Hyperpolarized Xe MRI of the Rat Brain with Chemical Shift Saturation Recovery and Spiral-IDEAL Readout

Purpose: To demonstrate the feasibility of Xe chemical shift saturation recovery (CSSR) combined with spiral-IDEAL imaging for simultaneous measurement of the time-course of red blood cell (RBC) and brain tissue signals in the rat brain.

Methods: Images of both the RBC and brain tissue Xe signals from the brains of five rats were obtained using interleaved spiral-IDEAL imaging following chemical shift saturation pulses applied at multiple CSSR delay times, τ. A linear fit of the signals to τ was used to calculate the slope of the signal for both RBC and brain tissue compartments on a voxel-by-voxel basis. Gas transfer was evaluated by measuring the ratio of the whole brain tissue-to-RBC signal intensities as a function of τ. To investigate the relationship between the CSSR images and gas transfer in the brain, the experiments were repeated during hypercapnic ventilation.

Results: Hypercapnia, affected the ratio of the tissue-to-RBC signal intensity (p = 0.026), consistent with an increase in gas transfer.

Conclusion: CSSR with spiral-IDEAL imaging is feasible for acquisition of Xe RBC and brain tissue time-course images in the rat brain. Differences in the time-course of the signal intensity ratios are consistent with gas transfer changes expected under hypercapnic conditions.