Positioning of electrode elements on the subject's body to provide a strong AC electric field (e.g., a TT field) without overheating

Abstract

Increasing the intensity of a tumor treating field (TT field) or other alternating current electric field treatment typically increases the effectiveness of the treatment. This application discloses methods for determining where to place electrode elements on a subject's body so that higher currents (generating higher intensity fields) flow through the electrode elements without overheating the electrode elements during a treatment session. The location selection is based on the fact that some areas on the surface of a given subject's body are better at removing heat from the electrode elements compared to other areas that may be only a short distance away. Additionally, the methods disclosed herein rely on placing electrode elements in areas that are better at removing heat from the electrode elements.

Description

[Technical Field]

[0001] The present application relates to the placement of electrode elements on a subject's body to provide a strong alternating electric field (eg, a TT field) without overheating. This application claims the benefit of U.S. Provisional Application No. 63 / 435,732, filed December 28, 2022, which is incorporated herein by reference in its entirety. [Background technology]

[0002] Tumor Treating Field (TT Field) therapy is a proven approach to treating tumors using alternating current electric fields at frequencies between 50 kHz and 1 MHz (e.g., 50 kHz to 1 MHz, 50 to 500 kHz, 75 to 300 kHz, or 150 to 250 kHz). Figure 1 shows the prior art Optune® system, which delivers TT fields to a patient via four transducer arrays 10 placed on the patient's skin near the tumor. The transducer arrays 10 are arranged in two pairs: one pair of transducer arrays 10L and 10R is placed on the left and right sides of the tumor, and the other pair of transducer arrays 10A and 10P is placed in front and behind the tumor. Each transducer array is connected to an AC signal generator 20 via a multi-wire cable. The AC signal generator (a) sends an AC current to the anterior / posterior (A / P) pair of the transducer array for 1 second to induce an electric field in the tumor in a first direction, and then (b) sends an AC current to the left / right (L / R) pair of the array for 1 second to induce an electric field in the tumor in a second direction, and then steps (a) and (b) are repeated throughout the treatment. Each transducer array contains multiple (e.g., between 9 and 30) electrode elements.

[0003] Alternating current electric fields can also be used to treat conditions other than tumors. For example, as described in U.S. Patent No. 10,967,167 (incorporated herein by reference in its entirety), alternating current electric fields can be used to increase the permeability of the blood-brain barrier, allowing, for example, chemotherapy drugs to reach the brain.

[0004] FIG. 2 shows a more detailed view of a set of four transducer arrays 10, with the individual electrode elements comprising each transducer array visible. In this example, each of the transducer arrays 10 includes nine circular electrode elements supported by a self-adhesive substrate. In particular, while FIG. 2 shows each of the four transducer arrays 10 positioned at a specific location on a patient's head, the exact placement of each of the transducer arrays 10 during use can vary by a few centimeters upward, downward, rightward, leftward, forward, and / or backward relative to the position shown in FIG. 2. Additionally, one or more of the transducer arrays 10 can be rotated (e.g., by 0-30° relative to the position shown in FIG. 2) to a different position (e.g., the position shown in FIG. 3 for the anterior transducer array 10A). Summary of the Invention [Problem to be solved by the invention]

[0005] Increasing the AC electric field strength typically increases the effectiveness of the treatment. Existing software (e.g., Novotal™) simulates the strength of the TT field within the subject's head and then accurately recommends where to place each of the transducer arrays 10 on the subject's head for a particular patient. This software operates by using the electrical properties of voxels within the subject's head to calculate the field strength in the relevant target region (e.g., within a tumor) when applying the TT field using different transducer array placements. The software then recommends transducer placements that maximize the field strength within the target region. Notably, while accepting the recommended positions from the field simulation software almost always improves the strength of the TT field reaching the target region, in many situations, the field strength improves only by a small amount (e.g., about 5-10%). [Means for solving the problem]

[0006] One aspect of the present invention relates to a first method for determining where to place electrode elements on a subject's body to allow higher current to flow through the electrode elements during a treatment session without overheating the electrode elements, the first method including identifying which areas of the subject's body where the electrode elements may be placed in connection with the treatment session have a relatively high heat dissipation capability adjacent the subject's skin, and selecting locations for the electrode elements based at least in part on the identification.

[0007] In some examples of the first method, the verifying includes obtaining a thermal image of the portion of the subject's body.

