Abstract:
The vest provides a simple and intuitive coil support assuring proper alignment of the coils with the patient and providing support for coil elements encircling the opposed arms. 
     A coil for receiving and/or transmitting radio-frequency signals for magnetic resonance imaging of the chest, and particularly for ventilation studies of the lungs, is supported in a flexible vest having arm holes locating the coil elements about the patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on provisional application No. 60/283,452 filed Apr. 12, 2001 and entitled “Vest Coil” and claims the benefit thereof. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     BACKGROUND OF THE INVENTION 
     Whereas magnetic resonance imaging (MRI) most frequently images the protons of water molecules, these conventional techniques have trouble imaging lung tissue. MR imaging of the lung is difficult because of the low proton density, resulting in a weak MR signal, and significant susceptibility artifacts. 
     These problems have been overcome by using a contrast agent in the form of a hyperpolarized gas, such as Helium 3 or Xenon 129, polarized by optical pumping using a laser. Measurements of lung physiology and function using such hyperpolarized contrast agents are determined by lung ventilation studies and are known in the art. 
     While the signal provided by hyperpolarized gas is improved over that normally available from lung tissue, it would be desirable to provide for improved signal generation and detection during lung ventilation studies. 
     SUMMARY OF THE INVENTION 
     The present invention provides a radiofrequecy coil for magnetic resonance imaging where the coil structure is supported on a vest having opposed arm holes for receiving the patient&#39;s arms and wrapping around the patient&#39;s body to receive magnetic resonance image signals from the region of the patient&#39;s lungs. 
     It is one object of the invention to provide an intuitive and comfortable support for radio-frequency coils used to image the lungs. Another object of the invention is to provide an improved local coil suitable for lung ventilation studies. 
     The coil structure may include at least one coil encircling an armhole and preferably two coils, one passing around each of the opposed armholes. 
     Thus, it is another object of the invention to provide a coil support that gives good lateral coverage of the lungs such as requires coil conductors above and below the arms. It is another object of the invention to provide a simple and intuitive coil support that ensures proper alignment of the coils with respect to the patient. 
     The vest structure includes side panels having the armholes and a front and back panel extending between the side panels and wherein the front and back panels include coils. The coil elements encircling each of the opposed arm holes may provide a first Helmholtz coil pair and the front and back panels may support a second Helmholtz coil pair perpendicular to the first. Alternatively, the coil element encircling each of the opposed armholes and the coil elements in the front and back panels provide independent signals for phased array studies. 
     It is thus another object of the invention to provide flexible, multiple coil coverage of the lungs. 
     The vest structure is constructed of a flexible material to wrap around the patient. The vest structure includes a separable portion disposed between the opposed armholes along an opening of the vest structure so that the vest structure may be put on by a patient in part by wrapping it about the patient. A closure means holding the separable portions in varying spatial relationships when the vest structure is wrapped about the patient to accommodate patients of different chest sizes. 
     Thus, it is another object of the invention to provide a comfortable coil structure that is easy to put on and that accommodates many different patients. 
     The vest structure includes an outer fabric shell supporting therein a set of layered, independently slidable flexible leaves including at least one flexible printed circuit board. At least one of the leaves may be an elastomeric plastic foam which may include a sliding layer on at least one surface. 
     Thus, it is another object of the invention to incorporate a coil structure into a vest so that the coil is flexible, comfortable, and robust. 
     The foregoing and other objects and advantages of the invention will appear from the following description. In this description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment and its particular objects and advantages do not define the scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view of the vest coil of  FIG. 1  unwrapped prior to being worn by a patient and showing the coil locations in phantom as positioned with respect to the vest coil arm holes; 
         FIG. 2  is a perspective view of the vest coil of the present invention in position on a patient; 
         FIG. 3  is a simplified perspective view of the coils of the vest coil positioned as when the patient is wearing the vest coil per  FIG. 1 ; and 
         FIG. 4  is an exploded perspective view of the vest coil showing the layers from which it is assembled. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIGS. 1 and 2 , the present invention provides a local coil  10  incorporated into a vest  12  that may be worn by the patient  14 . 
     The vest  12  includes a generally rectangular front panel  16  joined at one vertical edge to the corresponding edge of a generally rectangular right side panel  18  having an arm hole  20  positioned near its upper edge. The opposite vertical edge of right side panel  18  is joined to a corresponding edge of a generally rectangular rear panel  24  that may fit adjacent to the back of the patient  14  in the manner of a conventional vest. The opposite vertical edge of the rear panel  24  joins in turn with the corresponding edge of a generally rectangular left side panel  22  having an armhole  20 . 
