Coronary MR imaging: breath-hold capability and patterns, coronary artery rest periods, and beta-blocker use

High on sparsity: Interbin compensation of cardiac motion for improved assessment of left-ventricular function using 5D whole-heart MRI

PURPOSE

Cardiac magnetic resonance is the gold standard for evaluating left-ventricular ejection fraction (LVEF). Standard protocols, however, can be inefficient, facing challenges due to significant operator and patient involvement. Although the free-running framework (FRF) addresses these challenges, the potential of the extensive data it collects remains underutilized. Therefore, we propose to leverage the large amount of data collected by incorporating interbin cardiac motion compensation into FRF (FRF-MC) to improve both image quality and LVEF measurement accuracy, while reducing the sensitivity to user-defined regularization parameters.

METHODS

FRF-MC consists of several steps: data acquisition, self-gating signal extraction, deformation field estimations, and motion-resolved reconstruction with interbin cardiac motion compensation. FRF-MC was compared with the original 5D-FRF method using LVEF and several image-quality metrics. The cardiac regularization weight (λ c $$ {\lambda}_c $$ ) was optimized for both methods by maximizing image quality without compromising LVEF measurement accuracy. Evaluations were performed in numerical simulations and in 9 healthy participants. In vivo images were assessed by blinded expert reviewers and compared with reference standard 2D-cine images.

RESULTS

Both in silico and in vivo results revealed that FRF-MC outperformed FRF in terms of image quality and LVEF accuracy. FRF-MC reduced temporal blurring, preserving detailed anatomy even at higher cardiac regularization weights, and led to more accurate LVEF measurements. Optimizedλ c $$ {\lambda}_c $$ produced accurate LVEF for both methods compared with the 2D-cine reference (FRF-MC: 0.59% [-7.2%, 6.0%], p = 0.47; FRF: 0.86% [-8.5%, 6.7%], p = 0.36), but FRF-MC resulted in superior image quality (FRF-MC: 2.89 ± 0.58, FRF: 2.11 ± 0.47; p < 10-3).

CONCLUSION

Incorporating interbin cardiac motion compensation significantly improved image quality, supported higher cardiac regularization weights without compromising LVEF measurement accuracy, and reduced sensitivity to user-defined regularization parameters.

Clinical utility of a rapid two-dimensional balanced steady-state free precession sequence with deep learning reconstruction

BACKGROUND

Cardiovascular magnetic resonance (CMR) cine imaging is still limited by long acquisition times. This study evaluated the clinical utility of an accelerated two-dimensional (2D) cine sequence with deep learning reconstruction (Sonic DL) to decrease acquisition time without compromising quantitative volumetry or image quality.

METHODS

A sub-study using 16 participants was performed using Sonic DL at two different acceleration factors (8× and 12×). Quantitative left-ventricular volumetry, function, and mass measurements were compared between the two acceleration factors against a standard cine method. Following this sub-study, 108 participants were prospectively recruited and imaged using a standard cine method and the Sonic DL method with the acceleration factor that more closely matched the reference method. Two experienced clinical readers rated images based on their diagnostic utility and performed all image contouring. Quantitative contrast difference and endocardial border sharpness were also assessed. Left- and right-ventricular volumetry, left-ventricular mass, and myocardial strain measurements were compared between cine methods using Bland-Altman plots, Pearson's correlation, and paired t-tests. Comparative analysis of image quality was measured using Wilcoxon-signed-rank tests and visualized using bar graphs.

RESULTS

Sonic DL at an acceleration factor of 8 more closely matched the reference cine method. There were no significant differences found across left ventricular volumetry, function, or mass measurements. In contrast, an acceleration factor of 12 resulted in a 6% (5.51/90.16) reduction of measured ejection fraction when compared to the standard cine method and a 4% (4.32/88.98) reduction of measured ejection fraction when compared to Sonic DL at an acceleration factor of 8. Thus, Sonic DL at an acceleration factor of 8 was chosen for downstream analysis. In the larger cohort, this accelerated cine sequence was successfully performed in all participants and significantly reduced the acquisition time of cine images compared to the standard 2D method (reduction of 37% (5.98/16) p < 0.0001). Diagnostic image quality ratings and quantitative image quality evaluations were statistically not different between the two methods (p > 0.05). Left- and right-ventricular volumetry and circumferential and radial strain were also similar between methods (p > 0.05) but left-ventricular mass and longitudinal strain were over-estimated using the proposed accelerated cine method (mass over-estimated by 3.36 g/m2, p < 0.0001; longitudinal strain over-estimated by 1.97%, p = 0.001).

CONCLUSION

This study found that an accelerated 2D cine method with DL reconstruction at an acceleration factor of 8 can reduce CMR cine acquisition time by 37% (5.98/16) without significantly affecting volumetry or image quality. Given the increase of scan time efficiency, this undersampled acquisition method using deep learning reconstruction should be considered for routine clinical CMR.

Feasibility study of the multishot gradient-echo planar imaging sequence in non-enhanced and free-breathing whole-heart magnetic resonance coronary angiography

AIM

To investigate the feasibility of non-enhanced and free-breathing whole-heart magnetic resonance coronary angiography (MRCA) using multishot gradient-echo planar imaging (MSG-EPI).

MATERIALS AND METHODS

In total, 29 healthy volunteers were recruited for free-breathing whole-heart MRCA acquisition using the MSG-EPI sequence and fast gradient echo (GRE) sequence. After the examination, the actual scanning times, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the left main (LM) coronary artery, subjective quality scores for each segment, and evaluable length of the coronary artery were recorded and statistically analysed.

RESULTS

There was no significant difference between the SNRLM of the MSG-EPI sequence and fast GRE sequence (p=0.130), but the CNRLM of the MSG-EPI sequence was higher (p=0.001). The subjective quality score of the mid- and distal left anterior descending branch as well as the distal circumflex branch of the coronary artery in the MSG-EPI sequence was higher than that in the fast GRE sequence (p=0.003, 0.001, and 0.003, respectively). The evaluable length of the left anterior descending branch and the circumflex branch was better using the MSG-EPI sequence than that of the fast GRE sequence (p=0.015 and < 0.001, respectively). Moreover, the scanning time of the MSG-EPI sequence was 54.5% less than that of the fast GRE sequence (p<0.001).

CONCLUSION

The MSG-EPI sequence improves the subjective and objective image quality of MRCA as well as reduces the scanning time.

Free-breathing 2D radial cine MRI with respiratory auto-calibrated motion correction (RAMCO)

PURPOSE

To develop a free-breathing (FB) 2D radial balanced steady-state free precession cine cardiac MRI method with 100% respiratory gating efficiency using respiratory auto-calibrated motion correction (RAMCO) based on a motion-sensing camera.

METHODS

The signal from a respiratory motion-sensing camera was recorded during a FB retrospectively electrocardiogram triggered 2D radial balanced steady-state free precession acquisition using pseudo-tiny-golden-angle ordering. With RAMCO, for each acquisition the respiratory signal was retrospectively auto-calibrated by applying different linear translations, using the resulting in-plane image sharpness as a criterium. The auto-calibration determines the optimal magnitude of the linear translations for each of the in-plane directions to minimize motion blurring caused by bulk respiratory motion. Additionally, motion-weighted density compensation was applied during radial gridding to minimize through-plane and non-bulk motion blurring. Left ventricular functional parameters and sharpness scores of FB radial cine were compared with and without RAMCO, and additionally with conventional breath-hold Cartesian cine on 9 volunteers.

