Absolute thermometry using hyperpolarized 129Xe free-induction decay and spin-echo chemical-shift imaging in rats
Agilo L. Kern, Marcel Gutberlet, Regina Rumpel, Inga Bruesch, Jens M. Hohlfeld, Frank Wacker, Bennet Hensen
Abstract
Purpose
To implement and test variants of chemical shift imaging (CSI) acquiring both free induction decays (FIDs) showing all dissolved-phase compartments and spin echoes for specifically assessing 129Xe in lipids in order to perform precise lipid-dissolved 129Xe MR thermometry in a rat model of general hypothermia.
Methods
Imaging was performed at 2.89T. T2 of 129Xe in lipids was determined in 1 rat by fitting exponentials to decaying signals of global spin-echo spectra. 4 rats (conventional CSI) and 6 rats (turbo spectroscopic imaging) were scanned at three time points with core body temperature 37/34/37°C. Lorentzian functions were fit to spectra from regions of interest to determine the water-referenced chemical shift of lipid-dissolved 129Xe in the abdomen. Absolute 129Xe-derived temperature was compared to values from a rectal probe.
Results
Global T2 of 129Xe in lipids was determined as 251.3 ms ± 81.4 ms. Friedman tests showed significant changes of chemical shift with time for both sequence variants and both FID and spin-echo acquisitions. Mean and standard deviation of 129Xe and rectal probe temperature differences were found to be -0.15°C ± 0.93°C (FID) and -0.38°C ± 0.64°C (spin echo) for conventional CSI as well as 0.03°C ± 0.77°C (FID) and -0.06°C ± 0.76°C (spin echo) for turbo spectroscopic imaging.
Conclusion
129Xe MRI using conventional CSI and turbo spectroscopic imaging of lipid-dissolved 129Xe enables precise temperature measurements in the rat’s abdomen using both FID and spin-echo acquisitions with acquisition of spin echoes enabling most precise temperature measurements.