Abstract:
A hybrid magnetic resonance (MR) and positron emission tomography (PET) imaging system reduces likelihood of artifact distortion in PET images attributable to MR local coil cables and connectors in the patient table. MR local coil cables coupling the MR scanner and the MR local coil connectors are oriented so that they are outside the scanner field of view when performing PET scans.

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Invention 
     The invention relates to hybrid combination magnetic resonance (MR) and positron emission tomography (PET) scanning systems, and more particularly to MR/PET scanning systems having patient tables with MR local coil connectors adapted for selective coupling of a so-called auxiliary MR local coil array to the table and the MR scanning portion of the hybrid scanner. 
     2. Description of the Prior Art 
     In the past, MR scanners have employed selectively auxiliary MR local coil array assemblies in order to achieve higher image resolution for imaging procedures to a patient&#39;s brain and other organ parts. A local coil assembly has been mechanically and electrically coupled to the patient table by way of local coil connectors mounted on the table. Often the local coil connectors are oriented at the head and foot of the patient table. The local coil connectors in turn were coupled to the MR scanner by local coil cables. 
     In order to inhibit radio frequency (RF) electromagnetic coupling of the local coil cables and an MR scanner, the cables have been shielded in metalized plastic coated faraday cages having RF traps to inhibit distortion of or interference with MR scanner data acquisition. Traditionally local coil cables have been routed down the axial centerline of an MR scanner: the location of a patient&#39;s spine during scan data acquisition. While such local coil cable routing is satisfactory for MR scanner mode of a dual mode MR/Pet scanner, it can cause unwanted image artifacts when the hybrid seamier is operated as a PET seamier. It is believed that the such artifacts are attributable to high spatial frequency attenuation and scatter from the centerline-oriented cables, shielding and associated RF trap structures within the PET scan field of view FOV). 
     It would not be practical to remove and reinstall MR local coil connectors, cabling and related shielding from scanners only when imaging procedures requiring MR local coils are performed, as those components are permanently installed in the patient table structure. Existing RF shielding and traps are expensive to manufacture, relatively complex to install during scanner manufacture, and they occupy considerably higher volume within the patient table than the relatively thin MR local coil cables. 
     There is a need in the hybrid MR/PET scanner field to minimize formation of PET image artifacts attributable to MR local coil connectors, local MR coil cables and RF related shielding/trap structure without compromising ability to utilize MR local coil structures when needed for MR scanning procedures. 
     There is also a need in the hybrid MR/PET scanner field to minimize volume and construction complexity of MR local coil connectors, local MR coil cables and RF related shielding/trap structure. 
     SUMMARY 
     Accordingly, an object of the invention is to reduce risk of unwanted PET image artifacts when a hybrid combination MR/PET scanner is operational in PET scanning mode for a patient, yet retain the capability of performing MR scanning procedures with patient table mounted MR local coil arrays for other patients. 
     Another object of the present invention is to risk of unwanted PET image artifacts when a hybrid combination MR/PET scanner is operational in PET scanning mode for a patient without removal and reinstallation of MR local coil connectors, cables and shielding. 
     Yet another object of the present invention is to simplify RF shielding and RF trap structures in hybrid MR/PET image scanners and space occupied by such components. 
     These and other objects are achieved in accordance with embodiments of the present invention by the hybrid MR/PET scanner with patient table split cable feed of the present invention that provides MR local coil array connectivity for MR scanning procedures in a manner that does not interfere with PET scanning procedures. In the present invention the local MR coil connectors, cables and related RF traps/shielding are routed to the patient table outside the PET scanning field of view (FOV) when performing PET scans. 
     One aspect of the present invention is directed to a hybrid PET/MR imaging system including a PET scanning system having a PET scanning field of view and an MR scanning system having an MR scanning field of view. The scanner has a patient table having front and back ends, the table translatable from a first position outside the respective scanning fields to a second position wherein at least a portion of the table mediate the ends is inside the respective scanning fields. First and second MR local coil connectors are coupled respectively to the table proximal the respective front and back ends. The connectors are adapted for connection to an MR local coil oriented on the table during an MR imaging scan. First and second MR local coil cables coupled to the MR scanning system and respectively to the first and second MR local coil connectors. Both the MR local coil cables are oriented with respect to the imaging system so that the first cable passes through the PET scanning field of view when the patient table is in the first position and is displaced outside the PET scanning field of view when the patient table is in the second position. The second cable remains outside the PET scanning field in either patient table position. 
