Patent ID: 12251583

DETAILED DESCRIPTION

The following detailed description of the present disclosure is made with reference to the accompanying drawings, in which particular embodiments for practicing the present disclosure are shown for illustration purposes. These embodiments are described in sufficiently detail for those skilled in the art to practice the present disclosure. It should be understood that various embodiments of the present disclosure are different but do not need to be mutually exclusive. For example, particular shapes, structures and features described herein in connection with one embodiment can be embodied in other embodiment without departing from the spirit and scope of the present disclosure. It should be further understood that changes can be made to positions or placement of individual elements in each disclosed embodiment without departing from the spirit and scope of the present disclosure. Accordingly, the following detailed description is not intended to be taken in limiting senses, and the scope of the present disclosure, if appropriately described, is only defined by the appended claims along with the full scope of equivalents to which such claims are entitled. In the drawings, similar reference signs denote same or similar functions in many aspects.

The terms as used herein are general terms selected as those being now used as widely as possible in consideration of functions, but they may vary depending on the intention of those skilled in the art or the convention or the emergence of new technology. Additionally, in certain cases, there may be terms arbitrarily selected by the applicant, and in this case, the meaning will be described in the corresponding description part of the specification. Accordingly, it should be noted that the terms as used herein should be interpreted based on the substantial meaning of the terms and the context throughout the specification, rather than simply the name of the terms.

Hereinafter, exemplary embodiments of a device and method for tissue removal using intensity modulated focused ultrasound will be described in detail with reference to the accompanying drawings.

FIG.1shows schematically the configuration of a focused ultrasound based tissue removal device that supports a variety of output modes according to an embodiment of the present disclosure.FIG.1shows only necessary elements for describing the present disclosure, and does not depict all essential elements for operating the device or obtaining the effect of the present disclosure. That is, in addition to the disclosed elements, the device may further include elements including a variety of components, modules, devices or software.

Referring toFIG.1, the tissue removal device1according to an embodiment includes a focused ultrasound output unit10, a mode setting unit20to set an output mode of focused ultrasound, a control unit30to control the output characteristics of focused ultrasound according to the set mode, an ultrasound imaging unit40to monitor the formation of vapor bubbles in tissue, and a display unit50to display an ultrasound image.

The focused ultrasound output unit10includes an ultrasonic transducer to convert alternating current energy into mechanical vibration. According to an embodiment, the focused ultrasound output unit10may include a single transducer or an array of transducers to focus ultrasound onto at least one focal point. The focused ultrasound output unit10is configured to receive a control signal that determines the characteristics of ultrasound, for example, acoustic pressure, waveform, frequency and pulse length from the control unit30, and output the ultrasound of the characteristics according to a set value.

In general, the ultrasonic transducer is a device which converts alternating current energy of 20 KHz or above to mechanical vibration of the same frequency using the piezoelectric effect or magnetostrictive effect. For example, the transducer includes a body with one open side and piezoelectric elements, the body is filled with air, and each piezoelectric element is connected with an electric wire to apply voltage. The piezoelectric element uses a material exhibiting a piezoelectric effect such as quartz and tourmaline, and the transducer generates and outputs ultrasound using the piezoelectric effect of the piezoelectric element. The outputted ultrasound forms a plane wave or a focused ultrasound beam according to the structure of the transducer.

As shown inFIG.1, the focused ultrasound output unit10emits high intensity focused ultrasound (HIFU) to a target tissue T such as a fat cell or a tumor. A focal point position F is a point to which the output ultrasound beam is focused, and vibration energy by ultrasound converges on the single point to produce a strong nonlinear shockwave. Vapor bubbles of a few hundred μm to a few mm in size are formed at the focal point position F by the thermal effect of the shockwave (acoustic cavitation phenomenon), and as the bubbles vibrate and collapse/disappear, mechanical shocks are applied to the tissue. The characteristics of the output ultrasound differ depending on the output mode and it will be described in detail below.

The output characteristics of ultrasound differ depending on the output mode selected by the mode setting unit20, and the direct control of the output characteristics of ultrasound according to the mode selection is performed by the control unit30.

The existing ultrasound based lipolysis device does not actively control the output characteristics of ultrasound, and simply generates a predetermined level of thermal energy to burn off fats (about 65° C.). This method may have a risk of damaging the surrounding tissues (blood vessels, nerve cells, etc.) by heat dispersion, and it is difficult to predict the range and extent to which ultrasound breaks down fats and it is impossible to precisely remove only adipose tissues in a local area.

