Transmission Line Coupled Antennas and Detuning Circuits

Abstract

A radio frequency (RF) circuit for use with a magnetic resonance imaging (MRI) scanner to transmit an RF receive signal to an amplifier circuit, the RF circuit comprising: a transmission line, an antenna electrically connected to a first end of the transmission line, an impedance transformation circuit, and an impedance matching detuning circuit electrically connected between the transmission line and the impedance transformation circuit, the impedance matching detuning circuit comprising a plurality of reactive impedance elements and two or more switches operable to controllably switch between configurations of the plurality of reactive impedance elements to effect matching of an overall impedance of the RF circuit to a predetermined input impedance seen by the amplifier circuit at a predetermined RF frequency during a receive mode of the MRI scanner, while effecting an increase in impedance at the antenna to reduce the sensitivity of the antenna to RF signals at a predetermined frequency during an excitation mode of the MRI scanner.

Description

[Technical field]

[0001] The present invention relates to a transmission line coupled antenna and a detuning circuit. [Background technology]

[0002] (Related Applications) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 310,867, filed February 16, 2022, entitled "FAIL-SAFE REMOTE MATCHING AND BLOCKING CIRCUIT FOR MAGNETIC RESONANCE IMAGING SURFACE COILS," which is incorporated by reference in its entirety herein.

[0003] Magnetic resonance imaging (MRI) is used to image biological tissues by creating an environment in which nuclear magnetic resonance (NMR) signals are generated. To do this, a specimen (sample), such as a patient or animal, is placed in a uniform magnetic field (B0) oriented along the Z-axis of x / y / z orthogonal space, creating a net magnetic moment parallel to the magnetic field of the nuclear magnetic spins in the specimen. A high power radio frequency (RF) excitation pulse is applied in the B0 field, creating Larmor precession of protons in the xy plane. This is known as the transmit mode of an MRI scan, and is commonly referred to as the transmit pulse, transmit field, or B1. + An RF excitation pulse, called the magnetic field, is applied to the sample. The transmit pulse is applied at a frequency known as the Larmor frequency. The Larmor frequency is determined by the scanner magnetic field strength (B0) and the gyromagnetic ratio of the nuclei of interest in the sample according to the following equation: where γ is a known constant for a given element.

[0004]

number

[0005] Due to the nuclear properties of water and hydrogen, which are abundant in the human body, the majority of clinical MR images are acquired using signals from hydrogen nuclei (γ = 42.6 MHz / Tesla). Therefore, for clinical MRI at 1.5T and 3T, ラーモア are approximately 64MHz and 128MHz, respectively.

[0006] When the transmit field is turned off, the excited nuclei slowly relax back to their resting state parallel to the B0 field. This period of slow relaxation is known as the RF receive mode of the MRI scan. The transmit field excitation pulse "tilts" the spins of the nuclei, creating a localized changing magnetic moment in the nuclei. This generated magnetic signal decays as it relaxes. The difference in decay times between different materials is how MRI achieves contrast between different tissues in the body. The localized changing magnetic moment can be converted into an electrical signal, called the receive signal, by placing a loop of wire near the sample using Faraday's law of induction. Loops of wire, known as receive antennas, channels, elements, or antennas, can be placed at different locations on the sample, for example, over different parts of the patient's body, to capture the magnetic energy emanating from such different locations. In practice, other RF antennas that have sensitivity to magnetic and electric fields at the Larmor frequency can also be used as receive antennas (e.g., dipoles, striplines, birdcage, patch antennas, etc.).

[0007] MRI acquires images by manipulating the magnetic field during the transmit mode of the scan using gradient antennas that manipulate B0 in the x, y, and z directions to encode the spins with spatial information. In the RF receive mode, the signals generated by the nuclei of interest are converted into electrical RF receive signals by a local receive antenna. The signals are then passed to the processing circuitry of the MRI scanner and decoded to reconstruct a cross-sectional or volumetric image of the sample.

[0008] Since the received signal acquired by the receiving antenna is directly converted into an image, the quality of the received signal directly affects the quality of the clinical image. To increase the quantity 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 receiving antenna is typically tuned to resonate at the Larmor frequency by adjusting the amount of inductance and / or capacitance in the receiving loop.

[0009] However, to place the receiving antenna as close as possible to the area of ​​interest, it is usually necessary to place the receiving antenna in the high-power transmitting field B1 + The surface antenna must be placed directly within the MRI system. Because the transmit pulses are applied at the Larmor frequency, they can drive large currents through the receive antenna, which resonates at the Larmor frequency. These currents can pose a significant safety risk to the patient and the MRI system by distorting the transmit magnetic field and corrupting the resulting image. Therefore, to function properly, the surface antenna must be sensitive to the low-power magnetic energy present during the receive portion of the scan as the excited nuclei relax back to their quiescent state, and invisible to the high-power magnetic energy present during the transmit portion of the scan.

[0010] In practice, this is generally accomplished by using active and passive detuning circuits, often referred to as decoupling or blocking circuits. US Pat. No. 5,399,433, entitled "Decoupling Circuit for Magnetic Resonance Imaging Local Coil," discloses a local receiving antenna operatively coupled to an active decoupling circuit and a passive decoupling circuit. The active detuning circuit is typically turned on and off by an external DC signal provided via wires to one or more PIN diodes in the decoupling circuit that are connected to the surface receiving antenna. The PIN diodes act like solid-state switches in this circuit and are designed to present a high impedance that effectively detunes the antenna. The transmit field could cause a large current to flow through the receive loop, which could damage sensitive electronics, spoil the image, or harm the patient. Thus, to prevent the transmit field from causing a large current to flow through the receive loop, a DC signal is turned on during the transmit mode of the scan to activate the active detuning circuit. The DC signal is turned off during RF receive mode, deactivating the active detuning circuit, thus allowing the loop tuned to the Larmor frequency to resonate in response to the magnetic energy emanating from the sample. A passive detuning circuit is typically used to detune the antenna during transmit mode if the active detuning circuit is not operational. Passive detuning is often accomplished by using a cross-coupled diode pair. The diodes are biased by a high power voltage induced in the antenna during the transmit mode of the scan if there is no active detuning circuit in operation. In this way, the combination of active and passive detuning circuits can provide a relatively fail-safe mechanism to keep the receive antenna from resonating during transmit mode. The active detuning circuit generally serves as the primary mechanism for detuning the receive antenna during transmit mode. The passive detuning circuit generally serves as a backup to automatically detune the antenna if the active detuning circuit fails to detune during transmit mode. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 6,747,452 Summary of the Invention [Problem to be solved by the invention]

[0012] Modern MRI receive arrays are often multi-channel (i.e., have multiple antennas in close proximity to the patient) to take advantage of modern image acceleration techniques that allow for shorter exam times. In multi-channel arrays, it is necessary to ensure that the channels are isolated from each other to minimize RF energy shared between the channels. More specifically, it is necessary to ensure that the current induced in one antenna loop is not parasitically shared with the coils of other nearby antenna loops. To prevent this, amplifiers are commonly used in conjunction with the receive circuitry to present a high impedance to the antenna during the receive mode of the MRI scan. The high impedance at the receive antenna during receive mode limits the flow of current in that antenna, thereby reducing the RF electromagnetic energy transmitted by that antenna, thus limiting the induction of parasitic currents by that antenna in nearby antennas.

[0013] Detuning circuits, whether active, passive, or amplifier, are typically comprised of relatively large discrete components (inductors, capacitors, diodes, etc.), which often result in relatively large and fragile circuits. To protect the detuning circuits from mechanical damage, the detuning circuits are often encased in plastic or metal housings, which can be relatively large, bulky, heavy, and inflexible. In contrast, receive antennas must typically be placed as close as possible to the imaging region of interest to maximize image quality. Thus, the individual loops of the receive antenna themselves are typically configured to be lightweight and flexible to facilitate conforming to the contours of the sample, e.g., the contours of the patient's body. Unfortunately, detuning circuits coupled to the receive antenna and housed in bulky protective housings may compete for space near the patient's anatomy, limiting the flexibility of the receive antenna placement and therefore the clinical image quality. [Means for solving the problem]

[0014] In one embodiment, a radio frequency (RF) circuit for use with a magnetic resonance imaging (MRI) scanner is provided to transmit an RF receive signal to an amplifier circuit. The RF circuit includes a transmission line having a first end portion and a second end portion, an antenna electrically connected in parallel to the transmission line at the first end portion of the transmission line, and an impedance transformation circuit. The RF circuit further includes an impedance matching and detuning circuit. The impedance matching and detuning circuit is electrically connected between the transmission line and the impedance transformation circuit, and is also connected in parallel to the transmission line at the second end portion of the transmission line and in parallel to the impedance transformation circuit. The impedance matching and detuning circuit includes a plurality of reactive impedance elements and two or more switches. The two or more switches are operable to controllably switch between RF connection configurations between the reactive impedance elements, the RF connection configurations comprising a first RF connection configuration for RF connecting a first set of the reactive impedance elements to a second end of the transmission line to match an overall impedance of the RF circuit to a pre-defined input impedance seen by the amplifier circuit at a predetermined RF frequency during a receive mode of the MRI scanner, and a second RF connection configuration for RF connecting a second set of the reactive impedance elements to the second end of the transmission line to cause an increase in impedance at the antenna to reduce sensitivity of the antenna to RF signals at the predetermined frequency during an excitation mode of the MRI scanner.

[0015] In another aspect, a radio frequency (RF) circuit is for use with a magnetic resonance imaging (MRI) scanner to transmit an RF receive signal to an amplifier circuit. The RF circuit includes a transmission line having a first end and a second end, an antenna electrically connected in parallel with the transmission line at the first end of the transmission line, and an impedance transformation circuit. The RF circuit includes an impedance matching detuning circuit. The impedance matching detuning circuit is electrically connected between the transmission line and the impedance transformation circuit, as well as connected in parallel with the transmission line at the second end of the transmission line and in parallel with the impedance transformation circuit. The impedance matching detuning circuit includes a first reactive impedance element, a second reactive impedance element, and a third reactive impedance element, an active switch including a PIN diode electrically connected in series with the third reactive impedance element, and a first passive switch including a first cross-coupled PIN diode pair electrically connected between a first node and a third node. The series-connected PIN diode and the third reactive impedance element are electrically connected in parallel at a second end of the transmission line between a first node in a signal conductor of the transmission line and a second node in a relative ground of the transmission line. The first reactive impedance element is electrically connected between the first node and the third node. The second reactive impedance element is electrically connected between the third node and the second node.

