Reports about using optical techniques for imaging of arthritic joints can be found in the literature.5–8 However, the reported techniques utilized monochromatic light, and thus did not explore the richness of the spectral information obtained using a broadband light. Spectroscopic data carry useful information about tissue optical properties such as absorption, scattering, and tissue composition. Specifically for an arthritic joint, the features, which can significantly alter spectral information, include vessel proliferation (increased hemoglobin concentration), hypoxia, and quantitative and qualitative change of synovial fluid (SF) (edema, increased scattering). In addition, a joint shape changes when the synovial membrane thickens and SF collections are present. More specific details about the changes typical for an arthritic joint can be found in the Background and Methods sections. Thus, by considering both spectral and spatial data, the reliability of the arthritis diagnosis could be increased. A suitable spectral imaging modality for arthritis diagnostics is hyperspectral imaging (HSI). The technique provides both spectral and spatial information in one measurement and does not require contact between the object and the sensor. It has been demonstrated that the technique is very sensitive for detecting pathological conditions such as hypoxia9 or enhanced vascularization,10 both being important characteristics of an arthritic joint. In addition, the technique is not harmful to the patient (no ionizing radiation), is fast, and does not depend on the operator’s experience. The cost is less than MRI or x-ray and is probably comparable to ultrasound.