Examination of postmortem changes in the lungs, trachea, and bronchi in a rat model imaged with small-animal computed tomography.

Objectives: As less autopsies are performed, the need for postmortem computed tomography (PMCT) as an alternative is increasing. It is important to know how postmortem changes over time are reflected on CT, in order to improve the diagnostic capability of PMCT and replace forensic pathology evaluations such as time of death estimation. Methods: In this study, we examined temporal changes on postmortem chest CT images of a rat model. After acquiring antemortem images under isoflurane inhalation anesthesia, the rats were euthanized with a rapid intravenous injection of anesthetics. From immediately after death to 48 hours postmortem, chest images were acquired using small-animal CT. The 3D images were then evaluated on a workstation to measure the antemortem and postmortem air content in the lungs, trachea, and bronchi over time. Results: The air content in the lungs decreased, but the air content of the trachea and bronchi temporarily increased 1-12 hours postmortem, then decreased at 48 hours postmortem. Therefore, the measurement of trachea and bronchi volumes on PMCT could be an objective way to estimate the time of death. Conclusions: While the air content of the lungs decreased, the volume of the trachea and bronchi temporarily increased after death, indicating the potential to use such measurements to estimate time of death.

Optimization of HU threshold for coronary artery calcium scans reconstructed at 0.5-mm slice thickness using iterative reconstruction.

PURPOSE: This work investigated the simultaneous influence of tube voltage, tube current, body size, and HU threshold on calcium scoring reconstructed at 0.5-mm slice thickness using iterative reconstruction (IR) through multivariate analysis. Regression results were used to optimize the HU threshold to calibrate the resulting Agatston scores to be consistent with those obtained from the conventional protocol. METHODS: A thorax phantom set simulating three different body sizes was used in this study. A total of 14 coronary artery calcium (CAC) protocols were studied, including 1 conventional protocol reconstructed at 3-mm slice thickness, 1 FBP protocol, and 12 statistical IR protocols (3 kVp values*4 SD values) reconstructed at 0.5-mm slice thickness. Three HU thresholds were applied for calcium identification, including 130, 150, and 170 HU. A multiple linear regression method was used to analyze the impact of kVp, SD, body size, and HU threshold on the Agatston scores of three calcification densities for IR-reconstructed CAC scans acquired with 0.5-mm slice thickness. RESULTS: Each regression relationship has R2 larger than 0.80, indicating a good fit to the data. Based on the regression models, the HU thresholds as a function of SD estimated to ensure the quantification accuracy of calcium scores for 120-, 100-, and 80-kVp CAC scans reconstructed at 0.5-mm slice thickness using IR for three different body sizes were proposed. Our results indicate that the HU threshold should be adjusted according to the imaging condition, whereas a 130-HU threshold is appropriate for 120-kVp CAC scans acquired with SD = 55 for body size of 24.5 cm. CONCLUSION: The optimized HU thresholds were proposed for CAC scans reconstructed at 0.5-mm slice thickness using IR. Our study results may provide a potential strategy to improve the reliability of calcium scoring by reducing partial volume effect while keeping radiation dose as low as reasonably achievable.

Survey of Careers and Achievements on Delegates in JSRT International Delegation Projects.

Japanese society of radiological technology (JSRT) categorizes three international delegation projects; short-term studying abroad program (STSAP), international academic society visit program (overseas) (IASVP), and international internship visit program (Stanford University) (IIVP) for driving globalization of JSRT. In this survey, we conducted a questionnaire evaluating effectiveness of the international delegations. The survey covered 50 delegates of STSAP, 180 delegates of IASVP, and 100 delegates of IIVP. This survey includes detailed histories of career, current position, academic articles, and presentations as a first presenter before and on, and after each program. We categorized into six groups (change career, promoted in a position in hospital, kept a current position in hospital, promoted in a position in university, kept a current position in university, and others) in three programs. The response rate is approximately 58% (191/330 delegators). In all programs, almost all the delegates were radiological technologists in the hospital. They had reported a lot of academic articles and made a lot of presentations, and promoted in the hospital and/or university. STSAP, IASVP and IIVP were descending order of the average number of the articles as a first author and presentations as a first presenter. They published more the academic articles in Japanese than in English compared to JJRT and RPT. Therefore, research achievements and human resource conducted by this project provide great technologists and technique, and education. For further JRST globalization, it is desirable that we can continue these international delegations and verify the effectiveness.

