[Multi-facility Survey on Accuracy and Calibration Method for Dose Area Product Meter of Angiography Systems].

In many facilities, the displayed dose of dose-area product (DAP) is used for the dose management of interventional radiology. In this study, we investigated the measured dose at the patient entrance reference point (interventional reference point) and the displayed dose on each angiography systems. Also, we investigated the calibration method of each DAP. The errors of the measured dose and the displayed dose were less than 35%, but that dispersion was wide between the systems. The calibration methods varies according to a system. And even in the same manufacturer, the calibration methods were different. Therefore, to use the displayed dose of DAP for patient dose management, we need to compare that with the measured dose regularly. The differences of calibration methods induce the wide dispersion of the errors of the measured and the displayed dose. So the standardization of the calibration method in each manufacturer is expected.

[Measurement of Head and Neck Exposure in CT Guided IVR].

In April 2011, the International Radiological Protection Committee recommended that "The equivalent dose of the crystalline lens should not exceed 20 mSv/year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv". Based on this recommendation, it is predicted that the equivalent dose limit of our crystalline lens can be lowered in the near future. Therefore, it is important to grasp the current situation of radiation exposure. The purpose of this study is to measure the crystalline lens of surgeons by focusing on the CT-fluoroscopy guided interventional radiology's (IVRs). We also examined whether the exposure dose of the crystalline lens can be correctly evaluated by measuring the unequal exposure dose of the neck, which is usually used for the unequal exposure measurement. Results of the analysis of 200 CT-fluoroscopy guided IVR procedures showed that the unequal exposure dose of the neck was significantly correlated with the exposure dose of the crystalline lens which was measured near the left eye ball (R=0.83). However, the exposure dose of the crystalline was 33% lower than those of the neck. Therefore, although the individual dosimeter worn on the neck can be used as the useful index of the exposure dose of the crystalline lens, the results can be overestimated.

The Measurement of X-ray Fluoroscopy Input-output Characteristics in Angiography System.

PURPOSE: Determination of X-ray fluoroscopy radiation dose and contrast with angiographic system automatically depending on the objects, and to control setting manually, which is difficult for the measurement of characteristics. Therefore, we examined the method to adjust the conditions of fluoroscopy and measured the input-output characteristics. METHOD: To adjust and fix the condition of fluoroscopy, the exposure adjustment area at the center of the irradiation field was moved to the left side and attached the copper plates to regulate the exposure dose. The area to measure the digital value was selected at the center of the irradiation field, and the dosimeter was placed at the right side of the area, which was selected to measure the digital value. To regulate the entrance dose progressively, the acryl plates were inserted into the irradiation field except for the exposure adjustment area. We obtained a characteristic curve from the measured dose and the digital value. Difference of lookup table (LUT), dose dependency, and tube voltage dependency were checked by the digital characteristic curves. RESULT: Each LUT showed different curves, but they all saturated with 4095, which is the maximum value of 12 bits. Dose dependency was measured as an increase in the permitted dose level with an increase in the setting dose. Tube voltage dependency improved with the tube voltage rises. Each characteristic curve became same by converting the relative exposure dose. As a result, measuring the shape of LUT would be possible. CONCLUSION: The method is useful for measuring the characteristic curve with the X-ray fluoroscopy of angiographic system.

[The Time Sequence Noise Characteristics of the X- ray Fluoroscopic Image].

The role of the X-ray fluoroscopic image during interventional radiology (IVR) is not only the real-time dynamic image for the catheter operation but also to confirm the vascular anatomy using stored image, so that the importance increases more. For the purpose of measuring the time sequence characteristics of X-ray fluoroscopic image, we sampled the digital value of the same coordinate from each X-ray fluoroscopic image and calculated the frequency properties of the noise for the time sequence order as NPStime by performing Fourier transform on the digital value. The parameters, except k-factor which is the time sequence filter, did not influence NPStime. NPStime, which was examined in this study, showed that it is valuable for the method to analyze the time sequence noise characteristics. And, it also showed that it is possible to evaluate the time sequence image processing parameters of X-ray fluoroscopic image by NPStime. Nowadays, each manufacture of the X-ray angiographic system performs the original image processing to their own X-ray fluoroscopic images. The results of the discussion in this study could show the quantitative analysis on the frequency modulation. And it is possible to calculate NPStime by measuring the digital value of stored X-ray fluoroscopic image. The analysis by this method is also technically convenient for the time sequence noise characteristics of the X-ray fluoroscopic image.

Radioprotective Effects of a Semicircular X-ray Shielding Device for Operators During CT Fluoroscopy-Guided Interventional Procedures: Experimental and Clinical Studies.

PURPOSE: To evaluate, experimentally and clinically, the radioprotective effects of a semicircular X-ray shielding device for operators during CT fluoroscopy-guided IR procedures. MATERIALS AND METHODS: During experimentation, the reduction rates of scattered radiation rates from CT fluoroscopy were evaluated using a humanoid phantom. Two shielding device positions were tested: "shielding close to the CT gantry" and "shielding close to the operator". The scattered radiation rate without shielding was also evaluated. The clinical study retrospectively evaluated the operator's radiation exposure during 314 CT-guided IR procedures. With a semicircular X-ray shielding device (with shielding group, n = 119) or without it (no shielding group, n = 195), CT fluoroscopy-guided IR procedures were performed. Radiation dose measurements were taken using a pocket dosimeter placed near the operator's eye. For shielding and no shielding groups, the procedure time, dose length product (DLP), and the operator's radiation exposures were compared. RESULTS: Experimentation revealed the respective mean reduction rates of "shielding close to the CT gantry" and "shielding close to the operator" as 84.3% and 93.5% compared with the no-shielding setting. Although no significant differences were found in the procedure time and the DLP between "no shielding" and "with shielding" groups in the clinical study, the operators' radiation exposure in the "with shielding" group (0.03 ± 0.04 mSv) was significantly lower than in the "no shielding" group (0.14 ± 0.15 mSv; p < .001). CONCLUSION: The semicircular X-ray shielding device provides valuable radioprotective effects for operators during CT fluoroscopy-guided IR.