Publications – Page 2

June 13, 2023

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

© 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…]

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

June 13, 2023June 13, 2023

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

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…]

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 Engineering – https://doi.org/10.1038/s44172-022-00030-7

July 29, 2021July 29, 2021

Single pixel imaging at megahertz switching rates via cyclic Hadamard masks.

2021 nature communications

Abstract
Optical imaging is commonly performed with either a camera and wide-field illumination or with a single detector and a scanning collimated beam; unfortunately, these options do not exist at all wavelengths. Single-pixel imaging offers an alternative that can be performed with a single detector and wide-field illumination, potentially enabling imaging applications in which the detection and illumination technologies are immature. However, single-pixel imaging currently suffers from low imaging rates owing to its reliance on configurable spatial light modulators, generally limited to 22 kHz rates. We develop an approach for rapid single-pixel imaging which relies on cyclic patterns coded onto a spinning mask and demonstrate it for in vivo imaging of C. elegans worms. Spatial modulation rates of up to 2.4 MHz, imaging rates of up to 72 fps, and image-reconstruction times of down to 1.5 ms are reported, enabling real-time visualization of dynamic objects.

[Read more…]

a Video capturing of vertically shifted resolution target, 101 × 103 resolution and 72 fps frame rate. Total recording rate of 0.75 M pixels per second. Frames 1, 30, 60, 90, 110, and 142 out of the 142 captured frames are presented. The red and blue circles mark constant positions on the resolution target. b, c Videos capturing the motion of C. elegans worms at a frame rate of 10 fps, corresponding to a total recording rate of 0.7 M pixels per second. Frames 5, 10, 15, 20, 25, and 30 out of 31 frames are presented.

Evgeny Hahamovich*, Sagi Monin*, Yoav Hazan & Amir Rosenthal
*equal contribution

2021 nature communications – https://doi.org/10.1038/s41467-021-24850-x

July 29, 2021July 29, 2021

Single-pixel imaging of dynamic objects using multi-frame motion estimation.

2021 Scientific Reports

Abstract
Single-pixel imaging (SPI) enables the visualization of objects with a single detector by using a sequence of spatially modulated illumination patterns. For natural images, the number of illumination patterns may be smaller than the number of pixels when compressed-sensing algorithms are used. Nonetheless, the sequential nature of the SPI measurement requires that the object remains static until the signals from all the required patterns have been collected. In this paper, we present a new approach to SPI that enables imaging scenarios in which the imaged object, or parts thereof, moves within the imaging plane during data acquisition. Our algorithms estimate the motion direction from inter-frame cross-correlations and incorporate it in the reconstruction model. Moreover, when the illumination pattern is cyclic, the motion may be estimated directly from the raw data, further increasing the numerical efficiency of the algorithm. A demonstration of our approach is presented for both numerically simulated and measured data.

[Read more…]

Schematic of the two proposed algorithms (a) Flow of the algorithm in case of global motion. (b) Flow of algorithm in case of local motion..

Sagi Monin, Evgeny Hahamovich & Amir Rosenthal

2021 Scientific Reports – https://doi.org/10.1038/s41598-021-83810-z

July 6, 2020

Grüneisen-relaxation photoacoustic microscopy at 1.7 µm and its application in lipid imaging.

Schematic of the GR-PAM experimental system

Abstract
We report the first, to the best of our knowledge, demonstration of Grüneisen relaxation photoacoustic microscopy (GR-PAM) of lipid-rich tissue imaging at the 1.7 µm band, implemented with a high-energy thulium-doped fiber laser and a fiber-based delay line. GR-PAM enhances the image contrast by intensifying the region of strong absorbers and suppressing out-of-focus signals. Using GR-PAM to image swine-adipose tissue at 1725 nm, an 8.26-fold contrast enhancement is achieved in comparison to conventional PAM. GR-PAM at the 1.7 µm band is expected to be a useful tool for label-free high-resolution imaging of lipid-rich tissue, such as atherosclerotic plaque and nerves.

[Read more…]

Fig. Swine muscular tissue images under (a)-(c) OR-PAM and (d)-(f) GR-PAM at (a), (d) 1700; (b), (e) 1725; and (c), (f) 1750 nm. (g) Reference confocal microscopy image at the same region.

