WO2014181904A1

WO2014181904A1 - Method and apparatus for controlling output of ultrasonic transducer on base of blood flow change information

Info

Publication number: WO2014181904A1
Application number: PCT/KR2013/004133
Authority: WO
Inventors: 손건호; 강국진; 김태호; 전석환; 김종훈
Original assignee: 알피니언메디칼시스템 주식회사
Priority date: 2013-05-10
Filing date: 2013-05-10
Publication date: 2014-11-13
Also published as: KR101462024B1

Abstract

Disclosed are a method and an apparatus for controlling the output of an ultrasonic transducer on the base of blood flow change information . Provided are a method and an apparatus for controlling the output of an ultrasonic transducer, the method according to one aspect of the present invention controlling the output of an ultrasonic transducer on the base of blood flow change information, of the area of the body with which the transducer comes into contact, to prevent damage to the skin, such as a burn, during an ultrasound treatment and such others.

Description

Method and device for controlling output of ultrasonic transducer based on blood flow change information

The present embodiment relates to a method and an apparatus for adjusting the output of a high intensity focused ultrasound transducer based on change information of blood flow. More specifically, in order to prevent skin damage such as burns during High Intensity Focused Ultrasound (HIFU) treatment, a method of controlling the output of the transducer based on information on changes in blood flow in the human body that the transducer contacts. And to an apparatus.

The contents described in this section merely provide background information on the present embodiment and do not constitute a prior art.

In general, the diagnosis and treatment of the human body using ultrasound has been actively conducted in terms of the incision and surgical scar caused by the use of scalpel, and there is no fear of secondary infection. Examples of the application of ultrasound in the medical field include diagnostic fields such as fetal diagnosis and cancer tissue diagnosis, and therapeutic fields such as fat removal or cancer tissue or malignant tumor destruction.

Among them, High Intensity Focused Ultrasound (hereinafter, referred to as HIFU) treatment is applied to ultrasound in lesions such as tumors, thrombus, and cerebral infarction, and degeneration (for example, cauterization or destruction) by heat. It is a treatment. HIFU therapy has been developed for the treatment of prostate cancer, but is gradually expanding its application to non-solid cancers such as brain cancer, myoma and arrhythmia, including solid cancers such as liver cancer, breast cancer and pancreatic cancer. In particular, HIFU treatment has shown excellent results in the treatment of liver cancer and pancreatic cancer, which cannot be surgically operated.

The effects of HIFU treatment include thermal effects, cavitation effects, mechanical effects, peri-tumoral capillary destruction, and immune effects. Here, the thermal effect is to induce blood vessel coagulation and necrosis tumor cells to heat of 65 degrees or more, the cavitation effect is to increase the pressure in the cell to denature the protein structure of the cell and destroy the DNA of the tumor. In addition, the mechanical effect is to destroy the chemical linkage between the cancer cells, the capillary destruction around the tumor is to prevent the growth of the tumor by destroying the peripheral capillaries that nourish the tumor as well as the treatment lesion, the immune effect is postoperative Recognizing destroyed tumor cells as antigens means increasing immunity such as increased lymphocytes. Among them, the effect of using HIFU due to the thermal effect is the most representative.

In the case of HIFU treatment, a significant amount of energy is applied to the patient's body to heat the lesion, which may cause a side effect of heating the patient's skin due to an acoustic impedance mismatch between the patient's skin and the coupling agent (eg, hydrogel). . This acoustic impedance mismatch causes the patient to receive significant heating of the skin surface, which sometimes makes the patient uncomfortable, as well as causing burns to the skin or mucous membranes. These side effects may be exacerbated by bubbles that may be present between the skin and the coupling agent, or by hair on the skin. Thus, HIFU treatment requires a method that can effectively prevent overheating of tissues (such as skin or mucous membranes) of such patients.

Thermocouple monitoring and visual inspection of skin redness may be used to monitor skin temperature. However, the thermocouple approach is incomplete for HIFU treatment because the thermocouple electrodes are acoustically opaque and can interfere with the acoustic pathway. Monitoring skin color changes is not appropriate as a way to monitor skin temperature during HIFU treatment. Not only is the skin color different from person to person, but the skin color does not change until the patient's skin suffers any damage. That is, after finding redness of the skin tissue, the skin tissue may have already been burned. In addition, the appearance of redness in skin tissues with respect to skin heating belongs to a relatively slow response, so fast feedback control on skin heating during HIFU treatment is not easy.

