INTRACAVITY PROBES AND INTERFACES THEREFOR FOR USE IN OBTAINING IMAGES AND SPECTRA OF INTRACAVITY STRUCTURES USING HIGH FIELD MAGNETIC RESONANCE SYSTEMS

• US 20090076378A1
• Filed: 11/15/2005
• Published: 03/19/2009
• Est. Priority Date: 11/15/2004
• Status: Active Grant

• Current Assignee: DxTx Medical Inc.
• Original Assignee: Medrad Incorporated (Bayer AG)
• Inventors: Misic, George J.
• Granted Patent: US 7,885,704 B2
• Time in Patent Office: Days
• US Class Current: 600/423
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/6856 with a distal loop
• CPC Class Codes: G01R 33/34 Constructional details, e.g. resonators , specially adapted to MR
• CPC Class Codes: G01R 33/34084 implantable coils or coils being geometrically adaptable to the sample, e.g. flexible coils or coils comprising mutually movable parts
• CPC Class Codes: G01R 33/34092 RF coils specially adapted for NMR spectrometers
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels
• CPC Class Codes: G01R 33/3628 Tuning/matching of the transmit/receive coil
• CPC Class Codes: G01R 33/3642 Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification

Abstract

An intracavity probe for use with an MR system allows images or spectra of a region of interest within a cavity of a patient to be obtained. The probe includes a shaft, a balloon at one end thereof, and a coil loop within the balloon. The coil loop preferably includes two drive capacitors and a tuning capacitor, all of which in series. A junction node between the drive capacitors serves as a ground for electrically balancing the coil loop. Diametrically opposite the junction node, the tuning capacitor enables the coil loop to resonate at the operating frequency of the MR system. Across each drive capacitor is connected an output cable having an electrical length of S_L+n(λ/4). The output cables terminate in a plug that is used to connect the coil loop to an interface device for the intracavity probe.

Claims

1. An intracavity probe for use with a magnetic resonance (MR) system for obtaining images or spectra of a region of interest within a cavity of a patient, said intracavity probe comprising:

(a) a first coil loop for receiving MR signals from the region of interest, said first coil loop having a plurality of capacitors therein, said plurality of capacitors including (i) a first drive capacitor and a second drive capacitor of approximately equal value serially connected within said first coil loop and at a junction node thereof forming a virtual ground for electrically balancing and impedance matching said first coil loop and (ii) a tuning capacitor serially connected within said first coil loop diametrically opposite said junction node of said drive capacitors and having a value selected to resonate said first coil loop at an operating frequency of said MR system;

(b) a first output cable connected at one end thereof across said first drive capacitor; and

(c) a second output cable connected at one end thereof across said second drive capacitor;

wherein said first and said second output cables (i) each have an electrical length of S_L+n(λ

/4) wherein S_L is a supplemental length whose reactance is of a same magnitude as a reactance of said drive capacitor corresponding thereto, n is an odd integer, and λ

is a wavelength of the operating frequency of said MR system; and

(ii) terminate in a plug therefor for connecting said first coil loop to an interface device for said intracavity probe.

2. The intracavity probe of claim 1 further comprising:

(a) a flexible shaft having a tip at a distal end thereof, said tip being substantially more flexible than a remainder of said flexible shaft;

(b) an inner balloon connected to said distal end of said flexible shaft and enclosing said tip thereof;

(c) a non-stretchable material for securing said first coil loop to an anterior surface of said inner balloon; and

(d) an outer balloon connected to said distal end of said shaft enclosing both said inner balloon and said first coil loop secured thereto, said outer balloon for use in positioning said inner balloon within the cavity of the patient;

such that said non-stretchable material affects inflation of said inner balloon within said outer balloon to enable said first coil loop therein to be positioned approximate the region of interest for optimal reception of said MR signals therefrom.

