MR spectroscopy of the breast. Quantitation of choline using tissue water as a reference

Previous magnetic resonance spectroscopy (MRS) studies of the breast have shown elevated choline to be a possible diagnostic marker of malignancy and index of therapeutic effect. Issues related to evaluating choline signal intensity in breast MRS include lack of other metabolite signal in most of the breast MRS and possible variation in detection sensitivity among measurements. Phantom studies using choline solutions showed that choline signal could be corrected by water signal at various voxel localizations, which indicated that water signal could thus serve as an internal standard for quantifying choline. Consistency of choline concentration calculated from MRS signal and actual concentration was good, ranging 1.5 to 50.0 mM/kg. In clinical breast MRS, Baik's group reported using tissue water signal obtained in the same voxel as an internal standard to determine choline, correcting relaxation using T1 and T2 relaxation times for both metabolites. In this study, choline signal was positive (signal-to-noise ratio >2) in 8 of 9 malignancies before chemotherapy and negative in 5 of 5 benign cases. Choline concentrations in the 8 malignancies ranged from 1.80 to 26.7 mM/kg (average 14.0 mM/kg). These values, obtained in voxels from 1.73 to 3.38 mL, were in the same range of concentration as those previously reported in voxels of a fixed size, 8 mL. It would be more practical to adjust voxel size according to lesion size in clinical settings. This study showed that in vivo MR spectroscopic quantification of choline in breast tissue can successfully be performed for voxels of reduced size down to 2 mL. (author)