[0016] Aspects of the present disclosure are best understood from the following detailed description when read in conjunction with the accompanying figures. It is emphasized that, according to standard practice in the industry, various features are not drawn to scale. In fact, dimensions of various features may be arbitrarily increased or decreased for clarity of discussion. Further, the present disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed. [Brief description of the drawings]

[0017] [Figure 1] 1 is an exemplary diagram showing an RF transmit antenna and an RF receive antenna positioned relative to a patient in an MRI scanner. [Figure 2A] 1 is an exemplary circuit diagram illustrating a first exemplary receiver circuit operably coupled to an amplifier circuit that is operably coupled to an MRI signal processing system. [Figure 2B] FIG. 2B is an example circuit diagram showing additional details of example second and third switches of the circuit of FIG. 2A. [Diagram 3] 2B is an example diagram of an example effective RF receive mode circuit configuration of the receive circuit of FIG. 2A. [Figure 4] FIG. 2B is an example diagram of an effective RF active detuning mode circuit configuration of the receiver circuit of FIG. 2A. [Diagram 5] FIG. 2B is an illustration of an effective RF passive detuning mode circuit configuration of the receiver circuit of FIG. 2A. [Figure 6A] 2B is an exemplary diagram showing a break in the transmission line of the receiving circuit of FIG. 2A. [Figure 6B] 6B is an exemplary diagram illustrating a shift in resonant frequency due to the occurrence of an exemplary break in the transmission line depicted in FIG. 6A. [Figure 7] 2B is an example diagram of an effective RF passive detuning mode circuit resulting from failure of the third reactive impedance element of the first receiver circuit of FIG. 2A. [Figure 8] 4 is an example circuit diagram illustrating a second example receiver circuit according to some embodiments. [Figure 9] 4 is an example circuit diagram illustrating a third example receiving circuit according to some embodiments. [Figure 10A] FIG. 2 is an exemplary diagram illustrating a first exemplary impedance transformation circuit. [Figure 10B] FIG. 4 is an exemplary diagram illustrating a second exemplary impedance transformation circuit. [Figure 10C] FIG. 13 is an exemplary diagram illustrating a third exemplary impedance transformation circuit. [Figure 10D] FIG. 13 is an exemplary diagram showing a fourth exemplary impedance transformation circuit. [Figure 10E]FIG. 5 is an exemplary diagram showing an exemplary impedance transformation circuit. [Figure 10F] FIG. 6 is an exemplary diagram showing an example impedance transformation circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] FIG. 1 is an exemplary diagram showing an RF transmit antenna 110 and an RF receive antenna 112 positioned relative to a patient in an MRI scanner 100 system. Note that in the context of MRI, antennas are often referred to as "coils." A subject patient 102 is shown lying on a platform 104 in an MRI chamber 106. A main magnet 108 is positioned to generate a static B0 magnetic field. During an excitation mode, one or more RF transmit antennas 110 transmit excitation magnetic field pulses that generate a B1 magnetic field perpendicular to the static B0 magnetic field at a frequency of interest. Multiple RF receive antennas 112 are positioned in close proximity to the patient's body. During an RF receive mode, magnetic flux changes caused by precession (Larmor) motion of the net nuclear magnetization in the subject following RF excitation induce MR currents in the RF receive antennas 112, which can then be post-processed to extract frequency, phase, and amplitude information used to construct an MR image.

[0019] FIG. 2A is an exemplary circuit diagram showing a first example receiver circuit 202. The receiver circuit 202 is operably connected to an amplifier circuit 204. The amplifier circuit 204 is operably connected to an MRI signal processing system 206. The receiver circuit 202 includes an antenna 208, a first transmission line 210, an impedance matching and detuning circuit 212, and an impedance conversion circuit 215. The first transmission line 210 includes a first end 210-1 and a second end 210-2. The antenna 208 is operably connected to the first end 210-1 of the first transmission line 210. The impedance matching and detuning circuit 212 is operably connected to the second end 210-2 of the first transmission line 210. The impedance transformation circuit 215 is operatively connected between the impedance matching detuning circuit 212 and the amplifier circuit 204. More specifically, a third node, labeled as node D, of the impedance matching detuning circuit 212 and a second node, labeled as node E, of the impedance matching detuning circuit 212 are electrically connected to input terminals of the impedance transformation circuit 215. Each of the first and second output terminals of the impedance transformation circuit 215 is electrically coupled to the first and second input terminals of the amplifier circuit 204 at respective first and second input nodes F and G. The amplifier circuit 204 includes an output terminal 270 operatively coupled to the MRI signal processing system 206. The output terminal 270 can be configured to perform additional amplification, analog-to-digital conversion, and digital signal processing to construct a corresponding MRI image.

[0020] During receive mode operation, the receive circuit 202 acts as a matched resonant circuit that presents an input impedance to the amplifier circuit 204 that matches a prescribed input impedance of the amplifier circuit 204 at a given frequency to optimize the amplifier gain, i.e., the amplifier noise figure at the given frequency. The impedance elements of the receive circuit 202 are selected to achieve a particular voltage-current relationship at the input to the amplifier circuit 204 at the given frequency to achieve a reactance that creates resonance. The Larmor frequency is the given frequency for the exemplary receive circuit 202. The exemplary amplifier has a noise-matched input impedance of 50 ohms. In this case, the noise-matched resonant receive circuit (202) presents 50 ohms to the input of the amplifier circuit 204 at the given frequency. The reactive elements of the receiver circuit 202 are selected or tuned to make the receiver circuit 202 resonant at a given frequency. That is, the relationship phase between the voltage and current of the signal is changed at various locations within the receiver circuit 202 to ultimately achieve a particular relationship at the amplifier circuit 204. An exemplary input to the amplifier circuit 204 has a real input impedance (i.e., R=V / I) that is substantially free of imaginary components at a given Larmor frequency. The reactive elements of the exemplary receiver circuit 202 are selected to transform the voltage and current components of the RF receive signal at the Larmor frequency to be as in-phase as possible at the input to the amplifier circuit 204 to optimize amplifier performance at the Larmor frequency.

[0021] It is well known in the art that impedance describes the relationship between voltage and current (i.e., electric and magnetic fields). Impedance is specific to a given frequency. Resistance is the real part and describes the difference in voltage-current measurements caused by losses due to heat. Reactance is the imaginary part and describes the change in timing between the peaks and valleys of the voltage and current measurements (i.e., phase difference).

[0022] The antenna 208 consists of a loop or coil of conductive material and is positioned within the EM field generated during an MRI scan. The antenna 208 is sensitive to variations in the EM field at the Larmor frequency. In an RF receive mode, magnetic flux due to the precession of excited nuclei back to a quiescent state induces an RF receive signal at the receive signal frequency of the antenna 208. The receive signal at the Larmor frequency is transformed as described above by the receive circuitry 202 to tune to a specific impedance at the input to the amplifier circuitry 204.

[0023] The exemplary antenna 208 includes discrete antenna reactive impedance elements 222 electrically connected in a loop configuration by conductors 221. In the exemplary antenna 208, the antenna reactive impedance elements 222 include respective discrete capacitors 224 and the conductors 221 that may exhibit a unique inductive impedance. Alternative antenna reactive impedance elements (not shown) may include multi-capacitor circuits, inductor circuits, or circuits including a combination of capacitors and inductors. Different ones of the antenna reactive impedance elements 222 may have different values. One or more of the inductances of the antenna reactive impedance elements 222 and / or the conductor segments (221) may be adjustable to tune the resonant frequency of the antenna 208 to a predetermined received signal frequency, such as the Larmor frequency used by the exemplary MRI scanner 100.

[0024] The exemplary first transmission line 210 comprises a coaxial cable. Each one of the antenna reactive impedance elements (224) shown in line (222) is electrically connected in parallel to the first end 210-1 of the first transmission line 210 between a fifth node, labeled as node A, at a first end of the inner coaxial signal conductor (226) (shown by a line) and a sixth node, labeled as node B, at a first end of the outer coaxial relative to ground (228). Alternative first transmission lines (not shown) may comprise, for example, twisted pair, microstrip, or stripline.

[0025] The exemplary impedance transformation circuit 215 comprises reactive circuit elements configured to present an input impedance to the amplifier circuit 204 that matches a predetermined input impedance of the amplifier circuit 204 at a predetermined frequency to optimize the amplifier amplification, i.e., optimize the amplifier noise figure at the predetermined frequency. Additionally, the exemplary impedance transformation circuit 215 is configured to transform the small input impedance of the amplifier circuit 204 to a higher impedance than that at the antenna 208 located at the first end 210-1 of the first transmission line 210 (e.g., the impedance presented to the antenna 208 by the amplifier circuit 204). For amplifier decoupling, minimizing the current in the antenna 208 prevents the antenna 208 from generating parasitic RF signal coupling at one or more other nearby antennas (not shown). The configuration of reactive impedance elements to achieve impedance matching and transformation of the amplifier impedance sufficient to block current flow in the antenna 208 will be understood to depend on the particular physical and electrical implementation of the receiver circuit 202 and the characteristics of the amplifier circuit 204, as understood by those skilled in the art. During receive mode operation of the MRI scanner 100, the particular reactive impedance elements of the impedance matching detuning circuit 212 operate together with the impedance transformation circuit 215 to match the impedance of the receive circuit 202 to a particular impedance seen by the amplifier circuit 204 at a given frequency, for example, at the Larmor frequency. During operation of the MRI scanner 100 in an excitation mode, the particular reactive impedance elements of the impedance matching detuning circuit 212 operate to detune the receive circuit 202 from resonance at a given frequency. The exemplary impedance matching detuning circuit 212 is enabled to achieve RF detuning during the excitation mode by either active detuning or passive detuning. RF operation of the receive circuit 202 will now be described with reference to FIGS. 3-5. FIG. 3 is an exemplary diagram of an RF receive mode circuit 300.The RF receive mode circuit 300 shows only those components of the impedance matching detuning circuit 212 that operate to impedance match the signal received by the antenna 208 to a predetermined input impedance of the amplifier circuit 204 during the RF receive mode of an MRI scan. Figure 4 is an example diagram of an effective RF active detuning (mode) circuit 400 that shows only those RF components of the impedance detuning matching network (212) that operate to provide active detuning during the excitation mode of an MRI scan. Figure 5 is an example diagram of an effective RF passive detuning (mode) circuit 500 that shows only those RF components of the impedance detuning matching network (212) that operate to provide passive detuning during the excitation mode of an MRI scan.

