Quantitative sodium MRI of the mouse prostate.

A method was developed for quantitative sodium MRI of the mouse prostate at 9.4 T. A small loop-gap radiofrequency coil was constructed and dual-tuned to both the proton and sodium frequencies. The location and boundary of the mouse prostate were localized using high-resolution T(2)-weighted proton images, and sodium images were acquired with 1mm isotropic resolution using a short echo time (0.6 ms) and a long pulse repetition time (300 ms) for sodium density weighting with minimal T(1) and T(2) contrast. Sodium concentration in the prostate was estimated by comparing pixel intensities within the prostate to the pixel intensities in a pair of reference vials with known sodium concentrations, and a radiofrequency field inhomogeneity correction was performed based on field maps of a homogeneous phantom. In a group of five healthy, 5-month-old BALB/c mice, the average sodium concentration within their prostates was measured to be 173 +/- 38 mM. Muscle tissue and bladder were also clearly visible in the sodium images, and their sodium concentrations were estimated to be 40 +/- 15 mM and 210 +/- 72 mM, respectively.