Low Dose CT Colonography(LDCTC)를 이용한 Automatic Exposure Controll(AEC)와 Beam Collimation의 변화에 따른 유용성 평가와 Effective Dose의 평가치에 대한 연구

여상근(Sang Geun Yeo),정한별(Han Byeol Jeong),대창민(Chang Min Dae),민관홍(Kwan Hong Min),김성룡(Seong Ryong Kim) 대한CT영상기술학회 2008 대한CT영상기술학회지 Vol.10 No.1

Purpose To considerate the efficiency of Automatic Exposure Controller(AEC) and Beam Collimation with the value of Effective Dose obtained with the alteration of Automatic Exposure Controller(AEC) and Beam Collimation. Materials and methods 50 out-patients (Male:36, Female:14, mean age:45 years) underwent Low Dose CT Colonography with 16 MDCT from 1st June 2007 to 31th July 2007 were selected. The Effective Dose was produced with the alteration of DoseRight Automatic Current Selector(ACS) & DoseRight D-Dose modulation(D-DOM), Beam Collimation in same patients. Results On the assumption that Effective Dose without AEC is 100%, 8% was decreased with only ACS, 9% was declined with D-DOM, and 16% was decreased with using ACS & D-DOM. On the same condition, 8% was decreased with the Beam Colliniation increased double. Conclusion 8%~16% of Effective Dose was decreased with AEC Program(ACS, D-DOM) and Beam Collimation. Although 30%-40% of decrease effectiveness was not obtained like the previous papers about dose, the use of Automatic Exposure Controller and Beam Collimation decrease effective dose. The use of AEC and Beam Collimation maintain the high quality of images and extend the tube life time of CT modality.

Eclipse Collimator에 의한 Z-축 방향 Over Scan Range 감소가 선량과 영상의 질에 미치는 영향

정주현(Joo Hyun Jung),여상근(Sang Geun Yeo),김영옥(Young Ok Kim),대창민(Chang Min Dae),민관홍(Kwan Hong Min) 대한CT영상기술학회 2010 대한CT영상기술학회지 Vol.12 No.2

Purpose The purpose of this study was to research deacrease effect of radiation dose and quality of image by application of Eclipse collimator that reduce z-axis over scan range by interpolation. Materials and methods Using 256 MlXT applied Edipse col limator, We researched difference of radiation dose that patient was delivered with and without Eclipse collimator by Rando phantom, and measured equivalent dose that is different in decrease of z-axis over scan range by Eclipse collimator using thermo-luminescence dosimeter(TLD) and evaluated change of quality of image by radiation dose decrease using AAPM phantom. Results According to the application of Eclipse collimator in an experiment that use Rando phantom. CTDIvol reduced radiation dose of approximately 0.06% by 0.2 mGy from 32.9 mGy to 33.1 mGy. DLP reduced radiation dose of approximately 11% by 75mGyㆍcm from 626.86 mGyㆍcm to 701.86 mGyㆍcm. 10.23 mSv’s equivalent dose decreased by application of Eclipse collimator appeared in an experiment that use TLD, This result displayed decrease of equivalent dose of approximately 8.9%. Region of over scan range reduced equivalent dose of approximately 9.47 mSv. also this result displayed radiation decreased effect of approximately 22.86%. Image estimation of CT number(p=0.344) and noise(p=0.375) by decreased radiation dose was exposed that big difference does not exist. Conclusion By Eclipse collimator that reduce z-axial over scan range reduced radiation dose without decline of image quality exposure that was exceeded to patient could be line approximately 9~11%. If apply Eclipse collimator in various region for example young child examination, examination of organ that radiation sensitivity is high, and examination who wanted follow up case etc, we will get a high radiation dose efficiency.

