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Pohlman RM, Hinshaw JL, Ziemlewicz TJ, Lubner MG, Wells SA, Lee FT, Alexander ML, Wergin KL, Varghese T. Differential Imaging of Liver Tumors before and after Microwave Ablation with Electrode Displacement Elastography. ULTRASOUND IN MEDICINE & BIOLOGY 2021; 47:2138-2156. [PMID: 34011451 PMCID: PMC8243838 DOI: 10.1016/j.ultrasmedbio.2021.03.027] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 03/18/2021] [Accepted: 03/23/2021] [Indexed: 05/17/2023]
Abstract
Liver cancer is a leading cause of cancer-related deaths; however, primary treatment options such as surgical resection and liver transplant may not be viable for many patients. Minimally invasive image-guided microwave ablation (MWA) provides a locally effective treatment option for these patients with an impact comparable to that of surgery for both cancer-specific and overall survival. MWA efficacy is correlated with accurate image guidance; however, conventional modalities such as B-mode ultrasound and computed tomography have limitations. Alternatively, ultrasound elastography has been used to demarcate post-ablation zones, yet has limitations for pre-ablation visualization because of variability in strain contrast between cancer types. This study attempted to characterize both pre-ablation tumors and post-ablation zones using electrode displacement elastography (EDE) for 13 patients with hepatocellular carcinoma or liver metastasis. Typically, MWA ablation margins of 0.5-1.0 cm are desired, which are strongly correlated with treatment efficacy. Our results revealed an average estimated ablation margin inner quartile range of 0.54-1.21 cm with a median value of 0.84 cm. These treatment margins lie within or above the targeted ablative margin, indicating the potential to use EDE for differentiating index tumors and ablated zones during clinical ablations. We also obtained a high correlation between corresponding segmented cross-sectional areas from contrast-enhanced computed tomography, the current clinical gold standard, when compared with EDE strain images, with r2 values of 0.97 and 0.98 for pre- and post-ablation regions.
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Affiliation(s)
- Robert M Pohlman
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
| | - James L Hinshaw
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Timothy J Ziemlewicz
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Meghan G Lubner
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Shane A Wells
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Fred T Lee
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Marci L Alexander
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Kelly L Wergin
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Tomy Varghese
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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Mirzaei M, Asif A, Rivaz H. Accurate and Precise Time-Delay Estimation for Ultrasound Elastography With Prebeamformed Channel Data. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2020; 67:1752-1763. [PMID: 32248101 DOI: 10.1109/tuffc.2020.2985060] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Free-hand palpation ultrasound elastography is a noninvasive approach for detecting pathological alteration in tissue. In this method, the tissue is compressed by a handheld probe and displacement of each sample is estimated, a process which is also known as time-delay estimation (TDE). Even with the simplifying assumption that ignores out of plane motion, TDE is an ill-posed problem requiring estimation of axial and lateral displacements for each sample from its intensity. A well-known class of methods for making elastography a well-posed problem is regularized optimization-based methods, which imposes smoothness regularization in the associated cost function. In this article, we propose to utilize channel data that have been compensated for time gain and time delay (introduced by transmission) instead of postbeamformed radio frequency (RF) data in the optimization problem. We name our proposed method Channel data for GLobal Ultrasound Elastography (CGLUE). We analytically derive bias and variances of TDE as functions of data noise for CGLUE and Global Ultrasound Elastography (GLUE) and use the Cauchy-Schwarz inequality to prove that CGLUE provides a TDE with lower bias and variance error. To further illustrate the improved performance of CGLUE, the results of simulation, experimental phantom, and ex-vivo experiments are presented.
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Martelletti C, Armandi A, Caviglia GP, Saracco GM, Pellicano R. Elastography for characterization of focal liver lesions: current evidence and future perspectives. Minerva Gastroenterol (Torino) 2020; 67:196-208. [PMID: 32677420 DOI: 10.23736/s2724-5985.20.02747-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Focal liver lesions (FLLs) are a common finding during routine abdominal ultrasound (US). The differential diagnosis between diverse types of FLLs, especially between benign and malignant ones, is extremely important and can often be particularly challenging. Radiological techniques with contrast administration and/or liver biopsy are mostly necessary for establishing diagnosis, but they have several contraindications or complications. Due to limitations of these tools, there is urgent and still unmet need to develop a first line, non-invasive and simple method to diagnose FLLs. Elastography is an US-based imaging modality that provides information about the physical parameter corresponding to the tissue stiffness and can be considered a virtual biopsy. Several elastographic approaches have been developed, such as transient elastography, strain imaging and share wave imaging, which include point shear wave elastography and 2D shear wave elastography. These tools are already in use for evaluating liver fibrosis and in the assessment of focal lesions in other organs, like breast and thyroid gland. This review aims to assess the current evidence of different techniques based on elastography in the setting of FLLs, in order to evaluate accuracy, limitations and future perspectives. In particular, we focused on two contexts: the ability of discriminating between benign and malignant lesions, especially hepatocellular carcinoma and liver metastasis, and the surveillance after percutaneous therapy. This could have a high clinical impact making elastography crucial to identify the appropriate management of FLLs.
