Rapid, accurate and simultaneous noninvasive assessment of right and left ventricular mass with nuclear magnetic resonance imaging using the snapshot gradient method

RV mass measurement at end-systole: Improved accuracy, Reproducibility, and reduced segmentation time

PURPOSE

To evaluate the accuracy, reproducibility, and contouring time of RV mass in end-systole (ES) and end-diastole (ED). Magnetic resonance imaging (MRI) has been shown to be accurate and reproducible for the evaluation of right ventricular (RV) volume and function. RV mass, assessed in end-diastolic (ED) phase, is one of the least reproducible variables. The choice of end-systolic (ES) phase could offer an alternative to improve reproducibility, since the selection of the basal slice and the visualization of the usually thin RV wall are easier in this phase.

MATERIALS AND METHODS

To evaluate accuracy, 11 sheep were imaged in vivo and their RV free walls were weighed after removing epicardial fat. To evaluate reproducibility, 30 normal subjects and 30 subjects with pulmonary arterial hypertension (PAH) were imaged and interobserver and intraobserver variabilities were assessed in the ES and the ED. Segmentation time was recorded after visual selection of ES and ED phases.

RESULTS

ES RV mass measurement has less absolute variability (5.2% ± 3.2) compared to ED (10.6% ± 6.3) using weighed RV mass in sheep as the gold standard (P < 0.001). ES segmentation yielded higher intraobserver (intraclass correlation coefficients [ICC] = 0.94-0.99; coefficient of variability [CoV] = 6-7.3%) and interobserver (ICC = 0.85-0.98; CoV = 10.9-11.7%) reproducibility than ED segmentation. Segmentation time in humans was 25-28% faster in ES (P < 0.001).

CONCLUSION

The MRI assessment of RV mass is more accurate, reproducible, and faster in the ES phase.

The importance of trabecular hypertrophy in right ventricular adaptation to chronic pressure overload

To assess the contribution of right ventricular (RV) trabeculae and papillary muscles (TPM) to RV mass and volumes in controls and patients with pulmonary arterial hypertension (PAH). Furthermore, to evaluate whether TPM shows a similar response as the RV free wall (RVFW) to changes in pulmonary artery pressure (PAP) during follow-up. 50 patients underwent cardiac magnetic resonance (CMR) and right heart catheterization at baseline and after one-year follow-up. Furthermore 20 controls underwent CMR. RV masses were assessed with and without TPM. TPM constituted a larger proportion of total RV mass and RV end-diastolic volume (RVEDV) in PAH than in controls (Mass: 35 ± 7 vs. 25 ± 5 %; p < 0.001; RVEDV: 17 ± 6 vs. 12 ± 6 %; p = 0.003). TPM mass was related to the RVFW mass in patients (baseline: R = 0.65; p < 0.001; follow-up: R = 0.80; p < 0.001) and controls (R = 0.76; p < 0.001). In PAH and controls, exclusion of TPM from the assessment resulted in altered RV mass, volumes and function than when included (all p < 0.01). Changes in RV TPM mass (β = 0.44; p = 0.004) but not the changes in RVFW mass (p = 0.095) were independently related to changes in PAP during follow-up. RV TPM showed a larger contribution to total RV mass in PAH (~35 %) compared to controls (~25 %). Inclusion of TPM in the analyses significantly influenced the magnitude of the RV volumes and mass. Furthermore, TPM mass was stronger related to changes in PAP than RVFW mass. Our results implicate that TPM are important contributors to RV adaptation during pressure overload and cannot be neglected from the RV assessment.

Improved reproducibility of right ventricular volumes and function estimation from cardiac magnetic resonance images using level-set models

This study aims to assess whether an alternative method, that is based on volumetric surface detection (VoSD) without tracing and is totally free of geometric assumptions, can improve the reproducibility of right ventricular (RV) volume quantification from cardiac magnetic resonance (CMR) images, in comparison with a conventional disk-area technique. In a sample of 23 patients, with wide variability of RV end-diastolic volume (EDV: 47-131 ml), end-systolic volume (ESV: 20-76 ml), and ejection fraction (EF: 29-73%), using the standard method (Argus, Siemens) as the reference, the VoSD method showed good agreement for EDV, ESV, and EF estimations (correlation coefficient: 0.91, 0.94, and 0.94; Bland-Altman biases: 1 ml, 1 ml, and 0%; limits of agreement: +/-16 ml, +/-11 ml, and +/-11%, respectively). An analysis of the reproducibility of the two methods showed lower intraobserver variability for the VoSD method than for the conventional method, as evidenced by the coefficient of variability (CoV) values (2-6% vs. 8-15%; P < 0.05). In addition, the VoSD method showed improved interobserver reproducibility (7-10% vs. 8-15%), but the difference was statistically significant only for EF estimation variability (8 vs. 15%, P < 0.05). In conclusion, the newly developed VoSD technique allows accurate measurements of RV volumes and function, and appears to be more reproducible than the conventional methodology.

Intra-observer and interobserver reproducibility of right ventricle volumes, function and mass by cardiac magnetic resonance

OBJECTIVES

Cardiac magnetic resonance (CMR) allows quick and non-invasive evaluation both of right ventricle (RV) volume and function, which are important in many heart diseases. We have evaluated CMR intra- and interobserver reproducibility in different conditions of RV dimension and function.

