Patent Description:
Each transducer array is configured as a set of capacitively coupled electrode elements (about <NUM> in diameter) that are interconnected via flex wires. Each electrode element includes a ceramic disk that is sandwiched between a layer of an electrically conductive medical gel and an adhesive tape. When placing the arrays on the patient, the medical gel adheres to the contours of the patient's skin and ensures good electric contact of the device with the body. The adhesive tape holds the entire array in place on the patient as the patient goes about their daily activities.

The amplitude of the alternating current that is delivered via the transducer arrays is controlled so that skin temperature (as measured on the skin below the transducer arrays) does not exceed a safety threshold of <NUM> degrees Celsius. The temperature measurements on the patient's skin are obtained using thermistors placed beneath some of the disks of the transducer arrays. In the existing Optune® system, each array includes <NUM> thermistors, with one thermistor positioned beneath a respective disk in the array. (Note that most arrays include more than <NUM> disks, in which case the temperature measurements are only performed beneath a sub-set of the disks within the array).

The thermistors in each of the four arrays are connected via long wires to an electronic device called the "cable box" where the temperature from all <NUM> thermistors (<NUM> arrays × <NUM> thermistors per array) is measured and analog-to-digital converted into digital values for each thermistor. These measurements are then transmitted from the cable box to the field generator via an additional two wires that facilitate two-way digital serial communications between the cable box and the field generator. The controller in the field generator uses the temperature measurements to control the current to be delivered via each pair of arrays in order to maintain temperatures below <NUM> degrees Celsius on the patient's skin. The current itself is delivered to each array via an additional wire (i.e., one wire for each array) that runs from the field generator through the cable box to the array.

In the existing Optune® system there are four long <NUM>-wire cables (each of which runs between a respective array and the cable box) and one <NUM>-wire spiral cord that runs between the field generator and the cable box. Each of the <NUM>-wire cables has <NUM> wires for carrying signals from the <NUM> thermistors, <NUM> wire for the common of all <NUM> thermistors, plus <NUM> wire for providing the TTFields signal to the array. The <NUM>-wire spiral cord has <NUM> wire for power to the cable box (Vcc), <NUM> wire for ground to the cable box, <NUM> wires for data communication (to send the temperature readings to the field generator), plus <NUM> wires for TTFields signal (i.e., one for each of the four arrays).

<CIT> discloses an electrode for applying electric fields to a patient which includes a plurality of ceramic elements that are designed to be positioned against the patient's skin, and temperature sensors are provided at at least some of the ceramic elements to sense the temperature at the skin beneath the ceramic elements, so that appropriate action can be taken if an overtemperature condition is detected.

<CIT> discloses an electrosurgical return electrode which includes a conductive pad including a patient-contacting surface configured to conduct electrosurgical energy, and a temperature sensing circuit coupled to the conductive pad.

<CIT> discloses a medical system which includes a device positionable in at least a portion of a bodily organ (e.g., a heart) and including a plurality of transducer elements, a computing system configured to computationally discriminate between fluid and non-fluid tissue, and at least one communications path communicatively coupling the transducer elements and the computing system, utilizing a multiplexer/ demultiplexer.

<CIT> discloses an endocardial mapping and/or ablation system for introduction into a chamber of the heart which comprises a catheter probe, and an interface module which supplies and receives appropriate signals to and from a computer, utilizing a multiplexer/demultiplexer.

One aspect of the invention is directed to an apparatus for use together with an AC signal generator for imposing electric fields through a target region in a subject's body according to claim <NUM>.

<FIG> is a block diagram of an embodiment that relies on distal circuits <NUM> positioned in close proximity to each of the four transducer arrays <NUM> to obtain the temperature readings from the temperature sensors in the transducer arrays <NUM>. Each of the transducer arrays <NUM> includes a plurality of capacitively coupled electrode elements <NUM> and a plurality of temperature sensors <NUM> (both shown in <FIG>, <FIG>, and <FIG>). The temperature sensors <NUM> are positioned to detect the temperature at respective electrode elements <NUM>. In some preferred embodiments, the temperature sensors <NUM> are thermistors.