Photoplethysmography (PPG), on the other hand, refers to a simple and inexpensive optical technique that can be used to non-invasively monitor changes in blood flow mainly in peripheral blood vessels. PPG signals detect peripheral blood vessel disease affecting arterial blood circulation by tracking volume changes in arterial blood in the peripheral arteries, assessing peripheral blood vessels and aortic elasticity, blood flow resistance in the vascular system, functioning blood pressure and cardiac output, oxygen It is widely used in medical device fields such as saturation measurement.

The principle of this measurement technique was used for the first time by Hertzman (1938), in which the light source and the photodetector were brought into contact with the skin and the change of the amount of light from the light source by transmission, reflection, dispersion, and absorption was transferred through the photodetector. Change to voltage. The intensity of light detected varies by factors such as solid tissue, skin, bone, and total amount of the vascular system. Blood has a higher Absorption Coefficient than other tissue constructs. It is therefore well known that pulse changes in blood volume in tissues can be observed from the transmission or reflection of light.

This embodiment has a main object to provide a method and apparatus for adjusting the output of the transducer based on the change information of the blood flow of the human body contacted by the transducer in order to prevent skin damage such as burns during HIFU treatment.

According to an aspect of the present embodiment, an ultrasonic transducer having a plurality of transducer elements, a drive unit connected to the ultrasonic transducer and driving the plurality of transducer elements to radiate ultrasonic waves to a target portion, and the ultrasonic waves are transmitted. It provides an ultrasound therapy apparatus including a control unit for controlling the drive unit to adjust the output of some or all of the plurality of transducer elements in response to changes in blood flow in the skin tissue.

If it is determined that the blood flow change is different from the normal state, the controller may control the driving unit to stop driving of some or all of the plurality of transducer elements or to lower the intensity of the output.

In addition, the controller may monitor the blood flow change by using one or more Photothythysmography (PPG) signals.

In addition, the PPG signal may be measured in a region adjacent to the skin tissue through which the ultrasonic waves pass, so as not to disturb the acoustic path of the ultrasonic waves radiated from the plurality of transducer elements.

The controller may include a peak-to-peak value of an AC component included in the PPG signal, a peak of a DC component included in the PPG signal, and a DC component included in the PPG signal. At least one of the floor value DC Foot may be calculated, and a change trend of the calculated value may be monitored.

The control unit may control the driving unit to stop some or all of the plurality of transducer elements or lower the intensity of the output when it is determined that the change in the calculated value is different from the normal state. Can be.

In addition, the ultrasound therapy apparatus may include a plurality of PPG sensors coupled to a membrane or a housing provided in the ultrasound transducer to approach or contact skin tissue during ultrasound therapy.

According to another aspect of the present embodiment, the process of radiating focused ultrasound to the target site, the process of monitoring the blood flow changes of the skin tissue transmitted by the ultrasound, and when the blood flow changes different from the normal state, the skin tissue It provides an ultrasound therapy method comprising the step of adjusting the output of the ultrasound radiated to.

The monitoring of the blood flow change may use one or more PPG signals measured in an area adjacent to skin tissue through which the ultrasound is transmitted.

In addition, the adjusting of the output of the ultrasonic wave may be to stop the emission of the ultrasonic wave corresponding to the area where the PPG signal showing a change in the state different from the normal state among the one or more PPG signals or to lower the intensity of the ultrasonic wave emitted. have.

As described above, according to the present embodiment, the blood flow of capillaries in the tissues in direct contact with the membrane of the ultrasonic treatment apparatus during ultrasound treatment can be monitored, and the skin treatment can be prevented by controlling the ultrasonic treatment according to the monitoring result. There is.

In particular, since the blood flow is very similar in the skin tissue through which ultrasound directly penetrates, and the adjacent skin tissue that does not directly penetrate, ultrasound is transmitted directly by using PPG information measured at the skin area that does not interfere with the acoustic path of ultrasound. It is possible to estimate the blood flow of skin tissue.

