Patent Publication Number: US-2022214412-A1

Title: Dual Frequency Coil Package for Magnetic Resonance Imaging System Upgrade

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/994,997, filed on Aug. 17, 2020, entitled “Mononuclear MRI Upgrade System and Method”, which is a continuation of U.S. patent application Ser. No. 15/909,351, filed on Mar. 1, 2018, entitled “Dual Tuned MRI Resonator and Coil Package and Method”, which claimed the benefit of U.S. Provisional Patent Application Ser. No. 62/465,441, filed on Mar. 1, 2017, entitled “Dual Tuned MRI Resonator and Coil Package”, the contents of each are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Magnetic resonance imagining (MRI) has become a recognized and very useful tool for the diagnosis of numerous disease processes and pathologies of the human body, relying on the natural abundance of hydrogen in the body and its nature to precis, or spin, about in quasi-alignment with the strong magnetic field of MRI. MRI provides three-dimensional images of internal structures of a patient (e.g., human or animal). The internal structures may be bone structures, soft tissue (tendons, ligaments, and the like), and organs. MRI is a non-invasive diagnostic test that may determine the state of a disease (e.g., chronic obstructive pulmonary disease (COPD), cancer, and the like), or determine an abnormality in an internal structure (tendon rupture, stress bone fractures, and the like) without subjecting a patient to an invasive procedure, such as a needle biopsy or exploratory surgery. 
     Many conventional MRI systems are configured for transmitting and receiving radio frequency (RF) at a single RF (e.g., mononuclear systems). Such conventional MRI systems typically transmit and receive RF at the frequency of hydrogen, as this is the most common nuclei in a patient to image. However, hydrogen is not the only nuclei which recesses and can give off a signal in an MRI system, and certainly isn&#39;t the only nuclei occurring in the human body. Calcium, carbon, and phosphorous are three others occurring in sufficient quantities that have been exploited to generate signals of clinical interest from the body in a process known as MR spectroscopy, and, of late, actual images based upon the amount and bonding of such nuclei in the body. 
     Each nuclei has its own precessional frequency that is associated with the magnetic field strength of the MRI system according to the formula ω=σBo, in which ω is the precessional frequency f times 2π, or the radian frequency, o is the unique gyromagnetic ratio of the element in units Hz/Tesla, and σ is the strength of the magnetic field in units Tesla. The most commonly installed and operable field strengths are 1.5 Tesla and 3 Tesla systems. While these systems are described in terms of 1.5 or 3 Tesla, their actual magnetic field strength may vary according to different manufacturers. MRI systems typically are designed to provide easy and temporary connection for various MRI antennae designed to improve the signal quality from different human anatomies; hence, they are anatomically specific antennae which the MRI operator places upon these various anatomies and then connects the antennae to the common ports on the MRI system. These antennae now utilize multiple resonators contained within which connect to multiple receiver inputs on the receiver port of the MRI system and, similarly, anatomic specific transmit antennae connect to the transmit output port so as to focus the transmit energy to a smaller local anatomy versus the entire body, which is the purpose of the MRI system&#39;s built-in body transmit/receive coil. 
     There is an increasing need in clinical MRI which relies upon the use of nuclei, other than hydrogen, occurring naturally within the body, or those temporarily injected or inhaled. Only imaging at the single RF of hydrogen does not always provide sufficient imaging of a patient. For example, when imaging a patient&#39;s lungs it is at times preferable to have spatial and temporal imaging, which requires imaging nuclei at a first frequency (e.g., hydrogen) and nuclei at a second frequency (a nuclei other than hydrogen, such as fluorine, xenon, and the like). Flourine-19 is an example of such an element that can be inhaled in an inert form, mixed with air, and due to its natural resonance in MRI, can be exploited to generate images of the lungs and associated parenchyma. However, a mononuclear MRI system is not capable of transmitting and receiving at the second frequency. 
     A major hurdle preventing more common use of other nuclei is the significant expense associated with making MRI systems able to operate at dual or multiple frequencies associated with different nuclei. This expense is largely due to the significant additional hardware and firmware associated with duplicating the radio frequency (RF) transmit and receiver chains for each additional frequency, or providing more expensive broad-band chains that can operate at substantially different frequencies. Primarily for this reason, most MRI systems are manufactured and installed which operate on a singular frequency—the precessional frequency of hydrogen. 
     Additionally, conventional MRI systems that have the ability to generate an MRI excitation signal and receive from at least two nuclei frequencies (e.g., a multinuclear capable system) do not always have the ability to switch the frequency for receiving and transmitting contemporaneously when the patient is undergoing an MRI scan. This contemporaneous switching is typically limited by the receiving and transmitting coils of the MRI system. Therefore, in order to upgrade a multinuclear capable system, a transmission coil and receiving coil must be configured to allow the MRI system to transmit and receive at at least two nuclei frequencies. 
     Some conventional multinuclear capable MRI systems further include a multinuclear transmit body coil. However, these multinuclear capable MRI systems with a multinuclear transmit body coil, typically include multi-channel receiver coils. The multi-channel receiver coils include multiple resonators that typically only have the ability to receive at a frequency for a single nucleus. To configure a multinuclear capable MRI system to receive and transmit at a second frequency, the patient must be removed and a separate, distinct receiver coil having resonators that receive RF from a second, distinct nucleus must be placed on the patient. This causes positioning changes and the ability to spatially compare the images of the first nucleus frequency and the second nucleus frequency may be lost. 
     Finally, the minority of conventional multinuclear MRI systems that have the ability to contemporaneously switch frequencies that are transmitted and received utilize an intermediate frequency in the receiving coil. Such multinuclear MRI systems utilize a resonator in a receiver coil that does not include a tuned preamplifier, such that the signal received by the resonator is converted to an intermediate frequency prior to amplification. In such a multinuclear MRI system, the intermediate frequency must be converted to MRI system receiver frequency. This two-step frequency conversion, from the frequency of a nucleus to an intermediate frequency, and from the intermediate frequency to the MRI system receiver frequency requires a specialized receiver for the two-step conversion, or alternatively the MRI system receiver, itself, must be modified to accept and process the intermediate frequency generated by the first step of the conversion. This means that either the multinuclear MRI system must come with such a specialized receiver, or that the multinuclear system must further be retrofitted for a receiver with the two-step conversion, or, alternatively, the modification of the existing MRI system receiver increases the complexity of the MRI system, increases the complexity of converting a mononuclear system, and increases the cost associated with each. 
     Therefore, it would be desirable to have an MRI coil package that may be used to alter a mononuclear MRI system to a multinuclear MRI system that may contemporaneously switch between transmitting and receiving RF at a first nuclei and a second nuclei frequency, in which the receiver coil of the MRI coil package has one or more resonators that receive at least two frequencies from a first nuclei and a second nuclei. It would be further desirable to have an MRI coil package that may alter a multinuclear capable MRI system to a multinuclear functional MRI system, which may contemporaneously switch between transmitting and receiving RF at a first nuclei and a second nuclei frequency, in which the receiver coil of the MRI coil package has one or more resonators that receive at least two frequencies from a first nuclei and a second nuclei. Further, it would be desirable that the MRI coil package alter the mononuclear MRI system and the multinuclear capable MRI system to a multinuclear system without the use of an intermediate frequency. Finally, it would be desirable that the MRI coil package provide spatial and temporal imaging of a patient from at least two RF. 
     BRIEF SUMMARY 
     According to various example embodiments of the present general inventive concept, a dual frequency coil package system may be provided for use in transmitting and receiving at least two frequencies in an MRI system, including a frequency converter coupled to the MRI system to receive a first frequency through the local transmit coil port and convert the first frequency to a second frequency, a second frequency transmit coil to receive the second frequency from the frequency converter and to transmit the second frequency, a dual tuned receiver coil to receive and to output the at least two frequencies, and a switchable receiver to receive the at least two frequencies output from the dual tuned receiver coil and to transmit the first frequency received from the dual tuned receiver coil directly to the MRI system, and to convert the second frequency received from the dual tuned receiver coil to the first frequency before transmission to the MRI system. 
     The foregoing and/or other aspects and advantages of the present general inventive concept may be achieved by a dual frequency coil package used in transmitting and receiving at least two frequencies in an MRI system, the dual frequency coil package including a dual tuned receiver coil configured to receive at least two frequencies, including at least a first frequency and a second frequency, in operative communication with the MRI system through a first local port of the MRI system, and a second frequency transmit coil configured to transmit the second frequency in operative communication with the MRI system through a second local port of the MRI system. 
     The foregoing and/or other aspects and advantages of the present general inventive concept may also be achieved by a frequency converter and receiver system for use with a dual frequency coil package used in an MRI system, the frequency converter and receiver system including, a switchable receiver configured with one or more channels each configured to receive at least two frequencies, including at least a first frequency and a second frequency, each of the one or more channels including, an input configured to receive the at least two frequencies, an output configured output the second frequency, a first frequency path configured to pass the first frequency between the input and the output, a second frequency path configured to convert the second frequency to the first frequency between the input and the output, a first switch configured to switch electrical communication from the input between the first and second frequency paths, and a second switch configured to switch electrical communication to the output between the first and second frequency paths, and a frequency converter configured to receive the first frequency, convert the first frequency to the second frequency, and output the second frequency, wherein the switchable receiver and the frequency converter are configured to be in electrical communication such that the first and second frequencies are in phase after frequency conversions. 
     The foregoing and/or other aspects and advantages of the present general inventive concept may also be achieved by a dual frequency coil package system for use in transmitting and receiving at least two frequencies in an MRI system, the dual frequency coil package system including a frequency converter selectively coupled to a local transmit coil port of the MRI system, to receive a first frequency through the local transmit coil port, to convert the first frequency to the second frequency, and to output the second frequency, a second frequency transmit coil in electrical communication with the frequency converter so as to receive the second frequency from the frequency converter and to transmit the second frequency in operative communication with the MRI system, a dual tuned receiver coil configured to receive at least two frequencies, including at least the first frequency and the second frequency, and to output the at least two frequencies, and a switchable receiver configured to receive the at least two frequencies output from the dual tuned receiver coil, including at least the first frequency and the second frequency, and in electrical communication with the dual tuned receiver coil and selectively coupled to a local receiver coil port of the MRI system such that the switchable receiver and dual tuned receiver coil are in operative communication with the MRI system, wherein the switchable receiver transmits the first frequency received from the dual tuned receiver coil directly to the MRI system and converts the second frequency received from the dual tuned receiver coil to the first frequency before transmission to the MRI system. 
     The foregoing and/or other aspects and advantages of the present general inventive concept may also be achieved by a method of using a dual frequency coil package in an MRI system, the method including connecting a dual tuned coil package to local transmit and receive ports of the MRI system, converting a first frequency transmit power signal transmitted from the MRI system through the local transmit port to a second frequency transmit power signal, switching dual tuned resonators to a second frequency signal operating mode, converting second frequency signals received from resonators during a transmit pulse to the first frequency, and transmitting received first and converted first frequency signals to the local receive port of the MRI system for image processing. 
     Other features and aspects may be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The following example embodiments are representative of example techniques and structures designed to carry out the objects of the present general inventive concept, but the present general inventive concept is not limited to these example embodiments. In the accompanying drawings and illustrations, the sizes and relative sizes, shapes, and qualities of lines, entities, and regions may be exaggerated for clarity. A wide variety of additional embodiments will be more readily understood and appreciated through the following detailed description of the example embodiments, with reference to the accompanying drawings in which: 
         FIG. 1  illustrates an MRI system having a dual tuned coil package; 
         FIG. 2  illustrates a dual tuned resonator of a dual tuned receiver coil; 
         FIG. 3  illustrates a dual tuned resonator of a dual tuned receiver coil; 
         FIG. 4  illustrates a dual tuned resonator of a dual tuned receiver coil; 
         FIG. 5  illustrates an example of a single pole double throw (SPDT) switch used in various examples; 
         FIG. 6  illustrates a second frequency transmit coil of a dual tuned coil package; 
         FIG. 7  illustrates the switchable receiver and frequency converter of  FIG. 1 ; 
         FIG. 8  illustrates a switchable receiver and frequency converter; 
         FIG. 9  illustrates a switchable receiver and frequency converter; and 
         FIG. 10  illustrates a method of dual tuned MRI resonator and coil package. 
