REVIEW ARTICLE J Surg Ultrasound 2017;4:12-17 JSU Journal of Surgical Ultrasound 자동유방초음파의임상적의의 전북대학교의과대학외과학교실유방ㆍ갑상선외과 강상율, 이승주, 윤현조, 정성후 Clinical Significance of Automated Breast Ultrasound Sang Yull Kang, Seung Ju Lee, Hyun Jo Youn, Sung Hoo Jung Division of Breast ㆍ Thyroid Surgery, Department of Surgery, Chonbuk National University Medical School, Jeonju, Korea Received April 17, 2017 Revised May 3, 2017 Accepted May 7, 2017 Correspondence to: Hyun Jo Youn Division of Breast ㆍ Thyroid Surgery, Department of Surgery, Chonbuk National University Medical School, Jeonju 54907, Korea Tel: +82-63-250-2389 Fax: +82-63-271-6197 E-mail: yhj0903@jbnu.ac.kr Breast ultrasound is a well-established diagnostic tool that is coupled with mammography for evaluation of breast abnormalities. This technique is widely available, painless, well-tolerated and does not involve ionizing radiation. However, it has several faults. Because of its dependence on operator techniques for hand-held ultrasound (HHUS), the skill and knowledge of the operator influence the diagnostic accuracy, while poor standardization and reproducibility reduce the diagnostic yield. To overcome these problems, state-of-the-art equipment such as an automated breast ultrasound (ABUS) has been introduced. Automated breast ultrasound acquires a series of consecutive B-mode pictures and reconstructs three-dimensional datasets of the entire breast volume. These data can then be sent to a separate workstation for analysis by a radiologist. Automated breast ultrasound can produce objective and responsible images and is expected to minimize operator dependency. Several studies have demonstrated the feasibility of ABUS and shown equal performance when comparing ABUS with HHUS. Moreover, some physicians suggested that it could be used not only for follow-up of benign lesions, but also for screening of breast cancer. However, ABUS also possesses certain limitations, including difficulty in clearly visualizing tissue in the axilla and behind the nipple, corrugation artifacts, and absence of flow information. Based on these limitations, other physicians have claimed that ABUS cannot currently displace HHUS and still requires further evaluation. Here, we review previous studies of ABUS and discuss its clinical significance as it relates to breast lesions. Keywords: Automated, Hand, Breast, Ultrasonography 서론 유방암은전세계적으로여성에서가장흔한빈도로발생하는암으로치료기술의발전에도불구하고사망률은감소하지않고있다.(1) 그러나국내에서는최근유방암에대한관심증가와초음파를포함한영상기기의발전으로조기에유방암을발견하여치료하는경우가늘어나면서 생존율도증가하는추세이다.(2) 이와같이조기에유방암을발견하는것은유방암으로인한사망률을줄일뿐만아니라수술후항암화학요법등의보조요법 (adjuvant therapy) 을축소할수있기때문에매우중요하며, 따라서유방암의조기발견을위해적절한영상의학검사를시행하는것이필수적이다.(3) 유방촬영술 (mammography) 은오랜동안유방암의기 Journal of Surgical Ultrasound is an Open Access Journal. All articles are distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright c 2017 by The Korean Surgical Ultrasound Society ISSN 2288-9140