1 is a view schematically showing an ultrasound therapy apparatus according to an embodiment of the present invention.

2A, 2B and 2C show schematic configurations of a typical PPG measurement system.

3 is a diagram illustrating a form of a PPG signal measured by the transmission method.

4 is a diagram illustrating an AC component and a DC component extracted from a PPG signal.

5 is a view showing a change in the PPG component measured in capillaries according to the temperature change of the skin tissue.

6 is a flowchart schematically illustrating an ultrasound treatment method according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

Throughout the specification, when a part is said to include, 'include' a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated. . In addition, as described in the specification. The terms 'unit' and 'module' refer to a unit that processes at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software.

As shown in FIG. 1, in the present embodiment, the ultrasound therapy apparatus includes an ultrasound transducer 110, a driver 120 connected to the ultrasound transducer 110, and a controller 130 connected to the driver 120. do.

The ultrasound transducer 110 is configured to emit an ultrasound beam 140 toward the target tissue 151 in the body of the patient 150. The ultrasound beam 140 is used to treat target tissues such as tumors in organs or other tissues by coagulation, necrosis, heating, or the like. The ultrasound transducer 110 is mounted to the support 160 of the patient 150 by a mechanical Link mechanism (not shown), and the ultrasound transducer 110 of the ultrasound transducer 110 with respect to the support 160 of the patient 150. The position can be adjusted. Alternatively, the ultrasound transducer 110 may be installed on a mechanical arm independent from the support 160 of the patient 150.

In the illustrated embodiment, the ultrasonic transducer 110 includes a structure 112 and a plurality of transducer elements 111 secured to the structure 112. This structure 112 is shown to have a curved shape. In other embodiments, the structure 112 may have other shapes, shapes, and structures as long as it provides a surface on which the transducer element 111 can be fixed. In some cases, the ultrasonic transducer 110 includes a membrane (not shown) to remove the heat generated by the transducer element 111 when emitting the focused ultrasound beam, and the transducer element 111 and the patient. Acoustic impedance coupling between the skins of 150 may be improved.

The transducer element 111 is connected to the driving unit 120 and the control unit 130 so that the generation and / or intensity of the emitted ultrasonic beam 140 is controlled. For example, the driver 120 may generate one or more electrical driving signals controlled by the controller 130. The transducer element 111 converts the driving signal input from the driver 120 into ultrasonic energy. The control unit 130 and the driving unit 120 may be embodied as each or an integral part.

The driving unit 120 may be configured as an electric oscillator, and generates a driving signal of a frequency spectrum of ultrasonic waves, for example, about 50 KHz or about 10 MHz. When a drive signal is output to the transducer element 111, the transducer element 111 emits ultrasonic waves from each exposed surface.

The controller 130 may control the intensity or output of the ultrasonic wave emitted from the transducer element 111 by controlling the amplitude of the signal. In addition, the controller 130 controls, for example, the shape or size of the focus area formed by the transducer element 111 by controlling the phase component of the driving signal input to each transducer element 111, It is also possible to move the focus area to a desired position. For example, the controller 130 may adjust the focal length through the phase shift of the driving signal.

In addition, the controller 130 may stop some or all of the plurality of transducer elements 111 or control the amplitude and / or phase of each transducer element 111 to lower the intensity of ultrasonic waves emitted from some or all of them. Can be. In particular, the controller 130 stops the transducer element 111 so that the ultrasound beam does not penetrate the skin tissue when tissue damage due to an unintentional temperature rise is predicted in the skin tissue through which the ultrasound passes. The driving unit 120 may be controlled to lower the intensity of the ultrasonic beam passing through the skin tissue. According to the embodiment, in this case, in order to increase the efficiency of ultrasound treatment, other elements emitting ultrasound to tissues other than the skin tissue may increase the intensity of the ultrasound.

In order to monitor whether the skin tissue is heated, which may cause tissue damage as described above, the controller 130 may use a photoplethysmography (PPG) signal measured from the skin tissue near the acoustic path through which the ultrasound passes. . Hereinafter, the measurement of the PPG signal and its analysis method will be described in detail.

