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Watt FT, Mackle EC, Zhang EZ, Beard PC, Alles EJ. Towards clinical application of freehand optical ultrasound imaging. Sci Rep 2024; 14:18779. [PMID: 39138339 PMCID: PMC11322517 DOI: 10.1038/s41598-024-69826-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2024] [Accepted: 08/09/2024] [Indexed: 08/15/2024] Open
Abstract
Freehand optical ultrasound (OpUS) imaging is an emerging ultrasound imaging paradigm that uses an array of fibre-optic, photoacoustic ultrasound sources and a single fibre-optic ultrasound detector to perform ultrasound imaging without the need for electrical components in the probe head. Previous freehand OpUS devices have demonstrated capability for real-time, video-rate imaging of clinically relevant targets, but have been hampered by poor ultrasound penetration, significant imaging artefacts and low frame rates, and their designs limited their clinical applicability. In this work we present a novel freehand OpUS imaging platform, including a fully mobile and compact acquisition console and an improved probe design. The novel freehand OpUS probe presented utilises optical waveguides to shape the generated ultrasound fields for improved ultrasound penetration depths, an extended fibre-optic bundle to improve system versatility and an overall ruggedised design with protective elements to improve probe handling and protect the internal optical components. This probe is demonstrated with phantoms and the first multi-participant in vivo imaging study conducted with freehand OpUS imaging probes, this represents several significant steps towards the clinical translation of freehand OpUS imaging.
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Affiliation(s)
- Fraser T Watt
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, London, UK.
- Department of Medical Physics & Biomedical Engineering, University College London, London, UK.
| | - Eleanor C Mackle
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, London, UK
- Department of Medical Physics & Biomedical Engineering, University College London, London, UK
| | - Edward Z Zhang
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, London, UK
- Department of Medical Physics & Biomedical Engineering, University College London, London, UK
| | - Paul C Beard
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, London, UK
- Department of Medical Physics & Biomedical Engineering, University College London, London, UK
| | - Erwin J Alles
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, London, UK
- Department of Medical Physics & Biomedical Engineering, University College London, London, UK
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2
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Zhang S, Bodian S, Zhang EZ, Beard PC, Noimark S, Desjardins AE, Colchester RJ. Miniaturised dual-modality all-optical ultrasound probe for laser interstitial thermal therapy (LITT) monitoring. BIOMEDICAL OPTICS EXPRESS 2023; 14:3446-3457. [PMID: 37497509 PMCID: PMC10368049 DOI: 10.1364/boe.494892] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Revised: 06/09/2023] [Accepted: 06/13/2023] [Indexed: 07/28/2023]
Abstract
All-optical ultrasound (OpUS) has emerged as an imaging paradigm well-suited to minimally invasive imaging due to its ability to provide high resolution imaging from miniaturised fibre optic devices. Here, we report a fibre optic device capable of concurrent laser interstitial thermal therapy (LITT) and real-time in situ all-optical ultrasound imaging for lesion monitoring. The device comprised three optical fibres: one each for ultrasound transmission, reception and thermal therapy light delivery. This device had a total lateral dimension of <1 mm and was integrated into a medical needle. Simultaneous LITT and monitoring were performed on ex vivo lamb kidney with lesion depth tracked using M-mode OpUS imaging. Using one set of laser energy parameters for LITT (5 W, 60 s), the lesion depth varied from 3.3 mm to 8.3 mm. In all cases, the full lesion depth could be visualised and measured with the OpUS images and there was a good statistical agreement with stereomicroscope images acquired after ablation (t=1.36, p=0.18). This work demonstrates the feasibility and potential of OpUS to guide LITT in tumour resection.
