scholarly journals Synthetic Aperture Imaging Using High-Frequency Convex Array for Ophthalmic Ultrasound Applications

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2275
Author(s):  
Hae Gyun Lim ◽  
Hyung Ham Kim ◽  
Changhan Yoon
Keyword(s):  
Image Quality ◽  
Penetration Depth ◽  
Spatial Resolution ◽  
High Frequency ◽  
Imaging System ◽  
Ex Vivo ◽  
Synthetic Aperture ◽  
Single Element ◽  
High Frequency Ultrasound ◽  
Synthetic Aperture Imaging

High-frequency ultrasound (HFUS) imaging has emerged as an essential tool for pre-clinical studies and clinical applications such as ophthalmic and dermatologic imaging. HFUS imaging systems based on array transducers capable of dynamic receive focusing have considerably improved the image quality in terms of spatial resolution and signal-to-noise ratio (SNR) compared to those by the single-element transducer-based one. However, the array system still suffers from low spatial resolution and SNR in out-of-focus regions, resulting in a blurred image and a limited penetration depth. In this paper, we present synthetic aperture imaging with a virtual source (SA-VS) for an ophthalmic application using a high-frequency convex array transducer. The performances of the SA-VS were evaluated with phantom and ex vivo experiments in comparison with the conventional dynamic receive focusing method. Pre-beamformed radio-frequency (RF) data from phantoms and excised bovine eye were acquired using a custom-built 64-channel imaging system. In the phantom experiments, the SA-VS method showed improved lateral resolution (>10%) and sidelobe level (>4.4 dB) compared to those by the conventional method. The SNR was also improved, resulting in an increased penetration depth: 16 mm and 23 mm for the conventional and SA-VS methods, respectively. Ex vivo images with the SA-VS showed improved image quality at the entire depth and visualized structures that were obscured by noise in conventional imaging.

scholarly journals Frequency-Domain Synthetic Aperture Focusing Techniques for Imaging with Single-Element Focused Transducers

2021 ◽  
Author(s):  
Elyas Shaswary
Keyword(s):  
Image Reconstruction ◽  
Image Quality ◽  
Frequency Domain ◽  
Spatial Resolution ◽  
Imaging System ◽  
Synthetic Aperture ◽  
Single Element ◽  
Diffraction Effect ◽  
Sidelobe Level ◽  
Synthetic Aperture Focusing

Synthetic aperture focusing techniques (SAFT) make the lateral spatial resolution of the conventional ultrasound imaging from a single-element focused transducer more uniform. In this work, two new frequency-domain SAFT (FD-SAFT) algorithms are proposed, which are based on 2D matched filtering techniques. The first algorithm is the FD-SAFT virtual disk source (FD-VDS) that treats the focus of a focused transducer as a finite sized virtual source and the diffraction effect in the far-field is accounted for in the image reconstruction. The second algorithm is the FD-SAFT deconvolution (FD-DC) that uses the simulated point spread function of the imaging system as a matched filter kernel in the image reconstruction. These algorithms were implemented for pulsed and linear frequency modulated chirp excitations. The performance of these algorithms was studied using a series of simulations and experiments, and it was compared with the conventional B-mode and time-domain virtual point source SAFT (TD-VPS) imaging techniques. The image quality was analyzed in terms of spatial resolution, sidelobe level, signal-to-noise ratio (SNR), contrast resolution, contrast-to- speckle ratio, and ex vivo tissue image quality. The results showed that the FD-VDS had the highest spatial resolution and FD-DC had the second highest spatial resolution. In addition, FD-DC had generally the highest SNR. The computation run time of the proposed methods was significantly lower than the TD-VPS. Furthermore, chirp excitation improves the SNR of all methods by about 8 dB without significantly affecting the spatial resolution and sidelobe level. Thus, the FD-VDS and FD-DC methods offer efficient solutions to make the spatial resolution of conventional B-mode imaging more uniform.

scholarly journals Frequency-Domain Synthetic Aperture Focusing Techniques for Imaging with Single-Element Focused Transducers

2021 ◽  
Author(s):  
Elyas Shaswary
Keyword(s):  
Image Reconstruction ◽  
Image Quality ◽  
Frequency Domain ◽  
Spatial Resolution ◽  
Imaging System ◽  
Synthetic Aperture ◽  
Single Element ◽  
Diffraction Effect ◽  
Sidelobe Level ◽  
Synthetic Aperture Focusing

Synthetic aperture focusing techniques (SAFT) make the lateral spatial resolution of the conventional ultrasound imaging from a single-element focused transducer more uniform. In this work, two new frequency-domain SAFT (FD-SAFT) algorithms are proposed, which are based on 2D matched filtering techniques. The first algorithm is the FD-SAFT virtual disk source (FD-VDS) that treats the focus of a focused transducer as a finite sized virtual source and the diffraction effect in the far-field is accounted for in the image reconstruction. The second algorithm is the FD-SAFT deconvolution (FD-DC) that uses the simulated point spread function of the imaging system as a matched filter kernel in the image reconstruction. These algorithms were implemented for pulsed and linear frequency modulated chirp excitations. The performance of these algorithms was studied using a series of simulations and experiments, and it was compared with the conventional B-mode and time-domain virtual point source SAFT (TD-VPS) imaging techniques. The image quality was analyzed in terms of spatial resolution, sidelobe level, signal-to-noise ratio (SNR), contrast resolution, contrast-to- speckle ratio, and ex vivo tissue image quality. The results showed that the FD-VDS had the highest spatial resolution and FD-DC had the second highest spatial resolution. In addition, FD-DC had generally the highest SNR. The computation run time of the proposed methods was significantly lower than the TD-VPS. Furthermore, chirp excitation improves the SNR of all methods by about 8 dB without significantly affecting the spatial resolution and sidelobe level. Thus, the FD-VDS and FD-DC methods offer efficient solutions to make the spatial resolution of conventional B-mode imaging more uniform.

