This was a prospective study for assessing the usefulness of MRI-guided VABB, approved by the Institutional Review Board of our hospital. Informed consent was obtained from all patients. A total of 13 patients with 15 lesions scheduled for MRI-guided VABB and surgical excision between September 2009 and November 2011 were asked to participate in this prospective study. The patients ranged in age from 35 to 73 years and the median age was 51.4 years.
Breast MRI technique and lesion characteristics before biopsy
The MRI scans were acquired with the patient in the prone position with a 1.5 T scanner (Achieva; Philips Medical Systems, Best, the Netherlands) equipped with a breast coil.
The MRI images with the Achieva scanner were acquired using the following sequences: sagittal, fat-suppressed, and fast spin-echo T2-weighted imaging sequence (Repetition time/echo time 6,000/100 ms, flip angle 90°, 30 slices, field of view of 320 mm, matrix 424 × 296, number of excitations of 1, 4 mm slice thickness with 0.1 mm interslice gaps, and acquisition time of 2 minutes 56 seconds) and precontrast and postcontrast dynamic axial T1-weighted three-dimensional, fat-suppressed, fat-spoiled gradient-echo sequence (Repetition time/echo time 6.9/3.4, flip angle of12°, 2.0 mm slice thickness with no gap, acquisition time of 1 minute 31 seconds). The images were obtained before and at 0, 91, 182, 273, 364, and 455 seconds after a rapid bolus injection of gadolinium–diethylenetriamine pentaacetic acid (Magnevist; Schering, Berlin, Germany) at 0.1 mmol/kg of body weight.
Two breast radiologists analyzed the imaging findings according to the American College of Radiology Breast Imaging Reporting and Data System categories for MRI . All lesions were classified into category 4 or category 5 on MRI. For all cases, the following lesion characteristics were recorded: type (focus, mass or nonmass enhancement), size, location, and kinetic analysis.
MRI-guided vacuum-assisted breast biopsy procedure
Biopsies were performed with a 9-gauge MRI-compatible vacuum-assisted biopsy device (Automated Tissue Excision and Collection; Suros Surgical Systems, Indianapolis, IN, U.S). All biopsies were performed by two radiologists specializing in breast imaging (BJK, SHK); all had previous experience in breast MRI and percutaneous biopsies under stereotactic and sonographic guidance. The two radiologists had not previously performed the procedure but had observed or assisted one or more of the experienced radiologists.
The MRI biopsy technique has been previously described in detail . The patient was positioned prone in the 1.5 T magnet (Signa, GE Medical Systems, Milwaukee, WI, USA). The affected breast was placed in a dedicated biopsy compression device using a commercially available grid localizing system. The protocol for MRI-guided VABB at our institution comprised the following six steps: step 1, targeting images (breast compression by the biopsy guidance grid, marking the expected lesion site with a fiducial marker on the skin, and a sagittal T1 fat-saturated three-dimensional spoiled gradient echo image before and after intravenous administration of 20 ml gadodiamide (Omniscan; GE Healthcare, Oslo, Norway) plus 10 ml saline); step 2, determining lesion location and desired depth of probe insertion; step 3, preparing the probe; step 4, placing the device, and performing imaging to confirm the lesion location (sterilization and anesthetization of the breast, placement of the introducer and stylet through the needle guide, removal of the stylet and placement of the obturator inside the introducer, and axial scan to confirm accurate targeting); step 5, performing the biopsy, postexamination images and collecting the specimens (removal of the obturator and insertion of the biopsy device, tissue sampling, and post-biopsy sagittal scan to assess the completeness of tissue acquisition and to examine for the presence of postprocedural complications); and step 6, post-biopsy care of the breast (compression with ice and application of a sterile dressing on the biopsy site).
Data collection – including clinical indications for breast MRI, patient age, menopausal status, lesion size and type on MRI, biopsy parameters, histologic results of vacuum-assisted biopsy and surgical excision, and complications – was performed by reviewing medical records. The time of the biopsy (minutes) was determined by calculating the interval between the beginning of the MRI localizing sequence and the end of the final MRI sequence acquired. The radiologist performing the biopsy reviewed the MRIs obtained during and after the biopsy to determine the presence and extent of postbiopsy changes, to assess whether the MRI target was sampled or possibly excised.