Objectives: While computed tomography colonography (CTC) has become a non-invasive alternative to traditional colonoscopy, superficial lesions tend to be harder to detect, with reports of lesions <2 mm in height being missed. Therefore, for the evaluation of lesion detectability using CTC, optimizing scan parameters becomes important. In this study, we investigate the effect of the reconstructed matrix size from CTC on the lesion conspicuity. Methods: A CTC phantom was scanned, and images were reconstructed with 512, 768 and 1024 matrix sizes with the same raw data. The image data in each matrix size were compared in terms of physical assessment of the task-transfer function (TTF) and the noise power spectrum (NPS), and of visual assessment using Scheffé’s paired comparison. Results: Comparing 768 and 1024 matrix sizes with that of 512, NPS was higher in high-frequency components. On the other hand, TTF was improved using these larger matrix sizes along with significant statistical differences in the visual assessment. Conclusion: Larger matrix sizes (768 and 1024) improve the lesion conspicuity, thereby helping to detect superficial and small lesions (size<2 mm) in CTC.

Purpose: This study investigated whether real-time variable shape tungsten rubber (STR) could be applied for nail radiation protection in total skin electron beam (TSEB) therapy. Methods: Simulated finger phantoms were made from syringes filled with physiological saline of volumes 5, 10, 20, and 30 ml (inner diameters of 14.1, 17.0, 21.7, and 25.3 mm, respectively). Gafchromic film was applied to the phantom, and lead (thickness 1–3 mm) or STR (thickness 1–4 mm) with an area of 4´1.5 cm was used to cover the film. A 6 MeV electron beam with an 8 mm acrylic board was then used to irradiate the phantom. The source-surface distance (SSD) was 444 cm, the field size was 36´36 cm at SSD of 100 cm without an electron applicator, and the monitor unit was 2000 MU. The shielding rates were obtained from the dose profiles. Results: The mean values of the shielding rate values for all phantoms were 50.1, 97.6, and 98.7% for 1, 2, and 3 mm of lead, respectively, and -13.6, 53.9, 91.2, and 99.4% for 1, 2, 3, and 4 mm of STR, respectively. Conclusion: STR with a thickness of 4 mm had the same shielding properties as lead with a thickness of 3 mm, which was an approximately 100% shielding rate. STR could therefore be used in TSEB therapy instead of lead.

Purpose: Because of the promotion of cancer screening, the number of patients with lung cancer detected at the early stage has increased. However, it was reported that 30-40% of the lung cancer patients at stage I relapsed. If the recurrence risk can be accurately predicted, it is possible to give medical care for improving the prognosis of lung cancer patients. The purpose of this study was to develop a method for the prediction of recurrence risk of patients with lung cancer by using survival analysis of radiomics approach. Method: A public database was used in this study. Fifty patients (25 recurrences and 25 censored cases) classified as stage I or II were selected and their pretreatment computed tomography (CT) images were obtained. First, we selected one slice containing the largest tumor area and manually segmented the tumor regions. We subsequently calculated 367 radiomic features such as tumor size, shape, CT values, and texture. Radiomic features were selected by using least absolute shrinkage and selection (Lasso). Cox regression model and random survival forest (RSF) with the selected radiomic features were used for estimating the recurrence functions of fifty patients. Result: The experimental result showed that average area under the curve (AUC) values of Cox regression model and RSF for the prediction accuracy were 0.81 and 0.93, respectively. Conclusion: Since our scheme can predict recurrence risk of patients with lung cancer by using non-invasive image examinations, it would be useful for the selection of treatment and the follow-up after the treatment.

Purpose: To investigate the actual condition of the crystalline lens equivalent dose and effective dose according to the type of job and the type of duties in a medical institution. We also sought to clarify effective exposure reduction strategies. Methods: Equivalent crystalline lens doses, effective doses, job type, and duties for 8656 persons · year were obtained from 17 medical facilities. We analyzed the relationship between the effective dose and the crystalline lens equivalent dose in uniform exposure control and non-uniform exposure control conditions. Exposure data were obtained for 13 unique job types and duties. Results: The ratio of the lens equivalent dose to the effective dose of non-uniform exposure managers was 2 to 6 times and varied depending on the occupation. The percentage of persons whose annual lens equivalent dose exceeded 20 mSv was 4.75% for medical doctors, 1.17% for nurses, and 0.24% for radiological technologists. Highly exposed tasks included doctors in cardiology and gastroenterology performing angiography and endoscopy, nurses in endoscopy, and radiological technologists in radiography and CT examinations. Conclusion: Thorough unequal exposure control for operations with high crystalline lens exposure, radiation protection education, and effective use of proper personal protective equipment such as the use of radiation protection glasses may reduce lens exposure levels.

Quantitative evaluation of myocardial native T₁ value by measuring modified Look-Locker inversion recovery (MOLLI) method is clinically useful and is used for follow-up of various myocardial diseases. The heart rate during the scan can vary even in the same subjects. Therefore, it is important to know the effects of the heart rate on the native T₁ value of the myocardium. In this study, we evaluated the effect of the heart rate on the T₁ value in the 5s (3s) 3s scheme, time control data collection period of the MOLLI method, using phantom experiments and experiments of healthy volunteers. The 5s (3s) 3s scheme of the MOLLI method is considered to have little dependence on the heart rate, but the T₁ value still varied up to about 7% depending on the heart rate, and was underestimated up to 8% during low heart rate using phantom experiments.

We studied the image resolution properties in digital mammography using the variance and edge response function methods. The associated measurements were made using a polymethylmethacrylate phantom of 0–40 mm thickness while maintaining the incident dose to the detector constant, as well as with and without using the phantom but by varying the level of exposure to the detector. The results obtained using the two methods were compared on the object plane of the mammography unit with compensation for the magnification and rejection of the scattered radiation. In this unit, the imaging process of resolution enhancement may be performed according to the phantom thickness, shape of test device, exposure level, and so on. The modulation transfer function values of the variance method were slightly higher than those of the edge method, approximately 6% at 2 cycles/mm and 8% at 4 cycles/mm without resolution enhancement processing. We concluded that the variance method is more suitable than the edge method for the constancy test or quality control because of its lower coefficient of variation.