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(Radiology. 1999;211:129-135.)
© RSNA, 1999

Cardiac Imaging

Hypertrophic Cardiomyopathy: MR Measurement of Coronary Blood Flow and Vasodilator Flow Reserve in Patients and Healthy Subjects1

Nanaka Kawada, MD, Hajime Sakuma, MD, Tetsu Yamakado, MD, Kan Takeda, MD, Naoki Isaka, MD, Takeshi Nakano, MD and Charles B. Higgins, MD

1 From the Departments of Radiology (N.K., H.S., K.T.) and Internal Medicine (T.Y., N.I., T.N.), Mie University School of Medicine, 2-174 Edobashi, Tsu, Mie 514-8507, Japan; and the Department of Radiology, University of California, San Francisco (C.B.H.). From the 1997 RSNA scientific assembly. Received May 11, 1998; revision requested July 10; revision received September 9; accepted October 27. Address reprint requests to N.K.


   Abstract
TOP
 Abstract
Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
PURPOSE: To evaluate coronary blood flow per gram of myocardial mass and vasodilator flow reserve in patients with hypertrophic cardiomyopathy (HCM) and in healthy subjects by using breath-hold velocity-encoded cine (VEC) magnetic resonance (MR) imaging.

MATERIALS AND METHODS: Twenty-nine patients with HCM and nine healthy volunteers were examined. Fast VEC MR images were obtained in an oblique imaging plane perpendicular to the coronary sinus before and after intravenous injection of dipyridamole (0.56 mg/kg). The products of mean velocity and cross-sectional area of the vessel were integrated to measure blood flow. Breath-hold cine MR images encompassing the entire left ventricle were acquired to quantify the left ventricular mass.

RESULTS: In the basal state, the coronary blood flow per gram of myocardial mass was 0.74 mL/min/g ± 0.23 in healthy subjects and 0.62 mL/min/g ± 0.27 in patients with HCM. After administration of dipyridamole, coronary blood flow in patients with HCM increased to a level significantly less than that in healthy subjects (1.03 mL/min/g ± 0.40 vs 2.14 mL/min/g ± 0.51; P < .01), resulting in a severely depressed flow reserve ratio in patients with HCM compared with that in healthy subjects (1.72 ± 0.49 vs 3.01 ± 0.75; P < .01).

CONCLUSION: Breath-hold VEC MR imaging is a noninvasive technique for evaluating coronary flow per gram of myocardial mass and coronary flow reserve.

Index terms: Coronary vessels, flow dynamics, 511.12144, 547.12144 • Coronary vessels, MR, 511.12144, 547.12144 • Heart, cardiomyopathy, 51.12144, 51.86, 524.12144 • Heart, hypertrophy, 51.12144, 524.87 • Myocardium, blood supply, 511.12144 • Myocardium, MR, 511.12144


   Introduction
TOP
 Abstract
 Introduction
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Hypertrophic cardiomyopathy (HCM) is a genetic cardiac disease characterized by left ventricular hypertrophy in the absence of another cause of the increased cardiac mass (1). Previous studies demonstrated myocardial ischemia (2,3) and reduced coronary vasodilator flow reserve (3) in patients with HCM. However, absolute measurement of coronary blood flow and coronary flow reserve requires invasive catheterization of the coronary sinus or positron emission tomography (PET). A noninvasive, widely available method for measuring coronary blood flow and flow reserve would be useful in the evaluation of patients with HCM.

Velocity-encoded cine (VEC) magnetic resonance (MR) imaging allows noninvasive measurement of blood flow in the cardiovascular system without the use of intravascular catheterization or ionizing radiation. VEC MR imaging has been shown to be effective for quantifying blood flow in the aorta (4), pulmonary artery (5), and peripheral vessels (6). MR assessment of blood flow in the coronary sinus, which represents approximately 96% of the total myocardial blood flow, was reported by van Rossum et al in 1992 (7) with the use of a conventional VEC MR sequence without breath holding in healthy volunteers in the resting state. Recently, a more rapid VEC MR sequence has become available, which can acquire phasic flow data during a single breath hold (fast VEC MR) (8,9). This breath-hold method is better for evaluating blood flow in the coronary sinus during pharmacologic stress.

The purposes of the current study were (a) to evaluate absolute coronary blood flow per gram of myocardial mass in patients with HCM and in healthy subjects by quantifying blood flow in the coronary sinus with fast VEC MR imaging and by measuring left ventricular mass with fast cine MR imaging and (b) to compare coronary flow reserve in patients with HCM with that in healthy subjects.


