Journal of Radiation Industry 12 (1) : 97 ~ 102 (2018) Technical Paper 복부팬텀영상에서장비별피폭선량및노이즈비교 문일봉 1 신지윤 1 곽종길 2,3 장상현 4 류영환 5 동경래 1, * 1 광주보건대학교방사선과, 2 동신대학교보건의료학과, 3 KS 병원종합건진센터, 4 구자성정형외과의원, 5 서울의료원영상의학과 A Noise and Quantity of Exposed Ray for Abdominal Phantom Image Il-Bong Moon 1, Ji-Yun Shin 1, Jong-Gil Kwak 2,3, Sang-Hyun Jang 4, Young-Hwan Ryu 5 and Kyung-Rae Dong 1, * 1 Department of Radiological Technology, Gwangju Health University, 73, Bungmun-daero 419 Beon-gil, Gwangsan-gu, Gwangju 62271, Republic of Korea 2 Department of Public Health and Medicine, Dongshin University Graduate School, 185, Geonjae-ro, Naju-si, Jeollanam-do 58245, Republic of Korea 3 Comprehensive Medical Examination Center, KS Hospital, 220, Wangbeodeul-ro, Gwangsan-gu, Gwangju 62248, Republic of Korea 4 Department of Radiology, Dr. Koo s Orthopaedic & Sportsclinic, 179, Eungam-ro, Eunpyeong-gu, Seoul 03485, Republic of Korea 5 Department of Radiology, Seoul Medical Center, 156, Sinnae-ro, Jungnang-gu, Seoul 02053, Republic of Korea Abstract - This research is to compare noise and quantity of exposed ray at abdomen with two medical equipment company, GE and Siemens. As well as figuring out which one has high or low quantity of exposed ray and advantages of each equipment in certain areas. This research used SIEMENS (Somatom Definition Flash, Germany) and GE (Discovery CT 750 HD, USA) in C University as CT equipments. For dummy, this research used Rando phantom (Art-20x fluke biomedical, USA) in condition of care dose 4D and care Kv System with Siemens and GE respectively. For slice thickness, this research used 3 mm for Siemens and 3.75 mm for GE and scanned abdomen 4 times with same FOV 38 cm and 80, 100, 120, 140 kvp. This research is to figure out correlation between noise and quantity of rays from changes of tube voltage in each company s equipment for abdominal phantom. Also this paper got the results that average value of noise decreases and values of CTDlvol and DLP increases by increasing tube voltage to 80, 100, 120, 140 kvp respectively. From above research, there is a difference in quantity of ray for patients by type of equipment, even scanning same area. Therefore, there should be appropriate management criteria. With this perception, the limitation of this research used only two different companies equipment and used standardized phantom that excludes different characteristics by each patient. To increase quality of image with decreasing unnecessary quantity of rays, there should be additional technology development. Key words : CT, Rando phantom, CTDIvol, DLP * Corresponding author: Kyung-Rae Dong, Tel. +82-62-958-7668, Fax. +82-62-958-7669, E-mail. krdong@hanmail.net 97