     The panels  18 ,  24  and  22  and  16  provide for fabric hinges at their joined edges to wrap about the patient with the patient&#39;s arms through the armhole  20 . A connection between panels  16  and  22  is provided by a series of hook and loop fastener (Velcro) surfaced straps  26  providing loops extending from the uncommitted vertical edge of left side panel  22  attaching to corresponding hooks  28  on the outer surface of the front panel  16 . The straps and Velcro allow the vest to be adapted to patients of differing chest sizes. 
     The rectangular rear panel  24  includes a tab  33  extending below the edges of the front panel  16 , the right side panel  18  and the left side panel  22 . 
     Placement of the vest about the patient  14  is in the manner of a standard vest to cover the vertical extent of the lungs of the patient  14 . The connection between panels  16  and  12  is offset to the right of the patient  14  to provide for an uninterrupted front panel  16  for coil support. 
     Referring now to  FIGS. 1 and 3 , panels  16 ,  18 ,  24 , and  22  may support coils  36 ,  30 ,  32 , and  34 , respectively. The coils  34  and  30  are sized to encompass armholes  20  for panels  18  and  22  and of equal size to extend above and below the lung volume of the patient  14  when the vest is in place about the patient  14 . 
     Referring now to  FIG. 3 , in one embodiment, pairs of the coils  30 ,  32 ,  34 , and  36  are connected in Helmholtz configuration with coil  30  connected to opposing coil  34  along a first axis  35  and coil  32  connected to opposing coil  36  along axis  37  perpendicular to axis  35  and crossing the patient. Thus, coils  30  and  34  will obtain a sensitivity across the patient from arm to arm whereas coils  32  and  36  will obtain the sensitivity in the anterior/posterior direction. Connecting conductors  40  and  42  join the coils to provide co-cyclic current flows through the opposing coil pairs per this Helmholtz configuration. 
     The coil pairs  30  and  34  may be excited and/or may provide a signal through a coupling network  44  held in tab  33  of a type well known in the art and coil pairs  32  and  36  may be excited and/or may provide a signal through coupling network  46  also of a type well known in the art. The signals from coupling network  44  and  46  through leads  41  may be combined by a network  50  (shifting one signal by 90 degrees) to provide a quadrature signal on lead  52  improving signal-to-noise ratio. 
     In an alternative embodiment, the coils  30 ,  32 ,  34 , and  36  are connected to provide separate output signals and may be used, for example, in four channel, or phased array operation according to methods known in the art. 
     Coils  30 ,  32 ,  34 , and  36  may be tuned to the Lamor frequency of the hyperpolarized gas by series capacitors (not shown), but of a type well known in the art. In addition, decoupling networks may be attached to the coils  30 ,  32 ,  34 , and  36  (not shown) to shield the coil from sensitivity to an exciting RF pulse when an external RF field is used in a magnetic resonance imaging machine. 
     Referring now to  FIG. 4 , the coil  10  may be constructed in laminated form of a number of layers laminated together and held within a fabric shell  55 . A top layer  54  may comprise a layer of elastomeric foam (for example, polyurethane) to provide cushioning in the outer surface of the coil adjacent to the inner surface of the fabric shell  55 . Next, a layer  56  may provide for a fluoro-glass separator providing a smooth surface to prevent frictional shear between layer  56  and succeeding polyurethane foam layer  58 . The fluoro-glass separator of layer  56  may be glued to foam layer  54  but is separate from and presents a slick surface to succeeding layers. 
     Succeeding polyurethane foam layer  58  provides a second layer of foam which is followed by a succeeding layer of fluoro-glass  60  (adhered to layer  58  only) which again provides flexibility and protection to the next layer which is a flexible printed circuit board layer  62  printed with the coil patterns shown in  FIG. 1 . The flexible printed circuit board layer  62  may be of a conventional design having copper foil etched or laminated to a polymide film (Kapton) sheet that may flex as the coil form is formed about the patient and includes leads  40  and  42  and coupling networks  44  and  56 . 
     These layers are repeated in reverse order for the obverse side of printed circuit board  62  starting with layer  64  which is a fluoro-glass divider attached to the top of layer  66  which is an additional layer of polyurethane foam followed by layer  68  which provides a plastic reinforcement followed by layer  70  which is a fluoro-glass layer followed by and attached to, in turn, an outer second layer  72  of polyurethane foam. 
     Each of the layers (except as noted) is free to slide with respect to the other layers so that the vest  10  may be easily wrapped around the patient  14  without crushing or stretching of a given layer or undue resistance to bending. Flexibility is further enhanced by the thinness of the layers which add to about one-half inch total thickness. 
     The lead  41  extends from the rear of the coil  10  on the printed circuit board layer  62  and may pass to the tab  33  shown in  FIG. 1  holding the hybrid networks  44 ,  46  and  50  and supporting lead  52  which extends downward therefrom. 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.