Improving the Concentration of MR Contrast in the Arteries

This project will build and validate a tool designed to optimize the use of magnetic resonance (MR) contrast agents for contrast-enhanced magnetic resonance angiography (CE-MRA). As with most angiography methods, contrast agents selectively highlight a patient's arteries as compared to surrounding tissue. In CE-MRA the contrast agent is injected into an arm vein using a programmable injector and transported by the body's circulation to the arteries of interest, at which point a MR acquisition depicts the arteries distinctly from surrounding soft tissue. At present, the clinically accepted method of injecting the contrast agent is essentially the same for every patient, and has not been systematically evaluated or optimized. For most chest and abdominal CE-MRA studies contrast is injected over 5-15 seconds, and the resultant concentration of contrast agent in the arteries over the duration of the MR acquisition is not well known. What this concentration is and how it varies over time, however, has a large impact on the quality and clarity of the resulting images. This project is designed to optimize the concentration of contrast agent in the arteries during the MR scan by using the predictive results of a small "test bolus" injection to tailor the actual contrast injection for each individual patient such that concentration remains as high and as constant as possible during the time of MR acquisition. This will be accomplished by developing algorithms and software tools to tailor the optimal, patient-specific injection parameters. The method will be validated in a preliminary clinical study. We propose that we can predict what the contrast bolus will look like (i.e., its "concentration vs. time") by first administering a small (1cc) test bolus, taking pictures as the contrast passes through the blood vessels, and analyzing the results. Using this information, we believe that an individually patient-tailored injection given in multiple phases (i.e., a "multi-phasic" injection) can create constant contrast concentration (and therefore constant signal intensity) throughout the scan, eliminating this source of image blurring, and improving the sharpness and likely the diagnostic quality of first-pass CE-MRA. Moreover, by tailoring the contrast to the duration of the scan, the contrast agent is used most efficiently and not wasted outside the acquisition duration, potentially recouping any contrast-to-noise ratio (CNR) loss. It is important to note the results of this study are generalizable to CT Angiography (CTA) as well, where similar efficient use of the contrast will reduce cost and excessive patient exposure to iodinated contrast. We plan to compare an "optimized" multiphasic contrast administration to a standard single phase contrast administration.