Altaire Performance Paper

VASCULAR

IMAGING

DIAGNOSTIC

NEURORADIOLOGY

BREAST

IMAGING

MUSCULOSKELETAL

TECHNIQUES

November 2004

PerformanceA Hitachi Medical Systems America Publication

THE THIRD WAY:HIGH-FIELD OPEN MR IMAGING WITH THE ALTAIRE®

MR

A Hitachi Medical Systems America Publication

Introduction: High-fi eld open MR imagingwith the Altaire

MR angiography with theAltaire high-fi eld open MR systemGen J. Maruyama, MD

Mary Moncilovich-Greer, RT(R)(MR), CRT

Anthony Stauffer, MD

Diagnostic neuroradiology withthe Altaire high-fi eld open MR systemC. Douglas Phillips, MD

Breast imaging with the Altaire high-fi eldopen MR systemHugo E. Isuani, MD

Musculoskeletal techniques and studieswith the Altaire high-fi eld open MR systemGen J. Maruyama, MD

Glossary of abbreviations

5

7

16

27

35

43

THE THIRD WAY:HIGH-FIELD OPEN MR IMAGING WITH THE ALTAIRE®

PerformanceMR

4 A Hitachi Medical Systems America publication

The third way: High-field open MR imaging with the Altaire®

A Hitachi Medical Systems America publication 5

Contributors and institutions

©2004 Hitachi Medical Systems America, Inc.

Mission Regional Imaging Center provides magnetic-resonance imaging services for Mission Hospital Medical Center, a regional pediatric-care facility serving a broad range of patients. A member of the St. Joseph healthcare family, Mission Hospital is the largest medical center in south Orange County and the area’s designated trauma center.

Gen J. Maruyama, MD

Director, Musculoskeletal Imaging


Lead MRI Technologist


Director, Neuroimaging

Mission Regional Imaging CenterMission Viejo, California

C. Douglas Phillips, MD

Professor of RadiologyChief of Diagnostic NeuroradiologyUniversity of Virginia Health Sciences CenterCharlottesville, Virginia

The University of Virginia Health System embodies the leadership and inventiveness personified by its founder, Thomas Jefferson. The busy multispecialty tertiary-care health system includes a large neurosciences staff, and the 600-bed hospital is a major mid-Atlantic referral site in neurosurgical, craniofacial, and otolaryngological care. There is an active neuroradiologic training program, with diagnostic and interventional and neuroradiology fellows.

Hugo E. Isuani, MD

Staff RadiologistSierra–Providence–TotalCare NetworkEl Paso, Texas

TotalCare is a service of Sierra Medical Center. Opened in 1976 at the foot of the Rocky Mountains, Sierra Medical Center is a 365-bed acute-care hospital providing advanced healthcare services not only to El Paso but also to the outlying communities of west Texas, to southern New Mexico, and to northern Mexico.




Background

Open magnetic resonance (MR) imaging is well established as an alternative for the increasing number of patients who are unable or unwilling to undergo tube-type closed MR imaging and for the radiologists and technologists who want direct access for visual and auditory patient monitoring. In contemporary diagnostic imaging, high-field open MR systems, having advanced right along with closed systems in terms of their capabilities, are being effectively used in regular rotation with those closed systems for most imaging situations — brain disorders, traumatic injuries, eye abnormalities, spine diseases, tumor detection, liver and other abdominal diseases, knee and shoulder injuries, facial/neck abnormalities, cardiac malformations, blood flow and vessel disorders. In these situations, high-field open MR systems deliver comparable image quality in comparable scan times for comparable patient throughput.

The best high-field open MR systems offer state-of-the-art imaging techniques:

• Long echo train fast spin echo forfast T2 imaging

• Echo-planar imaging (EPI)

• Diffusion-weighted imaginguseful in neurological diagnosis

• Time-of-flight, phase contrast, and contrast-enhanced MR angiography for advanced vascular studies

• Radiofrequency (RF) fat saturation for enhanced visualization of musculoskeletal pathology

Historically, the status of open MR systems has been challenged by the theoretical correlation of magnetic field strength with signal-to-noise ratio (SNR). Of the three basic characteristics of an MR image —contrast, SNR, and spatial resolution —it is the SNR that is the measure for the overall quality of the image. The SNR increases with increases in the strength of the main magnetic field — almost quadratically at lower field strengths, linearly at higher field strengths. In the past, engineering challenges dictated the tunnel shape for maximum homogeneity and efficiency, resulting in designs that restrict access. Early attempts to provide greater patient comfort and surgeon access withan open MR design had field strengths<0.3 T. Since that time, innovative concepts in superconducting magnet design have yielded higher field strengths for open MR systems, and the manufacturers of open systems have also increased SNR by refining RF systems and coil technology, deploying advanced pulse sequences consistent with those of tunnel type systems, and implementing modifications in imaging parameters that accentuate the strengthsof the open MR paradigm.

The leading open MR systems that are now realizing the benefits of these research directions may best be viewed as representing a totally new MR system concept — a third way — combining advantages previously possessed separately by conventional low-field open systems and high-field closed systems. The advance is exemplified by the Altaire high-field open MR system (Hitachi Medical Systems

America, Inc., Twinsburg, Ohio). The Altaire has one of the highest field strengths achieved to date for open MR (0.7 T), and it incorporates an extremely refined noise-reduction technology. Further, the Altaire is designed with a high-performance gradient subsystem, which yields optimal spatial and contrast resolution and supports advanced imaging applications. Among the practical consequences are shorter repetition time (TR) selections and a reduction in time to echo (TE), minimizing dephasing and increasing T1 contrast.

Primer: The physicsof the Altaire

The Altaire technology — known as “vertical-field with optimized subsystem integration” (VOSI) — employs noise reduction and enhanced RF signal detection to improve SNR and thus yield images comparable in quality to those from closed MR systems.

An integral part of any MR system is its RF subsystem for delivering the excitation pulse and receiving the MR signal from the tissue by means of coils functioning as near-field antennae. Employing a vertical quadrature (circularly polarized) solenoid design for its volumetric coils (Figure 1, page 6), the Altaire realizes an increase of 40% more SNR compared to systems with conventional coils. As a general rule, the smaller the coil and the closer it is to the patient — that is, the better the coil fill factor, the relationship of the receiver’s coil size to the size of the object being imaged — the higher the SNR. By incorporating a wide range of anatomically specific coils, the Altaire takes advantage of this higher SNR.

In general, narrowing the bandwidth reduces the amount of noise sampled relative to the signal, thereby increasing SNR. The Altaire uses a variable bandwidth setting, which provides an important “power-tool” parameter for adjusting image quality without the chemical shift artifacts that result from the use of narrower bandwidths in 1.5 T high-field closed systems.

Introduction:High-field open MR imagingwith the Altaire®

Introduction: High-field open MR imaging with the Altaire®




Figure 1. The vertical-field orientation of the Altaire enables the use of solenoid radiofrequency coils instead of the less efficient saddle-type coils usually employed in horizontal-field systems. In order to maximize detection of transverse magnetization, the orientation of the receiving coil must be perpendicular to that of the main magnetic field. With horizontal-field systems, because the long axis of the patient is parallel to the magnetic field, it is often not possible to use the solenoid coils in volume (as opposed to surface) applications, with the coil completely enclosing the anatomical region. With this limitation overcome in the Altaire vertical-field system, volumetric application of solenoid coils can increase signal-to-noise ratio and produce an image quality that surpasses expectations for a field strength of 0.7 T.

The Altaire VOSI technology also incorporates a high-performance gradient subsystem such as is found on high-field closed MR systems. In order to perform the newer techniques such as EPI that have revolutionized MR imaging, it is important to have both high gradient amplitude and high gradient slew rates.The maximum gradient strength of the Altaire is 22 mT/m, much higher than the gradient strengths of previous open MR systems and comparable to the gradient strengths of high-field closed MR systems. Moreover, the maximum slew rate of the Altaire — the ratio of gradient strength to rise time — is 55 T/m/s, much higher than the slew rates of previous open MR systems and comparable to the slew rates of closed MR systems.

As with all advanced MR imagers, the Altaire uses various fast-scan and MR signal-data-management techniques that speed image acquisition — including fast spin-echo imaging, EPI, and partial k-space techniques that enable reduction in scan time with no loss of resolution.

The articles in this monograph demonstrate the quality and versatility of the imaging that the VOSI features make possible when the Altaire is utilized as part of the regular scanner rotation in a variety of diagnostic areas — vascular imaging, diagnostic neuroradiology, breast imaging, and musculoskeletal imaging.


The third way: High-fi eld open MR imaging with the Altaire®


MR angiography

Imaging of the vascular system has changed dramatically over the past decade as catheter-based angiography has been replaced for many purposes by the rapidly advancing, less invasive modalities of ultrasound, computerized tomography, and magnetic resonance (MR) imaging.1-4 MR angiography (MRA) is often the procedure of choice for initial noninvasive assessment of the intracranial vasculature.5,6 Now advances in high-fi eld open MR have allowed performance of high-quality peripheral MRA, once reserved for high-fi eld closed MR.

Available for years, and based on fl ow-related enhancement that distinguishes moving from stationary spins, time-of-fl ight (TOF) MRA is performed with either spin-echo or gradient-echo pulse sequences. TOF MRA can be performed as a two-dimensional (2D) or three-dimensional (3D) acquisition. The 2D acquisition collects information from a thin slice of tissue while 3D acquisition collects information from a slab of tissue.

In the more frequently utilized gradient-echo “bright-blood” method, the stationary spins (vessel wall and surrounding soft-tissue structures) in a slice or slab receive multiple radiofrequency (RF) pulses within a very short repetition time (TR) (T1 weighting) and

MR angiography with the Altaire® high-fi eld open MR systemGen J. Maruyama, MD

Director, Musculoskeletal Imaging


Lead MRI Technologist


Director, Neuroimaging

Mission Regional Imaging CenterMission Viejo, California

thus become saturated and produce little MR signal. Since the blood is moving, these spins are continuously fl owing out of the slice or slab and are replaced by fresh, fully magnetized blood spins that produce a high MR signal and have not been saturated by the applied RF pulse.1-3 These magnetized blood spins are then used to create the MRA image.

Once a series of 2D slices or a 3D slab has been acquired, the slices can be stacked and processed for image display in an angiographic format.1,3 To date, the most commonly employed projection techniques for this purpose have been the maximum intensity projection (MIP) algorithm and multiplanar reformations. The MIP technique has been enhanced by the volume-rendering algorithm, which incorporates the entire data set into a 3D image — thus making it possible to visualize the vascular surface and intravascular details while preserving spatial relationships.7

With 2D TOF MRA, it is possible to obtain images of blood fl ow over large areas (common carotid arteries, pelvis, lower extremities) in overall scan times of 5 to 10 minutes, depending on the number of slices.1,2 However, resolution is limited by the usual minimum slice thickness of about 1.5 mm,3 and signal may not be adequate to allow diagnosis in tortuous vessels.2

The volume acquisition of 3D TOF MRA (slabs up to 6 cm thick) makes for a higher signal-to-noise ratio (SNR) than 2D TOF, and the ability to partition the slab into slices less than 1 mm thick yields higher spatial resolution.1,3 Volume rendering increases sensitivity for detection of small intracranial aneurysms.8,9 3D TOF has been improved with the hybrid technique of multiple overlapping thin slab acquisition.1,3 The drawback associated with the 3D TOF slab thickness is a more limited area of coverage. In addition, motion during the sequence will affect the entire slab rather than just an individual slice.

