Gamma-ray imaging technologies based on the use of radiotracers enable us to clearly determine the physiological function of an organ not only during pre-clinical and clinical studies but also in the field of plant science. Serial time-course images can be used to indicate the changing spatial distribution of a radiotracer within a living plant system and to describe the dynamics and kinetics of a substance in an intact plant. Gamma-rays almost completely penetrate a plant body, and the image data obtained using them can potentially be used to quantitatively analyze physiological function parameters. This paper briefly reviews recent progress in the field of plant science to explore the use of positron emission tomography, a gamma camera, and the positron-emitting tracer imaging system, which is one of the most advanced gamma-ray imaging systems available for studying plant physiology, for solving problems in the field of environment and agriculture.

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  Positron emission tomography (PET) plays important roles in cancer diagnosis and molecular imaging research; but potential points remain for which big improvements could be made, including resolution, sensitivity and costs. Therefore, research on next generation PET technologies remains a hot topic worldwide. In this paper, we introduce some research trends by describing PET physics research in the National Institute of Radiological Sciences (NIRS). A depth-of-interaction (DOI) detector, for which various methods have been studied, will be a key device to get any significant improvement in sensitivity while maintaining high spatial resolution. DOI measurement also has a potential to expand PET application fields because it allows for more flexible detector arrangement. As an example, we are developing the world's first, open-type PET geometry “OpenPET”, which is expected to lead to PET imaging during treatment. The DOI detector itself continues to evolve with the help of recently developed semiconductor photodetectors, often referred to as silicon photomultipliers (SiPMs).

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  Measuring the radioactive contamination and the effect of decontamination are important to recover from the disaster caused by the nuclear accident at the Fukushima Dai-ichi Nuclear Power Plant. At present, the measurement has been carried out with survey meter. However the survey meter can only measure the dose rate at the position and cannot identify the direction of gamma-ray, and it is difficult to find the contaminated area. The gamma camera can identify the gamma-ray direction and make the image of contamination distribution. With combining the optical image with the gamma camera image, the contamination area can be easily identified. We have developed the gamma camera with semiconductor detectors, and checked the specification in the lab and fields.

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  Cadmium Telluride (CdTe) is one of the most promising semiconductor materials for hard X-ray and gamma-ray detection because of the high detection efficiency, and of the good energy resolution. Moreover, CdTe detectors with Schottky junction work as diode detectors, and show superior energy resolution. Based on the CdTe diode devices, we have developed CdTe pixel/strip imagers, and also realized a Si/CdTe Compton camera. These devices will be used for the Hard X-ray Imager (HXI) and the Soft Gamma-ray Detector (SGD) onboard ASTRO-H X-ray satellite to be launched in 2015. These developments are briefly reported in this article. We also describe our recent development of low-noise analog readout ASICs to be used for future development of CdTe gamma-ray imagers.

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  Recently gamma ray detection technologies become very important in the fields of medical application, space, and environment. Pixelated detectors and electronics are necessary to achieve high-resolution gamma ray detectors. Especially high resolution PET (positron emission tomography) system has been a driving force for developing pixel gamma-ray detectors. A pixel gamma detector is composed of granulated crystals and photo-detectors with highly integrated circuits (ASIC) to process the large number of channels. Recent development of these technologies is reviewed here.

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