Abstract:
A magnetic resonance imaging (MRI) array coil system and method for breast imaging are provided. The MRI array coil system includes a top coil portion with two openings configured to receive therethrough objects to be imaged. The MRI array coil system further includes a bottom coil portion having two openings configured to access from sides of the bottom coil portion the objects to be imaged. The top coil portion and bottom coil portion each have a plurality of coil elements configured to provide parallel imaging.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to and the benefit of the filing date of U.S. Provisional Application No. 60/523,456 filed on Nov. 19, 2003 and which is hereby incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to Magnetic Resonance Imaging (MRI) systems, and more particularly, to Radio-Frequency (RF) coils in MRI systems. 
   In MRI, the RF receive coil is one of the most important hardware components in the imaging system. A special-purpose receive coil for a region of interest is typically used for reception to enhance the signal-to-noise ratio (SNR) at that region. 
   For RF receive coils, it is known to further increase SNR using quadrature reception. In quadrature reception, NMR signals are detected in two orthogonal directions, which are in the transverse plane or perpendicular to the main magnetic field. The two signals are detected by two independent individual coils that cover the same volume of interest. With quadrature reception, the SNR can be increased, for example, by up to √2 over that of the individual linear coils. 
   Known receive coils are designed to provide higher image SNR. Further, with the use of parallel imaging techniques, not only is higher image quality provided, but higher scan speeds are provided without corresponding reduction in SNR. 
   Sensitivity Encoding (SENSE) is one techniques for parallel imaging that uses multiple coils to scan faster. Using SENSE, spatial sensitivity information provided by each coil element of a multiple-coil array system is used to substitute for the information provided by the encoding gradient in the k-space, therefore saving scanning time. The aliased or wrapped images generated by omitting the k-space lines are reconstructed by spatial sensitivity information provided by coil elements. Systems having SENSE compatible coils typically include a number of coil elements, with each of the coil elements providing distinctive spatial sensitivity information. 
   SENSE imaging may be used in different imaging applications, for example, for breast MRI. Breast MRI provides, for example, higher sensitivity when compared to other modalities. Changing magnetic resonance techniques and updated clinical imaging protocols result in a need for RF coils for breast imaging that provide high-resolution images, provide fast scanning speed with the application of the SENSE technique, and facilitate image guided biopsy and needle localization. The SENSE technique can greatly reduce the scan time, but typically requires arrays of multiple receiver coils that surround the tissue of interest. Known coils dedicated to breast MRI have very limited SENSE capability, if any at all, limited coverage, reduced SNR, more complex designs or decoupling arrangements, and/or are configured having a closed coil geometry that is unable to provide or provides limited biopsy access. Thus, these known coil designs for breast imaging are often complex and do not provide adequate or sufficient openness of the coils to allow medial and lateral biopsy access. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one embodiment, an MRI array coil system is provided having a top coil portion with two openings configured to receive therethrough objects to be imaged. The MRI array coil system further includes a bottom coil portion having two openings configured to access from sides of the bottom coil portion the objects to be imaged. The top coil portion and bottom coil portion each have a plurality of coil elements configured to provide parallel imaging. 
   In another embodiment, a method for magnetic resonance imaging is provided and includes configuring openings in a top coil portion of a coil array to receive breasts therethrough. The method further includes providing at least one of lateral and medial access to the breasts through a bottom coil portion of the coil array. The top coil portion and bottom coil portion each have a plurality of coil elements configured to provide parallel imaging. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an MRI array coil system in accordance with an embodiment of the present invention. 
       FIG. 2  is a perspective view of a main coil chamber of the MRI array coil system of  FIG. 1 . 
       FIG. 3 . is a perspective view of the MRI array coil system of  FIG. 1  showing the main coil chamber detached. 
       FIG. 4  is a side elevation view of the MRI array coil system of  FIG. 1 . 
       FIG. 5  is a front elevation view of a top coil portion of the MRI array coil system of  FIG. 1 . 
       FIG. 6  is a front elevation view of the top coil portion of the MRI array coil system of  FIG. 1  showing a body therein. 
