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High Resolution Elastography for Eye
Abstracts
T7. Elastography Symposium
T7-16-IN01 Elastography Basic Principles Giovanna Ferraioli Ultrasound Unit, Department of medical sciences and infectious diseases, Fondazione IRCCS Policlinico San Matteo, University of Pavia, Pavia, Italy Elastography displays the biomechanical properties of the tissue whereas B-mode ultrasound displays the acoustic properties. These properties are not related to each other. Elastography can be considered a virtual palpation: under a stress, stiffer tissues show less longitudinal displacement and higher speed of transverse displacement. Elastography techniques are based or on the assessment of the longitudinal displacement of the tissue induced by a stress, as in strain elastography and acoustic radiation force impulse (ARFI) imaging, or on the assessment of the speed of the transverse displacement of the tissue as in shear wave elastography. In strain elastography a part of the body is compressed axially by pressing across its surface and the internal tissue displacement is converted to a strain image (percentage of deformation), because the percentage of deformation will be constant whereas displacement decays with depth. In the ARFI imaging, the acoustic radiation force generates a localized displacement of a few microns in the ultrasound axial direction. ARFI generates also shear wave displacement at one point (point shear wave elastography) or along several lines (2D-shear wave elastography). Shear waves can be generated by an external mechanical push as well, as in vibration controlled transient elastography (VCTE), magnetic resonance elastography (MRE) or vibro-elastography. T7-16-IN02 High Resolution Elastography for Eye Chih-Chung Huang National Cheng Kung University, Taiwan Estimating the corneal elasticity can provide valuable information for corneal pathologies and treatments. Ophthalmologic pathologies such as keratoconus and the phototoxic effects of ultraviolet radiation on the cornea caused the corneal elasticity change. Not only the corneal pathologies but also the efficacy evaluation of corneal treatment, such as evaluating the recovery of corneal refractive surgery and the efficacy of corneal collagen crosslinking treatment are related to corneal elasticity. This makes quantitative estimation of the elasticity of the human cornea important for ophthalmic diagnoses. The present study investigated the use of a proposed high-resolution shear-wave imaging (HR-SWI) method based on a dual-element transducer (comprising an 8-MHz element for pushing and a 32-MHz element for imaging) for measuring the elasticity of the human cornea. The distance between these elements was 1.5 mm. Due to the image lateral resolution being limited by the distance between the pushing and imaging beams, a spatial algorithm named the Pseudo-Sudoku Algorithm (PSA) was used to improve the lateral resolution. The gelatin-phantom results showed the ability of the PSA to distinguish the elasticity distribution of a small two-side phantom (2.2 mm 3 3.5 mm). The image resolutions of HR-SWI in the axial and lateral directions were 301 and 129 mm, respectively. The elasticity values of corneas from six human donors were also measured by HR-SWI, with all of the ex vivo results demonstrating the potential of HR-SWI in clinically measuring the elasticity of the human cornea.
