[Improvement of Beam Hardening Effects of Virtual Monochromatic Image in Dual-energy CT: A Electron Density Phantom Study].

PURPOSE: A virtual monochromatic image (VMI) is acquired from two different types of polychromatic energy X-rays, not a monochromatic X-ray. The effective energy of monochromatic X-ray does not vary in passing through the patient's body. On the other hand, beam hardening effects are seen in images because of the change of polychromatic X-ray energy. The purpose of the present study was to evaluate the beam hardening improvement effect of VMI using a phantom with a bone mimicking ring. METHOD: We used a water equivalent electron density phantom with a hole in the center for inserting various measurement materials (i.e. fat, two types of bone with differing densities, contrast medium, blood, and water). Then, the CT numbers of each measurement materials were obtained from single energy CT (SECT) images and VMIs, respectively. Also, an additional bone-mimetic ring was used to obtain the CT numbers for evaluation of beam hardening effect. The CT number change rates were calculated from the obtained CT numbers with and without beam hardening effect. RESULT: The rate of CT number, change of VMI was significantly lower than that of SECT for all measured materials. CONCLUSION: In this study, VMI minimized changes in CT numbers due to the beam hardening effect and showed a higher beam hardening reduction effect.

A more accurate and safer method for the measurement of scattered radiation in X-ray examination rooms.

Advancements in and increasing usage of complex diagnostic examinations with interventional procedures and surgeries has led to an increase in the occupational radiation doses received by physicians and other medical staff. Measuring the scattered radiation doses received by these staff is vital for the development-effective radiation protection programs. In this study, we measured scattered doses during angiography and digital breast tomosynthesis examinations with small-type dosimeters using our jungle gym (JG) method with measurement points at 50-cm intervals. The results were compared with measurements taken using the conventional ion chamber method. The JG method uses paper pipe tubes and a plastic joint structure and allows measurements at different points inside an examination room. The difference between measurements can be attributed to the radiation absorption characteristics of the components used in the JG method. A maximum radiation dose reduction of 20% was observed due to absorption by the JG components. This effect was smaller than the measurement error produced because of reproducibility issues and other limitations of the conventional method. The conventional measurement has disadvantages that are associated with the reproducibility of measurement points, equipment load, and the radiation exposure experienced by the measurer. The proposed JG method exhibits significant improvements in all these aspects. Furthermore, the measurer does not have to be present in the measurement room; therefore, the JG method is extremely safe and useful for radiation protection.