Reproducibility of total choline/water ratios in mouse U87MG xenograft tumors by 1 H‐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 1 H‐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 ≈0.018 across all of the groups. The average percent difference between the two scans in each condition was always less than ≈3.0%, and the coefficient of variation was always less than ≈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 ≈12% when animals were maintained in the same position and immediately rescanned 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;36:459–467. ©2012 Wiley Periodicals, Inc.