Soonchonhyang Medical Science 16(2):241-247, December 2010 pissn: 2095-0179 I eissn: 2095-0187 CASE REPORT 스텐트내경측정시다양한다절편전산화단층촬영알고리즘의영향 김동훈 1, 백상현 1, 정명진 2 1 순천향대학교의과대학부천병원영상의학과학교실, 2 조선대학교의과대학조선대학교병원영상의학과 Effect of Various Multi-Detector Computed Tomography Algorithms on Measuring In-Stent Diameter Dong Hun Kim 1, Sang Hyun Paik 1, Myoung Jin Jeong 2 1 Department of Radiology, Soonchunhyang University Bucheon Hospital, Soonchunhyang University College of Medicine, Bucheon; 2 Department of Radiology, Chosun University Hospital, Chosun University School of Medicine, Gwangju, Korea This study was carried out to measure diameters of stents within phantom and to know proper algorithm for evaluating patency of stent by using multi-detector computed tomography (MDCT). Phantom model that stent was located in plastic pite with mixed saline and contrast (10:1) and total 80 patients (man:woman = 53:27, mean age, 60.8 years old) who undertaken percutaneous coronary intervention (stenting) were included in this study. Computed tomography scans were performed with 16- and 64-slice MDCT scanner with retrospective electrocardiography gating. Standard scanning protocols were applied. Cardiac radiologist and radiologic technician measured internal diameters of stents. Also, image qualities of stents as 8 points were scored. For evaluation of images, window width and window center were used as 900± 100 and 400± 100, respectively. In phantom model, average maximal diameters measured by each algorithms were 2.35 mm (B50f in Siemens AG, Medical Solutions [S company]) and 2.53 mm (Xres standard [XCB] in Phillips Medical Systems [P company]), respectively. In patients, in-stent resolution processed by Xres sharp (XCC) was scored as 7.67 (highest). In this study, B40f, B50f (16 slice MDCT in S company), XCB and XCC (64 slice MDCT in P company) are appropriate algorithms for evaluating internal patency of stents. Keywords: Computed tomography; Coroanry artery; Stent; Algorithm 서론서구화된식생활과스트레스등으로심혈관질환에의한입원과사망이늘고있으며이와연관된심혈관연구역시활발히진행되고있다 [1]. 수년동안선진국에서는질병으로인한입원및사망원인중에서관상동맥질환으로인한요인이증가하고있다 [2]. 우리나라의경우에도 2000년대초반이전 10년과비교하여관상동맥질환이 2배이상증가한것으로보고되고있다 [3]. 관상동맥질환은대부분동맥경화반에동반된혈전에의한폐색또는협착으로나타나는데가장주된치료방법이스텐트삽입술이다. 스텐트삽 입시술은 Sigwart 등 [4] 이인간에게처음으로시작한이후급성혈관폐쇄및재협착의발생을줄이는데획기적인시술방법으로알려졌다 [5]. 최근에는약물용출스텐트 (drug eluting stent) 가도입되어재협착률이낮아지고있지만아직도재협착병변이발생하며특히길이가긴경우, 작은혈관, 당뇨병환자, 개구부병변, 분지병변, 기저질환으로당뇨병이있는경우에는재협착률이 10-20% 로높다 [6]. 