Vincent Cunningham

Laser optoacoustic spectroscopy of gold nanorods within a highly scattering medium

We describe a spectroscopic comparative analysis based on the optoacoustic technique over the wavelength range from 410nm to 1000nm using a Q-switched Nd:YAG pumped optical parametric oscillator tunable source on a gold nanostructure solution located within a highly scattering medium. The advantages of this method over standard spectroscopy techniques are the possibility to localize and monitor the spectroscopic response of absorbing materials located within turbid media. The operation is confirmed using a comparative analysis with the spectroscopic results obtained from a reference measurement scheme, based on a highly sensitive collimated optical transmission setup in parallel and under the same experimental conditions as the optoacoustic technique.

Efficient combination of multiple high power semiconductor laser sources for photoacoustic signal generation in biomedical phantoms

There is increasing interest in photoacoustic techniques for non-invasive soft tissue investigation, this in part is due to the successful in vivo trials and investigation using biomedical soft tissue phantoms. The work presented in this paper focuses on the construction and calibration of a semiconductor laser system for the generation of high power optical pulses required for photoacoustic signal generation in biomedical phantoms. Such energy levels are achieved using combination of commercial semiconductor laser sources. Results presented in this paper show that this combination process is effective and an efficient means to obtain photoacoustic signals in biomedical samples.

Comparative analysis of optical absorption and optoacoustic signal generation in nanoparticles

Use of gold nanoparticles (GNPs) as a contrast agent for medical imaging is shown to improve the efficiency of optoacoustic signal generation; signal enhancement allows differentiation between different tissue types. This aspect of medical imaging is important when concerned with early cancer detection. The present paper presents a comparative analysis of two different optical techniques, optical transmission and optoacoustics, to define the different components associated with the attenuation of light in GNPs. This attenuation of light is first studied for a pure absorber where the results are shown to be in agreement for both optical methods, thus showing the effectiveness of the measurement technique. A comparative analysis is also carried out on spherical GNPs which have been synthesized to have peak absorption at the laser wavelength.

Analysis of photoacoustic signal frequencies in deep tissue phantoms using high sensitive interferometric optical sensors

Laser optoacoustics is based on the interaction of light with materials producing the thermoelastic effect forming acoustic waves which are characteristic of the medium in which they traverse. This technique is currently on trial for use in biomedical imaging applications and is achieving great success. The work presented here develops an innovative technique for wideband acoustic detection using a fibre optic sensor in a high sensitive multi-coil Mach-Zehnder interferometric configuration. A comparative analysis is performed using both electrical and optical detection techniques on gels which are commonly used to mimic human soft tissue. Indications of future work in this area will be presented throughout this paper.

Laser optoacoustic scheme for highly accurate characterization of gold nanostructures in liquid phantoms for biomedical applications

Abstract. Optoacoustic spectroscopy can overcome the drawbacks of all-optical techniques for biomedical spectroscopy, as the acoustic waves generated from the optical absorption and thermoelastic expansion of the targeted medium are attenuated very little. The spectral information can be resolved using a high energy, short-pulsed tunable laser, operating over a spectral range from 410 nm to 1000 nm. The amplitude of the induced pressure waves is directly proportional to the absorbed optical energy at each wavelength.

Modelling and characterization of photothermal effects assisted with gold nanorods in ex vivo samples and in a murine model

We discuss in this article the implementation of a laser-tissue interaction and bioheat-transfer 2-D finite-element model for Photothermal Therapy assisted with Gold Nanorods. We have selected Gold Nanorods as absorbing nanostructures in order to improve the efficiency of using compact diode lasers because of their high opto-thermal conversion efficiency at 808 and 850 nm. The goal is to model the distribution of the optical energy among the tissue including the skin absorption effects and the tissue thermal response, with and without the presence of Gold Nanorods. The heat generation due to the optical energy absorption and the thermal propagation will be computationally modeled and optimized. The model has been evaluated and compared with experimental ex-vivo data in fresh chicken muscle samples and in-vivo BALB/c mice animal model.

Analysis of the diffuse light and optoacoustic signal generation in nanoparticles

Use of gold nanoparticles (NPs) as a contrast agent for medical imaging is shown to improve the efficiency of optoacoustic signal generation; this signal enhancement allows differentiation between different tissue types. This aspect of medical imaging is important when concerned early cancer detection. The present paper presents the results on the interaction process between the laser light and gold NPs, providing valuable information necessary for improved and more efficient NP synthesis. The attenuation of laser is studied for NP solutions of different geometrical characteristics and concentrations where the study is based on both optical and optoacoustic characterization techniques. First results show that the absorption and scattering are correlated by increasing the size of the nanoparticles between 5nm and 60nm. The optoacoustic signals we have been obtained demonstrate similar behavior for gold NP diameters of 5nm to 12nm.

Preliminary tests on a low-cost and compact optoelectronic system for optical mammography

The work that is presented in this paper proposes a new low-cost and compact optoelectronic system for optical mammography trials. This system is based on the use of cost-off-the-shelf (COTS) optoelectronic and electronic components which are commonly used in the telecommunications industry. The main components of this novel system are based on low cost semiconductor laser diodes and avalanche photodiodes (APDs). This is backed up by the use of a versatile electronic architecture also based on telecommunication low cost components and techniques. Such methods allow research into the optimum modulation frequency for improved signal to noise ratio (SNR). To date the system has been tested on liquid phantoms formed by different concentrations of milk solutions. Results obtained from preliminary tests are within 10% of values obtained in previous publications.

Conception and description of a low-cost and compact optoelectronic frequency-domain system for optical mammography

In this work we propose a new low-cost and compact optoelectronic system for optical mammography trials based on the use of low-cost semiconductor lasers and Si photodetectors. This system is completed using a versatile electronic architecture based on COTS (Cost-Off-The-Shelf) telecom components and techniques. The system is also designed for experimental studies on the dependence of the modulation frequency and the optimum signal to noise ratio (SNR). Results presented in this paper show the effect the modulation frequency and index has on the phase of the signal when passing through a commonly used scattering medium.