Sang Yull Kang, et al.: Clinical Significance of Automated Breast Ultrasound 초검사로여겨졌으며선별검사 (screening test) 로써유일하게사망률을낮출수있는검사로알려져있다.(4) 그러나치밀유방 (dense breast) 에서의낮은민감도 (sensitivity), 높은위양성률 (false positive rate) 로인한불필요한조직검사와환자의불안유발, 방사선노출및검사시심한통증등의제한점으로선별검사시행을감소시킬수있는단점이있다.(5,6) 이러한유방촬영술의단점을보완하기위해유방초음파 (ultrasound) 를추가로시행하며, 유방촬영술과유방초음파를함께사용하는경우유방암을포함한유방병변 (lesion) 의발견을유의하게증가시킬수있다.(7,8) 하지만전통적인수동유방초음파검사 (hand-held ultrasound; HHUS) 의경우높은검사자 (operator) 의존도, 낮은재현성 (reproducibility), 표준화 (standardization) 의부재, 긴검사시간등의단점이존재해새로운초음파양식들의개발이요구된다.(4) 최근소개되고있는자동유방초음파 (Automated Breast Ultrasound; ABUS) 는영상의학과전문의가아닌방사선사 (radiographer) 가촬영할수있기때문에상대적으로덜숙련된인력으로표준화되고일관성있는영상을얻을수있는장점이있어 HHUS의단점을보완할수있는새로운기술로각광받고있다.(9-11) 이에저자들은문헌고찰을통해유방암을포함한유방병변의진단에있어 ABUS 의유용성을알아봄으로써실제임상적용에도움이되고자한다. 본론 1. ABUS의소개 1980 년 Maturo 등 (12) 에의해 ABUS 가처음소개된이후초창기에는주로실험적인접근방법으로연구가이루어졌다. 그후 ABUS에관한많은임상결과가발표되었고그유용성이입증되면서현재는전세계적으로세종류의기기가널리사용되고있다. 2008년 SonoCiné 가유방촬영술의보조적인사용적응증으로미국식약청 (U.S. Food and Drug Administration; FDA) 의허가를처음받았고, 이후 Siemens Healthcare 사의 Automated Breast Volume Scanner (ABVS) 가유방의 3차원입체영상을얻는시스템을구축하였다. 가장최근인 2012년에 FDA 승인을받은 U-System의 somo.v 는 ABVS 와마찬가지로 3 차원영상을제공하며치밀유방을가진무증상여성의유방암선별검사를위한기기로공식인정을받았다.(13) 본연구는이중에서현재까지가장많은임상연구가발표된 ABVS 를대상으로살펴보고자한다. 1) ABUS 의구성지금까지 ABUS에관하여발표된많은연구들은 Siemens Healthcare사의 ACUSON S200 (Siemens Medical Solution, Mountain View, CA) 을사용하였다. 이시스템은주파수 5-14 MHz, 길이 15.4 cm의탐촉자 (probe) 로 6 cm 깊이, 16.8 cm 범위영역을자동으로스캔 (scan) 하여 0.5 mm 두께의고해상도영상을만들어낸다 (Fig. 1). 최적화된영상을얻기위해 tissue harmonic imaging, advanced SieClear TM spatial compounding, dynamic tissue contrast enhancement, inferior-nipple image correction 그리고 3D image brightness auto-correction 과같은다양한기술을이용한다. 얻어진영상들은 ABUS에서작업단말기 (workstation) 로자동으로전송된후전체유방을볼수있도록 3차원영상으로변환되어다면재구성 (multiplanar reconstruction) 방식으로보여진다 (Fig. 2). 2) ABUS 의검사방법환자는편안히누운 (supine) 자세에서양손을머리위로올린상태로압박판으로유방을압박하여고정한후넓은탐촉자가압박판위를가로지르며자동으로영상을획득한다. 일반적으로양측유방의횡단면 (transverse plane), 종단면 (longitudinal plane), 관상면 (coronal plane) 의세영상을기본으로얻는다 (Fig. 3). 환자의유방크기에따라검사자는적절한스캔수를결정하며검사하는동안환자가숨을참을필요는없다. 실시간으로다면재구성을이용한 3차원적영상구성이가능하며, 한쪽유방을검사하는데약 3-5분, 한명의환자를검사하는데약 10-15 분의시간이소요된다. 3) ABUS 의장점 ABUS 는 HHUS 에비해검사자오류가적은자동화되고표준화된영상을제공하며지연판독 (delayed interpretation) 이가능하고재구성된이미지의보존과전달이용이해원격협진 (remote consultation) 이가능한장점이있다.(14,15) 또한 ABUS 는재현성이높으며전체유방을포함하는넓은영역의영상을보여주기때문에병변을간과할가능성이적다.(16) ABUS의관상면영상에서는 13
J Surg Ultrasound Vol. 4, No. 1, 2017 Fig. 1. Installation of the ACUSON S2000 automated breast volume scanner (ABVS). (A) The overview of ABVS system. (B) The transducer that has been designed for the ABVS. Fig. 2. Multiplanar reconstruction of the volume data displayed on the automated breast volume scanner. Fig. 3. Three standard images using automated breast volume scanner. Cononal view (left), longitudinal (right, upper) and transverse views (right, lower) are synchronously visualized on the screen. 