JP5252985B2 - Elasticity measurement method inside skin - Google Patents

Description

  The present invention relates to a method for non-invasively measuring the internal elasticity of each part of the skin.

Various methods have been devised for non-invasive measurement of skin flexibility. For example, a suction method that measures skin deformation by sucking the skin under reduced pressure, a traction / squeeze method that measures skin deformation by mechanically lifting or pushing the skin, and a weight perpendicular to the skin surface. The ballist method that measures the attenuation of vibration when dropping an object, the ultrasonic vibration method that uses an ultrasonic transducer to apply vibration to the skin vertically and measures the return of the vibration, one on the skin Alternatively, an extension method in which two metal contacts are brought into close contact with each other and stretched to measure the stress, a twisting method in which a disk-shaped disk is applied to the skin and a rotational torque is applied to measure the stress or phase shift, A wave propagation method is known in which a wave is propagated horizontally to the skin and the speed of vibration and the phase shift of the vibration are measured. Among these, the suction method has established its position as a general evaluation method for measuring skin tension and sagging, and when the displacement of the skin deformed with a constant suction pressure and time is analyzed, the return elastic ratio In (Ur / Uf), it is reported that the return ratio decreases with aging (Non-Patent Documents 1 and 2).
However, since the skin has a multi-layer structure, the contribution of each layer (epidermis, dermis, subcutaneous tissue) affects each other, and they are synthesized and detected by any method. It is unclear how the part contributes and is detected, and it is impossible to calculate the internal elasticity of the skin in a non-invasive manner according to layers such as epidermis, dermis, and subcutaneous tissue.

  On the other hand, an ultrasonic diagnostic apparatus is generally used in a medical institution as a diagnostic apparatus for displaying a structure inside a living body. Recently, not only the static in-vivo information (structure) but also dynamics inside the living body. A technique called tissue elasticity imaging method (for example, TSI: Tissue Strain Imaging) that captures information (flexibility of heart valve membrane, diagnosis of tumor such as breast cancer) has been developed (Patent Documents 1, 2, and 3).

Tissue elasticity imaging method is a method of visualizing and quantifying local elasticity by using ultrasonic images and tracking the distortion by applying internal force to the inside of the living body by vibration or the like. According to this, it is possible to measure and display the hardness and softness of the living tissue by generating an elastic image based on the strain and elastic modulus data of the tissue.
However, these methods are measurement methods that require skill because reproducibility and accuracy may be significantly lost depending on how the force is applied to the inside of the living body by vibration or the like from the outside. Further, these methods have a problem that it is difficult to accurately measure and visualize the elasticity inside the skin, which is a relatively shallow part even inside the living body.
JP 2007-105400 A JP 2004-57652 A JP 2005-144155 A Takema Y, Yoritomo Y, Kawai M, Imokawa G. Age-related changes in the elastic properties and thickness of human facial skin.Br J Dermatol 1994; 131; 641-8. Takema Y, Yoritomo Y, Kawai M. The relationship between age-related changes in the physical properties and development of wrinkles in humanfacial skin.J Soc Cosmet Chem 1995; 46: 163-73.

  The present invention relates to a method for accurately measuring and visualizing the elasticity of local areas inside the skin.

  The present inventors examined an elastic imaging method for skin tissue using ultrasonic waves. As a result, an inclusion having specific acoustic characteristics was sandwiched between the skin of the subject and the ultrasonic probe, and the inside of the skin was fixed at a certain period. It was found that the elasticity of the local area inside the skin can be visualized and digitized with high accuracy and good reproducibility.

That is, the present invention relates to the following 1) to 3).
1) A method for measuring elasticity inside a skin using an ultrasonic diagnostic apparatus capable of imaging distortion inside a subject, and having a sound speed of 1500 to 1600 m / s by a pressurizing / vibrating means provided on the ultrasonic probe. A method for measuring elasticity inside a skin, comprising pressurizing a subject with a certain period through an inclusion and measuring an elastic modulus inside the subject.
2) The method according to 1), wherein the inclusion is an ultrasonic phantom having a thickness of 5 to 30 mm.
3) The method of 1) or 2) in which the subject is pressurized so as to be pushed in at 1 mm to 10 mm for 1 to 30 seconds / once.