Contrast enhancement is a further advance for MRA. Whereas TOF MRA depicts blood infl ow, contrast-enhanced (CE) MRA (CEMRA) is based on the reduction of the T1 relaxation time of blood relative to surrounding tissues following the rapid bolus injection of a paramagnetic contrast agent (a gadolinium chelate). When MR signals are collected with a short TR value, the signal from the tissue surrounding the blood vessels is very small relative to that of the CE blood due to its longer T1 value.4 Because the veins enhance shortly after the arteries and shortly thereafter the contrast diffuses into the adjacent soft tissues, successful use of contrast enhancement requires very fast data acquisition sequences.3 With a TR <10 milliseconds, it is possible to complete some CEMRA sequences within the span of a single breath-hold (~30 seconds), thereby avoiding respiratory motion.1,2 In CEMRA, the time to the echo (TE) is kept at a minimum (~1 millisecond) in order to eliminate dephasing artifacts and minimize T2 decay.2 It is frequently possible with CEMRA to image lesions not visualized with noncontrast MRA.

The following sections detail four protocols for CEMRA that we have had success with as performed on an Altaire 0.7 T high-fi eld open magnet. Our standard protocols for CEMRA are listed. All patients are connected to our power injector via a60-inch-length OPTISTAR Y tubing and a right antecubital 20G angiocatheter in order

Maruyama / Moncilovich-Greer / Stauffer MR angiography with the Altaire® high-fi eld open MR system




to help standardize injection times. K space is acquired in ADA format (3/4 K-space acquisition). Injection rates for gadolinium and saline flush are set at 2 cc per second.

MRA of thecarotid arteries

A major application of MRA is screening the carotid arteries for arteriosclerotic disease. A common source of transient ischemic attacks and stroke is atheromatous disease at the carotid bifurcation in the neck, which has been imaged primarily using 2D TOF, 3D TOF, and CEMRA in addition to ultrasound, computed tomographic (CT) angiography, and conventional angiography. With MR, 2D TOF may offer the best edge definition and sensitivity to slow blood flow, but its dependability is often limited by flow voids, susceptibility to artifacts based on patient movement, and signal loss along horizontal portions of a vessel or along tortuous vessels. When CEMRA is performed of the carotids, a 3D spoiled gradient-echo technique is used. A limitation of 3D CEMRA is the loss of edge definition and an apparent decrease in lumen diameter in both diseased and nondiseased areas.10

Figure 1. Coronal-plane images of the carotid arteries of a 72-year-old patient who presented with a single episode of confusion. Contrast-enhanced (CE) MRA of the carotid arteries was performed (see Protocol 1). Figure 1A is a maximum intensity projection from the CEMRA; the image in Figure 1B was processed with the volume-rendering algorithm. The arrow in each image indicates changes in keeping with a high-grade stenosis of the proximal left common carotid artery, approximately 2 cm from its origin.

Protocol 1

Phased array neurovascular coil

FOV: 230-260 mm (to cover from proximal arch to circle of Willis).

Sequence 1: Scanogram or scout of neck and routine 2D TOF of carotids.

Sequence 2: Test injection performed using dynamic 2D coronal RF spoiled SARGE (RSSG) of neck. Record time when contrast enters into the proximal common carotid arteries. Injection rate: 2 cc gadolinium @ 2 cc per second with 20 cc saline flush.

Sequence 3: Add 3 to 5 seconds to the time recorded during the test injection and use this value as the contrast transit time (ctt)/time delay before imaging begins. Perform a mask run prior to contrast and two consecutive postcontrast 3D coronal RSSG CEMRA runs. Injection rate: 20 cc gadolinium @ 2 cc per second with 20 cc saline flush.

Figure 1 shows coronal-plane images of the carotid arteries of a 72-year-old patient who presented with a single episode of confusion. CEMRA of the carotid arteries was performed, using the Altaire high-field open MR system and protocol 1. A high-grade stenosis was seen 2 cm distal to the left common carotid origin.

Figure 1BFigure 1A




Figure 2. Sagittal-plane images of a normal thoracic aorta in a 45-year-old patient who presented with chest pain. Contrast-enhanced (CE) MRA was performed (see Protocol 2). Figure 2A is a maximum intensity projection from the CEMRA; the image in Figure 2B was processed with the volume-rendering algorithm. The images clearly show a normal ascending aorta, aortic arch, and descending thoracic aorta.

Protocol 2

CTL phased array coil, wrap quadrature coil, or peripheral vascular phased array coil can be used based on patient anatomy.

FOV: 300 mm

Sequence 1: Coronal localizer of thorax.

Sequence 2: Axial T2 gradient echo of thorax used as scout to identify flow in aorta.

Sequence 3: Test injection performed using dynamic 2D coronal RSSG at the apex of the aortic arch off of sequence 2. Record time when contrast reaches aortic arch. Injection rate: 2 cc gadolinium @ 2 cc per second with 20 cc saline flush.

Sequence 4: Add 5 to 7 seconds to the time recorded during the test injection and use this value as the contrast transit time (ctt)/time delay before imaging begins. Perform a mask run prior to contrast and two or three consecutive postcontrast coronal or oblique sagittal 3D coronal RSSG CEMRA runs. Injection rate: 30 to 35 cc gadolinium @ 2 cc per second with 20 cc saline flush.

MRA of the thoracic aorta

CEMRA is being used increasingly instead of digital subtraction angiography (DSA) for first-line imaging of the thoracic aorta in nontraumatic patients or in patients unable to undergo CT angiography. Diverse pathology including aortic dissection, aneurysm, intramural hematoma, stenosis, and congenital abnormalities can be evaluated. The advances in gradient strength, making possible shorter TR and acquisition times, have allowed CEMRA to be implemented with subsecond temporal resolution,11 which is useful for evaluating high-flow vascular lesions such as shunts and dissections. Patient positioning for MRA of the thoracic aorta is similar to positioning for MR imaging of the chest, and these patients generally have MR imaging of the chest along with the MRA study.

Figure 2 shows sagittal-plane images from a CEMRA of a normal thoracic aorta. Figure 3 (page 10) shows a type III descending thoracic aortic dissection. In each case, CEMRA was performed on the Altaire high-field open MR system utilizing protocol 2.

MR angiography with the Altaire® high-field open MR systemMaruyama / Moncilovich-Greer / Stauffer

Figure 2A Figure 2B




Figure 3. Sagittal-plane images of the thoracic aorta of a 61-year-old patient with a history of thoracic aneurysm. Contrast-enhanced MRA was performed (see Protocol 2). Figures 3A and 3B are maximum intensity projections; the images in Figures 3C and 3D were processed with the volume-rendering algorithm. The images show ectasia of the ascending aorta and extensive type III dissection of the thoracic aorta. The proximal portion of this dissection is immediately distal to the takeoff of the left subclavian artery (sca). There is a small true lumen (tl) with delayed filling of the false lumen (fl).

MRA of the renal arteries

Since its introduction, CEMRA has established itself as a safe and reliable technique for detecting and grading renal artery stenosis, with sensitivities ranging from 91% to 100% and specificities ranging from 89% to 100%.2 Because of the lack of ionizing radiation and relatively low nephrotoxicity of gadolinium at doses used for MRA, this technique is particularly attractive for the patient with a kidney transplant or with renal failure and an elevated creatinine level.

Technical parameters for renal CEMRA are similar to those for other abdominal CEMRA studies. However, the imaging volume is placed more posterior within the abdomen to cover the retroperitoneum and the expected course of the

renal arteries from the aorta. The straight coronal or slight coronal oblique acquisition volume is placed with its anterior margin just anterior to the aorta as a reference structure to ensure coverage of the left renal vein. Typical slab thickness ranges from 60 to 100 mm.

Figure 4 shows coronal-plane images of the normal abdominal aorta and renal arteries of a 54-year-old patient with a history of hypertension. Figure 5 shows a coronal-plane image of a 60-year-old patient with a history of elevated blood pressure and a right renal artery stenosis. In each case, CEMRA was performed on the Altaire high-field open MR system utilizing the T1-weighted gradient-echo technique in protocol 3.

Figure 3A

sca

tl

Figure 3B

sca

tl

Figure 3Csca

fl

tl

Figure 3D sca

fltl




Figure 4. Coronal-plane images of the normal abdominal aorta and renal arteries of a 54-year-old patient with a history of hypertension. Contrast-enhanced (CE) MRA was performed utilizing a 3D T1-weighted gradient-echo technique (see Protocol 3). Figure 4A is a maximum intensity projection from the CEMRA; the image in Figure 4B was processed with the volume-rendering algorithm. The images show symmetric and normal perfusion of both kidneys and no evidence of renal artery stenosis.

Figure 5. Coronal-plane image of the abdominal aorta and renal arteries of a 60-year-old patient with a history of elevated blood pressure. Contrast-enhanced MRA was performed utilizing a T1-weighted gradient-echo technique (see Protocol 3). The image, displayed using the maximum intensity projection algorithm, shows high-grade stenoses (arrows) near the originsof both the left and right renal arteries.

Protocol 3

Quadrature wrap coil or peripheral vascular phased array coil can be used.

FOV: 300 mm

Sequence 1: Coronal Scanogram of abdomen.

Sequence 2: T1 and T2 axial gradient-echo breath-hold (20 seconds) of abdomen. T2 axial centered at the renal artery level.

Sequence 3: Test injection performed using dynamic 2D coronal RSSG at the level of the renal artery referenced from the T2 axial in sequence 2. Injection rate: 2 cc gadolinium @ 2 cc per second with 20 cc saline flush. Record time when contrast reaches the aorta at the level of the renal artery.

Sequence 4: Add 7 seconds to the time recorded during the test injection and use this value as the contrast transit time (ctt)/time delay before imaging begins. Perform a mask run prior to contrast and two or three consecutive postcontrast coronal or oblique sagittal 3D coronal RSSG CEMRA runs. Injection rate: 30 to 35 cc gadolinium @ 2 cc per second with 20 cc saline flush.


Figure 4A

Figure 4B

Figure 5




Protocol 4

Peripheral vascular phased array coil.

FOV: 400 mm

Important to position legs in the coil by building up ankles so that legs are centered at the same height and are level.

First stage: Lower leg protocol

Sequence 1: Lower leg (station C of peripheral vascular coil)3-plane Scanogram.

Sequence 2: Axial T2 gradient echo to record flow in vessel from knee to ankle.

Sequence 3: Test injection performed using dynamic 2D coronal RSSG at the level of the popliteal artery as referenced from sequence 2. Injection rate: 2 to 3 cc gadolinium @ 2 cc per second with 20 cc saline flush. Record time when contrast reaches popliteal artery.

Sequence 4: Add 7 seconds to the time recorded during the test injection and use this value as the contrast transit time (ctt)/time delay before imaging begins. Perform a mask run prior to contrast and two or three consecutive postcontrast 3D coronal RSSG CEMRA runs. Injection rate: 20 cc gadolinium @ 2 cc per second with 20 cc saline flush.

Second stage: Pelvis and thigh protocol

Sequence 1: Use station A of four-station peripheral vascular coil. 3-plane Scanogram of pelvis.

Sequence 2: Table moves to station B, and obtain 3-plane Scanogram of thigh.

Sequence 3: Table moves back to station A. 3D coronal RSSG mask image obtained.

Sequence 4: Table moves back to station B. 3D coronal RSSG mask image obtained.

