Abstract:
Apparatus for collimating an X-ray beam, the apparatus comprising:
       a multi-slit rotatable collimator comprising:
           a semi-tubular structure extending coaxially along a longitudinal axis, the semi-tubular structure being formed out of an X-ray impermeable material;   at least one slit formed in the semi-tubular structure, wherein the at least one slit extends parallel to the longitudinal axis of the semi-tubular structure;   a mount for rotatably supporting the semi-tubular structure in the path of an X-ray beam; and   a drive mechanism for selectively rotating the semi-tubular structure about the longitudinal axis of the semi-tubular structure, whereby to selectively (i) position the at least one slit in the path of the X-ray beam so as to tailor the X-ray beam to the width of the at least one slit, and (ii) position a solid portion of the semi-tubular structure in the path of an X-ray beam so as to block an X-ray beam.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATION 
       [0001]    This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/727,436, filed Nov. 16, 2012 by Andrew Tybinkowski et al. for COMPUTERIZED TOMOGRAPHY (CT) IMAGING SYSTEM WITH MULTI-SLIT ROTATABLE COLLIMATOR (Attorney&#39;s Docket No. NEUROLOGICA-4349 PROV), which patent application is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to imaging systems in general, and more particularly to computerized tomography (CT) imaging systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    In many situations, it can be desirable to image the interior of opaque objects. By way of example but not limitation, in the medical field, it can be desirable to image the interior of a patient&#39;s body so as to allow viewing of internal body structures without physically penetrating the skin. 
         [0004]    Computerized Tomography (CT) has emerged as a key imaging modality in the medical field. CT imaging systems generally operate by directing X-rays into the body from a variety of positions, detecting the X-rays passing through the body, and then processing the detected X-rays so as to build a three-dimensional (3D) data set and a 3D computer model of the patient&#39;s anatomy. The 3D data set and 3D computer model can then be visualized so as to provide images (e.g., slice images, 3D computer images, etc.) of the patient&#39;s anatomy. 
         [0005]    By way of example but not limitation, and looking now at  FIGS. 1 and 2 , there is shown a mobile CT imaging system  5  of the sort disclosed in U.S. Pat. No. 7,397,895, issued Jul. 8, 2008 to Eric M. Bailey et al. for MOBILE COMPUTERIZED TOMOGRAPHY (CT) IMAGING SYSTEM WITH CORDLESS AND WIRELESS CAPABILITIES (Attorney&#39;s Docket No. NEUROLOGICA-7), which patent is hereby incorporated herein by reference. Mobile CT imaging system  5  generally comprises a torus  10  which is supported by a base  15 . Torus  10  and base  15  together comprise a frame for mobile CT imaging system  5 . A center opening  20  is formed in torus  10 . Center opening  20  receives the patient anatomy which is to be scanned. 
         [0006]    Looking next at  FIG. 3 , torus  10  generally comprises an X-ray tube assembly  25 , an X-ray detector assembly  30 , and a rotating drum assembly  35 . X-ray tube assembly  25  and X-ray detector assembly  30  are mounted to rotating drum assembly  35  in diametrically-opposing relation, such that an X-ray beam  40  (generated by X-ray tube assembly  25  and detected by X-ray detector assembly  30 ) is passed through the patient anatomy disposed in center opening  20 . Furthermore, since X-ray tube assembly  25  and X-ray detector assembly  30  are mounted on rotating drum assembly  35  so that they are rotated concentrically about center opening  20 , X-ray beam  40  will be passed through the patient&#39;s anatomy along a full range of radial positions, so as to enable mobile CT imaging system  5  to create a “slice” image of the anatomy penetrated by the X-ray beam. Furthermore, by moving mobile CT imaging system  5  relative to the patient during scanning, a series of slice images can be acquired, and thereafter appropriately processed, so as to create a 3D computer model of the scanned anatomy. 
         [0007]    The various electronic hardware and software for controlling the operation of X-ray tube assembly  25 , X-ray detector assembly  30 , and rotating drum assembly  35 , as well as for processing the acquired scan data so as to generate the desired slice images and 3D computer model, may be of the sort well known in the art and may be located in torus  10  and/or base  15 . 
