Interstudy reproducibility of dimensional and functional measurements between cine magnetic resonance studies in the morphologically abnormal left ventricle

Magnetic resonance microimaging for noninvasive quantification of myocardial function and mass in the mouse

The purpose of this work was to develop high-resolution cardiac magnetic resonance imaging techniques for the in vivo mouse model for quantification of myocardial function and mass. Eight male mice were investigated on a 7-Tesla MRI scanner. High-quality images in multiple short axis slices (in-plane resolution 117 microm2, slice thickness 1 mm) were acquired with an ECG-gated cine sequence. Left ventricular end-diastolic and end-systolic volumes and mass were calculated from segmented slice volumes. There was precise agreement of left ventricular mass determined ex vivo and by MRI. Intraobserver (5%) and interobserver (5%) variability of in vivo MR measurements were low.

Congenital heart disease: measuring physiology with MRI

Cine MRI and VEC MRI can be used to quantitate the physiology of the heart and great vessels in patients with CHD. This information can be a valuable adjunct to anatomical imaging for preoperative planning as well as postoperative monitoring. Some important clinical applications of quantitative cardiovascular functional MRI include measurement of ventricular masses, stroke volumes, and ejection fractions; estimation of shunts and valvular regurgitation; assessment of collateral blood flow and pressure gradients in aortic coarctation; and postsurgical evaluation of conduit blood flow and pressure gradients.

Reproducibility of right and left ventricular volume measurements by electron-beam CT in patients with congestive heart failure

The applicability and reproducibility of electron-beam computed tomography (EBCT) was tested to define left and right ventricular volumes in patients with congestive heart failure in a clinical setting.

METHODS

Ten patients (mean age 64 +/- 11 years) with dilated hearts and stable congestive heart failure (functional class III-IV) were studied. After determination of the individual circulation time, two serial short axis polytomographic EBCT studies were performed within a mean interval of 14.8 +/- 10 days. Following intravenous contrast administration, biventricular end-diastolic volumes (LVEDV, RVEDV), end-systolic volumes (LVESV, RVESV), and left ventricular muscle mass (LVMM) were determined using previously developed techniques.

RESULTS

Adequate contrast opacification in both ventricular cavities was obtained in all patients at baseline and at follow-up. Values were 323.4 +/- 99.3 (mean +/- SD) and 332.6 +/- 105.4 ml for LVEDV, 249.3 +/- 75.6 and 250.5 +/- 79.3 ml for LVESV, 236.8 +/- 56.2 and 251.2 +/- 72.7 ml for RVEDV, 179.8 +/- 76.4 and 188.3 +/- 64.0 ml for RVESV, and 207.7 +/- 70.6 and 204.9 +/- 81.9 g for LVMM (p = NS, respectively, paired t-test). Linear regression analysis correlating biventricular volumes and left ventricular muscle mass measurements in the serial scans yielded r-values in the range of 0.89 to 0.95 and a small SEE. The SE of the mean differences between left and right ventricular ejection fraction measurements was 1 point, respectively.

CONCLUSION

EBCT studies of ventricular volumes in patients with dilated hearts and congestive heart failure are highly reproducible and offer the potential for serial assessment of these patients in whom quantitation of ventricular volumes has been shown to be of prognostic value.

Cardiac MR imaging in congenital heart disease

Magnetic resonance imaging is a unique and insightful tool for the assessment of structure and function in congenital heart disease. For anatomic assessment, the large field of view, lack of limitation by patient size, and ability to create three-dimensional surface displays from routine imaging acquisitions offer several advantages over other modalities. The ability of magnetic resonance imaging to assess the volume and mass of bizarre ventricular shapes accurately and myocardial tissue and blood tagging as well as phase encoded velocity mapping has enhanced research in pediatric cardiology. Newer techniques, such as oxygen-sensitive magnetic resonance imaging and echo-planar magnetic resonance imaging, promise even further advances in research and in clinical applications.

Integrated approach to ischemic heart disease. The one-stop shop

Magnetic resonance imaging is unique in its variety of applications for imaging the cardiovascular system. A thorough assessment of myocardial structure, function, and perfusion; assessment of coronary artery anatomy and flow; and spectroscopic evaluation of cardiac energetics can be readily performed by magnetic resonance imaging. One key to the advancement of cardiac magnetic resonance imaging as a clinical tool in the evaluation, the so called one stop shop. Improvements in magnetic resonance hardware, software, and imaging speed now permit this integrated examination. Cardiac magnetic resonance is a powerful technique with the potential to replace or complement other commonly used techniques in the diagnostic armamentarium of physicians caring for patients with ischemic heart disease.

Imaging cardiac structure and pump function

This article describes magnetic resonance imaging approaches for assessing cardiac structure and myocardial pump function. The article is divided into cardiac structure and ventricular function. Throughout, representative images are included. There are numerous applications of magnetic resonance imaging for assessing cardiac structure and function, and magnetic resonance imaging compared favorably to other imaging modalities.

Atrial natriuretic peptide release is more dependent on atrial filling volume than on filling pressure in chronic congestive heart failure

BACKGROUND

The mechanism of atrial natriuretic peptide (ANP) release has been difficult to demonstrate in patient studies because of inaccuracies in measuring atrial volumes using conventional techniques.

METHODS

Magnetic resonance imaging was performed in 28 clinically stable patients (New York Heart Association class 3) with chronic heart failure to determine right atrial (RA), left atrial (LA), and ventricular volumes. In addition, right heart catheterization was serially performed and plasma ANP levels (in picograms per milliliter) were drawn from the right atrium.