       FIG. 7  is a front elevation view of a top coil portion of an MRI array coil system in accordance with another embodiment of the invention. 
       FIG. 8  is a front elevation view of the MRI array coil system of  FIG. 1  showing a torso therein. 
       FIG. 9  is a front elevation view of the MRI array coil system of  FIG. 1  showing access from a side window in accordance with one embodiment of the invention. 
       FIG. 10  is a side elevation view of the MRI array coil system of  FIG. 1  showing access from another window in accordance with an embodiment of the invention. 
       FIG. 11  is a schematic diagram of the MRI array coil system of  FIG. 1 . 
       FIG. 12  is another schematic diagram of the MRI array coil system of  FIG. 1 . 
       FIG. 13  is a schematic diagram of another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 14  is another schematic diagram of the MRI array coil system of  FIG. 13 . 
       FIG. 15  is a schematic diagram of another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 16  is a schematic diagram of another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 17  is a schematic diagram of another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 18  is a schematic diagram of another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 19  is a schematic diagram of another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 20 . A schematic diagram of another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 21  is a schematic diagram of another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 22  is a schematic diagram of the another embodiment of the MRI array coil system of  FIG. 1 . 
       FIG. 23  is a schematic diagram of another embodiment of the MRI coil array system of  FIG. 1 . 
       FIG. 24  is a schematic diagram of another embodiment of the MRI coil array system of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows an MRI array coil system  1  constructed in accordance with one embodiment of the present invention. The MRI array coil system  1  generally includes a main coil chamber  2 , a main bottom coil housing  6 , a right wing  7  and a left wing  8 . The main coil chamber  2 , as shown in  FIG. 2 , is formed by a top coil portion, for example, a top coil plate  3  and a bottom coil portion, for example, a bottom coil former  4 . The top coil plate  3  and the bottom coil former  4  are fixedly (e.g., permanently) connected in this embodiment. A right opening  13  and a left opening  14  are provided on the top coil plate  3  to receive the imaged objects (e.g., the left and right breasts of a human). The ends of the main coil chamber  2  also are open forming two windows  11  (right window) and  12  (left window), to allow access from both ends of the main coil chamber  2 . Two wings  7  and  8  may be provided on rigid or semi-flexible formers that may be attached to the two ends of the top coil plate  3  as shown in  FIG. 1 . 
   In another embodiment, as shown in  FIG. 3 , the main coil chamber  2  may be formed by two separate pieces: a top coil portion, for example, a top coil former  5  and a bottom coil portion, for example, a bottom coil former  4  that may be removably connected together. It should be noted that the bottom coil former  4  may be fixedly or removably connected to the main bottom coil housing  6 . The two ends of the top coil former  5  may be bent upward to form the two wings  7  and  8  or the two wings may be provided on two separate rigid or semi-flexible formers and may be attached to the two ends of the top coil plate  3  defined by a former. The left and right ends of the main coil chamber  2  are open forming the windows  11  (for the right end) and  12  (for the left end), to allow access from both ends of the main coil chamber  2  as illustrated in  FIG. 3  by two arrows. 
   The shape of the cross-section of the main coil chamber  2  may be semi-elliptical, as shown in  FIG. 4 . In one embodiment, the main coil chamber  2  has a long-axis D 1  of about 15 cm to about 25 cm along the superior-inferior direction and a short-axis D 2  of about 7 cm to about 15 cm along the up-down direction. The patient contact surface of the top coil plate  3  or the top coil former  5  may be curved or flat. The shape of the top coil plate  3 , as shown in  FIG. 5 , and in one embodiment, may be defined by a length B 1  of about 28 cm to about 36 cm and a height B 3  of about 0 cm to about 5 cm or by the length B 1  and an angle A 1  of about zero degrees to about twenty degrees formed between a tangential line at a region close to an end of the top coil former  5  and a horizontal line. The shape and the position of the two wings  7  and  8  may be defined, as shown in  FIG. 5 , by a distance B 2  of about 5 cm to about 15 cm between a top edge and a horizontal line and an angle A 2  of about twenty degrees and about eighty degrees between a tangential line along a side of a wing  7  or  8  and a horizontal line.  FIGS. 6 and 7  illustrate, respectively, a top coil plate  3  with A 2  being about eighty degrees for example, for a small size patient, and A 2  being about twenty degrees for example, for a large size patient. The wings  7  and  8  may be provided on flexible or semi-flexible formers so that their shapes and positions can be adjusted, for example, by a user, based on a patient&#39;s size and body profile. 
