A generalized procedure for calibrated MRI incorporating hyperoxia and hypercapnia

Area of Science:

• Neuroimaging
• Physiology
• Medical Physics

Background:

• Calibrated MRI techniques estimate resting deoxyhemoglobin (M) and cerebral metabolic rate of oxygen consumption (CMRO2) using BOLD and CBF signals during respiratory challenges.
• Previous methods relied on hypercapnia or hyperoxia alone, limiting accuracy and requiring significant extrapolation.
• Accurate M estimation is crucial for reliable CMRO2 change quantification during functional tasks.

Purpose of the Study:

• To present a generalized BOLD signal model applicable to simultaneous hypercapnia and hyperoxia.
• To enable more robust and accurate estimation of M and subsequent CMRO2 changes.
• To validate the generalized model against previous hypercapnia and hyperoxia-only approaches.

Main Methods:

• Developed a generalized BOLD signal model accommodating hybrid respiratory challenges (simultaneous hypercapnia and hyperoxia).
• Applied the model to estimate M and CMRO2 changes during a visual task.
• Compared results with those obtained using hypercapnia or hyperoxia alone.

Main Results:

• The generalized model yielded higher M estimates (7.6 ± 2.6) compared to hypercapnia (5.6 ± 1.8) or hyperoxia alone (4.5 ± 1.5) in visual areas.
• The new approach provided more robust spatial distribution of M, reflecting tissue deoxyhemoglobin more accurately.
• Improved accuracy in estimating evoked CMRO2 changes during the visual task.

Conclusions:

• The generalized BOLD signal model offers a more accurate and robust method for estimating M and CMRO2 changes.
• Utilizing simultaneous hypercapnia and hyperoxia reduces extrapolation, leading to improved neuroimaging analysis.
• This technique enhances the reliability of quantitative MRI measurements of brain metabolism.