98 문일봉 신지윤 곽종길 장상현 류영환 동경래 서 론 연구대상및방법 컴퓨터단층촬영 (Computed tomography; CT) 검사는환자의진단과치료에도움을주는반면에방사선조사에따른위험을내포하고있다. 1990년대후반에등장한 MDCT (Multi-detector computed tomography) 는기존의 CT 장비에비하여검사시간을대폭단축시키고환자의움직임에의한허상을감소시키며, 종축의해상도가증가하는장점이있었다 (Hu et al. 2000). 그러나 MDCT에서높은해상력을가진영상을구현하기위해서는매우얇은절편과많은절편의수가필요한데이는선량의증가로이어지는단점이있다 (Dawson 2004; Yates et al. 2004). 따라서 CT 검사의진단적이득에대한이해와함께검사에의한위험도를함께숙지하고있어야한다 (Goo 2005). CT 검사에서환자선량은전체방사선검사에서차지하는비율은낮은반면, 전체방사선량에서차지하는비율은상대적으로높다 (Kalra et al. 2004). 이러한 CT는의심받는질병을밝히는데자주사용되는데 CT 검사로얻어진정보가방사선노출로인한위험보다훨씬더가치가있겠지만정확한진단뿐아니라위험을최소화하는것도중요하다 (Lee et al. 2004). 이에합리적으로달성가능한피폭선량을낮게유지하여최대한환자피폭을줄이려는노력이필요하고영상의최적화를위해적정피폭선량의기초자료나피폭선량감소방법을마련해야한다 (ICRP 2006; Wang et al. 2013). 방사선량과관련된 CT 영상변수에는스캐너구조, 관전압, 관전류 rotation time, collimation, pitch, scan length, 검출기효율, 필터, 그리고차폐등이있다. 영상질을결정하는데도관련이있는이변수들은최소한의방사선량으로진단적가치가있는 CT 검사를시행하는영상기법의최적화를이해하고계획하는데중요하다 (Kwon et al. 2010). CT에서영상의질은인체의미세구조를명료하고정확하게영상으로나타낼수있느냐에따라좌우된다. 영상의질을결정하는중요한요소로는공간분해능과대조도분해능, Pixel, 노이즈등이있다 (Schaller et al. 2003). 과거에는흉부 CT 검사에서는많은검사시간을소요하였으나최근에는같은정보를 1회의호흡시간내에얻을수있게되었다 (Moon et al. 2017). 이처럼혁신적인 CT 기술발전으로인한진단적가치의향상으로검사건수가크게증가하여전체방사선검사에서 CT 검사의비중이크게증가하고있다. 이로인한방사선피폭또한중요한문제로대두되고있으나여전히대부분의병원에서는 CT 검사로인해환자가받는방사선피폭은영상정보량의확대와영상의질향상이라는측면에가리어져간과되고있는실정이다 (Moon et al. 2016). 이에본연구는복부팬텀을이용하여적정피폭선량및노이즈를알아보고자하였다. 1. 검사방법 CT 장비는 C대학에서사용되고있는 S사 (Somatom Definition Flash, Germany), GE (Discovery CT 750 HD, USA) 를사용했으며, 인체모형인 Rando phantom (Art-20x fluke biomedical, USA) 을사용하여각회사별노이즈와선량변화를측정하였다 (Fig. 1). 2. 검사조건실험을위해사용한장비의프로토콜은 Table 1과같다. 노이즈와선량측정을위한조건으로 slice thinkness는 S 사 3 mm, G사는 3.75 mm, Kernel값은 S사는 B40f, G사는 standard, FOV는 38 cm로동일하게하고관전압을 80, 100, 120, 140 kvp로변화를주었다. 3. 측정방법 3. 1 노이즈측정노이즈는 CT 계수 (Housfield Unit) 의표준편차로영상의 ROI (Region of interest) 에서 SD (Standard deviation) 값은노이즈이다. 각장비의관전압을 80, 100, 120, 140 kvp 로변화시켜노이즈를측정하였고, 측정방법은 Calibration 의 ROI를 99.70 mm 2 로일정하게설정하여각조건마다 10 회측정하여평균값으로타나내었다. 3. 2 선량측정선량측정은노이즈측정과같이장비의관전압을 80, 100, 120, 140 kvp로변화시켜 CTDIvol값과 DLP값으로나타내었다. CTDI (Computed Tomography Dose Index) 는단일슬라이스스캔에서공기중또는 CT선량측정용팬텀에서측정된선량의 Z축방향의적분값을절편두께로나눈값이다. CTDIvol은환자선량의평가를더욱정확하게하기위해도입되어사용되는스캔축에서의 CTDI로 Z축에서노출의변동을감안한값으로다음식 1, 2로정의하며단위로는 mgy를사용한다. CTDIvol = CTDI*NT/I (1) CTDIvol = CTDIw/pitch (2) I = 나선형 CT에서 rotation당테이블이움직인거리 DLP는모든영상에대한총선량의측정값으로 CTDIvol 에스캔한길이를곱한값으로이값은유효선량을측정하는데이용되며단위는 mgy*cm를사용한다 ( 식 3) (Kim et al. 2005).