[0026] 3, during an RF receive mode of an MRI scan, the first reactive impedance element 230 is RF coupled in series to the center conductor 226 of the first transmission line 210 between a first node, labeled as node C, and a third node, labeled as node D, of the center conductor 226 at the second end 210-2 of the first transmission line 210. The second reactive impedance element 232 is RF coupled between the third node, labeled as node D, and a second node, labeled as node E, of the relative ground conductor 228 of the first transmission line 210 at the second end 210-2 of the first transmission line 210. The first reactive impedance element 230 and the second reactive impedance element 232, together with the impedance transformation circuit 215, may be selected to maximize the received signal power transfer on the first transmission line 210 as well as minimize the received signal reflection on the first transmission line 210. The input impedance seen by the amplifier circuit 204 may be specified by the user or manufacturer requirements to maximize the received signal power transfer or minimize the amplifier noise figure as well as minimize the received signal reflection. An example of an optimal input impedance for the amplifier circuit 204 may be measured between a first input node F to the amplifier circuit 204 and a second input node G to the amplifier circuit 204 as shown in FIG. 2A. The first reactive impedance element 230 and the second reactive impedance element 232 are included in a first set of reactive impedance elements used to cause the overall impedance of the RF receiver circuit (202) to match a given input impedance seen at the amplifier circuit 204 at a given RF frequency during a receive mode of the MRI scanner 100. The third reactive impedance element 240 is not part of the first set of reactive impedance elements.

[0027] More specifically, the antenna reactive impedance element 222 and the first and second reactive impedance elements 230, 232 cooperate together with the first transmission line 210 to transform the impedance of the antenna 208, as further transformed by the impedance transformation performed by the impedance transformation circuit 215, such that the impedance presented by the receive circuit 202 between a third node labeled as node D and a second node labeled as node E is optimal for the amplifier circuit 204. More specifically, the first reactive impedance element 230 and the second reactive impedance element 232 are coupled in an exemplary L-network between the first transmission line 210 and the impedance transformation circuit 215. The impedance values ​​of the first reactive impedance element 230 and the second reactive impedance element 232 in the exemplary L-network are selected to operate with the impedance transformation circuit 215 to present an optimal impedance to the amplifier circuit 204. The combination of the antenna reactive impedance element 222 and the first and second reactive impedance elements 230, 232, the first transmission line 210, and the impedance transformation circuit 215 allows the antenna 208 to be located away from the amplifier circuit 204 while presenting an optimal input impedance to the amplifier circuit 204.

[0028] Thus, during operation of the RF receive mode circuit 300 shown in FIG. 3, the first reactive impedance element 230 and the second reactive impedance element 232 operate as impedance matching components. Additionally, these impedance elements also function as tuning components for the resonant circuit. However, as described below with reference to FIGS. 4-5, the circuit connections within the impedance matching detuning circuit 212 are reconfigurable to convert the first reactive impedance element 230 and the second reactive impedance element 232 to behave as detuning components during active and / or passive RF detuning. During an MRI scan, the first reactive impedance element 230 and the second reactive impedance element 232 alternate between performing a dual role as an RF impedance matching component during receive mode and as an RF detuning component during excitation mode.

[0029] The exemplary first reactive impedance element 230 and the exemplary second reactive impedance element 232 may each comprise a single capacitor 231 and 233, as shown. An alternative first series reactive impedance element (not shown) may comprise a multi-capacitor circuit, an inductor circuit, or a circuit comprising a combination of capacitors and inductors. Similarly, an alternative second reactive impedance element (not shown) may comprise a multi-capacitor circuit, an inductor circuit, or a circuit comprising a combination of capacitors and inductors.

[0030] 2A, the active detuning circuit includes a first switch 234 consisting of a PIN diode 235. The PIN diode 235 is connected to a third reactive impedance element 240 to contribute to a detuning function in the RF active detuning circuit. The PIN diode 235 is enabled during active detuning to change the circuit connection of the first reactive impedance element 230 and the second reactive impedance element 232 to convert from contributing to RF impedance matching to contributing to RF active detuning. The active detuning circuit further includes the third reactive impedance element 240 and a first blocking inductor 244. The PIN diode 235 has an anode electrically connected to a first node labeled as node C, as well as a cathode electrically connected to a fourth node labeled as node H. The first blocking inductor 244 has a first terminal connected to node H and a second terminal connected to a second node labeled as node E at ground potential. Thus, the first switch 234 and the third reactive impedance element 240 are connected in series with each other and in parallel with the second end 210-2 of the first transmission line 210. Furthermore, the third reactive impedance element 240 and the first blocking inductor 244 are connected in parallel with each other between a fourth node, labeled as node H, present at the cathode of the PIN diode 235 and a second node, labeled as node E, which is at ground potential.

[0031] The exemplary third reactive impedance elements 240 shown in Figures 3-5 each include a single capacitor 241. Alternate third reactive impedance elements (not shown) can include a multi-capacitor circuit, an inductor circuit, or a circuit including a combination of capacitors and inductors.

[0032] During RF receive mode, the first switch 234 comprising the PIN diode 235 is turned off so that the effective RF active detuning circuit 400, described below with reference to FIG. 4, is not operational. More specifically, referring to FIG. 2A, no DC turn-on voltage is applied to the PIN diode 235, thereby turning off the first switch 234. Thus, in the position of the first switch 234 that disconnects the third reactive impedance element 240 from the second connection with the first transmission line 210 during RF receive mode operation, an RF open circuit is created for RF current. Thus, RF active detuning is inoperative during receive mode. In contrast, during active detuning during pump mode, as described in more detail below, a DC turn-on voltage turns on the PIN diode 235 and connects the third (parallel) reactive impedance element 240 in parallel with the second end 210-2 of the first transmission line 210.

[0033] 2B, the passive detuning circuit includes second and third switches 236, 237. The second and third switches 236, 237 include respective first and second cross-coupled PIN diode pairs 238, 239. The first and second cross-coupled PIN diode pairs 238, 239 are enabled during passive detuning to connect the third reactive impedance element 240 to contribute to the detuning function in the RF passive detuning circuit. The first and second cross-coupled PIN diode pairs 238, 239 change the circuit connections of the first reactive impedance element 230 and the second reactive impedance element 232 to convert the function of the first reactive impedance element 230 and the second reactive impedance element 232 from contributing to RF impedance matching to contributing to RF active detuning. The passive detuning circuit also includes first and second passive detuning inductors (inductances) 242, 243 and first and second blocking capacitors 250, 252. The passive detuning circuit includes a first branch circuit 255′. The first branch circuit 255′ includes a second switch 236, a first passive detuning inductor 242, and a first blocking capacitor 250, which are connected in series. The first passive detuning inductor 242 is connected between the second switch 236 and the first blocking capacitor 250. The passive detuning circuit includes a second branch circuit 257′. The second branch circuit 257′ includes a third switch 237, a second passive detuning inductor 243, and a second blocking capacitor 252, which are connected in series. The second passive detuning inductor 243 is connected between the third switch 237 and the second blocking capacitor 252. The second switch 236 has a terminal connected to a first node labeled as node C and a terminal connected to a first terminal of a first passive detuned inductor 242. The third switch 237 has a terminal connected to a first node labeled as node C and a terminal connected to a first terminal of a second passive detuned inductor 243.The first blocking capacitor (capacitance) 250 has a terminal connected to the second terminal of the first passive detuned inductor 242 and a terminal connected to a fourth node labeled as node H. The second blocking capacitor (capacitance) 252 has a terminal connected to the second terminal of the second passive detuned inductor 243 and a terminal connected to a third node labeled as node D. Thus, the first branch circuit 255′ is connected in series with the third reactive impedance element 240 between a first node labeled as node C and a second node labeled as node E at ground potential. The second branch circuit 257′ is connected in series with the second reactive impedance element 232 between a first node labeled as node C and a second node labeled as node E at ground potential. Thus, the series-connected first branch circuit 255′ and the third reactive impedance element 240 are connected in parallel with the series-connected second branch circuit 257′ and the second reactive impedance element 232. Furthermore, both the series-connected first branch circuit 255' and the third reactive impedance element 240 and the series-connected second branch circuit 257' and the second reactive impedance element 232 are coupled in parallel to the second end 210-2 of the first transmission line 210.

[0034] Still referring to FIG. 2B, during RF receive mode operation, the second and third switches 236, 237 are turned off to prevent the RF passive detuning circuit 500, described below with reference to FIG. 5, from operating. The exemplary RF passive detuning circuit 500 is inoperable during RF receive mode because the RF receive signal has a voltage level below the threshold turn-on voltage required to turn on the first and second cross-coupled PIN diode pairs 238, 239. As a result, each of the second and third switches 236, 237 is turned off during RF receive mode. Turning off the second switch 236 decouples the first passive detuned inductor 242 and the third reactive impedance element 240 from being RF coupled in parallel with the first transmission line 210. Similarly, turning off the third switch 237 decouples the second passive detuned inductor 243 and the second reactive impedance element 232 from being RF coupled in parallel with the first transmission line 210. In contrast, during RF passive detuning in the RF excitation mode, as described in further detail below, the RF excitation signal induces an RF voltage level large enough to turn on the first and second cross-coupled PIN diode pairs 238, 239 of the respective second and third switches 236, 237. As described in further detail below, turning on the first cross-coupled PIN diode pair 238 RF couples the first passive detuned inductor 242 and the third reactive impedance element 240 in parallel to the first transmission line 210. Turning on the second cross-coupled PIN diode pair 239 RF couples the second passive detuned inductor 243 and the second reactive impedance element 232 in parallel to the first transmission line 210.

