Real‐time functional optical‐resolution photoacoustic microscopy using high‐speed alternating illumination at 532 and 1064 nm

Abstract

Optical-resolution photoacoustic microscopy (OR-PAM), which has been widely used and studied as a noninvasive and in vivo imaging technique, can yield high-resolution and absorption contrast images. Recently, metallic nanoparticles and dyes, such as gold nanoparticles, methylene blue, and indocyanine green, have been used as contrast agents of OR-PAM. This study demonstrates real-time functional OR-PAM images with high-speed alternating illumination at 2 wavelengths. To generate 2 wavelengths, second harmonic generation at 532 nm with an LBO crystal and a pump wavelength of 1064 nm is applied at a pulse repetition rate of 300 kHz. For alternating illumination, an electro-optical modulator is used as an optical switch. Therefore, the A-line rate for the functional image is 150 kHz, which is half of the laser repetition rate. To enable fast signal processing and real-time displays, parallel signal processing using a graphics processing unit (GPU) is performed. OR-PAM images of the distribution of blood vessels and gold nanorods in a BALB/c-nude mouse's ear can be simultaneously obtained with 500 × 500 pixels and real-time display at 0.49 fps.

Parallel Computing for Quantitative Blood Flow Imaging in Photoacoustic Microscopy

“…Parallel computing based on GPU is proven effective to improve computational efficiency and is extensively adopted in PAT imaging systems, for which the image reconstruction algorithm is usually designed with a high computation complexity to obtain a better image quality [19][20][21][22][23]. In PAM system, GPU has been applied for the real-time structure imaging (MAP) of blood vessels in a mouse's ear [24,25]. Different from these works, our parallel computation design generates both the structural image (MAP) and functional image (blood flow) and the latter accounts for over 60% of the entire computational time (shown in Figure 10).…”

“…Currently, several parallel computing methods with GPU have been implemented to reconstruct images in PAT systems such as back-projection (BP)-based PAT [19], finite element method (FEM)-based time-domain quantitative PAT [21] and double-state delay-multiply-and-sum (DS-DMAS)-based PAT [23]. In PAM system, GPUs are mainly adopted for the real-time structure imaging such as displaying maximum amplitude projection (MAP) images of blood vessels in a mouse's ear [24,25]. High performance computation of quantitative blood flow imaging in PAM has not been reported and remains a challenge.In this work, we propose a GPU-based parallel computing design for quantitative blood flow imaging in PAM.…”

Photoacoustic imaging in the second near-infrared window: a review

“…The first NIR window (NIR-I) from 700 to 1000 nm was extensively investigated for deep-tissue imaging. [74][75][76][77] Owing to the reduced blood absorption in this region, the penetration depth was improved with a small sacrifice in contrast. Several contrast agents based on metallic, inorganic (carbon nanotubes, quantum dots), organic small molecules (Indocyanine green-ICG, IRDye800, methylene blue), and semiconducting nanoparticles were developed for the NIR-I window, not only to enhance the contrast but also for targeted molecular imaging, drug delivery, therapy, etc.…”

Quickly Alternating Green and Red Laser Source for Real-time Multispectral Photoacoustic Microscopy

“…An ultrasound transducer detects these waves, and images are reconstructed to provide structural, functional, and molecular information of the underlying tissues [ 5 ]. The OR-PAM is sensitive to the optical absorption contrast, while conventional high-resolution imaging techniques, such as optical coherence tomography, confocal microscopy, and two-photon excitation fluorescence microscopy, are sensitive to optical scattering and fluorescence contrast [ 2 , 6 , 7 ]. To date, OR-PAM has been applied to many clinical applications based on endogenous biomolecules such as oxyhemoglobin, deoxyhemoglobin, lipids, and melanin.…”

“…Recently, new methods have been described to switch the excitation wavelengths of the SRS laser source by using a delay line [ 24 ], polarization modulation [ 6 , 25 ], and frequency-domain approaches [ 26 ]. In the delay-line method, light with multiple wavelengths of 532, 545, and 558 nm at PRR of 1 MHz was obtained by passively switching the wavelengths using an optical delay line composed of long optical fibers [ 24 ].…”