Abstract:
An magnetic resonance apparatus in embodiments of the invention may include one or more of the following features: (a) a coil having at least two sections, (b) the at least two sections having a resonant circuit, (c) the at least two sections being wirelessly coupled or decoupled, (d) the at least two sections being separable, (e) several openings allowing a subject to see and be accessed through the coil, (f) at least one cushioned head restraint, and (g) a subject input/output device providing visual data from in front and behind of the coil respectively; wherein the input/output device is selected from the group consisting of mirrors, prisms, video monitors, LCD devices, and optical motion trackers.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a cavity resonator coil for use in magnetic resonance systems.  
         BACKGROUND OF THE INVENTION  
         [0002]    There are many previously known resonators for use in magnetic resonance (MR) systems for imaging and spectroscopy. For example, one previously known device is commonly known as a birdcage resonator. These previously known birdcage resonators typically comprise a plurality of circumferentially spaced inductive/capacitive elements connected by inductive/capacitive end ring elements, which are driven at resonance by a Larmor radio frequency useful for nuclear magnetic resonance (NMR) systems. The object to be analyzed, e.g. the brain, is positioned within the resonator during the operation of the MR system.  
           [0003]    One disadvantage of these previously known resonators, however, is that they typically use lumped element circuits (with discrete inductors and capacitors) to achieve resonance at the selected radio frequency. Because lumped element circuits lose more energy to radiation at high frequencies where the circuit is greater than {fraction (1/10)} wavelength, the lumped element resonator is less efficient for high field MR imaging applications compared to lower field strengths. Because lumped element circuits are more radiative, they are electrically less efficient and have a lower Q factor. Similarly because conventional lumped element circuits such as the birdcage are more inductive, they resonate at lower frequencies than do the less inductive transmission line (TEM) circuits.  
           [0004]    These previously known resonators, which use lumped element circuits, suffer from several additional disadvantages. One such disadvantage is non-uniform current distributions which result in decreased homogeneity, decreased fill factor, and increased electric field losses. Especially at higher frequencies and for larger (clinical) volumes, lumped element resonators may achieve self-resonance below the desired frequency of operation as well as increased electromagnetic radiation losses.  
           [0005]    A distributed circuit, cavity resonator for NMR systems disclosed by Vaughan in U.S. Pat. No. 5,744,957 overcomes the above-mentioned disadvantages of the previously known devices. Vaughan discloses a cavity resonator having coaxial inner and outer cylindrical walls separated by a dielectric region. Spaced conductive end walls extend across the inner and outer walls at each axial end of the coil so that the inner, outer, and end walls together form an approximate cavity. The inner, outer, and end walls can, for example, be coated with a thin foil conductive material, such as copper, silver, or gold. In doing so, the coil imitates a coaxial line segment made resonant at Larmor frequencies useful for MR, such as 64 MHz (1.5 T), 175 MHz (4.1 T) or 170 MHz (4 T).  
           [0006]    The apparatus disclosed by Vaughan provides a cavity resonator coil overcoming the problems of conventional coils discussed above, providing for a substantial improvement in signal to noise ratio (SNR). The coil will also resonate and operate efficiently at higher Larmor frequencies for the higher static magnetic now available at 3T and above. Because the SNR from MR samples increases with the magnet field strength, the ability of this coil to resonate and operate efficiently at higher frequencies means that it can be used at high field strengths to obtain further SNR gains. This increase in signal to noise ratio provides a substantially improved image of the object to be analyzed within the resonator during the operation of the MR system, for example.  
           [0007]    The resonator disclosed by Vaughan has proven effective in MR systems providing increased SNR, homogeneity, transmit efficiency, fill factor, decreased electric field losses, and higher operational frequencies. However, there are still some problems associated with both the resonator disclosed by Vaughan and the previously known lumped element resonators.  
