Abstract:
A mobile CT imaging system comprising a housing having a center opening; and a CT imaging unit mounted to the housing, wherein the CT imaging unit is adapted to scan anatomical objects located within the center opening and generate images of the same, wherein the CT imaging unit comprises: a rotatable drum assembly disposed within the housing, concentric with the center opening; an X-ray tube mounted on the rotatable drum assembly and configured to emit an X-ray beam; and an X-ray detector mounted on the rotatable drum assembly in alignment with the X-ray beam; wherein the X-ray beam is disposed in an “off-center” configuration, adjacent to an entrance of the center opening.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS 
     This patent application is a continuation of prior U.S. patent application Ser. No. 11/653,706, filed Jan. 16, 2007 now U.S. Pat. No. 7,568,836 by Eric M. Bailey et al. for MOBILE COMPUTERIZED TOMOGRAPHY (CT) IMAGING SYSTEM WITH OFF-CENTER X-RAY BEAM, which in turn is: 
     (i) a continuation-in-part of prior U.S. patent application Ser. No. 11/193,941, filed Jul. 29, 2005 now U.S. Pat. No. 7,175,347 by Andrew P. Tybinkowski et al. for ANATOMICAL IMAGING SYSTEM WITH CENTIPEDE DRIVE, which patent application in turn claims benefit of:
         (a) prior U.S. Provisional Patent Application Ser. No. 60/670,164, filed Apr. 11, 2005 by Andrew P. Tybinkowski et al. for ANATOMICAL IMAGING SYSTEM WITH CENTIPEDE DRIVE; and   (b) prior U.S. Provisional Patent Application Ser. No. 60/593,001, filed Jul. 30, 2004 by Bernard Gordon et al. for ANATOMICAL SCANNING SYSTEM; and       

     (ii) a continuation-in-part of prior U.S. patent application Ser. No. 11/399,283, filed Apr. 6, 2006 now U.S. Pat. No. 7,396,160 by Andrew P. Tybinkowski et al. for COMPUTERIZED TOMOGRAPHY (CT) IMAGING SYSTEM WITH MONOBLOCK X-RAY TUBE ASSEMBLY. 
     The five above-identified patent applications are hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to anatomical imaging systems in general, and more particularly to Computerized Tomography (CT) imaging systems. 
     BACKGROUND OF THE INVENTION 
     Strokes are currently the third leading cause of death in the United States, causing approximately 177,000 deaths per year, and strokes are currently the number one cause of long-term disability in the United States, currently affecting nearly 5 million people. Strokes are caused by an abrupt interruption of the blood supply to the brain or spinal cord, thereby depriving the tissue of oxygen and resulting in tissue damage. 
     Strokes typically occur in one of two forms: (i) hemorrhagic stokes, which occur with the rupture of a blood vessel; and (ii) ischemic strokes, which occur with the obstruction of a blood vessel. 
     Rapid diagnosis is a key component of stroke treatment. This is because the treatment for an ischemic stroke may be contra-indicated for the treatment for a hemorrhagic stroke and, furthermore, the effectiveness of a particular treatment may be time-sensitive. More particularly, the current preferred treatment for an acute ischemic stroke, i.e., the administration of tPA to eliminate blood clots, is contra-indicated for a hemorrhagic stroke. Furthermore, the clinical data suggests that the medication used to treat ischemic strokes (i.e., tPA) is most effective if it is administered within 3 hours of the onset of the stroke. However, current diagnosis times, i.e., the time needed to identify that the patient is suffering from a stroke and to identify the hemorrhagic or ischemic nature of the stroke, frequently exceeds this 3 hour window. As a result, only a fraction of current ischemic stroke victims are timely treated with tPA. 
     Imaging is generally necessary to properly diagnose (and hence properly treat) a stroke. More particularly, imaging is generally necessary to: (i) distinguish strokes from other medical conditions; (ii) distinguish between the different types of strokes (i.e., hemorrhagic or ischemic); and (iii) determine appropriate treatments (e.g., the administration of tPA in the case of an ischemic stroke). 
     Computerized Tomography (CT) has emerged as the key imaging modality in the diagnosis of strokes. 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 computer model of the patient&#39;s anatomy. This computer model can then be visualized so as to provide images of the patient&#39;s anatomy. It has been found that such CT scanning, including non-enhanced CT scanning, CT angiography scanning and CT perfusion scanning, is able to provide substantially all of the information needed to effectively diagnose (and hence properly treat) a stroke. 
