Repeatability of a dual gradient‐recalled echo MRI method for monitoring post‐isometric contraction blood volume and oxygenation changes

The purpose of this study was to assess the repeatability of a dual gradient‐recalled echo (GRE) muscle functional MRI technique. On 2 days, subjects ( n  = 8) performed 10 s isometric dorsiflexion contractions under conditions of: (1) maximal voluntary contraction (MVC), (2) 50% MVC (50% MVC), or (3) 50% MVC with concurrent proximal arterial cuff occlusion (50% MVC cuff ). Functional MRI data were acquired using single‐slice dual GRE (TR/TE = 1000/6, 46 ms)‐echo planar imaging for 20 s before, during, and for 180 s after each contraction. The mean signal intensity (SI) time courses at each TE (SI 6 and SI 46 , reflecting variations in blood volume and %HbO 2 , respectively) from the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles were characterized with the post‐contraction change in SI and the time‐to‐peak SI (ΔSI and TTP, respectively). ΔSI 6 following an MVC was 36% higher than that obtained after a 50% MVC ( p  = 0.048). For ΔSI 6 , the highest intraclass correlation coefficients (ICCs) were observed for the TA muscle in the 50% MVC and MVC conditions, with values of 0.83 ( p  = 0.01) and 0.88 ( p  = 0.005), respectively. Bland–Altman plots revealed repeatability coefficients (RCs) for the 50% MVC and MVC conditions in the TA muscle of 1.9 and 1.4, respectively. The most repeatable measures for ΔSI 46 were obtained for the 50% MVC and MVC conditions in the EDL muscle ( p  = 0.01 and p  = 0.04, respectively). Bland–Altman plots revealed RC's for 50% MVC and MVC conditions in the EDL muscle of 3.9 and 5.7, respectively. ΔSI 6 and ΔSI 46 increased as a function of the contraction intensity. The repeatability of the method depends on the muscle and contraction condition being evaluated, and in general, is higher following an MVC. Copyright © 2009 John Wiley & Sons, Ltd.