Blood-oxygenation-level-dependent (BOLD) MRI responses to CO₂ and O₂ inhalation in brain gliomas

Cerebrovascular abnormalities are intricately involved in gliomas. While static cerebrovascular properties such as cerebral blood flow, volume, and permeability have been extensively studied, dynamic vascular parameters have not been fully understood. This study aimed to characterize the vascular responses to CO₂ and O₂ inhalation in brain gliomas.

In 15 glioma patients, concomitant CO₂ and O₂ inhalation was applied while BOLD MR images were continuously acquired for nine minutes, resulting in the measurement of O₂-reactivity, CO₂-reactivity, and bolus arrival time (BAT). Vascular parameters were compared between the tumor regions and contralateral healthy tissue using Student t-tests. The dependence of vascular parameters on glioma grade, glioma subtypes, and molecular biomarkers were assessed using a multiple linear regression.

Visual inspection suggested that reliable O₂-reactivity, CO₂-reactivity, and BAT maps could be obtained in every patient. Compared to the contralateral healthy tissue, glioma regions on average revealed a diminished O₂-reactivity (p < 0.001) and CO₂-reactivity (p < 0.001), but a lengthened BAT (p < 0.001). Intra-tumoral heterogeneity in the vascular parameters between core and periphery was also observed. Astrocytomas had a lower CO₂-reactivity (p = 0.014) and a longer BAT (p = 0.012) relative to oligodendrogliomas. Glioma grade had no association with O₂-reactivity, CO₂-reactivity, or BAT. Patients who lost ATRX expression had a lower CO₂- and O₂-reactivity (p = 0.005 and p = 0.035) compared to patients who retained ATRX expression.

Gliomas are associated with abnormal CO₂- and O₂-reactivity measured with MRI. These dynamic parameters may provide new insights into the vascular pathophysiology in gliomas.