METHODS

We have analysed CMR exams of 45 subjects, randomly selected from our database according to RV end-diastolic volume (EDV; 15-subject groups with EDV < 25th, 25-75th and > 75th percentiles of a normal control population). Selected subjects were of both sexes (male/female 33/12) and of variable age (8-83 years) and body surface (0.9-2.3 m). RV end-diastolic and end-systolic volumes (ESV), ejection fraction (EF) and mass were blindly evaluated by two operators. Bland-Altman bias and coefficient of variability (CoV) were used to assess intra- and interobserver reproducibility.

RESULTS

A wide range of EDV (range = 46-239 ml), ESV (20-129 ml) and EF (6-64%) was observed. The intra-observer bias was -5 ml for EDV, -2 ml for ESV, -1% for EF and 5 g for mass, with a CoV of 7-12%. The interobserver bias was 5 ml for EDV, 2 ml for ESV, 2% for EF and 6 g for mass, with a CoV of 8-13%. Analysis by tertiles showed EF assessment variability to be higher in the lower tertiles at intra-observer (P < 0.036) and, above all, at interobserver (P < 0.000) analysis. Mass assessment variability was higher in the upper tertile (P < 0.004) at intra-observer analysis.

CONCLUSIONS

Intra- and interobserver reproducibility of RV parameters assessed by CMR are adequate in a wide range of RV dimensions and function. However, caution is required with respect to the significance of small changes of EF and mass in the case of poor function and hypertrophy of the RV, respectively.

Quantification of left ventricular mass using cardiac magnetic resonance imaging compared with echocardiography in domestic cats

The hypotheses were that cardiac magnetic resonance imaging (cMRI) would accurately determine LV mass in domestic cats and would do so more accurately than echocardiography (ECHO). ECHO was performed on seven sedated cats. LV mass was calculated using the truncated ellipse formula from a right parasternal long-axis view. T1 weighted gradient echo cMRI was acquired from anesthetized cats during multiple phases of the cardiac cycle. Short-axis images were obtained by acquiring 3 mm thick contiguous slices perpendicular to the cardiac long axis. LV mass was determined using Simpson's rule. Endocardial and epicardial borders were traced on each slice at end-systole, end-diastole, and mid-cycle and the difference in areas was myocardial area. Myocardial area was multiplied by slice thickness to calculate myocardial volume. Total (summated) myocardial volume was multiplied by myocardial density (1.05) to obtain LV mass at three measured phases of the cardiac cycle. Cats were euthanized and the LV was dissected and weighed to determine true mass. CMRI at end-systole most accurately quantified LV mass and was more accurate than echocardiography (P = 0.0078). Actual LV mass ranged from 6.5 to 10.5 g (mean = 8.5 g, SD = 1.6 g) compared with MRI LV mass at end-systole, which ranged from 6.7 to 11.1 g (mean = 8.7 g, SD = 1.7 g) and echocardiographic LV mass at enddiastole, which ranged from 5.2 to 9.1 g (mean= 7.1 g, SD = 1.8 g). Inter- and intraobserver variability for cMRI was 2%. CMRI obtained at end-systole accurately and reliably quantifies LV mass in domestic cats. It is more accurate than the echocardiographic method used in this study.

Estimation of right ventricular mass by two-dimensional echocardiography

BACKGROUND

This report describes two original echocardiographic approaches to measure right ventricular (RV) mass (RVM).

METHODS

In the bullet formula (5/24 pi D1 D2 L), where D1 and D2 are short axes and L the log axis, the RVM is obtained by subtracting the cavity volume from the RV total volume and subsequently multiplying the difference by myocardium density. The second method uses 3 endocardium segments measured at: (1) short axis plane of the aortic valve and left atrium (b1); (2) short axis plane at the midpoint between the tricuspid valve annulus and the apex (b2); and (3) 4-chamber view (h). Those segment lengths are applying in the formula A = [(b1 + b2)/2] x h. The result is multiplied by the wall thickness and by myocardium density.

RESULTS

Both formulas were primarily tested in 30 mongrel dogs and have shown good correlation with the true mass ( r = 0.869 with the segments formula and r = 0.819 with the bullet formula). The same method was used in 20 human patients before heart transplant with similar results ( r = 0.810 with the segments formula and r = 0.836 with the bullet formula).

CONCLUSIONS

The RVM can be satisfactorily estimated by 2-dimensional echocardiography. The linear regression between the calculated mass (using the smoothest and thinner myocardium thickness) and the actual mass may provide the correction factor for the RVM calculation. Two echocardiographic methods were used to measure right ventricular mass. One of them used a bullet formula variant (5/24 pi D1 D2 L). The second method used 3 endocardium segments measured in 3 2-dimensional echocardiographic planes (short axis of aortic valve and left ventricle, and 4-chamber view), and applied in the formula A = [(b1 + b2)/2] x h. Both formulas have shown good correlation with the true mass in 30 mongrel dogs ( r = 0.869 with the segments formula and r = 0.819 with the bullet formula) and in 20 human patients before heart transplant ( r = 0.810 and r = 0.836, respectively).