RESULTS

FB radial cine with RAMCO had similar sharpness scores as conventional breath-hold Cartesian cine and the left ventricular functional parameters agreed. For FB radial cine, RAMCO reduced respiratory motion artifacts with a statistically significant difference in sharpness scores (P < 0.05) compared to reconstructions without motion correction.

CONCLUSION

2D radial cine imaging with RAMCO allows evaluation of left ventricular functional parameters in FB with 100% respiratory efficiency. It eliminates the need for breath-holds, which is especially valuable for patients with no or impaired breath-holding capacity. Validation of the proposed method on patients is warranted.

Neural network-based fully automated cardiac resting phase detection algorithm compared with manual detection in patients

Background

A cardiac resting phase is used when performing free-breathing cardiac magnetic resonance examinations.

Purpose

The purpose of this study was to test a cardiac resting phase detection system based on neural networks in clinical practice.

Material and Methods

Four chamber-view cine images were obtained from 32 patients and analyzed. The rest duration, start point, and end point were compared between that determined by the experts and general operators, and a similar comparison was done between that determined by the experts and neural networks: the normalized root-mean-square error (RMSE) was also calculated.

Results

Unlike manual detection, the neural network was able to determine the resting phase almost simultaneously as the image was obtained. The rest duration and start point were not significantly different between the neural network and expert (p = .30, .90, respectively), whereas the end point was significantly different between the two groups (p < .05). The start point was not significantly different between the general operator and expert (p = .09), whereas the rest duration and end point were significantly different between the two groups (p < .05). The normalized RMSEs of the rest duration, start point, and end point of the neural network were 0.88, 0.64, and 0.33 ms, respectively, which were lower than those of the general operator (normalized RMSE values were 0.98, 0.68, and 0.51 ms, respectively).

Conclusions

The neural network can determine the resting phase instantly with better accuracy than the manual detection of general operators.

Non-contrast free-breathing whole-heart 3D cine cardiovascular magnetic resonance with a novel 3D radial leaf trajectory

PURPOSE

To develop and validate a non-contrast free-breathing whole-heart 3D cine steady-state free precession (SSFP) sequence with a novel 3D radial leaf trajectory.

METHODS

We used a respiratory navigator to trigger acquisition of 3D cine data at end-expiration to minimize respiratory motion in our 3D cine SSFP sequence. We developed a novel 3D radial leaf trajectory to reduce gradient jumps and associated eddy-current artifacts. We then reconstructed the 3D cine images with a resolution of 2.0mm³ using an iterative nonlinear optimization algorithm. Prospective validation was performed by comparing ventricular volumetric measurements from a conventional breath-hold 2D cine ventricular short-axis stack against the non-contrast free-breathing whole-heart 3D cine dataset in each patient (n = 13).

RESULTS

All 3D cine SSFP acquisitions were successful and mean scan time was 07:09 ± 01:31 min. End-diastolic ventricular volumes for left ventricle (LV) and right ventricle (RV) measured from the 3D datasets were smaller than those from 2D (LV: 159.99 ± 42.99 vs. 173.16 ± 47.42; RV: 180.35 ± 46.08 vs. 193.13 ± 49.38; p-value≤0.044; bias<8%), whereas ventricular end-systolic volumes were more comparable (LV: 79.12 ± 26.78 vs. 78.46 ± 25.35; RV: 97.18 ± 32.35 vs. 102.42 ± 32.53; p-value≥0.190, bias<6%). The 3D cine data had a lower subjective image quality score.

CONCLUSION

Our non-contrast free-breathing whole-heart 3D cine sequence with novel leaf trajectory was robust and yielded smaller ventricular end-diastolic volumes compared to 2D cine imaging. It has the potential to make examinations easier and more comfortable for patients.

Accelerating multi-echo chemical shift encoded water-fat MRI using model-guided deep learning

PURPOSE

To accelerate chemical shift encoded (CSE) water-fat imaging by applying a model-guided deep learning water-fat separation (MGDL-WF) framework to the undersampled k-space data.

METHODS

A model-guided deep learning water-fat separation framework is proposed for the acceleration using Cartesian/radial undersampling data. The proposed MGDL-WF combines the power of CSE water-fat imaging model and data-driven deep learning by jointly using a multi-peak fat model and a modified residual U-net network. The model is used to guide the image reconstruction, and the network is used to capture the artifacts induced by the undersampling. A data consistency layer is used in MGDL-WF to ensure the output images to be consistent with the k-space measurements. A Gauss-Newton iteration algorithm is adapted for the gradient updating of the networks.

RESULTS

Compared with the compressed sensing water-fat separation (CS-WF) algorithm/2-step procedure algorithm, the MGDL-WF increased peak signal-to-noise ratio (PSNR) by 5.31/5.23, 6.11/4.54, and 4.75 dB/1.88 dB with Cartesian sampling, and by 4.13/6.53, 2.90/4.68, and 1.68 dB/3.48 dB with radial sampling, at acceleration rates (R) of 4, 6, and 8, respectively. By using MGDL-WF, radial sampling increased the PSNR by 2.07 dB at R = 8, compared with Cartesian sampling.

CONCLUSIONS

The proposed MGDL-WF enables exploiting features of the water images and fat images from the undersampled multi-echo data, leading to improved performance in the accelerated CSE water-fat imaging. By using MGDL-WF, radial sampling can further improve the image quality with comparable scan time in comparison with Cartesian sampling.

Cardiac magnetic resonance using fused 3D cine and 4D flow sequences:Validation of ventricular and blood flow measurements

PURPOSE

Current cardiovascular magnetic resonance (CMR) examinations require expert planning, multiple breath holds, and 2D imaging. To address this, we sought to develop and validate a comprehensive free-breathing 3D cine function and flow CMR examination using a steady-state free precession (SSFP) sequence to depict anatomy fused with a spatially registered phase contrast (PC) sequence for blood flow analysis.

METHODS

In a prospective study, 25 patients underwent a CMR examination which included a 3D cine SSFP sequence and a 3D cine PC (also known as 4D flow) sequence acquired during free-breathing and after the administration of a gadolinium-based contrast agent. Both 3D sequences covered the heart and mediastinum, and used retrospective vectorcardiogram gating (20 phases/beat interpolated to 30 phases/beat) and prospective respiratory motion compensation confining data acquisition to end-expiration. Cardiovascular measurements derived from the 3D cine SSFP and PC images were then compared with those from standard 2D imaging.

RESULTS

All 3D cine SSFP and PC acquisitions were completed successfully. The mean time for the 3D cine sequences including prescription was shorter than that for the corresponding 2D sequences (21 min vs. 36 min, P-value <0.001). Left and right ventricular end-diastolic volumes and stroke volumes by 3D cine SSFP were slightly smaller than those from 2D cine SSFP (all biases ≤5%). The blood flow measurements from the 3D and 2D sequences had close agreement in the ascending aorta (bias -2.6%) but main pulmonary artery flow was lower with the 3D cine sequence (bias -11.2%).

CONCLUSION

Compared to the conventional 2D cine approach, a comprehensive 3D cine function and flow examination was faster and yielded slightly lower left and right end-diastolic volumes, stroke volumes, and main pulmonary artery blood flow. This free-breathing 3D cine approach allows flexible post-examination data analysis and has the potential to make examinations more comfortable for patients and easier to perform for the operator.

CArtesian sampling with Variable density and Adjustable temporal resolution (CAVA)

PURPOSE

To develop a variable density Cartesian sampling method that allows retrospective adjustment of temporal resolution for dynamic MRI applications and to validate it in real-time phase contrast MRI (PC-MRI).