S87
T7-16-IN03 Ultrasound Shear Wave Elastography: Principles and New Technologies Shigao Chen Department of Radiology, Mayo Clinic, Rochester, MN Tissue stiffness measured by ultrasound shear wave elastography is useful for many clinical applications such as liver fibrosis staging and cancer imaging. This presentation gives an overview of various technical components of shear wave elastography, including the relationship between shear wave speed and tissue mechanical properties, generation of shear wave by ultrasound radiation force and mechanical vibration, detection of shear wave by ultrasound scanner, and methods for calculation of shear wave speed. Commercial shear wave technologies covered in this talk include SuperSonic Imagine, Fibroscan, and Comb-push Shearwave Ultrasound Elastography (CUSE). Examples of new technologies under development will also be given. Confounding factors for shear wave elastography will be discussed. T7-16-IN04 Evaluation of Shear Wave Dispersion Caused by Liver Fibrous Structure Using Hepatic Fibrosis Progression Model Makoto Yamakawa, Shiori Fujii, Tsuyoshi Shiina Graduate School of Medicine, Kyoto University, Kyoto, Japan In chronic hepatitis diagnosis, shear wave elastography is utilized for evaluating fibrosis progression. Not only the elasticity but also the viscosity of liver tissue is considered to be useful information for its diagnosis. Therefore, in recent years, a method of evaluating tissue viscosity using shear wave dispersion has been used clinically. However, the shear wave dispersion also occurs due to tissue viscosity, but also due to the microstructure of tissue. Therefore, we quantitatively evaluated the shear wave dispersion caused by the liver fibrous structure using a hepatic fibrosis progress model. At that time, in order to evaluate only the shear wave dispersion caused by the liver fibrous structure, the viscosity in the model was set to zero. As a results, the shear wave dispersion (shear wave dispersion slope) were 0.0260.003, 0.3260.20, 0.6260.25, 1.2560.89, and 0.7361.53 m/s/kHz for stage F0, F1, F2, F3, and F4. The dispersion slope tended to increase with progress of the hepatic fibrosis stage. However, in stage F4, the result was greatly affected by the location of the ROI, so the variance increased. The shear wave dispersion caused by the liver fibrous structure was about 10-20 % of that in in vivo measurement. Therefore, we confirmed that the shear wave dispersion is influenced by the liver fibrous structure together with the liver viscosity. T7-16-IN05 Analysis of Acoustic Properties of Liver Organelles Including NASH Tadashi Yamaguchi Center for Frontier Medical Engineering, Chiba University, Chiba, Japan Accurate diagnosis of non-alcoholic steatohepatitis (NASH) is a critical issue in current clinical practice. Non-invasive diagnosis of NASH can be achieved by quantitative ultrasound (QUS), which requires a detailed understanding tissue-specific acoustic microstructure at cellular scale (i,e., 10 mm). Therefore, QUS methods would benefit from the knowledge of the acoustic properties of organelles in NASH livers because they may represent the dominant scattering source at conventional frequencies used for in vivo assessments (i.e., , 15 MHz). This study focuses on obtaining speed of sound (c) of organelles (i.e., nucleus, cytoplasm, and fibers) using above-mentioned 250-MHz
T7. Elastography Symposium
T7-16-IN01 Elastography Basic Principles Giovanna Ferraioli Ultrasound Unit, Department of medical sciences and infectious diseases, Fondazione IRCCS Policlinico San Matteo, University of Pavia, Pavia, Italy Elastography displays the biomechanical properties of the tissue whereas B-mode ultrasound displays the acoustic properties. These properties are not related to each other. Elastography can be considered a virtual palpation: under a stress, stiffer tissues show less longitudinal displacement and higher speed of transverse displacement. Elastography techniques are based or on the assessment of the longitudinal displacement of the tissue induced by a stress, as in strain elastography and acoustic radiation force impulse (ARFI) imaging, or on the assessment of the speed of the transverse displacement of the tissue as in shear wave elastography. In strain elastography a part of the body is compressed axially by pressing across its surface and the internal tissue displacement is converted to a strain image (percentage of deformation), because the percentage of deformation will be constant whereas displacement decays with depth. In the ARFI imaging, the acoustic radiation force generates a localized displacement of a few microns in the ultrasound axial direction. ARFI generates also shear wave displacement at one point (point shear wave elastography) or along several lines (2D-shear wave elastography). Shear waves can be generated by an external mechanical push as well, as in vibration controlled transient elastography (VCTE), magnetic resonance elastography (MRE) or vibro-elastography. T7-16-IN02 High Resolution Elastography for Eye Chih-Chung Huang National Cheng Kung University, Taiwan Estimating the corneal elasticity can provide valuable information for corneal pathologies and treatments. Ophthalmologic pathologies such as keratoconus and the phototoxic effects of ultraviolet radiation on the cornea caused the corneal elasticity change. Not only the corneal pathologies but also the efficacy evaluation of corneal treatment, such as evaluating the recovery of corneal refractive surgery and the efficacy of corneal collagen crosslinking treatment are related to corneal elasticity. This makes quantitative estimation of the elasticity of the human cornea important for ophthalmic diagnoses. The present study investigated the use of a proposed high-resolution shear-wave imaging (HR-SWI) method based on a dual-element transducer (comprising an 8-MHz element for pushing and a 32-MHz element for imaging) for measuring the elasticity of the human cornea. The distance between these elements was 1.5 mm. Due to the image lateral resolution being limited by the distance between the pushing and imaging beams, a spatial algorithm named the Pseudo-Sudoku Algorithm (PSA) was used to improve the lateral resolution. The gelatin-phantom results showed the ability of the PSA to distinguish the elasticity distribution of a small two-side phantom (2.2 mm 3 3.5 mm). The image resolutions of HR-SWI in the axial and lateral directions were 301 and 129 mm, respectively. The elasticity values of corneas from six human donors were also measured by HR-SWI, with all of the ex vivo results demonstrating the potential of HR-SWI in clinically measuring the elasticity of the human cornea.
