Showing papers on "Photoacoustic spectroscopy published in 2013"
TL;DR: A preliminary test with healthy volunteers and volunteers suffering from diabetes mellitus demonstrates the viability of a noninvasive glucose monitoring for patients based on the combination of infrared QCL and photoacoustic detection.
Abstract: The noninvasive determination of glucose in the interstitial layer of the human skin by mid-infrared spectroscopy is reported. The sensitivity for this measurement was obtained by combining the high pulse energy from an external cavity quantum cascade laser (EC-QCL) tunable in the infrared glucose fingerprint region (1000–1220 cm–1) focused on the skin, with a detection of the absorbance process by photoacoustic spectroscopy in the ultrasound region performed by a gas cell coupled to the skin. This combination facilitates a quantitative measurement for concentrations of skin glucose in the range from 300 mg/dL, which is the relevant range for the glucose monitoring in diabetes patients. Since the interstitial fluid glucose level is representative of the blood glucose level and follows it without significant delay (<10 min), this method could be applied to establish a noninvasive, painless glucose measurement procedure that is urgently awaited by diabetes patients. We report here the design o...
177 citations
TL;DR: Under the optimized conditions described herein and using commercially available detectors, photoacoustic microscopy can detect as few as 100s of oxygenated hemoglobin molecules, and realizable improvements to the detector may enable single molecule detection of select molecules.
Abstract: The fundamental limitations of photoacoustic microscopy for detecting optically absorbing molecules are investigated both theoretically and experimentally. We experimentally demonstrate noise-equivalent detection sensitivities of 160,000 methylene blue molecules (270 zeptomol or 2.7×10^(−19) mol) and 86,000 oxygenated hemoglobin molecules (140 zeptomol) using narrowband continuous-wave photoacoustics. The ultimate sensitivity of photoacoustics is fundamentally limited by thermal noise, which can present in the acoustic detection system as well as in the medium itself. Under the optimized conditions described herein and using commercially available detectors, photoacoustic microscopy can detect as few as 100s of oxygenated hemoglobin molecules. Realizable improvements to the detector may enable single molecule detection of select molecules.
102 citations
TL;DR: Results suggest that photoacoustic imaging can be used to selectively detect the presence of monomers, and the implementation of the monomer–dimer contrast mechanism for the development of an enzyme-specific activatable probe is discussed.
Abstract: Activatable photoacoustic probes efficiently combine the high spatial resolution and penetration depth of ultrasound with the high optical contrast and versatility of molecular imaging agents. Our approach is based on photoacoustic probing of the excited-state lifetime of methylene blue (MB), a fluorophore widely used in clinical therapeutic and diagnostic applications. Upon aggregation, static quenching between the bound molecules dramatically shortens their lifetime by three orders of magnitude. We present preliminary results demonstrating the ability of photoacoustic imaging to probe the lifetime contrast between monomers and dimers with high sensitivity in cylindrical phantoms. Gradual dimerization enhancement, driven by the addition of increasing concentrations of sodium sulfate to a MB solution, showed that lifetime-based photoacoustic probing decreases linearly with monomer concentration. Similarly, the addition of 4 mM sodium dodecyl sulfate, a concentration that amplifies MB aggregation and reduces the monomer concentration by more than 20-fold, led to a signal decrease of more than 20 dB compared to a solution free of surfactant. These results suggest that photoacoustic imaging can be used to selectively detect the presence of monomers. We conclude by discussing the implementation of the monomer-dimer contrast mechanism for the development of an enzyme-specific activatable probe.
85 citations
TL;DR: Clear improvements in the magnitude and resolution of reconstructed photoacoustic images are seen when acoustic attenuation compensation is applied, using time-variant filtering.
