Diffusion weighted imaging of the normal breast: reproducibility of apparent diffusion coefficient measurements and variation with menstrual cycle and menopausal status.

Objectives: To establish the reproducibility of apparent diffusion coefficient (ADC) measurements in normal fibroglandular breast tissue and to assess variation in ADC values with phase of the menstrual cycle and menopausal status. Methods: Thirty-one volunteers (13 premenopausal, 18 postmenopausal) underwent magnetic resonance twice (interval 11-22 days) using diffusion-weighted MRI. ADC and a perfusion-insensitive ADC (omitting b = 0) were calculated. Reproducibility and inter-observer variability of mean ADC values were assessed. The difference in mean ADC values between the two phases of the menstrual cycle and the postmenopausal breast were evaluated. Results: ADC and ADC showed good reproducibility ( r% = 17.6, 22.4). ADC showed very good inter-observer agreement ( kappa = 0.83). The intraclass correlation coefficients (ICC) were 0.93 and 0.91. Mean ADC values were significantly lower in the postmenopausal breast (ADC 1.46 ± 0.3 × 10 mm/s, ADC 1.33 ± 0.3 × 10 mm/s) compared with the premenopausal breast (ADC 1.84 ± 0.26 × 10 mm/s, ADC 1.77 ± 0.26 × 10 mm/s; both P < 0.001). No significant difference was seen in ADC values in relation to menstrual cycle (ADC P = 0.2, ADC P = 0.24) or between postmenopausal women taking or not taking oestrogen supplements (ADC P = 0.6, ADC P = 0.46). Conclusions: ADC values in fibroglandular breast tissue are reproducible. Lower ADC values within the postmenopausal breast may reduce diffusion-weighted contrast and have implications for accurately detecting tumours. Key Points: • ADC values from fibroglandular breast tissue are measured reproducibly by multiple observers. • Mean ADC values were significantly lower in postmenopausal than premenopausal breast tissue. • Mean ADC values did not vary significantly with menstrual cycle. • Low postmenopausal ADC values may hinder tumour detection on DW-MRI. [ABSTRACT FROM AUTHOR]