복부팬텀영상에서장비별피폭선량및노이즈비교 99 Fig. 1. CT equipments (Siemens, GE). Table 1. Comparison of CT parameter by CT scanner equipments mas S equipment G equipment Care-dose 4D care KV kvp 80 100 120 140 80 100 120 140 Slice thickness (mm) 3 3 3 3 3.75 3.75 3.75 3.75 FOV (cm) 38 38 38 38 38 38 38 38 Kernal B40f B40f B40f B40f Standard Standard Standard Standard DLP = CTDIvol*Scan length (3) 결과 1. 관전압변화에의한노이즈평가 Rando phantom의 ROI를 99.70 mm 2 로일정하게설정하여각조건마다 10회의 SD를측정하여평균값으로나타낸결과는 Table 2와같다. S사장치에서 80, 100, 120, 140 kvp 의 SD값은각각 36.33, 25.22, 21.13, 19.03으로측정되었고, G사에서 80, 100, 120, 140 kvp의 SD값은각각 32.85, 27.2, 23.578, 21.81로측정되었다. 80 kvp를기준으로 100 kvp로증가시 S사는 30.6%, G 사는 17% 감소, 120 kvp로증가시 S사는 41.8%, G사는 28.2% 감소, 140 kvp로증가시 S사는 47.6%, G사는 33.6% 로감소하였다 (Figs. 2-5). 노이즈측정과같이장비의관전압을변화시켜 10회측정하여선량을평균값으로나타낸결과는 Table 2와같다. 먼저 CTDIvol값은 80 kvp일때, S사 2.58 mgy, G사 3.56 mgy, 100 kvp일때 S사는 5.25 mgy, G사는 3.55 mgy, 120 kvp일때 S사는 8.44 mgy, G사는 4.32 mgy, 140 kvp일때 S사는 12.47 mgy, G사는 5.69 mgy로측정되었고 80 kvp를기준으로 100 kvp로증가시 S사는 203.4%, G사는 0.3% 감 소, 120 kvp로증가시 S사는 327.1%, G사는 121.3% 증가, 140 kvp로증가시 S사는 483.3%, G사는 159.8% 증가하였다. 다음으로 DLP값은 80 kvp일때 S사는 123 mgy*cm, G 사는 184.82 Gy*cm, 100 kvp일때 S사는 251 Gy*cm, G사는 184.12 mgy*cm, 120 kvp일때 S사는 404 Gy*cm, G사는 224 mgy*cm, 140 kvp일때 S사는 597 mgy*cm, G사는 295.25 Gy*cm로측정되었고 80 kvp를기준으로 100 kvp 로증가시 S사는 204.1% 증가, G사는 0.004% 감소하였고, 120 kvp로증가시 S사는 328.5%, G사는 121.2% 증가, 140 kvp로증가시 S사는 485.3%, G사는 159.8% 증가하였다 (Figs. 6-8). 고찰 CT에서영상의질은인체의미세한구조를정확하게영상으로나타낼수있는가에의해좌우되며, 영상의질을결정하는중요한요소는노이즈, 균일도, 공간분해능, 대조도분해능, 인공물, 선량등이있으며이러한영상의질을결정하는요소들은객관적으로평가되어야한다. CT 검사시영상의화질과방사선피폭선량에영향을미치는기술적인요소로는 Slice thinkness, kvp, mas, 조사야, 환자의위치등이해당된다. CT에서고화질의영상을얻기위해서는고관
100 문일봉 신지윤 곽종길 장상현 류영환 동경래 Table 2. Comparison of radiation dose and noise by CT scanner equipments Equipment Measurement S G S G S G S G CT number 10.4 16.8 7.5 10 3.5 6.8 3 5.2 Noise 36.33 32.85 25.22 27.28 21.13 23.58 19.03 21.81 CTDIvol (mgy) 2.58 3.56 5.25 3.55 8.44 4.32 12.47 5.69 DLP (mgy*cm) 123 184.82 251 184.12 404 224.00 597 295.25 Effective mas 0.04 0.05 0.08 0.05 0.13 0.07 0.19 0.09 Fig. 2. S company 80 kvp. Fig. 5. G company 140 kvp. CT number 18 16 14 12 10 8 6 4 2 0 10.4 16.8 7.5 10 6.8 3.5 3 S equipment G equipment 5.2 Fig. 6. Comparison of CT number value by CT scanner equipments. Fig. 3. S company 100 kvp. Fig. 4. G company 120 kvp. 전압이사용되어야하는데최근피폭선량에대한관심이증가함에따라적은선량으로보다정확한영상정보를얻는것에초점을맞추고있다. 고선량 CT는저선량 CT에비해선명한영상을얻을수있다는장점이있지만진단적인가치는유사한데에비해환자선량이높다는단점이있다. 반면에과도하게환자선량을낮추게되면진단가치가떨어지는영상을얻게될수있다 (Yoo et al. 2010). 이에본연구는복부팬텀에서회사장비별로관전압의변화에따른노이즈와선량의상관관계를알고자하였고 C대학의 MDCT 장비 S사 (Somatom Definition Flash, Germany) 와 G사 (Discovery CT 750 HD, USA) 인체모형인 Rando phantom (Art-20x fluke biomedical, USA) 을이용해관전압의변화에따른노이즈와선량의변화를연구하여관전압이 80, 100,
