Showing papers on "Photoacoustic spectroscopy published in 2008"

Prospects of photoacoustic tomography

Abstract: Commercially available high-resolution three-dimensional optical imaging modalities—including confocal microscopy, two-photon microscopy, and optical coherence tomography—have fundamentally impacted biomedicine. Unfortunately, such tools cannot penetrate biological tissue deeper than the optical transport mean free path (∼1mm in the skin). Photoacoustictomography, which combines strong optical contrast and high ultrasonic resolution in a single modality, has broken through this fundamental depth limitation and achieved superdepth high-resolution optical imaging. In parallel, radio frequency-or microwave-induced thermoacoustic tomography is being actively developed to combine radio frequency or microwave contrast with ultrasonic resolution. In this Vision 20/20 article, the prospects of photoacoustictomography are envisaged in the following aspects: (1) photoacoustic microscopy of optical absorption emerging as a mainstream technology, (2) melanoma detection using photoacoustic microscopy, (3) photoacoustic endoscopy, (4) simultaneous functional and molecular photoacoustictomography, (5) photoacoustictomography of gene expression, (6) Doppler photoacoustictomography for flow measurement, (7) photoacoustictomography of metabolic rate of oxygen, (8) photoacoustic mapping of sentinel lymph nodes, (9) multiscale photoacoustic imagingin vivo with common signal origins, (10) simultaneous photoacoustic and thermoacoustic tomography of the breast, (11) photoacoustic and thermoacoustic tomography of the brain, and (12) low-background thermoacoustic molecular imaging.

Application of quantum cascade lasers to trace gas analysis

Abstract: Quantum cascade (QC) lasers are virtually ideal mid-infrared sources for trace gas monitoring. They can be fabricated to operate at any of a very wide range of wavelengths from ∼ 3 μm to ∼ 24 μm. Seizing the opportunity presented by mid-infrared QC lasers, several groups world-wide are actively applying them to trace gas sensing. Real world applications include environmental monitoring, industrial process control and biomedical diagnostics. In our laboratory we have explored the use of several methods for carrying out absorption spectroscopy with these sources, which include multipass absorption spectroscopy, cavity ring down spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), and quartz-enhanced photoacoustic spectroscopy (QEPAS).

Photoacoustic imaging and temperature measurement for photothermal cancer therapy

Abstract: Photothermal therapy is a noninvasive, targeted, laser-based technique for cancer treatment. During photothermal therapy, light energy is converted to heat by tumor-specific photoabsorbers. The corresponding temperature rise causes localized cancer destruction. For effective treatment, however, the presence of photoabsorbers in the tumor must be ascertained before therapy and thermal imaging must be performed during therapy. This study investigates the feasibility of guiding photothermal therapy by using photoacoustic imaging to detect photoabsorbers and to monitor temperature elevation. Photothermal therapy is carried out by utilizing a continuous wave laser and metal nanocomposites broadly absorbing in the near-infrared optical range. A linear array-based ultrasound imaging system is interfaced with a nanosecond pulsed laser to image tissue-mimicking phantoms and ex-vivo animal tissue before and during photothermal therapy. Before commencing therapy, photoacoustic imaging identifies the presence and spatial location of nanoparticles. Thermal maps are computed by monitoring temperature-induced changes in the photoacoustic signal during the therapeutic procedure and are compared with temperature estimates obtained from ultrasound imaging. The results of our study suggest that photoacoustic imaging, augmented by ultrasound imaging, is a viable candidate to guide photoabsorber-enhanced photothermal therapy.

Real-time in vivo photoacoustic and ultrasound imaging.

Abstract: A real-time photoacoustic imaging system is designed and built. This system is based on a commercially available ultrasound imaging system. It can achieve a frame rate of 8 frames/sec. Vasculature in the hand of a human volunteer is imaged, and the resulting photoacoustic image is combined with the ultrasound image. The real-time photo acoustic imaging system with a hybrid ultrasound probe is demonstrated by imaging the branching of subcutaneous blood vessels in the hand

Laser-based systems for trace gas detection in life sciences

Abstract: Infrared gas phase spectroscopy is becoming very common in many life science applications. Here we present three types of trace gas detection systems based on CO2 laser and continuous wave (cw) optical parametric oscillator (OPO) in combination with photoacoustic spectroscopy and cw quantum cascade laser (QCL) in combination with wavelength modulation spectroscopy. Examples are included to illustrate the suitability of CO2 laser system to monitor in real time ethylene emission from various dynamic processes in plants and microorganisms as well as from car exhausts. The versatility of an OPO-based detector is demonstrated by simultaneous detection of 13C-methane and 12C-methane (at 3240 nm) at similar detection limits of 0.1 parts per billion by volume. Recent progress on a QCL-based spectrometer using a continuous wave QCL (output power 25 mW, tuning range of 1891–1908 cm-1) is presented and a comparison is made to a standard chemiluminescence instrument for analysis of NO in exhaled breath.