[0008] In some examples of the first method, the verifying includes mapping a surface impedance or surface conductance of the portion of the subject's body. Optionally, in these examples, the mapping includes making impedance or conductance measurements within 5 mm of the surface of the subject's skin.

[0009] In some examples of the first method, the verifying includes obtaining a thermal image of the portion of the subject's body and mapping a surface impedance or surface conductance of the portion of the subject's body. In some examples of the first method, selecting the locations of the plurality of electrode elements is also based on multiple field strength simulations.

[0010] Another aspect of the invention relates to a second method for determining where to place electrode elements on a subject's body to allow higher current to flow through the electrode elements during a treatment session without overheating the electrode elements, the second method comprising: acquiring a thermal image of a portion of the subject's body where the electrode elements may be placed in connection with the treatment session; and selecting locations for the electrode elements based at least in part on the thermal image.

[0011] In some examples of the second method, selecting the locations of the plurality of electrode elements is also based on electrical properties of a volume within the subject's body. Optionally, in these embodiments, the electrical properties include impedance or conductance measurements within 5 mm of the surface of the skin of the subject's body.

[0012] In some examples of the second method, the acquiring occurs while the portion of the subject's body is located in an environment having an ambient temperature less than 25° C. In some examples of the second method, the selecting includes selecting positions where a majority of the electrode elements overlie a portion of the subject's body corresponding to the warmest 70% of the thermal image. In some examples of the second method, the selecting includes selecting positions where none of the electrode elements overlie a portion of the subject's body corresponding to the coolest 20% of the thermal image.

[0013] In some examples of the second method, the selecting includes selecting positions where a majority of the electrode elements overlie a portion of the subject's body corresponding to the warmest 70% of the thermal image, or where no portion of the electrode elements overlie a portion of the subject's body corresponding to the coolest 20% of the thermal image. In some examples of the second method, the selecting includes selecting positions that maximize the average temperature of all regions of the thermal image under the plurality of electrode elements.

[0014] In some examples of the second method, the acquiring occurs while the portion of the subject's body is located in an environment having an ambient temperature greater than 50°C.

[0015] In some examples of the second method, the acquiring occurs while the portion of the subject's body is located in an environment having an ambient temperature greater than 45° C. Optionally, in these examples, the selecting includes selecting positions where a majority of the electrode elements overlie a portion of the subject's body corresponding to the coolest 70% of the thermal image, or selecting positions where no portion of the electrode elements overlie a portion of the subject's body corresponding to the warmest 20% of the thermal image.

[0016] In some examples of the second method, the selecting includes selecting a position where none of the electrode elements overlap a portion of the subject's body corresponding to the coldest 70% of the thermal image. In some examples of the second method, the selecting includes selecting a position where none of the electrode elements overlap a portion of the subject's body corresponding to the coldest 20% of the thermal image.

[0017] In some examples of the second method, the selecting includes selecting locations that minimize an average temperature of all regions of the thermal image underlying the plurality of electrode elements.

[0018] Some examples of the second method further include positioning the plurality of electrode elements at the selected locations. Optionally, these examples further include applying an alternating current electric field to the subject's body at a frequency between 50 kHz and 1 MHz using the positioned plurality of electrode elements.

[0019] Some examples of the second method further include placing the plurality of electrode elements at the selected locations and applying an AC current to the body of the subject at a frequency between 50 kHz and 1 MHz using the placed plurality of electrode elements.

[0020] In some examples of the second method, selecting the locations of the plurality of electrode elements is also based on a plurality of electric field strength simulations.

[0021] Another aspect of the invention relates to a second method for determining where to place electrode elements on a subject's body to allow higher current to flow through the electrode elements during a treatment session without overheating the electrode elements, the third method comprising mapping a surface impedance or surface conductance for a portion of the subject's body where the electrode elements may be placed in connection with the treatment session, and selecting locations for the electrode elements based at least in part on the mapped surface impedance or surface conductance.

[0022] In some examples of the third method, selecting locations of the plurality of electrode elements is also based on a thermal image of the portion of the subject's body.

[0023] In some examples of the third method, the mapping includes placing at least one array of electrode elements on the portion of the subject's body, measuring current and / or voltage between each pair of the electrode elements in the at least one array, and generating a surface impedance map or a surface conductance map based on the measured current and / or voltage.

