Integrated heating/sensing catheter apparatus for minimally invasive applications

The present invention relates to a medical catheter device for minimally invasive applications, particularly relying on electromagnetic radiation to simultaneously perform controllable heating of a fluid or tissue adjacent to the catheter and detection of the temperature of the fluid or tissue. It relates to a body antenna / catheter system.

By placing a catheter in a region of interest in the human body, tumors, cardiac arrhythmias, benign prostatic hyperplasia (BPH), etc. can be detected, diagnosed, and treated.

When placed within the patient's vascular system, the catheter can be used to measure temperature or even to raise tissue temperature during heart surgery. Examples of known antenna catheter devices of this common type are described in Applicants' patents 5,683,382 and 6,932,776.

Obviously, to perform those functions, such catheters are small in diameter and highly flexible so that they can be inserted into the body through various natural passages in the body. Must have. Such catheters also need to facilitate a variety of ancillary processes such as catheter maintenance at a given or constant temperature, target site display, target site irrigation, and the like.

The antenna catheter of the type described above is always connected to an external control unit via a long cable, which transmits electromagnetic energy to the antenna catheter to heat fluid or tissue adjacent to the antenna catheter. It includes a transmitter and a receiver in the form of a radiometer that detects the thermal radiation captured by the antenna catheter that reflects the temperature of the fluid or tissue under examination. The receiver produces a corresponding output signal to control a display displaying its temperature. The signal can also be used to control the transmitter to maintain the selected heating profile.

For such devices that detect thermal radiation in the microwave region of primary interest in this document, the receiver is usually a Dicke-type radiometer. Such a radiometer is a comparative radiometer system that uses a switch to alternately connect to an antenna (an unknown temperature to be detected) and a reference temperature, which can be an invariant noise source or temperature sensor in the catheter.

Every component of such a radiometer produces noise power that contributes to the overall noise of the system. Therefore, the total output of the device includes not only the noise received by the antenna, but also the noise generated inside the device itself. Such fluctuations in the device can cause spurious output signal fluctuations that are larger than the signal level to be measured in some cases. To overcome this gain variation, Dicke has developed a common load comparison radiometer. This configuration significantly reduces the short-term gain fluctuation effect of the radiometer. More specifically, the switch provides a mechanism that allows both the reference signal and the unknown signal to pass through the device essentially simultaneously for the expected gain drift in the radiometer's amplifier. This ensures that any gain drift is applied equally to both the antenna signal and the reference signal.

The radiometer's input is switched between the antenna and the constant temperature reference load at a constant rate by the Dicke switch, so the switched or modulated RF signal is radio as close to the antenna as possible before RF amplification. Put in the meter. Any component or transmission line placed between the detected unknown temperature and the Dicke switch can introduce an error. One source of such error is a long coaxial cable that connects the antenna to the radiometer.

More specifically, the cable temperature contributes to the temperature measurement. The cable temperature is usually known and varies with the length of the cable. The part of the cable inside the human body is at body temperature, while the part of the cable outside the human body is at room temperature. All of these parameters can vary with the depth of bending and insertion of the probe into the human body. Further, when the device includes a transmitter, electric power is absorbed by the cable, and the cable is heated. If the loss on the cable is, for example, 3 dB (which can easily be that much), half of the antenna noise power comes from the desired tissue or fluid volume under inspection and the rest comes from within the cable. It will be.

Therefore, in the Dicke type radiometer, the error common to both measured values (that is, "unknown temperature" vs. "reference temperature") is eliminated, but the change or error between the unknown temperature and the Dicke switch is. It affects only the measured value of the unknown temperature and is not common to both measurement paths.

Therefore, to achieve accurate measurements, between the antenna and the radiometer to improve the overall performance and reliability of the device without increasing the size, weight, and cost of the device. It is highly desirable to minimize the loss of.