           [0008]    An ideal clinical head coil for example would lend itself to the easiest and most comfortable subject positioning, leave the subject&#39;s face uncovered once the subject is in position, and would include these access and comfort features without compromising coil performance, safety and reliability. It is preferable for a head coil to be both comfortable and accessible for the subject and easy to use for the technician. However, it is difficult to provide comfort and accessibility for the subject and ease of use for the technician and maintain a high coil performance. The ideal coil should have a removable top as well, to allow for comfortable subject positioning in the coil. Furthermore, some commercial systems don&#39;t provide the space for a coil that slides over a subject&#39;s head. Accordingly, several commercial coil designs already incorporate this “pop top” feature. However, these commercial coils that separate into halves are not popular with some research applications such as fMR. Apparently the electrical contacts that are broken and remade to open and close the coil each time a new subject is loaded, become unstable over time due to wear and oxidation, resulting in noise “spikes” and temporal instabilities often seen in EPI images for example. These electrical contacts are required to complete the end ring current paths in birdcages and similar coil structures. While commercial coils must meet rigorous FDA safety criteria, it could be imagined that electrical contacts in a coil might possibly pose safety risks in certain situations, especially where electrolytic bodily fluids were present.  
           [0009]    Similarly, an ideal body coil might be as small as possible and fit close enough to the human trunk for efficient transmission to and reception from a region of interest, but allow room for subject comfort and access. The present body coils are built very large to allow for access and comfort, but as a consequence are very inefficient and are poorly couplet the MR region of interest in a body. RF power amplifiers of 35 kW and more are required to compensate for the inefficiencies of a body coil used in a 3T magnet for example. Still, these coils provide little shoulder room for the largest human subjects.  
           [0010]    Limb coils, especially leg coils, are similarly limited by conventional practice. A leg volume coil for example must be oversized to make room for a leg with a foot to be threaded through the cylindrical structure. Or a leg coil has a removable top to provide easier access for a closer fitting, more efficient coil. This latter coil however by conventional designs requires the problematic electrical contacts described for the head coil above.  
           [0011]    Typical existing head only MR systems are one-piece units. A significant problem with this structure is that many medical subjects do not possess the physical ability to manipulate their heads and bodies into the positions required for the MR without significant difficultly or pain. Typically, the subject must try and navigate their head into the small diameter of the head only system. This can be painful or impossible for most medical subjects who are asked to do this while lying on their back.  
           [0012]    Because of the inherently low SNR of the MR signal, these signals must be acquired and averaged a sufficient number of times to improve the SNR to a significant value. MR data acquisition by signal averaging is highly intolerant of motion in the MR sample or subject. Accordingly, human subjects are required to remain motionless for the duration of an MR scan, sometimes lasting 30 minutes or more. Movement will result in lower resolution images and in image “ghosting”, thereby limiting the diagnostic quality of an image and often requiring a repeated imaging session. To minimize head motion for example, MR operators will often insert padding around the subject&#39;s head to provide head restraint. While this has the effect of reducing the subject&#39;s head movement, it does not eliminate all of the subject&#39;s head movement. Further, all of the padding placed around the subject&#39;s head can apply uncomfortable pressure and can intensify the subject&#39;s feelings of claustrophobia. Therefore, the purpose behind having a high performance coil with a better signal to noise ratio is defeated if the subject cannot remain still.  
           [0013]    Another, problem associated with many MR protocols, is they can be painfully loud. Typically, subjects are given earplugs or headphones to muffle the noise (in most MR centers the subject can even bring their own cassette or CD to listen to). The acoustic noise is attributed to the electro motive forces generated by switched electrical currents in the wires of the magnet&#39;s gradient coils. Stronger magnet fields and stronger or faster gradient current switching generate greater acoustic amplitudes. While the methods mentioned above are generally effective for gradient noise reduction, coils must be built to larger and less efficient dimensions to accommodate the head restraint and hearing protection devices placed about the head.  
           [0014]    Visual input/output is often required for a subject receiving an MR exam, for diagnostics or research. These I/O visual devices help to minimize claustrophobia, provide visual cues, and relay information from the MR operator. Visual I/O devices are typically mirrors, prisms, or active displays located above the subject&#39;s eyes. A problem with existing systems of this sort is that 1) they are often fixed in position which requires that a subject be adjusted to the device, and 2) they typically protrude above the head coil so as to preclude their use in close fitting head only MR systems, and in head gradient inserts used in whole body MR systems.  
