Simultaneous multi‐slice (SMS) acquisition enhances the sensitivity of hemodynamic mapping using gas challenges

Abstract

Hemodynamic mapping using gas inhalation has received increasing interests in recent years. Cerebrovascular reactivity (CVR), which reflects the ability of the brain vasculature to dilate in response to a vasoactive stimulus, can be measured with CO2 inhalation while continuously acquiring BOLD MRI images. Cerebral blood volume (CBV) can be measured with O2 inhalation. These hemodynamic mapping methods are appealing because of their absence of gadolinium contrast agent, ability to assess both baseline perfusion and vascular reserve, and utility in calibrating fMRI signal. However, like other functional and physiological indices, a major drawback of these measurements is their poor sensitivity and reliability. Simultaneous multi-slice (SMS) EPI is a fast-imaging technology that allows the excitation and acquisition of multiple 2D slices simultaneously, and has been shown to enhance the sensitivity of several MRI applications. To our knowledge, the benefit of SMS in gas inhalation imaging has not been investigated. In this work, we compare the sensitivity of CO2 and O2 inhalation data collected using SMS factor 2 (SMS 2) and SMS factor 3 (SMS 3) with those using conventional EPI (SMS 1). We showed that the sensitivity of SMS scans was significantly (p=0.01) higher than that of conventional EPI, although no difference was found between SMS 2 and SMS 3 (p=0.3). On a voxel-wise level, approximately 20-30% of voxels in the brain showed a significant enhancement in sensitivity when using SMS compared to conventional EPI, with other voxels showing an increase but not reaching statistical significance. When using SMS, the scan duration can be reduced by half while maintaining the sensitivity of a conventional EPI. The availability of a sensitive acquisition technique can further enhance the potential of gas inhalation MRI in clinical applications.

Evaluation of cerebrovascular reserve in patients with cerebrovascular diseases using resting-state MRI: A feasibility study

“…It should also be noted that rs-CVR method has been directly validated with CO2based CVR in healthy controls [18]. The spatial correlation between rs-CVR and CO2-based CVR was 0.88 in healthy controls, which was similar to the intra-subject correlations of rs-CVR maps (0.91) [18] and CO2-based CVR maps (0.93) [40].…”

Cerebrovascular Reactivity Measurement Using Magnetic Resonance Imaging: A Systematic Review

“…Use of EPI with parallel imaging compared to spiral imaging, reduced signal loss due to susceptibility-induced magnetic field gradients in BOLD-CVR measurements without affecting sensitivity, which was defined as the CVR t-statistic (n = 5) (Winter et al, 2009). Furthermore, one study (n = 5) showed that using simultaneous multi-slice acceleration of factor 2 and 3, can reduce scan duration by at least a half compared to conventional EPI while maintaining the CVR sensitivity (Ravi et al, 2016a). Compared to single-echo ASL or BOLD EPI, a multi-echo (four echoes) EPI acquisition followed by T2 * fitting of the signal decay had higher inter-scan repeatability of breath-hold CVR analysed across voxels, CVR sensitivity and test-retest reliability analysed using the intra-class correlation coefficient (n = 14) (Cohen and Wang, 2019).…”

Cerebrovascular reactivity measurement in cerebral small vessel disease: Rationale and reproducibility of a protocol for MRI acquisition and image processing

“…Finally, the increasing availability of simultaneous multislice and other parallel imaging techniques on commercial MR scanners will facilitate higher spatial and/or temporal resolution in future studies. 38 The ''HARNESS'' (Harmonising Brain Imaging Methods for Vascular Contributions to Neurodegeneration) collaboration, currently in progress, and ongoing discussions within the wider CVR community, should result in further recommendations and guidance relevant to the conduct of CVR experiments in SVD research.…”