Zuomin Zhao

The effects of optical scattering on pulsed photoacoustic measurement in weakly absorbing liquids

In this article, a photoacoustic technique, excited by a pulsed diode laser, is used in a study of optically absorbing and scattering liquids. The article discusses the effects of optical scattering on the photoacoustic source and signal. In the empirical part, varying amounts of milk and carbon powder were added to water to control the absorption and scattering coefficients of the resulting liquids. The results showed that scattering increases the duration of the photoacoustic signal while decreasing the signal amplitude to some degree. This paper also shows a quite simple method for measuring the scattering coefficient in weakly absorbing materials using a PZT transducer, which can be used to determine the concentration of highly scattering compositions in some cases.

Glucose sensing in aqueous Intralipid suspension with an optical coherence tomography system: experiment and Monte Carlo simulation

Peculiarities of light transport in IntralipidTM solutions and the effect of glucose on light scattering properties of the solution at two different IntralipidTM concentrations were studied with optical coherence tomography (OCT) technique in vitro. An open air OCT system using a superluminescent light source with center wavelength = 830 nm was used. 5% IntralipidTM solutions were used to simulate a biological tissue (skin) in our experiment. Glucose concentrations at the physiologically relevant level were added to IntralipidTM solutions. Increasing IntralipidTM concentration increases the scattering coefficient of the media meanwhile increasing glucose concentration increases the refractive index of the media and reduces the scattering coefficient of the media. The experimental data were compared to Monte Carlo simulations. We also made the simulations for 2% IntralipidTM solution. The results indicate that glucose added to 2 and 5% IntralipidTM solutions changes their scattering properties, which is manifested by a decrease in the slope of the OCT signal. This finding shows the ways of using OCT for sensing glucose and monitoring the alterations of its content in biotissues. Some discrepancies between measurements and simulations were found, which need further investigation.

Photoacoustic determination of glucose concentration in whole blood by a near-infrared laser diode

The near-infrared photoacoustic technique is recognized as a potential method for the non-invasive determination of human glucose, because near-infrared light can incident a few millimeters into human tissue, where it produces an acoustic wave capable of carrying information about the composition of the tissue. This paper demonstrates a photoacoustic glucose measurement in a blood sample as a step toward a non-invasive measurement. The experimental apparatus consists of a near-infrared laser diode operating with 4 micro joules pulse energy at 905 nm, a roller pump connected to a silicon plastic tube and a cuvette for circulating the blood sample. In addition, the apparatus comprises a PZT piezoelectric transducer integrated with a battery-powered preamplifier to receive the photoacoustic signal. During the experiment, a glucose solution is mixed into a human blood sample to change its concentration. Although the absorption coefficient of glucose is much smaller than that of blood in the near-infrared region, the osmotic and hydrophilic properties of glucose decrease the reduced scattering coefficient of blood caused by the dissolved glucose surrounding the blood cells. This changes the distribution of the absorbed optical energy in blood, which, in turn, produces a change in the photoacoustic signal. Our experiment demonstrates that signal amplitudes in fresh and stored blood samples in crease about 7% and 10%, respectively, when the glucose concentration reaches the upper limit of the physiological region (500 mg/dl).

Phase-delayed laser diode array allows ultrasonic guided wave mode selection and tuning

Selecting and tuning modes are useful in ultrasonic guided wave non-destructive testing (NDT) since certain modes at various center frequencies are sensitive to specific types of defects. Ideally one should be able to select both the mode and the center frequency of the launched waves. We demonstrated that an affordable laser diode array can selectively launch either the S0 or A0 ultrasonic wave mode at a chosen center frequency into a polymer plate. A fiber-coupled diode array (4 elements) illuminated a 2 mm thick acrylic plate. A predetermined time delay matching the selected mode and frequency was employed between the output of the elements. The generated ultrasound was detected by a 215 kHz piezo receiver. Our results imply that this array permits non-contacting guided wave ultrasonic NDT. The solution is small, affordable, and robust in comparison to conventional pulsed lasers. In addition, it does not require experienced operators.

Photoacoustic blood glucose and skin measurement based on optical scattering effect

Non-invasive blood glucose determination has been investigated by more than 100 research groups in the world during the past fifteen years. The commonly optical methods are based on the capacity of near-IR light to penetrate a few hundreds micrometers or a few millimeters into human tissue where it interacts with glucose. A change of glucose concentration may modify the optical parameters in tissue, with the result that its glucose concentration can be extracted by analyzing the received optical signals. This paper demonstrates that glucose affects on the scattering coefficient of human blood, by applying the streak camera and pulsed photoacoustic techniques; and drinking water seems also affecting on PA signal from skin surface.