           [0015]    It has been shown that back planes on RF coils can function as an RF mirror to extend the uniformity of the coil&#39;s transverse RF magnetic field along the rotational or “z” axis of the coil. A back plane, also known as an end cap, can be used in a coil to make a shorter, and therefore more ergonomic, better shielded, and more electrically efficient coil for a desired field of view. Conventional cylindrical birdcage head coil, as mentioned above, typically do not have a back plane. The lack of a back plane together with the inherently shorter axial field of a birdcage require the birdcage head coil to be longer typically covering the subject&#39;s mouth and chin. This increased length of the birdcage has many problems. It creates a head coil, which can increase feelings of claustrophobia for the subject. Once inside of the head coil the subject&#39;s mouth is located immediately in front of the inside coil wall. A subjects breath pushed back into their face by the inside coil wall creates a very uncomfortable/claustrophobic feeling for the subject. This is an undesirable result since the MR exam may take 20 to 90 minutes. Additionally, general medical access and vocal communications are impeded with the coil extending over the subject&#39;s mouth and chin. Further, if the subject has a large head, nose, and/or chin it becomes increasingly difficult to fit the subject&#39;s head inside of the coil. Another additional disadvantage for coils not having end caps is additional electromagnetic energy is lost from the top of the coil and thus the coil is less efficient at high frequencies.  
           [0016]    While a back wall in a head coil is more desirable for coil performance and ergonomics in relation to the subject&#39;s mouth and chin (i.e., with a back wall the head coil body can be shorter and thus the head coil does not have to extend over the chin), a back wall is undesirable for a couple of reasons. First, a back plane closes off one end of the coil giving the appearance of putting ones head into a bucket rather than an open cylinder. This can increase a feeling of claustrophobia for the subject. Second, the back plane limits access to the subject from the back of the magnet. In coils without back planes, leads for physiological monitors, anesthesia and/or respiratory hoses, EEG leads, communications lines, etc., can be passed. In these systems visual signal projection is often performed from the rear of a magnet and through the back of a coil to mirror or prism systems mounted above the subjects&#39; eyes. Therefore, presently, head coil manufacturers must choose between the benefits of having a coil back plane or end cap or the benefits associated with access to the subject provided by head coils with no end cap.  
           [0017]    As stated above, a problem associated with head coils is the amount of space provided inside of the coil. RF coils transmit MR stimulus to the subject and receive signals back most efficiently when the coil is as close as possible to the subject. Therefore, for RF coil performance considerations, space inside a coil should be only enough for subject comfort and for the inclusion of devices useful for safety, head stability, and communication with the subject. As stated above, normally a subject must wear earphones or plugs for hearing protection and have separate pads inserted around the head to hold the head motionless for the MR exam. Further, there is typically some sort of visual and/or audio communications device adjacent to the head so that the MR operator can communicate with the subject. However, the padding, hearing protection and communication equipment can not only make the MR experience uncomfortable for the subject but this equipment also occupies limited space within the head coil.  
           [0018]    All of these problems listed above, individually and collectively, degrade the overall quality of NMR images and spectra, add to the discomfort of the subject, and limit subject access for the physician or researcher. Therefore, what is clearly needed is a high performance apparatus, which provides for increased signal to noise ratios and improved MR image quality, while overcoming the problems discussed above.  
         SUMMARY OF THE INVENTION  
         [0019]    An magnetic resonance apparatus in embodiments of the invention may include one or more of the following features: (a) a coil having at least two sections, (b) the at least two sections having a resonant circuit, (c) the at least two sections being wirelessly coupled or decoupled, (d) the at least two sections being separable, (e) several openings allowing a subject to see and be accessed through the coil, (f) at least one cushioned head restraint, and (g) a subject input/output device providing visual data from in front and behind of the coil respectively; wherein the input/output device is selected from the group consisting of mirrors, prisms, video monitors, LCD devices, and optical motion trackers.  
           [0020]    A magnetic resonance apparatus in embodiments of the invention may include one or more of the following features: (a) a coil having at least one head restraint, (b) a means for audio communication to a subject connected to the head restraint, (c) a means for active or passive protection for a subject&#39;s hearing, (d) at least three head restraints to provide a three-point head restraint, (e) a means to secure said head restraint to a subject&#39;s head, and (f) a head cushion.  
           [0021]    A TEM coil providing MR imaging in embodiments of the invention may include one or more of the following features: (a) a coil providing at least two head restraints, (b) the head restraints having a means for audio communication to a subject, (c) a means for active or passive protection for a subject&#39;s hearing, (d) a head cushion to provide a three-point head restraint, (e) a means to secure said head restraints to a subject&#39;s head, and (f) a means to accept an audio signal input.  
           [0022]    A magnetic resonance apparatus in embodiments of the invention may include one or more of the following features: (a) a coil having at least two separable sections, (b) a input/output device, (c) a track system located within an open face area in the coil, and (d) the input/output device being slideably mounted on said track.  
