UltraLIGHT: New Frontiers of Medical Imaging?

68 the OCT technology is limited to approximately 2 millimeters. However, the thickness of the epithelial layer lining much of the body surface and cavities is within the reach of the UltraLIGHT imaging depth.11 Similarly, the endothelial layer of major blood vessels can also be a target.10 Therefore, UltraLIGHT can be used in dermatological, endoscopic and intravascular applications. In addition, UltraLIGHT can also be designed to operate in Doppler mode1-6 and image blood flow as slow as 0.2 millimeters per second (Figure 3) and blood vessels less than 20 micrometers in diameter, thereby approaching the flow speed and geometry of capillary vessels.7 Introduction The UltraLIGHT imaging system (see Figure 1) presently being developed at the Ontario Cancer Institute (OCI)/Princess Margaret Hospital (PMH) and Photonics Research Ontario (PRO) is based on the concept of optical coherence tomography (OCT).1-5 The name UltraLIGHT comes from ultrasound, a mature medical imaging modality. Analogous to ultrasound imaging in which a sound wave is transmitted through soft tissue and the image is formed by observing the reflected sound wave, the UltraLIGHT imaging system transmits light waves through biological tissues and the reflection forms the image (see Figure 2). Because the wavelength of light (0.8~1.3 um) is much shorter than that of sound (50~150 um), the imaging resolution of UltraLIGHT is superior to ultrasound. Conversely, since light waves cannot penetrate biological tissue as well as ultrasound, the imaging depth of all imaging systems based on UltraLIGHT: New Frontiers of Medical Imaging?