Medical imaging devices such as CT and MR have developed remarkably, and many of them have been used in clinical examination. At the same time, because computer performance has drastically improved, many of clinical applications for medical images have been developed actively. Many of these clinical applications are focused on throughput, and is designed so that the user can get the result without having to know the details. Therefore, many processes in these applications have been black box, users can not know the details of them. However, use of the basic knowledge about digital image processing, users can infer what kind of algorithms are used in clinical application. This article provides basic knowledge of digital image processing and medical image processing algorithms frequently used in clinical applications.
For Quality Assurance of clinical radiation therapy, it is necessary to accurately measure multiple doses, and evaluate and compare the results to the radiation treatment system. Based on the measurements using multiple dosimeters,there is no uncertainty estimation of the delivered dose for accurate analysis. In this study, we focused attention on smalltype optically stimulated luminescence（OSL）dosimeters, and clarified the relationship of uncertainties between the experimental variance associated with multiple data points and the variance predicted by Poisson distribution. The experiments were carried out as follows : fifteen dosimeters were placed in a water equivalent phantom, they were irradiated with X-rays having an acceleration voltage of 10-MV with 167.2 cGy（200 MU）and 2,090 cGy（2,500 MU）. Each dosimeter was read ten times and the experimental variance and predicted variance were analyzed. As a result, we found that the experimental uncertainties were 3.9 and 6.2 times higher than predicted uncertainty when irradiated at 167.2 cGy and 2,090 cGy, respectively. We discuss the relationship of measurement uncertainties. Then, we concluded that the uncertainty of OSL dosimeters was found to be 3%. We also conclude that the OSL dosimeter can be used to measure the absorbed dose in the radiation therapy region.
The purpose of this study was to investigate the effect of heavy metal filters for patient dose reduction and improving image contrast in digital radiography using a CsI based flat panel detector. The heavy metal filters used in this study were gadolinium, holmium, and ytteribium. These filters have a K-absorption edge in the range from 50 to 70 keV. Also, images without filters and images with conventional copper filter were obtained for comparative study. Iodine-water contrast and patient skin dose were measured in each combination of tube voltage（70and80kV）and filters. Compared with the condition of 80 kV tube voltage without filter, the combination of 80 kV tube voltage and holmium or ytteribium filter reduced patient skin dose by 35% without degrading image contrast. And the combination of 70 kV and ytteribium filter achieved improvement of the iodine-water contrast by 22% and a dose reduction of 8% compared with the condition of 80 kV tube voltage without filter. Appropriate additional heavy metal filters for digital radiography when using flat panel detectors can reduce patient dose without degrading image contrast.
June 7, 2015, Japan Network for Research and Information on Medical Exposures（J-RIME）published Diagnostic Reference Levels（DRLs 2015）for the first time in Japan. To operate the DRL, it is necessary to collect a great deal of radiation dose information of own facilities efficiently. The purpose of this study was to construct a system for collecting dose information in CT examination using Radiation Dose Structured Report（RDSR）. As a result of displaying the contents of RDSR using the free software, it was confirmed that there are differences in the information in RDSR by equipment and manufacturers. In-house software of dose management could be designed by focusing on the enumerated value, it was possible to extract information of interest from RDSR. For facilities which cannot introduce a commercial system, development of software for collecting radiation dose information using RDSR contributes greatly to the operation of DRL.
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