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Affiliation(s)
- Carolina Martelletti
- School of Gastroenterology, Department of Medical Sciences, University of Turin, Turin, Italy
| | - Angelo Armandi
- School of Gastroenterology, Department of Medical Sciences, University of Turin, Turin, Italy
| | | | - Giorgio M Saracco
- School of Gastroenterology, Department of Medical Sciences, University of Turin, Turin, Italy.,Department of Medical Sciences, University of Turin, Turin, Italy.,Unit of Gastroenterology, Molinette-SGAS Hospital, Turin, Italy
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Pohlman RM, Varghese T. Adaptation of Dictionary Learning for Electrode Displacement Elastography . ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020; 2020:2023-2026. [PMID: 33018401 PMCID: PMC7538652 DOI: 10.1109/embc44109.2020.9175319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Microwave ablation has become a common treatment method for liver cancers. Unfortunately, microwave ablation success is correlated with clinician's ability for proper electrode placement and assess ablative margins, requiring accurate imaging of liver tumors and ablated zones. Conventionally, ultrasound and computed tomography are utilized for this purpose, yet both have their respective drawbacks. As an alternate approach, electrode displacement elastography offers promise but is still plagued by decorrelation artifacts reducing lesion depiction and visualization. A recent filtering method, namely dictionary representation, has improved contrast-to-noise ratios without reducing delineation contrast. As a supplement to this recent work, this paper evaluates adaptations on this initial dictionary-learning algorithm and applies them to an EDE phantom and 15 in-vivo patient datasets. Two new adaptations of dictionary representations were evaluated, namely a combined dictionary and magnitude-based dictionary representation. When comparing numerical results, the combined dictionary representation algorithm outperforms the previous developed dictionary representation in signal-to-noise (1.54 dB) and contrast-to-noise (0.67 dB) ratios, while a magnitude dictionary representation produces higher noise levels, but improves visualized strain tensor resolution.
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Pohlman RM, Varghese T. Physiological Motion Reduction Using Lagrangian Tracking for Electrode Displacement Elastography. ULTRASOUND IN MEDICINE & BIOLOGY 2020; 46:766-781. [PMID: 31806499 PMCID: PMC7241290 DOI: 10.1016/j.ultrasmedbio.2019.11.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 09/19/2019] [Accepted: 11/04/2019] [Indexed: 05/03/2023]
Abstract
Minimally invasive treatments such as microwave ablation (MWA) have been growing in popularity for extending liver cancer survival rates in patients, when surgery is not an option. As a non-ionizing, real-time alternative to contrast-enhanced computed tomography, electrode displacement elastography (EDE) has shown promise as an imaging modality for MWA. Despite imaging efficacy, motion artifacts caused by physiological motion result in unintended speckle pattern variance, thereby inhibiting consistent and accurate ablated region visualization. To combat these unavoidable motion artifacts, a Lagrangian deformation tracking (LDT) approach based on freehand EDE was developed to track tissue movement and better define tissue properties. For validating LDT efficacy, a spherical inclusion phantom as well as seven in vivo data sets were processed, and strain tensor images were compared with identical time sampled images estimated using a traditional Eulerian approach. In vivo results revealed greater consistency among visualized LDT strain tensor images, with segmented ablated regions exhibiting standard deviation reductions of up to 98% when compared with Eulerian strain tensor images. Additionally, Lagrangian strain tensor images provided Dice coefficient improvements up to 25%, and success rates improved from approximately 50% to nearly 100% for ablated region visualization.
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Affiliation(s)
- Robert M Pohlman
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
| | - Tomy Varghese
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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Pohlman RM, Turney MR, Wu P, Brace CL, Ziemlewicz TJ, Varghese T. Two-dimensional ultrasound-computed tomography image registration for monitoring percutaneous hepatic intervention. Med Phys 2019; 46:2600-2609. [PMID: 31009079 PMCID: PMC6758542 DOI: 10.1002/mp.13554] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Revised: 04/14/2019] [Accepted: 04/15/2019] [Indexed: 01/03/2023] Open
Abstract
PURPOSE Deformable registration of ultrasound (US) and contrast enhanced computed tomography (CECT) images are essential for quantitative comparison of ablation boundaries and dimensions determined using these modalities. This comparison is essential as stiffness-based imaging using US has become popular and offers a nonionizing and cost-effective imaging modality for monitoring minimally invasive microwave ablation procedures. A sensible manual registration method is presented that performs the required CT-US image registration. METHODS The two-dimensional (2D) virtual CT image plane that corresponds to the clinical US B-mode was obtained by "virtually slicing" the 3D CT volume along the plane containing non-anatomical landmarks, namely points along the microwave ablation antenna. The initial slice plane was generated using the vector acquired by rotating the normal vector of the transverse (i.e., xz) plane along the angle subtended by the antenna. This plane was then further rotated along the ablation antenna and shifted along with the direction of normal vector to obtain similar anatomical structures, such as the liver surface and vasculature that is visualized on both the CT virtual slice and US B-mode images on 20 patients. Finally, an affine transformation was estimated using anatomic and non-anatomic landmarks to account for distortion between the colocated CT virtual slice and US B-mode image resulting in a final registered CT virtual slice. Registration accuracy was measured by estimating the Euclidean distance between corresponding registered points on CT and US B-mode images. RESULTS Mean and SD of the affine transformed registration error was 1.85 ± 2.14 (mm), computed from 20 coregistered data sets. CONCLUSIONS Our results demonstrate the ability to obtain 2D virtual CT slices that are registered to clinical US B-mode images. The use of both anatomical and non-anatomical landmarks result in accurate registration useful for validating ablative margins and comparison to electrode displacement elastography based images.