3. The intracavity probe of claim 2 wherein said non-stretchable material focuses inflation of said inner balloon to force a posterior surface of said outer balloon against a wall of the cavity then forcing an anterior surface of said outer balloon against a correspondingly-shaped interior contour of the cavity thereby bringing said first coil loop approximate the region of interest for optimal reception of said MR signals therefrom.

4. The intracavity probe of claim 2 wherein said outer balloon has an anterior surface for conformably fitting to a correspondingly-shaped interior contour of the cavity.

5. The intracavity probe of claim 4 wherein said outer balloon has a posterior surface, opposite said anterior surface thereof, comprising at least a pair of undulating folds.

6. The intracavity probe of claim 5 further comprising a means for controlling inflation of said inner balloon, said inflation control means being connected to said flexible shaft through which a fluid can be conveyed to inflate and deflate said inner balloon.

7. The intracavity probe of claim 6 wherein said inflation control means includes a stop cock for controlling passage of the fluid therethrough and release of the fluid therefrom.

8. The intracavity probe of claim 6 wherein said flexible shaft includes:

(a) a first lumen for interconnecting said inflation control means and said inner balloon; and

(b) a second lumen through which said first and said second output cables are routed from said first coil loop to be made available for connection to said interface device for said intracavity probe.

9. The intracavity probe of claim 8 wherein said inflation control means comprises a compressible inflator cuff and a tube therewith connected to said first lumen of said flexible shaft to deliver the gas to said inner balloon upon compression of said inflator cuff.

10. The intracavity probe of claim 5 wherein said non-stretchable material focuses inflation of said inner balloon to force said undulating folds of said outer balloon posteriorly against a wall of the cavity then forcing said anterior surface of said outer balloon anteriorly against said correspondingly-shaped interior contour of the cavity thereby bringing said first coil loop approximate the region of interest for optimal reception of said MR signals therefrom.

11. The intracavity probe of claim 10 wherein said anterior surface of said outer balloon is saddle-shaped and said correspondingly-shaped interior contour of the cavity is a rectal prostatic bulge of the patient.

12. The intracavity probe of claim 2 wherein said flexible shaft includes a scale printed on an outer surface thereof.

13. The intracavity probe of claim 2 wherein said inner and said outer balloons each comprise a non-paramagnetic, flame retardant, biocompatible medical grade material having low dielectric loss characteristics.

14. The intracavity probe of claim 2 further comprising an anti-migration disc attachable to said flexible shaft for preventing unwanted movement of said intracavity probe relative to the cavity of the patient.

15. The intracavity probe of claim 14 wherein said anti-migration means is a disc having a semi-spherical shape, said disc defining a slot for allowing said disc to be snapped onto said flexible shaft.

16. The intracavity probe of claim 2 further comprising a dilator element slidably mounted on said flexible shaft for dilating an orifice leading to the cavity to allow easy positioning of said intracavity probe within the cavity.

17. The intracavity probe of claim 2 wherein said outer balloon further comprises lateral indentations therein on which said first coil loop at least partially rests when said outer balloon is uninflated.

18. The intracavity probe of claim 1 further comprising:

(a) a flexible shaft;

(b) an inflatable balloon connected to a distal end of said flexible shaft, said inflatable balloon having (i) an anterior surface conformable to a correspondingly-shaped interior contour of the cavity and (ii) a posterior surface comprising at least a pair of undulating folds; and

(c) said first coil loop secured within said inflatable balloon approximate an underside of said anterior surface thereof;

such that when said inflatable balloon is inserted into the cavity and inflated said undulating folds thereof press against a wall of the cavity generally opposite the region of interest thus forcing said anterior surface of said inflatable balloon against said correspondingly-shaped interior contour of the cavity thereby bringing said first coil loop approximate the region of interest for optimal reception of said MR signals therefrom.

19. The intracavity probe of claim 1 wherein said first and said second drive capacitors each have a value in a range of approximately 62 pF to 82 pF and said tuning capacitor has a value in a range of approximately 12 pF to 15 pF.

