Analysis of myocardial motion based on velocity measurements with a black blood prepared segmented gradient-echo sequence: Methodology and applications to normal volunteers and patients

Original Research

Analysis of Myocardial Motion Based on Velocity Measurements with a Black Blood Prepared Segmented Gradient-Echo Sequence: Methodology and Applications to Normal Volunteers and Patients

Juergen Hennig, PhD Britta Schneider, MD Simone Peschl Michael Mark1 Thomas Krause Jorg Laubenberger, MD

The paper describes a strategy for measuring and characterizing myocardial motion in terms of velocity parameters derived from measurements with a segmented black blood prepared phase contrast gradient echo sequence. The characteristic parameters are calculated by transforming the velocities measured on a pixel-by-pixel basis across the left ventricle from the laboratory frame of reference into a cylindrical coordinate system, in which the motion velocities within the short axis plane are represented in polar coordinates and which is located at the center of the myocardium and moving with it over the ECG cycle. First results in a study with 12 healthy volunteers gave highly consistent values for the radial (expansion/ compression) as well as the rotational velocities. Ex- cept for one volunteer, motion at the R wave of the ECG starts with clockwise rotation, followed by contraction and expansion accompanied by counterclockwise rotation. First examinations of patients with global and focal disease demonstrate the potential to detect disturbances in the local as well as the overall motion patterns.

Index t-: Phase contrast - Heart wall motion * Myocardial motion * Ve- locity mapping

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Abbr~~htl0118: EF = ejection fraction, PET = positron emission tomography, RF = radiofrequency. TI-201 = Thallium-201, FDG-PET = F-18 Fluo- rodeoxyglucose-PET.

From Abt. ROntgendiagnosllk. MR-Tomographie. Department ofNuclear Med- idne, University Freiburg. Hugstettentr. 55, Freiburg, Germany. E-mail: hennigOnzl I.ukl.unl-freiburg.de. Received May 20, 1997: revision requested September 3 revision received November 1 0 accepted November 18. This work was supported by Grant He 187512 from the Deutsche Fonchungsge- meinschaff. The contents of this paper have been presented during the 5th annual meeting of the International Society for Magnetic Resonance in Med- icine, Vancouver, 1997. M d n ~ reprint requests to J.H.

0 ISMRM, 1998

VARIOUS TECHNIQUES EXIST to characterize the function of the myocardium. Positron emission tomography (PET) is the gold standard for measurements of regional perfusion and/or metabolism. As a crude albeit useful measure of the cardiac output, the ejection fraction can be measured using either ventriculography or echocardiography. Ultrasound can also be used to derive characteristic performance parameters like the circumferential shortening or segmental myocardial thickening, which can be used to detect motional defects caused by various focal or global disease.

A number of techniques have been proposed to non- invasively measure the mechanical performance of the heart by MR tomography. The most abundantly used approaches are tagging techniques, in which the images of the myocardium are labeled with a more or less regular grid by spatial modulation of the z magnetization before signal readout (1,2). Such tagging techniques can be used to observe the spatial displacement of the tagging labels over the ECG cycle. In addition to that, tagging allows the study of the mechanical properties of the myocardium, using a stress-strain analysis of myocardial regions defined by the comers of tagging points. A n in- trinsic disadvantage of tagging techniques is the fact that the spatial resolution of the functional information compared to the anatomical resolution of the underlying images is reduced by a factor of 3 to 5 in linear dimensions or a factor of 9 to 25 if the voxel areas are compared. Nevertheless, tagging methods have been used success- fully to describe the mechanical properties of the myocardium in healthy volunteers and patients (3-19).

