Shinji Motomura

A Compton camera for multi-tracer imaging

A high-energy resolution Compton camera consisting of two segmented Ge detectors is proposed for multitracer research. The basic parameters affecting its spatial resolution are described. Monte Carlo simulations were performed to optimize the detector system. Its suitability for multitracer technology was demonstrated by a test experiment.

Gamma-Ray Compton Imaging of Multitracer in Biological Samples Using Strip Germanium Telescope

The feasibility of using a Compton camera for multitracer imaging has been demonstrated with the results of two biological sample imaging experiments. The distribution of the multitracer administered to a soybean sample and a tumor-bearing mouse has been visualized for each nuclide simultaneously. Three-dimensional images of the multitracer have been obtained even though the samples were measured from a fixed direction.

Multiple molecular simultaneous imaging in a live mouse using semiconductor Compton camera

We have demonstrated the feasibility of semiconductor Compton cameras for multiple molecular imaging in nuclear medicine. The Compton camera used in this work comprises two double-sided orthogonal-strip germanium detectors, and their excellent energy resolution enabled discrimination of the nuclides and accurate determination of the scattering angle for γ rays in wide energy range. Three radioactive tracers of 65ZnCl2, 85SrCl2, and iodinated (131I) methylnorcholestenol were injected to a living mouse and were measured simultaneously. Both two- and three-dimensional images of each tracer were obtained by a fixed-angle imaging with a single Compton camera, which reflected the different in vivo behavior of them.

Improved imaging performance of a semiconductor Compton camera GREI makes for a new methodology to integrate bio-metal analysis and molecular imaging technology in living organisms

We have constructed the second prototype of the semiconductor Compton camera GREI that enables spectroscopic imaging of wide energy-range gamma-rays. The improved imaging performance has been demonstrated by an imaging experiment with a tumor-baring live mouse, where we were able to obtain the distribution images of the 64Cu-labeled antibody to the implanted three tumor sites of different cell lines, together with that of 65Zn, which was simultaneously administered as ZnCl2 solution. The imaging performance has been compared with that of the primary prototype of GREI, and the importance of the improvement for the simultaneous imaging of multiple radiotracers has been revealed. The methodology offered by GREI is expected to make a unique contribution toward establishing a new viewpoint for understanding life phenomena.

Visualization of biodistribution of Zn complex with antidiabetic activity using semiconductor Compton camera GREI

Various types of zinc (Zn) complexes have been developed as promising antidiabetic agents in recent years. However, the pharmacological action of Zn complex is not elucidated because the biodistribution of the complex in a living organism has not been studied. Nuclear medicine imaging is superior technology for the noninvasive analysis of the temporal distribution of drug candidates in living organisms. Gamma-ray emission imaging (GREI), which was developed by our laboratory as a novel molecular imaging modality, was adopted to visualize various γ-ray–emitting radionuclides that are not detected by conventional imaging techniques such as positron emission tomography and single-photon emission computed tomography. Therefore, we applied GREI to a biodistribution assay of Zn complexes. In the present study, 65Zn was produced in the natCu(p,n) reaction in an azimuthal varying field cyclotron for the GREI experiment. The distribution was then noninvasively visualized using GREI after the intravenous administration of a 65Zn-labeled di(1-oxy-2-pyridinethiolato)zinc [Zn(opt)2], ZnCl2, and di(l-histidinato)zinc. The GREI images were validated using conventional invasive assays. This novel study showed that GREI is a powerful tool for the biodistribution analysis of antidiabetic Zn complexes in a living organism. In addition, accumulation of 65Zn in the cardiac blood pool was observed for [Zn(opt)2], which exhibits potent antidiabetic activity. These results suggest that the slow elimination of Zn from the blood is correlated to the antidiabetic activity of [Zn(opt)2].