         [0008]    Still looking now at  FIG. 3 , base  15  comprises a transport assembly  50  for moving mobile CT imaging system  5  relative to the patient. More particularly, as disclosed in the aforementioned U.S. Pat. No. 7,397,895, transport assembly  50  preferably comprises (i) a gross movement mechanism  55  for moving mobile CT imaging system  5  relatively quickly across room distances, so that the mobile CT imaging system can be quickly and easily brought to the “bedside” of the patient, and (ii) a fine movement mechanism  60  for moving the mobile CT imaging system precisely, relative to the patient, during scanning, so that the patient can be scanned at their bedside, without being moved. As discussed in U.S. Pat. No. 7,397,895, gross movement mechanism  55  preferably comprises a plurality of free-rolling casters, and fine movement mechanism  60  preferably comprises a plurality of centipede belt drives (which can be configured for either stepped or continuous motion, whereby to provide either stepped or continuous scanning). Hydraulic apparatus  65  permits either gross movement mechanism  55  or fine movement mechanism  60  to be engaged with the floor, whereby to facilitate appropriate movement of mobile CT imaging system  5 . 
         [0009]    Looking next at  FIGS. 4 and 5 , there is shown another mobile CT imaging system  105  of the sort disclosed in U.S. patent application Ser. No. 13/304,006, filed Nov. 23, 2011 by Eric M. Bailey et al. for ANATOMICAL IMAGING SYSTEM WITH CENTIPEDE SCANNING DRIVE, BOTTOM NOTCH TO ACCOMMODATE BASE OF PATIENT SUPPORT, AND MOTORIZED DRIVE FOR TRANSPORTING THE SYSTEM BETWEEN SCANNING LOCATIONS (Attorney&#39;s Docket No. NEUROLOGICA-3337), which patent application is hereby incorporated herein by reference. Mobile CT imaging system  105  is generally similar to mobile CT imaging system  5  disclosed above, except that (i) mobile CT imaging system  105  is generally “scaled up” in size relative to mobile CT imaging system  5 , (ii) a bottom notch  170  is provided in skirt  175  of mobile CT imaging system  105 , and (iii) the casters of gross movement mechanism  55  of mobile CT imaging system  5  may be replaced by a pair of drive wheels  180 A,  180 B and a pair of casters  185 A,  185 B, and each of the centipede belt drives of fine movement mechanism  60  of mobile CT imaging system  5  may be replaced by a pair of parallel belt drives  190 A,  190 B disposed in side-by-side relation. Additional differences between mobile CT imaging system  105  of  FIGS. 4 and 5  and mobile CT imaging system  5  of  FIGS. 1-3  are disclosed in the aforementioned U.S. patent application Ser. No. 13/304,006. 
         [0010]    For the purposes of the present invention, it is generally immaterial whether the present invention is used in conjunction with the aforementioned mobile CT imaging system  5 , the aforementioned mobile CT imaging system  105  or another CT imaging system (e.g., a fixed position CT imaging system). 
         [0011]    With all CT imaging systems (i.e., with the aforementioned mobile CT imaging system  5 , the aforementioned mobile CT imaging system  105 , or another CT imaging system such as a fixed position CT imaging system), it is generally necessary to collimate the X-ray beam emitted by the X-ray tube assembly before the X-ray beam passes through the body. More particularly, X-ray tube assemblies generally emit their X-rays in a broad, relatively unfocused pattern, and the anatomy is imaged in a slice fashion, so it is generally desirable to restrict the X-rays reaching the patient to only those X-rays which are actually used for the slices being imaged, and to block the remaining X-rays emitted by the X-ray tube assemblies. This is typically done with a collimator, which is essentially an X-ray shield having a slit formed therein, which is interposed between the X-ray tube assembly and the patient. In this way, the slit permits the “useful” X-rays (i.e., those being used for the slices being imaged) to reach the patient, while the body of the collimator blocks the remainder of the X-rays emitted by the X-ray tube assembly. 
