Viscoelasticity measurement of heart wall in in vivo

Kanai, Hiroshi

doi:10.1109/ultsym.2004.1417767

Cited by 3 publications

(2 citation statements)

References 31 publications

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“…The mechanical stress that is applied to tissue can be produced either through internal sources of motion like respiration or cardiac pulsations (Bae et al, 2007; Kanai, 2004; Mai and Insana, 2002) or through external mechanical sources of motion (Bercoff et al, 2004; Kruse et al, 2008; Xu et al, 2007). The stimulus can also be classified based on the temporal characteristics of the excitation as static (or quasistatic) or dynamic.…”

Section: Elasticity Imagingmentioning

confidence: 99%

Magnetic resonance elastography: A review

2010

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Magnetic Resonance Elastography (MRE) is a rapidly developing technology for quantitatively assessing the mechanical properties of tissue. The technology can be considered to be an imaging-based counterpart to palpation, commonly used by physicians to diagnose and characterize diseases. The success of palpation as a diagnostic method is based on the fact that the mechanical properties of tissues are often dramatically affected by the presence of disease processes such as cancer, inflammation, and fibrosis. MRE obtains information about the stiffness of tissue by assessing the propagation of mechanical waves through the tissue with a special magnetic resonance imaging (MRI) technique. The technique essentially involves three steps: generating shear waves in the tissue,acquiring MR images depicting the propagation of the induced shear waves andprocessing the images of the shear waves to generate quantitative maps of tissue stiffness, called elastograms. MRE is already being used clinically for the assessment of patients with chronic liver diseases and is emerging as a safe, reliable and noninvasive alternative to liver biopsy for staging hepatic fibrosis. MRE is also being investigated for application to pathologies of other organs including the brain, breast, blood vessels, heart, kidneys, lungs and skeletal muscle. The purpose of this review article is to introduce this technology to clinical anatomists and to summarize some of the current clinical applications that are being pursued.

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Section: Elasticity Imagingmentioning

confidence: 99%

Magnetic resonance elastography: A review

2010

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“…The authors do not provide quantitative data on the muscle viscosity but a rough estimate that can be made from the experimental data shows that the viscosity change accompanying muscle contraction is far greater than one order of magnitude. The quantitative assessment of the contracting muscle viscosity changes has been made in the work of Kanai on imaging of the sound wavefront propagation along the heart wall [22]. It was estimated that during the cardiac cycle the viscosity of the myocardium changes from 0.1 kPa·s to about 2.1 kPa·s.…”

Section: Viscoelastic Properties Of Skeletal Musclementioning

confidence: 99%

Muscle as a molecular machine for protecting joints and bones by absorbing mechanical impacts

et al. 2014

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We hypothesize that dissipation of mechanical energy of external impact to absorb mechanical shock is a fundamental function of skeletal muscle in addition to its primary function to convert chemical energy into mechanical energy. In physical systems, the common mechanism for absorbing mechanical shock is achieved with the use of both elastic and viscous elements and we hypothesize that the viscosity of the skeletal muscle is a variable parameter which can be voluntarily controlled by changing the tension of the contracting muscle. We further hypothesize that an ability of muscle to absorb shock has been an important factor in biological evolution, allowing the life to move from the ocean to land, from hydrodynamic to aerodynamic environment with dramatically different loading conditions for musculoskeletal system. The ability of muscle to redistribute the energy of mechanical shock in time and space and unload skeletal joints is of key importance in physical activities. We developed a mathematical model explaining the absorption of mechanical shock energy due to the increased viscosity of contracting skeletal muscles. The developed model, based on the classical theory of sliding filaments, demonstrates that the increased muscle viscosity is a result of the time delay (or phase shift) between the mechanical impact and the attachment/detachment of myosin heads to binding sites on the actin filaments. The increase in the contracted muscle's viscosity is time dependent. Since the forward and backward rate constants for binding the myosin heads to the actin filaments are on the order of 100 s-1, the viscosity of the contracted muscle starts to significantly increase with an impact time greater than 0.01 s. The impact time is one of the key parameters in generating destructive stress in the colliding objects. In order to successfully dampen a short high power impact, muscles must first slow it down to engage the molecular mechanism of muscle viscosity. Muscle carries out two functions, acting first as a nonlinear spring to slow down impact and second as a viscous damper to absorb the impact. Exploring the ability of muscle to absorb mechanical shock may shed light to many problems of medical biomechanics and sports medicine. Currently there are no clinical devices for real-time quantitative assessment of viscoelastic properties of contracting muscles in vivo. Such assessment may be important for diagnosis and monitoring of treatment of various muscle disorders such as muscle dystrophy, motor neuron diseases, inflammatory and metabolic myopathies and many more.

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In vivo viscoelasticity estimation of myocardium

Kanai

IEEE Ultrasonics Symposium, 2005.

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Though myocardial viscoelasticity is essential in the evaluation of heart diastolic properties, it has never been noninvasively measured in vivo. By the ultrasonic measurement of the myocardial motion, we have already found that some pulsive waves are spontaneously excited by aortic-valve closure (AVC) at end-systole (T0). In this study, a sparse sector scan at a sufficiently high frame rate clearly reveals wave propagation along the heart wall. The propagation time of the wave along the heart wall is very small, namely, several milliseconds, and cannot be measured by conventional equipment. From the measured phase velocity, we estimate the myocardial viscoelasticity in vivo. In in vivo experiments applied to 6 healthy subjects, 3 patients with hypertrophic cardiomyopathy (HCM), and 3 patients with aortic stenosis (AS), the propagation of the pulsive wave was clearly visible in all subjects. For the frequency component up to 90 Hz, the typical propagation speed is about several m/s and rapidly decreased around the time of AVC. For the healthy subject, the typical value of elasticity was about 24-30 kPa and did not change around the time of AVC. The typical transient values of viscosity decreased rapidly from 400 Pa·s to 70 Pa·s around the time of AVC. The measured shear elasticity and viscosity in this study are comparable to those obtained for the human tissues using audio frequency in in vitro experiments reported in the literature. The method cannot be easily applied to these patients because there were inhomogeneities in the phase velocities due to the diseased myocardium. By applying the measurement of the phase velocity to each of 5 layers set in the heart wall, the phase velocity in the middle layer was lower than those in the LV-and RV-sides of the heart wall, which will corresponds to the change in myocardial fiber orientations. This method offers potential for in vivo imaging of the spatial distribution of the passive mechanical properties of the myocardium, which cannot be obtained by conventional echocardiography, CT, or MRI.

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Viscoelasticity measurement of heart wall in in vivo

Cited by 3 publications

References 31 publications

Magnetic resonance elastography: A review

Magnetic resonance elastography: A review

Muscle as a molecular machine for protecting joints and bones by absorbing mechanical impacts

In vivo viscoelasticity estimation of myocardium

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