Speaker
Description
In recent years, targeted radionuclide therapy (TRT) using alpha-particle–emitting radiopharmaceuticals, such as $^{211}$At, has attracted attention. To confirm the therapeutic efficacy of these agents, it is important to visualize the distribution of $^{211}$At in the body with high accuracy. In animal experiments, $^{211}$At imaging is typically performed using clinical SPECT systems designed for human imaging, which have a typical spatial resolution of approximately 5-10 mm. However, because small animals are much smaller than humans, it is desirable to establish an inexpensive and easy-to-use imaging device that provides an order-of-magnitude higher resolution, while still allowing whole-body imaging.
Therefore, we developed a high-resolution X-ray and gamma-ray camera with a $10 \times 10\ \mathrm{cm}^2$ imaging area specifically designed for mouse imaging and conducted animal experiments. This detector consists of four approximately $5 \times 5\ \mathrm{cm}^2$ MPPC (Multi-Pixel Photon Counter) arrays, a 0.5 mm-pitch diced GAGG scintillator, and a $\phi\,$98 mm tungsten parallel-hole collimator with the same pitch.
Using this device, $^{211}$At-NaAt or $^{211}$At-AuNPs were administered via the tail vein of anesthetized mice, and images were acquired targeting the 79 keV X-rays emitted by $^{211}$At. To further improve resolution, subpixel shift method was applied. This method involves overlaying images acquired at the initial position and a slightly shifted position, averaging the overlapping areas, halving the pixel size and improving resolution without changing the detector configuration. This method was applied to images taken after sacrifice, when the radiopharmaceutical distribution was no longer changing. As a result, accumulation of $^{211}$At in the stomach, thyroid, salivary glands, and bladder was confirmed with a high resolution of 0.25 mm pitch.
