Patent Application
20210346718
The present invention relates to energy-based treatments and, more specifically, systems and methods for improving the safety and efficacy of an energy-based dermatological treatment.
Sebaceous glands and other chromophores embedded in a medium, such as the dermis, can be thermally damaged by heating the chromophore with a targeted light source, such as a laser. However, the application of enough thermal energy to damage the chromophore can also be damaging to the surrounding dermis and the overlying epidermis, thus leading to epidermis and dermis damage as well as pain to the patient.
Previous approaches to prevent epidermis and dermis damage as well as patient pain during a photo-thermal treatment procedure include:
1. Cooling the epidermis, then applying the photo-thermal treatment; and
2. Cool the epidermis, also condition (i.e., preheat) the epidermis and dermis in a preheating protocol, then apply photo-thermal treatment in a distinct treatment protocol. In certain instances, the preheating protocol and the treatment protocol are performed by the same laser, although the two protocols would involve different laser settings and application protocols, thus leading to further complexity in the treatment protocol and equipment.
For either of these approaches, as well as in many energy-based dermatological procedures, measuring the temperature of the skin surface during the treatment provides valuable information that can be used to adjust the treatment protocol and/or equipment settings in real time. Such temperature-based treatment protocol adjustments can be made by a practitioner, as an example, every few seconds over an hour-long procedure or can be made automatically by the system itself in a closed-loop control fashion. However, any analytics of the underlying tissue based on skin surface measurements, or the use of skin surface temperature measurements to either suggest changes in settings or to make such adjustments automatically require a number of assumptions, such as the heat transfer coefficient and fluence (i.e., optical energy delivered per unit area), and these factors differ from system to system, even patient to patient. Particularly in photo-thermal targeted treatment systems involving both cooling and heating of the treatment area, inaccuracies in these assumed parameters can greatly influence the actual performance of the system during application of the treatment protocol.
In accordance with the embodiments described herein, there is described a method for operating a light source within a photo-thermal targeted treatment system for targeting a chromophore embedded within a medium. The method includes: 1) applying a treatment protocol to a skin surface; 2) measuring a skin surface temperature while applying the treatment protocol; 3) calculating parameters regarding a heat transfer provided by the photo-thermal targeted treatment system based on the skin surface temperature so measured; and 4) adjusting the light source and the treatment protocol in accordance with the information regarding the heat transfer.
In accordance with another embodiment, a photo-thermal targeted treatment system is described. The photo-thermal targeted treatment system includes a light source for providing a light output toward a treatment area, a cooling unit for providing a cooling mechanism at the treatment area, a temperature monitoring unit for measuring a skin surface temperature at the treatment area to provide a skin surface temperature measurement, and a controller for controlling the operating parameters of the light source, the cooling unit, and the temperature monitoring unit. The controller is configured for receiving the skin surface temperature measurement, calculating at least one heat transfer parameter of the photo-thermal targeted treatment system based on the skin surface temperature measurement, and adjusting at least one of the light source and the cooling unit, in accordance with the at least one heat transfer parameter so calculated.
The present invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout.
It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
Spatially relative terms, such as “beneath,” “below,” “lower,” “under,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” or “under” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary terms “below” and “under” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items, and may be abbreviated as “/”.
It will be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “adjacent to” another element or layer, it can be directly on, connected, coupled, or adjacent to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” “directly coupled to,” or “immediately adjacent to” another element or layer, there are no intervening elements or layers present. Likewise, when light is received or provided “from” one element, it can be received or provided directly from that element or from an intervening element. On the other hand, when light is received or provided “directly from” one element, there are no intervening elements present.
Embodiments of the invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Accordingly, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the invention.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present specification and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
When performing a dermatological treatment, it is preferable that the practitioner keeps his/her eyes continuously on the current treatment location. The reasons include:
1. Safety
2. Efficacy: The practitioner can ensure that no treatment areas are being skipped. For instance, keeping the practitioner's attention at the treatment location makes it less likely that the practitioner will lose track of where the next treatment location is if s/he is following a grid pattern.
3. Ergonomics: Having to constantly swivel his/her head to look at a screen is not a good ergonomic setup.
4. Economics: Currently, an assistant is required in the treatment room to call out temperatures, even if the temperature is displayed on the treatment system user interface. Having an assistant attend the procedure, even if the assistant is not required in the use of the treatment system, adds to the cost of operating the treatment system.
