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

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.

Three-dimensional coronary dark-blood interleaved with gray-blood (cDIG) magnetic resonance imaging at 3 tesla

PURPOSE

Three-dimensional (3D) dark-blood MRI has shown great potential in coronary artery plaque evaluation. However, substantial variability in quantification could result from superficial calcification because of its low signal. To address this issue, a 3D coronary dark-blood interleaved with gray-blood (cDIG) technique was developed.

METHODS

cDIG is based on a balanced steady-state free precession readout combined with a local re-inversion-based double-inversion-recovery (LocReInv-DIR) preparation. The LocReInv-DIR is applied every two RR intervals. Dark-blood and gray-blood contrasts are collected in the first and second RR interval, respectively. To improve the respiratory gating efficiency, two independent navigators were developed to separately gate the respiratory motion for the two interleaved acquisitions. In vivo experiments in eight healthy subjects and one patient were conducted to validate the technique.

RESULTS

cDIG provided dual-contrasts without compromise in scan time. The dark-blood images with cDIG demonstrated excellent wall and lumen signal performances and morphological measurements. Advantageously, cDIG yielded a second contrast that was shown to help identify the superficial calcification in the coronary plaque of a patient.

CONCLUSION

A novel technique was developed for obtaining 3D coronary vessel wall and gray lumen images. The additional contrast may aid in identifying calcified nodules and thus potentially improve the evaluation of coronary plaque burden.

The role of latency period in quality management for free-breathing coronary wall MRI

The aim of the present study was to determine the effects of the latency period on the performance of free-breathing coronary wall MRI. With the approval of IRB, 70 participants were recruited for coronary wall magnetic resonance imaging (MRI) and provided written informed consent. In 35 subjects, right coronary segments (RCA1-3) were imaged first; in the remaining subjects, the left coronary segments (LM and LAD1-3) were imaged first. The images were classified into groups; group 1 contained right coronary images from the subjects whose right coronary segments were imaged first and left coronary images from the subjects whose left coronary segments were imaged first. Group 2 contained the other coronary segments. The image scores (ranked1-3), latency periods, drift of the position of the navigator (NAV), scan efficiency were compared between image groups. Image group 1 has higher scores (1.66 ± 0.55 vs. 1.46 ± 0.51), shorter latency periods (32.04 ± 4.24 vs. 44.22 ± 5.57 min), lower drift in the location of the NAV (1.90 ± 1.27 mm vs. 2.61 ± 1.71 mm) and higher scan efficiency (32.7 ± 7.6 vs. 29.9 ± 7.9%) than group 2. Long latency periods have a significantly negative impact on the image quality of coronary wall MRI.

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.

The detection of coronary stiffness in cardiac allografts using MR imaging

OBJECTIVE

To test the hypothesis that biomechanical changes are quantitatively related to morphological features of coronary arteries in heart transplant (HTx) recipients.

MATERIALS AND METHODS

With IRB approval, three-dimensional (3D) magnetic resonance (MR) angiography and two-dimensional (2D) black-blood stead-state free precession (SSFP) MR imaging were performed to image coronary arteries of 36 HTx patients. Contours of coronary wall were manually drawn. For each coronary segment, coronary wall thickness, wall area, lumen area (in systole and diastole) were acquired. Coronary distensibility index (CDI) and the percent of the coronary wall occupying the vessel area (PWOV) were calculated.

RESULTS

There are totally 98 coronary segments eligible for quantitative analysis from 27 HTx patients. The CDI is 4.90 ± 2.44 mmHg(-1). The mean wall thickness is 1.49 ± 0.24 mm and the PWOV is 74.6% ± 7.5%. CDI has moderate correlations with wall thickness (r=-0.531, P<0.001) and with PWOV (R=-0.435, P<0.001).

CONCLUSIONS

Detected with coronary MR imaging, CDI is quantitatively correlated with the morphological features of the coronary artery in HTx patients. Coronary stiffness has the potential to become an alternative imaging biomarker for the quantitative assessment of the status of cardiac allografts.

