Measurement of lower-leg volume change by quantitative computed tomography.

BACKGROUND: Lower-leg edema is a common symptom in many diseases. A precise method with low variability for measurement of edema is warranted in order to obtain optimal conditions for investigation of treatment effects. PURPOSE: To evaluate computed tomography for precise measurement of lower-leg muscle and adipose tissue volumes using a very low level of effective radiation dose. MATERIAL AND METHODS: Eleven volunteers were examined three times during 1 day, either as two consecutive examinations in the morning and one single examination in the afternoon, or as one examination in the morning and two in the afternoon. Eleven scans with computed tomography were made at each examination, and lower-leg volumes were calculated from automatically measured scan areas and interscan distances. Volumes for muscle, adipose tissue, and bone were calculated separately. Minimal radiation dose was used. RESULTS: Mean difference between the repeated examinations was -0.1 ml for total volume, -1.4 ml for muscle, and 1.6 ml for adipose tissue volume. The corresponding 95% confidence intervals were -6.5 to 6.0 ml, -3.5 to 6.5 ml, and -7.0 to 4.0 ml, respectively. The resulting effective dose was 0.5 microSv to one leg. CONCLUSION: Computed tomography can be used as a precise quantitative method to measure small volume changes of the lower leg as a whole, and separately for muscle and adipose tissue. The results were obtained with a negligible effective dose, lower than that delivered by modern fan-beam dual-energy X-ray absorptiometry whole-body examinations and equal to a few hours of background radiation.