title: Repeatability of a dual gradient-recalled echo MRI method for monitoring post-isometric contraction blood volume and oxygenation changes.
abstract: 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 (DeltaSI and TTP, respectively). DeltaSI(6) following an MVC was 36% higher than that obtained after a 50% MVC (p = 0.048). For DeltaSI(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 DeltaSI(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. DeltaSI(6) and DeltaSI(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.
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA. otto.sanchez@vanderbilt.edu
authors.forename: O A
authors.initials: OA
authors.lastname: Sanchez
authors.forename: E A
authors.initials: EA
authors.lastname: Louie
authors.forename: E A
authors.initials: EA
authors.lastname: Copenhaver
authors.forename: B M
authors.initials: BM
authors.lastname: Damon
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001810:Blood Volume / Q000502:physiology*; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D009132:Muscles / Q000502:physiology; D010100:Oxygen / Q000378:metabolism*; D012044:Regression Analysis; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D010100:Oxygen