Circuit and apparatus for decoupling RF surface coils
A decoupling circuit for a radio frequency (RF) surface coil having a plurality of tuning capacitors includes at least two decoupling points and a DC source coupled to the at least two decoupling points. Each decoupling point is associated with one of the plurality of tuning capacitors. Each decoupling point includes a decoupling inductor connected in parallel with a tuning capacitor, a diode connected in series with the decoupling inductor and in parallel with the tuning capacitor, a resistor connected in parallel with the diode and at least one isolating inductor connected between the resistor and the diode to RF isolate the resistor. The value of the resistor in each decoupling point is selected to maintain a high quality factor (Q) of the RF surface coil and to reduce the switching speed of the decoupling circuit.
1. A decoupling circuit for a radio frequency (RF) surface coil in a magnetic resonance imaging (MRI) system, the RF surface coil having a plurality of tuning capacitors, the decoupling circuit comprising:
at least two decoupling points coupled to the RF surface coil in said magnetic resonance imaging system, each decoupling point associated with one of the plurality of tuning capacitors and comprising:
a decoupling inductor connected in parallel with a tuning capacitor;
a diode connected in series with the decoupling inductor and in parallel with the tuning capacitor;
a resistor connected in parallel with the diode; and
at least one isolating inductor connected between the resistor and the diode to isolate the resistor; and
a DC source coupled to the at least two decoupling points.
2. A decoupling circuit according to claim 1 , wherein the resistor has a first end and a second end and the diode has a first terminal and a second terminal and the at least one isolating inductor comprises:
a first isolating inductor connected between the first end of the resistor and the first terminal of the diode; and
a second isolating inductor connected between the second end of the resistor and the second terminal of the diode.
3. A decoupling circuit according to claim 1 , wherein the at least one isolating inductor is connected in series with the resistor.
4. A decoupling circuit according to claim 1 , wherein the diode is a PIN diode.
5. A decoupling circuit according to claim 1 , wherein the resistor has a resistance value and the resistance value is selected to reduce a switching time of the decoupling circuit.
6. A decoupling circuit according to claim 1 , wherein the resistor has a resistance value and the resistance value of the resistor in each decoupling point is the same.
7. A radio frequency (RF) surface coil apparatus for a magnetic resonance imaging (MRI) system, the RF surface coil assembly comprising:
a radio frequency (RF) coil of said magnetic resonance system, the RF coil comprising a plurality of tuning capacitors;
at least two decoupling points coupled to the RF coil, each decoupling point associated with one of the plurality of tuning capacitors and comprising:
a decoupling inductor connected in parallel with a tuning capacitor;
a diode connected in series with the decoupling inductor and in parallel with the tuning capacitor;
a resistor connected in parallel with the diode; and
at least one isolating inductor connected between the resistor and the diode; and
a DC source coupled to the at least two decoupling points.
8. An RF surface coil apparatus according to claim 7 , wherein the at least one isolating inductor is configured to RF isolate the resistor from the RF coil.
9. An RF surface coil apparatus according to claim 7 , wherein the at least two decoupling points are configured to maintain a quality factor (Q) of the RF coil.
10. An RF surface coil apparatus to claim 9 , wherein the resistor has a resistance value and the resistance value of the resistor in each decoupling point is the same.
11. An RF surface coil assembly apparatus to claim 7 , wherein the resistor has a resistance value and the resistance value is selected to reduce a switching time of the RF coil.
12. A resonance assembly comprising:
a superconducting magnet;
a gradient coil assembly disposed within an inner diameter of the superconducting magnet;
an RF body coil disposed within an inner diameter of the gradient coil assembly, the RF body coil configured to transmit RF excitation signals during a transmit mode;
an RF surface coil disposed within an inner diameter of the RF body coil and near an imaging subject, the RF surface coil comprising a plurality of tuning capacitors and configured to receive MR signals emitted from the imaging subject during a receive mode;
a decoupling circuit coupled to RF surface coil and configured to disable the RF surface coil during the transmit mode and enable the RF surface coil during the receive mode, the decoupling circuit comprising at least two decoupling points, each decoupling point associated with one of the plurality of tuning capacitors and comprising:
a decoupling inductor connected in parallel with a tuning capacitor;
a diode connected in series with the decoupling inductor and in parallel with the tuning capacitor;
a resistor connected in parallel with the diode; and
at least one isolating inductor connected between the resistor and the diode to isolate the resistor, and
a DC source coupled to the at least two decoupling points.
13. A resonance assembly according to claim 12 , further comprising an array of RF surface coils and a plurality of decoupling circuits, each decoupling circuit connected to one of the RF surface coils in the array of RF surface coils.
14. A resonance assembly according to claim 12 , wherein the resistor has a resistance value and the resistance value is selected to reduce a switching time for the RF surface coil between the transmit mode and the receive mode.