Continuous Flow-Driven Inversion for Arterial Spin Labeling Using Pulsed Radio Frequency and Gradient Fields

Abstract

Continuous labeling by flow driven adiabatic inversion is advantageous for arterial spin labeling (ASL) perfusion studies, but details of the implementation, including inefficiency, magnetization transfer, and limited support for continuous-mode operation on clinical scanners has restricted the benefits of this approach. Here a new approach to continuous labeling that employs rapidly repeated gradient and RF pulses to achieve continuous labeling with high efficiency is characterized. The theoretical underpinnings, numerical simulations, and in-vivo implementation of this pulsed continuous ASL (PCASL) are described. In-vivo PCASL labeling efficiency of 96% relative to continuous labeling with comparable labeling parameters far exceeded the 33% duty cycle of the PCASL RF pulses. Imaging at 3 Tesla with body coil transmission was readily achieved. This technique should help to realize the benefits of continuous labeling in clinical imagers.