복부팬텀영상에서장비별피폭선량및노이즈비교 101 Noise Effective mas 40 35 30 25 20 15 10 5 0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 36.33 32.85 25.22 27.28 21.13 23.58 Fig. 7. Comparison of noise by CT scanners. S equipment G equipment 19.03 S equipment G equipment 0.04 0.08 0.05 0.05 120, 140 kvp 로증가함에따라노이즈의평균값은감소하 고, CTDIvol, DLP 의값은증가한다는결과를얻었다. 본연 구와비슷한사례로 2014 년 Moon 의 MDCT 에서관전압변 화에따른노이즈와선량의변화연구결과에서관전압의감소에의한 Noise 변화는 140 kvp에서 120 kvp는평균 5.3% 증가하였고, 120 kvp에서 100 kvp는평균 7% 증가하였다. 관전압의감소에의한선량변화는 140 kvp에서 120 kvp 는평균 31.8% 가감소하였고, 120 kvp에서 100 kvp는평균 38.2% 감소하여선량감소효과에비해크게영상의질이감소되지않은결과가나타남으로써본연구와결과가일치함을알수있다 (Moon et al. 2014). 사용자는여러가지기술적인자들의최적사용을통해진단적연구와노력을계속해야겠다. 이를위해서는 CT 검사를, 추적검사와병리학적특성이이미알려져있는상황에서스캔범위와필요이상의스캔단면수를줄이고잘못된검사로인한반복노출을피해야할것이다. 현재 CT 검사의적용과수요가증가추세에있기때문에피폭선량감소에대한노력이더욱더절실할것이다. 그리고 CT 검사시각의료기관의장비의종류에따라서동일한부위를검사하는경우라도환자가받게되는선량에차이가발생한다. 그리므로적절한관리기준의설정되어야한다. 이런점에서본논문의한계는현재임상에서다른두회사의장비를각각사용하였고환자마다다른특징을제외하고일정하게정형화된팬텀을사용했다는점이다. 앞으로불필요한선량을줄이고영상의품질을향상시키기위한추가적인기술개발이필요하다고생각된다. 0.13 0.07 0.19 Fig. 8. Comparison of effective mas by CT scanners. 21.81 0.09 결 본연구결과, 노이즈는 80 kvp를기준으로 100 kvp, 120 kvp, 140 kvp로증가함에따라 S사는 (30.6%, 41.8%, 47.6%) 감소하였고 G사는 (17%, 28.2%, 33.6%) 감소하였다. CTDIvol은 80 kvp를기준으로 100 kvp, 120 kvp, 140 kvp 로증가함에따라 S사는 (203.4%, 327.1%, 483.3%) 증가하였고 G사는 ( - 0.3%, 121.3%, 159.8%) 증가하였다. DLP값은 80 kvp를기준으로 100 kvp, 120 kvp, 140 kvp로증가함에따라 S사는 (204.1%, 328.5%, 485.3%) 증가하였고 G 사는 ( - 0.004%, 121.2%, 159.8%) 증가하였다. 진단가치가높은영상획득을위해서적정한 CT 장비와적정한노이즈값과적정관전압을사용해환자선량을최소화해야할것으로사료된다. 사 This work was supported by the Nuclear Safety Research Program through the Korea Radiation Safety Foundation (KORSAFe) and the Nuclear Safety and Security Commission (NSSC), Republic of Korea (Grant No. 1305033). 론 사 참고문헌 Dawson P. 2004. Patient dose in multi-slice CT: Why is it increasing and does it matter?. Br. J. Radiol. 77(1):S10-S13. Goo HW. 2005. Pediatric CT : Understanding of radiation and optimization of imaging technupues. J. Korean Soc. Radiol. 52(1):1-5. Hu H, He HD, Foley WD and Fox SH. 2000. Four multidetector-row-helical CT: image quality and volume coverage speed. Radiology 215(1):55-62. ICRP. 2006. Managing Patient Dose in MultiDetector Computed Tomography (MDCT). ICRP Publication 102. Pergamoon Press, Oxpord. Kalra MK, Maher MM, Toth TL, Hamberg LM, Blake MA, Shepard JA and Saini S. 2004. Strategies for CT radiation dose optimization. Radiology 230(3):619-628. Kim YH, Choi JH, Kim SS, Oh YH, Lee CH, Cho OK, Kang DH, Lee YB, Kim HC and Kim CM. 2005. Patient exposure doses from medical x-ray examinations in Korea. J. Radiol. Sci. Technol. 28(3):241-248. Kwon SO, Dong KR, Kown DC, Goo EH, Choi JW and Chung WK. 2010. Estimate of Radiation Doses in MDCT Using Patient Weight. Prog. Med. Phys. 21(3):246-252. Lee CI, Haims AH, Monico EP, Brink JA and Forman HP. 2004.
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