[0035] The RF passive detuning circuit 500 is enabled during the drive mode in which the receive circuit 202 resonates at a predetermined frequency if the RF active detuning circuit 400 fails. Thus, it will be appreciated that a high voltage sufficient to turn on the first and second cross-coupled PIN diode pairs 238, 239 is induced. However, when the RF active detuning circuit 400 is operating during the transmit drive mode, the voltage at the first and second cross-coupled PIN diode pairs 238, 239 is not sufficient to turn on the first and second cross-coupled PIN diode pairs 238, 239. In some cases, only the first cross-coupled PIN diode pair 238 may have a high enough voltage to turn on. As a result, it will be apparent to one skilled in the art that the effective circuit will most closely resemble that of FIG. 4.

[0036] 4, during an RF excitation mode of an MRI scan, an active RF detuning circuit 400 includes first, second, and third reactive impedance elements 230, 232, 240, an antenna reactive impedance element 222, and a first transmission line 210. The antenna reactive impedance element 222 is coupled between a fifth node labeled as node A and a sixth node labeled as node B. The RF active detuning circuit 400 includes a first reactive impedance element 230 operatively connected in series to the first transmission line 210 between a first node labeled as node C and a third node labeled as node D. The RF active detuning circuit 400 includes second and third reactive impedance elements 232, 240 operatively connected in parallel at a second end 210-2 of the first transmission line 210 between a first node labeled as node C and a second node labeled as node E. The RF active detuning circuit 400 comprises an antenna reactive impedance element 222 operatively coupled in parallel to the first end 210-1 of the first transmission line 210 between a fifth node labeled as node A and a sixth node labeled as node B. The RF active detuning circuit 400 operates to detune the sensitivity of the receiving circuit 202 by blocking the flow of current on the antenna 208 by creating a high impedance between the fifth node labeled as node A and the sixth node labeled as node B at the antenna 208 located at the first end 210-1 of the first transmission line 210. This blocking is achieved primarily by the third reactive impedance element 240 in cooperation with the first transmission line 210 and the first and second reactive impedance elements 230 and 232. As used herein, "blocking" is defined as the process of reducing the sensitivity of the antenna 208 to RF signals by creating a high impedance on the antenna 208. The reduced sensitivity of antenna 208 reduces the risk of patient injury or circuit damage from excitation mode energy.Blocking is achieved by creating a high impedance at the Larmor frequency from the antenna 208 at the first end 210-1 of the first transmission line 210, as shown in Figure 4. Note that no circuit elements need be connected between the fifth node, labeled as node A, and the sixth node, labeled as node B, to create a high impedance between them. The first, second, and third reactive impedance elements 230, 232, and 240 are included in the second set of reactive impedance elements during active detuning and are used to increase the impedance at the antenna 208, thereby desensitizing the antenna 208 to RF signals at a predetermined frequency during the excitation mode of the MRI scanner 100.

[0037] 2A and 4, during an RF excitation mode, a first switch 234 constituting a PIN diode 235 is turned on to activate the RF active detuning circuit 400. The exemplary PIN diode 235 is electrically connected to the inner coaxial signal conductor (226) of the first transmission line 210 at a first node labeled as node C. The PIN diode 235 has a cathode connected to a fourth node labeled as node H. During the excitation mode, a DC turn-on signal provided via a Vcc voltage source to a third node labeled as node D is transmitted through a second blocking inductor 248 to the anode of the PIN diode 235, thereby turning on the PIN diode 235. The PIN diode 235 is selected to have characteristics such that when forward biased (i.e., turned on), it behaves as a short circuit to an RF signal, but when reverse biased (i.e., turned off), it behaves as an open circuit. The first blocking inductor 244 has a value selected to look like a wire (e.g., a short circuit) to DC currents, while looking like an RF blocking circuit element (e.g., an open circuit) to signals at a predetermined RF frequency. The reactance of the exemplary third reactive impedance element 240 resonates (or near resonates) with the coaxial cable (210) and antenna reactive impedance element 222 connected across a fifth node, labeled as node A, and a sixth node, labeled as node B, at the Larmor frequency. When the RF active detuning circuit 400 of FIG. 4 is operating with the PIN diode 235 turned on, the DC turn-on current flows through the second blocking inductor 248 connected in parallel with the first reactive impedance element 230, through the PIN diode 235, as well as through the first blocking inductor 244 to ground. Similar to the first blocking inductor 244, the second blocking inductor 248 acts as a short circuit to DC signals, but acts as an open circuit to RF signals.These blocking inductors (244, 248) allow DC current to pass through the capacitor elements (231 and 241), which are open circuits to DC current. If alternative first and third reactive impedance elements 230 and 240 are used such that there is a DC path through these elements (e.g., inductive elements), blocking inductors in parallel with these alternative first and third reactive impedance elements 230 and 240 may not be necessary. Also, when the PIN diode 235 is turned on, an RF signal path is formed through the series circuit of the turned on PIN diode 235 and the third reactive impedance element 240, which are connected in parallel with the first transmission line 210.

[0038] Additionally, during operation of the RF active detuning circuit 400, the first blocking capacitor 250 blocks DC current by turning on one of the diodes in the first cross-coupled PIN diode switch (238). The first blocking capacitor 250 is operatively connected between a fourth node, labeled as node H, and the first cross-coupled PIN diode switch (238). Similarly, the second blocking capacitor 252 is operatively connected between the second cross-coupled PIN diode switch (239) and a third node, labeled as node D, thereby blocking DC current by turning on one of the diodes in the second cross-coupled PIN diode switch (239).

[0039] 5, in the absence of a DC turn-on signal during an RF excitation mode of an MRI scan, the RF passive detuning circuit 500 is enabled. The excitation signal is enabled to momentarily induce an RF signal in the antenna 208 that causes the RF passive detuning circuit 500 to turn on. The first switch 234 may fail to turn on for any reason that may prevent sufficient DC current from flowing through the first switch 234. For example, the MRI scanner 100 system may fail to provide DC-bias to the RF active detuning circuit 400 due to failure of the receiver circuit 202 to be plugged into a power source or a broken connection to the DC bias input.

[0040] More specifically, during an RF excitation mode without turning on the first switch 234, an excitation signal is generated across the second and third switches 236, 237 having a voltage level high enough to turn on the cross-coupled PIN diode switches (238, 239). The first and second blocking capacitors 250, 252 have capacitance values ​​selected to act as short circuit elements for the RF signal. And, as explained above, the first blocking inductor 244 acts as an open circuit element for the RF signal. The first and second passive tuning inductors (elements) 242, 243 are tunable to adjust the frequency characteristics of the RF passive detuning circuit 500. The first and second passive tuning inductors 242, 243 can be used, for example, to compensate for small inherent capacitances and inductances of a circuit board (not shown) on which the receiver circuit 202 is formed. Thus, turning on the second and third switches 236, 237 activates the RF passive detuning circuit 500 of FIG.

[0041] The exemplary RF passive detuning circuit 500 includes first, second, and third reactive impedance elements 230, 232, 240, an antenna reactive impedance element 222, a first transmission line 210, and first and second passive tuning inductors 242, 243. The antenna reactive impedance element 222 is connected between a fifth node labeled as node A and a sixth node labeled as node B. It should be noted that the first and second passive tuning inductors 242, 243 may be replaced with other reactive elements such as capacitors. The first reactive impedance element 230 is operatively connected in series with the first transmission line 210 between a first node labeled as node C and a third node labeled as node D. The first RF subcircuit (255′) includes the third reactive impedance element 240 and the first passive tuning inductor 242 connected in series. The first RF sub-circuit (255') is operatively connected in parallel to the second end 210-2 of the first transmission line 210 and to node E between a first node, labeled as node C, and a second node, labeled as node E. The second RF sub-circuit (257') comprises a series-connected second reactive impedance element 232 and a second passive tuning inductor 243. The second RF sub-circuit (257') is operatively connected in parallel to the second end 210-2 of the first transmission line 210 between the first node, labeled as node C, and a second node, labeled as node E. The second passive tuning inductor 243 is also operatively connected between the first node, labeled as node C, and a third node, labeled as node D. The RF passive detuning circuit 500 is operable to detune the sensitivity of the receiving circuit 202 by blocking current flow on the antenna 208 by creating a high impedance between a fifth node, denoted as node A, and a sixth node, denoted as node B, at the antenna 208 located at the first end 210-1 of the first transmission line 210.This blocking is achieved primarily by the third reactive impedance element 240 in cooperation with the first transmission line 210 and the first and second reactive impedance elements 230 and 232. Blocking refers to creating a high resistance at the antenna 208, making the antenna 208 less sensitive to RF signals. The reduced sensitivity of the antenna 208 reduces the risk of patient injury or circuit damage from excitation mode energy. Blocking is achieved by creating a high resistance at the Larmor frequency from the antenna 208 to the first end 210-1 of the first transmission line 210, as shown in FIG. 5. It should be noted that no circuit element needs to be connected between the fifth node, labeled as node A, and the sixth node, labeled as node B, to create a high impedance between the fifth node, labeled as node A, and the sixth node, labeled as node B. The first, second and third reactive impedance elements 230, 232 and 240, and the first and second passive detuning inductors 242, 243, while included in a second set of reactive impedance elements during passive detuning, are used to increase the impedance at the antenna 208 to reduce the sensitivity of the antenna 208 to RF signals of a predetermined frequency during the excitation mode of the MRI scanner 100.

