Single Track Location Research Articles

On the Challenges Associated with Obtaining Reproducible Measurements Using SWEI in the Median Nerve

This work discusses challenges we have encountered in acquiring reproducible measurements of shear wave speed (SWS) in the median nerve and suggests methods for improving reproducibility. First, procedural acquisition challenges are described, including nerve echogenicity, transducer pressure and transmit focal depth. Second, we present an iterative, radon sum–based algorithm that was developed specifically for measuring the SWS in median nerves. SWSs were measured using single track location shear wave elasticity imaging (SWEI) in the median nerves of six healthy volunteers and six patients diagnosed with carpal tunnel syndrome. Unsuccessful measurements were associated with several challenges including reverberation artifacts, low signal-to-noise ratio and temporal window limitations for tracking the velocity wave. To address these challenges, an iterative convergence algorithm was implemented to identify an appropriate temporal processing window that removed the reverberation artifacts while preserving shear wave signals. Algorithmically, it was important to consider the lateral regression kernel size and position and the temporal window. Procedurally, both nerve echogenicity and transducer compression were determined to impact the measured SWS. Shear waves were successfully measured in the median nerve proximal to the carpal tunnel, but SWEI measurements were significantly compromised within the carpal tunnel itself. The velocity-based SWSs were statistically significantly higher than the displacement SWSs (p < 0.0001), demonstrating for the first time dispersion in the median nerve in vivo using SWEI.

Preclinical Imaging Using Single Track Location Shear Wave Elastography: Monitoring the Progression of Murine Pancreatic Tumor Liver Metastasis In Vivo.

Recently, researchers have discovered the direct impact of the tumor mechanical environment on the growth, drug uptake and prognosis of tumors. While estimating the mechanical parameters (solid stress, fluid pressure, stiffness) can aid in the treatment planning and monitoring, most of these parameters cannot be quantified noninvasively. Shear wave elastography (SWE) has shown promise as a means of noninvasively measuring the stiffness of soft tissue. However, stiffness is still not a recognized imaging biomarker. While SWE has been shown to be capable of measuring tumor stiffness in humans, much important research is done in small animal preclinical models, where tumors are often too small for the resolution of traditional SWE tools. Single-track location SWE (STL-SWE) has previously been shown to overcome the fundamental resolution limit of SWE imposed by ultrasound speckle, which may make it suitable for preclinical imaging. Using STL-SWE, in this work, we demonstrate, for the first time, that the stiffness changes occurring inside metastatic murine pancreatic tumors can be monitored over long time scales (up to 9 weeks). To prevent the respiration motion from degrading the STL-SWE estimates, we developed a real-time software-based respiration gating scheme that we implemented on a Verasonics ultrasound imaging system. By imaging the liver of three healthy mice and performing correlation analysis, we confirmed that the respiration-gated STL-SWE data was free from motion corruption. By performing coregistered power-doppler imaging, we found that the local variability in liver shear wave speed (SWS) measurements increased from 5.4% to 9.9% due to blood flow. We performed a longitudinal study using a murine model of pancreatic cancer liver metastasis to assess the temporal changes (over nine weeks) in SWS in two groups: a controlled group receiving no treatment (n=8), and an experimental group (n=6) treated with Gemcitabine, a chemotherapy agent. We independently evaluated tumor burden using bioluminescence imaging (BLI). The initial and endpoint SWS measurements were statistically different (p<0.05). Additionally, when the liver SWS exceeded 2.5 ± 0.3 and 2.73 ± 0.34 m/s in untreated and treated mice, respectively, the death of the mice was imminent within approximately 10 days. The time taken for the SWS to exceed the thresholds was 17 days (on average) longer in Gemcitabine treated mice compared to the untreated ones. The survival statistics corroborated the effectiveness of Gemcitabine. Spearman correlation analysis revealed a monotonic relationship between SWE measurements (SWS) and BLI measurements (radiance) for tumors whose radiance exceeded 1×107 photons/s/cm2/sr. Longitudinal measurements on the liver of four healthy mice revealed a maximum coefficient of variation of 11.4%. The results of this investigation demonstrate that with appropriate gating, researchers can use STL-SWE for small animal imaging and perform longitudinal studies using preclinical cancer models.

