MRI of the coronary vessel wall at 3 T: comparison of radial and cartesian k-space sampling

Free-breathing contrast-enhanced multiphase MRI of the liver in patients with a high risk of breath-holding failure: comparison of compressed sensing-accelerated radial and Cartesian acquisition techniques

BACKGROUND

Knowing the advantages and disadvantages of each magnetic resonance (MR) technique, would allow us to choose a sequence better suited in patients with a high risk of breath-holding failure.

PURPOSE

To compare the image quality of free-breathing contrast-enhanced multiphase MR imaging (MRI) using incoherent Cartesian k-space sampling combined with a motion-resolved compressed sensing reconstruction (XD-VIBE) and Golden-Angle Radial Sparse Parallel MRI (GRASP).

MATERIAL AND METHODS

A total of 67 patients were included. Overall image quality, motion artifacts, and liver edge sharpness on arterial and portal-venous phase were evaluated by two radiologists. We evaluated the signal intensity ratio between liver in the late arterial phase to aorta at peak enhancement and the detection rate of hypervascular lesions.

RESULTS

Overall image quality, artifact, and liver edge sharpness scores of XD-VIBE and GRASP were not significantly different (P = 0.070-0.397). Four (reviewer 1, 12.1%) and seven patients (reviewer 2, 21.2%) received non-diagnostic quality in the XD-VIBE group whereas one patient (reviewer 2, 2.9%) received non-diagnostic quality in the GRASP group. The ratio between the aorta and liver signal for GRASP was significantly higher than that of XD-VIBE (0.32 ± 0.10 vs. 0.47 ± 0.13; P < 0.001). The hypervascular lesion detection rate of XD-VIBE (86.7%) was higher than that of GRASP (57.1%) in the arterial phase without a statistically significant difference (P = 0.081).

CONCLUSION

Overall image quality of XD-VIBE and GRASP were not significantly different. More XD-VIBE examinations were rated non-diagnostic. On the other hand, the relative liver parenchymal enhancement to the aorta in the late arterial phase of GRASP was higher than that of XD-VIBE, which potentially leads to lower detectability of hypervascular lesions on arterial phase images.

Whole-heart coronary MR angiography using a 3D cones phyllotaxis trajectory

PURPOSE

To develop a 3D cones steady-state free precession sequence with improved robustness to respiratory motion while mitigating eddy current artifacts for free-breathing whole-heart coronary magnetic resonance angiography.

METHOD

The proposed sequence collects cone interleaves using a phyllotaxis pattern, which allows for more distributed k-space sampling for each heartbeat compared to a typical sequential collection pattern. A Fibonacci number of segments is chosen to minimize eddy current effects with the trade-off of an increased number of acquisition heartbeats. For verification, phyllotaxis-cones is compared to sequential-cones through simulations, phantom studies, and in vivo coronary scans with 8 subjects using 2D image-based navigators for retrospective motion correction.

RESULTS

Simulated point spread functions and moving phantom results show less coherent motion artifacts for phyllotaxis-cones compared to sequential-cones. Assessment of the right and left coronary arteries using reader scores and the image edge profile acutance vessel sharpness metric indicate superior image quality and sharpness for phyllotaxis-cones.

CONCLUSION

Phyllotaxis 3D cones results in improved qualitative image scores and coronary vessel sharpness for free-breathing whole-heart coronary magnetic resonance angiography compared to standard sequential ordering when using a steady-state free precession sequence.

Coronary artery plaque imaging: Comparison of black‐blood MRI and 64‐multidetector computed tomography

Objective

To comparatively evaluate black-blood coronary arterial wall MRI and 64-multidetector computed tomography (64-MDCT) for detection and classification of coronary artery plaques.

Methods

We included 15 patients with confirmed coronary artery plaques in the proximal or middle segments of coronary arteries by 64-MDCT, who underwent black-blood coronary wall MRI at 1.5 T within 10 days. Cross-sectional coronary wall images were acquired using a 2D double-inversion-recovery, electrocardiograph-triggered, navigator-gated, fat-suppressed, turbo-spin-echo sequence on the coronary arteries with lesions from the ostium to the middle segment continuously without gap. The vessel cross-sectional area (CSA), luminal CSA, maximal wall thickness, plaque burden, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) were measured in each slice and subsequently compared with computed tomography angiography (CTA) images. CTA images were divided into 5-mm segments for side-by-side comparison with MRI.

