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Jawli A, Aldehani W, Nabi G, Huang Z. Tissue-Mimicking Material Fabrication and Properties for Multiparametric Ultrasound Phantoms: A Systematic Review. Bioengineering (Basel) 2024; 11:620. [PMID: 38927856 PMCID: PMC11200625 DOI: 10.3390/bioengineering11060620] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2024] [Revised: 06/09/2024] [Accepted: 06/11/2024] [Indexed: 06/28/2024] Open
Abstract
Medical imaging has allowed for significant advancements in the field of ultrasound procedures over the years. However, each imaging modality exhibits distinct limitations that differently affect their accuracy. It is imperative to ensure the quality of each modality to identify and eliminate these limitations. To achieve this, a tissue-mimicking material (TMM) phantom is utilised for validation. This study aims to perform a systematic analysis of tissue-mimicking materials used for creating ultrasound phantoms. We reviewed 234 studies on the use of TMM phantoms in ultrasound that were published from 2013 to 2023 from two research databases. Our focus was on studies that discussed TMMs' properties and fabrication for ultrasound, elastography, and flow phantoms. The screening process led to the selection of 16 out of 234 studies to include in the analysis. The TMM ultrasound phantoms were categorised into three groups based on the solvent used; each group offers a broad range of physical properties. The water-based material most closely aligns with the properties of ultrasound. This study provides important information about the materials used for ultrasound phantoms. We also compared these materials to real human tissues and found that PVA matches most of the human tissues the best.
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Affiliation(s)
- Adel Jawli
- Division of Imaging Sciences and Technology, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK
- Department of Clinical Radiology, Sheikh Jaber Al-Ahmad Al-Sabah Hospital, Ministry of Health, Sulaibikhat 13001, Kuwait
| | - Wadhhah Aldehani
- Division of Imaging Sciences and Technology, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK
| | - Ghulam Nabi
- Division of Imaging Sciences and Technology, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK
| | - Zhihong Huang
- Division of Imaging Sciences and Technology, School of Medicine, Ninewells Hospital, University of Dundee, Dundee DD1 9SY, UK
- School of Science and Engineering, University of Dundee, Dundee DD1 4HN, UK
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Soloukey S, Generowicz B, Warnert E, Springeling G, Schouten J, De Zeeuw C, Dirven C, Vincent A, Kruizinga P. Patient-Specific Vascular Flow Phantom for MRI- and Doppler Ultrasound Imaging. ULTRASOUND IN MEDICINE & BIOLOGY 2024; 50:860-868. [PMID: 38471997 DOI: 10.1016/j.ultrasmedbio.2024.02.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2023] [Revised: 01/29/2024] [Accepted: 02/16/2024] [Indexed: 03/14/2024]
Abstract
OBJECTIVE Intraoperative Doppler ultrasound imaging of human brain vasculature is an emerging neuro-imaging modality that offers vascular brain mapping with unprecedented spatiotemporal resolution. At present, however, access to the human brain using Doppler Ultrasound is only possible in this intraoperative context, posing a significant challenge for validation of imaging techniques. This challenge necessitates the development of realistic flow phantoms outside of the neurosurgical operating room as external platforms for testing hardware and software. An ideal ultrasound flow phantom should provide reference-like values in standardized topologies such as a slanted pipe, and allow for measurements in structures closely resembling vascular morphology of actual patients. Additionally, the phantom should be compatible with other clinical cerebrovascular imaging modalities. To meet these criteria, we developed and validated a versatile, multimodal MRI- and ultrasound Doppler phantom. METHODS Our approach incorporates the latest advancements in phantom research using tissue-mimicking material and 3D-printing with water-soluble resin to create wall-less patient-specific lumens, compatible for ultrasound and MRI. RESULTS We successfully produced three distinct phantoms: a slanted pipe, a y-shape phantom representing a bifurcating vessel and an arteriovenous malformation (AVM) derived from clinical Digital Subtraction Angiography (DSA)-data of the brain. We present 3D ultrafast power Doppler imaging results from these phantoms, demonstrating their ability to mimic complex flow patterns as observed in the human brain. Furthermore, we showcase the compatibility of our phantom with Magnetic Resonance Imaging (MRI). CONCLUSION We developed an MRI- and Doppler Ultrasound-compatible flow-phantom using customizable, water-soluble resin prints ranging from geometrical forms to patient-specific vasculature.
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Affiliation(s)
- Sadaf Soloukey
- Department of Neuroscience, Erasmus MC, Rotterdam, The Netherlands; Department of Neurosurgery, Erasmus MC, Rotterdam, The Netherlands.
| | | | - Esther Warnert
- Deparment of Radiology and Nuclear Medicine, Erasmus MC, Rotterdam, The Netherlands; Erasmus MC Cancer Institute, Rotterdam, The Netherlands
| | - Geert Springeling
- Deparment of Experimental Medical Instrumentation, Erasmus MC, Rotterdam, The Netherlands
| | - Joost Schouten
- Department of Neurosurgery, Erasmus MC, Rotterdam, The Netherlands
| | - Chris De Zeeuw
- Department of Neuroscience, Erasmus MC, Rotterdam, The Netherlands; Netherlands Institute for Neuroscience, Royal Dutch Academy for Arts and Sciences, Amsterdam, Netherlands
| | - Clemens Dirven
- Department of Neurosurgery, Erasmus MC, Rotterdam, The Netherlands
| | - Arnaud Vincent
- Department of Neurosurgery, Erasmus MC, Rotterdam, The Netherlands
| | - Pieter Kruizinga
- Department of Neuroscience, Erasmus MC, Rotterdam, The Netherlands
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Phani D, Varadarajulu RK, Paramanick A, Paul S, Paramu R, Zacharia G, Shaiju VS, Muraleedharan V, Suheshkumar Singh M, Nair RK. Development and validation of a gel wax phantom to evaluate geometric accuracy and measurement of a hyperechoic target diameter in diagnostic ultrasound imaging. Phys Eng Sci Med 2024; 47:261-272. [PMID: 38150058 DOI: 10.1007/s13246-023-01362-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Accepted: 11/23/2023] [Indexed: 12/28/2023]
Abstract
Diagnostic ultrasound (US) scanners are generally evaluated using proprietary quality assurance (QA) phantoms, but their prohibitively high cost may prevent organizations to perform the necessary tests. This study aimed to develop a low-cost gel wax phantom with targets to determine the lateral and axial resolution and diameter of a hyperechoic target in an US scanner. The acoustic property (AP) of gel wax, which includes the speed of sound (cus), acoustic impedance (Z), and attenuation coefficient (µ), were determined for multiple transducers operating at 2.25, 5, 10, 15, and 30 MHz. These results were compared to the AP of soft tissue. Two polytetrafluoroethylene (PTFE) rectangular frames with holes separated by 5, 10, and 20 mm were constructed. Nylon filaments and stainless-steel disc (SS disc) (diameter = 16.8 mm) were threaded through the frames and suitably placed in gel wax to obtain orthogonal targets in the phantom. The target dimensions obtained from computerized tomography (CT) and US images of the phantom were compared for phantom validation. The average cus=1431.4 m/s, mass density ρ = 0.87 g/cm3, Z = 1.24 MRayls, and µ ranged from 0.7 to 0.98 dB/cm/MHz for gel wax at 22 °C. The US image measurement exhibited a maximum error in determining the diameter of the SS disc, resulting in a value of 18 mm instead of its actual value of 16.8 mm. The phantom volume decreased by 1.8% in 62 weeks. The present phantom is affordable, stable, customizable, and can be used to evaluate diagnostic US scanners across multiple centers.
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Affiliation(s)
- Debjani Phani
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India.
- Meenakshi Academy of Higher Education and Research, Chennai, Tamil Nadu, 600 078, India.
| | | | - Arijit Paramanick
- School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Thiruvananthapuram, Kerala, 695551, India
| | - Souradip Paul
- School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Thiruvananthapuram, Kerala, 695551, India
| | - Raghukumar Paramu
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
| | - George Zacharia
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
| | - V S Shaiju
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
| | - Venugopal Muraleedharan
- Department of Radio Diagnosis, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
| | - M Suheshkumar Singh
- School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Thiruvananthapuram, Kerala, 695551, India
| | - Raghuram Kesavan Nair
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
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von Haxthausen F, Rüger C, Sieren MM, Kloeckner R, Ernst F. Augmenting Image-Guided Procedures through In Situ Visualization of 3D Ultrasound via a Head-Mounted Display. SENSORS (BASEL, SWITZERLAND) 2023; 23:2168. [PMID: 36850766 PMCID: PMC9961663 DOI: 10.3390/s23042168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 02/09/2023] [Accepted: 02/10/2023] [Indexed: 06/18/2023]
Abstract
Medical ultrasound (US) is a commonly used modality for image-guided procedures. Recent research systems providing an in situ visualization of 2D US images via an augmented reality (AR) head-mounted display (HMD) were shown to be advantageous over conventional imaging through reduced task completion times and improved accuracy. In this work, we continue in the direction of recent developments by describing the first AR HMD application visualizing real-time volumetric (3D) US in situ for guiding vascular punctures. We evaluated the application on a technical level as well as in a mixed-methods user study with a qualitative prestudy and a quantitative main study, simulating a vascular puncture. Participants completed the puncture task significantly faster when using 3D US AR mode compared to 2D US AR, with a decrease of 28.4% in time. However, no significant differences were observed regarding the success rate of vascular puncture (2D US AR-50% vs. 3D US AR-72%). On the technical side, the system offers a low latency of 49.90 ± 12.92 ms and a satisfactory frame rate of 60 Hz. Our work shows the feasibility of a system that visualizes real-time 3D US data via an AR HMD, and our experiments show, furthermore, that this may offer additional benefits in US-guided tasks (i.e., reduced task completion time) over 2D US images viewed in AR by offering a vividly volumetric visualization.
