PROJECT SUMMARY -- KANDADAI Osteoporosis is a major problem with a high impact on human life, affecting over 48 million people in the United States. Normally, healthy bone constantly undergoes remodeling, which helps heal minor micro-fractures caused by day-to-day activity and keeps bones strong. Osteoporosis affects remodeling, increasing the probability of fracture. One of the common treatments for osteoporosis is bisphosphonates. However, while it has been shown to improve osteoporosis, long-term bisphosphonate treatment creates the risk of generating micro-cracks and increases the chance of hip fractures. Both the disease and treatment cause a change in the porosity of the bone, and currently, there are no viable techniques that accurately measure changes in the bone porosity. Currently, two techniques are used to study the deterioration of bone, magnetic resonance imaging (MRI) and computerized tomography (CT). Both techniques suffer from low resolution making micro-cracks in the bone difficult to detect. In addition, MRI and CT are not readily amenable to measuring the effects of day-to-day activity, load-bearing, and age on bone porosity, which would be needed to create a preventative treatment plan. In our proposed project we are investigating a novel visible-light imaging technique to study and differentiate a variety of bone porosity and micro-cracks. In our project, we will use a technique known as modulated photothermal radiometry (MPTR) that measures the porosity-dependent thermal conductivity of materials, such as bone. MPTR has two potential advantages over MRI and CT: 1) it uses visible light to study the deterioration of bone without harmful radiation, and 2) it is easier to implement in vivo with higher resolution. The work will have wide-reaching significance, both in the laboratory and in real life. Quantification of bone porosity and micro- cracks will improve the understanding of the effects of bone remodeling, a major issue in osteoporosis and other repetitive bone injuries.