METHODS AND SYSTEMS FOR DETERMINING FREEZING OF SKIN DURING COOLING

Abstract

The disclosure relates to applicators, cooling systems incorporating such applicators, and methods for a cooling treatment of a skin fold of a subject. Methods for determining a freezing event include measuring electrical impedance between a contact plate of an applicator and a return electrode. Methods include determining possible movements as well, which may also be based on measurements of electrical impedance.

Claims

1. A cooling system for reducing adipose tissue in a subject by cooling a skin portion of the subject, the cooling system comprising; a base station; an applicator that includes an electrically conductive cooling element having a cooling surface that is configured to contact the skin portion of the subject for the purpose of cooling the skin portion of the subject, the cooling surface of the cooling element being substantially electrically non-conductive having an electrical resistivity of 1,000 .Math.cm or more; and a controller that is configured to determine a freezing of the skin portion of the subject based on a time derivative of a first electrical impedance between the cooling element and a first return electrode configured to be placed on a body of the subject, the controller also being configured to determine a movement of the subject or a movement of the skin portion with respect to the cooling element by determining an electrical impedance between a movement sensor electrode and a movement sensor return electrode.

2. The cooling system according to claim 1, wherein the cooling element of the applicator is an aluminium contact plate.

3. The cooling system according to claim 2, wherein the cooling surface of the applicator is an anodized aluminium layer.

4. The cooling system according to claim 1, wherein the applicator includes an electrical cable attached to the cooling element and configured to deliver to the cooling element an electrical current of 35 mA or less, the controller being configured to determine the first electrical impedance between the cooling element and the first return electrode when the electrical current of 35 mA or less is delivered to the cooling element.

5. The cooling system according to claim 1, wherein the applicator is coupled to the base station with a flexible tube and wherein the flexible tube is configured to provide electric and/or electronic and/or a pneumatic connection between the base station and the applicator.

6. The cooling system of claim 1, wherein the first return electrode is configured to be placed on an extremity of the subject.

7. The cooling system according to claim 1, further comprising a mechanism for detecting the movement of the subject and/or the movement of the skin portion of the subject, wherein the controller is configured to determine the freezing of the skin portion by: determining the first electrical impedance between the cooling element and the first return electrode placed on the subject, determining a time derivative of the determined first electrical impedance, determining the movement of the subject and/or the movement of the skin portion of the subject with respect to the cooling element using the mechanism for detecting the movement of the subject and/or the movement of the skin portion of the subject, determining the freezing of the skin portion if the time derivative of the first electrical impedance satisfies at least one freezing condition during a first time slot, and when a distortion of the first electrical impedance due to the movement of the subject and/or the movement of the skin portion of the subject in the same time slot is discarded.

8. The cooling system of claim 7, wherein the time derivative of the first electrical impedance is a first order time derivative, and wherein the at least one freezing condition is that the first order time derivative of the first electrical impedance is above a first freezing threshold during a first time slot.

9. The cooling system of claim 8, wherein the first freezing threshold is determined based at least partially on measured values of the first order time derivative.

10. The cooling system according to claim 7, wherein the distortion due to the movement of the subject and/or the movement of the skin portion of the subject in the first time slot is discarded if no indication of a possible movement is derived from the mechanism for detecting movement, or if a possible movement derived from the mechanism for detecting movement is insufficient to cause satisfaction of the one or more freezing conditions.

11. The cooling system of claim 10, wherein the controller is configured to detect a possible movement if a first order time derivative of the electrical impedance between the movement sensor electrode and the movement sensor return electrode during the first time slot is above a movement threshold value.

12. A method for determining a freezing event during a cooling treatment, wherein a cooling element cools a skin portion of a subject, the method comprising: determining a first electrical impedance between the cooling element and a first return electrode placed on the subject; determining a time derivative of the determined first electrical impedance; determining a movement of the subject and/or a movement of a skin portion of the subject with respect to the cooling element by determining an electrical impedance between a movement sensor electrode and a movement sensor return electrode; and determining the freezing event exists if the time derivative of the first electrical impedance satisfies one or more freezing conditions during a first time slot, and when a distortion of the first electrical impedance due to the movement of the subject and/or the movement of the skin portion of the subject in the same time slot is discarded.

13. The method of claim 12, wherein the time derivative of the determined first electrical impedance is a second order time derivative of the first electrical impedance.

14. The method of claim 12, wherein the time derivative of the determined first electrical impedance is a first order time derivative of the first electrical impedance.

15. The method of claim 14, wherein a first freezing condition of the one or more freezing conditions is that the first order time derivative of the first electrical impedance is above a first freezing threshold during the first time slot.