RESULTS

Five patients had to be excluded from data analysis for technical reasons. The remaining 23 patients had the following hemodynamic measurements (mean +/- SD): RA mean pressure 7+/-5 mm Hg, pulmonary artery mean pressure 28+/-10, pulmonary capillary wedge pressure 21+/-8 mm Hg, and cardiac index 2.9+/-1.4 (L/min/m2), respectively. Plasma ANP levels were significantly elevated at 162+/-117 (normal range 20 to 65 pg/ml, p < 0.05), as were LA and RA volumes compared with healthy controls (RA volume 128+/-64 ml vs 82+/-25 ml, p < 0.05; LA volume 157+/-54 ml vs 71+/-24 ml, p < 0.01, respectively). ANP showed a stronger relation with atrial volumes (RA volume, r = 0.91, p = 0.0001; LA volume, r = 0.80, p = 0.001) than with atrial pressures (RA mean pressure, r = 0.45, p = 0.03; pulmonary capillary wedge pressure, r = 0.67, p = 0.001). A subgroup analysis of patients with increased RA or LA volumes (>1 SD of mean of controls) revealed a stronger relation between ANP and RA volumes than between ANP and LA volumes.

CONCLUSIONS

These data suggest that increased right heart volume with subsequent increased atrial stretch is the major determinant for ANP release in patients with stable CHF.

Hypertensive heart disease: quantitative evaluation of response to therapy with cine MR imaging

RATIONALE AND OBJECTIVES

To assess the ability of cine magnetic resonance (MR) imaging to help detect and quantity changes in left ventricular parameters in patients receiving antihypertensive therapy.

MATERIALS AND METHODS

After undergoing baseline cine MR imaging of the heart, 16 (12 men, four women) hypertensive patients participating in a prospective drug trial began isradipine therapy. Follow-up serial cine MR imaging was performed at 3 months and 6 months. Myocardial mass, end-systolic volume, end-diastolic volume, stroke volume, and ejection fraction were measured. Results from transaxially acquired three-dimensional data sets and monoplanar imaging were compared.

RESULTS

Three dimensional data showed reductions of 11% in end-systolic volume (P = .0051) and 17% in end-diastolic volume (P = .0023). These changes were not detected with monoplanar imaging. Changes in myocardial mass, stroke volume, and ejection fraction were not statistically significant.

CONCLUSION

Three-dimensional cine MR imaging can depict small yet statistically significant reductions in left ventricular volumes in response to antihypertensive therapy.

Comparison between manual and semiautomated analysis of left ventricular volume parameters from short-axis MR images

PURPOSE

The goal of this study was to evaluate a newly developed semiautomated contour detection algorithm for the quantitative analysis of cardiovascular MRI.

METHOD

Left ventricular function parameters derived from automatically detected endocardial and epicardial contours were compared with results derived from manually traced contours in short-axis multislice GRE MRI studies of 10 normal volunteers and 10 infarct patients.

RESULTS

Compared with manual image analysis, the semiautomated method resulted in the following systematic and random differences (auto-manual; mean +/- SD): end-diastolic volume: -5.5 +/- 9.7 ml; end-systolic volume: -3.6 +/- 6.5 ml; ejection fraction: 1.7 +/- 4.1%; left ventricular mass: 7.3 +/- 20.6 g. Total analysis time for a complete study was reduced from 3-4 h for the manual analysis to < 20 min using semiautomated contour detection.

CONCLUSION

Global left ventricular function parameters can be obtained with a high degree of accuracy and precision using the present semiautomated contour detection algorithm.

Simulation of two-dimensional tagged MRI

MR tagging is a recent imaging development that, in cardiac applications, makes possible the tracking of points in the myocardium during the cardiac cycle. Researchers have developed semiautomated, computer-based methods for analyzing tagged images, but the images are complex and present a challenge to automated tracking systems. Simulation can provide an inexhaustible supply of images for testing and validation of tag tracking software and preview the effect of parameter changes in acquisition. SIMTAG is an interactive computer program that simulates two-dimensional tagged-MR experiments. The mathematic model used in the simulation and algorithms for simulating image noise and object deformation are described. Examples of the use of simulated images in SPAMM parameter selection, a comparison of tag contrast in signal-averaged SPAMM and CSPAMM, and simulated images as test sets for tag-tracking software are presented.

Assessment of quantitative hypertrophy scores in hypertrophic cardiomyopathy: magnetic resonance imaging versus echocardiography

To compare the diagnostic value of spin-echo magnetic resonance (MR) imaging and transthoracic echocardiography in quantitative assessment of the extent of hypertrophy in patients with hypertrophic cardiomyopathy (HCM), we examined 52 consecutive patients with HCM. The Spirito-Maron and Wigle hypertrophy scores were calculated with wall thickness measurements obtained by both imaging modalities. MR imaging yielded complete assessment of anatomic features and allowed calculation of hypertrophy scores in 49 patients (94%). Adequate echocardiograms were obtained in 33 patients (63%) and correlated well with MR imaging for wall thickness measurements and for determination of the two hypertrophy scores (both r> 0.9). MR imaging provided additional information not available by echocardiography in 16 patients (31%). We conclude that the Spirito-Maron and Wigle hypertrophy scores correlated well between echocardiography and MR imaging. Because echocardiography was of insufficient quality for calculating adequate hypertrophy scores in 19 (37%) patients, MR imaging provided the most comprehensive diagnostic information in patients with HCM.