According to the proposed tissue removal device, it is possible to remove tissues (adipose tissues, tumor tissues, etc.) in a local area with high precision by controlling the output characteristics of focused ultrasound according to the mode selection. Hereinafter, three selectable output modes are described, but this is provided by way of example, and a variety of output modes may be added according to users' needs. Additionally, the term ‘first’, ‘second’ or the like is used to distinguish each output mode, and is not intended to indicate particular settings or the order of each mode.

In a first mode, the temperature in the tissue sharply rises using very high intensity focused ultrasound, and accordingly the tissue is removed using dynamic energy of formed vapor bubbles.

As opposed to the existing thermal ablation using thermal energy, this method mechanically removes the surrounding tissues by artificially generating cavitation through focused ultrasound. This technology also known as ‘focused ultrasound soft tissue removal’ or ‘boiling histotripsy’ forms vapor bubbles in a short time using ultrahigh intensity focused ultrasound having the acoustic pressure that is a few tens of times stronger than the existing method. Accordingly, it is possible to remove tissues in a shorter time than the existing method that ignites tissues by gradually increasing the temperature in the tissues, and monitor the treatment process in real time through cavitation monitoring.

FIGS.2A to2Eshow a process of removing the tissue using vapor bubbles formed by focused ultrasound in the first mode. As shown, when high intensity focused ultrasound is outputted to a target tissue (lesion in an adipose tissue or a cancer cell) using the ultrasonic transducer, a shockwave is produced at the focal point of ultrasound (FIG.2A), as water in the tissue is heated by the thermal effect of the shockwave, primary vapor bubbles are formed at the focal point (FIG.2B), and the vapor bubbles grow by the rise in vapor pressure in the bubbles due to negative pressure (tension) that is longer than positive pressure (compression) in the nonlinear shockwave waveform and vapor introduced into the bubbles (FIG.2C). The resulting bubbles form numerous secondary bubble clouds around the focal point by the shock scattering effect of ultrasound (FIG.2D), and as the bubble clouds vibrate or collapse with changes in acoustic pressure, shocks are applied to the surrounding tissues (FIG.2E).

According to an embodiment, in the first mode, the focused ultrasound is outputted with the center frequency of 0.1 to 30 MHz, and the pressure of the maximum positive pressure of 40 MPa or above and the maximum negative pressure of −10 MPa or below. Additionally, the pulse length may be 0.1 to 100 ms, the pulse repetition frequency may be 0.1 to 10 Hz, and the number of pulses may be one or more.

FIGS.3A to3Cshow the results of applying focused ultrasound according to the condition of the first mode to a tissue-mimicking gel. In the experimental example, an image is captured using a high speed camera (recording time is 0-13 ms) while emitting high intensity focused ultrasound having the fixed acoustic pressure of P+=92 MPa, P−=14 MPa and the frequency of 2 MHz to the tissue-mimicking gel for 10 ms. According to the simulation, the time required for the temperature of the gel to reach 100° C. is 3.84 ms. As shown, vapor bubbles are formed by an instantaneous temperature rise at the focal point position (indicated by the dashed circle) (FIG.3A) and scattering bubble clouds are formed by the shock scattering effect (FIG.3B). As the bubble clouds vibrate and collapse, mechanical shocks are applied to the tissue in the range of about 6-7 mm (FIG.3C).

A second mode is selected when removing tissue in a narrower area than the first mode. In the second mode, the formation of bubble clouds by the shock scattering effect may be suppressed by controlling the output characteristics of ultrasound immediately after vapor bubbles are formed by focused ultrasound, thereby selectively removing tissue in a narrow area of 1-3 mm on the basis of the focal point position.

According to an embodiment, in the second mode, focused ultrasound is outputted in the same condition (the pressure of the maximum positive pressure of 40 MPa or above and the maximum negative pressure of −10 MPa or below) as the first mode for a predetermined time, and immediately after vapor bubbles are formed, is adjusted to the acoustic pressure of the lower maximum positive pressure of 40 MPa or below and maximum negative pressure of −10 MPa or above.

