Light and Tissue
In our circulatory system, hemoglobin delivers oxygen to the tissue. Because of the differences in absorption between oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR), it is an excellent measure of tissue oxygenation. These values can then be used to calculate the arterial oxygenation (SaO2), which is one of the factors that reveals how the heart and lungs are functioning.
But there is more to the story.
Oxygen is also delivered and exchanged through the capillaries. At this level, the color and intensity of light output is no longer a simple function of hemoglobin absorption, but instead a complex combination of reflection, absorption, and light scattering (turbidity) from collagen and other tissue structures.
We see a similar scattering phenomenon every day when particles and clouds in the atmosphere scatter sunlight, making the sky appear different colors.
SFDI is a technique for clarifying turbidity non-invasively — like x-rays. However, unlike x-rays which use ionizing radiation, we use visible and near-infrared light, which are more benign and safer for patients and caregivers alike.