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Affiliation(s)
- Robert M. Pohlman
- Department of Medical PhysicsUniversity of Wisconsin School of Medicine and Public HealthUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Michael R. Turney
- Department of Medical PhysicsUniversity of Wisconsin School of Medicine and Public HealthUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Po‐Hung Wu
- Department of RadiologyUniversity of Wisconsin School of Medicine and Public HealthUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Christopher L. Brace
- Department of RadiologyUniversity of Wisconsin School of Medicine and Public HealthUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Timothy J. Ziemlewicz
- Department of RadiologyUniversity of Wisconsin School of Medicine and Public HealthUniversity of Wisconsin‐MadisonMadisonWI53706USA
| | - Tomy Varghese
- Department of Medical PhysicsUniversity of Wisconsin School of Medicine and Public HealthUniversity of Wisconsin‐MadisonMadisonWI53706USA
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Pohlman RM, Varghese T, Jiang J, Ziemlewicz TJ, Alexander ML, Wergin KL, Hinshaw JL, Lubner MG, Wells SA, Lee FT. Comparison of Displacement Tracking Algorithms for in Vivo Electrode Displacement Elastography. ULTRASOUND IN MEDICINE & BIOLOGY 2019; 45:218-232. [PMID: 30318122 PMCID: PMC6324563 DOI: 10.1016/j.ultrasmedbio.2018.09.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Revised: 08/21/2018] [Accepted: 09/03/2018] [Indexed: 05/09/2023]
Abstract
Hepatocellular carcinoma and liver metastases are common hepatic malignancies presenting with high mortality rates. Minimally invasive microwave ablation (MWA) yields high success rates similar to surgical resection. However, MWA procedures require accurate image guidance during the procedure and for post-procedure assessments. Ultrasound electrode displacement elastography (EDE) has demonstrated utility for non-ionizing imaging of regions of thermal necrosis created with MWA in the ablation suite. Three strategies for displacement vector tracking and strain tensor estimation, namely coupled subsample displacement estimation (CSDE), a multilevel 2-D normalized cross-correlation method, and quality-guided displacement tracking (QGDT) have previously shown accurate estimations for EDE. This paper reports on a qualitative and quantitative comparison of these three algorithms over 79 patients after an MWA procedure. Qualitatively, CSDE presents sharply delineated, clean ablated regions with low noise except for the distal boundary of the ablated region. Multilevel and QGDT contain more visible noise artifacts, but delineation is seen over the entire ablated region. Quantitative comparison indicates CSDE with more consistent mean and standard deviations of region of interest within the mass of strain tensor magnitudes and higher contrast, while Multilevel and QGDT provide higher CNR. This fact along with highest success rates of 89% and 79% on axial and lateral strain tensor images for visualization of thermal necrosis using the Multilevel approach leads to it being the best choice in a clinical setting. All methods, however, provide consistent and reproducible delineation for EDE in the ablation suite.
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Affiliation(s)
- Robert M Pohlman
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Tomy Varghese
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
| | - Jingfeng Jiang
- Department of Biomedical Engineering, Michigan Technological University, Houghton, Michigan, USA
| | - Timothy J Ziemlewicz
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Marci L Alexander
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Kelly L Wergin
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - James L Hinshaw
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Meghan G Lubner
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Shane A Wells
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Fred T Lee
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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Pohlman RM, Varghese T. Dictionary Representations for Electrode Displacement Elastography. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2018; 65:2381-2389. [PMID: 30296219 PMCID: PMC6400457 DOI: 10.1109/tuffc.2018.2874181] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Ultrasound electrode displacement elastography (EDE) has demonstrated the potential to monitor ablated regions in human patients after minimally invasive microwave ablation procedures. Displacement estimation for EDE is commonly plagued by decorrelation noise artifacts degrading displacement estimates. In this paper, we propose a global dictionary learning approach applied to denoising displacement estimates with an adaptively learned dictionary from EDE phantom displacement maps. The resulting algorithm is one that represents displacement patches sparsely if they contain low noise and averages remaining patches thereby denoising displacement maps while retaining important edge information. The results of dictionary-represented displacements presented with a higher signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) with improved contrast, as well as improved phantom inclusion delineation when compared to initial displacements, median-filtered displacements, and spline smoothened displacements, respectively. In addition to visualized noise reduction, dictionary-represented displacements presented with the highest SNR, CNR, and improved contrast with values of 1.77, 4.56, and 4.35 dB, respectively, when compared to axial strain tensor images estimated using the initial displacements. Following EDE phantom imaging, we utilized dictionary representations from in vivo patient data, further validating efficacy. Denoising displacement estimates are a newer application for dictionary learning producing strong ablated region delineation with little degradation from denoising.
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Yang W, Varghese T, Ziemlewicz T, Alexander M, Lubner M, Hinshaw JL, Wells S, Lee FT. Delineation of Post-Procedure Ablation Regions with Electrode Displacement Elastography with a Comparison to Acoustic Radiation Force Impulse Imaging. ULTRASOUND IN MEDICINE & BIOLOGY 2017; 43:1953-1962. [PMID: 28595851 PMCID: PMC5523876 DOI: 10.1016/j.ultrasmedbio.2017.04.021] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Revised: 04/12/2017] [Accepted: 04/20/2017] [Indexed: 05/03/2023]
Abstract
We compared a quasi-static ultrasound elastography technique, referred to as electrode displacement elastography (EDE), with acoustic radiation force impulse imaging (ARFI) for monitoring microwave ablation (MWA) procedures on patients diagnosed with liver neoplasms. Forty-nine patients recruited to this study underwent EDE and ARFI with a Siemens Acuson S2000 system after an MWA procedure. On the basis of visualization results from two observers, the ablated region in ARFI images was recognizable on 20 patients on average in conjunction with B-mode imaging, whereas delineable ablation boundaries could be generated on 4 patients on average. With EDE, the ablated region was delineable on 40 patients on average, with less imaging depth dependence. Study of tissue-mimicking phantoms revealed that the ablation region dimensions measured on EDE and ARFI images were within 8%, whereas the image contrast and contrast-to-noise ratio with EDE was two to three times higher than that obtained with ARFI. This study indicated that EDE provided improved monitoring results for minimally invasive MWA in clinical procedures for liver cancer and metastases.