New imaging techniques for assessing cardiac function

In summary, newer imaging technologies yield three-dimensional pictures of the left ventricle. Detailed information is provided on regional wall motion, wall thickening, and ventricular volumes, which can be helpful in managing patients with cardiac disease. MR imaging gives the highest resolution images, and MR angiography can be invaluable in assessing the anatomy of an aortic dissection. Gated tomography with a technetium-based myocardial perfusion tracer can be thought of as a low-resolution cine MR imaging study. Combined function and perfusion nuclear studies performed at rest in an ICU can give information on myocardial perfusion and stunning, which is helpful in managing patients with acute ischemic syndromes. First pass RNA is probably the most accurate method for measuring RVEF and can be performed at the bedside using a portable multicrystal camera. Serial measurements of RVEF may be helpful in managing patients with pulmonary hypertension of various causes. For patients with documented acute myocardial infarction or chest pain and no acute myocardial necrosis or for patients undergoing preoperative risk assessment, combined perfusion and function using nuclear techniques yields both stress-induced ischemia and resting ventricular function in a single procedure and is timely and cost effective.

Late ventricular geometry and performance changes of functional single ventricle throughout staged Fontan reconstruction assessed by magnetic resonance imaging

OBJECTIVES

We sought to test the hypothesis that late ventricular geometry and performance changes occur in functional single ventricles as they progress through staged Fontan reconstruction.

BACKGROUND

Indexes of ventricular geometry and performance are important in evaluating the functional state of the heart. Magnetic resonance imaging determines these indexes in complex ventricular shapes with minimal geometric assumptions. Previous studies have shown that 1 week after hemiFontan, the mass/volume ratio markedly increases.

METHODS

Multiphase, multislice, spin echo (n = 5) and cine (n = 30) magnetic resonance imaging was performed in 35 patients with a functional single ventricle (1 week to 12 years old) at various stages of Fontan reconstruction (15 in the pre hemiFontan stage, 11 after [6 to 9 months] the hemiFontan procedure and 9 after [1 to 2 years] the Fontan procedure). Volume and mass were calculated at end-systole and end-diastole. Ventricular output was then obtained. Ventricular centroid motion was also calculated.

RESULTS

No difference was noted (power > 72%) from the pre hemiFontan stage to 6 to 9 months after the hemiFontan procedure in (mean +/- SD) end-diastolic volume (104 +/- 24 vs. 123 +/- 40 cc/m2), mass (171 +/- 46 vs. 202 +/- 61 g/m2), ventricular output (7.9 +/- 2.2 vs. 6.6 +/- 2.4 liters/min per m2) or centroid motion (6.9 +/- 2.8 vs. 6.7 +/- 2. mm/m2). Patients in the Fontan group demonstrated a marked decrease in all indexes, indicating significant volume unloading and decrease in mass and ventricular performance. Mass/volume ratio was not significantly different among all three groups.

CONCLUSIONS

No geometric and performance changes from the volume-loaded stage are noted 6 to 9 months after the hemiFontan procedure; however, major changes occur 1 to 2 years after the Fontan procedure. The dramatic changes in the mass/volume ratio seen early after the hemiFontan procedure were not detected at 6 to 9 months. Furthermore diminution of mass, volume and ventricular performance are present at least 2 years after the Fontan procedure.

Magnetic resonance imaging in ischemic heart disease

The clinical use of MR imaging in ischemic heart disease is still limited, although this is the major cardiac disease afflicting populations of many countries. However, with the recent development of faster MR techniques, MR imaging provides multiple capabilities for the evaluation of most aspects of ischemic heart disease. We described the potential application of MR imaging for identifying and quantifying morphologic and functional alterations caused by myocardial infarction and ischemia; the contribution of MR contrast media to improve tissue characterization and to identify ischemic myocardium; and the application of fast MR imaging techniques for assessing anatomy and blood flow in the native coronary arteries and bypass conduits. With continued development of these capabilities, MR imaging has the potential to be a comprehensive noninvasive imaging modality in ischemic heart disease.

Accuracy of biplane long-axis left ventricular volume determined by cine magnetic resonance imaging in patients with regional and global dysfunction

Left ventricular (LV) volumes and ejection fraction can be obtained by applying Simpson's rule to multiple short-axis tomographic planes. A simpler method for determining LV volumes using the area-length equation is widely accepted and requires less time to acquire and analyze. Its accuracy, however, is questionable in deformed or asymmetrically contracting ventricles. This study compares biplane long-axis to serial short-axis computed LV volumes obtained by cine gradient-echo magnetic resonance imaging (MRI) in 2 distinct patient populations: (1) patients with global LV dysfunction, and (2) patients with regional LV dysfunction. A total of 114 patients were studied using both methods. Among 37 patients with global LV dysfunction, there was no statistically significant difference between methods (long axis vs short axis) for determining LV end-diastolic volume (203 +/- 91 vs 201 +/- 90 ml), end-systolic volume (142 +/- 81 vs 141 +/- 82 ml), and ejection fraction (33 +/- 12 vs 33 +/- 13%). However, in the 77 patients with regional dysfunction, LV end-diastolic volume was statistically slightly higher when obtained using the long-axis approach (157 +/- 53 vs 152 +/- 51 ml; p=0.004). Otherwise, end-systolic volume (97 +/- 49 vs 95 +/- 49 ml) and ejection fraction (40 +/- 13 vs 40 +/- 13%) were similar (p=NS). The correlation between LV volumes and ejection fractions for both groups was excellent (r >0.91). Thus, in this study group, biplane long-axis and serial short-axis computed LV volumes and ejection fractions were similar in patients with global or regional LV dysfunction. In critically ill patients unable to complete a comprehensive MRI examination, the biplane long-axis-derived volumes provide adequate data.

