Temperature sensing and control system for cardiac monitoring electrodes

• US 5,209,233 A
• Filed: 02/11/1991
• Issued: 05/11/1993
• Est. Priority Date: 08/09/1985
• Status: Expired due to Term

• Current Assignee: Picker International, Inc. (Koninklijke Philips N.V.)
• Original Assignee: Picker International, Inc. (Koninklijke Philips N.V.)
• Inventors: Reisker, Theodore J., Holland, G. Neil, Molyneaux, David A., Blakeley, Douglas M.
• Primary Examiner(s): Smith, Ruth S.
• Application Number:
  US07/653,628
• Time in Patent Office: 820 Days
• Field of Search: 128/653.2, 128/653.5, 128/696, 128/670, 128/671, 128/901, 128/908, 128/653.1
• US Class Current: 600/412
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/411 Detecting or monitoring allergy or intolerance reactions to an allergenic agent or substance
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence
• CPC Class Codes: A61B 6/541 involving acquisition triggered by a physiological signal
• CPC Class Codes: G01R 33/28 Details of apparatus provided for in groups G01R33/44 - G01R33/64
• CPC Class Codes: G01R 33/5673 Gating or triggering based on a physiological signal other than an MR signal, e.g. ECG gating or motion monitoring using optical systems for monitoring the motion of a fiducial marker
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A cardiac electrode (40) has a plug (48) which is frictionally received in a socket (50) of an electrical lead (56). An impedance (54) is connected in series between the electrical lead and the socket to pass ECG signals substantially unattenuated and for blocking radio frequency signals induced in the lead from reaching the socket and the electrode and heating the electrode to a sufficient temperature to burn the patient. The impedance includes an LC circuit (66, 68) which freely passes low frequency signals, such as cardiac signals, but which is tuned to resonance at radio frequencies, particularly at the frequency of resonance excitation and manipulation pulses of a magnetic resonance imager (A). Alternately, the impedance may include a resistive element for blocking the induced currents. A temperature sensor (60) is mounted in intimate contact with an electrically and thermally conductive socket portion (52) to sense the temperature of the electrode, indirectly. A temperature sensor lead (62), the cardiac lead (56), and a respiratory or other anatomical condition sensor are connected with a multiplexing means (140) which cyclically connects the output signals thereof with an analog to digital converter (142). The digital signals are converted to digital optical signals (102) to be conveyed along a light path (104) out of the examination region. The bits of the received digital signal are sorted (144) between an R-wave detector (120), a temperature limit check (122) which checks whether the temperature of the electrode exceeds preselected limits, and a respiratory detector (132).

Claims

1. A non-invasive diagnostic apparatus comprising:

a means for subjecting a region of interest of a patient to changing magnetic fields and radio frequency signals in order to induce and encode magnetic resonance of selected nuclei in the region of interest;

an electrode for engaging the patient to monitor ECG signals;

an electrically conductive lead having a clip means for selectively engaging and establishing electrical communication with the electrode, the radio frequency signals inducing radio frequency currents in the lead which currents can cause heating of the electrode;

a temperature sensing means mounted to the clip means for sensing temperature;

a means mounted in series between the electrically conductive lead and the electrode for passing the ECG signals while inhibiting the passage of the radio frequency currents;

a receiving means for receiving magnetic resonance signals from the region of interest;

a sequence control means for controlling application of magnetic field gradients and radio frequency pulses and processing the received magnetic resonance signals into diagnostic information.

2. The apparatus as set forth in claim 1 wherein the temperature sensing means is a resistive temperature device mounted in direct thermal contact with an electrically and thermally conductive portion of the clip means.

3. The apparatus as set forth in claim 1 wherein the means for passing ECG signals and inhibiting the passage of radio frequency currents includes an LC circuit having a radio frequency resonance frequency.

4. The apparatus as set forth in claim 1 wherein the means for passing ECG signals and inhibiting passage of radio frequency currents includes a resistance for attenuating the radio frequency currents.

5. A non-invasive diagnostic apparatus comprising:

a means for subjecting a region of interest of a subject to changing magnetic fields and radio frequency signals in a preselected resonance frequency band in order to induce magnetic resonance of selected nuclei in the region of interest;

an electrode disposed adjacent the region of interest to monitor ECG signals;

an electrically conductive lead having a clip means for selective connection to the electrode, the radio frequency signals inducing radio frequency currents in the lead which cause heating of the electrode;

a filter means mounted in series with the electrically conductive lead at the clip means for blocking the passage of the radio frequency currents more than the passage of the ECG signals;

a receiving means for receiving magnetic resonance signals from the region of interest;

a sequence control means for controlling the application of magnetic field gradients and radio frequency pulses and processing received magnetic resonance signals into diagnostic information.

6. The apparatus as set forth in claim 5 wherein the filter means includes an LC circuit and a resistor connected in parallel with the LC circuit.

7. The apparatus as set forth in claim 6 further including a second LC circuit connected in series with the first LC circuit, the first and second LC circuits presenting high impedance to the resonance frequency currents.