Abstract: Most reconstruction algorithms used in photoacoustic tomography do not account for the effects of acoustic attenuation on the recorded signals. For experimental measurements made in biological tissue, the frequency dependent acoustic attenuation causes high frequency components of the propagating photoacoustic waves to be significantly reduced. This signal loss manifests as a depth dependent magnitude error and blurring of features within the reconstructed image. Here, a general method for compensating for this attenuation using time-variant filtering is presented. The time-variant filter is constructed to correct for acoustic attenuation and dispersion following a frequency power law under the assumption the distribution of attenuation parameters is homogeneous. The filter is then applied directly to the recorded time-domain signals using a form of nonstationary convolution. Regularization is achieved using a time-variant window where the cutoff frequency is based on the local time-frequency distribution of the recorded signals. The approach is computationally efficient and can be used in combination with any detector geometry or reconstruction algorithm. Numerical and experimental examples are presented to illustrate the utility of the technique. Clear improvements in the magnitude and resolution of reconstructed photoacoustic images are seen when acoustic attenuation compensation is applied.
81 citations
TL;DR: It is demonstrated here that this approach can be used for continuous and non- invasive monitoring of the glucose level in human epidermis, and thus may form the basis for a non-invasive monitoring for diabetes patients.
Abstract: The application of a novel open, windowless cell for the photoacoustic infrared spectroscopy of human skin is described. This windowless cavity is tuned for optimum performance in the ultrasound range between 50 and 60 kHz. In combination with an external cavity tunable quantum cascade laser emitting in the range from ~1000 cm(-1) to 1245 cm(-1), this approach leads to high signal-to-noise-ratio (SNR) for mid-infrared spectra of human skin. This opens the possibility to measure in situ the absorption spectrum of human epidermis in the mid-infrared region at high SNR in a few (~5) seconds. Rapid measurement of skin spectra greatly reduces artifacts arising from movements. As compared to closed resonance cells, the windowless cell exhibits the advantage that the influence of air pressure variations, temperature changes, and air humidity buildup that are caused by the contact of the cell to the skin surface can be minimized. We demonstrate here that this approach can be used for continuous and non-invasive monitoring of the glucose level in human epidermis, and thus may form the basis for a non-invasive monitoring of the glucose level for diabetes patients.
76 citations
TL;DR: This study suggests that chromoproteins may have potential for providing genetically encoded photoacoustic contrast, by synthesizing and characterizing a range of commonly used fluorescent proteins and novel non-fluorescent chromoprotein and genetic expression of a chromop protein in mammalian cells.
Abstract: Genetically expressed fluorescent proteins have been shown to provide photoacoustic contrast. However, they can be limited by low photoacoustic generation efficiency and low optical absorption at red and near infrared wavelengths, thus limiting their usefulness in mammalian small animal models. In addition, many fluorescent proteins exhibit low photostability due to photobleaching and transient absorption effects. In this study, we explore these issues by synthesizing and characterizing a range of commonly used fluorescent proteins (dsRed, mCherry, mNeptune, mRaspberry, AQ143, E2 Crimson) and novel non-fluorescent chromoproteins (aeCP597 and cjBlue and a non-fluorescent mutant of E2 Crimson). The photoacoustic spectra, photoacoustic generation efficiency and photostability of each fluorescent protein and chromoprotein were measured. Compared to the fluorescent proteins, the chromoproteins were found to exhibit higher photoacoustic generation efficiency due to the absence of radiative relaxation and ground state depopulation, and significantly higher photostability. The feasibility of converting an existing fluorescent protein into a non-fluorescent chromoprotein via mutagenesis was also demonstrated. The chromoprotein mutant exhibited greater photoacoustic signal generation efficiency and better agreement between the photoacoustic and the specific extinction coefficient spectra than the original fluorescent protein. Lastly, the genetic expression of a chromoprotein in mammalian cells was demonstrated. This study suggests that chromoproteins may have potential for providing genetically encoded photoacoustic contrast.
