Optical coherence tomography(OCT)란?

[neonidas]

* OCT란 무엇인가?

Optical Coherence Tomography (OCT)는 인간 신체내에 있는 세포나 신경에 어떠한 문제가 발생하기 전에 미리 그것들에 대한 영상찍어 진단에 활용할 수 있도록 한 기기입니다.

만약 이 기기가 완전하게 활용이 된다면 질병의 진단과 병의 치료를 위해 밤낮주야로 노력하고 있는 의학자들, 연구자들, 과학자들에게 좀 더 깊이 있게 인간 신체에 대한 이해를 높이는데 커다란 기여를 할 수 있을 것 입니다. 

조금더 덧붙여 설명을 드리면 이 OCT는 초음파의 원리와 임상의들에게 친숙한 현미경 영상기술을 복합활용합니다.

초음파가 "Echoles"라는 후방 산란된 음파로 부터 이미지를 획득하는 기기라면, OCT는 생물학적 세포내의 미세구조에서 반사되어져 나오는 적외선(infrared)을 이용하여 이미지를 획득하는 기기입니다.

이 적외선 같은 경우 주파수(frequency)와 대역폭(bandwidth)에 있어서 초음파보다 훨씬 높은 값을 가지기 때문에 초음파 영상보다는 높은 해상도(resolution)의 이미지를 얻을 수 있습니다.

 적외선은 0.006인치 지름의 광섬유를 통해서 영상을 전달합니다. 이미지를 전달해주는 guidewire에는 다양한 이미지를 정확히 전달할 수 있는 렌즈들로 구성이 되어 있습니다. 이런 OCT는 biopsy가 안되는 부분에 대한 이미지를 편리하게 실시간으로 볼 수 있게 해줍니다.

Infrared light is delivered to the imaging site through a single optical fiber only .006" diameter (about the size of the period in this sentence). The imaging guidewire contains a complete lens assembly to perform a variety of imaging functions. The guidewire can be deployed independently or integrated into existing therapeutic or imaging catheters.

OCT imaging can be performed over approximately the same distance of a biopsy at high resolution and in real time making the most attractive applications for OCT those where conventional biopsies cannot be performed or are ineffective. (Huang, Science 254:1178, 1991)

초음파 같은 경우 음파의 속도로 전달이 되는 초음파 echo를 기존의 표준 전자적 기술로 처리할 수 있지만, OCT에 사용되는 적외석으로부터 신호를 추출하려면 간섭 기술이 필요합니다. 간섭계(interferometer)에 의해 측정된 신호는 축정 세포에 대한 높은 해상도와 3차원 영상의 실시간 구연을 위해 컴퓨터에서 다시 계산이 됩니다. 이렇게 함으로 해서 세포의 적출(excision)이나 견본(specimen)의 추출 없이 세포의 영상을 얻을 수 있습니다.

In addition to providing high-level resolutions for the eval‎uation of microanatomic structures OCT is inherently able to provide information regarding tissue composition. Using spectroscopy, users can eval‎uate the spectral absorption characteristics of tissue while simultaneously determining the orderliness of the tissue through the use of polarization imaging.

Avantages of OCT

HIGH RESOLUTION:
Current OCT systems have resolutions at 4-20 um compared to 110 um for high frequency ultrasound.

TISSUE CHARACTERIZATION:
Using information inherent to the returning photon signals, OCT can perform both spectroscopic and polarization imaging to better eval‎uate the composition of tissues and lesions.

SMALL SIZE:
The fiber-based design allows easy integration with small catheter/endoscopes.

REAL TIME IMAGING:
Imaging is at or near real time.

DOPPLER IMAGING:
Capable of simultaneous imaging and real time flow measurements.

LIGHTLAB DESIGN ADVANTAGES:
PC Based, Digital system architecture enables a compact, portable easily upgraded system.

Why Use OCT?

For more than three centuries, the microscope has been considered the ultimate tool to understand the origins of disease by examining tissue and microstructures in exquisite detail. While the technology contained within the microscope has evolved over time, enabling better resolution of smaller structures, one aspect has remained constant - material to be examined must be excised from the body and brought to the microscope.

New thinking concerning the origins of the world's two largest killers -- heart disease and cancer - expose the limitations of the current paradigm. Both diseases are thought to originate at the cellular level in the thin (20 - 200 micron) cellular layer covering the inner and outer surfaces of the body. Understanding these diseases on the microscopic level on an in vivo basis could lead to better diagnosis, earlier more precise treatments and development of novel therapies to help eradicate these diseases

For years, scientists, physicians and technology developers have struggled to achieve microscopic images from within the body. These attempts have met with limited success due to two primary factors: the size of the apparatus being deployed and the resolution of the images being obtained. Attempts to obtain microscopic images using external methodologies: magnetic resonance, X-ray, ultrasound, and nuclear imaging, have met with similar fates.

A New Weapon for Heart Disease and Cancer

While OCT has the potential to be used for a variety of medical applications, cancer and heart disease represent two of the most pressing, and promising application areas.