Routine breath-hold gradient echo MRI-derived right ventricular mass, volumes and function: accuracy, reproducibility and coherence study

Right ventricular (RV) dysfunction is a predictor of poor outcome in patients with heart disease. Conventional imaging modalities fail to assess RV volumes accurately. We sought to assess the accuracy and reproducibility of routine breath-hold gradient echo magnetic resonance imaging (MRI)-derived RV mass, volumes and function. We assessed: (1) The accuracy of in vivo MRI-derived RV mass in comparison to the RV weight in 9 minipigs. (2) Intra- and inter-observer reproducibility of RV mass, end-diastolic (EDV) and end-systolic (ESV) volumes and ejection fraction (EF) in 15 normal volunteers and 10 patients with heart disease. (3) Inter-study reproducibility of the former parameters in 25 coronary artery disease patients. (4) The correlation between right and left ventricular stroke volumes in the total population. Strong statistically significant correlations were found between: (1) MRI-derived RV mass and RV weight (r = 0.98, bias = 2.5 g), (2) Intra-observer measurements of RV mass (r = 0.96, bias = 0.5 g), EDV (r = 0.99, bias = -1.5 ml), ESV (r = 0.98, bias = 0.1 ml) and EF (r = 0.92, bias = -1.4%), (3) Inter-observer measurements of RV mass (r = 0.95, bias = 1.1 g), EDV (r = 0.98, bias = -1.1 ml), ESV (r = 0.98, bias = 1.2 ml) and EF (r = 0.87, bias = -1.9%), (4) Inter-study measurements of RV mass (r = 0.91, bias = -0.1 g), EDV (r = 0.96, bias = 3.8 ml), ESV (r = 0.98, bias = 0.3 ml) and EF (r = 0.90, bias = 0.9%), (5) MRI-derived right and left ventricular stroke volumes (r = 0.87). The assessment of the RV mass, volumes and function by routine breath-hold gradient echo MRI is accurate and highly reproducible. The correlation between left and RV MRI-derived stroke volumes indicates excellent coherence of simultaneous bi-ventricular volume measurements.

Assessment of biventricular remodeling by magnetic resonance imaging after successful primary stenting for acute myocardial infarction

Inferior acute myocardial infarction (AMI) is associated with a better outcome compared with anterior AMI, even in the presence of comparable infarct size. Whether left ventricular remodeling, a major predictor of poor outcome, and right ventricular (RV) remodeling depend on the site of an AMI remains unknown. Biventricular volumes were assessed by magnetic resonance imaging 7 +/- 2 days and 3.4 +/- 0.3 months after successful primary stenting in 51 consecutive patients with inferior or anterior AMI. This study documents RV involvement and biventricular reverse remodeling in patients with inferior AMI in the absence of RV infarction, as opposed to those with anterior AMI who show progressive biventricular remodeling.

Comparison of LV mass and volume measurements derived from electron beam tomography using cine imaging and angiographic imaging

PURPOSE

To estimate the variation of left ventricular (LV) mass and volume measurement with cine and angiography by electron beam tomography (EBT).

METHOD AND MATERIALS

Sixty-three consecutive patients (41 men, 22 women; age range 46-91) referred for cardiac imaging for clinical indications underwent cine and coronary artery electron beam angiography (EBA) studies on the same day. The cine images consisted of 144 images (12 slices/level x 12 levels), taken 12 frames/s for a full cardiac cycle. The EBA images consisted of 50-70 slices triggered at end-systole, with an acquisition time of 100 ms/slice. Slice thickness was 8 mm for the cine images and 1.5 mm for the EBA images. A total volume of 120-180 ml of nonionic contrast was used for each subject. The LV mass (myocardial tissue volume), LV cavity volume and total LV volume (tissue + cavity) measurements were completed using the software from the EBT computer console (G.E., S. San Francisco, CA).

RESULTS

The LV mass, cavity volume and total LV volumes at end-systole were 124.11 g, 45.66 and 163.86 ml when derived from the cine images and 130.74 g, 41.31 and 165.82 ml when derived from the EBA images. There were no significant differences between the cine and EBA-derived measurements, however the EBA-derived measurements showed slightly larger LV mass (mean 6.63 g), smaller cavity volume (mean -4.35 ml) and larger total LV volume (mean 1.96 ml, all p > 0.05) than did the cine-derived measurements. Based on case-by-case observations, these differences appear to be related to the higher spatial resolution of the thinner EBA images which allows better discrimination between papillary and trabecular muscle and LV. This leads to slightly smaller cavity size estimations and greater LV mass measurements. There was significant correlation between cine and EBA-derived measurements. Formulas were developed for relating the measurements made from the two modalities as follows: For LV mass: EBA value = 0.91 x cine value + 17.09, R = 0.95, p < 0.001; For LV cavity volume: EBA value = 1.06 x cine value - 6.91, R = 0.96, p < 0.001; For total LV volume: EBA value = 0.98 x cine value + 5.09 in ml, p < 0.001. The mean differences in measurements using the two modalities were 8.1, 18.2 and 6.5% for LV mass, LV cavity volume and total LV volume, respectively.

CONCLUSION

Both cine and EBA images were useful for measuring LV mass and volume with good intertest agreement. Cardiac volume and mass measurements derived from cine EBT studies probably slightly underestimate LV mass and overestimate LV volume.

Left Ventricular Mass: Manual and Automatic Segmentation of True FISP and FLASH Cine MR Images in Dogs and Pigs

PURPOSE

To evaluate the accuracy of manually and automatically segmented true fast imaging with steady-state precession (FISP) and fast low-angle shot (FLASH) cine magnetic resonance (MR) imaging in the determination of left ventricular (LV) mass.

MATERIALS AND METHODS

Nine dogs and five pigs underwent cine MR imaging of the entire LV from base to apex. Manual and automatic segmentation times were recorded, and LV masses determined with each were compared with each other and with the true LV mass at autopsy. Estimated mass and true mass at autopsy were compared by calculating the correlation coefficient and the mean difference between the two for each MR sequence and segmentation method.

