The Potential for Absolute Temperature Imaging Based on Brain Metabolites Using an FID-Shifting Approach in Gradient...

To implement and evaluate an efficient method for absolute temperature measurement using a gradient echo implementation of the echo planar spectroscopic imaging (EPSI) sequence.

The gradient echo EPSI sequence (GREPSI) utilizes an oscillating readout gradient together with continuous signal readout after slab selective excitation. The metabolite peaks are separated from the large water signal using a novel free induction decay (FID) time shifting method. SNR comparisons were made between spectra acquired with strong, weak, and no water suppression on a brain phantom with physiological metabolite concentrations. Measurements were made using no water suppression with the phantom at discrete temperatures between 22°C and 42°C. GREPSI was also compared with single voxel spectroscopy (SVS) and chemical shift imaging (CSI) pulse sequences. Finally, a healthy volunteer was scanned.

The FID shifting method allowed removal of the water spectrum and recognition of metabolite peak locations independent of water suppression. The standard deviation of the temperature measured at room temperature was 0.31°C, independent of water suppression, respectively. The absolute temperature measurements closely matched the corresponding water-bath temperature with accuracy within 2% at 42°C and precision on the order of 0.2°C using either NAA, Cre, or Cho as a reference. The in vivo temperature images of a normal volunteer were in the expected normal range.

This study indicates that accurate and precise temperature measurements can be obtained with GREPSI in a scan time on the order of 2-5 min, for an 8-slice slab, depending on the FOV imaged.