20. The intracavity probe of claim 1 further comprising a second coil loop identical in all respects to said first coil loop inclusive of two output cables connected thereto, with said first and said second coil loops being arranged in a phased array configuration.

21. The intracavity probe of claim 1 further comprising a second coil loop identical in all respects to said first coil loop inclusive of two output cables connected thereto, with said first and said second coil loops being oriented cooperatively to provide quadrature coverage of the region of interest.

22. An intracavity probe for use with a magnetic resonance (MR) system for obtaining images or spectra of a region of interest within a cavity of a patient, said intracavity probe comprising:

(a) a first coil loop for receiving MR signals from the region of interest, said first coil loop having a plurality of capacitors serially connected therein, said plurality of capacitors including (i) a drive capacitor for electrically balancing and impedance matching said first coil loop and (ii) a tuning capacitor positioned diametrically opposite said drive capacitor and having a value selected to resonate said first coil loop at an operating frequency of said MR system; and

(b) an output cable connected at one end thereof across said drive capacitor, said output cable (i) having an electrical length of S_L+n(λ

/4) wherein S_L is a supplemental length whose reactance is of a same magnitude as a reactance of said drive capacitor, n is an odd integer, and λ

is a wavelength of the operating frequency of said MR system; and

(ii) terminating in a plug therefor for connecting said first coil loop to an interface device for said intracavity probe.

23. The intracavity probe of claim 22 further comprising a second coil loop identical in all respects to said first coil loop inclusive of an output cable connected thereto, with said first and said second coil loops being arranged in a phased array configuration.

24. The intracavity probe of claim 22 further comprising a second coil loop identical in all respects to said first coil loop inclusive of an output cable connected thereto, with said first and said second coil loops being oriented cooperatively to provide quadrature coverage of the region of interest.

25. An interface device for interfacing an intracavity probe with a magnetic resonance (MR) system having a receive cycle and a transmit cycle of operation, said intracavity probe having a coil loop and a pair of output cables for connecting said coil loop to said interface device, said interface device comprising:

(a) a phase shifting network for enabling said coil loop (i) during said receive cycle to be coupled through said output cables to a probe input port of said MR system and enabling MR signals received from each of said output cables to be constructively combined and (ii) during said transmit cycle to be decoupled through said output cables from a transmit field of said MR system; and

(b) a preamplifier for providing gain and impedance matching between said phase shifting network and said probe input port so that said MR signals received from said phase shifting network are passed with enhancement of signal-to-noise ratio to said probe input port during said receive cycle.

26. The interface device of claim 25 wherein said phase shifting network includes:

(a) a pair of sub-networks of which a first sub-network is for connection to a first of said pair of output cables and a second sub-network is for connection to a second of said pair of output cables; and

(b) a pair of PIN diodes of which a first PIN diode is connected across an output of said first sub-network and a second PIN diode is connected across an output of said second sub-network;

wherein said PIN diodes are capable of being biased by said MR system such that (i) in a reverse biased state during said receive cycle, said PIN diodes enable said MR signals applied by said coil loop to said first and said second output cables to be phase-shifted relative to each other by said first and said second sub-networks and then provided constructively-combined to said preamplifier and (ii) in a forward biased state during said transmit cycle, said PIN diodes enable said coil loop to be decoupled through each of said first and said second output cables from said transmit field of said MR system.

27. The interface device of claim 25 wherein said preamplifier includes:

(a) a GASFET having a gate, a source and a drain; and

(b) a series resonant circuit connected between said phase shifting network and said gate, said series resonant circuit for coupling said intracavity probe to said gate so as to broaden a frequency response of said coil loop, said series resonant circuit comprising an input capacitor and an input inductor at a junction of which said gate of said GASFET is connected, said series resonant circuit during said receive cycle of said MR system for providing an optimum impedance to said GASFET when said coil loop is loaded.

