Hybrid optical parametrically-oscillating emitter at 1930 nm for volumetric photoacoustic imaging of water content

Schematic diagram of the hybrid optical parametrically-oscillating emitter (HOPE) at 1930 nm.

eLight 2, 6 (2022)
Jiawei Shi, Mingsheng Li, Huajun Tang, Jiqiang Kang, Najia Sharmin, Amir Rosenthal & Kenneth K. Y. Wong

Abstract:

Water plays a vital role in biological metabolism and it would be essential to trace the water content non-invasively, such as leveraging the vibrational absorption peak of the O–H bond. However, due to the lack of an efficient laser source, it was challenging to image the water content in the deep tissue with micron-level spatial resolution. To address this problem, we develop a high-power hybrid optical parametrically-oscillating emitter (HOPE) at 1930 nm, at which the vibrational absorption peak of the O–H bond locates. The maximum pulse energy is over 1.74 μJ with a pulse repetition rate of 50 kHz and a pulse width of 15 ns. We employ this laser source in the optical-resolution photoacoustic microscopy (OR-PAM) system to image the water content in the phantom and the biological tissue in vitro. Our 1930-nm OR-PAM could map the water content in the complex tissue environment at high spatial resolution, deep penetration depth, improved sensitivity, and suppressed artifact signal of the lipid.

PA image of (a) water acquired by 1930-nm OR-PAM

Fig. PA image of (a) water acquired by 1930-nm OR-PAM and b lipid acquired by 1750-nm OR-PAM; c Overlaid PA image of (a) and (b). d Photography of the adipose tissue. e–f Three-dimensional rendering view of (a, b). Scale bars, 500 µm

Read more – eLight 2, 6 (2022) 
Jiawei Shi, Mingsheng Li, Huajun Tang, Jiqiang Kang, Najia Sharmin, Amir Rosenthal & Kenneth K. Y. Wong

Burst-mode pulse interferometry for enabling low-noise multi-channel optical detection of ultrasound.

A schematic drawing of BM-PI.

© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement© 2019 Optics Express, OSA publishing.

Abstract
Ultrasound detection via optical resonators can achieve high levels of miniaturization and sensitivity as compared to piezoelectric detectors, but its scale-up from a single detector to an array is highly challenging. While the use of wideband sources may enable parallel interrogation of multiple resonators, it comes at the cost of reduction in the optical power, and ultimately in sensitivity, per channel. In this work we have developed a new interferometric approach to overcome this signal loss by using high-power bursts that are synchronized with the time window in which ultrasound detection is performed. Each burst is composed of a train of low-noise optical pulses which are sufficiently wideband to interrogate an array of resonators with non-overlapping spectra. We demonstrate our method, termed burst-mode pulse interferometry, for interrogating a single resonator in which the optical power was reduced to emulate the power loss per channel that occurs in parallel interrogation of 20 to 200 resonators. The use of bursts has led to up 25-fold improvement in sensitivity without affecting the shape of the acoustic signals, potentially enabling parallel low-noise interrogation of resonator arrays with a single source.

[Read more…]

The optical signal at the CM (blue) and BM (red)

Fig. The optical signal at the CM (blue) and BM (red) of the CRF output in the transition from the unlocked stated, in which the CRF blocks the optical pulses, to the locked state in which the CRF transmits the optical pulses and blocks only the ASE. Each of the spikes in the locked BM channel represents a burst with a width of 10 µs, shown in detail in Fig. 2(d), where the burst repletion rate was 8 kHz.