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Affiliation(s)
- Felix von Haxthausen
- Institute for Robotics and Cognitive Systems, University of Lübeck, 23562 Lübeck, Germany
| | - Christoph Rüger
- Department of Surgery, Campus Charité Mitte, Campus Virchow-Klinikum, Experimental Surgery, Charité–Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Berlin Institute of Health, 10117 Berlin, Germany
| | - Malte Maria Sieren
- Department of Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein Campus Lübeck, 23569 Lübeck, Germany
- Institute of Interventional Radiology, University Hospital Schleswig-Holstein Campus Lübeck, 23569 Lübeck, Germany
| | - Roman Kloeckner
- Institute of Interventional Radiology, University Hospital Schleswig-Holstein Campus Lübeck, 23569 Lübeck, Germany
| | - Floris Ernst
- Institute for Robotics and Cognitive Systems, University of Lübeck, 23562 Lübeck, Germany
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Arteaga-Marrero N, Villa E, Llanos González AB, Gómez Gil ME, Fernández OA, Ruiz-Alzola J, González-Fernández J. Low-Cost Pseudo-Anthropomorphic PVA-C and Cellulose Lung Phantom for Ultrasound-Guided Interventions. Gels 2023; 9:gels9020074. [PMID: 36826245 PMCID: PMC9957311 DOI: 10.3390/gels9020074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 01/11/2023] [Accepted: 01/13/2023] [Indexed: 01/19/2023] Open
Abstract
A low-cost custom-made pseudo-anthropomorphic lung phantom, offering a model for ultrasound-guided interventions, is presented. The phantom is a rectangular solidstructure fabricated with polyvinyl alcohol cryogel (PVA-C) and cellulose to mimic the healthy parenchyma. The pathologies of interest were embedded as inclusions containing gaseous, liquid, or solid materials. The ribs were 3D-printed using polyethylene terephthalate, and the pleura was made of a bidimensional reticle based on PVA-C. The healthy and pathological tissues were mimicked to display acoustic and echoic properties similar to that of soft tissues. Theflexible fabrication process facilitated the modification of the physical and acoustic properties of the phantom. The phantom's manufacture offers flexibility regarding the number, shape, location, and composition of the inclusions and the insertion of ribs and pleura. In-plane and out-of-plane needle insertions, fine needle aspiration, and core needle biopsy were performed under ultrasound image guidance. The mimicked tissues displayed a resistance and recoil effect typically encountered in a real scenario for a pneumothorax, abscesses, and neoplasms. The presented phantom accurately replicated thoracic tissues (lung, ribs, and pleura) and associated pathologies providing a useful tool for training ultrasound-guided procedures.
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Affiliation(s)
- Natalia Arteaga-Marrero
- Grupo Tecnología Médica IACTEC, Instituto de Astrofísica de Canarias (IAC), 38205 San Cristóbal de La Laguna, Spain
| | - Enrique Villa
- Grupo Tecnología Médica IACTEC, Instituto de Astrofísica de Canarias (IAC), 38205 San Cristóbal de La Laguna, Spain
- Correspondence:
| | - Ana Belén Llanos González
- Departamento de Neumología, Complejo Universitario de Canarias (HUC), 38320 San Cristóbal de La Laguna, Spain
| | - Marta Elena Gómez Gil
- Departameto de Radiología, Complejo Universitario de Canarias (HUC), 38320 San Cristóbal de La Laguna, Spain
| | - Orlando Acosta Fernández
- Departamento de Neumología, Complejo Universitario de Canarias (HUC), 38320 San Cristóbal de La Laguna, Spain
| | - Juan Ruiz-Alzola
- Grupo Tecnología Médica IACTEC, Instituto de Astrofísica de Canarias (IAC), 38205 San Cristóbal de La Laguna, Spain
- Instituto Universitario de Investigaciones Biomédicas y Sanitarias (IUIBS), Universidad de Las Palmas de Gran Canaria, 35016 Las Palmas de Gran Canaria, Spain
- Departamento de Señales y Comunicaciones, Universidad de Las Palmas de Gran Canaria, 35016 Las Palmas de Gran Canaria, Spain
| | - Javier González-Fernández
- Departamento de Ingeniería Biomédica, Instituto Tecnológico de Canarias (ITC), 38009 Santa Cruz de Tenerife, Spain
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6
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McDonald-Bowyer A, Dietsch S, Dimitrakakis E, Coote JM, Lindenroth L, Stoyanov D, Stilli A. Organ curvature sensing using pneumatically attachable flexible rails in robotic-assisted laparoscopic surgery. Front Robot AI 2023; 9:1099275. [PMID: 36686214 PMCID: PMC9849801 DOI: 10.3389/frobt.2022.1099275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Accepted: 12/19/2022] [Indexed: 01/07/2023] Open
Abstract
In robotic-assisted partial nephrectomy, surgeons remove a part of a kidney often due to the presence of a mass. A drop-in ultrasound probe paired to a surgical robot is deployed to execute multiple swipes over the kidney surface to localise the mass and define the margins of resection. This sub-task is challenging and must be performed by a highly-skilled surgeon. Automating this sub-task may reduce cognitive load for the surgeon and improve patient outcomes. The eventual goal of this work is to autonomously move the ultrasound probe on the surface of the kidney taking advantage of the use of the Pneumatically Attachable Flexible (PAF) rail system, a soft robotic device used for organ scanning and repositioning. First, we integrate a shape-sensing optical fibre into the PAF rail system to evaluate the curvature of target organs in robotic-assisted laparoscopic surgery. Then, we investigate the impact of the PAF rail's material stiffness on the curvature sensing accuracy, considering that soft targets are present in the surgical field. We found overall curvature sensing accuracy to be between 1.44% and 7.27% over the range of curvatures present in adult kidneys. Finally, we use shape sensing to plan the trajectory of the da Vinci surgical robot paired with a drop-in ultrasound probe and autonomously generate an Ultrasound scan of a kidney phantom.
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Affiliation(s)
- A. McDonald-Bowyer
- Welcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, London, United Kingdom,*Correspondence: A. McDonald-Bowyer, ; A. Stilli, ; S. Dietsch,
| | - S. Dietsch
- Welcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, London, United Kingdom,*Correspondence: A. McDonald-Bowyer, ; A. Stilli, ; S. Dietsch,
| | - E. Dimitrakakis
- Welcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, London, United Kingdom
| | - J. M. Coote
- Welcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, London, United Kingdom
| | - L. Lindenroth
- Department of Surgical & Interventional Engineering, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - D. Stoyanov
- Welcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, London, United Kingdom
| | - A. Stilli
- Welcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, London, United Kingdom,*Correspondence: A. McDonald-Bowyer, ; A. Stilli, ; S. Dietsch,
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7
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Chen C, Huang Y, Chen P, Hsu Y, Jaw F, Ho M. Modification of gelatin and photocured
3D
‐printed resin to prepare biomimetic phantoms for ultrasound‐guided minimally invasive surgeries. POLYM ENG SCI 2023. [DOI: 10.1002/pen.26216] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Chien‐Hua Chen
- Department of Biomedical Engineering National Taiwan University Taipei City Taiwan
| | - Yi‐Fan Huang
- Department of Chemical Engineering National Taiwan University of Science and Technology Taipei City Taiwan
| | - Po‐Hao Chen
- Department of Chemical Engineering National Taiwan University of Science and Technology Taipei City Taiwan
| | - Yu‐Tung Hsu
- Department of Chemical Engineering National Taiwan University of Science and Technology Taipei City Taiwan
| | - Fu‐Shan Jaw
- Department of Biomedical Engineering National Taiwan University Taipei City Taiwan
| | - Ming‐Hua Ho
- Department of Chemical Engineering National Taiwan University of Science and Technology Taipei City Taiwan
- R&D Center for Membrane Technology National Taiwan University of Science and Technology Taipei Taiwan
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8
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Nguyen CD, Edwards SA, Iorizzo TW, Longo BN, Yaroslavsky AN, Kaplan DL, Mallidi S. Investigation of silk as a phantom material for ultrasound and photoacoustic imaging. PHOTOACOUSTICS 2022; 28:100416. [PMID: 36386295 PMCID: PMC9649953 DOI: 10.1016/j.pacs.2022.100416] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 10/09/2022] [Accepted: 10/11/2022] [Indexed: 05/13/2023]
Abstract
Comprehensive characterization of biomedical imaging systems require phantoms that are easy to fabricate and can mimic human tissue. Additionally, with the arrival of engineered tissues, it is key to develop phantoms that can mimic bioengineered samples. In ultrasound and photoacoustic imaging, water-soluble phantom materials such as gelatin undergo rapid degradation while polymer-based materials such as polyvinyl alcohol are not conducive for generating bioengineered tissues that can incorporate cells. Here we propose silk protein-based hydrogels as an ultrasound and photoacoustic phantom material that has potential to provide a 3D environment for long-term sustainable cell growth. Common acoustic, optical, and biomechanical properties such as ultrasound attenuation, reduced scattering coefficient, and Young's modulus were measured. The results indicate that silk acoustically mimics many tissue types while exhibiting similar reduced optical scattering in the wavelength range of 400-1200 nm. Furthermore, silk-based materials can be stored long-term with no change in acoustic and optical properties, and hence can be utilized to assess the performance of ultrasound and photoacoustic systems.
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Affiliation(s)
| | - Skye A. Edwards
- Department of Biomedical Engineering, Tufts University, Medford, MA 02155, USA
| | - Tyler W. Iorizzo
- Department of Physics, University of Massachusetts Lowell, Lowell, MA 01854 USA
| | - Brooke N. Longo
- Department of Biomedical Engineering, Tufts University, Medford, MA 02155, USA
| | - Anna N. Yaroslavsky
- Department of Physics, University of Massachusetts Lowell, Lowell, MA 01854 USA
| | - David L. Kaplan
- Department of Biomedical Engineering, Tufts University, Medford, MA 02155, USA
| | - Srivalleesha Mallidi
- Department of Biomedical Engineering, Tufts University, Medford, MA 02155, USA
- Corresponding author.
