Sergio Rodríguez

Optoacoustic response of gold nanorods in soft phantoms using high-power diode laser assemblies at 870 and 905 nm: erratum

In the present paper we show the optoacoustic (OA) response of two solutions of gold nanorods dispersed in distilled water (0.8 mg/ml) and hosted in tissue-like phantoms by using small arrays of HPDLs at 870 and 905 nm as excitation sources. The HPDLs are coupled to a 7-to-1 optical fiber bundle with output diameter of 675 μm. Each solution of gold nanorods exhibits an absorption peak close to the operating wavelength, i.e. ~860 nm and ~900 nm, respectively, to optimize the generation of OA signals. The phantoms are made of agar, intralipid and hemoglobin to simulate a soft biological tissue with reduced properties of scattering. Three 3-mm diameter tubes done in the phantoms at different depths (0.9 cm, 1.8 cm, and 2.7 cm) have been filled with gold nanorods. In this way, OA signals with appreciable SNR are generated at different depths in the phantoms. The high OA response exhibited by gold nanorods suggests their application in OA spectroscopy as exogenous contrast agents to detect and monitor emerging diseases like metastasis and arteriosclerotic plaques.

System analysis of wavelength beam combining of high-power diode lasers for photoacoustic endoscopy

This paper, originally published on 27 April 2016, was replaced with a corrected/revised version on 8 June 2016. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. The purpose of wavelength-beam combining (WBC) is to improve the output power of a multi-wavelength laser system while maintaining the quality of the combined beam. This technique has been primarily proposed for industrial applications, such as metal cutting and soldering, which require optical peak power between kilowatts and megawatts. In order to replace the bulkier solid-state lasers, we propose to use the WBC technique for photoacoustic (PA) applications, where a multi-wavelength focused beam with optical peak power between hundreds of watts up to several kilowatts is necessary to penetrate deeply into biological tissues. In this work we present an analytical study about the coupling of light beams emitted by diode laser bars at 808 nm, 880 nm, 910 nm, 940 nm, and 980 nm into a .

Image reconstruction algorithms with wavelet filtering for optoacoustic imaging

Optoacoustic imaging (OAI) is a hybrid biomedical imaging modality based on the generation and detection of ultrasound by illuminating the target tissue by laser light. Typically, laser light in visible or near infrared spectrum is used as an excitation source. OAI is based on the implementation of image reconstruction algorithms using the spatial distribution of optical absorption in tissues. In this work, we apply a time-domain back-projection (BP) reconstruction algorithm and a wavelet filtering for point and line detection, respectively. A comparative study between point detection and integrated line detection has been carried out by evaluating their effects on the image reconstructed. Our results demonstrate that the back-projection algorithm proposed is efficient for reconstructing high-resolution images of absorbing spheres embedded in a non-absorbing medium when it is combined with the wavelet filtering.

ACCURATE DETERMINATION OF GOLD NANORODS CONCENTRATIONS FROM OPTOACOUSTIC SIGNALS DETECTED AT 870 NM AND 905 NM BY USING HIGH-POWER DIODE LASERS WITH FAST SWITCHING ELECTRONICS

Optoacoustic imaging (OAI) is an emerging biomedical technique that allows visualization of in-depth tissues by using ultrasonic signals generated by short laser pulses. In this work, the authors combine the optical power of several pulsed high-power diode lasers (HPDLs) at 870 nm and 905 nm to a 7-to-1 675-μm fiber bundle to generate optoacoustic (OA) signals from different mixtures of two gold nanorods solutions with absorbance peak at ∼ 860 nm and ∼ 900 nm, respectively. The pulses produced to generate OA signals are alternated between the two wavelengths by a microcontroller circuit with fast switching (0.5 ms). From the amplitude of the OA signals, the concentrations of the nanoparticles solutions are easily estimated with high accuracy using a fluence model. The results achieved with the proposed system show very good agreement between the concentrations of gold nanorods estimated from measurements and the expected values.