  According to the method of the present invention, it is possible to visualize and quantify the absolute elasticity of the skin internal region (epidermis / dermis, subcutaneous tissue, muscle layer) with high accuracy and good reproducibility.

The elasticity measurement method of the present invention can be performed using an ultrasonic diagnostic apparatus capable of imaging strain inside a subject, and having an ultrasonic probe provided with a pressurizing / vibrating means.
As an ultrasonic diagnostic apparatus, an ultrasonic beam is irradiated while contacting an ultrasonic probe on the surface of a subject, and the movement of each pixel of an ultrasonic image obtained from the reflected echo signal is tracked at the passing speed of the ultrasonic wave. There is no particular limitation as long as it is an ultrasonic diagnostic apparatus capable of calculating elastic properties from strain data inside the subject. For example, commercially available “Real Time Elastography” (Hitachi Medical), “Aprio” (Toshiba Medical Systems) Etc. In any of these methods, a static pressure is applied from the body surface to compressively deform the tissue, and a strain inside the tissue generated at that time is measured by ultrasonic waves, and an elastic characteristic of the tissue is calculated from the strain.

A general configuration example of the ultrasonic diagnostic apparatus is shown in FIG.
That is, the ultrasonic probe 1 is composed of an ultrasonic transmission unit 2 and an ultrasonic reception unit 3 in the ultrasonic probe 1, and distortion and distortion are generated from a signal processing unit 4 that processes an ultrasonic signal obtained from the ultrasonic probe 1. The result is displayed on the image display 6 which displays the strain and elastic modulus in the elastic modulus calculator 5. Further, the pressure / vibration device 7 for applying pressure / vibration through the inclusions includes a displacement measuring unit (not shown). The pressurizing / vibrating device 7 is composed of a device control interface unit 9 that controls the personal computer or the like.
With this configuration, it is possible to acquire elastic modulus data that is a ratio of the stress increment to the strain increment.

  The ultrasonic probe 1 is formed by arranging a large number of transducers in an array, and transmits and receives ultrasonic waves to a subject by performing beam scanning mechanically or electronically.

In the present invention, the pressurizing / vibrating means may be any means that can pressurize the inside of the skin at a constant cycle, and specifically, an electromagnetic type, an exciter driven by an ultrasonic motor, etc. It is preferably provided on the top or side of the ultrasonic probe (FIG. 2).
The pressurization may be of a level that can deform the skin, subcutaneous tissue, and muscle layer. Specifically, the pressure is such that the skin surface of the subject can be pushed into 10 cm or less, preferably 1 mm to 10 mm. Is preferred.
Further, the pressing speed is preferably 10 Hz or less, more preferably 1 Hz or less, and further preferably 0.08 to 0.25 Hz in terms of negligible viscosity.
By repeatedly applying pressure at a constant period, stable and reproducible pressurization can be performed.

The method of the present invention is performed via an inclusion having a thickness of 5 mm to 30 mm and a sound velocity of 1500 to 1600 m / s between the ultrasonic probe and the subject. Thereby, while performing ultrasonic transmission / reception with an ultrasonic probe, stress distribution can be effectively applied to the skin or skin tissue of the subject, and the epidermis / dermis can be measured well (Examples 1 and 2).
Examples of the inclusion include a base material having acoustic characteristics equivalent to human soft tissue, and a so-called ultrasonic phantom is preferable. It is preferable to use a hydrous hydrogel base material such as gelatin, agarose, agar, etc., rather than a low-damping rubber base material because the inclusion is easy to adjust the propagation speed of sound velocity (close to living tissue). .

Inclusions having an acoustic velocity of 1500 to 1600 m / s are used, but more preferably 1525 to 1545 m / s is close to the acoustic velocity of living tissue.
The measurement method of the sound speed of inclusions is that ultrasonic waves reflected from the boundary surface with the support through the inclusions are incident on the inclusions from the ultrasonic probe, which is a 1 to 100 MHz frequency sound wave that is an ultrasonic frequency for living bodies. Can be calculated by the time required to reciprocate within the inclusion and the distance that the ultrasonic wave has passed through the inclusion (twice the thickness of the inclusion) (FIG. 3).

  In addition, the inclusion is preferably in the range of 5 to 30 mm, more preferably 6 to 20 mm, and even more preferably 6 to 10 mm from the viewpoint of securing the focal length and the accuracy of tracking movement of the skin and subcutaneous tissue.

