Photoacoustic Spectrum Analysis Research Articles

Mid-infrared photoacoustic spectrum analysis of SF6 gas-decomposition system

Mid-infrared photoacoustic spectrum analysis of SF6 gas-decomposition system

Photoacoustic spectrum analysis for spherical target size and optical property determination: A feasibility study

The photoacoustic signal generated by an optically absorbing target is determined by the spatial profile of absorbed optical energy within the target. The analysis of the time profile and frequency content of the signal enables the recovery of the geometry of the object, as well as information about the optical properties. The photoacoustic response of spheres with a homogeneous absorbed optical energy profile is well described, and it is known that the width of the photoacoustic pulse is determined by the diameter of the sphere and its sound speed. In practice, the optical attenuation coefficients within the sphere will result in an inwardly decaying fluence profile leading to a similarly decaying absorbed optical energy profile. Further, the optical attenuation coefficients may be inhomogeneously distributed in the sphere. The implication for both cases is that the existing model for spheres does not fully apply. In this work, we developed analytical expressions for the photoacoustic time traces and amplitude spectra generated by a sphere with absorbed optical energy only in a spherical shell, and by a sphere with an inwardly decaying optical energy profile. Numerical simulations and experiments were conducted on these two imperfect sphere types. Fitting our model to the simulated or measured spectra allowed us to test our model’s ability to extract the sphere size and optical properties. We found that the radii can be recovered with high accuracy, even when the frequency response of the detector recording the photoacoustic pulse is not precisely known. The model was found to be less sensitive in recovering the optical attenuation coefficient, but it is feasible when the detector’s frequency response is well known.

Quick identification of prostate cancer by wavelet transform-based photoacoustic power spectrum analysis

Pathology is currently the gold standard for grading prostate cancer (PCa). However, pathology takes considerable time to provide a final result and is significantly dependent on subjective judgment. In this study, wavelet transform-based photoacoustic power spectrum analysis (WT-PASA) was used for grading PCa with different Gleason scores (GSs). The tumor region was accurately identified via wavelet transform time-frequency analysis. Then, a linear fitting was conducted on the photoacoustic power spectrum curve of the tumor region to obtain the quantified spectral parameter slope. The results showed that high GSs have small glandular cavity structures and higher heterogeneity, and consequently, the slopes at both 1210 nm and 1310 nm were high (p < 0.01). The classification accuracy of the PA time frequency spectrum (PA-TFS) of tumor region using ResNet-18 was 89% at 1210 nm and 92.7% at 1310 nm. Further, the testing time was less than 7 mins. The results demonstrated that identification of PCa can be rapidly and objectively realized using WT-PASA.

Theoretical Investigation of Photoacoustics From Cancer Cells: Modified Models

Photoacoustic (PA) technology has wide applications in cell study. However, photoacoustics from cancer cells lacks adequate understanding. Here, we establish two modified models for theoretical investigation of photoacoustics from cancer cells. The first model is based on endogenous absorbers of cancer cells, which can be measured by label-free PA microscopy. Different from previous studies about PA for cancer cells that are limited to melanoma cells, our model considers general cancer cells. Further, the feasibility of cancer cell cycle analysis via PA spectrum analysis is demonstrated. The second model is based on exogenous absorbers, e.g., nanoparticles (NPs), in cancer cells. The interactions between NPs and cells in PA signal generation are considered. The nucleus-to-cytoplasm ratio, refractive index, cellular uptake of NPs, NPs size heterogeneity and cell size are modeled to evaluate the contribution of each factor to the change of PA signal amplitudes, which is valuable to guide experiments for cancer cell identification by utilizing different PA signal amplitudes between normal cells and cancer cells. In conclusion, our study comprehensively investigates photoacoustics from cancer cells, which lays theoretical groundwork for future research on PA techniques for cancer cells and is expected to be useful for cancer diagnosis, treatment, and prognosis.

Prostate cancer identification via photoacoustic spectroscopy and machine learning

Photoacoustic spectroscopy can generate abundant chemical and physical information about biological tissues. However, this abundance of information makes it difficult to compare these tissues directly. Data mining methods can circumvent this problem. We describe the application of machine-learning methods (including unsupervised hierarchical clustering and supervised classification) to the diagnosis of prostate cancer by photoacoustic spectrum analysis. We focus on the content and distribution of hemoglobin, collagen, and lipids, because these molecules change during the development of prostate cancer. A higher correlation among the ultrasonic power spectra of these chemical components is observed in cancerous than in normal tissues, indicating that the microstructural distributions in cancerous tissues are more consistent. Different classifiers applied in cancer-tissue diagnoses achieved an accuracy of 82 % (better than that of standard clinical methods). The technique thus exhibits great potential for painless early diagnosis of aggressive prostate cancer.

