Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-02-14
2003-06-10
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S316010
Reexamination Certificate
active
06577042
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to medical devices and more particularly to a method and device for delivering ultrasound energy to a treatment location within a human or other mammal.
The use of ultrasound devices for lysing or removing material obstructing blood vessels in humans has been proposed in the art. These devices use ultrasound energy, either alone or with other aspects of a treatment procedure in an attempt to remove material blocking these blood vessels. One such device, an elongated ultrasound transmitting probe, has been used to lyse material obstructing blood vessels of humans or other mammals. The device consists of a cavitation generating tip at the end of an elongated transmission wire. A transducer is used to convert an electrical signal into longitudinal mechanical vibration in the transmission wire. This leads to the generation of a standing wave in the device and longitudinal displacement of the tip to transmit mechanical energy to the obstruction.
It is desirable for such an ultrasound probe to generate a wave with the maximum amplitude with a minimum of applied power. This maximum amplitude will generate the greatest lysing force and energy directed at any material being acted upon in the blood vessel. This will occur when the frequency of the ultrasound applied to the transmission wire of the probe by the transducer approaches the effective resonance frequency of the transmission wire of the probe. However, this effective resonance frequency will vary as the probe is moved within the blood vessel and among different blood vessels. Thus, the transmission wire of the probe may oscillate at less than its maximum amplitude at a given applied power. As a result, the probe will generate less than the maximum amount of ultrasonic energy within the blood vessel. The conditions which may affect the probe normally include bends in the transmission wire and compressions against the wire after the probe is fed through the various blood vessels in the body to the obstruction and moved within the blood vessel during treatment.
Additionally, conventional ultrasound probes do not measure the actual frequency or amplitude of oscillation at the probe tip. For example, space concerns generally preclude the use of features to transmit information regarding the action of the probe tip to a user. Users therefore will generally have no way to know what is actually happening at the probe tip.
One effort at maintaining suitable mechanical power transmitted by the tip is described in U.S. Pat. No. 5,477,509, the contents of which are incorporated herein by reference. This reference describes attempting to control the amplitude of the standing wave in the probe tip by monitoring the current input to the transducer, and varying the power input to the transducer so as to maintain the current input to the transducer at a constant level. Thus, when movement of the probe within the blood vessel decreases the current input to the transducer as a result of a change in the load of the transmission wire on the transducer, the power input to the transducer is increased in an effort to provide a constant power output at the tip of the probe. However, this reference fails to address the cause of the drop in supplied current. Rather the apparatus simply compensates for this decrease by inputting additional power. Thus, more power is required to be input to the transducer for the same output power which results in a decrease in the efficiency of the apparatus.
This prior art reference also describes monitoring the level of current input to the transducer to determine if there is a break in the transmission wire. If a break occurs in the transmission wire, the load of the transmission wire on the transducer will greatly decrease. This results in an extreme decrease in the required power input to achieve the supposed required power output at the tip of the probe. This change signals a problem, and the apparatus is shut down. However, such a system will not detect a problem in the transmission wire, such as a fracture, which might increase the load on the transducer. A fracture might increase the friction between the transmission wire and any other portion of the probe, for example, or any object the probe tip might come into contact with. While this fracture might be dangerous to the user, the required power input would not decrease below a predetermined level, and therefore would not be recognized as an event which would turn off the probe.
The optimal operating frequency of an ultrasonic device varies with the tolerances of the components of the device and the field of operation. In prior art ultrasonic devices, the optimal operating frequency is determined by scanning across the entire operating range of the device and locating the frequency which maximizes a particular operating parameter of the device, e.g. current. A significant drawback associated with the prior art approach of scanning across an entire operating frequency range is that a false optimum frequency may be selected which would result in sub-optimum performance for the device.
Accordingly, it would be beneficial to provide an ultrasound transmission device which can generate a maximum tip oscillation amplitude under a number of adverse conditions, and provide the feedback necessary to maintain maximum amplitude without increasing the power consumption of the apparatus, and which can monitor the system to notify the user of any fracture in the probe wire or other problem affecting the system.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, an ultrasound transmission apparatus in the form of a transmission member connectable to a transducer at its proximal end and having a tip at its distal end is provided. The apparatus includes an improved control system which can control the amplitude of oscillation at the tip of the probe. This control system comprises an electric power source which supplies constant power at a selected frequency to the transducer which converts the electrical energy to mechanical oscillation and generates a standing wave in the transmission member. The control system also includes a frequency measuring and adjusting instrument for continuously measuring the frequency of the mechanical oscillations output from the transducer. This frequency measuring instrument is also capable of varying the frequency of the oscillations of the transmission member and tip by fine tuning the frequency of the oscillations generated by the transducer. Finally, current and voltage monitoring instruments are also included for measuring current and voltage to determine power input to the transducer.
The control system maintains constant power (voltage times current) to the transducer and monitors the current and voltage input to the transducer. The oscillation frequency is varied over a predetermined range in order to maintain a frequency at which current input to the transducer, and thus power, is at a maximum. The resistance along the transmission member during oscillation is proportional to the load on the transducer and therefore electrical resistance at the transducer is proportional to the load on the transducer. Because power is maintained at a constant level, the load on the transducer will be at a minimum at maximum current. The amplitude of the oscillations of the transmission wire will also be at a maximum. Thus, as the frequency of the transducer is constantly adjusted to generate the greatest input current and thus maintain power at its maximum, the apparatus will always optimize the amplitude of the oscillation of the tip thereof at a given power.
This maximum will occur when the transducer vibrates at the effective resonance frequency of the transmission member. As the probe is moved within blood vessels in various parts of the body, the resonance frequency of the probe is slightly altered. By fine tuning the frequency of the oscillation frequency of the transducer, it is possible to oscillate the transmission member at a frequency approaching this new
Bell Phil
Klein Richard
Lee Weng
Popow John
Rosenschein Uri
Angiosonics Inc.
Dippert William M.
Dougherty Thomas M.
Reed Smith LLP
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