The effects of an initial depolarization pulse on dissolved phase hyperpolarized Xe brain MRI.

Purpose: To evaluate the effect of an initial 90° depolarization RF pulse on the dissolved-phase hyperpolarized (HP) xenon-129 ( Xe) brain imaging and to compare the SNR variability of HP Xe images acquired without an initial depolarization RF pulse to those following the initial depolarization pulse.

Methods: Five cognitive normal healthy volunteers were imaged using a Philips Achieva 3.0T MRI scanner during a single breath-hold following inhalation of 1 L of HP Xe. Each participant underwent six HP Xe scans. Three scans were performed using conventional single-slice projection HP Xe brain imaging, and the other three scans were performed using the HP Xe time-of-flight imaging with an initial rectangular depolarization pulse.

Results: Although the utilization of an initial depolarization results in the reduction of the mean image SNR, the presence of an initial depolarization RF pulse reduces the SNR variability of the HP Xe brain image by a factor of 2.26. The highest SNR variability was observed from the posterior brain region, where the anterior region possessed the lower level of signal variability.

Conclusion: An initial 90° depolarization RF pulse, applied prior to the HP Xe image acquisition, reduced the HP Xe signal variability more than two times between the different breath-hold images.