           [0023]    A TEM coil in embodiments of the invention may include one or more of the following features: (a) an input/output device, (b) a track system located within an open face area in the coil, (c) the input/output device being slideably mounted on said track, and (d) the input/output device is selected from the group consisting of visual transducers, olfactory transducers, gustatory transducers, or auditory transducers to provide two way communication or stimulus.  
           [0024]    An RF coil for magnetic resonance in embodiments of the invention may include one or more of the following features: (a) the coil comprising a plurality of sections, (b) the plurality of sections being with wireless connections and able to wirelessly couple electromagnetic energy between the plurality of sections or the plurality of sections being reactively decoupled, (c) the plurality of sections being separable, and (d) a guiding means to assure mutual alignment between said plurality of sections.  
           [0025]    A method of manufacturing a magnetic resonance device in embodiments of the invention may include one or more of the following steps: (a) providing a coil having a plurality of sections; the plurality of sections being separable, (b) attaching a head restraint means to prevent movement of a subject&#39;s head, provide communication with the subject, and protect said subject&#39;s hearing, (c) inserting a slideable input/output device within an open window on said top section to provide subject with two way communication, (d) creating a rear projection slot providing a channel positioned in a back plane of said coil to provide access for a rear visual projection system.  
           [0026]    A method of performing magnetic resonance imaging in embodiments of the invention may include one or more of the following steps: (a) providing a coil having a top section and a bottom section; said top section and bottom section being separable and wirelessly connected, (b) placing a subject within the bottom section, (c) placing the top section in electromagnetic communication with the bottom section, (d) providing a plurality of openings in the top section to allow a subject to see through said coil and be accessed through said coil, (e) providing at least one cushioned device for head restraint. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 is an exploded view of a construction of a resonator.  
         [0028]    [0028]FIG. 1 a  is a profile view of a construction of a resonator according to FIG. 1.  
         [0029]    [0029]FIG. 2 is an exploded view of an internal construction of a resonator according to an embodiment of the present invention.  
         [0030]    [0030]FIG. 2 a  is an exploded view of a resonator according to an embodiment of the present invention.  
         [0031]    [0031]FIG. 2 b  is a side profile diagram of a simulated subject&#39;s head within a resonator for the present invention.  
         [0032]    [0032]FIG. 2 c  is a profile view of a prior art bird cage coil.  
         [0033]    [0033]FIG. 2 d  is a profile view of a TEM cavity resonator.  
         [0034]    [0034]FIG. 2 e  is a profile view of a resonator according to an embodiment of the present invention.  
         [0035]    [0035]FIG. 2 f  is a profile view of a resonator according to an embodiment of the present invention.  
         [0036]    [0036]FIG. 3 is an enlarged view of the exploded view of a resonator as shown in FIG. 2 a.    
         [0037]    [0037]FIG. 4 is an exploded front profile of a resonator for the present invention.  
         [0038]    [0038]FIG. 5 is a rear side profile view of a resonator for the present invention.  
         [0039]    [0039]FIG. 6 is a front profile of a resonator for the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0040]    To assist in an understanding of the invention, a preferred embodiment or embodiments will now be described in detail. Reference will be frequently taken to the figures, which are summarized above. Reference numerals will be used to indicate certain parts and locations in the figures. The same reference numerals will be used to indicate the same parts or locations throughout the figures unless otherwise indicated.  
         [0041]    The present invention is not limited to only distributed circuit cavity resonator head coils, and may be employed in many of various types of MR head coil devices. It is to be further understood, moreover, the present invention may be employed in many of various types of MR devices and is not limited only to head coils. For purposes of illustration only, however, the present invention is below described in the context of cavity resonator head coils.  
         [0042]    With respect to FIGS. 1 &amp; 1 a,  a general construction of a cavity resonator is shown. Additional structures and teachings for construction of a cavity resonator, which can be utilized in the present invention are discussed in U.S. Pat. No. 5,557,247, U.S. Pat. No. 5,744,957, U.S. Pat. No. 5,886,596, U.S. Provisional Application 60/135,269, U.S. Provisional Application 60/222,144, U.S. Provisional 60/378,111, and U.S. Provisional 60/373,808, which are herein incorporated by reference in their entirety. Generally a cavity resonator (coil)  10  is comprised of an electrical circuit tube/board  12 , a front cavity wall component  14 , a lateral cavity wall component  16 , and a back cavity wall component  18  all contained within a coil shell  22 .  