     Unfortunately, in practice, the CT imaging system is typically located in the hospital&#39;s radiology department and the patient is typically received in the hospital&#39;s emergency room, and the “round-trip” time between the emergency room and the radiology department can frequently involve substantial delays, even in the best of hospitals. As a result, the time spent in transporting the patient from the emergency room to the radiology department and then back again can consume critical time which can compromise proper treatment of the patient (e.g., it can prevent ischemic stroke victims from being timely treated with tPA). 
     Thus, there is an urgent need for a new and improved CT imaging system which is particularly well suited for use in stroke applications. More particularly, there is an urgent need for a small, mobile CT imaging system which can be pre-positioned in the emergency room and moved to the patient so that the patient can be scanned at their current location, thus effectively eliminating “round-trip” delays and dramatically reducing the time needed to properly diagnose the patient. It is also important that the CT imaging system be relatively inexpensive, so as to facilitate its rapid proliferation and widespread use, e.g., pre-positioning in substantially all hospital emergency rooms and wide availability in outlying, low-volume settings (e.g., rural hospitals, ships, etc.). 
     In this respect it should also be appreciated that current CT imaging systems are generally quite large. This is due to (i) the general nature of CT imaging systems, and (ii) the anatomy that the current CT imaging systems are designed to scan. 
     More particularly, and looking now at  FIGS. 1 and 2 , current CT imaging systems generally comprise a housing A having a center opening B and enclosing a rotating drum assembly C, an X-ray tube assembly D adapted to emit X-rays, and an X-ray detector assembly E adapted to detect X-rays. X-ray tube assembly D and X-ray detector assembly E are mounted to rotating drum assembly C about center opening B, in diametrically-opposing relation, such that the X-ray beam F (generated by X-ray tube assembly D and detected by X-ray detector assembly E) is passed through the interior of the drum assembly C (i.e., across center opening B), and hence is passed through patient anatomy disposed within the interior of rotating drum assembly C (i.e., patient anatomy disposed within center opening B). Furthermore, since X-ray tube assembly D and X-ray detector assembly E are mounted on rotating drum assembly C so that they are rotated concentrically about the axis of rotating drum assembly C, X-ray beam F will be passed through the patient&#39;s anatomy along a full range of radial positions. As a result, by moving the patient longitudinally through center opening B while passing X-ray beam F through the anatomy along a range of radial positions, the CT imaging system can create the desired computer model of the scanned anatomy. Thus it will be appreciated that CT imaging systems must be large enough to fit, within the interior of drum assembly C, the patient anatomy which is to be scanned. Since conventional CT imaging systems are generally designed to scan any portion of the patient&#39;s anatomy, such CT imaging systems must have a center opening large enough to accept the torso of the patient B. Accordingly, conventional CT imaging systems are generally of substantial size. 
     Furthermore, since X-ray tube assembly D and X-ray detector assembly E are typically of substantial size and complexity (e.g., X-ray tube assembly D generally requires substantial power to penetrate the torso, and typically includes substantial power elements, cooling systems, etc., and X-ray detector assembly E typically includes substantial detector structure, etc.), and since X-ray tube assembly D and X-ray detector assembly E must remain fixed in position relative to one another with a high degree of precision even as drum assembly C is rotated at substantial speeds, X-ray tube assembly D and X-ray detector assembly E are typically mounted to rotating drum assembly C so that each assembly is concentric about the mid-point of the depth of the drum assembly. This arrangement minimizes cantilevering and provides the most stable mounting of X-ray tube assembly D and X-ray detector assembly E to rotating drum assembly C. Thus, with conventional CT imaging systems, X-ray beam F is positioned at the mid-point of the depth of the drum assembly. For purposes of the present invention, conventional CT imaging systems can be considered to have an “on-center” X-ray beam configuration. 
     The aforementioned construction of conventional CT imaging systems generally does not present a problem when the CT imaging system is a large, fixed-position installation designed to scan any portion of the patient&#39;s anatomy. However, such a construction presents a serious problem when trying to build a small, mobile CT imaging system intended to scan only the head of the patient, e.g., a potential stroke victim. This is because CT imaging systems having a center opening large enough to receive the torso of a patient must also have an overall size which makes it impractical to move the CT imaging system about the hospital. 