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Affiliation(s)
- Wenjun Yang
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA.
| | - Tomy Varghese
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Timothy Ziemlewicz
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Marci Alexander
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Meghan Lubner
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - James Louis Hinshaw
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Shane Wells
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Fred T Lee
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
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Yang W, Ingle A, Varghese T. Comparison of three dimensional strain volume reconstructions using SOUPR and wobbler based acquisitions: A phantom study. Med Phys 2016; 43:1615. [PMID: 27036561 DOI: 10.1118/1.4942814] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
PURPOSE Ultrasound strain imaging is a relatively low cost and portable modality for monitoring percutaneous thermal ablation of liver neoplasms. However, a 3D strain volume reconstruction from existing 2D strain images is necessary to fully delineate the thermal dose distribution. Tissue mimicking (TM) phantom experiments were performed to validate a novel volume reconstruction algorithm referred to as sheaf of ultrasound planes reconstruction (SOUPR), based on a series of 2D rotational imaging planes. METHODS Reconstruction using SOUPR was formulated as an optimization problem with constraints on data consistency with 2D strain images and data smoothness of the volume data. Reconstructed ablation inclusion dimensions, volume, and elastographic signal to noise ratio (SNRe) and contrast to noise ratio (CNRe) were compared with conventional 3D ultrasound strain imaging based on interpolating a series of quasiparallel 2D strain images with a wobbler transducer. RESULTS Volume estimates of the phantom inclusion were in a similar range for both acquisition approaches. SNRe and CNRe obtained with SOUPR were significantly higher on the order of 250% and 166%, respectively. The mean error of the inclusion dimension reconstructed with a wobbler transducer was on the order of 10.4%, 3.5%, and 19.0% along the X, Y, and Z axes, respectively, while the error with SOUPR was on the order of 2.6%, 2.8%, and 9.6%. A qualitative comparison of SOUPR and wobbler reconstruction was also performed using a thermally ablated region created in ex vivo bovine liver tissue. CONCLUSIONS The authors have demonstrated using experimental evaluations with a TM phantom that the reconstruction results obtained with SOUPR were superior when compared with a conventional wobbler transducer in terms of inclusion shape preservation and detectability.
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Affiliation(s)
- Wenjun Yang
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin 53705
| | - Atul Ingle
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Tomy Varghese
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin 53705 and Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
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Yang W, Ziemlewicz TJ, Varghese T, Alexander ML, Rubert N, Ingle AN, Lubner MG, Hinshaw JL, Wells SA, Lee FT, Zagzebski JA. Post-Procedure Evaluation of Microwave Ablations of Hepatocellular Carcinomas Using Electrode Displacement Elastography. ULTRASOUND IN MEDICINE & BIOLOGY 2016; 42:2893-2902. [PMID: 27592561 PMCID: PMC5116412 DOI: 10.1016/j.ultrasmedbio.2016.07.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Revised: 05/02/2016] [Accepted: 07/13/2016] [Indexed: 05/04/2023]
Abstract
Microwave ablation has been used clinically as an alternative to surgical resection. However, lack of real-time imaging to assess treated regions may compromise treatment outcomes. We previously introduced electrode displacement elastography (EDE) for strain imaging and verified its feasibility in vivo on porcine animal models. In this study, we evaluated EDE on 44 patients diagnosed with hepatocellular carcinoma, treated using microwave ablation. The ablated region was identified on EDE images for 40 of the 44 patients. Ablation areas averaged 13.38 ± 4.99 cm2 on EDE, compared with 7.61 ± 3.21 cm2 on B-mode imaging. Contrast and contrast-to-noise ratios obtained with EDE were 232% and 98%, respectively, significantly higher than values measured on B-mode images (p < 0.001). This study indicates that EDE is feasible in patients and provides improved visualization of the ablation zone compared with B-mode ultrasound.
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Affiliation(s)
- Wenjun Yang
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Timothy J Ziemlewicz
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Tomy Varghese
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA.
| | - Marci L Alexander
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Nicholas Rubert
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Atul N Ingle
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Meghan G Lubner
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - James L Hinshaw
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Shane A Wells
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Fred T Lee
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - James A Zagzebski
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin, USA
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Ingle AN, Ma C, Varghese T. Ultrasonic tracking of shear waves using a particle filter. Med Phys 2015; 42:6711-24. [PMID: 26520761 DOI: 10.1118/1.4934372] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE This paper discusses an application of particle filtering for estimating shear wave velocity in tissue using ultrasound elastography data. Shear wave velocity estimates are of significant clinical value as they help differentiate stiffer areas from softer areas which is an indicator of potential pathology. METHODS Radio-frequency ultrasound echo signals are used for tracking axial displacements and obtaining the time-to-peak displacement at different lateral locations. These time-to-peak data are usually very noisy and cannot be used directly for computing velocity. In this paper, the denoising problem is tackled using a hidden Markov model with the hidden states being the unknown (noiseless) time-to-peak values. A particle filter is then used for smoothing out the time-to-peak curve to obtain a fit that is optimal in a minimum mean squared error sense. RESULTS Simulation results from synthetic data and finite element modeling suggest that the particle filter provides lower mean squared reconstruction error with smaller variance as compared to standard filtering methods, while preserving sharp boundary detail. Results from phantom experiments show that the shear wave velocity estimates in the stiff regions of the phantoms were within 20% of those obtained from a commercial ultrasound scanner and agree with estimates obtained using a standard method using least-squares fit. Estimates of area obtained from the particle filtered shear wave velocity maps were within 10% of those obtained from B-mode ultrasound images. CONCLUSIONS The particle filtering approach can be used for producing visually appealing SWV reconstructions by effectively delineating various areas of the phantom with good image quality properties comparable to existing techniques.
