A study on fluoroscopic images in exposure reduction techniques ― Focusing on the image quality of fluoroscopic images and exposure images

Abstract The quality of the present day fluoroscopic images is sufficiently high for use as exposure images depending on the environment where the fluoroscopic images are recorded. In some facilities which use fluoroscopic images as exposure images they are recorded with a radiological x‐ray diagnostic device equipped with a fluoroscopic storage function. There are, however, cases where fluoroscopic images cannot be used as exposure images because the quality of the fluoroscopic image cannot be assured in the environment where the fluoroscopic images are recorded. This poses problems when stored fluoroscopic images are used in place of exposure images without any clearly established standard. In the present study, we establish that stored fluoroscopic images can be used as exposure images by using gray values obtained from profile curves. This study finds that replacement of stored fluoroscopic images with exposure images requires 20.1 or higher gray scale value differences between the background and signal, using a 20 cm thick acrylic phantom (here an adult abdomen as representing the human body) as the specific geometry. This suggests the conclusion that the gray value can be considered a useful index when using stored fluoroscopic images as exposure images.

the purpose to record the progress of the treatment being the record used for treatment assessments of the blood vessel in the diseased area and as image data for repeated observations following the treatment. For this reason, the imaging dose is set higher than the fluoroscopy dose. 8 Images are also used in documenting that appropriate treatment has been performed. However, the quality of the present day fluoroscopic images is sufficiently high for use as exposure images depending on the environment where the fluoroscopic images are recorded, 9

2.A | Definition of gray value
Digital images are collected as numerical data that need to be converted to brightness values to be observed as images. The brightness is expressed as the gray level. With x-ray images that have 8 bits per pixel of information, values from 0 to 256 in gray scale are represented by gradations from dark (black) to light (white). The representation with numerical values using this gradation is termed the gray value. 10,11 This study uses the gray value as a value to determine balloon expansion in coronary artery treatment, as depicted in fluoroscopic and exposure images obtained with a cardiovascular x-ray diagnostic device.

2.B | Equipment used
For the cardiovascular x-ray diagnosis device, we used the Allu-ra10/10 manufactured by Philips, Innova 2100IQ manufactured by GE, and the Trinias B8 MiX package manufactured by Shimazu Co., Ltd., Hamamatsu, Japan. For the video view, we used the kada-View manufactured by Photron M&E Solutions Inc., Tokyo, Japan, and ImageJ was used to analyze the images. We used a 20 cm thick acrylic phantom as the subject, and the area dose meter installed in the manufacturers' equipment as the dosimeter.
For visual and physical evaluations, we used the balloon for coronary artery treatment commonly used in clinical settings: 2.5/ 15 mm, 3.0/10 mm, 3.5/10 mm, and 4.0/10 mm (balloon diameter/ balloon length) manufactured by Kaneka Corporation, and Iovelin 350 (Teva Takeda Pharma Ltd., Nagoya, Japan) as the contrast agent.
2.C | Dose settings of x-ray diagnostic devices for circulatory organs Using each of the tested devices, we measured the x-ray doses of fluoroscopic and exposure images at the irradiation reference point of patients. Figure 1 shows the measurement geometry and Table 1 shows the conditions of the exposure and fluoroscopic imaging in the direction of imaging angles, Anterior-Posterior (AP).           Table 3, to be able to overcome the phenomenon with the tube voltage rises leading to blurring of images, which is a characteristic of the Flat Panel Detector (FPD).
The characteristic of the dose settings with device B is to control the x-ray dose with a large current, and the dose which patients are assuming device A, which has the lowest dose setting, as the standard, the device B setting is 1.6 times and for device C it is about 2.2 times higher than that of device A. Usually, when the dose rate is high, the image quality improves, but the evaluation of the balloons with small diameters in devices B and C with the higher dose rate was lower than in device A. This is because device A controls the image quality by controlling the x-ray dose. However, in devices B and C the signals of the balloons are flattened because these devices cut soft x-rays using an additional filter, and this may lower the visual evaluation due to poor control of the image quality with the digital filter as shown in Table 3.

| CONCLUSIONS
This study finds that replacement of stored fluoroscopic images with exposure images requires 20.1 or higher gray value differences between the background and signal, using an acrylic phantom of 20 cm thickness (representing the abdomen of a human adult) a specific geometry. This suggests the conclusion that the gray value can be considered a useful index when using stored fluoroscopic images as exposure images.

ACKNOWLEDGMENTS
We express our gratitude to physicians of the Cardio Vascular Center and radiological technologists of the Radiation Technology Division of the Showa University for cooperation in data collection and image evaluations in this study.

CONFLI CT OF INTEREST
The authors declare no conflicts of interest associated with this manuscript.