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9
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Zhong X, Cao Y, Zhou P. Thermochromic Tissue-Mimicking Phantoms for Thermal Ablation Based on Polyacrylamide Gel. ULTRASOUND IN MEDICINE & BIOLOGY 2022; 48:1361-1372. [PMID: 35623921 DOI: 10.1016/j.ultrasmedbio.2022.03.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Revised: 03/29/2022] [Accepted: 03/30/2022] [Indexed: 06/15/2023]
Abstract
In recent years, thermal ablation has played an increasingly important role in treating various tumors in the clinic. A practical thermochromic phantom model can provide a favorable platform for clinical thermotherapy training of young physicians or calibration and optimization of thermal devices without risk to animals or human participants. To date, many tissue-mimicking thermal phantoms have been developed and are well liked, especially the polyacrylamide gel (PAG)-based phantoms. This review summarizes the PAG-based phantoms in the field of thermotherapy, details their advantages and disadvantages and provides a direction for further optimization. The relevant physical parameters (such as electrical, acoustic, and thermal properties) of these phantoms are also presented in this review, which can assist operators in a deeper understanding of these phantoms and selection of the proper recipes for phantom fabrication.
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Affiliation(s)
- Xinyu Zhong
- Department of Ultrasound, Third Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Yuting Cao
- Institute of Ultrasound Imaging & Department of Ultrasound, Second Affiliated Hospital of Chongqing Medical University, Chongqing Key Laboratory of Ultrasound Molecular Imaging, Chongqing, China
| | - Ping Zhou
- Department of Ultrasound, Third Xiangya Hospital, Central South University, Changsha, Hunan, China.
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10
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Hacker L, Wabnitz H, Pifferi A, Pfefer TJ, Pogue BW, Bohndiek SE. Criteria for the design of tissue-mimicking phantoms for the standardization of biophotonic instrumentation. Nat Biomed Eng 2022; 6:541-558. [PMID: 35624150 DOI: 10.1038/s41551-022-00890-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2020] [Accepted: 02/07/2022] [Indexed: 01/08/2023]
Abstract
A lack of accepted standards and standardized phantoms suitable for the technical validation of biophotonic instrumentation hinders the reliability and reproducibility of its experimental outputs. In this Perspective, we discuss general criteria for the design of tissue-mimicking biophotonic phantoms, and use these criteria and state-of-the-art developments to critically review the literature on phantom materials and on the fabrication of phantoms. By focusing on representative examples of standardization in diffuse optical imaging and spectroscopy, fluorescence-guided surgery and photoacoustic imaging, we identify unmet needs in the development of phantoms and a set of criteria (leveraging characterization, collaboration, communication and commitment) for the standardization of biophotonic instrumentation.
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Affiliation(s)
- Lina Hacker
- Department of Physics, University of Cambridge, Cambridge, UK.,Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge, UK
| | - Heidrun Wabnitz
- Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany
| | | | | | - Brian W Pogue
- Thayer School of Engineering, Dartmouth, Hanover, NH, USA
| | - Sarah E Bohndiek
- Department of Physics, University of Cambridge, Cambridge, UK. .,Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge, UK.
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11
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Little CD, Mackle EC, Maneas E, Chong D, Nikitichev D, Constantinou J, Tsui J, Hamilton G, Rakhit RD, Mastracci TM, Desjardins AE. A patient-specific multi-modality abdominal aortic aneurysm imaging phantom. Int J Comput Assist Radiol Surg 2022; 17:1611-1617. [PMID: 35397710 PMCID: PMC9463301 DOI: 10.1007/s11548-022-02612-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Accepted: 03/15/2022] [Indexed: 11/29/2022]
Abstract
Purpose Multimodality imaging of the vascular system is a rapidly growing area of innovation and research, which is increasing with awareness of the dangers of ionizing radiation. Phantom models that are applicable across multiple imaging modalities facilitate testing and comparisons in pre-clinical studies of new devices. Additionally, phantom models are of benefit to surgical trainees for gaining experience with new techniques. We propose a temperature-stable, high-fidelity method for creating complex abdominal aortic aneurysm phantoms that are compatible with both radiation-based, and ultrasound-based imaging modalities, using low cost materials. Methods Volumetric CT data of an abdominal aortic aneurysm were acquired. Regions of interest were segmented to form a model compatible with 3D printing. The novel phantom fabrication method comprised a hybrid approach of using 3D printing of water-soluble materials to create wall-less, patient-derived vascular structures embedded within tailored tissue-mimicking materials to create realistic surrounding tissues. A non-soluble 3-D printed spine was included to provide a radiological landmark. Results The phantom was found to provide realistic appearances with intravascular ultrasound, computed tomography and transcutaneous ultrasound. Furthermore, the utility of this phantom as a training model was demonstrated during a simulated endovascular aneurysm repair procedure with image fusion. Conclusion With the hybrid fabrication method demonstrated here, complex multimodality imaging patient-derived vascular phantoms can be successfully fabricated. These have potential roles in the benchtop development of emerging imaging technologies, refinement of novel minimally invasive surgical techniques and as clinical training tools.
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Affiliation(s)
- Callum D Little
- Wellcome Trust-EPSRC Centre for Interventional and Surgical Sciences, London, W1W 7TS, UK
- Department of Medical Physics and Bioengineering, University College London, London, WC1E 6BT, UK
- Department of Cardiology, Royal Free Hospital, London, NW3 2QG, UK
| | - Eleanor C Mackle
- Wellcome Trust-EPSRC Centre for Interventional and Surgical Sciences, London, W1W 7TS, UK
- Department of Medical Physics and Bioengineering, University College London, London, WC1E 6BT, UK
| | - Efthymios Maneas
- Wellcome Trust-EPSRC Centre for Interventional and Surgical Sciences, London, W1W 7TS, UK
- Department of Medical Physics and Bioengineering, University College London, London, WC1E 6BT, UK
| | - Debra Chong
- Wellcome Trust-EPSRC Centre for Interventional and Surgical Sciences, London, W1W 7TS, UK
- Department of Vascular Surgery, Royal Free Hospital, London, NW3 2QG, UK
| | - Daniil Nikitichev
- Wellcome Trust-EPSRC Centre for Interventional and Surgical Sciences, London, W1W 7TS, UK
| | - Jason Constantinou
- Department of Vascular Surgery, Royal Free Hospital, London, NW3 2QG, UK
| | - Janice Tsui
- Wellcome Trust-EPSRC Centre for Interventional and Surgical Sciences, London, W1W 7TS, UK
- Department of Vascular Surgery, Royal Free Hospital, London, NW3 2QG, UK
| | - George Hamilton
- Wellcome Trust-EPSRC Centre for Interventional and Surgical Sciences, London, W1W 7TS, UK
- Department of Vascular Surgery, Royal Free Hospital, London, NW3 2QG, UK
| | - Roby D Rakhit
- Department of Cardiology, Royal Free Hospital, London, NW3 2QG, UK
| | - Tara M Mastracci
- Division of Surgery and Interventional Science, University College London, London, W1W 7TY, UK
| | - Adrien E Desjardins
- Wellcome Trust-EPSRC Centre for Interventional and Surgical Sciences, London, W1W 7TS, UK.
- Department of Medical Physics and Bioengineering, University College London, London, WC1E 6BT, UK.
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Paulsen SJ, Mitcham TM, Pan CS, Long J, Grigoryan B, Sazer DW, Harlan CJ, Janson KD, Pagel MD, Miller JS, Bouchard RR. Projection-based stereolithography for direct 3D printing of heterogeneous ultrasound phantoms. PLoS One 2021; 16:e0260737. [PMID: 34882719 PMCID: PMC8659365 DOI: 10.1371/journal.pone.0260737] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 11/16/2021] [Indexed: 01/17/2023] Open
Abstract
Modern ultrasound (US) imaging is increasing its clinical impact, particularly with the introduction of US-based quantitative imaging biomarkers. Continued development and validation of such novel imaging approaches requires imaging phantoms that recapitulate the underlying anatomy and pathology of interest. However, current US phantom designs are generally too simplistic to emulate the structure and variability of the human body. Therefore, there is a need to create a platform that is capable of generating well-characterized phantoms that can mimic the basic anatomical, functional, and mechanical properties of native tissues and pathologies. Using a 3D-printing technique based on stereolithography, we fabricated US phantoms using soft materials in a single fabrication session, without the need for material casting or back-filling. With this technique, we induced variable levels of stable US backscatter in our printed materials in anatomically relevant 3D patterns. Additionally, we controlled phantom stiffness from 7 to >120 kPa at the voxel level to generate isotropic and anisotropic phantoms for elasticity imaging. Lastly, we demonstrated the fabrication of channels with diameters as small as 60 micrometers and with complex geometry (e.g., tortuosity) capable of supporting blood-mimicking fluid flow. Collectively, these results show that projection-based stereolithography allows for customizable fabrication of complex US phantoms.