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Affiliation(s)
- Atul N Ingle
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53705 and Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705
| | - Chi Ma
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin 53705
| | - Tomy Varghese
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, and Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53705
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13
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Ingle A, Bucklew J, Sethares W, Varghese T. Slope Estimation in Noisy Piecewise Linear Functions. SIGNAL PROCESSING 2015; 108:576-588. [PMID: 25419020 PMCID: PMC4235795 DOI: 10.1016/j.sigpro.2014.10.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This paper discusses the development of a slope estimation algorithm called MAPSlope for piecewise linear data that is corrupted by Gaussian noise. The number and locations of slope change points (also known as breakpoints) are assumed to be unknown a priori though it is assumed that the possible range of slope values lies within known bounds. A stochastic hidden Markov model that is general enough to encompass real world sources of piecewise linear data is used to model the transitions between slope values and the problem of slope estimation is addressed using a Bayesian maximum a posteriori approach. The set of possible slope values is discretized, enabling the design of a dynamic programming algorithm for posterior density maximization. Numerical simulations are used to justify choice of a reasonable number of quantization levels and also to analyze mean squared error performance of the proposed algorithm. An alternating maximization algorithm is proposed for estimation of unknown model parameters and a convergence result for the method is provided. Finally, results using data from political science, finance and medical imaging applications are presented to demonstrate the practical utility of this procedure.
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Affiliation(s)
- Atul Ingle
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison WI 53706, USA
- Department of Medical Physics, University of Wisconsin-Madison, Madison WI 53705, USA
| | - James Bucklew
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison WI 53706, USA
| | - William Sethares
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison WI 53706, USA
| | - Tomy Varghese
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison WI 53706, USA
- Department of Medical Physics, University of Wisconsin-Madison, Madison WI 53705, USA
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14
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Zhou Z, Wu W, Wu S, Xia J, Wang CY, Yang C, Lin CC, Tsui PH. A survey of ultrasound elastography approaches to percutaneous ablation monitoring. Proc Inst Mech Eng H 2014; 228:1069-82. [DOI: 10.1177/0954411914554438] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Percutaneous thermal ablation has been widely used as a minimally invasive treatment for tumors. Treatment monitoring is essential for preventing complications while ensuring treatment efficacy. Mechanical testing measurements on tissue reveal that tissue stiffness increases with temperature and ablation duration. Different types of imaging methods can be used to monitor ablation procedures, including temperature or thermal strain imaging, strain imaging, modulus imaging, and shear modulus imaging. Ultrasound elastography demonstrates the potential to become the primary imaging modality for monitoring percutaneous ablation. This review briefly presented the state-of-the-art ultrasound elastography approaches for monitoring radiofrequency ablation and microwave ablation. These techniques were divided into four groups: quasi-static elastography, acoustic radiation force elastography, sonoelastography, and applicator motion elastography. Their advantages and limitations were compared and discussed. Future developments were proposed with respect to heat-induced bubbles, tissue inhomogeneities, respiratory motion, three-dimensional monitoring, multi-parametric monitoring, real-time monitoring, experimental data center for percutaneous ablation, and microwave ablation monitoring.
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Affiliation(s)
- Zhuhuang Zhou
- College of Life Science and Bioengineering, Beijing University of Technology, Beijing, China
| | - Weiwei Wu
- College of Electronic Information and Control Engineering, Beijing University of Technology, Beijing, China
| | - Shuicai Wu
- College of Life Science and Bioengineering, Beijing University of Technology, Beijing, China
| | - Jingjing Xia
- School of Electronic Information Engineering, Tianjin University, Tianjin, China
| | - Chiao-Yin Wang
- Department of Medical Imaging and Radiological Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Chunlan Yang
- College of Life Science and Bioengineering, Beijing University of Technology, Beijing, China
| | - Chung-Chih Lin
- Department of Computer Science and Information Engineering, Chang Gung University, Taoyuan, Taiwan
| | - Po-Hsiang Tsui
- Department of Medical Imaging and Radiological Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan
- Medical Image Research Center, Institute for Radiological Research, Chang Gung University, Taoyuan, Taiwan
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15
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Considering angle selection when using ultrasound electrode displacement elastography to evaluate radiofrequency ablation of tissues. BIOMED RESEARCH INTERNATIONAL 2014; 2014:764320. [PMID: 24971347 PMCID: PMC4058241 DOI: 10.1155/2014/764320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Accepted: 05/07/2014] [Indexed: 11/22/2022]
Abstract
Percutaneous radiofrequency ablation (RFA) is a minimally invasive treatment to thermally destroy tumors. Ultrasound-based electrode-displacement elastography is an emerging technique for evaluating the region of RFA-induced lesions. The angle between the imaging probe and the RFA electrode can influence electrode-displacement elastography when visualizing the ablation zone. We explored the angle effect on electrode-displacement elastography to measure the ablation zone. Phantoms embedded with meatballs were fabricated and then ablated using an RFA system to simulate RFA-induced lesions. For each phantom, a commercial ultrasound scanner with a 7.5 MHz linear probe was used to acquire raw image data at different angles, ranging from 30° to 90° at increments of 10°, to construct electrode-displacement images and facilitate comparisons with tissue section images. The results revealed that the ablation regions detected using electrode-displacement elastography were highly correlated with those from tissue section images when the angle was between 30° and 60°. However, the boundaries of lesions were difficult to distinguish, when the angle was larger than 60°. The experimental findings suggest that angle selection should be considered to achieve reliable electrode-displacement elastography to describe ablation zones.
