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

Slice encoding for the reduction of outflow signal artifacts in cine balanced SSFP imaging

PURPOSE

Standard balanced SSFP (bSSFP) cine MRI often suffers from blood outflow artifacts. We propose a method that spatially encodes these outflowing spins to reduce their effects in the intended slice.

METHODS

Bloch simulations were performed to characterize through-plane flow and to investigate how the use of phase encoding along the slice select's direction ("slice encoding") could alleviate its issues. Phantom scans and in vivo cines were acquired on a 3T system, comparing the standard 2D acquisition to the proposed slice-encoding method. Nineteen healthy volunteers were recruited for short-axis and horizontal long-axis oriented scans. An expert radiologist evaluated each slice-encoded/standard cine pairs in a rank comparison test and graded their quality on a 1-5 scale. The grades were used for a nonparametric paired evaluation for independent samples with a null hypothesis that there was no statistical difference between the two quality-grade distributions for α = 0.05 significance.

RESULTS

Bloch simulation results demonstrated this technique's feasibility, showing a fully resolved slice profile given a sufficient number of slice encodes. These results were confirmed with the phantom experiments. Each in vivo slice-encoded cine had a higher quality than its corresponding standard acquisition. The nonparametric paired evaluation came to 0.01 significance, encouraging us to reject the null hypothesis and conclude that slice-encoding effectively works in reducing outflow effects.

CONCLUSION

The slice-encoding balanced SSFP technique is helpful in mitigating outflow effects and is achievable within a single breath hold, being a useful alternative for cases in which the flow artifacts are significant.

Severe right ventricular dilatation after repair of Tetralogy of Fallot is associated with increased left ventricular preload and stroke volume

Aims

Pulmonary regurgitation (PR) and right ventricular (RV) dilatation are common in repaired tetralogy of Fallot (rTOF). Left ventricular (LV) dysfunction is an important risk factor in rTOF. The effect of PR/RV dilatation on LV performance and RV-LV interactions in rTOF are incompletely understood. We examined LV responses and exercise capacity in rTOF, both before and after pulmonary valve replacement (PVR).

Methods and results

Cardiac magnetic resonance imaging scans in 126 rTOF patients (age 17.3 ± 7.6 years) were analysed, comparing subjects with indexed RV end-diastolic volume (RVEDVi) <170 mL/m2 (mild/moderate dilatation, n = 95) and RVEDVi ≥170 mL/m2 (severe dilatation, n = 31). Indexed PR volume (PRVi), RV end-systolic (RVESVi), RV end-diastolic (RVEDVi), RV stroke volume (RVSVi), net pulmonary forward flow (NPFFi), LV end-diastolic (LVEDVi), LV end-systolic (LVESVi), LV stroke volume (LVSVi), RV and LV ejection fraction (EF), and diastolic septal curvature were obtained. Peak aerobic capacity (VO2 max) was measured. In a subset (n = 30), measures were obtained pre-and-post surgical PVR. Compared to those with mild/moderate RV dilatation, patients with severe RV dilation had greater PRVi (38 ± 12 vs. 24 ± 9 mL/m2, P < 0.0001), NPFFi (53 ± 9 vs. 44 ± 11 mL/m2, P < 0.0001), LVEDVi (87 ± 14 vs. 73 ± 13 mL/m2, P < 0.0001), LVESVi (39 ± 12 vs. 30 ± 8 mL/m2, P < 0.0001), and LVSVi (48 ± 7 vs. 43  ±  8 mL/m2, P = 0.002) but lower RV ejection fraction (46 ± 8 vs. 53 ± 7%, P < 0.0001). Septal curvature and VO2 max were similar in both groups. After PVR, there was no change in LVEDVi, LVSVi, septal curvature, or VO2 max.

Conclusions

Chronic PR with severe RV dilatation is associated with increased NPFFi, LVEDVi, and LVSVi. This may potentially explain preserved exercise capacity in rTOF with severe PR and RV dilatation.

Heart filling exceeds emptying during late ventricular systole in patients with systolic heart failure and healthy subjects - a cardiac MRI study

Background

Total heart volume (THV) within the pericardium is not constant throughout the cardiac cycle and THV would intuitively be lowest at end systole. We have, however, observed a phase shift between ventricular outflow and atrial inflow which causes the minimum THV to occur before end systole. The aims were to explain the mechanism of the late‐systolic net inflow to the heart and determine whether this net inflow is affected by increased cardiac output or systolic heart failure.

