Reliability And Validity Of Ultrasound Cross-sectional Area Measurements For Long-duration Spaceflight

Abstract

Limb muscle atrophy and the accompanying decline in function can adversely affect the performance of astronauts during mission-related activities and upon re-ambulation in a gravitational environment. Previous characterization of spaceflight-induced muscle atrophy has been performed using pre- and post-flight magnetic resonance imaging (MRI). In addition to being costly and time consuming, MRI is an impractical methodology for assessing in-flight changes in muscle size. Given the mobility of ultrasound (US) equipment, it may be more feasible to evaluate changes in muscle size using this technique. PURPOSE: To examine the reliability and validity of using a customized template to acquire panoramic US images for determining quadriceps and gastrocnemius anatomical cross-sectional areas (CSA). METHODS: Vastus lateralis (VL), rectus femoris (RF), medial gastrocnemius (MG), and lateral gastrocnemius (LG) CSAs were assessed in 10 healthy individuals (36 ± 2 yr) using US (CX50 Philips) and MRI. Panoramic US images were acquired by 2 sonographers using a customized template placed on the thigh and calf and analyzed by the same 2 sonographers. MRI images of the leg were acquired while subjects were supine in a 1.5T scanner (Signa Horizon LX, General Electric) and were analyzed by 3 trained investigators. The average of the 2 US and 3 MRI values were used for validity analysis. RESULTS: High inter-experimenter reliability was found for both the US template and MRI analysis, as coefficients of variation across muscles, ranged from 2.4% to 4.1% and 2.8% to 3.8%, respectively. Significant correlations were found between US and MRI CSA measures (VL, r = 0.85; RF, r = 0.60; MG, r = 0.86; LG, r = 0.73; P < 0.05). Furthermore, the standard error of measurement between US and MRI ranged from 0.91 to 2.09 cm2 with high limits of agreement analyzed by Bland-Altman plots. However, there were significant differences between absolute values of MRI and US for all muscles. CONCLUSION: The present results indicate that using a customized US template provides reliable measures of leg muscle CSA, and thus could be used to characterize changes in muscle CSA both in flight and on the ground.