Microcoil NMR Detectors

• US 20080272788A1
• Filed: 05/02/2008
• Published: 11/06/2008
• Est. Priority Date: 05/03/2007
• Status: Active Grant

• Current Assignee: ABQMR, Inc.
• Original Assignee: ABQMR, Inc.
• Inventors: McDowell, Andrew F.
• Granted Patent: US 8,067,938 B2
• Time in Patent Office: Days
• US Class Current: 324/322
• CPC Class Codes: G01R 33/34053 Solenoid coils; Toroidal coils
• CPC Class Codes: G01R 33/3628 Tuning/matching of the transmit/receive coil
• CPC Class Codes: G01R 33/4808 Multimodal MR, e.g. MR combined with positron emission tomography [PET], MR combined with ultrasound or MR combined with computed tomography [CT]
• CPC Class Codes: Y10T 29/49071 by winding or coiling

Abstract

The present invention provides resonance circuits, detection devices incorporating such circuits, and methods for their design, construction, and use.

Claims

1. A resonant circuit comprising

(a) a closely wound microcoil, wherein the closely wound microcoil is an effective magnetic resonance transmitter or receiver coil;

(b) an auxiliary inductor coil electrically connected in series to the closely wound microcoil; and

(c) a tuning capacitor electrically connected to the closely wound microcoil and the auxiliary inductor coil to form a resonant circuit.

2. The resonant circuit of claim 1, wherein the closely wound microcoil comprises wire with a diameter less than or equal to 2.5 times a skin-depth of the wire material.

3. The resonant circuit of claim 1 wherein the closely wound microcoil has a total length of between 148 μ

m and 648 μ

m.

4. The resonant circuit of claim 3, wherein the closely wound microcoil is wound around a capillary with an outer diameter of between 170 and 550 μ

m.

5. The resonant circuit of claim 1, wherein the auxiliary inductor coil comprises wire of a larger diameter than a diameter of the closely wound microcoil wire.

6. The resonant circuit of claim 5, wherein the auxiliary inductor coil has a radius of 0.3 cm to 0.6 cm.

7. The resonant circuit of claim 1 mounted on a mechanical support.

8. The resonant circuit of claim 7, installed in one or more shielded probe bodies.

9. The resonant circuit of claim 8, wherein the one or more shielded probe bodies comprise two shielded probe bodies, wherein a first shielded probe body shields the closely wound microcoil, wherein a second shielded body shields the shielded probe body shields the auxiliary inductor and the capacitor.

10. A resonant circuit comprising

(a) a microcoil comprising wire with a diameter less than or equal to 2.5 times a skin-depth of the wire material, wherein the microcoil is an effective magnetic resonance transmitter or receiver coil;

(b) an auxiliary inductor coil electrically connected in series to the microcoil; and

(c) a tuning capacitor electrically connected to the microcoil and the auxiliary inductor coil to form a resonant circuit.

11. The resonant circuit of claim 10, wherein the microcoil is a closely wound microcoil.

12. The resonant circuit of claim 10 wherein the microcoil has a total length of between 148 μ

m and 648 μ

m.

13. The resonant circuit of claim 12, wherein the microcoil is wound around a capillary with an outer diameter of between 170 and 550 μ

m.

14. The resonant circuit of claim 10, wherein the auxiliary inductor coil comprises wire of a larger diameter than a diameter of the microcoil wire.

15. The resonant circuit of claim 14, wherein the auxiliary inductor coil has a radius of 0.3 cm to 0.6 cm.

16. The resonant circuit of claim 10 mounted on a mechanical support.

17. The resonant circuit of claim 16, installed in one or more shielded probe bodies.

18. The resonant circuit of claim 17, wherein the one or more shielded probe bodies comprise two shielded probe bodies, wherein a first shielded probe body shields the closely wound microcoil, wherein a second shielded body shields the shielded probe body shields the auxiliary inductor and the capacitor.

19. A detection device, comprising:

(a) a permanent magnet possessing a field strength of 1-2 Tesla; and

(b) a resonant circuit comprising;

(i) a closely wound microcoil, wherein the closely wound microcoil is disposed proximate to the magnetic field generated by the permanent magnet, and wherein the closely wound microcoil is an effective magnetic resonance transmitter or receiver coil;

(ii) an auxiliary inductor coil electrically connected in series to the closely wound microcoil; and

(iii) a tuning capacitor electrically connected to the closely wound microcoil and the auxiliary inductor coil to form a resonant circuit; and

(c) a capillary with an inner diameter of between 100 μ

m and 400 μ

m, wherein the closely wound microcoil is wound around the capillary.

21. The detection device of claim 19 further comprising an NMR imaging system.

23. The detection device of claim 19, further comprising fluid handling tubing in fluid communication with the capillary.

25. A method for detection comprising:

(a) delivering a sample fluid to the detection system of claim 23;

(b) resonating the resonant circuit at low frequency; and

(c) detecting resonance signals from the sample, wherein the resonance signals correlate with a presence of one or more targets of interest in the sample fluid.

20. A detection device, comprising:

(a) a permanent magnet possessing a field strength of 1-2 Tesla; and

(b) a resonant circuit comprising;

(i) a microcoil comprising wire with a diameter less than or equal to 2.5 times a skin-depth of the wire material, wherein the microcoil is disposed proximate to the magnetic field generated by the permanent magnet, and wherein the microcoil is an effective magnetic resonance transmitter or receiver coil;

(ii) an auxiliary inductor coil electrically connected in series to the microcoil; and

(iii) a tuning capacitor electrically connected to the microcoil and the auxiliary inductor coil to form a resonant circuit; and

(c) a capillary with an inner diameter of between 100 μ

m and 400 μ

m, wherein the microcoil is wound around the capillary

22. The detection device of claim 20 further comprising an NMR imaging system.

24. The detection device of claim 20, further comprising fluid handling tubing in fluid communication with the capillary.

26. A method for detection comprising:

(a) delivering a sample fluid to the detection system of claim 24;

(b) resonating the resonant circuit at low frequency; and

(c) detecting resonance signals from the sample, wherein the resonance signals correlate with a presence of one or more targets of interest in the sample fluid.

27. A method for designing an auxiliary tuning inductor for use in an NMR microcoil resonant circuit, comprising:

(a) preparing a microcoil with wire of a first diameter;

(b) determining an RF resistance of the microcoil;

(c) winding an auxiliary inductor coil with wire of a second diameter, where the second diameter is greater than the first diameter, and wherein a radius of the auxiliary inductor coil is determined using the formula;

$r_{\mathrm{coil}}=\sqrt{\frac{25<br><br><br><br>l_{\mathrm{wire}}<br><br>{\mathrm{kd}}_{\mathrm{wire}}}{46<br><br><br><br>\mathrm{\pi <br><br>}}}$

where l_wire is the wire length, d_wire is the wire diameter, and kd_wire is the turn-to-turn wire spacing.

28. A method for forming a closely wound microcoil, comprising:

(a) mounting a microcapillary tube to a headstock of a miniature lathe via an optical fiber chuck appropriately sized to hold a microcapillary tube;

(b) attaching a first end of a wire to the optical fiber chuck;

(c) attaching a second end of the wire to a support controlled by a saddle and cross-feed of the miniature lathe; and

(d) turning the headstock and repositioning the cross-feed of the lathe until close winding of the microcoil around the microcapillary tube is complete.