     FIG. 8  shows a patient positioned in the MRI array coil system  1  with lateral access to the breasts of a patient thereby provided. A patient lies face downward (i.e., prone) on the MRI array coil system  1 , which provides support to the patient&#39;s torso  100 , with a chest  103  of the patient torso  100  contacting or touching the top coil plate  3 . It should be noted that the superior direction is out of the plane of the  FIG. 8  and the inferior direction is into the plane of  FIG. 8 . The right and left openings  13  and  14  on the top coil plate  3  receive the right and left breasts  101  and  102  of the patient torso  100  and the breasts  101  and  102  enter the main coil chamber  2 . The right breast  101  of the patient is accessible from the right window  11  as illustrated in  FIG. 8  by the arrow through the right window  11 . The left breast  102  of the patient is accessible from the left window  12  as illustrated in  FIG. 8  by the arrow through the left window  12 . 
     FIGS. 9 and 10  illustrate medial access to the breasts of a patient. In  FIG. 9 , the right portion of the patient&#39;s torso  100  and the right breast  101  are elevated to a suitable height to allow the left breast  102  of the patient to be accessed from the right window  11 . In  FIG. 10 , the left portion of the patient&#39;s torso  100  and the left breast  102  are elevated to a suitable height to allow the right breast  101  of the patient to be accessed from the left window  12 . 
   The electrical arrangement of the coil elements of the MRI array coil system  1  of various embodiments of the present invention include at least eight coil elements (e.g., RF coil elements).  FIGS. 11 and 12  show an eight-element MRI array coil system  1  in accordance with one embodiment that includes four loop coils  21 ,  22 ,  23  and  24  for right breast imaging and four loop coils  30 ,  27 ,  28  and  29  for left breast imaging.  FIG. 11  shows the eight coil elements separated for ease in illustrating and  FIG. 12  shows the eight coil elements in an operational position. Loop coils  21  and  30  are provided, respectively, around the right and left openings  13  and  14  (shown in  FIGS. 1 and 2 ) of the top coil plate  3  (shown in  FIGS. 1 and 2 ) for imaging the right breast  101 , left breast  102  and chest  103  of a human. Loop coils  24  and  27  are provided, respectively, around the right and left windows  11  and  12  (shown in  FIGS. 1 and 2 ) of the main coil chamber  2  (shown in  FIGS. 1 and 2 ) to provide lateral coverage for the right and left breasts  101  and  102 . Loop coils  22  and  23  are provided in the superior-inferior direction on the bottom coil former  4  to receive signals mainly from the lower portion of right breast  101 . Loop coils  28  and  29  are similarly provided in the superior-inferior direction on the bottom coil former  4  to receive signals mainly from the lower portion of left breast. 
   In operation, the four loop coils for right breast  21 ,  22 ,  23  and  24  distribute in all the three directions (i.e., left-right, superior-inferior and up-down directions). The four loop coils for left breast  27 ,  28   29  and  30  also distribute in all three directions. This arrangement allow the four coil elements around a breast to provide sensitivity encoding capability in all three directions for the breast and allow, for example, 3D SENSE imaging for unilateral breast imaging. SENSE imaging efficiency is the same in both the superior-inferior and up-down directions for bilateral breast imaging as that for unilateral breast imaging. In the bilateral imaging mode, SENSE imaging efficiency in the left-right direction is higher than in unilateral imaging mode. 