A second approach to characterization of heart wall motion is offered by the sensitivity of the phase of the MR signal to motion. This can be used to directly measure the local velocity of the myocardium by MR interferomet- ric techniques on a pixel-to-pixel basis (20). Phase contrast techniques (21) have also been used for such velocity measurements (22,23). It should be noted that

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Pigun. 1. Short axis images of the left ventricle of a normal volunteer during systole (t, = 90 msec) acquired with a black blood prepared segmented gradient-echo sequence (TE = 6.8 msec, TR = 11.25 msec, eight phase-encoding steps per ECG cycle, breath- hold examination in 16 ECG cycles). fa) The flow-compensated image: @, e, d) images with velocity encoding in x, y. and z direction, respectively. The bottom row represents the phase difference images of @), (e). and (d) to (a), respectively.

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Figure 2. PLXel-by-pixel plot of the rotation velocities (in units of 1 /sec = 1 cm/sec per cm radius) in a slice located halfway between the base and the apex in a normal volunteer in systole (tffg = 90 msec) (a). early diastole ( t , = 360 msec) @), and late diastole (tq = 630 msec) (c) as a function of the polar angle + in a polar coordinate system. The small diagram at the top right represents the reference for +: positive values of + represent clockwise rotation, + = 0 is defined at the mediolateral position of the left ventricle, + fs running counterclockwise. + = 1 to 2.5 thus corresponds to the anterior wall, 2.5 to 4 corresponds to the septal wall, 4 to 5.5 corresponds to the posterior wall, and 6 to 1 corresponds to the lateral wall.

phase contrast techniques and MR interferography are generically equivalent, because both approaches use the phase difference between a motion-com~nsated signal and a motion-sensitized signal for measuring velocities. In MR interferographic techniques, the two signals are acquired within the same acquisition window, whereas phase contrast methods are based on the phase differences between successive scans. An advantage of MR interferography is thus the avoidance of artifacts from nonreproducibility between the measurements. Phase contrast methods offer the advantage that they can be implemented in a way that one measurement can be performed within one breath-hold. Artifacts from breathing motion are thus avoided.

An excellent comparison of tagging methods and velocity-based approaches is found in ref. 24.

The commonly applied procedure to localize myocardial areas with compromised function used both in tagging techniques as well as in velocity-based approaches is stress-strain analysis for the detection of local variations in the motional performance of the myocardium.

The purpose of this paper is to explore the possibility to directly use ~ee-dimensional velocity data for the characterization of myocardial motion. Our initial study was designed to test the following hypothesis:

A dark blood prepared segmented breath-hold gradient-echo technique is a reliable technique to produce quantitative velocity data about the intramural motion

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of the myocardium, not only in healthy and cooperative volunteers, but also in patients.

0 The considerable interindividual variance in the overall motion of the heart can be considerably removed, ifthe measured velocity data are transformed into an internal coordinate system of the myocardium.

0 The velocity data and the parameters derived therefrom are sensitive measures to detect and characterize focal and global disease of the heart. For that purpose, the

Figure 3. Pixel-by-pixel plot of the radial velocities in the same slice and at the same time points as in Figure 2 as a function of the polar angle +. The diagram at the top right represents the reference for u; positive velocities represent motion toward the center of the myocardium (compression).

F'igure 4. Pixel-by-pixel plot of the rotational velocities u, and the radial velocities u, as a function of the distance r to the center of the myocardium at t- = 0 (left) and 90 msec (right). The straight lines are the result of a linear regression to the data points.

quantitative velocity measurements were compared with the results of conventional approaches for the diagnosis of functional impairment of the heart, such as PET, scintigraphy, or echocardiography. As a prerequisite for routine clinical use, two boundary

conditions must be fulfilled for the implementation of the technique. First of all, experiments should be performed within one breath-hold to avoid artifacts caused by re- positioning of the heart during the acquisition. For ex-

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amination of patients, the breath-hold time should not exceed 8 to 16 ECG cycles.

