Functional MRI using intravascular contrast agents: detrending of the relative cerebrovascular (rCBV) time course

Area of Science:

• Neuroimaging
• Pharmacology
• Biophysics

Background:

• Pharmacological fMRI in animal models uses blood pool contrast agents to measure cerebral blood volume changes.
• Background signal drift from contrast agent washout can confound interpretation of neural activation signals.
• Time-course detrending is crucial for accurate analysis when signal drift is significant.

Purpose of the Study:

• To evaluate detrending methods for estimating background signal drift caused by contrast agent washout in animal fMRI.
• To identify a robust approach for correcting signal drift in pharmacological fMRI experiments.

Main Methods:

• Comparison of different detrending approaches, including constant background approximation, unconstrained fits, and a constrained fit of a mono-exponential washout model.
• Application of methods to fMRI studies in rats investigating responses to rapid pharmacological challenges (cocaine, amphetamine).

Main Results:

• A constrained fit of a mono-exponential washout model demonstrated higher accuracy than constant background approximation and unconstrained fits.
• The constrained fitting approach enabled accurate estimation of contrast agent washout.
• Shorter baseline periods were required with the constrained fitting method compared to unconstrained extrapolation.

Conclusions:

• Constrained mono-exponential washout model fitting is a robust and accurate detrending method for pharmacological fMRI in rats.
• This approach improves the interpretation of functional responses to rapid pharmacological challenges.
• The method reduces overall experiment duration by allowing shorter baseline recordings.