[0024] In some examples of the third method, the mapping includes performing impedance tomography of a volume within the subject's body. Optionally, in these examples, the mapping includes performing impedance or conductance measurements within 5 mm of the surface of the skin of the subject's body.

[0025] In some examples of the third method, the selecting includes selecting positions where a majority of the electrode elements overlap a portion of the subject's body corresponding to the lowest 70% of the impedance of the mapping. In some examples of the third method, the selecting includes selecting positions where none of the electrode elements overlap a portion of the subject's body corresponding to the highest 20% of the impedance of the mapping.

[0026] In some examples of the third method, the selecting includes selecting a position where a majority of the electrode element overlaps a portion of the subject's body corresponding to the lowest 70% of the impedance of the mapping, or selecting a position where no portion of the electrode element overlaps a portion of the subject's body corresponding to the highest 20% of the impedance of the mapping.

[0027] In some examples of the third method, the selecting includes selecting locations that minimize an average impedance of all regions of the subject's body underlying the plurality of electrode elements.

[0028] Some examples of the third method further include positioning the plurality of electrode elements at the selected locations. Optionally, these examples further include applying an alternating current electric field to the subject's body at a frequency between 50 kHz and 1 MHz using the positioned plurality of electrode elements.

[0029] Some examples of the second method further include placing the plurality of electrode elements at the selected locations and applying an AC current to the body of the subject at a frequency between 50 kHz and 1 MHz using the placed plurality of electrode elements.

[0030] In some examples of the third method, selecting the locations of the electrode elements is also based on electric field strength simulations. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a block diagram of a prior art Optune® system for delivering a TT field. [Figure 2] 1 shows a set of transducer arrays that can be used to deliver TT fields, positioned at respective locations on the subject's head. [Figure 3] The same set of transducer arrays is shown placed at different locations on the subject's head. [Figure 4]1 shows a schematic diagram of a transducer array for delivering a TT field to a subject's body, and a thermal image of a portion of the subject's body on which the transducer array can be positioned. [Figure 5] 1 is a histogram showing the coldest 20% and warmest 70% of the total area of ​​an exemplary data set. [Figure 6] Three possible arrangements of the transducer array in FIG. 4 are shown, each showing where each of the electrode elements E1-E9 is located on portion 50 for each of three positions A, B, C. DETAILED DESCRIPTION OF THE INVENTION

[0032] Various embodiments will now be described in detail with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0033] This application describes a new approach for determining where to place each of the transducer arrays on a given subject's head (or other body part), which relies on local variations in the ability of a given subject's body to remove heat from the electrode elements on the transducer array.

[0034] When applying a TT field to a subject's body (e.g., using Optune®), the amplitude of the AC current that can be applied to a given subject's body is typically limited by thermal considerations. More specifically, Optune® transducer arrays heat up as the amplitude of the AC current applied to their transducers increases, eventually reaching a safe temperature threshold (e.g., 39°C). And that temperature threshold has traditionally been the limiting factor that prevents Optune® from operating at higher amplitudes.

[0035] The inventors have recognized that some areas on the surface of a given subject's body are better at removing heat (i.e., dissipating heat) from the transducer array electrode elements compared to other areas that may be only a short distance (e.g., 5 cm) away. Additionally, these differences between the heat dissipation capabilities of different areas of a subject's body can allow for a dramatic increase in the amplitude of AC current that can be applied to a given subject's body. This is because electrode elements placed over areas that are more effective at removing heat can have a higher current without reaching a safe temperature threshold.

[0036] Taking this phenomenon into account, it is possible to increase the amplitude of the TT field that can be delivered to a given subject by shifting the position of the transducer array so that all (or at least the majority) of the electrode elements are positioned over areas that are more effective at removing heat, and only a few (or none) of the electrodes are positioned over areas that are less effective at removing heat. In particular, when the electrode elements are positioned as described above, the heat dissipation provided by the subject's body can facilitate an increase in current flow of as much as 20% without overheating (compared to when the electrode elements are positioned over areas that are less effective at removing heat).

[0037] The use of the former approach can provide better results than the latter approach, since the approximately 20% increase in current provided by this heat dissipation-based approach can exceed the increase in current provided by the prior art approach based on field strength simulation, which outweighs the 5-10% loss in field strength that results from placing the transducer array in a suboptimal position (from a field strength simulation perspective).

