RF receiving coil circuit for MRI system

Abstract

An apparatus and method for receiving magnetic resonance (MR) signals for imaging a patient, the MR signals including MR frequencies. A radio frequency (RF) coil has a first end and a second end. An impedance transformer is in electrical communication with the RF coil. A preamplifier in electrical communication with the impedance transformer has gain. At least one resonant circuit is electrically connected to at least one end of the RF coil.

Description

[Technical field]

[0001] This application was filed as a PCT patent international application on March 23, 2022, and claims the benefit of priority to U.S. Non-provisional Application No. 17 / 211,534, filed on March 24, 2021, the disclosure of which is incorporated by reference in its entirety.

[0002] Generally, this patent document relates to MRI systems, and more particularly, to RF receive coil circuits for MRI systems. [Background technology]

[0003] MRI systems generate images of tissues and structures within a patient's body and are a very important tool in diagnosing and treating the patient. MRI systems are very complex and sensitive pieces of equipment that require precision to produce high quality images. As would be expected, there is a constant need to improve MRI systems to produce more accurate and detailed images that make the tissues and structures depicted in the images easier to see and understand. Furthermore, increased image clarity and precision allows for more accurate diagnosis and treatment.

[0004] The MRI system includes a tube apparatus on which the patient lies on a table. The tube apparatus includes a series of strong magnets, gradient coils, RF transmit coils, and RF receive coils. These magnets and coils are operated in contact with cells in the patient's body. Most of the cells in the body contain hydrogen atoms, which have nuclei that rotate around axes. Normally, these axes are randomly located throughout the patient's body. However, by exposure to the generally uniform magnetic field of the strong magnets, all of the hydrogen nuclei align so that their axes are parallel to the z-axis (i.e., the axis of the MRI machine). Additionally, the hydrogen nuclei resonate or vibrate at a relatively uniform frequency.

[0005] When one of the gradient coils is excited with an RF signal, a gradient in the magnetic field is created along a slice extending through the patient's body. A gradient is a change in the magnetic field caused by a strong magnet. This magnetic field gradient allows a slice through the patient's body to be imaged.

[0006] The angular orientation of the hydrogen nuclei within a slice of the patient's body is different from other hydrogen nuclei within the patient's body, and the hydrogen nuclei within the slice resonate or vibrate at a different frequency than the hydrogen nuclei outside the slice.

[0007] The RF transmit coil is then excited with a pulse having a relatively narrow bandwidth of frequencies that includes frequencies that correspond to the frequencies at which the nuclei of the hydrogen atoms in the slice resonate or vibrate. The nuclei of the hydrogen atoms in the slice increase in resonance or vibration and absorb the excess energy from the pulse. When the pulse ends, the nuclei of the hydrogen atoms release the excess energy, inducing an electrical or MRI signal in the RF receive coil.

[0008] The MRI signal induced in the RF receiver coil typically has multiple frequency components including magnetic resonance (MR) frequencies that are generated by the nuclei of hydrogen atoms in the slice resonating or vibrating and that carry information about the patient's tissue in the slice. The MRI machine uses the information in the electrical signals and MR frequencies to generate images of the body that can be used by medical personnel to diagnose and treat patients.

[0009] Frequency components other than the MR frequency of the induced signal produce noise that reduces the clarity and accuracy of the resulting MRI image. Noise is the unwanted part of a signal that obscures the information contained in the signal. It is technically the ratio of the desired signal power to the noise power and is defined as:

number

[0010] where SNR is the signal-to-noise ratio and P signal is the average power of the meaningful or useful part of the signal, and P noise is the average power of the noise that is unwanted and obscures the useful parts of the signal.

[0011] The problem is that as MRI designers use more channels in MRI systems to increase image clarity and detail, noise increases. Each channel uses a separate RF receive coil. For example, an MRI system may use 64 or more RF receive coils. These coils are typically stacked to fit the MRI system. When the coils are stacked, the mutual inductance between the coils increases. Due to the mutual inductance, the signal of one RF receive coil affects the amplitude of the signal of another mutually coupled coil. Thus, the signal of one RF receive coil distorts the signal induced in the other RF receive coils, increasing noise.

[0012] To minimize noise and coupling between the RF receiving coils, the output of each RF receiving coil is typically fed through a balun and a low impedance preamplifier. This structure increases the blocking impedance through the preamplifier, increasing the mutual isolation of the RF receiving coils and the SNR of the signal output by the preamplifier. The low input impedance of the preamplifier helps to isolate the RF coils, but as described herein, it can also cause dog-ear peaks in the gain of the preamplifier at frequencies other than the MR frequency. These peaks can cause the preamplifier to oscillate and become unstable.

[0013] 1 and 2 show the source impedance and gain profile of a typical low impedance preamplifier used in current MRI systems to process the MRI signal output by the RF receive coil. FIG. 1 plots the gain and source impedance against the frequency of the MRI signal. In this example, the preamplifier operates in a 21° C. environment and has a gain of 28 dB over a specified operating bandwidth that includes the MR frequency of 63.8 MHz. The design source impedance of the preamplifier is approximately 125 ohms. Other typical low impedance preamplifiers and associated circuits have different gains and different operating frequencies. Furthermore, they can be used in circuits with different designed source impedances, such as 50 ohms, 100 ohms, 150 ohms, 200 ohms, or 300 ohms. However, these alternative low impedance preamplifiers have similar performance profiles as shown in FIG. 1 and FIG. 2. Summary of the Invention [Problem to be solved by the invention]

[0014] A first trace 100 plots source impedance versus frequency of the input signal. The source impedance peaks at the MR frequency (63.8 MHz in the illustrated example) and then drops off from the peak as the frequency increases or decreases. A second trace 104 plots the gain of the preamplifier versus signal frequency. In the second trace 104, the gain of the preamplifier is shown to have a camel hump or dog-ear profile with a first dog-ear peak 102 and a second dog-ear peak 106 at a first dog-ear frequency 108 and a second dog-ear frequency 110, respectively. The first dog-ear frequency 108 and the second dog-ear frequency 110 are frequencies at which the preamplifier is unstable or oscillates. The first dog-ear frequency 108 is below the MR frequency of 63.8 MHz, and the second dog-ear frequency 110 is above the MR frequency of 63.8 MHz. The gain of the preamplifier at the first dog-ear frequency 108 and the second dog-ear frequency 110 is higher than the gain at the MR frequency, and the gain at the dog-ear frequencies 108, 110 can be 10 dB or more higher than the gain at the MR frequency. [Means for solving the problem]

[0015] The cause of the dog-ear profile of the preamplifier gain is shown in FIG. 2. Trace 112 plots the gain of the preamplifier against the source impedance. In the illustrated example, the preamplifier has an operating gain of 28 dB with a designed source impedance of 125 ohms. As shown in the plot, the gain of the preamplifier increases as the source impedance decreases from the designed source impedance, and reaches a maximum gain when the source impedance is conjugate matched to the input impedance of the preamplifier, which is lower than the designed source impedance at the operating frequency corresponding to the MR frequency. Additionally, the frequency of the signal being processed affects the source impedance seen by the preamplifier. As the frequency of the signal deviates from the MR frequency, the source impedance of the preamplifier decreases. The decrease in source impedance causes the gain of the preamplifier to increase, resulting in the first dog-ear peak 102 and the second dog-ear peak 106. Another problem is that the MRI data used to create the image slices is transmitted at the MR frequency. High gain and oscillations at frequencies on either side of the MR frequency make it difficult to extract the MRI data from the signal, resulting in poor quality images or no images at all. MRI system developers have attempted to address this problem using various signal processing techniques, such as introducing a small insertion loss to reduce the power of the signal input to the preamplifier. This technique reduces the signal-to-noise ratio and relatively increases the amount of noise in the MRI signal. Another technique that has been attempted is to pass the signal output by the preamplifier through a very narrow bandpass filter to suppress the gain corresponding to the dog-ear peaks 102 and 106. However, the bandpass filter also introduces insertion loss. Yet another technique that has been attempted is to use negative feedback to reduce the gain at the dog-ear frequencies 108 and 110, but this approach has also not been able to effectively reduce the effect of the dog-ear peaks 102 and 106 in the MRI system. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 plots source impedance and preamplifier gain against frequency, with the preamplifier gain having two dog-ear peaks at selected frequencies.