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Affiliation(s)
- Samantha J. Paulsen
- Department of Bioengineering, Rice University, Houston, TX, United States of America
| | - Trevor M. Mitcham
- Department of Imaging Physics, Division of Diagnostic Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, United States of America
- The University of Texas MD Anderson Cancer Center Graduate School of Biomedical Sciences, Houston, TX, United States of America
| | - Charlene S. Pan
- Department of Bioengineering, Rice University, Houston, TX, United States of America
| | - James Long
- Department of Imaging Physics, Division of Diagnostic Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, United States of America
| | - Bagrat Grigoryan
- Department of Bioengineering, Rice University, Houston, TX, United States of America
| | - Daniel W. Sazer
- Department of Bioengineering, Rice University, Houston, TX, United States of America
| | - Collin J. Harlan
- Department of Imaging Physics, Division of Diagnostic Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, United States of America
- The University of Texas MD Anderson Cancer Center Graduate School of Biomedical Sciences, Houston, TX, United States of America
| | - Kevin D. Janson
- Department of Bioengineering, Rice University, Houston, TX, United States of America
| | - Mark D. Pagel
- The University of Texas MD Anderson Cancer Center Graduate School of Biomedical Sciences, Houston, TX, United States of America
- Department of Cancer Systems Imaging, Division of Diagnostic Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, United States of America
| | - Jordan S. Miller
- Department of Bioengineering, Rice University, Houston, TX, United States of America
- * E-mail: (RRB); (JSM)
| | - Richard R. Bouchard
- Department of Imaging Physics, Division of Diagnostic Imaging, The University of Texas MD Anderson Cancer Center, Houston, TX, United States of America
- The University of Texas MD Anderson Cancer Center Graduate School of Biomedical Sciences, Houston, TX, United States of America
- * E-mail: (RRB); (JSM)
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Hacker L, Joseph J, Ivory AM, Saed MO, Zeqiri B, Rajagopal S, Bohndiek SE. A Copolymer-in-Oil Tissue-Mimicking Material With Tuneable Acoustic and Optical Characteristics for Photoacoustic Imaging Phantoms. IEEE TRANSACTIONS ON MEDICAL IMAGING 2021; 40:3593-3603. [PMID: 34152979 DOI: 10.1109/tmi.2021.3090857] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Photoacoustic imaging (PAI) standardisation demands a stable, highly reproducible physical phantom to enable routine quality control and robust performance evaluation. To address this need, we have optimised a low-cost copolymer-in-oil tissue-mimickingmaterial formulation. The base material consists of mineral oil, copolymer and stabiliser with defined Chemical Abstract Service numbers. Speed of sound c(f) and acoustic attenuation coefficient α (f) were characterised over 2-10 MHz; optical absorption μa ( λ ) and reduced scattering μs '( λ ) coefficients over 450-900 nm. Acoustic properties were optimised by modifying base component ratios and optical properties were adjusted using additives. The temporal, thermomechanical and photo-stabilitywere studied, alongwith intra-laboratory fabrication and field-testing. c(f) could be tuned up to (1516±0.6) [Formula: see text] and α (f) to (17.4±0.3)dB · cm -1 at 5 MHz. The base material exhibited negligible μa ( λ ) and μs '( λ ), which could be independently tuned by addition of Nigrosin or TiO2 respectively. These properties were stable over almost a year and were minimally affected by recasting. The material showed high intra-laboratory reproducibility (coefficient of variation <4% for c ( f ), α ( f ), optical transmittance and reflectance), and good photo- and mechanical-stability in the relevant working range (20-40°C). The optimised copolymer-in-oil material represents an excellent candidate for widespread application in PAI phantoms, with properties suitable for broader use in biophotonics and ultrasound imaging standardisation efforts.
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Dantuma M, Kruitwagen SC, Weggemans MJ, Op’t Root TJPM, Manohar S. Suite of 3D test objects for performance assessment of hybrid photoacoustic-ultrasound breast imaging systems. JOURNAL OF BIOMEDICAL OPTICS 2021; 27:JBO-210239SSR. [PMID: 34889084 PMCID: PMC8655513 DOI: 10.1117/1.jbo.27.7.074709] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Accepted: 11/16/2021] [Indexed: 06/13/2023]
Abstract
SIGNIFICANCE During the development and early testing phases of new photoacoustic (PA) breast imaging systems, several choices need to be made in aspects of system design and measurement sequences. Decision-making can be complex for state-of-the-art systems such as 3D hybrid photoacoustic-ultrasound (PA-US) breast imagers intended for multispectral quantitative imaging. These systems have a large set of design choices and system settings that affect imaging performance in different ways and often require trade-offs. Decisions have to be made carefully as they can strongly influence the imaging performance. AIM A systematic approach to assess the influence of various choices on the imaging performance in carefully controlled laboratory situations is crucial before starting with human studies. Test objects and phantoms are used for first imaging studies, but most reported structures have a 2D geometry and are not suitable to assess all the image quality characteristics (IQCs) of 3D hybrid PA-US systems. APPROACH Our work introduces a suite of five test objects designed for hybrid PA-US systems with a 3D detection aperture. We present the test object designs and production protocols and explain how they can be used to study various performance measures. To demonstrate the utility of the developed objects, measurements are made with an existing tomographic PA system. RESULTS Two test objects were developed for measurements of the US detectors' impulse responses and light distribution on the breast surface. Three others were developed to assess image quality and quantitative accuracy of the PA and US modes. Three of the five objects were imaged to demonstrate their use. CONCLUSIONS The developed test objects allow one to study influences of various choices in design and system settings. With this, IQCs can be assessed as a function of measurement sequence settings for the PA and US modes in a controlled way. Systematic studies and measurements using these objects will help to optimize various system settings and measurement protocols in laboratory situations before embarking on human studies.
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Affiliation(s)
- Maura Dantuma
- University of Twente, Multi-Modality Medical Imaging, Technical Medical Centre, Enschede, The Netherlands
| | - Saskia C. Kruitwagen
- University of Twente, Multi-Modality Medical Imaging, Technical Medical Centre, Enschede, The Netherlands
- Medisch Spectrum Twente Hospital, Enschede, The Netherlands
| | - Marlies J. Weggemans
- University of Twente, Multi-Modality Medical Imaging, Technical Medical Centre, Enschede, The Netherlands
| | | | - Srirang Manohar
- University of Twente, Multi-Modality Medical Imaging, Technical Medical Centre, Enschede, The Netherlands
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Cabrelli LC, Uliana JH, da Cruz Junior LB, Bachmann L, Carneiro AAO, Pavan TZ. Glycerol-in-SEBS gel as a material to manufacture stable wall-less vascular phantom for ultrasound and photoacoustic imaging. Biomed Phys Eng Express 2021; 7. [PMID: 34496358 DOI: 10.1088/2057-1976/ac24d6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Accepted: 09/08/2021] [Indexed: 11/12/2022]
Abstract
Styrene-ethylene/butylene-styrene (SEBS) copolymer-in-mineral oil gel is an appropriate tissue-mimicking material to manufacture stable phantoms for ultrasound and photoacoustic imaging. Glycerol dispersion has been proposed to further tune the acoustic properties and to incorporate hydrophilic additives into SEBS gel. However, this type of material has not been investigated to produce wall-less vascular flow phantom for these imaging modalities. In this paper, the development of a wall-less vascular phantom for ultrasound and photoacoustic imaging is reported. Mixtures of glycerol/TiO2-in-SEBS gel samples were manufactured at different proportions of glycerol (10%, 15%, and 20%) and TiO2(0% to 0.5%) to characterize their optical and acoustic properties. Optical absorption in the 500-950 nm range was independent of the amount of glycerol and TiO2, while optical scattering increased linearly with the concentration of TiO2. Acoustic attenuation and speed of sound were not influenced by the presence of TiO2. The sample manufactured using weight percentages of 10% SEBS, 15% glycerol, and 0.2% TiO2was selected to make the vascular phantom. The phantom proved to be stable during the pulsatile blood-mimicking fluid (BMF) flow, without any observed damage to its structure or leaks. Ultrasound color Doppler images showed a typical laminar flow, while the B-mode images showed a homogeneous speckled pattern due to the presence of the glycerol droplets in the gel. The photoacoustic images of the phantom showed a well-defined signal coming from the surface of the phantom and from the vessels where BMF was flowing. The Spearman's correlations between the photoacoustic and tabulated spectra calculated from the regions containing BMF, in this case a mixture of salt solutions (NiCl2and CuSO4), were higher than 0.95. Our results demonstrated that glycerol-in-SEBS gel was an adequate material to make a stable vascular flow phantom for ultrasound photoacoustic imaging.
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Affiliation(s)
- Luciana C Cabrelli
- Departamento de Física, FFCLRP, Universidade de São Paulo, Ribeirão Preto, Brazil
| | - Joao H Uliana
- Departamento de Física, FFCLRP, Universidade de São Paulo, Ribeirão Preto, Brazil
| | | | - Luciano Bachmann
- Departamento de Física, FFCLRP, Universidade de São Paulo, Ribeirão Preto, Brazil
| | - Antonio A O Carneiro
- Departamento de Física, FFCLRP, Universidade de São Paulo, Ribeirão Preto, Brazil
| | - Theo Z Pavan
- Departamento de Física, FFCLRP, Universidade de São Paulo, Ribeirão Preto, Brazil
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Development of Custom Wall-Less Cardiovascular Flow Phantoms with Tissue-Mimicking Gel. Cardiovasc Eng Technol 2021; 13:1-13. [PMID: 34080171 PMCID: PMC8888498 DOI: 10.1007/s13239-021-00546-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 05/12/2021] [Indexed: 10/26/2022]
Abstract
PURPOSE Flow phantoms are used in experimental settings to aid in the simulation of blood flow. Custom geometries are available, but current phantom materials present issues with degradability and/or mimicking the mechanical properties of human tissue. In this study, a method of fabricating custom wall-less flow phantoms from a tissue-mimicking gel using 3D printed inserts is developed. METHODS A 3D blood vessel geometry example of a bifurcated artery model was 3D printed in polyvinyl alcohol, embedded in tissue-mimicking gel, and subsequently dissolved to create a phantom. Uniaxial compression testing was performed to determine the Young's moduli of the five gel types. Angle-independent, ultrasound-based imaging modalities, Vector Flow Imaging (VFI) and Blood Speckle Imaging (BSI), were utilized for flow visualization of a straight channel phantom. RESULTS A wall-less phantom of the bifurcated artery was fabricated with minimal bubbles and continuous flow demonstrated. Additionally, flow was visualized through a straight channel phantom by VFI and BSI. The available gel types are suitable for mimicking a variety of tissue types, including cardiac tissue and blood vessels. CONCLUSION Custom, tissue-mimicking flow phantoms can be fabricated using the developed methodology and have potential for use in a variety of applications, including ultrasound-based imaging methods. This is the first reported use of BSI with an in vitro flow phantom.