         [0043]    With reference to FIG. 2, an exploded view of an internal construction of a resonator according to an embodiment of the present invention is shown. Generally coil  24  is comprised of electrical circuit tube/board  12  and  12 ′, front cavity walls  14  &amp;  14 ′, lateral cavity walls  16  &amp;  16 ′, and back cavity wall  18  &amp;  18 ′ all contained within coil shell  22  &amp;  22 ′. Electrical circuit tubes  12  and  12 ″ are generally comprised of circuit elements which may be transmission line elements including coaxial line, flat line, stripline, microstrip, wave guide or other distributed elements, inductors, capacitors, PIN diodes, or other lumped elements, printed or etched circuit boards, preamps, TR switches, phase shifters, amplitude modulators, and other electronics devices. Tubes  12  and  12 ′ are inductively coupled by mutual inductance of the current elements in each. Cavity walls  14 ,  14 ′, lateral cavity walls  16 ,  16 ′, and back cavity wall  18 ,  18 ′ are all electromagnetic shields or conductive strips comprised of conductive foil to complete the circuit, to limit radiative losses and to provide a Faraday shield for the coil  24 . Coil shells  22 ,  22 ′ are comprised of a nonconducting packaging material such as plastic or fiberglass to house the internal components of coil  24 , which are discussed above. When combined, front wall  14 ′, tube  12 ′, lateral wall  16 ′, back wall  18 ′, and coil shell  22 ′ are combined to form top section  28 . In addition, front wall  14 , tube  12 , lateral wall  16 , back wall  18 , and coil shell  22  are combined to form bottom section  26 . The internal construction of coil  24  is only essential to the present invention to the extent that it agrees with the external construction as shown in FIGS. 2 a - 6  and provides for some preferred manufacturing methods and materials. It is contemplated that coil  24  can have most any type of internal MR structure, however, preferably resonator  24  has a general internal structure similar to that of the teachings of U.S. Pat. No. 5,557,247, U.S. Pat. No. 5,744,957, U.S. Pat. No. 5,886,596, U.S. Provisional Application 60/135,269, U.S. Provisional Application 60/222,144, U.S. Provisional 60/378,111, or U.S. Provisional 60/373,808.  
         [0044]    Through research it has been found that hospitals, physicians, and MR system operators prefer to have a coil, which comes apart in two halves for ease of subject accessibility. With respect to FIG. 2 a,  an exploded view of an embodiment for a coil of the present invention is shown. In a preferred embodiment, coil  24  is comprised of a top section  28 , and a bottom section  26 . While FIGS.  2 - 6  show coil  24  having only a top  28  and bottom section  26 , it is fully contemplated that coil  24  could have a plurality of sections without departing from the spirit of the invention. However, for the purposes of this discussion, coil  24  is characterized as having a top  28  and bottom section  26 . Generally, since the two halves of coil  24  are wirelessly coupled through inductive or capacitive coupling, there is no need for electrical contacts to bind top section  28  with bottom section  26 . Basically coil  24  is comprised of conductor elements located in top section  28  mutually coupled to elements in bottom section  26 . This reactive coupling is possible utilizing structures similar to those in U.S. Pat. No. 5,557,247, U.S. Pat. No. 5,744,957, U.S. Pat. No. 5,886,596, U.S. Provisional Application 60/135,269, U.S. Provisional Application 60/222,144, U.S. Provisional 60/378,111, or U.S. Provisional 60/373,808. Coil  24  can be viewed as an array of resonant units (each unit comprised of a conductive element with cavity segment) all reactively coupled to each other. Thus there is no need for hard electrical contacts to transfer energy between top section  28  and bottom section  26 , thus the energy is transferred wirelessly. Alternately, as shown in FIGS. 2 e  and  2   f,  a plurality of sections  112  are reactively decoupled and driven by independent transmitters, or received by independent receivers or both transmit and receive such as is used in parallel imaging. These separate resonant circuits not only make top section  28  and bottom section  26  separable from one another they also have the added benefit of preventing switched gradient current induced eddy currents in coil  24 .  
