Dual-Phase ADC Modelling of Breast Masses in Diffusion-Weighted Imaging: Comparison with Histopathologic Findings

Abstract

IntroductionDiffusion-weighted imaging (DWI) utilizes diffusion signal attenuated due to the random microscopic motion of water molecules influenced by cell density, membrane integrity, tissue microstructure, perfusion and diffusion heterogeneity within the tissue (1). When compared with benign lesions and healthy tissue, more restricted water mobility of malignant lesions engenders slower attenuation of the diffusion signal captured from a set of images acquired with different degrees of diffusion weighting (reported as b-value) (2).Quantitative diagnosis of cancer from DWI relies on metrics computed as the parameters of a "signal attenuation" model fitted to the diffusion signal data. The need for reliable and precise metrics motivates new studies on development of advanced models for better fittings to the diffusion signal data or advanced methods for optimized estimation of diffusion metrics (3). There exist several advanced exponential signal attenuation models such as stretched exponential (4), bi-exponential (known as intravoxel incoherent motion) (5), statistical (6) and kurtosis (7) capable of describing complex diffusion processes of the breast tissue. However, the parameters derived from these models are difficult to estimate and quite complex for use in diagnosis. For instance, physiological basis of the heterogeneity index of the stretched exponential model is reported to be uncertain and likewise pseudo-diffusion coefficient of the biexponential model is thought to be unreliable (8). On the other hand, these models involve several parameters that complicate both the diffusion estimation process and the diffusion weighted imaging protocol. To get accurate diffusion estimates, the initial value and the limits for any model parameter should be determined very carefully and an appropriate optimization method should be employed (9). To reach consistent numerical solutions, the number of b-values of the diffusion weighted imaging protocol must set to be more than the number of parameters in the model and Eur J Breast Health 2018; 14: 85-92 DOI: 10.5152/ejbh.2018.3829 85 ABSTRACT Objective: To investigate the diagnostic value of dual-phase apparent diffusion coefficient (ADC) compared to traditional ADC values in quantitative diffusion-weighted imaging (DWI) for differentiating between benign and malignant breast masses. Materials and Methods:Diffusion-weighted images of pathologically confirmed 88 benign and 85 malignant lesions acquired using a 3.0T MR scanner were analyzed. Small region-of-interests focusing on the highest signal intensity of lesions were used. Lesion ADC estimates were obtained separately from all b-value images (ADC; b=50, 400 and 800s/mm 2 ), lower b-value images (ADC low ; b=50 and 400s/mm 2 ) and higher b-value images (ADC high ; b=400 and 800s/mm 2 ). A set of dual-phase ADC (dpADC) models were constructed using ADC low , ADC high and a perfusion influence factor ranging from 0 to 1. Results:Strong positive correlation is observable between ADC and all dpADCs (ρ=0.80-1.00). ...