Sequence 5: Table moves back to station A. Subtract 2 seconds from the test injection time obtained in sequence 3 of the first-stage lower-leg protocol, and use this value as the travel time for the pelvis (this step avoids the need for a repeat test injection). Perform a 3D coronal RSSG CEMRA of the pelvis and then the thigh during a two-stage contrast injection. Injection rate: 27 cc gadolinium @ 2.5 cc per second, followed by 10 cc gadolinium @ 1.5 cc per second, followed by 40 cc saline flush @ 2.5 cc per second.

Sequence 6: During the injection, the table moves through station B to obtain thigh CEMRA.

MRA of the lower extremities

Peripheral vascular disease (PVD) is a common condition with variable morbidity, affecting as many as 10 million people in the United States. Most affected people are over 50 years12 and are also at high risk of stroke, myocardial infarction, and cardiovascular death.13 Imaging of PVD requires complete visualization of the vessels, from the origin of the renal arteries down to the distal arteries of the lower leg, in different projections. Previously the standard method for examining the vessels of the legs was intra-arterial DSA. More recently, with the introduction of new examination techniques — including fast scanning, CEMRA, and automatic table movement14 — the use of 3D CEMRA has become practical.

Prior to contrast injection, plain (mask) images are collected, and after an application of contrast agent, contrast images are acquired in precisely the same positions and then subtracted from the mask images in a manner similar to that used in DSA. The scanning proceeds in two coronal steps from pelvis to ankle. However, at our center, we reverse this order of imaging, acquiring images of

the lower legs first, to minimize confounding venous flow, and then perform a two-stage CEMRA of the pelvis and thighs. Using this method, we have little venous contamination of the entire peripheral run-off. The Altaire table automatically steps between scan acquisitions. Screening peripheral MRA can identify which patients may need further catheter angiography/intervention.

Figure 6 shows a coronal-plane image of a normal peripheral run-off study. Figure 7 (page 14) shows a coronal-plane MRA of the lower extremities for a 64-year-old patient with severe stenosis of the left femoral-popliteal graft anastamosis with the popliteal artery. Occlusion of the left popliteal artery below the knee was present. Multifocal segmental stenosis of the right superficial femoral artery, anterior tibial artery, and tibioperoneal trunk was also present. This patient subsequently obtained a catheter angiogram, confirming these findings. In each case, CEMRA (40 cc gadolinium) was performed on an Altaire high-field open MR system utilizing a peripheral vascular coil and a T1-weighted spoiled gradient-echo technique, with automatic table movement per protocol 4.




Figure 6. Coronal-plane image of a normal peripheral run-off study of a middle-aged female. Contrast-enhanced MRA was performed utilizing a peripheral vascular coil and a T1-weighted spoiled gradient-echo technique, with automatic table movement and a biphasic injection of 20 cc and 10 cc gadolinium (see Protocol 4). The image is displayed using the maximum intensity projection algorithm.

Dedicated peripheral vascular coil is fitted for peripheral run-off study utilizing the Altaire® high-field open MR system for contrast-enhanced MRA. The coil provides 141 cm of coverage, typically from the renal arteries to the feet.


Figure 6




Figure 7. Coronal-plane MRA of the lower extremities for a 64-year-old patient with severe peripheral vascular disease. Figure 7A shows the abdominal aorta at the level of the renal arteries and aortic bifurcation. Figure 7B is at the level of the iliac bifurcation; there is occlusion of the left superficial femoral artery, with partial flow in a femoral-popliteal bypass graft (gr). Figure 7C shows severe stenosis of the left femoral-popliteal graft anastamosis with the politeal artery (arrow). Occlusion of the left mid superficial femoral artery

(SFA) was present. Multifocal segmental stenosis of the right SFA, anterior tibial artery, and tibioperoneal trunk was also present. Contrast-enhanced MRA was performed utilizing a peripheral vascular coil and a T1-weighted spoiled gradient-echo technique, with automatic table movement (see Protocol 4). The images are displayed using the maximum intensity projection algorithm. This patient subsequently obtained a catheter angiogram, confirming these findings.

Figure 7A

Figure 7D

Figure 7B

gr

Figure 7C




References

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2. Montgomery ML, Case RS. Magnetic resonance imaging of the vascular system: a practical approach for the radiologist. Top Magn Reson Imaging. 2003;14:376-385.

3. Bradley WG, ed. MR angiography. Applied Imaging. 2000;1(3):1-4.

4. Hornak JP. The basics of MRI. Accessed September 27, 2004, at http://www.cis.rit.edu/htbooks/mri.

5. Barboriak DP, Provenzale JM. MR arteriography of intracranial circulation. AJR. 1998;171:1469-1478.

6. Bhadelia RA, Bengoa F, Gesner L, et al. Efficacy of MR angiography in the detection and characterization of occlusive disease in the vertebrobasilar system. J Comput Assist Tomogr. 2001;25:458-465.

7. Mallouhi A, Felber S, Chemelli A, et al. Detection and characterization of intracranial aneurysms with MR angiography: comparison of volume-rendering and maximum-intensity-projection algorithms. AJR. 2003;180:55-64.

8. White PM, Teasdale EM, Wardlaw JM, Easton V. Intracranial aneurysms: CT angiography and MR angiography for detection — prospective blinded comparison in a large patient cohort. Radiology. 2001;219:739-749.

9. Raaymakers TWM, Buys PC, Verbeeten B Jr, et al. MR angiography as a screening tool for intracranial aneurysms: feasibility, test characteristics, and interobserver agreement. AJR. 1999;173:1469-1475.

10. Rapp JH, Saloner D. Current status of carotid imaging by MRA. Cardiovascular Surgery.2003;11:445-447.

11. Finn JP, Baskaran V, Carr J, et al. Thorax: low-dose contrast-enhanced three-dimensional MR angiography with subsecond temporal resolution—initial results. Radiology. 2002;224:896-904.

12. Weitz JI, Byrne J, Clagett GP, et al. Diagnosis and treatment of chronic arterial insufficiency of the lower extremities: a critical review. Circulation. 1996;94:3026-3049.

13. De Sanctis JT. Percutaneous interventionsfor lower extremity peripheral vascular disease.Am Fam Physician. 2001;64:1965-1972.

14. Ho KYJAM, Leiner T, de Haan MW, Kessels AGH, Kitslaar PJEHM, van Engelshoven JMA. Peripheral vascular tree stenoses: evaluation with moving-bed infusion-tracking MR angiography. Radiology. 1998;206:683-692.





Diagnostic neuroradiology with the Altaire® high-fi eld open MR systemC. Douglas Phillips, MD

Professor of RadiologyChief of Diagnostic NeuroradiologyUniversity of Virginia Health Sciences CenterCharlottesville, Virginia

Diagnostic neuroradiologywith MR imaging at UVA

The busy multispecialty tertiary-care health system at the University of Virginia (UVA) includes a large neurosciences staff, and the 600-bed hospital is a major mid-Atlantic referral site in neurosurgical, craniofacial, and otolaryngological care. There is an active neuroradiology training program, with diagnostic and interventional neuroradiology fellows. We perform all diagnostic neuroradiologic examinations, such as computed tomography (CT), magnetic resonance (MR) imaging, diagnostic cerebral angiography, myelography, and percutaneous biopsy procedures of the head and neck, skull base, and spinal column.

The indications for MR imaging of the brain and spine are wide ranging and include back and neck pain, radicular pain, recent spine or joint injury, headaches, dizziness, stroke, the evaluation of primary CNS neoplasms, metastatic disease, arteriovenous malformations (AVMs), and a broad list of neurological disorders including movement disorders, neurodegenerative conditions, and multiple sclerosis (MS). Working with UVA neurologists, neurosurgeons, and others, we regularly identify multiple brain tumor types as well as vascular and infectious disease, cervical and lumbar disc herniations, intrinsic spinal cord disease, and other conditions, and we also monitor the status of many of these diseases through routine follow-up examinations. With our MR

scanners, equipped with high-performance gradient subsystems and anatomically specifi c radiofrequency (RF) coils, we can perform a full and up-to-date range of techniques and sequences — from more traditional T1-weighted and T2-weighted images in different planes, with and without contrast, to gradient-echo and fast spin-echo techniques, inversion recovery sequences, diffusion-weighted imaging (DWI), balanced SARGE (BASG), MR angiography (MRA), and other innovative sequences.

Since September 2003, we have been using the 0.7 T Altaire high-fi eld open MR system (Hitachi Medical Systems America, Inc., Twinsburg, Ohio) in regular rotation with our conventional high-fi eld closed scanners ranging up to 1.5 T in fi eld strength — for a broad range of primary and follow-up imaging for brain tumors, strokes, spinal injuries, spinal degerative disease, other neurosurgery patients, and for initial evaluations and follow-up examinations for a large number of neurologic conditions. With some exceptions such as MR spectroscopy, and research studies already in progress and mandating high-fi eld imaging, the majority of our work is not prioritized for a particular scanner but is assigned to whatever system is available when the patient is scheduled. The Altaire high-fi eld open system has been easily and successfully customized for our site so that we can assign and perform exactly the same imaging sequences as on the

closed systems — in a seamless manner, with little difference in patient throughput, and with basically indistinguishable results — allowing us to transparently meet the high expectations of our referring specialists for diagnostic-quality images.

In some instances, our new or repeat patients insist on the comfort and convenience of the Altaire high-fi eld open system. In other cases, the Altaire is the only system that we can use because of patient size. As is true in many referral hospital practices, and increasingly in community practice, it is not unusual for us to be called on to image patients weighing well in excess of 300 pounds, patients whose girth prohibits their being imaged in a conventional closed MR system. In our experience, to deal with the growing signifi cant population of obese (and morbidly obese) patients, it is essential to have a high-quality open scanner. MR imaging is not otherwise possible for these patients, and that must be a patient-care consideration.

In the following sections, I describe in general terms our standard protocols for imaging of the brain, the cervical spine, and the lumbar spine. In association with each of these areas, our special protocols for various indications are described, exemplary resultant images from the Altaire high-fi eld open MR system are displayed, and our fi ndings in the cases represented by those images are summarized.




CASE 1

Indication: Persistent headaches following head trauma.

This elderly patient presented with headache associated with a fall 2 months previous, without a loss of consciousness. The patient was referred for MRI imaging of the brain with and without contrast. The clinical suspicion of a significant but previously unrecognized head injury was based on the persistent nature of the headaches. MR has typically been utilized in the evaluation of more chronic manifestations of trauma, while CT is more commonly utilized in the acute setting.

Procedure

Precontrast sequences: Sagittal T1,axial T2, axial 2D gradient echo, axial FLAIR, axial T1.

Postcontrast sequences: Axial T1, coronal T1, sagittal T1; DWI with apparent diffusion coefficient (ADC) maps.

MR imaging of the brainwith and without contrast

For our routine head imaging, after acquiring a three-axis scout image, we start with a sagittal T1-weighted sequence, then we follow with an axial fast spin-echo T2 sequence, an axial FLAIR sequence, and then an axial or coronal T1 sequence. Contrast is commonly indicated for MR in a number of conditions and in a large number of clinical settings. For instance, the routine evaluation of many patients with inflammatory, infectious, or known neoplastic conditions mandates contrast administration. Patients of advanced age being examined for often nonspecific indications commonly benefit from the inclusion of contrast-enhanced images. The increased incidence of tumors, both benign and malignant, is the likely explanation. If the provided clinical indications mandate contrast administration, we typically perform three-plane postcontrast T1 images. We utilize fat suppression if that is indicated for the anatomic area, such as the orbit or temporal bones, that we are studying. Common indications for our inclusion of fat-suppressed T1 images include detailed evaluation of the central skull base, orbits, temporal bones, and extracranial head and neck. Fat suppression is also useful in the evaluation of postoperative spines.

