iman Rafati - Academia.edu (original) (raw)
Papers by iman Rafati
Journal of the Acoustical Society of America, Mar 1, 2023
Assessment of ultrasound shear wave attenuation (SWA) can increase the accuracy of liver steatosi... more Assessment of ultrasound shear wave attenuation (SWA) can increase the accuracy of liver steatosis grading. Recent developments allowed to propose the revisited frequency shift method for SWA imaging. This method was tested on force-fed ducks for foie gras production (n = 6), and a feasibility study on patients with non-alcoholic steatohepatitis (NASH n = 27 + 13 healthy volunteers) was conducted. Liver biopsy and magnetic resonance imaging proton density fat fraction (MRI-PDFF) were available as reference standards. For the human study, shear wave dispersion (SWD) was also computed. A subset of participants had repeated measurements (<1-month) to assess repeatability. The mean SWA (coefficient of variation within the attenuation map) for healthy duck livers were 0.77 (0.66), 1.18 (0.22), and 1.52 Np/m/Hz (0.14), and for fatty duck livers they were higher at 3.13 (0.55), 3.16 (0.24), and 4.84 Np/m/Hz (0.23). Receiver operating characteristic (ROC) curves using biopsy as reference were compared for steatosis grades >0 (>S0), >S1, and >S2. SWA was as good as MRI-PDFF, and both were better than SWD for steatosis grading (p < 0.05). The repeatability of SWA was very good (mean intraclass correlation coefficient of 0.97). In summary, SWA seems promising to become an ultrasound reference standard for steatosis grading in NASH.
Frontiers in Physics, Jun 21, 2021
Changes in biomechanical properties of biological soft tissues are often associated with physiolo... more Changes in biomechanical properties of biological soft tissues are often associated with physiological dysfunctions. Since biological soft tissues are hydrated, viscoelasticity is likely suitable to represent its solid-like behavior using elasticity and fluid-like behavior using viscosity. Shear wave elastography is a non-invasive imaging technology invented for clinical applications that has shown promise to characterize various tissue viscoelasticity. It is based on measuring and analyzing velocities and attenuations of propagated shear waves. In this review, principles and technical developments of shear wave elastography for viscoelasticity characterization from organ to cellular levels are presented, and different imaging modalities used to track shear wave propagation are described. At a macroscopic scale, techniques for inducing shear waves using an external mechanical vibration, an acoustic radiation pressure or a Lorentz force are reviewed along with imaging approaches proposed to track shear wave propagation, namely ultrasound, magnetic resonance, optical, and photoacoustic means. Then, approaches for theoretical modeling and tracking of shear waves are detailed. Following it, some examples of applications to characterize the viscoelasticity of various organs are given. At a microscopic scale, a novel cellular shear wave elastography method using an external vibration and optical microscopy is illustrated. Finally, current limitations and future directions in shear wave elastography are presented.
The Journal of the Acoustical Society of America
Assessment of ultrasound shear wave attenuation (SWA) can increase the accuracy of liver steatosi... more Assessment of ultrasound shear wave attenuation (SWA) can increase the accuracy of liver steatosis grading. Recent developments allowed to propose the revisited frequency shift method for SWA imaging. This method was tested on force-fed ducks for foie gras production (n = 6), and a feasibility study on patients with non-alcoholic steatohepatitis (NASH n = 27 + 13 healthy volunteers) was conducted. Liver biopsy and magnetic resonance imaging proton density fat fraction (MRI-PDFF) were available as reference standards. For the human study, shear wave dispersion (SWD) was also computed. A subset of participants had repeated measurements (<1-month) to assess repeatability. The mean SWA (coefficient of variation within the attenuation map) for healthy duck livers were 0.77 (0.66), 1.18 (0.22), and 1.52 Np/m/Hz (0.14), and for fatty duck livers they were higher at 3.13 (0.55), 3.16 (0.24), and 4.84 Np/m/Hz (0.23). Receiver operating characteristic (ROC) curves using biopsy as reference...