RESULTS

True LV mass at autopsy correlated well with masses determined with manual and automatic contours on true FISP MR images. Mean differences between true LV mass and masses determined from manual contours on true FISP and FLASH images were -0.8 g +/- 2.6 and 3.7 g +/- 6.8, respectively. When manually drawn end-diastolic contours were automatically propagated to end systole, mean differences were 2.0 g +/- 3.6 (P =.05) and 9.1 g +/- 6.5 (P <.05) for true FISP and FLASH images, respectively. For automatic contours, mean differences were 10.6 g +/- 8.5 (P <.05) and 27.7 g +/- 13.4 (P <.05) for true FISP and FLASH images, respectively. Mean automatic segmentation time was six times less than mean manual segmentation time.

CONCLUSION

LV mass was determined most accurately by using manual contours on true FISP images. In these animal models, fully automatic segmentation of true FISP images was performed in one-sixth of the time of manual segmentation and yielded LV masses with a mean error of approximately 5% of true LV mass.

Interstudy reproducibility of right ventricular volumes, function, and mass with cardiovascular magnetic resonance

BACKGROUND

Cardiovascular magnetic resonance (CMR) has shown excellent results for interstudy reproducibility in the assessment of left ventricular (LV) parameters. However, interstudy reproducibility data for the more complex-shaped right ventricle in a large study group have not yet been reported. We sought to determine the interstudy reproducibility of measurements of right ventricular (RV) volumes, function, and mass with CMR and compare it with correspondent LV values.

METHODS

Sixty subjects (47 men; 20 healthy volunteers, 20 patients with heart failure, 20 patients with ventricular hypertrophy) underwent 2 CMR studies for assessment of RV measurements with a minimum time interval between each study.

RESULTS

The overall interstudy reproducibility (range between groups) for the RV was 6.2% (4.2%-7.8%) for end-diastolic volume, 14.1% (8.1%-18.1%) for end-systolic volume, 8.3% (4.3%-10.4%) for ejection fraction (EF), and 8.7% (7.8%-9.4%) for RV mass. RV reproducibility was not as good as for the LV for all measures in all 3 groups, but this was only statistically significant for EF (P <.01).

CONCLUSIONS

CMR showed good interstudy reproducibility for RV function parameters in healthy subjects, patients with heart failure, and patients with hypertrophy, which suggests that CMR is reliable for serial RV assessment. These data can be used to power sample sizes for longitudinal research studies of RV volume and function. The reproducibility values were similar to, but generally lower than, the reproducibility values for the LV in the same study population, which indicates that sample sizes for RV studies are in general larger than those for LV studies.

Accurate Quantification of Right Ventricular Mass at MR Imaging by Using Cine True Fast Imaging with Steady-State Precession: Study in Dogs

PURPOSE

To assess the accuracy of cine magnetic resonance (MR) imaging with a segmented true fast imaging with steady-state precession (FISP) technique for right ventricular (RV) mass quantification.

MATERIALS AND METHODS

Fourteen dogs were imaged with a 1.5-T clinical MR imaging unit by using an electrocardiographically gated true FISP sequence. Contiguous segmented k-space cine images were acquired from the base of the RV to the apex during suspended respiration (repetition time msec/echo time msec, 3.2/1.6; section thickness, 5 mm; in-plane resolution, 1.0 x 1.3 mm2). After imaging, each dog was sacrificed, and the RV free wall was isolated and weighed. Each MR imaging data set was analyzed twice by each of two independent observers who were blinded to the results of RV mass measurement at autopsy, and the mass measurements at MR imaging were compared with the autopsy results by using linear regression and Bland-Altman analysis.

RESULTS

RV mass measurements calculated by using the true FISP cine MR images were nearly identical to those at autopsy (R = 0.82, standard error of the estimate = 1.7 g, P >.05), with a mean difference between the autopsy and MR imaging measurements of 0.3 g +/- 1.7 (1.9% +/- 8.2) (P >.05). Inter- and intraobserver variations were small, with a mean interobserver variability of -0.1 g +/- 2.3 and a mean intraobserver variability of 0.2 g +/- 1.6 at every-section analysis.

CONCLUSION

In this animal model, true FISP cine MR imaging enabled accurate quantification of RV mass.

Real-time MR image acquisition during high-dose dobutamine hydrochloride stress for detecting left ventricular wall-motion abnormalities in patients with coronary arterial disease

PURPOSE

To compare the accuracy of real-time magnetic resonance (MR) imaging with that of standard echo-planar MR imaging for detecting myocardial wall-motion abnormalities at rest and during dobutamine hydrochloride-induced stress in patients with coronary arterial disease.

MATERIALS AND METHODS

In 22 patients with coronary arterial disease, left ventricular wall motion was examined at rest and during dobutamine hydrochloride stress, by using echo-planar MR imaging and a new technique with real-time segmented k-space turbo gradient-echo echo-planar MR imaging (repetition time, 16.5 msec; echo time, 6.8 msec). Wall-motion abnormalities were determined visually for each perfusion territory, and Cohen kappa coefficients were calculated for real-time imaging in comparison with echo-planar imaging. Coronary angiography was performed in all patients. Sensitivity and specificity for real-time and echo-planar imaging were calculated for detecting significant coronary arterial stenosis.

RESULTS

kappa values for detecting wall-motion abnormalities at real-time imaging, in comparison with echo-planar MR imaging, were 0.97 at rest and 0.94 at maximum dobutamine hydrochloride stress. At comparison with those of angiography, the sensitivity and specificity for detecting significant coronary arterial stenosis were 88% (14 of 16 patients) and 83% (five of six patients), respectively, for echo-planar imaging and 81% (13 of 16 patients) and 83% (five of six patients), respectively, for real-time imaging.

