Magnetic resonance imaging guided breast biopsy using a frameless stereotactic technique

The high sensitivity but poor specificity of contrast enhanced magnetic resonance (MR) imaging for delineating malignant breast lesions is increasing the demand for MR guide breast biopsy. However, the poor patient access offered by conventional MR systems makes such procedures extremely difficult. We describe a method of performing breast biopsy outside the bore of the magnet using the 3-D MR imaging data. This involves a frameless stereotactic technique using an ultrasonic localizer. The position in space of the tip of a pointer with a handle which incorporates two ultrasound emitters can be tracked using an array of ultrasound detectors. MR visible marker beads (fiducials) placed on the breast and imaged at the same time are identified to the computer in relation to images of the breast. The ultrasonic localizer is used to register the position in space of the fiducials by touching them with the tip of the pointer. The image of the lesion within the breast can then be displayed in relation to the position of the tip of the pointer and the needle approach planned. Nine women with foci of enhancement on their dynamic contrast enhanced MR images underwent frameless stereotactic breast cytology. Needle placement within 2 mm of the lesion was achieved at first pass in eight out of nine (89%) cases: in one case the needle had to be re-positioned prior to sampling. This technique provides a means of targetting MR visible lesions using the MR imaging data whilst performing the procedure outside the magnet bore.