  In the ultrasonic phantom preferably used as the inclusion, various targets having different acoustic impedances from the base material are arranged in a hydrophilic urethane rubber or gel base material having the same sound speed as the human skin or muscle tissue. It is often used for quality control of ultrasound imaging systems and training of doctors and medical technicians. For example, an ultrasonic phantom (Japanese Patent Laid-Open No. 11-155856) using a polymer gel (polyvinyl alcohol) in which powder is suspended, a water-based polymer or the like in a case made of hard and elastic material such as ABS Plastic An ultrasonic phantom (Japanese Unexamined Patent Publication No. 2003-180591) filled with a tissue mimicking material is known. These ultrasonic phantoms are obtained when a general skin elasticity measuring device shown in FIG. 4 made by Courage and Khazaka (Germany) Cutometer SEM474 is suctioned with a suction diameter of 6 mm and 300 mb for 5 seconds and then released. The deformation of the deformed skin is analyzed, and the return elastic ratio (Ur / Uf) is adjusted to 0.05 to 0.095 which shows the same elastic modulus as the skin.

  The skin elasticity is generally measured by placing a hollow attachment on the skin, sucking the inside of the attachment under reduced pressure, and measuring the deformation of the skin while changing the suction pressure and time. A typical instrument available on the market is the Courage and Khazaka (Germany) Cutometer SEM474, which measures the skin's elastic deformation as a measurement parameter for the skin elasticity of this Cutometer. Thus, the return elastic ratio (Ur / Uf) obtained in this way is generally used. Typically, the return elastic ratio (Ur / Uf) obtained by analyzing the displacement of the deforming skin when the suction diameter is 6 mm and the suction pressure of 300 mb is sucked for 5 seconds and then released is used. 0.05 to 0.095. Moreover, the value decreases with aging. Therefore, the ultrasonic phantom used in the present invention preferably has a return elastic ratio (Ur / Uf) of 0.05 to 0.095, which is the same as that of skin, and is 0.95 which is a value of teenage skin. What is -0.60 is more preferable.

  The inclusions may be interposed between the ultrasonic transmission / reception surface of the ultrasonic probe and the subject, but are preferably installed in parallel to the skin as shown in FIG.

  The ultrasonic probe 1 is pressurized and vibrated at a constant cycle perpendicularly to the skin through the pressurizing / vibrating device 7 from above the inclusion 8 placed in contact with the skin. It is desirable that the pressurization / vibration is previously controlled by inputting the pressurization / vibration speed and distance from a personal computer or the like and controlling from the apparatus control interface unit 9. While applying pressure and vibration, ultrasonic waves are transmitted from the ultrasonic transmission unit 2 inherent in the ultrasonic probe 1 to the skin through the inclusions. The ultrasonic signal from the ultrasonic transmission unit 2 is detected by the ultrasonic reception unit 3 included in the ultrasonic probe 1 as an ultrasonic reflection signal from the skin and inclusions. The ultrasonic signal is digitally processed by the signal processing unit 4, the time variation of the two-dimensional ultrasonic signal is calculated by the strain and elastic modulus calculation unit 5, and the distortion rate is displayed on the image display. It has become. And the relative elasticity modulus with respect to the elasticity modulus of the inclusion inside skin can be calculated | required from the inclusion measured simultaneously and the distortion rate inside skin.

Example 1
A linear electronic scan probe (ultrasound probe) PLT-1202S was attached to an ultrasonic diagnostic apparatus Aprio 80XV manufactured by Toshiba Medical Systems Co., Ltd., and elasticity analysis software TDI-Q was used. As the vibration device, a 2-axis stage controller KUMICON and a miniature actuator KUMI manufactured by KS Corporation were used. The ultrasonic phantom is a general skin elasticity measuring device shown in Fig. 4 (Courage and Khazaka (Germany)) Cutometer SEM474, sucking 300mm suction pressure for 6 seconds with 6mm suction diameter, and then analyzing the displacement when released. And the thing of 0.05-0.095 which shows the same elasticity modulus as skin with a return elastic ratio (Ur / Uf) was obtained from OST Corporation.
The speed of sound of the ultrasonic phantom is the method shown in FIG. 3, that is, a 1 to 100 MHz frequency sound wave, which is an ultrasonic frequency for living body, is incident on an inclusion from an ultrasonic probe and passes through the inclusion to the boundary with the support. The ultrasonic wave reflected on the surface was detected by an ultrasonic probe, and calculated from the time required to reciprocate within the inclusion and the distance that the ultrasonic wave passed through the inclusion (twice the thickness of the phantom), 1540 m / s.
14MHz linear electronic scanning probe (ultrasonic probe) PLT-1202S is inserted between the skin and the probe with a known phantom thickness of 7mm, and the moving distance of 4mm is pushed in for 3.7 seconds / once (about 2 seconds) ), An ultrasonic image was acquired (FIG. 5). Using the tissue Doppler imaging TDI (Tissue Strain Imaging) manufactured by Toshiba Medical System Co., Ltd., the phantom, skin, subcutaneous fat, and muscle regions are specified from the ultrasonic image, and the strain value (strain value). The change with time is shown in FIG. 5 (right).