PPG measuring system is composed of photo detector which converts light transmitted or reflected from light source and skin tissue into electric current signal by using photo detector and signal processing circuit that processes output of photo detector. .

FIG. 2A illustrates a light source including two light emitting

elements

211 and 212 capable of operating at a red light and a near infrared wavelength. The two

light emitting elements

211 and 212 constituting the light source include a constant current source; 213 to drive light of a constant brightness. In general, an LED light emitting device operating in a red light and a near infrared wavelength is mainly used as a light source.

2B illustrates a transimpedance amplifier 231 for converting the output current of the photodetector 220 into an amplifier output voltage. The photodetector 220 may be configured as a photo diode (PD), and converts light energy into an electrical signal, that is, a current. The converted current is converted into a DC voltage via a transimpedance amplifier 231 and then signal processed.

2C illustrates a signal processing circuit 230 of a PPG signal as a functional block, and has a low pass filter having a predetermined cutoff frequency (eg, approximately 20 Hz) from an output signal of the transimpedance amplifier 231. DC components extracted via 232 are separated through a predetermined interface 236. In addition, the AC component is extracted via a high pass filter 233 having a predetermined cutoff frequency (eg, approximately 0.05 Hz). In the case of the AC component, the amplifier is amplified to a predetermined size through the amplifier 234, and the signal amplified through the inverter / interface 235 is inverted and separated into a final signal of the AC component through a predetermined interface. . Since the process of extracting the AC component and the DC component by signal processing the PPG signal is a technique generally known in the art, a detailed description thereof will be omitted.

The PPG measurement method includes a transmission mode in which light transmitted through a tissue of light emitted from a light emitting device is detected by a photodetector on the opposite side, and light reflected from a tissue of light emitted from a light emitting device and returned back. There is a reflection mode detected by the detection element. In the transmission method, a tissue (eg, a finger) is positioned between the light source and the photodetector, and in the reflection method, the light source and the photodetector are located side by side. Ultrasound therapy usually targets lesions in the human organs, and therefore, unlike the case where a PPG signal is measured by a finger, a reflection method is more preferable. In general, a PPG sensor refers to a device provided with a light emitting device and a photodetecting device except for a signal processing circuit.

As can be seen in Figure 3, the electrical signal obtained in the photodetector is an AC component indicating the absorption of pulsating arterial blood due to heart rhythm and DC component by absorption of non-pulsating arterial blood, venous blood, skin, bone, tissue, etc. Can be distinguished.

The AC component of the PPG signal represents the amount of dynamic blood change caused by the heartbeat, and may be caused by the flow of blood volume in the arterial blood vessel, thereby reflecting the state of the arterial blood vessel. In addition, the DC component of the PPG signal may reflect the volume of static blood in veins and capillaries as well as arterial vessels. Therefore, the change of DC component is directly inversely related to blood volume.

As described above, the AC component signal extracted from the PPG signal represents the amount of blood change due to the heartbeat, and therefore, the AC Gap representing the peak to peak voltage in the AC component reflects the state of arterial vessels. Done. In addition, the DC peak and the DC foot of the DC component extracted from the PPG signal reflect blood volume information of the measurement site.

As is well known, as ultrasound energy is converted from skin tissue on the acoustic pathway to heat energy, the temperature of the tissue rises and the function of the cells is enhanced. As the temperature of the tissue rises, the capillaries expand and the tissue blood flow increases. Metabolism is enhanced early in tissue temperature rise, but metabolism decreases when temperature rises above a certain limit. This is because the chemical reaction occurs as the temperature rises and the enzyme activity changes. Especially, when the temperature of the tissue exceeds about 45 ℃, protein denaturation occurs.

In response to the metabolism of the tissue according to the temperature, the PPG signal measured from the tissue also appears to change depending on the temperature of the tissue.

According to the experimental results, as shown in FIG. 5, it can be seen that as the tissue temperature increases, the AC Gap value of the AC component included in the PPG signal increases. This is because the AC Gap value reflects the flow of blood at the measurement site, that is, the state of capillaries at the measurement site. In addition, the DC component of the PPG signal decreases as the capillary enlarges and the blood flow increases due to the temperature rise. On the other hand, if the tissue temperature rises above a certain limit (approximately 40 ° C) out of the normal metabolic range, the blood flow of the capillaries decreases, and thus the AC Gap value of the AC component included in the PPG signal decreases. It can be seen that the DC peak and DC foot of the DC component increase.

