Direct comparisons between MRI and other imaging techniques in the evaluation of EF have further bolstered the value of MRI in clinical practice. One of the first such studies compared MRI with ventricular angiography in calculating EF using the area-length method and found excellent correlation between the two (r = 0.88).¹¹ More recently, MRI assessment of EF using Simpson’s rule has proved more reproducible (less interstudy, intraobserver, and interobserver variability) than two-dimensional echocardiography, currently the most widely available imaging modality to assess cardiac function.¹²^,¹³ Also of note, direct comparisons among MRI, echocardiography, and radionuclide ventriculography revealed considerable differences in calculated EF, suggesting that MRI is the more accurate and preferred method to assess cardiac function, especially in dilated ventricles.¹⁴ Because of its consistent performance in clinical evaluations, MRI assessment of LV volumes using Simpson’s rule is now widely accepted as the most accurate and precise noninvasive estimation of EF.¹⁵

These benefits of MRI have research and clinical implications. Better reproducibility has resulted in the need for smaller sample sizes (sometimes by a factor of 80% to 90%) in studies using MRI measures of ventricular volumes than in those using other imaging modalities.³ Furthermore, MRI is now routinely used as the gold standard when evaluating other imaging techniques, such as three-dimensional echocardiography.¹⁶^,¹⁷ MRI may be particularly important in evaluating patients for prophylactic implantable cardioverter-defibrillator placement,¹⁸ in which an EF of 35% is commonly used to guide the implantation of a device. MRI may also be useful in serial evaluations to detect changes in EF that are smaller than the limits of sensitivity of echocardiography. This can be especially relevant in identifying the subclinical cardiotoxic effects of chemotherapy.¹⁹

Contraindications

Because no stimulant or contrast agent is required to assess resting EF, the contraindications for this technique coincide with those pertaining to any MRI scan, such as the presence of certain metal implants or devices (see Chapter 19) or severe claustrophobia.

Technique Description

Determination of resting EF by MRI requires no intravenous contrast agent or stimulant. The protocols that are most commonly used include steady-state free precession (SSFP) and gradient echo sequences, which are discussed in detail in Chapter 13.

Pitfalls and Solutions

Although generally very useful in accurately determining global EF, MRI does occasionally present obstacles that need to be overcome. The most frequent pitfall in MRI is inferior quality images because of respiratory motion artifact. One often-used remedy is a free-breathing protocol that uses respiratory gating or the use of real-time imaging rather than postacquisition reconstruction. Either of these techniques can improve image quality by reducing artifacts introduced by suboptimal breath-holding.

Image Interpretation

Once acquired, the global EF is determined by calculating volumes at end-diastole and end-systole. Most frequently, postprocessing involves using Simpson’s rule to determine ventricular chamber volumes. The function is then reported as a percentage (calculated by dividing the stroke volume by the end-diastolic volume and multiplying by 100), with 50% to 70% considered to be the normal range.

RESTING REGIONAL WALL MOTION ABNORMALITIES

Indications and Clinical Utility

Although ventricular EF provides a global assessment of cardiac function, it is still a relatively insensitive index of myocardial pathology. A patient with an EF of 50% may have regional wall motion abnormalities indicative of underlying coronary disease. Because of its excellent spatial resolution, cine MR images of the left ventricle allow a qualitative assessment of regional cardiac function without the acoustic limitations inherent in echocardiography.²⁰ In addition, because the quality and resolution of white blood MR images is not closely related to body habitus or cardiac orientation, images can be acquired in almost any tomographic plane, allowing for a more comprehensive evaluation of regional function.³

Quantitation of regional myocardial function can be accomplished with MRI using a variety of techniques (see Chapter 14). Local wall thickening can be assessed and has been shown to correlate well with the size and extent of myocardial infarction, as measured by enzymatic release.²¹ Myocardial tagging can also be used to calculate regional strain, an appealing concept because the dynamics of ventricular systole are complex and consist not only of thickening but also of contraction, expansion, twisting, and through-plane motion.²⁰ Strain calculation can potentially detect more subtle wall motion abnormalities than visual qualitative assessment and may provide valuable functional information in patients who have infarctions, hypertension, and nonischemic cardiomyopathies.²²^–²⁴ It is again worth noting that many of these patients may have a preserved global EF, despite having abnormal segmental myocardial mechanics. Although myocardial tagging and quantification of regional wall function is currently not a routine part of the cardiac MRI examination at most centers, considerable data suggest that it may have significant clinical utility in the future.