In laser treatment of acne, the operating thermal range is generally bound on the upper end at the epidermis and dermis damage threshold temperature of approximately 55° C., and at the lower end by the temperature required to bring the sebaceous gland to its damage threshold temperature of approximately 55° C. Based on clinical data, the operating temperature range for acne treatment expressed in terminal skin surface temperature is approx. 45° C. to 55° C., as an example. At skin surface temperatures below 45° C., it has been determined that there is no damage to the sebaceous gland. When the skin surface temperature is between 45° C. and 55° C., there are varying degrees of sebaceous gland damage, with no epidermal damage. Above 55° C., there is epidermal damage in addition to damage to the sebaceous gland. By adjusting the treatment system, such as the light source operating parameter settings, in real time during treatment, the practitioner can avoid damaging the epidermis and dermis surrounding the treatment area, while effectively administering the treatment protocol.
Exemplary System
Still referring to
Controller 122 further controls other components within photo-treatment unit 120, such as a laser 124, a display 126, a temperature monitoring unit, a foot switch 130, a door interlock 132, and an emergency on/off switch. Laser 124 provides the laser power for the photo-treatment protocol, and controller 122 regulates the specific settings for the laser, such as the output power and pulse time settings. Laser 124 can be a single laser or a combination of two or more lasers. If there more than one laser is used, the laser outputs are combined optically to function as one more powerful laser. Display 126 can include information such as the operating conditions of cooling unit 110, laser 124, and other system status. Temperature monitoring unit 128 is used to monitor the temperature of the skin surface in the treatment area, for example, and the measured skin surface temperature at the treatment area is used by controller 122 to adjust the photo-treatment protocol. Controller 122 also interfaces with footswitch 130 for remotely turning on or off laser 124 and/or cooling unit 110. Additionally, door interlock 132 can be used as an additional safety measure such that, when the door to the treatment room is ajar, door interlock 132 detects the condition and instructs controller 122 to not allow photo-treatment unit 120, or at least laser 124, to operate. Furthermore, emergency on/off switch 134 can be provided to quickly shut down photo-thermal targeted treatment system 100 in case of an emergency. In another modification, additional photodiodes or other sensors can be added to monitor the power level of the energy emitted from laser 124.
Continuing to refer to
Additionally, photo-treatment unit 120 may further include an audio out circuitry 150 for providing an audio output, such as a skin surface temperature reading as recorded at temperature monitoring unit 128. Audio out circuitry 150 provides a signal to, for example, an ear piece 152 through a wired or wireless connection such that the practitioner using the system can listen to the audio output. Ear piece 152 can be replaced, for instance, by a speaker system or other audio communication means. Audio out circuitry can also convey other information such as the status of the photo-treatment unit, any emergency warnings, or other messages to be conveyed to the user of photo-thermal targeted treatment system 100.
Many laser treatment systems rely on a thermal balance provided by thermal energy input via a laser and thermal energy removal via a cooling mechanism. In order to optimize both the safety and efficacy of such laser treatment systems, it would be desirable to have close control over both sides of this thermal balance equation. While the thermal energy input via the laser is relatively simple to measure and adjust via a closed-loop control system, cooling systems more challenging to control. The amount of thermal energy removal provided by a cooling mechanism, particularly air cooling systems, is difficult to quantify. Ideally, a measurement of the heat transfer (i.e., how much heat in W or J is being removed) provided by the cooling mechanism would be desirable.
System Fluence Metric T_Rise/W
Skin surface temperature measurements of the treatment area during application of the treatment protocol can assist in the prevention of patient injury while improving efficacy of the treatment. However, in evaluating the actual performance of the photo-thermal targeted treatment system in use, it is difficult to separate the thermal effects of cooling and fluence. Especially given the interwoven nature of the cooling and heating mechanisms in a photo-thermal targeted treatment system such as shown in
Rather than directly using the raw skin surface measurements, we recognize herein that the rise temperature T_rise, the epidermal temperature rise upon delivery of a treatment pulse, per watt (W) of energy delivered by the treatment pulse (i.e., T_rise/W) provides a suitable metric for fluence or a particular photo-thermal targeted treatment system, irrespective of the heat transfer coefficient.
