Metal immune system for tracking spatial coordinates of an object in the presence of a perturbed energy field

• US 6,373,240 B1
• Filed: 10/31/2000
• Issued: 04/16/2002
• Est. Priority Date: 10/15/1998
• Status: Expired due to Term

• Current Assignee: Biosense, Inc. (Cardinal Health, Inc.)
• Original Assignee: Biosense, Inc. (Cardinal Health, Inc.)
• Inventors: Govari, Assaf
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): Zaveri, Subhash
• Application Number:
  US09/702,973
• Time in Patent Office: 532 Days
• Field of Search: 324/207-17, 324/260, 324/461, 324/67, 342/442, 342/448, 342/459, 336/5, 607/422, 607/122, 702/150, 702/152, 702/153
• US Class Current: 324/207.17
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 5/06 Devices, other than using radiation, for detecting or locating foreign bodies for removing same A61B17/50 ; determining position of probes within or on the body of the patient
• CPC Class Codes: A61B 5/062 using magnetic field
• CPC Class Codes: A61B 90/36 Image-producing devices or illumination devices not otherwise provided for
• CPC Class Codes: G01D 5/2086 by movement of two or more coils with respect to two or more other coils

Abstract

A method for tracking an object, including producing an unperturbed energy field at a plurality of predetermined frequencies in the vicinity of the object and determining a characteristic of a perturbing energy field induced responsive to the unperturbed field, due to introduction of an article, responsive to the unperturbed field, into the vicinity of the object. The method further includes receiving a plurality of resultant signals responsive to the unperturbed and perturbing energy fields generated at a location of the object after introduction of the article, determining an optimal frequency for the unperturbed energy field from amongst the plurality of predetermined frequencies responsive to a parameter of the resultant signals, and determining spatial coordinates of the object responsive to the resultant signal at the optimal frequency.

Claims

1. A method for tracking an object, comprising:

producing an unperturbed energy field at a plurality of predetermined frequencies in the vicinity of the object;

measuring a baseline phase value φ

_ω

of each of the plurality of resultant signals at the respective plurality of predetermined frequencies before introduction of the article;

determining a characteristic of a perturbing energy field induced responsive to the unperturbed field, due to introduction of an article responsive to the unperturbed field into the vicinity of the object;

receiving a plurality of resultant signals responsive to the unperturbed and perturbing energy fields generated at a location of the object after introduction of the article;

measuring a phase shift φ

_ω

^total at the respective plurality of predetermined frequencies after introduction of the article, so that the parameter comprises a term |φ

_ω

^total−

φ

_ω

| for each of the plurality of predetermined frequencies;

determining an optimal frequency for the unperturbed energy field from amongst the plurality of predetermined frequencies responsive to a parameter of the resultant signals by determining a frequency ω

at which |φ

_ω

^total−

φ

_ω

| a is a minimum; and

determining spatial coordinates of the object responsive to the resultant signal at the optimal frequency.

2. A method according to claim 1, wherein producing the unperturbed energy field at the plurality of predetermined frequencies comprises scanning the frequencies sequentially.

3. A method according to claim 1, wherein producing the unperturbed energy field at the plurality of predetermined frequencies comprises multiplexing at least some of the frequencies.

4. A method according to claim 1, wherein determining spatial coordinates of the object comprises determining spatial coordinates responsive to an amplitude of a signal |M_ω

| at the frequency ω

.

5. A method according to claim 1, wherein determining spatial coordinates of the object comprises determining spatial coordinates responsive to a phase of a signal M_ω

at the frequency ω

.

6. A method according to claim 1, wherein producing the energy fields comprises producing magnetic fields.

7. A method according to claim 6, wherein receiving the signals comprises receiving electrical signals which are generated responsive to the magnetic fields.

