The effect of orientation on quantification of muscle creatine by ¹H MR spectroscopy

Creatine is a central energy metabolite whose N-CH₃ group can be detected with ¹H MR spectroscopy (¹H MRS) with relatively high sensitivity. Prior studies suggest that muscle fiber orientation can influence the appearance of other resonances attributed to total creatine (CR). Our purpose was to determine whether muscle fiber orientation affects muscle CR concentration quantification by ¹H MRS with the commonly used N-CH₃ resonance at 3.0 ppm. Skeletal muscle CR was quantified with water-referenced ¹H MRS in normal subjects with different forearm muscle orientations relative to the static magnetic field at 1.5T. There were no significant differences in mean total [CR] in two different series of experiments separately including two orthogonal orientations and four orientations (0°^, 30°^, 60°^, 90°) of the forearm relative to the static field using either short (TE = 15 ms) or long (TE = 100 ms) echo times for voxels containing or centered on the same tissues. Subtle differences in CR line-width and T2 correction factors were observed with orientation. These observations are consistent with the primary hypothesis that careful water-referenced [CR] quantification, accounting for T2 effects and using the N-CH₃ peak at 3.0ppm, is not affected by muscle orientation.