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Affiliation(s)
- Shaoyan Zhang
- Department of Medical Physics and Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, Charles Bell House, University College London, 43-45 Foley Street, London W1W 7TY, UK
| | - Semyon Bodian
- Department of Medical Physics and Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, Charles Bell House, University College London, 43-45 Foley Street, London W1W 7TY, UK
- Materials Chemistry Centre, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - Edward Z. Zhang
- Department of Medical Physics and Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, UK
| | - Paul C. Beard
- Department of Medical Physics and Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, Charles Bell House, University College London, 43-45 Foley Street, London W1W 7TY, UK
| | - Sacha Noimark
- Department of Medical Physics and Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, Charles Bell House, University College London, 43-45 Foley Street, London W1W 7TY, UK
- Materials Chemistry Centre, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - Adrien E. Desjardins
- Department of Medical Physics and Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, Charles Bell House, University College London, 43-45 Foley Street, London W1W 7TY, UK
| | - Richard J. Colchester
- Department of Medical Physics and Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, Charles Bell House, University College London, 43-45 Foley Street, London W1W 7TY, UK
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Zhang Q, Wu C, Long K, Huang C, Zhong X, Bai X, Cheng L, Jin L, Liang Y, Guan BO. In vivo endoscopic ultrasound imaging with a rotational-scanning, all-optical ultrasound probe. OPTICS LETTERS 2023; 48:1926-1929. [PMID: 37221801 DOI: 10.1364/ol.484841] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 02/24/2023] [Indexed: 05/25/2023]
Abstract
All-optical ultrasound manipulates ultrasound waves based on laser and photonics technologies, providing an alternative approach for pulse-echo ultrasound imaging. However, its endoscopic imaging capability is limited ex vivo by the multifiber connection between the endoscopic probe and the console. Here, we report on all-optical ultrasound for in vivo endoscopic imaging using a rotational-scanning probe that relies on a small laser sensor to detect echo ultrasound waves. The acoustically induced lasing frequency change is measured via heterodyne detection by beating the two orthogonally polarized laser modes, enabling a stable output of ultrasonic responses and immunity to low-frequency thermal and mechanical disturbances. We miniaturize its optical driving and signal interrogation unit and synchronously rotate it with the imaging probe. This specialized design leaves a single-fiber connection to the proximal end and allows fast rotational scanning of the probe. As a result, we used a flexible, miniature all-optical ultrasound probe for in vivo rectal imaging with a B-scan rate of 1 Hz and a pullback range of ∼7 cm. This can visualize the gastrointestinal and extraluminal structures of a small animal. This imaging modality offers an imaging depth of 2 cm at a central frequency of ∼20 MHz, showing promise for high-frequency ultrasound imaging applications in gastroenterology and cardiology.
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Barbosa RCS, Mendes PM. A Comprehensive Review on Photoacoustic-Based Devices for Biomedical Applications. SENSORS (BASEL, SWITZERLAND) 2022; 22:9541. [PMID: 36502258 PMCID: PMC9736954 DOI: 10.3390/s22239541] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Revised: 12/02/2022] [Accepted: 12/03/2022] [Indexed: 06/17/2023]
Abstract
The photoacoustic effect is an emerging technology that has sparked significant interest in the research field since an acoustic wave can be produced simply by the incidence of light on a material or tissue. This phenomenon has been extensively investigated, not only to perform photoacoustic imaging but also to develop highly miniaturized ultrasound probes that can provide biologically meaningful information. Therefore, this review aims to outline the materials and their fabrication process that can be employed as photoacoustic targets, both biological and non-biological, and report the main components' features to achieve a certain performance. When designing a device, it is of utmost importance to model it at an early stage for a deeper understanding and to ease the optimization process. As such, throughout this article, the different methods already implemented to model the photoacoustic effect are introduced, as well as the advantages and drawbacks inherent in each approach. However, some remaining challenges are still faced when developing such a system regarding its fabrication, modeling, and characterization, which are also discussed.
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Zhang S, Zhang EZ, Beard PC, Desjardins AE, Colchester RJ. Dual-modality fibre optic probe for simultaneous ablation and ultrasound imaging. COMMUNICATIONS ENGINEERING 2022; 1:s44172-022-00020-9. [PMID: 37033302 PMCID: PMC7614394 DOI: 10.1038/s44172-022-00020-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 07/13/2022] [Indexed: 11/08/2022]
Abstract
All-optical ultrasound (OpUS) is an emerging high resolution imaging paradigm utilising optical fibres. This allows both therapeutic and imaging modalities to be integrated into devices with dimensions small enough for minimally invasive surgical applications. Here we report a dual-modality fibre optic probe that synchronously performs laser ablation and real-time all-optical ultrasound imaging for ablation monitoring. The device comprises three optical fibres: one each for transmission and reception of ultrasound, and one for the delivery of laser light for ablation. The total device diameter is < 1 mm. Ablation monitoring was carried out on porcine liver and heart tissue ex vivo with ablation depth tracked using all-optical M-mode ultrasound imaging and lesion boundary identification using a segmentation algorithm. Ablation depths up to 2.1 mm were visualised with a good correspondence between the ultrasound depth measurements and visual inspection of the lesions using stereomicroscopy. This work demonstrates the potential for OpUS probes to guide minimally invasive ablation procedures in real time.
