Truncated correlation photoacoustic coherence tomography: An axial resolution enhancement imaging modality

In this report we present a novel photoacoustic (PA) modality using pulsed chirp excitation at a fixed wavelength and spectral analysis based on frequency-domain (FD) processing. We introduce Truncated Correlation Photoacoustic Coherence Tomography (TC-PACT), a PA axial resolution enhancement methodology, with an application to closely stacked subsurface multilayers of plexiglass coated with a thin layer of graphite acting as surface absorber. The experimental results demonstrated that the SNR and the axial resolution were higher in TC-PACT than in conventional FD photoacoustics. A ns pulsed laser was also used as PA excitation source with axial resolution results found to be commensurate with TC-PACT. However, the separation distance between adjacent absorbers when the latter approached the axial resolution limit of the transducer was only resolved in TC-PACT compared to pulsed laser PA owing to the lower uncertainty in the former modality involved in determining the location of the absorbers.