Surgery – Diagnostic testing – Measuring anatomical characteristic or force applied to or...
Utility Patent
1999-01-08
2001-01-02
Hindenburg, Max (Department: 3736)
Surgery
Diagnostic testing
Measuring anatomical characteristic or force applied to or...
Utility Patent
active
06168572
ABSTRACT:
The present invention relates to a device for examining the viscoelasticity and anisotropy of an area of an external surface of a living tissue, e.g., skin or artificial tissue.
The complex functions of the skin require maximum strength, as well as maximum flexibility. Many local or systemic lesions in the skin alter its structure and function. This may be reflected by significant changes in the mechanical properties of the affected skin area. Therefore, non-invasive assay of the mechanical properties of the skin such as hardness, stiffness and rigidity may be useful for monitoring skin disorders and lesions, as well as for the evaluation of skin changes relating to the physiological status of the individuals, in addition to their age, sex and race. So far, mostly subjective means are employed in clinical practice, including visual and palpating examinations of the skin lesion without discrete quantitative criteria. Histopathology, which may contribute more detailed information is invasive, complicated, expensive and needs special clinical skills, and moreover, by its nature is not repetitive or quantitative.
The relationship between the mechanical properties of viscoelastic matrices from different materials and the speed of propagation of shear surface waves (elastic waves) in the acoustic frequency range along the vector of the initial displacement of the material tested, was analyzed. According to the physical basis of the mechanics of elastic wave propagation, the speed of propagation of these waves in viscoelastic materials with constant mass density could be calculated from the expression:
v
2
=Y(1−m)/(1+m)(1-2m)p
where:
v=speed of propagation of longitudinal elastic surface shear wave;
Y=Young's modules of elasticity;
m=Poison coefficient of the material
p=Mass density of the material.
The viscoelastic properties of the material is characterized by one part of the equation:
Y(1−m)/(1+m)(1-2m)=&sgr;
Consequently, the speed of propagation of elastic waves is proportional to the viscoelasticity of the material (&sgr;=modules of elasticity) and its mass density is defined by:
v
2
=&sgr;/p
Therefore, the measurement of the speed of elastic wave propagation allows the determination of the modules of elasticity of an external tissue examined by the expression:
&sgr;=pv
2
Viscoelastic matrices with homogenous mechanical properties have isotropic modules of elasticity. Inhomogenous viscoelastic materials are characterized by the variations of the mechanical properties in different spatial orientations: this effect of anisotropy is exhibited by the modules of anisotropic elasticity. In the real biological tissues (for example, skin), the value of modules of elasticity in one direction can be several hundred percents greater than in the other direction.
A number of methods for the quantitative evaluation of the mechanical properties of tissues have been introduced but they have limited applications. These methods include identometry, uniaxial tensiometry, skin surface topography, torsion measurements, skin compliance to suction and others. A most promising approach for the evaluation of the mechanical properties of the viscoelastic materials is the measurement of the speed of propagation of elastic surface sheer waves (in acoustic frequency range) along the external tissues.
Accordingly, there is proposed a new multi-point probe and device for a non-invasive and safe measurement of the mechanical properties and anisotropy of an area of external layer of tissues. The device is based on the correlation between the tissue elasticity and the speed of propagation of a shear mechanical wave on its surface. The measurement is effected by a multi-directional (e.g., bi-directional) simultaneous examination of an array of points in the external tissue.
It is therefore a broad object of the present invention to provide a more advanced device for the measurement of the speed of propagation of elastic waves for the evaluation of the mechanical properties of living and artificial tissue for different applications.
The invention provides a probe for examining viscoelasticity and anisotropy of an area of an external layer of a living or artificial tissue, comprising an assembly including at least one group of piezoelectric spaced-apart transducers, each having a surface contact making edge, wherein one of said transducers operates as a transmitter and at least one other transducer operates as a receiver, and wherein said assembly is movable both axially, as well as angularly, means for effecting the controlled axial movement of said assembly, means for controlling the contact pressure to be exerted by the transducers on the surface of an area of a tissue to be examined, and means for effecting angular movement of said assembly at a selected axial displacement.
The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.
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O.A. Lindahl et al. :“Impression Techinque for the assesment of oedema: comparison with a new tactile sensor that measures physical property of tissue”,Medical and Biological Engineering and Computing, vol. 33, No. 1, pp. 27-32, Jan. 1995.
Gorodetsky Raphael
Polyansky Igor
Vexler Akiva
Davidson Davidson & Kappel LLC
Hadasit & Medical Research Services & Development Company, Ltd.
Hindenburg Max
Szmal Brian
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