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Ultrasound shear wave (SW) elastography has been widely studied and implemented on clinical syste... more Ultrasound shear wave (SW) elastography has been widely studied and implemented on clinical systems to assess elasticity of living organs. Imaging of SW attenuation reflecting viscous properties of tissues has received less attention. A revisited frequency shift method (R-FS) is proposed to improve robustness of SW attenuation imaging. Performances are compared with the frequency-shift (FS) method that we originally proposed, and to the two-point frequency shift (2P-FS) and attenuation measuring ultrasound SW elastography (AMUSE) methods. In the proposed R-FS method, the shape parameter of the gamma distribution fitting SW spectra is assumed to vary with distance, in contrast to FS. Secondly, an adaptive random sample consensus (A-RANSAC) line fitting method is used to prevent outlier attenuation values in the presence of noise. Validation was made on ten simulated phantoms with two viscosities (0.5 and 2 Pa.s) and different noise levels (15 to -5 dB), two experimental homogeneous gel phantoms, and six in vivo liver acquisitions on awake ducks (including three normal and three fatty duck livers). According to conducted experiments, R-FS revealed mean reductions in coefficients of variation (CV) of 62.6% on simulations, 62.5% with phantoms, and 62.3% in vivo compared with FS. Corresponding reductions compared with 2P-FS were 45.4%, 77.1%, and 62.0%, respectively. Reductions in normalized root-mean-square errors for simulations were 63.9% and 48.7% with respect to FS and 2P-FS, respectively.
Ultrasound in Medicine & Biology
2020 IEEE International Ultrasonics Symposium (IUS), 2020
Constructing an attenuation map based on local attenuation coefficient slope (ACS) in quantitativ... more Constructing an attenuation map based on local attenuation coefficient slope (ACS) in quantitative ultrasound (QUS) has shown potential in the diagnosis of liver steatosis. Detecting tumors in the liver and differentiating abnormalities in tissues are some other applications for these maps. In this work, we considered the construction of semantic parametric maps and a recent method providing a phantom-free estimation of local ACS. The main goal was to propose a methodology for constructing regularized phantom-free local ACS maps based on this framework. The proposed method was tested on two tissue mimicking (#1 and #2) with different attenuation: i) homogeneous phantoms; and ii) side-by-side phantoms. Modifications brought to previous works include: a) a linear interpolation of the power spectrum in log-scale; b) the relaxation of the underlying hypothesis on the diffraction factor; c) a generalization to nonhomogeneous local ACS; and d) an adaptive restriction of frequencies to a m...
Changes in biomechanical properties of biological soft tissues are often associated with physiolo... more Changes in biomechanical properties of biological soft tissues are often associated with physiological dysfunctions. Since biological soft tissues are hydrated, viscoelasticity is likely suitable to represent its solid-like behavior using elasticity and fluid-like behavior using viscosity. Shear wave elastography is a non-invasive imaging technology invented for clinical applications that has shown promise to characterize various tissue viscoelasticity. It is based on measuring and analyzing velocities and attenuations of propagated shear waves. In this review, principles and technical developments of shear wave elastography for viscoelasticity characterization from organ to cellular levels are presented, and different imaging modalities used to track shear wave propagation are described. At a macroscopic scale, techniques for inducing shear waves using an external mechanical vibration, an acoustic radiation pressure or a Lorentz force are reviewed along with imaging approaches prop...
2019 27th Iranian Conference on Electrical Engineering (ICEE), 2019
Passive dynamic walking is the simplest and the most efficient form of biped locomotion. Albeit t... more Passive dynamic walking is the simplest and the most efficient form of biped locomotion. Albeit the simplicity, the walking gait of passive dynamic walkers resembles human walking in slops very well. The most important drawbacks of these robots is their sensitivity on initial conditions and the limited range of slopes they can have a stable walking cycle on. The aim of this work is to alleviate these problems by adding a link that resembles a torso and controlling it using a Neuroevolutionary algorithm. To achieve this goal, initially the dynamical equations governing this robot was extracted. Then the control algorithm is applied. The reason to use this control strategy is to mimic how natural evolution could play a role in robust biped walking. It was observed that this strategy improved both shortcomings associated with passive dynamic walkers and interestingly the robot shows torso movements familiar to that of humans when facing steep slopes or zero slope.
