체질량지수및관전압변화에따른 CT 관상동맥조영술의영상의질및방사선피폭량비교 1 김윤경 김유경 2 목적 : 체질량지수 (Body mass index, 이하 BMI) 와관전압의변화에따른 CT 관상동맥조영술 (Coronary CT angiography, 이하 CCTA) 의영상의질및방사선피폭량에대하여알아보고자하였다. 대상과방법 : 64열다중검출 CT로후향적심동조화를이용한 CCTA를시행받은 139명의환자를 BMI 및관전압에따라세개의군으로나누었다 [A군(n=48), BMI < 25, 100 kvp; B 군 (n=45), BMI > 25, 120 kvp; C군 (n=46), BMI < 25, 120 kvp]. 대동맥및관상동맥근위부의조영증강정도와잡음을측정하였으며관상동맥 9분절의영상의질을 1-5점으로평가하였고 4점과 5점을진단에적합한것으로하였다. 각환자군간의영상의질지표와방사선피폭량을 t-검정과카이제곱검정을이용하여비교하였다. 결과 : 혈관의조영증강정도는 A군에서 B군과 C군보다높았다 (group A, 592 ± 85 HU; group B, 437 ± 46 HU; group C, 469 ± 62 HU, p < 0.001). 영상잡음은 A군과 B군사이에는유의한차이가없었으나 (23 ± 5 HU와 22 ± 6 HU, p=0.427), A군에서 C군에비해유의하게높았다 (23 ± 5 HU 와 17 ± 4 HU, p < 0.001). 신호대잡음비는평균 A군 24 ± 6, B군 19 ± 3, C군 27 ± 5로세군간에각각유의한차이가있었다. 조영증강대잡음비는평균 A군 18 ± 5, B군 14 ± 3, C군 20 ± 4로 A군에서 B군에비해유의하게높았으나 (p < 0.001) A군과 C군사이에는유의한차이가없었다 (p=0.127). 진단에적합한영상을보인관상동맥분절은 A군 97.9%, B군 96.0%, C군 99.0% 였으며영상질의평균점수는 A군 4.5 ± 0.5, B군 4.1 ± 0.4, C군 4.2 ± 0.4로세군간에각각유의한차이가있었다 (p < 0.001). 유효방사선량은 A군 8.5 ± 0.8 msv, B군 14.3 ± 1.3 msv, C군 14.9 ± 1.3 msv로, A군이다른두군에비하여약 42% 낮았다. 결론 : BMI가 25 이하인환자에서관전압을 100 kvp로낮추어 CCTA를시행하는경우진단에적절한영상을얻을수있으며효과적으로방사선피폭량을줄일수있다. 다중검출 CT (multidetector CT, 이하 MDCT) 를이용한이증가한다는단점이있으며이러한점은특히비만환자에서 CT 관상동맥조영술은관상동맥질환의진단및선별검사로영상잡음이크게증가한다 (6). 따라서 CT 관상동맥조영술시그정확도가인정되고있으며사용빈도및범위가점차로확행시환자의체질량지수에맞추어서로다른관전압을적용대되고있다 (1-3). 그러나 CT 관상동맥조영술은다른부위의하는프로토콜이연구되고있다 (7-9). 최근의이중-에너지 CT 검사보다방사선피폭량이높다는문제가있으며이를극 (dual-source) CT나전향적심동조화를이용한연구에서체복하기위한 CT 프로토콜과방사선피폭량의관계에관한여질량지수가 25 이하인환자는관전압을 120 kvp에서 100 러연구가있었다 (4-6). 관전압을낮추어촬영하는 CT 관상동 kvp로낮추어촬영하여도영상의질및진단능에유의한차이맥조영술은환자의방사선피폭량을낮출수있는유용한방가없다는보고가있었다 (7-9). 법중하나로서대두하고있으나관전압을낮출수록영상잡음우리의연구는 64열다중검출 CT로후향적심동조화를이용한연구로서, 본연구의목적은체질량지수가 25 이하로낮 1 고려대학교의과대학영상의학교실 2 은환자에있어서관전압을 100 kvp로낮추어촬영한 CT 관이화여자대학교의과대학영상의학교실이논문은 2009년 4월 26일접수하여 2009년 7월 26일에채택되었음. 상동맥조영술의영상의질을평가하고관전압 120 kvp로촬 29
김윤경외 : 체질량지수및관전압변화에따른 CT 관상동맥조영술의영상의질및방사선피폭량비교 영한 CT 관상동맥조영술과비교하는것이다. 또한, 관전압을 100 kvp로낮추어 CT 관상동맥조영술을시행할때방사선피폭량을어느정도줄일수있는지알아보고자하였다. 대상과방법 2008년 10월부터 2009년 3월까지 CT 관상동맥조영술을시행받은 139명의성인을대상으로후향적연구를하였다. 139명중여성은 41명, 남성은 98명이었으며, 연령분포는 28 세에서 83세로평균연령은 52.2세였다. CT 관상동맥조영술을시행받은이유는건강검진 (n=90), 흉통 (n=35), 흉부불편감 (n=9), 기타 (n=5) 등이었다. CT 촬영시측정한신장과체중을바탕으로체질량지수를계산하였으며, 체질량지수가 25 이하인환자는 94명, 체질량지수 25 이상인환자는 45명이었다. 체질량지수가 25 이하인환자 94명중 2008년 11월이후에 CT 관상동맥조영술을시행받은환자 48명에서는관전압을 100 kvp로낮추어촬영하였다. 