     
    
    
     DETAILED DESCRIPTION 
     The described systems may provide a dual frequency coil package system for use in transmitting and receiving at least two frequencies in an MRI system, the dual frequency coil package system including a frequency converter coupled to the MRI system to receive a first frequency through the local transmit coil port and convert the first frequency to a second frequency, a second frequency transmit coil to receive the second frequency from the frequency converter and to transmit the second frequency, a dual tuned receiver coil to receive and to output the at least two frequencies, and a switchable receiver to receive the at least two frequencies output from the dual tuned receiver coil and to transmit the first frequency received from the dual tuned receiver coil directly to the MRI system, and to convert the second frequency received from the dual tuned receiver coil to the first frequency before transmission to the MRI system. 
     The described systems may provide a dual tuned coil package, and a method of using the dual tuned coil package, to allow existing MRI systems to perform magnetic resonance imaging using nuclei of a plurality of different types of atoms. Various example embodiments of the present general inventive concept may be retrofitted to existing MRI systems by simply plugging into existing ports and allowing the existing MRI system to operate using the same processes otherwise used in detecting, for example, hydrogen nuclei, to detect other nuclei. To achieve these and other aspects of the present general inventive concept, various example embodiments may provide a dual tuned coil package having a dual tuned receiver coil. The dual tuned coil package and dual tuned receiver may transmit and receive two or more nuclei frequencies. Throughout these descriptions, signals having certain frequencies may be referred to simply as frequencies, e.g., a signal having a first frequency may be referred to simply as a first frequency, for a first frequency signal, and so on. The dual tuned coil package may include a dual tuned receiver coil and a second frequency transmit coil. The dual tuned coil package may include a frequency converter, and a switchable receiver. The dual tuned receiver coil may have one or more dual tuned resonators configured to receive at least two radio frequencies (RF) associated with two or more MRI nuclei. The one or more dual tuned resonators may operate at RF that are close in value (e.g., within approximately 7%, or approximately 15%, of one another in regard to the hydrogen Larmor frequency). The one or more dual tuned resonators may operate at RF that are far (e.g., more than approximately 7%, or more than approximately 15%) apart. The one or more dual tuned resonators may be configured to receive and transmit at the at least two RF to provide spatial and temporal imaging of a patient using an MRI system. The dual tuned resonators may include switching additional parallel capacitances across existing resonant capacitors, shorting out series capacitors to increase the total capacitance, driving varactors in parallel with tuning capacitors with precision voltages to tune to various frequencies, and combinations thereof to tune the dual tuned resonators to two or more frequencies. The dual tuned resonators may include switches, such as solid state single pole, single throw (SPST) switches, single pole double throw (SPDT), single pole triple throw (SPTT) switches, diode combinations, and combinations thereof to switch resonance of the dual tuned resonator to two or more frequencies. 
       FIG. 1  illustrates an MRI system having a dual tuned coil package. As illustrated in  FIG. 1 , an MRI system  1  is provided with a dual tuned coil package  2  that may include various componentry described herein. The dual tuned coil package  2  may be configured to convert a mononuclear MRI system to a system that may transmit and receive at least two nuclei frequencies (multinuclear ready system). The dual tuned coil package  2  may be configured to convert a multinuclear capable system to a multinuclear ready system. In the example embodiment illustrated in  FIG. 1 , the MRI system  1  includes an operator console  3 , a system controller  4 , a gradient driver  5   a , gradient axes  5   b , a transmit power amplifier  6 , a data acquisition component  7 , a frequency switch assembly  8 , a local transmit coil port  9 , an analog converter receiver  13 , a scanner receiver coil port  14 , a system body coil  17   b , and the dual tuned coil package  2 . The system body coil  17   b  may be interchangeable referred to throughout these descriptions as the first frequency transmit coil  17   b , as the frequency conventionally transmitted from the transmit power amplifier  6  to the system body coil  17   b  or local transmit coil port  9  is described as the first frequency in relation to the second frequency which may be applied to the transmit coil of the dual tuned coil package  2  as described herein. 
     The operator console  3  includes a computer and programmable configuration software, and is configured to display images. For example, the MRI system  1  may be programed to image a patient via an input received at the operator console  3 . As used herein the computer may refer to a general-purpose device that can be programmed to carry out various sets of arithmetic or logical operations. Further, the computer may include one or more processing elements (e.g., processors, central processing unit (CPU)) and some form of memory (e.g., data storage device, database), the memory being connected to (e.g., communicatively coupled with) the processing element(s). The computing device may further include one or more user interface devices (e.g., user input devices), such as a keyboard, mouse, display, and/or the like, which are connected to (e.g., communicatively coupled with) the processing element(s). 
     The system controller  4  is configured to activate and deactivate the gradient driver  5   a , the data acquisition component  7 , and the transmit power amplifier  6 . The system controller  4  is in operative communication with the operator console  3 . 
     The data acquisition component  7  is configured to process RF received from the dual tuned coil package  2 . The data acquisition component  7  is configured to be in operative communication with the operator console  3  and the analog converter receiver  13 . The gradient driver  5   a  is configured to drive current and voltages of the gradient axes  5   b . The gradient driver  5   a  is configured to be in operative communication with the system controller  4  and the gradient axes  5   b . The gradient axes  5   b  are configured to modulate the static magnetic field to produce three dimensional (3D) spatial encoding. The gradient axes  5   b  are in operative communication with the gradient driver  5   a.    
     The transmit power amplifier  6  may amplify a first frequency to transmit to the frequency switch assembly  8  to be routed to the system body coil  17   b  or through the local transmit coil port  9 . The transmit power amplifier  6  is in operative communication with the system controller  4  and the frequency switch assembly  8 . The analog converter receiver  13  converts the analog RF signal from the scanner receiver coil port  14 , which is in communication with the dual tuned coil package  2 , to a digital signal. The analog converter receiver  13  is in operative communication with the MRI scanner receiver coil port  14 , and the system controller  4 . The receiver coil port  14  includes a plurality of channels to respectively receive signals from, and to control, multiple resonance elements in a receiver coil, and the analog converter receiver  13  includes respective amplifiers and analog to digital converters for each channel of the receiver coil port  14 , based on the MRI system channel count. The first frequency transmit coil  17   b  is configured to transmit a first frequency into the patient to excite nuclei of a first frequency. The first frequency transmit coil  17   b  may transmit at the frequency of hydrogen nuclei, which is approximately 123.2 megahertz (MHz) for a 3 Tesla MRI system, and which may be referred to herein as the hydrogen frequency. 
     The dual tuned coil package  2  includes a second frequency transmit coil  17   a , and a dual tuned receiver coil  18 . The dual tuned coil package  2  may further include a frequency converter  16 , which may be referred to herein as a switchable power amplifier, having frequency conversion logic  16   a  and a second frequency power amplifier  16   b , and a switchable receiver  15  having a switch  15   a  and a frequency converter and amplifier  15   b.    
     The second frequency transmit coil  17   a  transmits a second frequency relative to the first frequency transmitted by the system body coil, or first frequency transmit coil,  17   b . The second frequency transmit coil  17   a  may further transmit two or more frequencies. The second frequency may be close (within, for example, 7%, or 15%) to the first frequency, such as approximately 115.9 MHz, which is the frequency of fluorine nuclei for a 3 Tesla MRI system. The second frequency may be far apart (e.g., more than 7%, or 15%) from the first frequency, such as approximately 15 MHz, which is the frequency of xenon nuclei for a 3 Tesla MRI system. The second frequency transmit coil  17   b  may be in operative communication with the second frequency power amplifier  16   b . An example embodiment of the second frequency transmit coil  17   b  is illustrated in  FIG. 6 , and is described herein. 
     The dual tuned receiver coil  18  may receive at least two different RF from excited nuclei of the patient. The dual tuned receiver coil  18  may receive at least two RF from nuclei that are close together. The dual tuned receiving coil  18  may receive at least two RF that are far apart. The dual tuned receiving coil  18  may be in operative communication with the switchable receiver  15 . The dual tuned receiving coil  18  may have one or more dual tuned resonators  10 , example embodiments of which are illustrated in  FIGS. 2-5 , and are described herein. 
     The frequency conversion logic  16   a , which may be referred to at times simply as the frequency converter, may convert the first frequency pulses from the transmit power amplifier  6  to pulses of the second frequency. The frequency conversion logic  16   a  may further deliver synchronization signals to the switchable receiver  15  to maintain a proper phase relationship (e.g., phase locking between the transmit and receive signals) between the transmission and receipt of the second frequency, such as via a direct, operative connection. The frequency conversion logic  16   a  may be in operative communication with the system controller  4  and the second frequency power amplifier  16   b , and may be in operative communication with the switchable receiver  15 . 
     The second frequency power amplifier  16   b  amplifies the transmission of the second frequency to the second frequency transmit coil  17   a . The second frequency power amplifier  16   b  may amplify the transmission of one or more frequencies. The second frequency power amplifier  16   b  is in operative communication with the frequency conversion logic  16   a  and the second frequency transmit coil  17   a , and the second frequency power amplifier  16   b  may be in operative communication with the frequency conversion logic  16   a  and the second frequency transmit coil  17   a  via the local transmit coil port  9 , sometimes referred to as an MRI system port, that is in electrical communication with the frequency switch assembly  8 , which may be used to switch transmit modes in the MRI system. 
     The switchable receiver  15  may include multiple channels to respectively receive signals from receiver coil resonators and communicate with the channels of the receiver coil port  14 , and each channel may include a switchable receiver switch  15   a  and a second frequency converter and amplifier  15   b . In the descriptions herein, the signal development in only one of the channels is typically described for the sake of clarity. The switchable receiver  15  may transmit the first frequency to the analog converter receiver  13  without amplification or conversion. The switchable receiver switch  15   a  engages or bypasses the second frequency converter and amplifier  15   b . When the dual tuned receiver coil  18  receives at the first frequency the switchable receiver switch  15   a  bypasses the second frequency converter and amplifier  15   b . When the dual tuned receiver coil  18  receives at the second frequency, the switchable receiver switch  15   a  engages the second frequency converter and amplifier  15   b . The switchable receiver switch  15   a  may be a bipolar logic switch in operative communication with the system controller  4 . 
     The second frequency converter and amplifier  15   b  may amplify the second frequency and convert the second frequency to the first frequency when the dual tuned receiver coil  18  receives at the second frequency. The second frequency converter and amplifier  15   b  may be in operative communication with the dual tuned receiver coil  18  and the analog converter receiver  13 . The switchable receiver  15  may be in operative communication with the dual tuned receiver coil  18  via the scanner receiver coil port  14 . 
     The frequency switch assembly  8  routes the first frequency transmit pulse from the power amplifier  6  to either the first frequency transmit coil, or system body coil,  17   b  or to the local transmit coil port  9 . The frequency switch assembly  8  may be a bipolar logic switch in operative communication with the system controller  4 . When the frequency switch assembly  8  is in a first position it routes the first frequency transmit pulse to the first frequency transmit coil  17   b  coil. When the frequency switch assembly  8  is in a second position it routes the first frequency transmit pulse to the local transmit coil port  9 , to be received by the second frequency conversion logic  16   a.    
