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The distortions of the free water model for diffusion MRI data when assuming single compartment relaxometry and

Uran Ferizi1, Eva M Müller-Oehring1, Eric T Peterson2

  • 1Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA, United States of America.

Physics in Medicine and Biology
|January 13, 2023
PubMed

Insights

A specific diffusion MRI model improves accuracy by including proton density, T1, and T2 parameters. This enhanced model reduces bias in free water fraction estimation compared to simplified models.

Area of Science:

  • Diffusion MRI (dMRI) and quantitative imaging.
  • Biophysical modeling of biological tissues.
  • Medical image analysis and interpretation.

Background:

  • Diffusion MRI (dMRI) models often simplify the underlying biophysical processes.
  • The simplified free water model assumes uniform proton density (PD), T1, and T2.
  • Accurate estimation of tissue microstructural properties is crucial for dMRI applications.

Purpose of the Study:

  • To quantify the bias introduced by a simplified free water diffusion MRI model.
  • To compare the simplified model against a specific model incorporating compartment-specific PD, T1, and T2.
  • To evaluate the impact of model choice on diffusion parameter estimation in synthetic and in vivo data.

Main Methods:

  • Development and comparison of a simplified and a specific free water diffusion MRI model.
  • Simulation of dMRI data with varying PD, T1, T2, and signal-to-noise ratio (SNR).
  • Fitting both models to synthetic data and an in vivo healthy brain dMRI dataset.

Main Results:

  • The specific model demonstrated higher accuracy and precision in estimating the free water volume fraction (f).
  • Bias in simplified model's f estimation increased with SNR and was most pronounced for mid-range ground-truth f.
  • In vivo white matter regions showed lower specific f compared to simplified f estimates.

Conclusions:

  • Incorporating compartment-specific PD, T1, and T2 into dMRI models significantly improves parameter estimation.
  • The specific model effectively reduces the bias in free water compartmental volume fraction estimation.
  • Diffusion parameters remain robust to minor model specification differences, but volume fraction estimation benefits from specificity.
Keywords:
T1 and T2 relaxometrybrain microstructurediffusion MRIfree waterproton density

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