Figure 1A. Axial FLAIR (70-degree flip angle) with driven equilibrium fast spin-echo readout, 1-mm in-plane acquired resolution; 14000/2300/112 (TR/TI/TE).

Figure 1A

Figure 1C. Axial T2 acquired in 2 min 35 sec with driven equilibrium fast spin-echo readout; image enhanced with 512x512 reconstruction; 6094/112 (TR/TE).

Figure 1C

Figure 1D. Axial T2 acquired in 2 min 35 sec with driven equilibrium fast spin-echo readout; slice position 5.5 mm superior to the image in Figure 1C; image enhanced with 512x512 reconstruction; 6094/112 (TR/TE).

Figure 1D

Figure 1B. Axial FLAIR (70-degree flip angle) with driven equilibrium fast spin-echo readout, 1-mm in-plane acquired resolution; slice position 5.5 mm superior to the image in Figure 1A; 14000/2300/112 (TR/TI/TE).

Figure 1B

C. Douglas Phillips Diagnostic neuroradiology with the Altaire® high-field open MR system




Case 1 findings

The brain parenchyma was within normal limits, and there was no abnormal contrast enhancement. The ventricles were normal. There were no extra-axial collections. The paranasal sinuses and orbits are within normal limits. The gradient-echo sequences demonstrated no evidence of blood products within the brain that would be suggestive of chronic blood-degradation products that might accompany significant head injury.

Impression: Normal MR examinationof the brain.

Figure 1E. Axial T2 acquired in 2 min 35 sec with driven equilibrium fast spin-echo readout; slice position 11 mm superior to the image in Figure 1C; image enhanced with 512x512 reconstruction; 6094/112 (TR/TE).

Figure 1E

Figure 1H. Postcontrast axial spin-echo T1; contrast enhanced with MTC pulse; slice position 11 mm superior to image in Figure 1F; 550/13 (TR/TE).

Figure 1H

Figure 1F. Postcontrast axial spin-echo T1; contrast enhanced with MTC pulse;550/13 (TR/TE).

Figure 1F

Figure 1I. Postcontrast sagittal T1; conventional fast spin-echo readout;380/12 (TR/TE).

Figure 1I

Figure 1G. Postcontrast axial spin-echo T1; contrast enhanced with MTC pulse; slice position 5.5 mm superior to the image in Figure 1F; 550/13 (TR/TE).

Figure 1G

Figure 1J. Axial T2 gradient echo with25-degree flip angle; 600/33 (TR/TE).

Figure 1J




CASE 2

Indication: Tumor follow-up — the patient had undergone chemotherapy and radiation therapy for known metastatic involvement of the brain by nongestational trophoblastic disease.

This young female patient with a nongestational trophoblastic tumor metastatic to the brain underwent MR examination 18 days previous. The follow-up MR imaging of the brain with and without contrast was performed due to a recent alteration in sensorium following radiation therapy. Follow-up of patients undergoing treatment of CNS neoplasms, both primary and metastatic to the brain, is a large volume of our practice. These patients may undergo more traditional chemotherapy regimens or conventional external beam radiation therapy; alternatively, they may undergo more novel therapies, including focused gamma radiation (Gamma Knife), tumor vaccine therapy, intra-arterial chemotherapies, and other innovative therapies for tumor treatment. These patients require high-quality imaging in their evaluation and follow-up, and consistency of the imaging procedures across a number of platforms is very important.

Procedure

Precontrast sequences: Axial T2 weighted, axial FLAIR, axial T1 weighted.

Postcontrast sequences: Axial T1 weighted, sagittal T1 weighted, coronalT1 weighted; DWI.

Figure 2C. Precontrast axial T1 with MTC; 583/13 (TR/TE).

Case 2 findings

The examination again demonstrated a large mass centered in the right temporal lobe. This large metastatic lesion had minimally increased in size. However, there had been the development of an overall increase in the heterogeneous enhancement as well as increased surrounding edema. Further, two small metastases in the right frontal lobe had enlarged and were more prominent. The degree of midline shift had not significantly changed. No new lesions were identified. Presumed postoperative leptomeningeal enhancement was again noted overlying the tumor. Postoperative changes in the right temporal cranium are also again noted. The right mastoid air cells remained opacified.

Impression:

• Although only minimally changed in size, the large right temporal lobe mass demonstrated increased heterogeneous enhancement and surrounding edema.

• The small right frontal lobe metastases had slightly enlarged in the interval.

Figure 2B. Axial T2 FLAIR with driven equilibrium fast spin-echo readout; echo factor of 16 contributes to short scan time; 14000/2300/112 (TR/TI/TE).

Figure 2B

Figure 2C

Figure 2A. Axial T2 with driven equilibrium fast spin-echo readout; image enhanced with 512x512 reconstruction; 6602/112 (TR/TE).

Figure 2A

Figure 2D. Postcontrast axial T1 at same location as the image in Figure 2C; lesion enhancement maximized with combinationof gadolinium and MTC; 586/13 (TR/TE).

Figure 2D





CASE 3

Indication: Suspected pituitary neoplasm — based on a number of hormonal abnormalities and pertinent clinical history.

This 37-year-old female was diagnosed with Forbes-Albright syndrome (ICD-9 253.1) based on the finding of galactorrhea and amenorrhea and was referred for MR imaging of the brain with attention to the sella and the pituitary gland. A number of endocrine abnormalities suggested disease of the hypothalamic-pituitary axis, and the diagnostic test of choice in these patients is high-resolution imaging of the pituitary gland with MR. Our protocol consists of very thin-section coronal T1 and T2 images through the sella turcica before contrast administration, followed by thin-section T1 images in the coronal and sagittal planes. Our slice thickness for all of our imaging platforms is 3 mm. Optimally, these images are performed without an interslice gap but with traditional or fast 2D spin-echo techniques, a very thin interslice gap improves the overall image quality.

Procedure

Sella protocol: Sagittal and coronal precontrast T1 weighted, sagittal and coronal postcontrast T1 weighted, and coronal and axial T2 weighted.

Case 3 findings

There was a 3.7-mm area of low T1 signal within the left anterior-inferior pituitary gland that demonstrated diminished enhancement compared with the rest of the gland on the postcontrast images. The lesion demonstrated hyperintense T2 signal. There was no evidence of cavernous sinus involvement. The suprasellar cistern appeared normal. The pituitary infundibulum remained midline and normal in appearance. There were no other significant findings, such as hypothalamic abnormalities, and there were no extra-axial fluid collections. The appearance of the remainder of the CNS structures were within normal limits.

Impression: The findings were consistent with microadenoma in the left anterior-inferior pituitary gland.

Figure 3A. Precontrast coronal T1; conventional spin-echo sequence with 3-mm slice thickness and submillimeter in-plane resolution; 350/17 (TR/TE).

Figure 3A

Figure 3B. Postcontrast coronal T1; 350/17 (TR/TE); at the same slice location as the image in Figure 3A.

Figure 3B

Figure 3C. Coronal T2 with driven equilibrium fast spin-echo readout for T2 weighting and fast acquisition time; 3-mm slice thickness; 4100/112 (TR/TE).

Figure 3C




CASE 4

Indication: Follow-up MR examination of a vestibular schwannoma that had undergone prior Gamma Knife treatment.

This middle-aged patient with a right vestibular schwannoma measuring 22 by 3 by 14 mm had undergone an MR examination 5 months previous, at which time the schwannoma had been targeted for focused radiation treatment with the Gamma Knife. The follow-up examination was performed with and without contrast. Our facility has a very active Gamma Knife program, with a large number of AVMs, benign and malignant primary brain tumors, and vestibular schwannomas treated over the years. The findings of successfully treated schwannomas include diminished central enhancement and decrease in tumor size over time. The first follow-up examination may demonstrate a slight increase in tumor size, perhaps reflecting some tumor edema. We commonly perform follow-up MR examinations in these patients at 6 months following therapy and on a yearly basis after the lesion has become stable in size and appearance. The results following Gamma Knife therapy compare favorably with surgical figures, and this treatment modality has gained increased acceptance for a wide range of patients, notably those who are poor surgical candidates or who have lost considerable hearing.

Procedure

Precontrast sequences: Sagittal T1 weighted, axial T2 weighted, axial T1 weighted.

Postcontrast sequences (fat saturation): Axial T1 weighted, coronal T1 weighted; 3D balanced SARGE (BASG) with axial reconstructions.

Case 4 findings

The examination demonstrated a right internal auditory canal lesion with extension into the cerebellopontine angle, which had slightly increased in size in the interval. The enhancement pattern was fairly typical for post-treatment schwannomas, with peripheral enhancement and a low signal intensity center, and it was approximately 1 mm greater in diameter than on the previous examination. Mass effect upon the cerebellar peduncle was noted; however, there was no radiation change in the adjacent parenchyma. No other lesionswere identified. There was no evidenceof hemorrhage.

Impression: Since the previous exami-nation, there was minimal enlargement of the right vestibular schwannoma, with findings representative of the Gamma Knife therapy.

Figure 4C. Postcontrast coronal T1;401/17 (TR/TE).

Figure 4C

Figure 4A. Precontrast axial T1; high resolution (0.6 mm in-plane); 3-mm slice thickness; image enhanced with 512x512 reconstruction; 400/16 (TR/TE).

Figure 4A

Figure 4B. Postcontrast axial T1 with radiofrequency fat saturation, at same position as the image in Figure 4A;350/15 (TR/TE).

Figure 4B





CASE 5

Indication: Headaches, occasional gait disturbances,and blurred vision.

This 40-year-old patient presented with some relatively nonspecific neurologic symptoms and blurred vision (ICD-9 368.8) and was subsequently referred for MR imaging of the brain with and without contrast. With these nonspecific neurologic symptoms, this patient was referred for cranial MR imaging to investigate a number of possible etiologies. Nonspecific neurologic symptoms can be the most difficult problems for the clinician to investigate, and MR, being the most sensitive examination for evaluating the brain, is the most frequently utilized diagnostic test. While more specific neurologic symptoms may lead to a more detailed and specific examination, it is still useful to have a protocol for the overall evaluation of the entirety of the brain in a thorough and expeditious fashion. In this case, the clinical suspicion was actually that of a demyelinating disease, such as MS, and the examination was tailored to exclude MS as a primary consideration.

Procedure

Precontrast sequences: Axial T1 weighted, axial T2 weighted, sagittal and axial FLAIR; axial DWI with ADC maps.

Postcontrast sequences: Axial T1 weighted, coronal T1 weighted.

Case 5 findings

The cerebellar tonsils extended at least 6 mmbelow the level of the foramen magnum, resulting in relative “crowding” of the tonsils and brainstem and a relative paucity of the cerebrospinal fluid (CSF) spaces. There was no evidence of a syrinx within the visualized portion of the upper cervical cord. There was no hydrocephalus. The signal and configuration of the brain substance was otherwise normal. There was no mass effect or space-occupying lesion and no evidence of hemorrhage. The remaining CSF-containing spaces were normal. There was no evidence of restricted diffusion on the diffusion-weighted images. No signal abnormalities were demonstrated after intravenous contrast administration. Mild inflammatory changes were noted within the frontal sinuses and bilateral anterior ethmoid air cells.

Impression:

• The crowding of the foramen magnum with inferior displacement of the cerebellar tonsils 6 mm below the foramen was compatible with the diagnosis of Arnold-Chiari type I malformation.