       FIG. 2  illustrates a dual tuned resonator of a dual tuned receiver coil. In the example embodiment of  FIG. 2 , the dual tuned resonator  10  configured to be provided to the dual tuned receiver coil  18  receives at least two RF that are substantially close together, e.g., within approximately 7%, or within approximately 15%, of one another in regard to the hydrogen Larmor frequency. While it is to be understood that the dual tuned receiver coil  18  may include one or more dual tuned resonators  10 , for illustration purposes a single dual tuned resonator is described and illustrated in  FIG. 2 . The dual tuned resonator  10 , which may be formed with an inductive wire  11 , includes one or more constant capacitors  12 ,  31 ,  43  and  51 , at least one variable frequency circuit  20 , a first frequency decoupler  50 , and a second frequency decoupler  30 . The dual tuned resonator  10  further includes a preamplifier circuit  40 . The dual tuned resonator  10  may be made of a material with high conductivity properties, such as copper tape, copper strip etched on rigid substrate, copper strips etched on flexible substrate, and so on. 
     In this embodiment, the one or more constant capacitors  12 ,  31 ,  43 , and  51  generate resonant frequency of the dual tuned resonator  10  at a first RF, such as approximately 123.2 MHz, which is the RF of hydrogen on conventional 3 Tesla MRI systems. At least one of the constant capacitors  12 ,  31 ,  43  and  51  may be of any capacitance to generate resonant frequency of the first RF for the dual tuned resonator  10 . In various example embodiments of the present general inventive concept, it may be beneficial to configure the dual tuned resonator  10  such that the one or more capacitors  12 ,  23 ,  31 ,  43 , and  51  are of substantially the same capacitance. 
     The at least one variable frequency circuit  20  shifts the resonant frequency of the dual tuned resonator  10  to a second RF, such as approximately 115.9 MHz, which is the RF resonance frequency of fluorine on conventional 3 Tesla MRI systems. The variable frequency circuit  20  may include a variable capacitor  22  arranged to be in parallel with a variable capacitor  23 , and a switch  21 . The variable capacitor  22  may be of any capacitance to generate a resonant frequency of the second RF for the dual tuned resonator  10  when it is activated. The variable frequency circuit  20  may also be a voltage-controlled varactor (not pictured) which is activated at both the first and the second frequency. The varactor is controlled by application of a tuning voltage, where a voltage is applied to the varactor in parallel with the variable capacitor  22  to provide resonance at the second frequency. 
     The switch  21  of the variable frequency circuit  20  activates and deactivates the variable frequency circuit  20 . The switch  21  may be any mechanism for activating and deactivating the variable frequency circuit  20 , such as a single pole single throw switch (SPST), microelectromechanical system (MEMS) switch, or a PIN diode. When the switch  21  is in an open position the additional capacitance  22  is deactivated, and the dual tuned resonator  10  has a resonant frequency at the first frequency. When the switch  21  is in a closed position the additional capacitance of variable capacitor  22  is activated, and the dual tuned resonator  10  has a resonant frequency at the second frequency. The switch  21  may be engaged by DC control from the MRI system  1  via common DC control signals provided at the MRI system receiver coil port  14 . 
     The first frequency decoupler  50  performs passive decoupling of the dual tuned resonator  10  during the transmit cycle of the first frequency. The first frequency decoupler  50  generates a high impedance resonance circuit for the first frequency during the transmit cycle of the first frequency. The first frequency decoupler  50  includes a first frequency variable inductor  52 , crossed PIN diodes  53 , and at least one constant capacitor, such as constant capacitor  51 . To passively decouple, a capacitive reactance of constant capacitor  51  is selected to equal the inductive reactance of inductor  52  to create a resonant circuit when connected in parallel. The constant capacitor  51  and the first frequency variable inductor  52  are connected in parallel when the crossed PIN diodes  53  are activated at the onset of the transmit pulse from the MR system  1  (not pictured) which develops voltage across the constant capacitor  51 , which biases the crossed PIN diodes  53  and creates a parallel resonant tank circuit in the first frequency decoupler  50 . 
     The second frequency decoupler  30  performs active decoupling of dual tuned resonator  10  during transmission of the second frequency. The second frequency decoupler  30  may further perform passive decoupling of the dual tuned resonator  10  during transmission of the second frequency. The second frequency decoupler  30  includes a second frequency variable inductor  35 , at least one constant capacitor, such as constant capacitor  31 , a crossed PIN diode  33  to perform passive decoupling, an actively biased diode  32 , and a direct current (DC) blocking capacitor  34 . 
     This second frequency decoupler  30  operates substantially similar to the first frequency decoupler  50  when passively decoupling at the second frequency via the cross-PIN diode  33  and DC blocking capacitor  34 . The second frequency decoupler  30  may further actively decouple, wherein a direct current (DC) control voltage generated by the MRI system  1 , and synchronized with the transmit pulse timing, is connected across active diode  32  via separate control lines (not pictured). Therefore, the second frequency variable inductor  35  is configured to generate a high impedance resonance circuit with the constant capacitor  31  during transmission of the second frequency. The second frequency variable inductor  35  may be any inductance to generate the high impedance resonance circuit with capacitance of constant capacitor  31  when in parallel. Further, the second frequency variable inductor  35  may be actively switched into parallel circuit with the synchronization of the DC control voltage across the PIN diode  32 . 
     The second frequency decoupler  30  includes the active and passive decoupling for safety. The active and passive decoupling is redundant. Specifically, the second frequency decoupler  30  will still operate and decouple without the DC control voltage from the MRI system, for active decoupling, via passive decoupling using the crossed PIN diodes  33 . This improves the safety of the dual tuned resonator  10  and the dual tuned receiver coil  18  in the event of a faulty DC control voltage or broken DC pathway. The active and passive decoupling of the second frequency decoupler  30  may be employed on each dual tuned resonator  10 , where such a decoupler may be tuned to the first and the second frequencies. Likewise, the first frequency decoupler  50  may be configured to actively and passively decouple similar to the second frequency decoupler  30 . 
     The preamplifier circuit  40  is configured to develop the MRI signal of the dual tuned resonator  10  for a preamplifier  71 . The MRI signal may be amplified from 20 to 30 decibels (dB) as determined by the MRI system receiver requirements, and to match output impedance from the preamplifier  71  of the dual tuned resonator  10  to the MR system analog converter receiver  13  of MRI system  1 . The preamplifier circuit  40  includes a preamplifier circuit inductor  44 , and the preamplifier  71 . The preamplifier circuit  71  further includes at least one constant capacitor, such as constant capacitor  43 . 
     The preamplifier input circuit  40  may develop the MRI signal across constant capacitor  43  and deliver it through isolation inductor  44  to the preamplifier  71 . Constant capacitor  43  is selected by its relative real component of resonance impedance of the first and second frequencies. This value may be from 50 to 200 ohms during resonance. The isolation inductor  44  is configured to match the resonance of constant capacitor  43 . The isolation inductor  44  is a low Q or broadband inductor selected to equal the average reactance of the capacitor  43 , where the average is the average of the reactance at the first frequency and the second frequency. Matching reactances of constant capacitor  43  and isolation inductor  44  at the average resonant frequencies of the first and second frequencies creates a high impedance condition in the preamplifier input circuit  40  due to the connection of the preamplifier  71 . This effectively places constant capacitor  43  in parallel with inductor  44  creating a high impedance tank circuit of the preamplifier circuit  40 . The high impedance tank circuit of the preamplifier circuit  40  then develops the RF signals received by the dual tuned resonator  10 , while impeding any undesirable currents induced in other nearby dual tuned resonators, substantially similar to dual tuned resonator  10 . This prevents undesired mutual coupling between dual tuned resonators. 
     The preamplifier  71  amplifies both the first and second frequencies as well as match the output impedance of the dual tuned resonator  10  to the MR system receiver  13  of MR system  1  to within 5 ohms, where the MR system receiver  13  is approximately 50 ohms. The preamplifier  71  may be either a narrowband or broadband preamplifier. In this  FIG. 2 , the preamplifier  71  is a low-input impedance broadband preamplifier, which has a resistance of less than 10 ohms from its input to ground. In various example embodiments it may be beneficial to configure the preamplifier  71  to have a resistance of less than  1  ohm from its input to ground. The preamplifier  71  may operate using the DC voltage provided by the MR system  1  on a connecting cable center pin (not pictured). 
       FIG. 3  illustrates a dual tuned resonator of a dual tuned receiver coil. Similar to the example embodiment illustrated in  FIG. 2 , the example embodiment illustrated in  FIG. 3  shows a dual tuned resonator  10 - 1  that is configured to receive at least two RF that are close together, such as, for example, within 7%, or within 15%, of the hydrogen frequency. This may account for output impedance changes due to frequency bandwidth shift in narrow band amplifiers, wherein the larger the shift, the greater the output impedance shift. While a dual tuned receiver coil  18  may include one or more dual tuned resonators, for illustration purposes a single dual tuned resonator  10 - 1  is described in this  FIG. 3 . Like the dual-tuned resonator  10  illustrated in  FIG. 2 , the dual tuned resonator  10 - 1  includes one or more constant capacitors  12 ,  31 ,  43  and  51 , at least one variable frequency circuit  20 , first frequency decoupler  50 , second frequency decoupler  30 , and preamplifier circuit  40 . The dual tuned resonator  10 - 1  may be made of a material with high conductivity properties, such as copper tape, copper strip etched on rigid substrate, copper strips etched on flexible substrate, and so on. The at least one constant capacitor  12 ,  31 ,  43 , and  51 , the at least one variable frequency circuit  20 , the first frequency doupler  50 , and the second frequency decoupler  30  are substantially the same as their corresponding elements in  FIG. 2 . 
     The preamplifier circuit  40  of the dual tuned resonator  10 - 1  includes at least one constant capacitor, such as constant capacitor  43 , and the preamplifier circuit inductor  44 , which are substantially the same as their corresponding elements in  FIG. 2 . The preamplifier circuit  40  further includes a variable preamplifier capacitor  42 , a preamplifier circuit inductor  44 , a reactance  46 , input capacitor  48 , one or more preamplifier switches  41 ,  45 , and  47 , the preamplifier  70 , and a MR inductor  61 . 
     The preamplifier capacitor  42  is configured to assist in shifting the resonant frequency of the dual tuned resonator  10 - 1  to the second frequency. Further, preamplifier capacitor  42  also alters the input impedance of resonator  10 - 1  to the preamplifier  70  to match the second frequency when the dual tuned resonator  10 - 1  has resonant frequency at the second frequency. The capacitor  42  may be of any capacitance to shift the resonant frequency of the dual tuned resonator  10 - 1  and shift the input impedance of the dual tuned resonator  10 - 1  to the preamplifier  70 . 
     The preamplifier capacitor  48  shifts the center of the preamplifier  70  operating bandwidth to the second frequency of the dual tuned resonator  10 - 1 , such as approximately 115.9 MHz, which is the RF of fluorine on conventional 3 Tesla MRI systems. The preamplifier capacitor  48  is switched into the preamplifier  70  input when switch  47  is closed. This switch closes simultaneously or nearly simultaneously with the switches  21 ,  41 ,  45 , and  62  to create a second operating mode for the preamplifier  70  at the second frequency. The switch  47  may be engaged by DC control from the MRI system  1 . The preamplifier capacitor  48  may be of any capacitance required to operate in parallel with the preamplifier&#39;s  70  internal input capacitance in order to shift the preamplifier  70  operating bandwidth to the second frequency, when the second frequency is close to the first frequency for the dual tuned resonator  10 - 1 . 
     The reactance  46  alters input inductance to the preamplifier  70  when activated. The reactance  46  is activated when the switch  45  is closed, placing the reactance  46  in parallel with the preamplifier circuit inductor  44 . When in parallel, the reactance  46  matches the negative reactance of the constant capacitor  43 , which is parallel with and matches the variable capacitor  42  when the dual tuned resonator  10 - 1  has a resonant frequency at the second frequency. The reactance  46  may be any reactance (inductive of capacitive) that creates parallel reactance to match that of the combined negative reactance of variable capacitor  42  and constant capacitor  43  to create an isolation circuit to reduce undesired mutual coupling between dual tuned resonators. 