[0017] [Diagram 2] FIG. 2 plots the source impedance versus the gain of the preamplifier.

[0018] [Diagram 3] FIG. 3 shows an MRI system.

[0019] [Figure 4] FIG. 4 is a circuit diagram showing an RF receiving coil circuit of the MRI system shown in FIG.

[0020] [Diagram 5] FIG. 5 shows a coupling circuit included in the RF receiving coil circuit shown in FIG.

[0021] [Figure 6] FIG. 6 is an alternative embodiment of the RF receive coil circuit shown in FIG.

[0022] [Figure 7] FIG. 7 is another alternative embodiment of the RF receive coil circuit shown in FIG.

[0023] [Figure 8] FIG. 8 is a top view of a circuit board on which the RF receiving coil circuit shown in FIG. 4 is mounted.

[0024] [Figure 9] FIG. 9 is a plot modeling the source impedance of the RF receive coil circuit shown in FIG.

[0025] [Figure 10]FIG. 10 is a plot from an example comparing the performance of the RF receive coil circuit shown in FIG. 4 with and without a resonant circuit. [Figure 11] FIG. 11 is a plot from an example comparing the performance of the RF receive coil circuit shown in FIG. 4 with and without a resonant circuit. [Figure 12] FIG. 12 is a plot from an example comparing the performance of the RF receive coil circuit shown in FIG. 4 with and without a resonant circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Various embodiments will be described in detail below with reference to the drawings. References to the drawings and various embodiments in this specification are not intended to limit the scope of the claims appended hereto. Moreover, the examples described herein are not intended to be limiting, but merely to illustrate some of the many possible embodiments for the scope of the appended claims.

[0027] For the purposes of this patent document, the terms "or" and "and" shall mean "and / or" unless otherwise stated or clearly intended otherwise by the context of their use. Whenever appropriate, terms used in the singular include the plural and vice versa. Use of the term "a" means "one or more" unless otherwise stated or where the use of "one or more" is clearly inappropriate. Use of the term "or" means "and / or" unless otherwise stated. The terms "comprises," "comprises," "comprising," "includes," "including," "including," "having," and "having" are interchangeable and not intended to be limiting. For example, the term "including" means "including but not limited to." The term "such as" is also not intended to be limiting.

[0028] All ranges provided herein include the upper and lower limits of the range unless expressly stated otherwise. Although values ​​are disclosed herein in disclosing certain exemplary embodiments, other embodiments within the scope of the pending claims may have values ​​other than the specific values ​​disclosed herein or values ​​outside the ranges disclosed herein.

[0029] Terms such as "approximately," "substantially," or "about" when used in conjunction with values ​​or structural elements provide for tolerances normally found during testing and manufacturing due to variations and imprecise tolerances in factors such as materials, devices, manufacturing processes, and equipment. These terms also provide allowance for variations due to environmental conditions such as temperature and humidity. Such variations may also result from normal wear and tear over the life of a device embodying the appended claims. Additionally, all values ​​disclosed herein are approximations, whether or not they are expressly stated to be so.

[0030] Generally, one aspect of this patent document relates to an apparatus and method for increasing the source impedance at a selected frequency of a preamplifier of an RF receive coil circuit. Another aspect relates to increasing the source impedance at a selected frequency while substantially maintaining the source impedance at an operating frequency of the preamplifier corresponding to the MR frequency. Yet another aspect relates to increasing the blocking impedance at a selected frequency of an RF receive coil of an RF receive coil circuit. Yet another aspect relates to decreasing the gain of the preamplifier at a selected frequency. Yet another aspect relates to decreasing the gain of the preamplifier at a selected frequency while substantially maintaining the gain at an operating frequency of the preamplifier corresponding to the MR frequency.

[0031] 3, a magnetic resonance imaging (MRI) system 114 generally includes a bore 118 and a tube assembly 116 that defines a coordinate system having x, y, and z axes. A patient table 122 is disposed within the bore 118. The z-axis is horizontal and extends longitudinally generally parallel to the length of the bore 118 and patient table 122, the y-axis extends vertically, and the x-axis extends horizontally from side to side.

[0032] The tube assembly 116 includes a strong magnet 124, a gradient coil 126, an RF transmit coil 128, and an RF receive coil 130. The strong magnet 124 generates a very strong and uniform magnetic field. The strong magnet 124 can be any suitable magnet, such as a permanent magnet, an electromagnet (sometimes called a resistive magnet), a superconducting magnet, which is an electric coil formed from a superconductor, or a combination of different types of magnets. The strong magnet 124 can be a single magnet or can be a plurality of magnets working together to generate a strong magnetic field. In various embodiments, the strong magnet 124 generates a strong magnetic field, such as a magnetic field of about 0.1 Tesla, about 0.5 Tesla, about 1 Tesla, about 1.5 Tesla, about 3 Tesla, about 4.7 Tesla, about 7 Tesla, about 8 Tesla, about 9.4 Tesla, about 10.5 Tesla, about 11.4 Tesla, about 11.7 Tesla, about 14 Tesla, or more.

[0033] The gradient magnetic field coils 126 typically include at least three coils. Typically, there is at least one gradient magnetic field coil 126 parallel to each of the x-axis, y-axis, and z-axis. Typically, the gradient magnetic field coils 126 are generally orthogonal to one another. Alternative embodiments may have different numbers and arrangements of gradient magnetic field coils 126. For example, there may be multiple gradient magnetic field coils 126 parallel to a given axis of the tube assembly 116. Embodiments may also have gradient magnetic field coils 126 arranged at oblique angles relative to one or more axes or relative to other gradient magnetic field coils 126.

[0034] In an exemplary embodiment, the RF transmit coil 128 extends along the z-axis for a length sufficient to extend the entire length of the patient's body. In other embodiments, the RF transmit coil assembly 128 is shorter. For example, the RF transmit coil assembly 128 can have a length sufficient to extend along the length of a typical patient's head, torso, limbs, or any other portion of the anatomy being imaged. In at least some exemplary embodiments, the RF transmit coil 128 can extend around the entire circumference of the patient's body or around only a portion of the patient's body. In an exemplary embodiment of the MRI system 114, the RF transmit coil 128 can be a single RF transmit coil or multiple RF transmit coils.

[0035] In various embodiments of the MRI system 114, the RF receiving coil 130 can be a single RF receiving coil or multiple RF receiving coils. The RF receiving coil 130 is described in more detail herein. In at least some exemplary embodiments, the multiple RF receiving coils 130 are arranged in a coil array, and the individual coils 130 in the array can overlap each other. Alternatively, in at least some embodiments, the RF receiving coils 130 in the coil array can be parallel to each other without overlapping. The RF receiving coils 130 can be integrated into the structure of the tube assembly 116, or the RF receiving coils 130 can be freely placed in various locations, such as in proximity to a particular anatomical structure of interest. Other arrangements of the RF receiving coils 130 are also possible. When the MRI system 114 has multiple RF receiving coils 130, the MRI system 114 can have any suitable number of coils, such as 8 coils, 16 coils, 32 coils, 64 coils, 128 coils, or 256 coils.

[0036] In at least some embodiments, the same RF coil can be used as both an RF transmit coil and an RF receive coil.