[0038] Optionally, the improvement provided by the placement recommendation based on the heat dissipation characteristics of different regions of the subject's skin can be compared to the improvement provided by prior art field simulation software. If the increase in current provided by placing the transducer array based on the heat dissipation characteristics of different regions of the subject's skin exceeds the increase in field strength provided by prior art field simulation software, the former approach should be implemented. On the other hand, if the increase in current provided by placing the transducer array based on the heat dissipation characteristics of different regions of the subject's skin is less than the increase in field strength provided by prior art field simulation software, the latter approach should be implemented. Alternatively, a hybrid approach that considers both heat dissipation characteristics and field simulation can be implemented.

[0039] Without being limited to this theory, the inventors believe that one factor affecting the ability of various regions to remove heat from the electrode elements is the difference in the amount of blood flowing adjacent to the surface of those regions (i.e., within a few millimeters of the surface of those regions). Regions with higher blood flow are more effective at removing heat from electrode elements placed in those regions. Therefore, by determining which regions have relatively high blood flow adjacent to the subject's skin, it is also possible to identify regions that are more effective at removing heat.

[0040] One suitable approach for identifying such regions relies on thermal imaging to identify which regions of a subject's body have relatively high blood flow adjacent to the subject's skin. The first step in this approach is to place the subject in an environment having an ambient temperature below the subject's body temperature (e.g., in a room below 35°C, below 30°C, below 25°C, below 22°C, or below 20°C). Next, a thermal image of the portion of the subject's body where the transducer array is located is acquired (e.g., using an infrared camera). Because the subject's blood is warmer than the ambient temperature, regions of the subject's body with higher blood flow will appear warmer in the thermal image, and regions of the subject's body with lower blood flow will appear cooler in the thermal image. The locations of the electrode elements are then selected at least in part based on the thermal image (e.g., by placing most or all of the electrode elements on the warmer regions and only a few (or none) of the electrode elements on the cooler regions).

[0041] Regions of a subject's body having relatively high blood flow adjacent to the subject's skin can also be detected using reverse thermal imaging. In this example, the subject is placed in an environment having an ambient temperature significantly higher than the subject's body temperature (e.g., greater than 40°C, greater than 45°C, greater than 50°C, greater than 55°C, or greater than 60°C, or in a room under a heating blanket, sauna, etc.). A thermal image of the portion of the subject's body where the transducer array is placed is then acquired (e.g., using an infrared camera). Because the subject's blood is cooler than the ambient temperature, regions of the subject's body having higher blood flow will appear cooler in the thermal image, and regions of the subject's body having lower blood flow will appear warmer in the thermal image. The locations of the electrode elements are then selected at least in part based on the thermal image (e.g., by placing most or all of the electrode elements on the cooler regions and only a few (or none) of the electrode elements on the warmer regions).

[0042] Another suitable approach relies on impedance tomography to identify which regions of the subject's body adjacent to the subject's skin may have a relatively good heat dissipation capability for heat generated in or near the electrodes during TT field treatment. This approach uses impedance tomography to determine the impedance of voxels located adjacent to the surface of the subject's body (e.g., at a depth of <1 mm, <2 mm, <3 mm, <4 mm, or <5 mm into the subject's body, e.g., 0.5-5 mm, 1-5 mm, 2-5 mm, 3-5 mm, or 4-5 mm from the surface of the subject's body). Notably, the impedance measurement does not need to be performed while TT field treatment is being administered. Any conventional approach for performing impedance tomography may be used. Regions of the body that exhibit low impedance paths close to the surface of the subject's body have lower impedance (and higher conductance) and better heat dissipation capabilities for heat from TT field treatment. The locations of the electrode elements are then selected based at least in part on the impedance (or conductance) adjacent to the surface of the subject's body (e.g., by placing most or all of the electrode elements on low impedance regions and only a few (or none) of the electrode elements on higher impedance regions).