Methods and Results

Healthy controls (n = 21) and patients with EF<35% (n = 14) underwent magnetic resonance imaging with flow measurements in vessels to and from the heart, and this was repeated in nine controls during 140 μgram kg⁻¹ min⁻¹ adenosine infusion. Minimum THV occurred 78 ± 6 ms before end of systolic ejection (8 ± 1% of the cardiac cycle) in controls. The late‐systolic net inflow was 12·3 ± 1·1 ml or 6·0 ± 0·5% of total stroke volume (TSV). Cardiac output increased 66 ± 8% during adenosine but late‐systolic net inflow to the heart did not change (P = 0·73). In patients with heart failure, late‐systolic net inflow of the heart′s left side was lower (3·4 ± 0·5%) compared to healthy subjects (5·3 ± 0·6%, P = 0·03).

Conclusions

Heart size increases before end systole due to a late‐systolic net inflow which is unaffected by increased cardiac output. This may be explained by inertia of blood that flows into the atria generated by ventricular systole. The lower late‐systolic net inflow in patients with systolic heart failure may be a measure of decreased ventricular filling due to decreased systolic function, thus linking systolic to diastolic dysfunction.

Echocardiographic Linear Dimensions for Assessment of Right Ventricular Chamber Volume as Demonstrated by Cardiac Magnetic Resonance

BACKGROUND

Echocardiography-derived linear dimensions offer straightforward indices of right ventricular (RV) structure but have not been systematically compared with RV volumes on cardiac magnetic resonance (CMR).

METHODS

Echocardiography and CMR were interpreted among patients with coronary artery disease imaged via prospective (90%) and retrospective (10%) registries. For echocardiography, American Society of Echocardiography-recommended RV dimensions were measured in apical four-chamber (basal RV width, mid RV width, and RV length), parasternal long-axis (proximal RV outflow tract [RVOT]), and short-axis (distal RVOT) views. For CMR, RV end-diastolic volume and RV end-systolic volume were quantified using border planimetry.

RESULTS

Two hundred seventy-two patients underwent echocardiography and CMR within a narrow interval (0.4 ± 1.0 days); complete acquisition of all American Society of Echocardiography-recommended dimensions was feasible in 98%. All echocardiographic dimensions differed between patients with and those without RV dilation on CMR (P < .05). Basal RV width (r = 0.70), proximal RVOT width (r = 0.68), and RV length (r = 0.61) yielded the highest correlations with RV end-diastolic volume on CMR; end-systolic dimensions yielded similar correlations (r = 0.68, r = 0.66, and r = 0.65, respectively). In multivariate regression, basal RV width (regression coefficient = 1.96 per mm; 95% CI, 1.22-2.70; P < .001), RV length (regression coefficient = 0.97; 95% CI, 0.56-1.37; P < .001), and proximal RVOT width (regression coefficient = 2.62; 95% CI, 1.79-3.44; P < .001) were independently associated with CMR RV end-diastolic volume (r = 0.80). RV end-systolic volume was similarly associated with echocardiographic dimensions (basal RV width: 1.59 per mm [95% CI, 1.06-2.13], P < .001; RV length: 1.00 [95% CI, 0.66-1.34], P < .001; proximal RVOT width: 1.80 [95% CI, 1.22-2.39], P < .001) (r = 0.79).

CONCLUSIONS

RV linear dimensions provide readily obtainable markers of RV chamber size. Proximal RVOT and basal width are independently associated with CMR volumes, supporting the use of multiple linear dimensions when assessing RV size on echocardiography.

QUANTITATIVE PLANAR AND VOLUMETRIC CARDIAC MEASUREMENTS USING 64 MDCT AND 3T MRI VS. STANDARD 2D AND M-MODE ECHOCARDIOGRAPHY: DOES ANESTHETIC PROTOCOL MATTER?

Cross-sectional imaging of the heart utilizing computed tomography and magnetic resonance imaging (MRI) has been shown to be superior for the evaluation of cardiac morphology and systolic function in humans compared to echocardiography. The purpose of this prospective study was to test the effects of two different anesthetic protocols on cardiac measurements in 10 healthy beagle dogs using 64-multidetector row computed tomographic angiography (64-MDCTA), 3T magnetic resonance (MRI) and standard awake echocardiography. Both anesthetic protocols used propofol for induction and isoflourane for anesthetic maintenance. In addition, protocol A used midazolam/fentanyl and protocol B used dexmedetomedine as premedication and constant rate infusion during the procedure. Significant elevations in systolic and mean blood pressure were present when using protocol B. There was overall good agreement between the variables of cardiac size and systolic function generated from the MDCTA and MRI exams and no significant difference was found when comparing the variables acquired using either anesthetic protocol within each modality. Systolic function variables generated using 64-MDCTA and 3T MRI were only able to predict the left ventricular end diastolic volume as measured during awake echocardiogram when using protocol B and 64-MDCTA. For all other systolic function variables, prediction of awake echocardiographic results was not possible (P = 1). Planar variables acquired using MDCTA or MRI did not allow prediction of the corresponding measurements generated using echocardiography in the awake patients (P = 1). Future studies are needed to validate this approach in a more varied population and clinically affected dogs.