Returning to <FIG>, each distal circuit <NUM> interfaces with the temperature sensors that are incorporated into the respective transducer array <NUM> to obtain the temperature readings from each temperature sensor. The distal circuit <NUM> then analog-to-digital converts those temperature readings and forwards the digitized temperature readings along to a central hub <NUM>. The central hub <NUM> then forwards these digitized temperature readings to the field generator <NUM> via a serial communication link so that the field generator <NUM> can determine, based on the temperature readings, if the current to the transducer arrays <NUM> has to be adjusted.

There are <NUM> short conductors that extend distally in the wiring <NUM> beyond the distal circuit <NUM> into the transducer array <NUM> itself. Those <NUM> conductors include <NUM> conductor for each of the <NUM> temperature sensors, <NUM> conductor for the temperature sensors' common ground, and <NUM> conductor for the TTFields signal (i.e., the AC current for the electrode elements). In some preferred embodiment, the distal circuit <NUM> is implemented using a single-chip microcontroller or Programmable System on Chip (PSoC) with a built in analog front end and multiplexer. Suitable part numbers for this purpose include the CY8C4124LQI-<NUM>. In this case, no other active components are needed in the distal circuit <NUM>. In alternative embodiments, other microcontrollers may be used with either built-in or discrete analog front ends and multiplexers, as will be apparent to persons skilled in the relevant arts. The analog front end and multiplexer obtains temperature readings from the temperature sensors. Those temperature readings are then digitized and transmitted to the central hub <NUM>, preferably via a serial data link. In addition, each distal circuit <NUM> also has an associated pass-through conductor (<NUM>, shown in <FIG> and <FIG>) for routing the TTFields signal that originated in the field generator <NUM> to the transducer array <NUM>.

In the <FIG> embodiment, each of the four distal circuits <NUM> is connected to the central hub <NUM> via a respective cable <NUM>. Notably only <NUM> conductors are required in each of the cables <NUM> that run between a distal circuit <NUM> and the hub <NUM> (i.e., one for Vcc, one for ground, one for serial data communication, and one for the TTFields signal). The distal circuits <NUM> therefore dramatically reduce the wire count that is needed to interface with each transducer array <NUM>.

<FIG> is a schematic diagram of a circuit that is suitable for use as the hub <NUM> depicted in <FIG>. In general terms, the hub <NUM> accepts the temperature readings from each of the distal circuits <NUM> (shown in <FIG>) and sends those temperature readings along to the field generator <NUM> (shown in <FIG>). Any of a wide variety of architectures may be used to accept and send the temperature readings. For example, in the illustrated embodiment, a controller <NUM> sends a signal to a digital multiplexer <NUM> that commands the digital multiplexer <NUM> to select one of the four inputs, which sets the hub <NUM> up to receive digital data from one of the distal circuits <NUM> (shown in <FIG>). After that, the controller <NUM> accepts all eight temperature readings from the selected input and transmits those temperature readings along to the field generator <NUM> (shown in <FIG>) via the transceiver <NUM>. After all the temperature readings from the selected input (i.e., the selected distal circuit) have been transmitted to the field generator, the controller <NUM> updates the control signal to digital multiplexer <NUM> and commands the digital multiplexer to select another one of the four inputs (i.e., another distal circuit). The controller <NUM> then accepts all eight temperature readings from the newly selected input and transmits those temperature readings to the field generator. Corresponding sequences are then performed to obtain eight temperature readings from the third input and eight temperature readings from the fourth input.

In some preferred embodiments, the controller <NUM>, the digital multiplexer <NUM>, and the transceiver <NUM> may be integrated together into a single chip. In alternative embodiments, the controller <NUM> and the digital multiplexer <NUM> are integrated together into a single chip, and a separate transceiver <NUM> is used. For example, the controller <NUM> and the digital multiplexer <NUM> may be implemented using a CypressCY8C4244LQI-<NUM>, and the transceiver <NUM> may be implemented using a Linear Technology LTC2856CMS8-<NUM>#PBF.

