標的アイソトープ治療に向けたアスタチン211イメージングのためのコンプトンカメラの開発

Tohoku University渡部浩司課

Rice immediately adapts the dynamics of photosynthates translocation to roots in response to changes in soil water environment

Rice is susceptible to abiotic stresses such as drought stress. To enhance drought resistance, elucidating the mechanisms by which rice plants adapt to intermittent drought stress that may occur in the field is an important requirement. Roots are directly exposed to changes in the soil water condition, and their responses to these environmental changes are driven by photosynthates. To visualize the distribution of photosynthates in the root system of rice plants under drought stress and recovery from drought stress, we combined X-ray computed tomography (CT) with open type positron emission tomography (OpenPET) and positron-emitting tracer imaging system (PETIS) with 11C tracer. The short half-life of 11C (20.39 min) allowed us to perform multiple experiments using the same plant, and thus photosynthate translocation was visualized as the same plant was subjected to drought stress and then re-irrigation for recovery. The results revealed that when soil is drier, 11C-photosynthates mainly translocated to the seminal roots, likely to promote elongation of the root with the aim of accessing water stored in the lower soil layers. The photosynthates translocation to seminal roots immediately stopped after rewatering then increased significantly in crown roots. We suggest that when rice plant experiencing drought is re-irrigated from the bottom of pot, the destination of 11C-photosynthates translocation immediately switches from seminal root to crown roots. We reveal that rice roots are responsive to changes in soil water conditions and that rice plants differentially adapts the dynamics of photosynthates translocation to crown roots and seminal roots depending on soil conditions

Copper-Catalyzed gamma-Selective and Stereospecific Allylic Cross-Coupling with Secondary Alkylboranes

The scope of the copper-catalyzed coupling reactions between organoboron compounds and allylic phosphates is expanded significantly by employing triphenylphosphine as a ligand for copper, allowing the use of secondary alkylboron compounds. The reaction proceeds with complete gamma-E-selectivity and preferential 1,3-syn stereoselectivity. The reaction of gamma-silicon-substituted allylic phosphates affords enantioenriched alpha-stereogenic allylsilanes

Development of a cost-effective Compton camera using a positron emission tomography data acquisition system

In nuclear-medical imaging, most clinically applied gamma rays have energies less than or equal to 511 keV. There is growing interest in the applications of radioisotopes emitting higher-energy gamma rays for pretherapeutic and therapeutic imaging. Compton cameras have the capability of imaging gamma rays with a wide range of energies. Since sensitivity of Compton cameras decrease with increase in gamma-ray energy, high sensitivity is required to image such radioisotopes. In this study, we developed a cost-effective Compton camera using high-sensitive inorganic scintillators and a commercially available data acquisition system for a positron emission tomography camera. An imaging experiment of a Mn-54 point source was performed to demonstrate the imaging capability for the camera, and the source was successfully imaged

Measurements of intensity of produced light in water during irradiations of electron beams with energies above and below the Cerenkov-light threshold

Luminescence of water during irradiation with particles having energies below the Cerenkov-light threshold was recently found for various types of radiations. However, the relation between the intensities of Cerenkov light and of the luminescence of water at the beam energy below the Cherenkov threshold is not well known. To clarify this point, we measured the produced light irradiating a water sample with electron beams having maximum energies above and below the Cerenkov-light threshold. The intensities of light during irradiation of electron beams with different energies increased rapidly at higher energy than ~260 keV while very small intensity was observed at the beam energy below the Cerenkov-light threshold. We conclude that the intensities of light produced in water during irradiation of electron beams with energies below the Cherenkov threshold from the luminescence of water are much lower than those of Cerenkov light

Astatine-211 imaging by a Compton camera for targeted radiotherapy

Astatine-211 is a promising radionuclide for targeted radiotherapy. It is required to image the distribution of targeted radiotherapeutic agents in a patient\u27s body for optimization of treatment strategies. We proposed to image 211At with high-energy photons to overcome some problems in conventional planar or single-photon emission computed tomography imaging. We performed an imaging experiment of a point-like 211At source using a Compton camera, and demonstrated the capability of imaging 211At with the high-energy photons for the first time

Performance improvement of Compton imaging of astatine-211 by optimising coincidence time windows

Astatine-211 is one of the promising radioisotopes for targeted alpha therapy. Optimising treatment strategies as well as determining the suitability of a given agent for a particular patient requires to image the time-dependent distribution of the targeted radiotherapeutic agent both in tumours and in normal tissues. Since the biodistribution of astatine is different from that of iodine, imaging astatine-211 directly is essential. In the previous study of astatine-211 Compton imaging, random coincidence events due to polonium K-shell X-rays were dominant and seemed to cause saturation of counts. Thus optimisation of the coincidence time windows is important to reduce random coincidence events. In this study, we have optimised the coincidence time windows of a Compton camera and improved the sensitivity, noise and spatial resolution of astatine-211 imaging