         [0012]    In addition to the foregoing, with “modern” CT imaging systems, it is possible to conduct multi-slice scanning of a patient by using a collimator having a slit wide enough to provide an X-ray beam which simultaneously encompasses multiple scan slices. In general, scanning with a wider X-ray beam (i.e., a higher slice count) yields faster scanning of a patient than scanning with a narrower X-ray beam (i.e., a lower slice count), but this is generally at the expense of subjecting the patient to a higher X-ray dose. For this reason, in some situations it may be desirable to make a high slice scan (e.g., a 32 slice scan) of a patient, whereas in other circumstances it may be desirable to make a low slice scan (e.g., an 8 slice scan) of a patient. 
         [0013]    Since the width of the X-ray beam is determined by the width of the slit in the collimator, varying the slice count of the scan requires the use of a plurality of collimator slits each having different widths. 
         [0014]    Thus there is a need for a fast, simple and reliable way to change collimator slits when the slice count of the scan is to be changed. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention provides a fast, simple and reliable way to change collimator slits when the slice count of the scan is to be changed. 
         [0016]    More particularly, the present invention comprises the provision and use of a novel multi-slit rotatable collimator, wherein each of the slits of the multi-slit rotatable collimator has a different size opening (i.e., each slit has a different width), and wherein the multi-slit collimator is rotated about an axis so as to selectively interpose a given slit between the X-ray tube assembly and the patient, whereby to allow scans of different slice counts to be made. In this way, the present invention provides a fast, simple and reliable way to change collimator slits when the slice count of the scan is to be changed. 
         [0017]    Additionally, the multi-slit rotatable collimator may be rotated about an axis so as to not interpose a given slit between the X-ray tube assembly and the patient, whereby to selectively shield the patient from the X-rays generated by the X-ray tube assembly. In this way, the present invention provides a fast, simple and reliable way to shield the patient from the X-rays generated by the X-ray tube assembly. 
         [0018]    In one preferred form of the invention, there is provided apparatus for collimating an X-ray beam, the apparatus comprising:
       a multi-slit rotatable collimator comprising:
           a semi-tubular structure extending coaxially along a longitudinal axis, the semi-tubular structure being formed out of an X-ray impermeable material;   at least one slit formed in the semi-tubular structure, wherein the at least one slit extends parallel to the longitudinal axis of the semi-tubular structure;   a mount for rotatably supporting the semi-tubular structure in the path of an X-ray beam; and   a drive mechanism for selectively rotating the semi-tubular structure about the longitudinal axis of the semi-tubular structure, whereby to selectively (i) position the at least one slit in the path of the X-ray beam so as to tailor the X-ray beam to the width of the at least one slit, and (ii) position a solid portion of the semi-tubular structure in the path of an X-ray beam so as to block an X-ray beam.   
               
 
         [0024]    In another preferred form of the invention, there is provided apparatus for imaging a patient, the apparatus comprising:
       a CT machine comprising an X-ray source; and   a multi-slit rotatable collimator comprising:
           a semi-tubular structure extending coaxially along a longitudinal axis, the semi-tubular structure being formed out of an X-ray impermeable material;   at least one slit formed in the semi-tubular structure, wherein the at least one slit extends parallel to the longitudinal axis of the semi-tubular structure;   a mount for rotatably supporting the semi-tubular structure in the path of the X-ray beam; and   a drive mechanism for selectively rotating the semi-tubular structure about the longitudinal axis of the semi-tubular structure, whereby to selectively (i) position the at least one slit in the path of the X-ray beam so as to tailor the X-ray beam to the width of the at least one slit, and (ii) position a solid portion of the semi-tubular structure in the path of an X-ray beam so as to block an X-ray beam.   