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Wang S, Noh Y, Brown J, Roujol S, Li Y, Wang S, Housden R, Ester MC, Al-Hamadani M, Rajani R, Rhode K. Development and Testing of an Ultrasound-Compatible Cardiac Phantom for Interventional Procedure Simulation Using Direct Three-Dimensional Printing. 3D PRINTING AND ADDITIVE MANUFACTURING 2020; 7:269-278. [PMID: 33409338 PMCID: PMC7774877 DOI: 10.1089/3dp.2019.0097] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Organ phantoms are widely used for evaluating medical technologies, training clinical practitioners, as well as surgical planning. In the context of cardiovascular disease, a patient-specific cardiac phantom can play an important role for interventional cardiology procedures. However, phantoms with complicated structures are difficult to fabricate by conventional manufacturing methods. The emergence of three-dimensional (3D) printing with soft materials provides the opportunity to produce phantoms with complex geometries and realistic properties. In this work, the aim was to explore the use of a direct 3D printing technique to produce multimodal imaging cardiac phantoms and to test the physical properties of the new materials used, namely the Poro-Lay series and TangoPlus. The cardiac phantoms were first modeled using real data segmented from a patient chest computer tomography (CT) scan and then printed with the novel materials. They were then tested quantitatively in terms of stiffness and ultrasound (US) acoustic values and qualitatively with US, CT, and magnetic resonance imaging systems. From the stiffness measurements, Lay-fomm 40 had the closest Young's modulus to real myocardium with an error of 29-54%, while TangoPlus had the largest difference. From the US acoustics measurements, Lay-fomm 40 also demonstrated the closest soft tissue-mimicking properties with both the smallest attenuation and impedance differences. Furthermore, the imaging results show that the phantoms are compatible with multiple imaging modalities and thus have potential to be used for interventional procedure simulation and testing of novel interventional devices. In conclusion, direct 3D printing with Poro-Lay and TangoPlus is a promising method for manufacture of multimodal imaging phantoms with complicated structures, especially for soft patient-specific phantoms.
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Affiliation(s)
- Shu Wang
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
- Address correspondence to: Shu Wang, School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, 4th Floor, Lambeth Wing, Westminster Bridge Road, London SE1 7EH, United Kingdom
| | - Yohan Noh
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Jemma Brown
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Sébastien Roujol
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Ye Li
- British Heart Foundation Centre, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Shuangyi Wang
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Richard Housden
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Mar Casajuana Ester
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Maleha Al-Hamadani
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Ronak Rajani
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
| | - Kawal Rhode
- School of Biomedical Engineering & Imaging Sciences, St Thomas' Hospital, King's College London, London, United Kingdom
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Pavan TZ, Evertsson M. Oil-Based Gel Phantoms and the Speed of Sound. ULTRASOUND IN MEDICINE & BIOLOGY 2020; 46:3170-3171. [PMID: 32782089 DOI: 10.1016/j.ultrasmedbio.2020.07.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Revised: 07/07/2020] [Accepted: 07/08/2020] [Indexed: 06/11/2023]
Affiliation(s)
- Theo Z Pavan
- Department of Physics, FFCLRP, University of São Paulo, Ribeirão Preto, SP, Brazil.
| | - Maria Evertsson
- Biomedical Engineering, Department of Clinical Sciences Lund, Lund University, Lund, Sweden
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Kaschwich M, Dell A, Matysiak F, Bouchagiar J, Bayer A, Scharfschwerdt M, Ernst F, Kleemann M, Horn M. Development of an ultrasound-capable phantom with patient-specific 3D-printed vascular anatomy to simulate peripheral endovascular interventions. Ann Anat 2020; 232:151563. [DOI: 10.1016/j.aanat.2020.151563] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2020] [Revised: 05/26/2020] [Accepted: 05/27/2020] [Indexed: 12/19/2022]
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La Torre A, Visioli CB. Neonatal brain ultrasound training for beginners: Could a head phantom be useful? ULTRASOUND : JOURNAL OF THE BRITISH MEDICAL ULTRASOUND SOCIETY 2020; 28:180-186. [PMID: 32831891 DOI: 10.1177/1742271x19894612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 10/21/2019] [Indexed: 11/16/2022]
Abstract
Background The traditional method of teaching the technique of neonatal brain ultrasonography is based upon the interaction between the practitioner and the neonate under the supervision of a tutor. This approach has disadvantages in that it may result in a longer imaging examination and the patient may become agitated. As demand for ultrasound services escalates and departments get busier, this often means that the trainee and supervisor are under pressure to work rapidly. Such environments are common but not conducive to the development of adequate skills and competencies. A neonatal head phantom used as part of a dedicated study day could help the beginner to learn basic elements of the ultrasound examination within a safe stress-free environment. It offers the opportunity to repeat the examination as often as the trainee wishes without time pressures and the distraction of a moving and potentially very sick baby. Aim The aim of this study is to evaluate the efficacy of a commercial phantom as a means for the practitioner to acquire the fundamental principles of neonatal brain ultrasound. Method A total of 17 participants attending a one day neonatal ultrasound course aimed at beginners were invited to complete a short two-part questionnaire that assessed their perceived improvement in scanning ability before and after using a commercially available head phantom. Results Of the 14 returned questionnaires, the overall perceived understanding, ability and confidence improved and anxiety levels about the procedure fell. The median pre-training score was 9.0 compared with the median post-training score of 12.0 (P = 0.005, Wilcoxon signed-rank test). At least 79% (up to 86%) of participants valued their experience with the phantom and would recommend the course to colleagues. Furthermore, about two-thirds reported that they would like to have additional practise with the phantom. Preliminary data from this study suggest that beginners found the head phantom useful for mastering some of the early skills required for neonatal brain ultrasound examinations, which in turn improved their confidence and reduced anxiety.
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Affiliation(s)
- Antonio La Torre
- Department of Neonatology, AOU Careggi Hospital, Florence, Italy
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21
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Phani D, Varadarajulu RK, Thomas A, Paramu R, Singh MS, Shaiju VS, Muraleedharan V, Nair RK. Acoustic and ultrasonographic characterization of polychloroprene, beeswax, and carbomer-gel to mimic soft-tissue for diagnostic ultrasound. Phys Eng Sci Med 2020; 43:1171-1181. [PMID: 32809141 DOI: 10.1007/s13246-020-00919-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 08/09/2020] [Indexed: 10/23/2022]
Abstract
Materials with acoustic properties similar to soft-tissue are essential as tissue-mimicking materials (TMMs) for diagnostic ultrasound (US). The velocity (cus), acoustic impedance (AI) and attenuation coefficient of US (µ) in a material collectively define its acoustic property. In this work, the acoustic properties of polychloroprene rubber, beeswax, and Carbomer-gel are determined. The pulse-echo technique is used to estimate cus and µ. The product of a sample density (ρ) and cus gives its AI. Using a reference based on the International Commission on Radiation Units and Measurements Report-61, Tissue Substitutes, Phantoms and Computational Modelling in Medical Ultrasound, the results are evaluated. The acceptance criteria are 1.043 ± 0.021 g/cm3 (ρ), 1561 ± 31.22 m/s (cus), 1.63 ± 0.065 MRayls (AI) and µ within 0.5-0.7 dB/cm/MHz. Sample computerized tomography (CT) and US scanning are performed to evaluate their similarities (contrast and speckle pattern) with respective images of the human liver (a clinical soft-tissue). The average errors in measuring cus and µ were 0.14% and 1.2% respectively. From the present findings, acoustic properties of polychloroprene and beeswax are unacceptable. However, the results of Carbomer-gel ρ = 1.03 g/cm3, cus = 1567 m/s, AI = 1.61 MRayls are satisfactory and µ = 0.73 dB/cm/MHz, is higher than the reference (4.3%). Carbomer-gel could produce CT and US images, efficiently mimicking the respective liver images. Carbomer-gel containing 95% water is a low-cost material with a simple formulation. Present results suggest, Carbomer- gel mimics soft-tissue and can be used as a TMM for diagnostic US.
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Affiliation(s)
- Debjani Phani
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India.
- Meenakshi Academy of Higher Education and Research, Chennai, Tamilnadu, 600 078, India.
| | | | - Anjali Thomas
- School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Vithura, Thiruvananthapuram, Kerala, 695551, India
| | - Raghukumar Paramu
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
| | - M Suheshkumar Singh
- School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Vithura, Thiruvananthapuram, Kerala, 695551, India
| | - V S Shaiju
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
| | - Venugopal Muraleedharan
- Department of Radio Diagnosis, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
| | - Raghuram Kesavan Nair
- Department of Radiation Physics, Regional Cancer Centre, Thiruvananthapuram, Kerala, 695011, India
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22
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Mackle EC, Shapey J, Maneas E, Saeed SR, Bradford R, Ourselin S, Vercauteren T, Desjardins AE. Patient-Specific Polyvinyl Alcohol Phantom Fabrication with Ultrasound and X-Ray Contrast for Brain Tumor Surgery Planning. J Vis Exp 2020. [PMID: 32744524 PMCID: PMC7610642 DOI: 10.3791/61344] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Phantoms are essential tools for clinical training, surgical planning and the development of novel medical devices. However, it is challenging to create anatomically accurate head phantoms with realistic brain imaging properties because standard fabrication methods are not optimized to replicate any patient-specific anatomical detail and 3D printing materials are not optimized for imaging properties. In order to test and validate a novel navigation system for use during brain tumor surgery, an anatomically accurate phantom with realistic imaging and mechanical properties was required. Therefore, a phantom was developed using real patient data as input and 3D printing of molds to fabricate a patient-specific head phantom comprising the skull, brain and tumor with both ultrasound and X-ray contrast. The phantom also had mechanical properties that allowed the phantom tissue to be manipulated in a similar manner to how human brain tissue is handled during surgery. The phantom was successfully tested during a surgical simulation in a virtual operating room. The phantom fabrication method uses commercially available materials and is easy to reproduce. The 3D printing files can be readily shared, and the technique can be adapted to encompass many different types of tumor.