The entire sequence of obtaining all of the temperature measurements from each of the four inputs is repeated periodically (e.g., every <NUM> second, <NUM> seconds, or <NUM> seconds) to update the temperature readings that are provided to the field generator <NUM>. The hub <NUM> communicates with the field generator <NUM> using any conventional communication technique (e.g., RS485). The hub <NUM> also includes pass-through conductors <NUM> that pass the TTField signals directly from the field generator <NUM> to each of the transducer arrays <NUM>. In one example, the hub <NUM> communicates with the field generator <NUM> via an <NUM>-conductor spiral cable <NUM> (which includes <NUM> wires for TTFields signal from each array, <NUM> wire for ground, <NUM> wire for Vcc to the distal circuits <NUM> and <NUM> wires for communication). Notably, this embodiment can be made backwards compatible with previous versions of TTField delivery systems.

In the embodiment described above, two wires are used to implement data communications between the hub <NUM> and the field generator <NUM> (i.e., for the temperature data). This may be accomplished, for example, by using one wire to implement communication in each direction. In alternative embodiments, the wire count between the hub <NUM> and the field generator <NUM> can be reduced by replacing the two data communication wires in the embodiments described above with a single data wire that implements two-way communication (using a conventional single wire communication protocol).

<FIG> is a schematic diagram of a circuit for interfacing the hub (shown in <FIG>) with any given transducer array <NUM>. Each transducer array <NUM> includes a plurality of capacitively coupled electrode elements <NUM> and a plurality of temperature sensors <NUM> positioned to sense temperatures at respective ones of the plurality of electrode elements. In some preferred embodiments, these temperature sensors <NUM> are thermistors.

An analog multiplexer <NUM> has an analog output and a plurality of selectable analog inputs, and each of the plurality of the analog inputs is connected to a respective one of the plurality of temperature sensors <NUM>. The second terminal of each temperature sensor <NUM> goes to a common ground. The output of the analog multiplexer <NUM> goes to an amplifier <NUM>, preferably with a high input impedance (e.g., an op amp that is configured as a voltage follower). The output of the amplifier <NUM> is provided to the input of an analog to digital converter <NUM>, and the output of the analog to digital converter is provided to a controller <NUM>.

The controller <NUM> orchestrates the operation of all of the components within the dashed line <NUM>. The controller <NUM> sends a command to the analog multiplexer <NUM> to select one of the temperature sensors <NUM>, in order to obtain a temperature reading from that temperature sensor.

In embodiments where thermistors are used as the temperature sensors <NUM>, temperature readings may be obtained by routing a known current through the thermistor and measuring the voltage that appears across the thermistor. In the illustrated embodiment, this may be achieved using a programmable current source <NUM>, which may be programmed to generate a known current (e.g., <NUM>µA). The analog multiplexer <NUM> is bidirectional, so this known current will be routed into whichever thermistor is selected by the analog multiplexer.

Temperature readings from all eight temperature sensors <NUM> may be obtained using the following procedure. The controller <NUM> sends a command to the analog multiplexer <NUM> to select the first thermistor, and configures the current source <NUM> to generate a known current. Because the first thermistor has been selected, the known current from the current source <NUM> will flow through the analog multiplexer <NUM> into the first thermistor. This will cause a voltage to appear across that thermistor. Because the first thermistor is selected, this voltage will appear at the output of the analog multiplexer <NUM>. The amplifier <NUM> provides this voltage to the input of the analog to digital converter <NUM>. The controller <NUM> instructs the analog to digital converter <NUM> to digitize this voltage. The controller <NUM> obtains this reading from the analog to digital converter <NUM> and temporarily stores the digitized reading (which corresponds to the first thermistor) in a buffer. This procedure is then repeated, sequentially, for each of the other thermistors until digitized readings from each of the eight thermistors are sitting in the buffer.

