Quantitative Dynamic MR Angiography using ASL based TrueFISP

Introduction Contrast-enhanced dynamic MR angiography (CE-dMRA) has received considerable attention recently owing to its ability to provide temporal information in addition to the otherwise "static" high-resolution 3-D contrast-enhanced MRA for a variety of clinical indications [1]. While the spatial resolution can reach millimeter and sub-millimeter level, the temporal resolution in CE-dMRA is generally on the order of seconds and the method requires intravenous injection of contrast agent. As a non-contrast alternative, dynamic MRA can be performed with pulsed arterial spin labeling (PASL) in combination with a continuous Look-Locker readout [2]. The appealing feature of spin-labeling based dMRA is the high temporal resolution (on the order of tens of milliseconds), yet the spatial resolution and SNR are not satisfactory due to the low flip angle and/or saturation effects during Look-Locker read-out. TrueFISP [3] is a balanced steady-state free precession (bSSFP) technique that offers high SNR and imaging efficiency. It is ideal for blood vessel imaging due to the intrinsically high T2/T1 ratio of the blood signal. In addition, the T1 recovery of tagged blood is minimally affected by the trueFISP readout, allowing a dynamic temporal window up to 3 blood T1s [4]. Here we show that quantitative dMRA with millimeter spatial resolution and millisecond temporal resolution can be achieved by marrying PASL with a multi-phase inversion-recovery (IR) trueFISP readout.