Method to automatically tune MRI RF coils

• US 6,184,684 B1
• Filed: 02/16/2000
• Issued: 02/06/2001
• Est. Priority Date: 01/27/1997
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Iben, Icko Eric Timothy, Dumoulin, Charles Lucien, El-Hamamsy, Sayed-Amr Ahmes, Watkins, Ronald Dean, Edelstein, William Alan
• Primary Examiner(s): ARANA, LOUIS M
• Application Number:
  US09/505,975
• Time in Patent Office: 356 Days
• Field of Search: 324/318, 324/319, 324/320, 324/322, 324/300, 324/307, 324/309, 600/421, 600/422
• US Class Current: 324/318
• CPC Class Codes: G01R 33/3628 Tuning/matching of the transmit/receive coil

Abstract

A sweep generator 230 applies a range of frequencies to an rf coil 140 to detect the resonant frequency of a field generated by a magnet 125a,b. A frequency to current converter 220 applies an auxiliary magnetic field to tune an MRI apparatus to the resonant frequency of the rf coil. A flexible coil of one turn (300) or two or more turns (500) has a plurality of segments (301-307; 501-513). One of the belt has a contact k0, (k0′), which is electrically connectable to one or more contacts k1, (k1′), k2, (k2′), etc. located between the ends of the segments. For each connection to successive contacts, the length of the coil and its inductance increases by the added impedance DL_ij between contacts k_i and k_j. That increase of inductance is nullified by capacitors DC_sij located between segments.

Claims

1. A flexible coil for magnetic resonance imaging comprising:

a continuous belt having a first layer of insulating material and a second layer comprising an rf coil for generating or receiving an rf MRI imaging signal, the belt comprising a series of joined segments including a first active segment that establishes a minimum active length and one or more serial intermediate segments that extend the active length of the belt between a minimum physical length and a maximum physical length;

the first segment having an inductance and a capacitance that establishes a resonant frequency for said minimum physical length;

means for adjusting the active length of the belt to an intermediate length compatible with the circumference of a sample, said intermediate length including one or more serial segments of the belt;

each serial segment being electrically connected in series with the first segment and with any intervening segments, each serial segment providing an incremental inductance and an incremental capacitance that substantially cancel one another so that the resonant frequency of the coil at each intermediate length and at the maximum length is substantially the same as the resonant frequency for the minimum length.

2. The flexible coil of claim 1 wherein each segment has the same fixed inductance and the same fixed capacitance.

3. The flexible coil of claim 1 wherein at least one segment has a fixed inductance and a fixed capacitance different from the fixed inductance and the fixed capacitance of at least one other segment.

4. The flexible coil of claim 1 wherein each segment has at least one inductor and at least one capacitor connected in series and a contact disposed on the segment for connecting the segment to one end of the belt.

5. The flexible coil of claim 1 further comprising a preamplifier with a source impedance selected to minimize the noise figure of the preamplifier and coupled to the flexible coil wherein the impedance of the flexible coil is in a range of about one-half to two times the source impedance of the preamplifier.

6. The flexible coil of claim 1 further comprising a preamplifier coupled to the flexible coil and an external tuning circuit coupled to the coil for adjusting phase shift by selectively adjusting reactance at the input of the preamplifier to minimize the noise figure of the preamplifier.

7. The flexible coil of claim 1 further comprising one or more variable reactive elements located within the minimum active length of the flexible coil in series with the series inductance of the flexible coil and selectively adjustable to vary the inductance of the flexible coil for altering the resonant frequency of the flexible coil.

8. The flexible coil of claim 7 wherein the variable reactive elements comprise at least one switched capacitor.

9. The flexible coil of claim 8 wherein the switched capacitor(s) further comprises PIN diode(s) for switching a capacitor into or out of the electrical circuit.

10. The flexible coil of claim 1 further comprising a phase tuning circuit coupled to the flexible coil for adjusting the phase of a signal received by the coil.

11. The flexible coil of claim 10 further comprising a preamplifier coupled to the phase tuning circuit.

12. The flexible coil of claim 10 wherein the phase tuning circuit comprises a variable reactance.

13. The flexible coil of claim 12 wherein the variable reactance comprises an inductor and variable capacitor.