Abstract
PurposeWhen using simultaneous multi‐slice (SMS) EPI for background suppressed (BGS) arterial spin labeling (ASL), correction of through‐plane motion could introduce artefacts, because the slices with most effective BGS are adjacent to slices with the least BGS. In this study, a new framework is presented to correct for such artefacts.MethodsThe proposed framework consists of 3 steps: (1) homogenization of the static tissue signal over the different slices to eliminate most inter‐slice differences because of different levels of BGS, (2) application of motion correction, and (3) extraction of a perfusion‐weighted signal using a general linear model. The proposed framework was evaluated by simulations and a functional ASL study with intentional head motion.ResultsSimulation studies demonstrated that the strong signal differences between slices with the most and least effective BGS caused sub‐optimal estimation of motion parameters when through‐plane motion was present. Although use of the M0 image as the reference for registration allowed 82% improvement of motion estimation for through‐plane motion, it still led to residual subtraction errors caused by different static tissue signal between control and label because of different BGS levels. By using our proposed framework, those problems were minimized, and the accuracy of CBF estimation was improved. Moreover, the functional ASL study showed improved detection of visual and motor activation when applying the framework as compared to conventional motion correction, as well as when motion correction was completely omitted.ConclusionWhen combining BGS‐ASL with SMS‐EPI, particular attention is needed to avoid artefacts introduced by motion correction. With the proposed framework, these issues are minimized.
Highlights
Simultaneous multi‐slice (SMS, a.k.a multiband) EPI excites multiple slices at the same time and reduces the number of excitation pulses per TR.[1,2] This approach has been proven to be very advantageous for FMRI and DTI.[1,3] Whereas for FMRI and DTI, the prime advantage of simultaneous multi‐slice (SMS)‐ EPI is the acceleration of the acquisition by shortening TR, for arterial spin labeling (ASL) this is much less beneficial because the preparation module for labeling and post‐labeling delay (PLD) is the main time‐consuming part of the sequence and not the readout
Whereas for FMRI and DTI, the prime advantage of SMS‐ EPI is the acceleration of the acquisition by shortening TR, for arterial spin labeling (ASL) this is much less beneficial because the preparation module for labeling and post‐labeling delay (PLD) is the main time‐consuming part of the sequence and not the readout
In multi‐slice ASL, optimal background suppression (BGS) is usually timed to occur for the first slice, whereas longitudinal relaxation will reduce the effectiveness of BGS for more distal slices that are typically acquired hundreds of milliseconds later than the first slice
Summary
Horizon2020 program CDS‐QUAMRI, Grant/Award Number 634541; EPSRC UK, Grant/Award Number: EP/ P012361/1; UK Royal Academy of Engineering; Wellcome Trust, Grant/Award Number: 203139/Z/16/Z. Purpose: When using simultaneous multi‐slice (SMS) EPI for background suppressed (BGS) arterial spin labeling (ASL), correction of through‐plane motion could introduce artefacts, because the slices with most effective BGS are adjacent to slices with the least BGS. Use of the M0 image as the reference for registration allowed 82% improvement of motion estimation for through‐plane motion, it still led to residual subtraction errors caused by different static tissue signal between control and label because of different BGS levels. KEYWORDS arterial spin labeling (ASL), background suppression, perfusion image, simultaneous multi‐slice (SMS).
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