Gamma cameras for intraoperative localization of sentinel nodes: technical requirements identified through operating room experience

Various nuclear medicine techniques are used for localization of sentinel lymph nodes (SLNs). Procedures that include high-quality preoperative imaging and skilled intraoperative use of a gamma counting probe are almost always successful. Those that involve only the intraoperative use of a gamma probe are generally less successful. For a variety of reasons, high-quality preoperative imaging is not possible at many institutions and thus many institutions use procedures that involve only intraoperative use of a gamma probe. It has been proposed that procedures involving intraoperative imaging be developed and evaluated. To better identify technical requirements for an intraoperative imaging system and protocol, five breast cancer patients were imaged intraoperatively, as well as preoperatively. The intraoperative imaging was performed using a small (127 mm × 127 mm) field-of-view (FOV) gamma camera mounted on an articulating arm (Gamma Medica GammaCAM/OR). Intraoperative imaging was performed following administration of anesthesia and following preparation of a sterile surgical field about the involved breast. The camera and arm were draped in a sterile sheath, and the operators of the camera were attired in sterile surgical wear. Intraoperative images were acquired pre-incision and post-excision. Images were acquired for 2 to 3 minutes each. Members of the surgical/nuclear medicine team observed and assessed the ease or difficulty of the acquisitions of images. Conclusions included that a camera for SLN localization should exhibit low noise, should have very good shielding from all non-imaging directions, should have very low collimator penetration, and should have very good sensitivity at 140 keV. The system should have tools for flexible display windowing, convenient region-of-interest definition, and rapid image analysis. These features should be readily available and be easily controlled by the individual positioning the camera. The FOV should be at least 127 mm × 127 mm but probably no larger than 200 mm × 200 mm. A system should also have a means by which its camera can be easily repeatably positioned.