68 citations
TL;DR: In this article, the suitability of photoacoustic spectroscopy (PAS) for aerosol absorption measurement at high relative humidity (RH) was evaluated and the bias was attributed to water evaporation impacting the PAS signal.
Abstract: Laboratory experiments were conducted to assess the suitability of photoacoustic spectroscopy (PAS) for aerosol absorption measurement at high relative humidity (RH). Initial experiments characterized the PAS sensitivity that increased strongly by ∼1.25 between dry conditions and 90% RH. Correction procedures were validated by measuring RH-independent absorption for hydrophobic absorbing particles. Absorption measured by PAS for a range of hygroscopic particles, including different morphologies, hygroscopicities, and absorbing entities, showed strong low biases at high RH (down to 0.4 at 90% RH). The bias was due to water evaporation impacting the PAS signal. Cooling samples to lower absolute humidity while maintaining a constant RH did not significantly reduce the bias magnitude within the temperature range 11–25°C. The magnitude and RH dependence of the bias were not reproduced well using a model of PAS response incorporating coupled heat and mass transfer in the transition regime. This was attributed, ...
65 citations
TL;DR: In this paper, an external cavity quantum cascade laser (EC-QCL) coupled with a mid-infrared (mid-IR) fiber and quartz enhanced photoacoustic spectroscopy (QEPAS) is described.
Abstract: An innovative spectroscopic system based on an external cavity quantum cascade laser (EC-QCL) coupled with a mid-infrared (mid-IR) fiber and quartz enhanced photoacoustic spectroscopy (QEPAS) is described. SF6 has been selected as a target gas in demonstration of the system for trace gas sensing. Single mode laser delivery through the prongs of the quartz tuning fork has been obtained employing a hollow waveguide fiber with inner silver–silver iodine (Ag–AgI) coatings and internal core diameter of 300 μm. A detailed design and realization of the QCL fiber coupling and output collimator system allowed almost practically all (99.4 %) of the laser beam to be transmitted through the spectrophone module. The achieved sensitivity of the system is 50 parts per trillion in 1 s, corresponding to a record for QEPAS normalized noise-equivalent absorption of 2.7 × 10−10 W cm−1 Hz−1/2.
63 citations
TL;DR: Highly sensitive cantilever-enhanced photoacoustic detection of hydrogen cyanide and methane in the mid-infrared region is demonstrated.
Abstract: Highly sensitive cantilever-enhanced photoacoustic detection of hydrogen cyanide and methane in the mid-infrared region is demonstrated. A mid-infrared continuous-wave frequency tunable optical parametric oscillator was used as a light source in the experimental setup. Noise equivalent detection limits of 190 ppt (1 s) and 65 ppt (30 s) were achieved for HCN and CH(4), respectively. The normalized noise equivalent absorption coefficient is 1.8 × 10(-9) W cm(-1) Hz(-1/2).
61 citations
TL;DR: It is found that the photoacoustic signal from aggregated silica-coated gold nanoparticles is greatly enhanced in comparison to disperse silica -coatedgold nanoparticles.
Abstract: Photoacoustic imaging, using targeted plasmonic metallic nanoparticles, is a promising noninvasive molecular imaging method. Analysis of the photoacoustic signal generated by plasmonic metallic nanoparticles is complex because of the dependence upon physical properties of both the nanoparticle and the surrounding environment. We studied the effect of the aggregation of gold nanoparticles on the photoacoustic signal amplitude. We found that the photoacoustic signal from aggregated silica-coated gold nanoparticles is greatly enhanced in comparison to disperse silica-coated gold nanoparticles. Because cellular uptake and endocytosis of nanoparticles results in their aggregation, these results have important implications for the application of plasmonic metallic nanoparticles towards quantitative molecular imaging.
60 citations
TL;DR: Compared to other approaches, the photoacoustic thermometric method has the advantage of not requiring custom-developed temperature-sensitive biosensors, which should facilitate the conversion of single-cell thermometry into a routine lab tool and make it accessible to a much broader biological research community.