In addition, signal from blood should be sufficiently suppressed to avoid artifacts from nonperiodic blood flow over the breath-hold period. Conventional black blood preparation is based on the T1 of blood and uses an inversion recovery prepulse with an inversion delay of ap- proximately 350 msec (25). This approach leads either to doubling of the overall examination time by acquiring image data only every other ECG cycle or to the cutting off of the last 350 msec during diastole. Both alternatives were found to be inappropriate for the purpose of our study. Strategies for suppressing blood signal by appli- cation of broad spatial saturation pulses across the left atrium and the pulmonary veins (24) have not given consistent good suppression for our particular sequence. We have thus used a slightly different approach using a spatially selective preparation pulse, which nulls all signal from blood directly outside of the observed slice. This was achieved by using a “sandwich pulse,” in which the pro- files of a 90” pulse acting on the slice under observation was added to that of a -90” pulse acting on a co-centric thicker slice. As a result, spins inside the examined slice are not affected and the z magnetization immediately ad- jacent to the observed slice is nulled. The transverse magnetization generated by the pulse is destroyed with an appropriate spoiler gradient.

The measurement technique and the postprocessing algorithm has been evaluated in a study with 12 normal volunteers. In addition to that, examinations have been performed on patients with focal and global disease.

0 MATERIALS AND METHODS

Data Acquisition All experiments were performed on a 1.5-T system

(Magnetom Vision, Siemens, Erlangen, Germany) equipped with a gradient system with 25 mT/m and 0.6 msec rise time. The available high performance booster for the gradients was not used to keep noise emission to a level comfortable for the patients. A four-element phased array body coil was used for optimizing the signal-to-noise ratio. Images were acquired in short axis

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Figure 5. Average values for the mean radial and rotation velocities u, and u,, for 1 1 volunteers. The error bars represent the SD. The dotted line gives the result of one volunteer, who differed significantly from the rest of the group, especially with respect to the rotation velocities. (a) A slice 2 cm from the base of the heart; (b) a slice 4 cm closer to the apex.

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0 180 360 540 720 Figure 6. Average values for the transmural velocity gradient du,/dr over 12 volunteers in a slice slightly displaced from the apical-basal midpoint toward the apex (7 cm from the base).

view of the myocardium with first order motion compensation as well as with selective motion sensitivity in the x, g, and z directions, respectively.

The basic pulse sequence for the reference data set consists of an radiofrequency (RF) spoiled gradient-echo sequence with first order motion compensation along all three dimensions (TE = 6.8 msec, TR = 11.25 msec, 8- mm slice thickness, 25.6-cm field of view, acquisition matrix = 128 X 512 reconstructed with zero filling to 256 X 256; oversampling in the read direction was used to avoid wraparound artifacts). For measurements of velocities, a bipolar gradient was added to the otherwise iden- tical sequence in any of the three dimensions. Motion sensitization was performed using a strong bipolar gradient (uenc = 20 cm/sec) to get a sensitivity sufficient for myocardial velocities. Eight phase-encoding steps per image were acquired within each ECG cycle, such that the


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total acquisition could be performed within 16 heart- beats. The width of the saturation slice used for black blood preparation was experimentally optimized to 32 mm for an observation slice thickness of 8 mm.

In the experimental protocol used, velocity measurements were performed in five parallel slices (8-mm thickness, 2-mm interslice gap) starting 2 cm from the base of the left ventricle and moving downward toward the apex in l-cm intervals. For each slice, breath-hold examinations were performed for the reference scan and the three motion-sensitized acquisitions.

For the human studies on normal volunteers (age range, 27-37 years: mean age, 30.5 years) and patients, consent was granted by the local ethical committee of the university. Volunteers with no clinical history of any myocardial disease were selected. All volunteers received a standard examination of their myocardial status, including ECG and transthoracic ultrasound. The purpose of the volunteer study was to measure the interindividual reproducibility of myocardial motion and to establish standard data for this age group.

In addition, explorative examinations have been performed on patients with focal ischemia (n = 5: two pos- terolateral, two anteroseptal, one posterior and anterolateral) as well as on patients with global impairment of myocardial function (n = 4: one with meningococcic tox- emia with pericardial edema: two with generalized ischemic heart disease, including globally reduced left ventricular function; one with cardiomyopathy). The results of the MR measurements were compared to the results from other examinations (echocardiography, scintigraphy, PET) performed on the patients in the course of their routine clinical workup.