Speckle-free estimation of tissue elasticity with single track location shear wave elasticity imaging

Shear Wave Elasticity Imaging (SWEI) is commonly used to characterize tissue elasticity, but conventional, multiple-track-location SWEI (MTL-SWEI) techniques are resolution-limited by speckle. MTL-SWEI techniques use plane wave ultrasound to monitor an induced shear wave as it propagates across a set of tracking beams within a region of interest. The scattering process creates a random, yet stationary, spatial sensitivity pattern for each beamformed location, called speckle bias, which causes errors in MTL-SWEI shear wave speed estimates that cannot be improved through averaging. Single Track Location SWEI (STL-SWEI) overcomes speckle bias by using a single track beam, subsequently exciting and tracking different push locations, and comparing the timing of the recorded shear wave signals from different push locations to estimate shear wave speed. Two and three-dimensional STL-SWEI imaging techniques are presented and compared to MTL-SWEI and Acoustic Radiation Force Impulse (ARFI) imaging in phantoms and in vivo experiments. Tradeoffs and techniques for sequencing, beamforming, shear wave speed estimation, and image formation are discussed. For applications where tissue heating and motion are not limiting factors, STL-SWEI provides superior imaging in terms of lateral resolution and contrast-to-noise ratio compared to MTL-SWEI and ARFI. [This work was supported by NIHR37HL096023 and NIHR01EB01248.]Shear Wave Elasticity Imaging (SWEI) is commonly used to characterize tissue elasticity, but conventional, multiple-track-location SWEI (MTL-SWEI) techniques are resolution-limited by speckle. MTL-SWEI techniques use plane wave ultrasound to monitor an induced shear wave as it propagates across a set of tracking beams within a region of interest. The scattering process creates a random, yet stationary, spatial sensitivity pattern for each beamformed location, called speckle bias, which causes errors in MTL-SWEI shear wave speed estimates that cannot be improved through averaging. Single Track Location SWEI (STL-SWEI) overcomes speckle bias by using a single track beam, subsequently exciting and tracking different push locations, and comparing the timing of the recorded shear wave signals from different push locations to estimate shear wave speed. Two and three-dimensional STL-SWEI imaging techniques are presented and compared to MTL-SWEI and Acoustic Radiation Force Impulse (ARFI) imaging in phantoms and ...

Measurement of Liver Stiffness Using Shear Wave Elastography in a Rat Model: Factors Impacting Stiffness Measurement with Multiple- and Single-Tracking-Location Techniques

The clinical use of elastography for monitoring fibrosis progression is challenged by the subtle changes in liver stiffness associated with early-stage fibrosis and the comparatively large variance in stiffness estimates provided by elastography. Single-tracking-location (STL) shear wave elasticity imaging (SWEI) is an ultrasound elastography technique previously found to provide improved estimate precision compared with multiple-tracking-location (MTL) SWEI. Because of the improved precision, it is reasonable to expect that STL-SWEI would provide improved ability to differentiate liver fibrosis stage compared with MTL-SWEI. However, this expectation has not been previously challenged rigorously. In this work, the performance of STL- and MTL-SWEI in the setting of a rat model of liver fibrosis is characterized, and the advantages of STL-SWEI in staging fibrosis are explored. The purpose of this study was to determine what advantages, if any, arise from using STL-SWEI instead of MTL-SWEI in the characterization of fibrotic liver. Thus, the ability of STL-SWEI to differentiate livers at various METAVIR fibrosis scores, for ex vivo postmortem measurements, is explored. In addition, we examined the effect of the common confounding factor of fluid versus solid boundary conditions in SWEI experiments. Sprague-Dawley rats were treated with carbon tetrachloride over several weeks to produce liver disease of varying severity. STL and MTL stiffness measurements were performed ex vivo and compared with the METAVIR scores from histological analysis and the duration of treatment. A strong association was observed between liver stiffness and weeks of treatment with the liver toxin carbon tetrachloride. Direct comparison of STL- and MTL-SWEI measurements revealed no significant difference in ability to differentiate fibrosis stages based on SWEI mean values. However, image interquartile range was greatly improved in the case of STL-SWEI, compared with MTL-SWEI, at small beam spacing.

