Events Calendar

Medical Imaging Seminar Series

Speaker: Dr. Rohan Dharmakumar, Cedars-Sinai Medical Center

Talk Title: "Blood-Oxygen-Level-Dependent MRI for Ischemic Heart Disease: Current State-of-the-Art"

Abstract: Coronary artery disease is the leading cause of death in the Western world. It is estimated that nearly 7 million people are living with coronary artery disease (CAD) in the United States and about half a million people die from it each year. The most common form of CAD leads to narrowing of the coronary arteries (stenosis) resulting in reduced blood flow and oxygen supplied to the heart muscle. Accurate early detection of flow deficits may permit interventional revascularization procedures (pharmacological intervention, percutaneous transluminal angioplasty, and/or bypass surgery) to re-establish flow to the hypo-perfused regions. The absence of revascularization increases the risk of sudden cardiac death.
Accurate non-invasive methods for detecting coronary artery disease are necessary to determine which patients should undergo revascularization therapy. The gold standard for detecting coronary artery stenosis is x-ray angiography with iodinated contrast agent which is expensive, invasive, and does not provide information regarding the functional status of the myocardium, which is perhaps more important than morphological information in treating the disease.

In order to identify CAD on the basis of functional status of the myocardium, significant research efforts have been devoted to the development of noninvasive methods, but the establishment of such methods remains challenging. Current approaches include computed positron emission tomography (PET), single photon emission computed tomography (SPECT), and myocardial contrast echocardiography (MCE). PET is a promising method for detecting regional myocardial blood flow differences. However, PET studies are limited by low spatial resolution, limited availability, and administration of ionizing radiation. SPECT imaging is the technique most widely used for detecting both metabolic activity and perfusion. However, like PET, SPECT techniques are also limited by low spatial resolution and/or potentially harmful ionizing radiation.

First-pass MRI with gadolinium conjugates has been used for assessing perfusion changes due to coronary artery disease. First-pass methods rely on the detection of changes in myocardial perfusion reserve due to coronary artery disease and thus typically require the use of pharmacological stress agents, such as adenosine or dipyridamole. Unfortunately, since these agents impart physical discomfort in patients, the infusion time of the agent is limited to only six minutes. This method is evaluated most commonly using rapid imaging techniques with multi-slice capabilities. While this approach can identify regions of perfusion deficits, the method is limited by inadequate myocardial coverage and sub-optimal temporal and spatial resolution because of the need to capture the first passage of the contrast media at relatively high temporal resolution (1 frame/heartbeat). These limitations can decrease the diagnostic sensitivity and specificity.

An alternate method for identifying perfusion deficits relies on endogenous contrast mechanism mediated by red blood cells. It is known that magnetic susceptibility of red blood cells is determined by the oxygen saturation (%O2) of the hemoglobin. Differential %O2 of hemoglobin molecules affects the local magnetic field variations in the intra- and the extra-vascular spaces. The changes in field inhomogeneities, due to changes in %O2, are realized as MR signal changes. This is known as blood-oxygen-level-dependent (BOLD) MRI and has enabled the detection of regional activation patterns in the brain. The potential benefits of BOLD MRI for detecting global or regional myocardial ischemia due to coronary artery disease were demonstrated over two decades ago. In this talk, I will chronicle the development of myocardial BOLD MRI for characterization of ischemic heart disease over the past decades.


Biography: Dr. Rohan Dharmakumar obtained his BSc in Theoretical Physiology and Physics, MSc in Mathematics and PhD in Medical Biophysics at the University of Toronto. Subsequently he went onto complete a postdoctoral fellowship in cardiac MRI and was appointed as Assistant Professor of Radiology and Biomedical Engineering at Northwestern University. Currently, he is an Associate Professor at Depts of Biomedical Sciences, Imaging, and Heart Institute and the Associate Director of Biomedical Imaging Research Institute at Cedars-Sinai Medical Center. At Cedars he heads a lab focused on translational cardiac imaging with the specific goal of extending our current understanding of ischemic heart disease using MRI. His research efforts are continually funded by the National Heart, Lung, and Blood Institute of the NIH and American Heart Association.

Host: Prof. Krishna Nayak

Location: Hughes Aircraft Electrical Engineering Center (EEB) - 248

Audiences: Everyone Is Invited

Contact: Talyia Veal