Accuracy of 3D lesion localization in molecular breast imaging (MBI) for biopsy needle guidance

Objectives Direct Conversion Molecular Breast Imaging (DC-MBI) is a functional modality, which uses two planar cameras that detect gamma ray emissions from intravenous injection of Tc99m-sestamibi to identify biochemical abnormalities associated with breast cancer. Currently, commercial DC-MBI systems do not have the ability to localize suspected lesions in all three dimensions and guide a biopsy needle. We are developing a biopsy guidance capability for DC-MBI using only two planar images and this paper will present the quantitative accuracy of 3D lesion localization using this method.

Methods DC-MBI consists of a pair of opposed semiconductor (CZT, Cadmium Zinc Telluride) gamma photon cameras that mildly compress the breast between them in standard planar mammographic views. For 3D lesion targeting, we have modified the design of the collimators, such that the lesion depth information is encoded in the planar images generated by the opposing detectors. The graphical user interface allows the physician to select the region of interest in the two planar images and a computer algorithm calculates the 3D coordinates of the lesion. A needle guide provides lateral access between the two MBI cameras for hub-to-hub insertion of the biopsy sampling device parallel to the chest wall. Breast phantoms shaped as semi-cylinders, 6 cm thick and 20 cm in diameter, were fabricated from agarose gel mixed with a Tc-99m solution. Color dyed lesions with Tc-99m activity concentrations 5 to 20 times background and 5 mm to 20 mm in size were embedded inside the phantoms. The phantoms were biopsied using MBI guidance using a 9 gauge needle and 20 mm sampling core.

Results The optimized collimator design allows the centroid of the lesion to be determined to within 2 mm in all three dimensions. The biopsied samples, visually inspected for color and also with MBI imaging, confirmed localization accuracy.

Conclusions A simple and effective method for MBI-guided biopsy has been demonstrated with phantom studies.