Jiawei Shi, Can Li, Huade Mao, Yuxuan Ren, Zhi-Chao Luo, Amir Rosenthal, and Kenneth K. Y. Wong

July 6, 2020

Increased SNR in acousto-optic imaging via coded ultrasound transmission.

Abstract

Acousto-optic imaging (AOI) is a non-invasive method that uses acoustic modulation to map the light fluence inside biological tissue. In many AOI implementations, ultrasound pulses are used in a time-gated measurement to perform depth-resolved imaging without the need for mechanical scanning. However, to achieve high axial resolution, it is required that ultrasound pulses with few cycles are used, limiting the modulation strength. In this Letter, we develop a new approach to pulse-based AOI in which coded ultrasound transmission is used. In coded-transmission AOI (CT-AOI), one may achieve an axial resolution that corresponds to a single cycle, but with a signal-to-noise ratio (SNR) that scales as the square root of the number of cycles. Using CT-AOI with 79 cycles, we experimentally demonstrate over four-fold increase in SNR in comparison to a single-cycle AOI scheme.

One of the fundamental limitations of optical imaging of biological tissue is light scattering due to optical heterogeneity. At depths exceeding several transport lengths, scattering leads to the diffusion of light, which severely limits the imaging resolution that may be achieved [1]. Additionally, optical imaging with diffused light often requires solving nonlinear optimization problems in order to map tissue parameters.

Acousto-optic imaging (AOI) is a hybrid approach that overcomes the limitations of light diffusion by using acoustic modulation [2]. Conventionally, AOI is performed by illuminating the tissue with a highly coherent continuous-wave (CW) laser and using ultrasound to locally modulate the phase of the laser light inside the tissue. In AOI, the ultrasound-induced phase modulation is a result of two mechanisms [3]: pressure-induced modulation of the refractive index and periodic movement of the optical scatterers. When the coherence length of the laser is sufficiently long, the local ultrasound-induced phase modulation inside the tissue is translated into an intensity modulation of the speckle pattern on the tissue boundary. Thus, by measuring the modulation depth of the speckle on the tissue boundary, it is possible to quantify the light fluence within the tissue at the positions in which the acoustic modulation was performed [4].

AOI is capable of identifying both highly absorbing and highly scattering structures through their effect on the light fluence [5], facilitating applications such as early assessment of osteoporosis [6]. Additionally, AOI can provide information on blood flow in the acoustically modulated regions through analysis of the spectral broadening of the speckle modulation [7]. While in most applications AOI is used as an independent technique for assessing tissue parameters, it may also be used as a complimentary technique to optoacoustic tomography (OAT). In previous works [8,9], it has been shown that the information provided by AOI can remove the bias in OAT images due to light attenuation, thus enabling OAT-image quantification.

[Read more…]

Fig. 1D profile of the modulated light along the ultrasound propagation path for single-pulse AOI (blue) and CT-AOI (red) with corresponding FWMH values of 4.32 mm and 4.07 mm, respectively.

Ahiad Levi, Sagi Monin, Evgeny Hahamovich, Aner Lev, Bruno G. Sfez, and Amir Rosenthal

July 6, 2020June 18, 2023

Ultrasound Detection Arrays Via Coded Hadamard Apertures.

Abstract
In the medical fields, ultrasound detection is often performed with piezoelectric arrays that enable one to simultaneously map the acoustic fields at several positions. In this work, we develop a novel method for transforming a single-element ultrasound detector into an effective detectionarray by spatially filtering the incoming acoustic fields using a binary acoustic mask coded with cyclic Hadamard patterns. By scanning the mask in front of the detector, we obtain a multiplexed measurement dataset from which a map of the acoustic field is analyticallyconstructed. We experimentally demonstrate our method by transforming a single-element ultrasound detector into 1D arrays with up to 59 elements.

[Read more…]

Fig. Normalized waveform shape comprasion of the strongest signal for a single vs. multiplexed aperture detection. The plots are for (a) an aperture with 1.5 mm diameter and 31 elements and (b) an aperture with 1 mm diameter and 59 elements.