Contraindications

As for global EF, because no stimulants or contrast agents are required, contraindications for this technique coincide with those pertaining to any MRI scan.

Description

Also as for the assessment of global EF, evaluation of regional wall motion abnormalities usually involves SSFP or gradient echo sequences. Although qualitative visual assessment of wall motion is most often used and is often feasible, given the formidable spatial resolution of MRI, quantitation of wall thickening using myocardial tagging may have a more significant clinical role in the future (see earlier, “Indications and Clinical Utility”). Myocardial tagging techniques are discussed in detail in Chapter 13.

Pitfalls and Solutions

The challenges pertaining to the determination of global cardiac function also apply to the assessment of regional wall motion abnormalities—namely the need to acquire good-quality images, free of artifact. Evaluating for regional wall motion abnormalities can also be particularly daunting to those who are inexperienced because it is sometimes difficult to discern true wall thickening from simple translation. It is thus important to have interpreters who are well versed in assessing regional cardiac function.

Image Interpretation

The interpretation of wall motion is often done in a qualitative manner, as noted. Reporting wall motion entails the use of a bull’s-eye diagram, with the left ventricle divided into 17 segments from the base to the apex, and assigning a score to each segment, ranging from normal to aneurysmal.

RIGHT VENTRICULAR FUNCTION

Indications and Clinical Utility

Just as for the left ventricle, RV function has important clinical and therapeutic implications. A depressed RV function predisposes patients to hypotension and confers a poor prognosis for patients with acute myocardial infarctions and chronic LV dysfunction.²⁵ In addition, RV function is a focus of attention in those with congenital heart disease. Because of its geometry and location beneath the sternum, the right ventricle is particularly difficult to assess with echocardiography and radionuclide ventriculography (Fig. 15-1). MRI is not bound by these constraints and thus allows for an accurate assessment of this cardiac chamber.

FIGURE 15-1 Short-axis MRI image of the right and left ventricles in end-diastolic phase (A) and representation of healthy adult ventricles (with the right ventricle on the left side of the picture) as geometrically reconstructed from MRI images (B). The bulging of the septum to the right side creates an irregular meniscus-shaped right ventricle that is not always amenable to certain imaging modalities.

MRI-derived volumes and mass of the right ventricle have shown robust correlations with in vitro casts and with clinical standards, such as invasive dilution techniques and radionuclide ventriculography.²⁶^,²⁷ Studies have also shown high reproducibility, with low intraobserver, interobserver, and interstudy variability in normal volunteers²⁸ and low interstudy variability in a diverse patient population.²⁹ The accuracy and precision of MRI allow for rigorous clinical evaluation of the right ventricle while obviating the risk of invasive procedures and radiation exposure.

Contraindications

Contraindications to the assessment of RV function by MRI are the same for any MR scanning procedure not requiring contrast, inotropic, or vasoactive agents.

Pitfalls and Solutions

Challenges associated with the assessment of RV function by MRI are the same as those presented by left ventricular evaluation.

Image Interpretation

Unless otherwise requested, RV function is usually not quantified but is graded subjectively as normal or mildly, moderately, or severely depressed. When a more precise assessment is warranted, RV volumes can be measured using short-axis slices and an EF can thus be calculated. An EF ranging from 47% to 80% is considered normal for the right ventricle.

DIASTOLIC FUNCTION

Indications and Clinical Utility

Although echocardiography is currently the established technique for diastolic assessment, there are inherent limitations to ultrasound that may be overcome with MRI, which can be used to evaluate the ventricle in three dimensions, taking into account the untwisting, longitudinal, and radial movement that occurs in diastole. Using myocardial tagging, strain assessment in these different orientations can be determined, thereby yielding a potentially more comprehensive evaluation of ventricular diastole than that offered by echocardiography. Transmitral flow velocities can also be determined, as in echocardiography, to ascertain the LV filling pattern and degree of diastolic dysfunction.

Contraindications

Contraindications to assessment of diastolic function are the same as for any MRI scan not requiring contrast, inotropic, or vasoactive agents.

