Development of a novel, dual-modality image guidance system by combining a focussed gamma probe with ultrasound imaging

During breast cancer surgery, there are several modalities that a clinician can choose from to detect and localize cancerous tissue intraoperatively, with one of the most common being non-imaging gamma probes. However, deficiencies in the existing modalities make it difficult for clinicians to completely resect the tumour with clean margins, meaning the patient may have to undergo a revision surgery. We describe a novel, dual-modality image guidance system comprising a non-imaging, focussed gamma probe and an ultrasound transducer that simultaneously acquires molecular and anatomical data for a complete surgical guidance system. The custom-designed focussed gamma probe features a highly convergent collimator that achieves high-resolution in a remote focal region. Monte Carlo simulations show a 3.5 mm full width at half maximum resolution and a maximum sensitivity of approximately 7.8 cps/kBq for a 45 mm focal length collimator. The unique focal point design of the gamma probe enables the region with the highest resolution to be aligned within the ultrasound imaging plane for simultaneous, dual-modality acquisition. The first proof-of-concept computer-aided design for the hybrid imaging system is presented. Simultaneous acquisition was realized using a custom-designed holder that allows the focussed gamma probe and any commercially available ultrasound probe to be connected into a single, hand-held unit. The system also contains a translational stage that allows the focal point of the gamma probe to be adjusted axially within the ultrasound plane for optimal assessment. The development of this novel, dual-modality image guidance system should facilitate more accurate real-time, intraoperative tumour margin assessment.