Optical Imaging Visible light penetrates into biological tissues more than one might think. Red and near infrared light penetrates deeper than green, blue or violet light. You can visualize this phenomenon by shining a flashlight through your hand, observing a red glow on the other side. Red light penetrates more because it is not strongly absorbed by blood and because it tends to scatter more. Optical diagnosis relies on the structural and biochemical differences between cancer tissue and normal tissue that can be probed with visible or near infrared light.
Cancerous cells are more active and reproduce at an abnormally high rate.
They also tend to have larger and more numerous nuclei. On the tissue level, tumors have immature collagen as well as immature blood vessels. Tumor detection Exogenous substances that accumulate in tumor tissue can enhance the optical contrast between tumors and normal surrounding tissue. Fluorescent dyes have been developed that can be used to delineate tumor borders. Determination of optical properties for light dosimetry Many diagnostic and therapeutic applications require knowledge of the light flux through tissue.