Sulfates as chromophores for multiwavelength photoacoustic imaging phantoms

Abstract

Abstract. As multiwavelength photoacoustic imaging becomes increasingly widely used to obtain quantitative estimates, the need for validation studies conducted on well-characterized experimental phantoms becomes ever more pressing. One challenge that such studies face is the design of stable, well-characterized phantoms and absorbers with properties in a physiologically realistic range. This paper performs a full experimental characterization of aqueous solutions of copper and nickel sulfate, whose properties make them close to ideal as chromophores in multiwavelength photoacoustic imaging phantoms. Their absorption varies linearly with concentration, and they mix linearly. The concentrations needed to yield absorption values within the physiological range are below the saturation limit. The shape of their absorption spectra makes them useful analogs for oxyand deoxyhemoglobin. They display long-term photostability (no indication of bleaching) as well as resistance to transient effects (no saturable absorption phenomena), and are therefore suitable for exposure to typical pulsed photoacoustic light sources, even when exposed to the high number of pulses required in scanning photoacoustic imaging systems. In addition, solutions with tissue-realistic, predictable, and stable scattering can be prepared by mixing sulfates and Intralipid, as long as an appropriate emulsifier is used. Finally, the Grüneisen parameter of the sulfates was found to be larger than that of water and increased linearly with concentration. © The Authors.Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Multiple illumination learned spectral decoloring for quantitative optoacoustic oximetry imaging

“…Variations in the Grüneisen parameter were also not part of the training set, even though it does vary significantly with rCu, because Γðc wb ðNiSO 4 ÞÞ ≈ 0.21 and Γðc wb ðCuSO 4 ÞÞ ≈ 0.14 at room temperature. 27 This results in a systematically higher SNR for low rCu-an effect not present in sO 2 , 37 which may explain why high rCu estimations are systematically worse in all of our phantom test sets. Laser noise levels are also wavelength dependent, which is reinforced by the pulse energy correction, e.g., resulting in a factor two SNR when measuring at 800 nm compared with 680 nm.…”

“…The relative copper sulfate model solution was based on a 2.2-molar nickel sulfate (NiSO 4 ) water solution, produced using nickel(II) sulfate hexahydrate (>98%, Sigma-Aldrich), and on a 0.25 molar copper sulfate (CuSO 4 ) water solution, produced using copper(II) sulfate pentahydrate (>98%, Sigma-Aldrich). 27 As shown in Fig. 2, these chromophores are mimicking the NIR absorption spectra of oxy-and deoxyhemoglobin in average whole blood with a hemoglobin concentration c wb ðHbTÞ ¼ 150 gl −1 .…”

“…The scattering in this wavelength range is negligible. 27 The initial reference measurements were done in 2 nm steps, with a 10-s integration time and using a photomultiplier tube sensor. The absorption spectroscopy measurements were repeated on the solutions after 70 days to verify their stability over time.…”

“…Γðx 0 Þ, as a material property is also independent of the illumination wavelength. 27 The LSD model, which was trained on the in silico training set tuples ðĤ; rCu tube Þ, is then presented (1) unseen in silico test set spectraĤ or (2) spectraŜ from an unseen phantom data test set to estimate the corresponding rCu LSD est . Note that A actually does depend on the fluence distribution ϕðx; μ a ðx; λÞ; μ 0 s ðx; λÞÞ.…”

Three-dimensional quantitative photoacoustic tomography using an adjoint radiance Monte Carlo model and gradient descent

“…The absorption coefficient is related to the chromophore concentrations via the specific absorption coefficient, α k ðλÞ, i.e., E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 4 ; 3 2 6 ; 6 9 6 μ a ðλ;rÞ ¼ X N k k c k ðrÞα k ðλÞ; (4) where N k is the number of chromophores and k indicates the chromophore type. The Grüneisen parameter Γ is assumed to be linearly dependent on chromophore concentrations, 15,34,35 i.e., E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 5 ; 3 2 6 ; 6 0 2…”