     Furthermore, it is not possible to solve the aforementioned problem by simply reducing the size of the CT imaging system so that it has a center opening just large enough to receive only the head of the patient. This is because the shoulders of the patient limit the extent to which the patient&#39;s head can be advanced into the center opening of the CT scanner. Thus, the conventional approach of locating the X-ray beam at the mid-point of the depth of the drum assembly (i.e., the aforementioned “on-center” configuration) prevents the lower portion of the head from being passed through the “on-center” X-ray beam. See  FIG. 2A . This can be unacceptable for many potential stroke victims, who may be affected in the lower portion of the brain or the upper portion of the neck. 
     Thus, there is a need for a new and improved approach for positioning the X-ray tube assembly and the X-ray detector assembly within a CT imaging system, so as to facilitate the provision of a mobile (i.e., small) CT imaging system which can scan the entire head of a patient. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a novel approach for positioning the X-ray tube assembly and the X-ray detector assembly within a CT imaging system, so as to facilitate the provision of a mobile (i.e., small) CT imaging system which can scan the entire head of a patient. 
     And there is provided a novel mobile CT imaging system having a significantly reduced size but which is still capable of scanning substantially the full range of the anatomy placed within the center opening of the CT imaging system, e.g., the entire head and upper neck of a patient. 
     In one form of the invention, there is provided a mobile CT imaging system comprising: 
     a housing having a center opening; and 
     a CT imaging unit mounted to the housing, wherein the CT imaging unit is adapted to scan anatomical objects located within the center opening and generate images of the same, wherein the CT imaging unit comprises:
         a rotatable drum assembly disposed within the housing, concentric with the center opening;   an X-ray tube mounted on the rotatable drum assembly and configured to emit an X-ray beam; and   an X-ray detector mounted on the rotatable drum assembly in alignment with the X-ray beam;   wherein the X-ray beam is disposed in an “off-center” configuration, adjacent to an entrance of the center opening.       

     In another form of the invention, there is provided a CT imaging system comprising: 
     a housing having a center opening larger than the head of a patient and smaller than the shoulders of a patient; and 
     a CT imaging unit mounted to the housing, wherein the CT imaging unit is adapted to scan anatomical objects located within the center opening and generate images of the same, wherein the CT imaging unit is configured to scan substantially the full range of the anatomy placed within the center opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
         FIG. 1  is a schematic external view of a conventional CT imaging system; 
         FIG. 2  is a schematic top view of the conventional CT imaging system shown in  FIG. 1 ; 
         FIG. 2A  is a schematic top view of the conventional CT imaging system shown in  FIG. 1 , but reduced in size so as to have a center opening just large enough to receive the head of a patient; 
         FIGS. 3 ,  4  and  5  are schematic views of a novel CT imaging system formed in accordance with the present invention; 
         FIG. 6  is a schematic top view of the novel CT imaging system shown in  FIGS. 3-5 ; 
         FIGS. 7 and 8  are schematic views showing the X-ray tube assembly and rotating drum assembly of the novel CT imaging system in  FIGS. 3-5 ; 
         FIGS. 9-11  are schematic views of the X-ray tube assembly shown in  FIG. 7 ; 
         FIGS. 12 and 13  are schematic views showing the mount of the X-ray tube assembly shown in  FIG. 7 ; 
         FIGS. 14-16  are schematic views showing the mount and the power connector of the X-ray tube assembly shown in  FIG. 7 ; 
         FIGS. 17 and 18  are schematic views showing the X-ray tube of the X-ray tube assembly shown in  FIG. 7 ; 
         FIGS. 19 and 20  are schematic views showing various aspects of the heat sink of the X-ray tube assembly shown in  FIG. 7 ; 
         FIG. 21  is a schematic view showing the heat sink mounted to the X-ray tube; 
         FIGS. 22-25  are schematic views showing the X-ray tube and heat sink secured to the mount and the power connector of the X-ray tube assembly shown in  FIG. 7  (but with the heat sink rendered transparent in  FIGS. 24 and 25  so as to reveal further aspects of the construction); and 
         FIGS. 26-28  are schematic views showing various aspects of the collimator and the collimator support of the X-ray tube assembly shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The Mobile CT Imaging System In General 
     Looking now at  FIGS. 3-5 , there is shown a novel mobile CT imaging system  5  formed in accordance with the present invention. 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, i.e., the head of the patient when mobile CT imaging system  5  is to be used in stroke applications. 