[0043] Yet another suitable approach relies on an array of electrode elements to identify which regions of the subject's body may have a relatively good heat dissipation capability adjacent to the subject's skin for heat generated in or near the electrodes during TT field treatment. This approach uses a set of electrodes to measure the surface impedance (or surface conductance) of the subject's body. In these embodiments, an array of electrode elements is placed on the subject's body at the location where the transducer array will be placed. The electrodes may be, for example, standard electrocardiogram electrodes, and are optionally attached to a flexible substrate configured to fit a particular body part. The current and / or voltage between each pair of electrode elements in the array is then measured, and a map of surface impedance (or surface conductance) is generated based on the measured current and / or voltage. Again, regions of the subject's body that exhibit low impedance paths close to the surface of the body have lower impedance (and higher conductance) and better heat dissipation capability for heat from TT field treatment. The locations of the electrode elements are then selected based at least in part on the impedance (or conductance) adjacent to the surface of the subject's body (e.g., by placing most or all of the electrode elements on low impedance regions and only a few (or none) of the electrode elements on higher impedance regions).

[0044] Either of these approaches can be used to determine where to place the electrode elements on the subject's body so that higher currents flow through the electrode elements without overheating them during a TT field therapy session.

[0045] Figures 4-6 show an example of how the first of these approaches (i.e., the thermal imaging approach) can be used to identify which areas of a subject's body have relatively high blood flow adjacent to the subject's skin, and how this information can be used to determine where to place electrode elements on the subject's body to allow higher currents to flow through the electrode elements.

[0046] The left half of Figure 4 shows an example of a transducer array 10 in which electrode elements E1-E9 may be arranged in a particular pattern. The right half of Figure 4 is an exemplary schematic diagram of a thermal image of a subject's body part 50 (e.g., a thermal image of the left side of a subject's head being treated using a TT field) in which multiple electrode elements may be arranged in connection with a treatment session. In this example, region t1 is the coolest region in the thermal image, region t2 is warmer than region t1, region t3 is warmer than region t2, and region t4 is warmer than region t3 (making region t4 the warmest region).

[0047] Based on the relative temperatures of regions t1-t4, we conclude that region t1 has the lowest blood flow, region t2 has higher blood flow than region t1, region t3 has higher blood flow than region t2, and region t4 has the highest blood flow.

[0048] In this example (not drawn to scale), the two t1 regions collectively occupy 20% of the total area of ​​portion 50, t2 region occupies 10% of the total area, t3 region occupies 50% of the total area, and t4 region occupies 20% of the total area. This means that region t1 corresponds to the coldest 20% of the total area, and regions t3 and t4 collectively correspond to the warmest 70% of the total area.

[0049] 5 is an example histogram to clarify what is meant by the coolest 20% of the total area and the warmest 70% of the total area. This histogram shows an example in which a portion of a subject's body on which multiple electrode elements are placed is divided into 50 equal regions, and the temperature of each of these regions is measured. In this example, three of the regions have a temperature of 30°C, four of the regions have a temperature of 30.5°C, three of the regions have a temperature of 31°C, five of the regions have a temperature of 31.5°C, seven of the regions have a temperature of 32°C, ten of the regions have a temperature of 32.5°C, ten of the regions have a temperature of 33°C, five of the regions have a temperature of 33.5°C, and three of the regions have a temperature of 34°C. Thus, in this example, the ten regions below 31°C correspond to the coolest 20% of the total area, and the 35 regions above 32°C correspond to the warmest 70% of the total area.

[0050] Because areas with higher blood flow are more efficient at removing heat from the electrode elements on the transducer array, it is best to place as many electrode elements as possible over areas with higher blood flow and as few elements as possible over areas with lower blood flow. One example of how to achieve these two goals is to position the transducer array in a location that maximizes the average temperature of all areas of the thermal image under the electrode elements.

[0051] Another example of how to achieve these two goals is to position the transducer array according to two guidelines: (a) the majority of the electrode elements should overlap the portion of the subject's body that corresponds to the warmest 70% of the thermal image (i.e., regions t3 and t4 in FIG. 4 ), and (b) the majority of the electrode elements should overlap the portion of the subject's body that corresponds to the coolest 20% of the thermal image (i.e., region t1 in FIG. 4 ). Ideally, choosing a layout that meets both guidelines (a) and (b) may not be possible in certain situations (depending on the layout of the thermal image). In these situations, following only one of the guidelines is sufficient.

[0052] The transducer array 10 shown in Figure 4 can be positioned anywhere on the portion 50, and Figure 6 shows three possible placements of the transducer array on the portion 50. Here, the inventors have considered where each of the electrode elements E1-E9 would be located relative to each of the three positions A, B, and C shown in Figure 6, taking into account guidelines (a) and (b).

