Development of a z-axis tilting technique using a chest phantom to reduce radiation exposure during computed tomography coronary angiography.

Japan has the highest estimated exposure frequency of diagnostic X-rays in the world. Furthermore, the volumetric computed tomography dose index (CTDIvol) and dose length product (DLP) of computed tomography coronary angiography are relatively high in Japanese diagnostic reference levels, and it is important to reduce both dose indices. This study proposed a new exposure reduction technique, the vanishing liver position (VLP), where the body is tilted to the right in the z-axis. The VLP advantages include reduction in the scanning range and overlap between the heart and the liver. Three different electrocardiogram protocols were employed, and changes in the tube current in the z-axis were measured during each protocol. Additionally, changes in the radiation exposure caused by z-axis tilting were evaluated. Our results indicate that this technique reduced CTDIvol and DLP by 6.2 and 8.9%, respectively, at most, indicating that this technique can reduce radiation exposure.

SIMPLE METHOD OF MEASURING SSDE FOR HEAD CT: FACILITATING PRE-CT SCAN DOSE CALCULATION USING SPECIALIZED HEAD SCAN BAND.

In this study, scaled scan band was developed to provide size-specific dose estimation (SSDE) values based on head circumference of patients undergoing computed tomography (CT) scans. The scan band was tested in 40 consecutive head CT examinations. The accuracy of the specialized scan band method was determined by comparing SSDEband with SSDE293,forehead, SSDEmean and SSDEcenter. SSDE293,forehead was used as the control value. The results of the linear fit of SSDEband, SSDEmean and SSDEcenter against SSDE293, forehead, were R2 = 0.958, R2 = 0.984 and R2 = 0.936, respectively. There was no significant difference between SSDEband, SSDEmean and SSDEcenter for SSDE293,forehead. Use of the proposed scan band method makes it possible to accurately determine the required radiation dose before a CT examination is performed.

DEVELOPMENT OF A SPECIALISED TAPE MEASURE TO ESTIMATE THE SIZE-SPECIFIC DOSE ESTIMATE.

The risk in computed tomography (CT) examinations is radiation exposure. We aimed to develop a specialised tape measure for determining the size-specific dose estimate (SSDE) for patients undergoing CT scans. The scanning parameters used were those of the abdominal protocol in our institute. With this method, the SSDE220 and standard deviations obtained from CT images for the liver, pelvic and lung areas, corresponded closely to the SSDEtape and standard deviations obtained using the tape measure. We thus devised a new idea that allows the estimation of the SSDE220 using a specialised tape measure before the CT examination, allowing for an informed explanation of the radiation dose to the patient. Although the tape measure developed in this study is specific to one particular CT instrument, the method could be adapted to a wide range of radiography applications.

Effect of table height displacement and patient center deviation on size-specific dose estimates calculated from computed tomography localizer radiographs.

The aim of this study is to evaluate the effect of table height displacement and patient center deviation along the [Formula: see text]-axis on size-specific dose estimate (SSDE) calculations based on computed tomography (CT) localizer radiographs in pediatric and adult abdominal CT examinations. CT localizer radiographs and CT axial images were acquired with table heights of - 5.0, - 2.5, 0.0 (center), 2.5, and 5.0 cm using two acrylic self-made phantoms filled with water. Water-equivalent diameters ([Formula: see text]) were calculated from the CT localizer radiographs and CT axial images. Relative errors of SSDEs from the CT localizer radiographs to SSDEs from the CT axial images were calculated to evaluate the effect of table height displacement. Furthermore, patient center deviations and indices of SSDE overestimation were measured from the clinical data of 110 abdominal CT examinations. The relative errors of SSDEs in phantoms equivalent to 1-year-old and 20-year-old Japanese reference persons ranged from - 2.45% (table height of 50 mm) to + 1.88% (- 50 mm) and from - 4.22% (50 mm) to + 3.79% (- 50 mm), respectively. The largest center deviation in all patients ranged from - 43.1 to 21.5 mm (median: - 14.4 mm). The indices of SSDE overestimation for all patients ranged from - 16.2 to 6.9 mm (median: - 2.2 mm). We found that the effects of table height displacement and patient center deviation along the [Formula: see text]-axis on SSDEs calculated from CT localizer radiographs in pediatric phantoms were smaller compared to adult phantoms. In order to correct these patient center deviations, it is necessary to apply an appropriate correction technique in each section along the [Formula: see text]-axis.

Analysis of Image Gently Abdominal CT Protocol With the Use of Body Phantom Adapted to the Japanese Size.

OBJECTIVE: The purpose of this study was to analyze in detail the quality of abdominal CT images obtained using three protocols reported by Image Gently in 2014 (hereafter referred to as Image Gently 2014), with the use of a handmade body phantom adapted to typical body sizes of the Japanese population. Moreover, we converted the findings of Image Gently 2014 to match Japanese body sizes and referred to our converted findings as Image Gently Japan. MATERIALS AND METHODS: We scanned each phantom in a mechanical isocenter in accordance with the Image Gently 2014 abdominal imaging protocol. We changed the tube current-exposure time product per rotation from 25 to 250 mAs. The bowtie filter was set with a minimum FOV for the phantom size. We then analyzed the volume CT dose index (CTDIvol)-measured CT number curve. We then used this CT number curve to calculate the CT number recommended by Image Gently Japan for each of the designated patient ages. RESULTS: The CTDIvol-measured CT number curve showed that, as the CTDIvol increased with each age, image noise decreased. When we assumed that the CTDIvol value for adults was 20 mGy, the measured CT number was 12.5 HU. We then multiplied each reduction coefficient by age (neonate and 1, 5, 10, and 15 years). The measured CT numbers for Image Gently Japan performed to attain limited dose reduction were 3.0, 3.9, 4.9, 6.0, and 9.0 HU, respectively, whereas those for Image Gently Japan performed to achieve moderate dose reduction were 3.3, 4.3, 5.3, 6.3, and 9.3 HU, respectively, and those for Image Gently Japan performed to attain aggressive dose reduction were 4.1, 5.1, 5.8, 6.8, and 9.5 HU, respectively. CONCLUSION: We analyzed the abdominal image quality demanded by Image Gently 2014, and we were able to adapt the results to the Japanese population and present them as our own Image Gently Japan recommendations. If the results of the present study become a foundation for scanning parameters for Japanese patients, we believe that they will eventually lead to a reduction in medical radiation exposure for this patient population.

[Method for evaluating the mechanical isocenter of the gantry of a radiotherapy machine with motion picture trace analysis software].

In recent years, development of advanced radiotherapy technology has resulted in an improvement in radiotherapy. Although the radiotherapy system has improved, the effect of the gap, the gyration center, and distortion of the rotation orbit cannot be neglected. Therefore, a verification method for a geometrical isocenter and rotation orbit in a three-dimension (3D) space is required. We developed a verification method for determination of the geometrical isocenter. In this method, the rotation of the gantry that applied the measured target from two directions was imaged and analyzed using animation pursuit analysis software. The measurement targets were pursued by analysis, and the rotation orbit of the target was visually evaluated from obtained coordinates and displacement distance. The gyration center in 3D space was calculated from pursued coordinates and compared with the intersection in the side laser and crosshair. In this verification method, the rotation orbit and geometrical isocenter in the 3D space were confirmed, and visually evaluated. Thus, this method was effective in verifying the geometrical isocenter by solving the problem of the measurement precision and reproducibility.