Abstract: A novel photoacoustic thermometric method is presented for simultaneously imaging cells and sensing their temperature. With three-seconds-per-frame imaging speed, a temperature resolution of 0.2°C was achieved in a photo-thermal cell heating experiment. Compared to other approaches, the photoacoustic thermometric method has the advantage of not requiring custom-developed temperature-sensitive biosensors. This feature should facilitate the conversion of single-cell thermometry into a routine lab tool and make it accessible to a much broader biological research community.
TL;DR: A blue light-emitting diode (LED)-based incoherent broad- band cavity-enhanced spectroscopy (IBBCEAS) approach for broad-band measurements of wavelength-resolved aerosol extinction over the spectral range of 445-480 nm and allows for simultaneous measurement of trace gases absorption present in the air sample using the same instrument.
Abstract: Despite the significant progress in the measurements of aerosol extinction and absorption using spectroscopy approaches such as cavity ring-down spectroscopy (CRDS) and photoacoustic spectroscopy (PAS), the widely used single-wavelength instruments may suffer from the interferences of gases absorption present in the real environment. A second instrument for simultaneous measurement of absorbing gases is required to characterize the effect of light extinction resulted from gases absorption. We present in this paper the development of a blue light-emitting diode (LED)-based incoherent broad-band cavity-enhanced spectroscopy (IBBCEAS) approach for broad-band measurements of wavelength-resolved aerosol extinction over the spectral range of 445-480 nm. This method also allows for simultaneous measurement of trace gases absorption present in the air sample using the same instrument. On the basis of the measured wavelength-dependent aerosol extinction cross section, the real part of the refractive index (RI) can be directly retrieved in a case where the RI does not vary strongly with the wavelength over the relevant spectral region. Laboratory-generated monodispersed aerosols, polystyrene latex spheres (PSL) and ammonium sulfate (AS), were employed for validation of the RI determination by IBBCEAS measurements. On the basis of a Mie scattering model, the real parts of the aerosol RI were retrieved from the measured wavelength-resolved extinction cross sections for both aerosol samples, which are in good agreement with the reported values. The developed IBBCEAS instrument was deployed for simultaneous measurements of aerosol extinction coefficient and NO(2) concentration in ambient air in a suburban site during two representative days.
TL;DR: In this paper, the standoff photoacoustic spectrum of hazardous molecules adsorbed at diffused surfaces from a distance of up to 25m was recorded for a Signal to Noise Ratio (SNR) of 10.
TL;DR: In this paper, a photoacoustic ozone sensor based on quartz-enhanced photo-acoustic spectroscopy is presented, where instead of a laser, a UV-LED at 285 nm is utilized as light source.
Abstract: A photoacoustic ozone sensor based on quartz-enhanced photoacoustic spectroscopy is presented. Instead of a laser, a UV-LED at 285 nm is utilized as light source. Using an acoustical resonator in off-beam configuration, it is feasible to align the light of the LED through the resonator tube. The sensor is integrated in a miniaturized flow-through gas cell which allows fast gas exchange. The sensor performance and the influence of the speed of sound on the measurement signal are investigated. For the detection of ozone in the Hartley band, a detection limit of S = 1.27 ± 0.08 ppmv (1σ) and a noise equivalent absorption sensitivity of D = (3.02 × 10−8 ± 1 × 10−10) cm−1W(Hz)−1/2 have been achieved.
TL;DR: In this paper, a photoacoustic spectroscopy-based detector of hydrogen sulfide (H2S) in biogas, natural gas and oil process technology is described, which is capable of measuring H2S concentrations over four orders of magnitude (from a few ppm level up to several per cent) in changing gas mixtures.