Results

Of the 15 patients, 12 were enrolled in the study. Coronary plaques were found in 46 slices on both CTA and MRI. Plaques were classified to 3 groups based on CTA: calcified plaques (n = 11), soft plaques (n = 23), and mixed plaques (n = 12). In MRI, the plaque burden, maximal wall thickness, SNR, and CNR in the coronary walls containing plaques were greater than in the normal coronary walls (0.83 ± 0.08 vs. 0.73 ± 0.08, 1.88 ± 0.51 vs. 1.51 ± 0.26 mm, 12.95 ± 2.78 vs. 9.93 ± 2.31, and 6.76 ± 2.52 vs. 3.89 ± 1.54, respectively; P < 0.05). The luminal CSA at the plaque was smaller than in normal coronary walls (2.50 ± 1.50 vs. 4.72 ± 2.28 mm²; P < 0.05). The SNR in the soft plaque was significantly greater than in calcified and mixed plaques (P < 0.05).

Conclusions

Coronary wall MRI can identify coronary plaques in the proximal and middle segments and has the potential to differentiate plaque types based on signal intensity.

Golden angle dual-inversion recovery acquisition coupled with a flexible time-resolved sparse reconstruction facilitates sequence timing in high-resolution coronary vessel wall MRI at 3 T

PURPOSE

The need for performing dual-inversion recovery (DIR) coronary vessel wall MRI in correspondence to minimal cardiac motion and optimal blood signal nulling is a major challenge. We propose to address this hurdle by combining DIR with a prolonged acquisition window in conjunction with a golden angle radial trajectory and k-t sparse sensitivity encoding (SENSE) reconstruction to enable a flexible a-posteriori selection of optimized imaging parameters.

METHODS

Coronary vessel wall data acquisition was performed with DIR golden angle radial imaging in n=15 healthy subjects. Images reconstructed using k-t sparse SENSE and different reconstruction window settings were quantitatively (vessel wall conspicuity, thickness, acquisition, and reconstruction window settings) compared with those obtained with more conventional radial DIR imaging.

RESULTS

A flexible retrospective selection of the reconstruction window width and position improved vessel wall conspicuity with respect to baseline acquisitions (P < 0.01). Vessel wall thickness remained unchanged (P = nonsignificant (NS)). Temporal window widths were similar for both approaches (P = NS), yet their position within the cardiac cycle differed significantly (P < 0.02).

CONCLUSIONS

A flexible DIR coronary vessel wall MRI technique that alleviates constraints associated with sophisticated sequence timing was proposed. When compared with a more conventional approach, the technique significantly improved image quality. Magn Reson Med 77:961-969, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Breath-hold imaging of the coronary arteries using Quiescent-Interval Slice-Selective (QISS) magnetic resonance angiography: pilot study at 1.5 Tesla and 3 Tesla

BACKGROUND

Coronary magnetic resonance angiography (MRA) is usually obtained with a free-breathing navigator-gated 3D acquisition. Our aim was to develop an alternative breath-hold approach that would allow the coronary arteries to be evaluated in a much shorter time and without risk of degradation by respiratory motion artifacts. For this purpose, we implemented a breath-hold, non-contrast-enhanced, quiescent-interval slice-selective (QISS) 2D technique. Sequence performance was compared at 1.5 and 3 Tesla using both radial and Cartesian k-space trajectories.

METHODS

The left coronary circulation was imaged in six healthy subjects and two patients with coronary artery disease. Breath-hold QISS was compared with T2-prepared 2D balanced steady-state free-precession (bSSFP) and free-breathing, navigator-gated 3D bSSFP.