-tP-ng For image postprocessing, we have developed a stand-

alone software package running on an external worksta- tion (Sun Sparc 20, Sun Microsystems, Mountain View, CAI. This postprocessing package is to provide a user- friendly interface for the analysis of the functional studies. The program analyzes the measured velocity data with a minimum of user interaction. The ultimate goal is to calculate a set of parameters that can be used to characterize the motional performance of the heart and to aid diagnosis in patients with functional deficits (26).

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Figure 7. Average values of the rotational velocity twist du,/dz defined as the linear gradient of the mean rotational velocity as a function of the long axis z position over 1 1 volunteers along the ECG cycle. Positive values of du+,/dz represent higher (clockwise) rotation velocities of the apical slices. The open squares connected by a dotted line corresponds to the velocity twist in a patient with focal ischemia but nearly normal EF of 40%.

The following was the working hypothesis in the devel- opment of the program. To obtain meaningful velocity data for the description of the internal dynamics of myocardial motion, the measured velocities in the laboratory frame must be translated into an internal coordinate system positioned at the center of mass of the moving myocardium to get rid of bulk motional components, which reflect the overall morphology of the heart and its attach- ment to the surrounding tissue more than the actual internal performance of the heart muscle.

The first step in data analysis is the semiautomatic segmentation of the myocardium. The only user interaction required for this step is selection of a point inside of the left ventricle. The inner and outer contour of the myocardial wall are then found automatically using a contour- tracing algorithm.

In the second step, the velocity data inside of the segmented myocardial wall in Cartesian coordinates are con- verted into a local coordinate system in the center of mass of the left ventricle. The measured velocity data dx, IJ, z) in the laboratory frame are decomposed into the following components:

dx, IJ, 2) = u, + u, + u, + u,,

where u, is the average velocity in the short axes (x, IJ) plane, u, and u, are the angular and radial velocities in a polar coordinate system with the origin at the center of the myocardium, and u, is the through-plane velocity component.

After conversion into this internal system of coordinates, the overall motional components u,,. u,, and u, and their variance were calculated from the pixel values in each slice at each time frame over the ECG cycle. Fi- nally the "velocity twist" du,,/dz in the apical-to-basal rotation velocities was calculated by linear regression of uw as a function of the long axes (2) coordinate.

For further interpretation, the results can be viewed on various levels of abstraction:

Color-coded velocity maps of all velocity components can be used to visually inspect any regional variations.

0 Diagrams of u,, u,, and u, as well as the absolute velocity u,, = V(v", + 3, + g) as a function of +, r, and z can be used to visualize the uniformity of motion.

0 The overall performance of the myocardium is charac- terized by plots of u,~. u,, u,, and durn/& versus the time t after the R wave.

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The transmural velocity gradients du,/dr and du,/dr are calculated and can be visualized as a diagram or a color-coded parametric image.

RESULTS

Normal Volunteers The results of the black blood prepared segmented gra-

dient-echo experiment performed on a normal volunteer in a slice located halfway between the apex and the basis at time 90 msec after the R wave (systole) are shown in Figure 1. The images demonstrate adequate suppression of the blood signal using the spatially selective sandwich pulse. In general, we noted that the suppression works better in the slices close to the heart base, where stronger exchange of blood across the slice occurs compared to slices closer to the apex.