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16
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Rivaz H, Boctor EM, Choti MA, Hager GD. Ultrasound elastography using multiple images. Med Image Anal 2013; 18:314-29. [PMID: 24361599 DOI: 10.1016/j.media.2013.11.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Revised: 11/20/2013] [Accepted: 11/25/2013] [Indexed: 01/20/2023]
Abstract
Displacement estimation is an essential step for ultrasound elastography and numerous techniques have been proposed to improve its quality using two frames of ultrasound RF data. This paper introduces a technique for calculating a displacement field from three (or multiple) frames of ultrasound RF data. To calculate a displacement field using three images, we first derive constraints on variations of the displacement field with time using mechanics of materials. These constraints are then used to generate a regularized cost function that incorporates amplitude similarity of three ultrasound images and displacement continuity. We optimize the cost function in an expectation maximization (EM) framework. Iteratively reweighted least squares (IRLS) is used to minimize the effect of outliers. An alternative approach for utilizing multiple images is to only consider two frames at any time and sequentially calculate the strains, which are then accumulated. We formally show that, compared to using two images or accumulating strains, the new algorithm reduces the noise and eliminates ambiguities in displacement estimation. The displacement field is used to generate strain images for quasi-static elastography. Simulation, phantom experiments and in vivo patient trials of imaging liver tumors and monitoring ablation therapy of liver cancer are presented for validation. We show that even with the challenging patient data, where it is likely to have one frame among the three that is not optimal for strain estimation, the introduction of physics-based prior as well as the simultaneous consideration of three images significantly improves the quality of strain images. Average values for strain images of two frames versus ElastMI are: 43 versus 73 for SNR (signal to noise ratio) in simulation data, 11 versus 15 for CNR (contrast to noise ratio) in phantom data, and 5.7 versus 7.3 for CNR in patient data. In addition, the improvement of ElastMI over both utilizing two images and accumulating strains is statistically significant in the patient data, with p-values of respectively 0.006 and 0.012.
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17
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Dewall RJ, Varghese T, Brace CL. Visualizing ex vivo radiofrequency and microwave ablation zones using electrode vibration elastography. Med Phys 2013; 39:6692-700. [PMID: 23127063 DOI: 10.1118/1.4758061] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
PURPOSE Electrode vibration elastography is a new shear wave imaging technique that can be used to visualize thermal ablation zones. Prior work has shown the ability of electrode vibration elastography to delineate radiofrequency ablations; however, there has been no previous study of delineation of microwave ablations or radiological-pathological correlations using multiple observers. METHODS Radiofrequency and microwave ablations were formed in ex vivo bovine liver tissue. Their visualization was compared on shear wave velocity and maximum displacement images. Ablation dimensions were compared to gross pathology. Elastographic imaging and gross pathology overlap and interobserver variability were quantified using similarity measures. RESULTS Elastographic imaging correlated with gross pathology. Correlation of area estimates was better in radiofrequency than in microwave ablations, with Pearson coefficients of 0.79 and 0.54 on shear wave velocity images and 0.90 and 0.70 on maximum displacement images for radiofrequency and microwave ablations, respectively. The absolute relative difference in area between elastographic imaging and gross pathology was 18.9% and 22.9% on shear wave velocity images and 16.0% and 23.1% on maximum displacement images for radiofrequency and microwave ablations, respectively. CONCLUSIONS Statistically significant radiological-pathological correlation was observed in this study, but correlation coefficients were lower than other modulus imaging techniques, most notably in microwave ablations. Observers provided similar delineations for most thermal ablations. These results suggest that electrode vibration elastography is capable of imaging thermal ablations, but refinement of the technique may be necessary before it can be used to monitor thermal ablation procedures clinically.
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Affiliation(s)
- Ryan J Dewall
- Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705, USA.
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18
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DeWall RJ, Bharat S, Varghese T, Hanson ME, Agni RM, Kliewer MA. Characterizing the compression-dependent viscoelastic properties of human hepatic pathologies using dynamic compression testing. Phys Med Biol 2012; 57:2273-86. [PMID: 22459948 DOI: 10.1088/0031-9155/57/8/2273] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Recent advances in elastography have provided several imaging modalities capable of quantifying the elasticity of tissue, an intrinsic tissue property. This information is useful for determining tumour margins and may also be useful for diagnosing specific tumour types. In this study, we used dynamic compression testing to quantify the viscoelastic properties of 16 human hepatic primary and secondary malignancies and their corresponding background tissue obtained following surgical resection. Two additional backgrounds were also tested. An analysis of the background tissue showed that F4-graded fibrotic liver tissue was significantly stiffer than F0-graded tissue, with a modulus contrast of 4:1. Steatotic liver tissue was slightly stiffer than normal liver tissue, but not significantly so. The tumour-to-background storage modulus contrast of hepatocellular carcinomas, a primary tumour, was approximately 1:1, and the contrast decreased with increasing fibrosis grade of the background tissue. Ramp testing showed that the background stiffness increased faster than the malignant tissue. Conversely, secondary tumours were typically much stiffer than the surrounding background, with a tumour-to-background contrast of 10:1 for colon metastases and 10:1 for cholangiocarcinomas. Ramp testing showed that colon metastases stiffened faster than their corresponding backgrounds. These data have provided insights into the mechanical properties of specific tumour types, which may prove beneficial as the use of quantitative stiffness imaging increases.
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Affiliation(s)
- Ryan J DeWall
- Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, USA.
