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The nuclear accident that occurred in Fukushima, Japan, in 2011, resulted in considerable radiation leaks and mass exposure owing to an insufficient initial response to the disaster. To prevent similar disasters in the future, their cause should be identified, analyzed, and addressed using radiation-monitoring systems. The core component of a radiation-monitoring system is the gamma camera. It consists mainly of a gamma detector and a collimator. We proposed a diverging collimator that incorporates a novel concept of a curved surface such that the collimator hole length is constant for all the incident hole angles. Therefore, the sensitivity is likely to be more uniform across the field of view (FOV) compared with the case of the conventional flat collimator. Through a simulation study, we determined the collimator parameters and compared the performance of the curved collimator with that of the conventional flat collimator. The results revealed the feasibility of achieving higher uniform sensitivity, up to 10.5% at the edge of the FOV by using the proposed curved collimator. The average peak-to-background ratio (PBR) of the curved collimator was determined to be higher by 10.8% across the entire FOV. This indicates that it produced a more distinct signal than the flat collimator. In our future research, we intend to fabricate a curved collimator and evaluate its performance experimentally.

Crystal area segmentation is one of the critical procedures for decoding the detector module coupled with scintillation crystal. However, the blurring effect makes the decoding procedure challenging. For precise decoding, we propose a crystal area segmentation method based on convolutional neural network (CNN). The method is divided into training stage and evaluation stage. In the training stage, data set was extracted from five flood maps in blocks. These blocks went over preprocessing with bandpass filter (BPF) and thresholding. Then the processed blocks were used to train and test the CNN. In evaluation stage, flood map from 2 positron emission tomography (PET) scanners were tested. The method showed 99.5% and 99.4% of peak detection accuracy for each test samples while existing method achieved 91.1% and 95.4%. The proposed algorithm detected center peaks almost perfectly and improved detectability of boundary peaks. Also, the whole decoding process was done in short amount of time. However, the algorithm proposed in this paper only considered the spatial information of the peaks in flood map. In further studies we will develop improved algorithm with using both spatial and energy information to develop more precise and practical decoding algorithm.

This study evaluated the shielding effect of a newly developed dose-reduction fiber (DRF) made from barium sulfate, in terms of radiation doses delivered to patients’ radiosensitive organs and operator during C-arm fluoroscopy and its impact on the quality of images. A C-arm fluoroscopy unit was placed beside a whole-body phantom. Radiophotoluminescent glass dosimeters were attached to the back and front of the whole-body phantom at 20 cm intervals. Radiation doses were measured without DRF and with it applied to the back (position 1), front (position 2) or both sides (position 3) of the phantom. To investigate the impact of DRF on the quality of fluoroscopic images, step-wedge and modulation transfer function phantoms were used. The absorbed radiation doses to the back of the phantom significantly decreased by 25.3–88.8% after applying DRF to positions 1 and 3. The absorbed radiation doses to the front of the phantom significantly decreased by 55.3–93.6% after applying DRF to positions 2 and 3. The contrast resolution values for each adjacent step area fell in the range 0.0119–0.0209, 0.0128–0.0271, 0.0135–0.0339 and 0.0152–0.0339 without and with DRF applied to positions 1, 2 and 3, respectively. The investigated DRF effectively reduces absorbed radiation doses to patients and operators without decreasing the quality of C-arm fluoroscopic images. Therefore, routine clinical use of the DRF is recommended during the use of C-arm fluoroscopy.

Single-photon emission computed tomography (SPECT) is a nuclear medical imaging method enabling the user to view functional images of patients. The collimator, which is an essential component of the SPECT, limits the direction of the incident gamma rays, such that the distribution of the gamma photons from the body can be observed. Collimators are composed of shielding materials with high atomic number and density, thus it is difficult to fabricate them in complex shapes. Among the existing collimators, the pinhole collimator consists of a small aperture perforated in a shielding material, and the modification of the pinhole parameters, such as the hole diameter and acceptance angle, during the scan is also challenging. A variable pinhole (VP) collimator comprises several thin tungsten layers with various hole sizes. Thus, the pinhole parameters can be varied for the region of interest (ROI) by forming the desired pinhole shape using a combination of holes. In this study, we implemented the concept of a VP collimator and applied it in a SPECT system to enhance its performance. The collimator was composed of five layers of with a diameter of 170 mm and thickness of 1 mm and with six holes of different sizes in each layer. Two point sources (Co-57, 122 keV) were used for the performance analysis by changing the system parameters. The spatial resolution and sensitivity of the SPECT system were affected by the variation of the pinhole diameters, with the peak-to-valley ratio increasing by up to 3.3 times with the increase in the magnification of the SPECT system. Two line source phantoms (Tc-99m, 140 keV) with an internal diameter of 1 mm were used for the performance evaluation of the system. The phantoms were positioned 20 mm apart inside the ROI with a diameter of 50 mm at a position of 29 mm from the object center. By applying the VP collimator, the resolution and the sensitivity performance were improved, achieving a full width at half maximum value of 2.7 times and counts of 2.8 times those of the conventional SPECT system. In future research, we aim to improve the system efficiency by conducting simultaneous experimental driving test of the dual-head VP collimator SPECT system.