A plot of the pixel-by-pixel rotational velocities as a function of the spatial angle 4 in the polar coordinate system along the ECG cycle is shown in Figure 2. These parameter plots are derived from the phase difference images shown in Figure 1 by transformation of the measured velocities into the internal coordinate system of the heart. High coherence of the rotational motion all over the myocardium is demonstrated. At the time of the R wave, the observed rotational velocity ( tecg = 0) is on the order of 1 to 2 cm/sec (= 1 cm/sec per cm radius), which trans-

Figure 8. Color-coded image of u, in a slice 3 cm from the base of the left ventricle in a patient with a posterior infarction acquired at tq = 90 msec (top) (a) compared to a velocity image of a normal volunteer acquired at corresponding position and time point (b) and to a TI-201 scintigram (c). The scintigrams represent two parallel sections during two time frames in systole. The nominal slice position of the MR image as measured from the base of the heart lies between the two scintigraphic images shown. A comparison of the velocity scale with the diagram in Figure 3 shows the much higher variation of u, over the myocardium. The infarcted region is akinetic or even dyskinetic (outward motion = blue).

lates to a tangential velocity of 2.5 to 5 cm/sec at a radius of 2.5 cm. In the later phases, some systematic velocity differences in different sectors are shown. Diastolic counter-rotation sets in first at the lateral wall (+ = 0-1 and 5-6 at tecg = 270 msec) and then moves on to the posterior and anterior parts at tecg = 360 msec.

A similar plot is shown for the radial velocities corresponding to contraction and expansion (Fig. 3). Following the local velocities over the different time frames, some subtle differences in the motional behavior in different segments can be appreciated. Compression velocities in the first three time frames (t, = 0-180 msec) are slightly higher at the posterior segments. Diastolic expansion sets in the posterior and the anterior segments, followed by the septal and lateral segments.

In Figure 4, the rotational (Fig. 4, top) and radial (Fig. 4, bottom) velocities u, and u, as a function of the distance to the center at the time of maximum rotation (t, = 0 msec) and after the onset of systolic compression ( t, = 90 msec) are shown. The gradient in the rotational velocity reflects the initial “iris shutter” motion of the myocardium. At the time of maximum systolic velocity (t, = 90 msec), this is already reduced and the main transmural velocity gradient is now in the radial direction, re- flecting myocardial thickening.

The cumulative result of the average rotational and radial velocities u+,, and u, over 12 normal volunteers is demonstrated in Figure 5. Note the small error bars,


which show the very high consistency of interindividual motion. This is in marked contrast to the measured velocities in the laboratory frame, which varied considerably between volunteers and did not reveal any significant interindividual reproducibility.

The diagrams show that normal heart action begins with clockwise rotation, even before the onset of contraction (time frame 1). Immediately after the onset of systole, the rotational velocity is reduced and even slightly in- verted in the more basal slices.

One volunteer (female, 37 years of age) fell out of line with respect to the rotational motion, which deviated significantly from the rest of the group. The anatomical images of this individual were normal, and she has no known pertinent clinical symptoms.

The interindividual transmural gradient of the radial velocity is found to be less consistent between individuals for the two basal slices but very consistent for the two apical slices (Fig. 6). The interindividual variation of the transmural velocity gradient in the basal slices does not necessarily reflect a greater interindividual variability of motion but might be an artifact of the very simple calculation method. A linear regression of u, versus r will yield true values for the transmural gradient only if the observed section of the myocardium has rotational sym- metry. For more basal slices, in which the shape of the myocardium is noncircular, a plot of velocities versus the distance to the center will mix data points of the inner and outer myocardium at different positions around the circumference, and the measured slope of u, versus r will thus not represent the true transmural gradient. A reliable calculation of the transmural gradient for the basal slices therefore requires more sophisticated analysis, which takes the anatomical eccentricity into account. This is, however, not (yet) part of our evaluation package. Pathologies leading to variations in this particular parameter will thus remain undetected with our current approach.

For the more apical slices, higher compression velocities of the inner myocardium in systole and a reversal in diastole as expected for compression and expansion, accompanied by wall thickening (systole) and thinning (diastole), are demonstrated in Figure 6.

From the mean rotational velocities at each time point as a function of the slice position, the rotational velocity twist can be calculated by linear regression (Fig. 7). Again, a very high interindividual consistency of the data

is observed. Counter-rotation between the basal and apical slices OCCUTS at teq = 90 msec and 180 msec and again at t, = 450 msec (see also Fig. 5, right column).

