Medical system having improved telemetry

A medical system having improved telemetry, the medical system featuring a programmer having a programming head. The system provides improved telemetry due to the unique antenna scheme within the programmer head. The antenna scheme utilizes a first antenna and a second antenna, the antennas disposed in a concentric and co-planar manner. This concentric and co-planar disposition permits the programmer head to be of much smaller and, thus, a more portable size than was previously possible. The antenna is further coupled with circuitry or software or both to reduce far field response (noise). The antenna may be constructed using printed circuit board, and thus be integrated with circuitry.

FIELD OF THE INVENTION
 The invention relates generally to system having two-way communication
 between devices. More specifically, the invention relates to external
 transceivers which remotely communicate with implanted medical devices.
 Part of this two-way communication link consists of control or programming
 signals transmitted from the external device to the implanted device for
 the purpose of altering the operation of the implanted device. The
 remainder of the link consists of low-level telemetry transmissions from
 the implant to the external device for the purpose of conveying
 information such as current status, battery level, or patient data.
 BACKGROUND OF THE INVENTION
 Two-way communication with implanted medical devices imposes special
 problems which become even more acute in an interference-prone
 environment, especially where the medical devices are essential to
 maintaining life functions. Necessarily, implanted medical devices require
 ultra-low power levels from long-lived batteries. The most common
 implanted telemetry system employs a single, multi-turned coil to
 externally receive the low-level telemetry signals. These single-coil,
 receiving antennas are quite susceptible to interference from electric,
 magnetic and electromagnetic field sources which are present in the
 clinical environment.
 The present invention employs two noise-canceling, antenna coils, which
 improve the signal-to-noise ratio significantly, and a circuit which
 permits transmission and reception of signals through the same antenna
 coil network without interactive tuning problems and without the
 employment of any switching devices. The improved, external transceiver
 circuit permits two-way communications with implanted medical devices in
 close proximity (on the order of 4 inches to 2 feet) to common
 interference sources such as cathode ray tubes and video monitors.
 Moreover, because the antenna coils reside within the same plane and our
 preferably co-axial they require a minimum amount of volume, leading to a
 much smaller, more portable programmer head. Finally, a system featuring
 the present invention may be cheaper, due to the fact that the disclosed
 antenna may be constructed using printed circuit board, and thus be
 integrated with circuitry.
 SUMMARY OF THE INVENTION
 A medical system having improved telemetry, the medical system featuring a
 programmer having a programming head. The system provides improved
 telemetry due to the unique antenna scheme within the programmer head. The
 antenna scheme utilizes a first antenna and a second antenna, the antennas
 disposed in a concentric and co-planar manner. This concentric and
 co-planar disposition permits the programmer head to be of much smaller
 and, thus, a more portable size than was previously possible. The antenna
 is further coupled with circuitry or software or both to reduce far field
 response (noise). The antenna may be constructed using printed circuit
 board, and thus be integrated with circuitry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1A depicts the general configuration of a programmer in which the
 present invention may be used. Typical programmer currently used, such as
 the Medtronic.TM. model 9790 programmer feature a keyboard 10 and display
 12. A series of one or more leads 16 are provided to provide direct
 electrical coupling to the patient, e.g. to collect ECG signals. Finally,
 a programmer head 14 is provided. This head transmits and receives signal
 through which the programmer may communicate with an implanted device 30.
 In the present system head 14 transmits and receives RF signals.
 FIG. 1B is a detailed view of programmer head 14. As seen head 14 possesses
 a pair of push button switches 23 and 25 labeled INTERROGATE and PROGRAM
 respectively. In use, the physician depresses one or the other of the two
 buttons to initiate a series of communications with an implanted device.
 Also commonly provided on programming heads 14 is a light 22 to indicate
 the position of the head relative to the implanted device. That is the
 light may illuminate or change color depending upon the proximity of the
 head to an implanted device.
 Referring now to FIG. 1C, there is shown a block diagram of a system
 incorporating the telemetry receiver of this invention. While the
 invention is described in the context of an external device which receives
 telemetry signals from an implanted medical device, the invention is not
 limited to the environment of medical devices.