RESULTS

Approximately 10 2.1-mm thick slices were acquired in a single ~20-s breath-hold using two-shot QISS. QISS contrast-to-noise ratio (CNR) was 1.5-fold higher at 3 Tesla than at 1.5 Tesla. Cartesian QISS provided the best coronary-to-myocardium CNR, whereas radial QISS provided the sharpest coronary images. QISS image quality exceeded that of free-breathing 3D coronary MRA with few artifacts at either field strength. Compared with T2-prepared 2D bSSFP, multi-slice capability was not restricted by the specific absorption rate at 3 Tesla and pericardial fluid signal was better suppressed. In addition to depicting the coronary arteries, QISS could image intra-cardiac structures, pericardium, and the aortic root in arbitrary slice orientations.

CONCLUSIONS

Breath-hold QISS is a simple, versatile, and time-efficient method for coronary MRA that provides excellent image quality at both 1.5 and 3 Tesla. Image quality exceeded that of free-breathing, navigator-gated 3D MRA in a much shorter scan time. QISS also allowed rapid multi-slice bright-blood, diastolic phase imaging of the heart, which may have complementary value to multi-phase cine imaging. We conclude that, with further clinical validation, QISS might provide an efficient alternative to commonly used free-breathing coronary MRA techniques.

Coronary artery wall imaging

Like X-Ray contrast angiography, MR coronary angiograms show the vessel lumens rather than the vessels themselves. Consequently, outward remodeling of the vessel wall, which occurs in subclinical coronary disease before luminal narrowing, cannot be seen. The current gold standard for assessing the coronary vessel wall is intravascular ultrasound, and more recently, optical coherence tomography, both of which are invasive and use ionizing radiation. A noninvasive, low-risk technique for assessing the vessel wall would be beneficial to cardiologists interested in the early detection of preclinical disease and for the safe monitoring of the progression or regression of disease in longitudinal studies. In this review article, the current state of the art in MR coronary vessel wall imaging is discussed, together with validation studies and recent developments.

Contrast-enhanced cardiovascular magnetic resonance imaging of coronary vessel wall: state of art

Coronary wall imaging by cardiovascular magnetic resonance (CMR) emerges as a promising method to detect vascular injury and remodeling directly within the coronary vascular wall. In this review, the current evidence on coronary wall enhancement using CMR is presented and summarized, with particular focus on its ability to detect inflammation in atherosclerosis, Takayasu's arteritis, acute coronary syndromes and immune-mediated inflammatory vasculitides. The authors review the possible mechanisms of coronary wall contrast enhancement on CMR and discuss the technical considerations and limitations. Lastly, the potential clinical applications and possibilities for future research are proposed.

Accuracy of MRI to identify the coronary artery plaque: a comparative study with intravascular ultrasound

PURPOSE

To evaluate the ability of black-blood coronary arterial wall MRI to identify the coronary artery plaque, using intravascular ultrasound (IVUS) as the golden standard.

MATERIALS AND METHODS

Nineteen consecutive patients underwent IVUS and coronary artery wall MRI. Cross-sectional images were acquired on the lesion of coronary artery from the ostium to the middle segment continuously. The vessel cross-sectional area (CSA), luminal CSA, plaque burden, contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were measured in each slice which was then compared with the IVUS images.

RESULTS

Sixteen of 19 patients completed coronary artery MRA and wall imaging. 41 of 67 slices were found plaques on both IVUS and MRI; The maximal wall thickness, plaque burden, SNR, CNR in the coronary wall containing plaque were greater compared with the normal coronary wall (1.70 ± 0.51 versus 1.24 ± 0.24; 0.71 ± 0.13 versus 0.59 ± 0.12; 1.86 ± 0.41 versus 1.47 ± 0.23; 5.10 ± 2.21 versus 2.99 ± 1.17; respectively, P < 0.05). The matched MRI and IVUS showed good correlation for vessel CSA (16.77 ± 10.67 versus 16.97 ± 8.36; r = 0.79; P < 0.01), luminal CSA (5.18 ± 5.01 versus 7.13 ± 5.14; r = 0.88; P < 0.01), plaque burden (0.71 ± 0.13 versus 0.59 ± 0.15; r = 0.67; P < 0.01). in segments containing plaques, especially the luminal CSA were strongly correlated.

CONCLUSION

MRI coronary artery wall imaging can identify coronary plaque in the proximal segments. It also has the potential to assess coronary artery size.

