MAGNETIC-RESONANCE-IMAGING QUANTITATION OF CHANGES IN MUSCLE VOLUME DURING 7 DAYS OF STRICT BED REST

Background: Prolonged bed rest results in a loss of leg lean body mass . Previous studies using bed rest as a model for microgravity have sho wn decreases in leg mass after 12 and 14 d, 5 and 17 wk. Hypothesis: A s magnetic resonance imaging (MRI) can provide a precise and non-invas ive means of determining muscle volume, we sought to determine if chan ges in leg muscle volume could be detected in bed rest periods as shor t as 7 d. Methods: Five young, healthy, male volunteers were subjected to 7 d of absolute bed rest. Each subject underwent MRI quantitation of segmental muscle Volumes of the calves and thighs before and after bed rest. Eleven (calf) and nine (thigh) contiguous 1-cm thick transax ial images were generated over prescribed regions using a Technicare M RI imager with a 0.6T superconducting magnet and body coil. Image proc essing was performed using a generalized 8-bit medical image analysis package developed at University of Texas Medical Branch. Images were a nalyzed for muscle and non-muscle volumes (including fat, blood vessel , and bone marrow volumes). Results: The MRI quantitation demonstrated bed rest-induced significant decreases in segmental thigh muscle (app roximate to 3.0%, p < 0.05) volume. Conclusions: We conclude that comp uterized image analysis of MRI images provides a sensitive tool capabl e of detecting leg Volume changes of as little as 3.0% over a 7-d peri od of strict bed rest.