S87
T7-16-IN03 Ultrasound Shear Wave Elastography: Principles and New Technologies Shigao Chen Department of Radiology, Mayo Clinic, Rochester, MN Tissue stiffness measured by ultrasound shear wave elastography is useful for many clinical applications such as liver fibrosis staging and cancer imaging. This presentation gives an overview of various technical components of shear wave elastography, including the relationship between shear wave speed and tissue mechanical properties, generation of shear wave by ultrasound radiation force and mechanical vibration, detection of shear wave by ultrasound scanner, and methods for calculation of shear wave speed. Commercial shear wave technologies covered in this talk include SuperSonic Imagine, Fibroscan, and Comb-push Shearwave Ultrasound Elastography (CUSE). Examples of new technologies under development will also be given. Confounding factors for shear wave elastography will be discussed. T7-16-IN04 Evaluation of Shear Wave Dispersion Caused by Liver Fibrous Structure Using Hepatic Fibrosis Progression Model Makoto Yamakawa, Shiori Fujii, Tsuyoshi Shiina Graduate School of Medicine, Kyoto University, Kyoto, Japan In chronic hepatitis diagnosis, shear wave elastography is utilized for evaluating fibrosis progression. Not only the elasticity but also the viscosity of liver tissue is considered to be useful information for its diagnosis. Therefore, in recent years, a method of evaluating tissue viscosity using shear wave dispersion has been used clinically. However, the shear wave dispersion also occurs due to tissue viscosity, but also due to the microstructure of tissue. Therefore, we quantitatively evaluated the shear wave dispersion caused by the liver fibrous structure using a hepatic fibrosis progress model. At that time, in order to evaluate only the shear wave dispersion caused by the liver fibrous structure, the viscosity in the model was set to zero. As a results, the shear wave dispersion (shear wave dispersion slope) were 0.0260.003, 0.3260.20, 0.6260.25, 1.2560.89, and 0.7361.53 m/s/kHz for stage F0, F1, F2, F3, and F4. The dispersion slope tended to increase with progress of the hepatic fibrosis stage. However, in stage F4, the result was greatly affected by the location of the ROI, so the variance increased. The shear wave dispersion caused by the liver fibrous structure was about 10-20 % of that in in vivo measurement. Therefore, we confirmed that the shear wave dispersion is influenced by the liver fibrous structure together with the liver viscosity. T7-16-IN05 Analysis of Acoustic Properties of Liver Organelles Including NASH Tadashi Yamaguchi Center for Frontier Medical Engineering, Chiba University, Chiba, Japan Accurate diagnosis of non-alcoholic steatohepatitis (NASH) is a critical issue in current clinical practice. Non-invasive diagnosis of NASH can be achieved by quantitative ultrasound (QUS), which requires a detailed understanding tissue-specific acoustic microstructure at cellular scale (i,e., 10 mm). Therefore, QUS methods would benefit from the knowledge of the acoustic properties of organelles in NASH livers because they may represent the dominant scattering source at conventional frequencies used for in vivo assessments (i.e., , 15 MHz). This study focuses on obtaining speed of sound (c) of organelles (i.e., nucleus, cytoplasm, and fibers) using above-mentioned 250-MHz