<p> Therefore, an object of the present invention is to provide a minimally invasive antenna catheter device that enables simultaneous control of heating a fluid or tissue in a human or animal body and detecting the temperature of the fluid or tissue.</p><p> Another object of the present invention is a device comprising an antenna catheter and an external control unit that can be inserted into a patient, eliminating the need for a long, lossy coaxial cable between the catheter and the external unit. The purpose is to provide a device configured to be such.</p><p> A further object of the present invention is to provide a minimally invasive temperature detector comprising an antenna catheter and a receiver in the form of a radiometer fully integrated within the catheter.</p><p> Yet another object of the present invention is an integrated antenna catheter that includes a built-in diplexer and microwave receiver to heat fluid or tissue adjacent to the catheter when connected to an external control unit that includes a transmitter. It is an object of the present invention to provide an integrated antenna catheter capable of simultaneously detecting the temperature of the fluid or tissue.</p><p> Other objectives are partly self-evident and partly appear below.</p><p> Therefore, the present invention includes the features of the configuration, the combination of the components, and the arrangement of the respective parts, which are illustrated in the following detailed description, and the scope of the present invention is shown in the claims.</p>

<p> Simply put, the present invention comprises an antenna catheter for insertion into a human or animal patient. The catheter, sometimes referred to as a probe, can be connected by an external control unit that can include a transmitter and a display. As before, the device also includes a receiver (preferably a Dicke-type radiometer). However, rather than incorporating the receiver into an external control unit as is conventionally done, all components of the receiver are fully incorporated into the catheter and preferably (although not required) said transmission. The machine transmits RF signals (ie signals below 300MHz). This not only minimizes the electrical distance between the antenna and the receiver, but also eliminates the need for long coaxial cables that have the problem of signal loss and cause measurement errors as described above. It becomes. Thus, the device is simpler and cheaper to manufacture and maintain, despite having a higher signal-to-noise ratio and sensitivity than comparable conventional devices of its kind.</p><p> If the device is intended to heat tissue and detect its temperature, the radixer is also fully integrated within the catheter, as described in more detail below, which allows the same catheter to be transmitted externally. The energy received from the machine is radiated at one frequency to heat the tissue, and at the same time, the heat radiation from the tissue (indicating the tissue temperature) can be detected at various frequencies.</p>

<figref num="1">Schematic representation of an integrated catheter device for minimally invasive applications, including antenna catheters for controlled heating and temperature detection.</figref><figref num="2">It is an enlarged view of a partial longitudinal sectional view showing the antenna catheter of FIG. 1 in more detail.</figref><figref num="3">It is a partial cross-sectional perspective view which shows the catheter of FIG. 2 further enlarged and partially cut out.</figref><figref num="4">It is a similar figure which shows a part of the catheter of FIG. 2 in a further enlarged scale.</figref><figref num="5">FIG. 2 is a schematic showing specific electrical components incorporated within the catheter of FIG.</figref><figref num="6">It is a similar figure which shows the specific component of the control unit of this apparatus.</figref><figref num="7">It is a graph which shows the return loss of the antenna catheter of FIG.</figref>

For a complete understanding of the essence and purpose of the present invention, the following detailed description will be referred to in connection with the accompanying drawings.

With reference to FIG. 1, the device comprises a minimally invasive flexible antenna catheter or probe 10 configured to be inserted into the patient through a natural or incised passage within the patient's body . Includes external control unit 12. The catheter is connected to the unit 12 by a flexible cable 14, which has an end connector 14a that connects to a corresponding connector 12a on the unit 12. Typically, the catheter 10 can be about 12.7 to 25.4 mm (0.5 to 1.0 inch) in length and about 2.0 to 2.54 mm (0.08 to 0.10 inch) in diameter.

With reference to FIGS. 2 and 3, catheter 10 includes an inner conductor 16 and a coaxial tubular outer conductor 18. The conductor 16 is longer than the conductor 18, and its front end or tip 16a is spaced from the front side of the outer conductor 18 (the space is filled with the disk-shaped dielectric spacer member 24). It is connected to the center of the space by soldering or welding. A hemispherical conductive shell 26 is attached to the front of the toe plate 22. Together they form the conductive anterior end or tip 10a of the catheter 10. The shell 26 also defines a fluid-sealing space 28 between the wall of the shell and the toe plate.