Pitfalls and Solutions

Given the rapidity of diastolic flow propagation, the limited temporal resolution of MRI can be a hindrance in accurately assessing diastolic function. This can be overcome by adjusting the views per segment, compromising some degree of spatial resolution, and/or using a free-breathing as opposed to a breath-hold protocol, so a longer time of acquisition can be used. Generally, a temporal resolution of at least 35 ms is warranted for diastolic evaluation.

Image Interpretation

In addition to evaluating the motion and strain of the myocardial tissue, which is currently not widely used clinically for diastole, MRI can also determine LV flow velocities and propagation during diastole. Using phase contrast imaging (see Chapter 17), the transmitral flow pattern can be determined much like it is with echocardiography. It is important to note, however, that some aspects of the transmitral E signal, such as acceleration and deceleration time, have not been validated with phase contrast MRI. Further characterization of diastolic LV flow can be achieved using a combination of phase contrast imaging and color vector mapping (Fig. 15-2). This is an experimental technique at present and is not yet widely used in clinical practice, but it does represent the potential of phase contrast imaging for assessing flow propagation in LV diastole. There is currently no standardized method of reporting diastolic function assessed by MRI.

FIGURE 15-2 Sequential frames of diastole in a normal (A) and dilated ventricle (B). In the normal example, note how the streamlines extend all the way to the apex. By contrast, flow propagation is markedly less and degenerates into a vortex in the middle of the dilated left ventricle.

DYNAMIC LEFT VENTRICULAR FUNCTION USING DOBUTAMINE

Indications and Clinical Utility

Like resting cardiac function, LV response to chronotropic and inotropic stimulation provides considerable clinical information, both physiologic and prognostic. Advances in software and hardware, specifically the development of phased-array surface coils, faster scanning, and advanced gating have increased the practicality and clinical utility of cardiac MRI wall motion stress testing.³ The focus of this subject will be the use of dobutamine and exercise stress testing in clinical practice. See Chapter 53 for a discussion of myocardial contrast perfusion imaging.

Physiology and Safety Profile of Dobutamine

Dobutamine is a synthetic catecholamine with mild β₁ receptor selectivity.³⁰^,³¹ It is a positive inotrope and, because of its peripheral vasodilatory effects, it induces a reflex tachycardia.³² At doses of up to 10 µg/kg/min, dobutamine augments myocardial contractility and promotes coronary vasodilation; doses of 20 to 40 µg/kg/min increase heart rate and myocardial oxygen demand³³ and, in the setting of significant epicardial coronary artery stenoses, can induce wall motion abnormalities by way of a supply-demand mismatch (Fig. 15-3).³⁴^,³⁵ Several large- scale investigations have evaluated the safety of dobutamine as a stress agent and have found a low incidence (often less than 1%) of major complications.³⁶^,³⁷

FIGURE 15-3 Wall motion abnormality during dobutamine infusion. A, At baseline, the end-systolic frame shows all segments contracting normally. B, The apex (arrow) becomes akinetic at peak dobutamine infusion, however.

Dobutamine Magnetic Resonance Imaging and Myocardial Ischemia

Perhaps the most common use of dobutamine stress imaging is to identify those patients who have physiologically significant coronary stenoses. The first clinical trials investigating the use of MRI in dobutamine studies were relatively small but showed excellent agreement between wall motion abnormalities seen on MRI at peak dobutamine levels and areas of abnormal myocardial perfusion as assessed by dobutamine thallium perfusion.³⁸^,³⁹ The sensitivity of dobutamine MRI compared favorably with that of dipyridamole MRI in detecting coronary stenoses in another study consisting exclusively of patients with high-grade (70% or more) lesions of at least one major coronary vessel.⁴⁰ In this series, the sensitivity of dobutamine MRI in detecting this degree of coronary stenosis was higher than 80% and increased with multivessel involvement. These early studies implied the safety and effectiveness of dobutamine as a pharmacologic stress agent and the utility of cardiac MRI in assessing for wall motion abnormalities.

A larger, more recent study compared dobutamine MRI with dobutamine stress echocardiography (DSE),⁴¹ a routinely used method of detecting inducible ischemia. In this study, 208 consecutive patients underwent DSE, dobutamine MRI, and biplane coronary angiography within a 14-day period. Dobutamine MRI demonstrated better sensitivity (86% vs. 74%) and specificity (86% vs. 70%) than DSE in detecting coronary artery disease (defined as more than 50% luminal narrowing) seen on angiography. Examinations were feasible in approximately 90% of patients with both DSE and dobutamine MRI, although the reasons for exclusion differed for the two techniques. Insufficient image quality was the major reason for exclusion from DSE and claustrophobia for dobutamine MRI. On the basis of these results, it was concluded that dobutamine MRI can detect wall motion abnormalities with significantly higher diagnostic accuracy than DSE because of improved image quality.