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Affiliation(s)
- Shaoyan Zhang
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London, WC1E 6BT UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, Foley Street, London, W1W 7TY UK
| | - Edward Z. Zhang
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London, WC1E 6BT UK
| | - Paul C. Beard
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London, WC1E 6BT UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, Foley Street, London, W1W 7TY UK
| | - Adrien E. Desjardins
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London, WC1E 6BT UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, Foley Street, London, W1W 7TY UK
| | - Richard J. Colchester
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London, WC1E 6BT UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, Foley Street, London, W1W 7TY UK
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Arjas A, Alles EJ, Maneas E, Arridge S, Desjardins A, Sillanpaa MJ, Hauptmann A. Neural Network Kalman Filtering for 3-D Object Tracking From Linear Array Ultrasound Data. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2022; 69:1691-1702. [PMID: 35324438 DOI: 10.1109/tuffc.2022.3162097] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Many interventional surgical procedures rely on medical imaging to visualize and track instruments. Such imaging methods not only need to be real time capable but also provide accurate and robust positional information. In ultrasound (US) applications, typically, only 2-D data from a linear array are available, and as such, obtaining accurate positional estimation in three dimensions is nontrivial. In this work, we first train a neural network, using realistic synthetic training data, to estimate the out-of-plane offset of an object with the associated axial aberration in the reconstructed US image. The obtained estimate is then combined with a Kalman filtering approach that utilizes positioning estimates obtained in previous time frames to improve localization robustness and reduce the impact of measurement noise. The accuracy of the proposed method is evaluated using simulations, and its practical applicability is demonstrated on experimental data obtained using a novel optical US imaging setup. Accurate and robust positional information is provided in real time. Axial and lateral coordinates for out-of-plane objects are estimated with a mean error of 0.1 mm for simulated data and a mean error of 0.2 mm for experimental data. The 3-D localization is most accurate for elevational distances larger than 1 mm, with a maximum distance of 6 mm considered for a 25-mm aperture.
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Thompson D, Nagel J, Gasteau D, Manohar S. Laser-induced ultrasound transmitters for large-volume ultrasound tomography. PHOTOACOUSTICS 2022; 25:100312. [PMID: 34868873 PMCID: PMC8626690 DOI: 10.1016/j.pacs.2021.100312] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/27/2021] [Accepted: 10/27/2021] [Indexed: 06/13/2023]
Abstract
We present a protocol for the design, fabrication and characterisation of laser-induced ultrasound transmitters with a specific, user-defined frequency response for the purpose of ultrasound tomography of large-volume biomedical samples. Using an analytic solution to the photoacoustic equation and measurements of the optical and acoustic properties of the materials used in the transmitters, we arrive at a required mixture of carbon black and polydimethylsiloxane to achieve the desired frequency response. After an in-depth explanation of the fabrication and characterisation approaches we show the performance of the fabricated transmitter, which has a centre frequency of 0.9 MHz, 200% bandwidth and 45.8 ∘ opening angle, multi-kPa pressures over a large depth range in water.
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Affiliation(s)
- D. Thompson
- Correspondence to: University of Twente, Technical Medical centre, Enschede, Netherlands.