16. The method of claim 15, wherein a second freezing condition of the one or more freezing conditions is that an integral of a logarithmic value of the first order time derivative during a second time slot is above a second freezing threshold, wherein the second time slot is longer than the first time slot.

17. The method of claim 12, wherein the movement sensor return electrode is the first return electrode.

18. The method of claim 12, further comprising interrupting the cooling treatment of the skin portion upon a freezing event being detected.

19. The method of claim 12, further comprising temporarily heating the cooling element upon a freezing event being detected.

20. The method of claim 12, wherein the skin portion of the subject is selected from the group consisting of one or more of a thigh, a buttocks, an abdomen, a submental tissue, a knee, a back, a face and an arm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Non-limiting examples of the present disclosure will be described in the following, with reference to the appended drawings, in which:

[0043] FIG. 1 schematically illustrates an example of a cooling system;

[0044] FIGS. 2A and 2B schematically illustrate an example of an applicator and a cooling system including such an applicator;

[0045] FIG. 3 schematically illustrates a method for reducing adipose tissue according to an example;

[0046] FIG. 4 schematically illustrates a method for determining a freezing event during a cooling treatment according to an example;

[0047] FIGS. 5 and 6 schematically illustrate further examples of methods for determining a freezing event during a cooling treatment; and

[0048] FIGS. 7A and 7B schematically illustrate signals of impedance sensors and a method for evaluating such signals according to an example.

DETAILED DESCRIPTION

[0049] FIG. 1 schematically illustrates an example of a cooling system which may be used in a method for reducing adipose tissue, particularly a cosmetic method for reducing adipose tissue.

[0050] The method may comprise providing a cooling system as illustrated in FIG. 1. The cooling system of FIG. 1 comprises a base station 100 and one or more applicators 110, 120. The base station may include a user interface 150 including a screen which may indicate information regarding the cooling treatment.

[0051] The user interface 150 may include a tactile screen. A tactile screen and/or one or more control buttons or handles may be used to select a suitable cooling treatment and/or adjust parameters for the cooling treatment.

[0052] The applicators 110, 120 may each be connected to the base station through a flexible tube or hose 105, 115. Such a flexible tube 105, 115 may be configured to provide electric and/or electronic and/or a pneumatic connection between the base station and applicators.

[0053] The base station may have an electrical supply, e.g. an electric cable with a plug.

[0054] Applicators may have different sizes and shapes adapted for cooling of different parts of a subject's body. In a method for reducing adipose tissue, a skin fold of a subject may be introduced in a cavity of the applicator and a portion of the skin of the subject may be brought into contact with a cooling element of the applicator.

[0055] A cooling treatment may include cooling the skin portion of the subject during a period of up to 90 minutes. Depending on the skin portion to be cooled, and depending on the objective of the treatment, duration and other settings (e.g. temperature) may be varied.

[0056] In examples, cooling the skin portion comprises controlling a temperature of the cooling element to between 0 and 15 C., specifically between 5 C. and 13 C. The skin portion of the subject may be one or more of thigh, buttocks, abdomen, submental tissue, knees, back, face, and arms. A cooling system may include a plurality of applicators and a plurality of skin folds can be treated at the same time.

[0057] With temperatures below 0 C. for a prolonged period of time, freezing of the skin may occur. To avoid such freezing, a pad or absorbent with a cryoprotectant may be used. The cryoprotectant may be provided between skin and cooling element to protect the skin.

[0058] In examples of the present disclosure, throughout a cooling treatment, a method for determining a freezing event may be continuously carried out. If a freezing event is detected, the cooling treatment may be interrupted, or otherwise altered to avoid damage or injury to a subject's skin. The cooling of the skin portion may be interrupted if a freezing event is detected. In examples, a method may include temporarily heating up the cooling elements if a freezing event is detected. In examples, an audible or visual alarm may be generated so that if a freezing event is detected such that an operator can intervene by manually altering the treatment, interrupting the treatment, disconnecting the base station or other.

[0059] FIGS. 2A and 2B schematically illustrate an example of an applicator 10, and a cooling system for treating a skin fold of a subject 90. As in the example of FIG. 1, the cooling system of FIG. 2B may include a base station 100 with a user interface 150, and multiple applicators 110, 120, 160. The applicators may be similar to the applicator 10 shown in FIG. 2A.

