Nonlinear optoacoustic readings from diffusive media at near-infrared wavelengths

5 years ago

Nonlinear optoacoustic readings from diffusive media at near-infrared wavelengths

Jaya Prakash, Jaber Malekzadeh-Najafabadi, Vasilis Ntziachristos

Optoacoustic (photoacoustic) imaging assumes that the detected signal varies linearly with laser energy. However, nonlinear intensity responses as a function of light fluence have been suggested in optoacoustic microscopy, that is, within the first millimeter of tissue. In this study, we explore the presence of nonlinearity deeper in tissue (~4 mm), as it relates to optoacoustic mesoscopy, and investigate the fluence required to delineate a switch from linear to nonlinear behavior. Optoacoustic signal nonlinearity is studied for different materials, different wavelengths and as a function of changes in the scattering and absorption coefficient of the medium imaged. We observe fluence thresholds in the mJ/cm2 range and preliminary find that different materials may exhibit different nonlinearity patterns. We discuss the implications of nonlinearity in relation to image accuracy and quantification in optoacoustic tomography. Nonlinearity is observed in optoacoustic tomography in diffusive media by increasing light fluence. The nonlinearity shows a piecewise linear function and there is a certain fluence threshold needed to trigger the transition from linear to nonlinear regime. The optoacoustic signal shows prominent nonlinearity by increasing absorption and scattering coefficient. Different materials can have different nonlinear trend and the laser wavelength has effect on the trend.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/jbio.201600310