Musculoskeletal Examination with MRI

Steven J. Gould, D.C., D.A.C.B.R. Central Plains Radiologic Services,

P.A.

Magnet

Magnetic strength measured in Tesla. MRI units in High, Mid and Low field strengths

High field – 1 Tesla and above Mid field - .3 – 1.0 Tesla Low field – below .3 Tesla

1 Tesla = 10,000 gauss (20,000 Xs earth’s magnetic pull)

earth’s magnetic pull = .3 gauss at equator and .7 gauss at the poles.

Parts of the MRI unit

Fonar upright

Types of Magnets; Super-conducting magnets - generally high

field, up to 8 Tesla. Most medical imaging with this type of magnet is done with 1 or 1.5 Tesla. Newer 3 Tesla units are now in use.

Liquid helium and nitrogen cooled. Narrow gantry or bore.

Problems with claustrophobia Building requirements are more costly Signal to noise ratio is higher for more

detailed images, but also artifacts are more difficult to contend with.

Images from 3T MRI

Resistive magnets - mid and low field strengths up to .4

Tesla. Based on electromagnets. Produce heat and need a coolant as

well.

Installation of magnetic core weighing 52,000 lbs.

Permanent magnets - solid magnet, like a magnet that we

usually think of. No outside power source needed. Low field strengths because too

heavy to make big enough to go over .3 Tesla.

MRI Magnetic Strength Example of MRI strength: Tennis Ball http://www.youtube.com/watch?v=V9UJ6JAeVuE&featu

re=related

Pallet Jack in the bore!

Oxygen Bottle and Watermelon http://www.youtube.com/watch?v=_lBxYtkh4ts&NR=1

MRI Magnetic Strength

Chair http://www.youtube.com/watch?v=

4uzJPpC4Wuk&feature=related

CT Scanner motion: http://www.youtube.com/watch?v=2CWp

ZKuy-NE&feature=related This is a C.T. scanner and NOT an MRI

scanner. Both units do have the smooth covering. MRI gantry/bore is “deeper”. C.T. gantry is “shorter”

Physics in brief:

Before being in the magnet all of the patient’s hydrogen atoms (unbound) are spinning like little planets or tops, but the orientation of each atom’s axis is randomly oriented compared to the others. When the patient is placed in the magnet, their hydrogen atoms will become aligned with the magnetic field, and some against or opposite (this will cause some of the charges to cancel). However, there is always a majority of atoms that align with the magnetic field. The atoms are not only spinning like planets but they actually have a wobble like a slowing top (precession).

AAPM/RSNA Physics Tutorial for Residents; Fundamental Physics of MR Imaging1 Robert A. Pooley, PhD, RadioGraphics 2005; 25:1087–1099 ● Published online 10.1148/rg.254055027 ●

The wobbling or precession is randomly oriented, even in the initial magnetic field. So we add a radio frequency to the magnetic field, the frequency of the RF is at the same frequency as the wobble or precession of the atoms and they then start wobbling together or come into phase. The RF also pulls the axes of the spinning atoms off of alignment with the magnetic field through energy that is imparted to them.

When the RF pulse is turned off the atoms lose their coherence or phase and give off energy (or a signal) because they release the energy imparted to them by the previous RF pulse. This signal is measured and can then be converted to a picture. Different tissues will permit the atoms to move back to the original magnet field alignment at different speeds or time frames. This is how fat can look different than blood or water on the image. Cortical bone has, essentially no unbound hydrogen atoms, so no signal is given off and therefore cortical bone is black.

Absorption of RF energy. Left: Prior to an RF pulse, the net magnetization (small black arrow) is aligned parallel to the main magnetic field and the z axis. Center and right: An RF pulse at the Larmor frequency will allow energy to be absorbed by the protons, thus causing the net magnetization to rotate away from the z axis.

AAPM/RSNA Physics Tutorial for Residents; Fundamental Physics of MR Imaging1 Robert A. Pooley, PhD, RadioGraphics 2005; 25:1087–1099 ● Published online 10.1148/rg.254055027 ●

Gradient system

-Three gradient coils (X,Y, and Z) -Gradient coils are electronically

controlled to determine the plane (sagittal, coronal, or oblique) of the image to be made.

Rapid switching off and on of electricity in the coils causes the coils of wire to vibrate within their plastic housing, causing the tapping/knocking sounds.

