In Vivo Compartmental Relaxation in a Model of Graded Muscle Edema

Abstract

MRI provides an excellent way of visualizing muscle inflammation; however, there are few techniques that serve to quantitatively assess edematous muscle. In this thesis, integrated relaxation measurements were made in vivo on edematous rat muscle with varying degrees of swelling. To investigate the effect of exchange on the observed relaxation parameters a two pool model was created and the Bloch-McConnell equations were solved for the varying amounts of swelling. Results from the simulation of the exchange model were compared to the observed data to extract fitted parameters for the compartmental relaxation times. These simulations also provided a comparison for the observed changes in the long-lived apparent T1. Edematous muscle was found to display both multiexponential T1 and multiexponential T2. Normal muscle, however, was found to exhibit only a single T1-T2 component. It was shown that the apparent T1 of the long-lived signal component in edematous muscle increased monotonically with an increase in the amount of edema. Knowledge of changes in T1 and the exchange kinetics in edematous muscle might help in further characterizing the micro-anatomy of muscle tissue in various stages of injury.