               
 
         [0031]    In another preferred form of the invention, there is provided a method for collimating an X-ray beam, the method comprising:
       providing a multi-slit rotatable collimator comprising:
           a semi-tubular structure extending coaxially along a longitudinal axis, the semi-tubular structure being formed out of an X-ray impermeable material;   at least one slit formed in the semi-tubular structure, wherein the at least one slit extends parallel to the longitudinal axis of the semi-tubular structure;   a mount for rotatably supporting the semi-tubular structure in the path of an X-ray beam; and   a drive mechanism for selectively rotating the semi-tubular structure about the longitudinal axis of the semi-tubular structure, whereby to selectively (i) position the at least one slit in the path of the X-ray beam so as to tailor the X-ray beam to the width of the at least one slit, and (ii) position a solid portion of the semi-tubular structure in the path of an X-ray beam so as to block an X-ray beam;   
           providing an X-ray beam; and   using the drive mechanism to selectively rotate the semi-tubular structure about the longitudinal axis of the semi-tubular structure.       
 
         [0039]    In another preferred form of the invention, there is provided a method for imaging a patient, the method comprising:
       providing a CT machine comprising an X-ray source, and a multi-slit rotatable collimator comprising a semi-tubular structure extending coaxially along a longitudinal axis, the semi-tubular structure being formed out of an X-ray impermeable material; at least one slit formed in the semi-tubular structure, wherein the at least one slit extends parallel to the longitudinal axis of the semi-tubular structure; a mount for rotatably supporting the semi-tubular structure in the path of the X-ray beam; and a drive mechanism for selectively rotating the semi-tubular structure about the longitudinal axis of the semi-tubular structure, whereby to selectively (i) position the at least one slit in the path of the X-ray beam so as to tailor the X-ray beam to the width of the at least one slit, and (ii) position a solid portion of the semi-tubular structure in the path of an X-ray beam so as to block an X-ray beam;   using the drive mechanism to selectively rotate the semi-tubular structure about the longitudinal axis of the semi-tubular structure; and   scanning the patient using the CT machine.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    These and other features and advantages of the present invention will become more readily apparent during the following detailed description of the preferred embodiments of the invention, which is to be considered in conjunction with the accompanying drawings wherein like numbers refer to like parts and further wherein: 
           [0044]      FIGS. 1-3  are schematic views showing an exemplary mobile CT imaging system; 
           [0045]      FIGS. 4 and 5  are schematic views showing another exemplary mobile CT imaging system; and 
           [0046]      FIGS. 6-23  are schematic views showing a novel multi-slit rotatable collimator assembly formed in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    The present invention provides a fast, simple and reliable way to change collimator slits when the slice count of the scan is to be changed. 
         [0048]    More particularly, the present invention comprises the provision and use of a novel multi-slit rotatable collimator, wherein each of the slits of the multi-slit rotatable collimator has a different size opening (i.e., each slit has a different width), and wherein the multi-slit collimator is rotated about an axis so as to selectively interpose a given slit between the X-ray tube assembly and the patient, whereby to allow scans of different slice counts to be made. In this way, the present invention provides a fast, simple and reliable way to change collimator slits when the slice count of the scan is to be changed. 
         [0049]    Additionally, the multi-slit rotatable collimator may be rotated about an axis so as to not interpose a given slit between the X-ray tube assembly and the patient, whereby to selectively shield the patient from the X-rays generated by the X-ray tube assembly. In this way, the present invention provides a fast, simple and reliable way to shield the patient from the X-rays generated by the X-ray tube assembly. 
         [0050]    In one preferred form of the invention, and looking now at  FIGS. 6-23 , there is provided a novel multi-slit rotatable collimator assembly  205  which generally comprises a base  210  having an opening  215 , a pair of spaced supports  220 ,  225  mounted to base  210 , a multi-slit rotatable collimator  230  rotatably mounted to supports  220 ,  225  so as to be movably disposed in front of opening  215 , a drive mechanism  235  for rotating multi-slit rotatable collimator  230 , and a position detector  240  for detecting the rotational disposition of multi-slit rotatable collimator  230 . Preferably, multi-slit rotatable collimator assembly  205  is covered with a housing  242  having an opening  243 , e.g., by securing housing  242  to base  210 , with opening  243  in housing  242  being aligned with opening  215  in base  210 . 