Abstract: This paper describes a photoacoustic spectroscopy-based detector of hydrogen sulfide (H2S) in biogas, natural gas and oil process technology. The instrument is capable of measuring H2S concentrations over four orders of magnitude (from a few ppm level up to several per cent) in changing gas mixtures. Problems caused by harsh industrial circumstances, contamination and widely varying composition of gases can be overcome by optimizing wavelength modulation, resonance frequency tracking and an easy-to-use method enabling in situ monitoring calibration. A diode laser emitting around 1.57 µm served as the excitation source; at this wavelength spectral overlap between H2S and CO2 is substantial. Spectral interference was eliminated by optimizing the amplitude of wavelength modulation; furthermore, a simplified calibration method was implemented taking advantage of a nearby absorption line of CO2 providing fast and economical measurements. Frequency dependence of the photoacoustic signal was determined by two methods to ensure accuracy. For 10 s integration time and 6800 Hz modulation frequency, the minimum detectable concentration was 6 ppm (3σ).
TL;DR: A new DND by He+ ion beam irradiation with very high NIR absorption was synthesized, which produced a 71-fold higher PA signal on a molar basis than similarly dimensioned gold nanorods and could be clearly imaged 3 mm below the skin surface with PA signal enhancement of 567% using an 820-nm laser wavelength.
Abstract: Radiation-damaged nanodiamonds (DNDs) are potentially ideal optical contrast agents for photoacoustic (PA) imaging in biological tissues due to their low toxicity and high optical absorbance. PA imaging contrast agents have been limited to quantum dots and gold particles, since most existing carbon-based nanoparticles, including fluorescent nanodiamonds, do not have sufficient optical absorption in the near-infrared (NIR) range. A new DND by He þ ion beam irradiation with very high NIR absorption was synthesized. These DNDs produced a 71-fold higher PA signal on a molar basis than similarly dimensioned gold nanorods, and 7.1 fmol of DNDs injected into rodents could be clearly imaged 3 mm below the skin surface with PA signal enhancement of 567% using an 820-nm laser wavelength. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.
TL;DR: This cross-correlation-based method to quantitatively measure transverse flow velocity using optical resolution photoacoustic (PA) microscopy enhanced with a digital micromirror device shows an accuracy of 0.35 mm/s at 0.3-mm depth in scattering chicken breast, making it promising for measuring flow in biological tissue.
Abstract: A cross-correlation-based method is proposed to quantitatively measure transverse flow velocity using optical resolution photoacoustic (PA) microscopy enhanced with a digital micromirror device (DMD). The DMD is used to alternately deliver two spatially separated laser beams to the target. Through cross-correlation between the slow-time PA profiles measured from the two beams, the speed and direction of transverse flow are simultaneously derived from the magnitude and sign of the time shift, respectively. Transverse flows in the range of 0.50 to 6.84 mm/s 6.84 mm/s are accurately measured using an aqueous suspension of 10-μm-diameter microspheres, and the root-mean-squared measurement accuracy is quantified to be 0.22 mm/s
0.22 mm/s. The flow measurements are independent of the particle size for flows in the velocity range of 0.55 to 6.49 mm/s
6.49 mm/s, which was demonstrated experimentally using three different sizes of microspheres (diameters: 3, 6, and 10 μm). The measured flow velocity follows an expected parabolic distribution along the depth direction perpendicular to the flow. Both maximum and minimum measurable velocities are investigated for varied distances between the two beams and varied total time for one measurement. This technique shows an accuracy of 0.35 mm/s
0.35 mm/s at 0.3-mm depth in scattering chicken breast, making it promising for measuring flow in biological tissue.
TL;DR: In this paper, a cantilever enhanced photoacoustic spectrometer with mid-infrared quantum cascade laser was applied for selective and sensitive formaldehyde (CH2O) gas measurement.
