Steven M. Shea

3D magnetization-prepared true-FISP: A new technique for imaging coronary arteries

The purpose of this work was to develop an ECG‐triggered, segmented 3D true‐FISP (fast imaging with steady‐state precession) technique to improve the signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) of breath‐hold coronary artery imaging. The major task was to optimize an appropriate magnetization preparation scheme to permit saturation of the epicardial fat signal. An α/2 preparation pulse was used to speed up the approach to steady‐state following a frequency‐selective fat‐saturation pulse in each heartbeat. The application of dummy cycles was found to reduce the oscillation of the magnetization during data acquisition. The fat saturation and magnetization preparation scheme was validated with simulations and phantom studies. Volunteer studies demonstrated substantially increased SNR (55%) and CNR (178%) for coronary arteries compared to FLASH (fast low‐angle shot) with the same imaging time. In conclusion, true‐FISP is a promising technique for coronary artery imaging. Magn Reson Med 46:494–502, 2001.

Three‐dimensional true‐FISP imaging of the coronary arteries: Improved contrast with T2‐preparation

To evaluate the effectiveness of a T2‐magnetization preparation scheme for improving coronary artery imaging with true fast imaging with steady‐state precession (True‐FISP).

Reduction of transient signal oscillations in true-FISP using a linear flip angle series magnetization preparation

An electrocardiogram (ECG)‐triggered, magnetization‐prepared, segmented, 3D true fast imaging with steady‐state precession (true‐FISP) sequence with fat saturation was recently proposed for coronary artery imaging. A magnetization preparation scheme consisting of an α/2 radiofrequency (RF) pulse followed by 20 constant flip angle dummy RF cycles was used to reduce signal oscillations in the approach to steady state. However, if large resonance offsets on the order of 70–100 Hz are present, significant magnetization oscillations will still occur during data acquisition, which will result in image ghosting and blurring. The goal of this work was to validate that a linear flip angle (LFA) series can be used during magnetization preparation to reduce these image artifacts. Computer simulations, phantom studies, and coronary artery imaging in healthy volunteers were performed to compare this magnetization preparation scheme with that of an α/2 pulse followed by constant flip angle dummy RF cycles. The results demonstrated substantial reduction in the apparent image artifacts when using linearly increasing flip angles during magnetization preparation. Magn Reson Med 49:151–157, 2003.

Artifact reduction in true‐FISP imaging of the coronary arteries by adjusting imaging frequency

The presence of resonance frequency offsets often causes artifacts in images acquired with true fast imaging with steady‐state precession (true‐FISP). One source of resonance offsets is a suboptimal setting of the synthesizer frequency. The goal of this work was to demonstrate that shifting the synthesizer frequency could minimize the off‐resonance related image artifacts in true‐FISP. A simple scouting method was developed to estimate the optimal synthesizer frequency for the volume of interest (VOI). To improve fat suppression, a similar scouting method was also developed to determine the optimal frequency offset for the fat saturation pulse. Coronary artery imaging was performed in healthy subjects using a 3D true‐FISP sequence to validate the effectiveness of the frequency corrections. Substantial reduction in image artifacts and improvement in fat suppression were observed by using the water and fat frequencies estimated by the scouting scans. Frequency shifting is a useful and practical method for improving coronary artery imaging using true‐FISP. Magn Reson Med 49:803–809, 2003.

Myocardial perfusion imaging based on the blood oxygen level-dependent effect using T2-prepared steady-state free-precession magnetic resonance imaging

Background—The decision to perform coronary revascularization procedures may hinge on assessment of myocardial perfusion reserve. Blood oxygen level–dependent (BOLD) MRI is a potential method to detect the effects of regional variations in myocardial blood flow during vasodilation. Methods and Results—We imaged dogs (n=13) on a 1.5-T whole-body MRI scanner using a new T2-prepared steady-state free-precession (SSFP) MRI pulse sequence sensitive to BOLD contrast. Images (in-plane resolution ≈1 mm2) of 5 short-axis and 2 long-axis slices of the heart were acquired during graded levels of adenosine infusion via a surgically placed left circumflex (LCx) catheter (n=11) or via a right atrial catheter in animals with an LCx occluder (n=2). Relative myocardial perfusion was measured with the use of fluorescent microspheres. Signal intensity changes in myocardium subtended by the left anterior descending coronary artery were compared with those in the LCx region. Unprocessed T2-weighted images revealed changes in signal intensity corresponding to areas of regional vasodilation or reduced myocardial perfusion reserve during systemic vasodilation. At maximal vasodilation, the signal intensity ratio in the LCx versus left anterior descending territories increased by 33±4% compared with baseline, corresponding to a 3.8±0.3-fold increase in relative perfusion (P<0.01). MR intensity at progressive levels of vasodilation demonstrated good agreement with microsphere flow (R=0.80, P<0.01). Conclusions—T2-prepared SSFP BOLD imaging is a promising method to determine an index of myocardial perfusion reserve in this animal model.

