Simultaneous multi-slice (SMS) imaging has been attempted for arterial spin labeled (ASL) perfusion MRI in conjunction with either 2D EPI [1] or GRE readout [2]. It was found that SMS-ASL can reduce T1 relaxation effect of the label, improve image coverage and resolution with little penalty in SNR. However, it has been shown that the temporal SNR of SMS-EPI ASL is still inferior to that of 3D background suppressed (BS) GRASE [3]. Moreover, pseudo-continuous ASL (pCASL) with 3D GRASE can be advantageous for the implementation of BS to further improve the sensitivity of ASL, as recommended by the ASL white paper [4]. Here we present a novel simultaneous multi-slab (SMSB) 3D GRASE sequence for volumetric pCASL imaging with high spatial resolution. The image quality of SMSB-GRASE was evaluated and compared to a standard 3D GRASE pCASL sequence. Preliminary results demonstrated the feasibility for whole-brain volumetric perfusion imaging at a high spatial resolution, although the drop in RF slice profiles in the overlapped boundary slices still needs to be addressed in future work.Figure 1a illustrates the scheme of the presented SMSB technique, including simultaneously excited 3D slabs (yellow and blue), pCASL labeling plane (red) and receiver coil array elements (orange) for a SMSB factor of two. Within each slab, conventional 3D imaging is applied to acquire multiple slices. Given the minimal overlap in the coil sensitivity profiles from the two 3D slabs (Fig. 1b), the aliased slices can be unfolded with a low g-factor penalty. Using a 32-channel head receiver coil, whole-brain 32 axial GRASE images were acquired on a Siemens Prisma system with the following parameters: two simultaneously excited slabs each has 16 slices, distance between the center of the two slabs was 48mm, slice oversampling=50%, FOV=290mm2, voxel size=3x3x3mm3, TR/TE=2940/36ms, BW=2604Hz/Px, segments=3, post label delay=1s, pCASL label duration=1.5s, labeling offset=90mm, and 20 pairs of label and control pCASL image volumes were acquired in 6mins. In addition to SMSB GRASE without FOV shift, a FOV/2 shift along the in-plane phase encoding direction was also implemented using blipped-CAIPIRINHA [5]. For comparison, standard 3D GRASE pCASL was performed for the two slabs individually with the same parameters and the whole-brain imaging took doubled scan time compared to that of SMSB. The aliased slices were then reconstructed using the slice-GRAPPA algorithm [5] with a kernel size of 3x3. Different from 2D SMS reconstruction, inter-slice shift also appears along the slice encoding direction in SMSB 3D acquisition, i.e., an additional term $$$\exp(-i2\pi\cdot{p}\frac{\triangle{z}}{FOV_{z}})$$$ for the k-space signal, where p is the slice index, and ∆Z is the distance between two simultaneously excited slabs. The performance of SMSB 3D GRASE sequences was evaluated by quantifying the spatial SNR (sSNR) and temporal SNR (tSNR) of both control and perfusion images. Whole-brain volumetric pCASL images using the SMSB 3D GRASE readout with and without a FOV/2 CAIPIRIHNA shift are shown in Fig. 2a and Fig. 2b, respectively. Compare to standard 3D GRASE (Fig. 3), high-resolution pCASL images with similar image quality were obtained using the proposed SMSB techniques. Non-blipped SMSB shows more residual artifact (arrows) due to higher g-factor comparing with the blipped case. Overall, the two imaging slabs (1st, 2nd rows & 3rd, 4th rows) are clearly distinguishable due to the RF profile effect for 3D slab excitations, which appear in both standard and SMSB GRASE images. Moreover, a more severe signal dropout in the central slices (white box) is observed in SMSB images, see Fig. 2. This finding can be further confirmed by the slice profile of 3D GRASE signal intensity along slice encoding direction, as presented in Fig. 4. In current implementation, although the two slabs were positioned with no gaps in between, the oversampled slices from one slab did overlap with the imaging slices from the second slab, and vise versa. This can be improved by interleaving multiple slabs and/or custom designed RF pulses with improved profiles in future work. As expected, quantified temporal and spatial SNR from 3D GRASE control and perfusion images all show a slight decrease in SMSB implementations, relative to the non-accelerated results (Table 1).A novel scheme for achieving 3D volumetric pCASL imaging with high resolution is presented by simultaneously exciting multiple 3D GRASE slabs. With 3D imaging within each slab, SMSB can potentially reach much higher spatial resolution than 2D SMS imaging, while minimizing the blurring effect caused by the T2 relaxation occurs during the 3D readout. In addition, SMSB 3D imaging facilitates the implementation of background suppression to further improve the temporal stability of pCASL.