QUANTITATIVE ASSESSMENT OF ATHEROSCLEROSIS VIA MRI

The primary objective of this work is to develop a quantitative method
for the assessment of atherosclerosis that can noninvasively detect and
quantify the disease in its early stages, before the vessel is occluded
or severely stenotic. Magnetic resonance imaging (MRI) and magnetic
resonance angiography (MRA) are effective for imaging vessels with
advanced atherosclerotic disease.The focus of this work is on the
development and evaluation of a new MRI technique that can directly
image the subintimal lipid deposits of atherosclerotic disease. Lipid
deposits, primarily cholesteryl esters, are characteristic of early
stage atherosclerosis, and the amount of these lipids can potentially
provide a quantitative measure of disease. The new MRI method is based on a stimulated-echo diffusion-weighted
(STED) sequence that suppresses water and allows direct visualization
of the less mobile lipids. The research aims to: (1) optimize and
improve the sequence for lipid imaging, (2) demonstrate that accurate
quantitation of the lipid accumulation is possible, (3) show that
detection and quantitation of the lipid is possible in an in-vivo
animal model, and (4) develop the technique on a whole-body imaging
system. Investigation of the properties of the water signal will
complement the work on the tissue lipids. One of the main tasks will be to investigate several improvements to
the basic technique to make it less sensitive to the effects of non-
random motion, and then to optimize the timing of the technique based
on accurate knowledge of the physical properties of the tissue water
and the lipid. In-vivo imaging will be demonstrated in an animal model
of atherosclerosis. Evaluation of the quantitative accuracy and
sensitivity of the imaging method will be accomplished using phantoms,
excised human tissue samples, and the rabbit model. The final component
of the research will be to implement the technique on a clinical whole-
body imaging system. This will require construction of a special-
purpose gradient coil to provide a higher diffusion gradient field than
is available on conventional MRI systems. The result of this research will be the development of an accurate
noninvasive method for quantitative evaluation of atherosclerosis. Such
a method would be useful both as a general-purpose diagnostic test and
as a tool for studying the factors that influence disease progression
and regression in animal models and in man.