• Cardiovascular Imaging
  OCT imaging has the potential to improve current cardiovascular therapies such as stenting and balloon angioplasty, by providing vascular images in real time to guide stent placement and balloon inflation. Given its small size, the OCT imaging guidewire could be integrated into an existing therapeutic catheter or deployed alongside during a procedure.

  New cardiac research indicates that unstable plaques - arterial lesions that do not constrict the blood vessel but rather burst releasing a bolus of lipids into the blood stream - may be responsible for up to 70 percent of all heart attacks. OCT has the potential to clearly identify plaques and help differentiate unstable plaques from stable plaques.

  In addition to providing exquisite morphological detail, LightLab is incorporating other capabilities of OCT such as spectroscopic imaging, polarization imaging and Doppler to provide further information regarding tissue composition and flow.
   

• Cancer Detection

  It is estimated that more than 85 percent of all cancers originate in the epithelium, the thin (20-200 micron) cellular layer covering the inner and outer surfaces of the body. Excisional biopsy, removing tissue from the body and examining it under a microscope, is the gold standard for cancer diagnosis. However, many biopsies are done on a hit or miss basis, small pieces of tissue are excised at random and dissected to check for cancerous cells.

OCT has the potential to greatly improve conventional biopsy by more precisely identifying the areas to be excised based on images of the epithelial layers, reducing the number of biopsies and making earlier and more accurate diagnosis possible. As the technology matures, it may be possible to perform biopsies using OCT imaging alone, making possible point of care biopsy.

LightLab Licensing Agreements Expand Clinical Applications

OCT imaging was invented by Professor James Fujimoto, Eric Swanson and their colleagues at MIT. The first medical application resulting from this work, ophthalmology, is licensed to Humphrey Instruments, which is a subsidiary of Carl Zeiss, Inc. The product, introduced to the market in 1996, is currently used to diagnose macular degeneration, an incurable eye disease that is the leading cause of blindness for those aged 55 and older in the United States. Macular degeneration affects more than 10 million Americans.

In 2000, Asahi Optical Company, Ltd. and LightLab Imaging announced a product development alliance with the goal of providing gastroenterologists a new class of high-resolution endoscopic imaging technology utilizing OCT. Under the terms of the agreement, the Pentax Medical Instrument Division of Asahi Optical Company gained access to LightLab Imaging's intellectual property and proprietary optical probe technology for endoscopic Optical Coherence Tomography. The two companies are co-developing intraluminal OCT systems for gastrointestinal and pulmonary applications.

In 2001, LightLab Imaging and Lantis Laser, Inc., announced a licensing agreement related to the use of Optical Coherence Tomography in the field of dentistry. Under the terms of the agreement, Lantis Laser gained license to LightLab Imaging's intellectual property portfolio related to OCT in the field of dentistry. Lantis believes that OCT will provide dentists with an unprecedented level of image resolution to assist in the eval‎uation of periodontal disease, dental restorations and in the detection of caries

Comparison between OCT (left) and Ultrasound (right). Tearney, G.J., et. al. Circ. 4256, 1997

망막(Retina)의 구조적인 변화를 실시간으로 관찰할 수 있는 기기로 제조사에서는 다음과 같이 소개하고 있습니다.

STRATUSOCT™
			Humphrey'의 Optical Coherence Tomography Scanner는 이전에는 가능치 않았던 안구 진단 정보를 제공합니다. 검사 자로 하여금 더욱 특수한 진단 및 치료, vitreoretinal diseases와 glaucoma에 대한 망막구조하의 정량적이고 세밀한 관리를 가능하게 합니다.이 장비는 cross-sectional한 망막 이미지를 획득하기위해 비접촉, 비침습적인 방법을 사용해서 망막의 단층 영상을 실시간으로 제공합니다. Cross-sectional scan of living tissue 다른 방법으로는 직접 관찰할 수 없는 구조를잘 보여줌 Multiple Document Screen side-by-side comparisons of scans, red-free fundus images와 numerical data를 허용 Removable optical mass storage seamless retrieval‎와 correlation analysis Enhanced image management 고해상도 칼라 프린트와 인터넷기반의 telemedicine Automated nerve fiber layer/retinal thickness 질병의 치료와 관리를 위한 정확한 모니터링 No injections of exposure to painful high-intensity light 환자의 안전 보장과 감소된 phototopia Imaging of ocular tissue at micron-resolution 뛰어난 Ultrasound B-scan으로 10배이상의 세부적인 이미지를 제공 Reveals tissue detail previously unavailable and undetectable 손상부분을 일찍 발견하여 쉽게 치료 PC-based computer interface patient throughput와 data archiving가 용이 Three-point reference system 반복 스캔을 위한 망막의 표면 기록과 맵핑 Non-contact, non-invasive scan obtained in one second 환자의 불편함을 최소화시키면서 살아있는 조직을 보여줌