In keeping with this hypothesis, another large-scale, single-center trial evaluated 163 patients referred for DSE who did not have adequate imaging windows, despite the use of second harmonic imaging and contrast agents.⁴² These patients underwent dobutamine MRI instead and the vast majority (more than 80%) were able to complete their study without complications. Of patients who underwent coronary angiography, dobutamine MRI had a sensitivity and specificity higher than 80% in the detection of coronary arterial luminal narrowing of at least 50%, similar to the results of the study detailed earlier. Of note, this study included patients who had resting wall motion abnormalities, whereas the study by Nagel and colleagues⁴¹ specifically excluded patients with previous myocardial infarction and reduced resting EF. The authors concluded that dobutamine MRI could be performed safely using fast imaging techniques and that dobutamine MRI had potentially greater clinical utility than DSE, without compromising sensitivity or specificity.

Further studies have increasingly substantiated the clinical utility of dobutamine MRI. In a small series consisting exclusively of patients with known epicardial coronary disease, low-dose dobutamine MRI was effective in differentiating normal, ischemic, hibernating, and nonviable myocardium.⁴³ There was also robust correlation seen with stress perfusion in these patients. In another study, which looked exclusively at patients with known coronary disease, Wahl and associates⁴⁴ performed high-dose dobutamine MRI prior to coronary angiography on 160 consecutive patients who had undergone prior coronary revascularization and had resting wall motion abnormalities. The sensitivity and specificity of dobutamine MRI in detecting coronary luminal narrowing of at least 50% was 89% and 84%, respectively. This patient population (with underlying wall motion abnormalities and low EF) is especially difficult to evaluate with DSE because of frequently poor acoustic windows. The fact that the diagnostic accuracy of dobutamine MRI is maintained in this group further broadens its clinical utility (Table 15-1).

TABLE 15-1 Summary of Studies Validating the Clinical Utility of Dobutamine Magnetic Resonance Imaging in Detecting Significant Coronary Disease

In these studies and in current routine clinical practice, wall motion abnormalities are identified and graded in a qualitative manner. The heightened image clarity of MRI, however, is well suited for quantitative analysis; this may attenuate the subjectivity involved in dobutamine stress assessment. Dobutamine MRI was performed in 39 consecutive patients referred for coronary angiography and in 10 normal volunteers; wall thickening was quantified using the modified center line technique.⁴⁵ This technique yielded a sensitivity of 91% and specificity of 80% in the detection of significant coronary artery disease. Myocardial tagging has also been applied to dobutamine MRI studies and yields significantly different strain and strain rates in ischemic and infarcted myocardium than in remote normal segments.⁴⁶ Comparing tagged and nontagged images in dobutamine MRI studies, Kuijpers and coworkers⁴⁷ found that tagged images detected inducible wall motion abnormalities in 10 patients who were judged to have normal nontagged studies. All these patients were found to have coronary disease on subsequent coronary angiography. Of note, this trial did not use quantitative methods to determine strain via the tagged images. Further studies are required to determine whether myocardial tagging and quantitative techniques are truly superior to visual assessment of wall motion and whether they should become a standard part of clinical practice (Fig. 15-4).

FIGURE 15-4 Strain assessment by way of myocardial tagging. Tagged end-diastolic (A) and end-systolic (B) images are seen, along with the quantitative assessment of strain (C).

Dobutamine Magnetic Resonance Imaging and Myocardial Viability

Following an ischemic event, differentiating between viable and nonviable myocardial tissue is an important clinical distinction that can help determine the utility of revascularization. Early studies evaluating the use of cardiac MRI for this found that wall thinning and shortened T2 relaxation time at rest could identify regions of chronic infarction (i.e., nonviable myocardium).⁴⁸ Corroborating the importance of wall thickness in assessing for myocardial viability was a study by Baer and colleagues,⁴⁹ which correlated a diastolic wall thickness more than 2.5 standard deviations below the normal mean value and systolic akinesis to markedly reduced technetium uptake.