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Affiliation(s)
- Eleanor C Mackle
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London; Department of Medical Physics and Biomedical Engineering, University College London;
| | - Jonathan Shapey
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London; Department of Medical Physics and Biomedical Engineering, University College London; Department of Neurosurgery, National Hospital for Neurology and Neurosurgery; School of Biomedical Engineering & Imaging Sciences, King's College London
| | - Efthymios Maneas
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London; Department of Medical Physics and Biomedical Engineering, University College London
| | - Shakeel R Saeed
- Department of Neurosurgery, National Hospital for Neurology and Neurosurgery; The Ear Institute, University College London; The Royal National Throat, Nose and Ear Hospital, London
| | - Robert Bradford
- Department of Neurosurgery, National Hospital for Neurology and Neurosurgery
| | - Sebastien Ourselin
- School of Biomedical Engineering & Imaging Sciences, King's College London
| | - Tom Vercauteren
- School of Biomedical Engineering & Imaging Sciences, King's College London
| | - Adrien E Desjardins
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London; Department of Medical Physics and Biomedical Engineering, University College London
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Wang C, Komninos C, Andersen S, D'Ettorre C, Dwyer G, Maneas E, Edwards P, Desjardins A, Stilli A, Stoyanov D. Ultrasound 3D reconstruction of malignant masses in robotic-assisted partial nephrectomy using the PAF rail system: a comparison study. Int J Comput Assist Radiol Surg 2020; 15:1147-1155. [PMID: 32385597 PMCID: PMC7316668 DOI: 10.1007/s11548-020-02149-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Accepted: 03/31/2020] [Indexed: 12/11/2022]
Abstract
Purpose In robotic-assisted partial nephrectomy (RAPN), the use of intraoperative ultrasound (IOUS) helps to localise and outline the tumours as well as the blood vessels within the kidney. The aim of this work is to evaluate the use of the pneumatically attachable flexible (PAF) rail system for US 3D reconstruction of malignant masses in RAPN. The PAF rail system is a novel device developed and previously presented by the authors to enable track-guided US scanning. Methods We present a comparison study between US 3D reconstruction of masses based on: the da Vinci Surgical System kinematics, single- and stereo-camera tracking of visual markers embedded on the probe. An US-realistic kidney phantom embedding a mass is used for testing. A new design for the US probe attachment to enhance the performance of the kinematic approach is presented. A feature extraction algorithm is proposed to detect the margins of the targeted mass in US images. Results To evaluate the performance of the investigated approaches the resulting 3D reconstructions have been compared to a CT scan of the phantom. The data collected indicates that single camera reconstruction outperformed the other approaches, reconstructing with a sub-millimetre accuracy the targeted mass. Conclusions This work demonstrates that the PAF rail system provides a reliable platform to enable accurate US 3D reconstruction of masses in RAPN procedures. The proposed system has also the potential to be employed in other surgical procedures such as hepatectomy or laparoscopic liver resection.
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Affiliation(s)
- Chongyun Wang
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS), University College London, 43-45 Foley St., Fitzrovia, London, W1W 7EJ, UK
| | - Charalampos Komninos
- Department of Electrical and Computer Engineering, University of Patras, 26504, Rio, Patras, Greece
| | - Stephanie Andersen
- Department of Computer Science, Stanford University, 353 Serra Mall, Stanford, CA, 94305, USA
| | - Claudia D'Ettorre
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS), University College London, 43-45 Foley St., Fitzrovia, London, W1W 7EJ, UK
| | - George Dwyer
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS), University College London, 43-45 Foley St., Fitzrovia, London, W1W 7EJ, UK
| | - Efthymios Maneas
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS), University College London, 43-45 Foley St., Fitzrovia, London, W1W 7EJ, UK
| | - Philip Edwards
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS), University College London, 43-45 Foley St., Fitzrovia, London, W1W 7EJ, UK
| | - Adrien Desjardins
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS), University College London, 43-45 Foley St., Fitzrovia, London, W1W 7EJ, UK
| | - Agostino Stilli
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS), University College London, 43-45 Foley St., Fitzrovia, London, W1W 7EJ, UK.
| | - Danail Stoyanov
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences (WEISS), University College London, 43-45 Foley St., Fitzrovia, London, W1W 7EJ, UK
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Dong J, Zhang Y, Lee WN. Walled vessel-mimicking phantom for ultrasound imaging using 3D printing with a water-soluble filament: design principle, fluid-structure interaction (FSI) simulation, and experimental validation. Phys Med Biol 2020; 65:085006. [PMID: 32106096 DOI: 10.1088/1361-6560/ab7abf] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The geometry and stiffness of a vessel are pertinent to blood dynamics and vessel wall mechanical behavior and may alter in diseased conditions. Ultrasound-based ultrafast Doppler (uDoppler) imaging and shear wave imaging (SWI) techniques have been extensively exploited for the assessment of vascular hemodynamics and mechanics. Their performance is conventionally validated on vessel-mimicking phantoms (VMPs) prior to their clinical use. Compared with commercial ones, customized VMPs are favored for research use because of their wider range of material properties, more complex lumen geometries, or wall structures. Fused deposition modeling (FDM) 3D printing technique with plastic filaments is a promising method for making VMPs with a complex vessel lumen. However, it may require a toxic solvent or a long dissolution time currently. In this paper, we present a safe, efficient and geometrically flexible method where FDM 3D printing with a water-soluble polyvinyl alcohol (PVA) filament is exploited to fabricate a walled three-branch VMP (VMP-I). As a key step in fabrication, to avoid dissolution of the PVA-printed vessel core by the solution of the tissue-mimicking material, paraffin wax was used for isolation. Paraffin wax is easy to coat (i.e. without any special equipment), of satisfactory thickness (∼0.1 mm), chemically stable, and easy to remove after fabrication, thus making the proposed method practicable for ultrasound imaging studies. VMP-I was examined by B-mode imaging and power Doppler imaging (PDI) to verify complete dissolution of PVA-printed vessel core in its lumen, confirming good fabrication quality. The flow velocities in VMP-I were estimated by uDoppler imaging with a -0.8% difference, and the shear wave propagation speeds for the same phantom were estimated by SWI with a -6.03% difference when compared with fluid-structure interaction (FSI) simulation results. A wall-less VMP of a scaled and simplified coronary arterial network (VMP-II) was additionally fabricated and examined to test the capability of the proposed method for a complex lumen geometry. The proposed fabrication method for customized VMPs is foreseen to facilitate the development of ultrasound imaging techniques for blood vessels.
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Affiliation(s)
- Jinping Dong
- Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong
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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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Manohar S, Dantuma M. Current and future trends in photoacoustic breast imaging. PHOTOACOUSTICS 2019; 16:100134. [PMID: 31871887 PMCID: PMC6909206 DOI: 10.1016/j.pacs.2019.04.004] [Citation(s) in RCA: 81] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 02/19/2019] [Accepted: 04/10/2019] [Indexed: 05/14/2023]
Abstract
Non-invasive detection of breast cancer has been regarded as the holy grail of applications for photoacoustic (optoacoustic) imaging right from the early days of re-discovery of the method. Two-and-a-half decades later we report on the state-of-the-art in photoacoustic breast imaging technology and clinical studies. Even within the single application of breast imaging, we find imagers with various measurement geometries, ultrasound detection characteristics, illumination schemes, and image reconstruction strategies. We first analyze the implications on performance of a few of these design choices in a generic imaging system, before going into detailed descriptions of the imagers. Per imaging system we present highlights of patient studies, which barring a couple are mostly in the nature of technology demonstrations and proof-of-principle studies. We close this work with a discussion on several aspects that may turn out to be crucial for the future clinical translation of the method.
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Dantuma M, van Dommelen R, Manohar S. Semi-anthropomorphic photoacoustic breast phantom. BIOMEDICAL OPTICS EXPRESS 2019; 10:5921-5939. [PMID: 31799055 PMCID: PMC6865090 DOI: 10.1364/boe.10.005921] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Revised: 09/18/2019] [Accepted: 09/20/2019] [Indexed: 05/04/2023]
Abstract
Imaging parameters of photoacoustic breast imaging systems such as the spatial resolution and imaging depth are often characterized with phantoms. These objects usually contain simple structures in homogeneous media such as absorbing wires or spherical objects in scattering gels. While these kinds of basic phantoms are uncluttered and useful, they do not challenge the system as much as a breast does, and can thereby overestimate the system's performance. The female breast is a complex collection of tissue types, and the acoustic and optical attenuation of these tissues limit the imaging depth, the resolution and the ability to extract quantitative information. For testing and challenging photoacoustic breast imaging systems to the full extent before moving to in vivo studies, a complex breast phantom which simulates the breast's most prevalent tissues is required. In this work we present the first three dimensional multi-layered semi-anthropomorphic photoacoustic breast phantom. The phantom aims to simulate skin, fat, fibroglandular tissue and blood vessels. The latter three are made from custom polyvinyl chloride plastisol (PVCP) formulations and are appropriately doped with additives to obtain tissue realistic acoustic and optical properties. Two tumors are embedded, which are modeled as clusters of small blood vessels. The PVCP materials are surrounded by a silicon layer mimicking the skin. The tissue mimicking materials were cast into the shapes and sizes expected in the breast using 3D-printed moulds developed from a magnetic resonance imaging segmented numerical breast model. The various structures and layers were assembled to obtain a realistic breast morphology. We demonstrate the phantom's appearance in both ultrasound imaging as photoacoustic tomography and make a comparison with a photoacoustic image of a real breast. A good correspondence is observed, which confirms the phantom's usefulness.
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Affiliation(s)
- Maura Dantuma
- Multi-Modality Medical Imaging group, TechMed Centre, University of Twente, Enschede, The Netherlands
- Biomedical Photonic Imaging group, TechMed Centre, University of Twente, Enschede, The Netherlands
| | - Rianne van Dommelen
- Biomedical Photonic Imaging group, TechMed Centre, University of Twente, Enschede, The Netherlands
| | - Srirang Manohar
- Multi-Modality Medical Imaging group, TechMed Centre, University of Twente, Enschede, The Netherlands
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de Jong TL, Moelker A, Dankelman J, van den Dobbelsteen JJ. Designing and validating a PVA liver phantom with respiratory motion for needle-based interventions. Int J Comput Assist Radiol Surg 2019; 14:2177-2186. [PMID: 31297650 PMCID: PMC6858400 DOI: 10.1007/s11548-019-02029-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 07/03/2019] [Indexed: 11/30/2022]
Abstract
Purpose The purpose is to design and validate an anthropomorphic polyvinyl alcohol (PVA) liver phantom with respiratory motion to simulate needle-based interventions. Such a system can, for example, be used as a validation tool for novel needles. Methods Image segmentations of CT scans of four patients during inspiration and expiration were used to measure liver and rib displacement. An anthropomorphic liver mold based on a CT scan was 3D printed and filled with 5% w/w PVA-to-water, undergoing two freeze–thaw cycles, in addition to a 3D-printed compliant rib cage. They were both held in place by a PVA abdominal phantom. A sinusoidal motion vector, based on the measured liver displacement, was applied to the liver phantom by means of a motion stage. Liver, rib cage and needle deflection were tracked by placing electromagnetic sensors on the phantom. Liver and rib cage phantom motion was validated by comparison with the CT images of the patients, whereas needle deflection was compared with the literature. Results CT analysis showed that from the state of expiration to inspiration, the livers moved predominantly toward the right (mean: 2 mm, range: − 11 to 11 mm), anterior (mean: 15 mm, range: 9–21 mm) and caudal (mean: 16 mm, range: 6–24 mm) direction. The mechatronic design of the liver phantom gives the freedom to set direction and amplitude of the motion and was able to mimic the direction of liver motion of one patient. Needle deflection inside the phantom increased from 1.6 to 3.8 mm from the initial expiration state to inspiration. Conclusions The developed liver phantom allows for applying different motion patterns and shapes/sizes and thus allows for patient-specific simulation of needle-based interventions. Moreover, it is able to mimic appropriate respiratory motion and needle deflection as observed in patients. Electronic supplementary material The online version of this article (10.1007/s11548-019-02029-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Tonke L de Jong
- BioMechanical Engineering Department, Delft University of Technology, Delft, The Netherlands.
