Abstract
A method is described for quantifying the cellular phosphorus‐31 (^31^P) concentration in human skeletal muscle based on RARE (rapid acquisition with relaxation enhancement) image intensities. The ^31^P concentrations were calculated using relaxation rates, RF coil spatial characteristics, and RARE signal intensities from foot muscle and an external ^31^P standard. ^31^P RARE and ^1^H T~2~‐weighted images of the foot muscles in 11 normal subjects were acquired at 3.0 T using a double‐tuned (^31^P/^1^H) birdcage coil. ^31^P PRESS (point‐resolved spectroscopy) spectra were acquired to verify the measurable ^31^P concentrations in a multiecho acquisition. The mean measured concentration was 26.4 ± 3.1 mM (mean ± SD) from RARE signal intensities averaged over the entire imaged foot anatomy and 27.6 ± 4.1 mM for a 3 × 3 pixel region‐of‐interest measurement. The ^31^P RARE image acquisition time was 4 min with a 0.55 cm^3^ voxel size. These results demonstrate that the ^31^P concentration can be accurately measured noninvasively in human muscle from RARE images acquired in short scan times with relatively high spatial resolution. Magn Reson Med 52:1036–1042, 2004. © 2004 Wiley‐Liss, Inc.