Aspiration methods and devices for assessment of viscoelastic properties of soft tissues

Abstract

Methods for assessing viscoelastic properties of soft tissues are based on detecting an inflection point on a pressure-time plot when air is aspirated from a cavity placed over the tissue sample. A small diameter tube through which air aspiration is conducted is ultimately closed off by tissue being drawn into the cavity causing an abrupt change in pressure slope. First or second derivatives of the pressure-time plot can be used to detect the inflection point. Repeating the test with a different aspiration rates or after a predetermined relaxation time allows determining tissue viscosity and tissue creep in addition to tissue elasticity expressed as Young's modulus.

Description

BACKGROUND OF INVENTION[0001]The invention relates to methods and devices for assessing viscoelastic properties of soft tissues. In particular, the invention relates to using aspiration methods to detect elasticity, viscosity, creep and other properties of accessible living tissues such as skin, cervix, vaginal wall, etc.[0002]Mechanical properties of skin (e.g., elasticity of skin) may change due to disease, stress, or dehydration. When the body becomes dehydrated as a result of diseases such as those that cause diarrhea or reduced liquid intake such as famine or marathon running, the skin becomes “doughy” and does not snap back when pinched. In a test for dehydration called the “pinch test” or “turgor test,” the skin is grasped and pulled up in a pinch-like manner and then released. Healthy skin will quickly snap back to its undeformed state, whereas dehydrated skin returns to its undeformed state slowly. Such conventional test is subjective and inaccurate. Objective determination...

AI Technical Summary

Benefits of technology

[0010]It is another object of the invention to provide an aspiration method for objective evaluation of viscoelastic properties of soft tissues allowing for comprehensive tissue evaluation beyond determination of tissue elasticity by Young's modulus. Other properties of interest that can be determined using the method of the invention include tissue viscosity and tissue creep.

[0011]A novel aspiration method for measuring soft tissue mechanical properties uses a probe having a cavity with an outer edge adapted to sealingly come in contact with the tissue test area. A small diameter tube enters the cavity in its center and extends inside thereof to end at a specific distance from the plane defined by the outer edge of the cavity. A vacuum pump and pressure sensor are connected to other end of the tube. The vacuum pump is activated to aspirate air from the cavity placed over the tissue test area. This draws tissue inside the probe cavity. The aspiration rate is constant creating a linear relationship between the negative pressure inside the probe cavity and time. The domed tissue keeps moving into the cavity until it finally reaches the inner tube and closes its opening. At this point, the remaining cavity volume is isolated from the pump, the drop in pressure inside the cavity is stopped and the tissue remains in the same position despite continuous draw of the vacuum pump. The small volume inside the tube is the only volume exposed to continuing aspiration. An abrupt change in volume under continuing vacuum is detected by the pressure sensor as an abrupt change in slope of continuous pressure drop. The device monitors negative pressure in the probe to identify the inflection point in its slope indicating the touching of the end of the tube by the tissue. The Young's modulus is then calculated based for example on a predetermined calibration data and displayed on a screen. Performing successive measurements with different rates of air aspiration and with variable intervals between successive measurements allows determination of other rheological characteristics of tissue such as viscosity and shear creep.

[0022]Additional steps allow detecting other tissue parameters like viscosity and creep from repeated test measurements conducted at different rates of aspiration and with different waiting periods between the tests.

Problems solved by technology

Such conventional test is subjective and inaccurate.

The occurrence of cervical ripening before 34 weeks of gestation leading to preterm delivery represents a serious medical problem.

Preterm delivery is a major cause of perinatal morbidity and mortality.

Premature babies are at increased risk for newborn health complications, as well as lasting disabilities, such as mental retardation, cerebral palsy, lung and gastrointestinal problems, vision and hearing loss, and even death.

The process of cervical ripening, consisting of softening of the connective tissue components, is not easily identifiable with present methods.

However, the true etiology of prolapse and differences seen among individuals are not entirely understood.

These devices however lack the ability for a comprehensive assessment of tissue which goes beyond simple elasticity measurements.

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