악성 병변을 감별하는데 중요한 뒷당김 현상(retraction phenomenon) 을 좀 더 명확히 관찰할 수 있는 장점이 있 할 수 있으며 유관을 따라 스캔할 수 없다는 단점이 있다. 으며(Fig. 4), 피부부터 흉벽까지 해부학적 구조를 연속적 또한 혈류(blood flow) 정보를 얻을 수 없어 악성 병변을 이고 체계적으로 볼 수 있기 때문에 유방 수술 시 효과적인 감별하기 위해 Color Doppler flow imaging (CDFI) 또는 정보를 제공해 준다.(17) Pulsed Doppler Unit (PDU)와 같은 추가 영상을 필요로 4) ABUS의 단점 한다.(18) 검사자에 의한 실시간 판독이 아닌 지연 판독을 유두 아래와 겨드랑이 병변의 명확한 관찰이 어려우며 시행하기 때문에 검사 시 문진을 통한 특정 부위의 자세한 환자가 너무 마르거나 팔을 위로 충분히 올리지 못하는 경 검사를 추가로 시행할 수 없고 의심되는 병변이 검사 이후 우 전체 유방을 완벽하게 촬영하기가 어렵다.(14) 환자의 에 발견될 경우 2차(second-look) 초음파를 요하는 빈도 호흡으로 인한 주름 결함(corrugation artifact) 이 발생 가 높다. 14
Sang Yull Kang, et al.: Clinical Significance of Automated Breast Ultrasound Fig. 4. Retraction phenomenon in standard automated breast volume scanning images. Three standard view of a right breast with an invasive ductal carcinoma lesion. Glandular tissue surrounding the lesion shows loss of its normal distribution pattern. This phenomenon (red arrow) is easier to visualize in the coronal as opposed to other planes. 성모두에서발견될수있는데특히악성석회화의경우크기가작은미세석회화가많아초음파상에서후방음향감소 (posterior acoustic shadow) 를관찰하기어려워유방촬영술에비해큰제약점으로인식되어왔다.(22) 그러나최근에는해상도가좋은초음파기기의도입과배경음영에의한발견의존도가줄어들어유방초음파의석회화병변발견정확도가증가하고있는데,(23) ABUS 는 HHUS 에비해횡단면, 종단면, 관상면뿐만아니라다양한각도의영상을선택적으로볼수있어서석회와의위치와수그리고모양을좀더정확하게알수있어유방의석회화병변을진단하는데매우유용한것으로알려져있다.(24,25) 요약하면 ABUS는병변의경계를좀더잘볼수있는관상면영상을추가로얻을수있고각각의구획단면 (sectional plane) 을관찰할수있기때문에 HHUS 에비해좀더높은정확도를보일수있다.(16,18) 2. ABUS와 HHUS의비교앞서기술한바와같이 ABUS는여러장점과단점들을가지고있기에지금까지기존의 HHUS 를대체할수있는새로운기기인지에관한많은논란이있어왔다. ABUS와 HHUS의정확도를비교한초창기예비조사 (pilot study) 의연구결과를살펴보면 Wojcinski 등 (19) 은 ABUS의 100% 민감도와 52.8% 의특이도, 66.0% 의정확도로 HHUS 와동등한유용성을보고하였고, Kim 등 (9) 은두검사방법사이에 Breast Imaging Reporting and Data System (BI-RADS) 범주 (category) 2와 3에서는 66.2%, 범주 4와 5에서는 100% 의일치율을보여 ABUS 가향후유방병변을진단하는데유용한방법이될수있을것으로예상하였다. 이후 ABUS의병변발견율과진단정확도가 HHUS 와유사하거나오히려높다는연구결과가많이보고되었는데 Lin 등 (20) 은 ABUS의진단정확도로 100% 의민감도와 95.0% 의특이도를보고하였고, 5566 명의대규모환자를대상으로한 Choi 등 (21) 의보고에따르면유방암의진단정확도 (97.7% vs. 96.5%) 와특이도 (97.8% vs. 96.7%) 에서모두 ABUS가 HHUS에비해우월한결과를보였고재검률 (recall rate) 도 ABUS (2.57/1,000예) 가 HHUS (3.57/1,000예) 에비해통계적으로낮은결과를보였다. 유방에형성되는석회화를동반하는병변은양성및악 3. 판독자간의일치율 ABUS는검사자의존도를최소화할수있는장점이있지만이는병변의위치와크기그리고특징을판독자들이얼마나일관성있게판독할수있느냐는또다른중요한문제점을낳았다. ABUS와 HHUS 의판독자간의일치율 (interobserver agreement) 을비교한많은연구에서 ABUS가 HHUS 에비해병변의모양, 경계, 에코발생 (echogenicity), 후방음향과 BI-RADS 최종평가등의모든항목에서동등하거나우월한일치율을보고하였다.(26-28) 특히, Shin 등 (11) 은 ABUS 영상을다섯명의판독자가분석하였을때병변의발견율, 특징및병변의위치, 크기등을보고하는데있어판독자간의일치율이높다고보고하였다. 이러한결과는 ABUS가다양한각도의삼차원적영상을표준화된다중절편영상 (multislice imaging) 으로얻을수있고 뒷당김현상 을포함한구조적왜곡 (architectural distortion) 을좀더잘관찰할수있는장점이있기때문이다. 그러나이와달리병변의모양과경계측면에서 ABUS의판독자간일치율이낮다는보고도있었다.(29) 최근에판독자간의일치율과관련된체계적고찰 (systemic review) 을시행한 Meng 등 (30) 에따르면 ABUS 는양성과악성유방병변을감별하는민감도 (92.0%) 와특이도 (84.9%) 는높지만판독자간의신뢰도 (reliability) 는각검사마다매우이 15