[0053] When the transducer array 10 is attached to the subject's body at location A, the majority of electrode elements E1-E9 overlap regions T3 and T4, which satisfies guideline (a). However, guideline (b) is not satisfied because electrode element E2 overlaps region t1 (corresponding to the coldest 20% of the thermal image).

[0054] When transducer array 10 is attached to the subject's body at location B, the majority of electrode elements E1-E9 overlap regions t3 and t4, which satisfies guideline (a), and none of the electrode elements overlap region t1, which satisfies guideline (b).

[0055] Finally, when the transducer array 10 is attached to the subject's body at location C, electrode elements E3, E5, E6, E8, and E9 are not located in region t3 / t4, which means that guideline (a) is not met. Also, guideline (b) is not met because electrode element E9 is located in region t1 (corresponding to the coldest 20% of the thermal image).

[0056] Based on the previous few paragraphs, we can see that the only position that satisfies both guideline (a) and guideline (b) is position B. Therefore, we can conclude that position B is superior to positions A and C. After reaching this conclusion, the transducer array is placed on the subject's body at whichever position is found to be superior. Thus, the electrode elements are over the selected positions.

[0057] Another approach is to place as many electrode elements as possible over areas with higher blood flow and / or as few electrode elements as possible over areas with lower blood flow. This can be achieved by selecting locations where the majority of the electrode elements (i.e., 50% of the total collective area of ​​the electrode elements) overlap the portion of the subject's body corresponding to the warmest 70% of the thermal image, or by selecting locations where no electrode elements overlap the portion of the subject's body corresponding to the coolest 20% of the thermal image. Yet another approach is to select locations where (a) the majority of the electrode elements overlap the portion of the subject's body corresponding to the warmest 70% of the thermal image, and (b) no electrode elements overlap the portion of the subject's body corresponding to the coolest 20% of the thermal image.

[0058] After the transducer array is positioned on the subject's body, the transducer array can be used to apply an AC electric field to the subject's body at a frequency between 50 kHz and 1 MHz (e.g., 50 kHz to 1 MHz, 50 to 500 kHz, 75 to 300 kHz, or 150 to 250 kHz). This can be achieved by applying AC current to transducer arrays positioned on either side of the target region at the corresponding frequency.

[0059] It should be noted that the values ​​in the above guidelines (a) and (b) are merely exemplary and may be modified (e.g., based on the nature of the thermal image for a given patient). For example, for guideline (a), the warmest 70% of the thermal image may be replaced with the warmest 50%, 65%, 75%, or 80%. And, for guideline (b), the coolest 20% of the thermal image may be replaced with the coolest 5%, 10%, 15%, or 25%.

[0060] Of course, if the subject is placed in an environment with an ambient temperature significantly higher than the subject's body temperature (e.g., greater than 40°C, greater than 45°C, greater than 50°C, greater than 55°C, or greater than 60°C, or the temperature under a heating blanket), the roles of the warmest and coolest regions are reversed. In this case, the transducer array can be positioned to minimize the average temperature of all regions of the thermal image under the multiple electrode elements. Alternatively, the transducer array can be positioned such that (i) the majority of the electrode elements should overlap the portion of the subject's body corresponding to the coldest 70% of the thermal image, and (ii) no portion of the electrode elements should overlap the portion of the subject's body corresponding to the warmest 20% of the thermal image. While selecting a layout that satisfies both conditions (i) and (ii) is ideal, in certain situations this may not be possible (depending on the layout of the thermal image). In these situations, satisfying only one of the conditions is sufficient.

[0061] Another approach is to place as many of the electrode elements as possible over areas with higher blood flow and / or as few of the electrode elements as possible over areas with lower blood flow. In a "hot room" embodiment, this can be achieved by selecting locations where the majority of the electrode elements (i.e., 50% of the total collective area of ​​the electrode elements) overlap the portion of the subject's body corresponding to the coolest 70% of the thermal image, or by selecting locations where no portion of the electrode elements overlaps the portion of the subject's body corresponding to the warmest 20% of the thermal image. Yet another approach is to select locations where (a) the majority of the electrode elements overlap the portion of the subject's body corresponding to the coolest 70% of the thermal image, and (b) no portion of the electrode elements overlap the portion of the subject's body corresponding to the warmest 20% of the thermal image.