Curved array photoacoustic tomographic system for small animal imaging

Abstract: We present systematic characterization of a photoacoustic imaging system optimized for rapid, high-resolution tomographic im- aging of small animals. The system is based on a 128-element ultra- sonic transducer array with a 5-MHz center frequency and 80% band- width shaped to a quarter circle of 25 mm radius. A 16-channel data- acquisition module and dedicated channel detection electronics enable capture of a 90-deg field-of-view image in less than 1s and a complete 360-deg scan using sample rotation within 15 s. Measure- ments on cylindrical phantom targets demonstrate a resolution of bet- ter than 200 m and high-sensitivity detection of 580-m blood tub- ing to depths greater than 3c min a turbid medium with reduced scattering coefficient s=7.8 cm 1 . The system is used to systemati- cally investigate the effects of target size, orientation, and geometry on tomographic imaging. As a demonstration of these effects and the system imaging capabilities, we present tomographic photoacoustic images of the brain vasculature of an ex vivo mouse with varying measurement aperture. For the first time, according to our knowledge, resolution of sub-200-m vessels with an overlying turbid medium of greater than 2c mdepth is demonstrated using only intrinsic biologi- cal contrast. © 2008 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2907157

Standoff photoacoustic spectroscopy

Abstract: Here, we demonstrate a variation of photoacoustic spectroscopy that can be used for obtaining spectroscopic information of surface adsorbed chemicals in a standoff fashion. Pulsed light scattered from a target excites an acoustic resonator and the variation of the resonance amplitude as a function of illumination wavelength yields a representation of the absorption spectrum of the target. We report sensitive and selective detection of surface adsorbed compounds such as tributyl phosphate and residues of explosives such as trinitrotoluene at standoff distances ranging from 0.5–20m, with a detection limit on the order of 100ng∕cm2.

Fast 3-D dark-field reflection-mode photoacoustic microscopy in vivo with a 30-MHz ultrasound linear array

Abstract: We present an in vivo dark-field reflection-mode photoacoustic microscopy system that performs cross-sectional (B-scan) imaging at 50Hz with real-time beamforming and 3-D imaging consisting of 166 B-scan frames at 1Hz with postbeamforming. To our knowledge, this speed is currently the fastest in photoacoustic imaging. A custom-designed light delivery system is integrated with a 30-MHz ultrasound linear array to realize dark-field reflection-mode imaging. Linear mechanical scanning of the array produces 3-D images. The system has axial, lateral, and elevational resolutions of 25, 70, and 200μm, respectively, and can image 3mm deep in scattering biological tissues. Volumetric images of subcutaneous vasculature in rats are demonstrated in vivo. Fast 3-D photoacoustic microscopy is anticipated to facilitate applications of photoacoustic imaging in biomedical studies that involve dynamics and clinical procedures that demand immediate diagnosis.

Ammonia monitoring at ppb level using photoacoustic spectroscopy for environmental application

Abstract: A novel photoacoustic (PA) trace-ammonia analyzer for measuring ambient ammonia concentration in the lower ppb concentration range has been developed. It is based on a wavelength-modulated, telecommunication type, room temperature-operated diode laser light source, an acoustically optimized, longitudinal resonator type small volume photoacoustic cell and a compact multi-functional electronics unit, which ensures the fully automatic long-term operation of the system. It has a response time below 2 min, which is achieved by using a photoacoustic cell made of polyvinylidene fluoride (PVDF) and gas-handling tubes made of polyamide 11 (PA-11). A dual wavelength measurement method with optimized measurement wavelengths and laser modulation parameters was introduced, which proved to efficiently suppress cross-sensitivity to other atmospheric components, most importantly to water vapor, while improving the sensitivity of the system. The developed PA system was tested with reference to a continuous-flow denuder system (AMANDA) under both laboratory and simulated field conditions, and it featured highly reliable, fully automatic operation with a detection limit of about 50 ppb of ammonia.

Optically multiplexed multi-gas detection using quantum cascade laser photoacoustic spectroscopy.