Measurement of ventricular volumes by cine magnetic resonance imaging in complex congenital heart disease with morphologically abnormal ventricles

This study assessed the validity of cine magnetic resonance imaging (MRI) for measuring right and left ventricular volumes by using Simpson's rule in children with complex congenital heart disease. Forty-five patients with complex congenital heart disease (average age 2.6 years) and 10 controls (average age 2.3 years) were evaluated. The whole heart was encompassed by contiguous transverse sections. Ventricular volumes were calculated by adding luminal areas determined in each section at end diastole and end systole. End-diastolic and end-systolic volumes by MRI in both groups correlated well with those by ventriculography (r>0.89). Comparison of the ejection fraction in both ventricles in both groups yielded a good correlation between MRI and ventriculography (r>0.67). MRI technique in both groups had low intraobserver and interobserver variation (<6%). Cine MRI provides a suitable noninvasive means of quantifying ventricular volume in children with complex congenital heart disease.

Rapid assessment of left ventricular volume by short axis cine MRI

MRI is an established and accurate method of measuring left and right ventricular volumes by summing chamber areas in multiple contiguous slices. Acquisition time may be up to 45 min. We have estimated volumes with gradient echo imaging to test the accuracy of a more rapid method (total acquisition time 15 min) using a recognized echocardiographic algorithm. The results were compared with the spin echo method. We studied 20 patients (mean age 52 years, 15 male) within 6 months of anterior myocardial infarction and 20 normal subjects (mean age 40 years, 19 males). For the rapid method, cine acquisitions were made in the horizontal long axis plane and in two short axis planes which divided the long axis into three equal parts. Volume was calculated assuming the ventricle to be composed of a cylinder, a truncated cone and a cone. There was good agreement between the two methods at end diastole with a mean difference (+/- standard error, +/- 95% confidence interval for limits of agreement) of -3 ml (+/- 8.3, +/- 37%) for normal subjects and 1.5 ml (+/- 4.2, +/- 25%) for patients. Agreement was less good at end systole with mean difference of 12.1 (+/- 3.5, +/- 41%) for normal subjects and 25.7 (+/- 3.7, +/- 47%) for patients. The rapid method, therefore, significantly underestimated end systolic volume compared with the previous method. Rapid measurements of end diastolic volume are more accurate than those of end systolic volume and hence ejection fraction. Provided the potential error is recognized, the rapid technique can be used in routine clinical practice in both normal and abnormal ventricles.

Improved reproducibility in measuring LV volumes and mass using multicoil breath-hold cine MR imaging

There is a generally recognized need for improvement in quality of fast cardiac MR images. Consequently, breath-hold cine MR images were obtained with multiple surface coils connected to phased array receivers, and C/N, intra-observer and inter-observer variabilities for LV volumes and mass were evaluated. Two sets of short-axis images of the LV, one with multiple surface coils and another with a body coil, were acquired in eight subjects with a fast cine MR sequence using k-space segmentation (TR/TE = 7/2.2 msec, temporal resolution = 56 msec). C/N with multicoil imaging was 32.2 +/- 7.6 (mean +/- SD), significantly higher than that with a body coil (11.0 +/- 3.3, P < .01). The mean percentage differences in intra-observer and inter-observer measurements with multicoil imaging were significantly better than those with a body coil. In conclusion, multicoil imaging provides significant gain in C/N on breath-hold cine MRI of the heart. In addition, intra-observer and inter-observer reproducibilities are improved with multicoil imaging.

Low-dosage dobutamine magnetic resonance imaging as an alternative to echocardiography in the detection of viable myocardium after acute infarction

The objective of this study was the evaluation of the feasibility of magnetic resonance (MR) imaging of the heart with low-dosage dobutamine stimulation for the detection of viability after acute myocardial infarction. Gradient echo MR images were obtained in 37 patients with recent myocardial infarction. Images of wall motion abnormalities and their reaction to low-dosage dobutamine stimulation were analyzed and compared with two-dimensional echocardiograms. Follow-up echocardiography at 3 to 6 months was available in 24 patients. Concordant diagnosis of viability between the two techniques was obtained in 30 (81%) of 37 patients. MR correctly predicted evolution of wall motion in 19 (79%) of 24 patients, a result not significantly different from echocardiography: 20 (83%) of 24. It was concluded that low-dosage dobutamine MR imaging is a safe alternative to echocardiography to predict recovery of wall motion abnormalities after myocardial infarction.

M-mode magnetic resonance imaging: a new modality for assessing cardiac function

Magnetic resonance imaging (MRI) studies of the heart have been used for some years, but there are few tools available to quantify cardiac motion. A method has been developed that creates an M-mode MRI image, analogous to the one used in echocardiography, to display motion along a line as a function of time. The M-mode image is created from MRI images acquired with an ordinary gradient echo cine sequence. In a cinematographic display of the images, a cursor line can be positioned in order to determine the orientation of the measurement. A resampling algorithm then calculates the appearance of the M-mode image along the cursor line. The MRI method has been compared to echocardiographic M-mode in a phantom study and by measuring mitral and tricuspid annulus motion in 20 normal subjects. The phantom study showed no significant differences between MRI and echocardiographic M-mode measurements (difference < 1 mm). The annulus motion exhibits a similar pattern using both methods and the measured amplitudes are in close agreement. M-mode MRI provides similar information to echocardiography, but the cursor line can be placed arbitrarily within the image plane and the method is thus not limited to certain acoustic windows. This makes M-mode MRI a promising technique for assessing cardiac motion.