Laser-Induced Damage on Fused Silica With Photo-Acoustic Spectrum Analysis

Laser-induced damage on fused silica is studied with photo-acoustic spectrum. The damage characteristics are evaluated with the spectral analysis of photo-acoustic signal. The experimental results show that the damage threshold of fused silica samples is about 20.9 J/cm2 at 1-ON-1 condition at the wavelength of 1064 nm and the pulse duration of 10 ns. The damage morphology observed with confocal microscopy is gray haze, and the diameter and depth of the largest crater in gray haze are $6.7~\mu \text{m}$ and 200 nm, respectively. The reproducibility of photo-acoustic spectrum analysis and the characteristic spectral peak is discussed. Compared to the photo-acoustic method judged by signal amplitude, the photo-acoustic spectrum is more sensitive, which may provide an effective support for the study on laser-generated thermal explosion and shock wave propagation. Moreover, the photo-acoustic spectrum may provide a clue for early-damage judgment.

Photoacoustic imaging and photoacoustic spectrum analysis in mouse models of cutaneous squamous cell carcinoma

Objective To establish a photoacoustic detection system and data processing methods for skin tumors, and to explore photoacoustic imaging and photoacoustic spectrum in mouse models of cutaneous squamous cell carcinoma (CSCC) . Methods A total of 60 healthy specific pathogen-free (SPF) female BALB/C nude mice aged 6-8 weeks were randomly and equally divided into 2 groups to be inoculated with a murine CSCC cell line XL50 and a human CSCC cell line A431 respectively on the right back near the upper limbs, and mouse models of murine CSCC (n = 20) and human CSCC (n = 20) were successfully established. The 850-nm photoacoustic detection system was applied in the above 2 kinds of mouse models, and photoacoustic imaging and photoacoustic spectrum data were collected. The fitted slope of acoustic power spectrum curves was compared between squamous cell carcinoma tissues and normal skin on the left back of the mouse model. After the photoacoustic detection, tumor tissues and normal skin at the opposite side were excised from the 2 kinds of mouse models, and subjected to histopathological examination. The fitted slope of different tissues was compared by using t test. Results Photoacoustic imaging showed higher photoacoustic signals of hemoglobin in squamous cell carcinoma tissues compared with the normal skin tissues. In the model of murine CSCC, the fitted slope of acoustic power spectrum curve was significantly lower in the tumor tissues (-1.827 ± 0.153 1) than in the normal skin tissues (-1.059 ±0.117 8, t = 3.973, P < 0.001) . In the model of human CSCC, the fitted slope of acoustic power spectrum curve was also significantly lower in the tumor tissues (-1.537 ± 0.125 5) than in the normal skin tissues (-0.960 ± 0.259 7, t = 2.166, P = 0.043) . Histopathological examination showed that the number of vessels increased in the tumor tissues compared with the normal skin tissues. Conclusion CSCC tissues are different from normal skin tissues in photoacoustic imaging signals and the fitted slope of acoustic power spectrum, which may lay a foundation for non-invasive photoacoustic diagnosis of CSCC. Key words: Neoplasms, squamous cell; Photoacoustic techniques; Photoacoustic imaging; Photoacoustic spectrum; Fitted slope

Comparison study of photoacoustic and ultrasound spectrum analysis in osteoporosis detection

Osteoporosis is a progressive bone disease, which is characterized by a decrease in the bone mass and deterioration in bone micro-architecture. In theory, photoacoustic (PA) analysis has the potential to obtain the characteristics of the bone effectively. In this study, we try to compare the PA spectral analysis (PASA) method with the quantitative ultrasound (QUS) method in osteoporosis assessment. We compare the quantified parameter slope from the PASA and broadband ultrasound attenuation from QUS among different bone models, respectively. Both the simulation and ex vivo experiment results show that bone with lower bone mineral density has the higher slope in the PASA method. Our comparison study proves that the PASA method has the same efficiency as QUS in osteoporosis assessment.

Characterizing cellular morphology by photoacoustic spectrum analysis with an ultra-broadband optical ultrasonic detector.

Photoacoustic spectrum analysis (PASA) has been demonstrated as a new method for quantitative tissue imaging and characterization. The ability of PASA in evaluating micro-size tissue features was limited by the bandwidth of detectors for photoacoustic (PA) signal acquisition. We improve upon such a limit, and report on developments of PASA facilitated by an optical ultrasonic detector based on micro-ring resonator. The detector's broad and flat frequency response significantly improves the performance of PASA and extents its characterization capability from the tissue level to cellular level. The performance of the system in characterizing cellular level (a few microns) stochastic objects was first shown via a study on size-controlled optically absorbing phantoms. As a further demonstration of PASA's potential clinical application, it was employed to characterize the morphological changes of red blood cells (RBCs) from a biconcave shape to a spherical shape as a result of aging. This work demonstrates that PASA equipped with the micro-ring ultrasonic detectors is an effective technique in characterizing cellular-level micro-features of biological samples.

