CN-122003615-A - RF receive circuit for MRI for single circuit Q-value destruction and preamplifier decoupling

CN122003615ACN 122003615 ACN122003615 ACN 122003615ACN-122003615-A

Abstract

A Radio Frequency (RF) receive circuit for use in a Magnetic Resonance Imaging (MRI) scanner includes an antenna including a plurality of reactive impedance elements coupled in a loop configuration, an amplifier input impedance, a first transmission line coupled in parallel with at least one reactive impedance element, a second transmission line coupled in parallel with the amplifier input impedance, a first reactive impedance circuit between the first transmission line and the second transmission line, an RF switch configured to isolate a second combined impedance including the second transmission line and the amplifier input impedance from a first combined impedance including the first transmission line and the first reactive impedance circuit when the RF switch is closed and to couple the second combined impedance to the first combined impedance when the RF switch is open, wherein the first combined impedance transforms the impedance of the RF switch to resonate with the at least one antenna impedance element when the RF switch is closed, and wherein the first combined impedance and the second combined impedance together transform the amplifier input impedance to resonate with the at least one antenna impedance element when the RF switch is open.

Inventors

Trasi Arlin temperature
Gillian gentry Heimer
Joseph Russell Correa
Phuket Malik

Assignees

墨迹空间成像公司

Dates

Publication Date: 20260508
Application Date: 20240918
Priority Date: 20230919

Claims (20)