• There was no evidence of demyelinating disease.

Figure 5A. Sagittal T1 with fast spin-echo readout; image enhanced with 512x512 reconstruction; 420/12 (TR/TE).

Figure 5A

Figure 5B. Axial T2 with driven equilibrium fast spin-echo readout; image enhanced with 512x512 reconstruction; 5078/112 (TR/TE).

Figure 5B

Figure 5C. Axial T1 with MTC pulse; image enhanced with 512x512 reconstruction;485/16 (TR/TE).

Figure 5C




CASE 6

Indication: Worsening gait instability in an elderly patient with prior strokes.

This elderly patient, with a history of cerebrovascular accident in the left cerebellum in 1990, presented with progressive gait instability over the previous 5 days (ICD-9 780.4) and was referred for MR imaging of the brain with and without contrast. The evaluation of patients who have had the acute or subacute onset of new neurologic symptoms may suggest a cerebral infarction. This suspicion is increased with increasing age or with the presence of vascular risk factors. We typically view the evaluation of a stroke patient as a study not only of the brain but also of the cerebral vasculature. This means the examination will typically be MR imaging of the brain and also MRA of the extracranial and intracranial vasculature. Obviously, this examination is tailored to the clinical suspicion and to other tests that may have already been performed. Many clinicians request Doppler ultrasound of the carotid bifurcations as a primary diagnostic modality and perform MR imaging only of the brain.

Procedure

Precontrast sequences: Axial T1 weighted, axial T2 weighted, axial FLAIR; axial DWI.

Postcontrast sequences: Axial T1 weighted, sagittal T1 weighted, coronalT1 weighted.

Case 6 findings

No areas of restricted diffusion were identified to suggest an acute infarct. Increased signal was present within the superior left cerebellar hemisphere and in the inferior right cerebellar hemisphere, consistent with encephalomalacia from the old infarction. There was mild generalized cortical atrophy. Minimal spotty bilateral white matter T2 signal abnormalities were present, likely due to chronic small-vessel ischemic injury. The brain and brain stem were otherwise normal in morphology and signal characteristic. There were no masses and no extra-axial collections. There were normal flow voids in the major intracranial vessels. There were no areas of abnormal enhancement. No MRA was requested or performed in this case.

Impression:

• There was no evidence of acute infarction.

• There were multiple old cerebellar infarctions.

Figure 6A. Axial T2 with driven equilibrium fast spin-echo pulse sequence; image enhanced with 512x512 reconstruction;6094/112 (TR/TE).

Figure 6A

Figure 6B. Axial FLAIR with driven equilibrium fast spin-echo readout and reduced flip angle; 14000/2300/112 (TR/TI/TE).

Figure 6B

Figure 6C. Postcontrast sagittal T1 with conventional fast spin-echo readout;380/12 (TR/TE).

Figure 6C





MR imaging of the spinewith and without contrast

In imaging the spine, we find that the following routine imaging sequences generally allow adequate evaluation of discogenic disease, trauma, inflammation, osseous metastases, other marrow abnormalities, and congenital malformations. We like to perform sagittal T1 and T2 imaging. The T2 images are fast spin-echo T2, with a long time to the echo (TE) only. Short TE images are not a part of our routine protocols. We may perform sagittal short-tau-inversion-recovery (STIR) imaging with a history of trauma and may also perform postcontrast sagittal T1 imaging in postoperative spine cases or with the history of neoplasia. We then perform axial T1 imaging and an axial fast spin-echo T2 or an axial gradient-echo sequence. Similar protocols are utilized for the cervical, thoracic, and lumbar spines. I have found imaging of the spine to be of a very high quality on the Altaire high-field open MR system. The coil performance is exceptional.

CASE 7

Indication: Torticollis —rule out cervical spine pathology.

This middle-aged patient presented with torticollis, a painful twisting or contracture of the neck (ICD-9 723.5), and MR imaging of the cervical spine without contrast was ordered to rule out cervical spine disk disease or primary spinal cord pathology.

Procedure

Sagittal T1 weighted, sagittal T2 weighted, axial T1 weighted, axial gradient echo.

Case 7 findings

The overall marrow signal, vertebral alignment, cord signal, and visualized paraspinal soft tissue structures appeared within normal limits. No significant degenerative change, central canal stenosis, or neural foraminal narrowing was seen involving the cervical spine.

Impression: The patient had a normal MR examination of the cervical spine. In the absence of significant findings on the spinal MR examination, the patient could be treated conservatively, with a good chance of return of normal function.

Figure 7C. Axial gradient echo with MTCand 40-degree flip angle; 633/15 (TR/TE).

Figure 7D. Axial T1 spin echo; image enhanced with 512x512 reconstruction;452/17 (TR/TE).

Figure 7C

Figure 7D

Figure 7A. Sagittal T2 with driven equilibrium fast spin-echo readout; echo factor of 24 contributes to heavy T2 weighting and short scan (~3 min); 3-mm slice thickness; submillimeter in-plane resolution;3002/120 (TR/TE).

Figure 7A

Figure 7B. Sagittal T1 with conventional fast spin-echo readout; 3-mm slice thickness; image enhanced with 512x512 reconstruction; 605/14 (TR/TE).

Figure 7B




CASE 8

Indication: Neck pain and radicular arm pain and weakness — evaluate for disk injury

This patient, a college football player, presented with persistent right trapezoid pain (ICD-9 723.1) and weakness, with the distribution of symptoms in the C4-5 distribution. MR imaging of the cervical spine without contrast was ordered to evaluate for bony degenerative disease, disk herniation, or evidence of a spinal cord injury. Neck and back pain are common ailments in the developed world and typically respond to conservative therapy. Persistent pain or accompaniment of this pain with either motor weakness or radicular symptoms is indicative of nerve root compression. MR has proven to be a sensitive and specific examination of the cervical and lumbar spine in the setting of possible nerve root compression.

Procedure

Sagittal T1-weighted and T2-weighted sequences with axial T1-weighted and gradient-echo sequences performed from skull base to the inferior end plate of T4.

Case 8 findings

The spinal canal was remarkable for a mild to moderate developmental stenosis. There were relatively diminutive pedicles, with an overall decrease in the anteroposterior dimensions of the central spinal canal. There were superimposed diffuse broad-based disco-osteophytic bulges extending from C2-3 through T1-2. There was, in addition, minimal anterolisthesis of T1 on

T2. The midcervical vertebrae had lost their normal lordotic curve and were relatively straightened in alignment. The paraspinous soft tissues were grossly within normal limits as was the posterior fossa. No definite cord signal abnormalities were defined.

Impression: There was diffuse mild congenital central canal stenosis. Multiple osseous segmentation anomalies were noted in the cervicothoracic junction, for which CT evaluation was recommended. There was moderate right C3-4 neuroforaminal stenosis with moderate bilateral C4-5 neural foraminal stenosis. The C4 and C5 nerve roots would be affected by stenosis at these levels.

Figure 8C. Axial gradient echo with MTC and 40-degree flip angle; image enhanced with 512x512 reconstruction;711/15 (TR/TE).

Figure 8C

Figure 8A. Sagittal T1 with fast spin-echo readout; 3-mm slice thickness; image enhanced with 512x512 reconstruction;530/14 (TR/TE).

Figure 8A

Figure 8B. Sagittal T2 with driven equilibrium fast spin-echo; echo factor of 24; 3-mm slice thickness; image enhanced with 512x512 reconstruction; 3000/120 (TR/TE).

Figure 8B





CASE 9

Indication: Sacroiliac pain and progressive weakening in the right lower extremity.

This patient, a 62-year-old female, presented with a history of sacroiliac pain and progressive weakening in the right lower extremity (ICD-9 722). She had undergone prior lumbar spine surgery. The patient was referred for MR imaging of the lumbar spine. As previously described, the combination of pain and weakness increases the confidence in clinical diagnosis of significant disk disease and nerve root compression. Alternatively, bony stenosis may result in this presentation.

Procedure

Sagittal and axial T1- and T2-weighted sequences through the lumbar spine.

Figure 9A. Sagittal T2 (30-cm field of view); echo factor of 16; image enhanced with 512x512 reconstruction; 3000/112 (TR/TE).

Case 9 findings

The thecal sac was capacious. In the inferior aspect of the thecal sac, the nerve roots appeared abnormal, with some evident clumping and roots that appeared to be focally adherent to adjacent roots and to the theca. Axial images also incidentally demonstrated L5-S1 bilateral spina bifida occulta. The thecal sac protruded posteriorly and demonstrated an irregular convex contour. The remainder of the lumbar spine demonstrated normal alignment. Vertebral body heights and intervertebral disk spaces were well maintained. No abnormal signal was identified within the cord. The conus was normal and terminated at the L1-2 level. Axial images demonstrated no focal disk abnormality, spinal stenosis, or foramina narrowing.

Impression:

• The thecal sac was capacious, with focal contour deformity, and there was associated spina bifida occulta at theL5-S1 level.

• There was focal clumping of the nerve roots inferiorly, which was felt indicative of arachnoiditis.

Figure 9C. Sagittal T2 (30-cm field of view); echo factor of 16; image enhanced with 512x512 reconstruction; 3000/112 (TR/TE).

Acknowledgment

The author wishes to thank Francis Schmit, RT(R)(MR)(CT), chief technologist/manager for CT/MRI at UVa Imaging, Charlottesville, Virginia, for his expertise in perfecting our standard neuroimaging protocols for the Altaire. All featured images from the Altaire were acquired at UVa Imaging.

Figure 9B. Sagittal T1 with driven equilibrium fast spin-echo readout; same location as the image in Figure 9A; image enhanced with 512x512 reconstruction; 605/14 (TR/TE).

Figure 9B

Figure 9A Figure 9C




Breast imaging with the Altaire® high-fi eld open MR systemHugo E. Isuani, MD

Staff RadiologistSierra–Providence–TotalCare NetworkEl Paso, Texas

MR: Extra dimensionfor breast imaging

I have been reading 4000 to 5000 mammograms per year for over 10 years. I have been reading ultrasounds for the same period. Over the past 2 years, I have also been reading magnetic resonance (MR) images of the breast.

The development of the capabilities of MR imaging systems has added an extra dimension to breast imaging — as a secondary diagnostic measure improving on the limitations of mammography and ultrasound in certain cases, and perhaps now soon as a primary screening measure for women with high cancer risk. The sensitivity of screening mammography for breast cancers in BRCA mutation carriers has been estimated at less than 50%, and 50% of the cancers in mutation carriers are said to appear in the interval between annual mammograms and to grow rapidly.1-4 The shortcomings of mammography — for example, sensitivity inversely related to breast density — are compounded for at-risk younger women, who in general have denser breasts than postmenopausal women.5-7

MR imaging has also been useful in guiding biopsies and other interventional procedures, and as more open MR systems become located in hospital surgical settings or in outpatient surgery centers for preoperative localization and intraoperative use, the utility of such imaging will be increased due to improved access.

The keys to MR imaging of the breast are high spatial resolution and the capacity for satisfactory temporal resolution. High spatial resolution allows the imaging of very thin slices and a close scrutiny of lesion morphology. The capacity for temporal resolution, which allows us to distinguish whether masses are malignant, depends on gradient technology and slew rates and on the receiver apparatus. These keys unlock the all-important use of enhancement, digital subtraction, and dynamic region-of-interest calculation.

As it happens, most breast MR imaging in El Paso is performed on open MR systems. Besides allowing for easier patient positioning and largely eliminating the experience of claustrophobia while promoting patient relaxation, the new high-fi eld open MR systems — with their advanced gradient technology and highly refi ned receiver coils — well support the state-of-the-art sequences available for breast imaging.