[0037] In addition to the tube assembly 116, the MRI system 114 typically includes gradient amplifiers 132, RF processing circuitry 134, a system controller 136, a computer system 138, a memory 140, and a computer terminal 139. The gradient amplifiers 132 include amplifiers for each set of gradient coils 126 that have a particular orientation. For example, there is an amplifier for the gradient coil 126 that corresponds to the x-axis, an amplifier for the gradient coil 126 that corresponds to the y-axis, and an amplifier for the gradient coil 126 that corresponds to the z-axis. Each amplifier excites a corresponding gradient coil 126 to produce a gradient in the magnetic field. As described herein, the gradients define the location of a slice through the patient's body for imaging.

[0038] The RF processing circuitry 134 includes components for exciting the RF transmit coil 128 and for processing signals received from the RF receive coil 130. For example, at least some embodiments of the RF processing circuitry 134 include a signal generator, waveform generator, or pulse generator that generates signals for exciting the RF transmit coil 128. An amplifier amplifies these signals input to the RF transmit coil 128. The RF processing circuitry 134 includes amplifiers, signal filters, such as bandpass filters, and analog-to-digital circuits (ADCs) that process the MRI signals received from the RF receive coil 130. The RF processing circuitry 134 digitizes the MRI signals and transmits the digitized MRI signals to the system controller 136.

[0039] A system controller 136 communicates with the gradient amplifiers 132, the RF processing circuitry 134, and a computer system 138. The system controller 136 receives digitized MRI signals from the RF processing circuitry 134 and extracts MRI image data from the digitized signals. The system controller 136 transmits the MRI image data to the computer system 138 for storage in memory 140 and further processing. When sufficient MRI image data has been collected, the computer system 138 generates an MRI image for display on a computer terminal 139. The system controller 136 also communicates with a patient positioning system which controls the position of the patient table 122.

[0040] The computer terminal 139 communicates with the system controller 136 and the computer system 138 and provides an interface through which an operator can enter commands and control the MRI system 114 to scan the patient's body and display MRI images. The computer terminal 139 can also be used to view the MRI images.

[0041] 3 and disclosed herein is one of many possible embodiments. Other embodiments of the MRI system 114 may have hardware components, software components, system architectures, and functionality other than those described herein.

[0042] 4, in at least some embodiments, the RF receive coil 130 and the power supply circuit 144 form an RF receive coil circuit 142. Although the term "RF receive coil" is used, those skilled in the art will understand that in at least some exemplary embodiments, the same coil may be used as both an RF receive coil and an RF transmit coil.

[0043] In at least some embodiments, the RF receive coil 130 is a single conductive loop having a first end 148 and a second end 150 that terminate in a first terminal 152 and a second terminal 154, respectively. In alternative embodiments, the RF receive coil 130 may have multiple conductive loops. The RF receive coil 130 may have any suitable shape, such as rectangular, circular, oval, or any other suitable shape. The shape and dimensions of the RF receive coil 130 may depend on various factors, such as the magnetic field strength of the MRI system 114, the part of the patient's body being imaged (e.g., torso, limbs, head, etc.), the type of tissue or organ being imaged, or packaging requirements for fitting the RF receive coil 130 into the tube assembly 116. Additionally, the RF receive coil 130 may be formed from any suitable form of transmission line, such as stripline, wire, or cable.

[0044] The RF receive coil 130 may have any suitable configuration. For example, the RF receive coil 130 may be a volume coil, a circularly polarized coil, a phased coil, a birdcage coil, a single-turn solenoid coil, or a surface coil. The RF receive coil 130 may also be adapted to be placed outside the patient's body or within the patient's body, such as in a cavity or blood vessel.

[0045] In at least some embodiments, the feeding circuit 144 includes a preamplifier 158, a coupling circuit 160, a first resonant circuit 162, and a second resonant circuit 164. The preamplifier 158 is a low noise amplifier having a low input impedance Z a and a low noise figure.

[0046] In at least some exemplary embodiments, for an MRI system 114 having a magnetic field of about 1.5 Tesla, the preamplifier 158 has a bandwidth of operating frequencies including the MR frequency of 63.8 MHz, an overall bandwidth in the range of about 17 MHz to about 500 MHz, an input impedance Za of about 1.5 ohms, a gain of about 28 dB, and a noise figure of about 0.5 dB or less. In at least some other exemplary embodiments, the preamplifier 158 has an input impedance Za in the range of about 50 ohms or less, a gain in the range of about 25 dB to about 35 dB, and a noise figure in the range of about 0.0 dB to about 1.0 dB. Other example embodiments have operating frequencies, input impedances Za, gains, or noise figures higher or lower than these ranges. One example of a preamplifier 158 suitable for use in the RF receive coil 130 of the MRI system 114 is amplifier model WMA1R5A from WanTcom Inc., having its principal place of business in Chanhassen, Minnesota.

[0047] In at least some exemplary embodiments, the first resonant circuit 162 and the second resonant circuit 164 are electrically connected between the first terminal 152 and the second terminal 154 of the RF receiving coil 130. The first resonant circuit 162 and the second resonant circuit 164 each have an inductor 166 and an inductor 167 arranged in series with a capacitor 168 and a capacitor 169, respectively. The inductors 166 and 167 and the capacitors 168 and 169 can be arranged in any order. For example, in some embodiments, the inductor 166 of the first resonant circuit 162 is connected to the first terminal 152 and the capacitor 168 is connected between the inductor 166 and the second terminal 154. Similarly, the inductor 167 of the second resonant circuit 164 is connected to the first terminal 152 and the capacitor 169 is connected between the inductor 167 and the second terminal 154. In other exemplary embodiments, the positions of inductor 166 and inductor 167 and capacitors 168 and 169, respectively, may be reversed.

[0048] In at least some alternative embodiments, the first resonant circuit 162 and the second resonant circuit 164 have configurations other than series resonant circuits as shown in Figure 4 and disclosed herein. In some embodiments, for example, the first resonant circuit 162 and the second resonant circuit 164 can be parallel resonant circuits.

[0049] In at least some exemplary embodiments, capacitors 168 and 169, inductors 166 and 167, or both capacitors 168 and 169 and inductors 166 and 167 are adjustable so that resonant circuits 162 and 164 resonate at a determined resonant frequency.

[0050] In at least some exemplary embodiments, the first resonant circuit 162 is tuned to resonate at a frequency approximately equal to a first dog-ear frequency 108 corresponding to the first dog-ear peak 102 (see, e.g., FIG. 1 ), and the second resonant circuit 164 is tuned to approximately equal a second dog-ear frequency 110 corresponding to the second dog-ear peak 106 (see, e.g., FIG. 1 ). In exemplary embodiments, the first resonant circuit 162 is tuned to a frequency in the range of about 58 MHz to about 61 MHz, and the second resonant circuit 164 is tuned to a frequency in the range of about 68 MHz to about 70 MHz for a coil of a 1.5 Tesla MRI system.

[0051] The first dog-ear frequency 108 and the second dog-ear frequency 110 may vary depending on various factors such as the impedance values ​​of the RF receive coil circuit 142, the preamplifier 158, the impedance converter 160, the coil 130, the strength of the magnetic field produced by the strong magnet 124, variations and tolerances in the operating values ​​of the electrical components, variations and tolerances in the manufacturing process, and environmental factors. An advantage of tuning the resonant frequency is that it can be approximately or exactly matched to a particular dog-ear frequency of the RF receive coil circuit 142.

