Reproducibility of total choline/water ratios in mouse U87MG xenograft tumors by 1H-MRS.

Purpose: To evaluate the reproducibility of the measurement of the total choline-to-water ratio, and the effect of repositioning the subject between scans, using 1H-magnetic resonance spectroscopy in a mouse U87MG xenograft model. Materials and Methods: In vivo single-voxel MR spectra at 7T from xenograft tumors were obtained using both a water-suppressed and a nonwater-suppressed point-resolved spectroscopy (PRESS) sequence. Reproducibility of the total choline/water ratio was evaluated under the conditions of immediate rescan with no change in position of the animal or voxel, immediate reposition, and reposition after 1 or 7 days. Results: Total choline-to-water ratios in U87MG tumor xenografts averaged approximate to 0.018 across all of the groups. The average percent difference between the two scans in each condition was always less than approximate to 3.0%, and the coefficient of variation was always less than approximate to 12%. Bias was unrelated to the testing condition and relatively negligible in magnitude (<3%). Due to heteroscedasticity in the ratios, the limits of agreement were calculated after log transformation of the data and ranged from approximate to 12% when animals were maintained in the same position and immediately rescanned to approximate to 52% when the two scans were 7 days apart. Conclusion: The total choline-to-water ratio provides a reproducible measure of choline-containing metabolites in subcutaneous U87MG xenograft tumors in mice. J. Magn. Reson. Imaging 2012;36:459467. (c) 2012 Wiley Periodicals, Inc.