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Alles EJ, Mackle EC, Noimark S, Zhang EZ, Beard PC, Desjardins AE. Freehand and video-rate all-optical ultrasound imaging. ULTRASONICS 2021; 116:106514. [PMID: 34280811 PMCID: PMC7611777 DOI: 10.1016/j.ultras.2021.106514] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Revised: 04/30/2021] [Accepted: 06/30/2021] [Indexed: 06/13/2023]
Abstract
All-optical ultrasound (AOUS) imaging, which uses light to both generate and detect ultrasound, is an emerging alternative to conventional electronic ultrasound imaging. To date, AOUS imaging has been performed using paradigms that either resulted in long acquisition times or employed bench-top imaging systems that were impractical for clinical use. In this work, we present a novel AOUS imaging paradigm where scanning optics are used to rapidly synthesise an imaging aperture. This paradigm enabled the first AOUS system with a flexible, handheld imaging probe, which represents a critical step towards clinical translation. This probe, which provides video-rate imaging and a real-time display, is demonstrated with phantoms and in vivo human tissue.
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Affiliation(s)
- Erwin J Alles
- Department of Medical Physics & Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, United Kingdom; Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 43-45 Foley Street, London W1W 7TS, United Kingdom.
| | - Eleanor C Mackle
- Department of Medical Physics & Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, United Kingdom; Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 43-45 Foley Street, London W1W 7TS, United Kingdom
| | - Sacha Noimark
- Department of Medical Physics & Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, United Kingdom; Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 43-45 Foley Street, London W1W 7TS, United Kingdom
| | - Edward Z Zhang
- Department of Medical Physics & Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, United Kingdom; Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 43-45 Foley Street, London W1W 7TS, United Kingdom
| | - Paul C Beard
- Department of Medical Physics & Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, United Kingdom; Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 43-45 Foley Street, London W1W 7TS, United Kingdom
| | - Adrien E Desjardins
- Department of Medical Physics & Biomedical Engineering, University College London, Malet Place Engineering Building, London WC1E 6BT, United Kingdom; Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 43-45 Foley Street, London W1W 7TS, United Kingdom
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Rajagopal S, Cox BT. Modelling laser ultrasound waveforms: The effect of varying pulse duration and material properties. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2021; 149:2040. [PMID: 33765774 DOI: 10.1121/10.0003558] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2020] [Accepted: 01/29/2021] [Indexed: 06/12/2023]
Abstract
Optical generation of ultrasound using nanosecond duration laser pulses has generated great interest both in industrial and biomedical applications. The availability of portable laser devices using semiconductor technology and optical fibres, as well as numerous source material types based on nanocomposites, has proliferated the applications of laser ultrasound. The nanocomposites can be deposited on the tip of optical fibres as well as planar hard and soft backing materials using various fabrication techniques, making devices suitable for a variety of applications. The ability to choose the acoustic material properties and the laser pulse duration gives considerable control over the ultrasound output. Here, an analytical time-domain solution is derived for the acoustic pressure waveform generated by a planar optical ultrasound source consisting of an optically absorbing layer on a backing. It is shown that by varying the optical attenuation coefficient, the thickness of the absorbing layer, the acoustic properties of the materials, and the laser pulse duration, a wide variety of pulse shapes and trains can be generated. It is shown that a source with a reflecting backing can generate pulses with higher amplitude than a source with an acoustically-matched backing in the same circumstances when stress-confinement has not been satisfied.
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Affiliation(s)
- Srinath Rajagopal
- Ultrasound and Underwater Acoustics, National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, United Kingdom
| | - Ben T Cox
- Department of Medical Physics and Biomedical Engineering, University College London, Malet Place Engineering Building, Gower Street, London, WC1E 6BT, United Kingdom
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Abstract
Purpose: Photoacoustics (optoacoustics) is a hybrid technology utilizing light excitation of acoustic responses in targets of interest. It has found numerous applications in biomedicine, including eye research, because of its ability to report both morphological and functional data about the interrogated tissue. This presentation will give an overview of current applications. Methods: Wavelength-dependent absorption of light in a tissue chromophore causes local heating, leading to a thermoelastic expansion-contraction cycle. If nanosecond pulses of light are used to excite this process, the resulting pressure wave is an ultrasound signal propagating through the tissue and detectable at the tissue surface. This is highly advantageous because of the known properties of ultrasound propagation in tissue and the ability to use standard, medical ultrasound equipment for detection. The time of arrival and amplitude of ultrasound signals provide information about the location and nature of the absorber. Results: Due to the wavelength dependence of the photoacoustic response, functional and physiological applications are possible. For example, retinal oximetry can be determined from the different optical absorption properties of oxy- and deoxyhemoglobin. Multispectral imaging of the posterior segment can identify pigments such as melanin or lipofuscin or the nature of foreign bodies. The technique can be combined with other imaging modalities such as ultrasound and optical coherence tomography to produce high-resolution images of retinal structures along with functional information. Conclusion: Photoacoustic technology is a powerful noninvasive tool for ocular research and to study ocular morphology, fundamental physiological parameters, cellular responses, and molecular expression.