Therefore, during ultrasound treatment, abnormal temperature rises of tissue located on the acoustic path through which ultrasound passes through the ultrasound transducer and the target site, in particular, skin tissue in direct contact with the ultrasound transducer, are measured. The change pattern of the AC gap, the DC peak of the DC component, or the DC foot of the AC component included in the PPG signal may be used.

Referring back to the ultrasound treatment apparatus of FIG. 1, the controller 130 may estimate an abnormal temperature rise of the skin tissue through which the ultrasound passes, using the PPG signal measured near the skin tissue through which the ultrasound passes. More specifically, the controller 130 continuously extracts the AC component and the DC component from the PPG signal measured in the vicinity of the skin tissue through which the ultrasound transmits during the ultrasound treatment, and the AC Gap, DC from the extracted AC and DC components. The change trend of at least one of the peak and the DC foot may be monitored. As a result, when it is determined that the change in the monitored value shows a different pattern from the normal state, it may be determined that an abnormal temperature rise may occur that may damage the tissue. Accordingly, the drive unit 120 may be controlled to stop some or all of the plurality of transducer elements 111 or lower the output intensity of some or all of the plurality of transducer elements 111 to eliminate abnormal temperature rise of the tissue.

The PPG sensor for measuring the PPG signal is preferably located in an appropriate skin region near the skin tissue through which the ultrasound passes, so as not to obstruct the acoustic path through which the ultrasound proceeds. The PPG sensor may be in direct contact with the skin, or may be in proximity to the skin. In addition, the PPG sensor may be configured in a form coupled to the membrane or the housing so that the membrane provided on the front surface of the ultrasonic transducer 110 for the ultrasound treatment can be in contact with the skin at the same time when the contact with the skin.

According to an embodiment, the controller 130 may be configured to determine whether a change in blood flow due to abnormal temperature rise occurs in a portion of skin tissue through which ultrasound is transmitted, using a plurality of PPG signals. That is, the PPG sensors are disposed at a plurality of sites near the skin tissue through which the ultrasound passes, and the controller 130 analyzes the PPG signals received from the plurality of PPG sensors, respectively. It can be configured to selectively control only the transducer element 111. According to the embodiment, in this case, in order to increase the efficiency of ultrasound treatment, other elements emitting ultrasound to tissues other than the skin tissue may increase the intensity of the ultrasound. In another embodiment, it is also possible to increase the output intensity of the transducer elements 111 stepwise when the temperature rise range of the skin tissue through which the ultrasound passes is within the normal range. That is, by adjusting the output intensity of the transducer elements 111 adaptively to the PPG signal, it is possible to increase the efficiency of ultrasound treatment without damaging the skin tissue.

6 is a flowchart schematically illustrating an ultrasound treatment method according to an embodiment of the present invention. The processes of FIG. 6 will be described with reference to the ultrasound therapy apparatus of FIG. 1.

As shown in FIG. 6, first, ultrasound is radiated to a target area from the plurality of transducer elements 111 to treat a lesion (S610).

The controller 130 continuously monitors blood flow changes of the skin tissue through which the ultrasonic waves are transmitted during the ultrasonic radiation (S620). That is, the change in blood flow of the skin tissue is observed from the PPG signal measured near the skin tissue through which the ultrasound passes. As described above, the controller 130 may extract the AC component and the DC component from the PPG signal, and monitor the change trend of at least one of AC Gap, DC Peak, and DC Foot from the extracted AC and DC components. .

As a result of monitoring the blood flow change of the skin tissue, when the blood flow change shows a different pattern from the normal state (YES in S630), the controller 130 controls the plurality of transducer elements 111 to remove abnormal temperature rise of the tissue. The driving unit 120 is controlled to stop some or all of the control panel or lower the output intensity of some or all of the control panel (S640). On the other hand, if the blood flow change is determined to be normal (No at S630), the monitoring continuously monitors the change in blood flow rate of the skin tissue through which ultrasound is transmitted and continues to perform ultrasound treatment through ultrasonic radiation at the target site.

