Development of a novel handheld intra-operative laparoscopic Compton camera for18F-Fluoro-2-deoxy-2-D-glucose-guided surgery

Compton imaging for medical applications

Compton imaging exploits inelastic scattering, known as Compton scattering, using a Compton camera consisting of a scatterer detector in the front layer and an absorber detector in the back layer. This method was developed for astronomy, and in recent years, research and development for environmental and medical applications has been actively conducted. Compton imaging can discriminate gamma rays over a wide energy range from several hundred keV to several MeV. Therefore, it is expected to be applied to the simultaneous imaging of multiple nuclides in nuclear medicine and prompt gamma ray imaging for range verification in particle therapy. In addition, multiple gamma coincidence imaging is expected to be realized, which allows the source position to be determined from a single coincidence event using nuclides that emit multiple gamma rays simultaneously, such as nuclides that emit a single gamma ray simultaneously with positron decay. This review introduces various efforts toward the practical application of Compton imaging in the medical field, including in vivo studies, and discusses its prospects.

One-by-One Comparison of Lymph Nodes Between 18F-FDG Uptake and Pathological Diagnosis in Esophageal Cancer

Esophagectomy with extended lymph node (LN) dissection is a standard treatment for resectable esophageal cancer to prevent recurrence, but severe, potentially life-threatening postoperative complications are still important issues. Accurate diagnosis of LN metastases would enable the decision to dissect or leave the LNs in regions with high risk of complications. Advancements in intraoperative gamma probe and radioactivity detectors have made intraoperative navigation surgery possible using a radiotracer as a marker. ¹⁸F-FDG is one such candidate markers, and the diagnostic power of FDG through counting the radioactivity close to each LN should be elucidated.

Development and evaluation of a prototype detector for an intraoperative laparoscopic coincidence imaging system with PET tracers

PURPOSE

Conventional positron emission tomography can be used only preoperatively to identify lymph node metastases, and hence, these growths are difficult to locate intraoperatively. Previously, an intraoperative laparoscopic coincidence imaging system, with an external fixed detector array and a detector probe that can be moved and inserted into the stomach, was proposed to identify lymph node metastases during stomach cancer surgery. This paper proposes a prototype detector for this system.

METHODS

GAGG:Ce (Gd₃Al₂Ga₃O₁₂:Ce) scintillator crystals, one to one coupled with silicon photomultipliers (SiPMs), were used to identify 511 keV photons. An optical tracking system followed the position and orientation of the movable detector. SiPM outputs were read out by time-over-threshold (TOT)-based application-specific integrated circuits, which converted the electrical charges into digital pulses. To identify the arrival time, channel number, and pulse width, which indicate the energy information of each TOT output, a data acquisition system was developed based on a field-programmable gate array.

RESULTS

The spatial resolution of the reconstructed images in lateral direction was better than 7 mm, but that of depth direction was limited, owing to inadequate projections. The prototype successfully reconstructed 44 kBq ¹⁸F-fluorodeoxyglucose sources during a 2-min scan.

CONCLUSION

We developed a prototype detector for an intraoperative laparoscopic coincidence imaging system. The prototype detector was evaluated successfully, and the produced images were similar to those obtained in the simulation results, thereby suggesting that this method offers a new possibility of imaging lymph node metastases intraoperatively.

In vivo simultaneous imaging with 99mTc and 18F using a Compton camera

We have been developing a medical imaging technique using a Compton camera. This study evaluates the feasibility of clear imaging with ^99mTc and ¹⁸F simultaneously, and demonstrates in vivo imaging with ^99mTc and/or ¹⁸F. We used a Compton camera with silicon and cadmium telluride (Si/CdTe) semiconductors. We estimated the imaging performance of the Compton camera for 141 keV and 511 keV gamma rays from ^99mTc and ²²Na, respectively. Next, we simultaneously imaged ^99mTc and ¹⁸F point sources to evaluate the cross-talk artifacts produced by a higher energy gamma-ray background. Then, in the in vivo experiments, three rats were injected with ^99mTc-dimercaptosuccinic acid and/or ¹⁸F-fluorodeoxyglucose and imaged. The Compton images were compared with PET images. The rats were euthanized, and the activities in their organs were measured using a well counter. The energy resolution and spatial resolution were measured for the sources. No apparent cross-talk artifacts were observed in the practical-activity ratio (^99mTc:¹⁸F  =  1:16). We succeeded in imaging the distributions of ^99mTc and ¹⁸F simultaneously, and the results were consistent with the PET images and well counter measurements. Our Si/CdTe Compton camera can thus work as a multi-tracer imager, covering various SPECT and PET probes, with less cross-talk artifacts in comparison to the conventional Anger cameras using a collimator. Our findings suggest the possibility of human trials.