Application of modulated optical excitation in the investigation and cure of diseases

Various optical phenomena such as reflection, scattering, absorption, fluorescence, etc., occur when light strikes a tissue surface. Investigation of light-tissue interactions thus can be used to study/understand tissue pathophysiology and health. Since the first in vivo examples were published, optical spectroscopy techniques have undergone a massive transformation in technology and clinical and commercial applications for more than 2 decades. Optical spectroscopy tools are now used for disease diagnosis in vivo, avoiding invasive biopsy procedures. Optical fibers could be inserted into minimally invasive clinical instruments like endoscopes to precisely deliver light into desired tissues for optical spectroscopy assessments. Additionally, light in the visible to the near-infrared range can treat various ailments. This chapter discusses how various techniques, including spectroscopy (laser-induced fluorescence, photoacoustic spectroscopy), imaging (fluorescence lifetime imaging, and time-correlated single-photon counting, photoacoustic), photobiomodulation, etc., can be utilized to diagnose, monitor disease states of tissues, and also to treat various ailments in vivo.