Optical Imaging

Optical imaging encompasses a host of light-based imaging modalities, including diffuse optical imaging, optical coherence tomography, two-photon microscopy and more.

The Martinos Center has played a major role in the development of diffuse optical imaging (DOI). DOI takes advantage of the optical properties of light to image inside the body. If you shine a flashlight on your hand, you'll see that light can travel through centimeters of tissue and still be detected. Based on our understandings of light migration through tissue we can use this detected light to measure changes in hemodynamics - changes in blood volume or blood oxygenation, for example - which can tell us a great deal about what's going on in the body.

Thus DOI can contribute to a variety of applications. In the brain, for example, it can detect and localize important events such as ischemic/hemorrhagic stroke or hyper-/hypoxia. It can also detect and localize vascular responses to brain activation - and in this way help to advance brain mapping efforts. Because a tight coupling exists between vascular and metabolic responses to activation, these measurements can reveal considerable information about the latter and may even provide some clues as to the underlying neural responses.

Researchers are exploring the potential of DOI for optical breast imaging. Here, the technique can reveal changes in blood volume and oxygen saturation that are specific to early stages of cancer. Because it focuses on these functional changes, it can - in theory - identify cancers before they are structurally evident (that is, before they are visible on X-ray or discernable by palpation). In addition to potential detection of cancers, DOI offers a means to explore the physiology of the breast. The literature includes, for example, studies on changes in the optical properties associated with age, exogenous hormone levels and menopausal status.

Optical recording offers several attractions over other imaging methods, including simplicity, low cost and portability. DOI systems can consist of little more than a probe with fiber-optic sources and detectors, a piece of dedicated hardware about the size of a small suitcase and a laptop computer. (Systems can be much larger, depending primarily on the type of laser source employed, but the approach generally offers a degree of portability unobtainable with many other modalities.) For this reason, the technique could be ideally suited to clinical applications such as bedside monitoring of cerebral oxygenation.