FIGS.4A to4Cshow a process of removing tissue in a local area by controlling the formation of vapor bubbles using pressure modulated focused ultrasound in the second mode. Referring toFIG.4A, when high intensity focused ultrasound produces a strong shockwave at the focal point position, the temperature of the tissue rises due to the shockwave (the center frequency of ultrasound: 0.1-5 MHz). Alternatively, focused ultrasound having the pressure that is not high enough to produce a shockwave but the center frequency that is high enough to rapidly increase the temperature may be used (the center frequency of ultrasound: 5-30 MHz, in this case, the focal length may be shorter). Referring toFIG.4B, when the temperature of water in the tissue increases, vapor bubbles are formed at the focal point position. Referring toFIG.4C, when the vapor bubble formation or the temperature reaching the threshold is sensed, the control unit controls the intensity of focused ultrasound below the setting value. As a result, the shock scattering effect does not occur, consequential bubble clouds are not formed, and the removal area by the bubbles is limited to the focal point position.

FIGS.5A to5Cshow the experimental results of applying focused ultrasound of the condition of the second mode to a tissue-mimicking gel. In the experimental example, from the beginning until vapor bubbles are formed, high intensity focused ultrasound of P+=92 MPa, P−=−14 MPa and the frequency of 2 MHz is emitted to the tissue-mimicking gel (the same condition as the first mode), and immediately after bubbles are formed, the acoustic pressure of ultrasound is adjusted to P+=30 MPa, P−=−9.4 MPa. As shown, vapor bubbles are formed at the focal point position (indicated by the dashed circle), but the shock scattering effect does not occur through the control of the ultrasound intensity (FIG.5A), and accordingly, the formation of secondary bubble clouds is suppressed at other areas than the focal point position (FIG.5B). As a result, shocks are only applied within the radius of 1 mm from the focal point position (FIG.5C).

Data related to the output characteristics of focused ultrasound in the second mode and the time required to form vapor bubbles may be determined based on biomechanics information, thermodynamics information and bubble dynamics information. For example, in the experimental example ofFIG.5, the time point at which the output characteristics of ultrasound are controlled upon formation of vapor bubbles is about 3.84 ms, which is the calculated time required for the temperature at the focal point part to reach 100° C. when high intensity ultrasound having the frequency of 2 MHz and the acoustic pressure characteristics of the maximum positive pressure of 92 MPa and the maximum negative pressure of −14 MPa is outputted to the tissue (or a tissue-mimicking gel having similar physical properties) through simulation.

The rising temperature trend of the tissue by ultrasound and vapor bubble dynamics may be predicted using Bioheat transfer equation and Gilmore bubble equation. In other words, in a specific ultrasound irradiation condition (acoustic pressure, waveform, frequency and irradiation time of ultrasound), it is possible to predict information, for example, the time required for the focal point part to reach a specific temperature, the size of a vapor bubble that will be formed, and a motion change of the vapor bubble in a given acoustic field. It is possible to automatically control the intensity of ultrasound without a senor by inputting time information required to accomplish the condition beforehand.

According to another embodiment, the ultrasound pressure may be lowered at the moment at which vapor bubbles are formed while monitoring the vapor bubble formation time in the form of a signal/image using an additional ultrasonic sensor (or ultrasound imaging equipment) without pre-setting when to control the output characteristics of ultrasound.

According to the second mode setting, in the same way as the first mode, vapor bubbles are artificially formed using a strong nonlinear shockwave produced by the ultrasonic transducer, but a motion change of vapor bubble may be controlled by reducing the intensity of focused ultrasound below the set value by instantaneously changing the acoustic pressure and waveform of ultrasound when a specific condition (a preset time is reached or a vapor bubble is observed) is reached. After the control, the acoustic pressure of ultrasound is lower than the absolute pressure value at which the shock scattering effect occurs, so acoustic cavitation does not occur in other areas than vapor bubbles formed at the focal point of ultrasound. Accordingly, it is possible to precisely strike tissue (a fat cell or a tumor tissue) in a narrow area using only mechanical shocks generated by movement of predictable and controllable vapor bubbles.

In a third mode, heating is generated in the subcutaneous fat layer without directly damaging the tissue using focused ultrasound of lower intensity and longer pulse length than the first mode and the second mode. For example, in case that a fat cell is removed by ultrasound in the first mode or the second mode, the tissue density reduces and the skin layer sags or loses elasticity, and in the third mode, it is possible to obtain the body tightening effect that firms up the skin by tightening the skin tissues and regenerating collagen and elastin fibers by thermal energy using ultrasound having weak intensity and long pulse length.

Although the output characteristics and effects of ultrasound in the first to third output modes have been described, a variety of output modes may be added according to environments and purposes of use as described above.

Referring back toFIG.1, the tissue removal device1according to an embodiment may include an ultrasound imaging unit40to monitor the formation of vapor bubbles and the tissue, and a display unit50to display an ultrasound image acquired by the ultrasound imaging unit.

