Patent Application
20070255085
The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:
One or more ultrasound sources are disposed in the center of interface 10. In some embodiments, the ultrasound sources will be focused on the axon of interest to create a Hall Effect current. The ultrasound source may be a single transducer, a con-focal transducer, two separate transducers, or two separate arrays operating at slightly different frequencies, with a resultant wave at the difference frequency representing the stimulation profile. The embodiment shown in
This embodiment also uses surface electrodes 24 and 26 to add a baseline electric field in order to decrease the stimulation amplitudes required by the localized Hall Effect phenomenon. Electrodes 24 and 26 communicate with the controller via conductors 28 and 30, respectively. In use, these surface electrodes are adhered to the patient's skin or other tissue surface and may use conductive gel to create electric current uniformity at the electrode/tissue interface.
Other elements of the system of this embodiment include a power supply 218, a DC step up 220, an ultrasound beamformer circuit 222, a TENS generator 224, a magnetic coil drive circuit 226 and flash ROM 228.
In one embodiment, shown in
Up to two ultrasonic beamformers could be used in this device, and as few as one transducer depending on the clinical application. In one embodiment, each beam former is operating at a slightly different frequency than the other. As documented earlier by Fatemi and Greenfield, the interaction of the two co-incident waves results in a third wave generated non-linearly at the difference frequency. There is a fourth wave that is not of interest to this application oscillating at the sum of the two frequencies. A typical array factor pointing at 180 degrees is shown in
Beam forming architecture is shown in the block diagram shown in
The ultrasound sources are intended to operate in continuous wave mode, thus justifying the use of programmable phase shifters. In another embodiment, pulsed ultrasound may also be used to generate a dampened sinusoidal response. With pulsed ultrasound, the microprocessor drives the transducers through an array of FET push-pull transistor-pairs, with each pulse delayed as a function of the transducer phase angle.
The third modality of the device of this invention is that of the transcutaneous neural stimulator. As mentioned earlier, this modality is only used to provide subthreshold stimulation, aiding the Hall Effect to trigger action potentials in the targeted axons. In DBS applications, for example, the use of surface electrodes may generate undesirable outcomes, while in spinal cord and peripheral applications, it may be programmed in a complex manner to exhibit a variety of neuromodulation mechanisms.
The surface electrodes could produce a variety of waveforms commonly used in neural stimulation, such as trapezoidal, asymmetric, and half-wave. The waveforms are generated by the host and downloaded into memory. The microcontroller reads the digitized waveforms, converts them to analog and sends them to the electrode pair, via current-controlled amplifiers.
In operation, the system is first set up by connecting the three major modules together: the device to the PC-host and the device to the patient-interface module. Both device and host are powered up, and the Graphical User Interface (GUI) software is run on the PC-host. The GUI contains a mathematical model that estimates magnetic induced current density due to magnetic coil operating parameters. The following parameters are then set for the magnetic drive circuit shown in
(1) Amplitude of input voltage (Amc);
(2) Frequency of input voltage (Fmc);
(3) Discharge output voltage (Vo); and
(4) Discharge repetition rate (DRR).
Both Amc and Fmc influence the operation of the charging circuit and are limited by a model of that circuit for optimal and safe operation. Vo and DRR determine the physiologic response to the magnetic coils. Larger Vo results in larger coil currents, thus introducing larger fluctuation in magnetic flux. The induced current in the target membrane is proportional to dB/dt. DRR determines the steady-state response of the axon, and may result in the following physiologic effects: (1) subthreshold stimulation; (2) hyperpolarization; and/or (3) sensitization. The preferred operation of the system is the first response so that subthreshold non-localized stimulation of many nerves in the magnetic field is aided by an incremental addition of the Hall Effect voltage introduced by the ultrasound sources at the target.
Next, the ultrasound sources are programmed for continuous operation. In one embodiment, a single ultrasound source operates at a stimulation frequency much greater than the fluctuation frequency of the magnetic flux density, but is considered effective for the targeted axon according to the nerve stimulation strength-duration curve shown in
In another embodiment, two ultrasound sources, whether single element or phased arrays, are programmed to operate at a wavelength that achieves desired localization. Ultrasound propagating in an axis transverse to that of the magnetic field, as shown in equation (1), will introduce a Hall Effect electric current. This localized phenomenon acts similar to a physical electrode, referred to herein as a “virtual electrode.” The two sources operate at slightly different frequencies, and the difference of the two is the stimulation frequency determined by the strength-duration curve shown in
Depending on the clinical application, stimulation sites may be too responsive to the induced current by the magnetic coils, thus requiring a decrease in flux density to a point where the Hall Effect voltage strength becomes less dominant. This situation may require the assistance of another subthreshold stimulation source, generated by the surface electrodes shown in
This application claims priority under 35 U.S.C. §119 to U.S. Application No. 60/745,829, filed Apr. 27, 2006, the disclosure of which is incorporated by reference as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 60745829 | Apr 2006 | US |