[0052] In at least some exemplary embodiments of the 1.5 Tesla MRI system, the inductor 166 of the first resonant circuit 162 has a value in the range of about 1.5 μH to about 3 μH, and the capacitor 168 has a value in the range of about 0.5 pF to about 3 pF. The inductor 167 of the second resonant circuit 164 has a value in the range of about 1.5 μH to about 3 μH, and the capacitor 169 has a value in the range of about 0.5 pF to about 3 pF. An example of an inductor that can be used for the first resonant circuit 162 and the second resonant circuit 164 is model 1008CS-222XGLC available from Coilcraft, Inc., having a principal place of business in Cary, Illinois. An example of a capacitor that can be used for the first resonant circuit 162 and the second resonant circuit 164 is model JR030 available from Voltronics, Inc., having a principal place of business in Chicago, Illinois.

[0053] The coupling circuit 160 provides an electrical coupling between the RF receive coil 130 and the preamplifier 158. In an exemplary embodiment, the coupling circuit 160 converts a balanced signal from the RF receive coil 130 to an unbalanced signal for amplification by the preamplifier 158.

[0054] One example of a coupling circuit 160 is a 90° lattice balun as shown in Figure 5. The lattice balun is an LC network having a first inductor 170 in electrical communication from the first terminal 152 of the RF receive coil 130 to the preamplifier 158 and a second inductor 172 in electrical communication from the second terminal 154 of the RF receive coil 130 to ground. A first capacitor 174 is in electrical communication from the first terminal 152 of the RF receive coil 130 to ground and a second capacitor 176 is in electrical communication from the second terminal 154 of the RF receive coil 130 to the input of the preamplifier 158.

[0055] In other exemplary embodiments, the coupling circuit 160 uses a balun other than a lattice balun. Yet other exemplary embodiments use a coupling circuit 160 other than a balun or have a direct electrical connection from the RF receive coil 130 to the preamplifier 158.

[0056] An advantage of the coupling circuit 160 is that it can provide a high blocking impedance Zb that helps isolate the RF receive coil 130 from other RF receive coils when the MRI system 114 uses multiple RF receive coils 130. This isolation reduces noise that is caused by mutual inductance between the RF receive coils 130 and that gets into the MRI signal. The high blocking impedance Zb can be created, at least in part, by providing a high source impedance Zs and a low input impedance Za. The relationship between these impedance values ​​can be defined as follows:

number

[0057] In an example embodiment, the impedance values ​​for an MRI system with a 1.5 Tesla magnetic field are Zc of 2.5 ohms, Za of 1.5 ohms, and Zs of 150 ohms. These values ​​result in a blocking impedance Zb of 250 ohms. In other example embodiments, the blocking impedance Zb ranges from about 100 ohms to about 5000 ohms.

[0058] Figure 6 illustrates an alternative embodiment of the RF receive coil circuit 142. This exemplary embodiment is substantially similar to the embodiment illustrated in Figure 4 and includes an RF receive coil 130, a first resonant circuit 162 and a second resonant circuit 164, a coupling circuit 160, and a preamplifier 158. However, the first resonant circuit 162 is electrically connected between the first terminal 152 of the RF receive coil 130 and ground, and the second resonant circuit 164 is electrically connected between the second terminal 154 of the RF receive coil 130 and ground.

[0059] Figure 7 illustrates an alternative embodiment of the RF receive coil circuit 142. This exemplary embodiment is substantially similar to the embodiment illustrated in Figure 4 and includes an RF receive coil 130, a first resonant circuit 162 and a second resonant circuit 164, a coupling circuit 160, and a preamplifier 158. However, the second terminal 154 of the RF receive coil 130 is connected to ground instead of the coupling circuit 160. Furthermore, both the first resonant circuit 162 and the second resonant circuit 164 are connected between the first terminal 152 of the RF receive coil 130 and ground.

[0060] 8, the RF receive coil 130 and the power supply circuitry 144 are mounted on a circuit board 178 having a coil portion 180 and a power supply board portion 182 formed into a loop having substantially the same shape and dimensions as the RF receive coil 130. The RF receive coil 130 is mounted on the coil portion 180 and the power supply circuitry 144 is mounted on the power supply board portion 182. In at least some exemplary embodiments, the RF receive coil 130 is formed from a stripline 156. The width and length of the stripline 156 can vary depending on various factors, such as the strength of the magnetic field generated by the MRI system 114. In an alternative embodiment, the coil portion 180 and the power supply board portion 182 are separate circuit boards with transmission lines or other electrical paths between them.

[0061] In an exemplary embodiment, the circuit board 178 is a printed circuit board (PCB) formed of a dielectric material. The circuit board 178 can have a single layer or multiple layers of material. One surface of the circuit board 178 has transmission lines for forming the RF receive coil 130 and conductive paths for electrically connecting various electrical components. Another surface, typically the bottom surface, of the feed board portion 182 has a ground plane that is a coating of a conductive material. The coil portion 180 of the circuit board 178 typically does not include a ground plane. The transmission lines, conductors, and ground planes can be formed of copper or any other suitable conductive material and can be laminated. The transmission lines can be provided on the surface of the circuit board 178 or the transmission lines can be disposed between layers of the circuit board 178. The electrical components forming the feed circuit 144 can be attached to the surface of the circuit board 178 or between layers of the circuit board 178. In various embodiments, the circuit board 178 can be a rigid circuit board or a flexible circuit board.

[0062] In at least some alternative embodiments, the circuit board 178 does not include the coil portion 180. For example, in embodiments when the RF receive coil 130 is formed from a wire or cable, the circuit board 178 does not include the coil portion 180 and the coil is electrically connected to the power supply circuit 144 via a terminal, connector, solder, or other connection structure.

[0063] Figure 9 models the source impedance Zs of the RF receiving coil circuit 142 of Figure 4 operating in a 21°C environment with and without the first resonant circuit 162 and the second resonant circuit 164. In this model, the preamplifier 158 has a bandwidth of operating frequencies including a MR frequency of 63.8MHz, a gain of 28dB, and an input impedance Za of 1.5ohms. The coupling circuit 160 is a 90° lattice balun formed by inductors 170 and 172 with inductances of about 90nH and capacitors 174 and 176 with capacitances of about 68pF. The first resonant circuit 162 and the second resonant circuit 164 are formed by an inductor 166 with an inductance of about 90nH and a capacitor 168 with a capacitance of about 68pF.

[0064] A first trace 184 plots the source impedance Zs when the RF receive coil circuit 142 does not include the first resonant circuit 162 and the second resonant circuit 164. This plot is substantially similar to the performance of the prior art system as shown by the first trace 100 of FIG. 1. The source impedance Zs at the first dog-ear frequency 108 and the second dog-ear frequency 110 is low. A second trace 186 plots the source impedance Zs when the RF receive coil circuit 142 includes the first resonant circuit 162 and the second resonant circuit 164. The second trace 186 shows how the first resonant circuit 162 and the second resonant circuit 164 increase the source impedance Zs at the first dog-ear frequency 108 and the second dog-ear frequency 110.

[0065] The model also shows that the source impedance Zs at an operating frequency corresponding to the MR frequency of the preamplifier 158 (e.g., 63.8 MHz) is not substantially changed by the addition of the first resonant circuit 162 and the second resonant circuit 164 to the RF receive coil circuit 142. The model also shows that the operating frequency corresponding to the MR frequency of the preamplifier 158 is not substantially changed when the RF receive coil circuit 142 includes the first resonant circuit 162 and the second resonant circuit 164. Increasing the source impedance Zs at the dog-ear frequencies 108 and 110 reduces the gain of the preamplifier 158 at the dog-ear frequencies 108 and 110, reducing the likelihood of oscillation of the preamplifier 158 and increasing the stability of the feed circuit 144.

