Collecting back-reflected photons in photoacoustic microscopy

Department of Electrical Engineering and Computer Science, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA.
Optics Express (Impact Factor: 3.49). 01/2010; 18(2):1278-82. DOI: 10.1364/OE.18.001278
Source: PubMed

ABSTRACT Since the photoacoustic effect relies only on the absorbed optical energy, the back-reflected photons from samples in optical-resolution photoacoustic microscopy are usually discarded. By employing a 2 x 2 single-mode fiber optical coupler in a laser-scanning optical-resolution photoacoustic microscope for delivering the illuminating laser light and collecting the back reflected photons, a fiber-optic confocal microscope is integrated with the photoacoustic microscope. Thus, simultaneous multimodal imaging can be achieved with a single light source and images from the two modalities are intrinsically registered. Such capabilities are demonstrated in imaging both phantoms and small animals in vivo.

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Available from: Tan Liu, Mar 11, 2014
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    • "The eye has an abundance of endogenous contrasts such as hemoglobin, melanin, and vascular tissue. All can be readily quantified and imaged by the PAT technique (de la Zerda et al., 2010; Hu et al., 2010; Jiao et al., 2010; Jiang et al., 2010; Rao et al., 2010; Silverman et al., 2010; Song et al., 2013; Xie et al., 2009; Zhang et al., 2010a, 2010b). PAT imaging of ex vivo sectioned pig eyes demonstrates that using focused laser beam short pulse irradiation with a ring ultrasonic transducer provides sharper ocular images than an unfocused laser (Kong et al., 2009a). "
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    ABSTRACT: This study evaluated in vivo imaging capabilities and safety of qualitative monitoring of oxygen saturation of hemoglobin (sO2) of rabbit ciliary body tissues obtained with acoustic resolution (AR) photoacoustic tomography (PAT). AR PAT was used to collect trans-scleral images from ciliary body vasculature of seven New Zealand White rabbits. The PAT sO2 measurements were obtained under the following conditions: when systemic sO2 as measured by pulse oximetry was between 100% and 99% (level 1); systemic sO2 as measured by pulse oximetry was between 98% and 90% (level 2); and systemic sO2 as measured by pulse oximetry was less than 90% (level 3). Following imaging, histological analysis of ocular tissue was conducted to evaluate for possible structural damage caused by the AR PAT imaging. AR PAT was able to resolve anatomical structures of the anterior segment of the eye, viewed through the cornea or anterior sclera. Histological studies revealed no ocular damage. On average, sO2 values (%) obtained with AR PAT were lower than sO2 values obtained with pulse oximetry (all p < 0.001): 86.28 ± 4.16 versus 99.25 ± 0.28, 84.09 ± 1.81 vs. 95.3 ± 2.6, and 64.49 ± 7.27 vs. 71.15 ± 10.21 for levels 1, 2 and 3 respectively. AR PAT imaging modality is capable of qualitative monitoring for deep tissue sO2 in rabbits. Further studies are needed to validate and modify the AR PAT modality specifically for use in human eyes. Having a safe, non-invasive method of in vivo imaging of sO2 in the anterior segment is important to studies evaluating the role of oxidative damage, hypoxia and ischemia in pathogenesis of ocular diseases. Copyright © 2015. Published by Elsevier Ltd.
    Experimental Eye Research 06/2015; 138. DOI:10.1016/j.exer.2015.05.022 · 2.71 Impact Factor
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    • "The energy of each laser pulse was sampled by the photodiode PD2 (DET10A, Thorlabs) to compensate for the pulse energy instability. As reported in our previous work, the lateral resolution of the LSOR-PAM is 2.8 µm, and the axial resolution is 23 µm [18]. "
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    ABSTRACT: We proposed to measure the metabolic rate of oxygen (MRO(2)) in small animals in vivo using a multimodal imaging system that combines laser-scanning optical-resolution photoacoustic microscopy (LSOR-PAM) and spectral-domain optical coherence tomography (SD-OCT). We first tested the capability of the multimodal system to measure flow rate in a phantom made of two capillary tubes of different diameters. We then demonstrated the capability of measuring MRO(2) by imaging two parallel vessels selected from the ear of a Swiss Webster mouse. The hemoglobin oxygen saturation (sO(2)) and the vessel diameter were measured by the LSOR-PAM and the blood flow velocity was measured by the SD-OCT, from which blood flow rate and MRO(2) were further calculated. The measured blood flow rates in the two vessels agreed with each other.
    Biomedical Optics Express 05/2011; 2(5):1359-65. DOI:10.1364/BOE.2.001359 · 3.65 Impact Factor
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    • "PAM detects the ultrasonic waves (PA waves) generated by pulsed laser-induced localized thermal expansion in biological tissues as a result of specific optical absorption. Recently, we developed the optical coherence tomography (OCT) guided photoacoustic ophthalmoscopy (PAOM) [7], which extended the laser scanning optical-resolution PAM (LSOR-PAM) [8–10] to retinal imaging. We have successfully used PAOM to image the retinal vasculature and the melanin distribution in the retinal pigment epithelium (RPE) of rat eye in vivo. "
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    ABSTRACT: We have developed an adaptive optics photoacoustic microscope (AO-PAM) for high-resolution imaging of biological tissues, especially the retina. To demonstrate the feasibility of AO-PAM we first designed the AO system to correct the wavefront errors of the illuminating light of PAM. The aberrations of the optical system delivering the illuminating light to the sample in PAM was corrected with a close-loop AO system consisting of a 141-element MEMS-based deformable mirror (DM) and a Shack-Hartmann (SH) wavefront sensor operating at 15 Hz. The photoacoustic signal induced by the illuminating laser beam was detected by a custom-built needle ultrasonic transducer. When the wavefront errors were corrected by the AO system, the lateral resolution of PAM was measured to be better than 2.5 µm using a low NA objective lens. We tested the system on imaging ex vivo ocular samples, e.g., the ciliary body and retinal pigment epithelium (RPE) of a pig eye. The AO-PAM images showed significant quality improvement. For the first time we were able to resolve single RPE cells with PAM.
    Optics Express 10/2010; 18(21):21770-6. DOI:10.1364/OE.18.021770 · 3.49 Impact Factor
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