3D arterial spin labeling imaging with DANTE preparation pulse
Tsuyoshi Matsuda1, Hirohiko Kimura2, Masayuki Kanamoto3, and Hiroyuki Kabasawa1

1MR Applications and Workflow, GE Healthcare Japan Corporation, Tokyo, Japan, 2Department of Radiology, University of Fukui, Fukui, Japan, 3Radiological Center, University of Fukui Hospital, Fukui, Japan

### Synopsis

DANTE preparation pulse for the arterial spin-labeling (ASL) sequence was developed to reduce the intravascular signal based on the hypothesis that DANTE could enable sufficient vascular signal suppression without any technical drawback. Phantom and human volunteer experiments were performed to evaluate the proposed method. A similar level of vascular suppression effect was observed with both MSDE and DANTE-prepared ASL sequence from phantom experiment. A signal intensity uniformity of vascular suppressed perfusion weighted images was superior with DANTE compared to MSDE. These results indicated that DANTE-preparation could be used as a vessel signal suppression method for ASL.

### Purpose

On the arterial spin label (ASL) imaging, the bright intravascular signal contributes to the overestimation of perfusion signal. ASL with Motion-sensitized Driven-equilibrium (MSDE) (1) has been used to suppress the vascular signal, however, it is sensitive to B1 and B0 field uniformity as well as eddy current. DANTE (Delays Alternating with Nutation for Tailored Excitation) preparation pulse (2) is an effective flow signal suppression method that does not affect static tissue signal. In this study, DANTE-enabled ASL sequence was prepared and evaluated using phantom and healthy human subjects to see whether DANTE preparation would bring a sufficient vascular suppression into effect comparing to MSDE method.

### MATERIAL & METHODS

DANTE pulse train was inserted between background suppression pulses as shown in Figure1. The parameters for DANTE module were as follows: RF pulse duration=100us, Tp: 1ms, Number of DANTE pulses = 200. For ASL, the following parameters were used: FOV = 240 x 240 mm, slice thickness = 4mm, # of slices = 32, TE= 10msec, Post labeling time Delay= 700msec, labeling durations= 3sec, acquisition = 7 arms x 512 sampling points. After the ASL sequence, a reference image without ASL module was acquired to provide M0. All scans were performed on a 3.0 Tesla Discovery750 (GE Healthcare) with 32-channel Receive only head coil. Phantom experiment: A flow phantom consisting of static water chamber and flow tubes which run through the chamber was used. 2.5 cm/s water flow was generated in the tubes. T1 value measured inside the static chamber was 2442msec, and the flowing part was 2054msec. The flip angle (FA) of DANTE RF pulse was changed to 0, 2, 4, 6, 8, 10, 12.5, and 15 [degree], and the gradient area of 28.6 [msec·mT/m] were used. To compare DANTE against MSDE, ASL scan using MSDE (1) was performed with the b value of MSDE varying from 0.005, 2.5, 5.0, 7.5, up to 10.0 [sec/mm$^2$]. Static water signal was measured inside the static chamber area on the reference image. Flow signal was measured inside the flow tubes on the ASL image. Volunteer study: A healthy volunteer was scanned with DANTE-ASL and MSDE-ASL. The study was approved by the local IRB and written informed consent was obtained from all subjects. NEX of two was used for human scan and the rest of ASL parameters were kept the same as phantom scan. The b value of 10 [sec/mm$^2$] was used for MSDE, and FA of 10 [degree] and the gradient area of 28.6 [msec·mT/m] were used for DANTE. The signal uniformity and intensity of DANTE-ASL and MSDE-ASL images were compared and evaluated against each other.

### RESULTS

The changes in signal intensity measured in the phantom images with MSDE or DANTE are shown in Figure 2. The signal decay patterns of flow component were similar in both DANTE and MSDE. As for the signal decay in the static area, rapid signal reduction was observed around b=7.5 [sec/mm$^2$] with MSDE preparation while gradual signal decay along FA change was seen with DANTE. The signal intensity ratio of DANTE with FA of 5 [degree] was similar to MSDE with b value of 5 [sec/mm$^2$] in the case of 2.5 cm/s flow. Similarly, DANTE with FA7.5 [degree] was close to MSDE with b value 10 [sec/mm$^2$]. Figure.3 shows the comparison of human ASL images without vascular suppression preparation, with MSDE, and with DANTE preparation pulse. The signal intensity ratio of the bilateral gray matter was 1.23 with MSDE, and 1.07 with DANTE. The signal intensity ratio of the bilateral gray matter was not as uniform in MSDE as DANTE. It was also observed that vascular signal was decreased with both methods.

### Discussion

It was demonstrated that the proposed DANTE- ASL imaging worked for both phantom and human imaging. DANTE-ASL reduced the intravascular signal while keeping the signal uniformity whereas conventional MSDE preparation generated less uniform ASL images. Local B1+ inhomogeneity caused signal loss (3) and nonuniformity with MSDE sequence. DANTE uses a small FA pulses resulting in smaller B1+ inhomogeneity. The results suggest that DANTE preparation works for reducing the intravascular signal for ASL. In conclusion, we have demonstrated that the DANTE preparation can be used as a vessel signal suppression method for ASL.

### Acknowledgements

No acknowledgement found.

### References

1. Dai W, Robson PM, Shankaranarayanan A, Alsop DC. Reduced resolution transit delay prescan for quantitative continuous arterial spin labeling perfusion imaging. Magn Reson Med. 2012;67(5):1252-65.

2. Li L, Miller KL, Jezzard P. DANTE-prepared pulse trains: a novel approach to motion-sensitized and motion-suppressed quantitative magnetic resonance imaging. Magn Reson Med 2012;68(5):1423–38.

3. Wang J , Yarnykh VL , Yuan C. Enhanced image quality in black-blood MRI using the improved motion-sensitized driven-equilibrium (iMSDE) sequence. J Magn Reson Imaging.2010 May ; 31(5):1256-63.

### Figures

Figure 1: a) DANTE diagram. The gradient area Gz is an area of gradient pulse (msec·mT/m) between each RF pulse indicated as a hatched area. b) ASL sequence timing diagram. DANTE pulse train was inserted between background suppression pulses (BK).

Figure 2: The normalized signal intensity curve for DANTE and MSDE. The lower horizontal axis shows the Flip Angle of DANTE and the upper horizontal axis shows the b value of MSDE. A rapid signal reduction was observed around b=7.5s/mm2 with MSDE (red dotted line) in the static area.

Figure 3: Comparison of human ASL images without vascular suppression (left), with MSDE (middle), and with DANTE (right) preparation pulse. The vascular signal was decreased with both methods (Blue arrow). The distribution of the signal intensity was not as uniform in MSDE (Yellow arrow) as DANTE.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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