64 slice MDCT에서 Beam Collimation 변화가 선량과 화질에 미치는 영향 평가

• 영문명: Evaluate effect of dose and image quality at 64 slice MDCT according to change of beam collimation
• 발행기관: 대한CT영상기술학회
• 저자명: 손춘봉(Choon Bong Son) 김문찬(Moon Chan Kim) 남윤철(Yoon Chul Nam)
• 간행물 정보: 『대한CT영상기술학회지』대한전산화단층기술학회지 제15권 제1호, 99~108쪽, 전체 10쪽
• 주제분류: 의약학 > 방사선과학
• 파일형태: PDF
• 발행일자: 2013.04.30

국문 초록

목적 64 slice MDCT에서 beam collimation의 변화가 선량 및 화질에 미치는 영향에 대한 평가를 하고자 하였다. 대상 및 방법 CT장치는 각각의 장치제조사의 64 slice MDCT(GE LightSpeed VCT, Philips Brilliance 64, Toshiba Aquillion, Siemens sensation)를 대상으로 하였으며(120 kV, 100 mA, 1.0 second rotation time, small focal spot, standard algorithm)의 동일조건으로 axial scan 하여 각 장비의 beam collimation 변화에 따른 선량 및 화질평가를 하였다. 선량측정은 Monte Carlo Simulation 방법과 직접 ionization chamber를 이용한 측정선량을 장비에서 제공하는 선량과 비교하였으며, 화질평가는 ACR phantom과 Philips MATLAB을 사용하여 노이즈, SNR, CNR, 2% MTF의 정량적인 평가를 하였다. 결과 VCT, Brilliance, Aquillion 장비에서는 narrow beam collimation에서 wide beam collimation으로 변화시키면 선량이 선형적으로 감소하였다. VCT는 20 mm beam collimation에서 40 mm로 변화시 head scan mode에서는 각각의 선량 측정방법에 따라서 5.6~21.1%, body scan mode에서는 4.3~6.9% 감소하였다. Philips 장비는 25~40 mm로 변화시 head scan에서는 15.2~21.1%, body scan에서는 4.3~18.6% 감소하였다. Toshiba 장비는 16~32 mm로 변화시 head scan에서는 9.1~21.1%, body scan에서는 유의한 차이가 없었다. sensation 장비의 경우 wide beam collimation으로 변화시키면 선량이 선형적으로 감소하지 않았으며, 5~19.8 mm까지는 head와 body scan mode에서 선량이 선형적으로 증가하였으며, 19.8~28.8 mm로 변화시 head scan에서는 7.6~14.5%, body scan에서는 4.2~11.9% 감소하였다. 화질을 측정한 결과 검사에서 VCT에서 beam collimation을 20~40 mm, Brilliance 장비는 25~40 mm, Aquillion 장비는 16~32 mm, sensation 장비의 경우 19.8~28.8 mm로 변화시 head와 body scan에서 noise 값은 1.3~8.8% 증가하고 SNR는 1.3~8.5%, CNR값은 2~8.3% 감소하였으며 고대조도 분해능인 MTF는 오히려 좋아졌다. 결론 64 MDCT에서 wide beam collimation 사용시 overbeaming effect로 인해 narrow beam collimation 사용 시보다 0.8~21%까지 선량이 감소하였다. 그러나 overscanning dose로 인한 선량증가를 감안하면 선량감소의 장점은 없다고 할 수 있다. 또한, wide beam collimation의 사용은 noise의 증가로 인하여 SNR, CNR의 감소를 초래하였으며, 공간분해능은 오히려 좋아졌다.

영문 초록

Ⅰ. Purpose The purpose of this study is to evaluate effect of dose and image quality at 64 slice MDCT according to change of beam collimation. Ⅱ. Meterial and Methods We used each CT manufacturer’s 64 slice MDCT (GE LightSpeed VCT, Philips Brilliance 64, Toshiba Aquillion, Siemens sensation) and evaluated dose and image quality according to change of beam collimation in the same axial scan condition (120 kV, 100 mA, 1.0 second rotation time, small focal spot, standard algorithm). Dosimetry was conducted by Monte Carlo Simulation method and we compared dosimetry of ionization chamber to dose that each CT manufacturer provided. We also evaluated noise, SNR, CNR and 2% MTF for estimation of image quality by ACR phantom and philips MATLAB. Ⅲ. Result Dose was linearly decreased when changing to wide beam collimation from narrow beam collimation in VCT, Brilliance, Aquillion and sensation. 1. In GE LightSpeed VCT case, according to method of dosimetry when changing to 40 mm beam collimation from 20 mm, dose was decreased between 5.6% and 21.1% in head scan mode and decreased between 4.3% and 6.9% in body scan mode. 2. In Philips Brilliance 64 case, when changing to 40 mm beam collimation from 25 mm, dose was decreased between 15.2% and 21.1% in head scan mode and decreased between 4.3% and 18.6% in body scan mode. 3. In Toshiba Aquillion case, when changing to 32 mm beam collimation from 16 mm, dose was decreased between 9.1% and 21.1% in head scan, but there was no attentive difference in body scan. 4. In Siemens sensation case, dose was not decreased linearly when changing to wide beam collimation. Dose was linearly increased in head and body scan mode from 5 mm to 19.8 mm and decreased between 7.6% and 14.5% in head scan, between 4.2% and 11.9% in body scan from 19.8% to 28.8%. By results of measurement of image quality, when changing beam collimation from 20 mm to 40 mm in GE LightSpeed VCT, from 25 mm to 40 mm in Philips Brilliance, from 16 mm to 32 mm in Toshiba Aquillion and from 19.8 mm to 28.8 mm in Siemens sensation, noise index was increased between 1.3% and 8.8%, SNR was increased between 1.3% and 8.5%, CNR was decreased beween 2% and 8.3% and MTF was improved. Ⅳ. Conclusions According to the study, when wide beam collimation was used, a percentage of the measured dose reduction was from 0.8% to 21% than narrow beam collimation was used. but it’s not an advantage for dose reduction because of increasing the dose by overscanning dose. Also, SNR, CNR were decreased and MTF was improved when wide beam collimation was used.

목차

Abstract

Ⅰ. 서론

Ⅱ. 대상 및 방법

Ⅲ. 결과

Ⅳ. 고찰

Ⅴ. 결론

참고문헌

국문초록

키워드

beam collimation overbeaming overscanning