Pseudo-random arterial modulation (PRAM): A novel arterial spin labeling approach to measure flow and blood transit times

Purpose: To investigate blood flow and transit time measurement, using the pseudo-random arterial modulation (PRAM). Materials and Methods: PRAM is based on a pseudorandom sequence of inversions and noninversions of the arterial blood at a labeling plane inferior to the imaging plane. To accomplish this, a pseudo-continuous tagging is used to create inversion or noninversion prepulses before a gradient echo sequence and tested on phantoms and human volunteers. Results: We have shown here that the PRAM technique can measure the velocity profile and the transit time accurately and efficiently both in a phantom and in vivo in a human brain. Conclusion: PRAM does not require separate control and label acquisition as is common in arterial spin labeling (ASL) but rather measures the distribution of transit times to a voxel within one integrated scan. The PRAM method is a model-free approach in measuring transit time distributions, and therefore ultimately should provide more accurate perfusion measurements.