Heung Suk Seo

Experimental performance of double-scattering Compton camera with anthropomorphic phantom

In proton therapy, it is important to very accurately determine the range of the proton beam. Recently it was found that this range can be determined from the distribution of the prompt gammas generated along the beams passage. The Compton imaging technique can be considered to be a promising candidate for accurate determination of prompt gamma distributions, in that it produces a better image for higher-energy gammas when compared with conventional mechanical-collimation-type imagers. In the present study, the Compton imaging technique was evaluated by experimentally obtaining Compton images of relatively high-energy gamma sources positioned in an anthropomorphic phantom. Preparatory to that, two point-like gamma sources, 137Cs (662 keV) and 22Na (1275 keV), were placed in the brain region of the phantom at different depths and imaged using a double-scattering Compton camera. The Compton camera, recently developed as a prototype system, consists of two position-sensitive semiconductor detectors as scatterer detectors and a scintillation detector as an absorber detector. The evaluated imaging and angular resolutions for the source energies of 662 and 1275 keV were 13.7 mm and 5.9° FWHM and 11.4 mm and 3.8° FWHM, respectively.

Feasibility study on Compton imaging for visualization of flow patterns using radiotracers

The radiotracer technique could be used in studies on multiphase flow systems by three-dimensional visualization of flow patterns, and, relatedly, there have been attempts to develop an industrial-purpose single photon emission computed tomography (SPECT) system. Compton cameras also have a great potential for industrial applications, due specifically to their inherent three-dimensional imaging capability, multi-tracing capability, and higher imaging sensitivity than imaging devices based on mechanical collimation. In the present study, the feasibility of Compton imaging for visualization of detailed flow patterns was determined using a Geant4 Monte Carlo simulation toolkit. The Compton camera considered is a double-scattering type consisting of three gamma-ray detectors: two double-sided silicon strip detectors (DSSDs) as scatterer detectors and one NaI(Tl) scintillation detector as an absorber detector. The results showed that the three-dimensional source distributions can be determined with the Compton camera under various source conditions, including a point source at the center, and two cylinderial volume sources of different dimensions or energies.

Study on listmode OSEM reconstruction including image-space resolution recovery techniques for Compton camera

Although Compton camera may has a great potential as next generation imaging modality comparing to SPECT and PET, its fully three-dimensional image reconstruction requires the considerable computational burden and the spatial resolution is suffered from the various physical phenomena arising during detection process. In this study, we investigated the accelerated statistical image reconstruction in which system matrix included a resolution recovery (RR) technique. We considered 3D Gaussian resolution model for the integrated angular and geometric uncertainties. The angular uncertainty is closely related to the limited energy resolution of the Compton camera and Doppler broadening and the geometric uncertainty is due to the segmented detectors. For RR, the 3D Gaussian resolution model is incorporated into listmode OSEM (LMOSEM) using image-space convolution operation. We investigated two different RR approaches: one (denoted by LMOSEM-RRF) is when the convolution is only performed in forward projection step, and the other (denoted by LMOSEM-RRFB) is when it is performed in both forward and backward projection steps. The simulation results showed that both RR approaches gave an improvement on spatial resolution for the resolution-degraded data due to both angular and geometric uncertainties. Although LMOSEM-RRF provided better resolution than LMOSEM-RRFB, LMOSEM-RRFB could still useful for low counting statistics in measurement.

Extrapelvic and extraperitoneal spread of recurrent stomach cancer: Two case reports

We report two cases of unusual combined extrapelvic and extraperitoneal extension of recurrent gastric adenocarcinoma and describe the imaging findings of the preferential anatomic pathway of disease spread. Extrapelvic and extraperitoneal extension of recurrent gastric adenocarcinoma is rare, and its symptoms may be vague and nonspecific. If patients with a surgical history of gastrointestinal neoplasm present with diffuse abdominal pain or painful swelling of the lower extremities, disease spread to the extrapelvic and extraperitoneal spaces should be suspected.