THEORY AND METHODS

The proposed method, called CArtesian sampling with Variable density and Adjustable temporal resolution (CAVA), begins by producing a sequence of phase encoding indices based on the golden ratio increment. Then, variable density is introduced by nonlinear stretching of the indices. Finally, the elements of the resulting sequence are rounded up to the nearest integer. The performance of CAVA is evaluated using PC-MRI data from a pulsatile flow phantom and real-time, free-breathing data from ten healthy volunteers.

RESULTS

CAVA enabled image recovery at various temporal resolutions that were selected retrospectively. For the pulsatile flow phantom, image quality and flow quantification accuracy from CAVA were comparable to that from another pseudo-random sampling pattern with fixed temporal resolution. In addition, flow quantification results based on CAVA were in good agreement with a breath-held segmented acquisition.

CONCLUSIONS

By allowing retrospective binning of the MRI data, CAVA provides an avenue to retrospectively adjust the temporal resolution of PC-MRI.

Isotropic 3D Cartesian single breath-hold CINE MRI with multi-bin patch-based low-rank reconstruction

PURPOSE

To develop a novel acquisition and reconstruction framework for isotropic 3D Cartesian cardiac CINE within a single breath-hold for left ventricle (LV) and whole-heart coverage.

METHODS

A variable-density Cartesian acquisition with spiral profile ordering, out-inward sampling, and acquisition-adaptive alternating tiny golden/golden angle increment between spiral arms is proposed to provide incoherent and nonredundant sampling within and among cardiac phases. A novel multi-bin patch-based low-rank reconstruction, named MB-PROST, is proposed to exploit redundant information on a local (within a patch), nonlocal (similar patches within a spatial neighborhood), and temporal (among all cardiac phases) scale with an implicit motion alignment among patches. The proposed multi-bin patch-based low-rank reconstruction reconstruction is compared against compressed sensing reconstruction, whereas LV function parameters derived from the proposed 3D CINE framework are compared against those estimated from conventional multislice 2D CINE imaging in 10 healthy subjects and 15 patients.

RESULTS

The proposed framework provides 3D cardiac CINE images with high spatial (1.9 mm³ ) and temporal resolution (˜50 ms) in a single breath-hold of ˜20 s for LV and ˜26 s for whole-heart coverage in healthy subjects. Shorter breath-hold durations of ˜13 to 15 s are feasible for LV coverage with slightly anisotropic resolution (1.9 × 1.9 × 2.5 mm) in patients. LV function parameters derived from 3D CINE were in good agreement with 2D CINE, with a bias of -0.1 mL/0.1 mL, -0.9 mL/-1.0 mL, -0.1%/-0.8%; and confidence intervals of ±1.7 mL/±3.7 mL, ±1.2 mL/±2.6 mL, and ±1.2%/±3.6% (10 healthy subjects/15 patients) for end-systolic volume, end-diastolic volume, and ejection fraction, respectively.

CONCLUSION

The proposed framework enables 3D isotropic cardiac CINE in a single breath-hold scan of ˜20 s/˜26 s for LV/whole-heart coverage, showing good agreement with clinical 2D CINE scans in terms of LV functional assessment.

Interpretation and Reporting of Coronary Arteries in Transposition of the Great Arteries: Cross-sectional Imaging Perspective

Knowledge of coronary artery nomenclature in transposition of the great arteries is essential, given the increasing population of adults with congenital heart disease and greater utilization of imaging in these patients. This article reviews appropriate terminology for describing coronary artery anatomy, commonly encountered coronary artery patterns, and postoperative coronary complications in the setting of transposition of the great arteries.

3D self-gated cardiac cine imaging at 3 Tesla using stack-of-stars bSSFP with tiny golden angles and compressed sensing

PURPOSE

To develop and evaluate an accelerated 3D self-gated cardiac cine imaging technique at 3 Tesla without the use of external electrocardiogram triggering or respiratory gating.

METHODS

A 3D stack-of-stars balanced steady-state free precession sequence with a tiny golden angle sampling scheme was developed to reduced eddy current effect-related artefacts at 3 Tesla. Respiratory and cardiac motion were derived from a central 5-point self-gating signal extraction approach. The data acquired around the end-expiration phases were then sorted into individual cardiac bins and used for reconstruction with compressed sensing. To evaluate the performance of the proposed method, image quality (1: the best; 4: the worst) was quantitatively compared using both the proposed method and the conventional 3D golden-angle self-gated method. Linear regression and Bland-Altman analysis were used to assess the functional measurements agreement between the proposed method and the routine 2D breath-hold multi-slice technique.

RESULTS

Compared to the conventional 3D golden-angle self-gated method, the proposed method yielded images with much less streaking artifact and higher myocardium edge sharpness (0.50 ± 0.06 vs. 0.45 ± 0.05, P = 0.004). The proposed method provided an inferior image quality score to the routine 2D technique (2.13 ± 0.35 vs. 1.38 ± 0.52, P = 0.063) but a superior one to the conventional self-gated method (2.13 ± 0.35 vs. 3.13 ± 0.64, P = 0.031). Left ventricular functional measurements between the proposed method and routine 2D technique were all well in agreement.

CONCLUSION

This study presents a novel self-gating approach to realize rapid 3D cardiac cine imaging at 3 Tesla.

Combining cholesterol-lowering strategies with imaging data: a visible benefit?

Coronary artery disease is characterised by the development of atherosclerotic plaques and is associated with significant morbidity and mortality on a global level. However, many patients with atherosclerosis are asymptomatic and the prediction of acute coronary events is challenging. The role of imaging studies in characterising plaque morphology and stability is emerging as a valuable prognostic tool, while providing evidence for the beneficial effects of cholesterol-lowering therapy on plaque burden. This review provides an overview of contemporary studies describing the value of imaging strategies for atherosclerotic plaques. Coronary angiography is commonly used in the clinical setting, but requires a significant radiation dose (similar to computed tomography). Magnetic resonance imaging evaluation of coronary vessels would avoid exposure to ionising radiation, but is not yet feasible due to motion artefacts. The roles of alternative imaging techniques, including grey-scale intravascular ultrasound, optical coherence tomography and near-infrared spectroscopy have emerged in recent years. In particular, grey-scale intravascular ultrasound has been effectively applied to detect changes in plaque burden and features of plaques predictive of rupture, as well as plaque characteristics during cholesterol-lowering therapy, providing novel insights into factors that may contribute to treatment effectiveness. Challenges and limitations to the use of imaging techniques are considered in this context, along with future imaging strategies.

Free-breathing whole-heart 3D cine magnetic resonance imaging with prospective respiratory motion compensation

PURPOSE

To develop and validate a new prospective respiratory motion compensation algorithm for free-breathing whole-heart 3D cine steady-state free precession (SSFP) imaging.

METHODS

In a 3D cine SSFP sequence, 4 excitations per cardiac cycle are re-purposed to prospectively track heart position. Specifically, their 1D image is reconstructed and routed into the scanner's standard diaphragmatic navigator processing system. If all 4 signals are in end-expiration, cine image data from the entire cardiac cycle is accepted for image reconstruction. Prospective validation was carried out in patients (N = 17) by comparing in each a conventional breath-hold 2D cine ventricular short-axis stack and a free-breathing whole-heart 3D cine data set.

RESULTS

All 3D cine SSFP acquisitions were successful and the mean scan time was 5.9 ± 2.7 min. Left and right ventricular end-diastolic, end-systolic, and stroke volumes by 3D cine SSFP were all larger than those from 2D cine SSFP. This bias was < 6% except for right ventricular end-systolic volume that was 12%. The 3D cine images had a lower ventricular blood-to-myocardium contrast ratio, contrast-to-noise ratio, mass, and subjective quality score.