The human placenta: Function and morphological assessments using ultrasound and magnetic resonance elastography

s / Placenta 45 (2016) 63e133 74 P1.6 THE HUMAN PLACENTA: FUNCTION AND MORPHOLOGICAL ASSESSMENTS USING ULTRASOUND AND MAGNETIC RESONANCE ELASTOGRAPHY Richard K. Miller , Stephan McAleavey , Juvenal Ormachea , Eva Pressman, Loralei Thornburg , David Dombroski , Jianhui Zhong, Marvin Doyley , Ronald W. Wood, Jonathan Carrol-Nellenback , Ollivier Hyrien , Philip Katzman , Christopher Stodgell , Kam Szlachetka, Henry Wang, Kevin Parker . University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; University of Rochester Haijm School of Engineering, Rochester, New York, USA Objective: In utero evaluations of placental anatomy and function offer the promise of associating placental pathophysiology with neonatal outcomes, and thus potential for enhanced management of perinatal complications and improved long-term health of the mother and child. Ultrasound Elastography (USE) and Magnetic Resonance Elastography (MRE) provide means to evaluate tissue stiffness in utero. In conjunction with measures of vascular anatomy and perfusion, we can test mechanistic hypotheses about the relationship with anatomical function and deviations associated with disease states. For example, The Parker Hypothesis (Parker, Phys. Med. Biol. 59: 4443,14) proposes that viscoelastic measures of soft tissue stiffness are related to the fractal branching properties of the vascular anatomy. Methods: Term human placentae were obtained immediately upon delivery and evaluated directly either in a 3T GE MRI with Elastography or using a Siemens Antares US scanner and VF10-5 Probe with custom single track location shear wave elasticity imaging pulse sequences and accelerated processing. Other placentae were perfused through the umbilical cord and imaging, Doppler measures and elastography were conducted. At the end of the experiments, a barium gel was infused to enhance subsequent CT imaging of the fetal vasculature. Results: The utility of elastography in functional evaluation of the placenta are readily demonstrated in the following examples: 1) Placental tissue anomalies (e.g., infarcted areas) are stiff, and provided dramatic examples of the sensitivity USE and MRE methodologies for the detection of placental pathology; 2) Ex vivo placental perfusions have been used to relate placental stiffness to fetal vasculature when measured by USE, as seen when fetal vascular dynamics were pharmacologically manipulated. Clinical and high-resolution microCT systems can and have been used on placentae to provide additional post-delivery anatomical characterization and quantification of the vascular beds. These CT observations provide confirmation of in vivo Doppler US and the potential use of MR angiography for vascular characterization. We demonstrated that these datasets are amenable to automated identification and characterization of branching morphology, including centerline tree and Sholl analyses. Conclusion: These USE and MRE technologies enable promising new approaches for the prediction of risks during and after pregnancy. (Support: Goode Foundation) MRI localization of a placental infarct with associated elastographic ortho slice A: gross examination of placental lesion. B, MR segmented volume. C. Superimposed MRE. Yellow arrow directs attention to lesion.

Shear Wave Speed Measurements Using Crawling Wave Sonoelastography and Single Tracking Location Shear Wave Elasticity Imaging for Tissue Characterization.

Elastography provides tissue stiffness information that attempts to characterize the elastic properties of tissue. However, there is still limited literature comparing elastographic modalities for tissue characterization. This study focuses on two quantitative techniques using different vibration sources that have not been compared to date: crawling wave sonoelastography (CWS) and single tracking location shear wave elasticity imaging (STL-SWEI). To understand each technique's performance, shear wave speed (SWS) was measured in homogeneous phantoms and ex vivo beef liver tissue. Then, the contrast, contrast-to-noise ratio (CNR), and lateral resolution were measured in an inclusion and two-layer phantoms. The SWS values obtained with both modalities were validated with mechanical measurements (MM) which serve as ground truth. The SWS results for the three different homogeneous phantoms (10%, 13%, and 16% gelatin concentrations) and ex vivo beef liver tissue showed good agreement between CWS, STL-SWEI, and MM as a function of frequency. For all gelatin phantoms, the maximum accuracy errors were 2.52% and 2.35% using CWS and STL-SWEI, respectively. For the ex vivo beef liver, the maximum accuracy errors were 9.40% and 7.93% using CWS and STL-SWEI, respectively. For lateral resolution, contrast, and CNR, both techniques obtained comparable measurements for vibration frequencies less than 300 Hz (CWS) and distances between the push beams ( ∆x ) between 3 mm and 5.31 mm (STL-SWEI). The results obtained in this study agree over an SWS range of 1-6 m/s. They are expected to agree in perfectly linear, homogeneous, and isotropic materials, but the SWS overlap is not guaranteed in all materials because each of the three methods have unique features.