     Another aspect of the present invention is directed to a hybrid PET/MR imaging system including a PET scanning system having a PET scanning field of view and an MR scanning system having an MR scanning field of view overlapping at least a portion of the PET scanning field of view. A patient table, having front and back ends, is translatable from a first position outside the respective scanning fields to a second position wherein at least a portion of the table mediate the ends is inside the respective scanning fields. First and second MR local coil connectors coupled respectively to the table proximal the respective front and back ends, adapted for connection to an MR local coil oriented on the table during an MR imaging scan. First and second MR local coil cables are coupled to the MR scanning system and respectively to the first and second MR local coil connectors. Those cables have radio frequency (RF) shielding surrounding same and are oriented with respect to the imaging system so that the first cable passes through the PET scanning field of view when the patient table is in the first position and remains outside the PET scanning field of view when the patient table is in the second position; and the second cable remains outside the PET scanning field in either patient table position. 
     Yet another aspect of the present invention is directed to A hybrid magnetic resonance (MR) and positron emission tomography (PET) imaging system comprising a PET scanning system having a PET scanning field of view with first and second terminating sides thereof and an MR scanning system having an MR scanning field of view. The scanner has a patient table with a front end translatable through the PET scan field of view to the second terminating side thereof, and a back end. A first local coil connector is coupled to the MR imaging system proximal the table front end, and is adapted for connection to an MR local coil oriented on the table during an MR imaging scan. A first MR local coil cable, translatable with the table, couples the MR scanning system and the first MR local coil connector. The MR local coil cable is oriented so that it is outside the PET scan field of view when the patient table front end is translated to the second terminating side thereof. 
     An embodiment of the present invention is also directed to a method for reducing image artifacts during a PET scan performed in a hybrid MR/PET imaging system having overlapping PET and MR scanning fields of view (FOV) with first and second terminating sides of the FOV. The scanner used to perform the method has a patient table having a front end translatable through the overlapping fields to the second terminating side of the FOV, and a back end. First and second local coil connectors are coupled to the MR imaging system and the table, adapted for connection to an MR local coil oriented on the table during an MR imaging scan. The method is performed by first mounting the first and second MR local coil connectors respectively to the table proximal the respective front and back ends. Next, the first local coil connector is coupled to the MR scanning system with a first RF-shielded MR local coil cable routed through the overlapping fields of view to the second terminating side. Next the second local coil connector is coupled to the MR scanning system with a second RF-shielded MR local coil cable routed outside the overlapping fields of view. During a PET scan the table front end is translated through the overlapping scanning fields, so that the first MR local coil connector and first MR local coil cable are on the second terminating side of the PET scan FOV. 
     The objects, aspects and features of embodiments of the present invention can be used severally or jointly in any combination or subcombination by those skilled in the art at their discretion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings of embodiments of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic perspective view of the hybrid MR/PET imaging scanner in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic plan view of the hybrid MR/PET imaging scanner in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic elevational view of the hybrid MR/PET imaging scanner in accordance with an embodiment of the present invention; and 
         FIG. 4  is a schematic perspective view of an embodiment of a local MR coil cable reel of the hybrid MR/PET imaging scanner of the present invention and; 
       To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
         FIG. 5  is a schematic plan view of the hybrid MR/PET imaging scanner of the present invention with the patient table inserted within the scanning fields of view; and 
         FIG. 6  is a schematic elevational view of the hybrid MR/PET imaging scanner of the present invention with the patient table inserted within the scanning fields of view. 
     
    
    
     DETAILED DESCRIPTION 
     After considering the following description, those skilled in the art will clearly realize that the teachings of exemplary embodiments of the present invention can be readily utilized in hybrid MR/PET imaging scanners. 