Oleg Volodarsky, Yoav Hazan, Michael Nagli, and Amir Rosenthal.
Optics Express, Volume 30, Issue 6, Pages 8959-8973
https://opg.optica.org/oe/abstract.cfm?URI=oe-30-6-8959

 

Algebraic determination of back-projection operators for optoacoustic tomography

source: © 2018 Optical Society of America

The simplicity and computational efficiency of back-projection formulae have made them a popular choice in optoacoustic tomography. Nonetheless, exact back-projection formulae exist for only a small set of tomographic problems. This limitation is overcome by algebraic algorithms, but at the cost of higher numerical complexity. In this paper, we present a generic algebraic framework for calculating back-projection operators in optoacoustic tomography. We demonstrate our approach in a two-dimensional optoacoustic-tomography example and show that once the algebraic back-projection operator has been found, it achieves a comparable run time to that of the conventional back-projection algorithm, but with the superior image quality of algebraic methods.[Read More…]

Fig. 1 (a) The grid of the image and detector locations used for calculating the model matrix?. The image is divided into ??×?? square pixels with a pixel area of ???? and the acoustic signals are sampled at ?? positions over a line with a distance of?? between them. (b) The image grid on which the projection operator ? is calculated. Here, only a single back-projection is calculated, and the number of pixels in the x directions is increased to ??=??+??−1.

Amir Rosenthal, “Algebraic determination of back-projection operators for optoacoustic tomography,” Biomed. Opt. Express 9, 5173-5193 (2018)

Ultrasound detection via low-noise pulse interferometry using a free-space Fabry-Pérot

source: © 2018 Optical Society of America

Coherence-restored pulse interferometry (CRPI) is a recently developed method for optical detection of ultrasound that achieves shot-noise-limited sensitivity and high dynamic range. In principle, the wideband source employed in CRPI may enable the interrogation of multiple detectors by using wavelength multiplexing. However, the noise-reduction scheme in CRPI has not been shown to be compatible with wideband operation. In this work, we introduce a new scheme for CRPI that relies on a free-space Fabry-Pérot filter for noise reduction and a pulse stretcher for reducing nonlinear effects. Using our scheme, we demonstrate that shot-noise-limited detection may be achieved for a spectral band of 80 nm and powers of up to 5 mW. [Read More…]

Fig. 1 A schematic of CRPI. EDFA is erbium-doped fiber amplifier; PZ is piezoelectric fiber stretcher; CRF is coherence-restoring filter; and π-FBG is π-phase-shifted fiber Bragg grating. The pulse train from the laser is filtered to a bandwidth of 0.4 nm, amplified, and further filtered by the CRF. Shifts of resonance of the π-FBG are measured by optical demodulator, implemented by a Mach-Zehnder interferometer locked to quadrature.

Oleg Volodarsky, Yoav Hazan, and Amir Rosenthal, “Ultrasound detection via low-noise pulse interferometry using a free-space Fabry-Pérot,” Opt. Express 26, 22405-22418 (2018)

Looking at sound: optoacoustics with all-optical ultrasound detection

source: © 2018 Light: Science & Applications

Originally developed for diagnostic ultrasound imaging, piezoelectric transducers are the most widespread technology employed in optoacoustic (photoacoustic) signal detection. However, the detection requirements of optoacoustic sensing and imaging differ from those of conventional ultrasonography and lead to specifications not sufficiently addressed by piezoelectric detectors. Consequently, interest has shifted to utilizing entirely optical methods for measuring optoacoustic waves. All-optical sound detectors yield a higher signal-to-noise ratio per unit area than piezoelectric detectors and feature wide detection bandwidths that may be more appropriate for optoacoustic applications, enabling several biomedical or industrial applications. Additionally, optical sensing of sound is less sensitive to electromagnetic noise, making it appropriate for a greater spectrum of environments. In this review, we categorize different methods of optical ultrasound detection and discuss key technology trends geared towards the development of all-optical optoacoustic systems. We also review application areas that are enabled by all-optical sound detectors, including interventional imaging, non-contact measurements, magnetoacoustics, and non-destructive testing.[Read More…]

Fig. 1 a Intensity-sensitive detection of refractive index. b Single-beam deflectometry. c Phase-sensitive ultrasound detection with a Schlieren beam. d Phase-sensitive ultrasound detection with a decoupled optoacoustic source. AL acoustic lens, CMOS CMOS camera, FP Fourier plane, L lens, LA laser, P prism, PD photodiode, QPD quadrant photodiode, SB Schlieren beam, SF spatial filter, US ultrasound

Georg Wissmeyer, Miguel A. Pleitez, Amir Rosenthal & Vasilis Ntziachristos ,”Looking at sound: optoacoustics with all-optical ultrasound detection”, in Light: Science & Applications volume 7, Article number: 53 (2018)