환자를다음과같은세개의군으로나누었다 : A군, 체질량지수 25 이하이며관전압 100 kvp로촬영한군 (n=48); B군, 체질량지수 25 이상이며관전압 120 kvp로촬영한군 (n=45); C군, 체질량지수 25 이하이며관전압 120 kvp로촬영한군 (n=46). 모든환자에서 CT를시행하기 1시간전에베타차단제인 propranolol(pranol, Daewoong, Korea) 20 mg을경구투여하였고, 1시간후심박동수가계속분당 65회이상으로측정되면 20 mg을추가로투여하고시행하였다. 추가적투여후에도심박동수가분당 70회이상으로높게측정되거나부정맥을보이는환자에서는 CT 관상동맥조영술을시행하지않았다. CT 촬영직전에 nitroglycerin(nitroglycerin, MyungMoon, Korea) 0.6 mg을설하투여하였다. CT 촬영은 64열다중검출 CT(SOMATOM Sensation 64, Siemens Medical Solutions, Germany) 를이용하였으며, 후향적심전도동조화를사용하였다. 관전압은 A군 100 kvp, B군과 C군은 120 kvp, 관전류 180 mas, 검출기폭조절은 64 0.6 mm, 겐트리회전시간은 370 msec, pitch 0.24로촬영하였다. 18 게이지카테터를이용하여상완정맥으로 70 ml의비이온성조영제 (iopamidol, Iopamiro 370, Bracco, Milan, Italy) 를초당 4-5 ml 속도로주입하고이어서 20 ml의생리식염수를같은속도로주입하면서상행대동맥에서덩어리추적 (bolus tracking) 을실시하여 100 HU가 되는시점으로부터 6초후영상을얻기시작하였다. 호흡정지하에폐동맥간부터심저까지단면영상을얻었다. 영상의재구성은심장재구성소프트웨어 (Syngo, Software Version 2006A, Siemens Medical Solutions, Germany) 를이용하여재구성하였다. 65% RR 간격에서영상을재구성하여평가하고나서, 최적의영상이아닐때는다른 RR 간격에서재구성하여평가하였다. 영상의질의객관적평가를위해대동맥근위부, 좌주관상동맥, 좌전하행동맥근위부, 및우관상동맥근위부에서혈관의조영증강정도와잡음 (noise), 신호대잡음비 (signal-tonoise ratio, SNR), 조영증강대잡음비 (contrast-to-noise ratio, CNR) 를측정하였다. 잡음은관심영역의 CT 음영 (density) 의표준편차 (standard deviation) 로정의하였다. 대동맥근위부에는 3.0 cm 2 의관심영역을두어측정하였으며나머지혈관에는석회화와동맥경화반을피하여가능한한큰관심영역을두고측정하였다. 신호대잡음비는각혈관의 CT 밀도 (density) 를대동맥근위부의잡음으로나눈값으로계산하였다. 조영증강대잡음비는혈관의 CT density와관상동맥주변심근의 CT density와의차를대동맥근위부의잡음으로나눈값으로계산하였다. 영상의질의주관적평가를위해관상동맥을다음과같이 9개의분절로나누어분석하였다 : 좌주관상동맥 (LM), 좌전하행동맥의근위부 (plad), 중간부 (mlad), 및원위부 (dlad), 좌회선동맥의근위부 (plcx) 및원위부 (dlcx), 우관상동맥의근위부 (prca), 중간부 (mrca), 및원위부 (drca). 영상의질은다음과같이 5 단계로구분하였으며두명의영상의학과의사가협의로분석하였다 : 5점, 인공물이없는경우 ( 혈관의가장자리가흐려짐없이뚜렷하게보임 ); 4점, 경도의인공물 ( 혈관의가장자리가약간흐리게보임 ); 3점, 중등도인공물 ( 혈관의가장자리가심하게흐려보임 ); 2점, 심한인공물 (1점과 3점의중간정도 ); 1점, 심한인공물로인하여혈관을구별할수없음. 이중 4점과 5점을진단에적절한우수한질의영상으로간주하였다. 세환자군간의영상의질및방사선피폭량을비교하였다. 유효추정방사선량 (effective estimated dose) 은방사선량 길이 (dose-length product, DLP) 에흉부의전환계수 (conversion coefficient) 인 0.017을곱하여환산하였다. 통계학적분석은환자나이, 체질량지수, 혈관조영증강정도및잡음, 신호대잡음비, 조영증강대잡음비, 방사선피폭량, 영상질점수를비교하기위해 t-검정을사용하였으며각 Table 1. Patient Characteristics for the Three Groups Group A (n = 48) Group B (n = 45) Group C (n = 46) P Value Characteristics BMI<25, BMI>25, BMI<25, Group A vs Group A vs Group B vs 100 kvp 120 kvp 120 kvp Group B Group C Group C No. of female/ 14/34 15/30 12/34 male patients Age (year) 52.5 ± 11.5 53.4 ± 8.7 50.1 ± 10.6 <.666.494 <.225 BMI (kg/m 2 ) 22.0 ± 1.60 28.0 ± 3.3 22.4 ± 1.40 <.001.216 <.001 HR (bpm) 58.1 ± 4.50 58.9 ± 7.4 55.9 ± 5.90 <.798.376 <.337 30