Growth of organic nonlinear optical (NLO) ammonium D,L-tartrate (AMT) single crystal by conventional and unidirectional method and its characterization

High-quality, transparent uniaxial ammonium D,L-tartrate (AMT) single crystal having dimension of 15 mm diameter and 60 mm length was grown by Sankaranarayanan–Ramasamy (SR) method with a growth rate of 1 mm per day. Single-crystal X-ray diffraction was carried out to confirm the AMT crystals. The presence of functional groups of crystallized AMT molecules were identified by FTIR spectral analysis. The dislocation density of the AMT crystals grown by slow evaporation solution technique (SEST) and SR method were characterized using chemical etching analysis. A comparative laser damage threshold analysis was made on the AMT crystals grown by conventional and SR method which shows that the crystal grown by SR method has higher damage threshold. The SR method grown AMT crystal has higher microhardness and also higher optical transmittance compared to conventional method grown crystal. The thermal properties of the SEST and SR method grown AMT crystals were measured by photoacoustic spectrum analysis. The second harmonic generation efficiency of AMT was determined using the powder Kurtz–Perry technique.

The Functional Pitch of an Organ: Quantification of Tissue Texture with Photoacoustic Spectrum Analysis

To investigate the use of photoacoustic (PA) spectrum analysis (PASA) to identify microstructural changes corresponding to fat accumulation in mouse livers ex vivo and in situ. The laboratory animal protocol for this work was approved by the university committee on use and care of animals. Six mice with normal livers and six mice with fatty livers were examined ex vivo with a PA system at 1200 nm, and nine similar pairs of mice were examined at 532 nm. To explore the feasibility of this technique for future study in an in vivo mouse model, an additional pair of normal and fatty mouse livers was scanned in situ with an ultrasonographic (US) and PA dual-modality imaging system. The PA signals acquired were analyzed by using the proposed PASA method. Results of the groups were compared by using the Student t test. Prominent differences between the PASA parameters from the fatty and normal mouse livers were observed. The analysis of the PASA parameters from six normal and six fatty mouse livers indicates that there are differences of up to 5 standard deviations between the PASA parameters of the normal livers and those of the fatty livers at 1200 nm; for parameters from nine normal and nine fatty mouse livers at 532 nm, the differences were approximately 2 standard deviations (P < .05) for each PASA parameter. The results supported our hypothesis that the PASA allows quantitative identification of the microstructural changes that differentiate normal from fatty livers. Compared with that at 532 nm, PASA at 1200 nm is more reliable for fatty liver diagnosis. Online supplemental material is available for this article.

Double spectrum analysis of photoacoustic signal

Photoacoustic spectroscopy based on the photoacoustic effect is the combination of optical imaging and acoustical imaging, which has become a powerful medical diagnosis tool to distinguish different tissues and components with several different wavelength photoacoustic images. But photoacoustic spectroscopy is limited by the scanning speed, system stability and signal accuracy. To solve these limitation problems, in this paper we propose a new method called photoacoustic double spectrum analysis which can greatly improve the image contrast and identification capability with quantitative analysis of the detected photoacoustic signal frequency. The final experimental results indicate that this method has the feasibility to distinguish different tissues quickly and easily with better contrast, which will be helpful for improving the applications of photoacoustic imaging in various branches of physics, biology, engineering, medicine, etc. We also expect the theoretical and experimental research proposed in this paper to establish the foundation and method for photoacoustic frequency imaging.

Photoacoustic spectrum analysis for microstructure characterization in biological tissue: A feasibility study

This study investigates the feasibility of characterizing the microstructures within a biological tissue by analyzing the frequency spectrum of the photoacoustic signal from the tissue. Hypotheses are derived from theoretical analyses on the relationships between the dimensions/concentrations of the photoacoustic sources within the region-of-interest and the linear model fitted to the power spectra of photoacoustic signals. The hypotheses are validated, following the procedures of ultrasound spectrum analysis, by simulations and experiments with phantoms fabricated by embedding the polyethylene microspheres in porcine gelatin, indicating that photoacoustic spectrum analysis could be a potential tool for characterizing microstructures in biological samples.

Numerical analysis of absorption and transmission photoacoustic spectra of silicon samples with differently treated surfaces

AbstractThis paper presents results of the photoacoustic (PA) spectral studies, of a series of silicon samples with differently prepared surfaces, in two PA experimental configurations, so-called, absorption and transmission ones. The PA amplitude spectra of the samples indicated existence of the damaged surface layers. In the paper, the two layer mathematical models of a sample with a damaged surface layer that were used for numerical interpretation of the amplitude PA spectra of the investigated samples, are presented and discussed.