중복 부위 검사 시 선량감소를 위한 Resolution과 Filter의 변화에 따른 화질평가

구본승(Bon Seung Koo),여상근(Sang geun Yeo),대창민(Chang Min Dae),민관홍(Kwan Hong Min),김성룡(Sung Ryong Kim),조평곤(Pyong Kon Cho) 대한CT영상기술학회 2011 대한CT영상기술학회지 Vol.13 No.1

목 적 최근 교통사고, 급성중증 환자의 증상에 따른 빠르고 정확한 진단을 위해서, 여러 가지 CT 검사가 동시에 발행되고 있다. 하지만, 중복되는 검사 범위라 할지라도 서로 다른 스캔 프로토콜로 검사하기 때문에 환자의 피폭선량은 증가하고 있다. 따라서, 본 연구의 목적은 다양한 resolution과 filter 변화에 따른 영상의 화질을 평가하고, 적절한 프로토콜을 임상에 적용하여 중복되는 검사의 감소에 따른 선량감소효과에 관한 연구를 하고자 한다. 대상 및 방법 CT 장비는 256-MDCT(Brilliance iCT, Philips health care, USA)로 진행하였으며 영상의 화질평가는 AAPM 팬텀(Model 610, Nuclear Association LTD, USA)과 philips system head phantom을 이용하고, Extended Brilliance Workspace(Version 4.0, Philips Medical Systems, Netherlands)로 측정하였다. Resolution과 filter가 화질에 미치는 영향을 알아보기 위해서, scan parameter를 128 * 0.625 beam collimation, 120 kVp, 250 mAs, 0.5 sec, 250 mm FOV, 5 mm slice thickness로 동일하게 적용하였고, resolution는 standard, high, ultrahigh로, filter는 A, B, C, D, EB, EC, UA, UB, UC, YC, YD, YE, YF 등으로 바꿔가면서 재구성한 영상으로 CT 감약계수, 노이즈, 균일도, 직선성, 공간분해능, MTF(50%, 10%)를 측정하여 화질을 평가하였다. 임상 적용에 따른 평가는 brain CT와 facial CT 3D를 단 한번의 스캔으로 검사한 환자를 대상으로, 영상의 화질을 정량적으로 평가하였고, 장비에서 제공하는 total DLP를 유효선량으로 계산하여 피폭선량을 평가하였다. 결 과 AAPM 팬텀의 영상평가에서 CT 감약계수는 resolution의 종류에 따라 6.5~-0.8 HU로 다양하게 분포하였고, 노이즈는 7.4~36.7 HU까지, 공간 분해능은 1.0~0.6 mm까지 구별하였고, MTF 50%는 3.6~5.3 lp/cm까지, MTF 10%는 6.4~8.5 lp/cm까지 standard에서 ultrahigh resolution으로 갈수록 공간주파수가 높게 평가되었다. 동일한 resolution에서 filter의 변화에 따른 화질 평가에서는 CT 감약계수만 filter의 종류에 따라 다양하게 분포하였고, 그외 노이즈, 공간 분해능, MTF 값은 filter가 smooth에서 sharp로 증가할수록 함께 증가하였다. 필립스 QA 팬텀으로 brain CT검사 시 사용되는 standard resolution과 UB filter를 이용하여 얻은 영상을 평가한 것은 high resolution과 UA또는 UB filter를 사용하여 얻은 영상과 가장 유사한 값을 보였다. 임상에 적용하여 평가한 결과는 high resolution과 UB filter를 사용시 임상적 적용이 높게 평가되었고, 기존에 검사해오던 brain CT영상과는 큰 차이를 느끼지 못했다. 뿐만 아니라, 선량 평가에서도 brain의 중복 검사를 피하기 위해서, 한번에 검사한 경우의 DLP는 977.1±22.4 mGyㆍcm, 유효선량은 2.2±0.1 mSv로 전체적으로 약 31.25%의 선량감소효과를 나타냈다. 결 론 서로 다른 프로토콜로 검사하는 brain CT와 facial CT 같이 중복되는 부위를 갖는 검사들이 동시에 발행될 경우 resolution과 filter에 따른 영상의 질적 차이를 정확히 이해하고 응용하여, 최적의 프로토콜을 사용함으로써, 중복되는 CT 검사의 수를 감소시켜서 환자의 피폭선량을 최소화할 수 있도록 해야 한다. Ⅰ. Purpose For fast and accurate diagnosis, various CT order are applied at the same time. But, radiation dose of patient is increased because the same body parts are studied with different CT protocol. The purpose of this study is to investigate image quality and the change of radiation dose according to the various resolution and filter. Ⅱ. Materials and Methods 256-MDCT(Brilliance iCT, Philips health care, Cleveland. OH, USA) was used in this study. In phantom study, image quality of AAPM and Philips QA phantom was evaluated by EBW. To evaluate the effects on the quality by resolution and filter, We measured the CT attenuation coefficient, noise, uniformity, linearity, spatial resolution, MTF in reconstructed image depending on the type of resolution and filter. The kind of resolution are standard, high, ultrahigh and the filter are composed of A, B, C, D, EB, EC, UA, UB, UC, YC, YD, YE, YF. The patient were studying brain CT and facial CT at the same time. For clinical applications, image quality was assessed quantitatively and radiation dose was measured with total DLP provided by CT modality. Ⅲ. Results 1. CT attenuation coefficient was distributed 6.5~-0.8 HU and noise was 7.4~36.7 HU. Spatial resolution was distinguished 1.0~0.6 mm. MTF 50% was evaluated 3.6~5.3 lp/mm, and MTF 10% was evaluated 6.4~8.5 lp/cm. In the same resolution, Measurement of Noise, Spatial resolution, MTF value are increasing from smooth to sharp except CT attenuation coefficient. 2. Brain image obtained with standard resolution and UB filter is similar to image with high resolution and UA or UB. 3. In the results of clinical application, brain image with high resolution and UB filter was effective. There were no significant difference compared to before. In addition, the dose was reduced by 31.25%. Ⅳ. Conclusion If we examine the same body part with a different protocol, we should study the patient with appropriate protocol in consideration of the dose and image quality. Therefore We must know the relationship between various resolution and filter. We should reduce the number of scan the same region in order to reduce the effective dose.

