Based on technology from telecommunications, optical coherence tomography (OCT) systems have been modified to accommodate many medical specialties, ranging from ophthalmology and cardiology to orthopedics. The first two applications are FDA approved and are routinely used in patients. Since 1994 our lab has been developing OCT for nontransparent tissue, from engineering and physics to clinical trials.
Analogous to ultrasound, OCT is an imaging modality that utilizes infrared light rather than sound. As infrared light is generated, it is split into both a sample and reference arm. Light reflecting back from the sample combines with light from the precisely controlled reference arm mirror. The intensity of interference is measured using a technique called low-coherence interferometry, with this intensity plotted as a function of tissue depth as the reference arm mirror is moved. As the beam is scanned across the surface of the tissue, two and three dimensional data sets are derived [14
]. These image sets can then be used to interpret the microstructure of the tissue.
Current clinical imaging modalities such as MRI, CT, and X-ray are critical to the diagnosis of disease. However, early disease diagnosis requires micron-scale, real-time imaging. OCT has shown many advantages over current imaging modalities such as a resolution 25x higher than any clinical subsurface imaging modality, a data acquisition speed of 120 high-resolution images per second, and the ability to perform imaging through a 0.017-inch fiber-optic endocatheter with automated probe pull-back [15
]. These characteristics make OCT an ideal system for the clinical setting in terms of speed and volumes of information gathered on both target and auxiliary structures. Additionally, the OCT engine is comparative in size to a portable ultrasound machine, which allows easy transport into procedure rooms (). These advantages make OCT an ideal tool for both the clinical and research settings.
Image (a), schematics (b), and catheter (c) of LightLab OCT imaging engine. Courtesy of LightLab imaging.
Finally, OCT can be combined with many adjuvant techniques: Doppler OCT, OCT elastography, OCT spectroscopy, second-order correlation (SOC) OCT, and polarization-sensitive OCT (PS-OCT). These adjuvant technologies are described in further detail in the appendix. For the purposes of this paper, we will examine the ability of OCT, focusing primarily on structural OCT and PS-OCT, to identify and track early disease progression and its potential for the early diagnosis of OA, RA, and RCR.