Abstract: We report high-throughput, nondispersive optical multiplexing of laser beams using a scanning galvanometer. We have utilized this technique for multispecies trace-gas detection using multiple quantum cascade laser photoacoustic spectroscopy. We demonstrate switching from one laser to another in less than 1 s, a performance level needed for a comprehensive multispecies sensor, and a high signal-to-noise ratio detection of five gaseous components, NH3, NO2, dimethyl methyl phosphonate (DMMP, a simulant for nerve agents), acetone, and ethylene glycol, in a room air gas mixture containing ~3 ppb of NH3, ~8 ppb of NO2, ~20 ppb of DMMP, ~30 ppb of acetone, and ~40 ppb of ethylene glycol.

Photoacoustic probing of fluorophore excited state lifetime with application to oxygen sensing.

Abstract: A new method is developed to perform local measurements of fluorophore excited state lifetimes in turbid media without collecting the fluorescence emission. The method is based on a pump-probe approach where a first laser pulse excites the dye and then a second laser pulse is used for photoacoustic probing of the transient absorption. The photoacoustic response generated by the probe pulse is recorded by an ultrasound receiver. Repeating the measurement for increasing pump-probe time delays yields a series of photoacoustic signals that are used to extract the lifetime of the excited state. The method is validated by measuring the lifetime of an oxygen sensitive dye solution at different concentrations of dissolved oxygen. The dye is pumped with a 532-nm pulsed laser and the transient absorption at 740 nm is probed using a second pulsed laser system. The photoacoustic-based results are in close agreement with those obtained from time-dependent fluorescent measurements. The method can be extended to photoacoustic lifetime imaging by using a receiver array instead of a single receiver. Potential applications of this method include tissue oxygen imaging for cancer diagnostics and mapping molecular events such as resonant energy transfer and ion collisions in a biological environment.

Optical methods for measurements of skin penetration.

Abstract: Fourier transform infrared photoacoustic (PAS), photothermal deflection (PDS) and Raman spectroscopy belong to the modern innovative noninvasive analytical tools that are beginning to be recognized as

Fourier Transform Infrared Measurement of Solid-, Liquid-, and Gas-Phase Samples with a Single Photoacoustic Cell

Abstract: A photoacoustic detector based on the optical cantilever microphone has been built. The detector is capable of measuring solid-, liquid-, and gas-phase samples. Photoacoustic Fourier transform infrared (FT-IR) measurement with three samples in different phases was demonstrated. Example samples were polyethene, sunflower oil, and methane. The sensitivity of the cell was compared to a commercial photoacoustic FT-IR detector. With the standard carbon black sample the cantilever detector gave approximately five times higher signal-to-noise ratio than the reference detector. The sensitivity with methane was also compared to the DTGS detector of the FT-IR instrument corresponding to an absorption path of 6.3 cm. Simulation of the photoacoustic signal showed that a compromise has to be made in the cell design between sensitivity for solid- and gas-phase samples but it is possible to highly enhance the sensitivity for all types of samples by reducing cantilever dimensions.

Semiconductor Laser Based Trace Gas Sensor Technology: Recent Advances and Applications

Abstract: Recent advances in the development of sensors based on infrared diode and quantum cascade lasers for the detection of trace gas species is reported. Several examples of applications in environmental and industrial process monitoring as well as in medical diagnostics using quartz enhanced photoacoustic spectroscopy and laser absorption spectroscopy will be described.

Method and gas sensor for performing quartz-enhanced photoacoustic spectroscopy

Abstract: The present invention targets gas sensors based on quartz-enhanced photo-acoustics, notably for applications where a very low price procial. The underlying idea is to replace the photo diode normally used for laser intensity measurement by the wall noise which is generated on the tuning fork. This eliminates the costs of the photo diode. The wall noise generated by the laser beam incident on the tuning fork is proportional to the intensity of the laser beam. Depending on the gas to be measured the wall noise signal can be separated from the gas concentration signal by using only one fork or a second fork preferably behind the first fork.

Photoacoustic spectroscopy system

Abstract: A system for providing photoacoustic spectroscopy. A light source having a quantum dot filter may provide a band of infrared light which is to be reflected by a lamellar grating to a photoacoustic chamber. The light may be modulated by the grating. The chamber may contain a sample of fluid for which spectral information is sought. A sensor may detect acoustic pressures in the chamber which indicate the spectral information. Signals from the sensor may be processed and displayed. Identification and concentration of certain substances in the fluid may be obtained.

