People often automatically connects "optical imaging" with beautiful and colorful microscopic images of cells. It is true that traditional and emerging microscopy techniques (con-focal, 2-photon, photoacoustic microscopy, OCT etc) are important members of optical imaging, but there are more.
The COTI lab focuses on a particular type of optical imaging, called diffuse optical tomography (DOT). A unique capability of DOT is that it can "see through" several or even over a dozen centimetres of opaque tissues without needing to cut open the tissue (also known as non-invasiveness), kind of like x-ray CT or MRI. However, compared to x-ray CT, DOT only uses safe low-energy near-infrared photons, similar to the sunlight shining on your face when you take an outdoor walk. In comparison, x-ray photons are much more energetic and may damage cells if the radiation is prolonged. Using DOT, we can computationally reconstruct 3-D maps of blood concentrations (how much blood per volume) and oxygen saturation (the percentage of red blood cells that carry oxygen) in a thick tissue sample. These physiological information are excellent indicators for diseases such as the presence of malignant tumors, inflammation or vascular diseases. In comparison, most microscopy techniques can only see through tissues no deeper than 1 mm.
In our research, we primarily use red and infrared wavelengths in the light spectrum to perform DOT measurements. This is because the major light absorbers in the tissue, known as chromophores, are primarily oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (HbR), water (H2O), lipids, melanin (the pigment made up our skin and hair colors) etc, have a relatively low absorption between 600 nm (red-colored) and 1000 nm (infrared and invisible) in light wavelengths. This window is referred to as the (1st) optical window. The provides researchers an opportunity to image deeply embedded tissue structures using red and near-infrared light.
Although it sounds fantastic if one can use light to create tomographic (i.e. 3-D) images of tissues, DOT is actually pretty difficult to do in general. There are a lot of challenges to make this work.