The compensation for asynchronous cardiac quiescence in coronary wall MR imaging

The aim of the present study was to assess the incremental benefit of compensating asynchronous cardiac quiescence in coronary wall MR imaging. With the approval of IRB, black-blood coronary wall MR imaging was performed on 30 older subjects (90 coronary wall segments). For round 1 coronary wall MR imaging, acquisition windows were traditionally set within rest period(4-chamber). Totally 51 of 90 images were ranked as "good" images and resulted in an interpretability rate of 57%. Then, an additional cine-MR was centered at coronary segments to obtain rest period(cross-sectional). The rest period(overlap) (the intersection between rest period(4-chamber) and rest period(cross-sectional)) was measured for each coronary segment. The "good" images had a longer rest period(overlap) and higher acquisition coincidence rate (the percentage of acquisition window covered by the rest period(overlap)) than "poor" images. Coronary wall rescans (round 2) were completed at 39 coronary segments that were judged as having "poor" images in round 1 scans. The acquisition window was set within the rest period(overlap). For the round 2 images, 17 of 39 (44%) coronary segments were ranked as "good" images. The overall interpretability rate (68 of 90, 76%) was significantly higher than that of the round 1 images alone. Our data demonstrated that asynchronous cardiac quiescence adversely affects the performance of coronary wall MR imaging. Individualizing acquisition windows based on multi-plane cine-MR helps to compensate for this motion discrepancy and to improve image quality.

Effects of respiratory motion on coronary wall MR imaging: a quantitative study of older adults

The aim of the present study is to assess the effects of respiratory motion on the image quality of two-dimensional (2D), free-breathing, black-blood coronary wall magnetic resonance (MR) imaging. This study was compliance with the HIPPA. With the approval of the institution review board, 230 asymptomatic participants, including 164 male patients (72.9 ± 4.4 years) and 66 female patients (72.4 ± 5.1 years), were recruited. Written informed consent was obtained. A 2D navigator (NAV)-gated, black-blood coronary wall MR imaging sequence was run on the left main artery, the left anterior descending artery and the right coronary artery. The drift of the location of the NAV and scan efficiency were compared between good (scored 2 or 3) and poor images (scored 1). Age, body weight, body weight index, heart rate, length of the rest period of cardiac motion, diaphragm excursion and breathing frequency were compared using a t test between the "successful" (having 2 or 3 good images) and "unsuccessful" cases (having 1 or 0 good images). A logistic regression model was applied to identify the contributors to good image quality. The drift of the NAV location and the scan efficiency were higher in the 411 good images compared with the 279 poor images. Minimal drift of the NAV location and low body weight were identified as independent predictors of good images after using a logistic regression model to adjust for multiple physiological and technical factors. The stability of respiratory motion significantly influences the image quality of 2D, free-breathing, black-blood coronary wall MR imaging.

Potential quantitative magnetic resonance imaging biomarkers of coronary remodeling in older hypertensive patients

OBJECTIVE

To detect differences in potential magnetic resonance imaging biomarkers of coronary remodeling between older hypertensive patients and healthy controls.

METHODS AND RESULTS

Two-dimensional black-blood coronary wall magnetic resonance imaging and 3-dimensional whole-heart coronary magnetic resonance angiography were performed on 130 participants (65-84 years), including 65 hypertensive patients and 65 healthy controls. Coronary segments derived from hypertensive participants had a higher mean coronary wall thickness, a smaller vessel area, a smaller coronary wall area, a smaller lumen area, a lower coronary distensibility index, and a higher percent of the coronary wall occupying the vessel area (PWOV) than those from healthy controls. When the average PWOV was set as an ad hoc cutoff point, coronary segments with a high PWOV had a significantly higher mean wall thickness, a higher maximum wall thickness, a smaller vessel area, a smaller lumen area, a lower coronary distensibility index, and a higher coronary plaque index compared with coronary segments with a low PWOV.

CONCLUSIONS

Magnetic resonance techniques are able to noninvasively detect significant differences in potential imaging biomarkers of coronary remodeling between older hypertensive patients and healthy controls. The PWOV is a promising remodeling feature for quantitatively evaluating the progression of coronary atherosclerosis.

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.