Abstract: A novel cantilever enhanced photoacoustic spectrometer with mid-infrared quantum cascade laser was applied for selective and sensitive formaldehyde (CH2O) gas measurement. The spectrum of formaldehyde was measured from 1,772 to 1,777 cm−1 by tuning the laser with a spectral resolution of 0.018 cm−1. The band at 1,773.959 cm−1 was selected for data analysis, at which position the laser emitted 47 mW. In univariate measurement, the detection limit (3σ, 0.951 s) and the normalized noise equivalent absorption coefficient (3σ) for amplitude modulation (AM) were 1.6 ppbv and 7.32 × 10−10 W cm−1 (Hz)−1/2 and for wavelength modulation (WM) 1.3 ppbv and 6.04 × 10−10 W cm−1 (Hz)−1/2. In multivariate measurement, the detection limit (3σ) can be as low as 901 pptv (1,773.833–1,774.085 cm−1, 15 spectral points each 0.951 s) for AM and 623 pptv (1,773.743–1,774.265 cm−1, 30 spectral points each 0.951 s) for WM. Because measurement time increases in multivariate measurement, its application is justified only when interferents need to be resolved. Potential improvements of the system are discussed.
TL;DR: In this paper, a compact measurement system based on a combination of cantilever enhanced photoacoustic spectroscopy (CEPAS) and optical parametric oscillator (OPO) was applied to the gas phase measurement of benzene, toluene, and o-, m- and p- xylene (BTX) traces.
TL;DR: The ability of the hydrophobic functional groups in the polyacrylamide matrix to shield the molecular dye from being affected by the proteins in the plasma, and prevent the dye from leaching out, is demonstrated.
Abstract: Presented here is a novel method of in vivo pH sensing utilizing a hybrid optical imaging technique, photoacoustic imaging (PAI), and pH sensitive polymeric nanoprobes. Nanoprobes with hydrophobic core containing a pH sensitive dye were synthesized and used to measure the pH level ex vivo first and then in vivo by performing experiments on a rat joint model, with an achieved precision of less than 0.1 pH units. The ability of the hydrophobic functional groups in the polyacrylamide matrix to shield the molecular dye from being affected by the proteins in the plasma, and prevent the dye from leaching out, is also demonstrated.
16 Jun 2013
TL;DR: In this paper, a piezoelectric micromachined ultrasonic transducer (pMUT) array designed for photoacoustic imaging is presented, which consists of 0.6μm PZT layer, 1μm elastic layer (SiO2) and 5μm supporting layer.
Abstract: A piezoelectric micromachined ultrasonic transducer (pMUT) array designed for photoacoustic imaging is presented in this paper. Two-dimensional pMUT arrays containing 144 elements (12×12 array) were bulk micromachined in silicon substrate. The devices were formed using two backside masks with deep reactive ion etching to create PZT thin film membranes and suspended silicon beams. The membrane radius is 25μm, with an 80μm element pitch. The total area for the pMUT array is approximately 1.6×1.6mm2. This membrane consists of 0.6μm PZT layer, 1μm elastic layer (SiO2) and 5μm supporting layer. Impedence and vibration measurements shows the resonant frequency of the pMUT elements is around 10MHz. Acoustic signal is detected using Pulse-Echo method. This high density acoustic sensor array has high array spatial gain and wide reception angle that can be used in photoacoustic imaging systems.
TL;DR: In this paper, the discharge feature gases, such as C 2 H 2, CH 4, CO 2 and H 2 O, were measured with a tunable laser photoacoustic spectrometer at the 1530.3709nm transition line.
TL;DR: A versatile, continuous wave, optical parametric oscillator-based spectrometer is successfully tested for the detection of hydrogen cyanide emission from clover leaves, and Pseudomonas bacteria; in addition, the presence of HCN in exhaled human breath is measured.