Scholte wave generation during single tracking location shear wave elasticity imaging of engineered tissues.

The physical environment of engineered tissues can influence cellular functions that are important for tissue regeneration. Thus, there is a critical need for noninvasive technologies capable of monitoring mechanical properties of engineered tissues during fabrication and development. This work investigates the feasibility of using single tracking location shear wave elasticity imaging (STL-SWEI) for quantifying the shear moduli of tissue-mimicking phantoms and engineered tissues in tissue engineering environments. Scholte surface waves were observed when STL-SWEI was performed through a fluid standoff, and confounded shear moduli estimates leading to an underestimation of moduli in regions near the fluid-tissue interface.

Single tracking location acoustic radiation force impulse viscoelasticity estimation (STL-VE): A method for measuring tissue viscoelastic parameters.

Single tracking location (STL) shear wave elasticity imaging (SWEI) is a method for detecting elastic differences between tissues. It has the advantage of intrinsic speckle bias suppression compared with multiple tracking location variants of SWEI. However, the assumption of a linear model leads to an overestimation of the shear modulus in viscoelastic media. A new reconstruction technique denoted single tracking location viscosity estimation (STL-VE) is introduced to correct for this overestimation. This technique utilizes the same raw data generated in STL-SWEI imaging. Here, the STL-VE technique is developed by way of a maximum likelihood estimation for general viscoelastic materials. The method is then implemented for the particular case of the Kelvin-Voigt Model. Using simulation data, the STL-VE technique is demonstrated and the performance of the estimator is characterized. Finally, the STL-VE method is used to estimate the viscoelastic parameters of ex vivo bovine liver. We find good agreement between the STL-VE results and the simulation parameters as well as between the liver shear wave data and the modeled data fit.

On the use of local speckle field as a correction factor for shear modulus estimates based on multiple-track-locations methods

Acoustic-radiation-force impulse (ARFI) imaging for characterization of shear modulus of biological tissues employs either multiple-track-locations (MTL) methods or single-track-location (STL) methods. MTL estimates of shear modulus at different depths suffer from more variability compared to those of STL estimates. Our studies have shown a significant correlation between bias in shear-wave arrival time estimates and local speckle field lateral statistics. We propose using the local speckle field as a surrogate for the unknown bias apparent in MTL shear-wave speed estimates. This local speckle field is determined using a “swept-receive acquisition” that is produced by holding the transmit beam fixed while laterally translating the receive aperture. Application of various lateral weighting functions to the swept-receive image results in an approximate compensation to the tracking bias. In this study, we implement our technique on simulation and experimental data from gelatin phantoms. Additionally, the effect of varying transmit-receive aperture f/# on the accuracy of our compensation method is investigated in simulation. Finally, the quality of compensated MTL shear modulus images are quantified and compared to those of the uncompensated MTL and of STL methods in matched tissue mimicking phantom experiments.

Compensating for Scholte waves in single track location shearwave elasticity imaging

The estimation of shearwave velocity in biological tissues using Single Track Location Shearwave Elasticity Imaging (STL-SWEI) depends on the assumption that the ultrasonically observed particle displacements are due to the propagation of shearwaves in an approximately infinite space. When this assumption is violated, erroneous estimates of the shearwave speed may occur leading to image artifacts. One particularly troubling error occurs when slowly propagating Scholte waves are generated at solid-fluid interfaces. These interface waves travel at a slower speed than the shearwaves produced in STL-SWEI. However, the signals produced appear similar to that of shearwaves and cannot be readily distinguished in the typical STL-SWEI imaging sequence. Instead, alternative sequences are needed to identify and correct for these anomalous wave types. In this work, the surface wave phenomena is examined in the context of STL-SWEI imaging. The appearance of these waves is demonstrated in simulation, tissue mimicking phantoms, engineered tissues, and in liver tissue using a clinical scanner. The effect of the ultrasound beam geometry on the Scholte wave measurement is studied. Finally, a revised STL-SWEI reconstruction method utilizing Radon Sums is presented. Using this method, the simultaneous characterization of shear and Scholte waves is demonstrated for the above materials.