The observed velocities in the z direction reflect the motion of the basis to the apex during systole as known from echocardiography. Peak velocities of u, in the basal slices during systole were observed to be on the order of 5 to 8 cm/sec.

Patients In Figure 8, a color-coded velocity image of a 68-year-

old patient with a posterior myocardial infarction is shown, in comparison with a Tl-201 scintigram (Fig. 8c) displaying a local perfusion deficit. The patient had a mildly reduced ejection fraction (EF) of 40% and no disease findings on FDG-PET. The MR images show reduced velocities in the hypoperfused area. No major deviation of the global motional parameters from the values measured in volunteers were observed. The rotational velocity twist du,,(z) versus tees was in excellent agreement to the results of the volunteer study as shown in Figure 7.

The other infarct patients had more severe functional impairment with EF down to 20%. Figure 9 shows velocity images of a patient (male, 70 years of age) after two posterior infarcts (1986 and 1995). His EF was 30% and PET showed homogeneous FDG utilization, but anteroseptal and lateral hypoperfusion was measured with NH, (Fig. 10). The ECG reported anterolateral hypokinesia/ akinesia; coronary angiography revealed stenosis of the left anterior descending coronary artery.

Pronounced regional variations of the motional velocities, as shown in Figure 9, do not, however, exactly cor- relate with either the exact location or the extent of the hyperperfused areas in the PET.

In Figure 1 1, considerably reduced averaged radial and rotational velocities are demonstrated, compared to Fig- ure 5. Also note that the direction of initial rotation (t, = 0) is opposed to that in normal volunteers.

Findings in the other infarct patients were comparable to those of patient 2: all showed pronounced regional variations in the motional components as well as significant deviations of the global motion parameters compared to the volunteers.

Also shown in Figure 11 are the radial velocities in a 55-year-old patient with generalized ischemic heart disease as an example for the patient group with global disease. The patient suffers from hypertension and has an echocardial diagnosis of a globally reduced left ven-

FIgnre 9. Color-coded velocity images of the magnitude ot the velocities (a), the rotational velocity u, [DJ and the radial velocity u, (cJ in a patient with multiple infarcts.

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Figure 10. Ammonia PET of the same patient as in Figure 9 displaying hyperperfusion in the lateral and anteroseptal parts of the myocardium.

tricular function with an EF of 25%. The diagram demonstrates that the velocities are considerably reduced compared to the much younger normal volunteers (Fig. 5). The larger error bars indicate the increased anisotropy of radial motion (see Fig. 12). The plotted pixel velocities of u, at systole (90 msec after the R wave) show considerable regional variations with some areas moving away from the center, whereas others already show compres- sional movement. Qualitatively similar results were received from the other three patients with global disease.

To assess whether the measured velocities can be cor- related with other parameters used for characterizing myocardial performance, we have plotted the average values of the radial velocities during systole (time frames 2 and 3 after the R wave) against the EF values as measured by ECG (n = 5) and/or coronary angiography (n = 6). For one infarct patient, the EF was not known; for patients who had measures with both techniques, average values were used. A good correlation between the two values is shown in Figure 13. The diagram must be taken with a grain of salt, because the patient group was het- erogeneous and the normal volunteers were far from be- ing age-matched and do not show actual measured EF values.

DISCUSSION Our results demonstrate the very high consistency of ve-

locity data acquired with the black blood prepared segmented phase contrast gradient-echo technique. With proper prescreening of patients with respect to exclusion criteria ( a r r h m a , claustrophobia), artifact-free images can be acquired very consistently, even in patients with severe disease. This is a major improvement compared to our previous experience with non-breath-hold techniques.