CONCLUSION

Real-time MR imaging is possible under stress conditions and allows accurate detection of wall-motion abnormalities.

Breath-hold FLASH and FISP cardiovascular MR imaging: left ventricular volume differences and reproducibility

PURPOSE

To compare fast imaging with steady-state precession (FISP) and fast low-angle shot (FLASH) magnetic resonance acquisitions to quantify left ventricular volumes, mass, and function and to determine if the two techniques are comparable.

MATERIALS AND METHODS

Left ventricular volume studies were performed in 10 patients with heart failure and in 10 healthy subjects by using FISP and FLASH imaging. Identical section positions were used for section-by-section contour comparisons. Manual analysis was performed by two experienced observers. The study was repeated on a different day and interobserver and interstudy reproducibility assessed.

RESULTS

With FISP, end-diastolic volume was larger (healthy subjects: +18 mL [13%], P <.001; patients: +6 mL [3%], not significant), end-systolic volume larger (healthy subjects: +9 mL [17%], P =.001; patients: +8 mL [6%], P =.001) and left ventricular mass smaller (healthy subjects: -25 g (19%), P <.001; patients: -21 g (11%), P <.001). There were no significant differences in ejection fraction. Both sequences had excellent interstudy and interobserver reproducibility, with statistically better reproducibility for interstudy healthy-subject ejection fraction on FISP images (P =.05). Section-by-section analysis determined that at FISP, endocardial contours were drawn larger and the epicardial contours smaller than on FLASH images. FISP enabled better delineation of epicardial fat from myocardium, of blood-myocardium interface in areas of trabeculation or papillary muscles, and of the atrioventricular ring.

CONCLUSION

FISP produces small but significantly higher left ventricular volume measurements, as compared with FLASH imaging. FLASH imaging and FISP have similar reproducibility.

TrueFISP: assessment of accuracy for measurement of left ventricular mass in an animal model

PURPOSE

To test the accuracy of a high performance true fast imaging with steady-state precession (TrueFISP) pulse sequence for the assessment of left ventricular (LV) mass in a large animal model on 1.5-T scanners.

MATERIALS AND METHODS

We imaged dogs (N = 10) on a clinical 1.5-T clinical scanner using electrocardiogram (ECG)-gated TrueFISP. In all animals, contiguous segmented k-space cine images were acquired from base to apex (in-plane resolution 1 x 1 mm(2), slice thickness 5 mm, TR = 4.8 msec, TE = 1.6 msec) during repeated breath-holds. In nine of the 10 animals, single-shot images gated to end-diastole were also acquired from base to apex in a single breath-hold (in-plane resolution 1 x 1 mm(2), slice thickness 5 mm, TR = 3.2 msec, TE = 1.6 msec). After imaging, animals were killed, the left ventricle was isolated, and the true mass of the left ventricle (free wall and septum) was determined. Independently, two observers blinded to the post-mortem results computed LV masses based on analysis of the magnetic resonance (MR) images.

RESULTS

Comparison of the computed LV mass using TrueFISP to the actual mass showed excellent agreement. Cine-systole was the most accurate technique (mass = 98.6% +/- 4.5% actual, bias = 1.2 +/- 3.4 g) followed by cine-diastole (mass = 97.9% +/- 5.3% actual, bias = 1.8 +/- 4.1 g) and single shot (mass = 94.7% +/- 7.9% actual, bias = 4.2 +/- 6.3 g). Inter- and intra-observer variabilities were low (5.8% +/- 7.1% and 0.4% +/- 4.8%, respectively).

CONCLUSION

We conclude that TrueFISP imaging is an accurate, rapid method to determine ventricular mass. In single-shot mode, TrueFISP requires only one breath-hold to estimate the mass of the heart within 6% of the actual value, whereas the segmented k-space implementation measured LV mass to within 3% of the true value.

Assessment of left ventricular mass by cardiovascular magnetic resonance

Left ventricular hypertrophy is associated with significant excess mortality and morbidity. The study and treatment of this condition, in particular the prognostic implications of changes in left ventricular mass, require an accurate, safe, and reproducible method of measurement. Cardiovascular magnetic resonance is a suitable tool for this purpose, and this review assesses the technique in comparison with others and examines the clinical and research implications of the improved reproducibility.

Multi-slice dynamic imaging: complete functional cardiac MR examination within 15 seconds

A new magnetic resonance (MR) sequence was developed to acquire real-time images in a multi-slice dynamic imaging mode to cover the complete heart in 15 seconds without the need for electrocardiogram (ECG) triggering and multiple breath holds. In 34 patients, left ventricular function was assessed with the new technique and a standard technique. The new technique proved to be feasible and accurate for functional cardiac examinations.