Automatic cardiac segmentation using semantic information from random forests

We propose a fully automated method for segmenting the cardiac right ventricle (RV) from magnetic resonance (MR) images. Given a MR test image, it is first oversegmented into superpixels and each superpixel is analyzed to detect the presence of RV regions using random forest (RF) classifiers. The superpixels containing RV regions constitute the region of interest (ROI) which is used to segment the actual RV. Probability maps are generated for each ROI pixel using a second set of RF classifiers which give the probabilities of each pixel belonging to RV or background. The negative log-likelihood of these maps are used as penalty costs in a graph cut segmentation framework. Low-level features like intensity statistics, texture anisotropy and curvature asymmetry, and high level context features are used at different stages. Smoothness constraints are imposed based on semantic information (importance of each feature to the classification task) derived from the second set of learned RF classifiers. Experimental results show that compared to conventional method our algorithm achieves superior performance due to the inclusion of semantic knowledge and context information.

Quantification of right ventricular volume in dogs: a comparative study between three-dimensional echocardiography and computed tomography with the reference method magnetic resonance imaging

Background

Right ventricular (RV) volume and function are important diagnostic and prognostic factors in dogs with primary or secondary right-sided heart failure. The complex shape of the right ventricle and its retrosternal position make the quantification of its volume difficult. For that reason, only few studies exist, which deal with the determination of RV volume parameters. In human medicine cardiac magnetic resonance imaging (CMRI) is considered to be the reference technique for RV volumetric measurement (Nat Rev Cardiol 7(10):551-563, 2010), but cardiac computed tomography (CCT) and three-dimensional echocardiography (3DE) are other non-invasive methods feasible for RV volume quantification. The purpose of this study was the comparison of 3DE and CCT with CMRI, the gold standard for RV volumetric quantification.

Results

3DE showed significant lower and CCT significant higher right ventricular volumes than CMRI. Both techniques showed very good correlations (R > 0.8) with CMRI for the volumetric parameters end-diastolic volume (EDV) and end-systolic volume (ESV). Ejection fraction (EF) and stroke volume (SV) were not different when considering CCT and CMRI, whereas 3DE showed a significant higher EF and lower SV than CMRI. The 3DE values showed excellent intra-observer variability (<3%) and still acceptable inter-observer variability (<13%).

Conclusion

CCT provides an accurate image quality of the right ventricle with comparable results to the reference method CMRI. CCT overestimates the RV volumes; therefore, it is not an interchangeable method, having the disadvantage as well of needing general anaesthesia. 3DE underestimated the RV-Volumes, which could be explained by the worse image resolution. The excellent correlation between the methods indicates a close relationship between 3DE and CMRI although not directly comparable. 3DE is a promising technique for RV volumetric quantification, but further studies in awake dogs and dogs with heart disease are necessary to evaluate its usefulness in veterinary cardiology.

Ex vivo cardiovascular magnetic resonance measurements of right and left ventricular mass compared with direct mass measurement in excised hearts after transplantation: a first human SSFP comparison

BACKGROUND

CMR is considered the 'gold standard' for non-invasive LV and RV mass quantitation. This information is solely based on gradient-recalled echo (GRE) sequences while contrast dependent on intrinsic T1/T2 characteristics potentially offers superior image contrast between blood and myocardium. This study aims, for the first time in humans, to validate the SSFP approach using explanted hearts obtained from heart transplant recipients. Our objective is establish the correlation between and to validate steady-state free precession (SSFP) derived LV and RV mass vs. autopsy mass of hearts from cardiac transplants patients.

METHODS

Over three-years, 58 explanted cardiomyopathy hearts were obtained immediately upon orthotopic heart transplantation from the OR. They were quickly cleaned, prepared and suspended in a saline-filled container and scanned ex vivo via SSFP-SA slices to define LV/RV mass. Using an automatic thresholding program, segmentation was achieved in combination with manual trimming (ATMT) of extraneous tissue incorporating 3D cardiac modeling performed by independent and blinded readers. The explanted hearts were then dissected with the ventricles surgically separated at the interventricular septum. Weights of the total heart not excluding papillary and trabecular myocardium, LV and RV were measured via high-fidelity scale. Linear regression and Bland-Altman plots were used to analyze the data. The intra-class correlation coefficient was used to assess intra-observer reliability.

RESULTS

Of the total of 58 explanted hearts, 3 (6%) were excluded due to poor image quality leaving 55 patients (94%) for the final analysis. Significant positive correlations were found between total 3D CMR mass (450 ± 111 g) and total pathology mass (445 ± 116 g; r = 0.99, p < 0.001) as well as 3D CMR measured LV mass (301 ± 93 g) and the pathology measured LV mass (313 ± 96 g; r = 0.95, p < 0.001). Strong positive correlations were demonstrated between the 3D CMR measured RV mass (149 ± 46 g) and the pathology measured RV mass (128 ± 40 g; r = 0.76, p < 0.001). The mean bias between 3D-CMR and pathology measures for total mass, LV mass and RV mass were: 3.0 g, -16 g and 19 g, respectively.

