64 채널 Multi-Detector Computed Tomography를 이용한 관상동맥검사의 선량 : 검사 프로토콜 다변화에 따른 환자선량 감소 (Doses of Coronary Study in 64 Channel Multi-Detector Computed Tomography : Reduced Radiation Dose According to Varity of Examnination Protocols)

서지정보

· 발행기관 : 대한방사선과학회
· 수록지 정보 : Journal of Radiological Science and Technology / 32권 / 3호 / 299 ~ 306페이지
· 저자명 : 김문찬

초록

MDCT의 시간분해능 향상과 등방성 해상능(isotrophic resolution) 영상의 획득, 그리고 지능적인 심전도 동조를 바탕으로 하여 심혈관 질환의 효과적인 진단검사로 인정받고 있는 후향적 심전도 동조화(retrospective ECG gating) 하의 coronary CT angiography는 상대적으로 많은 환자선량을 제공함으로 인해 우수한 진단방법으로서의 장점을 반감시키고 있다. 이에 각 장치 제조사에서는 환자선량을 감소시키는 방법의 연구가 활성화되어 왔으며, 이의 일환으로 지능적인 cardiac dose modulation 기술과 전향적 심전도 동조화(prospective ECG gating)를 사용한 sequential scan이 도입되고 있다. 이에 본 연구에서는 64 채널 MDCT에서 54kg, 163cm인 여성 인체모형팬텀을 대상으로 하고 형광유리선량계를 사용하여 후향적 심전도 동조화 하의 coronary CT angiography 프로토콜에서 환자선량의 정량적 평가와 환자선량 감소를 위해 본원에서 선택적으로 적용하고 있는 5가지 검사 프로토콜을 적용하였을 경우의 effective dose와 중요 부위의 organ dose를 측정 비교하여 다음과 같은 결과를 얻었다.
1) Dose modulation없이 120kVp와 210mAs의 노출조건으로 retrospectively ECG gated helical scan으로 시행한 conventional coronary CT angiography 프로토콜의 effective dose는 17.8mSv였으며, 심장의 organ dose는 103.8mGy였다.
2) 관전압을 120kVp에서 100kVp로 낮추었을 경우 effective dose는 11.0mSv로 conventional coronary CT에 비해 38.2%가 감소하였으며, 심장은 67.3mGy로 45.2%가 감소하였다.
3) Cardiac dose modulation을 적용한 경우 effective dose는 13.3mSv로 conventional coronary CT에 비해 25.3%가 감소하였으며, 심장은 80.0mGy로 22.9%가 감소하였다.
4) 100kVp의 저관전압과 cardiac dose modulation을 적용한 경우 effective dose는 8.1mSv로 conventional coronary CT angiography에 비해 54.5%가 감소하였으며, 심장은 49.5mGy로 52.3%가 감소하였다.
5) Prospective ECG gating을 사용한 sequential scan을 시행하였을 때 effective dose는 4.9mSv로 conventional coronary CT에 비해 72.5%가 감소하였으며, 심장은 33.8mGy로 67.4%가 감소하였다.
6) 100kVp의 저관전압과 sequential scan을 적용하였을 때 effective dose는 3.0mSv로 conventional coronary CT angiography에 비해 83.2%가 감소하였으며, 심장은 17.7mGy로 82.9%가 감소하였다.

영어초록

Purpose : To compare radiation dose for coronary CT angiography (CTA) obtained with 6 examination protocols such as a retrospectively ECG gated helical scan, a prospectively ECG gated sequential scan, low kVp technique, and cardiac dose modulation technique.
Materials and Methods : Coronary CTA was performed by using 6 current clinical protocols to evaluate effective dose and organ dose in primary beam area with anthropomorphic female phantom and glass dosimetric system in 64 channel multi-detector CT. After acquiring topograms of frontal and lateral projection with 80kVp and 10mA, main coronary scan was done with 0.35sec tube rotation time, 40mm collimation (0.625mm×64ea), small scan field of view (32cm diameter), 105mm scan length. Heart beat rate of phantom was maintained 60bpm in ECG gating. In constant mAs technique 120kVp, 600mA was used, and 100kVp for low kVp technique. In a retrospectively ECG gated helical CT technique 0.22pitch was used, peak mA (600mA) was adopted in range of 40~80% of R-R interval and 120mA(80% reduction) in others with cardiac dose modulation. And 210mAs was used without cardiac dose modulation. In a prospectively ECG gated sequential CT technique data were acquired at 75% R-R interval (middle diastolic phase in cardiac cycle), and 120msec additional padding of the tube-on time was used. For effective dose calculation region specific conversion factor of dose length product in thorax was used, which was recommended by EUR 16262.
Results : The mean effective dose for conventional coronary CTA without cardiac dose modulation in a retrospectively ECG gated helical scanwas 17.8mSv, and mean organ dose of heart was 103.8mGy. With low kVp and cardiac dose modulation the mean effective dose showed 54.5% reduction, and heart dose showed 52.3% reduction, compared with that of conventional coronary CTA.
And at the sequential scan(SnapShot pulse mode) under prospective ECG gating the mean effective dose was 4.9mSv, this represents an 72.5% reduction compared with that of conventional coronary CTA. And heart dose was 33.8mGy, this represents 67.4% reduction. Inthe sequential scan technique under prospective ECG gating with low kVp the mean effective dose was 3.0mSv, this represents an 83.2% reduction compared with that of conventional coronary CTA. And heart dose was 17.7mGy, this represents an 82.9% reduction.
Conclusion : In coronary CTA at retrospectively ECG gated helical scan, cardiac dose modulation technique using low kVp reduced dose to 50% above compared with the conventional helical scan. And the prospectively ECG gated sequential scan offers substantially reduced dose compared with the traditional retrospectively ECG gated helical scan.

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