Comparing BOLD and VASO-CBV population receptive field estimates in human visual cortex

Ícaro A.F Oliveira,Yuxuan Cai,Shir Hofstetter,Jeroen C.W Siero,Wietske Van Der Zwaag,Serge O Dumoulin

doi:10.1016/j.neuroimage.2021.118868

Abstract

Vascular Space Occupancy (VASO) is an alternative fMRI approach based on changes in Cerebral Blood Volume (CBV). VASO-CBV fMRI can provide higher spatial specificity than the blood oxygenation level-dependent (BOLD) method because the CBV response is thought to be limited to smaller vessels. To investigate how this technique compares to BOLD fMRI for cognitive neuroscience applications, we compared population receptive field (pRF) mapping estimates between BOLD and VASO-CBV. We hypothesized that VASO-CBV would elicit distinct pRF properties compared to BOLD. Specifically, since pRF size estimates also depend on vascular sources, we hypothesized that reduced vascular blurring might yield narrower pRFs for VASO-CBV measurements. We used a VASO sequence with a double readout 3D EPI sequence at 7T to simultaneously measure VASO-CBV and BOLD responses in the visual cortex while participants viewed conventional pRF mapping stimuli. Both VASO-CBV and BOLD images show similar eccentricity and polar angle maps across all participants. Compared to BOLD-based measurements, VASO-CBV yielded lower tSNR and variance explained. The pRF size changed with eccentricity similarly for VASO-CBV and BOLD, and the pRF size estimates were similar for VASO-CBV and BOLD, even when we equate variance explained between VASO-CBV and BOLD. This result suggests that the vascular component of the pRF size is not dominating in either VASO-CBV or BOLD.

Highlights

The majority of functional MRI studies employ blood oxygenation level-dependent (BOLD) contrast (Glover, 2011; Ogawa et al, 1990)
The population receptive field (pRF) size changed with eccentricity for Vascular Space Occupancy (VASO)-cerebral blood volume (CBV) and BOLD, and the pRF size estimates were similar for VASO-CBV and BOLD, even when we equate variance explained between VASO-CBV and BOLD
We evaluated four different slice orientations to find the optimal orientation for visual responses in a VASO-CBV experiment: (I) Aligned with the Anterior-Posterior Commissure covering the calcarine sulcus with the phase encoding in the Anterior-Posterior direction, (II) parallel to the calcarine sulcus with phase encoding in the Anterior-Posterior direction, (III) aligned with the cerebellar superior surface, with phase encoding in the Right-Left direction, and (IV) perpendicular to the calcarine sulcus with phase encoding in the RightLeft direction (Fig. 1A)

Summary

Introduction

The majority of functional MRI (fMRI) studies employ blood oxygenation level-dependent (BOLD) contrast (Glover, 2011; Ogawa et al, 1990). The Gradient Echo (GE) BOLD sequence is the typical method of choice, mainly because of its superior sensitivity, available Signal-to-Noise Ratio (SNR), and high coverage (Havlicek and Uludağ, 2020). This sequence suffers from limited spatial specificity due to contamination of the functional signal with draining and pial veins effect (Kim and Ogawa, 2012; Menon, 2002; Uludaǧ et al, 2009 ). VASO-CBV contrast promises higher microvascular specificity since it is sensitive to arteriole and post-arterial CBV changes, resulting in better spatial localization of the neuronal activity with reduced draining vein contamination than BOLD (Huber et al, 2014; Jin and Kim, 2008)

Methods

Results

Discussion

Conclusion