The use of an adaptive filter for CT images is becoming a common procedure and is said to reduce image noise while preserving sharpness and helping to reduce the required X-ray dose. Although many reports support this view, the validity of such evaluations is arguable. When the linearity of a system is in question, physical performance indexes should be measured under conditions similar to those of clinical use. Evaluations of diagnosis using clinical images may be fallible because the non-filtered image used as the reference might not have been optimally reconstructed. We have chosen simple, but commonly used, adaptive filters for our evaluation. As a reference for comparing performance, we designed linear filters that best approximate the noise characteristics of the adaptive filters. MTF is measured through observation of the edge-spread function. Clinical abdominal images are used to compare the performance of adaptive filters and linear filters. We conclude that the performance of the type of adaptive filter we have chosen is virtually the same as that of the linear filter, as long as the image quality of soft tissues is our interest. Both the noise SD and MTF are virtually the same if the contrast of the object is not substantially higher than 150 HU. Images of soft tissues obtained with the use of adaptive filters are also virtually the same as those obtained by linear filters. The edge-preservation characteristic of this adaptive filter is not observable for soft tissues.
The number of examinations using interventional radiology (IVR) has increased recently. Because of the more advanced and more complex procedures for IVR, longer treatment time is required. Therefore, it is important to determine exposure doses. We measured operator exposure dose during IVR using a thermoluminescence dosimeter. The results revealed the dose equivalent to the operator’s hands and fingers to be higher than that of other parts, although the effective dose for the operator was low. Moreover, we looked into the factors that affected exposure dose to the operator’s fingers, and examined ways to reduce the dose. In regard to the exposed dose to the operator’s fingers, dose reduction was possible as a result of a geometric arrangement of the fluoroscopic unit, the radiation field size, using a radiation protective device and deliberation to exposure dose reduction of the operator. It is possible to carry out IVR more safely using the method of exposure dose reduction to the operator’s fingers.
The purpose of this study was to clarify the information literacy of undergraduate students and problems in information education. An annual questionnaire survey was carried out by an anonymous method from 2003 to 2006. The survey was intended for third-year students in the Department of Radiological Technology. The questionnaire items were as follows: (1) ownership of a personal computer (PC), (2) usage purpose and frequency of PC operation, (3) operation frequency and mechanism of the Internet, and (4) IT terminology. The response rate was 100% in each year. The ratio of PC possession exceeded 80%. The ratio of students who replied “nearly every day” for the use of a PC and the Internet increased twofold and threefold in four years, respectively. More than 70% of students did not understand the mechanism of the Internet, and more than 60% of students did not know about TCP/IP. In the future, we need to consider information literacy education in undergraduate education.
Purpose: In our institution a CT scanner was installed in the same room as the linear accelerator. In stereotactic body radiotherapy (SBRT) we confirmed the isocenter position by serial thin-slice and long-scan-time CT images before every treatment as well as in planning. In planning we constructed digitally reconstructed radiography (DRR) of both the anterior and lateral views. At the first treatment we also checked the isocenter with linacgraphy. Then we compared the isocenter positions obtained from the DRR and linacgraphy. Materials and methods: Between Feb. 2005 and Oct. 2006, we treated 75 lung and liver tumors with SBRT in this way. Based on bony structures, we measured the differences between in-isocenter positions for SI, LR, and AP directions between DRR and linacgraphy. Results: The median (min–max) of the differences in-isocenter positions for SI, LR, and AP directions between DRR and linacgraphy were 0.0 mm (0–6.0), 0.0 mm (0–10.0), and 0.0 mm (0–10.0), respectively, as well as 3.2 mm (0–12.3) for 3-dimensional distance. In 28 tumors (37%) the differences exceeded 5 mm in three-dimensional distance. The frequency of differences exceeding 5 mm in upper lung lesions tended to be more than that in liver lesions, and that in left pulmonary lesions was significantly more than that in right ones. Conclusion: This result suggests that the relative position of the target volume to the bony structure differ in planning and in every treatment. It was recommended to verify isocenter accuracy in institutions where isocenter position is checked only by orthogonal linacgraphy in SBRT.
With attention given to the fact that information on weight and height is available in advance from electronic medical charts, we devised a method for determining body thickness on the basis of a simple calculation. The formula is as follows: body thickness=weighta×heightb×f. In order to obtain body thickness from the above formula, it is necessary to determine optimal factors of a, b, and f. Therefore, the formula is modified to give f=body thickness/weighta×heightb. Then, a multiplier of a with b is changed to determine a combination in which f is varied to the smallest extent. Every site of the body is checked to find that an optimal multiplier of a with b is weight0.6×height–0.8. This multiplier is applicable to all sites of the body. Then, f is given as a median of 15 to 74 cases in which calculation is made for each case based on the formula of weight0.6×height–0.8 and the body thickness. A difference between calculation values and measured values is equivalent to the variation of f in which the median is given as 100%. The variation of f at all sites of the body is 3% to 11% in terms of average absolute deviation. The calculation difference is obtained by the formula of body thickness×average absolute deviation. Where the calculation difference is within the above range, clinical practices will be influenced to a small extent. Thus, this study will provide an effective method for determining body thickness.
The purpose of this study was to verify the shielding evaluation method for medical X-ray imaging facilities in Report No. 147 of the National Council on Radiation Protection and Measurements (NCRP). We investigated the concept of radiation protection and the major revised point in Report No. 147. The goal of radiation protection in Report No. 147 was compared with that in Japan. Using the data of the Imaging Performance Assessment of CT scanners (ImPACT) 2006 and the latest pre-installation manuals of several manufactures for different computed tomography (CT) scanner models, we verified the shielding method for CT installations. The concept of radiation protection in Report No. 147 was based on the recommendation of the International Commission on Radiological Protection (ICRP) Publication 60. On the shielding method for CT units, compared with the CT scatter fraction for the body phantom in Report No. 147 was approximately 10% less than the results of the computation. In conclusion, we should note the use of the CT scatter fraction for the body phantom provided by Report No. 147; however, it is possible to apply the fundamental concept of the shielding evaluation in Report No. 147 to the shielding evaluation method in Japan.