RF system -Radio Frequency Antennas (known as coils),

commonly function as both transmitters and receivers for the radio frequency.

-RF used is dependent on the strength of the

magnetic field and the Larmor frequency of the target atoms. -Hydrogen is used and has a precession frequency of... 42 MHz at 1.0T 64 MHz at 1.5T).

-TV and Radio-stations can interfere with MR signal

and shielding must be used.

Coils Head Coil Shoulder Coil Body Coil Knee Coil

Additional components 1. Computer system

2. Operating and evaluation console 3. Documentation system

Longitudinal (T1) relaxation time. Application of a 90° RF pulse causes longitudinal magnetization to become zero. Over time, the longitudinal magnetization will grow back in a direction parallel to the main magnetic field.

AAPM/RSNA Physics Tutorial for Residents; Fundamental Physics of MR Imaging1 Robert A. Pooley, PhD, RadioGraphics 2005; 25:1087–1099 ● Published online 10.1148/rg.254055027 ●

T1-weighted contrast. Different tissues have different rates of T1 relaxation. If an image is obtained at a time when the relaxation curves are widely separated, T1-weighted contrast will be maximized. Mag magnetization. •FAT has short T1 relaxation. (gives off signal quickly.) •WATER (CSF) has long T1 relaxation (gives off signal more slowly).

Sample time.

T1 = Relaxation time constant

T1 describes the re-growth of the longitudinal magnetization over time and its return to equilibrium following the RF pulse. (Toy tops getting taller after being knocked down by RF pulse). Also known as spin-lattice relaxation.

Different types of tissues have different relaxation times. This is key to the sharp image contrast obtained with MR. (T1 weighted image shows the results of atoms that are contrasted with the T1 relaxation, with fluid being black and fat being bright white).

T2 = Spin-Spin interaction T2 relaxation time (spin spin relaxation time or transverse relaxation time)

Transverse magnetization. When the RF pulse is turned off, the spinning atoms re-

align to the magnetic field, and get taller (T1 relaxation) but at the same time the width of their rotation is getting smaller (wide arc of a fallen but still spinning top). T2 is more about the relation between adjacent

atoms, because when the RF pulse is turned off then the coherence (all spinning in the same manner) is also stopped (dephasing) and the atoms start to wobble out of phase again. Different tissues respond differently.

T2-weighted contrast. Different tissues have different rates of T2 relaxation. If an image is obtained at a time when the relaxation curves are widely separated, T2-weighted contrast will be maximized. Mag magnetization.

Water (CSF) has long T2 relaxation (slower loss of signal)

White matter has short T2 relaxation (quick loss of signal)

T2 continued.

This signal gets weaker with time and eventually dies out. In solids the atoms are affected by the magnetic fields of near by atoms and therefore the T2 signal is short.

In fluids, the atoms are less affected by near by magnetic field fluctuations and there is a longer T2 signal (so they give off more signal before they become under the influence of adjacent atoms) (why water is white on T2).

Pulse sequence diagram

A pulse sequence diagram can be used to show the relative timing of certain events during an MR imaging acquisition. The timing of RF pulses, the signal formed from these pulses, and the digitization of the signal is shown. TE is shown as the time to the

echo, and the repetition time (TR) is shown as the time it takes to go through the pulse sequence once. This pulse sequence uses a 90° RF pulse with a 180° RF pulse to rephase spins to form an echo. T1- and T2-weighted images may be created with this pulse sequence. ADC analog-to-digital converter; in all pulse sequence diagrams, G gradient.

SPIN ECHO: …”If a proton experiences a local increase in magnetic

field strength that is not experienced by a neighboring proton, it will precess faster than its neighbor. Because this imperfection in the magnetic field is constant, the proton will always spin faster than its neighbor. Prior to the 180° RF pulse, the proton spins faster “away” from its neighbor. After the 180° RF pulse, the spins are “flipped” and their directions can be thought to be reversed, so that now the faster proton is “behind” its neighbor and can “catch up” to its neighbor because it is still spinning faster. On the other hand, spin-spin interactions are random interactions between protons that cause random local changes in the magnetic fields experienced by the protons, and this causes dephasing. Because this is a random process, dephasing due to this effect cannot be reversed”….

AAPM/RSNA Physics Tutorial for Residents; Fundamental Physics of MR Imaging1 Robert A. Pooley, PhD, RadioGraphics 2005; 25:1087–1099 ● Published online 10.1148/rg.254055027

TE is the time between the peak of the 90° RF pulse and the peak of the echo that is formed.

