Multiple photon coincidence tomography

A double photon coincidence detection method for medical gamma-ray imaging

Cascade nuclides emit two or more gamma rays successively through an intermediate state. The coincidence detection of cascade gamma rays provides several advantages in gamma-ray imaging. In this review article, three applications of the double photon coincidence method are reviewed. Double-photon emission imaging with mechanical collimators and Compton double-photon emission imaging can identify radioactive source positions with their angular-resolving detectors, and reduce the crosstalk between nuclides. In addition, a novel method of coincidence Compton imaging is proposed by taking coincidence detection between a Compton event and a photopeak events. Although this type of coincidence Compton imaging cannot specify the location, it can be useful in multi-nuclide Compton imaging.

Time of flight dual photon emission computed tomography

Time-of-flight dual photon emission computed tomography (TOF-DuPECT) is an imaging system that can obtain radionuclide distributions using time information recorded from two cascade-decay photons. The potential decay locations in the image space, a hyperbolic response curve, can be determined via time-difference-of-arrival (TDOA) estimations from two instantaneous coincidence photons. In this feasibility study, Monte Carlo simulations were performed to generate list-mode coincidence data. A full-ring positron emission tomography-like detection system geometry was built in the simulation environment. A contrast phantom and a Jaszczak-like phantom filled with Selenium-75 (Se-75) were used to evaluate the image quality. A TOF-DuPECT system with varying coincidence time resolution (CTR) was then evaluated. We used the stochastic origin ensemble (SOE) algorithm to reconstruct images from the recorded list-mode data. The results indicate that the SOE method can be successfully employed for the TOF-DuPECT system and can achieve acceptable image quality when the CTR is less than 100 ps. Therefore, the TOF-DuPECT imaging system is feasible. With the improvement of the detector with time, future implementations and applications of TOF-DuPECT are promising. Further quantitative imaging techniques such as attenuation and scatter corrections for the TOF-DuPECT system will be developed in future.

Comparison of transaxial resolution in 180 degrees and 360 degrees SPECT with a rotating scintillation camera

Using circular 180 degrees and 360 degrees SPECT acquisition modes the transaxial resolution of line sources in air and water were measured at different positions in the field of view. With the 180 degrees acquisition mode, all line sources in air located off the axis of camera rotation (AoR) showed an oval distortion. This distortion was systematically related to the starting point of the rotating detector. On axis line sources in air were undistorted, regardless of the 180 degrees acquisition starting angle. The 360 degrees acquisition images of the line sources in air showed a similar effect but in a very mild form. In water, transaxial reconstructions of line sources (off axis) showed an enhancement of the oval distortion for both the 180 degrees and 360 degrees acquisitions. Computer simulations of the line source measurements were performed and correlated well with the experimental data. The line source results are explainable by the inherent depth dependent response of the scintillation camera. In clinical SPECT studies, distortions of this nature will be most appreciable with 180 degrees imaging of small organs that are located off the AoR.