CONCLUSION

The novel prospective respiratory motion compensation method for 3D cine SSFP imaging was robust and efficient and yielded slightly larger ventricular volumes and lower mass compared to breath-hold 2D cine imaging. Magn Reson Med 80:181-189, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

An Open Benchmark Challenge for Motion Correction of Myocardial Perfusion MRI

Cardiac magnetic resonance perfusion examinations enable noninvasive quantification of myocardial blood flow. However, motion between frames due to breathing must be corrected for quantitative analysis. Although several methods have been proposed, there is a lack of widely available benchmarks to compare different algorithms. We sought to compare many algorithms from several groups in an open benchmark challenge. Nine clinical studies from two different centers comprising normal and diseased myocardium at both rest and stress were made available for this study. The primary validation measure was regional myocardial blood flow based on the transfer coefficient (Ktrans), which was computed using a compartment model and the myocardial perfusion reserve (MPR) index. The ground truth was calculated using contours drawn manually on all frames by a single observer, and visually inspected by a second observer. Six groups participated and 19 different motion correction algorithms were compared. Each method used one of three different motion models: rigid, global affine, or local deformation. The similarity metric also varied with methods employing either sum-of-squared differences, mutual information, or cross correlation. There were no significant differences in Ktrans or MPR compared across different motion models or similarity metrics. Compared with the ground truth, only Ktrans for the sum-of-squared differences metric, and for local deformation motion models, had significant bias. In conclusion, the open benchmark enabled evaluation of clinical perfusion indices over a wide range of methods. In particular, there was no benefit of nonrigid registration techniques over the other methods evaluated in this study. The benchmark data and results are available from the Cardiac Atlas Project ( www.cardiacatlas.org).

Free breathing whole-heart 3D CINE MRI with self-gated Cartesian trajectory

Purpose

To present a method that uses a novel free-running self-gated acquisition to achieve isotropic resolution in whole heart 3D Cartesian cardiac CINE MRI.

Material and methods

3D cardiac CINE MRI using navigator gating results in long acquisition times. Recently, several frameworks based on self-gated non-Cartesian trajectories have been proposed to accelerate this acquisition. However, non-Cartesian reconstructions are computationally expensive due to gridding, particularly in 3D. In this work, we propose a novel highly efficient self-gated Cartesian approach for 3D cardiac CINE MRI. Acquisition is performed using CArtesian trajectory with Spiral PRofile ordering and Tiny golden angle step for eddy current reduction (so called here CASPR-Tiger). Data is acquired continuously under free breathing (retrospective ECG gating, no preparation pulses interruption) for 4–5 min and 4D whole-heart volumes (3D + cardiac phases) with isotropic spatial resolution are reconstructed from all available data using a soft gating technique combined with temporal total variation (TV) constrained iterative SENSE reconstruction.

Results

For data acquired on eight healthy subjects and three patients, the reconstructed images using the proposed method had good contrast and spatio-temporal variations, correctly recovering diastolic and systolic cardiac phases. Non-significant differences (P > 0.05) were observed in cardiac functional measurements obtained with proposed 3D approach and gold standard 2D multi-slice breath-hold acquisition.

Conclusion

The proposed approach enables isotropic 3D whole heart Cartesian cardiac CINE MRI in 4 to 5 min free breathing acquisition.

•

A novel self-gated 3D Cartesian acquisition is proposed for free breathing whole-heart cardiac MRI

•

The proposed framework has efficient k-space sampling, better eddy current performance and high computational efficiency

•

The Proposed method is able to achieve high spatio-temporal resolution 3D cardiac CINE

•

The proposed method only requires four to five minute free breathing scan

In vivo diffusion-tensor MRI of the human heart on a 3 tesla clinical scanner: An optimized second order (M2) motion compensated diffusion-preparation approach

PURPOSE

To optimize a diffusion-prepared balanced steady-state free precession cardiac MRI (CMR) technique to perform diffusion-tensor CMR (DT-CMR) in humans on a 3 Tesla clinical scanner METHODS: A previously developed second order motion compensated (M2) diffusion-preparation scheme was significantly shortened (40%) yielding sufficient signal-to-noise ratio for DT-CMR imaging. In 20 healthy volunteers and 3 heart failure (HF) patients, DT-CMR was performed comparing no motion compensation (M0), first order motion compensation (M1), and the optimized M2. Mean diffusivity (MD), fractional anisotropy (FA), helix angle (HA), and HA transmural slope (HATS) were calculated. Reproducibility and success rate (SR) were investigated.

RESULTS

M2-derived left ventricular (LV) MD, FA, and HATS (1.4 ± 0.2 μm2 /ms, 0.28 ± 0.06, -1.0 ± 0.2 °/%trans) were significantly (P < 0.001) less than M1 (1.8 ± 0.3 μm2 /ms, 0.46 ± 0.14, -0.1 ± 0.3 °/%trans) and M0 (4.8 ± 1.0 μm2 /ms, 0.70 ± 0.14, 0.1 ± 0.3 °/%trans) indicating less motion corruption and yielding values more consistent with previous literature. M2-derived DT-CMR parameters had higher reproducible (ICC > 0.85) and SR (82%) than M1 (ICC = 0.20-0.85; SR = 37%) and M0 (ICC = 0.20-0.30; SR = 11%). M2 DT-CMR was able to yield HA maps with smooth transmural transition from endocardium to epicardium.

CONCLUSION

The proposed M2 DT-CMR reproducibly yielded bulk motion robust estimations of mean LV MD, FA, HA, and HATS on a 3T clinical scanner. Magn Reson Med 76:1354-1363, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Part 2 - Coronary angiography with gadofosveset trisodium: a prospective intra-subject comparison for dose optimization for 100 % efficiency imaging

Background

Three tesla (3T) coronary magnetic resonance angiography (MRA) may be optimized using gadolinium-based contrast agents (GBCA) such as gadofosveset trisodium. The goal of this study was to evaluate if there is a qualitative or quantitative improvement in the coronary arteries with variation in contrast dose.

Methods

Twenty-eight healthy volunteers were prospectively recruited for coronary MRA at 3T using a steady state injection technique for 3D radial whole-heart image acquisition with retrospective respiratory self-gating (ClinicalTrials.gov identifier: NCT01853592). Nineteen volunteers completed both single- and double-dose imaging instances (0.03 and 0.06 mmol/kg, respectively). Intra-individual comparison of image quality was assessed by measurement of apparent signal/contrast-to-noise ratio (aSNR/aCNR) and subjective evaluation of image quality by 2 independent reviewers.

Results

The average duration of coronary MRA acquisition was 7.2 ± 1.2 min. There was significantly higher (60 %, p < 0.001) aSNR of the aorta and right/left ventricle for the double dose compared to single dose injection scheme and aSNR of the coronary arteries increased by 70 % (p < 0.001) for the double dose injection. aCNR increased by +55 % and +60 % in the ventricles and coronary arteries, respectively (p < 0.001). Overall segmental artery visualization for single dose was possible 47 % of the time, which improved to 60 % with double dose (p = 0.019), predominantly driven by improvements in more distal segment visualization (+40 % improvement in mid arterial segments, p = 0.013).

Conclusions

Gadofosveset trisodium dose of 0.06 mmol/kg significantly quantitatively and qualitatively improves the coronary artery image quality compared to 0.03 mmol/kg at 3T for moderate duration (6–8 min) steady state contrast enhanced coronary MRA.

