An Intrinsic Shape Estimation Algorithm for Flexible Ultrasound Probes Intended for Clinical Applications

field of view [2] and the ability to adapt to deformations in the target object over time (e.g., as a muscle deforms during movement). In addition, if a conformal transducer could substantially surround an anatomical target, it could be used to create tomographic images with high spatial resolution. [3] Such advantages may be useful in a variety of applications, such as inspection of complex-shaped parts in nondestructive evaluation of materials, [4] neuromodulation, [5] ultrasound therapy, [6] touch screens, [7] and medical imaging. [8,9] Musculoskeletal conditions would represent a particularly intriguing field for conformal sonography as tomographic ultrasound could supplement computed tomography (CT) or magnetic resonance (MR) imaging, and its higher temporal resolution and lack of ionizing radiation could generate insights currently unavailable through these other imaging modalities (e.g., visualizing relative movements of adjacent tissues in near-real time). The earliest versions of flexible ultrasound arrays were built using piezoceramic transducers. Since these materials were essentially rigid, flexibility was achieved by connecting the rigid transducers with mechanical joints. [4,10] Flexible arrays for biomedical and healthcare applications were also made by embedding piezoelectric components in or on a soft material, [6,[11][12][13][14] but such devices typically had low array densities. The lack of a stiff backing layer in these designs may result in narrower bandwidths compared to conventional rigid Conventional ultrasound transducers are short and rigid, which limits their applications, especially in the area of musculoskeletal imaging where many of the structures to be imaged lie within long curved anatomical structures, such as limbs. In such cases, conformal ultrasound imaging can be advantageous. This paper presents a process for fabricating 1D and 2D flexible polymer-based capacitive micromachined ultrasound transducers (flexible CMUTs). As a proof of concept, all elements of a 32-element linear flexible array are shown to be functional (100% yield) and uniform in fundamental resonant frequency (SD = 1.8%). One-way and two-way acoustic responses during immersion tests in flat, convex, and concave array configurations (radii of curvature = 3 cm) show an average fractional bandwidth of 83% and 75%, respectively, across these bending conditions. The flexible array shows no signal drop after over 100 bending cycles and only 6% variation in pulse amplitude after over 14 h of continuous operation. Finally, the resulting transducers are shown to operate at up to 15 MHz. The findings demonstrate robust operation of flexible CMUT arrays and justify further development targeted at key imaging applications, particularly in the area of diagnosing musculoskeletal conditions.

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“…Our group is currently exploring an algorithm‐based method to estimate the array shape at a given time. [ 58 ]…”

Section: Discussionmentioning

confidence: 99%

Flexible PolyCMUTs: Fabrication and Characterization of a Flexible Polymer‐Based Capacitive Micromachined Ultrasonic Array for Conformal Ultrasonography

Omidvar

Cretu

Rohling

et al. 2022

Adv Materials Technologies

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“…Noda et al, Chang et al, and Omidvar et al have suggested algorithms aimed at reconstructing precise biomedical US images. These algorithms utilize various optimization techniques such as entropy, variance, and gradient to achieve accurate US imaging results [34][35][36] . Real-time imaging can be challenging due to the iterative nature of these algorithms.…”

Section: Introduction and Purposementioning

confidence: 99%

Real-time element position tracking of flexible array transducer for ultrasound beamforming

China

Feng

Hooshangnejad

et al. 2023

Medical Imaging 2023: Ultrasonic Imaging and Tomography

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Unlike traditional ultrasound (US) transducers with rigid casing, flexible array transducers can be deformed to patientspecific geometries, thus potentially removing user dependence during real-time monitoring in radiotherapy. Proper transducer geometry estimation is required for the transducer's delay-and-sum (DAS) beamforming algorithm to reconstruct B-mode US images. The main contribution of this work is to track each element's position of the transducer to improve the quality of reconstructed images. An NDI Polaris Spectra infrared tracker was used to localize the custom design optical markers and interfaced using the Plus toolkit to estimate the transducer geometry in real-time. Each marker was localized with respect to a reference marker. Each element's coordinate position and azimuth angle were estimated using a polygon fitting algorithm. Finally, DAS was used to reconstruct the US image from radio-frequency channel data. Various transducer curvatures were emulated using gel padding placed on a CIRS phantom. The geometric accuracy of localizing the optical markers attached to the transducer surface was evaluated using 3D Cone-Beam Computed Tomography (CBCT). The tracked element positions' deviations compared to the CBCT images were measured to be 0.50±0.29 mm. The Dice score for the segmented target structure from reconstructed US images was 95.1±3.3% for above mentioned error in element position. We have obtained a high accuracy (<1mm error) when tracking the element positions with different random curvatures. The proposed method can be used for reconstructing US images to assist in real-time monitoring of radiotherapy, with minimal user dependence.

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Flexible Polymer-based Capacitive Micromachined Ultrasound Transducers (polyCMUTs): Fabrication and Characterization

Omidvar

Gerardo

Rohling

et al. 2021

2021 IEEE International Ultrasonics Symposium (IUS)

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An Intrinsic Shape Estimation Algorithm for Flexible Ultrasound Probes Intended for Clinical Applications

Cited by 5 publications

References 14 publications

Flexible PolyCMUTs: Fabrication and Characterization of a Flexible Polymer‐Based Capacitive Micromachined Ultrasonic Array for Conformal Ultrasonography

Flexible PolyCMUTs: Fabrication and Characterization of a Flexible Polymer‐Based Capacitive Micromachined Ultrasonic Array for Conformal Ultrasonography

Real-time element position tracking of flexible array transducer for ultrasound beamforming

Flexible Polymer-based Capacitive Micromachined Ultrasound Transducers (polyCMUTs): Fabrication and Characterization

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