Brain MRI CO(2) Stress Testing: A Pilot Study in Patients with Concussion

BACKGROUND: There is a real need for quantifiable neuro-imaging biomarkers in concussion. Here we outline a brain BOLD-MRI CO(2) stress test to assess the condition. METHODS: This study was approved by the REB at the University of Manitoba. A group of volunteers without prior concussion were compared to post-concussion syndrome (PCS) patients – both symptomatic and recovered asymptomatic. Five 3-minute periods of BOLD imaging at 3.0 T were studied – baseline 1 (BL1– at basal CO(2) tension), hypocapnia (CO(2) decreased ∼5 mmHg), BL2, hypercapnia (CO(2) increased ∼10 mmHg) and BL3. Data were processed using statistical parametric mapping (SPM) for 1(st) level analysis to compare each subject’s response to the CO(2) stress at the p = 0.001 level. A 2(nd) level analysis compared each PCS patient’s response to the mean response of the control subjects at the p = 0.05 level. RESULTS: We report on 5 control subjects, 8 symptomatic and 4 asymptomatic PCS patients. Both increased and decreased response to CO(2) was seen in all PCS patients in the 2(nd) level analysis. The responses were quantified as reactive voxel counts: whole brain voxel counts (2.0±1.6%, p = 0.012 for symptomatic patients for CO(2) response < controls and 3.0±5.1%, p = 0.139 for CO(2) response > controls: 0.49±0.31%, p = 0.053 for asymptomatic patients for CO(2) response < controls and 4.4±6.8%, p = 0.281 for CO(2) response > controls). CONCLUSIONS: Quantifiable alterations in regional cerebrovascular responsiveness are present in concussion patients during provocative CO(2) challenge and BOLD MRI and not in healthy controls. Future longitudinal studies must aim to clarify the relationship between CO(2) responsiveness and individual patient symptoms and outcomes.