Japanese Journal of Radiological Technology

Exposure index (EI) is expected as important standard for the optimization of image quality and exposed dose in digital radiography. It is set a region of interest (ROI) in a radiograph, to obtain a histogram of pixel values within an ROI, it is computed as EI of the image representative value of the histogram. In this study, we examined the effects of setting the ROI for EI computing. We set five different ROIs in chest or cervical spine frontal radiograph, and compared the computed EI in each ROIs. From the result, in some cases, we found that EI varied greatly as those compared to the case of ROI set in full image. We should consider about setting the ROI for EI computing when we use EI as standard for optimization of image quality and exposed dose in digital radiography.

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There are two types of radiophotoluminescent glass dosimeters (RPLDs). One has a tin filter in the capsule (GD-352M) and the other has no filter (GD-302M). The purpose of our study was to evaluate the properties of these RPLDs for computed tomography (CT) dosimetry: energy dependence, variation, angular dependence, and dose distribution in a single slice. Energy dependence and variation were investigated for ratio of the air kerma measured by RPLDs to that by ion chamber. Angular dependence was investigated for RPLDs and ion chamber. RPLDs were irradiated at 90°, 60°, 30°, 0°, −30°, −60°, and −90°: 0° was vertical to long axial direction of the RPLD, and plus and minus meant clockwise and anti-clockwise, respectively. Dose distribution in a single slice of an anthropomorphic phantom was acquired using 46 RPLDs. The dose responses of GD-302M and GD-352M depended on beam energy and irradiation angle of X-ray, respectively. The dose variation among dosimeters was large with GD-352M. The dose obtained from GD-352M was lower than that from GD-302M. It was expected that the dose distribution of GD-352M was formed by the primary X-ray, so RPLD without tin filter should be used for CT dosimetry.

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Discovery NM 530c (CZT SPECT) is a new single photon emission computed tomography (SPECT) scanner using a cadmium-zinc-telluride (CZT) solid-state semiconductor detector technology. Due to multi-pinhole collimator design of this system, each CZT detector facing different direction and be able to get incidence radioactivity from radioisotopes (RIs) existing outside of effective field of view (EFOV). The purpose of this study is to verify its impact and compare it to a conventional Anger-type SPECT scanner (Discovery NM/CT 670 pro). We used ^99mTcO₄^– as radiation source and set it outside of the EFOV at several different positions (height and angle) and scanned by both the cameras. As a result, CZT SPECT got more influence compared to Anger-type SPECT. The impact was different according to its height. When using other RIs in CZT SPECT room, it is important to confirm the appropriate position against CZT SPECT during scan.

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