[0066] In an exemplary embodiment, when the first resonant circuit 162 and the second resonant circuit 164 are used in the RF receive coil circuit 142, the gain at the peak of the first dog-ear 102 and the second dog-ear 106 is not more than about 8 dB greater than the gain at the MR frequency. In other exemplary embodiments, the gain at the peak of the first dog-ear 102 and the second dog-ear 106 is not more than about 12 dB, about 10 dB, about 8 dB, about 6 dB, about 4 dB, or about 2 dB greater than the gain at the MR frequency. In other exemplary embodiments, the gain at the peak of the first dog-ear 102 and the second dog-ear is about equal to or less than the gain at the MR frequency. In other exemplary embodiments, the gain at the peak of the first dog-ear 102 and the second dog-ear is about 2 dB, about 4 dB, about 6 dB, about 8 dB, about 10 dB, about 12 dB, about 14 dB, about 16 dB, about 18 dB, or about 20 dB less than the gain at the MR frequency.

[0067] In other exemplary embodiments, the gain at the peaks of the first dog ear 102 and the second dog ear when the RF receive coil circuit 142 has the first resonant circuit 162 and the second resonant circuit 164 is about 8 dB, about 10 dB, about 12 dB, about 14 dB, about 16 dB, or about 20 dB less than the gain at the peaks of the first dog ear 102 and the second dog ear when the RF receive coil circuit 142 does not have the first resonant circuit 162 and the second resonant circuit 164.

[0068] The reduction in gain at the first and second dog-ear frequencies 108, 110 by the first and second resonant circuits 162, 164 depends on a variety of factors. Examples of factors that may affect the reduction in gain include the size of the MRI system 114 (e.g., magnetic field strength), the tolerances of the electrical components used in the RF powering coil circuit 144, the degree to which the first and second resonant circuits 162, 164 are closely tuned to the first and second dog-ear frequencies 108, 110 that correspond to the peaks of the first and second dog-ears 102, environmental factors, the physical and electrical characteristics of the RF receiving coil 130, the quality of the electrical connections of the circuit, the various impedance values ​​of the RF powering coil circuit 144, the performance and characteristics of the preamplifier 158, and other physical and electrical characteristics of the RF powering coil circuit 144. Similar factors also affect the levels of gain at the first and second frequencies relative to the MR frequencies.

[0069] In an embodiment, Figures 10-12 measure and compare the performance of the RF receive coil circuit 142 shown in Figure 4 with and without the first resonant circuit 162 and the second resonant circuit 164. In this embodiment, the preamplifier 158 of the RF receive coil circuit 142 is a WanTcom Inc. amplifier model WMA1R5A. The RF receive coil 146 is a stripline 156 having a length of about 59 cm and a width of about 5 mm. The impedance transformer 160 is a 90° lattice balun. The inductors 170 and 172 of the balun are model 2222SQ-90N air coil inductors, SQ series inductors available from Coilcraft, Inc., and have an inductance of about 90 nH, and the capacitors 174 and 176 are model 800B680FTN500 available from American Technical Ceramics Co. (ATC), having a principal place of business in Huntington Station, NY, and have a capacitance of about 68 pF. The inductors 166 and 167 used in the first resonant circuit 162 and the second resonant circuit 164 are model 222XGLC available from Coilcraft and have an inductance of approximately 2.2 μH and approximately 2.2 μH, respectively. The capacitors 168 and 169 are variable capacitors model JR030 available from Voltronics and have a capacitance range of approximately 1.5 pF to approximately 3 pF. The first resonant circuit 162 is tuned to a resonant frequency of approximately 59 MHz and the second resonant circuit 164 is tuned to a frequency of approximately 69 MHz.

[0070] 10 illustrates the measured response of source impedance Zs versus frequency in Smith chart format, with a first trace 188 plotting the source impedance Zs of the RF receive coil circuit 142 without the first resonant circuit 162 and the second resonant circuit 164, and a second trace 190 plotting the source impedance Zs of the RF receive coil circuit 142 with the first resonant circuit 162 and the second resonant circuit 164. The measured source impedance increases significantly near the first dog ear frequency 108 and the second dog ear frequency 110 (approximately 59 MHz and approximately 69 MHz), as shown at marker 1 and marker 2, respectively, on the second trace 190. The impedance plot illustrated in FIG. 10 was generated using an E8358A network analyzer available from Agilent Inc., having its principal place of business in Palo Alto, California.

[0071] FIG. 11 plots the gain of the preamplifier 158 when the RF receive coil circuit 142 does not include the first resonant circuit 162 and the second resonant circuit 164. The gains at the dog-ear frequency 108 and the dog-ear frequency 110 are 59 MHz and 69 MHz, respectively, which is about 16 dB higher than the gain at the MR frequency of 63.8 MHz. In comparison, FIG. 12 plots the gain of the preamplifier 158 when the RF receive coil circuit 142 includes the first resonant circuit 162 and the second resonant circuit 164. When the first resonant circuit 162 and the second resonant circuit 164 are added to the RF receive coil circuit 142, the gains at the dog-ear frequency 108 and the dog-ear frequency 110 are reduced, so that the gains at 59 MHz and 69 MHz are 8 dB higher than the MR frequency of 63.8 MHz. The plots shown in Figures 11 and 12 were generated using a Model 8594E Spectrum Analyzer available from HP Inc., having principal place of business in Palo Alto, California.

[0072] The methods, devices and uses disclosed herein have many aspects, as follows. Some examples of the various aspects include the following devices, systems and methods. One aspect is an apparatus for receiving magnetic resonance (MR) signals for imaging a patient, the MR signals including MR frequencies. The apparatus includes a radio frequency (RF) coil having a first end and a second end, an impedance transformer in electrical communication with the RF coil, a preamplifier in electrical communication with the impedance transformer, the preamplifier having a gain, and at least one resonant circuit electrically connected to at least one end of the RF coil.

[0073] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the RF coil and the at least one resonant circuit form at least a part of an RF receive coil circuit, and the at least one resonant circuit increases a source impedance of a preamplifier at least at a first frequency and a second frequency.

[0074] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the RF coil and the at least one resonant circuit form at least a part of an RF receive coil circuit, and the at least one resonant circuit reduces the gain of the preamplifier at least at the first frequency and the second frequency.

[0075] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the at least one resonant circuit increases the source impedance to about 5 ohms or more.

[0076] Another aspect is that at least one resonant circuit provides a source impedance of about 5 ohms or greater at the first frequency and the second frequency while the source impedance remains substantially constant at the MR frequency. Increase The present invention relates to an apparatus for detecting a blood vessel having ...

[0077] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the at least one resonant circuit reduces the gain of the preamplifier by approximately 3 dB or more.

[0078] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein at least one resonant circuit reduces the gain of the preamplifier by approximately 3 dB or more at the first frequency and the second frequency while the gain remains approximately constant at the MR frequency.

[0079] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the gain at the first dog-ear peak and the second dog-ear peak is not more than about 8 dB greater than the gain at the MR frequency.

[0080] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the gain at at least one of the first dog-ear frequency or the second dog-ear frequency is about equal to or less than the MR frequency.

[0081] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein a gain at at least one of the first dog-ear frequency or the second dog-ear frequency is adjusted to the determined gain.

[0082] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein a gain at the first dog-ear peak and the second dog-ear peak when the RF receive coil circuit has the first resonant circuit and the second resonant circuit is about 8 dB less than a gain at the first dog-ear peak and the second dog-ear peak when the RF receive coil circuit does not have the first and second resonant circuits.

[0083] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the at least one resonant circuit comprises a first and a second resonant circuit.

[0084] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the RF coil and the first resonant circuit and the second resonant circuit form at least a portion of an RF receive coil circuit, the first resonant circuit increasing a source impedance of the RF receive coil circuit at a first frequency and the second resonant circuit increasing a source impedance of the RF receive coil circuit at a second frequency.

[0085] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit increases a source impedance of the preamplifier at frequencies of at least a first frequency bandwidth, and the second resonant circuit increases a source impedance of the preamplifier at least at a second frequency bandwidth.