         [0051]    More particularly, base  210  generally comprises a plate-like structure having an inner surface  245  and an outer surface  250 . Opening  215  extends through base  210 , opening on inner surface  245  and outer surface  250 . A mounting plate  255  is preferably secured to outer surface  250  of base  210 , whereby base  210  may be secured to the X-ray tube assembly of a CT imaging system, e.g., the X-ray tube assembly  25  of the aforementioned mobile CT imaging system  5 , or the X-ray tube assembly of the aforementioned CT imaging system  105 , or another CT imaging system such as a fixed position CT imaging system. Mounting plate  255  comprises an opening  260  ( FIG. 14 ) aligned with opening  215  in base  210 , whereby X-rays emitted from X-ray tube assembly  25  may pass through opening  260  in mounting plate  255  and through opening  215  in base  210 . 
         [0052]    Spaced supports  220 ,  225  are mounted to inner surface  245  of base  210  so that they reside on either end of opening  215 . Spaced support  220  comprises an opening  265  ( FIGS. 15 and 16 ), and spaced support  225  comprises an opening  270 , wherein opening  265  in spaced support  220  is axially aligned with opening  270  in spaced support  225 . 
         [0053]    Multi-slit rotatable collimator  230  is rotatably mounted to supports  220 ,  225  so as to be movably disposed in front of opening  215 . More particularly, multi-slit rotatable collimator  230  comprises a semi-tubular structure  275  (e.g., a 120 degree arc segment of a tube) formed out of an X-ray impermeable material (e.g., a high density material such as tungsten, molybdenum, etc.) having a plurality of longitudinal slits  280 A,  280 B, etc. formed therein, wherein each slit  280 A,  280 B, etc. has a different width (e.g., one slit  280 A sized for a 32 slice scan, another slit  280 B sized for an 8 slice scan, etc.). The two ends of semi-tubular structure  275  are movably mounted to spaced supports  220 ,  225  (e.g., by fitting axles  285 ,  290  through openings  265 ,  270  in spaced supports  220 ,  225 , respectively) so that multi-slit rotatable collimator  230  may be rotated about its longitudinal axis, whereby to selectively position one of the slits  280 A,  280 B, etc. between X-ray tube assembly  25  and the patient, whereby to permit scans of different slice counts (e.g., 32 slice scans, 8 slice scans, etc.) to be made. Additionally, multi-slit rotatable collimator  230  may be rotated about its axis so as to not interpose a given slit  280 A,  280 B, etc. between the X-ray tube assembly and the patient, whereby to selectively shield the patient from the X-rays generated by the X-ray tube assembly. 
         [0054]    Drive mechanism  235  is provided to selectively rotate multi-slit rotatable collimator  230  about its axis. Preferably semi-tubular structure  275  of multi-slit rotatable collimator  230  is rotated about its longitudinal axis using a Geneva drive mechanism, e.g., such as of the sort shown in  FIG. 17-23 . More particularly, drive mechanism  235  preferably comprises a drive shaft  295  which turns a gear  300 , which in turn rotates a drive wheel  305  carrying a pin  310 , which in turn rotates a driven wheel  315  having slots  320  therein. Driven wheel  315  is mounted to axle  285  extending through opening  265  in spaced support  220 . Preferably the number and location of slots  320  in driven wheel  315  are coordinated with the number and location of slits  280 A,  280 B, etc. in semi-tubular structure  275 , such that rotation of drive shaft  295  can selectively align a particular slit  280 A,  280 B, etc. with the X-ray beam emitted from X-ray tube assembly  25 , whereby to selectively tailor the X-ray beam to a desired width. Furthermore, the number and location of slots  320  in driven wheel  315  are coordinated with the “solid” portions of semi-tubular structure  275 , such that rotation of drive shaft  295  can selectively interpose a solid portion of semi-tubular structure  275  with the X-ray beam emitted from X-ray tube assembly  25 , whereby to selectively block the X-ray beam emitted by X-ray tube assembly  25 . 