[0060] The applicator 10 may include a cavity 2 for receiving a skin fold. An orifice connected to a suction system may be provided in a bottom of the cavity 2. The pump and power for sucking the skin fold into the applicator may be incorporated in the base station. Flexible tube or hose 5 may connect the applicator 10 to a corresponding base station. The applicator 10 may comprise a suitable coupling for coupling to tube 5. Providing suction or a vacuum can help ensure contact between the skin fold to be treated and one or more contact plates 3 arranged within the cavity.

[0061] Depending on the skin fold to be treated, the applicator may include one or more straight contact plates, e.g. two contact plates at opposite positions of the cavity. In other examples, a single contact plate which may be curved and/or may be shaped like a cup.

[0062] The applicator 10 for a system for cooling a skin portion of a subject comprises a cooling element 3 with a cooling surface for entering into contact with the skin portion of the subject for cooling the skin portion of the subject. The cooling element is electrically conductive and the cooling surface has a lower electrical conductivity than a remainder of the cooling element. The cooling system may be configured to determine an electrical impedance between the cooling element 3 and a first return electrode 190 configured to be placed on a body of the subject.

[0063] The cooling element 3 may be a metallic contact plate, optionally an aluminium plate. An aluminium plate may have a relatively good thermal conductivity. The applicator may further comprise a thermoelectric cooler configured to cool the metallic contact plate. Each of the contact plates may be cooled with Peltier elements. By controlling the power supplied to the Peltier elements, the temperature of the contact plates and thus the cooling of the skin fold can be controlled. Temperature sensors may be arranged in contact with the skin, or alternatively may measure temperature of the contact plate, or of the Peltier elements.

[0064] The cooling surface may be substantially electrically non-conductive. A higher resistivity of the cooling surface means that the whole contact plate may act as an electrode for impedance measurement. The cooling surface comprises an electrically non-conductive coating. The cooling surface may be an anodized aluminium layer.

[0065] The applicator 10 may comprise an electrical cable for providing an electrical current to the cooling element, wherein the electrical cable is attached to the cooling element with a screw. A current for determining an electrical impedance may be less than 35 mA, specifically less than 1 mA, more specifically 0.5 mA or less.

[0066] The applicator 10 may further comprise a mechanism for determining a movement. A movement may include a movement of the applicator, a movement of a skin fold with respect to the applicator or a movement of the subject. Such movements can affect the measurement of electrical impedance, and can thus affect the reliability of the determination of a freezing event.

[0067] In some examples, the applicator 10 may include an accelerometer for measuring the movement of the subject. In other examples, a further impedance measurement may be used to detect movements.

[0068] In some examples, a first return electrode 190 may be configured to be placed on an extremity of the subject. Electrical impedance between the contact plate 3 and first return electrode 190 may be measured to determine a possible freezing of the skin.

[0069] The cooling system may be configured to determine a freezing of the skin of the subject based on the electrical impedance, specifically on a variation of the electrical impedance by receiving signals and analysing signals regarding electrical impedance from the applicators.

[0070] In examples, the cooling system may be configured to determine the freezing of the skin based on a time derivative of the electrical impedance. It has been found that particularly a variation of the electrical impedance can be a reliable indicator of a freezing event.

[0071] In examples, the cooling system is further configured to determine movements of the subject or movements of the skin portion with respect to the cooling element by determining an electrical impedance between a movement sensor electrode 14 (in FIG. 2A) and a movement sensor return electrode. In FIG. 2B, the movement sensor electrode 14 is integrated in an applicator. The movement sensor electrode may be attached to the applicator, e.g. by fasteners such as screw, or by adhesive or any other suitable means. In examples, a kit maybe provided with which an applicator can be upgraded or retrofitted with a suitable system for measuring electrical impedance to determine possible freezing.

[0072] In an alternative example, a movement sensor electrode 180 may be separate from an applicator.

[0073] In examples, the movement sensor return electrode may be the first return electrode 190 (i.e. the same return electrode used in combination with the contact plate).

[0074] FIG. 3 schematically illustrates a method for reducing adipose tissue according to an example. In any of the examples disclosed herein, a skin fold to be treated may be of one of the following areas of the subject: thigh, buttocks, abdomen, submental tissue, knees, back, face, arms. In any of the examples disclosed herein, several skin folds may be treated simultaneously. For example, a single treatment device may comprise more than one applicator, and the applicators may be applied simultaneously to different skin folds.

[0075] At block 210, the configuration for the cooling may be determined. The configuration may depend particularly on which body part is treated. Particularly, cooling temperature and cooling time may be configured. Cooling temperature may relate to a temperature of the body of the subject in the treated region (temperature measured e.g. at epidermis), or a temperature of the cooling element.