     The one or more preamplifier circuit switches  41 ,  45  and  47  activate and deactivate portions of the preamplifier circuit  40 , simultaneously or nearly simultaneously. The switches  41 ,  45  and  47  may be any mechanism for activating and deactivating the portions of the preamplifier circuit  40 , such as a single pole single throw switch (SPST), microelectromechanical system (MEMS) switch, pin diode, or voltage-controlled varactor such as previously described. When the switches  41 ,  45 , and  47  are in an open position in this embodiment, portions of the preamplifier circuit  40  are deactivated, such that preamplifier circuit capacitor  42 , reactance  46 , and input capacitor  48  are disengaged, and the preamplifier circuit  40  has input impedance to match the center frequency of the preamplifier  70  at the first frequency. 
     When the switches  41 ,  45 , and  47  are in a closed position portions of the preamplifier circuit  40  are activated, such that the preamplifier circuit capacitor  42 , reactance  46 , and input capacitor  48  are engaged. When the preamplifier circuit capacitor  42 , reactance  46 , and input capacitor  48  are engaged the center frequency of the preamplifier  70  shifts to match the center frequency of the second frequency, and the input impedance of the preamplifier circuit  40  matches the center frequency of preamplifier  70  at the second frequency. 
     The preamplifier  70  is configured to amplify both the first and second frequencies as well as match the output impedance of the dual tuned resonator  10 - 1  to the MR system receiver  13  of MR system  1  to within 5 ohms, where the MR system receiver  13  is approximately 50 ohms. The preamplifier  70  may match the output impedance in conjunction with the MR inductor  61  and output impedance circuit  60 . The preamplifier  70  may be either a narrowband or broadband preamplifier. In the example embodiment illustrated in  FIG. 3 , the preamplifier  70  is a narrowband preamplifier. The preamplifier  70  may provide a gain of between 20 and 30 dB as required by the MRI system receiver  13  and operate using the DC voltage provided by the MRI system  1  on the connecting cable center pin (not pictured). 
     The MRI inductor  61  substantially matches (within 5 ohms) the output impedance from the preamplifier  70  to the MRI system  1 . The MRI inductor  61  may be any inductance to substantially match the output impedance from the preamplifier  70  to the MRI system  1 . 
     The output impedance circuit  60  matches the output impedance of the preamplifier  70  to the MRI system  1  to within 5 ohms when the dual tuned resonator  10 - 1  has a resonant frequency at the second frequency. The output impedance circuit  60  includes an output impedance capacitor  63 , an output impedance inductor  64 , and an output impedance switch  62 . 
     The output impedance capacitor  63  is configured to provide a shift in output reactance in conjunction with the output impedance inductor  64  when activated. The output impedance capacitor  63  may be of any capacitance to offset the inherent shift of the preamplifier output reactance when the preamplifier  70  operates at the second frequency. 
     The output impedance inductor  64  provides a shift in output reactance in conjunction with the output impedance capacitor  63  when activated. The output impedance inductor  64  may be of any inductance to offset the inherent shift of the preamplifier output reactance when the preamplifier  70  operates at the second frequency. 
     The output impedance switch  62  activates and deactivates the output impedance circuit  60 . The switch  62  may be any mechanism for activating and deactivating the portions of the preamplifier circuit  60 , such as a single pole single throw switch (SPST), microelectromechanical system (MEMS) switch, pin diode, or voltage-controlled varactor. When the switch  62  is in an open position the output impedance circuit is deactivated, and the output impedance of the preamplifier  70  matches within 5 ohms to the MRI system  1  for the first frequency. When the switch  62  is in a closed position the output impedance circuit  60  is activated, and output impedance of the preamplifier  70  is shifted to match within 5 ohms the MRI system  1  for the second frequency. 
       FIG. 4  illustrates a dual tuned resonator of a dual tuned receiver coil. In the example embodiment of  FIG. 4 , a dual tuned resonator  10 - 2  receives at least two frequencies that are far apart, such as, for example, over approximately 7%, or approximately 15%, apart, or at least not close together. The dual tuned resonator  10 - 2  includes the at least one constant capacitor  12 ,  31 ,  43 , and  51 , the at least one variable frequency circuit  20 , the first frequency decoupler  50 , the second frequency decoupler  30 , and the preamplifier circuit  40 . The dual tuned resonator  10 - 2  further includes one or more shorted capacitors  49 , one or more shorting switches  24 ,  29 ,  26 , and  27 . The at least one constant capacitor  12 ,  31 ,  43 ,  49 , and  51 , are substantially the same as their corresponding elements in  FIG. 2 . 
     The at least one variable frequency circuit  20  shifts the resonance of the dual tuned resonator  10 - 2  to a second RF, such as approximately 15.0 MHz, which is the RF of Xenon. The at least one variable frequency circuit  20  includes a variable capacitor  22  and a switch  21 . The variable capacitor  22  may be any capacitance to generate a resonant frequency of the second RF for the dual tuned resonator  10 - 2  when the variable frequency circuit  20  is activated. The switch  21  is substantially the same as the corresponding element of  FIG. 2 . 
     The first frequency decoupler  50  performs passive decoupling of the dual tuned resonator  10 - 2  when the dual tuned resonator  10 - 2  is transmitting the first frequency. The first frequency decoupler  50  may further perform passive decoupling of the second frequency when the two frequencies are far apart. The first frequency decoupler  50  generates a high impedance resonance circuit for the first frequency during the transmit cycle of the first frequency. The first frequency decoupler  50  includes a first frequency variable inductor  52 , at least one constant capacitor, such as constant capacitor  12 , and crossed PIN diodes  53  that are substantially the same as their corresponding components in  FIG. 2 . 
     The first frequency decoupler may further generate a high impedance resonance circuit for the second frequency during the transmit cycle of the second frequency. The first frequency decoupler may further include a variable inductor  39 , crossed PIN diodes  38 , and a first frequency decoupler switch  28  to generate the high impedance resonance circuit in substantially the same manner as the first frequency variable inductor  52  and first frequency crossed PIN diodes  53 . Further, the dual tuned resonator  10 - 2  may include one or more redundant first frequency passive decouplers, as shown in  FIG. 4  by constant capacitor  51 , first frequency variable inductor  52 , and first frequency crossed PIN diodes  53 . 
     The first frequency decoupler switch  28  activates the appropriate crossed PIN diode and inductor to decouple the dual tuned resonator  10 - 2  when it is transmitting the first and second RF. The first frequency decoupler switch  28  may be a single pole double throw switch (SPDT) as further described in  FIG. 5 . 
     The second frequency decoupler  30  performs active decoupling of the dual tuned resonator  10 - 2  during transmission of the second frequency. The second frequency decoupler  30  may further perform active decoupling of the dual tuned resonator  10 - 2  during transmission of the first frequency. The second frequency decoupler  30  includes a second frequency variable inductor  35 , at least one constant capacitor, such as constant capacitor  31 , and an actively based diode  32 . To actively decouple, a direct current (DC) control voltage generated by the MRI system  1 , and synchronized with the transmit pulse timing, is connected across active diode  32  via separate control lines (not pictured). Therefore, the second frequency variable inductor  35  is configured to generate a high impedance resonance circuit with the constant capacitor  31  during transmission of the second frequency. The second frequency variable inductor  35  may be any inductance to generate the high impedance resonance circuit with capacitance of constant capacitor  31  when in parallel. Further, the second frequency variable inductor  35  may be actively switched into parallel circuit by the synchronization of the DC control voltage across the PIN diode  32 . 
     Further, the second frequency decoupler  50  may perform active decoupling of the first frequency when the first frequency and second frequency are far apart. The second frequency decoupler  30  further includes a first frequency inductor  36 , a first frequency PIN diode  37 , and a second frequency decoupler switch  25 . The first frequency inductor  36  is configured to generate a high impedance resonance circuit with the constant capacitor  31  during transmission of the first frequency. To actively decouple, a direct current (DC) control voltage generated by the MRI system  1 , and synchronized with the transmit pulse timing, is connected across active diode  37  via separate control lines (not pictured). Therefore, the first frequency variable inductor  36  is configured to generate a high impedance resonance circuit with the constant capacitor  31  during transmission of the first frequency. The first frequency variable inductor  36  may be any inductance to generate the high impedance resonance circuit with capacitance of constant capacitor  31  when in parallel. Further, the first frequency variable inductor  36  may be actively switched into parallel circuit by the synchronization of the DC control voltage across the PIN diode  37 . 
     The second frequency decoupler switch  25  activates the appropriate PIN diode and inductor to decouple the dual tuned resonator  10 - 2  when it is transmitting the first and second frequencies. The first frequency decoupler switch  25  may be a single pole double throw switch (SPDT) as further described in  FIG. 5 . 
     The one or more series capacitors  49  provide and detract capacitance from the dual tuned resonator  10 - 2  to shift resonance of the dual tuned resonator from the first to the second frequency. The one or more shorted capacitors  49  add capacitance to the dual tuned resonator  10 - 2  when in circuit with the dual tuned resonator  10 - 2 . The one or more shorted capacitors  49  detract capacitance from the dual tuned resonator  10 - 2  when shorted out of the circuit of the dual tuned resonator  10 - 2 . Shorting the one or more shorted capacitors  49  removes the capacitive junctions from the circuit, lowering total net capacitance, and thereby shifting frequency of the circuit lower. 
     The one or more shorting switches  24 ,  29 ,  26 , and  27  short one or more constant capacitors  49 . The shorting switches may be any mechanism for shorting the one or more shorted capacitors  49 , such as a single pole single throw switch (SPST), microelectromechanical system (MEMS) switch, or a varactor or voltage-controlled PIN diode. When the shorting switches  24 ,  29 ,  26 , and  27  are open, the one or more constant capacitors  49  are not shorted. When the shorting switches  24 ,  29 ,  26 , and  27  are closed, the one or more constant capacitors  49  are shorted. The one or more shorting switches open and close simultaneously or nearly simultaneously. The one or more shorting switches  24 ,  29 ,  26 , and  27  may be engaged by DC control via the MRI system  1 . 
     The preamplifier circuit  40  is configured to develop the MRI signal of the dual tuned resonator  10 - 2  to a preamplifier  70  when the dual tuned resonator  10 - 2  resonates at a first frequency. The preamplifier circuit  40  may further be configured to develop the MRI signal of the dual tuned resonator  10 - 2  to a preamplifier  93  when the dual tuned resonator  10 - 2  resonates at a second frequency. The preamplifier circuit  40  includes a preamplifier circuit inductor  44 , a preamplifier  70 , and at least one constant capacitor, such as constant capacitor  43 . The preamplifier circuit inductor  44 , the preamplifier  70  and the constant capacitor  43  are substantially similar to their corresponding elements in  FIG. 3 . 
     The preamplifier circuit  40  further includes a second preamplifier circuit inductor  94 , and the second frequency preamplifier  93 . The second preamplifier circuit inductor  94  and the second frequency preamplifier  93  operate substantially similar to the preamplifier circuit inductor  44  and the preamplifier  7  when the dual tuned resonator  10 - 2  resonates at the second frequency. The preamplifier circuit  40  further includes one or more SPDT preamplifier switches  91  and  92 . The one more SPDT switches  91  and  92  are configured to activate or deactivate the preamplifier  70  and the second frequency preamplifier  93  in circuit with the dual tuned resonator  10 - 2  and system cable  95  of the MRI system  1  via the center pin  96  for signal transfer. The SPDT switches  91  and  92  may be a single pole double throw switch (SPDT) as further described in  FIG. 5 . The SPDT switches  91  and  92  may operate simultaneously or nearly simultaneously with the decoupler switches  25  and  28 , and the one or more shorting switches  24 ,  29 ,  26 , and  27 . The SPDT switches  91  and  92  may be engaged by DC control via the MRI system  1 . 