[0042] 2A-2B, additional details of the first RF subcircuit (255') and additional details of the second RF subcircuit (257') are shown. The first RF subcircuit (255') comprises a first blocking capacitor 250, a first passive tuning inductor 242, and a first cross-coupled PIN diode switch (236). The first blocking capacitor 250, the first passive tuning inductor 242, and the first cross-coupled PIN diode switch (236) are connected in series between a first node, labeled as node C, at the center conductor 226 of the first transmission line 210 and a fourth node, labeled as node H, at the terminal of the third reactive impedance element 240. The second RF subcircuit (257') comprises a second blocking capacitor 252, a second passive tuning inductor 243, and a second cross-coupled PIN diode switch (237). A second blocking capacitor 252, a second passive tuning inductor 243, and a second cross-coupled PIN diode switch (237) are connected in series between node C of the center conductor 226 of the first transmission line 210 and a third node, indicated as node D, at the terminal of the second reactive impedance element 232.

[0043] 6A-6B are example diagrams illustrating an open circuit in the first transmission line 210 (FIG. 6A) and a corresponding resonant frequency shift in the receiver circuit 202 (FIG. 6B). An open circuit in the first transmission line 210 is a potential failure event for the example receiver circuit 202. An example open circuit location in the first transmission line 210 is represented by a circle (602). When the first transmission line 210 breaks at location (602), or anywhere along the first transmission line 210, a new effective circuit is created as shown in FIG. 6A. The occurrence of such an open circuit 602 effectively removes the first reactive impedance element 230 and the second reactive impedance element 232 from the RF receive mode circuit 300 of FIG. 3. The elimination of these two impedance elements (230, 232) due to an open circuit in the first transmission line 210 circuit results in a substantially higher resonant frequency, as shown in FIG. 6B, where curve 610 without open circuit represents power versus resonant frequency without open circuit (i.e., normal operation), while curve 620 with open circuit represents power versus frequency when an exemplary open circuit 602 occurs in the first transmission line 210. In the exemplary receiver circuit 202, the open circuit in the first transmission line 210 results in a shift to a higher resonant frequency, or a resonance further away from a predetermined frequency, such as the Larmor frequency. FIG. 7 is an exemplary diagram of an effective RF passive detuning (mode) circuit 702 due to failure of the third reactive impedance element 240 in the first receiver circuit (202) of FIG. 2A. For example, referring to FIG. 2A, if the third reactive impedance element 240 fails, neither the RF active detuning circuit 400 nor the RF passive detuning circuit 500 are effective since they rely on the operation of the third reactive impedance element 240. The DC signal remains unchanged despite the break because the DC path through the first blocking inductor 244 remains. However, with no RF active detuning in the circuit, a high voltage is present across the cross-coupled diodes (238, 239). The first cross-coupled PIN diode pair 238 is essentially useless with the third reactive impedance element 240 removed.Meanwhile, the second cross-coupled PIN diode pair 239, which together with the reactive impedance elements (230, 232), the second passive tuning inductor 243, and the first transmission line 210 form an RF circuit, presents a high impedance to the first end 210-1 of the first transmission line 210, thereby blocking the current in the antenna 208. Now, referring to FIG. 7, when the third reactive impedance element 240 fails, the RF passive detuning circuit 702 includes the second reactive impedance element 232 and the second passive tuning inductor 243. The first reactive impedance element 230 is connected between a first node, labeled as node C, and a third node, labeled as node D. The second reactive impedance element 232 is connected between the third node, labeled as node D, and a second node, labeled as node E. The second passive tuning inductor 243 is connected between a first node labeled as node C and a third node labeled as node D. Thus, the second passive tuning inductor 243 connected between the first node labeled as node C and the third node labeled as node D can cause an increase in impedance in the antenna 208 sufficient to block current. More specifically, the RF passive detuning circuit 702 is operable to detune the sensitivity of the receiver circuit 202 by blocking current flow on the antenna 208 by creating a high impedance between a fifth node, denoted as node A, and a sixth node, denoted as node B, in the antenna 208 located at the first end 210-1 of the first transmission line 210. This blocking is achieved by the first transmission line 210, the first and second reactive impedance elements 230 and 232, and the second passive tuning inductor 243. "Blocking," as used herein, is defined as the process of creating a high resistance in the antenna 208 such that it becomes less sensitive to RF signals. Reducing the sensitivity of the antenna 208 reduces the risk of patient injury or circuit damage from excitation mode energy.Blocking is achieved by creating a high resistance at the Larmor frequency from the antenna 208 to the first end 210-1 of the first transmission line 210, as shown in Figure 7. Note that no circuit element connected between the fifth node, labeled as node A, and the sixth node, labeled as node B, is necessary to create a high impedance between the fifth node, labeled as node A, and the sixth node, labeled as node B.

[0044] FIG. 8 is an exemplary circuit diagram illustrating a second example receiver circuit (second receiver circuit 802) according to some embodiments. For economy of disclosure, only the parts of the second receiver circuit 802 that are different from the first receiver circuit (202) are described. Furthermore, to simplify the disclosure, neither the impedance transformation circuit 215 nor the amplifier circuit 204 are shown. However, it will be understood that the second receiver circuit 203 can be connected to the impedance transformation circuit 215 and the amplifier circuit 204 as described above. The active detuning circuit of the second receiver circuit 802 shown in FIG. 8 includes a first cross-coupled PIN diode switch (804) instead of the PIN diode switch (234) shown in FIG. 2A. Furthermore, the passive detuning circuit of the second receiver circuit 802 includes a first switch 804 and a third cross-coupled PIN diode switch (237) while omitting the first branch circuit 255 shown in FIG. 2A. During receive mode, the first and third switches 804 and 237 are both turned off, and the RF operation of the second receive circuit 802 is as described with reference to Fig. 3. During RF active detuning operation, the DC voltage turns on the first switch 804 but not the third switch 237, since the second blocking capacitor 252 blocks DC current. Thus, the RF operation of the second receive circuit 802 is as described with reference to Fig. 4. During RF passive detuning operation, the first blocking inductor 244 is selected to act as an open circuit for RF, while the second blocking capacitor 252 is selected to act as a short circuit for RF. Thus, the excitation signal causes the first switch 804 and the third switch 237 to turn on.

[0045] FIG. 9 is an exemplary circuit diagram illustrating a third example receiver circuit (third receiver circuit 902) according to some embodiments. For economy of disclosure, only the parts of the third receiver circuit 902 that are different from the receiver circuit 202 in the first example are described. The third receiver circuit 902 is identical to the receiver circuit 202 in the first example, except that the inductor 216 and the second transmission line 214 are electrically connected between the impedance matching detuning circuit 212. The inductor 216, which is a reactive impedance element, has a terminal coupled to a third node, denoted as node D, between the first reactive impedance element 230 and the second reactive impedance element 232. The inductor 216 also has a terminal connected to a fourth node, denoted as node L, at the center conductor (265) of the first end 214-1 of the second transmission line 214.

[0046] The inductor 216 is provided to optimize the impedance transformation through the second transmission line 214. A small variable impedance allows for tuning of the impedance transformation. The relative ground conductor 267 of the second transmission line 214 is coupled to a second node, labeled as node E, at relative ground potential. The exemplary impedance transformation circuit 215 is connected in parallel to the second end 214-2 of the second transmission line 214. More specifically, first and second input terminals of each of the impedance transformation circuits 215 are coupled across the signal conductor 265 and the relative ground conductor 267 at the second end 214-2 of the second transmission line 214 at nodes J and K, respectively. First and second output terminals of each of the impedance transformation circuits 215 are coupled to first and second input terminals of each of the amplifier circuits 204 at first and second input nodes F and G, respectively. The second transmission line 214 is enabled to be positioned to physically separate the amplifier circuit 204 from the second end 210 - 2 of the first transmission line 210 and the impedance matching detuning circuit 212 .

[0047] 10A-10F are exemplary circuits showing exemplary first through sixth impedance transformation circuits 215A-215F connected across the inputs to the exemplary amplifier circuit 204. More specifically, FIGS. 10A-10F show exemplary first through sixth impedance transformation circuits 215A-215F that are different from one another. The first through sixth impedance transformation circuits 215A-215F may be coupled across a third node, labeled as node D, and a second node, labeled as node E, in parallel with the second reactive impedance element 232 between the second reactive impedance element 232 and the input to the amplifier circuit 204. Additionally, the exemplary first through sixth impedance transformation circuits 215A-215F show coupling to a DC voltage source Vcc that may be activated during excitation mode operation of the MRI scanner 100. FIG. 10A shows an exemplary diagram of the first impedance transformation circuit 215A. The first impedance transformation circuit 215A includes only a signal conductor line between the second reactive impedance element 232 and the input to the amplifier circuit 204. FIG. 10B shows an example diagram of the second impedance transformation circuit 215B. The second impedance transformation circuit 215B includes a single inductor connected between a third node, labeled as node D, and the input to the amplifier circuit 204. FIG. 10C shows an example diagram of the third impedance transformation circuit 215C. The third impedance transformation circuit 215C includes a transmission line segment spanning a third node, labeled as node D, between the second reactive impedance element 232 and the input to the amplifier circuit 204, and a second node, labeled as node E. FIG. 10D shows an example diagram of the fourth impedance transformation circuit 215D. The fourth impedance transformation circuit 215D includes a first ladder network. The first ladder network includes two capacitors and two inductors. The two capacitors are coupled across the input to the amplifier circuit 204. The two inductors are coupled in series to be connected between a third node, labeled as node D, and the input to the amplifier circuit 204. Figure 10E shows an example diagram of a fifth impedance transformation circuit 215E.The fifth impedance transformation circuit 215E includes a second ladder network. The second ladder network includes two inductors and one capacitor. The two inductors are coupled in series to be connected between a third node, labeled as node D, and the input to the amplifier circuit 204. A capacitor is coupled across the input to the amplifier circuit 204 between the two inductors connected in series. FIG. 10F shows an exemplary diagram of the sixth impedance transformation circuit 215F. The sixth impedance transformation circuit 215F includes a first inductor, a second inductor, and a capacitor. The first inductor is coupled between a third node, labeled as node D, and the signal conductor 265 of the first end 214-1 of the second transmission line 214. The second inductor is coupled between the signal conductor 265 of the second end 214-2 of the second transmission line 214 and the input to the amplifier circuit 204. A capacitor is coupled across the inputs to the amplifier circuit 204 between the second end 214-2 of the second transmission line 214 and the second inductor. The exemplary first through sixth impedance transformation circuits 215A-215F are merely exemplary, and the exact circuit configuration may depend on the particular physical and electrical implementation of the receiver circuit 202 and the characteristics of the amplifier circuit 204. It will be further understood that the first and second reactive impedance elements 230, 232 are electrically connected to each of the exemplary first through sixth impedance transformation circuits 215A-215F and thereby contribute to the impedance transformation achieved by using the first through sixth impedance transformation circuits 215A-215F.