28. The interface device of claim 25 wherein said GASFET at said source thereof is connected to a biasing resistor therefor and at said drain thereof is connected to a coupling capacitor and an RF choke;

such that when said interface device is connected to said MR system said drain connects to said probe input port via said coupling capacitor and to a DC power source in said MR system via said RF choke.

29. The interface device of claim 25 wherein further including:

(a) a probe cable for connecting an output of said interface device to said probe input port of said MR system; and

(b) a cable trap for preventing undesired current from flowing on a shield conductor of said probe cable.

30. The interface device of claim 25 further comprising a preamp protection diode for protecting said preamplifier during said transmit cycle of said MR system.

31. An interface device for interfacing an intracavity probe with a magnetic resonance (MR) system having a receive cycle and a transmit cycle of operation, said intracavity probe having a coil loop and a pair of output cables for connecting said coil loop to said interface device, said interface device comprising:

a phase shifting network for enabling said coil loop (i) during said receive cycle to be coupled through said output cables to a probe input port of said MR system and enabling MR signals received from each of said output cables to be constructively combined and routed to said probe input port and (ii) during said transmit cycle to be decoupled through said output cables from a transmit field of said MR system.

32. An interface device for interfacing an intracavity probe and a coil system with a magnetic resonance (MR) system having a receive cycle and a transmit cycle of operation, said intracavity probe having a coil loop and a pair of output cables for connecting said coil loop to said interface device, said interface device comprising:

(a) a phase shifting network for enabling said coil loop (i) during said receive cycle to be coupled through said output cables to a probe input port of said MR system and enabling MR signals received from each of said output cables to be constructively combined for output to said probe input port and (ii) during said transmit cycle to be decoupled through each of said output cables from a transmit field of said MR system; and

(b) an array interface circuit for electrically interconnecting said coil system and said MR system.

33. The interface device of claim 32 wherein said array interface circuit includes:

(a) a first series resonant network for conveying MR signals from a first coil of said coil system to a first coil input port of said MR system;

(b) a second series resonant network for conveying MR signals from a second coil of said coil system to a second coil input port of said MR system;

(c) a pair of ¼

wavelength networks, one of said pair for receiving MR signals from a third coil of said coil system and an other of said pair for receiving MR signals from a fourth coil of said coil system; and

(d) a ¼

wavelength combiner for combining such MR signals received from said pair of ¼

wavelength networks and conveying such combined MR signals to a third coil input port of said MR system.

34. The interface device of claim 32 wherein said phase shifting network includes:

(a) a pair of sub-networks of which a first sub-network is for connection to a first of said pair of output cables and a second sub-network is for connection to a second of said pair of output cables; and

(b) a pair of PIN diodes of which a first PIN diode is connected across an output of said first sub-network and a second PIN diode is connected across an output of said second sub-network;

wherein said PIN diodes are capable of being biased by said MR system such that (i) in a reverse biased state during said receive cycle, said PIN diodes enable said MR signals applied by said coil loop to said first and said second output cables to be phase-shifted relative to each other by said first and said second sub-networks and then provided constructively-combined for output to said probe input port and (ii) in a forward biased state during said transmit cycle, said PIN diodes enable said coil loop to be decoupled through each of said first and said second output cables from said transmit field of said MR system.

35. The interface device of claim 32 wherein said ¼

wavelength combiner is a Wilkinson combiner.

36. The interface device of claim 32 wherein each of said first and said second series resonant networks are series resonant at the operating frequency of said MR system to thereby render an electrical length thereof effectively zero.

37. The interface device of claim 32 wherein said ¼

wavelength combiner and said ¼

wavelength networks connected thereto provide for such MR signals conveyed therethrough an electrical length of effectively zero at the operating frequency of said MR system.

38. The interface device of claim 32 further including:

(a) a probe cable having a shield conductor and a center conductor insulatively disposed therein such that at an end of said probe cable said shield and said center conductors are connected across an output of said phase shifting network, said probe cable having an electrical length of n(λ

/2); and

(b) a cable trap for preventing undesired current from flowing on said shield conductor of said probe cable.