   In other embodiments as shown in  FIGS. 13 and 14 , two lateral loop coils  25  and  27  for imaging the right breast and left breast, respectively, may be provided. The MRI array coil system  1  in these embodiments are a ten-element design.  FIG. 14  shows the coil elements in their operational positions. 
   In another embodiment, the four loop coils  22 ,  23 ,  29  and  28  on the bottom coil former  4  of the eight-element design shown in  FIGS. 11 and 12  may be replaced by four saddle coils  41 ,  42 ,  43  and  44 , as shown in  FIG. 15 . Similarly, the four loop coils  22 ,  23 ,  29  and  28  on the bottom coil former  4  of the ten-element design as shown in  FIGS. 13 and 14  also may be replaced by four saddle coils  41 ,  42 ,  43  and  44 , as shown in  FIG. 16 . Further, the four saddle coils  41 ,  42 ,  43  and  44  may be added to the ten-element design to form four quadrature (QD) pairs  51 ,  52 ,  53  and  54  with the four loop coils  22 ,  23 ,  29  and  28  as shown in  FIG. 17 . The MRI array coil system  1  in this embodiment is a fourteen-element design. 
   Two loop coils  31  and  32  may be provided to this fourteen-element design for the two wings  7  and  8 , as shown in  FIG. 18 , and which improves SNR and SENSE imaging efficiency in the left-right direction for chest region imaging. The MRI array coil system  1  in this embodiment is a sixteen-element design. 
   Fours loop coils  33 ,  34 ,  35  and  36  may be provided to fourteen-element design, as shown in  FIG. 19 , and improves SNR and SENSE imaging efficiency in the superior-inferior direction for chest region. As shown in  FIG. 19 , loop coils  33  and  34  are for right breast  101  and loop coils  35  and  36  are for left breast  102 . The MRI array coil system  1  in this embodiment is an eighteen-element design. 
   The four loop coils  33 ,  34 ,  35  and  36  in the eighteen-element design may be replaced by four saddle coils  45 ,  46 ,  47  and  48  as shown in  FIG. 20 . Further, the four saddle coils  45 ,  46 ,  47  and  48  may be added to the eighteen-element design to form four quadrature (QD) pairs  55 ,  56 ,  57  and  58  with the four loop coils  33 ,  34 ,  35  and  36  as shown in  FIG. 21 . The MRI array coil system  1  in this embodiment is a twenty-two-element design. Loop coils  31  and  32  may also be added to this twenty-two-element design for the two wings  7  and  8 , as shown in  FIG. 22 . The MRI array coil system  1  in this embodiment is a twenty-four-element design. 
   In operation, depending on the type of imaging system in connection with which the MRI array coil system  1  is used, and the number of coils provided in the MRI array coil system  1 , a MRI scanner having more than eight receivers, for example, a MRI scanner with a minimum of twenty-four receivers may be needed for the MRI array coil system  1  of the twenty-four-element design. For example, for a eight-receiver MRI scanner, the eight-element design as shown in  FIG. 12  may be used. However, with other embodiments having more than eight elements, an MRI scanner having more receivers or channels may be needed 
   Further, modifications may be provided to MRI array coil system  1 , for example, in order to improve the SNR and SENSE imaging efficiency in the left-right direction for chest region for the eight-element design. For example, the two lateral loop coils  24  and  27  may be extended upwards to form the two wings  7  and  8 , respectively, as shown in  FIG. 23 . The circuitry of the right wing  7 , shown in  FIG. 24 , may be formed partially (e.g., about one-half) by the right lateral loop  24  and partially (e.g., about one-half) by the right chest loop  21 . The circuitry of the left wing  8 , shown in  FIG. 24 , also may be formed partially (e.g., about one-half) by the left lateral loop  27  and partially (e.g., about one-half) by the left chest loop  30 . These circuitry configurations of the wings of the MRI array coil system  1  of, for example, the eight-element design, further improve SENSE imaging efficiency in the superior-inferior direction for chest region imaging. 
