Systematic analysis of frequency dependent differential photoacoustic cross-section data for source size estimation.

A frequency dependent differential photoacoustic cross-section (DPACS) over a large frequency band (100-1000 MHz) was computed, and subsequently, morphological parameters of a photoacoustic (PA) source were quantified. The Green's function approach was utilized for calculating the DPACS for spheroidal droplets with varying aspect ratios, Chebyshev particles with different waviness and deformation parameters, and normal red blood cells and cells affected by hereditary disorders (e.g., spherocytosis, elliptocytosis, and stomatocytosis). The theoretical framework considers that PA waves propagate through an acoustically dispersive and absorbing medium and are detected by a planar detector of finite size. The frequency dependent DPACS profile was fitted with tri-axial ellipsoid, finite cylinder, and toroid form factor models to obtain size and shape information of the PA source. The tri-axial ellipsoid form factor model was found to provide better estimates of the shape parameters compared to other models for a variety of sources. The inverse problem framework may motivate developing PA-based technology to assess single-cell morphology.