Application of magnetic resonance imaging technique in determining canine muscle and human free-flap viability

Magnetic resonance imaging technique is an exciting, new, safe clinical tool that provides a noninvasive way to monitor free-tissue transfers. Magnetic resonance imaging (MRI) produces a cross-sectional tomographic image at higher resolution than conventional CAT scans and provides a dynamic and physiologic assessment of transferred tissue. We first studied ischemic muscle in the beagle hindlimb gracilis muscles and found an incremental and definitive increase in signal strength both over time and in comparing complete devascularization to partial devascularization. In the right hindlimb (partially devascularized), there was an average increase in T2 (measured in milliseconds) of 2.5 percent at 1 hour, 16.72 percent at 3 hours, and 16.45 percent at 12 hours as compared to normal undisturbed muscle. Similarly, the left hindlimb (completely devascularized) measurements increased from 10.97 percent at 1 hour to 24.02 percent at 3 hours to 47.75 percent at 12 hours. Possible explanations for T2 increases include an increase in intercellular and intracellular water, a change in pH, and possible protein metabolism changes. Clinical studies in seven patients with free flaps have shown "normal" T2 values in healthy tissue comparable to undisturbed canine gracilis muscle and the change in contour and composition of tissue over time. The clinical usefulness of these data is apparent.