   MATERIALS AND METHODS
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Subjects
Twenty-nine patients with HCM (24 men, five women; age range, 40–73 years; mean age, 62 years ± 8) and nine healthy volunteers (five men, four women; age range, 24–71 years; mean age, 48 years ± 18) without a history of heart or lung disease were examined (age difference between groups not significant). The diagnosis of HCM was made with clinical, echocardiographic, and angiographic evaluation. The mean values (± SD) for the thickness of the interventricular septum, the thickness of the posterior free wall, and the septal-to-posterior wall ratio measured with echocardiography were 17.9 mm ± 3.8, 14.1 mm ± 3.9, and 1.3 ± 0.4, respectively. All patients had normal sinus rhythm. No patient with HCM had a narrowing of the left ventricular outflow tract at cine MR imaging and x-ray angiography. Patients with HCM had normal left ventricular systolic function and had no hemodynamically significant coronary artery stenosis (no more than 25% narrowing of the diameter in the major coronary arteries) at x-ray coronary angiography. The protocol for the study was approved by the institutional ethics committee. All patients and control subjects gave informed consent before entering the study.

Measurement of Blood Flow in the Coronary Sinus
MR imaging was performed with a 1.5-T clinical MR imager (Signa Horizon; GE Medical Systems, Milwaukee, Wis). After placement of electrocardiographic monitoring leads, subjects underwent imaging in the supine position with a 5-inch (12.7-cm) circular surface coil placed on the anterior chest and with a general-purpose flexible surface coil on the back. Electrocardiographic leads were attached to the chest for cardiac gating.

The pulse sequence for fast VEC MR imaging was a phase-contrast fast gradient-echo sequence with k-space segmentation (Fastcard-PC; GE Medical Systems). Oblique coronal VEC MR images were acquired in the imaging plane that was perpendicular to the coronary sinus (Fig 1), with a section thickness of 5 mm, a repetition time of 15 msec and an echo time of 5 msec (15/5), a field of view of 28 x 21 cm, 96 phase-encoding steps, and a reconstructed image matrix of 256 x 192. Uniform radio-frequency excitation was used in this sequence, which maintains the spins in a steady state, eliminates the need for dummy excitations before data collection, and enables the acquisition of data immediately after the electrocardiographic R-wave trigger.



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  		Figure 1. Axial scout MR image acquired from a 49-year-old healthy female volunteer, with a breath-hold cine MR sequence (9/2; section thickness, 5 mm; field of view, 28 x 28 cm; 128 phase-encoding steps; eight views per segment). The oblique coronal imaging plane (long white line) is perpendicular to the coronary sinus (short white line).

 
Velocity-encoding gradients were applied in the section-selective direction with a velocity window of ±100 cm/sec, which provided a sufficient signal-to-noise ratio for flow measurement in the coronary sinus. Four lines in k space were collected per trigger per segment. For each k-space view, positive and negative velocity-encoding data were acquired as a sequential pair. True temporal resolution, the time during which imaging data were acquired for each cine frame, was 120 msec. View-sharing reconstruction was used to improve the effective temporal resolution to 60 msec (9). Magnitude and phase cine images with nine to 13 temporal phases were reconstructed from the data acquired within a single breath hold (Fig 2).



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  		Figure 2a. Breath-hold VEC MR images obtained in the oblique coronal imaging plane from a 56-year-old man with HCM. a, Magnitude image and b, phase difference image (15/5). The blood flow velocity in the coronary sinus (arrow) is indicated as low signal intensity in b.

 


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  		Figure 2b. Breath-hold VEC MR images obtained in the oblique coronal imaging plane from a 56-year-old man with HCM. a, Magnitude image and b, phase difference image (15/5). The blood flow velocity in the coronary sinus (arrow) is indicated as low signal intensity in b.

 
After the subjects took a deep breath in and released it, VEC MR imaging data were acquired with suspended inspiration. The optimal imaging plane was chosen from three consecutive imaging planes so that the coronary sinus was imaged throughout the cardiac cycle, and the section location was as close to the right atrium as possible. After obtaining breath-hold VEC MR images with the patient in the baseline state, 0.56 mg of dipyridamole per kilogram of body weight was injected into the antecubital vein over 4 minutes. VEC MR images on the three consecutive imaging planes were obtained 2 minutes after finishing the injection of dipyridamole. Heart rate and blood pressure were monitored and recorded during the entire examination. No patient or control subject experienced marked adverse effects after the administration of dipyridamole.

