Optical absorbance measurements and photoacoustic evaluation of freeze-thawed polyvinyl-alcohol vessel phantoms

Abstract

Multispectral photoacoustic (MPA) imaging is a promising tool for the diagnosis of atherosclerotic carotids. Excitation of different constituents of a plaque with different wavelengths of the light may provide morphological information to evaluate plaque vulnerability. Preclinical validation of in vivo photoacoustic (PA) imaging requires a comprehensive phantom study. In this study, the design of optically realistic vessel phantoms for photoacoustics was examined by characterizing their optical properties for different dye concentrations, and comparing those to PA measurements. Four different concentrations of Indian ink and molecular dye were added to a 15 wt% PVA and 1 wt% orgasol mixture. Next, the homogeneously mixed gels were subjected to five freeze -thaw cycles to increase the stiffness of vessel phantoms (r inner = 2.5mm, r outer = 4mm). For each cycle, the optical absorbance was measured between 400 nm 990 nm using a plate reader. Additionally, photoacoustic responses of each vessel phantom at 808 nm were tested with a novel, hand-held, integrated PA probe. Measurements show that the PA signal intensity increases with the optical absorber concentration (0.3 to 0.9) in close agreement with the absorbance measurements. The freeze -thaw process has no significant effect on PA intensity. However, the total attenuation of optical energy increases after each freeze-thaw cycle, which is primarily due to the increase in the scattering coefficient. In future work, the complexity of these phantoms will be increased to examine the feasibility of distinguishing different constituents with MPA imaging.

Study of Polyvinyl Alcohol Hydrogels Applying Physical-Mechanical Methods and Dynamic Models of Photoacoustic Signals

“…Our results are supported by studies showing consistent values for the speed of sound [ 7 , 28 ] and PA amplitude [ 29 ]. However, it is important to note that while other researchers changed freezing cycles to determine the speed of sound and PA amplitude, we varied the concentration of PVA.…”

Tissue mimicking materials for imaging and therapy phantoms: a review

“…Weir et al added aluminium oxide to a 10% PVAc to achieve a speed of sound of 1524 ms −1 for a transcranial Doppler phantom (Weir et al 2015). Additionally, this TMM has been applied to photoacoustic phantoms (Arabul et al 2015), through optimizing FT cycles to increase turbidity and adding optical scatterers to tune optical properties.…”