[0076] In examples, contact plates of the treatment device may be maintained at a temperature below 0 C., more particularly below 5 C. for a period between 15 and 90 minutes. Specially, the contact plates may be maintained in contact with the skin for a period between 20 and 75 minutes. The treatment time may be adapted to the area of skin that is being treated. Treatment times for some areas of skin may be for example 30 to 50 minutes, and for other areas of skin, the treatment time may be for example 60 to 75 minutes.

[0077] In some examples, the base station of the cooling system may have a number of predefined and stored cooling programs. An operator may simply select the treatment of choice or the body part to be treated. Alternatively, the base station may be able to determine which applicator is activated or is connected to the base station. If the applicator can only be used in a single area, the base station may thus automatically recognize the area or body part is being treated and automatically select the suitable configuration. Alternatively, the base station can recognize the applicator, whereas an operator indicates (e.g. selects on the base station) which specific area, zone or body part will be treated of the different areas or zones which could be treated with the specific applicator.

[0078] The skin fold(s) may be introduced into the applicator(s). A cryoprotectant may be arranged between the skin fold and the contact plates in the applicators. At block 220, the skin fold may be cooled particularly with the objective of cooling adipose tissue to locally reduce fat.

[0079] During the cooling treatment, continuous monitoring may take place at block 230 to detect a freezing event. If such a freezing event is detected at block 230, the freezing may be mitigated at block 240 in any of a variety of ways commented herein including disconnecting the cooling system, warming up the contact plates (temporarily), shutting of the cooling system and other.

[0080] FIG. 4 schematically illustrates a method for determining a freezing event during a cooling treatment according to an example. During the cooling treatment, impedance may be measured substantially continuously. Measuring impedance at block 310 means that an electrical impedance is measured between a metal contact plate and a first return electrode. Measuring impedance may be carried out with a frequency of, for example, 1 kHz to 1000 kHz, specifically between 10 kHz and 200 kHz.

[0081] At block 320, based on the measured impedance, a possible freezing event of a user's skin may be determined. If the electrical impedance develops in such a way that is not suspicious of a freezing event, the flow diagram passes to block 340 and the conclusion is that there is no freezing event. It should be clear that the method is continuous, i.e. measuring impedance may be performed continuously and thus continuously conclusions may be reached with respect to freezing.

[0082] If at block 320, a possible freezing event is detected, a determination may be made whether there is a possible movement at block 350. In examples, movements may be continuously measured at block 330. If electrical impedance measured at block 310 develops in such a way that freezing is detected, and at the same time no movement is detected, the conclusion may be reached at block 360 that there is a freezing event. A reason for checking for possible movement is to reduce false positives because movements can cause similar impedance changes as a freezing event.

[0083] In accordance with this example, possible movements may be measured continuously, but an evaluation of the possible movements is only made if a freezing event is suspected.

[0084] An alternative example is shown in FIG. 5. As in FIG. 4, movements and electrical impedance between the cooling element and a first return electrode placed on the subject may be continuously measured (blocks 310, 330). Movements may be measured by determining an electrical impedance between a movement sensor electrode and a movement sensor return electrode. The movement sensor return electrode may be the first return electrode.

[0085] Independently from one another, and continuously, possible freezing elements may be detected, and possible movements may be detected (blocks 320, 350).

[0086] As long as no freezing event is suspected, the conclusion is reached at block 340 that there is no freezing event, and thus no reason to interrupt or modify the cooling treatment. If a freezing event is suspected, it is verified whether a movement might have affected the determination of the freezing event. If at the same time, a freezing element is suspected and the determination is made that a movement cannot have caused this, then the conclusion is reached at block 360 that a freezing event has occurred or is occurring.

[0087] In the example of FIG. 5, a further block 370 is introduced. If a freezing event is suspected and at the same a movement is suspected, a further check is made to determine whether there is an actual freezing event or not. At block 370 a further evaluation may be made by comparing the development or variation of electrical impedance measured for movement detection and electrical impedance measured for determining a freezing event. If a freezing event occurs, the electrical impedance may increase in both measurements, but it may be more pronounced between the cooling element and the return electrode.

[0088] In any of the examples of FIGS. 4 and 5, a freezing event may be suspected, if one or more freezing conditions are met for the electrical impedance.

[0089] In any of the examples, a method for determining a freezing event during a cooling treatment, wherein a cooling element cools a skin portion of a subject comprises determining (block 310) a first electrical impedance between the cooling element and a first return electrode placed on the subject, and determining a time derivative of the determined first electrical impedance.

[0090] In particular, the first order time derivative may be used. The first order time derivative indicates a speed of change of the first electrical impedance and has been found to be able to reliably indicate a possible freezing event if the first order time derivative is above a threshold.

