Evaluating the Diagnostic Performance of MR Cytometry Imaging in Differentiating Benign and Malignant Breast Tumors.

Abstract

Background: MR cytometry is a class of diffusion-MRI-based methods that characterize tumor microstructures at the cellular level. It involves multicompartmental biophysical modeling of multi-b and multiple diffusion time data to generate microstructural parameters, which may improve differentiation of benign and malignant breast tumors.

Purpose: To implement MR cytometry imaging with transcytolemmal water exchange (JOINT and EXCHANGE) to differentiate benign and malignant breast tumors, and to compare the classification efficacy of IMPULSED, JOINT, and EXCHANGE.

Study type: Prospective.

Subjects: 115 patients with pathologically confirmed breast tumors (25 benign and 90 malignant).

Field strength/sequence: 3T; pulsed gradient spin-echo (PGSE) diffusion-weighted imaging (DWI) and oscillating gradient spin-echo (OGSE) DWI at 25 and 50 Hz.

Assessment: Tumor regions were delineated by two radiologists on DWI. Time-dependent ADC and microstructural parameters (cell diameter $d$ , intracellular volume fraction $v_{\text{in}}$ , water exchange rate constant $k_{\text{in}}$ , extracellular diffusivity $D_{\mathrm{ex}}$ and intracellular intrinsic diffusivity $D_{\text{in}}$ ) were calculated. Classification performance was assessed in the original cohort and in an age-adjusted cohort (excluding older malignant patients to eliminate significant age differences).

Statistical tests: Mann-Whitney U-tests compared benign and malignant tumor values. Multivariable logistic regression used a stepwise approach based on the likelihood ratio test. The area under the receiver operating characteristic (AUC) was computed and compared by using the DeLong test.

Results: In the full analysis (25 benign, 90 malignant), microstructural parameters from methods incorporating transcytolemmal water exchange (JOINT and EXCHANGE) demonstrated superior performance (AUC: ADC, 0.822; IMPULSED, 0.840; JOINT, 0.902; EXCHANGE, 0.905). Combining different metrics further improved classification (AUC: IMPULSED [ $d$ , $v_{\text{in}}$ ], 0.942; JOINT [ $d$ , $v_{\text{in}}$ ], 0.956; EXCHANGE [ $d$ , $k_{\text{in}}$ ], 0.954; [ ${\mathrm{ADC}}_{\text{PGSE}},{\mathrm{ADC}}_{25\mathrm{Hz}},\mathrm{AD}{C}_{50\mathrm{Hz}}$ ], 0.927). These improvements were also observed in the age-adjusted analysis (25 benign, 42 malignant).

Data conclusion: MR cytometry outperformed ADC in distinguishing benign and malignant breast tumors. Incorporating transcytolemmal water exchange into biophysical modeling further improved its diagnostic performance.

Evidence level: 1 Technical Efficacy: Stage 2.