MRI examination

All breast MRI examinations were performed on a 3.0-T system (GE Discovery MR750; GE Healthcare, Milwaukee, WI, USA), with an eight-channel dedicated breast coil. Patients were in the prone position, and both breasts were imaged simultaneously. For premenopausal females, imaging was performed between day 7 and day 14 of the menstrual cycle. An MRI plain scan was performed with the axial T2-weighted single-shot fast spin echo sequence using a modified Dixon technique (T₂ IDEAL) for intravoxel fat-water separation, using the following parameters: Repetition time (TR), 2,500 msec; echo time (TE), 53.5 msec; slice thickness, 6 mm; layer spacing, 1.0 mm; field of view, 360×360 mm; matrix size, 320×192 pixels; and number of excitations (NEX), 3. Similarly, the parameters for the axial T1-weighted fast spin-echo were as follows: TR, 569 msec; TE, 15.6 msec; slice thickness, 6 mm; layer spacing, 1.0 mm; field of view, 360×360 mm; matrix size, 256×192; NEX, 4.

In order to obtain dynamic contrast-enhanced (DCE) MRI scans, a dynamic examination was performed using the axial T1-weighted 3D dynamic gradient echo fat sequence. The parameters for this examination were as follows: TR/TE, 3.9/1.7; flip angle, 5°; field of view, 360×360 mm; matrix size, 348×348; and slice thickness, 1.8 mm. Subsequent to unenhanced acquisition, Gadodiamide (0.2 mmol/kg body weight, GE Healthcare Life Sciences, Little Chalfont, UK) was intravenously injected at the rate of 2 ml/sec, followed by 20 ml saline flush. DCE image acquisition was initiated immediately after the saline injection. The sequence was repeated for seven times without time gaps, and each sequence lasted for 60 sec.

DWI was performed with an axial single-shot fat suppressed echo-planar diffusion weighted sequence (TR, 3,000 msec; TE, 49.5 msec; slice thickness, 6 mm; layer spacing, 1.0 mm; field of view, 360×360 mm; matrix size, 128×96; and NEX, 4). The diffusion-sensitizing gradient was applied along the x, y and z axes, while b-values of 0 and 800 sec/mm² were used.