Another study by this group sought to determine which markers could predict contractile recovery of dysfunctional myocardium following revascularization, a functional definition of myocardial viability.⁵⁰ In this series, 43 patients who suffered a remote myocardial infarction underwent resting and low-dose dobutamine cardiac MRI as well as a follow-up resting MRI after a revascularization procedure (either bypass grafting or angioplasty). A resting diastolic wall thickness of 5.5 mm or more was 92% sensitive but only 56% specific in predicting contractile recovery on postrevascularization MRI. Dobutamine-induced systolic wall thickening of 2 mm or more was highly sensitive (89%) but also very specific (94%) in predicting functional recovery. The authors concluded that low-dose dobutamine cardiac MRI provided more information on myocardial viability than resting MRI alone. Other studies evaluating the use of low-dose dobutamine MRI in assessing for contractile recovery in patients with a recent myocardial infarction have also yielded favorable results, with diagnostic accuracy exceeding 80%.⁵¹^,⁵²

Just as for the detection of coronary stenoses, DSE is also widely used to identify myocardial viability. An early study comparing dobutamine MRI with DSE found a high degree of concordance in the diagnosis of viability.⁵³ Baer and associates⁵⁴ compared dobutamine transesophageal echocardiography (TEE) with dobutamine MRI using positron emission tomography (PET) scanning as the reference standard for viability. Both modalities yielded similar results but MRI was slightly more sensitive and specific than echocardiography. In a follow-up study, a similar head-to-head comparison was performed, this time using contractile recovery following revascularization as the end point. The investigators determined that there was no significant difference between dobutamine TEE and dobutamine MRI in the assessment of viability.⁵⁵ These studies indicated that dobutamine MRI compared favorably with an already accepted technique in the assessment of myocardial viability.

Dobutamine MRI has also been compared with contrast MRI imaging for the assessment of viability (Fig. 15-5). Delayed hyperenhancement techniques using gadolinium contrast are widely used in determining the extent of viable and scarred myocardium, discussed in detail in Chapter 57. Partial wall thickness enhancement (less than 75%) represents an area of uncertainty in predicting contractile recovery, which may be clarified with low-dose dobutamine testing. Kaandorp and colleagues sought to investigate the relevance of intermediate degrees of enhancement⁵⁶ and found that regions with only subendocardial enhancement (encompassing 1% to 50% of total ventricular wall thickness) often exhibited contractile reserve with low-dose dobutamine, whereas areas with transmural involvement (enhancement extending to 76% to 100% of wall thickness) did not improve with dobutamine. Segments with 51% to 75% enhancement varied in their response, with 61% of these segments improving with dobutamine and 39% demonstrating no contractile reserve. The authors concluded that in cases of intermediate hyperenhancement, assessment of contractile reserve with dobutamine may allow optimal identification of segments that are likely to improve with revascularization.

FIGURE 15-5 Viability study using dobutamine to evaluate contractile reserve. End-systolic frames of the four-chamber view at baseline (A) and with low-dose dobutamine (B) show persistent akinesis of the inferior septum (arrows). There is extensive transmural delayed enhancement of this area with gadolinium (C), confirming the lack of viability.

In keeping with this hypothesis, two studies have compared dobutamine MRI with delayed contrast-enhanced MRI in predicting functional improvement after a revascularization procedure in patients with coronary artery disease.⁵⁷^,⁵⁸ Dobutamine MRI exhibited a greater diagnostic accuracy than contrast enhancement; this advantage was largest in segments with intermediate degrees of enhancement (51% to 75%). Low-dose dobutamine MRI compares favorably with echocardiography and delayed hyperenhancement, which is a reflection of its clinical accuracy and utility in evaluating for myocardial viability.

Dobutamine Magnetic Resonance Imaging and Patient Prognosis

Aside from providing physiologic information, the results of a clinically relevant cardiac study should have prognostic implications and risk stratification value. To this end, Hundley and colleagues ⁵⁹ followed 279 patients over an average of 20 months after the completion of full-dose dobutamine MRI. Evidence of inducible ischemia or a resting EF lower than 40% was associated with myocardial infarction and cardiac death independently of the presence of coronary risk factors (Fig. 15-6). Of note, these patients had previous transthoracic echocardiography that was not adequate for wall motion analysis and so the authors concluded that in patients with poor echocardiograms, the results of dobutamine MRI stress tests can be used to forecast myocardial infarction or cardiac death.