       FIG. 5  illustrates a single pole double throw (SPDT) switch useful in the presently described system. The example in  FIG. 5  has a configuration that may be indicative of one or more of the SPDT switches described herein. The SPDT switch  25  utilizes PIN diodes  101  and  102  with a common node  103 . A control DC signal enters via connection  110 , and current is limited through resistor  104 . Frequency is filtered by capacitor  105  and RF choke  106 . These latter components prevent interference of the low impedance DC circuit with the RF circuit at node  103  where the common RF signal is passed to common node (2) through capacitor  109 . Choke  106  offers a high impedance to RF and low resistance to DC, while capacitor  105  effectively shorts any RF signals to ground, to prevent them from entering into the DC bias path  110 . 
     When the bipolar control signal from the MRI system at  110  is positive with respect to ground, diode  102  is forward biased with its cathode connection to ground via RF choke  108 , thus enabling the RF signal to pass with limited impedance from switch node (2) to node (3). Positive voltage at  103  also reverse biases diode  101  effectively ensuring good isolation between the two ports at node (2) and (3). Similarly, when the bipolar control signal from the MRI system at  110  is negative with respect to ground, diode  101  is forward biased with its node connection to ground via RF choke  107  to enable the RF signal to pass with limited impedance from switch node (2) to node (1). Negative voltage at  103  also reverse biases diode  102  similarly ensuring good isolation between the two ports at node (2) and (3) while operating in this mode. 
       FIG. 6  illustrates a second frequency transmit coil of a dual tuned coil package. As previously described, this example embodiment of the second frequency transmit coil  17   a  transmits at a second frequency relative to a first frequency transmitted by the system body coil, or first frequency transmit coil. Various example embodiments of the second frequency transmit coil  17   a  may further be configured to transmit two or more frequencies. In the example embodiment illustrated in  FIG. 6 , the second frequency transmit coil  17   a  may include one or more balanced resonators  130  and  140 , one or more DC blocking diodes  123  and  125 , a high voltage PIN diode  124 , a series match capacitor  126 , and a parallel match capacitor  127 . It may be beneficial to configure the components such that the parallel drive resonators are balanced in order to provide more efficient transmit power distribution of the MRI power from the MRI system  1 , due to quadrupling the drive currents around a parallel circuit compared to a series circuit given the same reactances in each resonator and a common input impedance. The MRI system  1  delivers the excitation signal from the second frequency power amplifier  16   b  via MRI system  1  local transmit coil port  9  through a cable  121 . 
     The one or more balanced resonators  130  and  140  may be of a shape to proximately fit and image a particular anatomy of a patient, such as the patient&#39;s lungs. The balanced resonator  130  may include one more diodes  131 ,  133  and  136 , an adjustable capacitor  132 , a fixed capacitor  135 , one or more series capacitors  134 , and one or more shorting circuits  150 . The balanced resonator  140  may include one or more diodes  141 ,  143  and  146 , an adjustable capacitor  142 , a fixed capacitor  145 , one or more series capacitors  144 , and one or more shorting circuits  160 . 
     When the high voltage PIN diode  124  is forward biased, the match capacitor  126  is in series with the input signal from the MRI system  1 . The parallel match capacitor  127  is in parallel to the input signal from the MRI system  1 . 
     During transmission of the second frequency signal to the transmit coil  17   a  via the cable  121 , the DC control signals from the MRI system  1  heavily biases on the one or more diodes  131 ,  133 ,  136 ,  141 ,  143 ,  146 , and the high voltage PIN diode  124 . During transmission of the first frequency signal and receiving by the receiver coil  18 , the bi-polar control signal of MRI system  1  reverse biases the diodes  131 ,  133 ,  136 ,  141 ,  143 ,  146 , and the high voltage PIN diode  124 . Biasing makes the one or more balanced resonators  130  and  140  break into several shorter conductor lengths, due to reverse biased diodes acting like open circuits. This makes the transmit coil  17   a  transparent to both the first frequency transmit coil  17   b  of the MRI system  1 , and the receiver coil  18 , which decreases interference of coupling between these devices. 
     The second frequency signal to the transmit coil  17   a  may be transmitted via the cable  121  is delivered across capacitor  127 , and the voltage developed drives second frequency currents around the one or more balanced resonators  130  and  140  in phase and with equal magnitude due to the total impedance and resonant frequency of the one or more balanced resonators  130  and  140  being substantially equal. These impedances and frequencies are equal due to the fixed capacitor  135  being substantially equal to the fixed capacitor  145 , and the series capacitor  134  being substantially equal to the series capacitor  144 , with the adjustable capacitors  132  and  142  tuned to ensure balance (e.g., absolute balance) of currents while maintaining resonance at the second frequency. 
     The shorting circuits  150  and  160  are configured so that the transmit coil  17   a  transmits two or more frequencies. Each balanced resonator  130  and  140  may be balanced with equal capacitance values as previously described, such that one or more series capacitors, such as  134  and  144 , may be shorted, via the shorting circuit  150  and  160  via switches  151  and  161 . When the switches  151  and  161  are closed, capacitors  134  and  144  are shorted, which effectively increases the frequency of the resonator  17   a . The switches  151  and  161  are opened and closed via control signals from the MRI system  1  via the local transmit coil port  9  and MR scanner receiver coil port  14 . Capacitor selection, combined with one or more switches  151  and  161 , may create two or more resonant frequencies for the second frequency transmit coil  17   a , while maintaining balance between balanced resonators  130  and  140 . 
     As previously described, the dual tuned receiver coil  18  may be provided with multiple resonators, such as, for example,  8  resonators,  16  resonators, and so on. The purpose of the multiple resonators is to provide improved signal quality, from a target tissue volume, compared to fewer larger resonators. These multiple resonators may be connected to independent MRI system receiver channels which further amplify, analog-to-digital convert, and image process. Further, due to more modern and advanced digital signal image acquisition and processing techniques such as parallel imaging, these multiple resonator signals can be acquired much faster than those of fewer resonators, and, hence, significantly improving the temporal response of the MRI system, and enabling the imaging of rapid biological functions such as beating hearts and respiration. 
       FIG. 7  illustrates the switchable receiver and frequency converter of  FIG. 1 . As illustrated in  FIG. 7 , the frequency converter  16  includes frequency conversion logic  16   a  and a second frequency power amplifier  16   b . A transmit power signal transmitted from the transmit power amplifier  6 , and having the first frequency, may be transmitted in the same manner whether it is destined for the system body coil  17   b  or the second frequency transmit coil  17   a , and the frequency switch assembly  8   a  is controlled to route the transmit power signal to one or the other. If the switch assembly  8   a  is controlled to route the transmit power signal through the local transmit coil port  9 , the signal is received by the frequency conversion logic  16   a  to be converted from the first frequency to the second frequency. After converting the first frequency signal to the second frequency, the frequency conversion logic  16   a  sends the second frequency signal to the second frequency power amplifier  16  to be amplified and transmitted to the second frequency transmit coil  17   a . The transmit power signal is typically applied to the transmit coils in pulses. After the second frequency transmit coil  17   a  has received and transmitted the second frequency power signal, the signal from the one or more dual tuned resonators  10  is received by the switchable receiver  15 . If the signal received from the one or more dual tuned resonators  10  is transmitted at the second frequency, the switch  15   a  is controlled to route the received signal to an amplifier  180 , and the amplified signal is then passed to frequency converter logic  182  to be converted back to the first frequency and then transmitted through switch  184  to the scanner receiver coil port  14 . If the signal received by the switchable receiver has the first frequency, switches  15   a  and  184  are controlled to route the receive signal via line  186  through to the scanner receiver coil port  14  without the amplification and frequency conversion. Switches  15   a  and  184  may be controlled by a common control signals, one per channel and fully synchronized in their bi-polar switching, such that both switches are routing signals to/from the same line provided in the switchable receiver  15 . It is noted that the two, switchable path configuration and associated componentry is illustrated in  FIG. 7  only for the sake of clarity, but other variants of the switchable receiver  15  may have multiple paths to accommodate signals transmitted from a number of dual tuned resonators  10  of the dual tuned receiver coil. For example, the switchable receiver  15  may be configured with  16  such input and output paths so that each of  16  or fewer signals transmitted from the dual tuned receiver coil  18  to the switchable receiver  15  may be accommodated with paths switchable between the unaltered signal line and the amplified and frequency converted signal line. The receiver coil port  14  typically will be equipped to receive such a multiple number of lines as well, and the control logic for activating the lines received by the receiver coil port  14  may also be utilized as the switch control to control one or both of switches  15   a  and  184  to direct the signals from the resonators  10  to the receiver coil port  14 . 
     Because most anatomically specific antenna include unique features such as number of resonators, power requirements, and output capabilities, they are accompanied by unique software codes, known as configuration files, which are routinely installed on the MRI system via simple editing of the MRI coil configuration via the console and computer. When the antenna in question is connected to the MRI system via ports  9  and/or  14 , it is detected by the system program via unique identifying signals designed into the coil (such as programmable serial ID codes or resistor values), the system then pulls in the appropriate coil configuration file and utilizes it to drive the system controller  4  and thus provide control signals via the system receiver  13  and transmit power amplifier  6 . 
     Thus, the signal received by the receiver coil port  14  of the MRI system  1  has the same frequency as that transmitted out from the local transmit coil port  9  of the MRI system  1 . In various example embodiments of the present general inventive concept, the switchable receiver  15  and the frequency converter  16  may be in electrical communication and/operative control to cause the transmitted and received signals to be synchronized and in phase. Various example embodiments of the present general inventive concept provide such phase locking by a phase lock loop provided to one or both of the switchable receiver  15  and frequency converter  16 , examples of which will be discussed in more detail in  FIGS. 8 and 9 . The switchable receiver  15  and frequency converter may be provided in separate housings or a common housing with a plurality of connections and/or connection ports to connect to the MRI system  1  ports and the second frequency transmit coil  17   a . Therefore, various examples of the present general inventive concept provide a switchable receiver  15  and frequency converter  16  that may simply be plugged into the existing ports of an MRI system to convert a first frequency signal to a second frequency to be transmitted from the transmit coils and received by the receiver coils, and converted back to the first frequency such that the MRI system performs imaging as it normally would through the transmission and receipt of the first frequency signal throughout the entirety of the transmit and receive processes. 
       FIG. 8  illustrates a switchable receiver and frequency converter. As noted with the other various example embodiments discussed and/or illustrated herein, the present general inventive concept is not limited to the components illustrated in this example embodiment, as other example embodiments may be provided with more, fewer, and/or different componentry without departing from the spirit and scope of the present general inventive concept. For example, although the switchable receiver  15 - 1  and frequency converter  16 - 1  in  FIG. 8  are provided in separate housings in electrical communication with one another, other examples may provide these or similar components in a common housing. In the example of  FIG. 8 , and as discussed in the description of  FIG. 1 , the switch assembly  8  is in electrical communication with the transmit power amplifier  6  and is configured to route the signal from the transmit power amplifier  6  either to the local transmit coil port  9  or along the MRI system  1  wiring connected to the first frequency transmit coil  17   b . As previously described, the transmit power signal routed through the local transmit coil port will be delivered in this example to the frequency converter  16 - 1  to be converted to another frequency. The switch assembly  8  may typically be configured as part of the existing MRI system to allow an operator to selectively switch between routing the signal so as to transmit with the existing system body coil, referenced herein as the first frequency transmit coil  17   b , or to transmit through the local transmit coil port which in this example embodiment is connected the frequency converter to be ultimately transmitted at a different frequency to a local coil, which is a coil that is inserted into the scanner and onto the patient, referenced herein as the second frequency coil  17   a . Such a local coil could be placed over, for example, the patient&#39;s brain, elbow, knee, etc., and is a transmit as well as a receive coil. In the example embodiments described herein, portions of the local coil are typically differentiated between the second frequency coil  17   a  and the dual tuned receiver coil  18 . 