The high consistency of the velocity data in the examinations on normal volunteers after transformation into an internal coordinate system is encouraging. Although rotation and contraction/expansion are a quite crude ap- proximation to the actual biophysical mechanism of the contractile motion of the myocardial muscles, they seem to give an adequate and sensitive parameter for the pa- rametrization of myocardial motion.

The absolute values of the measured velocities (urosys = 2-3 cm/sec) seem to be quite low at first view. This is due, in part, to the fact that the velocity vectors nearly never point directly to the center of the myocardium. Typ- ical systolic absolute velocity values were observed to be in the order of 4 to 6 cm/sec. In addition, it should be kept in mind that the segmented acquisition mode necessary for doing breath-hold scans lead to a quite medi- ocre time resolution of 90 msec within the ECG cycle. The peak velocities therefore suffer quite significantly from low pass filtering.

The low temporal resolution is certainly one of the main disadvantages of our approach. Subtle differences in the temporal evolution of myocardial motion, especially during systole, can not be observed.

For the phase contrast imaging sequence used, the benefits of extremely consistent data afforded by breath- hold acquisition nevertheless seem to outweigh this disadvantage. Velocity-encoded hybrid echo-planar imaging sequences might lead to further improvements allowing the combination of high temporal resolution within the ECG cycle with breath-hold acquisition. Such an approach could also be the means to solve the further problem of slice misregistration between the velocity-coded scans on the same slice, which can occur if the position of the heart moves between breath-holds.


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The patient results confirm our working hypothesis ac- cording to which the observed intramural velocities in the local coordinate system of the myocardium show very lit- tle interindividual variations and are sensitive parameters to detect motional disturbances in focal and global disease. A definite assessment of the use of velocity measurements in the diagnosis and characterization of various diseases requires more extensive studies including standardized control examinations (echocardiography, scintigraphy, PET), as well as the acquisition of age-matched (and probably gender-selective) reference data.

Changes in the myocardial mobility far away from the area of infarction, as shown in Figure 9, have been observed in five patients using tagging techniques (12). Sim- ilar techniques have also been used to study intramural changes in patients with focal ( 1 2.14- 16) as well as global (18.19) disease. The results were qualitatively in agreement with our findings. A thorough discussion requires more extensive and thorough studies as well as an assessment of the relation between the stress-/strain-analysis used in the evaluation of tagging images as compared to our velocity measurements.

A basic problem in the evaluation of the clinical use- fulness of our technique is the fact that there is no real

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0 2 4 6 Figure 12. plxel-by-pixel plot of the radial velocities of u, at tffg = 90 msec for the patient with generalized ischemic heart disease, whose mean velocities are shown in Figure 1 1. A comparison with Figure 2 demonstrates that the lower mean values shown in Figure 11 is due mainly to a considerably larger variation of the velocities (including reversal) at different segments of the myocardium.

gold standard for intramural velocity measurements against which our approach could be measured. A comparison of the sensitivity and reliability of our velocity measurements with the results of tagging techniques is certainly interesting and will be performed in a future study.

Further studies are also necessary to study the functional correspondence between the areas of hypoperfusion and their effect on the local and global motion parameters.

For routine applications, an essential feature of our velocity-based approach and the postprocessing strategy used is the high degree of automation it allows. The parameters used for characterizing motion can be derived fully automatically after the one and only interaction of selecting one data point in the interior of the left ventricle. Patients with no deviations of their motional function can thus be identified automatically. For disease findings, the quite compact set of parameters used to characterize motion promises a more objective and practical approach to look at disease than the pitfalls involved in trying to make a diagnosis based on visual inspection of hundreds of images.

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McVei& ER. Zerhouni EA. Noninvasive measurement of trans-

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Finally, it should be noted that the images acquired with our technique also allow a morphologically based analysis similar to ECG by calculation of the EF and the regional segmental wall thickness, which might be useful adjunct to our postprocessing package in the future.

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Analysis of myocardial motion based on velocity measurements with a black blood prepared segmented gradient-echo sequence: Methodology and applications to normal volunteers and patients