Optical Coherence Tomography Provides an Active Window on the Brain

Optical Coherence Tomography (OCT) is a powerful new tool for monitoring both degenerative and malignant activities occurring deep within the brain -- by looking into the eyes. The OCT scanner uses two light beams (diodes or pulse lasers) to generate a 3d image of the depth of the retinas. This information tells medical specialists many different things about what is happening inside the skull.

One beam of light is fired at the tissue and another at a reference mirror. When the reflected beams have travelled an identical distance, interference will make their combined beam brighter than if the distances are different. So by reflecting one beam off of different layers of tissue, and moving the reference mirror until the combined reflected beam is brightest, the technique can measure the depths of each section of tissue and build up a detailed image of its structure. It has proved particularly useful in ophthalmology because the semi-transparent nature of retinal tissue makes it possible for OCT to penetrate to greater depths - up to several millimetres. When applied to the OND it can give information about both the shape and thickness of retinal nerve fibres, allowing even subtle changes to be tracked.

Such changes can be used to monitor the progression of diseases non-invasively and relatively cheaply. Unlike MRI, which is expensive and can require patients to remain still for an hour or more, OCT is increasingly available in clinics and can be carried out in a few minutes. "It's extremely inexpensive compared to other tests," says Valenti.

One possibility is to use OCT to monitor the effectiveness of treatments for neurodegenerative diseases, says Danesh-Meyer: "These drugs can have a lot of side effects, so if they are not having a benefit then you won't want to continue with them." _NS

The progress of brain tumours, multiple sclerosis, Alzheimer's, Parkinson's, and other brain diseases can be tracked over time using this non-invasive technique.

As the technology improves and allows for faster, less uncomfortable scans, it is likely that a routine baseline scan will be done on all adolescents as part of their permanent medical records. Should any new symptoms warrant it, later OCT scans can be compared with the baseline study to look for signs of brain pathology.

Longer lives mean more chances for new pathology. Pathology in the brain has been historically very hard and expensive to track over time. Newer technologies such as the OCT should allow medical scientists and practitioners to determine which persons need treatment, and which treatments provide the best result. The time saved by such new procedures should translate into a more functional lifespan.