Assessment of valvular heart disease by magnetic resonance imaging

MRI has developed very rapidly and now provides anatomic and functional information in cases of valvular heart disease. MRI has several important attributes that make it advantageous for the evaluation of valvular heart disease. First, the natural contrast between flowing blood and surrounding cardiovascular structures provides sharp delineation of endocardial and epicardial borders without the need for contrast media. This feature in combination with the essential three-dimensional nature of this imaging technique allows precise quantification of cardiac volumes, function, and mass without the use of any assumed formulas or geometric models. Second, blood flow-sensitive GRE techniques are able to identify areas of turbulent flow caused by stenotic or regurgitant valves. With this technique regurgitant jets can be visualized and semiquantitative grading can be performed as with color Doppler. Third, recently developed velocity-encoded techniques permit measurements of blood flow velocities across stenotic native and prosthetic heart valves and retrograde flow caused by regurgitation. Moreover, the close interstudy reproducibility of measurements of cardiac dimensions and valvular regurgitation suggests a role in assessing the effect of therapeutic interventions.

Evaluation of cardiac function with magnetic resonance imaging

A large body of evidence has accumulated to substantiate the accuracy of functional MR measurements of both ventricles. Because of good accuracy and superior reproducibility, MR imaging may be considered the gold standard for in vivo quantification of left and right ventricular ejection fraction, myocardial mass, and wall stress. New prospects for functional MR imaging include determination of the end-systolic volume-pressure relation as an index of myocardial contractility. The ability of MR imaging to detect wall motion disturbances may be enhanced further by combining myocardial tagging techniques with finite element analysis. Conventional MR imaging is limited by long examination times, but recent ultrafast modifications of echo-planar imaging allow completion of a functional heart study within seconds. Implementation of ultrafast MR imaging will greatly increase the usefulness of MR imaging for routine evaluation of cardiac function.

Quantification of collateral blood flow in coarctation of the aorta by velocity encoded cine magnetic resonance imaging

BACKGROUND

Knowledge about the volume of collateral flow provides insight into the severity of coarctation of the aorta and may be critical in planning the operative approach. There is currently no method for the quantification of collateral flow in coarctation of the aorta. In this study, we applied velocity encoded cine magnetic resonance imaging (VENC-MR) to establish the flow pattern and volume of collateral flow in the descending thoracic aorta in normal subjects and patients with coarctation, introducing a new possibility to quantify the severity of the coarctation by determining the amount of collateral flow.

METHODS AND RESULTS

VENC-MR was used to measure flow in the proximal and distal descending thoracic aorta in 10 normal subjects. In 23 patients with coarctation, flow was measured near the coarctation site and above the diaphragm. Patients were divided into a group with moderate to severe coarctation and a group with mild coarctation on the basis of clinical gradient between upper and lower extremities and the estimation of the gradient across the coarctation by Doppler echocardiography. The gradient across the coarctation and the degree of anatomic narrowing were also assessed by MR imaging. In normal volunteers, VENC-MR showed a 7 +/- 6% decrease in total flow, from proximal to distal aorta. The interobserver reproducibility was 3.9% to 4.9% (mean, 4.4%). In patients with moderate to severe coarctation, VENC-MR demonstrated an 83 +/- 50% increase in total flow from proximal to distal aorta, yielding a significant change compared with normal subjects (P < .01). Patients with mild coarctation showed a normal flow pattern and no significant change in total flow. There was a significant relation between the amount of flow increase in the distal aorta and the reduction in luminal diameter at the coarctation site (r = .94) as well as the clinical gradient (r = .84).

CONCLUSIONS

This study shows the normal flow pattern in the descending thoracic aorta and its reversal in coarctation due to collateral flow. Thus, VENC-MR can measure collateral flow in coarctation and serves as a unique method for providing this important measurement of the severity of coarctation of the aorta.

Evaluation of left atrial contribution to left ventricular filling in aortic stenosis by velocity-encoded cine MRI

Velocity-encoded cine MRI (VEC-MRI) can measure volume flow at specified site in the heart. This study used VEC-MRI to measure flow across the mitral valve to compare the contribution of atrial systole to left atrial filling in normal subjects and patients with left ventricular hypertrophy. The study population consisted of 12 normal subjects (mean age 34.5 years) and nine patients with various degrees of left ventricular hypertrophy resulting from aortic stenosis (mean age 70 years). VEC-MRI was performed in double-oblique planes through the heart to measure both the mitral inflow velocity pattern (E/A ratio) and the volumetric flow across the mitral valve. The left atrial contribution to left ventricular filling (AC%) was calculated. The results were compared with Doppler echocardiographic parameters. The VEC-MRI-derived mitral E/A ratios showed a significant linear correlation with E/A ratios calculated from Doppler echocardiography (r = 0.94), and the VEC-MRI-derived E/A ratios (2.1 +/- 0.5 vs 1.0 +/- 0.4) and AC% values (24.9 +/- 7.2 vs 45.7 +/- 16.4) were significantly different between normal subjects and patients with aortic stenosis (p < 0.01 in both groups). The same differences were seen in the Doppler echocardiographic parameters. The VEC-MRI-derived E/A ratio and AC% showed significant hyperbolic and linear correlations with left ventricular mass indexes (r = 0.95 and 0.86). In addition, the VEC-MRI-determined E/A ratio and the volumetric AC% displayed a highly significant hyperbolic correlation (r = 0.95). Thus VEC-MRI can be used to evaluate left ventricular diastolic filling characteristics in normal subjects and patients with abnormalities of diastolic filling.