The ultrasound imaging unit40may include a transducer to output high frequency imaging ultrasound and a computing device to create an ultrasound image based on the time for the ultrasound to bounce off the tissue and return. Using the ultrasound imaging unit40, the focal point position of focused ultrasound may be detected or the presence or absence of cavitation may be monitored in real time. The display unit50outputs the ultrasound image acquired by the ultrasound imaging unit40in real time to allow the user to see the ultrasound image. The user can see the location of the target tissue, the focal point position of focused ultrasound and the presence or absence of a vapor bubble through the display unit50.

According to an embodiment, the tissue removal device may further include a laser pointer (not shown) for marking the focal point position of focused ultrasound on the body surface. The orientation of the laser pointer matches the orientation of the ultrasonic transducer, and is set such that an intersection of a criss-cross laser pointer is placed on a straight line with the focal point position of focused ultrasound. It is possible to improve the surgical accuracy and convenience of the user by visually guiding the focus of focused ultrasound.

FIG.6shows the tissue removal device according to an embodiment when viewed from the side. The tissue removal device1is a hand-held device including a handle300, and the handle300has an operation switch350for easy and simple output mode change and on/off.

According to an embodiment, the device may further include a multi-freedom compact operating system to enable fine-tuning of the focal point position of ultrasound without moving the focused ultrasound output unit, and the handle may further include a tuning switch used to fine-tune the position and angle of the focused ultrasound output unit through the multi-freedom compact operating system. The user can fine-tune the position and angle of the ultrasonic transducer through manipulation of the tuning switch attached to the handle while seeing the display.

Referring toFIG.6, the tissue removal device1includes an ultrasound guide unit100to support the focused ultrasound output unit (the transducer) and adjust the penetration depth of focused ultrasound, and the ultrasound guide unit100may be a structure having a water tube250through which water supplied through a water pump200passes.FIG.7shows the tissue removal device1according to an embodiment when viewed from the top.

FIGS.8A to8Cshows the ultrasound penetration depth varying depending on the shape of the ultrasound guide unit according to an embodiment. As shown, the ultrasound guide unit100has the shape of a truncated cone, and the truncation plane of the cone contacts the skin. Since ultrasound is focused onto the focal point position F, as the cone length of the guide unit is shorter, ultrasound is focused onto a deeper location in the body. In case that the focused ultrasound output unit includes an array of transducers, each having adjustable phase, it is possible to arbitrarily reduce or increase the focal length through phase control, but in case that the focused ultrasound output unit includes a single transducer, it is impossible to adjust the focal length at a fixed location. According to an embodiment, it is possible to adjust the focal length using a single transducer at a low price by replacing the ultrasound guide unit100of different shapes according to target focal point positions.

According to an embodiment, the ultrasound guide unit may be customized through 3D printing according to the user's body structure features.

According to an embodiment, the water pump200is configured to control the amount of water supplied to the ultrasound guide unit100based on the real-time ultrasound imaging results through the ultrasound imaging unit. The focal position of ultrasound may be changed by movement or breathing of a patient during treatment, and the change in focal point position of ultrasound may be compensated for by controlling the height of the ultrasound guide unit100by the control of the water pump amount according to the ultrasound imaging results as shown in an embodiment. To this end, the ultrasound guide unit100may be a variable structure that can expand or shrink with the introduction of water or an ultrasound gel.

According to the above-described acoustic cavitation based tissue removal device, it is possible to remove tissues, for example, adipose tissues in a non-invasive manner using high intensity focused ultrasound, and significantly reduce inflammation, swelling and blooding compared to the invasive method. Additionally, as opposed to the existing HIFU based devices, the acoustic cavitation based tissue removal device provides a variety of output modes, including the first mode for removing tissues in a relatively wide area using vapor bubbles formed by high intensity focused ultrasound, the second mode for selectively removing only tissues in a narrower area by reducing the ultrasound intensity using pressure modulated focused ultrasound at the moment at which vapor bubbles are formed, and the third mode for obtaining the body tightening effect using low intensity ultrasound. Additionally, it is possible to monitor the tissues and the formation of vapor bubbles (cavitation) in real time through ultrasound imaging. Accordingly, the user can remove tissues in a local area with high precision by controlling the output characteristics of focused ultrasound.

While the present disclosure has been hereinabove described with reference to the embodiments, it will be understood by those having ordinary skill in the corresponding technical field that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure defined by the appended claims.