In alternative embodiments, not shown, an alternative approach (e.g., the conventional voltage divider approach) for interfacing with the thermistors may be used in place of the constant current approach described above. In other alternative embodiments, a different type of temperature sensor may be used in place of the thermistors described above. Examples include thermocouples, RTDs, and integrated circuit temperature sensors such as the Analog Devices AD590 and the Texas Instruments LM135. Of course, when any of these alternative temperature sensors is used, appropriate modifications to the circuit (which will be apparent to persons skilled in the relevant arts) will be required.

In some embodiments, additional readings may be obtained and used for self-calibration to increase the accuracy of the temperature readings obtained from the thermistors. For example, in the illustrated embodiment, the bottom input of the analog multiplexer <NUM> is connected to ground, and the top input of the analog multiplexer <NUM> is connected to a precision resistor <NUM>. In some embodiments, the precision resistor <NUM> is a <NUM> kOhm, <NUM>,<NUM>% tolerance resistor. Readings from the precision resistor <NUM> may be obtained using the same procedure described above for obtaining a reading from any one of the thermistors. Obtaining readings from the grounded input of the analog multiplexer <NUM> is also similar, except that the current source <NUM> may be deactivated when the grounded input is selected. In these embodiments, the controller <NUM> temporarily stores the digitized readings from the precision resistor and the grounded input in a buffer (which means that a total of <NUM> readings are stored in the buffer). These additional readings may ultimately be used to calibrate the readings that were obtained from the thermistors. In some embodiments, this calibration is implemented in the controller <NUM> itself, prior to transmission of the digital data that corresponds to the temperature readings. In other embodiments, this calibration is implemented in a downstream processor (e.g., the controller <NUM> in the hub <NUM>, both shown in <FIG>), in which case the digital data corresponding to the precision resistor (and optionally the grounded input) is transmitted to the downstream processor along with the uncalibrated temperature readings that were obtained from the thermistors.

One suitable approach for performing calibration using the precision resistor <NUM> is to compare the actual voltage measured across that resistor with the expected voltage based on Ohm's law, the known value of the precision resistor <NUM>, and the expected value of the current being produced by the current source <NUM>. Any deviation between the actual measured voltage and the expected voltage could then be used as a multiplier for subsequent measurements from the thermistors <NUM>.

The controller <NUM> in the distal circuit <NUM> communicates with the hub <NUM> (shown in <FIG>) via UART <NUM>, and transmits the temperature readings obtained from the temperature sensors <NUM> to the hub. In some embodiments, the controller <NUM> may be programmed to operate autonomously, in which case it would automatically collect temperature readings from each of the temperature sensors <NUM> and store the result in a buffer as described above, and subsequently transmit the contents of the buffer (i.e., readings for each of the eight temperature sensors <NUM>, and optionally the additional readings described above) to the hub.

In alternative embodiments, the controller <NUM> may be programmed to operate as a slave to a master controller located in the hub. In these embodiments, the controller <NUM> starts out in a quiescent state, where all it does is monitor incoming commands from the master controller that arrive via the UART <NUM>. Examples of commands that can arrive from the master controller include a "collect samples" command and a "send data" command. When the controller <NUM> recognizes that a "collect samples" command has arrived, the controller <NUM> will initiate the procedure described above to obtain temperature readings from each of the eight temperature sensors <NUM> and store the result in its buffer. When the controller <NUM> recognizes that a "send data" command has arrived, the controller <NUM> will execute a procedure that transmits the previously collected temperature readings from the buffer to the hub via the UART <NUM>.

In those embodiments in which the controller <NUM> operates as a slave to a master controller located in the hub <NUM>, it becomes possible to synchronize the temperature measurements that are obtained from each of the four transducer arrays <NUM> (shown in <FIG>). One way to accomplish this would be to have the master controller in the hub <NUM> send a "collect samples" command to all four controllers <NUM> either simultaneously or in rapid succession, so that the temperature readings obtained from each of the transducer arrays will be obtained at or near the same time. The temperature readings can then be collected by the hub <NUM> in batches of eight from each of the four controllers <NUM>.

