Catheter‐directed contrast‐enhanced coronary MR angiography in swine using magnetization‐prepared True‐FISP

Abstract

Contrast-enhanced (CE) coronary magnetic resonance angiography (MRA) following intraarterial (IA) injection of contrast agent was compared using two sequences in swine: magnetization-prepared fast imaging with steady-state precession (True-FISP), and magnetization-prepared fast low-angle shot (FLASH). Thick-slice projection images were acquired with submillimeter in-plane spatial resolution (0.9 ؋ 0.8 mm 2 ). The magnetization-preparation scheme provided a clear delineation of the major coronary arteries with excellent background suppression. The True-FISP acquisition resulted in an increase in signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) by approximately a factor of 2 over FLASH (P < 0.05 Key words: magnetic resonance (MR); coronary vessels; interventional MR; True-FISP; MR angiographyDiagnostic coronary angiography is an essential component of interventional procedures for coronary artery stenoses, such as balloon angioplasty and stent placement. Coronary angiography is most commonly performed using injections of iodinated contrast agent through a catheter that has been guided into the coronary system with x-ray fluoroscopy. This technique provides excellent in-plane resolution for detection of disease. However, x-ray-guided coronary procedures expose the patient and medical team to ionizing radiation, and also require the use of potentially nephrotoxic contrast agents.Serfaty et al. (1) recently demonstrated the feasibility of coronary MR angiography (MRA) using catheter-directed intra-arterial (IA) injections of gadolinium (Gd)-based contrast agent. The use of MRI avoids ionizing radiation and potentially nephrotoxic iodinated contrast agents. Unlike x-ray fluoroscopy, MRI can also provide end-organ functional information at the time the endovascular procedure is performed (2).Most previous IA MRA techniques have used a 2D projection-imaging technique (1,3,4). Although this scheme obviates the need for rigorous coronary artery localization, signal from background tissues (myocardium and fat) must be reduced to prevent it from obscuring the coronary arteries. Segmented fast low-angle shot (FLASH) in conjunction with a magnetization-preparation scheme has been used to acquire coronary roadmaps in real time (5). Excellent background suppression was achieved, allowing a clear delineation of the coronary arteries. Thick-slice projection images were acquired without electrocardiogram (ECG) triggering to cover the relevant anatomy and to minimize the imaging time and contrast injection volume.Recently, fast imaging with steady-state precession (True-FISP) has been shown to improve the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of non-contrast-enhanced (CE) coronary MRA over FLASH (6). The purpose of this work was to further improve IA CE coronary MRA by testing the hypothesis that data acquisition using True-FISP improves SNR and CNR over FLASH. In addition, we aimed to improve the in-plane spatial resolution by eliminating the effects of cardiac motion via ECG triggering.

Three‐dimensional contrast‐enhanced steady‐state free precession for improved catheter‐directed coronary magnetic resonance angiography

“…This is followed by a train of 180°inversion pulses, separated by delay times TI 1 , TI 2 , TI 3 , and TI 4 . Linear flip angle (LFA) preparation pulses are applied at the end of TI 4 . Note that TS and TI 1 -TI 4 are not necessarily equal.…”

“…Linear flip angle (LFA) preparation pulses are applied at the end of TI 4 . Note that TS and TI 1 -TI 4 are not necessarily equal. …”

“…For two-dimensional imaging: slice thickness ϭ 4 cm. We used the magnetization preparation parameters determined by the computer simulation, with the exception of TI 4 , which was adjusted to 95 msec based on empirical results, and this discrepancy is likely due to the fact that in vivo, certain tissue types may be more prevalent than others.…”

Interventional MR: devices, applications, electromagnetic safety concerns

“…Notable exceptions are the small intracranial vessels as well as the coronary arteries due to the cardiac motion during the relatively long acquisition times for 3D MRA. A projection technique with direct intracoronary gadolinium injection may be one useful approach for coronary imaging, as shown in several studies [ [13][14][15]. Recently, MR guided coronary stent placement has successfully been performed in a pig model based on passive device tracking in combination with a real-time balanced gradient echo sequence [16].…”

Role of non-invasive imaging in the management of coronary artery disease: an assessment of likely change over the next 10 years. A report from the British Cardiovascular Society Working Group

“…While there are ongoing technology improvements (such as parallel imaging), these are unlikely to be sufficient to fully challenge CA, although there are some as yet not fully assessed technical advances that may well have an impact such as use of hyperpolarised 13 C, which may boost the signal by a factor of ,10 000. 29 Although it is difficult to estimate the probability of such developments entering the clinical arena, it may be prudent to plan for future options by expanding the development and installation of CMR scanners, with the potential for them to be adapted if and when developments in CAD imaging become available.…”