따라서스텐트삽입후추적검사가반드시필요하며오랫동안고식적심혈관조영술 (conventional coronary angiography) 이표준적인검사로알려져왔다. 하지만이검사는부정맥, 뇌졸중, 관상동맥혈전발생과같은부작용이있을수있으며약 0.1% 의환자 Correspondence to: Dong Hun Kim Department of Radiology, Soonchunhyang University Bucheon Hospital, Soonchunhyang University College of Medicine, 1174 Jung-dong, Wonmi-gu, Bucheon 420-767, Korea Tel: +82-32-621-5851, Fax: +82-32-621-5874, E-mail: dhk0827@schbc.ac.kr Received: Jul 9, 2010 / Accepted: Nov 9, 2010 2010 Soonchunhyang Medical Research Institute This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/). http://jsms.sch.ac.kr 241
Kim DH, et al. Effect of MDCT Algorithms on Coronary Stent 가사망할수있는침습적인방법이며시술을위해서꼭입원을요한다는불편함이있다 [7]. 최근에는비침습적인관상동맥영상법으로다절편전산화단층촬영 (multi-detector row computed tomography, MDCT) 이개발되어유용하게사용되고있다. 고밀도해상도와빠른시간안에영상획득과재구성이가능한 MDCT로인해비침습적인관상동맥영상촬영이가능해졌는데 [8], 관상동맥뿐만아니라심기능검사와함께우회술을시행한혈관과삽입된스텐트의재협착여부를판별할수있게되었다. MDCT는관상동맥의협착이나폐색을진단하는데 90% 이상의민감도와 93-98% 의특이도를보이며, 스텐트개통성에대한민감도는 90-100%, 특이도는 80-90%, 재협착의민감도는 70-100%, 특이도는 80-100% 로매우우수한비침습적검사로보고되고있다 [9-13]. 최근들어빠른 0.3초의 computed tomography (CT) 튜브회전시간과전향적심장동조화 (prospective cardiac gating) 가가능한 MDCT가도입되면서저선량으로빠르고정확하게관상동맥을비침습적으로검사할수있게되었다 [10,14,15]. 관상동맥내스텐트시술혹은수술후에우회술을시행한이식혈관이나스텐트의협착및개존성을추적조사하는것은환자들의예후를판정하는데매우중요하다 [16]. 저자들은관상동맥내시술되는스텐트내부의협착이나폐색을확인하는데있어서영향을줄수있는다양한영상알고리즘을적용하고특징을관찰하였다. 대상및방법 1. 대상 1) 팬텀 (phantom) 제작스텐트 (JOSTENT Coronary Stent Graft, ABBOTT Vascular Instuments Deutschland GMBH, Rangendingen, Germany) 의재질은스테인레스이며벽두께는 0.09 mm, 펴지않았을때두께는 1.8 mm인상용제품을이용하였다. 팬텀은작은유리병안에생리식염수와조영제를 10:1 로혼합한조영제를채운후얇은관내부 안에풍선으로확장시킨실측내경 3.75 mm의스텐트 (Fig. 1) 를유리병에삽입하여제작하였다 (Fig. 2). 2) 환자대상군협심증을주소로 50% 이상의관상동맥협착이확인되어스텐트삽입시술을받은환자를대상으로추적관찰중비정형적흉통으로내원한 80명 ( 남자 53명, 여자 27명, 평균연령 60.8세 ) 환자를대상으로 64절편 MDCT를이용하여관상동맥 CT 혈관조영촬영을시행하였다. 스텐트시술후 CT 촬영까지소요시간은평균 8±2.5 개월이었다. 평균심박동수는 65±7회 / 분이었다. 2. MDCT 검사팬텀검사는 16절편, 64절편 MDCT를사용하였고, 스텐트삽입환자군검사는 64절편 CT를사용하였다. 16절편 MDCT (SO- MATOM Sensation16, Siemens AG, Medical Solutions, Forchheim, Germany) 와 64절편 MDCT (Brilliance-64, Phillips Medical Systems, Cleaveland, OH, USA) 를이용하였다. 16절편 MDCT 는 16 0.75 mm의검출조준기, 420 ms의회전시간, 관전압 120 kvp 와평균관전류 500 mas를사용하였고, 64절편 MDCT는 64 0.625 mm의검출조준기, 400 ms의회전시간과관전압 120 kvp 와평균관전류 476 mas를사용하였다. 팬텀측정시앞서언급된자체제작팬텀을검사대위에놓고고정시킨후심장 CT 검사와동일하게촬영하였다. 환자검사는관상동맥의조영상을얻기위해서비이온성조영제 (Optiray 350, Mallin ckrodt Inc., Hazelwood, Mo, USA) 를자동주입기 (CT 9000 ADV injector, Mallinckrodt Inc., Liebel-Flarsheim Business, Cincinnati, OH; STELLANT D CT Injection systems, Medrad Inc., Indianola, PA, USA) 에주입한후 16절편 MDCT는초당 4.7 ml의 Glass bottle Stent Straw Fig. 1. Stent after ballooning. Fig. 2. Structure of stent phantom. 242 http://jsms.sch.ac.kr Soonchonhyang Medical Science 16(2):241-247