Most systems that use TTFields to treat tumors switch the direction of the field that is being applied to the tumor periodically (e.g. every second). To minimize noise in the temperature measurements, a small gap in time during which the field is not applied in either direction may be introduced, and the temperature measurements can be made during that gap in time. In some preferred embodiments, the master controller located in the hub <NUM> synchronizes the timing of the "collect samples" command to all four controllers <NUM> so that each of the distal circuits <NUM> will obtain its temperature readings during this gap. In embodiments where the temperature readings are obtained from each of the four transducer arrays simultaneously, this approach can be used to minimize the duration of the gap. For example, if a system requires <NUM> to obtain a single measurement, taking all <NUM> measurements in sequence (i.e., <NUM> distal circuits × <NUM> thermistors at each circuit) would take <NUM>. In contrast, if each of the four distal circuits operates in parallel, each distal circuit can complete its job in <NUM>, in which case all <NUM> samples can be obtained in <NUM>. Note that because the "send data" command is not sensitive to noise, that command can be executed while the fields remain on, and is therefore not time-critical.

In some embodiments, some or all of the following components are implemented by a single integrated circuit: analog multiplexer <NUM>, amplifier <NUM>, analog to digital converter <NUM>, controller <NUM>, UART <NUM>, and current source <NUM>. One example of a single integrated circuit that includes all of these functional blocks is the Cypress CY8C4124LQI-443T programmable system on chip (PSoC).

Optionally, a connector may be included in the path between the hub <NUM> and each of the transducer arrays <NUM>, as shown in <FIG> for a single transducer array. In the <FIG> embodiment, a connector <NUM> is positioned distally beyond the distal circuit <NUM>; and in the <FIG> embodiment, a connector <NUM> is positioned on the proximal side of the distal circuit <NUM>.

<FIG> depicts a more detailed view to show exactly where the connector <NUM> is positioned in the <FIG> embodiment. In this embodiment, the connector <NUM> is positioned distally beyond the distal circuit <NUM>. Operation of the <FIG> embodiment is similar to the operation of the <FIG> embodiment discussed above, except that <NUM> signals traverse the connector <NUM>: one for the AC current that goes to the electrode elements <NUM>; one for each of the eight temperature sensors <NUM> (for a subtotal of eight); and one for a common ground that is used for all of the eight temperature sensors <NUM>.

<FIG> depicts a more detailed view to show exactly where the connector <NUM> is positioned in the <FIG> embodiment. In this embodiment, the connector <NUM> is positioned on the proximal side of the distal circuit <NUM>. Operation of the <FIG> embodiment is similar to the operation of the <FIG> embodiment discussed above, except that <NUM> signals traverse the connector <NUM>: one for the AC current that goes to the electrode elements <NUM>, one for data that travels between the UART <NUM> and the hub; one for power to the distal circuit <NUM>, and one for ground for the distal circuit <NUM>.

<FIG> depicts the mechanical layout for the <FIG>/<FIG> embodiment. In this embodiment, a substrate <NUM> supports a plurality of capacitively coupled electrode elements <NUM>. The electrode elements <NUM> are configured for placement against the subject's body, and the substrate <NUM> is configured to hold the plurality of electrode elements <NUM> against the subject's body. A plurality of temperature sensors <NUM> are positioned adjacent to and/or beneath respective ones of the electrode elements <NUM> so that the temperature sensors <NUM> can sense the temperatures of those electrode elements.

A cable <NUM> has a proximal end and a distal end. This cable <NUM> includes (i) a conductor <NUM> that permits AC current to flow between the proximal end of the cable and the distal end of the cable and (ii) a data path configured to carry the digital data corresponding to the plurality of temperature readings (which originates in the distal circuit <NUM>) from the distal end of the cable to the proximal end of the cable (i.e., in the direction of the hub).