CONCLUSIONS

SSFP-CMR accurately determines total myocardial, LV and RV mass as compared to pathology weighed explanted hearts despite variable surgical removal of instrumentation (left and right ventricular assist devices, AICD and often apical core removals). Thus, this becomes the first-ever human CMR confirmation for SSFP now validating the distinction of 'gold standard'.

Cardiac image segmentation from cine cardiac MRI using graph cuts and shape priors

In this paper, we propose a novel method for segmentation of the left ventricle, right ventricle, and myocardium from cine cardiac magnetic resonance images of the STACOM database. Our method incorporates prior shape information in a graph cut framework to achieve segmentation. Poor edge information and large within-patient shape variation of the different parts necessitates the inclusion of prior shape information. But large interpatient shape variability makes it difficult to have a generalized shape model. Therefore, for every dataset the shape prior is chosen as a single image clearly showing the different parts. Prior shape information is obtained from a combination of distance functions and orientation angle histograms of each pixel relative to the prior shape. To account for shape changes, pixels near the boundary are allowed to change their labels by appropriate formulation of the penalty and smoothness costs. Our method consists of two stages. In the first stage, segmentation is performed using only intensity information which is the starting point for the second stage combining intensity and shape information to get the final segmentation. Experimental results on different subsets of 30 real patient datasets show higher segmentation accuracy in using shape information and our method's superior performance over other competing methods.

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.

Management of adults with Tetralogy of Fallot

Tetralogy of Fallot is the most common form of cyanotic congenital cardiac disease. Patients with previously repaired tetralogy of Fallot are the most common patients seen in the Program for Adults with Congenital Heart Disease at The Johns Hopkins All Children's Heart Institute. Guidelines for the management of these patients are available from multiple sources including The American College of Cardiology (ACC) and The American Heart Association (AHA), The Canadian Cardiovascular Society, and The European Society of Cardiology (ESC). These guidelines describe multiple components related to the care for these patients including strategies for medical follow-up, the management of arrhythmias and electrophysiological diseases, and the treatment of chronic pulmonary insufficiency and stenosis. Several new strategies are available for replacement of the pulmonary valve including transcatheter replacement of the pulmonary valve and replacement of the pulmonary valve with a self-manufactured bicuspid polytetrafluoroethylene pulmonary valve.

Cardiac MRI segmentation using mutual context information from left and right ventricle

In this paper, we propose a graphcut method to segment the cardiac right ventricle (RV) and left ventricle (LV) by using context information from each other. Contextual information is very helpful in medical image segmentation because the relative arrangement of different organs is the same. In addition to the conventional log-likelihood penalty, we also include a "context penalty" that captures the geometric relationship between the RV and LV. Contextual information for the RV is obtained by learning its geometrical relationship with respect to the LV. Similarly, RV provides geometrical context information for LV segmentation. The smoothness cost is formulated as a function of the learned context which helps in accurate labeling of pixels. Experimental results on real patient datasets from the STACOM database show the efficacy of our method in accurately segmenting the LV and RV. We also conduct experiments on simulated datasets to investigate our method's robustness to noise and inaccurate segmentations.

Diagnosis and management of pulmonary arterial hypertension using MR imaging

Pulmonary arterial hypertension (PAH) is a syndrome that results from restricted blood flow through the pulmonary arterial circulation, which leads to a pathological increase in pulmonary vascular resistance (PVR) and ultimately to right heart failure. The prognosis of patients with PAH has improved with the recent development of new medications. The need for new noninvasive diagnostic tools is increasing. Magnetic resonance (MR) imaging is the gold standard for assessing the right ventricle (RV). Its high degree of reproducibility makes it ideal for monitoring changes in RV parameters in response to therapy. MR imaging can also provide both anatomical and functional information about pulmonary hemodynamics. This article reviews the current status of MR imaging of the right side of the heart and pulmonary circulation in patients with PAH and other associated pulmonary diseases.