         [0045]    With reference to FIG. 2 c,  previously known devices such as birdcage  100 , discussed above, require electrical contacts to complete an end ring  102  circuit on each end. Birdcage coil  100  design has one or more end ring  102  circuits at each end of the coil design, which provide current return paths to separate legs that traverse between two rings  102 . Thus, the operation of a birdcage coil  100  design relies on current flow through end rings  102 . Therefore, separating birdcage  100  into two halves requires hard electrical contacts between the two halves to be broken. Electrical contacts provide many problems including being prone to wear, oxidation, intermittency, and potential safety hazards for the subject.  
         [0046]    The current paths on conventional birdcage coils  100  are dependent on end rings  102  making birdcage  100  inductance dependent on the diameter of the coil. Large coils such as head and body coils are very inductive and therefore resonate at lower frequencies.  
         [0047]    With reference to FIGS. 2 d,    2   e,  and  2   f,  resonant cavity  110  circuit of the present invention does not depend on a current return path on an end ring  102 , as does a birdcage  100 . The current return in the preferred embodiment occurs on its associated cavity wall  108  segment, creating an electrically shorter, and therefore less inductive, more current uniform, higher frequency, and more efficient circuit than an equal sized birdcage  100 . The operational frequency of birdcage  100  is dependent on and limited by the inductive end ring  102 . TEM or cavity resonator  110  whose operational frequency is not dependent on or limited by an end ring  102  however can obtain much higher frequencies.  
         [0048]    The current paths on TEM resonator  110  are not dependent on end rings  102 , but rather on cavity wall  108  to provide a “return” path for current elements  109 . TEM coil  110  can therefore be arbitrarily large in diameter such as a large body coil, and still resonate at frequencies limited only by the size of an individual line element. Segmented TEM coils  110  shown in FIGS. 2 e  and  2   f  are shown to highlight the individual segments  108  or line elements  109  of which a TEM coil  110  is composed. Because the operation of TEM coil  110  does not depend on an end ring  102 , segments  112  from coil  110  can be removed as shown without affecting the operational coil.  
         [0049]    Therefore, the present invention utilizes top section  28  reactively coupled, inductively and/or capacitively, to bottom section  26  to allow for a separable design without the necessity of hard electrical contacts. The two sections of coil  24  are coupled reactively to one another so that all electrical circuits of coil  24  are sealed harmlessly inside dielectric coil packaging  27 . The present invention not only makes coil  24  more accessible to subjects, it also minimizes or prevents any electrical shock hazard to the subject. Further, the separation of top section  28  and bottom section  26  assists in preventing eddy currents.  
         [0050]    Another benefit of the reactive design of coil  24  is the ability to create an open window  29  substantially near the top of top section  28 . As discussed above, a common problem with present systems is the coil giving the subject either an increased feeling of claustrophobia or not providing enough room for subjects with large heads, noses, and/or chins. Since, top section  28  has several openings  25 , between inductively coupled elements of coil  24 , the subject can freely see out of coil  24  and thus the feeling of claustrophobia is significantly reduced. Additionally, general medical access and vocal communications are not impeded due to open sections  29  &amp;  25 . Further, if the subject has a large head, nose, and/or chin, open window  29  allows the subject to fit comfortably within coil  24  as is depicted in FIG. 2 b.  The use of open window  29  allows a larger head to fit, into a smaller, closer fitting, and therefore more efficient coil  24 .  
         [0051]    [0051]FIG. 3 shows an enlarged view of FIG. 2 a.  With respect to FIG. 3, combination head restraints  30  and head cupped cushion  31  are shown. As stated above, regardless of the amount of padding used to prevent motion of the subject&#39;s head there is inevitably still some motion. Moreover, the padding can cause the subject some discomfort from compression and an increased feeling of claustrophobia. Combination head restraints  30  and head cushion  31  of the present invention not only provide an improved cushioned 3-point head restraint system from an ergonomics&#39; viewpoint, but head restraints  30  also provide communications to the subject from the MR operator, relaxing music or other entertainment to the subject, and hearing protection by passive or active sound suppression means. Audio input into the head restraints  30  may be by cable, optic fiber, sound tube, or wireless means.  