A module <NUM> is mounted (either directly or through intervening components) to the distal end of the cable <NUM>. The distal circuit <NUM> is mounted in this module <NUM>. In some embodiments, power and ground for the distal circuit <NUM> is provided through the cable <NUM>. A first half of a connector <NUM> is provided at the distal end of the module <NUM>, and the second half of the connector <NUM> is provided on the substrate <NUM>. The first half of the connector <NUM> mates with the second half of the connector <NUM> so that electrical signals can pass through both halves of the connector <NUM>. When both halves of the connector <NUM> are mated, signals from the eight thermistors <NUM> will travel through wiring on the substrate <NUM>, through the connector <NUM>, and into the distal circuit <NUM>. This distal circuit <NUM> includes the analog multiplexer, the analog to digital converter, and the controller (described above in connection with <FIG>). In addition, a common ground signal for all the thermistors <NUM> is provided through the connector <NUM>. A path for the AC current for the electrode elements <NUM> is also provided through the connector <NUM>. This path continues through appropriate wiring on the substrate <NUM> so that the plurality of electrode elements <NUM> will be electrically connected to a corresponding conductor of the cable <NUM>.

A module <NUM> is mounted (either directly or through intervening components) to the substrate <NUM>. The distal circuit <NUM> is mounted in this module <NUM>. In some embodiments, power and ground for the distal circuit <NUM> are provided through the cable <NUM>. A first half of a connector <NUM> is provided at the distal end of the cable <NUM>, and the second half of the connector <NUM> is provided on the substrate <NUM>. The first half of the connector <NUM> mates with the second half of the connector <NUM> so that electrical signals can pass through both halves of the connector <NUM>. When both halves of the connector <NUM> are mated, signals from the cable <NUM> will travel through the connector <NUM>, and into the distal circuit <NUM>. This distal circuit <NUM> includes the analog multiplexer, the analog to digital converter, and the controller (described above in connection with <FIG>). In addition, a path for the AC current for the electrode elements <NUM> is also provided through the connector <NUM>. This path continues through appropriate wiring on the substrate <NUM> so that the plurality of electrode elements <NUM> will be electrically connected to a corresponding conductor of the cable <NUM>.

The connectorized design depicted in <FIG> provides a significant advantage over non-connectorized embodiments in that the patient or caregiver can attach the transducer arrays <NUM> to the patient's skin without being hindered by the presence of cables. In these embodiments, the cables <NUM> are preferably disconnected from the substrates <NUM> when the transducer arrays <NUM> are initially placed on the patient's body. Only after the transducer arrays <NUM> are affixed in their desired positions are the cables <NUM> connected to the transducer arrays <NUM> via the connectors <NUM> or <NUM>. The connectors are preferably waterproof to prevent moisture (e.g., perspiration, showers, etc.) from interfering with the electric circuitry.

Note that the <FIG>/<FIG>/<FIG> embodiment has an advantage over both the non-connectorized <FIG> embodiment and the <FIG>/<FIG>/<FIG> embodiment because the transducer arrays <NUM> are preferably sterilized before use. Sterilization is ordinarily performed using either radiation or gas. Since radiation can interfere with electronics, assemblies in which the distal circuit <NUM> cannot be disconnected from the transducer arrays <NUM> can only be sterilized with gas. On the other hand, if the distal circuit <NUM> is located on the proximal side of the connector <NUM> (as it is in the <FIG>/<FIG>/<FIG> embodiment), the portion that includes the distal circuit <NUM> will not require sterilization. This permits sterilization of the transducer arrays <NUM> in the <FIG>/<FIG>/<FIG> embodiment to be performed using either gas or radiation without risk of damage to the distal circuit <NUM>.

Each of the configurations described above has significant advantages over the prior art because only <NUM> conductors are needed in each of the cables <NUM> that interface with each transducer array <NUM>. Furthermore, because only <NUM> conductors are required, the cables <NUM> that extend distally beyond the hub <NUM> can be made thinner and smaller than the prior art cables. This makes it easier to mount the hub <NUM> on a portion of the body that is adjacent to the transducer arrays <NUM>, and to make small and lightweight interconnections between the hub <NUM> and the transducer arrays <NUM>. For example, when the transducer arrays <NUM> are affixed to the patient's scalp, it becomes possible to mount the hub <NUM> on the patient's head in the vicinity of the transducer arrays <NUM> without discomfort to the patient. In these embodiments, shorter cables <NUM> (e.g., less than <NUM> or even less than <NUM>) are preferably used to interconnect the hub <NUM> with both the transducer arrays <NUM> and the distal circuit <NUM>.