       FIGS. 1 ,  2 ,  5  and  6  show generally a hybrid MR/PET scanner  10  of known construction and operation, having a scanner gantry  20  that incorporates scanner components necessary to acquire patient images in both the MR and PET modalities. In this exemplary hybrid scanner, the MR and PET scan fields of view (FOV), respectively  22 ,  24 , are overlapping. For MR scanning of patient local areas of interest, such as for example a patient&#39;s cranium, a known MR local coil assembly may be attached to the patient table  30  and coupled to the MR scanner in a manner to be described in greater detail herein. 
     The patient table  30  has a front end  32  and a back end  34 . Front patient table support  36  supports the patient table  30  on one side of the scanner, flanking the MR and PET FOV&#39;s  22 ,  24 . Similarly, rear patient table support  38  supports the patient table  30  on the other side of the scanner, flanking the MR and PET FOV&#39;s  22 ,  24 . As shown in  FIGS. 2 and 3 , table  30  translates from a patient loading area on the front table support  36  side of the scanner  10 , where the table is entirely outside of the MR and PET FOV&#39;s  22 ,  24 . A patient is placed on the table  30  and thereafter the table is translated so that the front  32  thereof penetrates the FOV&#39;s  22 ,  24 , so that the portion of the patient&#39;s anatomy to be scanned is positioned in the relevant FOV for scanning. For example if it is desired to perform an MR scan on a patient&#39;s cranium utilizing a local coil assembly  26 , the coil assembly is attached to the patient table  30  and positioned with the patient within the MR FOV  22 . 
     The MR local coil assembly  26  is attached and electronically coupled to the scanner  10  by way of front local MR coil connectors  40 , located in the patient table  30  proximal the front end  32 . A similar set of rear local MR coil connectors  42  are provided in the patient table  30  proximal the back end  34 . The respective local coil connector pairs  40 ,  42  are electronically coupled to the MR modality of scanner  10  by respective MR local coil cables  50 ,  52 . The local coil cables  50 ,  52  have flexible RF shielding  54 , such as known braided metallic shielding, with RF traps  56  selectively oriented on the cable in cooperation with the shielding. 
     As shown in  FIGS. 1-3  and  5 - 6 , the local coil cables  50 ,  52  are of sufficient length to allow the patient table  30  to translate across its entire range of motion from front table support  36  (see  FIGS. 2 and 3 ) to rear table support  38  (see  FIGS. 4 and 5 ). Excess cable slack can be restrained dropped within cable recesses  39 . Alternatively, cable slack may be taken up by one or more cable reels  60  within an RF shielding cage  62  of known construction, and oriented in the front or rear table supports  36 ,  38 . Any other known means of excess cable slack take-up known in the art may be utilized at the discretion of those skilled in the art. 
     When an MR local coil assembly  26  or other type of local coil structure is not needed to perform a patient scan, it can be removed from the patient table  30  by disconnecting from one or more of the local coil connectors  40 ,  42 . It is intended that the MR local coil connectors  40 ,  42  and respective MR local coil cables  50 ,  52  remain in situ in the scanner  10 , even when PET scans are performed. 
     During PET scans anything other than the patient in the PET FOV  24  has the potential for causing one or more artifacts in the acquired PET image. Therefore during a PET scan the patient table  30  is positioned in the PET FOV  24  intermediate the table front and back ends  32 ,  34  so that the MR local coil connectors  40 ,  42  are not in the FOV  24 . The MR local coil cables  50 ,  52  are routed from the scanner  10  to their respective MR local coil connectors  40 ,  42  so that they do not pass through the PET scanning field of view  24  while conducting a PET scan. 
     As is shown in  FIGS. 1-3  the front local MR coil cable  50  passes through the scanner gantry  20  when the patient table  30  is in the patient loading position on the front patient table support  36  flanking side of the PET scan FOV  24 . When the patient table is inserted into the gantry  20  PET scan FOV  24  the front end  32  of patient table  30  is on the rear patient table support  38  back flanking side of the PET scan FOV  24 , along with the front local MR coil connectors  40  and the entire front local MR coil cable  50 . In the embodiment of the present invention shown in the figures herein, the rear local MR coil connectors  42  and the associated rear local MR coil cable  52  do not enter the PET scan field of view  24  in any patient table  30  position. 
     As neither of the front or rear local MR coil cables  50 ,  52  are in the PET field of view  24  when utilizing the PET imaging modality, they do not create PET image artifacts. 
     Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.