64 Slice MDCT에서 HR Variation이 Image Quality에 미치는 영향에 대한 고찰

김주현(Joo Hyun Kim),김상현(Sang Hyun Kim),여상근(Sang Geun Yeo),대창민(Chang Min Dae),민관홍(Kwan Hong Min),김성룡(Sung Ryong Kim) 대한CT영상기술학회 2007 대한CT영상기술학회지 Vol.9 No.1

Purpose 16 slice MDCT is Widely used for coronary CT angiography, however it is well known that image quality is more affected the variation of heart rate than heart rates. Recently, 64 slice MDCT has been introduced, it has the merit of faster scan time. Therefore, it might be improve image quality for minimizing the variation of heart rate during scan time. The purpose of this study is, (a) to analyze the variation of heart rate according to time-course during CT scanning (b) to evaluate how to impact to the image quality by the differences of heart rate variation. Materials and Methods Total 200 patients were enrolled in this study. 100 patients who underwent cardiac CT With 16 MDCT from Jan 2004 to Jul 2004(74 men, 26 women; mean age 55.15±12.75 years), 100 patients who underwent cardiac CT With 64 MDCT from Jun 8, 2006 to Jun 30, 2006(68 men, 32 women; mean age 58.4±11.56 years). Mean heart rate is no significant difference between two groups(16 MDCT 71.04±3.52bpm, 64 MDCT 69.31±4.71bpm). Equipments were used 16 MDCT(Mx8000 IDT, Philips) and 64 MDCT(Brilliance 64, Philips) which are the same rotation times(420msec, i.e. temporal resolution is same as 53msec). We recorded the variation of HR during pre and post scan as well as scanning period. We evaluated the image quality by dividing several groups according to the variation of HR ; Group I(0-5bpm), Group II(11-15bpm), Group III(11-5bpm), Group IV(16-20bpm), Group V(above 20bpm). The results are also compared for the evaluation of quality between 16 MDCT and 64 MDCT. For the qualitative analysis of image quality, we used 4 grade scoring system(Excellent : 4 points, Good : 3 points, Fair : 2 points, Bad : 1 point). For the quantitative analysis, we analyzed the presence and frequency of banding artifacts including stair-step artifact and acceleration artifact. Results The result of mean HR variation on 64 MDCT was significantly diminished comparing With 16 MDCT(5.48±4.20 bpm vs 10.31±5.90, P<0.05). For the qualitative analysis of image quality. The overall score of 64 MDCT is statistically larger than that of 16 MDCT(3.41±0.7 VS 2.84±0.9, P<0.05). For the quantitative analysis the frequency of stairstep artifacts is markedly occurred on 16 MDCT(64 MDCT: 0.5±1.04, 16 MDCT: 2.4±3.2, P<0.05). Furthermore, acceleration artifact was extremely rare on 64 MDCT (64 MDCT: 1, 16 MDCT : 11, P<0.05). Conclusion In this study, we suggest that 64 MDCT have the merit to improve image quality by reducing scan time and minimizing the variation of heart rate comparing With 16 MDCT. We conclude that 64 MDCT will be play an important role for the evaluation of ischemic heart disease due to markedly eliminating acceleration artifact which is frequently occurred in patients who could not sufficient breath-hold.