MR imaging of the coronary vasculature: imaging the lumen, wall, and beyond

The characteristics of coronary artery disease are gradual thickening of the coronary walls and narrowing of the vascular lumen by the buildup of atherosclerosis plaques. These morphologic changes can be noninvasively detected by coronary magnetic resonance (MR) imaging/MR angiography (MRA). In addition, functional changes, such as coronary wall distensibility and flow changes, may also be evaluated with MR imaging. However, the application of current MR imaging/MRA techniques is limited in clinical practice because of several adverse technical and physiologic factors, such as cardiac and respiratory motion. Many technical innovations have been adopted to address these problems from multiple aspects.

Whole left ventricular functional assessment from two minutes free breathing multi-slice CINE acquisition

Two major challenges in cardiovascular MRI are long scan times due to slow MR acquisition and motion artefacts due to respiratory motion. Recently, a Motion Corrected-Compressed Sensing (MC-CS) technique has been proposed for free breathing 2D dynamic cardiac MRI that addresses these challenges by simultaneously accelerating MR acquisition and correcting for any arbitrary motion in a compressed sensing reconstruction. In this work, the MC-CS framework is combined with parallel imaging for further acceleration, and is termed Motion Corrected Sparse SENSE (MC-SS). Validation of the MC-SS framework is demonstrated in eight volunteers and three patients for left ventricular functional assessment and results are compared with the breath-hold acquisitions as reference. A non-significant difference (P > 0.05) was observed in the volumetric functional measurements (end diastolic volume, end systolic volume, ejection fraction) and myocardial border sharpness values obtained with the proposed and gold standard methods. The proposed method achieves whole heart multi-slice coverage in 2 min under free breathing acquisition eliminating the time needed between breath-holds for instructions and recovery. This results in two-fold speed up of the total acquisition time in comparison to the breath-hold acquisition.

Cardiovascular magnetic resonance profiling of coronary atherosclerosis: vessel wall remodelling and related myocardial blood flow alterations

AIMS

To determine the association between coronary vessel wall morphology and haemodynamic consequences to the myocardium using a combined cardiovascular magnetic resonance (CMR) imaging protocol. Non-invasive CMR profiling of coronary atherosclerotic wall changes and related myocardial blood flow impairment has not been established yet.

METHODS AND RESULTS

Sixty-three patients (45 men, 61.5 ± 10.7 years) with suspected or known coronary artery disease underwent 3.0 Tesla CMR imaging. The combined CMR protocol consisted of the following imaging modules at rest: 3D vessel wall imaging and flow measurement of the proximal right coronary artery (RCA), myocardial T2*, and first-pass perfusion imaging. During adenosine stress coronary flow, T2* and first-pass perfusion imaging were repeated. Coronary X-ray angiography classified patient groups: (i) all-smooth (n = 19); (ii) luminal irregular (diameter reduction < 30%; n = 35); and (iii) stenosed RCA (diameter reduction ≥ 50%; n = 9). The ratio of CMR-derived vessel wall area-to-lumen area significantly increased stepwise for the comparison of all-smooth vs. luminal irregular vs. stenosed RCA (1.9 ± 0.6 vs. 2.6 ± 0.6 vs. 3.6 ± 0.9, P < 0.01). Epicardial coronary flow reserve exhibited a stepwise significant decrease (3.4 ± 0.5 vs. 2.9 ± 0.7 vs. 1.7 ± 0.3, P < 0.01). On the myocardial level, stress-induced percentage gain of T2* values (ΔT2*) was significantly decreased between groups (29.2 ± 10.6 vs. 9.0 ± 9.8 vs. 2.2 ± 11.8%, P < 0.01) while perfusion reserve index decreased in the presence of stenosed RCA only (2.2 ± 0.6 vs. 2.0 ± 0.4 vs. 1.3 ± 0.3, P = ns and P < 0.01, respectively).

CONCLUSION

The proposed comprehensive CMR imaging protocol provided a non-invasive approach for direct assessment of coronary vessel wall remodelling and resultant pathophysiological consequences on the level of epicardial coronary and myocardial blood flow in patients.

Self-gated free-breathing 3D coronary CINE imaging with simultaneous water and fat visualization

The aim of this study was to develop a novel technique for acquiring 3-dimensional (3D) coronary CINE magnetic resonance images with both water and fat visualization during free breathing and without external respiratory or cardiac gating. The implemented multi-echo hybrid 3D radial balanced Steady-State Free Precession (SSFP) sequence has an efficient data acquisition and is robust against motion. The k-space center along the slice encoding direction was repeatedly acquired to derive both respiratory and cardiac self-gating signals without an increase in scan time, enabling a free-breathing acquisition. The multi-echo acquisition allowed image reconstruction with water-fat separation, providing improved visualization of the coronary artery lumen. Ten healthy subjects were imaged successfully at 1.5 T, achieving a spatial resolution of 1.0×1.0×3.0 mm³ and scan time of about 5 minutes. The proposed imaging technique provided coronary vessel depiction comparable to that obtained with conventional breath-hold imaging and navigator gated free-breathing imaging.

Cardiac gating calibration by the Septal Scout for magnetic resonance coronary angiography

BACKGROUND

Electrocardiogram (ECG) gating is commonly used to synchronize imaging windows to diastasis periods over multiple heartbeats in magnetic resonance (MR) coronary angiography. Calibration of the ECG gating parameters is typically based on a cine cardiovascular MR (CMR) video of the beating heart. Insufficient temporal resolution in the cine-CMR method, however, may produce gating errors and motion artifacts.It was previously shown that tissue Doppler echocardiography (TDE) can identify accurate diastasis window timings by observing the movement of the interventricular septum (IVS). We present a new CMR technique, the Septal Scout, for measuring IVS motion. We demonstrate that cardiac gating windows determined by the Septal Scout produce sharper coronary MR angiography images than windows determined by cine-CMR.

METHODS

9 healthy volunteers were scanned on a GE Optima 450w 1.5T MR system. Cine-CMR was acquired and used to identify the start and end times of the diastasis window (Wcine). The Septal Scout employs a one-dimensional steady-state free precession (SSFP) readout along the ventricular septum prescribed from the 4-chamber view. The Septal Scout data is processed to produce a septal velocity function, from which the diastasis window was determined (Wsep). Non-contrast-enhanced MR angiography was performed twice for each volunteer: once gated to Wcine, once to Wsep. Vessel sharpness was assessed subjectively by two experienced observers, and quantitatively by full width half maximum (FWHM) measurements of cross-sectional vessel profiles. In addition, TDE was performed on a subcohort of 6 volunteers where diastasis windows (WTDE) were determined from the IVS velocity measured in the 4-chamber view. Wsep and WTDE were compared using Pearson's correlation.

RESULTS

MRA acquisitions were successful in all volunteers. Vessel segments produced smaller FWHM measurements and were deemed sharper when imaged during the Septal Scout gating windows (p < 0.05). Subjective assessment of sharpness also improved for the Septal Scout-gated scans (p < 0.01 for both observers). Lastly, Wsep and WTDE were highly correlated (R > 0.98, p < 0.001).

CONCLUSIONS

The MR Septal Scout technique was introduced and demonstrated to be more accurate at determining cardiac gating windows than cine-CMR, yielding sharper coronary MR angiography images.

High-resolution 3D whole-heart coronary MRA: a study on the combination of data acquisition in multiple breath-holds and 1D residual respiratory motion compensation

OBJECT

To study a scan protocol for coronary magnetic resonance angiography based on multiple breath-holds featuring 1D motion compensation and to compare the resulting image quality to a navigator-gated free-breathing acquisition. Image reconstruction was performed using L1 regularized iterative SENSE.