MR Image Analysis
The contour of the coronary sinus was manually traced on the magnitude images at each cine frame without knowledge of the identity of the subject. The traced region of interest was applied on the corresponding phase image, and the cross-sectional area and mean velocity were recorded. Although the effect of through-plane motion caused by cardiac contraction in the oblique coronary plane was relatively small, we measured flow velocity in the adjacent tissue to perform phase-offset correction. Volumetric coronary venous flow was calculated by integrating the products of cross-sectional area and mean velocity in the coronary sinus from the nine to 13 images acquired across the cardiac cycle (Fig 3). Coronary flow reserve was calculated as the ratio of the blood flow in the coronary sinus after injection of dipyridamole to the baseline blood flow.



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  		Figure 3. Curve of volume flow in the coronary sinus measured with breath-hold VEC MR imaging in a 56-year-old man with HCM. Biphasic blood flow pattern, with a first peak during systole and a second peak during diastole, was observed.

 
Measurement of Left Ventricular Myocardial Mass
Left ventricular mass was measured in all subjects in the baseline state with breath-hold cine MR imaging (10/2; section thickness, 10 mm; field of view, 32 x 32 cm; reconstructed image matrix, 256 x 128). Short-axis images were acquired from apex to base to cover the entire left ventricle. Epi- and endocardial borders were manually traced. Left ventricular mass was calculated as a product of the specific gravity of myocardium (ie, 1.05) and integrated left ventricular myocardial area. Left ventricular mass was measured on both end-diastolic images and end-systolic images, and the mean of the two measurements in systole and diastole was used for data analysis. The left ventricular mass index was calculated as left ventricular mass divided by body surface area.

Statistical Analysis
All data were expressed as the mean ± SD, except where noted. Group data were analyzed with the Student t test for paired or unpaired data. Statistical significance of the difference was defined as P < .05. Linear regression analysis was performed with the least-squares method.


   RESULTS
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Hemodynamics at Rest and after Dipyridamole Injection
The mean values for the basal systolic blood pressure, diastolic blood pressure, and heart rate were 138 mm Hg ± 22, 78 mm Hg ± 12, and 65 beats per minute ± 11, respectively, in patients with HCM and were 133 mm Hg ± 24, 69 mm Hg ± 13, and 60 beats per minute ± 6, respectively, in healthy subjects (differences between the two groups not significant). After injection of dipyridamole, the mean systolic blood pressure, diastolic blood pressure, and heart rate were 137 mm Hg ± 24, 73 mm Hg ± 13, and 75 beats per minute ± 12 in patients with HCM and were 129 mm Hg ± 21, 66 mm Hg ± 14, and 78 beats per minute ± 12 in healthy subjects (differences between the two groups not significant). No significant change was seen in systolic and diastolic blood pressure before and after dipyridamole injection in healthy subjects and patients with HCM. Heart rate was significantly increased after dipyridamole injection in both groups (P < .05), without significant differences between the two groups.

Left Ventricular Mass Measurements
Figure 4 shows short-axis images of the left ventricle acquired at the end of diastole and at the end of systole in a healthy subject, and Figure 5 shows those images in a patient with HCM. Left ventricular wall thickening was documented on breath-hold cine MR images for all patients with HCM. The mean left ventricular mass in patients with HCM (242.7 g ± 79.1) was significantly greater than that in healthy subjects (124.9 g ± 33.5; P < .01) (Table).



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  		Figure 4a. Short-axis MR images of the left ventricle obtained with a breath-hold cine MR sequence (10/2) in a 24-year-old healthy female volunteer. (a) End-diastolic image. (b) End-systolic image. A normal left ventricular wall (arrow) is demonstrated, with good contrast between the blood pool and the myocardium.

 


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  		Figure 4b. Short-axis MR images of the left ventricle obtained with a breath-hold cine MR sequence (10/2) in a 24-year-old healthy female volunteer. (a) End-diastolic image. (b) End-systolic image. A normal left ventricular wall (arrow) is demonstrated, with good contrast between the blood pool and the myocardium.

