Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-05-08
2001-06-12
Casler, Brian L. (Department: 1911)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C606S130000, C600S429000, C600S439000
Reexamination Certificate
active
06246898
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to a method for carrying out medical procedures, and more particularly to a method for carrying out medical procedures using a 3-D locating and imaging system.
BACKGROUND OF THE INVENTION
Using the time-of-flight principle of high frequency sound waves, it is possible to accurately measure distances within an aqueous medium, such as inside the body of a living being during a surgical procedure. High frequency sound, or ultrasound, is defined as vibrational energy that ranges in frequency from 100 kHz to 10 MHz. The device used to obtain three-dimensional measurements using sound waves is known as a sonomicrometer. Typically, a sonomicrometer consists of a pair of piezoelectric transducers (i.e., one transducer acts as a transmitter while the other transducer acts as a receiver). The transducers are implanted into a medium, and connected to electronic circuitry. To measure the distance between the transducers, the transmitter is electrically energized to produce ultrasound. The resulting sound wave then propagates through the medium until it is detected by the receiver.
The transmitter typically takes the form of a piezoelectric crystal that is energized by a high voltage spike, or impulse function lasting under a microsecond. This causes the piezoelectric crystal to oscillate at its own characteristic resonant frequency. The envelope of the transmitter signal decays rapidly with time, usually producing a train of six or more cycles that propagate away from the transmitter through the aqueous medium. The sound energy also attenuates with every interface that it encounters.
The receiver also typically takes the form of a piezoelectric crystal (with similar characteristics to the transmitter piezoelectric crystal), that detects the sound energy produced by the transmitter and begins to vibrate in response thereto. This vibration produces an electronic signal in the order of millivolts, that can be amplified by appropriate receiver circuitry.
The propagation velocity of ultrasound in an aqueous medium is well documented. The distance traveled by a pulse of ultrasound can therefore be measured simply by recording the time delay between the instant the sound is transmitted and when it is received.
Prior art ultrasound measurement systems suffer from a number of shortcomings which limit their utility. Firstly, conventional sonomicrometers use analog circuitry to transmit and receive signals (e.g., phase capacitative charging circuits). The voltage representing the measured distance is then output to a strip chart recorder in analog form. This data must then be digitized for computer analysis.
Secondly, conventional ultrasound measurement systems use analog potentiometers to adjust the inhibit time and the threshold voltage that triggers the receiver circuits. This often requires the use of an oscilloscope. Each time the sonomicrometer is used, these settings must be manually set and adjusted in order to tune the system. This can be time consuming and annoying. As a whole, the function of the tracking system cannot be changed. The repetition frequency is fixed, regardless of the number of channels used, and the tracking system is therefore very limited in terms both of the distances that can be measured, and the temporal precision with which the sonomicrometer system operates.
Thirdly, conventional sonomicrometers feature pairs of transmitter and receiver crystals that are energized sequentially at fixed repetition rates. As such, prior art tracking systems lack experimental flexibility. For example, before a pair of crystals is implanted in the medium (e.g., a bodily structure, such as a human organ), the user must decide the function of each crystal; similarly, the user must determine which distances are to be measured by which crystal pair. This can be awkward because surgery often necessitates changes during the procedure. If either of the receiver or transmitter crystals malfunctions, the distance between them cannot be measured. Critical measurements can therefore be lost after a significant amount of effort is put into setting up the surgery.
Fourthly, conventional ultrasound tracking systems measure only a straight line distance between any isolated pair of crystals. Three-dimensional information is therefore impossible to acquire. Even if multiple combinations of distances could somehow be linked together, the inherently analog nature of the data would necessitate the use of additional, complex hardware.
Finally, conventional ultrasound tracking systems use discrete elements, such as threshold capacitors and potentiometers requiring large plug-in units to increase the number of channels. The systems are very large, usually two feet wide by 18″ deep, and up to 12″ high. Additional hardware such as strip chart recorders must be used, for visualization and subsequent processing. This can be very awkward given the space constraints at busy research institutes and hospitals.
The foregoing drawbacks to prior art systems limited their utility, and hence limit the practicality of using the systems to perform various types of medical procedures.
SUMMARY OF THE INVENTION
According to the present invention there are provided a variety for methods for carrying out a medical procedure using a three-dimensional tracking and imaging system. The 3-D tracking and imaging system provides enhanced functionality for diverse clinical and medical research applications.
The 3-D tracking and imaging system of the present invention uses modern day digital electronics in conjunction with an integrated personal computer. External A/D converters are not required, as the data is acquired digitally, directly from the sensors. Due to the speed of the controlling computer, the tracking system of this invention is capable of detecting distance increments as small as 19 &mgr;m. The acquired data can be displayed on the computer screen as it is being obtained, and can be saved to the computer's storage media with a simple key stroke. After an experiment or surgical procedure, the saved data can be examined and manipulated according to the user's specifications.
According to a preferred embodiment of the present invention, virtually every function of the 3-D tracking and imaging system is digitally controlled, and therefore very flexible. To begin, a set-up menu is generated which allows the user to select which transducers are active as well as the function of each channel. Next, a data display program permits the parameters of the transducer to be customized for specific applications. For example, if very few channels are being used, the repetition frequency can be increased so that data can be acquired at several Khz. On the other hand, if the system is being used in vitro, where persistent echoes from a container vessel may present a problem, the repetition frequency can be reduced to allow the echoes to attenuate between successive measurements.
The duration of the power delivered to the transducers can be reduced for precision work or increased if greater distances are required to be measured. The duration of the delay required to overcome electromagnetic interference between transducer leads is adjustable by means of a variable inhibit feature. Additionally, the number of samples displayed and stored in any given data save is variable according to the length of time that a user's protocol demands. Finally, the resolution of the displayed information is variable in conjunction with the degree of motion of the measured specimen. All of these functions are controlled digitally by means of custom designed digital cards or modules discussed in greater detail below, which, in turn, are software controlled.
Additional customized software is included in the 3-D tracking and imaging system of the present invention for post processing and visualizing the acquired data. In these routines, stray data points can be easily removed, three point filters can be applied for smoothing, level shifts can remove areas of discontinuity, channe
Burkhoff Daniel
Klein George
Smith Wayne
Vesely Ivan
Arter & Hadden LLP
Casler Brian L.
Sonometrics Corporation
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