1. A Radio Frequency (RF) receive circuit for use in a Magnetic Resonance Imaging (MRI) scanner, the RF circuit comprising: An antenna comprising a plurality of reactive impedance elements electrically coupled in a loop configuration; an amplifier input impedance; a first transmission line electrically coupled in parallel with the at least one reactive impedance element; A second transmission line electrically coupled in parallel with the amplifier input impedance; A first reactive impedance circuit electrically coupled to the first transmission line and to the second transmission line between the first transmission line and the second transmission line; An RF switching circuit electrically coupled between a first combined impedance comprising the first transmission line and the first reactive impedance circuit and a second combined impedance comprising the second transmission line and the amplifier input impedance; Wherein the RF switch circuit is operable to electrically isolate the second combined impedance from the first combined impedance when the RF switch is closed and to electrically couple the second combined impedance to the first combined impedance when the RF switch is open; Wherein the first combined impedance transforms the impedance of the RF switch circuit to resonate with the at least one antenna impedance element when the RF switch is closed, and Wherein the first combined impedance and the second combined impedance together transform the amplifier input impedance to resonate with the at least one antenna impedance element when the RF switch is open.
2. The circuit of claim 1, further comprising: A matching impedance circuit positioned between the RF switching circuit and the second transmission line electrically coupled to the first reactive impedance and the second transmission line; Wherein the matching impedance is operable to match the first combined impedance to the second combined impedance when the RF switch is open to prevent reflection of a transmission line signal.
3. The circuit according to claim 1, Wherein the second combined impedance comprises a second reactive impedance circuit electrically coupled to the second transmission line between the second transmission line and the amplifier input impedance, and Wherein, when the RF switch is open, the second reactive impedance circuit imparts a phase length such that a common phase length of the first combined impedance and the second combined impedance transforms the amplifier input impedance to resonate with the at least one antenna impedance element.
4. The circuit according to claim 1, A matching impedance circuit electrically coupled to the first reactive impedance and the second transmission line between the RF switch circuit and the second transmission line, and A second reactive impedance circuit electrically coupled to the second transmission line between the second transmission line and the amplifier input impedance, and Wherein the second combined impedance comprises the second reactive impedance circuit; wherein the matching impedance is operable to match the first combined impedance and the second combined impedance to prevent reflection of a transmission line signal when the RF switch is open, and Wherein, when the RF switch is open, the second reactive impedance circuit impedance imparts a phase length such that a common phase length of the first combined impedance and the second combined impedance transforms the amplifier input impedance to resonate with the at least one antenna impedance element.
5. The circuit according to claim 1, Wherein the RF switching circuit comprises at least one diode.
6. The circuit according to claim 1, Wherein the RF switching circuit comprises a first cross-coupled diode and a second cross-coupled diode.
7. The circuit according to claim 1, Wherein the RF switch is configured to automatically close in response to an RF signal having a threshold received at the antenna, and Wherein the RF switch is configured to automatically open in response to an RF signal received at the antenna having a value below a threshold.
8. The circuit according to claim 1, Wherein the RF switch is configured to close in response to a control signal during an excitation mode operation of the MRI system, and Wherein the RF switch is configured to open in response to a control signal during a receive mode operation of the MRI system.
9. The circuit according to claim 1, Wherein the first transmission line comprises a first coaxial cable, and Wherein the second transmission line comprises a second coaxial cable.
10. The circuit according to claim 1, Wherein the first transmission line comprises a first coaxial cable; wherein the second transmission line comprises a second coaxial cable, and Wherein the switching circuit includes at least one diode electrically coupled between a signal line of the first coaxial transmission line and ground.
11. A Radio Frequency (RF) receive circuit for use in a Magnetic Resonance Imaging (MRI) scanner, the RF circuit comprising: An antenna comprising a plurality of reactive impedance elements electrically coupled in a loop configuration; an amplifier input impedance; a first transmission line comprising a first end and a second end, wherein at least one reactive impedance element is electrically coupled in parallel with the first transmission line at the first end of the first transmission line; A second transmission line electrically comprising a first end and comprising a second end, wherein the amplifier input impedance is electrically coupled in parallel with the second transmission line at the second end of the second transmission line; a first reactive impedance circuit electrically coupled to the first transmission line and the second transmission line between the second end of the first transmission line and the first end of the second transmission line; an RF switching circuit electrically coupled in parallel with the first transmission line and the second transmission line between a first combined impedance comprising the first transmission line and the first reactive impedance circuit and a second combined impedance comprising the second transmission line and the amplifier input impedance; Wherein the RF switch circuit is operable to electrically isolate the second combined impedance from the first combined impedance when the RF switch is closed and to electrically couple the second combined impedance to the first combined impedance when the RF switch is open; Wherein the first combined impedance transforms an impedance of the RF switching circuit seen at the first end of the first transmission line to resonate with the at least one antenna impedance element when the RF switch is closed, and Wherein when the RF switch is open, the first combined impedance and the second combined impedance together transform the amplifier input impedance seen at the first end of the first transmission line to resonate with the at least one antenna impedance element.
12. The circuit of claim 11, further comprising: A matching impedance circuit positioned between the RF switching circuit and the first end of the second transmission line electrically coupled to the first reactive impedance and the second transmission line; wherein the matching impedance is operable to match the first combined impedance to the second combined impedance when the RF switch is open to prevent reflection of a transmission line signal.
13. The circuit according to claim 11, Wherein the second combined impedance comprises a second reactive impedance circuit electrically coupled to the second transmission line between the second end of the second transmission line and the amplifier input impedance, and Wherein when the RF switch is open, the second reactive impedance circuit impedance imparts a phase length such that a common phase length of the first combined impedance and the second combined impedance transforms the amplifier input impedance seen at the first end of the first transmission line to resonate with the at least one antenna impedance element.
14. The circuit according to claim 11, A matching impedance circuit electrically coupled between the first reactive impedance and the second transmission line between the RF switch circuit and the first end of the second transmission line, and A second reactive impedance circuit electrically coupled to the second transmission line between the second end of the second transmission line and the amplifier input impedance, and Wherein the second combined impedance comprises the second reactive impedance circuit; wherein the matching impedance is operable to match the first combined impedance and the second combined impedance to prevent reflection of a transmission line signal when the RF switch is open, and Wherein, when the RF switch is open, the second reactive impedance circuit impedance imparts a phase length such that a common phase length of the first combined impedance and the second combined impedance transforms the amplifier input impedance seen at the first end of the first transmission line to resonate with the at least one antenna impedance element.
15. The circuit according to claim 11, Wherein the RF switching circuit comprises at least one diode.
16. The circuit according to claim 11, Wherein the RF switching circuit comprises a first cross-coupled diode and a second cross-coupled diode.
17. The circuit according to claim 11, Wherein the RF switch is configured to automatically close in response to an RF signal having a threshold received at the antenna, and Wherein the RF switch is configured to automatically open in response to an RF signal received at the antenna having a value below a threshold.
18. The circuit according to claim 11, Wherein the RF switch is configured to close in response to a control signal during an excitation mode operation of the MRI system, and Wherein the RF switch is configured to open in response to a control signal during a receive mode operation of the MRI system.
19. The circuit according to claim 11, Wherein the first transmission line comprises a first coaxial cable, and Wherein the second transmission line comprises a second coaxial cable.
20. The circuit according to claim 11, Wherein the first transmission line comprises a first coaxial cable; wherein the second transmission line comprises a second coaxial cable, and Wherein the switching circuit includes at least one diode electrically coupled between a signal line of the first coaxial transmission line and ground.