[0062] It should again be noted that the values ​​in this example are merely illustrative and may be changed (e.g., based on the nature of the thermal image for a given patient). For example, for condition (i), the 70% coolest portion of the thermal image may be replaced with 50%, 65%, 75%, or 80% of the coolest portion. And for condition (ii), the 20% warmest portion of the thermal image may be replaced with 5%, 10%, 15%, or 25% of the warmest portion.

[0063] 4-6 illustrate how a thermal imaging approach can be used to identify which areas of a subject's body have relatively high blood flow adjacent to the subject's skin, and how this information can be used to determine where to place electrode elements on the subject's body to allow higher currents to flow through the electrode elements. However, any of the other approaches described herein for identifying which areas of a subject's body have high heat dissipation capabilities adjacent to the subject's skin may also be used.

[0064] In one example, an approach based on impedance tomography is used, in which, instead of generating thermal images as described above in connection with Figures 4-6 and using the temperature of each region as a proxy for blood flow, impedance tomography is used to generate a map of surface impedance, and the impedance of each region is used as a proxy for heat dissipation capacity (the lower the impedance, the greater the heat dissipation capacity).

[0065] Another example uses an approach based on impedance measurements using an array of electrodes (e.g., electrodes similar to ECG electrodes), in which, instead of generating a thermal image as described above in connection with Figures 4-6 and using the temperature of each region as a proxy for blood flow, a map of surface impedance is generated by applying a current and / or voltage to the array of electrodes and measuring the impedance of each region, which is used as a proxy for the region's ability to dissipate heat (the lower the impedance, the better the ability to dissipate heat).

[0066] As explained above, areas with higher heat dissipation capacity are more efficient at removing heat from the electrode elements on the transducer array, so it is best to place as many electrode elements as possible on areas with higher heat dissipation capacity and as few elements as possible on areas with lower heat dissipation capacity. When either of these impedance-based approaches is used, these two goals can be achieved by placing the transducer array in a position that minimizes the average impedance of all regions of the impedance map under multiple electrode elements.

[0067] These two goals can also be achieved by positioning the transducer array according to two guidelines: (a) the majority of the electrode elements should overlap the portion of the subject's body corresponding to the lowest 70% of the impedance map, and (b) none of the electrode elements should overlap the portion of the subject's body corresponding to the highest 20% of the impedance map. While it would be ideal to select a layout that complies with both guidelines (a) and (b), in certain situations, this may not be possible (depending on the impedance map layout). In these situations, following only one of the guidelines is sufficient. Another approach is to select a location where the majority of the electrode elements (i.e., 50% of the total collective area of ​​the electrode elements) overlap the portion of the subject's body corresponding to the lowest 70% of the impedance map, or to select a location where none of the electrode elements overlap the portion of the subject's body corresponding to the highest 20% of the impedance map. Yet another approach is to select a region where (a) the majority of the electrode elements overlap the portion of the subject's body corresponding to the lowest 70% of impedances in the impedance map, and (b) no portion of the electrode elements overlaps the portion of the subject's body corresponding to the highest 20% of impedances in the impedance map.

[0068] It should be noted that the numerical values ​​in the above guidelines (a) and (b) are merely exemplary and may be modified (e.g., based on the nature of the impedance map for a given patient). For example, for guideline (a), the lowest 70% of the impedance map's impedance may be replaced with 50%, 65%, 75%, or 80% of the lowest impedance. And for guideline (b), the highest 20% of the impedance map's impedance may be replaced with 5%, 10%, 15%, or 25% of the highest impedance.

[0069] In some embodiments, data obtained using the thermal imaging approach described above can be combined with data obtained using the impedance or conductance measurement approach described above to determine where to place the transducer array.

[0070] After determining where to place the transducer array, the transducer array is placed on the subject's body at whichever location is found to be superior based on the impedance map. The electrode elements are then positioned over the selected location. After the transducer array is positioned on the subject's body, it can be used to apply an AC electric field to the subject's body at a frequency between 50 kHz and 1 MHz (e.g., 50 kHz to 1 MHz, 50 to 500 kHz, 75 to 300 kHz, or 150 to 250 kHz). This can be accomplished by applying AC currents to transducer arrays positioned on either side of the target region at the corresponding frequencies.

[0071] Headings are provided for convenience only and should not be construed as limiting the invention in any way. Embodiments shown under any heading or in any portion of this disclosure may be combined with embodiments shown under the same or other headings or in other portions of this disclosure. Unless otherwise specified herein or clearly contradicted by context, any combination of elements described herein in all its possible variations is encompassed by the invention.