Time course of structural adaptations in chronic AV block dogs: evidence for differential ventricular remodeling

To determine the nature and time course of biventricular hypertrophy and concomitant electrical and mechanical changes after creation of complete atrioventricular block (CAVB), six adult dogs (22–30 kg) were subjected to serial magnetic resonance imaging (MRI) and electrocardiography. After 6 days of CAVB, left ventricular (LV) mass, ejection fraction (EF), and Q-T time at a paced rhythm of 60 beats/min were already significantly increased. Maximal values were reached within 14–21 days of CAVB: LV mass, from 116 ± 11 to 143 ± 12 g; right ventricular (RV) mass, from 40 ± 3 to 55 ± 6 g; EF, from 68 ± 6% to 86 ± 5%; and Q-T time, from 285 ± 25 to 330 ± 35 ms, all P < 0.05. Cardiac output returned to baseline at day 14. End-diastolic wall thickness increased only in the RV, in which angiotensin type 1 (AT1) receptor mRNA expression was significantly greater. The autopsy correlated well with the MRI results ( r = 0.98, P≤ 0.01). In conclusion, electrophysiological, mechanical, and structural adaptation processes after bradycardia-induced volume overload develop rapidly and are completed within 3 wk. The degree of hypertrophy was greater in the RV, which was associated with an increase in AT1receptor mRNA.

Left ventricular mass in hypertrophic cardiomyopathy: assessment by three-dimensional and geometric MR methods

PURPOSE

The goals of this work were to evaluate the practical utility of MRI to quantify myocardial mass in patients with hypertrophic cardiomyopathy (HCM), define the differences in myocardial mass measurements obtained with three-dimensional and geometric MR methods in patients with normal left ventricular morphology and in patients with wall thickening, and establish the correlation between the two MR methods and the geometric echocardiographic method (GEM).

METHOD

The same protocol was followed to conduct prospective MR examinations on 72 patients. In 60 of the subjects suspected to have HCM, imaging was performed to confirm or rule out the preliminary clinical diagnosis; the other 12 were healthy volunteers. Multislice SE, single slice multiphase, and multislice multiphase GRE sequences were performed in all cases. Left ventricle mass was calculated using formulas that assume an ellipsoid geometry for the left ventricle (geometric method), and the results were compared with the mass found using the three-dimensional method and subsequent application of Simpson rule. Tests were run to evaluate intraobserver variability in the MR data obtained with the three-dimensional method. The measurements obtained with the two MR methods were compared with the results obtained with GEM.

RESULTS

Although the mean left myocardial mass values obtained using the three-dimensional MR method were smaller than the mean values found with the geometric MR method in all patients, the difference was significant only in patients with HCM. The correlation between the geometric MR method and GEM was very good both in patients with HCM and in those with normal wall thickening. The correlation between the three-dimensional MR method and GEM was good in patients whose left ventricle morphology was normal and poor in patients with HCM. Intraobserver agreement for three-dimensional mass values was excellent.

CONCLUSION

MR examinations should be a standard technique for calculating myocardial ventricular mass. In patients with normal ventricle wall thickness, the geometric method can be used to calculate myocardial mass because it is less time consuming. However, in patients with abnormal morphology of the left ventricle and/or asymmetric wall thickening such as found in HCM, in whom the geometric method overestimates myocardial mass, measurements should be made using the three-dimensional method.

MR gradient echo volumetric analysis of human cardiac casts: focus on the right ventricle

PURPOSE

Our goal was to assess the utility of different imaging directions in volumetric studies of the heart with MRI, in particular to identify the optimal imaging plane for studies of the right ventricle.

METHOD

We examined 12 sets of human four-chamber cadaveric cardiac casts. Gradient echo MRI was performed in four imaging planes: (a) perpendicular to the right ventricular inflow tract; (b) perpendicular to the right ventricular outflow tract; (c) in the left ventricular short axis view; and (d) in the axial view. The volumes of the right ventricle and other cardiac cavities were determined with the method of discs. The true cast volumes were measured with the water displacement technique. The agreement between true and measured volumes and the repeatability of image analysis were determined using the Bland-Altman method.

RESULTS

There were no statistically significant differences between the measured and true right ventricular volumes irrespective of the imaging plane. The axial plane gave the smallest mean absolute difference from the true right ventricular volume (3.2 +/-2.2 ml) and also the best repeatability of volume analysis (0.2+/-1.6 ml). However, the other imaging planes performed nearly as well, and the differences across the planes were not statistically significant (p > 0.05). Also, in studies of the left ventricle and left and right atrium, the axial view appeared to give the best results, but differences across the imaging planes remained small.

CONCLUSION

The present studies of human cardiac casts suggest that gradient echo MRI is well applicable to right ventricular volume measurements. Imaging the right ventricle in axial planes covering the entire heart gives good agreement with true right ventricular volumes and excellent analysis reproducibility. However, other imaging directions perform nearly as well, and thus selection of the imaging plane may not be of major importance to the accuracy of cardiac volume measurements with MR.

Comparison of fast spiral, echo planar, and fast low-angle shot MRI for cardiac volumetry at .5T

The application of fast imaging is necessary to reduce the scanning time for cardiac volumetric MRI. Fast spiral, echo planar imaging (EPI), and fast low-angle shot (FLASH) imaging are rapid MRI techniques that allow image acquisition within a fraction of a second. Performed as a multi-shot technique, breath-hold imaging with high temporal and spatial resolution is feasible. This study evaluated the accuracy of interleaved spiral, EPI, and FLASH imaging for measuring ventricular volume and mass at .5T. Breath-hold short-axis cines in parallel planes covering both ventricles were acquired in 16 volunteers with all three fast methods, as well as with conventional gradient-echo imaging for comparison. All fast techniques showed good agreement with conventional imaging. Despite its lower temporal resolution, FLASH imaging yielded higher image quality than EPI and spiral, making FLASH more reliable and suggesting that at .5T, it is the method of choice for rapid cardiac volumetric imaging.

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.