스텐트내경측정시전산화단층촬영알고리즘 김동훈외 속도로 100 ml의조영제를주입하였다. 64절편 MDCT는초당 4.5 ml의속도로 80 ml의조영제를먼저주입한후생리식염수와조영제를 1:1로혼합하여 40 ml, 총 120 ml를전완정맥 (antercubital vein) 을통하여주입하였다. 검사시작은상행동맥에관심영역을설정한후 CT 수치가 100 Hounsfield units (HU) 에도달한시간부터 6초후에주폐동맥분기부에서횡격막까지 15초정도의호흡정지시간에촬영하였다. 영상의재구성은 16절편 MDCT는 0.75 mm의절편두께와 0.5 mm 간격으로각 Kernel 값을적용하여 B10f, B20f, B30f, B40f, B50f, B60f, B70f, B80f로구분하여재구성하였고, 64절편 MDCT는 0.9 mm의절편두께와 0.45 mm 간격으로각필터값을적용하여 Cardiac sharp (CC), Cardiac detailed stent (CD), Y-sharp (YA), Y-detail (YB), Xres smooth (XCA), Xres standard (XCB), Xres sharp (XCC), Xres detailed stent (XCD) 로구분하여재구성하였다. 재구성영상은 EBW (Extended Brilliance Workspace V3.5.0.2250, Phillips Medical Systems) 에서최대강도투시영상 (maximum intensity projection) 기법을이용하여관찰하였다. 관상동맥의장축으로최대강도투시영상기법을이용하여 2 mm의절편두께와 1 mm 간격으로스텐트부위의장축에수직으로하여단면영상을얻었다. 평가방법은영상의학과전문의 1명, 방사선사 1명에의해평가하였으며, 2명이 3차례의반복측정으로오차를줄이려시도하였다. 팬텀실험에서는스텐트의내경을측정하기위해각알고리즘에따른같은위치의영상에서스텐트내경길이를측정하여평가하였고, 스텐트를삽입한환자검사에서는단축및 2방-, 4방-영상과최대투시강조영상, 3차원영상등을참고하여관상동맥내의스텐트에의한인공물이혈관내경에미치는정도가가장적은알고리즘에최고점수 8점을부여하였고, 나머지는차례로 1점단위로하위점수를부여하여알고리즘변화에따라평가하였다. 결과반복측정간에의미있는차이는없었다 (P< 0.05). 스텐트팬텀을가지고한실험에서각알고리즘값에따른평균내경이가장큰경우는 16절편 MDCT (Siemens AG, Medical Solutions) 의 B50f에서 2.35 mm, 64절편 MDCT (Phillips Medical Systems) 의 XCB (Xres standard) 에서 2.53 mm로나타났다 (Figs. 3, 4). 16 절편 MDCT 를이용한결과들에서실측 3.75 mm와는차이가큰평균 2.08 mm 를보였고, 64절편 MDCT에서는 2.36 mm를보였다. 최소치와최대치의차이는 16절편 MDCT에서 0.72 mm로 64절편 MDCT를이용한결과 0.25 mm와비교하여 3배정도의큰차이를보였다. 각각 16절편 MDCT (Siemens AG, Medical Solutions) 와 64절편 MDCT (Phillips Medical Systems) 에서의결과는 Tables 1과 2에나타냈다. 64절편 MDCT만을이용하여촬영한스텐트를삽입한 B10f B20f B30f B40f B50f B60f B70f B80f Fig. 3. Stent phantom image of 16-slice multi-detector row computed tomography. Although ring like artifacts occur around stent, relative good delineation and sharp margins of stent struts are seen in B40f, B50f, B60f, and B70f. Soonchonhyang Medical Science 16(2):241-247 http://jsms.sch.ac.kr 243