MATERIALS AND METHODS

The effects of respiratory motion on the Cartesian sampling scheme were minimized by performing data acquisition in multiple breath-holds. During the scan, repetitive readouts through a k-space center were used to detect and correct the respiratory displacement of the heart by exploiting the self-navigation principle in image reconstruction. In vivo experiments were performed in nine healthy volunteers and the resulting image quality was compared to a navigator-gated reference in terms of vessel length and sharpness.

RESULTS

Acquisition in breath-hold is an effective method to reduce the scan time by more than 30% compared to the navigator-gated reference. Although an equivalent mean image quality with respect to the reference was achieved with the proposed method, the 1D motion compensation did not work equally well in all cases.

CONCLUSION

In general, the image quality scaled with the robustness of the motion compensation. Nevertheless, the featured setup provides a positive basis for future extension with more advanced motion compensation methods.

Respiratory Motion Compensation Using Diaphragm Tracking for Cone-Beam C-Arm CT: A Simulation and a Phantom Study

Long acquisition times lead to image artifacts in thoracic C-arm CT. Motion blur caused by respiratory motion leads to decreased image quality in many clinical applications. We introduce an image-based method to estimate and compensate respiratory motion in C-arm CT based on diaphragm motion. In order to estimate respiratory motion, we track the contour of the diaphragm in the projection image sequence. Using a motion corrected triangulation approach on the diaphragm vertex, we are able to estimate a motion signal. The estimated motion signal is used to compensate for respiratory motion in the target region, for example, heart or lungs. First, we evaluated our approach in a simulation study using XCAT. As ground truth data was available, a quantitative evaluation was performed. We observed an improvement of about 14% using the structural similarity index. In a real phantom study, using the artiCHEST phantom, we investigated the visibility of bronchial tubes in a porcine lung. Compared to an uncompensated scan, the visibility of bronchial structures is improved drastically. Preliminary results indicate that this kind of motion compensation can deliver a first step in reconstruction image quality improvement. Compared to ground truth data, image quality is still considerably reduced.

Feasibility of free-breathing late gadolinium-enhanced cardiovascular MRI for assessment of myocardial infarction: navigator-gated versus single-shot imaging

OBJECTIVES

The aim of this study was to evaluate the feasibility of two free-breathing late gadolinium-enhanced cardiovascular magnetic resonance (LGE-CMR) techniques (two-dimensional segmented navigator-gated [NAV-LGE] and single-shot [SS-LGE]) by comparing with breath-hold LGE-CMR (BH-LGE) as reference.

METHODS

A total of 200 consecutive patients underwent the three LGE-CMR imaging techniques. BH patterns were assessed with dynamic navigator MR imaging. Image quality was graded on a 5-point scale (4=optimal; 0=not assessable). In patients with sufficient BH capability (diaphragmatic movement with a deviation of <3mm), hyperenhancement was scored with a 5-point scale, and global infarct size (%left ventricle) was quantified.

RESULTS

Compared to free-breathing LGE-CMR, BH-LGE had higher image quality grade in patients with sufficient BH capability (P<0.01 [vs. NAV-LGE]; P<0.001 [vs. SS-LGE]) but poorer image quality in patients with insufficient BH capability (P<0.001 [vs. NAV-LGE]; P<0.01 [vs. SS-LGE]). NAV-LGE had higher sensitivity for infarct detection than SS-LGE (97.1% vs. 88.4%, P<0.05), but specificity was not significantly different (97.3% vs. 94.7%, P=0.37). By Bland-Altman analysis, the average differences in global infarct size were 0.4% and 1.2%, and the limits of agreement were ± 4.0% and ± 5.9% for NAV- and SS-LGE, respectively.

CONCLUSIONS

Although both NAV- and SS-LGE improve the image quality in patients with insufficient BH capability, NAV-LGE is superior to SS-LGE in infarct detection and infarct size measurement. NAV-LGE can be a possible first-line technique for patients with inability to perform sufficient BH.

Comparison of three-dimensional volume-targeted thin-slab FIESTA magnetic resonance angiography and 64-multidetector computed tomographic angiography for the identification of proximal coronary stenosis

BACKGROUND

Based on recent clinical data, an imaging strategy of identifying proximal coronary disease allows further management decisions in patients with stable angina pectoris. We aimed to compare diagnostic accuracy of non-contrast fast steady-state (FIESTA) magnetic resonance angiography (MRA) with 64-multidetector computed tomographic angiography (CTA), using conventional coronary angiography (CA) as the reference standard.

METHODS

Thirty patients with suspected coronary artery disease consented to participate in an institutional review board-approved protocol. Coronary MRA was performed at 1.5 T using a respiratory navigator and electrocardiogram-gated three-dimensional FIESTA pulse sequence. CTA images were acquired using a 64-multidetector computed tomographic scanner, using beta blockade to reduce the heart rate to less than 70 bpm. Coronary luminal stenosis >50% was identified. Plaques were classified as non-calcified, mixed, or calcified on CTA, and as high-, intermediate-, or low-signal on FIESTA MRA.

RESULTS

Compared to CA, the sensitivity, specificity, and overall accuracy for detection of >50% proximal coronary stenoses were 83.0%, 86.9%, and 86.1% for MRA and 85.1%, 87.2%, and 86.8% for CTA, respectively. For the 24 calcified stenoses, MRA corrected 16 segments that overestimated on CTA and MRA had an accuracy of 75% in evaluating calcified plaques.

CONCLUSIONS

High-resolution three-dimensional FIESTA MRA and CTA have a similar accuracy in detecting proximal coronary stenosis. The clinical impact of identification of proximal disease in patients with stable CAD needs to be examined in future studies.

Free-breathing multiphase whole-heart coronary MR angiography using image-based navigators and three-dimensional cones imaging

Noninvasive visualization of the coronary arteries in vivo is one of the most important goals in cardiovascular imaging. Compared to other paradigms for coronary MR angiography, a free-breathing three-dimensional whole-heart iso-resolution approach simplifies prescription effort, requires less patient cooperation, reduces overall exam time, and supports retrospective reformats at arbitrary planes. However, this approach requires a long continuous acquisition and must account for respiratory and cardiac motion throughout the scan. In this work, a new free-breathing coronary MR angiography technique that reduces scan time and improves robustness to motion is developed. Data acquisition is accomplished using a three-dimensional cones non-Cartesian trajectory, which can reduce the number of readouts 3-fold or more compared to conventional three-dimensional Cartesian encoding and provides greater robustness to motion/flow effects. To further enhance robustness to motion, two-dimensional navigator images are acquired to directly track respiration-induced displacement of the heart and enable retrospective compensation of all acquired data (none discarded) for image reconstruction. In addition, multiple cardiac phases are imaged to support retrospective selection of the best phase(s) for visualizing each coronary segment. Experimental results demonstrate that whole-heart coronary angiograms can be obtained rapidly and robustly with this proposed technique.

Black-blood steady-state free precession (SSFP) coronary wall MRI for cardiac allografts: a feasibility study

PURPOSE

To assess the hypothesis that steady-state free procession (SSFP) allows for imaging of the coronary wall under the conditions of fast heart rate in heart transplantation (HTx) patients.

MATERIALS AND METHODS

With the approval of our Institutional Review Board, 28 HTx patients were scanned with a 1.5T scanner. Cross-sectional black-blood images of the proximal portions of the left main artery, left anterior descending artery, and right coronary artery were acquired with both a 2D, double inversion recovery (DIR) prepared turbo (fast) spin echo (TSE) sequence and a 2D DIR SSFP sequence. Image quality (scored 0-3), vessel wall area, thickness, signal-to-noise ratio (SNR, vessel wall), and contrast-to-noise ratio (CNR, wall-lumen) were compared between TSE and SSFP.