[0091] In other examples, the second order time derivative may be used. The second order time derivative indicates an acceleration of the first electrical impedance. Outliers over time of the second order time derivative may also indicate a possible freezing event. In one example, an absolute value of the second order time derivative may be compared with a threshold value.

[0092] The method may further include determining movements (block 350), including movement of the subject and/or movements of a skin portion of the subject with respect to the cooling element using a mechanism for detecting movement.

[0093] A freezing event may be determined if the first order time derivative of the first electrical impedance satisfies one or more freezing conditions during a first time slot, and if distortion of the first electrical impedance due to a movement in the same time slot is discarded. A first freezing condition is that the first order time derivative of the first electrical impedance is above a first freezing threshold during a first time slot.

[0094] In some examples, the first freezing threshold is determined based at least partially on measured values of the first time derivative. In examples, the first freezing threshold may vary over time.

[0095] A further example is shown in FIG. 6. At block 405, signals regarding electrical impedance between the cooling element and the first return electrode may be received. A filter may be applied to the received signal, at block 410. Particularly, an averaging filter may be applied, e.g. a number of individual measurement points may be summed and averaged and correlated to a single measurement time (in the middle of the averaged measurement points).

[0096] In an example, impedance measurements may be made at a frequency of 1 kHz to 1.000 kHz, and specifically between 50 to 200 kHz, and more specifically around 100 kHz.

[0097] The sample time of the averaging filter may be 0.1 seconds to a few seconds, and specifically between 0.5 and 2.5 seconds.

[0098] Similarly, at block 505, signals regarding electrical impedance between a movement sensor electrode and the movement return electrode are received. At block 510, a similar averaging filter may be applied. The measurement frequency and averaging may be the same or in the same order of magnitude for the impedance measurement for movements and the impedance measurements for detecting potential freezing events.

[0099] After filtering, at blocks 415, 515, a time derivative of both measurements may be determined, in particular a first order time derivative. A plurality of freezing conditions may be defined for the first order time derivative of the electrical impedance at blocks 430 and 440.

[0100] A first freezing condition, block 430, may be that the first order time derivative of the first electrical impedance is above a first freezing threshold, or between predefined first freezing thresholds during a first time slot. The freezing threshold thus corresponds to a value of rate of change of the electrical impedance. In some examples, the first freezing threshold may vary over time. Optionally, not individual values of the first order time derivative may be compared with the threshold, but rather an average value of two or more moments in time.

[0101] In one example:

Impedance_variation=(current impedance variationlast impedance variation)/2(Eq. 1)

Peak=impedance_variation/first_threshold_value(Eq. 2)

First_threshold_value=(fixed_threshold*gain_threshold)+(abs[impedance_variation]*gain_impedance) (Eq. 3)

[0102] Equation 1 expresses an averaging over two time slots of the first order time derivative of the electrical impedance. Equation 2 defines a peak value as a ratio between the first order time derivative of the electrical impedance and a threshold value. If a peak is at predefined levels, a freezing event may be detected. If a peak is low, then it is unlikely that freezing occurred, because the electrical impedance variation is too low. If the peak is too high, a freezing event is unlikely, because there must be another cause for a very rapid variation of the electrical impedance (e.g. lost contact between skin and cooling element or similar). Equation 3 indicates how the first threshold value may vary over time taking into account measurements from specific components in a specific cooling treatment.

[0103] A second freezing condition may be defined at block 440. A second freezing condition in this example is that an integral of a (natural) logarithmic value of the first order time derivative during a second time slot is above a second freezing threshold, wherein the second time slot is longer than the first time slot.

Ln_value=(ln(peak)/second time slot(Eq. 4)

[0104] The second time slot may be longer than the first time slot. The first time slot (for the first order time derivative) may be between 1 and 5 seconds, specifically between 1 and 4 seconds. The second time slot may be longer. In an example, the second time slot may be 5 seconds.

[0105] If both the first and second freezing conditions are satisfied, then the algorithm passes on to block 450 or block 540 as will hereinafter be explained. If either one of the freezing conditions is not satisfied, the conclusion is drawn at block 490, that no freezing has occurred.

[0106] Simultaneously, a first order time derivative of the electrical impedance between movement sensor electrode and return electrode may be determined at block 515, and at block 530, a first movement criterion may be defined.

[0107] A possible movement may be derived if a first order time derivative of the electrical impedance between the movement sensor electrode and the movement sensor return electrode during the first time slot is above a movement threshold value, or between predefined movement thresholds (block 530). At block 530, similar Equations 1-3 may be applied but to the signals relating to the movement sensors.

