The aim of this paper is to overcome the acoustic diffraction limit to achieve finer lateral resolution in and out of focus regions. For this purpose, a well-known structured-illumination method is used to increase the acoustic spatial bandwidth to improve the lateral resolution of the system. The illuminated optical beam is shaped by a digital micromirror device (DMD) to form sinusoidal patterns force to shift the object spatial spectrum. The shifted spectrum passes high spatial frequency components through the finite bandwidth of the system. Here, the phase compounding method is modified in comparison with [1] to increase the lateral resolution improvement from 2 to 5 times. To achieve this goal, adding the spatial frequency component of the second order to the fundamental component by considering phase shifts of 0,45,90 and 180 degree and orientations of 0,45,90, and 135 degree. The experimental results validate the performance of the system.
We report wide-field polygon-scanning optical-resolution photoacoustic microscopy (OR-PAM) that achieves 1-MHz A-line rate of oxygen saturation in vivo. We develop a polygon-scanning imaging probe. Using stimulated Raman scattering and optical delay in fiber, we develop a dual-wavelength pulsed laser that has proper wavelengths, sufficient pulse energy, high pulse repetition rate, and sub-microseconds wavelength switching time for fast imaging of oxygen saturation. The OR-PAM system offers a 478-Hz B-scan rate and a 1-Hz volumetric imaging rate over a 12×5 mm2 scanning area. We demonstrate dynamic imaging of oxygen saturation of fast response to epinephrine injection in the mouse ear. Results show fast hemodynamic and functional changes in centimeter-sized areas.
Optical-resolution photoacoustic microscopy (OR-PAM) can image the blood oxygen saturation (sO2) in vivo without labeling. OR-PAM assumes a linear relationship between the photoacoustic amplitude and the optical absorption coefficient and ignores the wavelength-dependent optical fluence attenuation in tissue. However, strong scattering in biological tissues may significantly change the optical energy deposition, leading to inaccurate sO2 measurement. Here, we report fluence-compensated OR-PAM to correct the sO2 imaging. In a narrow optical spectrum, we assume the scattered fluence is linearly related to the optical wavelength. Using three optical wavelengths, we can compensate for the scattering-induced photoacoustic signal change and thus improve the accuracy of sO2 measurement. We use a Monta Carlo model to validate the linear assumption of the scattered fluence. In in vivo experiments, we demonstrate that the optical fluence compensation can effectively improve the sO2 accuracy. The compensated arterial sO2 values are in the range of 0.95 ~ 0.99, which is consistent with normal physiological values. Compared with the uncompensated ones, the accuracy has been improved greatly. Enabled by the accurate sO2 imaging tool, we can reliably observe the sO2 gradient in the vascular network. We expect this new technique will further broaden the preclinical and clinical applications of functional OR-PAM.
Optical-resolution photoacoustic microscopy (OR-PAM) has been developed for anatomical, functional, and molecular imaging but usually requires multiple scanning for different contrasts. We present five-wavelength OR-PAM for simultaneous imaging of hemoglobin concentration, oxygen saturation, blood flow speed, and lymphatic vessels in single raster scanning. We develop a five-wavelength pulsed laser via stimulated Raman scattering. The five pulsed wavelengths, i.e., 532, 545, 558, 570, and 620 / 640 nm, are temporally separated by several hundreds of nanoseconds via different optical delays in fiber. Five photoacoustic images at these wavelengths are simultaneously acquired in a single scanning. The 532- and 620 / 640-nm wavelengths are used to image the blood vessels and dye-labeled lymphatic vessels. The blood flow speed is measured by a dual-pulse method. The oxygen saturation is calculated and compensated for by the Grüneisen-relaxation effect. In vivo imaging of hemoglobin concentration, oxygen saturation, blood flow speed, and lymphatic vessels is demonstrated in preclinical applications of cancer detection, lymphatic clearance monitoring, and functional brain imaging.
KEYWORDS: Photoacoustic spectroscopy, Acoustics, Photoacoustic microscopy, Laser energy, Signal to noise ratio, Microscopes, Ultrasonography, Pulsed laser operation, Signal detection, In vivo imaging
Due to limited ultrasound detection angle, photoacoustic microscopy may own a relatively low sensitivity. To break this limit, we develop an ultra-sensitive optical resolution photoacoustic microscopy based on a customized acoustic lens with high numerical aperture (0.74) (HNA-OR-PAM). The sensitivity of HNA-OR-PAM is improved to around 160% as the state-of-the-art OR-PAM. It has the capability to measure oxygen saturation of mice’s ear in vivo with ~10nJ pulse energy, reducing the nonlinear effect induced by high pulse energy. In addition, photoacoustic signal of tilted objects could be enhanced due to augmented ultrasound detection angle, which has been validated in our phantom study and the brain imaging experiment in vivo.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.