 


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  		Figure 5a. Short-axis MR images of the left ventricle obtained with a breath-hold cine MR sequence (10/2) in a 62-year-old man with HCM. (a) End-diastolic and (b) end-systolic images demonstrate that the left ventricular wall (arrow) is hypertrophic.

 


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  		Figure 5b. Short-axis MR images of the left ventricle obtained with a breath-hold cine MR sequence (10/2) in a 62-year-old man with HCM. (a) End-diastolic and (b) end-systolic images demonstrate that the left ventricular wall (arrow) is hypertrophic.

 

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  		Coronary Blood Flow Volume, Myocardial Mass, and Coronary Flow Reserve in Patients with HCM and Healthy Subjects
 
Coronary Blood Flow and Coronary Flow Reserve
In the baseline state, the coronary blood flow per gram of myocardial mass was 0.74 mL/min/g ± 0.23 in healthy subjects and 0.62 mL/min/g ± 0.27 in patients with HCM (not significant). After the administration of dipyridamole, the coronary blood flow per gram of myocardial mass was 2.14 mL/min/g ± 0.51 in healthy subjects, which was significantly higher than that in patients with HCM (1.03 mL/min/g ± 0.40; P < .01) (Fig 6). As demonstrated in Figure 7, the increase of coronary blood flow per gram of myocardial mass induced by dipyridamole injection was considerably greater in healthy subjects compared with that in patients with HCM, resulting in a significant difference in the coronary flow reserve ratio between the two groups, with a coronary flow reserve ratio of 1.72 ± 0.49 in the HCM group and 3.01 ± 0.75 in healthy subjects with normal myocardium (P < .01) (Fig 8, Table).



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  		Figure 6a. Graphs of the coronary blood flow per gram of myocardial mass (a) in the baseline state and (b) after dipyridamole injection. The mean coronary blood flow per gram of myocardial mass in patients with HCM was significantly lower than that in healthy subjects after dipyridamole administration. LV = left ventricle, NS = not significant.

 


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  		Figure 6b. Graphs of the coronary blood flow per gram of myocardial mass (a) in the baseline state and (b) after dipyridamole injection. The mean coronary blood flow per gram of myocardial mass in patients with HCM was significantly lower than that in healthy subjects after dipyridamole administration. LV = left ventricle, NS = not significant.

 


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  		Figure 7a. Graphs of the coronary blood flow per gram of myocardial mass before and after dipyridamole injection. The increase in coronary blood flow was more substantial in (a) healthy subjects than in (b) patients with HCM. LV = left ventricle.

 


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  		Figure 7b. Graphs of the coronary blood flow per gram of myocardial mass before and after dipyridamole injection. The increase in coronary blood flow was more substantial in (a) healthy subjects than in (b) patients with HCM. LV = left ventricle.

 


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  		Figure 8. Graph of the coronary flow reserve (CFR) ratios in healthy subjects and in patients with HCM. The mean coronary flow reserve ratio was significantly lower in patients with HCM than in healthy subjects.

 
Relationship between Coronary Flow Reserve and Left Ventricular Mass
A significant inverse relationship was found between the coronary flow reserve ratio and left ventricular mass index in healthy subjects and patients with HCM (r = -0.60; P < .01) (Fig 9).



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  		Figure 9. Graph of the correlation between the coronary flow reserve (CFR) ratio and the left ventricular (LV) mass index in all subjects. A significant negative correlation was found between the coronary flow reserve ratio and the left ventricular mass index (r = -0.60; P < .01). BSA = body surface area, {bigcirc} = healthy subject, • = patient with HCM.

 

   DISCUSSION
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
The results in the current study show that quantification of blood flow rate per gram of myocardial mass for the entire left ventricle is feasible by using breath-hold VEC MR imaging of the coronary sinus and breath-hold cine MR imaging of the left ventricle. We found that the coronary blood flow per gram of myocardial mass after pharmacologic stress and the vasodilator flow reserve are decreased in patients with HCM.

Measurements of Coronary Blood Flow Rate with MR Imaging and Comparison with Other Techniques
To our knowledge, no previous study has measured the coronary blood flow per gram of myocardial mass by using the VEC MR technique. The coronary blood flow in healthy subjects has been measured by several investigators noninvasively with PET (10–13). MR measurement of blood flow in control subjects was 0.74 mL/min/g ± 0.23 in the current study. Our data showed relatively good agreement with the values reported by Czernin et al (10) (0.76 mL/min/g ± 0.17), by Gewirtz et al (11) (0.81 mL/min/g ± 0.32), by de Silva et al (12) (0.97 mL/min/g ± 0.22), and by Nienaber et al (13) (0.99 mL/min/g ± 0.13).