Kim DH, et al. Effect of MDCT Algorithms on Coronary Stent Xres smooth (XCA) Xres standard (XCB) Xres sharp (XCC) Xres detailed stent (XCD) Cardiac sharp (CC) Cardiac detailed stent (CD) Y-sharp (YA) Y-detail (YB) Fig. 4. Stent phantom image of 64-slice multi-detector row computed tomography (MDCT). In images of 64-slice MDCT, artifacts that shown in 16-slice MDCT (Fig. 3) are not seen. Although little blurring around stent is, we can evaluate lumen of stent, well. Table 1. Internal diameter of stent measured by various algorithms of 16-slice multi-detector row computed tomography B10f B20f B30f B40f B50f B60f B70f B80f Inside diameter (mm) 1.63 1.78 2.02 2.28 2.35 2.25 2.23 2.12 환자검사에서는 XCC 에서 7.67 점으로실재혈관내스텐트를인지 하고내부를확인하는데가장높은해상능을보이는것으로평가 되었다 (Fig. 5). XCB (7.50 점 ), XCD (7.33 점 ), XCA (7.17 점 ) 도유사한 평가를받았다. 반면, CC (5.83 점 ), CD (4.67 점 ), YA (4.33 점 ), YB (3.33 점 ) 알고리즘을사용한결과는평균 (5.98 점 ) 보다낮은점수로 스텐트평가에는어려움이있을것으로평가되었다 (Table 3). 고찰 스텐트삽입의주된원인이되는동맥경화증은동맥의내벽손 상이생겨동맥내벽에콜레스테롤의침착, 섬유세포나평활근의 증식, 석회침착등이일어나동맥벽이두터워지고단단해짐으로써 내경이좁아지는상태로인해관상동맥내혈류감소가일어나고허 혈증상을발생시킨다 [17]. 관상동맥협착증의진단에있어서는현 재까지도관상동맥조영술이표준진단법으로이용되고있으나, 최 근개발된 MDCT 가높은해상능과기능검사를병행할수있다는 장점때문에새로운비침습적영상검사로관심을모으고있으며, Table 2. Internal diameter of stent measured by various algorithms of 64-slice multi-detector row computed tomography 관상동맥우회로수술후도관의개존성평가에도이용되고있다 [18-20]. XCA XCB XCC XCD CC CD YA YB Inside diameter (mm) 2.38 2.53 2.45 2.35 2.22 2.37 2.30 2.28 XCA, Xres smooth; XCB, Xres standard; XCC, Xres sharp; XCD, Xres detailed stent; CC, Cardiac sharp; CD, Cardiac detailed stent; YA, Y-sharp; YB, Y-detail. MDCT 는기존의관상동맥조영술에비해비침습적방법으로영 상을얻는다는장점이있으며, 수초의회전시간에얇은단면의나 선형컴퓨터단층촬영관상동맥조영이가능하며, 우수한종축방 향의공간해상도를기반으로어떠한방향에서도영상의재형성이 가능한장점이있다. 또한심전도동조화기술에의해이완기와수 축기의영상이쉽게만들어질수있고, 관상동맥에대한영상을획 득하면서추가적인비용이나추가적인조영제의사용, 추가적인방 사선노출없이좌심실기능의측정이가능한장점이있다 [21-23]. 또한, 전체촬영시간이 10 여초이내로짧으며호흡곤란이나심부전 이있는환자에서도시행가능하고, 심박동기나제세동기를가지고 있는환자에서도자기공명영상과달리검사가가능하다. 관상동맥 질환을가진환자에서형태학적이상의진단뿐만아니라동시에 기능적평가가가능하다는장점도있다 [24]. 한편, MDCT 는자기 공명영상에비하여움직이는심장의정지영상을얻기위해필요한 244 http://jsms.sch.ac.kr Soonchonhyang Medical Science 16(2):241-247
스텐트내경측정시전산화단층촬영알고리즘 김동훈외 Xres smooth (XCA) Xres standard (XCB) Xres sharp (XCC) Xres detailed stent (XCD) Cardiac sharp (CC) Cardiac detailed stent (CD) Y-sharp (YA) Y-dtail (YB) Fig. 5. Stent image of 64-slice multi-detector row computed tomography. In patient with stent insertion, we can see the lumen patency in XCA, XCB, XCC, and XCD algorithms. However, CC, CD, YA, and YB algorithms represent poor image quality because of blooming artifact (metal artifact). Table 3. Average score of instent resolution visualized by various algorithms of 64-slices multi-detector row computed tomography XCA XCB XCC XCD CC CD YA YB Scale 7.17 7.50 7.67 7.33 5.83 4.67 4.33 3.33 Resolution within stent was affected by blooming artifact. XCA, Xres smooth; XCB, Xres standard; XCC, Xres sharp; XCD, Xres detailed stent; CC, Cardiac sharp; CD, Cardiac detailed stent; YA, Y-sharp; YB, Y-detail. 