[0108] The movement threshold(s) may be determined based at least partially on measured values of the first time derivative. The first movement threshold may vary over time.

[0109] If at block 530 no movement is determined or suspected, and at block 430 and 440, freezing is suspected, a third freezing condition may be checked at block 450.

[0110] In examples, the first time derivative (particularly of the electrical impedance between cooling element and return electrode) may be determined over time windows with a first span, and over time windows with a second span, the second span being longer than the first span. In practice, different averaging filters may be applied. For example, a first averaging filter based on 32 measurement points may be applied, and at the same time a second averaging filter based on 64 measurements may be applied. It should be clear that 32 and 64 are merely mentioned as examples. In examples, a Haar filter is used.

[0111] The third freezing condition at block 450 may be defined in that during the first time slot, the first order time derivative determined over the first span (in this example, the averaging filter with 32 points) is substantially different from the first time derivative measured over the second span (the averaging filter with 64 points). If freezing occurs, the first order time derivative with the averaging filter over a shorter time span will be different from the first order time derivative with the averaging filter over the longer time span. If instead the averages are not significantly different, the third freezing condition is not satisfied, and the conclusion is reached at block 490 that there is no freezing event.

[0112] If the first and second freezing conditions are satisfied, at blocks 430, 440 and a movement criterion is satisfied at block 530, a further determination may be made whether a movement has distorted the electrical impedance measurement.

[0113] In examples, distortion due to a movement in the first time slot may be discarded if no indication of a possible movement is derived from the mechanism for detecting movement, or if a possible movement derived from the mechanism for detecting movement is insufficient to cause satisfaction of the freezing conditions.

[0114] The method may thus comprise checking an additional criterion based on the time derivative of the first electrical impedance and on the electrical impedance between the movement sensor electrode and the movement sensor return electrode.

[0115] The additional criterion is that a ratio of the time derivative of first electrical impedance and the time derivative of the electrical impedance between the movement sensor electrode and the movement sensor return electrode is above a threshold.

Ratio=Impedance_variation_freezing/impedance_variation_movement(Eq. 5)

[0116] If the ratio of Equation 5 is above a specific threshold, this indicates that the first order time derivative of the electrical impedance for freezing is significantly higher than the first order time derivative of the electrical impedance for movement.

[0117] In some examples, the additional criterion may be determined (block 540) for the first time slot i.e. the same time slot as for the first and second freezing conditions. In other examples, the additional criterion may be determined after the first time slot.

[0118] FIGS. 7A and 7B schematically illustrate signals of impedance sensors and a method for evaluating such signals according to an example. In FIG. 7A, at the top part, filtered signals of impedance measurements for freezing (between cooling element and return electrode, reference sign 600) and for movements (between movement electrode and corresponding electrode, reference sign 610) are shown.

[0119] After applying the averaging filters and deriving firs order time derivatives, the results are shown in the bottom of the figure, with reference signs 602, and 612 respectively. In FIG. 7A, two different time windows have been identified, A, and B in which freezing events may be suspected. Particularly, in window B, specific jumps or increases of the electrical impedance may be recognized.

[0120] The aforementioned examples of FIGS. 4, 5 and 6 of methods for determining freezing events may be applied to these three time windows as follows.

[0121] FIG. 7B illustrates time window A in more detail. Reference sign 620 indicates a threshold for a first order time derivative, which varies over time. With reference to Equations 1-3, the threshold may correspond to a minimum peak value. It may be seen in FIG. 7B that the resulting signals after applying the averaging filter allows identification of specific increases more readily than the unfiltered signals. With reference to the example of FIG. 6, in time window A, a first freezing condition may be found to be satisfied, but a second freezing condition may be found not to be satisfied. The result is that no freezing event is detected and the cooling treatment may continue as normal.

[0122] In time window B, first and second freezing conditions may be found to be satisfied. At the same time, also the movement sensor indicates a peak above a corresponding threshold. I.e. at block 530 of FIG. 6, a possible movement is detected because a sufficient increase of electrical impedance is also measured between movement sensor electrode and return electrode. Applying the example of FIG. 6, the algorithm would pass to block 540, and a comparison may be made of the first order time derivative of both electrical impedances. In the case of time window B, the ratio as defined in Equation 5 may be found to be satisfied and the conclusion can be reached that a freezing event has occurred or is occurring.

[0123] Measurements of the electrical impedance sensor(s) may also be used to determine a correct positioning of the applicator and skin fold. If measurements of the sensor(s) indicate an unusual pattern, particularly at the beginning of a treatment, this may indicate that the applicator is not correctly positioned, a cryoprotectant pad is not suitably positioned, or another problem and therefore that the skin of the user is not adequately protected and/or that the cooling treatment will not be effective.

