Contact sensing systems and methods
According to some embodiments, a medical instrument comprises an elongate body having a proximal end and a distal end and a pair of electrodes or electrode portions (for example, a split-tip electrode assembly). Systems and methods are described herein that perform contact sensing and/or ablation confirmation based on electrical measurements obtained while energy of different frequencies are applied to the pair of electrodes or electrode portions. The contact sensing systems and methods may calibrate network parameter measurements to compensate for a hardware unit in a network parameter measurement circuit or to account for differences in cables, instrumentation or hardware used.
1. A system for determining whether a medical instrument is in contact with tissue based, at least in part, on impedance measurements, the system comprising:
a signal source configured to deliver signals having different frequencies to a pair of electrodes of a medical instrument; and
a processing device configured to:
apply a transform to a resulting waveform that formulates across a pair of electrodes to obtain impedance measurements at a first frequency and a second frequency;
determine a ratio between the magnitude of the impedance at the second frequency and the first frequency;
if the determined ratio is below a predetermined threshold indicative of contact, generate a first output indicative of contact; and
if the determined ratio is above the predetermined threshold, generate a second output indicative of no contact.
2. The system of claim 1 , wherein the signal source comprises a radiofrequency energy source and wherein the first and second frequencies are between 5 kHz and 1000 kHz.
3. The system of claim 1 , wherein the signal source is configured to generate signals having a frequency adapted for tissue ablation.
4. The system of claim 1 , further comprising a second signal source configured to generate signals having a frequency adapted for tissue ablation.
5. The system of claim 4 , wherein the frequency adapted for tissue ablation is between 400 kHz and 600 kHz.
6. The system of claim 1 , wherein the predetermined threshold is a value between 0.5 and 0.9.
7. A method of determining whether a medical instrument is in contact with tissue based, at least in part, on impedance measurements, the method comprising:
applying signals having a first frequency and a second frequency to a pair of electrodes of medical instrument;
applying a transform to a resulting waveform to obtain impedance measurements at the first frequency and the second frequency;
determining a ratio between the magnitude of the impedance at the second frequency and the first frequency;
if the determined ratio is below a predetermined threshold indicative of contact, generating a first output indicative of contact; and
if the determined ratio is above the predetermined threshold, generating a second output indicative of no contact.
8. The method of claim 7 , wherein the first frequency and the second frequency are within a range between 5 kHz and 1000 kHz.
9. The method of claim 7 , wherein the second frequency is higher than the first frequency.
10. The method of claim 7 , wherein impedance measurements at the first frequency and the second frequency are obtained sequentially.
11. The method of claim 7 , wherein impedance measurements at the first frequency and the second frequency are obtained simultaneously.
12. The method of claim 7 , wherein the second frequency is at least 20 kHz higher than the first frequency.
13. The method of claim 7 , wherein the first frequency is 20 kHz and the second frequency is 800 kHz.
14. The method of claim 7 , wherein the predetermined threshold is a value between 0.5 and 0.9.
15. The method of claim 7 , wherein said steps of generating a first output and generating a second output further comprises causing the first output or the second output to be displayed on a display.
16. The method of claim 15 , wherein the output comprises textual information indicative of contact.
17. The method of claim 15 , wherein the output comprises a quantitative measurement indicative of contact.
18. The method of claim 15 , wherein the output comprises a qualitative assessment of contact.
19. The method of claim 7 , wherein the transform is a Fourier transform.