Magnetic resonance imaging quantitation of changes in muscle volume during 7 days of strict bed rest

Prolonged bed rest results in a loss of leg lean body mass. Previous studies using bed rest as a model for microgravity have shown decreases in leg mass after 12 and 14 d, 5 and 17 wk.

As magnetic resonance imaging (MRI) can provide a precise and non-invasive means of determining muscle volume, we sought to determine if changes in leg muscle volume could be detected in bed rest periods as short as 7 d.

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 transaxial images were generated over prescribed regions using a Technicare MRI imager with a 0.6T superconducting magnet and body coil. Image processing was performed using a generalized 8-bit medical image analysis package developed at University of Texas Medical Branch. Images were analyzed for muscle and non-muscle volumes (including fat, blood vessel, and bone marrow volumes).

The MRI quantitation demonstrated bed rest-induced significant decreases in segmental thigh muscle (approximately 3.0%, p < 0.05) volume.

We conclude that computerized image analysis of MRI images provides a sensitive tool capable of detecting leg volume changes of as little as 3.0% over a 7-d period of strict bed rest.