[0124] Examples of the methods disclosed herein may be implemented with hardware, software, firmware and combinations thereof.

[0125] Those of skill in the art would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application.

[0126] The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with one or more general-purpose processors, a digital signal processor (DSP), cloud computing architecture, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLC), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0127] Various aspects of the present disclosure are set out in the following numbered clauses:

[0128] Clause 1. An applicator for a system for cooling a skin portion of a subject, the applicator comprising: [0129] a cooling element with a cooling surface for entering into contact with the skin portion of the subject for cooling the skin portion of the subject, [0130] wherein the cooling element is electrically conductive and the cooling surface has a lower electrical conductivity than a remainder of the cooling element, wherein [0131] the cooling system is configured to determine an electrical impedance between the cooling element and a first return electrode configured to be placed on a body of the subject.

[0132] Clause 2. The applicator according to clause 1, wherein the cooling element is a metallic contact plate, optionally an aluminium plate.

[0133] Clause 3. The applicator according to clause 2, further comprising a thermoelectric cooler configured to cool the metallic contact plate.

[0134] Clause 4. The applicator according to clause 2 or 3, wherein the cooling surface is an anodized aluminium layer.

[0135] Clause 5. The applicator according to any of clauses 1-4, wherein the cooling surface is substantially electrically non-conductive.

[0136] Clause 6. The applicator according to clause 5, wherein the cooling surface comprises an electrically non-conductive coating.

[0137] Clause 7. The applicator according to any of clause 1-6, comprising an electrical cable for providing an electrical current to the cooling element, wherein the electrical cable is attached to the cooling element with a screw.

[0138] Clause 8. The applicator according to any of clauses 1-7, comprising a cavity configured to receive a skin fold, wherein the cooling element is arranged within the cavity and is configured to cool the skin fold.

[0139] Clause 9. The applicator according to any of clauses 1-8, wherein a current for determining an electrical impedance is less than 35 mA, specifically less than 1 mA, more specifically 0.5 mA or less.

[0140] Clause 10. The applicator according to any of clauses 1-9, comprising an accelerometer for measuring the movement of the subject.

[0141] Clause 11. A cooling system for cooling a skin portion of a subject comprising a base station, and one or more applicators according to any of clauses 1-10 configured to be coupled to the base station.

[0142] Clause 12. The cooling system of clause 11, wherein the applicators are coupled to the base station with a flexible tube.

[0143] Clause 13. The cooling system of clause 12, wherein the flexible tube is configured to provide electric and/or electronic and/or a pneumatic connection between the control base station and applicator.

[0144] Clause 14. The cooling system of any of clauses 11-13, wherein the first return electrode is configured to be placed on an extremity of the subject.

[0145] Clause 15. The cooling system according to any of clauses 11-14, further configured to determine a freezing of the skin of the subject based on the electrical impedance, specifically on a variation of the electrical impedance.

[0146] Clause 16. The cooling system according to clause 15, wherein the cooling system is further configured to determine the freezing of the skin based on a time derivative of the electrical impedance.

[0147] Clause 17. The cooling system according to any of clauses 11-16, wherein the cooling system is further configured to determine movements of the subject or movements of the skin portion with respect to the cooling element.

[0148] Clause 18. The cooling system according to clause 17, wherein the system is configured to determine the movements of the subject or the movements of the skin portion with respect to the cooling element by determining an electrical impedance between a movement sensor electrode and a movement sensor return electrode.

[0149] Clause 19. The cooling system according to clause 18, wherein the movement sensor return electrode is the first return electrode.

[0150] Clause 20. The cooling system according to clause 18 or 19, wherein the movement sensor electrode is arranged on the applicator.

[0151] Clause 21. The cooling system according to clause 20, wherein the movement sensor electrode is arranged in proximity of or around a cavity of the applicator configured to receive a skin fold.

[0152] Clause 22. The system according to claim 20 or 21, wherein the movement sensor electrode is attached to the applicator, specifically with adhesive or fasteners.

[0153] Clause 23. A method for determining a freezing event during a cooling treatment, wherein a cooling element cools a skin portion of a subject, the method comprising: [0154] determining a first electrical impedance between the cooling element and a first return electrode placed on the subject, [0155] determining a time derivative of the determined first electrical impedance, [0156] determining movements, including movement of the subject and/or movements of a skin portion of the subject with respect to the cooling element using a mechanism for detecting movement, [0157] determining the freezing event if the time derivative of the first electrical impedance satisfies one or more freezing conditions during a first time slot, and if distortion of the first electrical impedance due to a movement in the same time slot is discarded.