Estimating System Heat Transfer Coefficient
Referring now to
The resulting changes in skin surface temperature are shown in graph 200. As shown in
The nadir-peak combinations can be alternatively shown as in
T_rise=T_peak−T_nadir [Eq. 1]
For the first seven pulses, the T_rise values are summarized in Table 1 below, where the average of the T_rise(° C.) values for all pulses is considered T_rise (%)=100%:
It can be seen in Table 1 that T_rise is, to first order, independent of T_nadir and T_peak values and the derivation below will show that it is also virtually independent of any Heat Extraction, HE, effects. The HE can be characterized as a factor of the system Heat Transfer Coefficient (HTC), average skin surface temperature T_ave, and the air temperature T_air:
HE˜HTC*(T_ave−T_air) [Eq. 2]
Specifically related to the treatment system evaluated in
T_ave1=(T_peak+T_nadir)/2=(20.78° C.+0.32° C.)/2=10.55° C. [Eq. 3]
Cooling (heat extraction) is proportional to the heat transfer coefficient:
HE1=HTC*(10.55° C.−(−21° C.))=HTC*31.55° C. [Eq. 4]
Similarly for pulse 7 at t=12.6 seconds:
Despite there being a difference of 52.02° C./31.55° C.=65% in cooling between pulse 7 and pulse 1, T_rise for pulse 1 and pulse 7 differs by less than 1%. Thus, we assert that T_rise is for practical purposes independent of HTC.
In the above calculations, it is assumed that the cooling (i.e., heat extraction) is dominated by the cooling air provided to the skin surface, not diffusion into other parts of the tissue. We also assume the pulse itself is short, e.g., 150 milliseconds, limiting the effect of any diffusion from the skin tissue at the treatment site. Additionally, we assume the average temperature during the pulse is a close approximation of the actual temperature behavior. While we are aware the actual temperature behavior is an exponential decay, using the average value is consistent across the various pulses for the purposes of the present calculations.
Thought of in another way, in
P_laser=P_cooling [Eq. 7]
Similarly, the laser energy of the treatment pulse is delivered during the 150 ms pulse duration, and the cooling energy is delivered by the cooling mechanism in a uniform manner over the full period of 2.1 seconds. That is, over a full period of 2.1 seconds, including the applied pulse duration plus the period between treatment pulse applications, the laser energy would be equal to the cooling energy provided by the cooling mechanism:
E_laser=E_cooling [Eq. 8]
Thus, the cooling energy would only affect the treatment pulse only during the treatment pulse period of 150 ms, thus any change in cooling would only affect the pulse by a ratio of 150 ms/2.1 s=0.075 (i.e., 7.5%). Therefore, to a first order, moderate variations in HTC would only minimally affect the energy delivered in a treatment pulse and, thereby, variation in HTC would not affect T_rise to an appreciable degree.
One aspect of the treatment protocol which should be taken into account is the laser spot size, as the temperature sampling area to measure T_rise is sampled over a known area size. For instance, in using an IR camera to measure skin surface temperature, the temperature of a skin surface area corresponding to an area of 3.2 mm by 3.2 mm is measured, in accordance with an embodiment. Thus, T_rise/W is an appropriate metric for laser fluence as the area over which the skin surface temperature is measured is known, and any variance in the actual laser spot size and shape from system to system is irrelevant.
Relative Heat Transfer Coefficient h′
In order to more accurately compare and predict the performance of different systems, it would be desirable to have an understanding of the Heat Extraction, HE, characteristic of each system. While the actual HE value for each system is difficult to ascertain, a relative heat transfer coefficient, h′, can be calculated as a measure of the Heat Transfer Coefficient (HTC) for a single system. While the relative HTC (h′) does not allow comparison of HTC values between different systems, because it does not take into account variations in spot sizes and shapes delivered at the treatment area, h′ does allow the user to evaluate the performance of a given photo-thermal targeted treatment system with a known spot size and shape, especially over time. In other words, even without precise knowledge of the laser spot size and shape, since the way the laser deposits its energy is essentially constant with each laser pulse, h′ is a valid measurement for evaluating a given treatment system.
The value of the relative HTC h′ for a given system can be derived using the following method, for example. As shown in Eqs. 7 and 8, at thermal equilibrium, it is recognized that the heating power provided by the laser and the cooling power provided by the cooling mechanism are in balance such that the laser input power is equal to the cooling power. Similarly, over a full period of 2.1 seconds, the energy provided by the laser is equal to the energy provided by the cooling mechanism. Thus, we can conclude that, at thermal equilibrium,
E_cooling˜HTC*Temperature differential=HTC*∫[Tskin−Tair] [Eq. 9]
where the integral is over the time period of one pulse. As above, the integral over the skin temperature Tskin is approximated by the average temperature of the peak and nadir temperatures for a given pulse. For example, for the pulse around 35 s in
(T_peak+T_nadir)/2=(43.78° C.+23.74° C.)/2=33.76° C. [Eq. 10]
Consequently, cooling energy can be calculated:
E_cooling=HTC*Area_cooling*full period*(T_skin−T_air) [Eq. 11]
where T_air is the measured temperature of the cooling air in the case of an air-cooled system.