 An external device, such as a programmer used in cardiac pacing systems, is
 illustrated at 20. The device picks up data at t/r coil 21, which data has
 been telemetered from another device illustrated at 30, e.g., an implanted
 cardiac pacemaker. The data which is uplinked to device 20 is inputted to
 processor block 24 via receiver 89, where it may be stored, analyzed, etc.
 The data can be displayed by any suitable display or printer, as shown at
 15. Such programmer devices also have input capability, as by receiving
 tapes, discs, or data inputted by keyboard, as shown at 16. Device 30 also
 has a transmitter 22 for sending data to the implanted device 30. The
 portions of implanted device 30 that are important to this invention are
 illustrated within block 30. The transmitter 31 is controlled by block 25,
 and transmits encoded data through t/r coil 28 to the external device 20.
 In practice, the device 30 can also receive data from external device 20,
 through receiver 29 which is connected to processor 25. Processor 25 is
 also suitably used to control operation of pace sense circuits 17, which
 transmit pacing signals to a patient's heart through leads 18, and receive
 heart signals for processing. Block 25 suitably uses a microprocessor and
 associated memory 26, in a know fashion.
 FIG. 1D is a detailed view of programmer head 14 and in particular
 illustrates the transmitting and receiving components 20 found within the
 head and the particular subject of the present invention. As mentioned
 above, programmers communicate with implanted devices through the
 transmission and reception of telemetry. Often this telemetry is carried
 on RF waves, which require the provision of appropriately configured
 antennas in the programming head 14.
 FIG. 2 depicts the relation between the antenna coils 1 and 2 which would
 be within programming head 14 according to the present invention as they
 would relate to the transmitting antenna 3 from an implanted device. As
 seen, the transmitting antenna 3 creates a field depicted here with a
 variety of flux lines, generally 4. The coils 1 and 2 are in the same
 plane but do not have the same size. Moreover, these coils need not even
 have the same number of windings. Although shown as roughly square, coils
 may be in any appropriate shape, as discussed below more fully with
 regards to FIG. 9. As shown, coils 1 and 2 are coupled to compensatory
 electrical controls to provide the far field noise canceling effect. As
 can be appreciated, the different sizes of coils 1 and 2 result in a
 different pick up of the magnetic flux of the field and, thus, induces
 different voltages in each of the coils. These different voltages may be
 compensated for by the compensatory electrical controls to thus achieve
 far field noise canceling effect.
 FIGS. 3A-3C each disclose compensatory electrical controls which may be
 used to provide the desired far field cancellation result. Generally
 speaking, the voltage generated by a coil is linearly related to the
 number of turns and the area of the coil (assuming, for simplicity, a far
 field source which gives uniform magnetic flux per unit area.) Thus the
 more turns in a coil, or the larger the coil, the more voltage created.
 From this, we have found that coils of non-equal area can be compensated
 for by varying the number of windings in each. FIG. 3A is particularly
 beneficial when the inner coil antenna L1 is smaller than outer coil L2
 and inner coil L1 has more turns or windings to as to generate the same
 voltage for far fields, but in opposite phase. For example, a typical set
 of coils would have the following characteristics: The outer coil L2 would
 be circular and be six square inches in area and have 25 turns while the
 inner coil L1 would be on quarter the area, or one and one-half (1.5)
 square inches and have 100 turns.
 FIG. 3B shows an alternative embodiment for providing far field
 cancellation. In particular, this embodiment features the step-up
 transformer T1 which may be used to compensate for the small area of coil
 2. This use of a step-up transformer is particularly believed useful if
 the voltage loss cannot be made up for by providing coil 2 with more
 turns. Recall, the voltage induced in the coils by the field is a function
 of both the coil geometry as well as the number of turns in the coils.
 Thus the compensatory electrical control scheme used in the invention
 depends both upon the size of the coils as well as the number of turns
 used in each coil. Other factors which affect the ultimate design of a
 programmer head include, among other things, the carrier frequency,
 transmission power.
 FIG. 3C shows an alternative embodiment for providing the compensatory
 electrical controls. In particular, this embodiment approaches the desired
 far field noise canceling effect in a manner opposite to that shown in
 FIG. 3B. In particular, in this design, rather than stepping up the output
 from coil L2 the output from coil L1 is attenuated.
