2D beam excitation presaturation-pulse (hereafter Beam Sat pulse) was able to saturate the carotid artery selectively and visualized hemodynamics in brain such as collaterals via the circle of Willis in patients with the carotid stenosis ^1-2. In previous study, continuous Beam Sat pulses were applied to the portal venography and hepatic arteriography (Fig1a). And the portal vain (PV) was visualized clearly and selectively ³, but the right hepatic artery (RHA) was unclear ⁴. This is because T1 relaxation of saturated blood magnetizations in RHA is short. In this study, we applied the 2D beam excitation pulse to inversion recovery pulse (hereafter Beam IR). Effective visualization of the RHA by using the Beam IR pulse was shown with healthy volunteers.

Imaging sequence

Veins and Arteries Scans Contrast-Arterial Spin Labeling (VASC-ASL) is steady-state free precession (SSFP) sequence with slice selective IR (+180deg) to image non-contrast enhanced MRA in body region. In order to avoid the inflow signal saturation, Beam IR (-180def) is added immediately after slice selective IR pulse to restore longitudinal magnetization in selective region (Fig.1b). A 1.5T MRI scanner (Hitachi Medical Corporation, Tokyo, Japan) and 16ch body coil were used for all imaging.

Flow phantom evaluation

A glass tube (diameters = 10 - 5 mm) with flowing water (v = 27.5 - 109.4 cm/s) was placed in column-shaped phantom containing static water (Fig.2a). The Beam IR direction was parallel to the flow direction (Fig.2b), and perpendicular to the flow direction (Fig.2c). Typical scan parameters: TR/TE = 3.9 ms / 1.9 ms, TI = 500 ms, FA = 120 def, imaging matrix = 192 / 160, scan time 56 sec, beam diameter = 30 mm. We evaluated the visualized distance and signal intensity of flowing water.

Volunteer Study

Two healty volunteers were imaged. We explained the purpose and significance of this study to healthy volunteers and obtained written consent. Beam IR pulse overlapped with the descending aorta to restore longitudinal magnetization of inflow blood to HA[h1] (Fig.3), and did not overlap with PV, splenic vein (SpV) and the superior mesenteric vein (SMV) to avoid restoring. And slice selective IR was set from aortic arch to inguinal area to suppress inflow blood from veins. Typical scan parameters: TR/TE = 3.9 ms / 1.9 ms, TI = 800 ms, imaging matrix 192 / 160, Thickness = 4.0 mm, Slice# = 30, respiratory gating (RG), fat suppression = CHESS, scan time = 4:42, beam diameter = 30 mm. We evaluated the visibility of each blood vessel by making MIP images.

The flow phantom evaluation

Fig.4 shows the flow phantom images. The visualized distance D from Beam IR in Fig.4a was 13.8cm and in Fig.4b is 14.0 cm. It is almost equal to the calculated distance 13.2cm from flow velocity 27.5 cm/s and transit time 480 ms. The signal intensity in Fig.4b is lower than Fig.4a. When Beam IR direction is perpendicular to flow direction (Fig.4b), the restored region becomes smaller (only 30 mm), so signal intensity becomes lower. Beam IR should be overlapped with a straight artery to restore enough regions. The HA is a branch of the straight abdominal aorta, so the Beam IR should be set on abdominal aorta.

Volunteer Study

Fig.5a shows an image of VASC-ASL with Beam IR. The HA from common hepatic artery (CHA) to RHA was visualized clearly. The RHA, gastroduodenal artery (GDA) and splenic artery (SpA) were visualized in a subtraction image (Fig.5c, 5d) of with (Fig.5a) and without Beam IR image (Fig.5b). These vessels were not visualized in BeamSat VAS-ASL image (Fig.5e) clearly. The visualized distance of HA from the celiac artery was 15.2cm. It is almost equal to the calculated distance 16.0±7.8 cm from mean velocity 20.5±10 cm/s ⁵ and transit time 780 ms.

The more peripheral arteries than RHA (Fig.5d white arrow head) were not visualized in all images. It is supposed that the signal loss of peripheral arteries is caused by absence of inflow blood to the HA with RG. We assume that the visualization of peripheral arteries are improved by the increased inflow blood, when ECG gate is applied and a timing of IR is optimized.

We developed VASC-ASL with Beam IR pulse to selectively visualize RHA. The usefulness of the developed technique was demonstrated by applying it to phantom and volunteers.