The configurations described herein can advantageously reduce tangling of the cables that lead to the transducer arrays <NUM>, reduce the number of times that the cables will interfere with patients' everyday activities, reduce the overall cumbersomeness of the system, improve patient comfort, and improve maneuverability of the electrodes when they are affixed to the patient's body.

Returning to <FIG>, a display unit (not shown) may be added to the system. This display unit may be used to display information that the device provides to the patient including but not limited to device status (e.g., on/standby), error indications, status of battery charge, compliance metrics, etc. The display unit may be mounted at any point along the cable <NUM> between the hub <NUM> and the field generator <NUM>. In alternative embodiments, the display unit <NUM> may be mounted to the hub <NUM> itself.

In some alternative embodiments, the wires that provide power and ground to the distal circuit <NUM> can also be eliminated by diverting some of the energy from the TTFields signal (which is delivered via pass-through conductors) using a coil, storing that energy in a capacitor adjacent to the distal circuit <NUM>, and powering the distal circuit <NUM> using the stored energy. It is even possible to implement a one-wire communication protocol that transmits the temperature data over the TTFields signal wire. In such a configuration, the data communication signals and power for the distal circuits (Vcc) could all be removed from the cable that runs to the transducer array <NUM>. If all of these wire reduction techniques are implemented, only two wires will be needed between the hub <NUM> and each transducer array <NUM> (i.e., <NUM> for the TTField signal and <NUM> for ground). And the total number of wires that run back from the four transducer arrays <NUM> to the field generator <NUM> would be reduced to <NUM> (i.e., <NUM> for a common ground and a total of <NUM> for the TTField signals).

Claim 1:
An apparatus for use together with an AC signal generator (<NUM>) for imposing electric fields through a target region in a subject's body, the apparatus comprising:
a transducer array (<NUM>) comprising:
a plurality of capacitively-coupled electrode elements (<NUM>) configured for placement against the subject's body;
a substrate (<NUM>) configured to hold the electrode elements (<NUM>) against the subject's body; and
a plurality of temperature sensors (<NUM>) positioned to sense temperatures at respective ones of the electrode elements (<NUM>);
a cable (<NUM>) with multiple conductors and having a proximal end and a distal end, wherein the cable (<NUM>) includes a first conductor (<NUM>) that permits AC current to flow between the proximal end of the cable (<NUM>) and the distal end of the cable (<NUM>), and a data path configured to carry digital data from the distal end of the cable (<NUM>) to the proximal end of the cable (<NUM>);
a module (<NUM>) mounted directly or through intervening components to the distal end of the cable (<NUM>), wherein the module (<NUM>) includes a distal circuit (<NUM>) comprising:
an analog multiplexer (<NUM>) having an analog output and a plurality of selectable analog inputs, wherein each of the analog inputs is operatively connected to a respective one of the temperature sensors (<NUM>);
an analog-to-digital converter (<NUM>) configured to digitize signals from the analog output of the analog multiplexer (<NUM>); and
a controller (<NUM>) configured to sequentially select each of the analog inputs of the analog multiplexer (<NUM>), sequentially obtain, from the analog-to-digital converter (<NUM>), a plurality of temperature readings, each of the temperature readings corresponding to a respective one of the temperature sensors (<NUM>), and transmit digital data corresponding to the temperature readings; and
a connector (<NUM>) connecting the transducer array (<NUM>) to the module (<NUM>), whereby the first conductor (<NUM>) in the cable (<NUM>) is connected to the transducer array (<NUM>) and the temperature sensors (<NUM>) are connected to the analog multiplexer (<NUM>).