Coherent flow effects on IVIM-based perfusion measurements: A phantom study in 3 T

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Neuroimaging

Background:

• Quantitative, non-invasive measurement of perfusion is a challenge in MRI.
• Intravoxel Incoherent Motion (IVIM) technique, based on Diffusion-Weighted Imaging (DWI), estimates perfusion at the sub-voxel level.
• IVIM parameters like perfusion fraction (f) and pseudo-diffusion coefficient (D*) are key, but direct conversion to Cerebral Blood Flow (CBF) needs validation.

Purpose of the Study:

• Investigate the accuracy of IVIM-based perfusion measures.
• Explore the influence of coherent flow on voxel signal.
• Assess the relationship between ground truth CBF, IVIM parameters, and calculated CBF.

Main Methods:

• Constructed a phantom with agarose gel and tubes mimicking arterioles with regulated flow velocity.
• Simulated Cerebral Blood Volume (CBV) and CBF values by controlling flow in tubes.
• Scanned the phantom using an IVIM-optimized DWI protocol and processed data for IVIM measures.
• Proposed a model based on extended Bloch-Torrey equations with a coherent flow term.

Main Results:

• IVIM yielded reasonable estimates of CBF and CBV within physiological flow ranges (0.5-2 mm/s).
• Consistent overestimation of flow (up to 200%) was observed at higher velocities.
• Higher velocities showed significant overestimation, especially in arterial or vein-like flow conditions.

Conclusions:

• IVIM is a viable technique for estimating brain perfusion and blood volume within relevant physiological flow ranges.
• The accuracy of IVIM for CBF estimation is limited at higher flow velocities due to overestimation.
• Further research and model refinement are needed to address discrepancies at high flow rates.