[0048] <Various Examples> Examples of resonant traps may include: Example 1 includes a radio frequency (RF) circuit (202) for use with a magnetic resonance imaging (MRI) scanner (100) to transmit an RF receive signal to an amplifier circuit (204). The RF circuit (202) includes a transmission line (210) having a first end (210-1) and a second end (210-2), an antenna (208) electrically connected in parallel to the transmission line at the first end of the transmission line, an impedance transformation circuit (215), and an impedance matching detuning circuit (212). The impedance matching detuning circuit is electrically connected between the transmission line and the impedance transformation circuit, as well as electrically connected in parallel to the transmission line at the second end of the transmission line and in parallel to the impedance transformation circuit. The impedance matching detuning circuit includes a plurality of reactive impedance elements (230, 232, 240) and two or more switches (234, 236, 237). In a first RF connection configuration, the two or more switches RF connect a first set of the reactive impedance elements (230, 232) to the second end of the transmission line during a receive mode of the MRI scanner to match the overall impedance of the RF circuit to a predetermined input impedance seen by the amplifier circuit at a predetermined RF frequency, while in a second RF connection configuration, the two or more switches are operable to controllably switch between RF connection configurations between the reactive impedance elements (230, 232, 240) to RF connect a second set of the reactive impedance elements (230, 232, 240) to the second end of the transmission line during an excitation mode of the MRI scanner to increase an impedance at the antenna and thereby reduce the sensitivity of the antenna to RF signals at a predetermined frequency.

[0049] Example 2 may include the subject matter of example 1. The two or more switches include an active switch (234) controllable based on a DC control signal to switch between a first active switch configuration and a second active switch configuration, in which the active switch RF disconnects at least one of the reactive impedance elements (240) from the second end of the transmission line to configure the first set of the reactive impedance elements (230, 232) to contribute to matching the overall impedance of the RF circuit to a predetermined input impedance seen by the amplifier circuit at the predetermined RF frequency during the receive mode of the MRI scanner. In the second active switch configuration, the active switch (234) RF connects at least one of the reactive impedance elements (240) to the second end of the transmission line to configure a second set of the reactive impedance elements (230, 232, 240) to increase the impedance at the antenna to reduce the sensitivity of the antenna to RF signals during the excitation mode of the MRI scanner. The two or more switches comprise passive switches (236, 237) that are controllable between a first passive switch configuration and a second passive switch configuration based on a voltage level of the RF receive signal transmitted within the RF circuit (202). In the first passive switch configuration, when there is no RF signal transmitted within the RF circuit having a voltage equal to or greater than a threshold voltage, the passive switches (236, 237) RF-disconnect at least one (240) of the plurality of reactive impedance elements (230, 232, 240) from the second end (210-2) of the transmission line (210), thereby configuring the first set (230, 232) of the plurality of reactive impedance elements to contribute to matching the overall impedance of the RF circuit to the predetermined input impedance seen by the amplifier circuit (204) at the predetermined RF frequency during the receive mode of the MRI scanner (100).In the second passive switch configuration, the passive switches (236, 237) configure the second set (230, 232, 240) of the reactive impedance elements (230, 232, 240) to RF connect at least one (240) of the reactive impedance elements (230, 232, 240) to the second end (210-2) of the transmission line (210) in response to the occurrence of an RF signal transmitted in the RF circuit having a voltage equal to or greater than the threshold voltage, thereby increasing the impedance at the antenna (208) and reducing the sensitivity of the antenna (208) to RF signals during the excitation mode of the MRI scanner (100).

[0050] Example 3 may include the subject matter of example 1. The plurality of reactive impedance elements includes a first reactive impedance element (230), a second reactive impedance element (232), and a third reactive impedance element (240). The first set includes the first reactive impedance element and the second reactive impedance element. The second set includes the first reactive impedance element, the second reactive impedance element, and the third reactive impedance element.

[0051] Example 4 may include the subject matter of example 3. Two or more of the switches (236, 237) are operable to RF connect the first reactive impedance element (230) and the second reactive impedance element (232) in an L configuration. The first reactive impedance element is RF connected in series to the transmission line at the second end of the transmission line. The second reactive impedance element is RF connected in parallel to the transmission line after the first reactive impedance element at the second end of the transmission line. Thus, operable to cause matching of the overall impedance of the RF circuit to the predetermined input impedance seen by the amplifier circuit at the predetermined RF frequency during the receive mode of the MRI scanner. Two or more of the switches are operable to RF connect the third reactive impedance element such that it is RF connected in parallel to the transmission line at the second end of the transmission line, thereby causing an increase in the impedance at the antenna (208) from matching the overall impedance to reduce the sensitivity of the antenna to RF signals at a predetermined frequency during the excitation mode of the MRI scanner.

[0052] Example 5 may include the subject matter of example 3. The first reactive impedance element (230) and the second reactive impedance element (232) are operable to be RF coupled to contribute to matching the overall impedance of the RF circuit to the predetermined input impedance seen by the amplifier circuit at the predetermined RF frequency during the receive mode of the MRI scanner. The two or more switches include at least one active switch (234) and at least one passive switch (236, 237) controllable based on a voltage level of an RF signal transmitted in the RF receive circuit. The at least one active switch (234) is controllable in response to the generation of a DC signal to RF couple the third reactive impedance (240) to the second end of the transmission line to increase the impedance at the antenna from matching the overall impedance and reduce the sensitivity of the antenna to the RF signal during the excitation mode of the MRI scanner. At least one of the passive switches (236, 237) RF connects the third reactive impedance element to the second end of the transmission line in response to the occurrence of an RF signal in the RF receiver circuit having a voltage equal to or greater than a threshold voltage, thereby increasing the impedance at the antenna from matching the overall impedance and reducing the sensitivity of the antenna to RF signals during the excitation mode of the MRI scanner.

[0053] Example 6 may include the subject matter of example 5 and further includes a fourth reactive impedance element (243). The at least one passive switch includes a first passive switch (237) controllable based on a voltage level of an RF signal transmitted in an RF receiver circuit. The first passive switch RF couples the third reactive impedance element (240) in series with the fourth reactive impedance element (243) and in parallel with the second end of the transmission line in response to the occurrence of an RF signal in the RF receiver circuit having a voltage equal to or greater than a threshold voltage, thereby causing an increase in the impedance at the antenna and reducing the sensitivity of the antenna to RF signals.

[0054] Example 7 may include the subject matter of Example 6 and further include a fifth reactive impedance element (242). The at least one passive switch includes a second passive switch (236) controllable based on a voltage level of an RF signal transmitted in an RF receiver circuit. The second passive switch RF couples the fifth reactive impedance element in parallel to the second end of the transmission line and in series with the second reactive impedance element (232) in response to the occurrence of an RF signal in the RF receiver circuit having a voltage equal to or greater than a threshold voltage, thereby causing an increase in the impedance at the antenna and reducing the sensitivity of the antenna to RF signals.

[0055] Example 8 may include the subject matter of example 7. The first passive switch (237) and the second passive switch (236) are switches that are independently operable in response to the occurrence of an RF signal in an RF receiver circuit having a voltage equal to or greater than the threshold voltage.

[0056] Example 9 may include the subject matter of example 7. The first passive switch and the second passive switch are switches that are independently operable in response to the occurrence of an RF signal in an RF receiver circuit having a voltage equal to or greater than a threshold voltage. The fourth reactive impedance element (243) is operable to cause an increase in the impedance at the antenna from matching the overall impedance when a third reactive impedance element (240) fails to reduce the sensitivity of the antenna to RF.

[0057] Example 10 may include the subject matter of example 1. An RF receiver circuit resonates at the predetermined RF frequency having a predetermined frequency band and a predetermined center frequency when two or more of the switches RF connect the first set of the plurality of reactive impedance elements to the second end of the transmission line. A failure (602) of the impedance matching detuning circuit causes an electrical disconnection of one or more elements of the impedance matching detuning circuit from the transmission line connecting the impedance matching detuning circuit to the antenna, or an electrical disconnection of the entire impedance matching detuning circuit. The failure of the impedance matching detuning circuit causes a shift of the resonant frequency of the RF receiver circuit to a shifted resonant frequency having a shifted frequency band and a shifted center frequency different from each of the predetermined frequency band and the predetermined center frequency.

[0058] Example 11 may include the subject matter of Example 1. The transmission line is a differential transmission line comprising a signal conductor (226) and a relative ground conductor (228). The antenna is electrically connected across the signal conductor and the relative ground conductor at the first end of the transmission line. The increase in impedance at the antenna is for reducing the sensitivity of the antenna to RF signals from an overall impedance match. The increase in impedance at the antenna occurs at a location in the RF circuit where the antenna is electrically connected across the signal conductor and the relative ground conductor at the first end of the transmission line.

[0059] Example 12 may include the subject matter of example 1. The impedance transformation circuit transforms the input impedance of the amplifier circuit at the antenna to a higher impedance than at the antenna during transmission of an RF receive signal in the RF circuit, thereby minimizing currents at the antenna. Furthermore, the antenna is prevented from generating parasitic RF signal coupling at one or more other antennas.

[0060] Example 13 can include the subject matter of example 1. The predetermined frequency is a Larmor frequency. Example 14 may include the subject matter of example 2. The voltage threshold is an MRI RF excitation signal voltage level.

[0061] Example 15 may include the subject matter of Example 3. The two or more switches include an active switch (234) and a first passive switch (237). The active switch includes a PIN diode (235) electrically connected in series with a third reactive impedance element (240). The series connected PIN diode and the third reactive impedance element are electrically connected in parallel at a second end of the transmission line between a first node (C) in the signal conductor of the transmission line and a second node (E) in the relative ground of the transmission line. The first passive switch (237) includes a first cross-coupled PIN diode pair (239) electrically connected between the first node (C) and a third node (D). The first reactive impedance element (230) is electrically connected between the first node and the third node. The second reactive impedance element (232) is electrically connected between the third node (D) and the second node (E).