CT 관상동맥 조영술에서 환자의 심박동수 및 체질량 지수에 따라 심전도 동조화 방법과 관전압 변화에 따른 영상 평가와 피폭선량에 관한 고찰

박신호(Shin Ho Park),구본승(Bon Seung Koo),여상근(Sang Geun Yeo),대창민(Chang Min Dae),민관홍(Kwan Hong Min) 대한CT영상기술학회 2011 대한CT영상기술학회지 Vol.13 No.2

목적 256-MDCT를 이용한 관상동맥 CT 조영술(Coronary CT angiography, 이하 CCTA)에서 환자의 심박동수(Heart rate, 이하 HR) 및 체질량 지수(Body mass index, 이하 BMI)에 따라 심전도 동기화 방법과 관전압 변화에 따른 영상 화질과 선량 평가에 대하여 알아보고자 한다. 대상 및 방법 2010년 7월부터 8월까지 본원 건강증진센터를 방문하여 ECG-gated CCTA를 시행한 무증상 환자 208명을 대상으로 HR에 따라 심전도 동기화 방법을 변화시키고, BMI에 따라 kVp을 변화시켜 4개 군으로 나누었다. 장비는 256-MDCT(Brilliance iCT, Philips health care, Cleveland. OH. USA)를 사용하였고, phantom 연구에서는 관전압 변화에 따른 영상의 화질평가를 위해 American association of physicists in medicine(이하 AAPM) phantom을 사용하여, CT number와 noise값을 측정하였고, 선량측정을 위해 ionization chamber를 사용하여 CTDIvol(CT dose index volume) 값을 측정하였다. 임상 연구에서는 관전압 변화에 따른 영상의 화질평가를 위해, 관상동맥 근위부와 대동맥의 조영증강 정도, 잡음, 신호 대 잡음 비와 조영증강 대 잡음 비를 측정하였으며, 관상동맥 9분절의 영상의 질을 1~5점으로 평가하였고 4점과 5점을 진단에 적합한 것으로 하였다. 검사 종료 후 장비에서 제공하는 CTDIvol과 Dose Length Product(DIP)값을 이용하여 유효 선량으로 계산하여 선량감소효과를 평가하였다. 각 환자군 간의 영상의 질 지표와 방사선 피폭 량을 통계학적으로 분석하기 위해 Mann-whitney test를 이용하여 분석하였다. 결과 혈관의 조영 증강 정도는 A군이 B군보다 높았(group A, 452±74HU; group B, 333±45HU, p < 0.0001), C군이 D군보다 높았으며(group C, 441±77HU; group D, 355土75HU, p < 0.0001) 각각 유의한 차이가 있었다. 영상의 잡음은 A군과 B군 사이에 유의한 차이가 없었고(group A, 21土4HU; group B, 21土2HU, p=0.521), C군과 D군 사이에도 유의한 차이가 없었다(group C, 21±3HU; group D, 21±2HU, p = 0.561). 신호 대 잡음 비는 A군이 B군보다 높았고(group A, 22土4; group B, 17土3, p < 0.0001), C군이 D군보다 높았으며(group C, 21土4; group D, 17±4 HU, p < 0.0001), 각각 유의한 차이가 있었다. 조영 증강 대 잡음 비는 A군이 B군보다 높았고(group A, 17±3; group B, 12±2, p < 0.0001, C군이 D군보다 높았으며(group C, 16土4; group D, 12土3HU, p < 0.0001), 각각 유의한 차이가 있었다. 진단에 적합함을 평가한 영상 질의 평균 점수는 A군 4.6土0.4, B군 4.7土0.3, C군 4.3土0.5, D군 4.3土0.4으로 모든 군에서 진단에 적절한 영상을 보였다. 유효 선량은 A군 2.2±0.3 mSv, B군 4.4土0.4mSv, C군 8.6±1.2 mSv, D군 16.8±1.9 mSv로, 네 군 간의 각각 유의한 차이가 있었고(p < 0.0001), A군이 B군보다 약 50% 선량감소효과를 나타냈으며, C군이 D군보다 48.8%의 선량감소효과를 나타냈다. 