시간분해능이부족하여심박동수가빠른경우움직임에의한허 상이발생하는단점이있으나 [25], 적절한심박수를유지하는약물 전처치를할경우대부분문제없이검사를끝낼수있다. 또다른 제한점으로환자의검사전전처치상태와호흡상태또한환자의 심박동률과부정맥여부, 그리고검사장비의심전도동조화기능 에따라영상의질이달라질수있다. Giesler 등 [26] 은심박동수가 70 회 / 분미만인환자들은 13% 에서관상동맥영상의질저하가있 는반면 70 회 / 분이상인환자들은 33% 에서관상동맥영상의질저 하가발생된다고지적하였다. Nieman 등 [27] 은낮은심박동수에서 는관상동맥협착진단의민감도가 82% 인반면 80 회이상인환자 에서는단지 32% 의민감도를보인다고보고하였다. 그리고심박동 률이분당 74 회이하일때가장좋은영상을만들수있다고하였으 며, 심장영상의가장적절한재구성창은보통심박동률이 70 회이 하일때심장의확장기중간과후반부에서가장좋은영상을나타 내며, 심박동률이 70 회이상일때는심장주기의수축기후반부와 확장기전반부에서좋은영상을만들수있다 [26]. 본연구에서환자들의평균심박동수는 65±7회 / 분으로심박동수에의한영상질영향이적을것으로판단된다. 영상을관찰하기위하여사용한창구성 (window setting) 값은넓이 900 HU (±100 HU), 중앙값은 400 HU (±100 HU) 로평가하였고, 창구성값에따라스텐트의내경의크기가달라짐을확인하였다. 즉, 넓이가좁고중앙값이높으면스텐트표면에서일어나는번짐현상이감소하여스텐트내경은증가하는것처럼나타났다. 이번연구에서의제한점으로는관측자의측정과정에서오차가발생할수있다. 또다른제한점으로팬텀검사에서각알고리즘에따라스텐트내경을측정한결과치가실측스텐트내경크기인 3.75 mm에미치지못하는문제가있었다. 이는스텐트벽에서발생하는선경화허상 (beam hardening artifact) 으로내경에저음영의번짐현상이원인으로보이며영상대조도에영향을주는각알고리즘에따라조금씩차이가발생한것으로보인다. 본연구에서팬텀검사에의한결과값은스텐트내경측정과알고리즘의관계를알아보고자한연구이며측정치의정확도를평가하기위한것은아니므로추후추가연구가필요할것으로판단된다. 16절편 MDCT에서는 B50f에서가장가까운수치를나타냈고, 64절편 MDCT에서는 XCB 알고리즘에서가장가까운수치를기록하였다. 알고리즘값이대조도를높이는경계가분명한알고리즘값으로가까워질수록인공물에의해스텐트내경의크기가감소함을알수있었다. 또 Soonchonhyang Medical Science 16(2):241-247 http://jsms.sch.ac.kr 245
Kim DH, et al. Effect of MDCT Algorithms on Coronary Stent 한너무대조도가낮고경계가불분명해질수있는 B20f, B30f 나 XCA 등도명확한직경측정이어려워스텐트를관찰하는데는유 용하지않을것으로보인다. 따라서스텐트의변형및골절의여부 를보기위해서중간정도의대조도를보이고비교적경계가분명 해보이는알고리즘을사용하는것이좋은데, 16 절편 MDCT 에서 는 B40f, B50f 와 64 절편 MDCT 에서는 XCB, XCC 의알고리즘이 유용할것으로생각한다. 64 절편 MDCT 로측정한환자검사에서 는대조도가비교적큰알고리즘 XCC 에서영상질측정에서높은 점수 (7.67 점 ) 가나왔고, XCB, XCD, XCA 순으로약간의차이는있 었으나, 혈관내경의협착정도를관찰하는데는큰차이가없는것 으로나타났다. 이는팬텀검사에서와유사한결과이다. 관상동맥 에서번짐현상에의한스텐트내경의변화를알고리즘값에따라 측정하였을때 16 절편 MDCT 에서는 B40f 와 B50f, 그리고 64 절편 MDCT 에서는 XCB 와 XCC 에서스텐트실측크기에가까운값을 얻을수있었다. 결론적으로스텐트내경의협착정도를평가하기위해서는 16 절 편 MDCT 에서는 B40f, B50f, 그리고 64 절편 MDCT 에서는 XCB, XCC 알고리즘을사용하는것이효과적일것이다. 최근국내에도 입된 128 절편, 256 절편, 320 절편 MDCT 를이용한연구결과가기 대되는이때 64 절편 MDCT 를이용한각알고리즘의스텐트내경 측정에미치는영향에대한본연구는스텐트삽입후재협착이나 스텐트골절등의합병증진단과추적관찰을위한기초자료로활 용될수있고새로운장비를이용한앞으로의연구에참고연구로 기여하는바가클것으로기대된다. REFERENCES 1. Al Suwaidi J, Berger PB. Do stents reduce mortality compared with balloon angioplasty? A critical review of all the evidence. Am Heart J 2005; 150:7-10. 2. 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