Because enhancement in the breasts is very subtle, the digital subtraction algorithm, comparing precontrast with postcontrast images, is useful for highlighting the areas with increased signal due to the gadolinium. Then the high gradient slew rates and the refi ned breast receiver coils on the high-fi eld open MR systems allow three to fi ve acquisitions of the same slices over a 5- to 7-minute postcontrast time frame — thus providing the data for dynamic region-of-

interest graphing. Once we have identifi ed tumors and other masses and assessed their morphology (whether smooth/rough, round/irregular, homogeneous/heterogeneous)8 with the use of contrast and the digital-subtraction algorithm, this ability to track temporal resolution at the region of interest yields information about the pattern of enhancement over time, which information allows us to distinguish whether the lesions are benign or malignant.8 Whereas a benign lesion will enhance gradually and steadily over the acquisition period, a malignant lesion — due in part to the dynamic of its neovascularization — will enhance rapidly and then “wash out.” (A graph of temporal resolution that enhances rapidly but then plateaus instead of washing out may be indicative of overlapping benign and malignant regions in the mass.) Any number of areas (regions of interest) within the breast may be analyzed in this way to screen for malignancy.

Our protocols for breast imaging with the Altaire high-fi eld open MR system also include sagittal short-tau-inversion-recovery (STIR) sequences and axial fast spin-echo T2 sequences with fat saturation to aid detection of lesions and discrimination of their morphology.

The current indications for MR imaging of the breast include the staging of known tumors (on the basis of mammograph and/or ultrasound), work-up for lumpectomy, palpable lesions in dense breasts with negative mammography and ultrasound, and monitoring of response to chemotherapy.9 In general, the utility of MR imaging as a back-up diagnostic procedure increases with breast density, and the index of suspicion occasioning MR imaging is greater when the mammography report reads “extremely dense breast pattern and no evidence of malignancy” than it is when the report refers to a “fatty breast.” If a possible mass is felt upon breast palpation and the mammogram although negative demonstrates a dense breast, then ultrasound and MR, in sequence, are in order.

Hugo E. Isuani Breast imaging with the Altaire® high-fi eld open MR system




Two prominently published recent studies have documented the efficacy of MR imaging for breast cancer screening, particularly in high-risk women. Kriege and colleagues found that among 1909 women (including 358 carriers of germ-line mutations of the BRCA1 or BRCA2 gene) with a 15% or greater cumulative lifetime risk of breast cancer, the sensitivity of MR for detecting invasive breast cancer was 79.5%, versus 17.9% for clinical breast examination and 33.3% for mammography.10 The specificity is not as good as the sensitivity for MR imaging of the breast because there are other benign diseases that may mimic cancer.

Warner and associates have reported on a study involving 236 Canadian women aged 25 to 65 years with BRCA1 or BRCA2 mutations who underwent one to three annual screening examinations. Of the 22 cancers that were detected in these women (16 invasive, 6 ductal carcinoma in situ), 17 (77%) were detected by MR, versus 8 (36%) by mammography, 7 (33%) by ultrasound, and 2 (9.1%) by clinical breast examination.11

In further support of our positive experience with the high-field open MR systems, another recently published report concluded that using MR to screen women at high genetic risk for breast cancer meets the criterion for technology assessment — adopted by the Blue Cross-Blue Shield Association — that the technology in question should improve net health outcome.12

In MR imaging of the breast it is important to remember that because breast cancer tends to be multifocal with bilateral manifestations, particularly for women with a family history of cancer, both breasts should always be studied.

A few brief case summaries will serve to exemplify the utility of MR imaging for at-risk women and women with dense breasts. In one case, following negative mammogram, ultrasound biopsy identified a lobular carcinoma 6 mm in diameter. The woman was sent to us for preoperative staging. With our MR protocol, we found a second carcinioma 3 cm from the known tumor. This was important information in determining the foci for lumpectomy and judging the advisability of moving to mastectomy. If the woman has dense breasts and

positive tumors, an MR exam is a critical part of the decision-making process. Without MR imaging, it is not possible in such cases to confirm that there are no further tumors beyond those identified by mammography and/or ultrasound.

In another case, the woman presenting with a palpable thickening of the breast, the mammogram was equivocal and ultrasound showed a small 1-cm ill-defined abnormal mass that biopsied positive. When this patient was sent to us for a staging, we found on MR examination that the tumor mass was in fact 4 cm in diameter (rather than 1 cm) — a very large tumor, that is.

Another example involves a woman who had had a lumpectomy 15 years prior to our examining her. The most recent routine mammogram was equivocal, and it could not be determined whether the noted assymetrical density was an extension of the area of scar tissue related to the lumpectomy or instead a new tumor. The MR imaging revealed a new primary tumor.

In the following pages, two further cases are described, our protocols for MR imaging of the breast are detailed, and sample images are displayed.




CASE 1

Indication: Axillary lymph adenopathy of unknown origin in left breast; negative mammogram.

This 71-year-old patient presented with signs of axillary lymph adenopathy in the left breast, discovered by clinical examination. Mammography was negative. An ultrasound was not ordered. The patient was referred for MR imaging of the left breast with and without contrast, with digital subtraction and dynamic region-of-interest analysis.

Protocol: Single breast (no history of cancer)

Multiplanar multisequential MR imaging with attention to left breast. Comparison with previous mammogram.

(1) 3-plane localizer

(2) Axial fast spin-echo T2 with fat saturation (includes both breasts)

(3) Sagittal STIR (symptomatic breast)

(4) Sagittal fast spin-echo T2 (symptomatic breast)

(5) Sagittal three-dimensional (3D) dynamic RSSG sequence (symptomatic breast)

Figure 2. Precontrast sagittal short-tau-inversion-recovery images of the left breast; 1700/100/17 (TR/TI/TE). The image in Figure 2A is at the level of the nipple, midbreast. The image in Figure 2B is in the axillary tail. This breast shows a scattered fibroglandular pattern based on the amount of fat and breast tissue. The breast appears normal in these precontrast images. Prominent lymph nodes are noted in the upper right of Figure 2B (arrows), but postcontrast imaging with digital subtraction is necessary to assess them for possible malignancy.

Figure 1. Precontrast sagittal T2 of the left breast with driven equilibrium fast spin-echo readout; 4970/98 (TR/TE). The image in Figure 1A is at the level of the nipple, midbreast. The image in Figure 1B is in the axillary tail. The images reveal a scattered fibroglandular breast pattern without definite masses.

Figure 2A

Figure 1A Figure 1B

Hugo E. Isuani Breast imaging with the Altaire® high-field open MR system

Figure 2B




Figure 4. Sagittal digital subtraction three-dimensional gradient echo (RSSG), with flip angle of 60, in the axillary region of the left breast; 16/7 (TR/TE). The postcontrast acquisition for the image in Figure 4A was at 1:10 minutes; the postcontrast acquisition for Figure 4B was at 4:40 minutes. The lymph nodes that are visible in the upper right of these images are smooth, slightly lobulated, large, circumscribed. The time-vs-intensity graph in Figure 4C displays the dynamic of digitally subtracted enhancement over the 7-minute acquisition period (postcontrast acquisitions at 1:10, 2:20, 3:30, 4:40, 5:50) for the region of interest as noted by the arrows in Figures 4A and 4B. The shape (rapid rise followed by washout) of the solid-line curve in the graph is consistent with local metastasis from a primary breast tumor.

Figure 3. Sagittal digital subtraction three-dimensional gradient echo (RSSG), with flip angle of 60, in the axillary tail of the left breast; 16/7 (TR/TE). The postcontrast acquisition for the image in Figure 3A was at 1:10 minutes. The lymph nodes that are visible in the upper center-right of the image are smooth, slightly lobulated, circumscribed. The time-vs-intensity graph in Figure 3B displays the dynamic of digitally subtracted enhancement over the 7-minute acquisition period (postcontrast acquisitions at 1:10, 2:20, 3:30, 4:40, 5:50) for the region of interest as noted by the arrow in Figure 3A. The shape (rapid rise followed by washout) of the solid-line curve in the graph is consistent with local metastasis from a primary breast tumor.

Figure 3B

Figure 4B

Figure 4C

Figure 3A

Figure 4A Figure 4B




Case 1 findings

In the left breast 12:00 position at the distance of approximately 4 cm from the nipple, there is a 6- by 7-mm enhancing mass seen with characteristics consistent with malignancy. This mass demonstrates rapid enhancement with subsequent contrast washout. In the left axillary region, there are multiple borderline sized and enlarged lymph nodes that also demonstrate a malignant enhancement pattern consistent with axillary metastatic lymphadenopathy. The largest lymph node measures approximately 3 by 2 by 2.5 cm in size. The enlarged lymph nodes are visualized on the mammogram. The small enhancing lesion within the left breast, however, is not seen on the mammogram.

Impression:

• 6- by 7-mm mass in the left breast 12:00 position, 4 cm from the nipple, that is felt to represent a primary breast malignancy.

• Multiple enlarged left axillary lymph nodes with a malignant enhancement pattern suggestive of metastatic adenopathy.

Figure 5. Sagittal digital subtraction three-dimensional gradient echo (RSSG), with flip angle of 60, of the left breast; 16/7 (TR/TE). The postcontrast acquisition for the image in Figure 5A was at 2:20 minutes. The bright mass in the center of the image has volume (approximately 7-mm diameter) and irregular edges. The time-vs-intensity graph in Figure 5B displays the dynamic of digitally subtracted enhancement over the 7-minute

acquisition period (postcontrast acquisitions at 1:10, 2:20, 3:30, 4:40, 5:50) for the region of interest as noted by the arrow in Figure 5A. The shape (rapid rise followed by washout) of the solid-line curvein the graph is consistent with the impressionof a primary malignant tumor.


Figure 5B

Figure 5A




CASE 2

Indication: Right breast cyst; dense breasts; family history of cancer.

This 49-year-old patient presented with multiple cysts, extremely dense breast pattern on mammography, and a family history of cancer. The patient was referred for MR imaging of the right breast with and without contrast, with digital subtraction and dynamic region-of-interest analysis. Ultrasound was not performed.

Protocol: Single breast (history of breast cancer)

Multiplanar multisequential MR imaging with attention to left breast.

(1) 3-plane localizer

(2) Axial fast spin-echo T2 with fat saturation (includes both breasts)

(3) Sagittal STIR (affected breast)

(4) Sagittal fast spin-echo T2 (affected breast)

(5) Sagittal 3D dynamic RSSG sequence(affected breast)

Figure 6C

Figure 6A Figure 6B

Figure 6. All three images represent the same precontrast sagittal slice in the right breast. The image in Figure 6A is a sagittal T1 with conventional spin-echo readout; 400/20 (TR/TE); additional coverage provided with two-slice simultaneous acquisition feature (dual slice). The image in Figure 6B is a sagittal short-tau inversion recovery; 1500/100/17 (TR/TI/TE). The image in Figure 6C is a sagittal T2 with driven equilibrium fast spin-echo readout; 3727/98 (TR/TE). In Figure 6A, with only the fat and fibroglandular tissue bright, three dark homogeneous fluid masses at the back of the extremely dense breast tissue, next to the chest wall, can barely be noted. In Figure 6B, with the fat suppressed and dark, the dense breast tissue now appears bright, and the fluid cysts are even brighter. The cysts are most clearly pronounced in Figure 6C, the T2-weighted image, with the fluid bright as well as the fat.