FIGURE 15-6 Kaplan-Meier event-free survival curves in patients with an LVEF < 40% or ≥ 40%, with or without inducible ischemia. Compared with patients with an LVEF ≥ 40% and no evidence of inducible ischemia, event-free survival was significantly lower in patients with inducible ischemia (P < .0004) or an LVEF < 40% (P < .00005).

(Adapted from Hundley WG, Morgan TM, Neagle CM, et al. Magnetic resonance imaging determination of cardiac prognosis. Circulation 2002; 106:2328-2333.)

The results of another investigation by Kuijpers and associates ⁶⁰ further suggested the clinical utility of dobutamine MRI in patient risk stratification. Consecutive patients (299) suspected of myocardial ischemia but with indeterminate resting and bicycle exercise electrocardiograms underwent resting and full-dose dobutamine MRI. Patients who had resting wall motion abnormalities were at higher risk for major adverse cardiac events at 2-year follow-up than patients with normal resting wall motion (18% vs. 0.56%; P < .001). Furthermore, the results of dobutamine MRI could classify patients with unknown or intermediate risk (e.g., patients in this study with no prior history of coronary disease, indeterminate resting electrocardiograms, and no resting wall motion abnormalities) more definitively into a high or low coronary risk group. It was concluded that dobutamine MRI may be a valuable tool in risk-stratifying patients, especially those with unclear cardiac risk.

Dobutamine MRI has also been used in the assessment of preoperative cardiovascular risk in patients undergoing noncardiac surgery.⁶¹ In 102 consecutive patients unable to undergo stress echocardiography because of inadequate acoustic windows, 6 patients suffered a perioperative cardiac event and 5 of them had inducible ischemia on their dobutamine MRI. Just as in the earlier study, the investigators though that dobutamine MRI was a significant predictor of cardiac events and could be especially useful for clarifying risk in patients who have intermediate clinical predictors of perioperative cardiac events.

Contraindications

In addition to having the usual contraindications to any MR scan, dobutamine MRI also presents the added risk of an intravenous inotrope. Patients with ongoing ischemia, tachyarrhythmias, intracardiac thrombi, and severe baseline hypertension may not be suitable candidates for dobutamine infusion.

Pitfalls and Solutions

Image quality with dobutamine can be problematic because the tachycardia may decrease temporal and spatial resolution. Using different protocols, including those involving free-breathing sequences, may be a viable option. In cases in which the patient does not reach target heart rate (usually 85% of maximum predicted in tests for ischemia), administering atropine to decrease vagal tone may be required. On the other hand, if the patient develops persistent tachycardia or hypertension with dobutamine infusion, intravenous β blockade may be warranted.

Image Interpretation

In clinical practice, wall motion is assessed visually at rest and at peak stress. The left ventricle is divided into 17 segments and each is given a score ranging from normal to aneurysmal. If wall motion abnormalities are inducible with dobutamine, the location of coronary stenosis that corresponds to the wall motion territory in question is reported.

DYNAMIC LEFT VENTRICULAR FUNCTION USING EXERCISE

Indications and Clinical Utility

In patients who are capable of physical exertion, it may be possible to perform exercise rather than pharmacologic stress MRI. Both bicycle and treadmill exercise have been evaluated as stress agents (Fig. 15-7) and have shown favorable preliminary results. In one study, 16 healthy patients successfully completed supine bicycle stress tests and underwent MR imaging using an ultrafast sequence.⁶² Both the right and left ventricles demonstrated physiologic changes with exercise, such as increased stroke volume and EF and decreased end-systolic volumes, all of which were consistent with previous exercise physiology data. Because of the difficulty in imaging the right ventricle with conventional modalities, this is one of the few reports detailing the response of the right ventricle to exercise. In another trial, which used treadmill exercise, 27 patients with exertional chest pain completed an exercise protocol and subsequent MRI imaging.⁶³ The sequence was 79% sensitive and 85% specific for detecting more than 70% coronary artery stenoses on coronary angiography. These values are similar to those obtained by stress echocardiography and nuclear studies. The authors noted that one of the major limitations of performing treadmill MRI tests is the inability to acquire images within 60 to 90 seconds of cessation of exercise. This report suggests that treadmill MRI testing is at least feasible and further studies are needed to determine the clinical utility of exercise stress MRI in the evaluation of ischemic heart disease.