Note that the 180° RF pulse occurs at half of the echo time TE.

TR is the time that it takes to run through the pulse sequence one time.

1 time through the pulse sequence will produce one row of raw data. Must run through the pulse sequence as many times as needed to produce all rows required to make an image. For image matrix of 256 X 256 pixels we must repeat the pulse sequence 256 times for one image.

Imaging Sequences

Various imaging sequences are used to manipulate image appearance and tissue contrast by taking advantage of proton responses to RF signals within the Magnetic field. Common sequences in spinal and musculoskeletal imaging include:

Spin Echo Fast Spin Echo (Turbo spin echo) Proton Density Gradient Echo Inversion Recovery and/ or Fat Saturation

Imaging Sequences Spin Echo: T1 image = Short TE and Short TE TR <800msec ; TE <30msec

Multiecho spin-echo pulse sequence.

Proton Density = Short TE (TE1) and Long TR T2 image = Long TE (TE2) and Long TR

Imaging Sequences Tissue Signal Intensity T1 and T2 Fat Subacute hemorrhage Proteinaceous fluid

Fluid Fibrous tissue/scar or Cortical bone Chronic hemorrhage/ hemosiderin Air

Musculoskeletal MRI: Kaplan, Helms, Dussault, Anderson, Major: pub; Saunders 2001 page 6

Proton Density and T2 TR >1000msec TR >2000msec TE <30msec TE >60msec

Imaging Sequences

Turbo Spin Echo (also known as Fast spin echo)

This sequence uses a 90° RF pulse with multiple 180° RF pulses. Multiple echoes are formed, and the data are used to create a single data set. Multiple rows of raw data are filled during one TR period; this feature allows the pulse sequence to be run fewer times, thus saving imaging time.

This configuration is known as an “Echo Train”. This “train of 4 would reduce scanning to ¼ the original. Echo Train lengths of 8 and 16 are also used.

Fast spin echo: shows fat as bright signal Standard “second echo” T2 shows fat as

intermediate signal - Fluid remains Bright on both FSE and T2

Turbo Spin Echo (also known as Fast spin echo)

Gradient echo (AKA – T2*W) (TR Variable ; TE <30msec ; Flip Angle = 10 – 80 degrees) Used to decrease time to get T2 weighted

image Fluid is bright white Ligaments, cartilage, menisci, and labrum are well

shown. Susceptibility effects – accentuate differences at

tissue interfaces and show hemorrhage and hemoglobin breakdown. (iron in hemoglobin is low signal)

Drawback: over estimates the size of osteophytes Artifacts from metallic hardware can obscure near

by anatomy

Imaging Sequences

Gradient Echo Sequence

Imaging Sequences

Figure 1: An axial gradient-echo T2 weighted image (a) performed within one week of first presentation demonstrates a large hematoma in the left thalamic region. An axial spin-echo T2 weighted image (b) performed 14 weeks later demonstrates the resolving hematoma with no surrounding edema or other features to suggest an underlying tumor. The Internet Journal of Neurosurgery 2009 : Volume 5 Number 2

T1 and GR T2*. Left uncinate process hypertrophy

Imaging Sequences

IR and Fat Saturation

Imaging Sequences

Initial Scan- Fat Sat and follow-up IR 3 months later. Note resolution of bone contusion

Spin Echo T1 - FSE T2 - IR TE 25 / TR 350 TE125/ TR 3500 TE 25/TR 3600

Imaging Sequences

Acute/ active L3 Pedicle edema and pars fx

Biologic Effects:

No known long term effects. Some high field magnets have increased core body temperature with prolonged exposures. Scrotal warming in guinea pigs has been documented. (~4 T at research and development centers).

INDICATIONS:

Spinal disc disease- MRI has become the "gold standard"

Spinal cord- injury, neoplasm, infection, congenital,

and acquired lesions.

Extremities- muscle, ligament, menisci, joints, neoplasm, infection.

CNS/Brain- neoplasm/ organic disease, infection, trauma--hematoma.

Infection disc protrusion DDD

Indications continued…

Trauma: Limited MRI scan: scan only the region of

highest suspicion for fx, bone bruise etc...

MRI is more sensitive than C.T. for bone marrow edema.