[0158] Clause 24. The method of clause 23, wherein the time derivative of the determined first electrical impedance is a second order time derivative of the first electrical impedance.

[0159] Clause 25. The method of clause 23, wherein the time derivative of the determined first electrical impedance is a first order time derivative of the first electrical impedance,

[0160] Clause 26. The method of clause 25, wherein a first freezing condition is that the first order time derivative of the first electrical impedance is above a first freezing threshold during a first time slot.

[0161] 27. The method of clause 26, wherein the first freezing threshold is determined based at least partially on measured values of the first time derivative.

[0162] Clause 28. The method of clause 27, wherein the first freezing threshold varies over time.

[0163] Clause 29. The method of any of claims 26-28, wherein a second freezing condition is that an integral of a logarithmic value of the first order time derivative during a second time slot is above a second freezing threshold, wherein the second time slot is longer than the first time slot.

[0164] Clause 30. The method of any of claims 26-29, wherein the first order time derivative is determined over time windows with a first span, and over time windows with a second span, the second span being longer than the first span.

[0165] Clause 31. The method according to clause 30, wherein a third freezing condition is that during the first time slot, the first time derivative determined over the first span is substantially different from the first time derivative measured over the second span.

[0166] Clause 32. The method according to any of clauses 23-31, wherein distortion due to a movement in the first time slot is discarded if no indication of a possible movement is derived from the mechanism for detecting movement, or if a possible movement derived from the mechanism for detecting movement is insufficient to cause satisfaction of the freezing conditions.

[0167] Clause 33. The method of any of clauses 23-32, wherein detecting a possible movement comprises determining an electrical impedance between a movement sensor electrode and a movement sensor return electrode.

[0168] Clause 34. The method of clause 33, wherein the movement sensor return electrode is the first return electrode.

[0169] Clause 35. The method of clause 33 or 34, wherein a possible movement is derived if a first order time derivative of the electrical impedance between the movement sensor electrode and the movement sensor return electrode during the first time slot is above a movement threshold value.

[0170] Clause 36. The method of clause 35, wherein the movement threshold is determined based at least partially on measured values of the first order time derivative.

[0171] Clause 37. The method of clause 36, wherein the movement threshold varies over time.

[0172] Clause 38. The method of any of clauses 35-37, further comprising checking an additional criterion based on the time derivative of the first electrical impedance and on the electrical impedance between the movement sensor electrode and the movement sensor return electrode.

[0173] Clause 39. The method of clause 38, wherein the additional criterion is that a ratio of the time derivative of first electrical impedance and the time derivative of the electrical impedance between the movement sensor electrode and the movement sensor return electrode is above a threshold.

[0174] Clause 40. The method of clause 39, wherein the additional criterion is determined for the first time slot.

[0175] Clause 41. The method of clause 39, wherein the additional criterion is determined after the first time slot.

[0176] Clause 42. A method for reducing adipose tissue, particularly a cosmetic method for reducing adipose tissue, comprising: [0177] providing a cooling system according to any of clauses 11-22; [0178] providing contact between a skin portion of the subject and the cooling element of the cooling system; [0179] cooling the skin portion of the subject optionally during a period of up to 90 minutes; and [0180] carrying out the method according to any of clauses 23-41 during the cooling.

[0181] Clause 43. The method of clause 42, wherein cooling the skin portion comprises controlling a temperature of the cooling element to between 0 and 15 C., specifically between 5 C. and 13 C.

[0182] Clause 44. The method of clause 42 or 43, wherein the cooling of the skin portion is interrupted if a freezing event is detected.

[0183] Clause 45. The method of any of clauses 42-44 comprising temporarily heating up the cooling elements if a freezing event is detected.

[0184] Clause 46. The method of any of clauses 42-45, wherein an alarm is generated if a freezing event is detected.

[0185] Clause 47. The method of any of clauses 42-46, wherein the skin portion of the subject is one or more of thigh, buttocks, abdomen, submental tissue, knees, back, face, arms.

[0186] Clause 48. The method of any of clauses 42-47, further comprising checking correct functioning of the cooling system by determining the electrical impedance between the cooling element and a first return electrode and/or by determining the electrical impedance between the movement electrode and the movement return electrode.

[0187] Although only a number of examples have been disclosed herein, other alternatives, modifications, uses and/or equivalents thereof are possible. Furthermore, all possible combinations of the described examples are also covered. Thus, the scope of the present disclosure should not be limited by particular examples, but should be determined only by a fair reading of the claims that follow.