Citrate in Pediatric CNS Tumors?

Signal modulation of in vivo PRESS spectra of anaplastic astrocytoma (i) and DIBSG (ii + iii) acquired with different TE. In vivo spectra acquired at TE of 35 ms (A), 144 ms (B), and 316 ms (C) from the same ROI are compared with spectra obtained from a citrate model solution at the same conditions. The complex signal centered at 2.6 ppm in tumor spectra shows the same J-modulation as citrate. At a TE of 316 ms, the center peaks of citrate are inverted.

Time course of citrate in DIBSG. A, Nonrandom residual signal, not accounted for by standard metabolites included in the LCModel basis set and consistent with citrate, can be detected in the MR spectrum obtained from a representative patient at the time of initial diagnosis. This signal is less readily detected in follow-up studies of this patient at 7 and 11 months when there was clinical progression of disease. Spectra are scaled to measured absolute concentrations to allow direct comparison of peak areas. Shown are unfiltered raw data (thin line) and the LCModel fit to the data (thick line). B, Plotted are tumor citrate concentrations versus time after initial diagnoses obtained from 6 patients in whom studies were performed repeatedly. Concentrations of citrate decrease significantly with time.

MR spectroscopy of age-matched controls. There is no evidence for citrate in spectra of age-matched control subjects as illustrated in a representative PRESS (TE, 35 ms) spectrum of occipital gray matter (A). Spectra from model solutions of citrate and NAA are shown for comparison (B). Note that the NAA peak at approximately 2.7 ppm does not co-resonate with citrate.

MR spectroscopy of premature brain. A, An MR spectrum of a premature baby (gestational age, 33 weeks; 7 weeks premature) who underwent an MR examination to rule out white matter injury is shown. The MR images were interpreted as normal, and neurologic sequelae are not reported at this stage. A small signal at 2.6 ppm consistent with citrate is detected. Note that the low levels of NAA are normal for premature brain.²⁴ B, T2-weighted MR image indicating the ROI.