<p>Photoacoustic microscopy (PAM) is a fast-growing biomedical imaging technique that provides high-resolution <italic>in vivo</italic> imaging beyond the optical diffusion limit. Depending on the scalable lateral resolution and achievable penetration depth, PAM can be classified into optical resolution PAM (OR-PAM) and acoustic resolution PAM (AR-PAM). The use of a microelectromechanical systems (MEMS) scanner has improved OR-PAM imaging speed significantly and is highly beneficial in the development of miniaturized handheld devices. The shallow penetration depth of OR-PAM limits the use of such devices for a wide range of clinical applications. We report the use of a high-speed MEMS scanner for both OR-PAM and AR-PAM. A high-speed, wide-area scanning integrated OR-AR-PAM system combining MEMS scanner and raster mechanical movement was developed. A lateral resolution of 5 μm and penetration depth ∼0.9-mm <italic>in vivo</italic> was achieved using OR-PAM at 586 nm, whereas a lateral resolution of 84 μm and penetration depth of ∼2-mm <italic>in vivo</italic> was achieved using AR-PAM at 532 nm.</p>
The hemodynamics and oxygen saturation status of vascular are very important biomarkers for disease, such as brain glioma tumor and ischemia-reperfusion ulcer. Therefore, a high spatial resolution imaging tool for vascular imaging is demanded. Conventional optical imaging modalities, including confocal microscopy and two-photon microscopy, require external contrast agent to image blood vessels and are not sensitive to oxygen saturation. The development of photoacoustic microscopy provides a contrast-free, high-spatial resolution and functional vascular imaging tool. It’s gaining more and more popularity in biomedical research. In this paper, we introduce a dual-wavelength opticalresolution photoacoustic microscopy (OR-PAM) system for functional imaging of vasculature. This system has demonstrated its application in brain glioma tumor imaging, as well as skin ischemia-reperfusion imaging.
A Microelectromechanical Systems (MEMS)-based rapid scanning photoacoustic microscopy (PAM) is available to help life science research in neuroscience, cell biology, and in vivo imaging. MicroPhotoAcoustics (MPA; Ronkonkoma, NY), the only manufacturer and vendor of Optical Resolution (OR)-PAM systems, has developed a commercial PAM system with switchable optical and acoustic resolution (OR- and AR-PAM). To achieve real-time imaging capability without sacrificing high signal-to-noise ratios (SNRs), a 2-axis water-proofing MEMS scanner made of flexible polydimethylsiloxane (PDMS) was demonstrated by collaboration with Pohang University of Science and Technology (South Korea) that promises to dramatically increase the system’s imaging speed. This flexible scanner results in a wide scanning range and a fast imaging speed (5 B-scan images per second). Equipped with different excitation sources, in vivo PA images of microvasculatures in a mouse ear was obtained. The lateral and axial resolutions of the OR-PAM system are 4.38 μm. It is expected that this MEMS-based fast OR-PAM system can be significantly useful in both preclinical and clinical applications. With the continuation of new technological advancements and discoveries, MPA plans to further advance PAM to achieve faster imaging speed, higher spatial resolution at deeper tissue layer, and address a broader range of biomedical applications.
We present a water-proof Microelectromechanical systems (MEMS) based scanning optical resolution Photoacoustic Microscopy (OR-PAM) system and its application in glioma tumor mouse model study. The presented OR-PAM system has high optical resolution (~3 μm) and high scanning speed (up to 50 kHz A-scan rate), which is ideal for cerebral vascular imaging. In this study, the mice with glioma tumor are treated with vascular disrupting agent (VDA). OR-PAM system is utilized to image the cerebral with the whole skull intact before and after the injection of VDA. By image registration, the response of every single blood vessel can be traced. This will provide us deeper understanding of the drug effect.
A focused-scanning photoacoustic microscopy (PAM) is available to help advancing life science research in neuroscience, cell biology, and in vivo imaging. At this early stage, the only one manufacturer of PAM systems, MicroPhotoAcoustics (MPA; Ronkonkoma, NY), MPA has developed a commercial PAM system with switchable optical and acoustic resolution (OR- and AR-PAM), using multiple patents licensed from the lab of Lihong Wang, who pioneered photoacoustics. The system includes different excitation sources. Two kilohertz-tunable, Q-switched, Diode Pumped Solid-State (DPSS) lasers offering a up to 30kHz pulse repetition rate and 9 ns pulse duration with 532 and 559 nm to achieve functional photoacoustic tomography for sO<sub>2</sub> (oxygen saturation of hemoglobin) imaging in OR-PAM. A Ti:sapphire laser from 700 to 900 nm to achieve deep-tissue imaging. OR-PAM provides up to 1 mm penetration depth and 5 μm lateral resolution. while AR-PAM offers up to 3 mm imaging depth and 45 μm lateral resolution. The scanning step sizes for OR- and AR-PAM are 0.625 and 6.25 μm, respectively. Researchers have used the system for a range of applications, including preclinical neural imaging; imaging of cell nuclei in intestine, ear, and leg; and preclinical human imaging of finger cuticle. With the continuation of new technological advancements and discoveries, MPA plans to further advance PAM to achieve faster imaging speed, higher spatial resolution at deeper tissue layer, and address a broader range of biomedical applications.
Diffuse correlation spectroscopy (DCS) is an emerging noninvasive technique that probes the deep tissue blood flow, by using the time-averaged intensity autocorrelation function of the fluctuating diffuse reflectance signal. We present a fast Fourier transform (FFT)-based software autocorrelator that utilizes the graphical programming language LabVIEW (National Instruments) to complete data acquisition, recording, and processing tasks. The validation and evaluation experiments were conducted on an in-house flow phantom, human forearm, and photodynamic therapy (PDT) on mouse tumors under the acquisition rate of ∼400 kHz . The software autocorrelator in general has certain advantages, such as flexibility in raw photon count data preprocessing and low cost. In addition to that, our FFT-based software autocorrelator offers smoother starting and ending plateaus when compared to a hardware correlator, which could directly benefit the fitting results without too much sacrifice in speed. We show that the blood flow index (BFI) obtained by using a software autocorrelator exhibits better linear behavior in a phantom control experiment when compared to a hardware one. The results indicate that an FFT-based software autocorrelator can be an alternative solution to the conventional hardware ones in DCS systems with considerable benefits.