   Thus, various embodiments of the present invention provide open ends, for example, the two windows  11  and  12  of the MRI array coil system  1  that allow access to one window from the other window through the main coil chamber. This provides lateral access to the breasts being imaged (e.g., accessing the right breast from the right window or accessing the left breast from the left window), thereby allowing for lateral breast biopsy applications. Further, medial access to the breasts being imaged (e.g., accessing the right breast from the left window or accessing the left breast from the right window) also is provided with the MRI array coil system  1 . 
   The curved patient contact surface of the top coil plate  3  and flexible wings  7  and  8  of the MRI array coil system  1  accommodates various body profiles of patients, thus providing a more patient friendly design. 
   The semi-elliptical shaped cross-section of the bottom coil former  4  of the main coil chamber  2  allows the coil elements that are provided on the bottom coil former  4  to be closer to the imaged objects (e.g., breasts of a human), and to provide better SNR and coverage. 
   The MRI array coil system  1  also may provide eight to twenty-four coil elements (e.g., channels), to allow use in connection with an MRI scanner having eight or higher numbers of receivers. It should be noted that the coil elements are isolated from each other through geometric isolation and/or preamplifier decoupling and/or using transformers. Therefore, all the coil elements of the MRI array coil system  1  may be used simultaneously to provide imaging on a multi-channel MRI scanner. 
   The MRI array coil system  1  further provides two separate sets of coil elements: one set for the right breast and the other set for the left breast. Each set of coil elements can be used separately to achieve unilateral imaging for one of the two breasts of a patient. When both sets of coil elements are used, bilateral imaging for both the breasts of a patient can be obtained. The coil elements around each breast distribute in all the three directions (i.e., left-right, superior-inferior and up-down directions). These arrangements provide sensitivity encoding capability in all the three directions for the breast and allow for 3D SENSE unilateral breast imaging. Higher SENSE imaging efficiency in the left-right direction may be provided when both sets of coil elements are used for the bilateral imaging mode. 
   The two wings  7  and  8  of the MRI array coil system  1  also provide improved coverage for the chest wall region of a patient. The two wings  7  and  8  allow the coil elements to further distribute in the left-right direction around the chest region of a patient and improve SENSE imaging efficiency in the left-right direction for chest region. In addition, the four loop coils  33 ,  34 ,  35  and  36 , distributing in the superior-inferior direction around chest region, not only provide higher SNR and better coverage, but also enhance SENSE imaging efficiency in the superior-inferior direction for chest region. 
   The eight quadrature coil pairs  51 ,  52 ,  53 ,  54 ,  55 ,  56 ,  57  and  58 , formed by the eight loop coils  22 ,  23 ,  29 ,  28 ,  33 ,  34 ,  35  and  36  and the eight saddle coils  41 ,  42 ,  43 ,  44 ,  45 ,  46 ,  47  and  48 , provide higher SNR for the chest region by providing quadrature signal detection, and also provide improved SENSE imaging efficiency in the superior-inferior direction resulting from the additional information of the phase of the local sensitivity of each saddle coil. 
   Thus, a multiple channel MRI array coil system that can be used on a MRI scanner equipped with eight or higher numbers of receivers for both unilateral and bilateral breast imaging is provided. Lateral biopsy access is provided such that the left breast of a patient can be accessed from the left open end of the imaging chamber and the right breast of the patient can be accessed from the right open end of the imaging chamber. Medial biopsy access also is provided such that a patient&#39;s left breast can be accessed from the right open end of the imaging chamber, and the right breast can be accessed from the left open end of the imaging chamber. 
   The MRI array coil system  1  also further provides sensitivity encoding in all three, x, y, and z, directions and for both the unilateral and bilateral imaging modes. Coil elements are distributed in the left-right, superior-inferior and up-down directions for both left and right breasts such that 3D SENSE imaging can be performed in all the three directions for both breasts of a patient. Improved coverage for the chest wall and axilla regions of a patient is also provided. 
   Sensitivity encoding in all three, x, y, and z, directions for the chest wall regions is additionally provided. Thus, 3D SENSE imaging also may be performed for the chest wall regions. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.