Fast-scanning photoacoustic microscopy with a side-looking fiber optic ultrasound sensor

Abstract

Optical-resolution photoacoustic microscopy (OR-PAM) images biological tissue with sub-cellular resolution and optical absorption contrast. OR-PAM is limited by the tradeoff among imaging speed, field of view, and sensitivity. In this work, we present an OR-PAM technique based on an unfocused side-looking fiber optic ultrasound (FOUS) sensor, which achieves high imaging speed, large field of view, and good sensitivity for in vivo imaging. The FOUS sensor is developed based on a dual-polarized fiber laser and read out with real-time frequency demodulation. Via minimizing the readout noise, the sensor offers a noise-equivalent pressure of 43.6 Pa, enabling high detection sensitivity over a large field of view. High imaging speed is achieved via scanning the laser beam with a 2D galvo mirror in the ultrasound detection area. Microvascular imaging with a frame rate of 2 Hz over a 2 × 2 mm 2 area has been demonstrated in the mouse ear. The new OR-PAM technique may be used in the visualization of biological and physiologic dynamics.

Micro-rocket robot with all-optic actuating and tracking in blood

“…Taking advantage of scalable resolutions and depths, photoacoustic imaging of the micro-rocket robot in deep tissue may also be possible in the future using a photoacoustic computed tomographic system 32 . In addition, please note that real-time tracking with high resolution remains difficult to achieve by the current system due to its slow imaging speed, which can be improved by developing faster pulsed lasers and OR-PAM scanners 26,27 . In addition, the intensity of the actuation laser exceeds the safety threshold for in vivo applications, which is an open problem for light-driven microrobots.…”

“…Meanwhile, because longer wavelengths have weaker scattering, near-infrared photoacoustic excitation can also increase the penetration depth. In addition, in the future, a fast OR-PAM system can be used for real-time tracking of the microrocket [25][26][27][28] .…”

Dual-Polarized Fiber Laser Sensor for Photoacoustic Microscopy

“…The laser emits two linear polarization modes due to the weak birefringence of optical fiber. Each polarization mode can be expressed by [44,45]:4πcfx,y∫−∞+∞nx,yz||ez2dz=2Mπ where c is the light speed in vacuum, fx,y is the lasing frequency for each polarization mode x and y , nx,y is the refractive index, and M denotes the resonant order. The term ||ez2represents the longitudinal profile of intracavity intensity, which is normalized as ∫−∞+∞||ez2dz=1.…”

“…Considering the detection sensitivity, bandwidth, sensor size, and detection field of view [32,33,34,35,36,37,38,39,40,41,42], fiber laser sensors based on the dual-polarization principle have their unique advantages in OR-PAM. A fiber-laser-based ultrasound sensor can achieve a 40 Pa NEP over a 50 MHz bandwidth [43,44,45,46]. The smaller size makes it straightforward to combine the acoustic detection beam with the optical excitation beam.…”

Photoacoustic computed tomography with lens-free focused fiber-laser ultrasound sensor

“…Recently, fiber-laser ultrasound sensors (FUSs) interrogated using mature I/Q demodulation technique exhibited a strong immunity to environmental disturbances [25]. The FUS also showed great potential for in vivo OR-PAM imaging of vasculature in mouse ears [26]. However, the mouse ear needed to be placed extremely close to the fiber surface during the imaging process because the FUS sensitivity rapidly decayed with increasing working distance.…”