Differential modulation of right ventricular strain and right atrial mechanics in mild vs. severe pressure overload

Increased right atrial (RA) and ventricular (RV) chamber volumes are a late maladaptive response to chronic pulmonary hypertension. The purpose of the current investigation was to characterize the early compensatory changes that occur in the right heart during chronic RV pressure overload before the development of chamber dilation. Magnetic resonance imaging with radiofrequency tissue tagging was performed on dogs at baseline and after 10 wk of pulmonary artery banding to yield either mild RV pressure overload (36% rise in RV pressure; n = 5) or severe overload (250% rise in RV pressure; n = 4). The RV free wall was divided into three segments within a midventricular plane, and circumferential myocardial strain was calculated for each segment, the septum, and the left ventricle. Chamber volumes were calculated from stacked MRI images, and RA mechanics were characterized by calculating the RA reservoir, conduit, and pump contribution to RV filling. With mild RV overload, there were no changes in RV strain or RA function. With severe RV overload, RV circumferential strain diminished by 62% anterior (P = 0.04), 42% inferior (P = 0.03), and 50% in the septum (P = 0.02), with no change in the left ventricle (P = 0.12). RV filling became more dependent on RA conduit function, which increased from 30 ± 9 to 43 ± 13% (P = 0.01), than on RA reservoir function, which decreased from 47 ± 6 to 33 ± 4% (P = 0.04), with no change in RA pump function (P = 0.94). RA and RV volumes and RV ejection fraction were unchanged from baseline during either mild (P > 0.10) or severe RV pressure overload (P > 0.53). In response to severe RV pressure overload, RV myocardial strain is segmentally diminished and RV filling becomes more dependent on RA conduit rather than reservoir function. These compensatory mechanisms of the right heart occur early in chronic RV pressure overload before chamber dilation develops.

Imaging techniques and the evaluation of the right heart and the pulmonary circulation

Since the right side of the heart and the pulmonary circulation are regarded as secondary components of the circulatory system, their role in disease has traditionally not received the same attention as their counterparts in the systemic circulation. This was partly because precise noninvasive study of these structures was difficult. For many years, chest radiography and invasive angiography were the only techniques available for imaging the minor circulation. The development of transthoracic echocardiography and nuclear techniques has produced a significant leap forward for noninvasive imaging, particularly of the right ventricle. More recently, novel echocardiographic techniques, and advances in computed tomography and magnetic resonance imaging, in particular, have expanded our diagnostic armamentarium and provided new insights into the anatomy and function of the pulmonary circulation in both health and disease. This article contains a review of the current status of techniques for imaging the right side of the heart and the pulmonary circulation.

Interactive real-time mapping and catheter ablation of the cavotricuspid isthmus guided by magnetic resonance imaging in a porcine model

Aims

We investigated the feasibility of real-time magnetic resonance imaging (RTMRI) guided ablation of the cavotricuspid isthmus (CTI) by using a MRI-compatible ablation catheter.

Methods and results

Cavotricuspid isthmus ablation was performed in an interventional RTMRI suite by using a novel 7 French, steerable, non-ferromagnetic ablation catheter in a porcine in vivo model (n = 20). The catheter was introduced and navigated by RTMRI visualization only. Catheter position and movement during manipulation were continuously visualized during the entire intervention. Two porcine prematurely died due to VT/VF. Anatomical completion of the CTI ablation line could be achieved after a mean of 6.3±3 RF pulses (RF energy: 1807±1016.4 Ws/RF pulse, temperature: 55.9±5.9°C) in n = 18 animals. In 15 of 18 procedures (83.3%) a complete CTI block was proven by conventional mapping in the electrophysiological (EP) lab.

Conclusion

Completely non-fluoroscopic ablation guided by RTMRI using a steerable and non-ferromagnetic catheter is a promising novel technology in interventional electrophysiology.

Cardiac MR imaging: new advances and role of 3T

Over the last decade, cardiac magnetic resonance imaging has increasingly evolved into a useful diagnostic tool among the radiology and cardiology communities. Ongoing improvements in MR imaging hardware, processing speed, and pulse sequence development have laid the foundation for rapid progress in cardiac MR imaging. This article summarizes developing techniques and technique-related aspects, and the advantages and possible pitfalls of 3T in particular.

Prevalence and correlates of septal delayed contrast enhancement in patients with pulmonary hypertension

Using cardiac magnetic resonance, the presence of myocardial delayed contrast enhancement (DCE) has been described in the ventricular septum at the level of the right ventricular insertion points in patients with pulmonary hypertension (PH). The aim of this study was to investigate the prevalence, extent, and correlates of this finding. Septal DCE was evaluated in 55 patients with known or suspected PH of various causes. The extent of DCE was estimated visually with an insertion enhancement score (range 0 to 4) and quantified as DCE mass. The results were correlated with cine magnetic resonance and right-sided cardiac catheterization. Predictors of DCE were investigated using multivariate analysis. PH at rest was present in 42 patients (group 1) and absent in 13 (group 2). DCE was noted in 41 patients (97%) in group 1 and 3 (23%) in group 2 (p <0.0001). The extent of DCE was higher in group 1 than group 2 (median insertion enhancement score 3 vs 0, median DCE mass 8.7 vs 0 g, respectively; p <0.0001 for both). The extent of DCE showed moderate to good univariate correlations (r = 0.5 to 0.73) with pulmonary pressures and with right ventricular volumes, mass, and ejection fractions. In multivariate analysis, systolic pulmonary pressure was the only predictor of DCE. In conclusion, the presence of septal DCE at the right ventricular insertion points is common in PH of different causes, and the level of systolic pulmonary pressure elevation appears to be the main determinant of this finding.