Abstract: A versatile, continuous wave, optical parametric oscillator is used in combination with photoacoustic spectroscopy for long-term trace gas experiments of volatile compounds emitted by biological samples. The optical parametric oscillator-based spectrometer (wavelength near 3 μm, 8-MHz linewidth, output power ∼1 W) is suc- cessfully tested for the detection of hydrogen cyanide (HCN) emission from clover leaves, and Pseudomonas bac- teria; in addition, the presence of HCN in exhaled human breath is measured. For specific experiments, the spectrometer is operated continuously up to 10 days and has a detection limit of 0.4 parts-per-billion volume of HCN in air over 10 s, using the P8 rotational line in the ν3 vibrational band of HCN at 3287.25 cm −1 . This results in an overall sensitivity of the system of 2.5 × 10 −9 cm −1 Hz −1∕2 . © 2013 Society of Photo-Optical Instrumentation
TL;DR: In vivo dynamic process imaging using a label-free real-time optical-resolution photoacoustic microscope (OR-PAM) with ability to provide sustained imaging with near real- time feedback for focusing and positioning is demonstrated.
Abstract: The authors demonstrate in vivo dynamic process imaging using a label-free real-time optical-resolution photoacoustic microscope (OR-PAM). This reflection-mode system takes advantage of a 532-nm fiber laser source with a high pulse repetition rate of up to 600 kHz combined with a fast-scanning mirror system. Microvasculature in SCID mouse ears is imaged at near real-time (0.5 fps) for a 1×1 mm 2 field of view (FOV) with micron-scale lateral resolution. We also demonstrate imaging of cardiac-induced microhemodynamics in murine microvasculature at real-time frame-rates (30 fps) over a 250×250 μm 2 FOV using real-time C-scan OR-PAM with ability to provide sustained imaging with near real-time feedback for focusing and positioning.
TL;DR: In this article, the nonlinear scattering properties of carbon black suspensions (CBS) were studied using nanosecond photoacoustic (PA) and optical z-scan techniques, and the effective nonlinear extinction coefficients of CBS were determined.
Abstract: Nonlinear scattering properties of carbon black suspensions (CBS) are studied using nanosecond photoacoustic (PA) and optical z-scan techniques. When the laser is operated in multi-pulse mode, no nonlinear behavior is observed in PAZ-scans. However, in the single-pulse mode, we observed the nonlinear scattering in both PAZ and optical z- scans. Our results are in agreement with the well-known bleaching effect in CBS and demonstrate the importance of pulse repetition frequency for studying nonlinear scattering using photoacoustics. The effective nonlinear extinction coefficients of CBS were determined, and we found that PAZ-scan data are more sensitive and offer information on higher nonlinearities.
TL;DR: Specific features of cysts compared to malignancies are revealed, which can be exploited for discrimination of the two abnormalities in future modifications of the imager.
Abstract: In the search for improved imaging modalities for detection and diagnosis of breast cancer, a high negative prediction value is also important. Photoacoustic (optoacoustic) imaging is a relatively new technique that has high potential for visualizing breast malignancies, but little is known about the photoacoustic appearance of benign lesions. In this work, we investigate the visibility of benign breast cysts in forward-mode photoacoustic mammography using 1064-nm light, as currently applied in the Twente photoacoustic mammoscope. Results from (Monte Carlo and k-wave) simulations and phantom measurements were used to interpret results from patient measurements. There was a strong agreement among the results from simulations, phantom, and patient measurements. Depending on the absorption contrast between cyst and breast tissue, cysts were visible as either one or two confined high-contrast areas representing the front and the back of the cyst, respectively. This edge enhancement is most likely the consequence of the local sudden change in the absorbed energy density and Gruneisen coefficients. Although the current forward-mode single-wavelength photoacoustic mammoscope cannot always unambiguously discriminate cysts from malignancies, this study reveals specific features of cysts compared to malignancies, which can be exploited for discrimination of the two abnormalities in future modifications of the imager
TL;DR: In this article, the authors demonstrated the potential of using high power LEDs as an inexpensive and compact excitation source for biomedical photoacoustics and demonstrated the possibility of acquiring multi-wavelength data sets simultaneously when using Golay excitation methods.