The rear or tail end of the outer conductor 18 is closed by a disc-shaped heel cap 30 soldered or welded to the conductor 18 and to the rear end 16b of the inner conductor 16 and said to the inner conductor 16. The rear end 16b extends into a small opening 32 in the center of the heel cap 30. The rear end of the center conductor 16 is also connected to the tip of the inner conductor 33 of the cable 14. These two conductors meet at the opening 32 the end of the cable that is secured to the heel cap 30.

As best seen from FIGS. 2 and 4, the portion of the inner conductor 16 within the outer conductor 18 has a dielectric sleep 34 and fits snugly within the conductor 18 and is the length of the conductor 18. It is supported within the conductor 18 by a conductive insert 36 extending in the longitudinal direction. The conductor 16 and its sleeve 34 extend along the axial passage 38 in the insertion body. The insert 36 is in contact with both the outer conductor 18 and the heel cap 30.

As best seen from FIGS. 3 and 4, the insert 36 is approximately T-shaped in cross section and has a pair of arms 36a, 36a and legs 36b, which are the outer conductors 18. In cooperation with, define a pair of longitudinal passages 42, 42 extending in the longitudinal direction of the insert 36. These passages are capable of accommodating a pair of tubes 44, the front ends of which the tubes 44 are secured within the pair of holes 46,46 of the toe plate 22. The tube extends along passages 42, 42 into through holes 48, 48 of the heel cap 30 where it communicates with passages 49, 49 of cable 14.

The tube 44 provides a fluid passage between the catheter tip 10a and the space 28, thereby passing through the catheter to cool the catheter tip or to keep the catheter tip at a selected temperature. The fluid can circulate. In fact, the insert 36 through which those tubes 44 pass constitutes a heat sink. Therefore, it is possible to open the tube into the inserts 42, 42 to keep the catheter and its entire contents at the temperature of the fluid. As shown in FIG. 1, passages 49,49 in cable 14 extend to connector 14a, communicate with hose 50 at connector 14a, and the hose 50 is detachably coupled to control unit 12. Terminate at connector 50a.

Of course, the insert passages 42,42 and tubes 44,44 can also be used for other purposes. For example, the shell 26 can be provided with a small hole 26 to allow the cleaning fluid supplied by one or both tubes to be discharged from the catheter tip 10a. Also, passages and / or tubes can accommodate small wires leading to temperature sensors, ultrasonic transducers, or other electrical devices in space 28 at the tip of the catheter, depending on the particular application.

As best seen from FIGS. 2 and 3, the sheath 52 of the dielectric material (eg, PTFE) surrounds the outer conductor 18 of the catheter 10. However, the sheath does not extend all the way to the front end or tip of the conductor and is terminated at a predetermined distance from the tip for reasons apparent below. The posterior or caudal end of the sheath 52 fuses with the cable 14 so that there is no stepped boundary between the two, which allows the catheter to be easily inserted into the patient. It becomes.

With reference to FIGS. 2-4, a filter circuit 54 and a microwave radiometer circuit 56 (preferably in the form of a monolithic microwave integrated circuit chip (MMICS)) are mounted on top of the insert 36. The 36 acts as a support and heat sink for those chips. Further, the coupling capacitor 58 embedded in the spacer member 24 is directly attached to the inner conductor 16 immediately in front of the insert body 36. One terminal of the capacitor 58 is electrically connected to the conductor 16, the other terminal is connected to the filter circuit 54 via the lead strip 60, and then the filter circuit 54 is connected to the radiometer circuit 56. Output signals from the radiometer circuit 56, as well as specific bias and control voltages, are transmitted in conductors 64, which extend along the top of the insert 36 and through holes 66 in the heel cap 30. Exit the catheter through. These conductors combine with the corresponding conductors 68 (FIGS. 1 and 3) that extend along the cable 14 to the control unit 12. Also, the return conductor 69 from circuit 56 is connected to the corresponding conductor 70 in cable 14.

Preferably, the radiometer circuit 56 operates at frequencies in the microwave region (eg, 1 GHz to 26 GHz, most preferably a center frequency of 4 Gz). A conventional Dicke-type radiometer Cairo is disclosed in Japanese Patent No. 4,557,272 of the applicant. A similar chip radiometer configuration is available from Applicant Meridian Medical Systems, Inc.