Advanced Quartz-Enhanced Photoacoustic Trace Gas Sensor for Early Fire Detection

Abstract: A spectroscopic trace gas sensor using a distributed feedback diode laser at λ=1.53 μm and based on quartz enhanced photoacoustic spectroscopy technique is described. The sensor is capable of quasi-simultaneous quantification of trace ammonia, hydrogen cyanide, and acetylene (NH3, HCN, and C2H2, respectively) concentrations at ~100 ppbv levels with a 4s integration time. The sensor design, responsivity, noise, and crosstalk characteristics are reported.

Online Monitoring of Exhaled Breath Using Mid-Infrared Laser Spectroscopy

Abstract: This review describes the merits of laser-assisted analytical instrumentation for biomedical diagnostics. In particular, we present an overview of the recent progress on spec- troscopic online monitoring of exhaled breath with mid-infrared coherent sources. The current detection limits of laser spectroscopic approaches are in the picomolar to nanomolar range, de- pending on the molecular compound. The time resolution of the measurements is down to the sub-second range. This very high sensitivity and time resolution open up exciting perspectives for novel analytical tasks in biomedical research and clinical diagnosis.

Pressure-induced line broadening for the (30012)’(00001) band of CO2 measured with tunable diode laser photoacoustic spectroscopy

Abstract: Pressure-induced foreign-broadening lineshape parameters of the carbon dioxide rovibrational transitions belonging to the (30012)←(00001) overtone band near the 1.573 μm wavelength region are measured by using a tunable diode laser photoacoustic spectrometer. The spectroscopic analysis has concerned the first 11 lines of the R branch. For these lines, the air- and Ar-broadening coefficients are measured at room temperature (∼298 K). The measured broadening coefficients of all the transitions of 12 C 16 O 2 are compared with those given in the HITRAN04 database and former measurements with a different spectroscopic method. Agreements and discrepancies are underlined and briefly discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficient of carbon dioxide transitions.

Mid-infrared photoacoustic spectroscopy of solids using an external-cavity quantum-cascade laser.

Abstract: We describe the use of a pulsed external-cavity quantum-cascade laser (EC-QCL) for the acquisition of mid-IR photoacoustic (PA) spectra of solids. The EC-QCL employed in this work operates from 990 to 1075 cm−1 (9.30–10.10 μm). A gas-microphone PA cell was used as the detector, and the signal was demodulated using a lock-in amplifier. PA EC-QCL spectra of solids display bands significantly narrower than those in corresponding PA Fourier transform infrared spectra.

Discrimination of transgenic and conventional soybean seeds by fourier transform infrared photoacoustic spectroscopy.

Abstract: polymers and solutes, which leads to a strong partitioning effect, would actually slow down the diffusion process. The attraction force between the solution and the matrix becomes the molecular friction for the diffusion. Furthermore, those molecules that partition in the hair are larger than acetonitrile and 1-pentanenitrile. The size of the molecule could also contribute to the effect on the speed of diffusion as well as the molecular structure, like the difference between aliphatic hydrocarbons versus aromatic hydrocarbons. This brief study has illustrated the potential of this novel approach to investigate diffusion of solutes into micro fibers, such as human hair, in situ. The system could be further optimized by noting that a large area of the image was redundant in the analysis. A smaller FPA detector (e.g., a 32 3 32 array) would have collected the same information for a much shorter measurement time, and hence, a better temporal resolution. On the other hand, the large area measured could have been utilized for high throughput measurements by arranging several cross-sections of hair in the image field of view. Diffusion studies of different hair types or simply a larger number of repeat measurements can be carried out in parallel. Nevertheless, the idea of using this approach to study the diffusion of solutes in hair has been demonstrated. In summary, we have demonstrated the potential of in situ FT-IR spectroscopic imaging to study the diffusion of chemicals across the hair cross-section. All spectra were measured simultaneously, enabling the study of dynamic systems. The study of the diffusion of four model chemicals, acetonitrile, 1-pentanenitrile, 4-cyanophenol, and 4-cyanobenzoic acid, into hair cross-sections has been demonstrated. 4Cyanophenol and 4-cyanobenzoic acid require a much longer time to complete the diffusion process owing to their relatively larger molecular sizes and the possibility of the formation of Hbonds with the polar groups of the hair proteins. It is possible to further optimize this study by using a smaller FPA array for a better temporal resolution or arranging more hair crosssections into the field of view of the detector for high throughput studies. The demonstrated in situ approach can be applied to a wide range of diffusion studies, not limited to hair cross-sections but applicable to any biological tissues.