Current techniques for MR imaging of atherosclerosis

Vessel wall imaging of large vessels has the potential to identify culprit atherosclerotic plaques that lead to cardiovascular events. Comprehensive assessment of atherosclerotic plaque size, composition, and biological activity is possible with magnetic resonance imaging (MRI). Magnetic resonance imaging of the atherosclerotic plaque has demonstrated high accuracy and measurement reproducibility for plaque size. The accuracy of in vivo multicontrast MRI for identification of plaque composition has been validated against histological findings. Magnetic resonance imaging markers of plaque biological activity such as neovasculature and inflammation have been demonstrated. In contrast to other plaque imaging modalities, MRI can be used to study multiple vascular beds noninvasively over time. In this review, we compare the status of in vivo plaque imaging by MRI to competing imaging modalities. Recent MR technological improvements allow fast, accurate, and reproducible plaque imaging. An overview of current MRI techniques required for carotid plaque imaging including hardware, specialized pulse sequences, and processing algorithms are presented. In addition, the application of these techniques to coronary, aortic, and peripheral vascular beds is reviewed.

Coronary MR imaging: lumen and wall

Coronary MR imaging is a promising noninvasive technique for the combined assessment of coronary artery anatomy and function. Anomalous coronary arteries and aneurysms can reliably be assessed in clinical practice using coronary MR imaging and the presence of significant left main or proximal multivessel coronary artery disease detected. Technical challenges that need to be addressed are further improvements in motion suppression and abbreviated scanning times aimed at improving spatial resolution and patient comfort. The development of new and specific contrast agents, high-field MR imaging with improved spatial resolution, and continued progress in MR imaging methods development will undoubtedly lead to further progress toward the noninvasive and comprehensive assessment of coronary atherosclerotic disease.

Cardiac magnetic resonance imaging at 3.0 T

Cardiovascular magnetic resonance imaging (MRI) has gained widespread acceptance for the assessment of cardiovascular disease. Cardiac MRI requires fast data acquisition schemes because of constraints imposed by physiological motion of cardiac structures and blood flow, which dictate the suitable window of data acquisition. The ongoing improvement of MRI hardware and the development of tailored imaging techniques have been the cornerstones for rapid progress in cardiac MRI. Cardiac MRI at 3.0 T holds the promise to overcome some of the signal-to-noise (SNR) limitations, especially for techniques with borderline SNR at 1.5 T (eg, myocardial perfusion, assessment of viability, or imaging of coronary arteries). The improved SNR at 3.0 T can be used to increase the spatial resolution and/or reduce imaging time. It was shown that all applications of cardiac imaging at 1.5 T seem feasible also at 3.0 T and predominantly provide similar or improved image quality. Although specific absorption rate limitations and susceptibility effects remain a primary concern, the combination of high-field strength examinations with parallel imaging has increased the performance of techniques such as steady-state free-precession at 3.0 T. Therefore, the signal-to-noise and the contrast-to-noise ratios advantages at 3.0 T and the resulting potential benefit for an improved diagnostic value will constantly fuel further developments in this area and pave the way for novel, promising imaging techniques.

High-field-strength magnetic resonance: potential and limits

OBJECTIVE

To expatiate on the possible advantages and disadvantages of high magnetic field strengths for magnetic resonance imaging and, in particular, for magnetic resonance angiography.

METHODS AND RESULTS

A review of the available literature is given, presenting many of the advantages and disadvantages of imaging at higher field strengths. Focus is put on imaging at 3 to 7 T. Early results at 7 T are presented; these results indicate that several of the angiographic techniques commonly used at lower field strengths show promise for improvement by taking advantage of the higher signal and susceptibility sensitivity at 7 T.

CONCLUSIONS

The drive toward higher field strengths, both for the purpose of fundamental research and for clinical diagnostic imaging, is likely to continue. New applications using the unique properties of high field strength will almost certainly emerge as researchers gain more experience. The ultimate limiting factor is likely to be the physiological effects at high field strengths. However, this limit seems to lie at field strengths higher than 7 T because early experience shows good tolerance of 7 T examinations.