[0062] Example 16 can include the subject matter of Example 15 and further includes a first blocking capacitor (252) electrically connected in series between the first passive switch (237) and the third node (D). The first blocking capacitor behaves as a short circuit to the RF signal.

[0063] Example 17 can include the subject matter of Example 16 and further includes a first reactive tuning element (243) electrically connected in series between the first passive switch (237) and the first blocking capacitor (262).

[0064] Example 18 can include the subject matter of Example 15 and further includes a first blocking inductor (248) electrically connected in parallel with the first reactive impedance element (230). The first blocking inductor behaves as an open circuit to an RF signal.

[0065] Example 19 may include the subject matter of example 15. The two or more switches include a second passive switch (236). The second passive switch includes a second cross-coupled PIN diode pair (238) electrically connected between the first node (C) and a fourth node (H). The third reactive impedance element (240) is electrically connected between the fourth node (H) and the second node (E).

[0066] Example 20 may include the subject matter of Example 19 and further includes a first blocking capacitor (252) electrically connected in series between the first passive switch (237) and the third node (D) and a second blocking capacitor (250) electrically connected in series between the second passive switch (236) and the fourth node (H). Each of the first blocking capacitor and the second blocking capacitor behaves as a short circuit to an RF signal.

[0067] Example 21 can include the subject matter of Example 20 and further includes a first reactive tuning element (243) electrically coupled in series between the first passive switch (237) and the first blocking capacitor (252), and a second reactive tuning element (242) electrically coupled in series between the second passive switch (236) and the second blocking capacitor (250).

[0068] Example 22 may include the subject matter of Example 21 and further includes a first blocking inductor (248) electrically connected in parallel with the first reactive impedance element (230) and a second blocking inductor (244) electrically connected in parallel with the third reactive impedance element (240). Each of the first blocking inductor and the second blocking inductor behaves as an open circuit to an RF signal.

[0069] Example 23 may include the subject matter of Example 1 and further include a reactance element (222) electrically connected in parallel to the first end of the transmission line between a fifth node (A) on the signal conductor (226) of the transmission line and a sixth node (B) on the reference ground (228) of the transmission line.

[0070] Example 24 may include a radio frequency (RF) circuit for use with a magnetic resonance imaging (MRI) scanner to transmit an RF receive signal to an amplifier circuit. The RF circuit includes a transmission line having a first end and a second end, an antenna electrically connected in parallel to the transmission line at the first end of the transmission line, an impedance transformation circuit, and an impedance matching detuning circuit. The impedance matching detuning circuit is electrically connected in parallel to the transmission line at the second end of the transmission line and in parallel to the impedance transformation circuit between the transmission line and the impedance transformation circuit. The impedance matching detuning circuit includes a first reactive impedance element (230), a second reactive impedance element (232), a third reactive impedance element (240), an active switch (234), and a first passive switch (237). The active switch (234) includes a PIN diode (235) electrically connected in series with the third reactive impedance element. The first passive switch (237) includes a first cross-coupled PIN diode pair (239) electrically connected between a first node (C) and a third node (D). The series-coupled PIN diodes and a third reactive impedance are electrically connected in parallel to the second end of the transmission line between a first node (C) on the signal conductor of the transmission line and a second node (E) on the phase-to-ground of the transmission line. The first reactive impedance (230) is electrically connected between the first node (C) and the third node (D). The second reactive impedance (232) is electrically connected between the third node (D) and the second node (E).

[0071] Example 25 can include the subject matter of Example 24 and further includes a first blocking capacitor (252) electrically connected in series between the first passive switch (237) and the third node (D). The first blocking capacitor behaves as a short circuit to the RF signal.

[0072] Example 26 can include the subject matter of Example 25 and further includes a first tuning inductor (243) electrically connected in series between the first passive switch (237) and the first blocking capacitor (252).

[0073] Example 27 can include the subject matter of Example 24 and further include a first blocking inductor (248) electrically connected in parallel with the first reactive impedance element (230). The first blocking inductor behaves as an open circuit to an RF signal.

[0074] Example 28 may include the subject matter of Example 24. The two or more switches include a second passive switch (236). The second passive switch includes a second cross-coupled PIN diode pair (238) electrically connected between the first node (C) and a fourth node (H). A third reactive impedance element (240) is electrically connected between the fourth node (H) and the second node (E).

[0075] Example 29 may include the subject matter of Example 28 and further includes a first blocking capacitor (252) electrically connected in series between the first passive switch (237) and the third node (D) and a second blocking capacitor (250) electrically connected in series between the second passive switch (236) and the fourth node (H). Each of the first blocking capacitor and the second blocking capacitor behaves as a short circuit to the RF signal.

[0076] Example 30 may include the subject matter of Example 29 and further includes a first tuning inductor (243) electrically coupled in series between the first passive switch (237) and the first blocking capacitor (252), and a second tuning inductor (242) electrically coupled in series between the second passive switch (236) and the second blocking capacitor (250).

[0077] Example 31 can include the subject matter of Example 30 and further includes a first blocking inductor (248) electrically connected in parallel with the first reactive impedance element (230) and a second blocking inductor (244) electrically connected in parallel with the third reactive impedance element (240). Each of the first blocking inductor and the second blocking inductor behaves as an open circuit to an RF signal.

[0078] Example 32 may include the subject matter of Example 24 and further includes a reactance element (222) electrically connected in parallel to the first end (210-1) of the transmission line between a fifth node (A) in a signal conductor of the transmission line and a sixth node (B) in a phased earth of the transmission line.

[0079] The above description is presented to enable anyone skilled in the art to make and use the MRI-RF receiving circuit. Various modifications to the examples will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other examples and applications without departing from the scope of the present invention. In the above description, numerous details have been set forth for purposes of explanation. However, those skilled in the art will appreciate that the examples of the present disclosure can be practiced without these specific details. In other examples, well-known processes are shown in block diagram form so as not to obscure the description of the present invention with unnecessary detail. The same reference numerals have been used in several places to represent different views of the same or similar items in different drawings. Thus, the foregoing description and drawings of the embodiments and examples are merely illustrative of the principles of the present invention. Thus, it will be appreciated that various modifications can be made to the embodiments by those skilled in the art without departing from the scope of the present invention as defined in the appended claims.

Claims

1. 1. An RF circuit as a radio frequency circuit for use with a magnetic resonance imaging scanner as an MRI scanner to transmit an RF receive signal to an amplifier circuit, the RF circuit comprising: a transmission line having a first end and a second end; an antenna electrically connected in parallel to the transmission line at the first end of the transmission line; An impedance conversion circuit; an impedance matching and detuning circuit electrically connected between the transmission line and the impedance transformation circuit, and also connected in parallel to the transmission line at the second end of the transmission line and in parallel to the impedance transformation circuit; It is equipped with The impedance matching detuning circuit A plurality of reactive impedance elements; two or more switches operable to controllably switch between RF connection configurations between a plurality of said reactive impedance elements; The RF connection arrangements are a first RF connection arrangement for RF connecting a first set of the plurality of reactive impedance elements to the second end of the transmission line to match an overall impedance of the RF circuit to a predetermined input impedance seen by the amplifier circuit at a predetermined RF frequency during a receive mode of the MRI scanner; a second RF connection arrangement, RF connecting a second set of the reactive impedance elements to the second end of the transmission line to increase impedance at the antenna and desensitize the antenna to RF signals at the predetermined RF frequency during an excitation mode of the MRI scanner; Equipped with RF circuit.

2. The two or more switches are an active switch controllable based on a DC control signal to switch between a first active switch configuration and a second active switch configuration, in the first active switch configuration, the active switch RF disconnects at least one of the reactive impedance elements from the second end of the transmission line, thereby constituting the first set of reactive impedance elements that contribute to matching the overall impedance of the RF circuit to the predetermined input impedance seen by the amplifier circuit at the predetermined RF frequency during the receive mode of the MRI scanner; the active switch being a second active switch configuration, wherein the active switch configures the second set of the reactive impedance elements to RF connect the at least one of the reactive impedance elements to the second end of the transmission line to increase the impedance at the antenna and reduce the sensitivity of the antenna to RF signals during the excitation mode of the MRI scanner; a passive switch controllable between a first passive switch configuration and a second passive switch configuration based on a voltage level of the RF receive signal transmitted within the RF circuit, wherein in the first passive switch configuration, in the absence of an RF signal being transmitted within the RF circuit having a voltage equal to or greater than a threshold voltage, the passive switch RF disconnects at least one of the reactive impedance elements from the second end of the transmission line, thereby configuring the first set of the reactive impedance elements to contribute to matching the overall impedance of the RF circuit to the predetermined input impedance seen by the amplifier circuit at the predetermined RF frequency during the receive mode of the MRI scanner; the passive switch in a second passive switch configuration, wherein the passive switch configures the second set of a plurality of reactive impedance elements to RF connect at least one of the reactive impedance elements to the second end of the transmission line in response to an occurrence of an RF signal transmitted in the RF circuit having a voltage equal to or greater than the threshold voltage, thereby increasing the impedance at the antenna and decreasing the sensitivity of the antenna to RF signals during the excitation mode of the MRI scanner; The RF circuit of claim 1 , comprising:

3. The plurality of reactive impedance elements include A first reactive impedance element; A second reactive impedance element; A third reactive impedance element; It is equipped with the first set comprises the first reactive impedance element and the second reactive impedance element; the second set comprises the first reactive impedance element, the second reactive impedance element, and the third reactive impedance element. The RF circuit of claim 1 .

4. two or more of the switches are operable to RF connect the first reactive impedance element and the second reactive impedance element in an L configuration, the first reactive impedance element being RF connected in series to the transmission line at the second end of the transmission line and the second reactive impedance element being RF connected in parallel to the transmission line after the first reactive impedance element at the second end of the transmission line to match the overall impedance of the RF circuit to the predetermined input impedance seen by the amplifier circuit at a predetermined RF frequency during the receive mode of the MRI scanner; two or more of the switches are operable to RF connect the third reactive impedance element to be RF connected in parallel to the transmission line at the second end of the transmission line, thereby causing an increase in the impedance at the antenna from matching the overall impedance to reduce the sensitivity of the antenna to RF signals at the predetermined RF frequency during the excitation mode of the MRI scanner. The RF circuit of claim 3 .