RESULTS

The overall image quality of SSFP was higher than TSE (1.23 ± 0.95 vs. 0.88 ± 0.69, P < 0.001). SSFP had a higher coronary wall SNR (20.1 ± 8.5 vs. 14.9 ± 4.8, P < 0.001) and wall-lumen CNR (8.2 ± 4.6 vs. 6.8 ± 3.7, P = 0.005) than TSE.

CONCLUSION

Black-blood SSFP coronary wall MRI provides higher image quality, SNR, and CNR than traditional TSE does in HTx recipients. It has the potential to become an alternative means to noninvasive imaging of cardiac allografts.

Free-breathing single navigator gated cine cardiac magnetic resonance at 3 T: feasibility study in patients

BACKGROUND

Cardiac magnetic resonance imaging (CMRI) is an important tool to assess cardiac function. However, one of the limitations of CMRI is the need for frequent breath-holding (BH) steps. This may be inconvenient to some patients and limit the use of this modality in patients unable to cooperate because of cognitive reasons or physically incapable of performing the required BH steps. The purpose of this study is to overcome the intrinsic timing and computation limitations of dual-navigator cine imaging and demonstrate the feasibility of free-breathing (FB) cine cardiac left ventricular function with a single-respiratory-navigator gating at 3 T.

RESULTS

Eight participants underwent cine CMRI with both the conventional 2-dimensional cine BH and FB navigator-gated techniques. Scan parameters were identical, except in the FB technique, in which a respiratory navigator and only 2 signal averages were used. Images were scored for quality. Left ventricular end-systolic volume and end-diastolic volume were calculated. The differences in the end-systolic volume and end-diastolic volume assessed by the BH and FB were not statistically significant with P = 0.9 and 0.2, respectively. There was a good agreement between LV volumes with the limits of agreement (± 2 SD = ± 22.36 mL). Image quality score was not significantly different (P = 0.76).

CONCLUSIONS

Free-breathing cine imaging utilizing a single-respiratory-navigator gating technique is comparable to conventional BH technique in both qualitative and quantitative imaging measures. Therefore, the FB cine technique can be used as an alternative for children and patients who are unable to hold their breath.

Rapid quantification of myocardial lipid content in humans using single breath-hold 1H MRS at 3 Tesla

A rapid, proton magnetic resonance spectroscopy method to evaluate human myocardial lipid levels in a single breath-hold at 3 T using a commercial whole-body system is presented. During a 10 s breath-hold, water unsuppressed and suppressed spectra were acquired by two phased array coils using a short-echo time spectroscopic stimulated echo (STEAM) sequence electrocardiogram-triggered to mid-diastole. Lipid-to-water ratios were obtained in the septum of 15 healthy volunteers, (0.46 ± 0.19)%. These results agreed well with ratios obtained from averaged spectra acquired in seven multiple breath-holds, (0.45 ± 0.20)%, providing increased signal-to-noise ratio but requiring longer acquisition times. Excellent correlation was found between the two methods (r = 0.94, P < 0.05). Reproducibility of ¹H MRS for measuring myocardial lipid levels in a short breath-hold was acceptable in five repeated measurements within the same subject (coefficient of variation = 19%). Thus, single breath-hold proton spectroscopy allows reliable and quick quantification of myocardial lipids at 3 T. Magn Reson Med, 2011. © 2011 Wiley-Liss, Inc.

A prospective study for comparison of MR and CT imaging for detection of coronary artery stenosis

OBJECTIVES

the purpose of the present study was to directly compare the diagnostic accuracy of magnetic resonance imaging (MRI) and multislice computed tomography (CT) for the detection of coronary artery stenosis.

BACKGROUND

both imaging modalities have emerged as potential noninvasive coronary imaging modalities; however, CT-unlike MRI-exposes patients to radiation and iodinated contrast agent.

METHODS

one hundred twenty consecutive patients with suspected or known coronary artery disease prospectively underwent 32-channel 3.0-T MRI and 64-slice CT before elective X-ray angiography. The diagnostic accuracy of the 2 modalities for detecting significant coronary stenosis (≥ 50% luminal diameter stenosis) in segments ≥ 1.5 mm diameter was compared with quantitative invasive coronary angiography as the reference standard.

RESULTS

in the patient-based analysis MRI and CT angiography showed similar diagnostic accuracy of 83% (95% confidence interval [CI]: 75 to 87) versus 87% (95% CI: 80 to 92), p = 0.38; sensitivity of 87% (95% CI: 76 to 93) versus 90% (95% CI: 80 to 95), p = 0.16; and specificity of 77% (95% CI: 63 to 87) versus 83% (95% CI: 70 to 91), p = 0.06, respectively. All cases of left main or 3-vessel disease were correctly diagnosed by MRI and CT angiography. In the patient-based analysis MRI and CT angiography were similar in their ability to identify patients who subsequently underwent revascularization: the area under the receiver-operator characteristic curve was 0.78 (95% CI: 0.69 to 0.87) for MRI and 0.82 (95% CI: 0.74 to 0.90) for CT angiography.

CONCLUSIONS

thirty-two channel 3.0-T MRI and 64-slice CT angiography similarly identify significant coronary stenosis in patients with suspected or known coronary artery disease scheduled for elective coronary angiography. However, CT angiography showed a favorable trend toward higher diagnostic performance.

Coronary wall MR imaging in patients with rapid heart rates: a feasibility study of black-blood steady-state free precession (SSFP)

We assessed the hypothesis that black-blood steady-state free precession (SSFP) would provide coronary wall images comparable to images from TSE and have better performance than TSE under conditions of fast heart rate. With IRB approval, thirty participants without a history of coronary artery disease (19 men, 11 women, 26-83 y/o) were scanned with a 1.5 T MR scanner. Cross-sectional black-blood images of the proximal portions of coronary arteries were acquired with a two-dimensional (2D), double inversion recovery (DIR) prepared TSE sequence and a 2D DIR SSFP sequence on the same planes. Image quality (ranked with a 4-point system, scored from 0 to 3), vessel wall area and thickness, signal-to-noise ratio (SNR) of the wall and contrast-to-noise ratio (CNR, wall to lumen) were compared between SSFP and TSE with SPSS software (v 13.0). Totally 28 scans were completed. For SSFP and TSE, there was no difference in image quality. SSFP had a higher SNR (23.7 ± 10.1 vs. 14.4 ± 5.2, P < 0.001) and wall-lumen CNR (8.8 ± 4.5 vs. 6.7 ± 3.2, P = 0.001). Good agreements between measured wall area (r = 0.701, P < 0.001) and thickness (r = 0.560, P < 0.001) were found. For 10 participants with heart rate more than 80 beats/min, the image quality of SSFP was higher than TSE (P = 0.016). SSFP provided image quality and measurement accuracy that was comparable to TSE. With its higher performance under fast heart rate conditions, SSFP may break through the existing thresholds for heart rate and extend clinical applicability of coronary wall MR imaging to a larger population.

Detection of coronary artery anomalies in infants and young children with congenital heart disease by using MR imaging

PURPOSE

To evaluate the feasibility and accuracy of magnetic resonance (MR) coronary angiography for the detection of coronary artery anomalies in infants and children by using surgical findings as a reference.

