At a very basic level, Optical Coherence Tomography can be considered similar to ultrasound except that OCT uses infrared light instead of sound waves [6, 10]. The backscatter of light reflected by the tissue is detected and filtered such that only coherent waves are processed by the OCT system producing an ultra kinase inhibitor Y-27632 high-resolution (4�C20��m) digital image on a computer screen (Figure 1) [5, 6, 10, 18�C20]. In early OCT systems, the measurement of time-of-flight by the optical signal allows for production of a two-dimensional image and detection of spatial relationships between adjacent structures [10]. This OCT technology is referred to as time-domain OCT because the image production and resolution is based on a function of distance traveled over time by the infrared light signal.

In contrast, spectral-domain OCT detect differences in tissue composition based on changes in the frequency of backscattered light allowing for more efficient data acquisition and faster scan speeds producing near-real-time images [16, 21, 22]. In addition, polarization-sensitive OCT (PS-OCT) is another OCT technology that differs again by containing the ability to detect changes in the polarization state of the backscattered light permitting quantification of tissue birefringence. Figure 1 Cartilage OCT form birefringence. (a) OCT image of cartilage with OCT form birefringence where distinct dark bands create a multilayered appearance. (b) OCT image of cartilage without OCT birefringence. In cartilage graded to be without OCT form birefringence, … 4.

Optical Coherence Tomography of Articular Cartilage Articular cartilage exhibits natural birefringence that is detectable by light microscopy due to the organization of its collagen fibrils [21]. Herrmann et al. showed that normal cartilage is sensitive to the polarization state of the incident light of OCT and that the cartilage birefringence could be evaluated using polarization sensitive OCT [9]. Early in the progression of osteoarthritis, collagen fibrils of articular cartilage become disorganized. Drexler et al. examined the relationship between the polarization sensitivity of cartilage as detected by OCT and the changes seen in collagen organization as determined by polarized microscopy of human osteochondral explants [23].

They determined that collagen disorganization found in arthritic articular cartilage as detected by polarized microscopy is detectable by PS-OCT as a loss of normal form birefringence [23]. Using a polarized fiberoptic OCT system, Chu et al. evaluated healthy and degenerating cartilage in grossly normal appearing human articular cartilage and showed high intraobserver and interobserver reproducibility in detecting Drug_discovery the presence or absence of a discernible banding pattern described as cartilage OCT form birefringence [5]. Bear et al. showed that the degree of OCT form birefringence correlated with polarized microscopy [24].