Physiological basis of vascular autocalibration (VasA): Comparison to hypercapnia calibration methods

• Published in: Magnetic resonance in medicine Vol. 78; no. 3; pp. 1168 - 1173
• Main Authors: Kazan, Samira M., Huber, Laurentius, Flandin, Guillaume, Ivanov, Dimo, Bandettini, Peter, Weiskopf, Nikolaus
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.09.2017; John Wiley and Sons Inc
• Subjects: autorescaling; Blood volume; BOLD calibration; BOLD fMRI; Calibration; Functional magnetic resonance imaging; Hypercapnia; Magnetic resonance imaging; Mapping; Medical research; Medicine; Note—Biophysics and Basic Biomedical Research; Reactivity; SPM toolbox; Statistical methods; Statistics; Stimulation; VasA; VasA toolbox; vascular reactivity; Vascularization; vascularization differences; Visual stimuli; autorescaling; VasA; VasA toolbox; vascular reactivity; SPM toolbox; BOLD calibration; BOLD fMRI; vascularization differences
• ISSN: 0740-3194; 1522-2594; 1522-2594
• DOI: 10.1002/mrm.26494

Purpose The statistical power of functional MRI (fMRI) group studies is significantly hampered by high intersubject spatial and magnitude variance. We recently presented a vascular autocalibration method (VasA) to account for vascularization differences between subjects and hence improve the sensitivity in group studies. Here, we validate the novel calibration method by means of direct comparisons of VasA with more established measures of baseline venous blood volume (and indirectly vascular reactivity), the M‐value. Methods Seven healthy volunteers participated in two 7 T (T) fMRI experiments to compare M‐values with VasA estimates: (i) a hypercapnia experiment to estimate voxelwise M‐value maps, and (ii) an fMRI experiment using visual stimulation to estimate voxelwise VasA maps. Results We show that VasA and M‐value calibration maps show the same spatial profile, providing strong evidence that VasA is driven by local variations in vascular reactivity as reflected in the M‐value. Conclusion The agreement of vascular reactivity maps obtained with VasA when compared with M‐value maps confirms empirically the hypothesis that the VasA method is an adequate tool to account for variations in fMRI response amplitudes caused by vascular reactivity differences in healthy volunteers. VasA can therefore directly account for them and increase the statistical power of group studies. The VasA toolbox is available as a statistical parametric mapping (SPM) toolbox, facilitating its general application. Magn Reson Med 78:1168–1173, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.