Detection of regional left ventricular asynchrony in obstructive hypertrophic cardiomyopathy by magnetic resonance imaging

Cine magnetic resonance imaging was used to analyze global and regional left ventricular function in seven patients with obstructive hypertrophic cardiomyopathy (HC) and 10 normal subjects. In patients with HC a 38% higher left ventricular mass index (106.4 +/- 20.2 gm/m2 vs 77.0 +/- 16.1 gm/m2, p < 0.005) associated with a lower end-diastolic volume index (44.9 +/- 8.9 ml/m2 vs 58.3 +/- 9.0 ml/m2, p < 0.005) resulted in an 85% higher mass-to-volume ratio (2.4 +/- 0.52 vs 1.3 +/- 0.57, p < 0.0005). Stroke volume did not differ significantly, whereas ejection fraction was higher (80.4% +/- 6.5% vs 65.4% +/- 7.2%, p < 0.0005) in patients with HC. Although early diastolic filling fraction was smaller in patients with HC (61.0% +/- 22.8% vs 68.4% +/- 14.6%), the difference did not reach significance because of substantial variability. In patients with HC (in contrast to normal subjects) the time to maximal wall thickening was shorter (p < 0.025) in the hypertrophied basal region of the ventricle (223 +/- 42 msec) than in the apical region (267 +/- 35 msec), reflecting asynchrony between these regions. Additionally, in patients with HC the standard deviation of the time to maximal wall thickening in the basal region was significantly higher when compared with that of normal subjects (40.0 +/- 24 msec vs 16.9 +/- 17 msec, p < 0.0005), reflecting asynchrony even within one region. Thus magnetic resonance imaging can detect regional left ventricular asynchrony, an important cause of impaired diastolic function, in patients with HC and normal global systolic function.(ABSTRACT TRUNCATED AT 250 WORDS)

MRI-derived ventricular volume curves for the assessment of left ventricular function

To assess the utility of double oblique, ECG-gated 1H magnetic resonance (MR) derived volume curves for assessing LV function, cardiac short axis images were acquired with a fast field echo technique. We applied this methodology to assess left ventricular function in three groups: normals, patients with left ventricular hypertrophy, and dilated cardiomyopathy. Six slices with 16-20 phases per RR interval were analyzed, representing the initial 75-80% of the cardiac cycle. For each slice, the endocardial border of the left ventricular (LV) chamber was manually traced. Using Simpson's rule, the total LV volume at a given phase was determined considering the traced area, thickness and position in three-dimensional space of each of the six constituent slices. The calculated volumes were plotted against time and the stroke volume, ejection fraction and cardiac output were determined. The volume vs time plots for the systolic and diastolic portions of the curve were individually fit to third degree polynomials using a least squares approximation. From the fit curves, the following data were extracted: the mean slope (dV/dT) during filling and emptying, and the time to 1/4, 1/3 and 1/2 filling and emptying. These parameters are valuable indices of the functional status of the myocardium; thus, accurate and useful estimates of LV function can be obtained using MRI derived volume curves in normal and abnormal states.

Left ventricular volume calculation with integrated backscatter from echocardiography

Integrated backscatter analysis (IB) is a new echocardiographic method for automatically differentiating tissue from blood on the basis of differences in the amplitude of reflected ultrasound. Left ventricular volume was estimated with IB by use of a modification of Pappus' theorem and a summated ellipsoid method. IB measurements correlated well with a standard biplane area-length method derived off-line from endocardial borders drawn by hand from the same echocardiographic data (y = 1.09 x - 35, r = 0.95). Integrated backscatter measurement of ventricular volume derived from six imaging planes with both the Pappus' rule and the summated ellipsoid methods correlated well with magnetic resonance imaging volume estimates (r = 0.91 and r = 0.90, respectively), whereas use of one imaging plane correlated less well (r = 0.75). Automated analysis of integrated backscatter differentiates tissue from blood sufficiently to allow accurate volume calculations compared with magnetic resonance imaging and to standard hand-drawn echo techniques. This method provides accurate measurement of left ventricular volumes that should be useful in clinical hemodynamic assessments.

Magnetic resonance imaging and spectroscopy of the human heart

Magnetic resonance imaging and spectroscopy have a great potential both for clinical cardiac diagnostics and for research in cardiac physiology, metabolism and disease. At the present time, cardiac MRI already is the method of choice in several clinical conditions, especially in imaging central vasculature and intra- and paracardiac masses. With the recent development of contrast agents and ability to measure both flow velocities and flow volume, the cardiac MRI is likely to have a profound role in evaluating coronary arterial disease as well as valvular heart disease. The limitations due to long imaging times of cardiac MRI-studies are likely to be overcome with the development of ultrafast imaging techniques in the near future. On the other hand, cardiac MRS is still a research tool, which needs technical improvements before it can be widely utilized in clinical work. However, attempts to this aim are highly justified, when the possibility that MRS will provide metabolic information of the heart is considered and bearing in mind, that MR-magnets with sufficient field strength for MRS are increasingly in use in most modern hospitals. The role of magnetic resonance imaging (MRI) and spectroscopy (MRS) in the evaluation of heart diseases is still evolving. Some clear indications for clinical use of cardiac MRI have already become apparent, whereas cardiac MRS is still confined to research applications. The current paper consists of a review of the role of MRI for cardiovascular diagnosis together with a review of the currents status of cardiac MRS.