Description

RF receive circuit for MRI for single circuit Q-value destruction and preamplifier decoupling Cross Reference to Related Applications This patent application claims the benefit of U.S. provisional patent application No. 63/539,322 entitled "Diode-Isolated Single Circuit Q-Spoling AND PREAMP Decoupling (Diode isolation single circuit Q value destruction and preamplifier decoupling)" filed on 9/2023, which is expressly incorporated herein by reference in its entirety. Statement regarding federally sponsored research or development The present invention was completed with government support under 5R44EB028728-03 awarded by the National Institutes of Health (NIH). The government has certain rights in this invention. Background Magnetic Resonance Imaging (MRI) is used to image biological tissue by creating an environment that generates Nuclear Magnetic Resonance (NMR) signals. To this end, a sample, such as a patient or animal, is first placed in a uniform magnetic field (B 0) oriented along the Z-axis in x/y/Z cartesian space to create a net magnetic moment parallel to the nuclear magnetic spin field of the sample. When in the B 0 field, a high-power Radio Frequency (RF) excitation pulse of energy is applied to create larmor precession of protons in the x-y plane. This is referred to as the transmit mode of the MRI scan, wherein the applied RF excitation pulses are generally referred to as transmit pulses, transmit fields, or B 1+ fields. The transmitted pulse is applied at a frequency called the larmor frequency, which is determined by the field strength of the scanner (B 0) and the gyromagnetic ratio of the nuclei of the sample of interest according to the following equation, whereinIs a known constant for a given element: Due to the abundance of water and nuclear nature of hydrogen in the human body, most clinical MR images use nuclear energy from hydrogen =42.6 MHz/Tesla). Thus, for 1.5T and 3T clinical MRI,Approximately 64 MHz and 128 MHz, respectively. Once the emission field is off, the excited nuclei will gradually relax back to their resting state, oriented parallel to the B 0 field. This period of gradual relaxation is referred to as the RF receive mode of the MRI scan. One or more transmit field excitation pulses "tilt" the spins of the nuclei to create locally varying magnetic moments at the nuclei. Relaxation causes the created magnetic signal to decay. The difference in decay time between different materials is how MRI achieves contrast between different tissues in the body. The locally varying magnetic moment can be converted into an electrical signal called the received signal by placing a coil near the sample using the law of faraday induction. Coils, known as receive antennas, channels, elements or antennas, may be placed at different locations at the sample, for example, overlapping different portions of the patient's body, to capture magnetic energy emanating from such different locations. In practice, other RF antennas that are sensitive to magnetic and electric fields at larmor frequencies may also be used as receive antennas (e.g., dipoles, striplines, birdcages, patch antennas, etc.). Images are acquired in MRI by manipulating the field with gradient antennas during the transmit mode of scanning, which manipulate B 0 in the x, y, or z directions to encode the spins with spatial information. During the RF receive mode, the resulting signals are generated by the nuclei of interest and transformed in the local receive antenna into electrical RF receive signals, which may then be passed to MRI scanner processing circuitry, decoded and reconstructed into cross-sectional or volumetric images of the sample. Because the received signal acquired by the receiving antenna is directly converted into an image, the quality of the received signal directly affects clinical image quality. To help increase the amount and quality of the received signal, the receiving antenna is typically placed as close as possible to the surface of the sample volume of interest to increase the amount of faraday induction that occurs. The receive antenna is typically tuned to resonate at larmor frequency f Larmor by adjusting the amount of inductance and/or capacitance in the receive loop to further increase the sensitivity of the receive antenna to the frequency of interest. However, in order to place the receive antenna as close as possible to the region of interest, the receive antenna must typically be placed directly within the high power transmit field B 1+. Because the transmit pulse is applied at the larmor frequency, a significant current on the receiving antenna resonating at the larmor frequency can be driven. Such currents may distort the transmit field, destroy the resulting image, and present a significant safety risk to the patient and to the MRI system. Thus, to function properly, the surface antenna must be sensitive to the lower power magnetic energy present during relaxation of the excited nuclei back