Referring to FIG. 1, the control unit 12 includes a transmitter or generator 72 that powers the catheter 10 via a cable 14. The output signal from the transmitter 72 has a frequency that is different (preferably much lower) than the radiometer frequency. The transmitter shown has an output in the RF frequency range (ie, less than 300MHz, preferably 500KHz), which eliminates the need for the cable 14 to be a coaxial cable, which makes the cable 14 more than a coaxial cable. It is possible to have higher flexibility and lower loss. If that is not a problem for a given application, the generator 72 is capable of transmitting at higher frequencies in the microwave region. The transmitter 72 is controlled by the processor 74, which receives instructions from the control button 76a on the operator control panel 76 of the unit 12.

The control unit 12 also includes an amplifier 78 that receives an output signal indicating temperature from the radiometer circuit 56 via the conductor 68 of the cable 14. The amplifier 78 adjusts the signal and sends it to the processor 74, which in turn generates a control signal for controlling the output of the transmitter 72. The processor 74 can also apply the signal to the display 82, which can display the temperature of the fluid or tissue probed by the catheter 10 in real time.

Of course, the display 82 can also display other parameters related to the correct operation of the device (transmitter output, reflected power, catheter temperature, room temperature, elapsed time, etc.).

Preferably, the control unit 12 includes a heating / cooling device 84 that is controlled by the processor 74 and is connected to the joints 84b, 84b via the via holes 84a, 84a, and the connector 50a, to the joints 84b, 84b. 50a is connected. This allows the device 84 to circulate fluid through the catheter 10 to keep the catheter at a selected temperature above or below room temperature, or to a type of temperature change selected for a particular application. It becomes possible to obey.

Referring to FIG. 2, basically, the inner conductor 16 in the catheter 10 constitutes an RF transmission line terminating at a conductive rounded tip 10a. The transmission line operates at the output signal frequency of transmitter 72 (eg, 500 KHz). When the transmitter 72 is activated, the transmission line will radiate heating energy only from the bare portion of the catheter between the catheter tip 10a and the tip of the dielectric sheath 52. Thus, the bare portion constitutes an RF heating or transmitting antenna T, the length of which is determined by the anterior range of the sheath 52 on the outer conductor 18. In other words, increasing the length of the sheath 52 reduces the exposed length of the conductor 18, that is, the surface that can come into contact with the tissue, and thus the length of the antenna T. Since the outer conductor 18 is at the same RF potential as the conductor 16, it can provide an RF path between the antenna T and the transmitter 72.

Referring to FIGS. 2 and 4, the conductive catheter tip 10a also includes a temperature sensing microwave receiving antenna R capable of capturing heat radiation from tissue adjacent to the catheter 10. The portion of the conductor 16 from the tip 10a to the junction with the capacitor 58 constitutes a microwave reception path, which leads along the lead strip 60 to the filter circuit 54 and then to the radiometer circuit 56. .. The conductor 16 transmits both RF and microwave signals, but the conductor 33 transmits only the RF signal through the outer conductor 18 (although it is basically an extension of the conductor 16). Please note.

Depending on the application, the dielectric spacer member 24 is bridged with a small spiral wire (2 to 4 turns) wound in a groove around the member 24 as shown by a virtual line in reference numeral 25 in FIG. It may be desirable to connect 10a to conductor 18. As a result, the RF heating pattern of the antenna T is improved without significantly deteriorating the microwave antenna pattern of the receiving antenna R.

A passive diplexer D is incorporated into the catheter 10 to block transmitter signals from the microwave receiving path to allow the catheter 10 to simultaneously heat (transmit) and detect temperature (detection by radiometer). , And the microwave signal is isolated from the transmitter. The diplexer D has a 1/4 wavelength (λ) consisting of a coupling capacitor 58 and a portion of the catheter 10 extending from the capacitor 58 (more specifically, its connection to the connector 16) to the heel cap 30._R/ 4) Formed from short-circuit stub S. This 1/4 wavelength stub S should be tuned to the frequency of the radiometer circuit 56 (eg 4GHz).