Photoacoustic Spectroscopy to determine in vitro the non radiative relaxation time of protoporphyrin IX solution containing gold metallic nanoparticles

Abstract: In order to compare the non radiative relaxation time (NRRT) between standard protoporphyrin IX (PpIX) and protoporphyrin PpIX(1) solution containing gold metallic nanoparticles, we measured the photoacoustic spectroscopy (PAS) signal phase to determine, for each solution, the NRRT by using the Rosencwaig-Gesho theory, modified to include the effect of a finite non radiative deexcitation time. A NRRT average value, obtained for each solution, is reported and compared with some NRRT of triplet states reported in the literature for molecules with the same tetrapyrrolic structure. In the study was used PpIX disodium salt (DS) solution of 25% HCL. From each solution it was obtained its optical absorption spectrum, by using a UV-Vis spectrophotometer. After this, in the maximum observed optical absorption peak (404 nm), it was obtained the Photoacoustic (PA) signal phase as a function of the light modulation frequency, from 17 to 80 Hz. Our investigations are devoted to the improvement of the thermal treatments of drugs for medical applications.

Application of optical coherence tomography, pulsed photoacoustic technique, and time-of-flight technique to detect changes in the scattering properties of a tissue-simulating phantom.

Abstract: Intralipid is a well-known emulsion used as a tissue-simulating phantom in developing optical imaging and diagnostic techniques for medical applications. The optical coherence tomography (OCT), pulsed photoacoustic (PA), and time-of-flight (TOF) techniques were used to detect glucose-induced changes in the optical properties of Intralipid. A comparison of the applicability of these techniques to register changes in the scattering properties of Intralipid samples showed that OCT is the most effective method, whereas the sensitivity of the PA technique was less pronounced. Photon migration studies with the TOF technique showed changes in pulse amplitude, pulse width, and arrival time of the pulse maximum as a function of changes in Intralipid concentration. Also the measured signal parameters showed changes when measuring high glucose concentrations.

Molecular relaxation effects in hydrogen chloride photoacoustic detection

Abstract: A photoacoustic (PA) sensor has been developed to monitor hydrogen chloride at sub-ppm level in the 1740-nm region The system was designed to control the process in the novel low-water-peak optical fiber manufacturing process Relaxation effects in hydrogen chloride PA detection in oxygen–helium and nitrogen–helium gas mixtures are presented, showing that the generation of the PA signal is strongly affected by the ratio of these substances In addition, the role of water vapor in the PA signal is investigated

Modeling and Numerical Investigation of Photoacoustic Resonators

Abstract: Photoacoustic spectroscopy is based on the photoacoustic effect, that was discovered in 1880 by A. G. Bell (Bell, 1880). One year later, W. C. Rontgen published a paper on the application of photoacoustic spectroscopy on gas (Rontgen, 1881). Sensors based on the photoacoustic effect are devices which allow the detection of molecules of very low concentration. It is even possible to discriminate different isotopes of one molecule. In a photoacoustic sensor (PAS) a gas sample contained in the measuring cell is subjected to a laser beam. The wavelength of the laser is tuned to a vibrational or rotational line of the searched molecules. The technique takes advantage of the fact, that absorbed electromagnetic radiation is due to non-radiant transitions partially transferred into thermal energy of the surrounding molecules. This leads to an increase of the pressure in the sample. A modulated emission generates a sound wave. The resulting acoustic wave is detected by a microphone and phase-sensitively measured. A typical set-up for photoacoustic investigation is shown in Figure 1. To detect low molecule concentrations one enhances the microphone signal by utilizing the acoustic resonances of the measuring chamber. The achievable amplification depends on the shape of the resonator and on the precise coupling of the laser profile and the acoustic modes. Experimental investigations of different PAS set-ups are very time consuming and expensive. Addressing the related questions numerically is much more efficient. The theoretical treatment of PAS has a long history. Analytical calculations have been performed for cylinder shaped resonators, which play an important role among the variety of measuring chambers. Resonator shapes of higher complexity, however, are not amenable to these methods. Numerical techniques like the finite element method (FEM) represent a suitable tool to investigate such systems. Generally, the investigation of the excited gas requires the solution of a system of coupled partial differential equations. The FEM allows the treatment of such coupled problems. However, this is rather computer time consuming and, considering the numerous design variants, should be avoided. In literature, methods are discussed, that allow to circumvent the coupled problem. We combine these methods with the FEM and are now able to calculate the photoacoustic signal for arbitrary resonator shapes. This offers the possibility