     In the example embodiment illustrated in  FIG. 8 , the switch assembly  8  is illustrated as being in position to route the signal from the transmit power amplifier  6  through the local transmit coil port to the frequency converter  16 - 1 . The signal frequencies discussed regarding this example are related to a 3 Tesla operating frequency of a conventional MRI system. Other MRI systems may be based on larger or smaller operating frequencies, for which the frequencies produced in the frequency converter  16 - 1  may be adjusted accordingly. For example, in the 3 Tesla operating frequency, the system delivers a signal of 123.2 MHz from the transmit power amplifier  6  as the hydrogen excitation frequency, which may be referred to herein as the hydrogen signal. The hydrogen signal coming into the frequency converter  16 - 1  during the transmit pulse, which is a synchronized activity in which the synchronization is done by the existing MRI system  1 , is routed, or being sampled, from the local transmit coil port  9 . In the example embodiment illustrated in  FIG. 8 , the hydrogen signal will be converted to a fluorine signal, or fluorine excitation frequency, which is 115.9 MHz for this MRI system. Because the hydrogen signal is relatively close to the fluorine signal, the transmit power signal for hydrogen excitation will be stepped down by a large amount before being stepped back up to a level for fluorine excitation. Changing the signal frequency in two stages in this manner may be better for input and output signal frequencies of relatively close values, but in various examples, the frequency converter  16 - 1  may be configured to operate in a single stage, as will be discussed in regard to  FIG. 9 . 
     The frequency converter  16 - 1  includes a first mixer  202  to receive the hydrogen signal from the local transmit coil port  9 , and a first phase lock loop (PLL)  204  that also receives the hydrogen signal. The first PLL  204  includes a local crystal oscillator  206  as a reference oscillator producing a signal of 87.2 MHz. The first PLL  204  performs phase comparisons of the local oscillator  206  signal and the hydrogen signal and keep the two signals locked in phase, and supply the 87.2 MHz signal to the first mixer  202  such that the 87.2 MHz signal is synchronized and in phase with the 123.2 MHz hydrogen signal also supplied to the first mixer  202 . The first mixer  202  receives the hydrogen signal and the signal from the first PLL  204  and generates a signal having an intermediate frequency of 36 MHz by subtracting the signal from the first PLL  204  from the hydrogen signal. The signal output from the first mixer  202  is then passed through a low pass filter  214  that rejects any higher frequency signal components from the first mixer  202  and allows the 36 MHz signal to pass through to a second mixer  212 . A second PLL  208 , which includes a local crystal oscillator  210  as a reference oscillator producing a signal of 80 MHz, is in electrical communication with the first PLL  204  and the second mixer  212  such that an 80 MHz signal provided to the second mixer  212  is synchronized and in phase with the 36 MHz intermediate frequency signal passed to the second mixer  212  from the low pass filter  214 . The second mixer  212  receives the 36 MHz intermediate frequency signal and the 80 MHz signal from the second PLL  208  and generate the 115.9 MHz signal, which is the fluorine excitation frequency, by adding the intermediate frequency signal to the signal from the second PLL  208 . The 115.9 MHz signal is passed through a high pass filter  216  that rejects any lower frequency signal components from the second mixer  212  and allows the 115.9 MHz fluorine signal to pass through to a power amplifier  218 . The power amplifier  218  amplifies the fluorine signal to a desired level and transmits the amplified fluorine signal to the second frequency transmit coil  17   a . The power amplifier  218  may have a several hundred Watt output. In various example embodiments of the present general inventive concept, because the MRI system employs an automated transmit gain setting based upon receiving the peak signal return relative to adjusting transmit power settings (thus finding the 90 degree flip angle), the power amplifier  218  may be set to scale the power out according to input power from the local coil transmit port  9  of the system, thus continuing to employ the auto-gain setting routine of the MRI system. As previously noted, the two-stage mixer configuration is used in this example due to the relatively close frequencies of the hydrogen and fluorine signals. In this example, relatively high frequency local oscillators  206 , 210  are used to produce an intermediate frequency signal that is significantly lower in frequency than the hydrogen and fluorine signals. Such a configuration reduces the chances of having one signal corrupt the other in a single-stage mixer and filter configuration due to the signals being so relatively close to one another. 
     The components of the frequency converter  16 - 1  illustrated in  FIG. 8 , as well as a housing  200  containing the illustrated components, are preferably non-magnetic, because the frequency converter  16 - 1  may be formed of sufficient size and dimension to be placed inside the bore of the MRI and plugged directly into the local transmit coil port  9  of the MRI system  1 . The device may have no ferro-magnetic material at all, having a casing of plastic or aluminum or other such non-magnetic material, and be constructed of all non-magnetic parts. Similarly, the switchable receiver  15 - 1  may include a housing  201  containing the illustrated components therein, the housing  201  and components also being formed of non-magnetic material so as to be placed in close proximity to the scanner receiver coil port  14  of the MRI system. The frequency converter  16 - 1  and switchable receiver  15 - 1  may be provided in a common housing and separated by one or more shielding layers and/or materials, as the local transmit coil port  9  and receiver coil port  14  are typically located in close proximity to one another. In various examples in which the frequency converter  16 - 1  and switchable receiver  15 - 1  are provided in separate housings  200 , 201 , electrical connection ports may be provided so that one or more oscillators may be shared by the components in both housings  200 , 201 . 
     The output of the frequency converter  16 - 1  is the converted frequency of sufficient power to drive the second frequency coil  17   a , while the transmit power signal from the transmit power amplifier  6  was switched to the local transmit coil port  9  using the same switching logic that would otherwise be employed by the MRI system  1 . The transmit power signal was switched, or converted, to operate at the non-hydrogen frequency, which in this example is 115.9 MHz, the fluorine frequency. Thus, the existing MRI system  1  is essentially unaware of the change in the transmit power path and transmit power frequency after the signal has gone through the local transmit coil port  9 . 
     The switchable receiver  15 - 1  of the example illustrated in  FIG. 8  is switchable between a first path that receives a signal from the resonators tuned to the transmit power signal delivered to the first frequency transmit coil  17   b , and a second path that receives a signal from the resonators tuned to the transmit power signal delivered from the frequency converter  16 - 1  to the second frequency transmit coil  17   a . As the signal received through the resonators  10  from the frequency converter  16 - 1  is at a different frequency than that output at the local transmit coil port  9 , the switchable receiver  15 - 1  converts the frequency of the received signal back to the frequency of the transmit power signal delivered from the local transmit coil port  9 . In the example of  FIG. 8 , the frequency converter  16 - 1  is transmitting at 115.9 MHz, and therefore the signal received from the respective resonators of the dual tuned resonators  10  will also be at a frequency of 115.9 MHz, which is the fluorine frequency. The frequency converter  16 - 1  is a single channel system driving a transmit power signal, which could be implemented in various examples as a coaxial output. The switchable receiver  15 - 1 , however, uses low power, using an n-channel multi-nuclear coil as previously described in regard to the dual tuned resonators  10 . For example, if there are  8  resonators provided for the second frequency signal, e.g., the fluorine signal, in the receiver coil array  10 , then 8 channels will be provided to receive those respective signals from the 8 resonators, and so on. Each of those n channels are configured to be switchable at an input of the switchable receiver  15 - 1  between the unaltered path for the first frequency signal, e.g., the hydrogen signal, and the frequency conversion path for the second frequency signal, e.g., the fluorine signal. Each of the n channels are also configured to be switchable at the output of the switchable receiver  15 - 1  to deliver a signal having the first signal frequency level to the MRI scanner receiver coil port  14 . For the sake of clarity, only one of the n channels is illustrated for the example embodiment of  FIG. 8 . 
     For each of the n channels of the switchable receiver  15 - 1 , the respective signals from the dual tuned resonators  10  are received at the switch  234 , which is controlled by the existing switching logic provided in the MRI system for the receiver coil port  14 , indicated in  FIG. 8  by the line  236 . Typically, the MRI systems having multi-channel systems have receiver (input) coil ports  14  having paths for all the different RF pathways controlled by logic pins driving a TTL type of logic to engage and disengage the receiver elements or resonators according to whether the system is in a receive or transmit pulse of the cycle. Therefore, in the receive pulse the logic pins are controlled to make the receiver coil ports  14  on and operable to receive the respective signals from the resonators  10 . The independent DC output from the receive coil port  14  is used to control coil detuning during an input pulse, to activate diodes in the resonators  10  to detune and decouple resonator logic to change frequencies, and so on. Thus, the same logic coming from the MRI system that is synchronized with the transmit/receive toggling may also be used to drive the switches  234 , 235  to toggle between, for example, the hydrogen and fluorine modes described herein. If the transmit system is operating in the hydrogen mode, the receiver array is also operating in the hydrogen mode, and the signal does not need to be altered by the switchable receiver  15 - 1 . In such a case, the switches  234 , 235  illustrated in the switchable receiver  15 - 1  in  FIG. 8  would be in the opposite state to that illustrated so as to connect to line  238 , and the hydrogen signals would pass straight through to the MRI system receiver coil port  14  to be processed as normal. Alternatively, when the switches of the switchable receiver  15 - 1  are in the state illustrated in  FIG. 8 , in the non-hydrogen mode, the 115.9 MHz signal delivered from the resonators  10  are directed to an amplifier  220 . Although the 115.9 MHz signal has already been amplified by an onboard amplifier out in the dual tuned receiver coil  18  as previously described, the signal is still relatively small due to the fact that MRI coils work with very small signals. Thus, the signals are driven by a preliminary second stage provided by the amplifier  220  before being converted back to the first frequency. In various example embodiments of the present general inventive concept, the gain of the amplifier  220  may be set to compensate for the losses of the converter circuitry, and to deliver the same signal amplitude back to the receiver coil port  14  as the hydrogen signal, i.e., the first frequency, switched directly through. 
     The switchable receiver  15 - 1  includes first and second PLLs  224 , 226  that are configured to be in electrical communication with the frequency converter  16 - 1 . More specifically, in the example embodiment illustrated in  FIG. 8  the switchable receiver  15 - 1  includes a first PLL  224  in electrical communication with the second PLL  208  of the frequency converter  16 - 1 , and a second PLL  226  in electrical communication with the first PLL  204  of the frequency converter  16 - 1 . This electrical communication allows the PLLs  224 , 226  of the switchable receiver  15 - 1  to share the respective outputs of the local oscillators  210 , 206  of the PLLs  204 , 208  of the frequency converter  16 - 1  in phase lock loop control. The local oscillators may be configured in either of the switchable receiver  15 - 1  or frequency converter  16 - 1 . The 115.9 MHz signal output from the amplifier  220  is received by a first mixer  222  that also receives an 80 MHz signal from the first PLL  224  that is synchronized and in phase with the 115.9 MHz signal from the amplifier  220 . The first mixer  222  is configured to down convert the 115.9 MHz signal to the same 36 MHz intermediate frequency produced in the frequency converter  16 - 1  by subtracting the signal from the first PLL  224  from the signal received from the amplifier  220 . The generated signal output from the first mixer  222  is then passed through a low pass filter  230  that rejects any higher frequency signal components from the first mixer  222  and allows the 36 MHz signal to pass through to a second mixer  228 , which is in electrical communication with the second PLL  226  to receive the 87.2 MH signal that is synchronized and in phase with the 36 MHz signal received from the low pass filter  230 . The second mixer  212  receives the 36 MHz intermediate frequency signal and the 87.2 MHz signal from the second PLL  226  and generates a 123.2 MHz signal by adding the 36 MHz signal to the 87.2 MHz signal from the second PLL  226 . The 123.2 MHz signal is passed through a high pass filter  232  that rejects any lower frequency signal components from the second mixer  228  and allows the 123.2 MHz signal to pass through to be output by the switchable receiver  15 - 1  at the same frequency level as the transmit power signal originally output at the local transmit coil port  9 . Through such a conversion, the MRI system  1  is not “aware” of the change in the transmit power signal frequency generated in the frequency converter  16 - 1  and applied to the second frequency transmit coil  17   a , because the MRI system  1  is receiving signals at the same frequency at which the signals were transmitted. One valuable aspect of this construction is the ability to utilize all of the MRI system&#39;s existing features in operational capability, but being able to obtain information at a different resonant frequency, on both the transmit and receive sides of the MRI system. A transmitted power signal frequency can be translated to the nuclei of interest, and the frequency can be translated again after receiving the signal back from the coil package, and the MRI system will process the information as if it were the hydrogen signal frequency. It is noted that while the fluorine nuclei frequency is discussed throughout the description of the example embodiment illustrated in  FIG. 8 , different examples of the system can be configured to generate the resonant frequency for a host of other elements, such as calcium, phosphorous, sodium, and the like. 