결론 환자의 HR와 BMI를 기준으로 심전도 동기화 방법과 관전압을 적용할 때, HR가 70미만으로 유지되고 있는 환자에게 전향적 동조화 방식을 이용하고, BMI가 25 미만으로 낮은 환자에게 관전압을 100kVp로 낮추어 CCTA를 시행하면 영상의 질적인 저하 없이 진단에 적절한 영상을 얻을 수 있는 동시에 환자의 방사선 피폭선량을 효과적으로 줄일 수 있다. I. Purpose To investigate image quality and radiation dose with different ECG synchronization method and tube voltage(kVp) by heart rate(HR) and body mass index(BMI) in coronary computed tomographic angiography(CCTA) which is using 256-multi-detector computed tomography(MDCT). II. Meterial and Methods This study was proceeded with 208 patients in our health promotion center. ECG-gated CCTA was practiced by different ECG method varied by HR and different kVp varied by BMI. The patients were divided into 4 groups by HR and BMI. 256-MDCT(Brilliance iCT, Philips health care, Cleveland. OH, USA) was used in this study. In phantom study, American association of physicists in medicine(AAPM) phantom was used to evaluate the image quality by kVp variation. Moreover CT number and noise was measured. To measure CTDIvol, Ionization chamber was used. In clinical research, attenuation and image noise of the aorta and coronary arteries was masured. and, the image quality of 9 coronary segmenrs was graded on a scale of 1-5, where grade 4 or 5 was considered to be diagnostic. Image quallity parameters and radiation dose were compared using a Mann-whitney test. III. Result Attenuation was higher in group A and B(group A, 452±74 HU; group B, 333±45 HU, p < 0.0001), group C and D(group C, 441±77 HU; group D, 355±75 HU, p < 0.0001). Noise was similar in group A and B(group A, 21±4HU; group B, 21±2HU, p=0.521), group C and D(group C, 21±3HU; group D, 21±2HU, p = 0.561). SNR and CNR were higher in group A and group B(group A, 22±4; group B, 17±3, p < 0.0001), (group A, 17±3; group B, 12±2, p < 0.0001), group C and group D(group C, 21±4; group D, 17±4HU, p < 0.0001), (group C, 16±4; group D, 12±3 HU, p < 0.0001). Each of them has significant differences. Mean score of image quality was 4.6±0.4 in group A, 4.7±0.3 in group B, 4.3±0.5 in group C and 4.3±0.4 in group D. Effective dose was 2.2±0.3 mSv in group A, 4.4±0.4mSv in group B, 8.6±1.2mSv in group C and 16.8±1.9mSv in group D, which bad significant differences in each of all 4 groups(p < 0.0001). Effective radiation dose reduced 50% in group A and group B, 48.8% in group C and group D. IV. Conclusions In patients with HR under 70 and prospective ECG gating technique, with BMI less than 25 and CCTA with 100 kVp lead to signification reduction in radiation exposure without degradation of image quality.

