In Vitro and In Vivo Multispectral Photoacoustic Imaging for the Evaluation of Chromophore Concentration

Multispectral photoacoustic imaging is a powerful noninvasive medical imaging technique that provides access to functional information. In this study, a set of methods is proposed and validated, with experimental multispectral photoacoustic images used to estimate the concentration of chromophores. The unmixing techniques used in this paper consist of two steps: (1) automatic extraction of the reference spectrum of each pure chromophore; and (2) abundance calculation of each pure chromophore from the estimated reference spectra. The compared strategies bring positivity and sum-to-one constraints, from the hyperspectral remote sensing field to multispectral photoacoustic, to evaluate chromophore concentration. Particularly, the study extracts the endmembers and compares the algorithms from the hyperspectral remote sensing domain and a dedicated algorithm for segmentation of multispectral photoacoustic data to this end. First, these strategies are tested with dilution and mixing of chromophores on colored 4% agar phantom data. Then, some preliminary in vivo experiments are performed. These consist of estimations of the oxygen saturation rate (sO2) in mouse tumors. This article proposes then a proof-of-concept of the interest to bring hyperspectral remote sensing algorithms to multispectral photoacoustic imaging for the estimation of chromophore concentration.

Dual-Modal Photoacoustic Imaging and Optical Coherence Tomography [Review]

Optical imaging technologies have enabled outstanding analysis of biomedical tissues through providing detailed functional and morphological contrast. Leveraging the valuable information provided by these modalities can help us build an understanding of tissues’ characteristics. Among various optical imaging technologies, photoacoustic imaging (PAI) and optical coherence tomography (OCT) naturally complement each other in terms of contrast mechanism, penetration depth, and spatial resolution. The rich and unique molecular-specified absorption contrast offered by PAI would be well complemented by detailed scattering information of OCT. Together these two powerful imaging modalities can extract important characteristic of tissue such as depth-dependent scattering profile, volumetric structural information, chromophore concentration, flow velocity, polarization properties, and temperature distribution map. As a result, multimodal PAI-OCT imaging could impact a broad range of clinical and preclinical imaging applications including but not limited to oncology, neurology, dermatology, and ophthalmology. This review provides an overview of the technical specs of existing dual-modal PAI-OCT imaging systems, their applications, limitations, and future directions.

SISTEMA DE BAIXO CUSTO PARA EXECUÇÃO E MONITORAMENTO ON-LINE DE REAÇÕES FOTOCATALÍTICAS: APLICAÇÃO EM REDUÇÃO DE NITRO-FENOL

LOW-COST SYSTEM FOR ONLINE MONITORING OF PHOTOCALYTICAL REACTIONS: APPLICATION IN NITROPHENOL. There is a global concern with pollutants and organic contaminants and efficient and inexpensive methods are sought for the treatment of these toxic products. Generally, large volume reactors and the use of expensive equipment are required to monitor a photoreaction. The present work proposes the construction of a colorimetric equipment, which allows the online monitoring of photoreactions, using low-cost materials that allow the analysis from small aliquots. To show the applicability of the system, we studied the reduction reaction of 4-nitrophenol (4NP) with NaBH4. The impedimetric sensor enabled to construct the kinetic curve of the decrease in the chromophore band. It was possible to observe that the 4NP reduction reaction depends on: (i) chromophore concentration; (ii) stability of the reducing agent and; (iii) repulsion between the anions. The system developed here opens doors, as it can be used using a photocatalyst in the form of film, and it has also proved to be an inexpensive alternative for both research and teaching laboratories, as it allows the execution of chemical physics practices such as kinetic monitoring of reactions and mathematical adjustment of the curves.

Integrating Multispectral Hemodynamic Imaging for Bulk Tissue Oxygenation Analysis

Tissue perfusion and oxygenation are important factors in predicting patient outcomes, but current non-invasive devices for this type of measurement are limited to contact-based single-site monitoring. We present the co-integration of a multispectral optical-electronic subsystem into an existing non-contact coded hemodynamic imaging (CHI) device to enable image acquisition under different illuminants for spatial tissue oxygenation. Stability of the optical output for three illuminants over 10 mins was validated by the imaging system, with σmax=0.407 intensity units, reflecting stability in local fluctuations, and a maximal overall change of 3.1 units. Bulk tissue oxygenation measurement of the thenar eminence during a cuff occlusion experiment revealed relative changes in absorbance due to oxy- and deoxyhemoglobin consistent with concurrent physiological changes in chromophore concentration as described in a previous study.