High-resolution silicon photonics focused ultrasound transducer with a sub-millimeter aperture.

Schematic illustration of the developed transducer

2023 Optics Letters Vol. 48, Issue 10, pp. 2668-2671

Michael Nagli, Jürgen Koch, Yoav Hazan, Ahiad Levi, Orna Ternyak, Ludger Overmeyer, and Amir Rosenthal

Abstract
We present an all-optical focused ultrasound transducer with a sub-millimeter aperture and demonstrate its capability for high-resolution imaging of tissue ex vivo. The transducer is composed of a wideband silicon photonics ultrasound detector and a miniature acoustic lens coated with a thin optically absorbing metallic layer used to produce laser-generated ultrasound. The demonstrated device achieves axial resolution and lateral resolutions of 12 μm and 60 μm, respectively, well below typical values achieved by conventional piezoelectric intravascular ultrasound. The size and resolution of the developed transducer may enable its use for intravascular imaging of thin fibrous cap atheroma.

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Imaging experiments.

Fig. Imaging experiments. (a),(c) Optical images of acoustic targets. (b),(d) Ultrasound images of the targets shown in panels (a),(c). (a),(b) Images of 50-µm tungsten wires. (c),(d) Images of lamb meat and fat tissue; (d) is a 1D line scan image along the dotted line shown in panel (c); on the right side are three 0.5 mm × 0.5 mm close-up images. The image in panel (d) is “rolled” and shown in the polar coordinate system.

Michael Nagli, Jürgen Koch, Yoav Hazan, Ahiad Levi, Orna Ternyak, Ludger Overmeyer, and Amir Rosenthal

2023 Optics Letters Vol. 48, Issue 10, pp. 2668-2671
https://doi.org/10.1364/OL.486567

All-optical optoacoustic micro-tomography in reflection mode.

System Setup.

2023 Biomedical Engineering Letters

Tamar Harary, Yoav Hazan & Amir Rosenthal

Abstract
High-resolution optoacoustic imaging at depths beyond the optical diffusion limit is conventionally performed using a microscopy setup where a strongly focused ultrasound transducer samples the image object point-by-point. Although recent advancements in miniaturized ultrasound detectors enables one to achieve microscopic resolution with an unfocused detector in a tomographic configuration, such an approach requires illuminating the entire object, leading to an inefficient use of the optical power, and imposing a trans-illumination configuration that is limited to thin objects. We developed an optoacoustic micro-tomography system in an epi-illumination configuration, in which the illumination is scanned with the detector. The system is demonstrated in phantoms for imaging depths of up to 5 mm and in vivo for imaging the vasculature of a mouse ear. Although image-formation in optoacoustic tomography generally requires static illumination, our numerical simulations and experimental measurements show that this requirement is relaxed in practice due to light diffusion, which homogenizes the fluence in deep tissue layers.

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In-vivo Tomographic imaging.

Fig. In-vivo Tomographic imaging. Figure 8-a: Microscope images of mouse ear (left) and corresponding MIP of the optoacoustic image (right). Figure 8-b: Montage of four different tomographic depth. The depth difference between each consecutive slice was 50 μm. Figure 8-c. Typical raw OA signals from a mouse ear. Scale bar: 1 mm

Tamar Harary, Yoav Hazan & Amir Rosenthal

2023 Biomedical Engineering Letters
https://doi.org/10.1007/s13534-023-00278-8

Homodyne time-of-flight acousto-optic imaging for low-gain photodetector.

AOI system setup.

2023 Biomedical Engineering Letters volume 13, pages49–56 

Ahiad R.Levi, Yoav Hazan, Aner Lev, Bruno G. Sfez & Amir Rosenthal

Abstract
Acousto-optics imaging (AOI) is a hybrid imaging modality that is capable of mapping the light fluence rate in deep tissue by local ultrasound modulation of the diffused photons. Since the intensity of the modulated photons is relatively low, AOI systems often rely on high-gain photodetectors, e.g. photomultiplier tubes (PMTs), which limit scalability due to size and cost and may significantly increase the relative shot-noise in the detected signal due to low quantum yields or gain noise. In this work, we have developed a homodyne AOI scheme in which the modulated photons are amplified by interference with a reference beam, enabling their detection with a single low-gain photodetector in reflection-mode configuration. We experimentally demonstrate our approach with a silicon photodiode, achieving over a 4-fold improvement in SNR in comparison to a PMT-based setup. The increased SNR manifested in lower background noise level thus enabling deeper imaging depths. The use of a fiber-based configuration enables the integration of our scheme in a hand-held AOI probe.

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Normalized power spectrum measured

Figure – Normalized power spectrum measured in the spatial position in which the AOI was maximal using conventional ToF-AOI with a PMT (blue) and our homodyne approach with a PD (red). A consistent decrease in noise level measured in both cases in favour of PD. The 2nd and 3rd harmonics of the US signal are visible for both techniques. (Color figure online).

Ahiad R.Levi, Yoav Hazan, Aner Lev, Bruno G. Sfez & Amir Rosenthal

2023 Biomedical Engineering Letters volume 13, pages49–56 
https://doi.org/10.1007/s13534-022-00252-w