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

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 ×100 g−1 × 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.