The case of the missing glutamine

A theoretical study was performed to determine the accuracy and repeatability of multiple one-dimensional pulse sequences in the quantification of glutamine concentration at 3T. Variable repeatability (12% to>50%) and significant absolute error (-50% to +70%) were noted for the eight pulse sequences considered. Data acquired in vivo using three of the pulse sequences used for simulation matched the predicted repeatability well; among the pulse sequences considered, point-resolved spectroscopy (TE=80ms) offered minimal error and acceptable repeatability (12%) for brain glutamine measurements. Following correction for the expected bias of each pulse sequence, consistent glutamine measurements, in the 1-mM range, were reported with the three sequences. An explanation for the mismatch between in vivo ¹H MRS and in vitro ¹³C/¹H MRS at high field was attempted.