| | - Adriaan Moelker
- Radiology and Nuclear Medicine Department, Erasmus MC, University Medical Center, Rotterdam, The Netherlands
| | - Jenny Dankelman
- BioMechanical Engineering Department, Delft University of Technology, Delft, The Netherlands
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Taghizadeh S, Labuda C, Mobley J. Development of a Tissue-Mimicking Phantom of the Brain for Ultrasonic Studies. ULTRASOUND IN MEDICINE & BIOLOGY 2018; 44:2813-2820. [PMID: 30274683 DOI: 10.1016/j.ultrasmedbio.2018.08.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 08/15/2018] [Accepted: 08/17/2018] [Indexed: 06/08/2023]
Abstract
Constructing tissue-mimicking phantoms of the brain for ultrasonic studies is complicated by the low backscatter coefficient of brain tissue, causing difficulties in simultaneously matching the backscatter and attenuation properties. In this work, we report on the development of a polyvinyl alcohol-based tissue-mimicking phantom with properties approaching those of human brain tissue. Polyvinyl alcohol was selected as the base material for the phantom as its properties can be varied by freeze-thaw cycling, variations in concentration and the addition of scattering inclusions, allowing some independent control of backscatter and attenuation. The ultrasonic properties (including speed of sound, attenuation and backscatter) were optimized using these methods with talc powder as an additive. It was determined that the ultrasonic properties of the phantom produced in this study are best matched to brain tissue in the frequency range 1-3 MHz, indicating its utility for laboratory ultrasonic studies in this frequency range.
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Affiliation(s)
- Somayeh Taghizadeh
- National Center for Physical Acoustics and Department of Physics and Astronomy, University of Mississippi, University, Mississippi, USA
| | - Cecille Labuda
- National Center for Physical Acoustics and Department of Physics and Astronomy, University of Mississippi, University, Mississippi, USA.
| | - Joel Mobley
- National Center for Physical Acoustics and Department of Physics and Astronomy, University of Mississippi, University, Mississippi, USA
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Design of lymphedema ultrasound phantom with 3D-printed patient-specific subcutaneous anatomy: A-mode analysis approach for early diagnosis. Phys Med 2018; 55:73-81. [PMID: 30471822 DOI: 10.1016/j.ejmp.2018.10.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 09/27/2018] [Accepted: 10/23/2018] [Indexed: 11/22/2022] Open
Abstract
The secondary lymphedema is mostly caused due to injury of lymphatic system during cancer treatment and its psychological and cosmetic issues are very critical for patients since it can cause severe thickening and swelling of lesions, mostly upper and lower limbs. Therefore, early diagnosis of the secondary lymphedema is more important to treat the symptoms in advance. The amplitude-mode (A-mode) ultrasound is suggested as an early diagnostic modality because it is relatively more cost-effective, portable, and easy to use than other previous diagnostic modalities. In order to see features of the A-mode ultrasound forearly diagnosis of lymphedema, ultrasound lymphedema phantoms were designed and fabricated with patient-specific subcutaneous honeycomb structures at the sub-stages of the international society of lymphedema (ISL) stage II and gelatin- or gelatin-salt based phantom materials. The patent-specific honeycomb structures were segmented from computed tomography (CT) venography images using various image process technologies and printed using a three dimensional (3D) printer for which its printing material shows similar acoustic impedance range with human subcutaneous tissues. The lymphedema phantoms showed similar subcutaneous anatomical features to those of patient's imagesin brightness mode (B-mode) ultrasound examination, and acoustic information originated from the stage-specific honeycomb structures was well represented in A-mode ultrasound examination. In particular, the A-mode wave form well represented stage-specific honeycomb information even with higher impedance value of fibrous fat region. Such stage-specific wave form information of A-mode ultrasound for the corresponding stage-specific lymphedema phantoms at the ISL stage II can be useful for further development of an A-mode ultrasound applications for early diagnosis of the secondary lymphedema.
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Jones CJM, Munro PRT. Stability of gel wax based optical scattering phantoms. BIOMEDICAL OPTICS EXPRESS 2018; 9:3495-3502. [PMID: 30338134 PMCID: PMC6191636 DOI: 10.1364/boe.9.003495] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Revised: 05/24/2018] [Accepted: 06/11/2018] [Indexed: 05/27/2023]
Abstract
Phantoms with tuneable optical scattering properties are essential in the development and refinement of optical based imaging techniques. Mineral oil based 'gel wax' phantoms are the subject of increasing interest due to their ease and speed of manufacture, non-toxic nature, ability to cast into anatomically realistic shapes, as well as their cost-effective nature of production. The addition of scatterers such as titanium dioxide powder and monodisperse silica microspheres to the gel wax allows for the creation of phantoms with a controllable optical scattering coefficient. To enable repeated use of such phantoms, the stability of the scattering properties must be determined-a property which has yet to be investigated. We present an analysis of the stability of the reduced scattering coefficient (μ s ' ) of such phantoms over time. We conclude that due to the measurable reduction in scattering coefficient over time, gel wax phantoms embedded with silica spheres may not be suitable for repeated use over time, however gel wax-TiO2 phantoms are much more temporally stable.
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Affiliation(s)
- Charlotte J. Maughan Jones
- Department of Medical Physics and Biomedical Engineering, Malet Place Engineering Building, University College London, London WC1E 6BT, UK
| | - Peter R. T. Munro
- Department of Medical Physics and Biomedical Engineering, Malet Place Engineering Building, University College London, London WC1E 6BT, UK
- School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Highway, Perth, Western Australia 6009, Australia
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Filippou V, Tsoumpas C. Recent advances on the development of phantoms using 3D printing for imaging with CT, MRI, PET, SPECT, and ultrasound. Med Phys 2018; 45. [PMID: 29933508 PMCID: PMC6849595 DOI: 10.1002/mp.13058] [Citation(s) in RCA: 139] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Revised: 06/03/2018] [Accepted: 06/15/2018] [Indexed: 12/27/2022] Open
Abstract
PURPOSE Printing technology, capable of producing three-dimensional (3D) objects, has evolved in recent years and provides potential for developing reproducible and sophisticated physical phantoms. 3D printing technology can help rapidly develop relatively low cost phantoms with appropriate complexities, which are useful in imaging or dosimetry measurements. The need for more realistic phantoms is emerging since imaging systems are now capable of acquiring multimodal and multiparametric data. This review addresses three main questions about the 3D printers currently in use, and their produced materials. The first question investigates whether the resolution of 3D printers is sufficient for existing imaging technologies. The second question explores if the materials of 3D-printed phantoms can produce realistic images representing various tissues and organs as taken by different imaging modalities such as computer tomography (CT), positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), ultrasound (US), and mammography. The emergence of multimodal imaging increases the need for phantoms that can be scanned using different imaging modalities. The third question probes the feasibility and easiness of "printing" radioactive or nonradioactive solutions during the printing process. METHODS A systematic review of medical imaging studies published after January 2013 is performed using strict inclusion criteria. The databases used were Scopus and Web of Knowledge with specific search terms. In total, 139 papers were identified; however, only 50 were classified as relevant for this paper. In this review, following an appropriate introduction and literature research strategy, all 50 articles are presented in detail. A summary of tables and example figures of the most recent advances in 3D printing for the purposes of phantoms across different imaging modalities are provided. RESULTS All 50 studies printed and scanned phantoms in either CT, PET, SPECT, mammography, MRI, and US-or a combination of those modalities. According to the literature, different parameters were evaluated depending on the imaging modality used. Almost all papers evaluated more than two parameters, with the most common being Hounsfield units, density, attenuation and speed of sound. CONCLUSIONS The development of this field is rapidly evolving and becoming more refined. There is potential to reach the ultimate goal of using 3D phantoms to get feedback on imaging scanners and reconstruction algorithms more regularly. Although the development of imaging phantoms is evident, there are still some limitations to address: One of which is printing accuracy, due to the printer properties. Another limitation is the materials available to print: There are not enough materials to mimic all the tissue properties. For example, one material can mimic one property-such as the density of real tissue-but not any other property, like speed of sound or attenuation.
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Affiliation(s)
- Valeria Filippou
- Institute of Medical and Biological EngineeringFaculty of Mechanical EngineeringUniversity of LeedsLeedsLS2 9JTWest YorkshireUK
| | - Charalampos Tsoumpas
- Department of Biomedical Imaging ScienceSchool of MedicineUniversity of LeedsLeedsLS2 9NLWest YorkshireUK
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Liu Y, Ghassemi P, Depkon A, Iacono MI, Lin J, Mendoza G, Wang J, Tang Q, Chen Y, Pfefer TJ. Biomimetic 3D-printed neurovascular phantoms for near-infrared fluorescence imaging. BIOMEDICAL OPTICS EXPRESS 2018; 9:2810-2824. [PMID: 30258692 PMCID: PMC6154206 DOI: 10.1364/boe.9.002810] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Revised: 05/17/2018] [Accepted: 05/18/2018] [Indexed: 05/03/2023]
Abstract
Emerging three-dimensional (3D) printing technology enables the fabrication of optically realistic and morphologically complex tissue-simulating phantoms for the development and evaluation of novel optical imaging products. In this study, we assess the potential to print image-defined neurovascular phantoms with patent channels for contrast-enhanced near-infrared fluorescence (NIRF) imaging. An anatomical map defined from clinical magnetic resonance imaging (MRI) was segmented and processed into files suitable for printing a forebrain vessel network in rectangular and curved-surface biomimetic phantoms. Methods for effectively cleaning samples with complex vasculature were determined. A final set of phantoms were imaged with a custom NIRF system at 785 nm excitation using two NIRF contrast agents. In addition to demonstrating the strong potential of 3D printing for creating highly realistic, patient-specific biophotonic phantoms, our work provides insight into optimal methods for accomplishing this goal and elucidates current limitations of this approach.
