Purpose: The recent introduction of pseudo-continuous labeling has significantly improved the sensitivity of Arterial Spin Labeling (ASL) perfusion techniques, opening a great potential for wider clinical use. To date, clinical validation of this technique and comparison with established standards has been limited to 3D FSE and GRASE variants of pseudo-continuous ASL (pCASL). No such re-port is available for multi-slice Echo-Planar Imaging (MS-EPI) based pCASL implementations, which offer an interesting alternative in terms of scanning efficiency. Therefore, the aim of the present study is to compare the outcomes of MS-EPI -based pCASL and dynamic susceptibility contrast imaging (DSC) at 3.0 Tesla in diagnosis and follow up of brain tumors.
Materials and methods: We retrospectively reviewed 56 exams of 43 patients with histologically proven and contrast en-hancing brain tumors. All examinations were performed from February 2011 to March 2013 on MR Philips Achieva 3T TX including pCASL, DSC and contrastenhanced T1-weighted se-quences. A qualitative evaluation was conducted: maximum signal enhancement and the degree of suscep-tibility artifacts in the tumors were each scored visually from 0 to 2, in pCASL subtraction imag-es and rCBV maps. A semi-quantitative analysis was performed, correlating normalized pCASL signal differences with normalized DSC based regional blood flow (rCBF) and regional blood volume (rCBV) pa-rameters in the highest rCBV area. Normalization was achieved by dividing ASL and DSC measurements by equivalent measurements in the thalamus.
Results: The enhancement pattern was similar between pCASL, rCBV and rCBF maps in all patients, ex-cept in 4 cases. We observe a significant correlation between pCASL and rCBV visual enhancement scores, Spearman correlation coefficient 0.69, p<0.00001. The artifact scores are significantly lower in pCASL subtraction images than in rCBV maps: p<0.001, Wilcoxon signed rank test for paired samples. We observe however regional differences between enhancement patterns in DSC and pCASL. We observe a highly significant correlation between pCASL and CBV signal ratios: Spearman correlation coefficient 0.64, p<0.0001 and a highly significant correlation between pCASL and CBF signal ratios: Spearman correlation coefficient 0.68, p<0.0001. A Bland-Altman analysis of pCASL signal ratios and DSCbased CBF ratios revealed a mean difference of 0.79 (CBF ratios being larger than pCASL ratios). The 95% limits of agreement were -3.81 and 2.23.
Conclusion: MS-EPI pCASL may be an alternative to DSC imaging, as it provides similar information on tumor vascularization with no need for contrast medium injection and less susceptibility in the skull base. However, the origin of local discrepancies between DSC and MS-EPI pCASL in some cas-es needs further investigation.
Pierre Reginster, Bénédicte Martin and Vincent Denolin
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