     As seen in  FIG. 5 , torus  10  generally comprises a 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 the X-ray beam  40  (generated by X-ray tube assembly  25  and detected by X-ray detector assembly  30 ) is passed through 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. As a result, by passing the X-ray beam through the anatomy along a range of radial positions, while also passing the X-ray beam through the anatomy along a range of longitudinal positions, mobile CT imaging system  5  can create the desired computer model of the scanned anatomy. Significantly, with mobile CT imaging system  5 , scanning is conducted while the patient remains stationary and the CT imaging system is moved, as will hereinafter be discussed in further detail. 
     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 computer model, may be of the sort well known in the art and may be located in torus  10  and/or base  15 . 
     Still looking now at  FIG. 5 , base  15  comprises a transport assembly  50  for moving mobile CT imaging system  5  about relative to the patient. More particularly, as disclosed in the aforementioned U.S. patent application Ser. No. 11/193,941, which patent application is hereby incorporated herein by reference, 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 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 without being moved. As discussed in detail in the aforementioned U.S. patent application Ser. No. 11/193,941, 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 the mobile CT imaging system  5 . However, as also discussed in detail in the aforementioned U.S. patent application Ser. No. 11/193,941, gross movement mechanism  55  may be omitted entirely, and only fine movement mechanism  60  may be provided, in which case fine movement mechanism  60  is used to both (i) move mobile CT imaging system  5  to the patient prior to scanning, and (ii) move the mobile CT imaging system relative to the patient during scanning. 
     Base  15  preferably also includes other system components in addition to those discussed above, e.g., batteries  70  for powering the electrical components of CT machine  5 , etc. 
     The various components of CT imaging system  5  are engineered so as to provide a relatively small, mobile and inexpensive CT imaging system. Among other things, and as will hereinafter be discussed in further detail, mobile CT imaging system  5  is sized so that its center opening  20  is just large enough to receive the head of a patient. This permits the CT imaging system to be considerably smaller in size, thereby facilitating its mobility. 
     As noted above, if CT imaging system  5  utilized a conventional, “on-center” X-ray beam configuration, such a size reduction would result in only the top half of the head being scanned, since the patient&#39;s shoulders would prevent the lower half of the head from reaching the mid-point of the depth of rotating drum assembly  35 , i.e., from passing through the X-ray beam. 
     The present invention overcomes this problem by providing a novel approach for positioning the X-ray tube assembly and the X-ray detector assembly within the CT imaging system, so as to permit scanning substantially the full range of the anatomy placed within the center opening of the CT imaging system. As a result, the mobile CT imaging system can have a center opening just large enough to receive the head of a patient, yet permits scanning of the entire head of a patient. 
     More particularly, as seen in  FIG. 6 , and as will hereinafter be discussed in further detail, the present invention provides a novel mobile CT imaging system utilizing an “off-center” X-ray beam configuration, with the X-ray beam being positioned adjacent to the entrance of the center opening of the CT imaging system. This construction permits the CT imaging system to be constructed with a center opening just large enough to receive the head of a patient, yet permits scanning of the entire head of a patient. As a result, a mobile CT imaging system can be provided with a greatly reduced size, but which also permits scanning of the full head of the patient. 
     Off-Center X-Ray Beam Construction 
     As noted above, and looking now at  FIGS. 6 and 7 , mobile CT imaging system  5  comprises X-ray tube assembly  25 , X-ray detector assembly  30 , and rotating drum assembly  35 , wherein X-ray beam  40  is positioned “off-center” relative to the depth of the center opening of the CT imaging system, with the X-ray beam being positioned adjacent to the entrance of the center opening of the CT imaging system. 
     Looking now at  FIGS. 7 and 8 , X-ray tube assembly  25  and rotating drum assembly  35  are shown. Rotating drum assembly  35  comprises an annular drum  75  ( FIG. 8 ). A face plate  80  ( FIGS. 7 and 8 ) is secured to the front side of annular drum  75 , so that face plate  80  rotates in conjunction with annular drum  75 . X-ray tube assembly  25  is mounted to face plate  80  so that X-ray tube assembly  25  also rotates in conjunction with the drum. 
     Looking next at  FIGS. 7-11 , X-ray tube assembly  25  generally comprises a mount  100  for supporting the various components of X-ray tube assembly  25  and securing those components to face plate  80 ; a power connector  105  for delivering power from a power source to X-ray tube assembly  25 ; an X-ray tube  110  for emitting X-rays; a heat sink  115  for drawing heat away from X-ray tube  110 ; a collimator support  120 ; and a collimator  125  for collimating the X-rays emitted by X-ray tube  110  and “focusing” those X-rays on X-ray detector  30  ( FIG. 5 ). The various components of the X-ray tube assembly  25  are designed to interconnect with one another so as to collectively form a relatively compact, lightweight and inexpensive “monoblock” assembly, as shown in  FIGS. 7-11  and as discussed in further detail in pending U.S. patent application Ser. No. 11/399,283, which patent application is hereby incorporated herein by reference. 
