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

Silicon-photonics acoustic detector for optoacoustic micro-tomography.

Yoav _mouse_ear_left1_shr_450X450

© 2022 Nature  Communications

Technology developed at the Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering will allow the miniaturization of ultrasound transducers, thereby improving their resolution
New technology that allows for very high-resolution medical imaging (close to 10 µm) is expected to lead to the development of tiny and effective ultrasound systems and other medical applications. The innovative technology, SPADE, is based on research led by Professor Amir Rosenthal and Ph.D. student Yoav Hazan of the Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering at the Technion-Israel Institute of Technology. Their findings were published in Nature Communications.

Prof. Amir Rosenthal (left) and Ph.D. student Yoav Hazan of the Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering
Prof. Amir Rosenthal (left) and Ph.D. student Yoav Hazan of the Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering

Medical ultrasound is an accepted and common tool for monitoring various physiological conditions in internal tissues. Its great advantage is that unlike CT scans and x-rays, it is not based on ionizing radiation, which is considered dangerous in high doses. The main component of ultrasound systems is the transducer – an electro-mechanical device that transmits and receives ultrasound waves.

One of the technological challenges in the world of ultrasound is the development of endoscopic transducers – miniature transducers inserted through a tiny hole in the skin, or from one of the body’s natural orifices in a minimally invasive procedure. Such transducers are essential because the scan of deep tissue regions often requires a small transducer that comes close to the target tissue.

The challenge in developing these transducers stems in part from the fact that miniaturization impairs their sensitivity, making it difficult to create high-quality images. The SPADE (Silicon-Photonics Acoustic Detector) technology developed by the Technion researchers is based on optical components instead of electrical components that literally alter the image. It provides the possibility to perform ultrasound tests in resolutions not previously achieved. The researchers stress that the new technology could dramatically improve the resolution of additional diagnostic methods such as vascular imaging using optoacoustics. In this regard, the article in Nature Communications presents mapping of blood vessels in a mouse’s ear at an unprecedented resolution (about 10 microns).

image ear comparation

The study was supported by the Russell Berrie Nanotechnology Institute (RBNI), the National Science Foundation, the Polak Foundation, the Israel Innovation Authority,  the Israel Science Foundation and the Ollendorf Minerva Center.

Read more – © 2022 Nature Comunication -Silicon-photonics acoustic detector for optoacoustic micro-tomography. 

Hand-Held Optoacoustic System for the Localization of Mid-Depth Blood Vessels.

A photograph of the assembled optoacoustic probe.

Photonics 2022, 9(12), 907

Zohar Or,  Ahiad R.Levi,  Yoav Hazan and Amir Rosenthal

Abstract
The ability to rapidly locate blood vessels in patients is important in many clinical applications, e.g., in catheterization procedures. Optical techniques, including visual inspection, generally suffer from a reduced performance at depths below 1 mm, while ultrasound and optoacoustic tomography are better suited to a typical depth on the scale of 1 cm and require an additional spacer between the tissue and transducer in order to image the superficial structures at the focus plane. For this work, we developed a hand-held optoacoustic probe, designed for localizing blood vessels from the contact point down to a depth of 1 cm, without the use of a spacer. The probe employs a flat lens-free ultrasound array, enabling a largely depth-independent response down to a depth of 1 cm, at the expense of low elevational resolution. Specifically, while in lens-based probes, the acoustic signals from outside the focal region suffer from distortion, in our probe, only the amplitude of the signal varies with depth, thus leading to an imaging quality that is largely depth-independent in the imaged region. To facilitate miniaturization, dark-field illumination is used, whereby light scattering from the tissue is exploited to homogenize the sensitivity field.

[Read more…]

Optoacoustic images of the blood vessels in a human wrist.

Figure-Optoacoustic images of the blood vessels in a human wrist, at different depths and orientations. A cross-section of the radial artery can be seen clearly in real time at depths up to 7 mm, as in (a,c). A deep vein can be seen in (b) at a depth of 8 mm. In (d), we can see a vein diving from 3 to 7 mm in a longitudinal cross-section. The scale bar in subfigure (a) applies to all subfigures.

Zohar Or, Ahiad R.Levi, Yoav Hazan and Amir Rosenthal

Photonics 2022, 9(12), 907; https://doi.org/10.3390/photonics9120907

Silicon-photonics focused ultrasound detector for minimally invasive optoacoustic imaging.

ptoacoustic image of a double-loop-shaped

Biomedical Optics Express Vol. 13, Issue 12, pp. 6229-6244 (2022)
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Michael Nagli, Jürgen Koch, Yoav Hazan, Oleg Volodarsky, Resmi Ravi Kumar, Ahiad Levi, Evgeny Hahamovich, Orna Ternyak, Ludger Overmeyer, and Amir Rosenthal

Abstract
One of the main challenges in miniaturizing optoacoustic technology is the low sensitivity of sub-millimeter piezoelectric ultrasound transducers, which is often insufficient for detecting weak optoacoustic signals. Optical detectors of ultrasound can achieve significantly higher sensitivities than their piezoelectric counterparts for a given sensing area but generally lack acoustic focusing, which is essential in many minimally invasive imaging configurations. In this work, we develop a focused sub-millimeter ultrasound detector composed of a silicon-photonics optical resonator and a micro-machined acoustic lens. The acoustic lens provides acoustic focusing, which, in addition to increasing the lateral resolution, also enhances the signal. The developed detector has a wide bandwidth of 84 MHz, a focal width smaller than 50 µm, and noise-equivalent pressure of 37 mPa/Hz1/2 – an order of magnitude improvement over conventional intravascular ultrasound. We show the feasibility of the approach and the detector’s imaging capabilities by performing high-resolution optoacoustic microscopy of optical phantoms with complex geometries.