         [0055]    By way of example but not limitation, where semi-tubular structure  275  comprises a first slit  280 A, a second slit  280 B and a solid portion disposed between first slit  280 A and second slit  280 B, the Geneva drive mechanism may comprise a drive wheel  305  carrying a pin  310 , which in turn rotates a driven wheel  315  having slots  320  therein, such that (i) the solid portion disposed between first slit  280 A and second slit  280 B will be presented to the X-ray beam when drive wheel  305  and driven wheel  315  are in the position shown in  FIG. 17 , (ii) slit  280 A will be presented to the X-ray beam when drive wheel  305  and driven wheel  315  move through the positions shown in  FIGS. 18-20 , and (iii) slit  280 B will be presented to the X-ray beam when drive wheel  305  and driven wheel  315  move through the positions shown in  FIGS. 21-23 . 
         [0056]    Position detector  240  is provided for detecting the rotational disposition of multi-slit rotatable collimator  230 . More particularly, position detector  240  comprises a sensor element  325  mounted to base  210 , and a sensed element  330  mounted to axle  290  of multi-slit rotatable collimator  230 , such that the rotational disposition of multi-slit rotatable collimator  230  can be determined using position detector  240 . 
         [0057]    As noted above, multi-slit rotatable collimator assembly  205  is preferably covered with housing  242  having opening  243  therein, e.g., by securing housing  242  to base  210 , with opening  243  in housing  242  being aligned with opening  215  in base  210 . 
         [0058]    On account of the foregoing, when multi-slit rotatable collimator assembly  205  is mounted in front of the X-ray tube assembly of a CT imaging system so that X-rays emitted by the X-ray tube assembly pass through multi-slit rotatable collimator assembly  205 , and when it is desired to scan a patient with an X-ray beam of a first slice width (e.g., a high slice scan such as a 32 slice scan), drive mechanism  235  is activated so as to turn multi-slit rotatable collimator  230  about its axis so as to position a first slit between X-ray assembly  25  and the patient (e.g., slit  280 A). In this way multi-slit rotatable collimator  230  will tailor the width of the X-ray beam delivered to the patient to the desired first slice width. 
         [0059]    Correspondingly, when it is desired to scan a patient with an X-ray beam of a second slice width (e.g., a low slice scan such as an 8 slice scan), drive mechanism  235  is activated so as to turn multi-slit rotatable collimator  230  about its axis so as to position a second slit between X-ray assembly  25  and the patient (e.g., slit  280 B). In this way multi-slit rotatable collimator  230  will tailor the width of the X-ray beam delivered to the patient to the desired second slice width. 
         [0060]    Furthermore, when it is desired to shield the patient from the X-ray beam emitted by X-ray assembly  25 , drive mechanism  235  is activated so as to turn multi-slit rotatable collimator  230  about its axis so as to position a solid portion of semi-tubular structure  275  between X-ray assembly  25  and the patient. In this way multi-slit rotatable collimator  230  will block the X-ray beam from being delivered to the patient. 
         [0061]    In one preferred form of the invention, multi-slit rotatable collimator  230  comprises two slits  280 A,  280 B, wherein slit  280 A is sized to provide a 32 slice scan and slit  280 B is sized to provide an 8 slice scan. However, if desired, more or less slits may be provided, and/or the widths of the slits may be varied. By way of example but not limitation, three slits  280 A,  280 B,  280 C may be provided, with slit  280 A being sized to provide a 64 slice scan, slit  280 B being sized to provide an 32 slice scan and slit  280 C being sized to provide an 8 slice scan. Still other configurations will be readily apparent to one skilled in the art in view of the present disclosure. 
         [0062]    If desired, a filter may be interposed between X-ray assembly  25  and semi-tubular structure  275  of multi-slit rotatable collimator  230 . By way of example but not limitation, a bow-tie filter  335  may be interposed between X-ray assembly  25  and semi-tubular structure  275  of multi-slit rotatable collimator  230 . In one preferred form of the invention, bow-tie filter  335  ( FIG. 12 ) is mounted to base  210  in front of opening  215  and within the volume defined by semi-tubular structure  275 , such that X-rays emitted from X-ray assembly  25  are filtered prior to passing through a slit  280 A,  280 B, etc. in semi-tubular structure  275  or encountering a solid portion of semi-tubular structure  275 . 
       Modifications of the Preferred Embodiments 
       [0063]    It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.