 FIG. 4A shows the response of a prior art single loop receiving antenna as
 a function of the distance to a transmitter and FIG. 4B shows the response
 of a dual loop receiving antenna according to the present invention as a
 function of the distance to a transmitter. As can be seen in a comparison
 of these FIGS, a dual coil, concentric co-planar antenna of the present
 invention provides superior performance compared to a single coil version.
 This is seen specifically in FIG. 4A, where a single coil has a gain of 30
 versus FIG. 4B, where a dual coil antenna has a gain of 100, both being
 0.00 meters distance (Z).
 FIG. 5 shows an alternative embodiment of the present invention. In this
 embodiment a further third coil 97 is provided alongside and in the same
 plane as a co-planar and co-axial coil design 98, 99 as previously
 described above. In addition, third coil 97, besides being provided
 alongside and in the same plane as a co-planar and co-axial coil design
 98, 99, could also be provided co-planar and co-axial to coil 98, 99
 instead of alongside. In this last configuration there would be a tri-coil
 array in a single plane and all of which would be concentric. The
 additional third coil may be used to accommodate rotated uplink fields.
 This additional coil will be switched in, instead of the inner coil, upon
 such occurrence. Through this structure there is a butterfly type
 receiving type structure. It should be pointed out, this design does have
 a disadvantage to the concentric design in that it has two optimal
 positions and it does have a null output depending upon the rotation along
 the Z axis. Despite these limitations the additional third co-planar coil
 provides greater freedom in trading of far field, close field responses.
 The range of such structure, however, will be limited, as the turn's
 ratios cannot be very large.
 FIGS. 6A and 6B shows an alternative means for providing far field
 noise-canceling effects. In particular, FIG. 6A shows a structure in which
 two coils may have their signals processed within their digital domain.
 Coils L1, L2 (coil 1 and coil 2) are disposed in a co-planar, co-axial
 manner, as already described above. As seen, each coil itself is coupled
 through an amplifier to an analog/digital converter. Thereafter the
 digital signals of each coil are processed using a digital signal
 processor, as shown.
 FIG. 6B shows the steps used to process the signals gathered by the
 structure in FIG. 6A. As seen, the signals are received or taken from coil
 1 and coil 2 at 6-1. Thereafter, at 6-2 signals outside the band of
 telemetry frequencies are removed and the ratio of non-zero filtered
 signals is performed at 6-3. At 6-4 the result of the operation in 6-3 is
 processed along side the original sent signals from 6-1 so as to achieve
 the appropriate far field noise suppression, depicted here as processed
 signal at 6-5.
 FIG. 7 depicts an alternative embodiment for providing coils according to
 the present invention. While the invention disclosed above is preferably
 practiced using congruent coil shapes which are disposed co-axially, in a
 particular environment the invention may also be practiced using
 non-congruent or non co-axial or both coils. Examples of such coils are
 shown in FIGS. 7A-7E.
 FIG. 7A depicts a scheme in which dual oval coils are set in a non co-axial
 disposition.
 FIG. 7B shows co-axial disposition of a square outer coil and circular
 inner coil. In both FIGS. 7A and 7B the coils are set in a planar
 configuration.
 In FIG. 7C the coils are set in a manner in which they have different or
 varying thicknesses. In this configuration they would be co-planar and,
 indeed, they could even be congruent, although not necessarily. While
 depicted as co-axial it could also be imagined they could be in a non
 co-axial configuration.
 FIG. 7D depicts an alternative embodiment in which the coils are co-axial
 and planar but which have a ramped or increasing thickness within the
 plane.
 Finally, FIG. 7E depicts an embodiment in which the coils are disposed in a
 co-planar, co-axial configuration but with the outer coil having a greater
 thickness than the inner coil. It should be understood, as discussed
 above, that the windings of each coil may be suitably selected to obtain
 the desired output signals for the environment in which the antenna is to
 operate. Thus, the present invention has been described within the context
 of a medical system programmer. It should be understood, however, the
 antenna of the present invention is not limited merely to medical systems
 but could congruently be used in other applications as well, such as in a
 variety of wireless devices.