The quantitative relationship between longitudinal and radial function in left, right, and total heart pumping in humans

The total heart volume variation (THVV) during systole has been proposed to be caused by radial function of the ventricles, but definitive data for both ventricles have not been presented. Furthermore, the right ventricle (RV) has been suggested to have a greater longitudinal pumping component than the left ventricle (LV). Therefore, we aimed to compare the stroke volume (SV) generated by radial function to the volume variation of the left, right, and total heart. To do this, we also needed to develop a new method for measuring the contribution of the longitudinal atrioventricular plane displacement (AVPD) to the RVSV (RVSVAVPD). For our study, 11 volunteers underwent cine MRI in the short- and long-axis planes and MRI flow measurement in all vessels leading to and from the heart. The left, right, and total heart showed correlations between volume variation from flow measurements and radial function calculated as SV minus the longitudinal function ( r = 0.81, P < 0.01; r = 0.80, P < 0.01; and r = 0.92, P < 0.001, respectively). Compared with the LV, the RV had a greater AVPD (23.4 ± 0.8 vs. 16.4 ± 0.5 mm), center of volume movement (13.0 ± 0.7 vs. 7.8 ± 0.4 mm), and, RVSVAVPD(82 ± 2% vs. 60 ± 2%) ( P < 0.001 for all). We found that THVV is predominantly caused by radial function of the ventricles. Longitudinal AVPD accounts for ∼80% of the RVSV, compared with ∼60% for the LVSV. This difference explains the larger portion of THVV found on the left side of the heart.

Effects of steady state free precession parameters on cardiac mass, function, and volumes

PURPOSE

We aimed to investigate comparability of LV volumes, function, and mass acquired with three steady-state free precession (SSFP) pulse sequences, simulating typical vendor and protocol specific differences in data acquisition.

METHODS

Twenty-one healthy subjects (11 male and 10 female; age range 23-49) underwent cardiac magnetic resonance (CMR) imaging at 1.5 Tesla (T). A complete stack of short-axis views covering the entire left ventricle (LV) were acquired for each of the three SSFP sequences, differing in the interslice gap and slice thickness (7 mm with no gap (7/0 mm); 7 mm with a 3 mm gap (7/3 mm) and 6 mm with a 4 mm gap (6/4 mm)) with slight variations in acquisition parameters. For each sequence, the LV volumes, function, and mass were determined. Intra- and inter-observer variability and inter-study reproducibility were assessed for all protocols.

RESULTS

All LV volumes, function and mass parameters were similar for the three SSFP sequences (P > 0.05 for all). The LV ejection fraction for the 7/3 mm sequence was 67.2 +/- 6.0, 67.4 +/- 5.3 for the 7/0 mm sequence, and the 6/4 mm sequence was 69.2 +/- 5.7. The LV mass ranged from 119.8 +/- 32.4 for the 7/3 mm sequence to 122.2 +/- 34.0 for the 7/0 mm sequence. Variabilities were low with no difference in variability between the sequences.

CONCLUSION

The three SSFP pulse sequence techniques resulted in similar LV volume, function, and mass measurements with no difference in observer and interstudy variabilities. This may allow application and transfer of LV volume studies and databases based on different imaging parameters, at different CMR sites, with a given post-processing method. Future multi-centre studies may now be in a position to consider multi-vendor study designs for LV volume studies.

Cardiac MR imaging: state of the technology

Recent developments in magnetic resonance (MR) imaging of the heart have refocused attention on the potential of MR and continue to attract intense interest within the radiology and cardiology communities. Improvements in speed, image quality, reliability, and range of applications have evolved to the point where cardiac MR imaging is increasingly seen as a practical clinical tool. As is often the case with MR imaging, not all of the most powerful techniques are necessarily easy to master or understand, and many-nonspecialists and specialists alike-are challenged to stay abreast. This review covers some of the major milestones that have led to the current state of cardiac MR and attempts to put into context some concepts that, although technical, have a real impact on the diagnostic power of cardiac MR imaging. Topics discussed include functional imaging, myocardial viability and perfusion imaging, flow quantification, and coronary artery imaging. A review such as this can only scratch the surface of what is a dynamic interdisciplinary field, but the hope is that sufficient information and insight are provided to stimulate the motivated reader to take his or her interest to the next level.

Determination of cardiac volumes and mass with FLASH and SSFP cine sequences at 1.5 vs. 3 Tesla: a validation study

PURPOSE

To compare cardiac cine MR imaging using steady state free precession (SSFP) and fast low angle shot (FLASH) techniques at 1.5 and 3 T, and to establish their variabilities and reproducibilities for cardiac volume and mass determination in volunteers. To assess the feasibility of SSFP imaging in patients at 3 T and to determine comparability to volume data acquired at 1.5 T.