Measuring the optical parameters of weakly absorbing, highly turbid suspensions by a new technique: photoacoustic detection of scattered light

We present and apply a novel method, the scattering photoacoustic (SPA) technique, for measuring optical parameters in weakly absorbing, highly scattering suspensions. In this method, a solid absorber is in contact with a suspension sample to permit the photoacoustic detection of the samples light-scattering properties. We conducted measurements conducted to determine the reduced scattering coefficients of Intralipid suspensions with a concentration range of 0.1-5%, and the results are in good agreement with those achieved by other researchers. Moreover, we also illustrate the relationship between the amplitude of the SPA signal and absorption, scattering, and detection distance. Through a study of Intralipid-ink mixes, we demonstrate that the SPA technique has the ability to determine simultaneously the absorption and reduced scattering coefficients of turbid media. This new technique has low cost and is noninvasive, and it enables on-line measurements to be made.

Production and detection theory of pulsed photoacoustic wave with maximum amplitude and minimum distortion in absorbing liquid

The photoacoustic effect produced by laser-induced stress waves in liquids has found a variety of scientific and practical applications in industry, medicine, and environmental protection. The photoacoustic technique has the natural advantage of being less sensitive to scattering than traditional optical tools, thus offering increased accuracy and sensitivity. This paper aims to give a systematic outline of photoacoustic techniques, starting with the production and extending to the propagation and detection of photoacoustic waves. The focal point is the production of acoustic waves with maximum amplitude and minimum distortion. Maximum amplitude plays an essential role in photoacoustic spectroscopy and minimum distortion is the key to the determination of optical distribution and imaging in turbid media.

A free plate model can predict guided modes propagating in tubular bone-mimicking phantoms

The goal of this work was to show that a non-absorbing free plate model can predict with a reasonable accuracy guided modes measured in bone-mimicking phantoms that have circular cross-section. Experiments were carried out on uncoated and coated phantoms using a clinical axial transmission setup. Adjustment of the plate model to the experimental data yielded estimates for the waveguide characteristics (thickness, bulk wave velocities). Fair agreement was achieved over a frequency range of 0.4 to 1.6 MHz. A lower accuracy observed for the thinnest bone-mimicking phantoms was caused by limitations in the wave number measurements rather than by the model itself.

Photo-acoustic excitation and detection of guided ultrasonic waves in bone samples covered by a soft coating layer

Photo-acoustic (PA) excitation was combined with skeletal quantitative ultrasound (QUS) for multi-mode ultrasonic assessment of human long bones. This approach permits tailoring of the ultrasonic excitation and detection so as to efficiently detect the fundamental flexural guided wave (FFGW) through a coating of soft tissue. FFGW is a clinically relevant indicator of cortical thickness. An OPO laser with tunable optical wavelength, was used to excite a photo-acoustic source in the shaft of a porcine femur. Ultrasonic signals were detected by a piezoelectric transducer, scanning along the long axis of the bone, 20-50 mm away from the source. Five femurs were measured without and with a soft coating. The coating was made of an aqueous gelatin-intralipid suspension that optically and acoustically mimicked real soft tissue. An even coating thickness was ensured by using a specific mold. The optical wave length of the source (1250 nm) was tuned to maximize the amplitude of FFGW excitation at 50 kHz frequency. The experimentally determined FFGW phase velocity in the uncoated samples was consistent with that of the fundamental antisymmetric Lamb mode (A0). Using appropriate signal processing, FFGW was also identified in the coated bone samples, this time with a phase velocity consistent with that theoretically predicted for the first mode of a fluid-solid bilayer waveguide (BL1). Our results suggest that photo-acoustic quantitative ultrasound enables assessment of the thickness-sensitive FFGW in bone through a layer of soft tissue. Photo-acoustic characterization of the cortical bone thickness may thus become possible.

Noninvasive glucose sensing in scattering media using OCT, PAS, and TOF techniques

In this paper, optical measurement techniques, which enable non-invasive measurement, are superimposed to glucose sensing in scattering media. Used measurement techniques are Optical Coherence Tomography (OCT), Photoacoustic spectroscopy (PAS) and laser pulse Time-of-Flight (TOF) measurement using a streak camera. In parallel with measurements, a Monte-Carlo (MC) simulation models have been developed. Experimental in vitro measurements were performed using Intralipid fat emulsion as a tissue simulating phantom for OCT and TOF measurements. In PAS measurements, a pork meat was used as a subject but also preliminary in vivo measurements were done. OCT measurement results show that the slope of the OCT signals envelope changes as a function of glucose content in the scattering media. TOF measurements show that the laser pulse full width of half maximum (FWHM) changes a little as function of glucose content. An agreement with MC-simulations and measurements with Intralipid was also found. Measurement results of PAS technique show that changes in glucose content in the pork meat tissue can be measured. In vivo measurements with a human volunteer show that other factors such as physiological change, blood circulation and body temperature drift may interfere the PA response of glucose.