[0086] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first frequency bandwidth is in a range from about 0.5 MHz to about 5 MHz and the second frequency bandwidth is in a range from about 0.5 MHz to about 5 MHz.

[0087] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit and the second resonant circuit do not substantially affect the source impedance at MR frequencies.

[0088] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit increases a source impedance of the preamplifier at a first frequency and the second resonant circuit increases a source impedance of the preamplifier at a second frequency.

[0089] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit increases the gain of the preamplifier at a first frequency and the second resonant circuit increases the gain of the preamplifier at a second frequency.

[0090] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit increases a source impedance of the preamplifier at frequencies within a first frequency bandwidth, and the second resonant circuit increases a source impedance of the preamplifier at frequencies within a second frequency bandwidth.

[0091] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit increases the gain of the preamplifier at frequencies within a first frequency bandwidth, and the second resonant circuit increases the gain of the preamplifier at frequencies within a second frequency bandwidth.

[0092] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit and the second resonant circuit do not substantially affect the gain of the preamplifier at the MR frequency.

[0093] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the increase in source impedance of the preamplifier in the first frequency bandwidth and the second frequency bandwidth is in the range of about 5 ohms to about 100 ohms.

[0094] Another aspect is an apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the reduction in the gain of the preamplifier in the first frequency bandwidth is in the range of about 5 dB to about 12 dB, and the reduction in the gain of the preamplifier in the second frequency bandwidth is in the range of about 5 dB to about 12 dB.

[0095] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein each of the first resonant circuit and the second resonant circuit comprises a capacitor and an inductor.

[0096] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the capacitor and the inductor are arranged in series.

[0097] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein at least one capacitor of the first resonant circuit and the second resonant circuit is a variable capacitor.

[0098] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein at least one inductor of the first resonant circuit and the second resonant circuit is a variable inductor.

[0099] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein each of the first resonant circuit and the second resonant circuit is electrically connected between a first end and a second end of the RF coil.

[0100] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit is electrically connected between a first end of the RF coil and ground, and the second resonant circuit is electrically connected between a second end of the RF coil and ground.

[0101] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein a first end of the RF coil is in electrical communication with an input of the impedance converter and a second end of the RF coil is grounded.

[0102] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, wherein at least one of the first resonant circuit and the second resonant circuit is electrically connected between a first end and a second end of the RF coil, and the other of the first resonant circuit and the second resonant circuit is electrically connected between the first end of the RF coil and ground.

[0103] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, further comprising a 90° impedance transformer electrically connected between the first resonant circuit and the second resonant circuit and the preamplifier.

[0104] Another aspect is the apparatus of one or any combination of the above embodiments and aspects disclosed herein, further comprising a circuit board, wherein the RF coil, the first resonant circuit, the second resonant circuit, the impedance converter and the preamplifier are mounted on the circuit board.

[0105] Another aspect is an apparatus for processing magnetic resonance (MR) signals for imaging a patient, the apparatus comprising: a circuit board; a radio frequency (RF) coil having a first end and a second end, the RF coil formed at least in part by traces on the circuit board; a balun mounted on the circuit board, the balun in electrical communication with the first end and the second end of the RF coil; a preamplifier mounted on the circuit board, the preamplifier in electrical communication with the balun; and first and second resonant circuits mounted on the circuit board, the first resonant circuit connecting the RF coil between the first end of the RF coil and the balun. and a second resonant circuit in electrical communication with at least a first end of the RF coil between the second end of the RF coil and the balun, the first resonant circuit increasing a source impedance of the preamplifier in a first frequency bandwidth and the second resonant circuit increasing a source impedance of the preamplifier in a second frequency bandwidth, each of the first resonant circuit and the second resonant circuit comprising a capacitor arranged in series with an inductor.

[0106] Another aspect is a method of processing a radio frequency (RF) signal transmitted along a circuit of a magnetic resonance imaging (MRI) device, the circuit having an RF coil in electrical communication with a preamplifier, the RF signal comprising a magnetic resonance (MR) frequency, the circuit comprising at least a coil and a preamplifier, inducing an RF signal in the coil, the RF signal having a first frequency and a second frequency, the first frequency being less than the MR frequency and the second frequency being greater than the MR frequency, increasing a source impedance of the preamplifier at the first frequency and the second frequency, and amplifying the RF signal, of one or any combination thereof disclosed herein above.

[0107] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein the circuit has at least a first resonant circuit and a second resonant circuit in electrical communication with the RF coil, and increasing the source impedance of the preamplifier at the first frequency and the second frequency comprises tuning the circuit using the first resonant circuit and the second resonant circuit.

[0108] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein the circuit has at least a first resonant circuit and a second resonant circuit in electrical communication with the RF coil, and increasing the source impedance of the preamplifier at the first frequency and the second frequency comprises increasing the source impedance of the preamplifier at the first frequency and the second frequency by an amount of approximately 5 ohms or greater.

[0109] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein the circuit has at least a first resonant circuit and a second resonant circuit in electrical communication with the RF coil, and increasing the source impedance of the preamplifier at the first frequency and the second frequency comprises maintaining the source impedance at the MR frequency substantially constant.

[0110] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein the circuit has at least a first resonant circuit and a second resonant circuit in electrical communication with the RF coil, and increasing the source impedance of the preamplifier at the first frequency and the second frequency comprises increasing the source impedance of the preamplifier at the first frequency and the second frequency by an amount of approximately 5 ohms or greater while maintaining the source impedance at the MR frequency approximately constant.

[0111] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein the first resonant circuit has a first resonant frequency at least approximately equal to the first frequency, and the second resonant circuit has a second resonant frequency at least approximately equal to the second frequency.

[0112] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein the preamplifier has an operating frequency corresponding to the MR frequency, and the operating frequency is between the first frequency and the first frequency.

[0113] Another aspect is a method of one or any combination of the above embodiments and aspects disclosed herein, wherein tuning the circuit reduces the gain of the preamplifier at the first and second frequencies relative to the gain of the preamplifier at the first and second frequencies of an untuned circuit.

[0114] Another aspect is a method of one or any combination of the above embodiments and aspects disclosed herein, comprising adjusting the circuit to reduce the gain of the preamplifier at at least one of the first and second frequencies to a level that is no more than about 8 dB greater than the gain at the MR frequency.

[0115] Another aspect is a method of one or any combination of the above embodiments and aspects disclosed herein, comprising adjusting the circuit to make the gain of the preamplifier at at least one of the first frequency and the second frequency approximately equal to the gain at the MR frequency or to reduce the gain to a level lower than the gain at the MR frequency.

[0116] Another aspect is a method of one or any combination of the above embodiments and aspects disclosed herein, comprising adjusting a circuit to reduce a gain of the preamplifier at least one of the first frequency and the second frequency to a determined gain.

[0117] Another aspect is a method of one or any combination of the above embodiments and aspects disclosed herein, comprising adjusting the circuit to reduce the gain of the preamplifier by approximately 8 MHz or more at at least one of the first frequency and the second frequency.

[0118] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein the preamplifier of the regulated circuit has approximately the same gain as the preamplifier of the unregulated circuit.

[0119] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, further comprising reducing the gain of the preamplifier at the first frequency and the second frequency by about 3 dB or more.

[0120] Another aspect is a method of one or any combination of the above embodiments and aspects disclosed herein, further comprising reducing the preamplifier gain at the first frequency and the second frequency by about 3 dB or more while maintaining the preamplifier gain at the MR frequency substantially constant.

[0121] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein at least the first resonant circuit and the second resonant circuit do not affect the source impedance at the MR frequency.