[0072] While the present invention has been disclosed with reference to particular embodiments, numerous modifications, changes, and variations can be made to the described embodiments without departing from the scope of the invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but rather have the full scope defined by the language of the following claims and their equivalents.

Claims

1. 1. A method for determining where to place electrode elements on a subject's body to allow higher current to flow through the electrode elements during a treatment session without overheating the electrode elements, the method comprising: identifying regions of the subject's body on which the plurality of electrode elements may be positioned in association with the treatment session that have a relatively high heat dissipation capacity adjacent the subject's skin; and selecting locations for the plurality of electrode elements based at least in part on the confirmation.

2. The method of claim 1 , wherein the verifying comprises obtaining a thermal image of the portion of the subject's body.

3. The method of claim 1 , wherein the verifying comprises mapping a surface impedance or a surface conductance of the portion of the subject's body.

4. The method of claim 1 , wherein selecting the locations of the plurality of electrode elements is also based on a plurality of electric field strength simulations.

5. 1. A method for determining where to place electrode elements on a subject's body to allow higher current to flow through the electrode elements during a treatment session without overheating the electrode elements, the method comprising: acquiring a thermal image of a portion of the subject's body on which the plurality of electrode elements can be positioned in relation to the treatment session; selecting locations for the plurality of electrode elements based at least in part on the thermal image.

6. 6. The method of claim 5, wherein the acquiring occurs while the portion of the subject's body is located in an environment having an ambient temperature of less than 25°C.

7. 6. The method of claim 5, wherein the selecting comprises selecting positions where a majority of the electrode elements overlap a portion of the subject's body corresponding to the warmest 70% of the thermal image, or where the selecting comprises selecting positions where no portion of the electrode elements overlaps a portion of the subject's body corresponding to the coolest 20% of the thermal image.

8. The method of claim 5 , wherein said selecting comprises selecting locations that maximize an average temperature of all regions of said thermal image underlying said plurality of electrode elements.

9. 6. The method of claim 5, wherein the acquiring occurs while the portion of the subject's body is located in an environment having an ambient temperature greater than 45°C.

10. 10. The method of claim 9, wherein the selecting comprises selecting positions where a majority of the electrode elements overlap a portion of the subject's body corresponding to the coolest 70% of the thermal image, or where the selecting comprises selecting positions where no portion of the electrode elements overlaps a portion of the subject's body corresponding to the warmest 20% of the thermal image.

11. The method of claim 5 , further comprising positioning the plurality of electrode elements at the selected locations.

12. 12. The method of claim 11, further comprising applying an alternating electric field to the subject's body at a frequency between 50 kHz and 1 MHz using the arranged plurality of electrode elements.

13. The method of claim 5 , wherein selecting the locations of the plurality of electrode elements is also based on a plurality of electric field strength simulations.

14. 1. A method for determining where to place electrode elements on a subject's body to allow higher current to flow through the electrode elements during a treatment session without overheating the electrode elements, the method comprising: mapping a surface impedance or surface conductance for a portion of the subject's body on which the plurality of electrode elements can be positioned in relation to the treatment session; selecting locations of the plurality of electrode elements based at least in part on the mapped surface impedance or surface conductance.

15. 15. The method of claim 14, wherein the mapping comprises making impedance or conductance measurements within 5 mm of the surface of the skin of the subject's body.

16. 15. The method of claim 14, wherein the selecting comprises selecting a position where a majority of the electrode elements overlap a portion of the subject's body corresponding to the lowest 70% of the impedance of the mapping, or the selecting comprises selecting a position where no portion of the electrode elements overlaps a portion of the subject's body corresponding to the highest 20% of the impedance of the mapping.

17. 15. The method of claim 14, wherein said selecting comprises selecting locations that minimize an average impedance of all regions of the subject's body underlying the plurality of electrode elements.

18. The method of claim 14 , further comprising positioning the plurality of electrode elements at the selected locations.

19. 20. The method of claim 18, further comprising applying an alternating electric field to the subject's body at a frequency between 50 kHz and 1 MHz using the arranged plurality of electrode elements.

20. The method of claim 14 , wherein selecting the locations of the plurality of electrode elements is also based on a plurality of electric field strength simulations.

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