scholarly journals Implementation of a Rotational Ultrasound Biomicroscopy System Equipped with a High-Frequency Angled Needle Transducer — Ex Vivo Ultrasound Imaging of Porcine Ocular Posterior Tissues

2021 ◽  
Author(s):  
Tae-Hoon Bok ◽  
Juho Kim ◽  
Jinho Bae ◽  
Chong Hyun Lee ◽  
Dong-Guk Paeng
Keyword(s):  
Ultrasound Imaging ◽  
High Frequency ◽  
Ex Vivo ◽  
Focal Length ◽  
Ultrasound Biomicroscopy ◽  
Single Element ◽  
High Frequency Ultrasound ◽  
Scanning Angle ◽  
Distance Range ◽  
Minimal Incision

The mechanical scanning of a single element transducer has been mostly utilized for high-frequency ultrasound imaging. However, it requires space for the mechanical motion of the transducer. In this paper, a rotational scanning ultrasound biomicroscopy (UBM) system equipped with a high-frequency angled needle transducer is designed and implemented in order to minimize the space required. It was applied to ex vivo ultrasound imaging of porcine posterior ocular tissues through a minimal incision hole of 1 mm in diameter. The retina and sclera for the one eye were visualized in the relative rotating angle range of 270° ~ 330° and at a distance range of 6 ~ 7 mm, whereas the tissues of the other eye were observed in relative angle range of 160° ~ 220° and at a distance range of 7.5 ~ 9 mm. The layer between retina and sclera seemed to be bent because the distance between the transducer tip and the layer was varied while the transducer was rotated. Certin features of the rotation system such as the optimal scanning angle, step angle and data length need to be improved for ensure higher accuracy and precision. Moreover, the focal length should be considered for the image quality. This implementation represents the first report of a rotational scanning UBM system.

scholarly journals Implementation of a Rotational Ultrasound Biomicroscopy System Equipped with a High-Frequency Angled Needle Transducer — Ex Vivo Ultrasound Imaging of Porcine Ocular Posterior Tissues

2021 ◽  
Author(s):  
Tae-Hoon Bok ◽  
Juho Kim ◽  
Jinho Bae ◽  
Chong Hyun Lee ◽  
Dong-Guk Paeng
Keyword(s):  
Ultrasound Imaging ◽  
High Frequency ◽  
Ex Vivo ◽  
Focal Length ◽  
Ultrasound Biomicroscopy ◽  
Single Element ◽  
High Frequency Ultrasound ◽  
Scanning Angle ◽  
Distance Range ◽  
Minimal Incision

The mechanical scanning of a single element transducer has been mostly utilized for high-frequency ultrasound imaging. However, it requires space for the mechanical motion of the transducer. In this paper, a rotational scanning ultrasound biomicroscopy (UBM) system equipped with a high-frequency angled needle transducer is designed and implemented in order to minimize the space required. It was applied to ex vivo ultrasound imaging of porcine posterior ocular tissues through a minimal incision hole of 1 mm in diameter. The retina and sclera for the one eye were visualized in the relative rotating angle range of 270° ~ 330° and at a distance range of 6 ~ 7 mm, whereas the tissues of the other eye were observed in relative angle range of 160° ~ 220° and at a distance range of 7.5 ~ 9 mm. The layer between retina and sclera seemed to be bent because the distance between the transducer tip and the layer was varied while the transducer was rotated. Certin features of the rotation system such as the optimal scanning angle, step angle and data length need to be improved for ensure higher accuracy and precision. Moreover, the focal length should be considered for the image quality. This implementation represents the first report of a rotational scanning UBM system.

scholarly journals In vivo imaging of swimming micromotors using hybrid high-frequency ultrasound and photoacoustic imaging

2020 ◽  
Author(s):  
Azaam Aziz ◽  
Joost Holthof ◽  
Sandra Meyer ◽  
Oliver G. Schmidt ◽  
Mariana Medina-Sánchez
Keyword(s):  
High Frequency ◽  
Imaging System ◽  
Ex Vivo ◽  
Photoacoustic Imaging ◽  
Imaging Techniques ◽  
High Frequency Ultrasound ◽  
Living Organisms ◽  
And Function ◽  
Frequency Ultrasound

AbstractThe fast evolution of medical micro- and nanorobots in the endeavor to perform non-invasive medical operations in living organisms boosted the use of diverse medical imaging techniques in the last years. Among those techniques, photoacoustic (PA) tomography has shown to be promising for the imaging of microrobots in deep-tissue (ex vivo and in vivo), as it possesses the molecular specificity of optical techniques and the penetration depth of ultrasound imaging. However, the precise maneuvering and function control of microrobots, in particular in living organisms, demand the combination of both anatomical and functional imaging methods. Therefore, herein, we report the use of a hybrid High-Frequency Ultrasound (HFUS) and PA imaging system for the real-time tracking of magnetically driven micromotors (single and swarms) in phantoms, ex vivo, and in vivo (in mice bladder and uterus), envisioning their application for targeted drug-delivery.

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