MRI demonstrates soft tissues and can evaluate hyperflexion/ hyperextension (ligamentous) injuries. T2 weighted sagittal scan is done to show water (edema and hemorrhage).

Tear drop fracture with ligament tearing and hemorrhage. (MVC pt)

Supraspinatus tendon tear (farming injury)

Contraindications to MRI Large patients over 300 lbs (for conventional gantry

units). Some open units will accommodate patients ~450

lbs. Claustrophobic patients. 5-30% of patients, some

degree. Children and claustrophobic patients may need to be

sedated. Aneurysm clips (especially at the circle of Willis) Intra-occular foreign bodies (Welders, sheet metal workers, etc...)

Contraindications continued…

Subcutaneous metal shards / Shrapnel Cardiac pacemakers or defibrillators Implanted TENS (neurostimulators) Prosthetic heart valves (mitral) Cochlear Implants/ hearing aids Tattooed eyeliner and other make-ups

(cosmetics). First trimester of pregnancy Life support equipment Penile implants

Contraindications continued…

Most surgical clips now being used are non-ferromagnetic and do not prevent MRI.

Examples; Vasectomy Vagotomy Tubal ligation Lymph node resection Splenectomy Cholecystectomy Sympathectomy.

Contraindications continued. Joint prosthesis, Harrington rods, and most

orthopedic appliances are not contraindications to MRI. Pedicle screws with spinal surgery. Wait 6 weeks before another MRI can be done, so that screws have securely healed into the bone.

Some devices depend on scanner strength (strength of magnetic field) to be contraindicated or not.

Only direct indication to do MRI during pregnancy is if mother's life is at risk.

Artifacts Post-surgical arthrodesis: Pedicle screws Black artifacts noted in both planes.

Artifacts Close up images. Post-surgical arthrodesis with pedicle screws Psoas Abscess

Contrast Agents

Indications for contrast enhancement

Prior spinal surgery in the region of interest; Specifically to differentiate new vs.

recurrence disc herniation. Infections Tumors; certain tumors Vascular

T.B.

Axial T1 Sag. IR Axial T1 + C Axial T2

Complications with Gado.

Nephrogenic Systemic Fibrosis NSF leads to excessive formation of

connective tissue in the skin and internal organs. NSF is progressive and may be debilitating or fatal.

Complications with Gado.

Gadiolinium Contrast agent Risk of Nephrogenic Systemic Fibrosis With use in patients with Renal Disease Usually history of Dialysis Tx. Usually Middle aged (children and

elderly have been reported). Initially seen in 1997 and first

characterized in 2000. >250 reported cases by Sept 2007. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2007/uc

m108919.htm

Complications with Gado.

More than 90% of proven nephrogenic systemic fibrosis cases are related to;

gadodiamide (Omniscan) gadopentetate (Magnevist) gadoversetamide (Optimark).

Thomsen, http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncem

ents/2007/ucm108919.htm

Complications with Gado.

NSF symptoms include one or more of the following:

burning and/or itchy skin hardened, darkened, shiny skin tight, sensitive skin that may be painful to the

touch loss of joint flexibility joint pain (particularly deep pain in the hips or

ribs) impaired movement muscle weakness yellowed eyes

www.medscape.com/viewarticle/568775_3

Skin changes of NSF in patient before

(A, C and E)

and

after kidney transplant

(B, D and F).

emedicine.medscape.com/article/1097889-overview

Nephrogenic fibrosing dermopathy on the abdomen, demonstrating a peau d'orange appearance. Keloid scar in mid abdomen is present from a prior surgery.

Spine:

Neoplasms: A. Primary Intramedullary Ependymoma Astrocytoma Metastases Intradural Meningioma Neurinoma Neurofibroma Lipoma Metastases

Giant Cervical Intraspinal Schwannoma: A Case Report. The Internet Journal of Spine Surgery 2007 : Volume 3 Number 1

Spine continued.

Extradural Mets. Teratoma Epidermoid Lymphoma Lipomatosis or lipoma Other Arachnoid cyst Chordoma Pseudotumor

Spine continued. Presacral Masses

Teratoma Meningocele Hematoma Metastases or recurrent colonic neoplasm Fibrosis B. Metastatic Extradural Intradural

T1 Sag. L.spine / Mets.