흉부 CT검사 시 검사부위를 벗어난 Topogram 부위에 Automatic Exposure Control 적용이 선량 및 화질에 미치는 영향

박관중(Guan Jung Park),김영옥(Young Ok Kim),여상근(Sang Geun Yeo),대창민(Chang Min Dae),민관홍(Kwan Hong Min) 대한전산화단층기술학회 2011 대한CT영상기술학회지 Vol.13 No.2

목적 임상에서 많이 시행하고 있는 흉부 computed tomography(이하 CT) 검사 시, 세 개의 각기 다른 CT장비 제조사의 automatic exposure control(이하 AEC) system을 인체 등가phantom에 적용하여, 검사부위를 벗어난 topogram을 검사하였다. 검사부위를 벗어난 topogram에서 AEC작동유무 및 CT dose index volume(이하 CTDI) 변화를 측정하고, 영상의 노이즈값의 비교를 통하여 선량 및 화질 변화를 알아보고자 하였다. 대상 및 방법 사용된 각 장비 회사별 CT 장비는 Brilliance 64 MDCT(Philips healthcare, 이하 P사), LightSpeed VCT XT 64 MIDCT(General Electric Medical System, 이하 G사), Somatom Definition Dual CT(Siemens Healthcare, 이하 S사)를 사용하였다. Rando phantom을 대상으로 하여 본원에서 흉부 검사 범위로 정하고 있는 성대에서 부신이 충분히 포함된 topogram을 정상군으로 정하고, 정상군과 비교하여 폐첨부에서 머리 방향쪽으로 2cm 검사부위를 벗어난 군을 A군, 4cm는 B군, 6cm는 C군, 8cm를 D군으로 대조군을 정하였다. 선량 평가를 위해 각 장비 제조회사에서 제공하는 CTDI값과 ionization chamber를 이용하여 CTDI값을 실측한 후, 정상군의 CTDI값을 기준으로 대조군의 CTDI 증감률을 산출하였다. 화질 평가는 AAPM phantom을 이용하여 정상군 및 대조군 실험 영상의 6시 방향 1/4지점에서 4×4cm의 크기의 region of interest(이하 ROI)를 설정하여 모든 slice의 평균오차의 값을 노이즈값으로 계산하여 평가하였다. 결과 정상적인 topogram과 검사부위를 벗어난 topogram의 AEC적용 결과는 P사의 경우는 ACS만 적용 시 노이즈값은 정상군은 12.9, A군은 약 12.7(p=0.0273, B군은 약 12.6(p=0.0195), C군은 약 12.2(p=0.002), D군은 약 12.l(p=0.002)로 측정되었으며, 대조군의 CTDI 증감률은 정상군과 비교하여 각 군에서 약 8.9%, 11.1%, 14.4%, 15.6% 증가하였다. ACS combined Z-DOM 적용 시에는 정상군 비교하여 CTDI 증감률은 각 군에서 약 3.0%, 4.0%, 4.0%, 5.0% 증가하지만, 노이즈값은 각 군에서 약 13.3, 약 13.2(p=0.0216), 13.1(p=0.0078), 12.9(p=0.0195), 12.9(p=0.0039)로 측정되었다. ACS combined D-DOM 적용 시에는 CTDI 증감률은 정상군 비교하여 각 군에서 약 0.9%, 1.8%, 1.8%, 2.7% 증가하였고, 노이즈값은 정상군은 약 12.7, 대조군은 약 12.6(p=0.0301), 12.5(p=0.0392), 12.5(p=0.0391), 12(p=0.002)로 통계학적으로 유의한 차이가 없었다. S사의 경우에는 노이즈값은 각 군에서 약 8.0, 7.9(p=0.0376), 7.6(p=0.0277), 7.5(p=0.002), 7.3(p=0.002)로 통계학적으로 유의한 차이가 없었다. CTDI 증감률은 정상군 비교하여 각 군에서 약 1.2%, 3.4%, 2.3%, 6.9% 증가하였다. G사의 경우는 Auto mA 적용 시, 정상군의 노이즈값은 약 45.0, A군은 약 44.1(p<0.0001), B군은 약 44.1(p<0.0001), C군은 약 44.1(p<0.0001), D군은 약 44.1(p<0.0001)으로 대조군에서는 모두 동일한 결과로 측정되었다. 정상군과 비교하여 대조군 모두 통계학적으로 유의한 차이가 없이, CTDI 증감률은 정상군과 비교하여 모든 대조군에서 동일하게 약 8.1% 증가를 보였다. 결론 검사부위를 벗어난 topogram을 얻은 후, topogram에 포함되지 않은 영역에 AEC를 적용하게 되면, 각 장비 회사마다 다소 차이는 있지만 영상의 질적 차이 없이 방사선 피폭선량이 최소 약 0.9%에서 최대 15.6% 증가하였다. 따라서 AEC를 적용 시 정확한 환자의 위치잡이가 선행되어야 topogram을 통해 정확한 정보를 얻을 수 있다. 