         [0052]    As can be seen from FIG. 3, head restraint earpieces  30  can be positioned in any direction to accommodate the size of the subject&#39;s head. Furthermore, head restraints  30  and head cushion  31  may come in a variety of sizes for use on a variety of subjects. Head restraints  30  and head cushion  31  would be chosen, depending on the subject&#39;s head size to ensure that the subject&#39;s head is held snugly in coil  24  to prevent motion, but not so snug as to cause pain. Further, because head restraints  30  and head cushion  31  are compact they do not crowd coil  24 , thus allowing the use of a smaller more efficient coil while reducing any feeling of claustrophobia. Other methods of adjusting head restraints  30  and head cushion  31  are contemplated, such as having cushions that can expand and contract to the subject&#39;s head by simply rotating them in a clockwise-counterclockwise motion, cams, or other means without departing from the spirit of the invention. With further reference to FIG. 3, guiding slots  32  are shown. Guiding slots assist in assuring mutual alignment between top section  28  and bottom section  26 .  
         [0053]    With reference to FIGS. 4 &amp; 5, an I/O device of the present invention is shown. I/O device  40  can be any type of I/O device including but not limited to mirrors, prisms, video monitors, LCD devices, optical motion trackers, etc. In one embodiment I/O device  40  has a front mirror  44  and a rear mirror  46  facing the front and rear of coil  24  respectively and is mounted on track  42  over the subject&#39;s face. I/O device  40  can then be adjusted to multiple positions, directions, and configurations without moving the subject. Further, in contrast to prior systems where the outside radius of the coil is increased by mounting I/O device(s) on top of or extending from the top of a coil, I/O device  40  is mounted wholly or in part within the radius or outside dimensions of coil  24 . It can be seen from FIGS. 4 &amp; 5 that I/O device  40  is particularly well suited for mounting inside open window  29  (discussed in more detail above) above the face in coil  24 . I/O device  40  can be moved along track  42  from one end of the coil to the other. By sliding I/O device  40  along track  42 , it can be adjusted to any subject&#39;s useful viewing angle, including looking forward or backward. For example: receiving visual information projected to the subject from the front or the back of the MR magnet (discussed in more detail below). The versatile and low profile construction of I/O device  40  allows for coil  24  to be used in close fitting head only MR systems, and in head gradient inserts used in whole body MR systems. Further, it is contemplated I/O device  40  could be replaced or complemented by similar platforms to perform other I/O functions such as positioning temperature, air, oxygen, anesthesia, IV tubes, or the like relative to a subject&#39;s mouth or nose. It is further contemplated that input/output device  40  can be any visual, olfactory, gustatory, or auditory transducers providing two way communication or stimulus. I/O devices can also be used for delivery of therapy, robotic execution of surgery, and physiological monitoring including temperature, blood pressure, respiration, EEG, EKG, etc.  
         [0054]    With respect to FIG. 6, a front view of a resonator is shown. As discussed above, back planes on RF coils function as an RF mirror to extend the uniformity of the coil&#39;s transverse RF magnetic field along the rotational or “z” axis of the coil. The lack of end rings on a TEM coil further enhances the field extent on the z-axis. A back plane or end cap can be used in coil  24  located within back wall  62  to make the coil shorter on the z axis, and therefore more ergonomic, better shielded, and more electrically efficient coil for a desired field of view. In coil  24  for example, back wall  62  of coil  24  housing a back plane makes it possible to build a coil short enough to fully expose a subject&#39;s mouth, and make the coil more efficient at higher frequencies, while still covering the whole head field of view desired for a standard head coil. In contrast, a conventional cylindrical birdcage head coil without an end cap may be twice as long, less efficient at high frequencies, and more prone to promoting claustrophobia. A back wall in a head coil is more desirable for coil performance and ergonomics on the “mouth” end of the coil.  
         [0055]    Visual signal projection is often performed from the rear of a magnet and through the back of a coil to mirror or prism systems mounted above the subjects&#39; eyes. Blocking this access with a coil back plane or endcap therefore prevents visual signal projection. The present invention solves the rear magnet access problem; at least in part by providing a substantial channel  60  in back wall  62  of coil  24 . Opening  60  is located high in coil  24  to minimally affect the imaging performance in the head area of coil  24  while giving maximum access for rear visual projection systems. Therefore, opening  60  allows the coil  24  to preserve the advantages of a closed end coil, while allowing for most of the benefits of an open-ended coil. Further, channel  60  provides general medical access for temperature, air, oxygen, anesthesia, IV tubes, EEGleads, physiological monitors, or the like.  
         [0056]    It will be appreciated that the present invention can take many forms and embodiments. The true essence and spirit of this invention are defined in the appended claims, and it is not intended that the embodiment of the invention presented herein should limit the scope thereof.