3D Time-of-Flight MRA Using Inversion Recovery TrueFISP

A major drawback of 3D time-of-flight (TOF) sequences is progressive saturation of inflowing spins along the slab direction, and a sufficient long TR or shaped excitation pulses are required to compensate for this. Here we present a new TOF technique based on a combination of selective inversion and 3D acquisition with TrueFISP. The stationary tissue is partially suppressed by the inversion pulse while the non-inverted, inflowing blood shows the full SSFP signal. There is nearly no saturation of the blood signal during the segmented 3D TrueFISP acquisition which results in an excellent contrast between tissue and blood. INTRODUCTION Time-of-flight magnetic resonance angiography (TOF-MRA) is a noninvasive technique to image arterial or venous blood vessels without the need of a contrast agent. The contrast between flowing blood and stationaly tissue is obtained by unsaturated spins flowing into the imaged volume. RF-spoiled and T1-weighted gradient echo sequences are used for 3D TOF MRA, whereby the inflowing spins experience a series of RF pulses. Since T1 of blood is about one second an increasing saturation and thus a loss of contrast can be observed along the direction of flow (1). A new 3 0 TOF technique based on TrueFISP (FIESTA, balanced FFE) is proposed that does not show a significant saturation of blood even for very short repetition times TR and high flip angles. The signal of the stationaly background is suppressed by selective inversion of the imaging slab. METHOD The proposed 31) TOF technique consists of a preparation part and an acquisition part. Both parts are continuously repeated during the run of the sequence (Fig. 1). For the preparation a spatially selective n-pulse is applied that covers both the imaging slab and a region above or below the volume of interest to suppress either arterial or venous signals. The npulse inverts the magnetization of the stationary tissue that has to be suppressed, followed by free relaxation towards the equilibrium value. The acquisition part starts at a time TI after the inversion pulse to allow the inflow of non-inverted blood into the imaging slab.