E. Hahamovich and A. Rosenthal, “Ultrasound Detection Arrays Via Coded Hadamard Apertures,” in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, doi: 10.1109/TUFFC.2020.2993583.

June 12, 2023

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

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…]

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

September 25, 2019July 6, 2020

Simultaneous multi-channel ultrasound detection via phase modulated pulse interferometry.

The acoustic setup used to test the performance of PM-PI.

Abstract
In optical detection of ultrasound, resonators with high Q-factors are often used to maximize sensitivity. However, in order to perform parallel interrogation, conventional interferometric techniques require an overlap between the spectra of all the resonators, which is difficult to achieve with high Q-factor resonators. In this paper, a new method is developed for parallel interrogation of optical resonators with non-overlapping spectra. The method is based on a phase-modulation scheme for pulse interferometry (PM-PI) and requires only a single photodetector and sampling channel per ultrasound detector. Using PM-PI, parallel ultrasound detection is demonstrated with four high Q-factor resonators.

[Read more…]

Fig. A schematic drawing of the PM-PI system used in this work to interrogate 4 resonators, implemented with π-phase shifted fiber Bragg gratings (π-FBGs). A wideband pulse laser with band-pass filters (BPFs) and an erbium-doped fiber amplifier (EDFA) create a source with a high spectral power density and sufficient bandwidth to cover the spectra of all the resonators. The modulation unit is an unbalanced Mach-Zehnder interferometer (MZI), composed of optical fiber couplers (FC) and a phase modulator (PM). The input phase signal to the PM, shown in the top-right plot, alternates between two values with a difference of 𝜋/2. For each phase value, the pulses interfere differently at the output of each resonator depending on the phase difference in the MZI for the specific resonance wavelength of that resonator. The bottom-right plot, shows a typical voltage signal measured for one of the resonators, which alternates between two states that correspond to the two phase values. As the bottom-right plot shows, in the current implementation, the duration of each phase value delivered to the PM corresponded to 5 laser pulses. We note that the limited bandwidth of our measurement did not allow full separation between the pulses in the bottom-right plot.

Yoav Hazan and Amir Rosenthal.
Optics Express Vol. 27, Issue 20, pp. 28844-28854 (2019) https://doi.org/10.1364/OE.27.028844

September 19, 2019September 30, 2019

Enhanced Sensitivity of Silicon-Photonics-Based Ultrasound Detection via BCB Coating.

Impact Statement:
This paper gives a solution to one of the fundamental limitations of silicon-photonics based ultrasound detectors: the low photo-elastic response of silicon and silica. By using a BCB over-cladding, 5-fold increase in the acoustic sensitivity is achieved. We additionally provide a detailed analysis of the sensing mechanism, quantifying the different effects that contribute to the enhanced sensitivity.
Abstract:
Ultrasound detection via silicon waveguides relies on the ability of acoustic waves to modulate the effective refractive index of the guided modes. However, the low photo-elastic response of silicon and silica limits the sensitivity of conventional silicon-on-insulator sensors, in which the silicon core is surrounded by a silica cladding. In this paper, we demonstrate that the sensitivity of silicon waveguides to ultrasound may be significantly enhanced by replacing the silica over-cladding with bisbenzocyclobutene (BCB)-a transparent polymer with a high photo-elastic coefficient. In our experimental study, the response to ultrasound, in terms of the induced modulation in the effective refractive index, achieved for a BCB-coated silicon waveguide with TM polarization was comparable to values previously reported for polymer waveguides and an order of magnitude higher than the response achieved by an optical fiber. In addition, in our study, the susceptibility of the sensors to surface acoustic waves and reverberations was reduced for both TE and TM modes when the BCB over-cladding was used.

[Read more…]

Fig. – The measurement setup. For each of the polarizations, a Mach-Zehnder interferometer was constructed, where in each of the interferometer arms a chip with a different over-cladding material (BCB or silica) was connected. An ultrasound transducer was used to generate acoustic waves that impinged on only one of the chips, which were separated by more than 10 cm.

Resmi Ravi Kumar, Evgeny Hahamovich, Shai Tsesses, Yoav Hazan, Assaf Grinberg, Amir Rosenthal. IEEE Photonics Journal ( Volume: 11 , Issue: 3 , June 2019 )