Case 2 findings

The extreme density of this breast makes it very hard to examine by mammography, and the case suggests the importance of MR imaging with contrast for breast imaging of such patients. There are multiple cysts in the right breast. No solid nodules were demonstrated. No abnormal enhancement is seen to indicate carcinoma.

Impression: Multiple cysts, no evidence of breast carcinoma or other enhancing lesions.

Figure 7A Figure 7BFigure 7. Axial short-tau inversion recovery with large (32-cm) field of view of the breasts; 1703/100/17. The images in Figure 7A and Figure 7B represent two different transaxial locations and show different cysts. As in Figure 6B, the uniform fat suppression enhances the conspicuity of the cystic lesions, which appear bright along with the breast tissue.

Figure 8. Sagittal digital subtraction three-dimensional gradient echo (RSSG), with flip angle of 60, of the right breast; 16/7 (TR/TE). The postcontrast acquisition for the image in Figure 8A was immediate. The lack of enhancement in the image suggests that there is no malignancy associated with the cysts. The graph in Figure 8B displays the dynamic of digitally subtracted enhancement over the 7-minute acquisition period (postcontrast acquisitions immediately and at 1:00,2:00, 3:00, 4:00, 5:00) for the region of interest as noted by the arrow in Figure 8A. The shape (steady gradual ascent) of the solid-line curve in the graph represents a benign enhancement pattern.

Acknowledgment

The author wishes to thank Andres Salcedo, RT(R)(MR), CT/MRI supervisor at Total Care Outpatient Diagnostic Radiology, El Paso, Texas, for his expertise in perfecting our standard breast imaging protocols forthe Altaire.


Figure 8BFigure 8A




10. Kriege M, Brekelmans CTM, Boetes C, et al. Efficacy of MRI and mammography for breast-cancer screening in women with a familial or genetic predisposition. N Engl J Med. 2004;351:427-437.

11. Warner E, Plewes DB, Hill KA, et al. Surveillance of BRCA1 and BRCA2 mutation carriers with magnetic resonance imaging, ultrasound, mammography, and clinical breast examination. JAMA. 2004;292:1317-1325.

12. Blue Cross Blue Shield Association, Technology Evaluation Center. Magnetic resonance imaging of the breast in screening women considered to be at high genetic risk of breast cancer. December 2003; volume 18, number 15. Accessed September 27, 2004, at http://www.bluecares.com/tec/vol18/18_15.html.

References

1. Meijers-Heijboer H, van Geel B, van Putten WL, et al. Breast cancer after prophylactic mastectomy in women with a BRCA1 or BRCA2 mutation. N Engl J Med. 2001;345:159-164.

2. Brekelmans CTM, Seynaeve C, Bartels CCMM, et al. Effectiveness of breast cancer surveillance in BRCA1/2 gene mutation carriers and women with high familial risk. J Clin Oncol. 2001;19:924-930.

3. Scheuer L, Kauff N, Robson M, et al. Outcome of preventive surgery and screening for breast and ovarian canceer in BRCA mutation carriers. J Clin Oncol. 2002;20:1260-1268.

4. Komenaka IK, Ditkoff BA, Joseph KA, et al The development of interval breast malignancies in patients with BRCA mutations. Cancer. 2004;100:2079-2083.

5. Kolb TM, Lichy J, Newhouse JH. Comparison of the performance of screening mammography, physical examination, and breast US and evaluation of factors that influence them: an analysis of 27,825 patient evaluations. Radiology. 2002;225:165-175.

6. Mandelson MT, Oestreicher N, Porter PL, et al. Breast density as a predictor of mammographic detection: comparison of interval- and screen-detected cancers. J Natl Cancer Inst. 2000;92:1081-1087.

7. Rosenberg RD, Hunt WC, Williamson MR, et al. Effects of age, breast density, ethnicity and estrogen replacement therapy on screening mammographic sensitivity and cancer stage at diagnosis. Radiology. 1998;209:511-518.

8. ACR breast imaging reporting and data system atlas. Reston, Va: American College of Radiology; 2003.

9. Viehweg P, Paprosch I, et al. Contrast-enhanced magnetic resonance imaging of the breast: interpretation guidelines. Top Magn Reson Imaging. 1998;9:17-43.




Musculoskeletal techniques andstudies with the Altaire® high-fi eld open MR systemGen J. Maruyama, MD

Director, Musculoskeletal ImagingMission Regional Imaging CenterMission Viejo, California

Advantages of the Altaire for musculoskeletal imaging

Musculoskeletal imaging is challenging at all fi eld strengths: Numerous anatomic structures need to be demonstrated, and the pathology is diverse. Infl ammatory, infectious, and neoplastic conditions may be encountered, in addition to traumatic injuries.1,2 There is little doubt that MR, with its soft-tissue contrast and multiplanar capabilities, is the diagnostic modality best suited for the musculoskeletal system.

The Altaire provides several specifi c advantages for musculoskeletal imaging. At 0.7 T, there are fewer susceptibility effects, for two reasons. First, the Altaire has a highly uniform magnetic fi eld, enhanced by an active shimming capacity. The variable bandwidth setting and lower overall fi eld strength of the magnet allow metallic susceptibility artifacts to be diminished. This is extremely useful in postoperative cases where chemical shift from orthopedic hardware can degrade image quality. An additional advantage of the Altaire is seen with T1 imaging, as relative T1 contast of

nonfatty tissue is better discriminatedat 0.7 T than at 1.5 T.

The open vertical-fi eld geometry of the Altaire, coupled with its solenoid volume coil design, provides another advantage in musculoskeletal imaging. The volumetric application of the solenoid coil in the vertical-fi eld orientation of the Altaire results in a higher uniformity of image signal-to-noise ratio (SNR) when compared with images achieved with conventional high-fi eld closed MR systems and solenoid-type coils (see fi gure on page 5). When the fi eld orientation is horizontal, the design of solenoid coils is less effi cient. In our opinion, the uniformly high SNR obtained with the Altaire, an advantage of the system’s vertical-fi eld architecture, produces an image quality that surpasses expectations for a fi eld strength of 0.7 T.

Freedom of lateral positioning within the magnet is also an advantage for musculo-skeletal imaging. For any open MR system, the side-to-side movement of the table allows the body part of interest to be imaged at, or very close to, the magnet isocenter. Imaging at the isocenter takes advantage of the most homogeneous magnetic fi eld,

Figure 1. The positioning advantage of open architecture. The Altaire readily allows for true positional isocenter imaging, as seen in this schematicfor a shoulder study.

Gen J. Maruyama Musculoskeletal techniques and studies with the Altaire® high-fi eld open MR system

Open Bore




also optimizing uniformity of SNR. Patients presenting for certain examinations, like those of the wrist and elbow, can be imaged with their arms by their sides, significantly increasing patient comfort and cooperation, while the body part of interest is placed at the magnet isocenter. For shoulder imaging in particular, the wide table and lateral access of the Altaire make possible the achievement of isocenter without compromise (Figure 1) and increase the comfort of the abduction-external-rotation (ABER) position.

At the field strength of 0.7 T, the relative precession rates between fat and water protons can be distinguished, allowing for true chemical fat suppression. In contrast, most open systems with lower field

strengths make use of the Dixon method to obtain fat suppression.

High-field open imaging of the knee

The knee is perhaps the easiest of all the musculoskeletal structures to image, and solenoidal coils are extremely efficient. But detection of pathology can be far more difficult: Meniscal tears, ligamentous and tendon pathology, and cartilage defects can be subtle lesions. The utility of true chemical fat suppression by the Altaire offers a diagnostic advantage for orthopedic imaging over most lower field strength open MR imaging. Indeed, because of the quality of the magnetic field in the Altaire, there is a

limited need for sagittal gradient-echo scans for detecting and evaluating meniscal tears.

Our standard protocol for imaging the knee with the Altaire calls for proton-density-weighted (PD) and proton-density fat-suppressed (PD fatsat) scans in the axial, coronal, and sagittal planes. Obtaining PD fatsat images in exactly the same locations as PD images allows for comparison betweenthese images and increased conspicuity of pathologies with T2 prolongation — such as meniscal tears, ligament and tendon pathology, osteochondral injuries, and edema. Figures 2 to 6 demonstrate thefine detail of images — particularly those with fat suppression — achieved withthe Altaire.

Figure 2. Sagittal proton-density-weighted (PD) (Figure 2A) and PD fat-suppressed (Figure 2B) images of a high-grade sprain of the anterior cruciate ligament (ACL) (arrow). A thickened, amorphous appearance of the ACL is seen with increased intrasubstance signal. The ACL was brought into the sagittal plane by externally rotating the knee 10 to 15 degrees of external rotation within the knee coil.

Figure 3. Sagittal proton-density-weighted (PD) (Figure 3A) and PD fat-suppressed (Figure 3B) images of a complete tear of the posterior cruciate ligament (arrow). The joint effusion and debris within the fluid are compatible with a diagnosis of synovitis.

Figure 2A

Figure 3A

Figure 2B

Figure 3B




Figure 4. Coronal proton-density-weighted (PD) (Figure 4A) and PD fat-suppressed (Figure 4B) images of a complete tear of the proximal medial collateral ligament (arrow). A high-grade sprain of the anterior cruciate ligament and a tear of the medial meniscus are also visible. In Figure 4B, there is mild reactive hyperemia along the peripheral aspect of the medial tibial plateau.

Figure 5. Sagittal proton-density-weighted (PD) (Figure 5A) and PD fat-suppressed (Figure 5B) images of a full-thickness chondral defect (grade 4) involving the midtrochlear groove (arrow). Figure 5B shows the deep subcortical reactive hyperemia from the chondral defect. There is also a chondral defect (grade 3 to 4) involving the inferior patellar articular surface.

Figure 6. An axial proton-density-weighted fat- suppressed image of subcortical edema/reactive hyperemia along the lateral patellar facet. The image is of a postero-medial and postero-lateral corner injury, with bone-marrow edema involving the posterior medial and lateral tibial plateau(arrow). Injury to the anterior cruciate ligamentand synovitis are also visible.

Gen J. Maruyama Musculoskeletal techniques and studies with the Altaire® high-field open MR system

Figure 5A

Figure 4A Figure 4B

Figure 5B

Figure 6




High-field open imagingof the ankle

Our standard protocol for imaging the ankle with the Altaire also involves PD and PD fatsat scans in the axial, coronal, and sagittal planes. The ankle is usually imaged unilaterally for smaller field-of-view imaging. Although many of the tendons can be identified in the sagittal plane, axial images are most useful in identifying tendon pathology, especially when differentiating partial- from full-thickness tears.

In cases of trauma, short-tau-inversion-recovery (STIR) scans are complementary and present edema changes very homogeneously. Figure 7 shows axial images of normal ankle anatomy, and Figure 8 shows coronal images of a posterior tibial tendon tear.

Figure 7. Axial proton-density-weighted images of (Figure 7A) normal ligamentous anatomy and (Figure 7B) normal tendon anatomy of the ankle. In Figure 7A, normal anterior talofibular (1), posterior talofibular (2), and deltoid (3) ligaments can be seen. In Figure 7B, the normal posterior tibial (4), flexor digitorum longus (5), flexor hallicus longus (6), peroneus brevis (7), and pero-neus longus (8) tendons can be seen along the posterior aspect of the ankle. A normal Achilles tendon (9) can also be identified.

Figure 8. Coronal proton-density-weighted (PD) (Figure 8A) and PD fat–suppressed (Figure 8B) images of a partial posterior tibial tendon tear (arrow). Intrasubstance degeneration and edema are visible in the surrounding soft tissues.