군간의진단에적합한관상동맥분절수및진단에적합한영상을얻은환자수의비교를위해카이제곱검정을사용하였다. 체질량지수와혈관조영증강정도및잡음과의관계를분석하기위해 Pearson 상관분석을사용하였다. 통계학적유의수준은 0.05 미만으로하였다. C, 0.016; group B 와 group C, < 0.001). 조영증강대잡음비는평균 A군 18 ± 5, B군 14 ± 3, C군 20 ± 4로 A군에서 B군에비해유의하게높았으나 (p < 0.001) A군과 C군 결 과 환자군간에연령은유의한차이가없었으며 A군과 C군간에체질량지수는유의한차이가없었다 (group A, 22.0± 1.6; group C, 22.4 ± 1.4, p=0.216). 각군의평균체중은 A군 62.0 kg(44-78 kg), B군 76.5 kg(60-110 kg), C군 64.7 kg(50-79 kg) 이었고, 평균체중당요오드주입량은 A군 0.42 gi/kg, B군 0.34 gi/kg, C군 0.40 gi/kg이었다. 세군의평균분당심박동수는 A군 58.1 ± 4.5 회 (51-67 회 ), B 군 58.9 ± 7.4 회 (46-70회), C군 55.9 ± 5.9 회 (47-66 회 ) 로유의한차이가없었다 (Table 1). 혈관의평균조영증강정도는 100 kvp로촬영한 A군에서 120 kvp로촬영한 B군과 C군보다유의하게높게나타났다 (group A, 592 ± 85 HU; group B, 437 ± 46 HU; group C, 469 ± 62 HU: p < 0.001). 영상잡음은 A군과 B군사이에는유의한차이가없었으나 (23 ± 5 HU 와 22 ± 6 HU, p=0.427), A군에서 C 군에비해유의하게높았다 (23 ± 5 HU 와 17 ± 4 HU, p < 0.001). 신호대잡음비는평균 A군 24 ± 6, B군 19 ± 3, C군 27 ± 5로세군간에각각유의한차이가있었다 (p value; group A 와 group B, < 0.001; group A 와 group Fig 1. Linear regression plot of mean vessel attenuation against body mass index shows significant negative dependency (r=- 0.364, p<0.001). Solid line = mean; dashed lines = 95% confidence interval. Table 2. Objective Image Quality Parameters in Three Groups Parameter Group A (n = 48) Group B (n = 45) Group C (n = 46) P Value BMI<25, 100 kvp BMI>25, 120 kvp BMI<25, 120 kvp Gr. A vs Gr. B Gr. A vs Gr. C Gr. B vs Gr. C Attenuation (HU) Aorta 582 ± 86 441 ± 48 463 ± 61 <.001 <.001 <.062 LM 583 ± 91 442 ± 47 470 ± 61 <.001 <.001 <.013 plad 570 ± 83 430 ± 53 465 ± 65 <.001 <.001 <.005 prca 616 ± 98 431 ± 64 479 ± 81 <.001 <.001 <.002 Noise (HU) Aorta 26 ± 6 24 ± 5 18 ± 3 <.085 <.001 <.001 LM 21 ± 7 022 ± 11 17 ± 8 <.340 <.015 <.004 plad 023 ± 11 22 ± 9 17 ± 8 <.534 <.002 <.007 prca 021 ± 10 020 ± 10 016 ± 10 <.668 <.037 <.103 SNR Aorta 24 ± 6 19 ± 4 26 ± 5 <.001 0 0.017 <.001 LM 24 ± 6 19 ± 3 27 ± 5 <.001 0 0.011 <.001 plad 23 ± 6 19 ± 4 26 ± 5 <.001 0 0.006 <.001 prca 25 ± 7 19 ± 4 27 ± 6 <.001 0 0.088 <.001 CNR Aorta 18 ± 5 14 ± 3 20 ± 4 <.001 0 0.138 <.001 LM 18 ± 5 14 ± 3 20 ± 4 <.001 0 0.090 <.001 plad 18 ± 5 14 ± 3 20 ± 5 <.001 0 0.050 <.001 prca 20 ± 6 14 ± 3 20 ± 5 <.001 0 0.429 <.001 BMI=body mass index, HU=Hounsfield units, SNR=signal-to-noise ratio, CNR=contrast-to-noise ratio 31