Journal of the Acoustical Society of America, Mar 1, 2023
Assessment of ultrasound shear wave attenuation (SWA) can increase the accuracy of liver steatosi... more Assessment of ultrasound shear wave attenuation (SWA) can increase the accuracy of liver steatosis grading. Recent developments allowed to propose the revisited frequency shift method for SWA imaging. This method was tested on force-fed ducks for foie gras production (n = 6), and a feasibility study on patients with non-alcoholic steatohepatitis (NASH n = 27 + 13 healthy volunteers) was conducted. Liver biopsy and magnetic resonance imaging proton density fat fraction (MRI-PDFF) were available as reference standards. For the human study, shear wave dispersion (SWD) was also computed. A subset of participants had repeated measurements (<1-month) to assess repeatability. The mean SWA (coefficient of variation within the attenuation map) for healthy duck livers were 0.77 (0.66), 1.18 (0.22), and 1.52 Np/m/Hz (0.14), and for fatty duck livers they were higher at 3.13 (0.55), 3.16 (0.24), and 4.84 Np/m/Hz (0.23). Receiver operating characteristic (ROC) curves using biopsy as reference were compared for steatosis grades >0 (>S0), >S1, and >S2. SWA was as good as MRI-PDFF, and both were better than SWD for steatosis grading (p < 0.05). The repeatability of SWA was very good (mean intraclass correlation coefficient of 0.97). In summary, SWA seems promising to become an ultrasound reference standard for steatosis grading in NASH.
Frontiers in Physics, Jun 21, 2021
Changes in biomechanical properties of biological soft tissues are often associated with physiolo... more Changes in biomechanical properties of biological soft tissues are often associated with physiological dysfunctions. Since biological soft tissues are hydrated, viscoelasticity is likely suitable to represent its solid-like behavior using elasticity and fluid-like behavior using viscosity. Shear wave elastography is a non-invasive imaging technology invented for clinical applications that has shown promise to characterize various tissue viscoelasticity. It is based on measuring and analyzing velocities and attenuations of propagated shear waves. In this review, principles and technical developments of shear wave elastography for viscoelasticity characterization from organ to cellular levels are presented, and different imaging modalities used to track shear wave propagation are described. At a macroscopic scale, techniques for inducing shear waves using an external mechanical vibration, an acoustic radiation pressure or a Lorentz force are reviewed along with imaging approaches proposed to track shear wave propagation, namely ultrasound, magnetic resonance, optical, and photoacoustic means. Then, approaches for theoretical modeling and tracking of shear waves are detailed. Following it, some examples of applications to characterize the viscoelasticity of various organs are given. At a microscopic scale, a novel cellular shear wave elastography method using an external vibration and optical microscopy is illustrated. Finally, current limitations and future directions in shear wave elastography are presented.
The Journal of the Acoustical Society of America
Assessment of ultrasound shear wave attenuation (SWA) can increase the accuracy of liver steatosi... more Assessment of ultrasound shear wave attenuation (SWA) can increase the accuracy of liver steatosis grading. Recent developments allowed to propose the revisited frequency shift method for SWA imaging. This method was tested on force-fed ducks for foie gras production (n = 6), and a feasibility study on patients with non-alcoholic steatohepatitis (NASH n = 27 + 13 healthy volunteers) was conducted. Liver biopsy and magnetic resonance imaging proton density fat fraction (MRI-PDFF) were available as reference standards. For the human study, shear wave dispersion (SWD) was also computed. A subset of participants had repeated measurements (<1-month) to assess repeatability. The mean SWA (coefficient of variation within the attenuation map) for healthy duck livers were 0.77 (0.66), 1.18 (0.22), and 1.52 Np/m/Hz (0.14), and for fatty duck livers they were higher at 3.13 (0.55), 3.16 (0.24), and 4.84 Np/m/Hz (0.23). Receiver operating characteristic (ROC) curves using biopsy as reference...