8. The apparatus as set forth in claim 5 further including:

an analog to digital converter connected with the electrical lead for converting the signals passed along the lead to electrical digital signals;

a filter impedance means connected between the lead and the analog to digital converter for protecting the analog to digital converter from the induced radio frequency currents;

an electro-optical converter means for converting the electrical digital signals to optical digital signals and transmitting the optical digital signals along a light path.

9. A non-invasive diagnostic apparatus comprising:

a means for subjecting a region of interest of a subject to changing magnetic fields and radio frequency signals in order to induce magnetic resonance of selected nuclei in the region of interest;

an electrode for monitoring cardiac signals disposed adjacent the region of interest;

an electrically conductive lead having a clip means for selective connection to the electrode;

an impedance means mounted in series with the electrically conductive lead adjacent the clip means for inhibiting the passage of radio frequency currents and passing low frequency signals;

a temperature sensing means for sensing electrode temperature and generating an electrical temperature signal indicative thereof;

a multiplexing means for selectively connecting one of the electrical temperature and low frequency signals with an analog to digital converter, the analog to digital converter being connected with the lead to transmit digitized temperature and cardiac signals thereon;

a receiving means for receiving magnetic resonance signals from the region of interest;

a sequence control means for controlling the application of magnetic field gradients and radio frequency pulses and processing received magnetic resonance signals into diagnostic information.

10. A non-invasive diagnostic apparatus comprising:

a means for non-invasively examining an internal region of a subject in an examination region with radio frequency energy;

a monitoring means for monitoring a condition of the subject, the monitoring means including at least one electrically conductive monitor lead that extends into the examination region to a socket for selectively receiving an electrode which is mounted in contact with the subject;

a temperature sensing means for sensing a temperature at the socket.

11. The apparatus as set forth in claim 10 further including a bandpass filter means mounted closely adjacent the socket for passing monitored condition signals and blocking the passage of radio frequency currents induced in the monitor lead.

12. The apparatus as set forth in claim 10 further including a multiplexing means for selectively connecting one of the monitored condition and temperature signals to an analog to digital converter and an electrical to optical converter means for converting an output of the analog to digital converter to digital, optical signals for transmission along an optical transmission path.

13. The apparatus as set forth in claim 12 further including:

an optical signal receiving means for receiving the digital optical signals transmitted along the optical transmission path;

a sorting means for sorting bits of the received digital signal between a monitored condition signal detector and a temperature limit checking means for comparing the monitored temperature with preselected limits.

14. A non-invasive apparatus comprising:

a means for non-invasively examining an internal region of a subject in an examination region with radio frequency energy;

an electrode detachably mounted to the subject;

a monitoring means for monitoring a condition of the subject, the monitoring means including at least one electrically conductive monitor lead that extends into the examination region and is connected with the electrode;

a temperature sensing means for sensing a temperature of the electrode.

15. The apparatus as set forth in claim 14 wherein the temperature sensing means includes a temperature sensor and a temperature sensor lead extending from the temperature sensor to a temperature signal output means.

16. The apparatus as set forth in claim 15 wherein the temperature sensor is a fluoroptic sensor which generates light that changes in accordance with temperature and wherein the temperature sensor lead is an optic fiber.

17. The apparatus as set forth in claim 15 wherein the temperature sensing means is an electrical sensor and the temperature sensor lead is an electrically conductive lead and further including a filter means connected with at least one of the temperature sensor lead and the monitor lead for blocking the passage of radio frequency signals therethrough and passing low frequency signals.

18. The apparatus as set forth in claim 14 wherein the monitor lead has a socket at one end thereof, the temperature sensing means being mounted in the socket and wherein the electrode has a plug means which is releasably received in the socket.

19. The apparatus as set forth in claim 18 further including a bandpass filter means mounted closely adjacent the socket for passing monitored condition signals and blocking the passage of radio frequency currents induced in the monitor lead.

20. A method of non-invasive diagnostic examination comprising:

attaching an electrode which is connected to an electrical lead to a subject and positioning a portion of the subject to be examined in an examination region;

subjecting the examination region to changing magnetic fields and radio frequency signals in order to induce magnetic resonance of selected nuclei in the examination region, the radio frequency signals inducing radio frequency currents in the electrical lead;

monitoring a temperature of the electrode;

in response to the monitored electrode temperature exceeding preselected limits, controlling application of the radio frequency signals;

receiving magnetic resonance signals from the examination region; and

,

processing the received magnetic resonance signals into diagnostic information.

21. A method of non-invasive diagnostic examination comprising:

attaching an electrode which is connected by an impedance to an electrical lead to a subject and disposing a portion of the subject to be examined in an examination region;

subjecting the portion of the subject in the examination region to changing magnetic fields and radio frequency signals including a selected resonance frequency in order to induce magnetic resonance of selected nuclei of the subject, the radio frequency signals inducing radio frequency currents including the resonance frequency in the leads;

blocking passage of the radio frequency currents from the lead to the electrode while concurrently passing signals with frequencies below the selected resonance frequency from the electrode to the electrical lead;

receiving the magnetic resonance signals from the region of interest and receiving electrode signals with frequencies below the resonance frequency from the leads; and

,

processing the received magnetic resonance signals and electrode signals into diagnostic information.