Measurement of left ventricular mass: methodology and expertise

The strong relation between increased left ventricular mass and cardiovascular events makes accurate measurement of left ventricular mass a high priority, especially in patients with hypertension. M-mode echocardiography is used most widely to measure left ventricular mass because of its wide availability, moderate expense, anatomic and prognostic validation and lack of radiation or claustrophobia; however, this technique is expertise-dependent and may give erroneous results in distorted ventricles. Two-dimensional and especially three-dimensional echocardiography increase the precision with which left ventricular mass is measured but they are more time-consuming and difficult to perform on a large scale. Magnetic resonance imaging provides highly accurate left ventricular mass measurements and permits tissue imaging but its use is limited by expensive, fixed facilities and claustrophobia. Cine computed X-ray tomography also measures left ventricular mass accurately and permits perfusion assessment with contrast injection but it involves radiation and the use of fixed facilities of limited availability. Understanding the strengths and limitations of available techniques can facilitate selection of the most appropriate method to measure left ventricular mass in a particular setting.

Functional and bioenergetic consequences of postinfarction left ventricular remodeling in a new porcine model. MRI and 31 P-MRS study

BACKGROUND

The underlying mechanisms by which left ventricular remodeling (LVR) leads to congestive heart failure (CHF) are unclear. This study examined the functional and bioenergetic abnormalities associated with postinfarction ventricular remodeling in a new, large animal model.

METHODS AND RESULTS

Remodeling was induced by circumflex coronary artery ligation in young pigs. LV mass, volume, ejection fraction (EF), the ratio of scar surface area to LV surface area, and LV wall stresses were calculated from magnetic resonance imaging anatomic data and simultaneously measured LV pressure. Hemodynamics, transmural blood flow, and high-energy phosphates (spatially localized 31P-nuclear magnetic resonance) were measured under basal conditions, during hyperperfusion induced by pharmacological vasodilation with adenosine, and during pyruvate infusion (11 mg/kg per minute IV). Six of 18 animals with coronary ligation developed clinical CHF while the remaining 12 animals had LV dilation (LVR) without CHF. The results were compared with 16 normal animals. EF decreased from 55.9 +/- 5.6% in normals to 34.6 +/- 2.3% in the LVR group (P < .05) and 24.2 +/- 2.8% in the CHF group (P < .05 versus LVR). The infarct scar was larger in CHF hearts than in LVR hearts (P < .05). In normals, LV myocardial creatine phosphate (CP)/ATP ratios were 2.10 +/- 0.10, 2.06 +/- 0.16, and 1.92 +/- 0.12 in subepicardium (EPI), mid myocardium (MID), and subendocardium (ENDO), respectively. In LVR hearts, the corresponding ratios were decreased to 1.99 +/- 0.13, 1.80 +/- 0.14, and 1.57 +/- 0.15 (ENDO P < .05 versus normal). In CHF hearts, CP/ATP ratios were 1.41 +/- 0.14, 1.33 +/- 0.15, and 1.25 +/- 0.15; (P < .05 versus LVR in EPI and MID). The calculated myocardial free ADP levels were significantly increased only in CHF hearts.

CONCLUSIONS

Bioenergetic abnormalities in remodeled myocardium are related to the severity of LV dysfunction, which, in turn, is dependent on the severity of the initiating myocardial infarction.

Cardiac activation mapping by MRI

To establish cardiac MRI as a tool for noninvasive evaluation of activation patterns, 10 healthy volunteers were examined by cine segmented turboFLASH imaging sequences. Sequence modifications for low signal blood-pool appearance were applied, i.e., bilateral spatial saturation for segmented turboFLASH imaging. Pixelwise calculation of first-harmonic Fourier phase values (displayed as color-encoded maps) reveal either anterior septal or left ventricular free-wall sites as areas of earliest phase spreading towards posterior paraseptal sites in segmented turboFLASH scans. Phase scatter is lower in unsaturated than spatially presaturated segmented turboFLASH studies. Phase standard deviation in areas of endocardial displacement is higher in basal than apical slice positions in these scans. Early results indicate that first-harmonic Fourier phase analysis of cardiac-segmented turboFLASH MRI cine studies may provide a tool for noninvasive studies of cardiac activation sequence.

Bioenergetic consequences of left ventricular remodeling

BACKGROUND

Left ventricular (LV) remodeling is associated with LV dysfunction and decrease of coronary flow reserve. The underlying mechanisms responsible for these alterations are unclear. Changes in myocardial high-energy phosphate levels may be associated with these alterations.

METHODS AND RESULTS

Twelve dogs with LV remodeling secondary to discrete necrosis produced by transmyocardial DC shock were compared with 8 normal dogs. LV mass and end-diastolic volume were measured by magnetic resonance imaging 7 days before and 12.9 +/- 1.3 months after DC shock. Transmurally localized 31P nuclear magnetic resonance spectra from five layers across the LV wall were obtained simultaneously with transmural blood flow measurements (microspheres) under basal conditions and during pacing at 200 and 240 beats per minute. LV mass and end-diastolic volume were significantly increased after DC shock (33% and 26%, respectively, each P < .01). Under basal conditions, the subendocardial creatine phosphate (CP)/ATP ratio was significantly lower in remodeled LV compared with the control group (1.71 +/- 0.09 versus 2.04 +/- 0.09, P < .05). The subendocardial CP/ATP ratio was inversely correlated with both the increase in LV mass and LV end-diastolic volume (r = -.77 and r = -.70, P < .01 and P < .05, respectively). In remodeled myocardium, pacing induced a significant increase in LV end-diastolic pressure (from 8 +/- 1 to 20 +/- 3 mm Hg, P < .05), which was accompanied by a significant decrease of subendocardial/subepicardial (Endo/Epi) blood flow ratio (from 1.01 +/- 0.10 to 0.63 +/- 0.11, P < .05) and a significant decrease in subendocardial CP/ATP ratio (from 1.78 +/- 0.07 to 1.61 +/- 0.10, P < .05) and increase of delta P(i)/ATP ratio (from 0 to 0.24 +/- 0.05, P < .01). The decrease in subendocardial CP/ATP ratio was correlated with the decrease in Endo/Epi blood flow ratio (r = .79, P < .05).