MRI detects increased coronary wall thickness in asymptomatic individuals: The multi-ethnic study of atherosclerosis (MESA)

To evaluate the use of coronary wall MRI as a measure of atherosclerotic disease burden in an asymptomatic population free of clinical cardiovascular disease. Coronary wall magnetic resonance imaging (MRI) is a noninvasive method for evaluation of arterial wall remodeling associated with atherosclerosis.

Breath‐hold three‐dimensional true‐FISP imaging of coronary arteries using asymmetric sampling

To evaluate the feasibility of using asymmetric sampling in a three‐dimensional, magnetization‐prepared, segmented true‐FISP (fast imaging with steady‐state precession) sequence in order to reduce the sensitivity to resonance offsets, while simultaneously improving imaging speed.

Coronary artery imaging: 3D segmented k‐space data acquisition with multiple breath‐holds and real‐time slab following

The purpose of this work was to develop a multiple‐breath‐hold (BH) imaging method for coronary arteries in which a segment of k‐space is acquired in each BH. The goal was to increase the resolution, or the signal‐to‐noise ratio (SNR) and coverage, of three‐dimensional‐(3D)‐BH volume‐targeted scanning (VCATS). To correct for slab position differences, a real‐time slab following technique using navigator echoes for motion detection was used. Sixteen normal volunteers were imaged to compare the method with a single‐BH scan. Results showed that higher resolution, or larger coverage and higher SNR, were achieved by the multiple‐BH method without respiratory motion artifacts. In conclusion, 3D segmented k‐space data acquisition with multiple‐BHs and real‐time slab following is a promising approach for extending the capabilities of VCATS further. J. Magn. Reson. Imaging 2001;13:301–307.

Three-dimensional breathhold magnetization-prepared TrueFISP: A pilot study for magnetic resonance imaging of the coronary artery disease

Purpose:X-ray angiography is currently the standard test for the assessment of coronary artery disease. A substantial minority of patients referred for coronary angiography have no significant coronary artery disease. The purpose of this work was the evaluation of the accuracy of a three-dimensional (3D) breathhold coronary magnetic resonance angiography (MRA) technique in detecting hemodynamically significant coronary artery stenoses in a patient population with x-ray angiographic correlation. Materials and Methods:Sequential subjects (n = 33, M/F = 22/11, average age = 57) who were referred for conventional coronary angiography were enrolled in the study. The study protocol was approved by our institutional review board. Each subject gave written informed consent. Volume-targeted 3D breathhold coronary artery scans with ECG-triggered, segmented True Fast Imaging with Steady-state Precession (TrueFISP) were acquired for the left main (LM), left anterior descending (LAD), and right coronary arteries (RCAs). Coronary MRA was evaluated with conventional angiography as the gold standard. Results:The overall sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) for diagnosing any hemodynamically significant coronary artery disease (≥50% diameter reduction) with coronary MRA was 87%, 57%, 72%, 68%, and 80%, respectively. The sensitivity of the technique in the LM, LAD, and RCA was 100%, 83%, and 100%, respectively. The NPV of the technique in the LM, LAD, and RCA was 100%, 82%, and 100%, respectively. Conclusions:Three-dimensional breathhold True Fast Imaging with Steady-state Precession is a promising technique for coronary artery imaging. It has a relatively high sensitivity and NPV. Results of this study warrant further technical improvements and clinical evaluation of the technique.

Coronary Artery Imaging Using Contrast-Enhanced 3D Segmented EPI

The purpose of the work was to evaluate the effectiveness of extracellular contrast media in improving MR coronary angiography using breath‐hold segmented echo‐planar imaging (SEPI). Two protocols were designed to optimize the inversion recovery‐prepared contrast‐enhanced SEPI method. In 15 healthy volunteers, significant improvements in signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), vessel sharpness, and length of visualization were observed post‐contrast. The method with two targeted scans to cover the left and right arteries, respectively, following separate 20‐mL contrast injections, was found to yield thinner slices and longer right coronary artery (RCA) visualization than a single scan following a 40‐mL contrast injection without compromising SNR and CNR. In conclusion, extracellular contrast media substantially improves the delineation of coronary arteries with SEPI. J. Magn. Reson. Imaging 2001;13:676–681.