Figure 8A

Figure 7A

3

2

1

Figure 7B

4

5

6 78

9

Figure 8B




Figure 9. Spin-echo T1-weighted images in the axial plane (Figure 9A), oblique sagittal plane (Figure 9B), and abduction external rotation position after intra-articular administration of dilute gadolinium (Figure 9C) demonstrate an anterior labral periosteal sleeve avulsion injury (arrows).

High-field open imagingof the shoulder

Our standard protocol for imaging the shoulder with the Altaire employs PD scans and PD fatsat scans in the oblique sagittal and oblique coronal and axial planes. If intra-articular or intravenous gadolinium is administered, the MR arthrography protocol sequence changes to T1-weighted scans followed by PD fatsat scans in the axial, oblique sagittal, and oblique coronal planes. The ABER position is added to the protocol if intra-articular gadolinium is administered.

Administering intra-articular gadolinium distends the shoulder joint and increases the conspicuity of labral pathologies. There are four common indications for using intra-articular gadolinium in shoulder imaging. We prefer MR arthrography if the patient is under 40 years of age, if the

shoulder is postoperative, if there is concern for adhesive capsulitis, or if there is suspicion of microinstability that is difficult to diagnose both clinically and radiographically. When intravenous gadolinium is administered, the standard protocol calls for spin-echo T1-weighted scans followed by PD fatsat scans in three orthogonal planes. In patients for whom motion artifacts are problematic, ABER positioning early in the imaging sequence may result in better patient compliance. With ABER positioning, one can view the footplate of the supraspinatus muscle attachment site and the undersurface of the tendon. One can also possibly see fluid entering the tear.

Figure 9 shows an anterior labral periosteal sleeve avulsion injury. Figures 10 and 11 show superior labral injuries that extend from anterior to posterior (aka, SLAP tears). Figure 12 shows a tear of the distal supraspinatus tendon.


Figure 9A Figure 9C

Figure 9B




Figure 10A. An oblique coronal spin-echo T1-weighted image, after intra-articular administration of dilute gadolinium, of a superior labral tear (1) with contrast extending into the superior labrum tear at its glenoid attachment. Figure 10B. A spin-echo T1-weighted image, after intra-articular administration of dilute gadolinium, in the abduction external rotation position of a labral injury (2) extending into the anterior superior labrum adjacent to the attachment of the supraspinatus tendon to the greater tuberosity (3).

Figure 11. Axial spin-echo T1-weighted (Figure 11A) and spin-echo proton-density fat-suppressed images (Figure 11B), after intra-articular administration of dilute gadolinium, of a superior labral tear extending anterior to posterior (arrows). The fluid within this tear is clearly delineated.

Figure 12. Coronal proton-density-weighted (PD) (Figure 12A) and oblique sagittal PD fat-suppressed (Figure 12B) images of a partial-thickness articular-sided rotator-cuff tear of the distal suprapinatus tendon (arrows). A small joint effusion is present. In Figure 12B, there is increased conspicuity of the partial thickness tear.

Figure 10A

1

Figure 10B

3

2

Figure 11A Figure 11B





Figure 13. Sagittal spin-echo T1-weighted (Figure 13A) and T2-weighted (Figure 13B) images of a normal cervical spine.

Figure 14. A sagittal fast spin-echo T2-weighted image (Figure 14A), and an axial two-dimensional gradient-echo image through C5 and C6 (Figure 14B), showing a left paracentral/foraminal disk extrusion (1) with flattening of the left paracentral ventral cerebrospinal fluid (2).

High-field open imagingof the cervical spine

Our standard protocol for imaging the cervical spine with the Altaire employs spin-echo T1-weighted scans in the sagittal plane, fast spin-echo T2-weighted scans in the sagittal plane (excellent for seeing intrinsic cord pathology and lesions), and two-dimensional (2D) gradient-echo scans in the axial plane. Alternatively, a three-dimensional (3D) axial gradient-echo scan can be used, allowing for the acquisition of a thinner slice than the 2D technique due to the elimination of interslice cross-talk with a volumetric acquisition. However, since the 3D data are collected as a data volume rather than as individual slices, any motion artifact that occurs during screening will be propagated throughout the data set. Two-dimensional imaging allows the technologist to repeat only those slices

in which motion may have occurred. Therefore, patient selection becomes the most important parameter for our decision to use 2D or 3D axial imaging.

As alternatives to the above sequence, we sometimes perform a fast spin-echo T1-weighted scan in the sagittal plane to further decrease image acquisition time, a STIR scan in the sagittal plane (for evaluation of trauma, infection, or metastasis), or a T1- or T2-weighted scan in the axial plane when a metallic artifact is present, as the susceptibility artifact will be less prominent thanon standard gradient-echo images.

Figure 13 shows the normal cervical spine. Figure 14 displays a paracentral disk extrusion. Figure 15 shows a posttraumatic fracture through the anterior inferior C5 vertebra.



Figure 14A

1

Figure 14B

2




References

1. Stoller D. Magnetic Resonance Imaging in Orthopedics and Sports Medicine. Philadelphia: Lippincott-Raven; 1997.

2. Mitchell DG. MRI Principles. Philadelphia: WB Sanders Co; 1999.

Figure 15. Sagittal short-tau inversion-recovery images (Figure 15A and 15B) of a posttraumatic fracture through the anterior inferior C5 vertebral body. There is rupture of both the anterior and posterior longitudinal ligaments (arrows). Soft-tissue hematoma is seen in the paraspinal soft tissues of the upper cervical spine.

Summary

Recognizing the quality of the musculoskeletal images achieved with the Altaire is a first step toward acknowledging that the Altaire offers a welcome new third way of MR imaging. The demands that musculoskeletal imaging places on the Altaire are easily and readily met. In particular, the Altaire possesses several advantages over high-field closed MR systems: The open architecture allows for freedom of positioning and direct isocenter imaging, there is stronger relative T1 contrast, and there is better uniformity of SNR.

Acknowledgment

The author wishes to thank Mary Moncilovich-Greer, RT(R)(MR), CRT, lead MRI technologist at Mission Regional Imaging Center, for her expertise in perfecting our standard musculoskeletal protocols forthe Altaire.





Vascular Imaging Sequences

• RSSG: RF Spoiled SARGE (Steady-state Acquisition Rewinded Gradient Echo) —a dynamic 2D or 3D T1-weighted gradient-echo pulse sequence in which the T2 weighting is spoiled by an RF pulse. Dynamic RSSG acquisitions are used in conjunction with MR contrast media to obtain contrast-enhanced (CE) MRA studies.

• TOF: Time of Flight — 2D and 3D time-of-flight imaging is based on the RSSG pulse sequence and takes advantage of very short repetition time (TR) and time to the echo (TE) to image flowing blood within an anatomical region, without the use of contrast media. The background (stationary) spins are saturated by repetitive RF pulses, while the spins from flowing blood remain unsaturated and therefore exhibit a higher relative signal intensity.

• CEMRA k-space filling techniques

Sequential: k-space is filled sequentially,from bottom to top.

ADA: Asymmetric Data Allocation — the center of k-space filled at the beginning of the acquisition. ADA incorporates the use of half scan or three-quarter scan; therefore, choosing ADA decreases scan time.

PEAKS: PEak Artery enhancing K-space filling Sequence — 3D k-space divided into central, peripheral, and unsampled segments. The user selects the size of the unsampled segment relative to the fully sampled segments and whether to use zero filling or conjugation. During the acquisition, the prepeak phase is used to fill the peripheral segment adjacent to the unsampled segment. The central portion ofk-space is then acquired at peak arterial phase. The postpeak phase is used to fill most of thek-space periphery.

RPEAKS: Reverse PEak Artery enhancingK-space filling Sequence — a variation of the PEAKS filling method. In this variation, the postpeak phase is collected adjacent to the unsampled segment, while the prepeak phase is used to fill most of the k-space periphery.

Neurological imaging sequences

• SE with MTC: Spin Echo with Magnetization Transfer Contrast — a classic spin-echo pulse sequence with the addition of the MTC protocol parameter. MTC accentuates the image contrast produced by the magnetization transfer from bound water to free water.

• GE with MTC: A classic gradient-echo pulse sequence incorporating the MTC protocol parameter. MTC accentuates the image contrast produced by the magnetization transfer from bound water to free water.

• DE-FSE: Driven Equilibrium Fast Spin Echo —a fast spin-echo technique in which the residual magnetization is forced back to equilibrium by utilizing additional 90- and 180-degree RF refocusing pulses prior to each successive excitation. DE-FSE may be acquired with proton-density or T2 weightings.

• DE-FLAIR: Driven Equilibrium Fluid-Attenuated Inversion Recovery — a T1- or T2-weighted acquisition that utilizes a specific inversion time (TI) to null the signal from CSF.

• T2* GE: T2* Gradient Echo — a gradient-echo pulse sequence utilizing a relatively small flip angle to maximize signal from blood and blood products.

• DWI with RF fat sat: Diffusion-Weighted Imaging with RF fat saturation — DWI technique that detects minute differences in water-molecule movement by applying large gradient lobes or motion-probing gradients (MPGs) on opposite sides of the 180-degree RF pulse. The addition of fat saturation to the acquisition prevents artifacts from fatty tissue from appearing on the images.

• BASG: Balanced SARGE (Steady-state Acquisition Rewinded Gradient Echo) —2D and 3D BASG pulse sequence employing gradient rewinder lobes to preserve transverse and longitudinal magnetization components. The sequence employs very short TR and TE times. This is a mixed-contrast (T1/T2) sequence; fluid is bright, with the remainderof the tissues retaining their T1-weighted signal intensity.

• ADC trace maps: Apparent diffusion coefficient trace maps — postprocessed trace images that reduce T2 shine through.

Glossary of abbreviations Glossary of abbreviations

Breast imaging sequences

• DE-FSE: Driven Equilibrium Fast Spin Echo —a fast spin-echo technique in which the residual magnetization is forced back to equilibrium by utilizing additional 90- and180-degree RF refocusing pulses prior tothe next excitation. DE-FSE may be acquired with proton-density or T2 weightings.

• STIR: Short-Tau Inversion Recovery —an inversion-recovery pulse sequence that utilizes an inversion time such that signalfrom fat is suppressed.

• 3D RSSG: RF Spoiled SARGE (Steady-state Acquisition Rewinded Gradient Echo) —a dynamic 3D T1-weighted gradient-echo pulse sequence in which the T2 weighting is spoiled by an RF pulse. The pulse sequence is typically acquired once precontrast and then at predefined intervals postcontrast. The dynamic data sets can be subtracted from one another, and/or the data from a region of interest (ROI) can be plotted graphically to aid in diagnosis.

Musculoskeletal imaging sequences

• PD FSE with RF fat sat: Proton Density-weighted Fast Spin Echo with RF fat saturation — a classic fast spin-echo technique with proton-density weighting, with the additionof RF fat saturation to suppress signal from fatty tissue.

• STIR: Short-Tau Inversion Recovery — an inversion-recovery pulse sequence that utilizes an inversion time such that signal from fat is suppressed.

• SE with RF fat sat: A classic spin-echo pulse sequence with the addition of RF fat saturation to suppress signal from fatty tissue. Often used after intra-articular injection of a diluted MR contrast agent.

• SARGE: Steady-state Acquisition Rewinded Gradient Echo — a T2*-weighted gradient-echo pulse sequence in which the transverse magnetization is refocused before the nextTR with gradient rewinder lobes.


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