Volume CT를 이용한 관상동맥 CT 혈관조영술에서 Auto Exposure와 Manual Exposure의 선량비교

다국어 초록 (Multilingual Abstract)

Ⅰ. Purpose
The purpose of this study is to reduce Exposure dose of coronary artery CT angiography by comparing Exposure dose of Auto Exposure that was setted in the equipment with Exposure dose of Manual Exposure that the user sets when we use volume CT.
Exposure dose would be increased because we scan two or three times, if heart rate (HR) of the patient is high when we test a patient by Auto Exposure. Therefore, we try to know the difference of Exposure dose and a failure rate of the test when we test a patient by Manual Exposure and scan only one time though HR of the patient is high.
Ⅱ. Materials and Methods
The subjects were 100 adults who visit the hospital in outpatient and for a comprehensive medical testing from 2, Jan to 29, Feb, 2012.
We divided into two groups. One group is 50 adults for Auto Exposure, the other group is 50 adults for Manual Exposure. Of these patients, 59 were men and 41 were women. The average of ages was 55.3±10.6.
We excluded a patient had below HR 65 bpm by triggering heartbeat before we tested coronary artery CT angiography. The equipment was used by Aquilion ONE Cardiac Volume Scan 640MS (Toshiba, Japan). We reconstructed the images and evaluated the quality of images based on End Systolic and End Diastolic in 30~80% of R-R interval.
We tested by using one beat, two beat, and three beat scan method depending on HR in Auto Exposure mode and just one beat scan method in Manual Exposure mode, and then we reconstructed the images and investigated Exposure Dose. We used Dose report data coming out the test and measured Exposure dose. We analysed using PASW Statistics (SPSS) Ver. 18.0.
Ⅲ. Results
The failure rates of test were 5 (5%) of 100, Auto Exposure and Manual Exposure showed 3 (6%) of 50 and 2 (4%) of 50, respectively.
As a result of Independent Samples t-test about the failure rates of test between two groups, there was no difference.
As a result of analysing Exposure dose of Auto exposure and of Manual Exposure, Auto exposure had 413.5±259.4 mGyㆍcm and Manual Exposure had 97.9±66.1 mGyㆍcm. That means there was a significant difference of Exposure dose between two groups.
Therefore, when we compared two kinds of test method, Exposure Dose would be reduced as much as 76.4% in Manual Exposure method than in Auto Exposure method.
Ⅳ. Conclusion
There was no difference of failure rate of test between Auto Exposure method that was setted in the equipment and Manual Exposure method that the user sets in coronary artery CT angiography using Volume CT.
The images coming out Auto Exposure and Manual Exposure method were referred to Radiologists and evaluated and there was no difference.
If we use Auto Exposure method in coronary artery CT angiography, we should do 2 beat scan when a patient have above HR 65 bpm and 3 beat scan when a patient have above HR 85 bpm. However, we could reduce Exposure dose as much as 76.4% when we use Manual Exposure and do 1 beat scan regardless of HR without difference of failure rate of test.
We should reconstruct the images in Systolic period when HR of a patient is above 70 bpm, so the quality of images would get going down because of using Cardiac Modulation function if BMI index is above 31.
Therefore, we need to set mA in Manual when BMI index is above 31 and we don’t use Cardiac Modulation function instead.
It gets possible to test when there is high HR of a patient which it had been impossible before in coronary artery CT angiography when we use Volume CT, but the quality of images go down. The Manual Exposure method can reduce Exposure dose in coronary artery CT angiography by using Volume CT.