김윤경외 : 체질량지수및관전압변화에따른 CT 관상동맥조영술의영상의질및방사선피폭량비교 사이에는유의한차이가없었다 (p=0.127) (Table 2). 120 kvp로촬영한환자 91명에서체질량지수와평균혈관조영증강정도및영상잡음과의상관관계를보았을때, 체질량지수는혈관의조영증강정도와유의한음의상관관계를보였으며 (r = -0.364, p < 0.001), 영상잡음과는양의상관관계를보였다 (r = 0.498, p < 0.001) (Figs. 1, 2). 각각의관상동맥분절별로영상의질을평가한결과평균점수는 A군 4.5 ± 0.5, B군 4.1 ± 0.4, C군 4.2 ± 0.4로세군모두에서진단에적절한영상을보였다 (Fig. 3). 총 1251 분절중진단에적절한관상동맥분절 (4점이상 ) 은 1,222개 (97.7%), 진단에부적절한관상동맥분절 (3점이하 ) 은 29개 (2.3%) 였다. 29개분절은모두 3점이었으며 1점과 2점을받은분절은없었다. 진단에부적절한 29개분절은각각, A군 9개분절 (LM, 1; prca, 1; mrca, 3; mlad, 1; plcx, 2; dlcx, 1), B군 16개분절 (prca, 2; mrca, 8; drca, 2; plad, 1; mlad, 2; dlad, 1), C군 4개분절 (prca, 1; mrca, 1; drca, 1; mlad, 1) 이었다. 진단에부적절한영상을한분절도포함하지않는환자의빈도는 A군 87.5%(42/48), B군 80.0%(36/45), C군 95.7%(44/46) 이었다 (Table 3). 세군의유효방사선량은각각, A군 8.5 ± 0.8 msv, B군 14.3 ± 1.3 msv, C군 14.9 ± 1.3 msv로, 관전압을 100 kvp로낮추어촬영한 A군은 120 kvp로촬영한다른두군에비하여방사선피폭량이약 42% 낮았다 (Table 4). 고 찰 Fig. 2. Linear regression plot of image noise against body mass index shows significant positive dependency (r=0.498, p<0.001). Solid line = mean; dashed lines = 95% confidence interval. 체질량지수는 CT 검사시에영상의질에영향을미치는인자로알려져있다. 특히 CT 혈관조영술을시행할때에는체질량지수가높을때혈관조영증강의감소와영상잡음의증가로말미암아영상의질이저하됨이보고되었다 (10-12). CT 혈관조영술을저관전압으로촬영하면영상잡음이높아져영상의질이저하되지만, 혈관내조영증강역시높아지므로조영증강대잡음비는유지되어진단에적절한영상을얻을수있으며방사선피폭량을줄일수있는장점이있다 (5, 6). 우리의연구에서는체질량지수가 25 이하로낮은환자군에서관전압을 100 kvp로낮추어 CT 관상동맥조영술을촬영할 A B C Fig. 3. A-C. CT images in representative coronary CT angiography studies of group. A. 44-year-old man from group A with BMI of 24.0 kg/m 2. Axial CT image obtained at 100 kvp shows diagnostic image quality with vessel attenuation of 610 HU and image noise of 21 HU. Estimated radiation dose was 7.4 msv. B. 56-year-old woman from group B with BMI of 27.4 kg/m 2. Axial CT image obtained at 120 kvp shows diagnostic image quality with vessel attenuation of 495 HU and image noise of 28 HU. Estimated radiation dose was 12.5 msv. C. 41-year-old man from group C with BMI of 23.5 kg/m 2. Axial CT image obtained at 120 kvp shows diagnostic image quality with vessel attenuation of 518 HU and image noise of 14 HU. Estimated radiation dose was 14.6 msv. 32