Abstract: absorption is weak ( 10Watt peak power) are however not available in this wavelength range. High power LEDs could be a potential alternative as they are widely available in the visible wavelength range (400nm to 632nm) and relatively cheap. High power LEDs are generally operated in continuous wave mode and provide average powers of several Watts. The possibility of over driving them by tens of times their rated current when driven at a low duty cycle (<1%), offers the prospect of achieving similar pulse energies (tens of µJ) to that provided by high peak power pulsed laser diodes. To demonstrate the possibility of using high power LEDs as an excitation source for biomedical applications, single point measurements were implemented in a realistic blood vessel phantom. A four colour device was also used to demonstrate the possibility of using LEDs for making spectroscopic measurements. It was shown that when driving all four wavelengths at once, the generated photoacoustic signal could be used to design a filter in order to improve the SNR of the photoacoustic signals generated at each individual wavelength. The possibility of acquiring multiwavelength data sets simultaneously when using Golay excitation methods was also demonstrated. This preliminary study demonstrated the potential for using high power LEDs as an inexpensive and compact excitation source for biomedical photoacoustics.
TL;DR: In this paper, the performance of silicon cantilevers is investigated in photo-acoustic measurements of solid samples, and the signal strength is shown to increase tens of percent compared with the results obtained with previously reported cantilever microphones.
Abstract: Silicon cantilever sensors have been designed, fabricated and tested in acoustic wave detection. The principal application of the components is photoacoustic spectroscopy (PAS) which is a highly sensitive method in solid, liquid and gas analysis. The developed microfabrication process of the sensors is based on silicon-on-insulator (SOI) wafer etching, in which the challenge is to control and minimize the residual stress related curving in thin (5 μm) but large-area (few mm 2 ) components. The sensitivity of the fabricated cantilevers is investigated in photoacoustic measurements of solid samples, and the signal strength is shown to increase tens of percent compared with the results obtained with previously reported cantilever microphones. Improvement of the signal-to-noise ratio (SNR) verifies the advantage of the presented cantilevers in photoacoustic sensing.
TL;DR: This novel method employs HIFU to generate a heating impulse in the flow medium, followed by photoacoustic monitoring of the thermal decay process, which can be applied to a continuous medium, i.e., a medium without discrete scatterers or absorbers resolvable byphotoacoustic imaging.
Abstract: We report the development of photoacoustic flowmetry assisted by high-intensity focused ultrasound (HIFU). This novel method employs HIFU to generate a heating impulse in the flow medium, followed by photoacoustic monitoring of the thermal decay process. Photoacoustic flowmetry in a continuous medium remains a challenge in the optical diffusive regime. Here, both the HIFU heating and photoacoustic detection can focus at depths beyond the optical diffusion limit (~1 mm in soft tissue). This method can be applied to a continuous medium, i.e., a medium without discrete scatterers or absorbers resolvable by photoacoustic imaging. Flow speeds up to 41 mm⋅s^(-1) have been experimentally measured in a blood phantom covered by 1.5-mm-thick tissue.
TL;DR: The functional capability of a numerical model for the optimization of acoustic off-beam resonators in COMSOL Multiphysics® is presented and the influence on the resonance frequency and the Q-factor of the micro tuning fork is investigated.
Abstract: Temperature dependent measurements with a compact fiber coupled sensor for trace gas detection in the near-infrared based on tuning fork enhanced interferometric photoacoustic spectroscopy are presented. The temperature effects on the sensor have been investigated in a range from T = −41°C to T = 107°C, in particular the influence on the resonance frequency and the Q-factor of the micro tuning fork. The refined sensor head contains a combination of a silicon tuning fork and an acoustic off-beam resonator and permits methane detection with a detection limit of S = (3.85 ± 0.01) ppm. The functional capability of a numerical model for the optimization of acoustic off-beam resonators in COMSOL Multiphysics® is presented.