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19
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DeWall RJ, Varghese T, Brace CL. Quantifying local stiffness variations in radiofrequency ablations with dynamic indentation. IEEE Trans Biomed Eng 2011; 59:728-35. [PMID: 22167553 DOI: 10.1109/tbme.2011.2178848] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Elastographic imaging can be used to monitor ablation procedures; however, confident and clear determination of the ablation boundary is essential to ensure complete treatment of the pathological target. To investigate the potential for ablation boundary representation on elastographic images, local variations in the viscoelastic properties in radiofrequency-ablated regions that were formed in vivo in porcine liver tissue were quantified using dynamic indentation. Spatial stiffness maps were then correlated to stained histology, the gold standard for the determination of the ablation periphery or boundary. Regions of interest in 11 radiofrequency ablation samples were indented at 18-24 locations each, including the central zone of complete necrosis and more peripheral transition zones including normal tissue. Storage modulus and the rate of stiffening were both greatest in the central ablation zone and decreased with radial distance away from the center. The storage modulus and modulus contrast at the ablation outer transition zone boundary were 3.1 ± 1.0 kPa and 1.6 ± 0.4, respectively, and 36.2 ± 9.1 kPa and 18.3 ± 5.5 at the condensation boundary within the ablation zone. Elastographic imaging modalities were then compared to gross pathology in ex vivo bovine liver tissue. Area estimated from strain, shear-wave velocity, and gross pathology images were 470, 560, and 574 mm(2), respectively, and ablation widths were 19.4, 20.7, and 23.0 mm. This study has provided insights into spatial stiffness distributions within radiofrequency ablations and suggests that low stiffness contrast on the ablation periphery leads to the observed underestimation of ablation extent on elastographic images.
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Affiliation(s)
- Ryan J DeWall
- Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705, USA.
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20
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DeWall RJ, Varghese T, Madsen EL. Shear wave velocity imaging using transient electrode perturbation: phantom and ex vivo validation. IEEE TRANSACTIONS ON MEDICAL IMAGING 2011; 30:666-78. [PMID: 21075719 PMCID: PMC3066053 DOI: 10.1109/tmi.2010.2091412] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
This paper presents a new shear wave velocity imaging technique to monitor radio-frequency and microwave ablation procedures, coined electrode vibration elastography. A piezoelectric actuator attached to an ablation needle is transiently vibrated to generate shear waves that are tracked at high frame rates. The time-to-peak algorithm is used to reconstruct the shear wave velocity and thereby the shear modulus variations. The feasibility of electrode vibration elastography is demonstrated using finite element models and ultrasound simulations, tissue-mimicking phantoms simulating fully (phantom 1) and partially ablated (phantom 2) regions, and an ex vivo bovine liver ablation experiment. In phantom experiments, good boundary delineation was observed. Shear wave velocity estimates were within 7% of mechanical measurements in phantom 1 and within 17% in phantom 2. Good boundary delineation was also demonstrated in the ex vivo experiment. The shear wave velocity estimates inside the ablated region were higher than mechanical testing estimates, but estimates in the untreated tissue were within 20% of mechanical measurements. A comparison of electrode vibration elastography and electrode displacement elastography showed the complementary information that they can provide. Electrode vibration elastography shows promise as an imaging modality that provides ablation boundary delineation and quantitative information during ablation procedures.
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Affiliation(s)
- Ryan J. DeWall
- Department of Medical Physics and Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI 53705 USA ()
| | - Tomy Varghese
- Department of Medical Physics and Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI 53705 USA ()
| | - Ernest L. Madsen
- Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705 USA ()
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21
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van Vledder MG, Boctor EM, Assumpcao LR, Rivaz H, Foroughi P, Hager GD, Hamper UM, Pawlik TM, Choti MA. Intra-operative ultrasound elasticity imaging for monitoring of hepatic tumour thermal ablation. HPB (Oxford) 2010; 12:717-23. [PMID: 21083798 PMCID: PMC3003483 DOI: 10.1111/j.1477-2574.2010.00247.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
BACKGROUND Thermal ablation is an accepted therapy for selected hepatic malignancies. However, the reliability of thermal ablation is limited by the inability to accurately monitor and confirm completeness of tumour destruction in real time. We investigated the ability of ultrasound elasticity imaging (USEI) to monitor thermal ablation. OBJECTIVES Capitalizing on the known increased stiffness that occurs with protein denaturation and dehydration during thermal therapy, we sought to investigate the feasibility and accuracy of USEI for monitoring of liver tumour ablation. METHODS A model for hepatic tumours was developed and elasticity images of liver ablation were acquired in in vivo animal studies, comparing the elasticity images to gross specimens. A clinical pilot study was conducted using USEI in nine patients undergoing open radiofrequency ablation for hepatic malignancies. The size and shape of thermal lesions on USEI were compared to B-mode ultrasound and post-ablation computed tomography (CT). RESULTS In both in vivo animal studies and in the clinical trial, the boundary of thermal lesions was significantly more conspicuous on USEI when compared with B-mode imaging. Animal studies demonstrated good correlation between the diameter of ablated lesions on USEI and the gross specimen (r = 0.81). Moreover, high-quality strain images were generated in real time during therapy. In patients undergoing tumour ablation, a good size correlation was observed between USEI and post-operative CT (r = 0.80). CONCLUSION USEI can be a valuable tool for the accurate monitoring and real-time verification of successful thermal ablation of liver tumours.