[Development of automatic window level and width-setting system for abdominal CT scanning].

Window setting is a very important technique in CT examinations. However, most beginner technologists have difficulty in setting the optimal window. Now, thanks to technical progress, it is easy to obtain a great many CT images. On the other hand, it is impossible to provide the optimal window setting for all images. Therefore, our purpose is to offer optimal CT images for every patient by using the automatic window-level and width-setting system. As a result of this experiment, there was a considerable difference in window setting by an expert technologist and that by a beginner technologist. With our system, we were able always to obtain an optimal window setting, such as that set by an expert technologist, regardless of the CT experience of the radiological technologist. We think that this system will be effective in observing animated examinations even if film is no longer used in the future.

[Results of a questionnaire survey on window setting and FOV on CT images of examinations].

The use of CT as a general examination has spread widely and is even used in small institutions. However, it is difficult to determine the current situation of each institution. Therefore, we employed a questionnaire to investigate the current situation of a variety of institutions. From the results of the questionnaire, we determined that the window setting was difficult for beginner technologists. In addition, in many institutions, radiological technologists did not always use the same display FOV for the same patient. From this questionnaire, we were able to determine the present conditions in each institution. We consider these results very useful.

Development of a cardiac evaluation method using a dynamic flat-panel detector (FPD) system: a feasibility study using a cardiac motion phantom.

The purpose of this study is to investigate the feasibility of cardiac evaluation with a dynamic flat-panel detector (FPD), based on changes in pixel values during cardiac pumping. To investigate the feasibility of cardiac evaluation with a dynamic flat-panel detector (FPD), based on changes in pixel values during cardiac pumping. Sequential radiographs of a cardiac motion phantom and water-equivalent material step were obtained with an FPD system. Various combinations of cardiac output and heart rate were evaluated with and without contrast medium. The ventricular area and summation of pixel values in the ventricles were measured. The ejection fraction (EF) was calculated based on the rate of changes and then compared to EF obtained from computed tomography images. In addition, slight changes in pixel values were visualized by use of inter-frame subtraction and color-mapping. The result of a clinical case was examined according to cardiac physiology. There were strong correlations between EF and our results. There was no significant difference between the findings with and without contrast medium. When the heart rate was greater than 60 bpm, EF obtained with our method were underestimated. It is necessary for a patient to be examined at an imaging rate between 7.5 and 10 fps at least. In addition, a +/-1.2% change in pixel value was equivalent to a +/-10 mm change in the thickness of water. Color-mapping images were supported by cardiac physiology. Evaluating changes in pixel values on dynamic chest radiography with FPD has the potential to demonstrate cardiac function without contrast medium. Inter-frame subtraction and color-mapping are very useful for interpreting changes in pixel value as velocities of blood flow.

[Evaluation of time resolution in cardiac synchronized image reconstruction using multi-slice CT].

One of the newest CT application technologies is cardiac synchronized image reconstruction. In this technology, evaluation of time-resolution is very important. We developed a method of measuring time-resolution in cardiac synchronized reconstruction, and evaluated various scanning protocols. In our experiment, ECG-gated scanning was done by multi-slice CT (Aquilion16 Super Heart Edition, Toshiba Medical Systems Co., Ltd., Japan). The nominal slice thickness was 0.5 mm, and rotation time was 0.5 sec. Input heart rate was set at 40, 45, 50, 55, 60, 70, 75, 80, and 90 bpm, and helical pitch at 3.2, 4.0, and 4.8 (beam-pitch: 0.200, 0.250 and 0.300). We measured FWTM of the obtained sensitivity distribution and compared at each scanning protocol. Time resolution improved as helical pitch decreased and heart rate increased. However, phase-time resolution deteriorated as heart rate increased. The results of our experiment indicated that a segment center was determined by X-ray tube rotation time and heart rate, and the number of segments was determined by heart rate, helical pitch, and reconstruction position. Time resolution changed with X-ray tube rotation time, heart rate, helical pitch, and reconstruction position. In this report, we provide a reference for an optimal scanning protocol in cardiac synchronized image reconstruction.