Effect of region of interest size in quantitative diffusion-weighted magnetic resonance imaging of the breast

Introduction

In breast MRI, morphological and dynamic enhancement features determine whether a lesion is benign or malignant but specificity is low. Diffusion-weighted magnetic resonance imaging (DW-MRI) measures microscopic motion of water and gives quantitative measurement known as the apparent diffusion coefficient (ADC). This study was conducted to determine whether the whole of the lesion should be included within the region of interest (ROI) or whether a small ROI would differentiate benign from malignant disease.

Methods

Fifteen female patients with 15 suspicious lesions were imaged on a 3T MRI machine (Philips HealthCare, Best, the Netherlands). DWI-MRI was performed with b-values of 0, 150, 800 s/mm² using single-shot SE-EPI (TR/ TE = 9,543 ms/50 ms). The ROI of the lesion and of fibroglandular tissue was used to calculate ADC values. Histology or follow-up data were available for all lesions.

Results

The mean ADC value of malignant lesions (13) from two small ROIs was 0.954 ± 0.145 mm²/second and for benign (2) was 1.69 ± 0.17 mm²/ second (Figure 1a). The ADC values for the whole lesion were 1.027 ± 0.23 mm²/second and 1.78 ± 0.293 mm²/second, respectively (Figure 1b).

Figure 1

Box plot of ADC values for benign, malignant and normal tissue using (a) two small ROIs and (b) a large ROI.

Conclusions

There is a significant difference between ADC values from large and small ROIs (P <0.05), with small ROIs giving greater differentiation. DWI is a promising technique to improve specificity of breast MRI.