[Reduction of Operator Exposure Radiation Dose and Evaluation of Image Quality Using Half Scan in CT Fluoroscopy]

In recent years, the number of examinations and treatments using computed tomography fluoroscopy (CTF) has been increasing, and there is concern about an increase in the exposure radiation dose of the operator. Use of half scan CTF can be expected to reduce the exposure radiation dose, but there is no report. The purpose of this study was to evaluate the exposure radiation dose at the operator's position and image quality when using a half scan CTF. The left side facing the gantry was the operator's position, and the ambient dose equivalent at 160 cm, 130 cm, and 100 cm from the floor was measured using an ionization chamber survey meter. The absorbed dose at the forceps holding position of the operator was measured using a fluorescent glass dosimeter with the forceps holding position 15 cm caudal from the scan center. The imaging conditions used a tube voltage of 120 kV and a tube current of 50 mA. Half scan CTF was performed by changing the center angle of the half scan on the console every 45°. As a result, the set angles were 135°and 90°at the operator's position, and 135°at the operator's forceps holding position. In addition, we evaluated the effect of half scan CTF on image quality. CTF images were collected with a cryogenic needle used for cryotherapy punctured in a water-equivalent self-made phantom. The profile curves of the obtained images were drawn and compared using analysis software to evaluate the effects of artifacts. Then, the SD of the CT value of the region of interest with and without the artifact was measured, and the relative artifact index was calculated and evaluated. Using the same image, CT value and SD were tested to evaluate noise. Half scan CTF had no effect on the image quality due to artifacts and noise.