     More particularly, and looking now at  FIGS. 9-13 , mount  100  generally comprises a frame  130  which includes a canister  135  for receiving other components, as will hereinafter be discussed, and a pair of brackets  140  ( FIGS. 9 and 10 ) for securing frame  130  to face plate  80 . Additionally, and looking now at  FIGS. 9-11  and  14 - 16 , power connector  105  is attached to mount  100  so as to supply power contacts to, and close off, the rear end of canister  135 . 
     X-ray tube  110  is shown in  FIGS. 17 and 18 . X-ray tube  110  is preferably of the sort well known in the art of airport security scanners (e.g., it may be a RAD-12™ Rotating Anode X-ray Tube of the sort manufactured by Varian Medical Systems of Palo Alto, Calif.), and is generally characterized by a rear cylindrical portion  141 , a front cylindrical portion  142 , an annular face  143  formed at the intersection of rear cylindrical portion  141  and front cylindrical portion  142 , rear electrical connectors  145  for delivering power to X-ray tube  110 , an emitter opening  150  for emitting X-rays from the X-ray tube, and an alignment keyway  155  for use in appropriately aligning X-ray tube  110  in the X-ray tube assembly  25 , as will hereinafter be discussed. While not shown in the drawings, it will be appreciated by those skilled in the art that the X-ray tube&#39;s anode is disposed in front cylindrical portion  142 , adjacent to emitter opening  150 . 
     Looking next at  FIGS. 19 and 20 , heat sink  115  is characterized by a front cylindrical portion  170 , a rear cylindrical portion  175  terminating in an end surface  176 , an annular face  180  formed at the intersection of front cylindrical portion  170  and rear cylindrical portion  175 , an axial opening  183  extending along the length of heat sink  115 , a window  185  for passing X-rays through heat sink  115 , and a front recess  190  ( FIG. 19 ) for receiving a portion of collimator support  120 , whereby to connect collimator  125  to heat sink  115 , as will hereinafter be discussed. In order to increase the heat transfer capacity of heat sink  115 , it is preferable to have multiple openings formed in the heat sink, whereby to increase its effective surface area. These multiple openings are preferably in the form of a plurality of circumferential slots  195 , and a plurality of radial slots  200 , formed in both front cylindrical portion  170  and rear cylindrical portion  175 . 
     As seen in  FIG. 21 , heat sink  115  is mounted onto X-ray tube  110  by seating heat sink  115  on the X-ray tube&#39;s front cylindrical portion  142 , with the rear surface  176  ( FIG. 20 ) of heat sink  115  engaging annular face  143  ( FIG. 17 ) of the X-ray tube, and with window  185  ( FIGS. 19 and 20 ) of heat sink  115  aligned with emitter opening  150  ( FIG. 17 ) of X-ray tube  110 . This arrangement positions the heat-conveying mass of heat sink  115  adjacent to the heat-producing anode of X-ray tube  110 , and permits X-rays exiting emitter opening  150  to pass through the heat sink via window  185 . 
     As seen in  FIGS. 22 and 23 , X-ray tube  110  and heat sink  115  are positioned, as a subassembly, in canister  135  so that the X-ray tube&#39;s electrical connectors  145  electrically connect to power connector  105 , whereby to deliver electrical power to X-ray tube  110 . As seen in  FIGS. 24 and 25 , which show the assembly with the heat sink rendered transparent so as to show additional construction details, an alignment pin  156  ( FIG. 25 ) is used to align the alignment keyway  155  in X-ray tube  110  with a corresponding alignment keyway  157  formed in canister  135 , whereby to ensure proper orientation of the X-ray tube relative to mount  100 . A plurality of clamps  160  ( FIGS. 24 and 25 ), secured by bolts  165 , engage annular face  143  of the X-ray tube so as to secure X-ray tube  110  in position within canister  135 . Preferably Belleville washers (or other spring washers) are provided to accommodate any thermal expansion of the components. 