그 정보를 바탕으로 AEC가 올바르게 동작하여 선량의 최적화를 달성할 수 있을 것으로 사료된다. I. Purpose The purpose of this study is to investigate the change of radiation dose and image quality in outside topogram of scan range applying automatic exposure control (AEC) through phantom study in chest CT. II. Meterial and Methods A Rando anthropomorphic chest phantom and AAPM phantom was scanned on a 64 multi detector CT using the AEC systems from three different manufacturers: General Electric Healthcare, Philips Medical Systems and Siemens Medical Solutions. A general scanning protocol was created for each examination where as many as possible of the scanning parameters were set equal. Divided into 5 groups according to include and not be scan range of topogram. Topogram, normally including scan range, is defined normal group. If not was control group, the group which was 2 an outside topogram of scan range toward head from lung apex was designated as A group, B group in 4 cm off, C group in 6 an off, and D group in 8 an off. CTDI was measured using ionization chamber and provided by CT modality. CTDI fluctuation ratios of control groups were calculated based on the values of CTDI in normal group. For the evaluation of image quality, mean error value was assessed by the image noise from AAPM phantom. III. Result As a result of application of AEC to normal and control groups, in case of P, when applying only ACS, noise of normal group was 12.9, 12.7(p=0.0273) in A group, 12.6(p=0.0195) in B group, 12.2(p=0.002) in C group, 12.1(p=0.002) in D group. CTDI fluctuation ratios of control group was increased by 8.9%i, 11.1%, 14.4%, 15.6% respectively in each group compared to normal group. When applying ACS combined Z-OOM, the CTDI fluctuation ratios of control groups was increased by 3.0%, 4.0%, 4.0%, 5.0% respectively, compared to normal group. However, noise was appeared to be 13.3, 13.2(p=0.0216), 13.1(p=0.0078), 12.9(p=0.0195), 12.9(p=0.0039). When applying ACS combined D-DOM, the CTDI fluctuation ratios was increased by 0.9%, 1.8%, 1.8%, 2.7% while noise value in normal group was 12.7, 12.6(p=0.0301), 12.5(p=0.0392, 12.5(p=0.0391), 12(p=0.002). No statistical significant difference was found. In case of S, noise appeared to be 8.0, 7.9(p=0.0376), 7.6(p=0.0277), 7.5(p=0.002), 7.3(p=0.002) respectively in each group leading to no statistical significant difference. CTDI fluctuation ratios, comparing to normal group, was increased by 1.2%, 3.4%, 2.3%, 6.9%. In case of G, when applying AutomA, the noise of normal group was measured to be 4.0, and 44.1(p<0.0001) in A~D control groups, Compared to normal group, there was no statistical significant difference in control groups, and also the fluctuation ratio (%) of CTDI showed the same ratio of 8.1% in all control groups. IV. Conclusions Radiation dose by different mmufacturer was increased by at minimum 0.9% up to at maximum 15.6%. And it was little difference of image quality found at all. Consequently, projection of topogram, normally included scan range, is very important applying AEC in CT examination.