Table 3. Subjective Image Quality Assessment in Three Groups Group A Group B Group C (n = 48) (n = 45) (n = 46) P Value BMI<25, BMI>25, BMI<25, 100 kvp 120 kvp 120 kvp Gr. A vs Gr. B Gr. A vs Gr. C Gr. B vs Gr. C Total No. of segments 432 405 414 Mean score 4.5 ± 0.5 4.1 ± 0.4 4.2 ± 0.4 <.001 <.001 <.001 Diagnostic image quality (per segment) 97.9% (423/432) 96.0% (389/405) 99.0% (410/414).113.187.006 Non-diagnostic image quality (per segment) 2.1% (9/432)0 4.0% (16/405) 1.0% (4/414)0 Diagnostic image quality (per patient) 87.5% (42/48)00 80.0% (36/45)00 95.7% (44/46)00.326.157.022 Table 4. Radiation Dose Estimates in Three Groups Group A (n = 48) Group B (n = 45) Group C (n = 46) P Value BMI<25, 100 kvp BMI>25, 120 kvp BMI<25, 120 kvp Gr. A vs Gr. B Gr. A vs Gr. C Gr. B vs Gr. C Effective dose (msv) 8.5 ± 0.8 14.3 ± 1.3 14.9 ± 1.3 <.001 <.001.026 경우관상동맥분절의 97.9% 에서진단에적절한양질의영상 120 kvp 대신 100 kvp로낮추어촬영하는방법을통해영상을얻을수있다는것을확인하였다. 이는통상적인 120 kvp 의질저하없이방사선피폭량을약 42% 감소시킬수있었로촬영한환자군과비교하여유의한차이가없었으며체질량다. 지수가높은환자군과비교하여서는오히려좋은결과를보였요오드는원자번호가높아낮은 X-선에너지일수록요오드다. 영상잡음의경우체질량지수가 25 이하이며 100 kvp로조영제의감쇠를증가시키므로관전압을낮추어 CT 촬영을할촬영한 A군이체질량지수가 25 이하이며 120 kvp로촬영한경우요오드조영제의조영증강을증가시킨다는장점이있다 C군보다는높았지만, 체질량지수 25 이상이며 120 kvp로촬 (14, 15). 본연구에서도 100 kvp로촬영한환자군에서혈관영한 B군과비교하여서는유의한차이를보이지않았다. 따라조영증강이다른군에비해유의하게높았다. 이러한점을이서체질량지수가 25 이하로낮은환자는관전압을 100 kvp 용해저관전압으로촬영하는환자는조영제주입량을줄이는로낮추어촬영하여도영상의질에는부정적인영향을주지않프로토콜이연구되었으며, Stolzmann 등에따르면체질량지는다고볼수있다. 수가 25 이하로낮은환자에서관전압을 100 kvp로낮추어 Pflederer 등 (13) 은체중 85 kg 이하인환자는관전압 100 촬영할때조영제주입량을 1.0 ml/kg에서 0.8 ml/kg로 20% kvp로촬영한 CT관상동맥조영술과 120 kvp로촬영한 CT 줄여도체질량지수가 25 이상이며 120 kvp로촬영한환자와관상동맥조영술간에영상질에차이가없었다고하였으며조비교하였을때혈관조영증강에유의한차이가없었다 (7). 영증강정도와영상잡음이 100 kvp로촬영한군에서유의하높은체질량지수와낮은관전압은모두영상잡음을증가시게높았지만신호대잡음비나조영증강대잡음비는유의한켜영상의질에부정적인영향을끼치게된다. 저자들의연구차이가없었다고발표하였다. 또한, 관전압을낮춤으로써에서체질량지수가낮고낮은관전압으로촬영한 A군과체질 38.6% 의방사선피폭을줄일수있었다. Alkadhi 등 (8) 은체량지수가높고높은관전압으로촬영한 B군을비교하였을때질량지수및심박동수에따라관전압과관전류, 심동조화를영상잡음에는유의한차이가없었으나영상의질을비교하였서로다른다섯개프로토콜로세분하여촬영한결과각프로을때에는 A군의평균점수가더높았으며진단에적절한영토콜간에영상의질에는유의한차이가없었으며, 120 kvp, 상의빈도도높았다. 진단에적절한영상을얻는빈도는관전 330 mas, 후향적심동조화를사용한기존의프로토콜에비하압이달라도체질량지수가유사한 A군과 C군사이에는유의여 BMI < 25, 심박동수 70 이하인그룹에서 100 kvp, 190 한차이가없었지만, 같은관전압으로촬영하였어도체질량지 mas, 전향적심동조화프로토콜을사용하여방사선피폭이수가다른 B군과 C군사이에서는유의한차이가있었는데이 86% 감소하였다고보고하였다. 이처럼환자의체중이나체질는체질량지수가영상의질에미치는영향이크다는점을시량지수와같은개별적특성에따른 CT 프로토콜의변화를통사한다. 또한, 같은체질량지수임에도불구하고낮은관전압해방사선피폭량을최소한도로줄이면서영상의질을저하하으로촬영한 A군이 C군보다영상의질의평균점수가오히려지않는최적의프로토콜을찾기위한연구가계속되고있다. 높았는데, 이는낮은관전압으로인해혈관조영증강이증가우리의연구에서는체질량지수 25 이하인환자에서관전압을한효과로영상잡음이다소높아진점을극복하였다고생각해 33
