Citrate Level Measurement
Proton MRS were acquired using a single-voxel point-resolved spectroscopy (PRESS) with a short echo time (TE) of 35 milliseconds, a repetition time (TR) of 1.5 seconds, and 128 signal averages were used for all acquisitions(14). The total acquisition time, which included scanner adjustments, was less than five minutes per spectrum. All spectra were processed with fully automated LCModel (Stephen Provencher Inc., Oakville, Ontario, Canada, LCModel Version 6.3-1L) software and citrate was quantified as previously described(4, 15). MRS data was acquired prior to contrast injections using a 1.5T MR System (Sign LX; EG Healthcare). Patients aged less than 5 years were imaged under general anesthesia. Single voxel short TE was used to obtain signals with minimal signal loss due to T2 signal decay of metabolites. T2-weighed fast spin-echo, fluid-attenuated inversion recovery (FLAIR), and T1-weighed FLAIR magnetic resonance (MR) images were acquired in all cases and reviewed to determine the extent of the lesion prior to selecting the region of interest. This region was documented in three MRIs and reviewed to ensure that no partial volume for normal appearing tissue was enclosed. Sizes and shaped of this region were adjusted to the lesion sizes and typically varied from 5-10cm3(Figure 1).