[0122] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, further comprising converting the RF signal from a balanced RF signal to an unbalanced RF signal prior to amplifying the RF signal.

[0123] Another aspect is the method of one or any combination of the above embodiments and aspects disclosed herein, wherein converting the RF signal from a balanced RF signal to an unbalanced RF signal comprises passing the RF signal through a balun.

[0124] The various embodiments described above are provided for illustrative purposes only and should not be construed as limiting the scope of the claims appended hereto. Those skilled in the art will readily recognize various modifications and variations that may be made without following the exemplary embodiments and applications illustrated and described herein and without departing from the true spirit and scope of the following claims. Such modifications and equivalents are intended to be included in the scope of the claims. The inventions disclosed herein include the following: [Aspect 1] 1. An apparatus for receiving magnetic resonance (MR) signals for imaging a patient, the MR signals comprising MR frequencies; a radio frequency (RF) coil having a first end and a second end; an impedance converter in electrical communication with the RF coil; a preamplifier in electrical communication with the impedance converter, the preamplifier having a gain; at least one resonant circuit electrically connected to at least one end of the RF coil; An apparatus comprising: [Aspect 2] The apparatus of claim 1, wherein the RF coil and the at least one resonant circuit form at least a portion of an RF receiving coil circuit, and the at least one resonant circuit increases the source impedance of the preamplifier at least at a first frequency and a second frequency. [Aspect 3] The apparatus of claim 2, wherein the RF coil and the at least one resonant circuit form at least a portion of an RF receiving coil circuit, and the at least one resonant circuit reduces the gain of the preamplifier at least at a first frequency and a second frequency. [Aspect 4] 2. The apparatus of claim 1, wherein the at least one resonant circuit comprises a first resonant circuit and a second resonant circuit. [Aspect 5] The apparatus of claim 4, wherein the RF coil and the first resonant circuit and the second resonant circuit form at least a portion of an RF receive coil circuit, the first resonant circuit increasing a source impedance of the RF receive coil circuit at a first frequency and the second resonant circuit increasing a source impedance of the RF receive coil circuit at a second frequency. [Aspect 6] The apparatus of aspect 5, wherein the first resonant circuit increases a source impedance of the preamplifier at least at a frequency of a first frequency bandwidth, and the second resonant circuit increases a source impedance of the preamplifier at least at a second frequency bandwidth. [Aspect 7] 7. The apparatus of aspect 6, wherein a bandwidth of the first frequency is in a range from approximately 0.5 MHz to approximately 5 MHz and a bandwidth of the second frequency is in a range from approximately 0.5 MHz to approximately 5 MHz. [Aspect 8] 8. The apparatus of claim 7, wherein the first resonant circuit and the second resonant circuit do not substantially affect source impedance at the MR frequency. [Aspect 9] 6. The apparatus of claim 5, wherein the first resonant circuit increases a source impedance of the preamplifier at the first frequency and the second resonant circuit increases a source impedance of the preamplifier at the second frequency. [Aspect 10] The apparatus of claim 5, wherein the first resonant circuit increases a source impedance of the preamplifier at frequencies within a first frequency bandwidth, and the second resonant circuit increases a source impedance of the preamplifier at frequencies within a second frequency bandwidth. [Aspect 11] 11. The apparatus of claim 10, wherein the first resonant circuit and the second resonant circuit do not substantially affect the gain of the preamplifier at the MR frequency. [Aspect 12] 11. The apparatus of aspect 10, wherein the increase in source impedance of the preamplifier in the first frequency bandwidth and the second frequency bandwidth ranges from approximately 5 ohms to approximately 100 ohms. [Aspect 13] 5. The apparatus of embodiment 4, wherein each of the first resonant circuit and the second resonant circuit comprises a capacitor and an inductor. [Aspect 14] 14. The apparatus of claim 13, wherein the capacitor and the inductor are arranged in series. [Aspect 15] 14. The apparatus of claim 13, wherein at least one capacitor of the first resonant circuit and the second resonant circuit is a variable capacitor. [Aspect 16] 14. The apparatus of claim 13, wherein at least one inductor of the first resonant circuit and the second resonant circuit is a variable inductor. [Aspect 17] 5. The apparatus of claim 4, wherein each of the first resonant circuit and the second resonant circuit is electrically connected between the first end and the second end of the RF coil. [Aspect 18] 5. The apparatus of claim 4, wherein the first resonant circuit is electrically connected between the first end of the RF coil and ground, and the second resonant circuit is electrically connected between the second end of the RF coil and ground. [Aspect 19] 19. The apparatus of claim 18, wherein the first end of the RF coil is in electrical communication with an input of the impedance converter and the second end of the RF coil is grounded. [Aspect 20] The apparatus of aspect 4, wherein at least one of the first resonant circuit and the second resonant circuit is electrically connected between the first end and the second end of the RF coil, and the other of the first resonant circuit and the second resonant circuit is electrically connected between the first end of the RF coil and ground. [Aspect 21] 5. The apparatus of embodiment 4, wherein the impedance converter is a balun. [Aspect 22] Further comprising a circuit board; The apparatus of aspect 10, wherein the RF coil, the first resonant circuit and the second resonant circuit, the impedance converter, and the preamplifier are mounted on the circuit board. [Aspect 23] 1. An apparatus for processing magnetic resonance (MR) signals for imaging a patient, comprising: A circuit board; a radio frequency (RF) coil having a first end and a second end, the RF coil being formed at least in part by traces of the circuit board; a balun mounted on the circuit board, the balun being in electrical communication with the first end and the second end of the RF coil; a preamplifier mounted on the circuit board, the preamplifier being in electrical communication with the balun; a first resonant circuit and a second resonant circuit mounted on the circuit board, the first resonant circuit in electrical communication with at least the first end of the RF coil between the first end of the RF coil and the balun, the second resonant circuit in electrical communication with at least the second end of the RF coil between the second end of the RF coil and the balun, the first resonant circuit increasing a source impedance of the preamplifier at a first frequency bandwidth, the second resonant circuit increasing a source impedance of the preamplifier at a second frequency bandwidth, each of the first resonant circuit and the second resonant circuit comprising a capacitor in series with an inductor; An apparatus comprising: [Aspect 24] 1. A method for processing radio frequency (RF) signals transmitted along circuitry of a magnetic resonance imaging (MRI) device, the circuitry having an RF coil in electrical communication with a preamplifier, the RF signals comprising magnetic resonance (MR) frequencies, the circuitry comprising at least a coil and a preamplifier; inducing an RF signal in a coil, the RF signal having a first frequency and a second frequency, the first frequency being less than an MR frequency and the second frequency being greater than an MR frequency; increasing a source impedance of the preamplifier at the first frequency and at the second frequency; amplifying the RF signal; A method for providing the above. [Aspect 25] The circuit includes at least a first resonant circuit and a second resonant circuit in electrical communication with the RF coil, and increasing a source impedance of the preamplifier at the first frequency and the second frequency includes: 25. The method of embodiment 24, comprising tuning the circuit using the first resonant circuit and the second resonant circuit. [Aspect 26] 26. The method of claim 25, wherein the first resonant circuit has a first resonant frequency at least approximately equal to the first frequency, and the second resonant circuit has a second resonant frequency at least approximately equal to the second frequency. [Aspect 27] 26. The method of claim 25, wherein the preamplifier has an operating frequency corresponding to the MR frequency, the operating frequency being between the first frequency and the second frequency. [Aspect 28] 26. The method of claim 25, wherein tuning the circuit reduces a gain of a preamplifier at the first frequency and the second frequency relative to a gain in a first amplifier and a second amplifier of an untuned circuit. [Aspect 29] 30. The method of claim 28, wherein the preamplifier of the regulated circuit has approximately the same gain as the preamplifier of an unregulated circuit. [Aspect 30] 30. The method of claim 28, wherein at least the first resonant circuit and the second resonant circuit do not affect the source impedance at the MR frequency. [Aspect 31] 26. The method of embodiment 25, further comprising converting the RF signal from a balanced RF signal to an unbalanced RF signal prior to amplifying the RF signal. [Aspect 32] 32. The method of aspect 31, wherein converting the RF signal from the balanced RF signal to the unbalanced RF signal comprises passing the RF signal through a balun.

