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

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.

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.

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.

The method is useful for measuring the characteristic curve with the X-ray fluoroscopy of angiographic system.