5. the first reactive impedance element and the second reactive impedance element are operable to be RF coupled to contribute to matching the overall impedance of the RF circuit to the predetermined input impedance seen by the amplifier circuit at the predetermined RF frequency during the receive mode of the MRI scanner; The two or more switches are at least one active switch controllable based on a DC signal, the active switch responsive to generation of the DC signal to RF connect the third reactive impedance element to the second end of the transmission line to increase the impedance at the antenna from matching the overall impedance and to reduce the sensitivity of the antenna to RF signals during the excitation mode of the MRI scanner; at least one passive switch controllable based on a voltage level of an RF signal transmitted within the RF circuit, the at least one passive switch RF-connecting the third reactive impedance element to the second end of the transmission line in response to the occurrence of an RF signal within the RF circuit having a voltage equal to or greater than a threshold voltage, thereby increasing the impedance at the antenna and decreasing the sensitivity of the antenna to RF signals during the excitation mode of the MRI scanner; Equipped with The RF circuit of claim 3 .

6. the RF circuit further comprises a fourth reactive impedance element; at least one of the passive switches comprises a first passive switch controllable based on the voltage level of an RF signal transmitted within the RF circuit, the first passive switch RF-connecting the third reactive impedance element in series with the fourth reactive impedance element and in parallel with the second end of the transmission line in response to the occurrence of an RF signal within the RF circuit having a voltage equal to or greater than the threshold voltage, thereby causing an increase in the impedance at the antenna and reducing the sensitivity of the antenna to RF signals; The RF circuit of claim 5 .

7. the RF circuit further comprises a fifth reactive impedance element; at least one of the passive switches comprises a second passive switch controllable based on the voltage level of an RF signal transmitted within the RF circuit, the second passive switch RF-connecting the fifth reactive impedance element in parallel to the second end of the transmission line and in series with the second reactive impedance element in response to the occurrence of an RF signal within the RF circuit having a voltage equal to or greater than the threshold voltage, thereby causing an increase in the impedance at the antenna and reducing the sensitivity of the antenna to RF signals. The RF circuit of claim 6.

8. the first passive switch and the second passive switch are operable to switch independently of one another in response to the occurrence of an RF signal in the RF circuit having a voltage equal to or greater than the threshold voltage. The RF circuit of claim 7.

9. the first passive switch and the second passive switch are switches that are independently operable in response to the occurrence of an RF signal in the RF circuit having a voltage equal to or greater than the threshold voltage; the fourth reactive impedance element is operable to cause an increase in the impedance at the antenna from matching the overall impedance in the event of a failure of the third reactive impedance element to reduce the sensitivity of the antenna to RF. The RF circuit of claim 7.

10. the RF circuit is resonant at the predetermined RF frequency having a predetermined frequency band and a predetermined center frequency when two or more of the switches RF connect the first set of the plurality of reactive impedance elements to the second end of the transmission line; a failure of the impedance matching detuning circuit causing electrical disconnection of one or more elements of the impedance matching detuning circuit, or electrical disconnection of the entire impedance matching detuning circuit, from the transmission line connecting the impedance matching detuning circuit to the antenna causes a shift in the resonant frequency of the RF circuit to a shifted resonant frequency having a shifted frequency band and a shifted center frequency different from the respective predetermined frequency band and predetermined center frequency. The RF circuit of claim 1 .

11. the transmission line is a differential transmission line including a signal conductor and a relative ground conductor; the antenna is electrically connected between the signal conductor and the relative ground conductor at the first end of the transmission line; the increase in impedance at the antenna from the overall impedance matching to reduce the sensitivity of the antenna to RF signals occurs at a location in the RF circuit where the antenna is electrically connected between the signal conductor and the reference ground conductor at the first end of the transmission line; The RF circuit of claim 1 .

12. the impedance transformation circuit is configured to transform an input impedance of the amplifier circuit at the antenna to a higher impedance than at the antenna during transmission of an RF receive signal in the RF circuit, thereby minimizing currents in the antenna and preventing the antenna from generating parasitic RF signal coupling at one or more other antennas. The RF circuit of claim 1 .

13. The predetermined RF frequency is the Larmor frequency. The RF circuit of claim 1 .

14. The threshold voltage is an MRI RF excitation signal voltage level. The RF circuit of claim 2 .

15. The two or more switches include an active switch and a first passive switch; the active switch comprises a PIN diode electrically connected in series with the third reactive impedance element; the series-connected PIN diode and the third reactive impedance element are electrically connected in parallel to the second end of the transmission line between a first node in a signal conductor of the transmission line and a second node in a relative ground of the transmission line; the first passive switch comprises a first cross-coupled PIN diode pair electrically connected between the first node and a third node; the first reactive impedance element is electrically connected between the first node and the third node; the second reactive impedance element is electrically connected between the third node and the second node. The RF circuit of claim 3 .

16. The RF circuit further comprises: a first blocking capacitor electrically connected in series between the first passive switch and the third node; the first blocking capacitor behaves as a short circuit to RF signals; 16. The RF circuit of claim 15.

17. The RF circuit further comprises: a first reactive tuning element electrically connected in series between the first passive switch and the first blocking capacitor; 17. The RF circuit of claim 16.

18. the RF circuit further comprises a first blocking inductor electrically connected in parallel with the first reactive impedance element; the first blocking inductor behaves as an open circuit to an RF signal; 16. The RF circuit of claim 15.

19. The two or more switches include a second passive switch; the second passive switch comprises a second cross-coupled PIN diode pair electrically connected between the first node and a fourth node; the third reactive impedance element is electrically connected between the fourth node and the second node.

16. The RF circuit of claim 15.

20. The RF circuit further comprises: a first blocking capacitor electrically connected in series between the first passive switch and the third node; a second blocking capacitor electrically connected in series between the second passive switch and the fourth node; It is equipped with each of the first blocking capacitor and the second blocking capacitor behaves as a short circuit to an RF signal; 20. The RF circuit of claim 19.

21. The RF circuit further comprises: a first reactive tuning element electrically coupled in series between the first passive switch and the first blocking capacitor; a second reactive tuning element electrically coupled in series between the second passive switch and the second blocking capacitor; Equipped with 21. The RF circuit of claim 20.

22. The RF circuit further comprises: a first blocking inductor electrically connected in parallel with the first reactive impedance element; a second blocking inductor electrically connected in parallel with the third reactive impedance element; It is equipped with each of the first blocking inductor and the second blocking inductor behaves as an open circuit to an RF signal; 22. The RF circuit of claim 21.

23. The RF circuit further comprises: a reactance element electrically connected in parallel to the first end of the transmission line between a fifth node in the signal conductor of the transmission line and a sixth node at the relative ground of the transmission line; The RF circuit of claim 1 .

24. 1. An RF circuit as a radio frequency circuit for use with a magnetic resonance imaging scanner as an MRI scanner to transmit an RF receive signal to an amplifier circuit, the RF circuit comprising: a transmission line having a first end and a second end; an antenna electrically connected in parallel to the transmission line at the first end of the transmission line; An impedance conversion circuit; an impedance matching and detuning circuit electrically connected between the transmission line and the impedance transformation circuit, and also connected in parallel to the transmission line at the second end of the transmission line and in parallel to the impedance transformation circuit; It is equipped with The impedance matching detuning circuit comprises: A first reactive impedance element; A second reactive impedance element; A third reactive impedance element; an active switch comprising a PIN diode electrically connected in series with the third reactive impedance element; a first passive switch comprising a first cross-coupled PIN diode pair electrically connected between the first node and a third node; It is equipped with the series-connected PIN diode and the third reactive impedance element are electrically connected in parallel to the second end of the transmission line between the first node in a signal conductor of the transmission line and a second node at a relative ground of the transmission line; the first reactive impedance element is electrically connected between the first node and the third node; the second reactive impedance element is electrically connected between the third node and the second node. RF circuit.

25. The RF circuit further comprises: a first blocking capacitor electrically connected in series between the first passive switch and the third node; the first blocking capacitor behaves as a short circuit to RF signals; 25. The RF circuit of claim 24.

26. The RF circuit further comprises: a first tuning inductor electrically connected in series between the first passive switch and the first blocking capacitor; 26. The RF circuit of claim 25.

27. The RF circuit further comprises: a first blocking inductor electrically connected in parallel with the first reactive impedance element; the first blocking inductor behaves as an open circuit to an RF signal; 25. The RF circuit of claim 24.

28. The two or more switches include a second passive switch. the second passive switch comprises a second cross-coupled PIN diode pair electrically connected between the first node and a fourth node; the third reactive impedance element is electrically connected between the fourth node and the second node.

25. The RF circuit of claim 24.

29. The RF circuit further comprises: a first blocking capacitor electrically connected in series between the first passive switch and the third node; a second blocking capacitor electrically connected in series between the second passive switch and the fourth node; It is equipped with each of the first blocking capacitor and the second blocking capacitor behaves as a short circuit to an RF signal; 30. The RF circuit of claim 28.

30. The RF circuit further comprises: a first tuning inductor electrically coupled in series between the first passive switch and the first blocking capacitor; a second tuning inductor electrically coupled in series between the second passive switch and the second blocking capacitor; Equipped with 30. The RF circuit of claim 29.

31. The RF circuit further comprises: a first blocking inductor electrically connected in parallel with the first reactive impedance element; a second blocking inductor electrically connected in parallel with the third reactive impedance element; It is equipped with each of the first blocking inductor and the second blocking inductor behaves as an open circuit to an RF signal; 31. The RF circuit of claim 30.

32. The RF circuit further comprises: a reactance element electrically connected in parallel to the first end of the transmission line between a fifth node in the signal conductor of the transmission line and a sixth node at a relative ground of the transmission line; 25. The RF circuit of claim 24.

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