MATERIALS AND METHODS

Ten healthy volunteers underwent cardiac magnetic resonance imaging using SSFP and segmented gradient-echo FLASH, using both a 1.5 and a 3 T MR system on the same day. Ten patients with impaired left ventricular (LV) function were also studied at both field strengths with SSFP.

RESULTS

For both SSFP and FLASH, field strength had no effect on the quantification of LV and right ventricular (RV) volumes, mass, or function (P > or = 0.05 for field strength for all parameters). At both 1.5 and 3 T, SSFP yielded smaller LV mass (e.g., at 3 T 109 +/- 30 g vs. 142 +/- 37 g; P = 0.011) and larger LV volume (e.g., at 3 T end-diastolic volume 149 +/- 37 mL vs. 133 +/- 31 mL at 5 T; P = 0.041) measurements than FLASH. In patients with reduced LV function, all volume and mass measurements were again similar for SSFP sequences at 1.5 vs. 3 T. In volunteers and patients, measurement variabilities for LV parameters were small for both field strength and sequences, ranging between 3.7% and 10.7% for mass.

CONCLUSION

Compared to 1.5 T, cardiac cine MR imaging at 3 T, using either FLASH or SSFP sequences, is feasible and highly reproducible. Field strength does not have an influence on quantification of cardiac volume or mass, but the systematic overestimation of LV mass and underestimation of LV volume by FLASH compared to SSFP is present at both 1.5 and 3 T. Normal values for cardiac volumes and mass established at 1.5 T can be applied to scans obtained at 3 T.

Physiology of isolated anomalous pulmonary venous connection of a single pulmonary vein as determined by cardiac magnetic resonance imaging

The physiology of isolated partially anomalous pulmonary venous connection of a single pulmonary vein has yet to be fully characterized. This study assessed the magnitude of the left-to-right shunt and right ventricular (RV) dilation from a single anomalous pulmonary vein using cardiac magnetic resonance imaging. Subjects with >1 anomalous pulmonary vein or associated lesions, including atrial septal defects, were excluded. In the 6 subjects identified, the median pulmonary-to-systemic flow ratio was 1.55 (range 1.3 to 1.6). The mean RV end-diastolic volume indexed to body surface area in the subjects was significantly larger than in a normal reference cohort (108 +/- 16 vs 78 +/- 18 cm(3)/m(2), p = 0.0009) and greater than the upper limit of normal in all 6 subjects. Older age did not correlate with increased magnitude of shunting (r = 0.3, p = 0.5), but increased age did correlate with RV end-diastolic volume indexed to body surface area (r = 0.96, p = 0.01). Isolated partially anomalous pulmonary venous connection with only 1 vein connecting anomalously results in a modest left-to-right shunt and mild RV dilation.

Dual breath-hold magnetic resonance cine evaluation of global and regional cardiac function

The purpose of our study was to evaluate the accuracy of a multislice cine magnetic resonance imaging (MRI) technique with parallel imaging in regard to global and regional left ventricular function. Forty-two individuals underwent cine MRI on a 1.5-tesla scanner. Cine MRI used a steady-state free precession technique and was performed as a single-slice technique (nonTSENSE cine) and an accelerated multislice technique (TSENSE cine) with five slices per breath-hold. End diastolic volume (EDV), end systolic volume (ESV), and ejection fraction (EF) were evaluated for all data sets and in regard to regional wall motion and regional wall motion analysis, and quantitative regional wall thickness and systolic thickening were also assessed. EDV, ESV, and EF based on TSENSE cine showed excellent correlation to the nonTSENSE cine approach (all r(2)=0.99, P<0.001). While EDV evaluations showed a small underestimation for TSENSE cine, ESV and EF showed accurate results compared with nonTSENSE cine. Both readers showed good agreement (kappa=0.72) in regional wall motion assessment comparing both techniques. Data acquisition for the multislice approach was significantly shorter ( approximately 75%) that in single-slice cine. We conclude that accurate evaluation of regional wall motion and left ventricular EF is possible using accelerated multislice cine MR with high spatial and temporal resolution.

