Abstract
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Objectives While beta probes - after preoperative 18F-FDG administration - can be useful to identify occult small residual disease immediately after surgical resection, the necessary exploration of the operating field after resection is time consuming. We developed a prototype beta-imaging probe that may improve lesion detection using real-time imaging of the radioactivity distribution in the operating field. A particular theoretical advantage of imaging detectors over simple beta counting probes is a much larger active area and small individual detector elements.
Methods The 11 x 22 mm beta silicon-detector (assembled as 8 x 16 pad array) is coupled to custom readout electronics via a kapton flex cable with epoxy-encapsulated wirebonds. Detector performance was evaluated in simple phantom studies and performing in-vivo imaging studies using 4 subcutaneous 9L tumors in rats. Performance was compared with 18F-FDG microPET and high-energy gamma probe measurements. For probe evaluations, the tumor surface was surgically exposed.
Results Spatial resolution was dependent on point source distance to the detector surface with 1.4 mm resolution at direct contact. In-vivo imaging testing revealed that all primary tumors (weight range 2.6-3.7g) were clearly visually detected maintaining a minimal distance of 2-3 mm from the surface of the tumor in the surgical bed. Typical in-vivo peak tumor to muscle background (T/M) ratios were in the range of 2.5:1, which compared favorable to those obtained from the high-energy gamma probe (range 1.8:1 - 1.9:1). However, achievable T/M ratios obtained from microPET images were much higher (range 11.6:1 - 17.0:1).
Conclusions The prototype beta imaging probe provides 2-D images of the radioactivity distribution obtained from positron emitters such as 18F-FDG. An optimized system design holds promise for future human exploration.
Research Support UM-CC G00122