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Affiliation(s)
- Mark G van Vledder
- Departments of Surgery, The Johns Hopkins School of Medicine, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
| | - Emad M Boctor
- Departments of Radiology, The Johns Hopkins School of Medicine, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
| | - Lia R Assumpcao
- Departments of Surgery, The Johns Hopkins School of Medicine, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
| | - Hassan Rivaz
- Center for Computer Integrated Surgical Systems, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
| | - Pezhman Foroughi
- Center for Computer Integrated Surgical Systems, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
| | - Gregory D Hager
- Center for Computer Integrated Surgical Systems, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
| | - Ulrike M Hamper
- Departments of Radiology, The Johns Hopkins School of Medicine, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
| | - Timothy M Pawlik
- Departments of Surgery, The Johns Hopkins School of Medicine, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
| | - Michael A Choti
- Departments of Surgery, The Johns Hopkins School of Medicine, Whiting School of Engineering, The Johns Hopkins UniversityBaltimore, MD, USA
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22
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Rubert N, Bharat S, DeWall RJ, Andreano A, Brace C, Jiang J, Sampson L, Varghese T. Electrode displacement strain imaging of thermally-ablated liver tissue in an in vivo animal model. Med Phys 2010; 37:1075-82. [PMID: 20384243 DOI: 10.1118/1.3301603] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
PURPOSE Percutaneous thermal ablation is increasingly being used to destroy hepatic tumors in situ. The success of ablative techniques is highly dependent on adequate ablation zone monitoring, and ultrasound-based strain imaging could become a convenient and cost-effective means to delineate ablation zone boundaries. This study investigates in vivo electrode displacement-based strain imaging for monitoring hepatic ablation procedures that are difficult to perform with conventional elastography. METHODS a In our method, minute displacements (less than a millimeter) are applied to the unconstrained end of the ablation electrode, resulting in localized tissue deformation within the ablation zone that provides the mechanical stimuli required for strain imaging. This article presents electrode displacement strain images of radiofrequency ablation zones created in porcine liver in vivo (n = 13). RESULTS Cross-sectional area measurements from strain images of these ablation zones were obtained using manual and automated segmentation. Area measurements from strain images were highly correlated with areas measured on histopathology images, quantitated using linear regression (R = 0.894, P < 0.001 and R = 0.828, P < 0.001, respectively). CONCLUSIONS This study further demonstrates that electrode displacement elastography is capable of providing high-contrast images using widely available commercial ultrasound systems which may potentially be used to assess the extent of thermal ablation zones.
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Affiliation(s)
- N Rubert
- Department of Medical Physics, University of Wisconsin-Madison, 1111 Highland Avenue, Madison, Wisconsin 53706, USA
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23
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Carson PL, Fenster A. Anniversary paper: evolution of ultrasound physics and the role of medical physicists and the AAPM and its journal in that evolution. Med Phys 2009; 36:411-28. [PMID: 19291980 DOI: 10.1118/1.2992048] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Ultrasound has been the greatest imaging modality worldwide for many years by equipment purchase value and by number of machines and examinations. It is becoming increasingly the front end imaging modality; serving often as an extension of the physician's fingers. We believe that at the other extreme, high-end systems will continue to compete with all other imaging modalities in imaging departments to be the method of choice for various applications, particularly where safety and cost are paramount. Therapeutic ultrasound, in addition to the physiotherapy practiced for many decades, is just coming into its own as a major tool in the long progression to less invasive interventional treatment. The physics of medical ultrasound has evolved over many fronts throughout its history. For this reason, a topical review, rather than a primarily chronological one is presented. A brief review of medical ultrasound imaging and therapy is presented, with an emphasis on the contributions of medical physicists, the American Association of Physicists in Medicine (AAPM) and its publications, particularly its journal Medical Physics. The AAPM and Medical Physics have contributed substantially to training of physicists and engineers, medical practitioners, technologists, and the public.
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Affiliation(s)
- Paul L Carson
- Department of Radiology, University of Michigan Health System, 3218C Medical Science I, B Wing SPC 5667, 1301 Catherine Street, Ann Arbor, Michigan 48109-5667, USA.
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Bharat S, Fisher TG, Varghese T, Hall TJ, Jiang J, Madsen EL, Zagzebski JA, Lee FT. Three-dimensional electrode displacement elastography using the Siemens C7F2 fourSight four-dimensional ultrasound transducer. ULTRASOUND IN MEDICINE & BIOLOGY 2008; 34:1307-16. [PMID: 18374467 PMCID: PMC2597045 DOI: 10.1016/j.ultrasmedbio.2008.01.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2007] [Revised: 11/20/2007] [Accepted: 01/15/2008] [Indexed: 05/02/2023]
Abstract
Because ablation therapy alters the elastic modulus of tissues, emerging strain imaging methods may enable clinicians for the first time to have readily available, cost-effective, real-time guidance to identify the location and boundaries of thermal lesions. Electrode displacement elastography is a method of strain imaging tailored specifically to ultrasound-guided electrode-based ablative therapies (e.g., radio-frequency ablation). Here tissue deformation is achieved by applying minute perturbations to the unconstrained end of the treatment electrode, resulting in localized motion around the end of the electrode embedded in tissue. In this article, we present a method for three-dimensional (3D) elastographic reconstruction from volumetric data acquired using the C7F2 fourSight four-dimensional ultrasound transducer, provided by Siemens Medical Solutions USA, Inc. (Issaquah, WA, USA). Lesion reconstruction is demonstrated for a spherical inclusion centered in a tissue-mimicking phantom, which simulates a thermal lesion embedded in a normal tissue background. Elastographic reconstruction is also performed for a thermal lesion created in vitro in canine liver using radio-frequency ablation. Postprocessing is done on the acquired raw radio-frequency data to form surface-rendered 3D elastograms of the inclusion. Elastographic volume estimates of the inclusion compare reasonably well with the actual known inclusion volume, with 3D electrode displacement elastography slightly underestimating the true inclusion volume.
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Affiliation(s)
- Shyam Bharat
- Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
| | - Ted G. Fisher
- Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
| | - Tomy Varghese
- Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
| | - Timothy J. Hall
- Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
| | - Jingfeng Jiang
- Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
| | - Ernest L. Madsen
- Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
| | - James A. Zagzebski
- Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
| | - Fred. T. Lee
- Department of Radiology, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA
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