In the current study, MR measurement of coronary flow reserve was significantly lower in patients with HCM than in control subjects. These findings are consistent with those of some previous studies (14,15). Mammola et al (14) measured the coronary flow reserve ratio in the left main coronary artery with transesophageal Doppler flow imaging, demonstrating that the coronary flow reserve ratio was impaired in patients with hypertrophic obstructive cardiomyopathy when compared with that in normal hearts (1.8 ± 0.3 vs 3.1 ± 0.5; P < .01). In a study with PET, Camici et al (15) found that regional myocardial blood flow in patients with HCM increased significantly less than that in control subjects after pharmacologically (dipyridamole) induced vasodilation (1.63 mL/min/g ± 0.58 vs 2.99 mL/min/g ± 1.06; P < .001).

Advantages and Disadvantages of Breath-hold VEC MR Imaging versus Non–Breath-hold VEC MR Imaging
MR assessment of total myocardial blood flow in the resting state was re ported by van Rossum et al (7), who used a conventional VEC MR sequence. Because MR imaging data need to be acquired for more than 4 minutes, conventional VEC MR imaging may not be adequate for evaluating absolute myocardial blood flow after pharmacologic stress. With breath-hold VEC MR imaging, all data can be acquired during a single breath hold. Therefore, assessment of coronary blood flow after the administration of short-acting pharmacologic agents, such as dobutamine or adenosine, can be achieved with breath-hold VEC MR imaging. In addition, in a study comparing breath-hold and non–breath-hold VEC MR images, the breath-hold version of the sequence showed better overall image quality because respiratory blurring and ghosting artifacts can be suppressed with data acquisition over a single breath hold (16).

Breath-hold VEC MR imaging also has disadvantages. Breath holding changes the intrathoracic pressure, which can affect venous return to the heart and cardiac output. Therefore, the myocardial blood flow may be altered during a breath hold compared with the flow measured during regular breathing. Further studies are required to compare the coronary flow rate measured with breath-hold VEC MR imaging with the flow measured with respiratory-triggered VEC MR imaging. However, it is unrealistic to assert that breath holding should have any important influence on coronary flow reserve or on the depression of coronary flow reserve in patients with HCM, which is the major finding of the current study.

Limitations of Flow Measurement with Breath-hold VEC MR Imaging
Because the spatial resolution of the current breath-hold VEC MR image was approximately 1 x 2 mm, the effects of partial volume averaging along the border of the vessel could not be negligible in a small vessel. The limited spatial resolution of the MR image remains a major concern for the accuracy of measuring volume flow in the coronary artery with a phase-contrast MR technique. However, the coronary sinus is larger than the coronary artery; the coronary sinus measures approximately 7–10 mm in diameter and occupies more than 6 pixels. Therefore, errors caused by the limited spatial resolution are less important in quantifying flow volume in the coronary sinus than in quantifying flow volume in the coronary artery. Assessment of accurate peak flow velocity requires a good temporal resolution of the cine images. Fortunately, volume flow rate (in milliliters per minute) is generally less sensitive to the temporal resolution. In a previous study, investigators demonstrated that coronary arterial flow (in milliliters per minute) can be accurately quantified with VEC MR images with relatively low temporal resolution (17).

Although we did not have direct validation of MR measurement of blood flow in the coronary sinus in this study, we have compared MR assessments of flow volume in the coronary arteries with those measured by a transit-time ultrasound flow probe in open-chest dogs in a previous study (18). The results indicated that breath-hold VEC MR imaging can provide accurate quantification of coronary blood flow. Recently, Schwitter et al (19) measured blood flow in the coronary sinus with conventional VEC MR imaging and compared that with global myocardial perfusion assessed with nitrogen 13-labeled ammonia PET in five healthy volunteers. These investigators (19) found an excellent correlation (r = 0.95) between MR flow measurement of the coronary sinus and global myocardial perfusion assessed with PET.

The flow measurement for the coronary sinus reflects nearly total myocardial blood flow for the left ventricle, so regional distribution of the coronary blood flow cannot be evaluated. Assessment of the regional distribution of myocardial flow requires myocardial perfusion MR imaging with first-pass distribution of MR contrast medium or myocardial perfusion scintigraphy. However, flow measurement with VEC MR imaging seems especially attractive for the assessment of global myocardial perfusion abnormalities and dysfunction of coronary vasoactivity in diffuse myocardial disease, such as myocardial hypertrophy and other disease (20). To our knowledge, up until the time this article was written, the evaluation of generalized coronary vascular dysfunction has required PET or catheterization.

