Impact of fibroglandular tissue and background parenchymal enhancement on diffusion weighted imaging of breast lesions.

PURPOSE

To evaluate the influence of the amount of fibroglandular breast tissue (FGT) and background-parenchymal enhancement (BPE) on lesion detection, quantitative analysis of normal breast tissue and of breast lesions on DWI.

MATERIALS AND METHODS

IRB approved this retrospective study on focal findings at contrast-enhanced (CE)breast MR and DWI performed during July-December 2011. Patients with cysts, previous irradiation,silicone implants and current chemotherapy were excluded. DWI with fat suppression was acquired before dynamic acquisition (b factors: 0.1000 s/mm2) using 1.5 and 3 T scanners. Using correlation with dynamic and T2 images, ROIs were drawn free-hand within the borders of any visible lesion and incontralateral normal breast. Fisher's exact test to evaluate visibility and Wilcoxon-rank-sum test for comparison of ADC values were used. The amount of FGT and BPE was visually assessed by concurrent MRI. Analysis was stratified by menopausal status.

RESULTS

25/127 (20%) lesions were excluded for technical reasons. 65/102 (64%) lesions were visible on DWI (median diameter: 1.85 cm). Mass lesions (M) were more visible (43/60 = 72%) than non-mass enhancement (NME) (22/42 = 52%) and malignant lesions were more visible (55/72 = 76%) than benign(10/30 = 33%). BPE and FGT did not influence visibility of M (p = 0.35 and p = 0.57 respectively) as well as of NME (p = 0.54 and p = 0.10). BPE and FGT did not influence visibility of malignant (p = 0.96 and p = 1.0)and benign lesions (p = 1.0 and p = 0.10). Results were confirmed adjusting for menopausal status. The ADC value of normal breast tissue was not influenced by BPE, while it was lower in predominantly fatty breasts compared to dense ones (p = 0.002).

CONCLUSIONS

FGT affects the quantitative evaluation of ADC in normal breast tissue whereas BPE does not.Furthermore, both BPE and FGT do not influence visibility of benign or malignant findings, including both mass lesions and non-mass enhancement, on DWI.