     Looking next at  FIGS. 9 ,  11 , and  22 - 28 , collimator support  120  supports collimator  125  relative to X-ray tube  100  and heat sink  115 , with collimator opening  205  ( FIG. 28 ) aligned with window  185  ( FIGS. 19 and 20 ) of heat sink  115  (and hence with emitter opening  150  of X-ray tube  110 ). More particularly, an arm  210  of collimator support  120  is received in front recess  190  of heat sink  115 , with a base  215  ( FIGS. 26 and 27 ) of collimator support  120  being received in a recess  220  ( FIGS. 22 and 23 ) of mount  100 . As a result of this construction, collimator opening  205  is kept in alignment with window  185  of heat sink  115  and hence in alignment with emitter opening  150  of X-ray tube  110 , so that collimator  125  may “focus” the X-rays emitted by X-ray tube  110  onto X-ray detector  30  ( FIG. 5 ). 
     Heat sink  115  is preferably formed out of the same material as the anode of X-ray tube  110 , such that heat sink  115  will thermally expand at the same rate as the anode of X-ray tube  110 , thereby ensuring that window  185  of heat sink  115  remains in alignment with the anode of the X-ray tube  110  even if X-ray tube  110  gets hot and undergoes some thermal expansion. Furthermore, since collimator  125  is fixed to heat sink  115  via collimator support  120 , collimator opening  205  remains aligned with window  185  of heat sink  115  even if thermal expansion causes some change in the position of window  185  of heat sink  115 . Thus, by virtue of the foregoing construction, the emitter of X-ray tube  110  will remain in axial alignment with window  185  of heat sink  115  and opening  205  of collimator  125 , regardless of any thermal expansion occurring among the parts. 
     Thus, in accordance with the present invention, and as shown in  FIGS. 6-28 , X-ray tube assembly  25 , X-ray detector assembly  30 , and rotating drum assembly  35  are all constructed so that X-ray beam  40  is positioned “off-center” relative to the depth of the center opening of the CT imaging system, with the X-ray beam being positioned adjacent to the entrance of the center opening of the CT imaging system. As noted above, this construction permits the entire head of the patient to be scanned, even where the center opening of the CT imaging system is sized just large enough to accommodate the head of the patient. As a result, a significantly smaller, and hence mobile, CT imaging system can be constructed. 
     In addition to the foregoing, since the center opening of the novel CT imaging system  5  is smaller than conventional CT imaging systems, thereby resulting in the X-ray tube assembly being positioned closer to the tissue being scanned, and since the anatomy being scanned by the novel CT imaging system  5  is thinner than the range of anatomies scanned by conventional CT imaging systems (e.g., the head of the patient versus the torso of the patient), significantly lower X-ray energies can be used with the novel CT imaging system  5 . By way of example but not limitation, CT imaging system  5  can make excellent images using only 1 kW of power, versus the 36-80 kW of power normally used with conventional CT imaging systems. The use of lower X-ray energies further simplifies the creation of a small, highly mobile CT imaging system. 
     Use 
     The novel CT imaging system  5  is preferably used as follows. When a patient arrives at the emergency room presenting stroke-like symptoms, they are quickly scanned in the emergency room, on their gurney, using CT imaging system  5 , which is pre-positioned in the emergency room. More particularly, CT imaging system  5  is raised on its gross movement mechanism  55 , i.e., by actuating hydraulic actuators  65 . CT imaging system  5  is then moved on its casters to the patient, so that the patient (while still lying on their gurney) is positioned within the center opening  20  of CT imaging system  5 . As noted above, CT imaging system  5  is constructed so that center opening  20  is sized so as to be just larger than the head of the patient. Thereafter, hydraulic apparatus  65  is activated so that CT imaging system  5  is supported on its fine movement mechanism  60  (i.e., the centipede belt drives). Scanning is then commenced, with fine movement mechanism  60  precision-advancing CT imaging system  5  relative to the patient during scanning. Scanning of the full head of the patient is achieved, even though the center opening of the CT imaging machine is too small to receive the patient&#39;s shoulders, inasmuch as the CT imaging machine is provided with the “off-center” X-ray beam configuration discussed above. 
     Application To Other Types Of Scanning Systems 
     It should be appreciated that the present invention is not limited to use in medical applications or, indeed, to use with CT machines. Thus, for example, the present invention may be used in connection with CT machines used for non-medical applications, e.g., with CT machines which are used to scan inanimate objects. Furthermore, the present invention may be used with non-CT-type scanning systems. 
     Modifications 
     It will be appreciated that still further embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure. It is to be understood that the present invention is by no means limited to the particular constructions herein disclosed and/or shown in the drawings, but also comprises any modifications or equivalents within the scope of the invention.