Japanese Journal of Radiological Technology

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Plaque imaging using computed tomography (CT) is an important diagnostic method for predicting the risk of vascular events. However, the CT value variability of plaques, which depends on the scan parameters, remains a key challenge. The aim of this study was to evaluate the effect of reconstruction properties on the CT value, area, and shape reproducibility of plaques. In general, the types of reconstruction kernels in a CT system are limited, thus impeding the acquisition of the necessary resolution properties (modulation transfer functions: MTFs). We therefore obtained images with eight types (smoothed to edge-enhanced) of resolution property by applying frequency processing to the original CT images. We made phantoms of simulated 6-mm-diameter vessels with plaque and scanned them at different doses. The CT values, areas, and shape reproducibility of plaques were measured from each processed image. Enhanced-type resolution with no edge enhancement (not exceeding 1.0) effectively raised the CT value and shape reproducibility accuracies. However, edge-enhancement type resolution caused errors in the CT value, area and shape reproducibility.

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To prevent the recurrence of irradiation accidents, monitor-unit (MU) verification that is independent of the MU values calculated using the radiation treatment planning system (RTPS) is required. In this study, we investigated whether independent verification of MU values is being conducted in medical settings and examined the types and methods used. Our results indicate that 93.8% of facilities conduct independent MU verification. The methods used vary according to the facility: 30.4% conduct actual measurements, 18.6% use MS-Excel calculation sheets, 16.7% use specialized commercially-available software, 14.7% use spreadsheets 13.7% use calculators, and 5.9% use other methods. In this study, we were able to formulate basic data that can be used for information-sharing between facilities.

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Quality control (QC) detects changes in the performance of gamma cameras that could adversely affect interpretations of clinical studies. We used plate and sheet ⁵⁷Co flood sources to measure extrinsic uniformity during daily QC. Each source, when placed on the top of a collimated detector, allowed the acquisition of uniform images from both detectors, thus reducing the amount of time needed to perform daily QC. No serious problems with the gamma camera system were revealed by visual checks, and changes in detector sensitivity were rapidly determined by observing daily variations in the measured values of extrinsic uniformity. Furthermore, ⁵⁷Co flood sources confer advantages in that they shorten the time required for preparation of flood sources and reduce the consequent exposure of medical staff to radiation.

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