Over the past several years the use of magnetic resonance to image myocardial perfusion has become a routine and well-accepted clinical tool. Recent studies suggest that in appropriately selected patients that the sensitivity of MRI for the detection of significant coronary artery disease maybe superior to that of SPECT imaging. The vast majority of these studies, however, have required the administration of an exogenous contrast agent, such as gadolinium, in order to measure myocardial perfusion.
Myocardial perfusion can also be measured by MRI using endogenous contrast mechanisms. Our center has a long tradition in the use of these endogenous MR contrast mechanisms to image tissue perfusion, and the use of susceptibility-based BOLD imaging for functional brain imaging was in fact first described by Bruce Rosen, director of our center. We have previously used endogenous MR contrast mechanisms, including BOLD and Arterial Spin Labeling (ASL), to image myocardial perfusion in humans and large animals in-vivo.
Much of our current efforts aim to take advantage of recent advances in MRI hardware and software that have the potential to allow even higher quality images of myocardial perfusion to be obtained with either ASL or BOLD imaging. These advances include the advent of high field large bore scanners for cardiac imaging, and advances in gradient technology that permit rapid, single-shot and SSFP cardiac imaging. Selected images, acquired recently with these techniques, are shown below.
|Figure 1: Myocardial Ischemia detection using ASL and BOLD imaging at 3T: MRI detection of myocardial perfusion defect in a porcine model of coronary stenosis at 3 Tesla using T1-weighted based perfusion imaging (left image) and T2-weighted BOLD contrast imaging (middle image) during intravenous infusion of adenosine. Notice the close regional correspondence with the territory “at risk” delineated post LAD selective injection of Gd-DTPA (right image).
|Figure 2: Myocardial T2 measurement in humans with single shot SSFP and spin-echo EPI techniques. The use of single shot imaging has the potential to decrease motion related artifact and noise in the T2 maps.
Other areas of active investigation in the group include the use of susceptibility contrast to measure myocardial blood volume and regional myocardial oxygen consumption. The ability of MRI to evaluate myocardial blood volume, perfusion and oxygen consumption serially, non-invasively and without exposure to ionizing radiation constitute a very powerful tool for physiological and patho-physiological investigation. Several studies are currently being conducted in collaboration with colleagues in the MGH cardiology division.