Apparent diffusion coefficient (ADC) as a single predictor is insufficient to predict cellular density in gliomas

Area of Science:

• Neuro-oncology
• Medical imaging
• Histopathology

Background:

• Cellular density (CD) in gliomas is crucial for treatment decisions.
• Diffusion MRI, using Apparent Diffusion Coefficient (ADC) measurements, is a common method for estimating CD.
• Theoretically, higher CD should lead to lower ADC due to hindered diffusion by cell membranes.

Purpose of the Study:

• To empirically assess the relationship between cellular density and ADC in gliomas.
• To compare empirical findings with the theoretical inverse relationship between CD and ADC.

Main Methods:

• Collected 52 spatially localized biopsies from 23 untreated glioma patients.
• Measured CD using quantitative histopathology (nuclei/mm²).
• Included 52 "virtual biopsies" from normal white matter with CD inferred from literature for balance.

Main Results:

• Empirical data revealed a moderate positive correlation between CD and ADC (r=0.48).
• The observed slope was +4.6 x 10⁶ cells·s/mm⁴.
• This contradicts the theoretical prediction of a negative correlation with a slope of -1.72 x 10⁶ cells·s/mm⁴.

Conclusions:

• Empirical CD-ADC correlations in glioma differ from current theoretical models.
• The observed relationship is positive, reversing the theoretically expected negative correlation.
• Histopathological validation is essential for refining image-based CD estimation in gliomas.