The assumption that coronary sinus blood flow represents the entire left ventricular myocardial blood flow could be questioned. It is based on the observation by Hood (21) that 96% of the small veins arising from the left ventricular free wall and the ventricular septum drain into the coronary sinus. Thus, the coronary sinus blood flow can provide an adequate assessment of the left ventricular myocardial blood flow. In the current study, the imaging sections for flow measurements were located as close to the right atrial ostium of the coronary sinus as possible to detect the entire venous blood flow through the coronary sinus.

Administration of dipyridamole increases plasma adenosine levels and causes direct coronary vasodilation (22). The agent therefore uncouples blood flow from oxygen demand or from cardiac work. Consequently, pharmacologic stress with dipyridamole is physiologically different from the exercise stress test. The results of a previous study with PET demonstrated that the reduction in coronary flow reserve measured after the administration of dipyridamole is more pronounced in patients with HCM who have a history of chest pain than in those without a history of chest pain (15). Therefore, noninvasive MR assessment of the coronary flow and flow reserve with dipyridamole seems appropriate for evaluating the functional severity of the disease and possibly determining a prognosis for the patients.

Clinical Implications
Several explanations of myocardial ischemia and decreased coronary flow reserve in patients with HCM have been proposed previously. Capillary density in the hypertrophied heart may be inadequate relative to the increased myocardial mass (23), and abnormally narrowed intramural coronary arteries have been identified in the histologic specimens from patients with HCM (24). In addition, increased compression of intramyocardial coronary arteries in the systolic phase may cause decreased systolic coronary blood flow in patients with HCM (25). Impaired left ventricular relaxation in patients with HCM (26,27) may also limit the rapid increase in early diastolic perfusion, resulting in decreased coronary blood flow during the diastolic phase (28). Noninvasive flow measurement in the coronary sinus with VEC MR imaging may be useful in monitoring the physiologic state of perfusion abnormalities and in determining a prognosis for patients with myocardial hypertrophy.

A statistically significant correlation was seen between the coronary flow reserve and left ventricular myocardial mass. The relation between left ventricular mass and coronary flow reserve was studied previously by Houghton et al (29) in hypertensive patients with left ventricular hypertrophy. These investigators (29) observed no statistically significant linear relation between left ventricular mass and coronary flow reserve. To compensate for the difference in the size of patients, the left ventricular mass index was used to evaluate correlation with the coronary flow reserve ratio. We observed a relatively good correlation between the coronary flow reserve ratio and the left ventricular mass index (r = -0.60; P < .01). Further studies are required to address the clinical implications of this finding.

In conclusion, MR measurements of coronary blood flow per gram of myocardial mass in healthy subjects showed good agreement with the values previously reported with other methods. The absolute coronary blood flow rate per gram of myocardial mass was significantly lower in the group with HCM than in the healthy subjects after pharmacologic stress with dipyridamole administration. Vasodilator flow reserve was significantly lower in patients with HCM than in healthy subjects. Breath-hold VEC MR imaging is a noninvasive technique that can provide assessments of altered coronary blood flow per gram of myocardial mass and vasodilator flow reserve in patients with HCM and possibly other myocardial disease.


   Acknowledgments
 
We thank Stephan Maier, MD, PhD, and Ferenc A. Jolesz, MD, Brigham and Women's Hospital, Harvard Medical School, for allowing us to use XPHASE software.


   Footnotes
 
Abbreviations: HCM = hypertrophic cardiomyopathy VEC = velocity-encoded cine

Author contributions: Guarantors of integrity of entire study, N.K., H.S., K.T.; study concepts, H.S., T.Y., C.B.H.; study design, H.S.; definition of intellectual content, H.S., T.Y., T.N., C.B.H.; literature research, N.K., H.S., T.Y.; clinical studies, T.Y., N.I., T.N.; data acquisition, H.S.; data analysis, N.K., H.S.; statistical analysis, N.K., H.S.; manuscript preparation and editing, N.K., H.S.; manuscript review, K.T., T.Y., C.B.H.


   References
TOP
 Abstract
 Introduction
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

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