A new methodology for MBI guided biopsy: initial patient results

Introduction: Molecular breast imaging (MBI) uses a dual-head gamma camera to detect uptake of Tc-99m sestamibi in breast lesions. Previous work has established that MBI can detect breast cancers occult on mammography and ultrasound, thus direct-biopsy capability of lesions seen on MBI is desired. MBI guided biopsy allows for direct biopsy of a lesion without the need to find a correlate through another modality such as mammography, ultrasound, or MRI.

Methods: Design of MBI biopsy system: The CMR Navican MBI gantry was modified to allow access to the breast by rotating the upper detector vertically. The light breast compression usually achieved by the upper detector is now achieved through an independent compression paddle. This paddle allows for insertion of a needle using commercially available biopsy kits employed with vacuum assisted biopsy systems.

Determination of lesion depth: The opposing views provided by the dual-detector MBI system allow for accurate determination of the X and Y-coordinates of a lesion but provide no obvious estimate of lesion depth. Two independent methods were developed for estimation of lesion depth. Method 1 utilizes the relative lesion activity in the upper versus lower detector images to calculate lesion depth.¹ Method 2 utilizes triangulation. The upper detector can be rotated to 15^o. Comparison of the relative change in y-position of the lesion between the standard image (0^o) and that obtained at 15^o allows estimation of lesion depth.

Patient Biopsy Procedure: The patient is injected with 20mCi of Tc-99m sestamibi, which allows for rapid (≤2 minutes/view) imaging. Conventional views (CC and MLO) of both breasts are obtained and the radiologist selects the optimum gantry angle and breast orientation for biopsy of any lesion of interest. Enough compression is placed over the area of concern so that the breast is stabilized. Once positioned, opposing images are obtained with the upper detector at 0^o and an additional image is acquired with the upper detector at 15^o. Analysis of the opposing detector images, and the upper detector images at 0^o and 15^o provides two estimates of lesion depth. Once the depth of the lesion is confirmed the biopsy is performed by a radiologist using a vacuum assisted device. Once the biopsy samples have been obtained, they are placed in a dish and imaged by the upper detector to confirm the presence of activity in the samples. Samples are then placed in a formalin container and sent for histopathologic interpretation.

Results: Six patient studies have been completed to date. Three patients have been successfully biopsied with concordant pathology. In the other three patients no lesion was evident on imaging and biopsy was discontinued. All patients reported minimal if any discomfort with the process. From start of biopsy workflow to completion of sampling took about 30 minutes.

Conclusions: A methodology has been developed that allows for rapid biopsy of lesions identified on MBI images. Completion of additional patient studies is in progress to confirm this methodology. FDA approval of this methodology is also pending. This is an important next step in establishing MBI as a valuable screening tool that permits biopsy of lesions without the need for correlative imaging with other modalities.

References:

• Hruska CB, O'Connor MK. Quantification of lesion size, depth, and uptake using a dual-head molecular breast imaging system. Med Phys. 2008 Apr; 35 (4):1365-76 PMID: 18491531 PMCID: 2673627 DOI: 10.1118/1.2885371