Rationale for, and recent progress in, 3D reconstruction of the heart and lungs

Three-dimensional information of the structure and function of the heart and lungs is needed for several reasons including the following: (a) An apparent change in shape or location of the imaged ventricular wall may either be due to the heart moving through the imaged region, or because it truly represents that change in geometry, or a mixture of the two. In addition, as diseases of the heart and lungs are often heterogeneous in their spatial distribution, we expect the structural and functional consequences to also be heterogeneous in their spatial distribution; (b) Comparison of a selected anatomic feature (e.g., a coronary artery stenosis or pulmonary opacity) at long time intervals may make detection and/or quantitation of lesion progression questionable. The use of a 3D reconstruction to calculate a projection image with a reproducible angle of view is a particularly powerful consequence of 3D image reconstruction; (c) Use of image information from one imaging modality helps improve the quantitative characteristics of an image generated with another imaging modality; (d) Radiation treatment planning requires knowledge of the 3D distribution of radiation attenuation coefficients so that 3D distribution of the regional deposition of radiation energy can be quantitated; (e) Allows for indirect estimation of the physiological dimensions of one aspect of an organ so that the degree of disease of that part of the organ can be assessed.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation in left ventricular regional wall stress with cine magnetic resonance imaging: normal subjects versus dilated cardiomyopathy

We measured the variation of end-systolic wall stress and its relation to regional ejection fraction in short-axis planes through the left ventricle in normal subjects and in patients with dilated cardiomyopathy (DCM) by cine magnetic resonance imaging. There was a gradual increase in end-systolic wall stress but a gradual decrease in ejection fraction from apex to base in normal subjects (14 +/- 6 to 52 +/- 15 kdyne/cm2, 78% +/- 12% to 62% +/- 8%) and in patients with DCM (49 +/- 28 to 130 +/- 30 kdyne/cm2, 40 +/- 18 to 23% +/- 9%). The end-systolic wall stress in patients with DCM was higher than in normal subjects at every level (p < 0.01). We conclude that there is a variation in end-systolic wall stress in both normal subjects and patients with DCM with regional ejection fraction inversely related to regional end-systolic wall stress.

Velocity-encoded cine MRI in the evaluation of left ventricular diastolic function: measurement of mitral valve and pulmonary vein flow velocities and flow volume across the mitral valve

Left ventricular diastolic function has been evaluated by means of analysis of the flow pattern through the mitral valve. Velocity-encoded cine magnetic resonance imaging (VEC-MR) is a new method for characterizing flow patterns in the heart. The feasibility of using VEC-MR to measure early diastolic (E) and atrial systolic (A) peak flow velocities and E/A ratios in the mitral inflow, as well as systolic (X), early diastolic (Y), and atrial systolic (Z) peak flow velocities and X/Y ratios in the pulmonary vein, was evaluated in 10 normal volunteers. The VEC-MR-derived velocities and indexes were compared with Doppler-derived results. Volumetric flow across the mitral valve was also used to measure stroke volume, cardiac output, and the left atrial contribution of left ventricular filling. VEC-MR yielded lower peak velocities than Doppler echocardiography. The velocities of the two measurements showed a significant linear correlation (Doppler E velocity = 1.30 x VEC-MR + 1.6 cm/sec, r = 0.68; Doppler A velocity = 1.83 x VEC-MR - 5.2 cm/sec, r = 0.83; and Doppler X velocity = 0.45 x VEC-MR + 0.09 cm/sec, r = 0.74). Consequently the E/A and X/Y ratios measured by these two methods showed statistically significant linear correlations with r values of 0.94 and 0.83. The volume of blood flow across the mitral valve measured by VEC-MR (5610 +/- 620 ml/min) was not statistically different from the cardiac output measured from the ascending aorta by VEC-MR (5670 +/- 590 ml/min) or by left ventricular cine magnetic resonance imaging (5440 +/- 614 ml/min). The left atrial contribution to left ventricular filling was 25.9 +/- 7.5%. Our results indicate that VEC-MR can be used not only for evaluation of left ventricular diastolic filling from the mitral valve and pulmonary vein flow velocities but also for quantitative measurement of the volume of blood flow across the mitral valve.

Assessment of left ventricular diastolic function in dilated cardiomyopathy with cine magnetic resonance imaging: effect of an angiotensin converting enzyme inhibitor, benazepril

The effects of angiotensin converting-enzyme inhibitor, benazepril, on diastolic function in patients with dilated cardiomyopathy, with (n = 4) or without (n = 11) mitral regurgitation, were examined with the time-volume curve of the left ventricle derived from cine magnetic resonance images. Peak filling rate/end-systolic volume and ejection fraction were increased in the group without regurgitation (p < 0.01) but not in the group with regurgitation after treatment. There was a strong correlation between peak filling rate/end-systolic volume and ejection fraction (r = 0.89) and between the change in peak filling rate/end-systolic volume and that in ejection fraction after treatment (r = 0.74) in the group without regurgitation. These findings suggest that in some patients with dilated cardiomyopathy benazepril has favorable effects on diastolic function, which seem to be related to improvement in systolic function. This drug may not be as beneficial in patients with dilated cardiomyopathy complicated by mitral regurgitation.