  In addition, with this method, measuring the cheeks of women in their 20s and 60s and calculating the relative strain value (strain relative value) corrected with the phantom, the relative strain value decreased with age, It was possible to measure that the elasticity inside the skin was lowered. Further, it was found that the elasticity was large in the order of fat> muscle> skin in the skin (FIG. 6).

Example 2
We compared the usefulness of using a phantom with and without a phantom (with phantom) and without a phantom (without phantom). We examined whether or not a 7mm thick phantom with a cheek skin feel of a 20's female was sandwiched between the 14MHz ultrasonic probe and the inner skin of the forearm. The pushing condition was a pushing distance of 3.7 seconds / 1 stroke over a moving distance of 4 mm. FIG. 7 shows the degree of tissue deformation using tissue Doppler imaging TDI (Tissue Strain Imaging). As a result, when the phantom is not sandwiched (when none), the epidermis touches the probe surface, so the epidermis and dermis layers do not appear clear in the B-mode image, and the deformation degree of the epidermis and dermis layers is displayed in (-) It turned out that it was not caught correctly. Therefore, the usefulness by pinching a phantom was able to be confirmed.

Example 3
We compared the accuracy of mechanical pressing and manual pressing.
According to the example, a 7 mm thick phantom was sandwiched between a 14 MHz ultrasonic probe and the skin for comparison. For the manual push, the same person pushed in appropriately, and when using the device, the measurement was repeated 5 times by pushing the 4 mm moving distance in 3.7 seconds / once. FIG. 8 shows a graph of strain values (strain values) drawn from ultrasonic images acquired five times each, and the phantom strain values (strain values) are obtained and the coefficient of variation (CV value: standard deviation / average value × 100). The results of calculating are shown in Table 1. As a result, it was clarified that the CV value was smaller in the method of pressing with the device, and it was confirmed that the accuracy increased.

Configuration diagram of ultrasonic diagnostic equipment Configuration diagram of ultrasonic probe with pressurizing / vibrating means Diagram showing phantom sound velocity measurement method Diagram showing the measurement principle of the suction method and calculation of measurement parameters Chart showing temporal change of ultrasonic image and strain value (strain value) of skin tissue when pressurized through inclusion phantom The figure which shows the measurement result of the internal elasticity value of the skin corrected with the phantom of the face cheek Ultrasonic image of skin tissue with and without inclusion phantom and chart showing degree of deformation of internal elasticity Chart showing the stability of the internal elasticity with and without constant pressure exciter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 2 Ultrasonic transmitter 3 Ultrasonic receiver 4 Signal processor 5 Strain and elastic modulus calculator 6 Image display 7 Pressurizing / vibrating device 8 Inclusion 9 Device control interface unit

Claims (1)

An elastic measuring method of the skin internal local using imageable ultrasonic diagnostic apparatus distortions in the subject, by pressure-vibration means provided in the ultrasonic probe, the acoustic velocity 1500~1600m / s met Thus, the subject is 1 mm in a fixed cycle of 1 to 30 seconds / time through an ultrasonic phantom having a thickness of 5 to 30 mm and a return elastic ratio (Ur / Uf) of 0.05 to 0.095. A method for measuring the elasticity of a local area inside the skin that reaches the epidermis / dermis, subcutaneous tissue, and muscle layer, characterized by measuring the elastic modulus inside the subject by pressurizing to push 10 mm .