     As previously discussed, the two-stage frequency conversion illustrated in the example of  FIG. 8  may be desirable when the transmit power signal frequency of the MRI system and the desired transmit power signal frequency have relatively close values. In various examples where the desired transmit power signal frequency is much higher or lower than the transmit power signal frequency natively generated by the MRI system, a single-stage frequency conversion will likely be sufficient. As such, a single local oscillator may suffice for such an example embodiment, and a single PLL in each of the switchable power amplifier and switchable receiver. 
       FIG. 9  illustrates a switchable receiver and frequency converter. The overall configuration of the example of  FIG. 9  is similar to that illustrated in  FIG. 8 , except that the frequency conversion from the first frequency to the second frequency, as well as the conversion from the second frequency back to the first frequency, is performed in a single-stage, rather than a two-stage, operation. In various examples in which the second frequency is very different (for example, more than 7%, or 15% apart) from the first frequency, e.g., 15 MHz to 120 MHz apart, such a single-stage frequency conversion may be more acceptable. In  FIG. 9 , a 1.5 Tesla operational MRI system is assumed, and thus the frequency converter  16 - 2  converts a first frequency of 64 MHz, which is the hydrogen signal for this system, to a second frequency of 30 MHz, which is the phosphorous signal for this system. Thus, the frequency converter  16 - 2  and switchable receiver  15 - 2  are operable with a dual tuned receiver coil that detects phosphorous nuclei as well as hydrogen nuclei. Other than the single-stage frequency conversion, the switchable receiver  15 - 2  and the frequency converter  16 - 2  operate in roughly the same manner as the switchable receiver  15 - 1  and the converter  16 - 1  of  FIG. 8 . In this example, the switch assembly  8  is controlled by the MRI system  1  to route the hydrogen signal through the port  9 , which is therefore delivered to a mixer  302 , as well as to a PLL  304  including a local crystal oscillator  306  as a reference oscillator producing a signal of approximately 34 MHz. The PLL  304  performs phase comparisons of the local oscillator  306  signal and the hydrogen signal and keeps the two signals locked in phase, and supplies the 34 MHz signal to the mixer  302  such that the 34 MHz signal is synchronized and in phase with the 64 MHz hydrogen signal also supplied to the mixer  302 . The mixer  302  receives the hydrogen signal and the signal from the first PLL  204  and generates a signal having an intermediate frequency of 30 MHz by subtracting the signal from the PLL  304  from the hydrogen signal. The signal output from the mixer  302  is then passed through a high pass filter  308  that rejects any higher frequency signal components from the mixer  302  and allows the 30 MHz signal to pass through to an amplifier  310 . The amplifier  310  amplifies and transmits the second frequency signal to the second frequency transmit coil  17   a . The gain of the amplifier  310  may be set to compensate for the losses of the converter circuitry, and to deliver the same signal amplitude as the first frequency output from the local coil transmit port  9 . When the switchable receiver  15 - 2  receives a signal back from the resonators  10  at the second frequency, a switch  318  is controlled to pass the signal to an amplifier  312  to amplify and transmit the second frequency signal to a mixer  314 . The gain of the amplifier  312  may be set to compensate for various encountered losses and to deliver the same signal amplitude back to the mixer  314  as the hydrogen signal, i.e., the first frequency, that would be switched directly through line  322  of the switchable receiver  15 - 2 . 
     The mixer  314  is in electrical communication with a PLL  316  that is also in electrical communication with the PLL  304  so as to receive the 34 MHz signal that is synchronized and in phase with the second frequency signal. The mixer  314  adds the signals together to transmit the 64 MHz, or first frequency, signal to a low pass filter  324  that rejects any lower frequency signal components from the mixer  314  and passes the first frequency signal to the switch  320 , which in  FIG. 9  is controlled to pass the first frequency signal on to the receiver coil port  14 . It is noted that various examples may have more or less components as those illustrated in  FIG. 6 , and/or in a different configuration, and may include altogether different components. 
     A method of operating MRI systems at one or more switchable frequencies different than that generated and generally transmitted to the body system coil of the MRI system is provided. One goal is to provide a relatively low-cost upgrade or addition to existing MRI systems which will provide for the excitation and reception of MRI signals from more than one nuclei, in addition to that of hydrogen. Referring to  FIG. 1 , at least one aspect of such an upgrade is that it may utilize only the common connectivity ports, i.e., the local transmit coil port  9  and scanner receiver coil port  14 , provided by all MRI system manufacturers for the substitution of various anatomically specific MRI antenna. 
     Another aspect is the addition of antennae, otherwise referred to herein as dual tuned coils, which can operate in both transmit mode and receive mode at more than one frequency, and, in the case of the receive antennae, they are configured with multiple resonators which further improve the spatial and temporal resolution of the MRI scan for more than one nuclei. For these multi-nuclear antenna to operate in acquiring MRI data from nuclei other than the excitation and reception of hydrogen, an amplified transmit signal at a non-hydrogen frequency may be generated and applied to the second frequency transmit coil  17   a . Similarly, the receiver array of resonators  10  may be switched to a non-hydrogen operating mode, and the signals from the resonators may then be transmitted to a first stage of non-hydrogen pre-amplifiers which may be configured to be connected directly to, and built into, the resonator circuitry, before being transmitted to another stage of amplification configured in the housing of the switchable receiver  15 . The signal output of switchable receiver  15 , which may have been converted back to the first frequency, i.e., the hydrogen frequency, may be sent back to the common MRI system receiver coil port  14  which then delivers these converted signals back to the MRI system at the hydrogen frequency for image processing and display. The MRI system may remain operating at the hydrogen frequency as if the other frequency was never present. 
     Similarly, during the MRI pulse sequence (chosen by the operator from the operating console as normal), a small transmit signal of hydrogen frequency may be delivered to the local antenna transmit port  9  where it is connected to frequency converter  16  containing frequency conversion logic  16   a  and second frequency power amplifier  16   b , which amplifies the converted signal at the non-hydrogen frequency. This power is then applied to the second frequency transmit coil, or antenna,  17   a  that is operable at the non-hydrogen frequency. As MRI relies on timing synchronization of the transmit pulses and receiver signals, both of the switchable receiver  15  and frequency converter  16  may be maintained in frequency and phase synchronization via a direct connection to each other of a common local oscillator signal used in both units, which is also synchronized with the excitation signals delivered by the local transmit coil port  9  and commonly used receiver array control signals provided at the receiver coil port  14 . Another aspect is the use of completely non-magnetic components (magnetic or ferrous materials cannot be placed in the MRI bore as they substantially distort the desired homogeneity of the static magnetic field of the MRI as well as present safety hazards from becoming projectiles in the changing fields) in the switchable receiver  15  and frequency converter  16 , so that placement in or proximate to the MRI bore does not interfere with MRI processes. Another aspect is that the MRI system may simply use the described local coil configuration file to provide the control logic signals, via common ports  9  and  14 , necessary to activate either the hydrogen mode or the non-hydrogen mode of the units  10 ,  17   a ,  15  and  16  so that they may operate in either nuclei or frequency mode. In short, the receiver antenna array of multiple resonators may be switched between hydrogen frequency or non-hydrogen frequencies using these control signals, and the MRI signal outputs of  10  are either switched directly through unit  15  to port  14  for processing if operating in hydrogen mode, or if operating in non-hydrogen frequency, they are further amplified and converted from non-hydrogen frequency to hydrogen frequency and then routed to port  14 . 
     Similarly, the transmit signal at switch  8  can be routed to the system body coil for transmitting power at the hydrogen frequency through body coil transmit antenna  17   b , or routed through switch  8  and port  9  to unit  16  for frequency conversion and power amplification of non-hydrogen excitation signal before being sent to the local transmit antenna  17   a  operating at the non-hydrogen frequency. In some implementations, it may be beneficial to employ a post-processing algorithm to re-encode raw data sets obtained from non-hydrogen frequencies before presenting in true two or three-dimensional images. As implementation of the dual tuned coil package may result in MRI scanning without any changes regarding spatial localization accomplished with the gradient coils  5   b , some distortion to an image reconstructed from the non-hydrogen frequency system may be encountered due to the gradients being “calibrated” for hydrogen frequency spatial encoding. The post-processing algorithm may be implemented via post-processing software which communicates with the computer via a common ethernet port available on all MRI systems. In various examples, the image set may be sent out for the post-processing and then returned to the computer for display on the console in the traditional manner. Thus, with various examples, one can simply utilize the resonators, second frequency transmit coil, switchable receiver, and frequency converter in a similar fashion to that in which one might connect any transmit/receive antenna set to the common local transmit coil and receiver coil ports, and create a multiple nuclei MRI system from a single nuclei system on demand. 
       FIG. 10  illustrates a method of dual tuned MRI resonator and coil package. It is understood that the operations illustrated in  FIG. 10  are merely those of an example, and may include more or fewer operations, and/or in a different order, than those presented in  FIG. 10 . Further, for the sake of clarity, the operations illustrated in  FIG. 10  simply discuss the use of the second frequency that is converted from the first frequency transmitted by the MRI system in use. However, it is noted that, as discussed in regard to  FIGS. 8 and 9 , an alternative parallel path is used in the switchable receiver  15  when the dual tuned MRI resonator and coil package is connected to the MRI system but operating in the hydrogen (1H) frequency, such as when the transmit power is being transmitted by the system transmit coil. The dual tuned resonator and coil package can be used in such a case merely for convenience, but may still be beneficial in obtaining improved results in the imaging by the MRI system. For example, when the dual tuned resonator and coil package of the present general inventive concept is used with the hydrogen frequency from the system transmit coil, no frequency conversion is performed, but improved reception results may occur from using the high sensitivity, multi-channel dual tuned receiver coil (antenna)  18  operating at the hydrogen frequency. This is also convenient as no changing of coils or system set-up is required to easily switch back and forth between the first and second frequencies. 
     In operation  400  the dual tuned coil package is connected to the local transmit and receive ports of the MRI system. For example, in examples utilizing the switchable receiver  15  and frequency converter  16 , which may be in separate housings or combined into one housing, connections from the switchable receiver  15  may be plugged into the receiver coil port  14 , and the frequency converter  16  may be connected to the local transmit coil port  9 . In operation  402  the first frequency transmit power signal transmitted by the MRI system is received by the frequency converter  16  to be converted to a second frequency and amplified before being transmitted to the dual tuned coil package  2 . In operation  404 , the dual tuned resonators  10  in the dual tuned receiver coil  18  are switched to a second frequency signal operating mode. In various example embodiments, the switch to the second frequency signal operating mode may be implemented by switching logic supplied locally to the dual tuned coil package, or may be implemented through operational control from the system controller  4 . In operation  406 , the resonator signals of the second frequency are received by the switchable receiver  15  to be amplified and converted back to the first frequency. In operation  408 , the switchable receiver  15  transmits the first frequency image signals to the receiver coil port of the MRI system for image processing. Upon receiving the first frequency image signals, the MRI system then performs image processing as if in receipt of signals that were transmitted through the coils at the same frequency at which the MRI system originally generated, such as hydrogen signals. 