Claims

1. 1. An apparatus for receiving magnetic resonance (MR) signals for imaging a patient, the MR signals comprising MR frequencies; a radio frequency (RF) coil having a first end and a second end, the RF coil configured to output magnetic resonance imaging (MRI) signals including MR frequencies; an impedance converter in electrical communication with the RF coil; a preamplifier in electrical communication with the impedance converter, the preamplifier having a gain; at least a first resonant circuit and a second resonant circuit electrically connected to at least one end of the RF coil, the first resonant circuit being tuned to resonate at a first frequency and the second resonant circuit being tuned to resonate at a second frequency, the first frequency being lower than the MR frequency and corresponding to a first dog-ear frequency, and the second frequency being higher than the MR frequency and corresponding to a second dog-ear frequency, thereby reducing a gain of the preamplifier at the first frequency and the second frequency; Equipped with An apparatus, wherein the first resonant circuit increases a source impedance of the preamplifier at the first frequency and the second resonant circuit increases a source impedance of the preamplifier at the second frequency.

2. 2. The apparatus of claim 1, wherein the RF coil and the first resonant circuit and the second resonant circuit form at least a portion of an RF receive coil circuit, the first resonant circuit increasing a source impedance of the RF receive coil circuit at a first frequency and the second resonant circuit increasing a source impedance of the RF receive coil circuit at a second frequency.

3. 3. The apparatus of claim 2, wherein the first resonant circuit increases a source impedance of the preamplifier at least at frequencies of a first frequency bandwidth, the first frequency bandwidth including the first frequency, and the second resonant circuit increases a source impedance of the preamplifier at least at frequencies of a second frequency bandwidth, the second frequency bandwidth including the second frequency.

4. The apparatus of claim 1 , wherein the first resonant circuit and the second resonant circuit do not affect a source impedance at the MR frequency.

5. 3. The apparatus of claim 2, wherein the first resonant circuit increases a source impedance of the preamplifier at frequencies within a first frequency bandwidth, the first frequency bandwidth including the first frequency, and the second resonant circuit increases a source impedance of the preamplifier at frequencies within a second frequency bandwidth, the second frequency bandwidth including the second frequency.

6. The apparatus of claim 1 , wherein the first resonant circuit and the second resonant circuit do not affect the gain of the preamplifier at the MR frequency.

7. 2. The apparatus of claim 1, wherein the increase in source impedance of the preamplifier in the first frequency bandwidth and the second frequency bandwidth ranges from approximately 5 ohms to approximately 100 ohms.

8. The apparatus of claim 1 , wherein the first resonant circuit and the second resonant circuit each comprise a capacitor and an inductor.

9. The apparatus of claim 8 , wherein the capacitor and the inductor are arranged in series.

10. 9. The apparatus of claim 8, wherein at least one capacitor of the first resonant circuit and the second resonant circuit is a variable capacitor.

11. 9. The apparatus of claim 8, wherein at least one inductor of the first resonant circuit and the second resonant circuit is a variable inductor.

12. 2. The apparatus of claim 1, wherein each of the first resonant circuit and the second resonant circuit is electrically connected between the first end and the second end of the RF coil.

13. 2. The apparatus of claim 1, wherein the first resonant circuit is electrically connected between the first end of the RF coil and ground, and the second resonant circuit is electrically connected between the second end of the RF coil and ground.

14. 14. The apparatus of claim 13, wherein the first end of the RF coil is in electrical communication with an input of the impedance converter and the second end of the RF coil is connected to ground.

15. 2. The apparatus of claim 1, wherein at least one of the first resonant circuit and the second resonant circuit is electrically connected between the first end and the second end of the RF coil, and the other of the first resonant circuit and the second resonant circuit is electrically connected between the first end of the RF coil and ground.

16. The apparatus of claim 1 , wherein the impedance converter is a balun.

17. Further comprising a circuit board; The apparatus of claim 1 , wherein the RF coil, the first and second resonant circuits, the impedance converter, and the preamplifier are mounted on the circuit board.

18. 1. An apparatus for processing magnetic resonance (MR) signals for imaging a patient, comprising: A circuit board; a radio frequency (RF) coil having a first end and a second end, the RF coil being formed at least in part by traces of the circuit board and configured to output magnetic resonance imaging (MRI) signals including MR frequencies; a balun mounted on the circuit board, the balun being in electrical communication with the first end and the second end of the RF coil; a preamplifier mounted on the circuit board, the preamplifier being in electrical communication with the balun; a first resonant circuit and a second resonant circuit mounted on the circuit board, the first resonant circuit in electrical communication with at least the first end of the RF coil between the first end of the RF coil and the balun, the second resonant circuit in electrical communication with at least the second end of the RF coil between the second end of the RF coil and the balun, the first resonant circuit increasing a source impedance of the preamplifier in a first frequency bandwidth lower than the MR frequency and corresponding to a first dog-ear frequency, thereby increasing the impedance of the preamplifier in the first frequency bandwidth; a first resonant circuit and a second resonant circuit each comprising a capacitor in series with an inductor, the first frequency bandwidth corresponding to the first dog-ear frequency and the second frequency bandwidth corresponding to the second dog-ear frequency; An apparatus comprising:

19. 1. A method for processing radio frequency (RF) signals transmitted along circuitry of a magnetic resonance imaging (MRI) device, the circuitry having an RF coil in electrical communication with a preamplifier, the RF signals comprising magnetic resonance (MR) frequencies, the circuitry comprising at least a coil and a preamplifier; inducing an RF signal in a coil, the RF signal having a first frequency and a second frequency, the first frequency being less than an MR frequency and the second frequency being greater than an MR frequency, a bandwidth of the first frequency corresponding to a first dog-ear frequency and a bandwidth of the second frequency corresponding to a second dog-ear frequency; increasing a source impedance of the preamplifier at the first frequency and at the second frequency; decreasing a gain of the preamplifier at the first frequency and at the second frequency; amplifying the RF signal; A method for providing the above.

20. The circuit includes at least a first resonant circuit and a second resonant circuit in electrical communication with the RF coil, and increasing a source impedance of the preamplifier at the first frequency and the second frequency comprises:

20. The method of claim 19, comprising tuning the circuit using the first resonant circuit and the second resonant circuit.

21. 21. The method of claim 20, wherein the first resonant circuit has a first resonant frequency at least approximately the same as the first frequency, and the second resonant circuit has a second resonant frequency at least approximately the same as the second frequency.

22. 21. The method of claim 20, wherein the preamplifier has an operating frequency corresponding to the MR frequency, the operating frequency being between the first frequency and the second frequency.

23. 21. The method of claim 20, wherein tuning the circuit reduces a preamplifier gain at the first and second frequencies relative to a gain in a first and second amplifier of an untuned circuit.

24. 24. The method of claim 23, wherein the preamplifier of the regulated circuit has approximately the same gain as the preamplifier of an unregulated circuit.

25. 24. The method of claim 23, wherein at least the first resonant circuit and the second resonant circuit do not affect the source impedance at the MR frequency.

26. 21. The method of claim 20, further comprising converting the RF signal from a balanced RF signal to an unbalanced RF signal prior to amplifying the RF signal.

27. 27. The method of claim 26, wherein converting the RF signal from the balanced RF signal to the unbalanced RF signal comprises passing the RF signal through a balun.

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