A Digital Signal Processing Module for Ge Semiconductor Detectors

We have developed a digital signal processing module (APV7109) for a germanium semiconductor detector. The benchmark test of this module has shown good energy resolution and high throughput compared with conventional analog modules. By adding an extension module, the APV7109 can perform more advanced on-line calculations using the pulse shapes delivered by the on-board programmable logic. Therefore, user defined algorithms for pulse shape analysis can be used to adapt this module to various applications. Tests have demonstrated the feasibility of this extensible design.

Three-dimensional tomographic imaging by semiconductor Compton camera GREI for multiple molecular simultaneous imaging

We have investigated the possibility of three-dimensional (3D) tomographic imaging by semiconductor Compton cameras that we have been developing for multiple molecular simultaneous imaging. As a significant feature of Compton cameras, multi-directional projection of the γ-ray source distribution can be obtained even by a fixed-angle imaging with a single Compton camera unit. We have already implemented a 3D tomographic image reconstruction method applicable for both single- and multiple-unit Compton cameras, and succeeded in 3D tomographic imaging with a single Compton camera unit. In order to enlarge the field of view and to obtain more accurate images, we are constructing an array of multiple semiconductor Compton camera units.

Investigation of Biodistribution and Speciation Changes of Orally Administered Dual Radiolabeled Complex, Bis(5-chloro-7-[(131)I]iodo-8-quinolinolato)[(65)Zn]zinc

Many zinc (Zn) complexes have been developed as promising oral antidiabetic agents. In vitro assays using adipocytes have demonstrated that the coordination structures of Zn complexes affect the uptake of Zn into cells and have insulinomimetic activities, for which moderate stability of Zn complexes is vital. The complexation of Zn plays a major role improving its bioavailability. However, investigation of the speciation changes of Zn complexes after oral administration is lacking. A dual radiolabeling approach was applied in order to investigate the speciation of bis(5-chloro-7-iodo-8-quinolinolato)zinc complex [Zn(Cq)2], which exhibits the antidiabetic activity in diabetic mice. In the present study, 65Zn- and 131I-labeled [Zn(Cq)2] were synthesized, and their biodistribution were analyzed after an oral administration using both invasive conventional assays and noninvasive gamma-ray emission imaging (GREI), a novel nuclear medicine imaging modality that enables analysis of multiple radionuclides simultaneously. The GREI experiments visualized the behavior of 65Zn and [131I]Cq from the stomach to large intestine and through the small intestine; most of the administered Zn was transported together with clioquinol (5-chloro-7-iodo-8-quinolinol) (Cq). Higher accumulation of 65Zn for [Zn(Cq)2] than ZnCl2 suggests that the Zn associated with Cq was highly absorbed by the intestinal tract. In particular, the molar ratio of administered iodine to Zn decreased during the distribution processes, indicating the dissociation of most [Zn(Cq)2] complexes. In conclusion, the present study successfully evaluated the speciation changes of orally administered [Zn(Cq)2] using the dual radiolabeling method.

Millimeter-order imaging technique from 100 keV to MeV based on germanium Compton camera

A prototype molecular imaging system that features wide-band imaging capability from 100 keV to MeV was developed based on a germanium Compton camera. In this system, radiotracer imaging is performed through the Compton imaging technique above 300 keV and through the coded mask imaging technique below 200 keV. For practical use, small animal imaging requires spatial resolution of the order of millimeters. We conducted tests with a multiple-well phantom containing 99mTc (140 keV) and 54Mn (834 keV), and confirmed the spatial resolution of better than 3.2 mm for the phantom placed 35 mm above the detector. We also report imaging results of a living mouse into which we injected 99mTc (140 keV) and 54Mn (834 keV).

Development of multielemental imaging on semiconductor Compton telescope

The feasibility of using a Compton camera for multitracer imaging has been demonstrated with the results of two biological sample imaging experiments. The distribution of the multitracer administered to a soybean sample and a tumor-bearing mouse has been visualized for each nuclide simultaneously. 3D images of the multitracer have been obtained even though the samples were measured from a fixed direction.