RF Power Duty Cycle Restrictions of Continuous Arterial Spin Labeling Coil for 7.0 Tesla Perfusion Magnetic Resonance Imaging

摘要

Perfusion magnetic resonance imaging (MRI) is a powerful tool in diagnosing the physiological status of healthy and diseased tissues [1], [2]. Among the various perfusion imaging methods, the Continuous Arterial Spin Labeling (CASL) is a particularly attractive noninvasive approach in human whole-brain studies [3], [4]. CASL is performed by using a separate surface labeling coil on the neck, so that the 1{sup left}H magnetization in arterial blood is labeled by continuous perturbation. For perfusion imaging at high-field, the RF power duty cycle needs to be carefully determined to meet the FDA safety guidelines on the Specific Absorption Rate (SAR) [5]. Here, we applied the Finite-Difference Time-Domain (FDTD) method to study the duty cycle restrictions at 7.0 Tesla [6]. We first obtained the required transverse magnetic field (B{sub}1) field strength by FDTD simulations and experiments at 3.0 Tesla. The same B{sub}1 field strength is required at 7.0 Tesla and the maximum allowable power duty cycle is obtained by simulations.