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Affiliation(s)
- Randolph D Glickman
- Department of Ophthalmology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA
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Thompson D, Gasteau D, Manohar S. Spatially compounded plane wave imaging using a laser-induced ultrasound source. PHOTOACOUSTICS 2020; 18:100154. [PMID: 32071869 PMCID: PMC7013334 DOI: 10.1016/j.pacs.2019.100154] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Revised: 09/26/2019] [Accepted: 11/21/2019] [Indexed: 05/26/2023]
Abstract
This work presents spatially compounded plane wave imaging using a laser-induced ultrasound source. The plane wave source consisted of a 30 μm thick film of carbon black-doped PDMS cured on a 100 μm thick polyester substrate and presented a rectangular aperture of 40 × 3 mm. It was placed in front of a linear ultrasound array, passing through the imaging plane allowing overlap of the detection plane and the insonification plane. Illumination was provided by an array of optical fibre bundles placed above the imaging plane, at an angle. We will first present the general imaging set up and instrumentation used, after which details are given on the fabrication of the transmitter itself and on the objects that were imaged. Comparing laser-induced and conventional ultrasound images of wire phantoms shows the point-spread-function to be, in general, slightly better laterally in the conventional case but more homogeneous throughout the imaging plane with the laser-induced source. Imaging of a tissue-mimicking phantom shows a 55% improvement in contrast between a tumour and the background when using laser-induced ultrasound, as compared to the conventional case.
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Affiliation(s)
- David Thompson
- Biomedical Photonic Imaging, Technical Medical Centre, University of Twente, The Netherlands
| | - Damien Gasteau
- Biomedical Photonic Imaging, Technical Medical Centre, University of Twente, The Netherlands
- Multi-Modality Medical Imaging Group (M3I), Technical Medical Centre, University of Twente, The Netherlands
| | - Srirang Manohar
- Biomedical Photonic Imaging, Technical Medical Centre, University of Twente, The Netherlands
- Multi-Modality Medical Imaging Group (M3I), Technical Medical Centre, University of Twente, The Netherlands
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Alles EJ, Desjardins AE. Source Density Apodization: Image Artifact Suppression Through Source Pitch Nonuniformity. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2020; 67:497-504. [PMID: 31603778 PMCID: PMC7049469 DOI: 10.1109/tuffc.2019.2945636] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Conventional ultrasound imaging probes typically comprise finite-sized arrays of periodically spaced transducer elements which, in the case of phased arrays, can result in severe grating and sidelobe artifacts. Whereas side lobes can be effectively suppressed through amplitude apodization ("AmpA"), grating lobes arising from periodicity in transducer placement can only be suppressed by decreasing the element pitch, which is technologically challenging and costly. In this work, we present source density apodization ("SDA") as an alternative apodization scheme, where the spatial source density (and, hence, the element pitch) is varied across the imaging aperture. Using an all-optical ultrasound imaging setup capable of video-rate 2-D imaging as well as dynamic and arbitrary reconfiguration of the source array geometry, we show both numerically and experimentally how SDA and AmpA are equivalent for large numbers of sources. For low numbers of sources, SDA is shown to yield superior image quality as both side and grating lobes are effectively suppressed. In addition, we demonstrate how asymmetric SDA schemes can be used to locally and dynamically improve the image quality. Finally, we demonstrate how a nonsmoothly varying spatial source density (such as that obtained for randomized arrays or in the presence of source positioning uncertainty or inaccuracy) can yield severe image artifacts. The application of SDA can, thus, yield high image quality even for low channel counts, which can ultimately result in higher imaging frame rates using acquisition systems of reduced complexity.
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