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Affiliation(s)
- Yi Liu
- Department of Bioengineering, University of Maryland, Silver Spring, MD, USA
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
- Authors contributed equally to this work
| | - Pejhman Ghassemi
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
- Authors contributed equally to this work
| | - Andrew Depkon
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
- Marquette University, Milwaukee, WI, USA
| | - Maria Ida Iacono
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - Jonathan Lin
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - Gonzalo Mendoza
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - Jianting Wang
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - Qinggong Tang
- Department of Bioengineering, University of Maryland, Silver Spring, MD, USA
| | - Yu Chen
- Department of Bioengineering, University of Maryland, Silver Spring, MD, USA
| | - T Joshua Pfefer
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
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Xia W, Kuniyil Ajith Singh M, Maneas E, Sato N, Shigeta Y, Agano T, Ourselin S, J West S, E Desjardins A. Handheld Real-Time LED-Based Photoacoustic and Ultrasound Imaging System for Accurate Visualization of Clinical Metal Needles and Superficial Vasculature to Guide Minimally Invasive Procedures. SENSORS (BASEL, SWITZERLAND) 2018; 18:E1394. [PMID: 29724014 PMCID: PMC5982119 DOI: 10.3390/s18051394] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/10/2018] [Revised: 04/25/2018] [Accepted: 04/27/2018] [Indexed: 01/11/2023]
Abstract
Ultrasound imaging is widely used to guide minimally invasive procedures, but the visualization of the invasive medical device and the procedure’s target is often challenging. Photoacoustic imaging has shown great promise for guiding minimally invasive procedures, but clinical translation of this technology has often been limited by bulky and expensive excitation sources. In this work, we demonstrate the feasibility of guiding minimally invasive procedures using a dual-mode photoacoustic and ultrasound imaging system with excitation from compact arrays of light-emitting diodes (LEDs) at 850 nm. Three validation experiments were performed. First, clinical metal needles inserted into biological tissue were imaged. Second, the imaging depth of the system was characterized using a blood-vessel-mimicking phantom. Third, the superficial vasculature in human volunteers was imaged. It was found that photoacoustic imaging enabled needle visualization with signal-to-noise ratios that were 1.2 to 2.2 times higher than those obtained with ultrasound imaging, over insertion angles of 26 to 51 degrees. With the blood vessel mimicking phantom, the maximum imaging depth was 38 mm. The superficial vasculature of a human middle finger and a human wrist were clearly visualized in real-time. We conclude that the LED-based system is promising for guiding minimally invasive procedures with peripheral tissue targets.
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Affiliation(s)
- Wenfeng Xia
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ, UK.
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT, UK.
| | - Mithun Kuniyil Ajith Singh
- Research and Business Development Division, PreXion Corporation, Stationsplein 45 A4.004, 3013AK Rotterdam, The Netherlands.
| | - Efthymios Maneas
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ, UK.
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT, UK.
| | - Naoto Sato
- Research and Development Division, 1-14-1, Kandasudacho, Chiyoda-ku, Tokyo 101-0041, Japan.
| | - Yusuke Shigeta
- Research and Development Division, 1-14-1, Kandasudacho, Chiyoda-ku, Tokyo 101-0041, Japan.
| | - Toshitaka Agano
- Research and Development Division, 1-14-1, Kandasudacho, Chiyoda-ku, Tokyo 101-0041, Japan.
| | - Sebastian Ourselin
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ, UK.
- Centre for Medical Imaging Computing, University College London, Gower Street, London WC1E 6BT, UK.
| | - Simeon J West
- Department of Anaesthesia, University College Hospital, Main Theatres, Maple Bridge Link Corridor, Podium 3, 235 Euston Road, London NW1 2BU, UK.
| | - Adrien E Desjardins
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ, UK.
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT, UK.
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Gruijthuijsen C, Colchester R, Devreker A, Javaux A, Maneas E, Noimark S, Xia W, Stoyanov D, Reynaerts D, Deprest J, Ourselin S, Desjardins A, Vercauteren T, Vander Poorten E. Haptic Guidance Based on All-Optical Ultrasound Distance Sensing for Safer Minimally Invasive Fetal Surgery. JOURNAL OF MEDICAL ROBOTICS RESEARCH 2018; 3:10.1142/S2424905X18410015. [PMID: 30820482 PMCID: PMC6390942 DOI: 10.1142/s2424905x18410015] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
By intervening during the early stage of gestation, fetal surgeons aim to correct or minimize the effects of congenital disorders. As compared to postnatal treatment of these disorders, such early interventions can often actually save the life of the fetus and also improve the quality of life of the newborn. However, fetal surgery is considered one of the most challenging disciplines within Minimally Invasive Surgery (MIS), owing to factors such as the fragility of the anatomic features, poor visibility, limited manoeuvrability, and extreme requirements in terms of instrument handling with precise positioning. This work is centered on a fetal laser surgery procedure treating placental disorders. It proposes the use of haptic guidance to enhance the overall safety of this procedure and to simplify instrument handling. A method is described that provides effective guidance by installing a forbidden region virtual fixture over the placenta, thereby safeguarding adequate clearance between the instrument tip and the placenta. With a novel application of all-optical ultrasound distance sensing in which transmission and reception are performed with fibre optics, this method can be used with a sole reliance on intraoperatively acquired data. The added value of the guidance approach, in terms of safety and performance, is demonstrated in a series of experiments with a robotic platform.
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Affiliation(s)
| | - Richard Colchester
- Department of Medical Physics & Biomedical Engineering, University College London, UK
| | - Alain Devreker
- Department of Mechanical Engineering, KU Leuven, Belgium
| | - Allan Javaux
- Department of Mechanical Engineering, KU Leuven, Belgium
| | - Efthymios Maneas
- Department of Medical Physics & Biomedical Engineering, University College London, UK
| | - Sacha Noimark
- Department of Medical Physics & Biomedical Engineering, University College London, UK
| | - Wenfeng Xia
- Department of Medical Physics & Biomedical Engineering, University College London, UK
| | - Danail Stoyanov
- Centre for Medical Imaging Computing, University College London, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, London, UK
| | | | - Jan Deprest
- Department of Obstetrics and Gynecology, Division Woman and Child, Fetal Medicine Unit, KU Leuven, Belgium
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, London, UK
| | - Sebastien Ourselin
- Centre for Medical Imaging Computing, University College London, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, London, UK
| | - Adrien Desjardins
- Department of Medical Physics & Biomedical Engineering, University College London, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, London, UK
| | - Tom Vercauteren
- Department of Medical Physics & Biomedical Engineering, University College London, UK
- Wellcome/EPSRC Centre for Interventional and Surgical Sciences, London, UK
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36
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Maneas E, Xia W, Ogunlade O, Fonseca M, Nikitichev DI, David AL, West SJ, Ourselin S, Hebden JC, Vercauteren T, Desjardins AE. Gel wax-based tissue-mimicking phantoms for multispectral photoacoustic imaging. BIOMEDICAL OPTICS EXPRESS 2018; 9. [PMID: 29541509 PMCID: PMC5846519 DOI: 10.1364/boe.9.001151] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Tissue-mimicking phantoms are widely used for the calibration, evaluation and standardisation of medical imaging systems, and for clinical training. For photoacoustic imaging, tissue-mimicking materials (TMMs) that have tuneable optical and acoustic properties, high stability, and mechanical robustness are highly desired. In this study, gel wax is introduced as a TMM that satisfies these criteria for developing photoacoustic imaging phantoms. The reduced scattering and optical absorption coefficients were independently tuned with the addition of TiO2 and oil-based inks. The frequency-dependent acoustic attenuation obeyed a power law; for native gel wax, it varied from 0.71 dB/cm at 3 MHz to 9.93 dB/cm at 12 MHz. The chosen oil-based inks, which have different optical absorption spectra in the range of 400 to 900 nm, were found to have good photostability under pulsed illumination with photoacoustic excitation light. Optically heterogeneous phantoms that comprised of inclusions with different concentrations of carbon black and coloured inks were fabricated, and multispectral photoacoustic imaging was performed with an optical parametric oscillator and a planar Fabry-Pérot sensor. We conclude that gel wax is well suited as a TMM for multispectral photoacoustic imaging.
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Affiliation(s)
- Efthymios Maneas
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ,
UK
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
| | - Wenfeng Xia
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ,
UK
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
| | - Olumide Ogunlade
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
| | - Martina Fonseca
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
| | - Daniil I. Nikitichev
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ,
UK
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
- Translational Imaging Group, Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
| | - Anna L. David
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ,
UK
- Institute for Women’s Health, University College London, 86-96 Chenies Mews, London WC1E 6HX,
UK
- Department of Development and Regeneration, KU Leuven (Katholieke Universiteit),
Belgium
| | - Simeon J. West
- Department of Anaesthesia, University College Hospital, Main Theatres, Maple Bridge Link Corridor, Podium 3, 235 Euston Road, London NW1 2BU,
UK
| | - Sebastien Ourselin
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ,
UK
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
- Translational Imaging Group, Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
| | - Jeremy C. Hebden
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
| | - Tom Vercauteren
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ,
UK
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
- Translational Imaging Group, Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
| | - Adrien E. Desjardins
- Wellcome / EPSRC Centre for Interventional and Surgical Sciences, University College London, Charles Bell House, 67-73 Riding House Street, London W1W 7EJ,
UK
- Department of Medical Physics and Biomedical Engineering, University College London, Gower Street, London WC1E 6BT,
UK
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