Publications – Page 3

September 19, 2019September 30, 2019

Noise reduction in resonator-based ultrasound sensors by using a CW laser and phase detection.

The detection of ultrasound via optical resonators is conventionally performed by tuning a continuous-wave (CW) laser to the linear slope of the resonance and monitoring the intensity modulation at the resonator output. While intensity monitoring offers the advantage of simplicity, its sensitivity is often limited by the frequency noise of the CW laser. In this work, we develop an alternative CW technique that can significantly reduce measurement noise by monitoring variations in the phase, rather than intensity, at the resonator output. In our current implementation, which is based on a balanced Mach–Zehnder interferometer for phase detection, we demonstrate a 24-fold increase in the signal-to-noise ratio of the detected ultrasound signal over the conventional, intensity-monitoring approach.[Read more…]

Fig. – Signals detected using the IM and PM interrogation methods with an optical power of 0.1 mW. In the PM measurement, the OPD was set to zero to maximize the SNR.

Lucas Riobó, Yoav Hazan, Francisco Veiras, María Garea, Patricio Sorichetti, and Amir Rosenthal. Optics Letters Vol. 44, Issue 11, pp. 2677-2680 (2019) •https://doi.org/10.1364/OL.44.002677
© 2019 Optical Society of America

February 18, 2019September 30, 2019

The Impulse Response of Negatively Focused Spherical Ultrasound Detectors and its Effect on Tomographic Optoacoustic Reconstruction.

In optoacoustic tomography, negatively focused detectors have been shown to improve the tangential image resolution without sacrificing sensitivity. Since no exact inversion formulae exist for optoacoustic image reconstruction with negatively focused detectors, image reconstruction in such cases is based on using the virtual-detector approximation, in which it is assumed that the response of the negatively focused detector is identical, up to a constant time delay, to that of a point-like detector positioned in the detector’s center of curvature. In this work, we analyze the response of negatively focused spherical ultrasound detectors in three dimensions and demonstrate how their properties affect the optoacoustic reconstruction. Our analysis sheds new light on commonly reported experimental reconstruction artifacts in optoacoustic systems that employ negatively focused detectors. Based on our analysis, we introduce a simple correction to the virtual-detector approximation that significantly enhances image contrast and reduces artifacts. [Read more…]

Fig. (a) The geometry of the negative acoustic lens studied with full
acoustic simulations. The speed of sound of the surrounding medium and lens
material were 1500 m/s and 2757 m/s. respectively. (b) The detected acoustic
signals obtained when the lens was acoustically matched to the surrounding
medium (solid-blue curve) and when its acoustic impedance was 1.xx times that
of the surrounding medium (dashed-red curve), leading to internal reflections
in the lens structure. The reflection from the detection surface was 50% of the
pressure signal.

Gilad Drozdov, Ahiad Levi, Amir Rosenthal.
IEEE Transactions on Medical Imaging.DOI: 10.1109/TMI.2019.2897588

December 17, 2018September 30, 2019

Algebraic determination of back-projection operators for optoacoustic tomography

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)

December 17, 2018September 30, 2019

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

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)

December 17, 2018September 30, 2019

Looking at sound: optoacoustics with all-optical ultrasound detection

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)

December 17, 2018September 30, 2019

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.

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)

December 17, 2018June 18, 2023

Ultrasound Detection Using Acoustic Apertures

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 )

December 12, 2018September 30, 2019

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

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)

December 11, 2018September 30, 2019

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.

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 )

January 29, 2019September 30, 2019

Everolimus-eluting stents stabilize plaque inflammation in vivo: assessment by intravascular fluorescence molecular imaging.

Aims
Inflammation drives atherosclerosis complications and is a promising therapeutic target for plaque stabilization. At present, it is unknown whether local stenting approaches can stabilize plaque inflammation in vivo. Here, we investigate whether everolimus-eluting stents (EES) can locally suppress plaque inflammatory protease activity in vivo using intravascular near-infrared fluorescence (NIRF) molecular imaging.
Methods and results
Balloon-injured, hyperlipidaemic rabbits with atherosclerosis received non-overlapping EES and bare metal stents (BMS) placement into the infrarenal aorta (n = 7 EES, n = 7 BMS, 3.5 mm diameter x 12 mm length). Four weeks later, rabbits received an injection of the cysteine protease-activatable NIRF imaging agent Prosense VM110. Twenty-four hours later, co-registered intravascular 2D NIRF, X-ray angiography and intravascular ultrasound imaging were performed. In vivo EES-stented plaques contained substantially reduced NIRF inflammatory protease activity compared with untreated plaques and BMS-stented plaques (P = 0.006). Ex vivo macroscopic NIRF imaging of plaque protease activity corroborated the in vivo results (P = 0.003). Histopathology analyses revealed that EES-treated plaques showed reduced neointimal and medial arterial macrophage and cathepsin B expression compared with unstented and BMS-treated plaques.
Conclusions
EES-stenting stabilizes plaque inflammation as assessed by translational intravascular NIRF molecular imaging in vivo. These data further support that EES may provide a local approach for stabilizing inflamed plaques.[Read more…]

Fig. Ex vivo FRI analyses of plaque inflammatory cysteine protease activity in BMS-, EES-treated, and unstented plaque zones. (A–C) Ex vivo FRI alignments from three representative animals. All NIRF images were obtained with a one second exposure. Image windows optimized for individual images.

Marcella A. Calfon Press, Georgios Mallas, Amir Rosenthal, Tetsuya Hara, Adam Mauskapf, R. Nika Nudelman, Alexander Sheehy, Igor V. Polyakov, Frank Kolodgie, Renu Virmani, J. Luis Guerrero, Vasilis Ntziachristos, Farouc A. Jaffer.European Heart Journal – Cardiovascular Imaging, Volume 18, Issue 5, 1 May 2017, Pages 510–518.