In the illustrated example, the laser energy is E_laser=23 W*150 ms over an unknown yet constant spot area, and T_air is −21° C. We assume the cooling area is much larger than the laser spot, and the cooling provided by the cooling mechanism is uniform. Thus, at thermal equilibrium:
E_laser=E_cooling [Eq. 12]
→23 W*0.15 s=HTC*Area_cooling*2.1 s*(33.76° C.−(−21° C.)) [Eq. 13]
Solving for HTC*Area_cooling, we find:
HTC*Area_cooling=0.030=h′ [Eq. 14]
The relative HTC, h′, is a valuable metric in evaluating the performance of the photo-thermal targeted treatment system. For instance, h′ provides a direct measurement to infer the HTC for a particular system, thus allowing the application of closed-loop control for in situ adjustment of the cooling mechanism. As an example, a closed-loop control system can be implemented to control the operations of the cooling mechanism in order to compensate for any system performance variations due to environmental factors (e.g., temperature, humidity, altitude) and system factors (e.g., restriction of intake air due to frosting). Similarly, any other changes in the cooling mechanism performance can be quantified using h′.
Heat Extraction Rate Control
A First Alternate Approach to Estimating System Heat Transfer Coefficient
The heat transfer can be somewhat estimated by measuring the temperature of the cooling air (e.g., using a thermistor) and the air velocity at the air outlet of the cooling mechanism (e.g., using a heated pitot tube). However, variations in environmental factors (e.g., altitude, ambient temperature, ambient humidity, patient temperature at the treatment area) often lead to inaccuracies.
Newton's law of cooling formula is
T=T_equilibrium+(T_initial−T_equilibrium)*exp(−k*t) [Eq. 15]
where:
How quickly the object cools down depends on two factors. The first factor is the difference in the temperatures between the object (e.g., skin tissue) and the cooling medium (e.g., cold air applied to the skin). The larger the difference, the quicker the cooling. The second factor is the cooling coefficient k, which depends on the mechanism of the cooling and the amount of heat that is exchanged. The cooling coefficient can be expressed as:
k=h*A/C, [Eq. 16]
where:
We recognize herein that the fall time of the skin surface temperature from the onset of the pre-cooling period (e.g., as shown between time −15 to 0 second in
T=T_equilibrium+(T_initial−T_equilibrium)*exp(−k*t) [Eq. 17]
From the curve fit of Eq. 17, shown as a thick dashed line 410 in
A Second Alternate Approach to Estimating System Heat Transfer Coefficient
Using the same equations as above, but using the time interval between the pulses as opposed to the pre-cooling period, we can again estimate k, the cooling coefficient. A graph 500 in
Knowledge regarding h′ and k k, since both are direct metric of the Heat Extraction for a given photo-thermal targeted treatment system, can be directly used as an input for a closed-loop control of the cooling system. For instance, any changes in h′ can be used as an indicator of system changes, including cooling, over time. Thus, the information so derived above based on specific measurements and parameters of the particular photo-thermal treatment system and its use conditions can help protect the safety of the patient in ways heretofore unavailable to the system user. For example, the information so derived above can be used to adjust the cooling setting of cooling unit 110, power, pulse width, duty cycle or other operating parameters of laser 124, and other settings of system 100 as shown in
The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention.
Accordingly, many different embodiments stem from the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. As such, the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination.
For example, embodiments such as the below are contemplated:
1. A method for operating a light source within a photo-thermal targeted treatment system for targeting a chromophore embedded within a medium. The method includes: 1) applying a treatment protocol to a skin surface; 2) measuring a skin surface temperature while applying the treatment protocol; 3) inferring information regarding a heat transfer provided by the photo-thermal targeted treatment system; and 4) adjusting the light source and the treatment protocol in accordance with the information regarding the heat transfer.
2. The method of Item 1, wherein the information regarding the heat transfer is a system fluence metric.
3. The method of Item 1, wherein the information regarding the heat transfer is a relative heat transfer coefficient.
4. The method of Item 1, wherein the information regarding the heat transfer is a heat extraction rate.
In the specification, there have been disclosed embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the claimed invention
| Number | Date | Country | |
|---|---|---|---|
| 63021210 | May 2020 | US |