Cost-effective optoacoustic system based on the combination of high-power diode lasers

One of the main issues of the advances in optoacoustic (OA) applications is to reduce the high costs and the big sizes of solid state lasers. High-power diode lasers (HPDLs) have been demonstrated to be a valid alternative reducing enormously the expenses, besides other advantages such as smaller sizes and higher modulation frequencies. However, in some cases it is possible to furtherly reduce their costs. We present a cost-effective OA system based on the combination of several 905-nm HPDLs with direct coupling into a fiber bundle. These HPDLs have an internal pulse driver, based on an n-channel Mosfet and two charging capacitors, which needs an external Mosfet driver circuit and a voltage supply in order to improve the optical pulse shape and energy. We compare the performances and the prices of this OA system with another similar HPDL-based OA system built with commercial elements. Results indicate good OA signal generation (~15.6 mVpp) with pulse energy of 12.3 μJ and, especially, a cost reduction by a factor of ~15 if compared to the other HPDL-based system.

Multi-wavelength photoacoustic system based on high-power diode laser bars

Multi-wavelength laser sources are necessary for a functional photoacoustic (PA) spectroscopy. The use of high-power diode lasers (HPDLs) has aroused great interest for their relatively low costs and small sizes if compared to solid state lasers. However, HPDLs are only available at few wavelengths and can deliver low optical energy (normally in the order of μJ), while diode laser bars (DLBs) offer more wavelengths in the market and can deliver more optical energy. We show the simulations of optical systems for beam coupling of single high-power DLBs operating at different wavelengths (i.e. 808 nm, 880 nm, 910 nm, 940 nm, and 980 nm) into 400-μm optical fibers. Then, in a separate design, the beams of the DLBs are combined in a compact system making use of dichroic mirrors and focusing lenses for beam coupling into a 400-μm optical fiber. The use of optical fibers with small core diameter (< 1 mm) is particularly suggestive for future photoacoustic endoscopy (PAE) applications that require interior examination of the body.

Optoacoustic system based on 808-nm high energy short pulse diode laser stacks

In the last few decades, high power diode lasers (HPDL) have been introduced as alternative laser sources for optoacoustic imaging (OAI), due to their high repetition rates (a few kHz) for fast OA image acquisition, lower cost and size if compared to solid state lasers. Nevertheless, their drawbacks consist in a low energy per pulse (μJ) and a relatively highly divergent beam that needs collimation optics. At this purpose, the employment of diode laser stacks significantly increases the energy per pulse up to several mJ. The diode laser stacks imply a big challenge if compared to single emitters for several reasons. Firstly, they need very demanding electronic requirements, as forward voltages and currents of several tens of volts and hundreds of amperes, respectively. Secondly, their highly divergent beam profile requires precise collimation by means of fast axis and slow axis collimation. In this work, we show an 808-nm diode laser stack driven with 17 V and ~ 200 A by a low-cost current driver for emitting pulses of 1 mJ at 1 kHz. Particular emphasis will be attributed to the design of the high current pulses driver and the optics employed to collimate and after focus the beam in a spot. The light spot will be applied to an ink inclusion hosted in turbid phantom. We demonstrate that our system is able to generate appreciable OA signals in turbid phantoms. This aspect represents a novelty in OAI systems because it is demonstrated that HPDL sources can efficiently replace solid-state lasers.

Optoacoustic response from graphene-based solutions embedded in optical phantoms by using 905-nm high-power diode-laser assemblies

During the last two decades, optoacoustic imaging has been developed as a novel biomedical imaging technique based on the generation of ultrasound waves by means of laser light. In this work, we investigate the optoacoustic response from graphene-based solutions by using a compact and cost-effective system based on an assembly of several 905-nm pulsed high-power diode lasers coupled to a bundle of 200-μm diameter- core optical fibers. The coupled light is conveyed into a lens system and focused on an absorber consisting of graphene-based nanomaterials (graphene oxide, reduced graphene oxide, and reduced graphene-oxide/gold-nanoparticle hybrid, respectively) diluted in ethanol and hosted in slightly scattering optical phantoms. The high absorption of these graphene-based solutions suggests their potential future use in optoacoustic applications as contrast agents.