No abstract

For high-sensitivity brain imaging, we have developed a two-head single-photon emission computed tomography (SPECT) system using a CdTe semiconductor detector and 4-pixel matched collimator (4-PMC). The term, '4-PMC' indicates that the collimator hole size is matched to a 2 × 2 array of detector pixels. By contrast, a 1-pixel matched collimator (1-PMC) is defined as a collimator whose hole size is matched to one detector pixel. The performance of the higher-sensitivity 4-PMC was experimentally compared with that of the 1-PMC. The sensitivities of the 1-PMC and 4-PMC were 70 cps/MBq/head and 220 cps/MBq/head, respectively. The SPECT system using the 4-PMC provides superior image resolution in cold and hot rods phantom with the same activity and scan time to that of the 1-PMC. In addition, with half the usual scan time the 4-PMC provides comparable image quality to that of the 1-PMC. Furthermore, (99m)Tc-ECD brain perfusion images of healthy volunteers obtained using the 4-PMC demonstrated acceptable image quality for clinical diagnosis. In conclusion, our CdTe SPECT system equipped with the higher-sensitivity 4-PMC can provide better spatial resolution than the 1-PMC either in half the imaging time with the same administered activity, or alternatively, in the same imaging time with half the activity.

We propose a wide aperture parallel-hole collimator that we call a 4-pixel matched collimator (4-PMC) for high-sensitivity SPECT imaging. The hole size of the 4-PMC is matched to four detector pixels; that is, there are four (2 × 2) pixels per collimator hole. By contrast, a 1-pixel matched collimator (1-PMC) is defined as a collimator whose hole size is matched to one detector pixel. We evaluated four types of collimator (high-resolution collimator versions and high-sensitivity collimator versions of both 4-PMC and 1-PMC) by simulation. SPECT images of a cylindrical phantom with cold spots in the noise-free condition demonstrated that the 4-PMC provided a higher-contrast image than the 1-PMC for the same collimator version. In addition, SPECT images at the noise level corresponding to a human cerebral blood flow study suggested that the high-sensitivity version of the 4-PMC provided the highest contrast image among the four collimator types. In conclusion, the high-sensitivity SPECT system using the 4-PMC can improve the trade-off between spatial resolution and sensitivity and will consequently provide improved image contrast for clinical studies of the human brain compared with the SPECT system using the 1-PMC.

The basic performance of the CdTe-gamma camera system was evaluated, and its stability was verified. It was shown that the camera could be operated daily for several months without calibration.

Measurement of radioactive contamination and confirmation of the decontamination effects are important for the recovery from the nuclear accident at the Fukushima Dai-ichi Nuclear Power Plant. We have developed a gamma camera which can visualize the gamma-ray intensity distribution in real time. Experiments were conducted to investigate its performance. An energy resolution of 2.3 % and spatial resolution of 0.68 m at a distance of 5 m were confirmed. In addition, field tests were conducted in the Fukushima Dai-ichi Nuclear Power Plant. The gamma-ray intensity distribution was successfully visualized within as short a time as 10 seconds in an environment with an air dose rate of 1 -10 mSv/h. Prominent gamma-ray radiation was found from the penetration holes, which connect the inside and outside of the primary containment vessel. From this result, it was found that shielding the penetration holes will improve the work environment during decontamination and cleanup activities. These results indicate the gamma camera will contribute to decontamination work and radiation exposure reduction for workers.