Abstract:
A MRI array coil includes a plurality of first coils in a receive coil array and a plurality of second coils in a transmit coil array. The receive coil array and the transmit coil array are electrically disjoint.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. provisional patent application Ser. No. 60/274,523 filed Mar. 8, 2001. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to magnetic resonance imaging and, in particular, to radio frequency coils. 
   Radio frequency (RF) coils are used produce and/or sense the magnetic resonance (MR) signal used in magnetic resonance imaging (MRI). A main static magnetic field aligns the nuclei of interest, gradient coils provide indicia of spacial location and the transmit and receive RF coils produce the desired contrast signal. 
   A MR scanner with a horizontally directed main field will normally have the main field parallel with the scanner&#39;s main symmetry plane. These scanners are the original MR scanners. 
   A MR scanner with a vertically directed main field will normally have the main field orthogonal to the pole surface and to the main magnet&#39;s symmetry plane. These scanners are normally called open magnet MR scanners. 
   Signal to noise ratios (SNRs) for RF receive coils have been increased by the use of smaller receive coils. In order to preserve the desired field of view (FOV), such receive coils have been combined into a phased array of such coils. In some cases a large transmit RF coil is used for the entire FOV. In other cases, one or more of the receive coils is operated as a transceiver coil, both exciting the nuclei and sensing the resulting signal. 
   As main field strength has increased, it has become difficult to power a single large transmit coil for rapid imaging applications at high field strength. The alternative has been to use smaller transceiver coils as part of a coil array, but these have other problems. Because of coils being used for both transmitting and receiving, there is no means to optimize such factors as field uniformity for both transmitting and receiving. In addition, decoupling and phase correction of the coils in an array becomes more complicated and difficult. 
   SUMMARY OF THE INVENTION 
   A MRI array coil includes a plurality of first coils in a receive coil array and a plurality of second coils in a transmit coil array. The receive coil array and the transmit coil array are electrically disjoint. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of an array coil according to the invention having a whole body field of view. 
       FIG. 2  is a schematic diagram of another array coil according to the invention having a whole body field of view. 
       FIG. 3  is a schematic diagram of an array coil according to the invention having an upper body field of view. 
       FIG. 4  is a schematic diagram of an array coil according to the invention having a head and chest field of view. 
       FIG. 5  is a schematic diagram of an array coil according to the invention having a torso and/or pelvis field of view. 
       FIG. 6  is a schematic diagram of an array coil according to the invention having a knee and/or foot field of view. 
       FIG. 7  is a schematic diagram of an array coil according to the invention having a spine and/or neck field of view. 
       FIG. 8  is a schematic diagram of an array coil according to the invention having a cardiac and/or abdominal field of view. 
       FIG. 9  is a block diagram of a possible driver configuration for the array coils of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a MRI array coil  10  is shown positioned about the body  12  of a subject. The FOV of the coil  10  can include the whole of the body  12 . The transmit coil array  14  and the receive coil array  16  are integrated into a common support structure, which is not shown. The support structure may be, for example, plastic, foam or other suitable materials in such forms, for example, as clamshell, split-top, solid or split into various sections suitable for arranging about the subject. The individual coils may be chosen as linear or quadrature and surface or volume, depending on the desired application. The embodiment of  FIG. 1  has a one-to-one correspondence between transmit and receive coils. The transmit coil array  14  and the receive coil  16  are electrically disjoint. 
   During transmission selected transmit coils are turned on and all the receive coils are turned off and during receiving selected receive coils are turned on and all of the transmit coils are turned off. 
   The use of small coils with respect the overall FOV allows relatively low power to be applied to the transmit coil array  14  compared to a large coil encompassing the entire FOV and a high signal to noise ratio to be achieved with the receive coil array  16 . In addition, because the arrays  14 ,  16  are electrically disjoint, each array can be optimized for its function, transmit or receive. Also, decoupling and phase correction can be independently pursued for each array. The small size of all of the coils also permits optimal conformance with the subject with resulting improvements in SNR. 
   It should be apparent to one skilled in the art that an MRI array coil such as this can be used in horizontal as well as vertical field MR scanners. The use of such MRI array coils have the further advantage of limiting unnecessary RF leakage out of the imaging region and thus eliminating aliasing or cusp artifacts. 
   Referring to  FIG. 2 , a MRI array coil  20  similar to the array coil  10  is illustrated. This embodiment has unequal numbers of transmit and receive coils. In this case, a transmit coil may be associated with more than one receive coil. 
   Referring to  FIG. 3 , a similar MRI array coil  30  illustrates a MRI coil array having a FOV covering the upper half of the subject. 
   Referring to  FIG. 4 , a similar MRI array coil  40  illustrates a MRI coil array having a FOV covering the head and chest of the subject, suitable for neurovascular imaging. 
   Referring to  FIG. 5 , a similar MRI array coil  50  illustrates a MRI coil array having a FOV covering the torso and/or the pelvis of the subject. 
   Referring to  FIG. 6 , a similar MRI array coil  60  illustrates a MRI coil array having a FOV covering the knee and/or the foot of the subject. 
   Referring to  FIG. 7 , a similar MRI array coil  70  illustrates a MRI coil array having a FOV covering the spine and/or the neck of the subject. 
   Referring to  FIG. 8 , a similar MRI array coil  80  illustrates a MRI coil array having a FOV covering the cardiac and/or abdominal areas of the subject. 
   Referring to  FIG. 9 , a possible driver configuration for the transmit coil array is illustrated. An RF amplifier  92  provides RF power to a divider network  94  that divides the RF power for application to each of coils of the transmit array. The phase of the signal is adjusted with a phase shifter  96  and the amplitude is adjusted with the gain  98 . 
   It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.