A practical modification to a resting state fMRI protocol for improved characterization of cerebrovascular function.

Cerebrovascular reactivity (CVR), defined here as the Blood Oxygenation Level Dependent (BOLD) response to a CO2 pressure change, is a useful metric of cerebrovascular function. Both the amplitude and the timing (hemodynamic lag) of the CVR response can bring insight into the nature of a cerebrovascular pathology and aid in understanding noise confounds when using functional Magnetic Resonance Imaging (fMRI) to study neural activity. This research assessed a practical modification to a typical resting-state fMRI protocol, to improve the characterization of cerebrovascular function. In 9 healthy subjects, we modelled CVR and lag in three resting-state data segments, and in data segments which added a 2-3 minute breathing task to the start of a resting-state segment. Two different breathing tasks were used to induce fluctuations in arterial CO2 pressure: a breath-hold task to induce hypercapnia (CO2 increase) and a cued deep breathing task to induce hypocapnia (CO2 decrease). Our analysis produced voxel-wise estimates of the amplitude (CVR) and timing (lag) of the BOLD-fMRI response to CO2 by systematically shifting the CO2 regressor in time to optimize the model fit. This optimization inherently increases gray matter CVR values and fit statistics. The inclusion of a simple breathing task, compared to a resting-state scan only, increases the number of voxels in the brain that have a significant relationship between CO2 and BOLD-fMRI signals, and improves our confidence in the plausibility of voxel-wise CVR and hemodynamic lag estimates. We demonstrate the clinical utility and feasibility of this protocol in an incidental finding of Moyamoya disease, and explore the possibilities and challenges of using this protocol in younger populations. This hybrid protocol has direct applications for CVR mapping in both research and clinical settings and wider applications for fMRI denoising and interpretation.

Voxelwise optimization of hemodynamic lags to improve regional CVR estimates in breath-hold fMRI.

Cerebrovascular Reactivity (CVR), the responsiveness of blood vessels to a vasodilatory stimulus, is an important indicator of cerebrovascular health. Assessing CVR with fMRI, we can measure the change in the Blood Oxygen Level Dependent (BOLD) response induced by a change in CO2 pressure (%BOLD/mmHg). However, there exists a temporal offset between the recorded CO2 pressure and the local BOLD response, due to both measurement and physiological delays. If this offset is not corrected for, voxel-wise CVR values will not be accurate. In this paper, we propose a framework for mapping hemodynamic lag in breath-hold fMRI data. As breath-hold tasks drive task-correlated head motion artifacts in BOLD fMRI data, our framework for lag estimation fits a model that includes polynomial terms and head motion parameters, as well as a shifted variant of the CO2 regressor (±9 s in 0.3 s increments), and the hemodynamic lag at each voxel is the shift producing the maximum total model R2 within physiological constraints. This approach is evaluated in 8 subjects with multi-echo fMRI data, resulting in robust maps of hemodynamic delay that show consistent regional variation across subjects, and improved contrast-to-noise compared to methods where motion regression is ignored or performed earlier in preprocessing.Clinical Relevance- We map hemodynamic lag using breathhold fMRI, providing insight into vascular transit times and improving the regional accuracy of cerebrovascular reactivity measurements.

Feasibility of a Modified Ride-on Car Intervention on Play Behaviors during an Inclusive Playgroup.

AIMS: Children with mobility related disabilities often experience limited participation and access to social interactions. An emerging pediatric powered mobility device are modified ride-on cars that provide self-directed mobility experiences to children with disabilities. This study aimed to determine: (1) the feasibility of a modified ride-on car intervention during an inclusive playgroup, (2) the effect of a modified ride-on car intervention on the play behaviors of children with and without mobility related disabilities. METHOD: A single-subject research design was implemented. Thirteen children participated in a weekly inclusive playgroup. The five children with mobility related disabilities were provided modified ride-on cars during the intervention. Children's play behaviors were classified with Howes' Peer Play Scale. Intervention effects were examined using nonoverlap of all pairs (NAP). RESULTS: The intervention was feasible based on participants' good attendance, retention rates, and successful use of modified ride-on cars. Overall children did not experience significant changes in play behaviors, with a few exceptions for decreased solitary, and increased parallel play, and/or direct peer interaction, among children with mobility related disabilities. Future research could examine modified ride-on car use by children with mobility related disabilities focusing on changes in unique play interactions between children with and without disabilities.