J Surg Ultrasound Vol. 4, No. 1, 2017 질적 (heterogeneous) 이라고보고해 ABUS 의판독자간의일치율에관해서는잘고안된좀더많은전향적연구가필요할것으로생각한다. 4. 유방암선별검사로서 ABUS의유용성우리나라를포함한여러나라에서유방암의선별검사방법으로 40세이상의여성에서 1-2년간격의유방촬영술을권고하고있다.(31) 유방촬영술은유방암의사망률을낮추는유일한선별검사방법으로알려져있지만유방암발생위험도가높고젊은여성에서많이관찰되는치밀유방에서는정확도가떨어지는단점이있다.(4,5) 이러한제한점은외국에비해젊은여성에서의유방암발생률이높은우리나라에서더욱중요한문제이다.(32) 유방초음파는유방병변의진단정확도를높이기위한유방촬영술의보완적인영상검사로여겨져왔으며아직논란은있지만최근에는특히치밀유방에서유방암선별검사로서의유용성에관하여많이보고되고있다.(7,33) ABUS가 HHUS와비교해동등한진단정확도를보인다는연구결과들이보고된이후양성병변들의추적관찰뿐만아니라유방암의선별검사로서 ABUS의유용성을알아보려는연구가많이이루어졌다. Zang 등 (15) 은 ABUS가 HHUS 에비해검사자의존도가낮고검사시간이짧아선별검사로서유리하다고하였고, Kelly 등 (34) 은특히치밀유방을가진여성에서유방암의선별검사로유방촬영술에 ABUS를추가하면정확도를높이고재검률을낮출수있다고보고하였다. ABUS 는특히유방촬영술의민감도가떨어지는치밀유방조직을갖는여성에서유방암선별검사로서유방촬영술과함께시행한다면기존의 HHUS 보다더욱정확한결과를보일것으로예상된다. 5. ABUS의미래지금까지 ABUS의정확성및유용성에관한많은보고에도불구하고기존의 HHUS를대체할수있는방법으로 ABUS를권고하고있지는않다.(14) 즉, HHUS를대신해 ABUS를사용함으로써유방암의발견율을높이거나불필요한조직검사를줄일수있다는명확한연구결과는아직보고되지않았다. 그러나앞으로영상기술이더욱발전하고명확한진단기준이표준화된다면 ABUS의유용성은훨씬향상될것으로예상된다. 향후대규모의다기관, 전 향적연구를통한타당성검토가이루어진다면 ABUS의적절한임상적응증을확립할수있을것이다. 결 론 ABUS는일관성있고재현성이우수하며검사자의존도가낮은고화질의 3차원영상을제공한다. 판독자간의높은일치율이입증된다면 ABUS는유방암을포함한유방병변의정확한관찰을위한기존의유방촬영술과 HHUS 의효과적인보조기기가될수있다. ABUS가기존의 HHUS 를대체할수있는지에대해서는향후좀더많은연구가필요할것으로생각한다. REFERENCES 1. Youlden DR, Cramb SM, Dunn NA, Muller JM, Pyke CM, Baade PD. The descriptive epidemiology of female breast cancer: an international comparison of screening, incidence, survival and mortality. Cancer Epidemiol 2012;36:237-48. 2. Park EH, Min SY, Kim Z, Yoon CS, Jung KW, Nam SJ, et al. Basic facts of breast cancer in korea in 2014: the 10-year overall survival progress. J Breast Cancer 2017;20:1-11. 3. Chow LW, Yip AY, Ng EL. Prevention of oncological diseases: primary and secondary prevention. Int J Biol Markers 2012;27:e337-43. 4. Drukteinis JS, Mooney BP, Flowers CI, Gatenby RA. Beyond mammography: new frontiers in breast cancer screening. Am J Med 2013;126:472-9. 5. Kolb TM, Lichy J, Newhouse JH. Comparison of the performance of screening mammography, physical examination, and breast US and evaluation of factors that influence them: an analysis of 27,825 patient evaluations. Radiology 2002;225:165-75. 6. Feig SA. Adverse effects of screening mammography. Radiol Clin North Am 2004;42:807-19, v. 7. Berg WA, Blume JD, Cormack JB, Mendelson EB, Lehrer D, Böhm-Vélez M, et al. Combined screening with ultrasound and mammography vs mammography alone in women at elevated risk of breast cancer. JAMA 2008;299:2151-63. 8. Flobbe K, Bosch AM, Kessels AG, Beets GL, Nelemans PJ, von Meyenfeldt MF, et al. The additional diagnostic value of ultrasonography in the diagnosis of breast cancer. Arch Intern Med 2003;163:1194-9. 9. Kim YW, Kim SK, Youn HJ, Choi EJ, Jung SH. The clinical utility of automated breast volume scanner: a pilot study of 139 cases. J Breast Cancer 2013; 16:329-34. 16
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