Passive-demodulation pulse interferometry for ultrasound detection with a high dynamic range

(a) Schematic drawing of the system used for pulse interferometry. (b) Active-demodulation scheme consists of an unbalanced Mach–Zehnder interferometer (MZI) stabilized to quadrature using a wideband feedback circuit. PZ is piezoelectric fiber stretcher, and FC is 50/50 fused fiber coupler. (c) Passive-demodulation scheme consists of a dual-polarization unbalanced MZI, implementing a 90° optical hybrid. PBS is polarization beam splitter.

source: © 2018 Optical Society of America

In the optical detection of ultrasound, resonators with high Q-factors are often used to maximize sensitivity. However, increasing the Q-factor of a resonator may reduce the linear range of the interrogation scheme, making it more susceptible to strong external perturbations and incapable of measuring strong acoustic signals. In this Letter, a passive-demodulation scheme for pulse interferometry was developed for high dynamic-range measurements. The passive scheme was based on an unbalanced Mach–Zehnder interferometer and a 90° optical hybrid, which was implemented in a dual-polarization all-fiber setup. We demonstrated the passive scheme for detecting ultrasound bursts with pressure levels for which the response of conventional, active interferometric techniques became nonlinear. [Read More…]

Fig. 1. (a) Schematic drawing of the system used for pulse interferometry. (b) Active-demodulation scheme consists of an unbalanced Mach–Zehnder interferometer (MZI) stabilized to quadrature using a wideband feedback circuit. PZ is piezoelectric fiber stretcher, and FC is 50/50 fused fiber coupler. (c) Passive-demodulation scheme consists of a dual-polarization unbalanced MZI, implementing a 90° optical hybrid. PBS is polarization beam splitter.

Yoav Hazan and Amir Rosenthal, “Passive-demodulation pulse interferometry for ultrasound detection with a high dynamic range,” Opt. Lett. 43, 1039-1042 (2018)

Ultrasound Detection Using Acoustic Apertures

source: © 2018 IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Ultrasound detection is commonly performed by piezoelectric transducers that are optimized for a specific application. Since the piezoelectric technology is not configurable, transducers designed for one application may not be compatible with other applications. In addition, some designs of ultrasound transducers may be difficult to implement owing to production constraints. In this paper, we propose a simple, low-cost method to reconfigure the geometry of ultrasound transducers. The technique is based on using apertures in thin sheets of acoustic blockers. We experimentally demonstrate this method for an ultrasound transducer with a central frequency of 1 MHz and show that it can emulate detectors of various sizes. An added advantage of this technique is its capability to achieve semi-isotropic detection sensitivity due to diffraction when the aperture size is comparable to the acoustic wavelength even when the angular sensitivity of the transducer is inherently limited.[Read More…]

Fig. 1 (a) Side view illustration of the detection scheme used in this paper. An ultrasound blocking mask with an aperture is placed in front of a large-area ultrasound receiver, resulting in an emulated detector whose detection characteristics depend on the aperture geometry. (b) Illustration of the experimental setup in which the emulated detector was used to characterize the 2-D diffraction map from an ultrasound transmitter. (c) Illustration of the setup used for characterizing the angular sensitivity of the emulated detector. (b) and (c) Transmitter was scanned in the xy plane while keeping the same z value for the transmitter, the receiver, and the aperture mask centers.

E Hahamovich, A Rosenthal, “Ultrasound Detection Using Acoustic Apertures”,in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control ( Volume: 65 , Issue: 1 , Jan. 2018 )

Modeling the sensitivity dependence of silicon-photonics-based ultrasound detectors

source: © 2017 Optical Society of America

With recent advances in optical technology, interferometric sensing has grown into a highly versatile approach for ultrasound detection, with many interferometric detectors relying on optical waveguides to achieve high levels of sensitivity and miniaturization. In this Letter, we establish a practical model for assessing the sensitivity of silicon-photonics waveguides to acoustic waves. The analysis is performed for different polarizations, waveguide dimensions, and acoustic wave types. Our model was validated experimentally in the acoustic frequency band of 1–13 MHz by measuring the sensitivities of the two polarization modes in a silicon strip waveguide. Both the experimental results and theoretical prediction show that the transverse-magnetic polarization achieves a higher sensitivity and suppression of surface acoustic waves compared to the transverse-electric polarization for the geometries studied. [Read More…]

Fig. 2. Numerical calculation of normalized sensitivity ?? as a function of the waveguide width (??) and height (??) and polarization for (a), (b) the longitudinal acoustic wave in normal incidence and (c), (d) SAWs created in oblique incidence.

