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Abstract:
Purpose/Introduction: Arterial spin labeling (ASL) is a promising non-invasive approach for perfusion measurements1,2,3. However, liver perfusion imaging with ASL is limited by respiratory and cardiac motion artifacts. Background suppression (BS) can reduce the sensitivity
of ASL measurements to physiological motion4. Furthermore, the quantification of liver perfusion is challenging due to the relative long blood transit-time and the short T1-relaxation time of the liver5. The aim of this study was to investigate the capability of pseudo-continuous
ASL (pCASL) with BS to quantify the total liver perfusion and transit time of the blood delivery by varying the post-labeling delay.
Subjects and Methods: Three healthy volunteers were examined on a 3T MR scanner (MAGNETOM Prisma, Siemens Healthcare) with body- and spine-array coils. Liver perfusion was measured using a pCASL echo-planar imaging sequence6.. Six sagittal slices were acquired with the following parameters: TR/TE, 9000/14 ms; slicethickness/
gap, 8/4 mm; in-plane resolution, 3 9 3 mm2; matrix,
82 9 100; bandwidth, 2380 Hz/Pixel; tagging flip angle, 25; and gradient strength 7 mT/m. Tag duration was set to 2000 ms and postlabeling delays (PLDs) were 700, 1500, 2000, 2500, 3000, 3500 ms. 32 label-control image pairs and anM0 image were acquired within 5 min. BS for liver tissue (T1 = 800 ms) was utilized by a double inversion approach. The tagging plane was placed perpendicular to the portal vein
(Fig. 1). Images were acquired by employing a synchronized breathing protocol. Images with strong motion artefacts were discarded from subsequent analysis using MATLAB. A mask of liver parenchyma was created by segmenting averaged difference images. Mean perfusion and transit-time over the liver parenchyma mask were calculated based on a one-compartment perfusion model5,7,8.
Results: pCASL with BS allowed for hepatic perfusion assessment in all participants. Perfusion-weighted images and the corresponding model fitting is depicted in Figure 2a+b. Liver perfusion values and transit-times are presented in Table 1. For comparison, the perfusion values at a single PLD calculated with simplified assumptions are
shown. Model fitting provided a mean perfusion of 136 ml/100 g/min and a transit time of 1938 ms, whereas a perfusion of 73 ml/100 g/min was calculated based on a single PLD data.
