Correlation Between Minimum Apparent Diffusion Coefficient (ADC_min) and Tumor Cellularity: A Meta-analysis

Diffusion-weighted imaging (DWI) is a magnetic resonance imaging (MRI) technique based on measure of water diffusion that can provide information about tissue microstructure, especially about cell count. Increase of cell density induces restriction of water diffusion and decreases apparent diffusion coefficient (ADC). ADC can be divided into three sub-parameters: ADC minimum or ADC_min, mean ADC or ADC_mean and ADC maximum or ADC_max Some studies have suggested that ADC_min shows stronger correlations with cell count in comparison to other ADC fractions and may be used as a parameter for estimation of tumor cellularity. The aim of the present meta-analysis was to summarize correlation coefficients between ADC_min and cellularity in different tumors based on large patient data.

For this analysis, MEDLINE database was screened for associations between ADC and cell count in different tumors up to September 2016. For this work, only data regarding ADC_min were included. Overall, 12 publications with 317 patients were identified. Spearman's correlation coefficient was used to analyze associations between ADC_min and cellularity. The reported Pearson correlation coefficients in some publications were converted into Spearman correlation coefficients.

The pooled correlation coefficient for all included studies was ρ=-0.59 (95% confidence interval (CI)=-0.72 to -0.45), heterogeneity Tau²=0.04 (p<0.0001), I²=73%, test for overall effect Z=8.67 (p<0.00001).

ADC_min correlated moderately with tumor cellularity. The calculated correlation coefficient is not stronger in comparison to the reported coefficient for ADC_mean and, therefore, ADC_min does not represent a better means to reflect cellularity.