Cardiac MR Imaging Assessment Following Tetralogy of Fallot Repair

Survivors of tetralogy of Fallot (TOF) repair constitute a large and growing population of patients. Although postsurgical outcome is generally favorable, as these patients move into adulthood, late morbidity is becoming more prevalent and the notion that TOF has been "definitively repaired" is increasingly being challenged. Recent evidence suggests that adverse long-term postsurgical outcome is related to chronic pulmonary regurgitation, right ventricular dilatation, and deteriorating ventricular function. Cardiac magnetic resonance (MR) imaging has been established as an accurate technique for quantifying ventricular size, ejection fraction, and valvular regurgitation. Cardiac MR imaging does not expose the patient to ionizing radiation and is therefore ideal for serial postsurgical follow-up. Familiarity with the anatomic basis of TOF, the surgical approaches to repair, and postrepair sequelae is essential for performing and interpreting cardiac MR imaging examinations. For example, awareness of the complications and sequelae that can occur will assist in determining when to intervene to preserve ventricular function and will improve long-term outcome. Technical facility is necessary to tailor the examination to the individual patient (eg, familiarity with non-breath-hold modifications that allow evaluation of young and less compliant patients). The radiologist can play an essential role in the treatment of patients with repaired TOF by providing noninvasive anatomic and physiologic cardiac MR imaging data. Further technologic advances in cardiac MR imaging are likely to bring about new applications, better normative data, and more examinations that are operator independent.

Cardiac three-dimensional magnetic resonance imaging and fluoroscopy merging: a new approach for electroanatomic mapping to assist catheter ablation

BACKGROUND

Modern nonfluoroscopic mapping systems construct 3D electroanatomic maps by tracking intracardiac catheters. They require specialized catheters and/or dedicated hardware. We developed a new method for electroanatomic mapping by merging detailed 3D models of the endocardial cavities with fluoroscopic images without the need for specialized hardware. This developmental work focused on the right atrium because of the difficulties in visualizing its anatomic landmarks in 3D with current approaches.

METHODS AND RESULTS

Cardiac MRI images were acquired in 39 patients referred for radiofrequency catheter ablation using balanced steady state free-precession sequences. We optimized acquisition and developed software for construction of detailed 3D models, after contouring of endocardial cavities with cross-checking of different imaging planes. 3D models were then merged with biplane fluoroscopic images by methods for image calibration and registration implemented in a custom software application. The feasibility and accuracy of this merging process were determined in heart-cast experiments and electroanatomic mapping in patients. Right atrial dimensions and relevant anatomic landmarks could be identified and measured in all 3D models. Cephalocaudal, posteroanterior, and lateroseptal diameters were, respectively, 65+/-11, 54+/-11, and 57+/-9 mm; posterior isthmus length was 26+/-6 mm; Eustachian valve height was 5+/-5 mm; and coronary sinus ostium height and width were 16+/-3 and 12+/-3 mm, respectively (n=39). The average alignment error was 0.2+/-0.3 mm in heart casts (n=40) and 1.9 to 2.5 mm in patient experiments (n=9), ie, acceptable for clinical use. In 11 patients, reliable catheter positioning and projection of activation times resulted in 3D electroanatomic maps with an unprecedented level of anatomic detail, which assisted ablation.

CONCLUSIONS

This new approach allows activation visualization in a highly detailed 3D anatomic environment without the need for a specialized nonfluoroscopic mapping system.

Magnetic resonance imaging during untreated ventricular fibrillation reveals prompt right ventricular overdistention without left ventricular volume loss

BACKGROUND

Most out-of-hospital ventricular fibrillation (VF) is prolonged (>5 minutes), and defibrillation from prolonged VF typically results in asystole or pulseless electrical activity. Recent visual epicardial observations in an open-chest, open-pericardium model of swine VF indicate that blood flows from the high-pressure arterial system to the lower-pressure venous system during untreated VF, thereby overdistending the right ventricle and apparently decreasing left ventricular size. Therefore, inadequate left ventricular stroke volume after defibrillation from prolonged VF has been postulated as a major contributor to the development of pulseless rhythms.

METHODS AND RESULTS

Ventricular dimensions were determined by MRI for 30 minutes of untreated VF in a closed-chest, closed-pericardium model in 6 swine. Within 1 minute of untreated VF, mean right ventricular volume increased by 29% but did not increase thereafter. During the first 5 minutes of untreated VF, mean left ventricular volume increased by 34%. Between 20 and 30 minutes of VF, stone heart occurred as manifested by dramatic thickening of the myocardium and concomitant substantial decreases in left ventricular volume.

CONCLUSIONS

In this closed-chest swine model of VF, substantial right ventricular volume changes occurred early and did not result in smaller left ventricular volumes. The changes in ventricular volumes before the late development of stone heart do not explain why defibrillation from brief duration VF (<5 minutes) typically results in a pulsatile rhythm with return of spontaneous circulation, whereas defibrillation from prolonged VF (5 to 15 minutes) does not.

Évaluation de la fonction cardiaque en imagerie par résonance magnétique et scanner hélicoïdal multicoupe

Magnetic resonance imaging and multislice spiral computed tomography are ideal techniques for assessing cardiac function. The main objectives of this article are to describe the different aspects, global and regional systolic left ventricular function, diastolic left ventricular function and right ventricular function, and to introduce the agreed parameters for this evaluation.