Advancing Tissue Science and Engineering: A Foundation for the Future A Multi-Agency Strategic Plan

Tissue EngineeringVol. 13, No. 12 Advancing Tissue Science and Engineering: A Foundation for the Future A Multi-Agency Strategic PlanPublished Online:8 Dec 2007https://doi.org/10.1089/ten.2007.1503AboutSectionsPDF/EPUB ToolsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail "Advancing Tissue Science and Engineering: A Foundation for the Future A Multi-Agency Strategic Plan." , 13(12), pp. 2825–2826FiguresReferencesRelatedDetailsCited ByRegeneration of skin appendages and nerves: current status and further challenges3 February 2020 | Journal of Translational Medicine, Vol. 18, No. 1Overview of the US Food and Drug Administration Regulatory ProcessRegenerative Medicine and Rehabilitation for Tendinous and Ligamentous Injuries in Sport HorsesVeterinary Clinics of North America: Equine Practice, Vol. 34, No. 2Localized surface functionalization of polycaprolactone with atmospheric-pressure microplasma jet31 July 2015 | Biomedical Physics & Engineering Express, Vol. 1, No. 2Scholte wave generation during single tracking location shear wave elasticity imaging of engineered tissuesThe Journal of the Acoustical Society of America, Vol. 138, No. 2The utilization of decellularized tendon slices to provide an inductive microenvironment for the proliferation and tenogenic differentiation of stem cellsBiomaterials, Vol. 52USPIO-labeled textile materials for non-invasive MR imaging of tissue-engineered vascular graftsBiomaterials, Vol. 39Estimating Cell Concentration in Three-Dimensional Engineered Tissues Using High Frequency Quantitative Ultrasound14 March 2014 | Annals of Biomedical Engineering, Vol. 42, No. 6Hype and expectations in tissue engineeringRegenerative Medicine, Vol. 9, No. 1Mechanical characterization of bioprinted in vitro soft tissue models26 November 2013 | Biofabrication, Vol. 5, No. 4Towards a Richer Debate on Tissue Engineering: A Consideration on the Basis of NEST-Ethics15 November 2012 | Science and Engineering Ethics, Vol. 19, No. 3Thinking Inside the Box: Keeping Tissue-Engineered Constructs In Vitro for Use as Preclinical Models Michael C. Gibbons, Marcus A. Foley, and Kristen O'Halloran Cardinal5 November 2012 | Tissue Engineering Part B: Reviews, Vol. 19, No. 1US FDA outreach to the regenerative medicine community: challenges and opportunitiesRegenerative Medicine, Vol. 7, No. 4Regenerative Medicine Applied to Solid Organ Transplantation: Where Do We Stand?Transplantation Proceedings, Vol. 42, No. 4Synopsis of the Food and Drug Administration–National Institute of Standards and Technology Co-Sponsored “In Vitro Analyses of Cell/Scaffold Products” Workshop Brent McCright, Jiyoung M. Dang, Deborah A. Hursh, David S. Kaplan, Rabia Ballica, Kimberly A. Benton, and Anne L. Plant10 February 2009 | Tissue Engineering Part A, Vol. 15, No. 3 Volume 13Issue 12Dec 2007 InformationCopyright 2007, Mary Ann Liebert, Inc.To cite this article:Advancing Tissue Science and Engineering: A Foundation for the Future A Multi-Agency Strategic Plan.Tissue Engineering.Dec 2007.2825-2826.http://doi.org/10.1089/ten.2007.1503Published in Volume: 13 Issue 12: December 8, 2007Online Ahead of Print:December 1, 2007PDF download