김윤경외 : 체질량지수및관전압변화에따른 CT 관상동맥조영술의영상의질및방사선피폭량비교 볼수있다. 우리의연구에는제한점이있다. 이연구에포함된환자중다수는무증상선별검사를위한환자들이며이러한환자들은대부분고식적관상동맥조영술을시행받지않았다. 이에우리는영상의질만평가했을뿐관상동맥질환에대한진단적정확도를분석하지않았다. 향후관상동맥질환을앓고있는환자군에서고식적인관상동맥조영술과의비교를통한진단능평가에대한연구가이루어져야하겠다. 또한, 환자군별평균심박수나심박수의변동범위를기록하지않았다. 그러나베타차단제를사용하여심박수가 70 이하로유지되고, 부정맥이없는환자에게서만 CT를시행하였기때문에평균심박수나심박수의변동에따른영상질평가에의영향은적을것으로생각한다. 결론적으로, 체질량지수가 25 이하로낮은환자에서선택적으로관전압을 100 kvp로낮추어 CT 관상동맥조영술을시행하는경우영상의질저하없이진단에적절한영상을얻을수있는동시에효과적으로방사선피폭량을줄일수있다. 참고문헌 1. Mollet NR, Cademartiri F, van Mieghem CA, Runza G, McFadden EP, Baks T, et al. High-resolution spiral computed tomography coronary angiography in patients referred for diagnostic conventional coronary angiography. Circulation 2005;112:2318-2323 2. Leschka S, Alkadhi H, Plass A, Desbiolles L, Grünenfelder J, Marincek B, et al. Accuracy of MSCT coronary angiography with 64-slice technology: first experience. Eur Heart J 2005;26:1482-1487 3. Husmann L, Schepis T, Scheffel H, Gaemperli O, Leschka S, Valenta I, et al. Comparison of diagnostic accuracy of 64-slice computed tomography coronary angiography in patients with low, intermediate, and high cardiovascular risk. Acad Radiol 2008;15:452-461 4. Hausleiter J, Meyer T, Hadamitzky M, Huber E, Zankl M, Martinoff S, et al. Radiation dose estimates from cardiac multislice computed tomography in daily practice: impact of different scanning protocols on effective dose estimates. Circulation 2006;113: 1305-1310 5. Leschka S, Stolzmann P, Schmid FT, Scheffel H, Stinn B, Marincek B, et al. Low kilovoltage cardiac dual-source CT: attenuation, noise, and radiation dose. Eur Radiol 2008;18:1809-1817 6. Szucs-Farkas Z, Kurmann L, Strautz T, Patak MA, Vock P, Schindera ST. Patient exposure and image quality of low-dose pulmonary computed tomography angiography: comparison of 100- and 80-kVp protocols. Invest Radiol 2008;43:871-876 7. Stolzmann P, Leschka S, Scheffel H, Krauss T, Desbiolles L, Plass A, et al. Dual-source CT in step-and-shoot mode: noninvasive coronary angiography