Simultaneous measurement of perfusion and oxygenation changes using a multiple gradient-echo sequence: application to human muscle study.

ABSTRACT

We have developed a magnetic resonance imaging (MRI) technique based on a multiple gradient-echo sequence designed to probe perfusion and oxygenation simultaneously within skeletal muscle. Processing of the images acquired at successive echo times (TEs) generates two functional maps one of the signal intensity (SI) extrapolated to zero echo time, which is sensitive to perfusion; and a second one of R2*, which reflects oxygenation. An advantage of the processing procedure lies in the selection of tissue of interest through the profile of T2* decay, leading to automatic rejection of pixels containing small vessels. This allows a more specific assessment of tissue perfusion and oxygenation. This technique was demonstrated successfully during post-ischemic reactive hyperemia in human calf. A perfusion peak of 123 mL x 100 g(-)1 x min(-1) was measured immediately after ischemia, whereas R2* value showed an 11.5% decrease at the same time, essentially reflecting blood oxygenation changes. Differences in the time courses of reperfusion and re-oxygenation were observed, oxygenation presenting a slower recovery. The mechanisms responsible for such a differential dynamic response are discussed.