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Ultrasound shear wave (SW) elastography has been widely studied and implemented on clinical syste... more Ultrasound shear wave (SW) elastography has been widely studied and implemented on clinical systems to assess elasticity of living organs. Imaging of SW attenuation reflecting viscous properties of tissues has received less attention. A revisited frequency shift method (R-FS) is proposed to improve robustness of SW attenuation imaging. Performances are compared with the frequency-shift (FS) method that we originally proposed, and to the two-point frequency shift (2P-FS) and attenuation measuring ultrasound SW elastography (AMUSE) methods. In the proposed R-FS method, the shape parameter of the gamma distribution fitting SW spectra is assumed to vary with distance, in contrast to FS. Secondly, an adaptive random sample consensus (A-RANSAC) line fitting method is used to prevent outlier attenuation values in the presence of noise. Validation was made on ten simulated phantoms with two viscosities (0.5 and 2 Pa.s) and different noise levels (15 to -5 dB), two experimental homogeneous gel phantoms, and six in vivo liver acquisitions on awake ducks (including three normal and three fatty duck livers). According to conducted experiments, R-FS revealed mean reductions in coefficients of variation (CV) of 62.6% on simulations, 62.5% with phantoms, and 62.3% in vivo compared with FS. Corresponding reductions compared with 2P-FS were 45.4%, 77.1%, and 62.0%, respectively. Reductions in normalized root-mean-square errors for simulations were 63.9% and 48.7% with respect to FS and 2P-FS, respectively.
Ultrasound in Medicine & Biology
2020 IEEE International Ultrasonics Symposium (IUS), 2020
Constructing an attenuation map based on local attenuation coefficient slope (ACS) in quantitativ... more Constructing an attenuation map based on local attenuation coefficient slope (ACS) in quantitative ultrasound (QUS) has shown potential in the diagnosis of liver steatosis. Detecting tumors in the liver and differentiating abnormalities in tissues are some other applications for these maps. In this work, we considered the construction of semantic parametric maps and a recent method providing a phantom-free estimation of local ACS. The main goal was to propose a methodology for constructing regularized phantom-free local ACS maps based on this framework. The proposed method was tested on two tissue mimicking (#1 and #2) with different attenuation: i) homogeneous phantoms; and ii) side-by-side phantoms. Modifications brought to previous works include: a) a linear interpolation of the power spectrum in log-scale; b) the relaxation of the underlying hypothesis on the diffraction factor; c) a generalization to nonhomogeneous local ACS; and d) an adaptive restriction of frequencies to a m...
Changes in biomechanical properties of biological soft tissues are often associated with physiolo... more Changes in biomechanical properties of biological soft tissues are often associated with physiological dysfunctions. Since biological soft tissues are hydrated, viscoelasticity is likely suitable to represent its solid-like behavior using elasticity and fluid-like behavior using viscosity. Shear wave elastography is a non-invasive imaging technology invented for clinical applications that has shown promise to characterize various tissue viscoelasticity. It is based on measuring and analyzing velocities and attenuations of propagated shear waves. In this review, principles and technical developments of shear wave elastography for viscoelasticity characterization from organ to cellular levels are presented, and different imaging modalities used to track shear wave propagation are described. At a macroscopic scale, techniques for inducing shear waves using an external mechanical vibration, an acoustic radiation pressure or a Lorentz force are reviewed along with imaging approaches prop...
2019 27th Iranian Conference on Electrical Engineering (ICEE), 2019
Passive dynamic walking is the simplest and the most efficient form of biped locomotion. Albeit t... more Passive dynamic walking is the simplest and the most efficient form of biped locomotion. Albeit the simplicity, the walking gait of passive dynamic walkers resembles human walking in slops very well. The most important drawbacks of these robots is their sensitivity on initial conditions and the limited range of slopes they can have a stable walking cycle on. The aim of this work is to alleviate these problems by adding a link that resembles a torso and controlling it using a Neuroevolutionary algorithm. To achieve this goal, initially the dynamical equations governing this robot was extracted. Then the control algorithm is applied. The reason to use this control strategy is to mimic how natural evolution could play a role in robust biped walking. It was observed that this strategy improved both shortcomings associated with passive dynamic walkers and interestingly the robot shows torso movements familiar to that of humans when facing steep slopes or zero slope.