8. A method for tracking an object, comprising:

producing an unperturbed energy field comprising a plurality of predetermined frequencies in the vicinity of the object;

producing a perturbing energy field by introduction of an article responsive to the unperturbed field into the vicinity of the object;

receiving a respective plurality of signals responsive to the unperturbed and perturbing energy fields generated at a location of the object after introduction of the article;

determining one or more factors conditional on spatial coordinates of the object responsive to the plurality of signals and the respective frequencies by assuming a phasor {overscore (A)}_ω

of a signal responsive to the unperturbed energy field and a phasor {overscore (A)}′

_ω

of a signal responsive to the perturbing energy field to be directly proportional to a plurality of predetermined currents generating the fields; and

assuming a phase φ

_ω

of the signal responsive to the unperturbed energy field and a phase φ

_ω

of the signal responsive to the perturbing energy field to be linearly dependent on the plurality of predetermined frequencies.

9. A method according to claim 8, wherein the plurality of frequencies comprises at least four frequencies, and wherein the one or more factors comprise the spatial coordinates of the object.

10. A method according to claim 9, wherein receiving the plurality of signals comprises receiving at least four values of a signal M_i at the at least four frequencies, and wherein determining the one or more factors comprises:

determining a value of a position signal amplitude A₀, generated responsive to the unperturbed energy field, by substituting respective values of the signal M_i into an equation

11. Object tracking apparatus, comprising:

a radiator, which generates an energy field at a plurality of predetermined frequencies in the vicinity of the object;

a sensor, fixed to the object, which generates a plurality of signals responsive to the energy field and to an interfering article responsive to the energy field; and

signal processing circuitry, which receives the plurality of signals from the sensor and determines an optimal frequency for the energy field from amongst the plurality of predetermined frequencies responsive to a parameter of the signals by measuring a baseline phase value φ

_ω

of each of the plurality of resultant signals at the respective plurality of predetermined frequencies before introduction of the article; and

measuring a phase shift φ

_ω

^total at the respective plurality of predetermined frequencies after introduction of the article, so that the parameter comprises a term |φ

_ω

^total−

φ

_ω

| for each of the plurality of predetermined frequencies, and which determines position coordinates of the object responsive of the object responsive to the signal at the optimal frequency by determining a frequency ω

at which |φ

_ω

^total−

φ

_ω

| is a minimum.

12. Apparatus according to claim 11, wherein the radiator generates the energy field at the plurality of predetermined frequencies by scanning the frequencies sequentially.

13. Apparatus according to claim 11, wherein the radiator generates the energy field at the plurality of predetermined frequencies by multiplexing at least some of the frequencies.

14. Apparatus according to claim 11, wherein the parameter comprises a phase shift, and wherein the optimal frequency comprises the frequency where the phase shift is a minimum.

15. Apparatus according to claim 14, wherein the signal processing circuitry determines the position coordinates of the object responsive to an amplitude of one of the plurality of signals at the frequency where the phase shift is a minimum.

16. Apparatus according to claim 11, wherein the energy field comprises a magnetic field.

17. Apparatus according to claim 16, wherein the plurality of signals comprise a plurality of electrical signals which are generated responsive to the magnetic field.

18. Object tracking apparatus, comprising:

a radiator, which generates an energy field comprising a plurality of predetermined frequencies in the vicinity of the object;

a sensor, fixed to the object, which generates a respective plurality of signals responsive to the energy field and to an interfering article responsive to the energy field; and

signal processing circuitry, which receives the plurality of signals from the sensor and determines one or more factors conditional on spatial coordinates of the object responsive to the signals and their corresponding frequencies by assuming a phasor {overscore (A)}_ω

of a signal responsive to the unperturbed energy field and a phasor {overscore (A′

)}_ω

of a signal responsive to the perturbing energy field to be directly proportional to a plurality of predetermined currents generating the fields; and

assuming a phase φ

_ω

of the signal responsive to the unperturbed energy field and a phase φ

_ω

′

of the signal responsive to the perturbing energy field to be linearly dependent on the plurality of predetermined frequencies.

19. Apparatus according to claim 18, wherein the plurality of frequencies comprises at least four frequencies, and wherein the one or more factors comprise the spatial coordinates of the object.