     Various examples may provide a dual frequency coil package used in transmitting and receiving at least two frequencies in an MRI system, the dual frequency coil package including a dual tuned receiver coil configured to receive at least two frequencies, including at least a first frequency and a second frequency, in operative communication with the MRI system through a first local port of the MRI system, and a second frequency transmit coil configured to transmit the second frequency in operative communication with the MRI system through a second local port of the MRI system. The dual frequency coil package may further include one or more amplifiers included in the dual tuned receiver coil to amplify a signal transmitted by the dual tuned receiver coil. The dual frequency coil package may further include one or more resonators that are switchable so as to receive the first frequency in a first frequency mode, and to receive the second frequency in a second frequency mode. Each of the one or more resonators may include one or more fixed capacitors to generate resonance of the respective one or more resonators at the first frequency, and one or more variable frequency capacitors to shift the generated resonance of the respective one or more resonators to the second frequency in response to being activated. The one or more variable frequency capacitors may be in a variable frequency circuit including a switch to activate the one or more variable frequency capacitors. The one or more fixed capacitors may be in operative communication with the variable frequency circuit. Each of the one or more resonators may include a preamplifier circuit to respectively amplify the first and second frequencies and match an output impedance of the respective one or more resonators to a receiver of the MRI system. The preamplifier circuit may amplify a signal output by the respective one or more resonators from 20 to 30 decibels. Each of the one or more resonators may include a first frequency decoupler to passively decouple the respective one or more resonators at the first frequency, and a second frequency decoupler to decouple the respective one or more resonators at the second frequency. The second frequency decoupler may include a passive decoupler and an active decoupler. The dual tuned receiver coil may be switchable between a first frequency mode to receive the first frequency, and a second frequency mode to receive the second frequency. The dual frequency coil package may further include one or more dual frequency resonators each including switchable logic to switch a resonant frequency of the respective dual frequency resonators between the first and second frequency modes. 
     Various examples may provide a frequency converter and receiver system for use with a dual frequency coil package used in an MRI system, the frequency converter and receiver system including, a switchable receiver including one or more channels each channel receiving at least two frequencies, including at least a first frequency and a second frequency, each of the one or more channels including, an input configured to receive the at least two frequencies, an output configured to output the second frequency, a first frequency path configured to pass the first frequency between the input and the output, a second frequency path configured to convert the second frequency to the first frequency between the input and the output, a first switch to switch electrical communication from the input between the first and second frequency paths, and a second switch to switch electrical communication to the output between the first and second frequency paths, and a frequency converter to receive the first frequency, convert the first frequency to the second frequency, and output the second frequency, wherein the switchable receiver and the frequency converter are in electrical communication such that the first and second frequencies are in phase after frequency conversions. The first and second switches may be controlled by a logic signal from the MRI system. The frequency converter may include a first phase lock loop including a local oscillator, where the first phase lock loop receives the first frequency input to the frequency converter, locks the first frequency in phase with a first reference frequency from the local oscillator, and outputs the reference frequency, a first frequency mixer that receives the first frequency input to the frequency converter and the reference frequency and outputs the second frequency, and a first amplifier to amplify the second frequency. The second frequency path may include a second amplifier to receive the second frequency from the first switch and amplify the second frequency, a second phase lock loop configured to be in electrical communication with the first phase lock loop so as to lock the first reference frequency in phase with the first frequency, a second frequency mixer configured to receive the second frequency from the second amplifier and the first reference frequency from the second phase lock loop and output the first frequency to the second switch. The frequency converter may include a first phase lock loop including a first local oscillator, the first phase lock loop configured to receive the first frequency, lock the a first reference frequency from the first local oscillator in phase with the first frequency, and output the first reference frequency, a first frequency mixer that receives the first frequency input to the frequency converter and the first reference frequency and outputs a third frequency, a second phase lock loop including a second local oscillator, the second phase lock loop in electrical communication with the first phase lock loop, locks a second reference frequency from the second local oscillator with the first frequency, and outputs the second reference frequency, a second frequency mixer to receive the third frequency and the second reference frequency and output the second frequency, and a first amplifier to amplify the second frequency. The second frequency path may include a second amplifier to receive the second frequency from the first switch and amplify the second frequency, a third phase lock loop in electrical communication with the second phase lock loop so as to lock the second reference frequency in phase with the first frequency, a third frequency mixer to receive the second frequency from the second amplifier and the second reference frequency from the third phase lock loop and output the third frequency, a fourth phase lock loop in electrical communication with the first phase lock loop so as to lock the first reference frequency in phase with the first frequency, and a fourth frequency mixer configured to receive the third frequency from the third frequency mixer and the first reference frequency from the fourth phase lock loop and output the first frequency to the second switch. The outputs of the switchable receiver may be connected to a local receiver coil port of the MRI system. An input of the frequency converter may be connected to a local transmit coil port of the MRI system. 
     Various examples may provide a dual frequency coil package system for use in transmitting and receiving at least two frequencies in an MRI system, the dual frequency coil package system including a frequency converter to be selectively coupled to a local transmit coil port of the MRI system, to receive a first frequency through the local transmit coil port, to convert the first frequency to the second frequency, and to output the second frequency, a second frequency transmit coil configured be in electrical communication with the frequency converter so as to receive the second frequency from the frequency converter and to transmit the second frequency in operative communication with the MRI system, a dual tuned receiver coil to receive at least two frequencies, including at least the first frequency and the second frequency, and to output the at least two frequencies, and a switchable receiver to receive the at least two frequencies output from the dual tuned receiver coil, including at least the first frequency and the second frequency, and in electrical communication with the dual tuned receiver coil and selectively coupled to a local receiver coil port of the MRI system such that the switchable receiver and dual tuned receiver coil are in operative communication with the MRI system, wherein the switchable receiver transmits the first frequency received from the dual tuned receiver coil directly to the MRI system and converts the second frequency received from the dual tuned receiver coil to the first frequency before transmission to the MRI system. The dual tuned receiver coil may include one or more resonators that are switchable so as to receive the first frequency in a first frequency mode, and to receive the second frequency in a second frequency mode, the switchable receiver may include one or more channels each configured to receive at least the first and second frequencies, and each of the one or more resonators of the dual tuned receiver coil in respective communication with one of the one or more channels of the switchable receiver. 
     Various examples may provide a method of using a dual frequency coil package in an MRI system, the method including connecting a dual tuned coil package to local transmit and receive ports of the MRI system, converting a first frequency transmit power signal transmitted from the MRI system through the local transmit port to a second frequency transmit power signal, switching dual tuned resonators to a second frequency signal operating mode, converting second frequency signals received from resonators during a transmit pulse to the first frequency, and transmitting received first and converted first frequency signals to the local receive port of the MRI system for image processing. The method may further include controlling the switching of the dual tuned resonators and the converting of the signals received from the resonators through control logic connections of the local receive port. The method may further include locking the frequencies in phase during frequency conversions. 
     Various examples may include a dual frequency resonator that receives at least two frequencies, the dual frequency resonator including one or more fixed capacitors to generate resonance of the dual frequency resonator at a first frequency, a variable frequency circuit to generate resonance of the dual frequency resonator at a second frequency, wherein the one or more fixed capacitor are in operative communication with the variable frequency circuit, a preamplifier input circuit to amplify the first frequency and the second frequency received by the dual frequency resonator to match frequency and impedance of a magnetic resonance imaging system receiver, wherein the preamplifier input circuit is in operative communication with the one or more fixed capacitors and the variable frequency circuit, a first frequency decoupler circuit configured to passively decouple the dual tuned resonator at the first frequency, wherein the first frequency decoupler is in operative communication with the one or more fixed capacitors, the variable frequency circuit, and the preamplifier input circuit, a second frequency decoupler circuit to decouple the dual tuned resonator at the second frequency, the second frequency decoupler including a passive decoupler and an active decoupler, wherein the second frequency decoupler is in operative communication with the one or more fixed capacitors, the variable frequency circuit, and the preamplifier input circuit. 
     Various examples of the present general inventive concept may provide a dual frequency coil package for transmitting and receiving at least two frequencies to an MRI system, the dual frequency coil package including a dual tuned receiver coil configured to receive at least two frequencies, the dual tuned receiver including one or more dual tuned resonators, the one or more dual tuned resonators including one or more fixed capacitors to generate resonance of the dual frequency resonator at a first frequency, a variable frequency circuit to generate resonance of the dual frequency resonator at a second frequency, wherein the one or more fixed capacitor are in operative communication with the variable frequency circuit, a preamplifier input circuit to amplify the first frequency and the second frequency received by the dual frequency resonator to match frequency and impedance of a magnetic resonance imaging system receiver, wherein the preamplifier input circuit is in operative communication with the one or more fixed capacitors and the variable frequency circuit, a first frequency decoupler circuit to passively decouple the dual tuned resonator at the first frequency, wherein the first frequency decoupler is in operative communication with the one or more fixed capacitors, the variable frequency circuit, and the preamplifier input circuit, a second frequency decoupler circuit to decouple the dual tuned resonator at the second frequency, the second frequency decoupler comprising, a passive decoupler and an active decoupler, wherein the second frequency decoupler is in operative communication with the one or more fixed capacitors, the variable frequency circuit, and the preamplifier input circuit, and wherein the dual tuned receiver coil is in operative communication with the MRI system, a second frequency transmit coil configured to transmit the second frequency, wherein the second frequency transmit coil is in operative communication with the MRI system. 
     Various examples may provide a dual frequency coil package for transmitting and receiving at least two frequencies to an MRI system, the dual frequency coil package including a dual tuned receiver coil configured to receive at least two frequencies, the dual tuned receiver coil including one or more dual tuned resonators, the one or more dual tuned resonators including one or more fixed capacitors configured to generate resonance of the dual frequency resonator at a first frequency, a variable frequency circuit configured to generate resonance of the dual frequency resonator at a second frequency, wherein the one or more fixed capacitors are in operative communication with the variable frequency circuit, a preamplifier circuit configured to the first frequency and the second frequency received by the dual frequency resonator to match frequency and impedance of a magnetic resonance imaging system receiver, wherein the preamplifier input circuit is in operative communication with the one or more fixed capacitors and the variable frequency circuit, a first frequency decoupler circuit configured to passively decouple the dual tuned resonator at the first frequency, wherein the first frequency decoupler in operative communication with the one or more fixed capacitors, the variable frequency circuit, and the preamplifier input circuit, a second frequency decoupler circuit configured to decouple the dual tuned resonator at the second frequency, the second frequency decoupler including a passive decoupler and an active decoupler, wherein the second frequency decoupler is in operative communication with the one or more fixed capacitors, the variable frequency circuit, and the preamplifier input circuit, and wherein the dual tuned receiver coil is in operative communication with the MRI system, a second frequency transmit coil configured to transmit the second frequency, wherein the second frequency transmit coil is in operative communication with the MRI system, a switchable receiver configured to transmit the first frequency to an analog converter of the MRI system, the switchable receiver including a switchable receiver switch configured to engage a second frequency converter and amplifier when the dual tuned receiver coil receives at the second frequency, wherein the switchable receiver switch is in operative communication with the second frequency converter and amplifier and the dual tuned receiver coil, a second frequency converter and amplifier configured to convert the second frequency to the first frequency and amplify the converted second frequency, wherein the switchable receiver is in operative communication with the analog converter of the MRI system, a frequency converter configured to convert a first frequency of the MRI system to a second frequency when the dual tuned receiver receives at the second frequency, wherein the frequency converter is in operative communication with the MRI system, a second frequency power amplifier configured to amplify the second frequency of the MRI system when the frequency converter converts the first frequency to the second frequency, wherein the second frequency power amplifier is in operative communication with the frequency converter and the second frequency transmit coil. 
     Note that spatially relative terms, such as “up,” “down,” “right,” “left,” “beneath,” “below,” “lower,” “above,” “upper,” and the like may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over or rotated, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.