Effect of cilazapril on regional left ventricular wall thickness and chamber dimension following acute myocardial infarction: in vivo assessment using MRI

The primary goal of the current study was to assess in situ, using magnetic resonance imaging, the effect of a new angiotensin-converting enzyme inhibitor, cilazapril, in reducing left ventricular remodeling after acute myocardial infarction. Three groups of animals were investigated: (1) sham-operated rats (n = 19); (2) infarcted rats receiving no treatment (n = 23); and (3) infarcted rats receiving cilazapril (100 mg/L drinking water, n = 20). Treatment with cilazapril began on the third day postocclusion and continued for 3 to 4 months. Myocardial infarction was produced by ligation of the left coronary artery, and electrocardiographic (ECG)-gated short-axis images were acquired 3 to 4 months later. Sham-operated animals were subjected to the same procedure but the left coronary artery was not ligated. From the image acquired in the middle of the left ventricle (equatorial slice), left ventricular wall thicknesses, chamber diameters, and surface area measurements of the cavities were determined. At autopsy examination, infarct size and tissue water content were determined. The results demonstrate that magnetic resonance imaging has the potential to assess in situ the alterations of left ventricular dimensions and mass after acute myocardial infarction and can be used to document the influence of therapeutic interventions. Cilazapril provided protection against the deleterious remodeling changes such as ventricular dilation and wall thinning consequent to acute myocardial infarction.

Application of cine nuclear magnetic resonance imaging for sequential evaluation of response to angiotensin-converting enzyme inhibitor therapy in dilated cardiomyopathy

Cine nuclear magnetic resonance (NMR) imaging was used to serially measure cardiovascular function in 17 patients with New York Heart Association class II or III heart failure and left ventricular ejection fraction less than or equal to 45% who were treated for 3 months with benazepril hydrochloride, a new angiotensin-converting enzyme inhibitor, while continuing treatment with diuretic agents and digoxin. Interobserver reproducibilities for ejection fraction (r = 0.94, SEE 3.3%), end-systolic volume (r = 0.98, SEE 10.6 ml), end-diastolic volume (r = 0.99, SEE 8.29 ml), end-systolic mass (r = 0.96, SEE 15.4 g), end-systolic wall stress (r = 0.91, SEE 10 dynes.s.cm-5) and end-systolic stress/volume ratio (r = 0.85, SEE 0.13) demonstrated applicability of cine NMR imaging for the serial assessment of cardiovascular function in response to pharmacologic interventions in patients with heart failure. During 12 weeks of treatment with benazepril, ejection fraction increased progressively from 29.7 +/- 2.2% (mean +/- SEM) to 36 +/- 2.2% (p less than 0.05), end-diastolic volume decreased from 166 +/- 14 to 158 +/- 12 ml (p = NS), end-systolic volume decreased from 118 +/- 12 to 106 +/- 11 ml (p less than 0.05), left ventricular mass decreased from 235 +/- 13 to 220 +/- 12 g (p less than 0.05), end-systolic wall stress decreased 29% from 90 +/- 5 to 64 +/- 5 dynes.s.cm-5 (p less than 0.05), end-systolic pressure decreased from 92.6 +/- 3.7 to 78.8 +/- 5.3 (p less than 0.05) and end-systolic stress/volume ratio, a load-independent index of contractility, decreased from 0.83 +/- 0.05 to 0.67 +/- 0.06 (p less than 0.05), demonstrating that improved ejection fraction is due to afterload reduction.

Measurement of right ventricular mass in normal and dilated cardiomyopathic ventricles using cine magnetic resonance imaging

The accurate quantification of right ventricular (RV) mass has eluded conventional imaging modalities. Accordingly, cine magnetic resonance imaging was used for quantification of RV as well as left ventricular (LV) mass in 10 normal subjects and in 10 patients with dilated cardiomyopathy with an LV ejection fraction less than 0.40. Hearts were imaged with 10 mm thick short-axis slices from apex to base with a short echo delay time of 5 ms. Each slice was partitioned into 3 sections: RV free wall, ventricular septum and LV free wall, for calculation of end-diastolic and end-systolic mass and LV:RV free wall ratio. RV end-diastolic mass in normal subjects was 45 +/- 8 g, which was similar to the values determined in previously published postmortem studies, mean 46 g (range 23 to 68). The value determined in patients with dilated cardiomyopathy was higher (50 +/- 11 g), but this difference was not significant. LV:RV free wall ratio in cardiomyopathy (3.6 +/- 1.0) was greater than in normal subjects (2.4 +/- 0.3), because of the greater LV free wall mass in dilated cardiomyopathy, where LV free wall end-diastolic mass was 173 +/- 40 g vs 107.1 +/- 19.9 g in normal subjects (p less than 0.05). RV mass measurements had 6.4 +/- 3.6% interobserver and 7.3 +/- 6.1% intraobserver variability. There were no significant differences between end-diastolic and end-systolic mass measurements. Thus, cine magnetic resonance imaging can reproducibly calculate RV mass. The values in normal subjects correspond to previously reported postmortem values for a population without heart disease.

Cardiovascular applications of magnetic resonance imaging and phosphorus-31 spectroscopy

Recent advances in cardiovascular applications of magnetic resonance (MR) imaging and phosphorus-31 spectroscopy are reported. MR velocity mapping is a valuable adjunct to conventional imaging techniques, providing information on flow velocities as well as on absolute blood flow volume in the aorta and pulmonary arteries. Recently, ultrafast MR techniques have become available to evaluate myocardial perfusion with the aid of MR contrast agents as perfusion marker. Dynamic MR imaging is a powerful tool to assess cardiac function and ventricular mass. In particular, right ventricular function and mass can be evaluated with great accuracy, contributing to improved assessment of the significance of disease processes which may affect the right heart. The role of phosphorus-31 spectroscopy of the heart is expanding for the evaluation of ischemic myocardial disease and cardiomyopathies. The phosphocreatine to adenosine triphosphate ratio appears to be a marker of disease in patients with cardiac hypertrophy. In conclusion, MR imaging and phosphorus-31 spectroscopy is gaining widespread acceptance for evaluation of many cardiovascular disease processes.