In FIG. 6, processes S610 to S640 are described as being sequentially executed, but this is merely illustrative of the technical idea of the exemplary embodiment of the present invention. In other words, a person of ordinary skill in the art to which an embodiment of the present invention belongs may execute the process described in FIG. 6 by changing the order described in FIG. 6 without departing from the essential characteristics of the embodiment of the present invention. Since the above processes may be variously modified and modified to be executed in parallel, FIG. 6 is not limited to the time series order.

The above description is merely illustrative of the technical idea of the present embodiment, and those skilled in the art to which the present embodiment belongs may make various modifications and changes without departing from the essential characteristics of the present embodiment. Therefore, the present embodiments are not intended to limit the technical idea of the present embodiment but to describe the present invention, and the scope of the technical idea of the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present embodiment.

As described above, the present embodiment is applied to a method and apparatus for adjusting the output of the transducer based on the change information of the blood flow in the human body contacted by the transducer in the case of ultrasound therapy, thereby preventing skin damage such as burns. It is a useful invention that can be done.

(Explanation of the sign)

110: ultrasonic transducer 111: transducer element

112: structure 120: drive part

130: control unit 211: light emitting element

212: light emitting element 213: constant current source

220: photodetector 231: transimpedance amplifier

232: low pass filter 233: high pass filter

234: Amplifier 235: Invert / Interface

236: interface

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority under Patent Application No. 10-2013-0053031 filed to Korea on May 10, 2013 under Article 119 (a) (35 USC § 119 (a)). All content is incorporated by reference in this patent application. In addition, if this patent application claims priority for the same reason for countries other than the United States, all its contents are incorporated into this patent application by reference.

Claims

An ultrasonic transducer having a plurality of transducer elements;

A driving unit connected to the ultrasonic transducer and driving the plurality of transducer elements to radiate ultrasonic waves onto a target portion; And

Control unit for controlling the drive unit to adjust the output of some or all of the plurality of transducer elements in response to changes in blood flow in the skin tissue through which the ultrasound is transmitted

Ultrasound therapy device comprising a.
The method of claim 1,

The control unit,

And when it is determined that the blood flow change is different from the normal state, the driving unit is controlled to stop driving of some or all of the plurality of transducer elements or to lower the intensity of the output.
The method of claim 1,

The control unit,

Ultrasonic therapy device characterized in that for monitoring the blood flow changes using one or more photoplethysmography (hereinafter abbreviated as "PPG") signal.
The method of claim 3,

The PPG signal is,

And the ultrasonic wave is measured in an area adjacent to the skin tissue through which the ultrasonic wave is transmitted so as not to obstruct the acoustic path of the ultrasonic wave radiated from the plurality of transducer elements.
The method of claim 3,

The control unit,

Peak-to-Peak value of the AC component included in the PPG signal, DC Peak of the DC component included in the PPG signal, and the bottom value (DC) of the DC component included in the PPG signal And at least one of the foot, and monitoring the change in the calculated value.
The method of claim 4, wherein

The control unit,

When it is determined that the change in the calculated value is different from the normal state, the driving unit is controlled to stop some or all of the plurality of transducer elements or to lower the intensity of the output. Treatment device.
The method of claim 1,

The ultrasound therapy device,

And at least one PPG sensor coupled to a membrane or a housing provided in the ultrasound transducer to allow proximity or contact with skin tissue during ultrasound treatment.
Radiating focused ultrasound onto a target site;

Monitoring blood flow changes of the skin tissue through which the ultrasound penetrates; And

If the change in blood flow shows a different state from the normal state, the process of adjusting the output of the ultrasonic radiation emitted to the skin tissue

Ultrasound treatment method comprising a.
The method of claim 8,

The process of monitoring the blood flow changes,

And at least one PPG signal measured in an area adjacent to the skin tissue through which the ultrasound passes.
The method of claim 9,

The process of adjusting the output of the ultrasonic wave,

Ultrasound treatment method characterized in that to stop the emission of the ultrasonic wave corresponding to the region in which the PPG signal showing a change in the aspect different from the normal state of the one or more PPG signal or lower the intensity of the ultrasonic wave emitted.