Intravascular contrast agent T2* relaxivity in brain tissue

Area of Science:

• Magnetic Resonance Imaging
• Medical Physics
• Neuroimaging

Background:

• Dynamic susceptibility-weighted contrast-enhanced (DSC) MRI perfusion relies on contrast agent (CA) concentration estimation.
• Linearity assumptions between relaxation and CA concentration can be inaccurate due to compartmentalization and magnetic field effects.
• Existing methods for determining CA relaxivity in microvasculature are limited.

Purpose of the Study:

• To empirically test a non-linear expression based on the static dephasing regime (SDR) against a linear approximation for DSC MRI.
• To evaluate the accuracy of cerebral blood volume (CBV) estimation using both linear and non-linear models.
• To assess the performance of the non-linear model across different magnetic field strengths and echo times.

Main Methods:

• Converted signal-time curves from white matter (WM) and grey matter (GM) to concentration time curves (CTCs) using linear and non-linear formulations.
• Optimized parameters for both models by comparing WM-derived CBV with arterial CTCs in healthy subjects at 3T.
• Applied optimized parameters to calculate CBV in WM and GM of healthy subjects (3T) and meningioma patients (1.5T).

Main Results:

• The non-linear SDR formulation provided an acceptable functional form for tissue relaxivity.
• Reliable CBV estimates were achieved using the non-linear model at varying field strengths (1.5T and 3T) and echo times.
• The non-linear approach demonstrated improved accuracy compared to the linear approximation.

Conclusions:

• A non-linear SDR model offers a more accurate approach for DSC MRI perfusion measurements.
• This method enhances the reliability of CBV quantification in both healthy and diseased brain tissues.
• The findings support the use of non-linear relaxivity models for improved DSC MRI analysis.