Speaker
Description
In nuclear medicine, there is a growing need for imaging systems capable of visualizing gamma rays in the several-hundred keV range. One notable application is the imaging of radioactive gold nanoparticles, which emit 412-keV gamma rays. Although considered promising drug carriers, their biodistribution is not fully understood, making it important to visualize their distribution in animal experiments. However, high-resolution imaging devices for several-hundred keV gamma rays have not yet been developed. Single-photon emission computed tomography (SPECT) uses a gamma-ray detector with a collimator that limits the incident direction of photons. Although widely used in clinical practice, conventional SPECT typically has a spatial resolution of ~5 mm, which is insufficient for small-animal imaging. Moreover, SPECT is usually limited to photon energies below 200 keV, as high-energy gamma rays tend to penetrate the collimator walls. While thick collimator walls are required for high-energy photons, they significantly reduce the sensitivity of the system.
Therefore, we developed a high-contrast SPECT (HC-SPECT) for high-resolution imaging using high-energy gamma rays. The system employs a 1-mm pitch array of Gd₃(Ga,Al)₅O₁₂(Ce) (Ce:GAGG) scintillators coupled with a multi-pixel photon counter (MPPC) array. For whole-body imaging of mice, we assembled 10 × 10 cm² scintillator array and four 5 × 5 cm² MPPC arrays. To enable high-energy gamma-ray imaging, we also developed a novel collimator featuring hourglass-shaped holes, which are wider at the top and bottom surfaces and narrower in the middle. This design allows for thicker collimator walls while maintaining higher sensitivity than conventional parallel-hole collimators, enabling both high sensitivity and high resolution.
In this presentation, we will present performance evaluation results of HC-SPECT and compare its performance with that of conventional SPECT and a Compton camera, which is commonly used for high-energy gamma-ray imaging.