The adjusted length of the stub S (ie, the catheter portion between the capacitor 58 and the heel cap 30) is determined by the permittivity of the material in the sleeve 34 as well as the radiometer frequency. For example, if the radiometer frequency is 4 GHz and the sleeve 34 is PTFE (K = 2.1), the stub length will be about 12.7 mm (0.5 inch). On the other hand, when a material with K = 9 is used, the stub length will be shortened to about 6.4 mm (0.25 inch). For intermediate lengths (eg, about 9.7 mm (0.38 inches)), a material with K = 3.8 would be used.

FIG. 5 is a schematic diagram showing the components of the diplexer D, including the 1/4 wavelength stub S, the coupling capacitor 58, the lead strip 60, and the components of the bandpass filter circuit 54. As shown in the figure, in the configuration of the catheter 10, the stub S adjusted to the radiometer frequency is inserted into the transmission path from the transmitter 72 to the tip 10a. Inductance L in the stub S and circuit 54₁Form a low-pass filter that isolates high frequency (4GHz) signals from the RF path to transmitter 72. On the other hand, capacitor C and inductance L₂Both constitute a high-pass filter that blocks low-frequency (500 KHz) transmitter signals from the signal reception path to the radiometer circuit 56. For some applications, it is desirable that the chip of circuit 54 include the elements of radiometer circuit 56. Placing the radiometer components on separate chips prevents feedback caused by too high amplifier gain on a single chip.

2 and 4 show a capacitor 58 mounted directly on the center conductor 16. However, the capacitor 58 can be incorporated into the filter circuit 54, in which case the lead strip 60 of FIG. 4 extends directly from the conductor 16 to the circuit 54.

See FIG. 6 here. The figure shows the control unit 10 in some detail. The control unit includes various high-pass (HP) and low-pass (LP) filters, which together form a back-end diplexer to isolate the various signals sent to and received from the catheter 10. All of the signals are transmitted along a dedicated conductor in the cable 14. The illustrated back-end diplexer is only one that can be incorporated into the unit 10 and does not constitute the present invention and will not be described in detail. It should be noted that the RF ground conductor 70 from the catheter 10 reaches the ground electrode 12a connected to the unit 12. When the device is in use, the electrodes are placed in contact with the patient's skin to provide an RF return route between the catheter and the patient.

FIG. 7 is a graph showing the performance of Diplexer D. As shown in the figure, Diplexer D provides good impedance matching at a receive frequency of 4GHz (ie greater than 20dB), while blocking frequencies below 1GHz, including a transmitter frequency of 500KHz, or Remove.

The configuration described above allows essentially the same antenna elements to send and receive signals simultaneously, which can both heat the tissue or fluid and detect the temperature of the tissue or fluid in real time. It is possible, and this makes it possible to perform the various medical procedures described at the beginning. Due to the fact that the diplexer and radiometer are incorporated into the catheter probe 10 without significantly increasing the size and / or stiffness of the catheter, the device provides extremely accurate and noise-free temperature measurements in minimal time. It becomes possible.

As can be seen from the above, the applicant's catheter device is particularly for detecting the temperature of such tissue or fluid for monitoring and / or heating the tissue or fluid in the human or animal body in a controlled manner. Provide efficient and effective means. Even if the catheter includes a transmitting and receiving antennas, the entire microwave radiometer and diplexer electrically isolate the transmitter from the receiver, and the catheter is still very small and flexible. This makes it possible to use it in many minimally invasive medical applications.

It will be understood that the above-mentioned objectives, especially those obvious from the above description, are efficiently achieved. In addition, it is possible to make specific changes to the above configuration without departing from the scope of the present invention. For example, depending on the application, the transmitter 76 can transmit in the microwave region. However, in that case, the cable 14 becomes a coaxial cable, which is less flexible and more lossy. Also, of course, if the catheter is used only for detection, the diplexer including the stub S and the circuit 54 can be omitted.

Therefore, it is intended that all matters described above and shown in the accompanying drawings are exemplary and do not imply restrictions.

It will also be appreciated that the following claims are intended to cover all of the general and specific features of the invention described herein.