with low radiation dose. Radiology 2008;249:71-80 8. Alkadhi H, Stolzmann P, Scheffel H, Desbiolles L, Baümuller S, Plass A, et al. Radiation dose of cardiac dual-source CT: the effect of tailoring the protocol to patient-specific parameters. Eur J Radiol 2008;68:385-391 9. Tatsugami F, Husmann L, Herzog BA, Burkhard N, Valenta I, Gaemperli O, et al. Evaluation of a body mass index-adapted protocol for low-dose 64-MDCT coronary angiography with prospective ECG triggering. AJR Am J Roentgenol 2009;192:635-638 10. Jung B, Mahnken AH, Stargardt A, Simon J, Flohr TG, Schaller S, et al. Individually weight-adapted examination protocol in retrospectively ECG-gated MSCT of the heart. Eur Radiol 2003; 13:2560-2566 11. Irie T, Inoue H. Individual modulation of the tube current-seconds to achieve similar levels of image noise in contrast-enhanced abdominal CT. AJR Am J Roentgenol 2005;184:1514-1518 12. Bae KT, Seeck BA, Hildebolt CF, Tao C, Zhu F, Kanematsu M, et al. Contrast enhancement in cardiovascular MDCT: effect of body weight, height, body surface area, body mass index, and obesity. AJR Am J Roentgenol 2008;190:777-784 13. Pflederer T, Rudofsky L, Ropers D, Bachmann S, Marwan M, Daniel WG, et al. Image quality in a low radiation exposure protocol for retrospectively ECG-gated coronary CT angiography. AJR Am J Roentgenol 2009;192:1045-1050 14. Sigal-Cinqualbre AB, Hennequin R, Abada HT, Chen X, Paul JF. Low-kilovoltage multi-detector row chest CT in adults: feasibility and effect on image quality and iodine dose. Radiology 2004;231:169-174 15. Nakayama Y, Awai K, Funama Y, Hatemura M, Imuta M, Nakaura T, et al. Abdominal CT with low tube voltage: preliminary observations about radiation dose, contrast enhancement, image quality, and noise. Radiology 2005;237:945-951 34
J Korean Soc Radiol 2010;62:29-35 Image Quality and Radiation Exposure in Coronary CT Angiography According to Tube Voltage and Body Mass Index 1 Yoon Kyung Kim, M.D., Yookyung Kim, M.D. 2 1 Department of Radiology, Korea University Guro Hospital, Korea University College of Medicine 2 Department of Radiology, Ewha Womans University MokDong Hospital Purpose: To investigate the image quality and radiation dose of a coronary CT angiography (CCTA) according to tube voltage and body