MATERIALS AND METHODS

The data analysis was approved by the institutional review board. One hundred children with congenital heart disease underwent MR coronary angiography while under general anesthesia (mean age ± standard deviation, 3.9 years ± 3; age range, 0.2-11 years). A navigator-gated, T2-prepared, three-dimensional steady-state free precession whole-heart protocol (isotropic voxel size, 1.0-1.3 mm(3); mean imaging time, 4.6 minutes ± 1.2; mean navigator efficiency, 70%; 3-mm gating window) was used after injection of gadopentetate dimeglumine. The cardiac rest period (end systole or middiastole) and acquisition window were prospectively assessed for each patient. Coronary artery image quality (score of 0 [nondiagnostic] to 4 [excellent]), vessel sharpness, and coronary artery anomalies were assessed by two observers. Surgery was performed in 58 patients, and those findings were used to define accuracy. Variables were assessed between age groups by using either analysis of variance or Kruskal-Wallis tests.

RESULTS

Diagnostic image quality (score, ≥1 for all coronary artery segments) was obtained in 46 of the 58 patients (79%) who underwent surgery. The origin and course of the coronary artery anatomy depicted with MR imaging was confirmed at surgery in all 46 patients-including the four (9%) with substantial coronary artery anomalies. Diagnostic-quality images were obtained in 84 of the 100 patients. The rate of success improved significantly when patients were older than 4 months (88% for patients >4 months vs 17% for patients ≤4 months, P < .001).

CONCLUSION

Improved whole-heart MR coronary angiography enables accurate detection of abnormal origin and course of the coronary artery system even in very young patients with congenital heart disease.

Noninterleaved velocity encodings for improved temporal and spatial resolution in phase-contrast magnetic resonance imaging

A segmented k-space acquisition technique using noninterleaved velocity encodings is presented to reduce spatial and temporal blur in phase-contrast cardiovascular magnetic resonance imaging. A translating phantom with pulsatile flow was used to simulate imaging of coronary arteries on a 1.5-T GE Echospeed scanner, using both interleaved and noninterleaved velocity encodings. The results demonstrate that the use of noninterleaved velocity encodings reduces spatial and temporal blur by improving the temporal resolution.

Respiratory and cardiac self-gated free-breathing cardiac CINE imaging with multiecho 3D hybrid radial SSFP acquisition

A respiratory and cardiac self-gated free-breathing three-dimensional cine steady-state free precession imaging method using multiecho hybrid radial sampling is presented. Cartesian mapping of the k-space center along the slice encoding direction provides intensity-weighted position information, from which both respiratory and cardiac motions are derived. With in plan radial sampling acquired at every pulse repetition time, no extra scan time is required for sampling the k-space center. Temporal filtering based on density compensation is used for radial reconstruction to achieve high signal-to-noise ratio and contrast-to-noise ratio. High correlation between the self-gating signals and external gating signals is demonstrated. This respiratory and cardiac self-gated, free-breathing, three-dimensional, radial cardiac cine imaging technique provides image quality comparable to that acquired with the multiple breath-hold two-dimensional Cartesian steady-state free precession technique in short-axis, four-chamber, and two-chamber orientations. Functional measurements from the three-dimensional cardiac short axis cine images are found to be comparable to those obtained using the standard two-dimensional technique.

Genesis of multipeaked waves of the esophagus: repetitive contractions or motion artifact?

Multipeaked waves (MPW) in the distal esophagus occur frequently in patients with esophageal spastic motor disorders and diabetes mellitus and are thought to represent repetitive esophageal contractions. We aimed to investigate whether the relative motion between a stationary pressure sensor and contracted peristaltic esophageal segment that moves with respiration leads to the formation of MPW. We mathematically modeled the effect of relative movement between a moving pressure segment and a fixed pressure sensor on the pressure waveform morphology. We conducted retrospective analysis of 100 swallow-induced esophageal contractions in 10 patients, who demonstrated >30% MPW on high-resolution manometry (HRM) during standardized swallows. Finally, using HRM, we determined the effects of suspended breathing and hyperventilation on the waveform morphology in 10 patients prospectively. Modeling revealed that relative movement between a stationary pressure sensor and a moving contracted segment, contraction duration, contraction amplitude, respiratory frequency, and depth of respiration affects the waveform morphology. Retrospective analysis demonstrated a close temporal association with the onset of second and subsequent contractions in MPW with respiratory phase reversals. Numbers of peaks in MPW and respiratory phase reversals were closely related to the duration of contraction. In the prospective study, suspended breathing and hyperventilation resulted in a significant decrease and increase in the MPW frequency as well as the number of peaks within MPW respectively. We conclude that MPW observed during clinical motility studies are not indicative of repetitive esophageal contraction; rather they represent respiration-related movement of the contracted esophageal segment in relation to the stationary pressure sensor.

Influence of applying nitroglycerin in whole-heart free-breathing 3D coronary MR angiography

OBJECTIVE

The purpose of our study was to assess the impact of sublingual nitroglycerin (NTG) spray on free-breathing 3D whole-heart coronary MR angiography (MRA).

SUBJECTS AND METHODS

We compared the timing parameters; measured the lumen diameter of the major coronary arteries; calculated coronary vasodilation, apparent signal-to-noise ratio (SNR), and apparent contrast-to-noise ratio (CNR); and evaluated the image quality on pre- and post-NTG coronary MRA in 15 volunteers. Statistical analysis was performed with p value less than 0.05 considered significant.

RESULTS

The mean trigger delay and optimal acquisition window were shortened significantly and the mean scanning time was prolonged statistically after NTG administration. There was no significant alteration in terms of apparent SNR and apparent CNR. The lumen diameters were significantly larger in coronary MRA post-NTG than in that of pre-NTG, with an average 25.35% +/- 6.51% (SD) increase, and the left circumflex coronary artery (LCX) had slightly lower vasodilation in comparison with the right coronary artery. Image quality scores of 53 (39.3%, 53/135) segments were increased and 15 segments (11.1%, 15/135) decreased after NTG administration, and the remaining 67 segments (49.6%, 67/135) were unchanged.

CONCLUSION

In general, sublingual NTG is useful for improving visualization of the coronary artery lumen and alleviating the impact of artifact. However, several alterations and disadvantages should be taken into consideration in view of the disturbed assessment of vasodilatory response in the LCX and the impaired quality in a minority of segments after NTG administration. Further studies are needed to evaluate the effect of beta-blockade on eliminating the disadvantages of sublingual NTG.

Screening for proximal coronary artery anomalies with 3-dimensional MR coronary angiography

Under 35 years of age, 14% of sudden cardiac death in athletes is caused by a coronary artery anomaly (CAA). Free-breathing 3-dimensional magnetic resonance coronary angiography (3D-MRCA) has the potential to screen for CAA in athletes and non-athletes as an addition to a clinical cardiac MRI protocol. A 360 healthy men and women (207 athletes and 153 non-athletes) aged 18–60 years (mean age 31 ± 11 years, 37% women) underwent standard cardiac MRI with an additional 3D-MRCA within a maximum of 10 min scan time. The 3D-MRCA was screened for CAA. A 335 (93%) subjects had a technically satisfactory 3D-MRCA of which 4 (1%) showed a malignant variant of the right coronary artery (RCA) origin running between the aorta and the pulmonary trunk. Additional findings included three subjects with ventral rotation of the RCA with kinking and possible proximal stenosis, one person with additional stenosis and six persons with proximal myocardial bridging of the left anterior descending coronary artery. Coronary CT-angiography (CTA) was offered to persons with CAA (the CAA was confirmed in three, while one person declined CTA) and stenosis (the ventral rotation of the RCA was confirmed in two but without stenosis, while two people declined CTA). Overall 3D MRCA quality was better in athletes due to lower heart rates resulting in longer end-diastolic resting periods. This also enabled faster scan sequences. A 3D-MRCA can be used as part of the standard cardiac MRI protocol to screen young competitive athletes and non-athletes for anomalous proximal coronary arteries.