Shai Tsesses, Daniel Aronovich, Assaf Grinberg, Evgeny Hahamovich, and Amir Rosenthal “Modeling the sensitivity dependence of silicon-photonics-based ultrasound detectors”, Optics Letters Vol. 42, Issue 24, pp. 5262-5265 (2017)

Analysis of Negatively Focused Ultrasound Detectors in Optoacoustic Tomography

A schematic description of acoustic absorbers in increasing sizes and a quantitative demonstration of the low-pass effect caused by the convex acoustic detector.

source:© 2017 IEEE Transactions on Medical Imaging

In optoacoustic tomography, negatively focused transducers may be used for improving the tangential image resolution while preserving a high signal-to-noise ratio. Commonly, image reconstruction in such scenarios is facilitated by the use of the virtual-detector approach. Although the validity of this approach has been experimentally verified, it is based on an approximation whose effect on optoacoustic image reconstruction has not yet been studied. In this paper, we analyze the response of negatively focused acoustic detectors in 2D in both time and frequency domains. Based on this analysis, tradeoffs between the detector size, curvature, and sensitivity are formulated. In addition, our analysis reveals the geometrical underpinning of the virtual-detector approximation and quantifies its deviation from the exact solution. The error involved in the virtual-detector approximation is studied in image reconstruction simulations and its effect on image quality is shown. The theoretical tools developed in this work may be used in the design of new optoacoustic detection geometries as well as for improved image reconstruction.
[Read More…]

Schematic illustration of (a,b) tangential and (c,d) non-tangential impact between of an impinging acoustic wave on a convex detector. (a,c) An illustration of the intersection of the acoustic wavefront with the detector surface and (b,d) of the corresponding phase factor exp[ikL(θ)] . The figure illustrates the conclusion from the SPM analysis given in (16) and (17): In the case of tangential intersection L∼θ2 and the integration over exp[ikL(θ)] in (15) is not cancelled out, whereas in the case on non-tangential intersection L∼θ which causes nullification of exp[ikL(θ)] under integration.

G. Drozdov and A. Rosenthal “Analysis of Negatively Focused Ultrasound Detectors in Optoacoustic Tomography,†accepted to Transactions on Medical Imaging ( Volume: 36 , Issue: 1 , Jan. 2017 )

Modeling of ultrasound detection by silicon-photonics-based sensors

source: © 2018 Optical Society of America

We develop a simple model for assessing the sensitivity of silicon-photonics ultrasound interferometric detectors for two types of acoustic waves. The sensitivity of the two polarization modes of a waveguide are calculated and experimentally verified. [Read More…]

Fig. 2. (a) Microscope image of the SOI sensor. PMF is polarizationmaintaining fiber (b) Schematic illustration of the interferometric setup. PZ is piezoelectric fiber stretcher; VA is variable attenuator;DL is delay line. For each polarization state, two types of acoustic waves were detected: (c) longitudinal waves in normal incidence and (d) surface acoustic waves created in oblique incidence.

Fig. 3. Measured time-dependent acoustic responses (optical phase shift) for TE (solid) and TM (dashed) waveguide modes, obtained for (a) glass fiber, (b) silicon waveguide with normal incidence and (c) silicon waveguide with surface acoustic waves created in oblique incidence.

S. Tsesses, D. Aronovich, A. Grinberg, E. Hahamovich, and A. Rosenthal, “Modeling of ultrasound detection by silicon-photonics-based sensors,” in Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF), OSA Technical Digest (online) (Optical Society of America, 2018), paper JTu2A.43.