[Read more…]

The detector’s fabrication process.
Image generated by GPL Ghostscript (device=ppmraw)

Fig. The detector’s fabrication process. (a) Schematic description of the bonding and the substrate etching steps. (b) A waveguide array fabricated on top of an SOI die (left), an acoustic lens within a quartz substrate (center), and an etched waveguide array bonded to the acoustic lens (right). (c) Fiber bonding setup. The detector is placed under a microscope and between two rotating fiber holders, each connected to a 5-degree of freedom manipulator (x, y, z, pitch, yaw). (d) The assembled detector mounted on the scanning system (3D stage) inside a water tank.

Michael Nagli, Jürgen Koch, Yoav Hazan, Oleg Volodarsky, Resmi Ravi Kumar, Ahiad Levi, Evgeny Hahamovich, Orna Ternyak, Ludger Overmeyer, and Amir Rosenthal.

Biomedical Optics Express Vol. 13, Issue 12, pp. 6229-6244 (2022) •https://doi.org/10.1364/BOE.470295
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Miniaturized ultrasound detector arrays in silicon photonics using pulse transmission amplitude monitoring.

Tomographic imaging via PTAM.

© 2022 Optica Publishing Group 

Yoav Hazan, Michael Nagli, Ahiad Levi, and Amir Rosenthal

Abstract
Silicon photonics holds promise for a new generation of ultrasound-detection technology, based on optical resonators, with unparalleled miniaturization levels, sensitivities, and bandwidths, creating new possibilities for minimally invasive medical devices. While existing fabrication technologies are capable of producing dense resonator arrays whose resonance frequency is pressure sensitive, simultaneously monitoring the ultrasound-induced frequency modulation of numerous resonators has remained a challenge. Conventional techniques, which are based on tuning a continuous wave laser to the resonator wavelength, are not scalable due to the wavelength disparity between the resonators, requiring a separate laser for each resonator. In this work, we show that the Q-factor and transmission peak of silicon-based resonators can also be pressure sensitive, exploit this phenomenon to develop a readout scheme based on monitoring the amplitude, rather than frequency, at the output of the resonators using a single-pulse source, and demonstrate its compatibility with optoacoustic tomography.

[Read more…]

PTAM pressure measurements

Fig. PTAM pressure measurements. (a) Transmission spectrum of π-BG at different static pressures. The legend notes the pressure in kPa. (b) Normalized power transmission, (c) peak transmission, (d) resonance width, and (e) resonance wavelength of π-BG at different pressure calculated from the spectrum plotted in panel (a). (f) Schematic configuration of simultaneous ultrasound signal detection. Ultrasound signal, generated by a transducer, impinges the detection array at an angle. The setup results in a slight delay difference of the ultrasound signal along the detector array. (g) and (h) Measured ultrasound signals of the setup in panel (f), for resonators presented in Figs. 1(e) and 1(f), respectively.

Yoav Hazan, Michael Nagli, Ahiad Levi, and Amir Rosenthal

© 2022 Optica Publishing Group
Optics Letters Vol. 47, Issue 21, pp. 5660-5663 (2022) https://doi.org/10.1364/OL.467652https://doi.org/10.1038/s44172-022-00030-7

Single-detector 3D optoacoustic tomography via coded spatial acoustic modulation.

the measurement system setup

2022 Communications Engineering

Evgeny Hahamovich, Sagi Monin, Ahiad Levi, Yoav Hazan & Amir Rosenthal

Abstract
Optoacoustic tomography (OAT) is a hybrid imaging modality that combines optical excitation with ultrasound detection and enables high-resolution visualization of optical contrasts at tissue depths in which light is completely diffused. Despite its promise in numerous research and clinical applications, OAT is limited by the technological immaturity of ultrasound detection systems. It suffers from limited element count, narrow field of view and lack of technology for spatial modulation of acoustic signals. Here we report single-detector OAT capable of high-fidelity imaging using an amplitude mask in planar geometry coded with cyclic patterns for structured spatial acoustic modulation. Our image reconstruction method maximises sensitivity, is compatible with planar signal detection, and uses only linear operations, thus avoiding artefacts associated with the nonlinear compressed-sensing inversion. We demonstrate our method for 3D OAT of complex objects and living tissue performed with only a single ultrasound detector, effectively coded into a 2D array with 1763 elements. Our method paves the way for a new generation of high-fidelity, low-cost OAT systems.

[Read more…]

a photograph of the leg

Fig. A is a photograph of the leg. B is a subset over a vertical line of the measured signals, C is the de-multiplexed signals, and D is the MAP of the reconstructed optical density as a function of depth (z). The amplitudes are in arbitrary units.

Evgeny Hahamovich, Sagi Monin, Ahiad Levi, Yoav Hazan & Amir Rosenthal

2022 Communications Engineeringhttps://doi.org/10.1038/s44172-022-00030-7

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