The Internet Journal of Pediatrics and Neonatology 2009 : Volume 10 Number 1

Cervical meningocele with tethered cord in a seven-years old child: Case Report

Mehmet Senoglu MD Assist. Prof. Department of Neurosurgery KSU Medical School Kahramanmaras Turkey

Zeki Yilmaz MD Resident Department of Neurosurgery KSU Medical School Kahramanmaras Turkey

Citation: M. Senoglu & Z. Yilmaz : Cervical meningocele with tethered cord in a seven-years old child: Case Report. The Internet Journal of Pediatrics and Neonatology. 2009 Volume 10 Number 1

Cervical meningocele with tethered cord in a seven-years old child: Case Report

Spine continued.

C. Spinal Cord Atrophy

Hemiatrophy Anterior Atrophy Posterior and diffuse atrophy

Myelomalacia Hydromyelia and Syringomyelia

Spinal Trauma

Acute Fracture Cord Contusion Cord Transection Hematomyelia Subdural or Epidural Hematoma

Vertebroplasty @ L2– L4 --

TX for comp fx at L3.

Spine continued…

Chronic Stenosis Microcystic and Macrocystic Myelomalacia Atrophy Cord Fissure Pseudotumor Pseudomeningocele Epidermoid

Spinal discs

Discs Herniation: Imaging method of choice for degenerative disc disease and disc derangement. Recurrent Disc vs. scar tissue in the Post Op. patient.

Gadolinium contrast is used to enhance the vascular scar tissue, whereas the avascular herniated disc tissue should not enhance.

FIG 1. Axial view images of a patient with surgically confirmed recurrent herniated disk.

D, Obtained 5 min after the administration of contrast medium. Placement of cursor to measure recurrent disk (1) and scar (2) enhancement. Contrast ratio between scar and recurrent disk fragment is greater at 5 min than at 50 min.

TABLE 1: Contrast enhancement in recurrent disk fragment and scar after IV injection of ionic and nonionic contrast media

AJNR: 25, June/July 2004 SCAR VERSUS RECURRENT DISK

C, Obtained 50 min after

B, Obtained 5 min after the administration of contrast. A, Obtained before the administration of gadopentetate dimeglumine (0.1 mmol/kg).

Spine continued…

Multiple Sclerosis A-V Malformation Arachnoiditis (pseudocord sign, empty cord sign, and giant root sign) Osteomyelitis Congenital Anomalies Vertebral Hemangioma Bone and fat islands Rheumatoid arthritis Craniocervical junction anomalies Spinal dysraphisms

Shoulder; Rotator Cuff

evaluation, tear vs. tendonopathy

Glenoid labrum evaluation

Biceps tendon abnormalities

Impingement syndrome

Elbow:

Degenerative joint disease Intracapsular loose bodies Ligaments (collateral ligaments) Biceps and triceps muscle ruptures Lateral and medial epicondylitis

Coronal IR- MRI of elbow , midsubstance UCL tear (yellow arrow).

Wrist:

Degenerative joint disease Scaphoid or Lunate avascular necrosis Carpal tunnel syndrome Tumors Ganglion cyst Hemangioma of the wrist Intercarpal ligaments

http://afni.nimh.nih.gov/sscc/staff/rwcox/ISMRM_2006/Syllabus

Keinbock’s disease’ - AVN Luncate

Hip:

Avascular necrosis Stress fractures Degenerative joint disease Synovitis Infections Metastatic disease Prosthesis

Knee:

Degenerative joint disease and Chondromalacia patella

Meniscal injuries; MR is modality of choice for degenerative changes or tear.

Ligamentous injuries: medial and lateral collateral ligaments, and anterior and posterior cruciate ligaments.

Tendon injuries: Patellar tendon, quadriceps tendon.

Joint capsule assessment

Knee continued.

Baker's Cysts and Meniscal cysts Intra-articular loose bodies Bone bruise following trauma Osteochondritis dissecans Infectious arthritis Prosthesis

Ankle and Foot:

Achilles tendon tear / tendonitis / tendonopathy

Ligament and tendon assessment Soft tissue masses Ganglion cysts Osteomyelitis Avascular necrosis Osteochondritis dessecans

MRA

Carotid Artery disease Atherosclerosis

Vertebral arteries/ Basilar artery Intracranial

Aneurysm AV Malformation Occlusive disease Arterial Venous

Cervical spine MRA

Breast

Carcinoma This case has

carcinoma in right breast

Implant evaluation

Implant eval for leakage

No leak found

The End