mass index (BMI). Materials and Methods: This study included 139 patients who underwent CCTA using a retrospective electrocardiography-gating technique. A total of 48 patients (BMI <2 5, group A) were examined with 100 kvp, 45 patients (BMI > 25, group B) with 120 kvp, and 46 patients (BMI < 25, group C) with 120 kvp. Attenuation and image noise of the aorta and coronary arteries was measured. Moreover, the image quality of 9 coronary segments was graded on a scale of 1-5, where grade 4 or 5 was considered to be diagnostic. Image quality parameters and radiation dose were compared using a t-test or Chi-squared test. Results: Vessel attenuation in group A was significantly higher than in groups B or C (group A, 592 ± 85 HU; group B, 437 ± 46 HU; group C, 469 ± 62 HU, p<0.001). Image noise was similar in group A and group B (23 ± 5 HU versus 22 ± 6 HU, p=0.427), but significantly higher in group A compared to group C (23 ± 5 HU versus 17 ± 4 HU, p<0.001). A significant difference was observed in the signal-to-noise ratio between the three groups (group A, 24 ± 6; group B, 19 ± 3; group C, 27 ± 5: p<0.05). Moreover, the contrast-to-noise ratio was significantly higher in group A than group B (group A 18 ± 5 versus group B 14 ± 3, p < 0.001) but not significantly different between group A and group C (group C 20 ± 4, p=0.127). The percentage of coronary segments with diagnostic image quality was 97.9% in group A, 96.0% in group B, and 99.0% in group C. The mean image quality score was 4.5 ± 0.5 in group A, 4.1 ± 0.4 in group B, and 4.2 ± 0,4 in group C (p<0.001). The effective radiation doses were 8.5 ± 0.8 msv in group A, 14.3 ± 1.3 msv in group B, and 14.9 ± 1.3 msv in group C. A 42% reduction in mean effective radiation dose in group A was observed compared with groups B and C. Conclusion: In patients with BMI less than 25 and a low-dose CCTA with 100 kvp leads to a significant reduction in radiation exposure without degradation of image quality. Index words : Coronary Angiography Body mass index Radiation Dosage Address reprint requests to : Yookyung Kim, M.D., Department of Radiology, Ewha Womans University MokDong Hospital, 911-1 MokDong YangCheon-ku, Seoul 158-710, Korea. Tel. 82-2-2650-5174 Fax. 82-2-2650-5071 E-mail: yookkim@ewha.ac.kr 35