CONCLUSIONS

These results demonstrate that alterations in myocardial high-energy phosphate levels are correlated with the extent of LV remodeling. In remodeled hearts, pacing-induced tachycardia produces further changes of myocardial high-energy phosphate levels in the subendocardium that appear to be related to ventricular dysfunction and redistribution of blood flow away from the subendocardium.

Left ventricular quantification with breath-hold MR imaging: comparison with echocardiography

To evaluate the reproducibility of measurements of left ventricular (LV) dimensions, function, and myocardial mass, segmented k-space gradient-recalled-echo (GRE) magnetic resonance (MR) imaging was performed on two occasions on 12 healthy volunteers. To compare the MR data, all volunteers underwent a two-dimensional echocardiography with determination of LV dimensions and function. The left ventricle was imaged during breath-hold by consecutive, contiguous short-axis views at end-diastole and end-systole. An average of eight short-axis views was needed to encompass the whole left ventricle. This fast MR sequence limited the total acquisition time to 12 min. LV volumes and masses were calculated after manual delineation of epicardial and endocardial surfaces by two observers in a blinded fashion. Interstudy variability varied between 4.1% and 10.3% for LV end-diastolic volume and end-systolic volume, respectively. Differences in interobserver variability were smaller and varied between 3.6% and 7.3% for LV ejection fraction and end-diastolic volume, respectively. Intraobserver variabilities ranged between 2.0% and 7.0% for LV ejection fraction and end-systolic volume, respectively. These variability percentages agree very well with other studies in literature using other MR sequences. No significant differences in LV dimensions or function were found between MR imaging and echocardiography. In conclusion, this MR sequence allows fast and reproducible LV quantification.

Reproducibility of MRI-derived measurements of right ventricular volumes and myocardial mass

Magnetic resonance (MR) imaging has been shown to provide accurate measurements of right ventricular (RV) volumes and myocardial mass. The purpose of this study was to evaluate the reproducibility of MR imaging, which in clinical practice may be as important as its absolute accuracy. The reproducibility of MR imaging measurements of the right ventricle was assessed by analyzing 40 serial functional MR imaging examinations of the right ventricle with variance component analysis. Standard deviations and 95% ranges for change were: for RV myocardial mass, 5.9 and 16 g; and for RV ejection fraction, 6.0% and 16%, respectively. Reproducibility was similar for cine and spin-echo MR imaging. The intraobserver and interobserver errors were especially large, indicating that observer subjectivity is the limiting factor in the interpretation of the MR images. This study suggests that the reproducibility of RV measurements is adequate to detect RV hypertrophy and a low ejection fraction in the individual patient. For accurate follow-up examinations, whereby smaller changes are to be detected, the reproducibility of MR imaging measurements may not be sufficient. More effort is needed to improve the reproducibility of MR imaging measurements.

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.

Technical note: rapid measurement of left ventricular mass by spin echo magnetic resonance imaging

Magnetic resonance (MR) imaging provides an accurate measurement of left ventricular mass but imaging time can be up to 45 min. We tested a more rapid multislice spin echo technique on 16 volunteers without evidence of heart disease. Multislice short axis spin echo images were acquired in up to three sets of five, clustered around end systole. Total imaging time was 15 min. Myocardial areas were summed and specific gravity was assumed. Comparison was made with multiple single acquisitions timed to end systole. There was good agreement between the two measurements of left ventricular mass. Mean (+/- standard deviation (sd), range) values were 212 g (+/- 41.71, 152 to 311) by the multislice method and 213 g (+/- 44.26, 155 to 317) by the single slice method. The mean difference (+/- sd of difference) between measurements was -1.72 +/- 14.89 g (95% confidence interval for limits of agreement was +/- 14%). We have therefore established a more rapid and accurate method of measuring left ventricular mass.

Magnetic resonance measurement of velocity and flow: technique, validation, and cardiovascular applications

With a newly developed magnetic resonance (MR) technique for blood flow measurements, qualitative and quantitative information on both flow volume and flow velocity in the great vessels can be obtained. MR flow quantitation is performed with a gradient-echo MR sequence with high temporal resolution enabling measurements at frequent intervals throughout the cardiac cycle. MR flow quantitation uses the phase rather than the amplitude of the MR signal to reconstruct the images. These images, often referred to as MR velocity maps or velocity-encoded cine MR images, are two-dimensional displays of flow velocity. From these velocity maps, velocity and volume flow data can be obtained. Previous validation experiments have demonstrated the accuracy of MR velocity mapping, and this technique is now being applied successfully in several clinical fields. MR velocity mapping may be of considerable value when Doppler echocardiography results are unsatisfactory or equivocal, particularly because MR is suited for the analysis of volumetric flow and complex flow patterns. Among the vastly growing number of clinical cardiovascular applications that have been reported are the great arteries and veins, coronary vessels, valvular disease, and the abdominal and peripheral vessels. These items are reviewed, and some aspects of the technique that need improvement are discussed.