Judd-Ofelt Analysis of Photoacoustic Spectra of Powdered Neodymium Compounds

Photoacoustic (PA) spectra of powdered neodymium oxide: Nd2O3 (A type), neodymium hydrated chloride: NdCl3-6H2O and neodymium fluoride: NdF3 are reported. PA band shifts as compared to their positions in aqueous Nd(III) ion have been used to calculate the nephelauxetic parameters of their compounds. The variation of these parameters and correlation with the nature of metal-ligand bonding have been discussed. A novel method is introduced to determine relative values of Judd-Ofelt parameters and oscillator strengths of powdered samples using PA spectroscopy. It is found that a linear correlation exists between relative values of τ2 and relative oscillator strengths of hypersensitive transitions of the title compounds. It can be hoped that the new method of PA technique may serve for the Judd-Ofelt quantitative analysis of powdered rare earth compounds.

Analysis of photoacoustic IR spectra of aerogel and silica powder

Especially for solid-gas systems with a small volume fraction of the solid material, photoacoustic spectroscopy (PAS) is a very useful tool for the determination of the optical properties. For such materials, the photoacoustic signal is extremely large because of their low thermal conductivity. With other methods, the measurement of reflectance and transmittance is very difficult for such samples. The expansion of the interstitial gas in porous samples is responsible for a significant part of the photoacoustic signal. It is important to include this contribution in the quantitative interpretation of the PAS experiments. In addition to the optical properties of the sample, the interstitial gas expansion yields information about the structure of the pores. A model calculation is presented for the analysis of photoacoustic spectra in the infrared regime (ṽ = 400…2000 cm−1; λ = 5…25 μm) of silica powder, monolithic aerogel and opacified aerogel powder.

High resolution photoacoustic spectra of Ho_2O_3 and Nd_2O_3

A piezoelectric detection system for recording photoacoustic (PA) spectra of materials in the condensed phase was designed and fabricated. A Nd-YAG laser pumped tunable dye laser with a bandwidth of 0.05 nm was used for recording the fine structure of bands in the region between 610-680 nm in powdered microcrystalline samples of Ho(2)O(3) and Nd(2)O(3). Analysis of high resolution photoacoustic spectra obtained new information on the Stark components of the ground and excited states of Ho(3+) and Nd(3+) in the oxide matrix.

Infrared-laser photoacoustic spectroscopy

This paper reviews the applications of IR-laser photoacoustics to trace-gas monitoring as well as to spectroscopic studies on absorbing liquids. In the first part we present a stationary, dual-beam CO-laser and a mobile CO 2-laser photoacoustic system which have both been applied to the monitoring of various gaseous pollutants. Emphasis is put on selectivity, sensitivity and on temporal resolution. Novel cell designs and experimental techniques and an iterative procedure for the analysis of photoacoustic spectra of multicomponent mixtures are introduced. New results are presented for measurements on car and industrial exhausts as well as on ambient air. The second part is devoted to theoretical and experimental photoacoustic studies on strongly absorbing liquids, in particular on the investigation of different boundary conditions. A characteristic enhancement of the photoacoustic signal in the liquid is obtained if a liquid or solid surface layer is present. This new phenomenon permits the analysis of surface films with a thickness of ⩾ 1 μm. Furthermore, the photoacoustic in-situ monitoring of the polymerization process on a liquid surface is presented for the first time.

Quantitative analysis of photoacoustic IR spectra

Photoacoustic spectroscopy is a method for directly measuring the absorption properties of gases and condensed matter. We have developed a photoacoustic gas cell for a rapid-scan Fourier spectrometer. With this cell we can extend the spectral range down to 180 cm−1; more than one octave lower than previously reported useful broadband measurements. The photoacoustic spectrum of a microscope cover glass was measured from 180 ... 200 cm−1 and normalized with respect to the spectrum of carbon black as a reference material. Starting from the one-dimensional equation of heat conduction we derived an expression for the surface temperature of single and double-layer samples. We calculated the surface temperature of the glass lamella and divided it by the corresponding values for carbon black using the thermal conductivity of carbon black as a fitting parameter. We show that the one-dimensional model calculation reproduces the experimental spectrum over the whole spectral range.

Computer-assisted analysis of photoacoustic spectra of solid and solution state cyanide methemoglobin

A computer-assisted method for analyzing photoacoustic spectra has been developed. Using this analysis, the relative absorption spectrum and either the chromophore concentration or thermal diffusivity characteristic of a sample can be derived from its photoacoustic spectrum. We have demonstrated the accuracy of the method by analyzing photoacoustic spectra of solution and crystalline-phase bovine cyanide methemoglobin. BASIC and FORTRAN routines used to collect and to analyze photoacoustic spectra are described. Photoacoustic spectroscopy can be used in conjunction with the analytical method presented here to obtain accurate absorption spectra from a variety of solid, opaque, and/or turbid samples.