Hemodynamic modeling of aspirin effects on BOLD responses at 7T

Aspirin is considered a potential confound for functional magnetic resonance imaging (fMRI) studies. This is because aspirin affects the synthesis of prostaglandin, a vasoactive mediator centrally involved in neurovascular coupling, a process that underlies the blood oxygenated level dependent (BOLD) response. Aspirin-induced changes in BOLD signal are a potential confound for fMRI studies of patients (e.g. with cardiovascular conditions or stroke) who receive low-dose aspirin prophylactically and are compared to healthy controls that do not take aspirin. To examine the severity of this potential confound, we combined high field (7 Tesla) MRI during a simple hand movement task with a biophysically informed hemodynamic model. Comparing elderly volunteers with vs. without aspirin medication, we tested for putative effects of low-dose chronic aspirin on the BOLD response. Specifically, we fitted hemodynamic models to BOLD signal time courses from 14 regions of the human motor system and examined whether model parameter estimates were significantly altered by aspirin. While our analyses indicate that hemodynamics differed across regions, consistent with the known regional variability of the BOLD response, we neither found a significant main effect of aspirin (i.e., an average effect across brain regions) nor an expected drug×region interaction. While our sample size is not sufficiently large to rule out small-to-medium global effects of aspirin, we had adequate statistical power for detecting the expected interaction. Altogether, our analysis suggests that low-dose aspirin, as used for prophylactic purposes, does not strongly affect BOLD signals and may not represent a critical confound for fMRI studies. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by the René and Susanne Braginsky Foundation (KES) and the University of Zurich (KES) as well as by the ETH Zurich Postdoctoral Fellowship Program (SF), the Marie Curie Actions for People COFUND Program (SF), and the University of Zurich Forschungskredit Postdoc (SF). ### Author Declarations All relevant ethical guidelines have been followed; any necessary IRB and/or ethics committee approvals have been obtained and details of the IRB/oversight body are included in the manuscript. Yes All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Upon acceptance of this paper, the code used for the analysis as well as the BOLD signal time series data will be made publicly available. Furthermore, the code has been cross-checked internally for reproducibility. All analysis streams were performed on the Euler cluster at ETH Zurich. More information on the computational power can be found at .