Abstract:
A computed tomography scanner includes a base system and a rotor system. The rotor system has an axle that is rotationally mounted to the base system. At least one x-ray source is mounted to the rotor system. A power interface system at least partially disposed about the axle couples power to the x-ray source. The power interface may include a slip ring assembly or a cable assembly that winds and unwinds about the axle as the rotor system rotates.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX  
       [0003]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0004]     1. Field of the Invention  
         [0005]     The present invention relates to computed tomography (CT) scanners, more particularly, to portable CT scanners designed for use outside the typical diagnostic environment or where the examined subject is small.  
         [0006]     2. Description of the Related Art  
         [0007]     Computed tomography is a diagnostic procedure that uses special x-ray equipment to obtain cross-sectional axial images of a subject. The general classification of CT scanners is based upon the arrangement of components in the scanners and the mechanical motion required to collect data. The term “generation” with an associated number is applied to the CT scanners discussed below because of the order in which these designs were introduced. However, a higher generation number does not necessarily mean a higher performance system. Each generation scanner has a variety of advantages, including speed of data acquisition, as well as disadvantages, such as cost and susceptibility to imaging artifacts.  
         [0008]     Typically, first generation CT scanners have a single x-ray source, which is rigidly connected to a single x-ray detector. To collect one slice of imaging data, a pencil beam x-ray is passed from the source through the subject to the detector cell. The source and the detector are then moved slightly with respect to the subject and another pencil beam x-ray is passed from the source through the subject to the detector. This process is repeated until the necessary data is collected.  
         [0009]     Second generation CT scanners have an x-ray source rigidly connected to an array of x-ray detectors. The detectors all lie within the same scan plane, but are not necessarily contiguous nor do they span the entire circumference of a subject being examined. To collect one slice of imaging data, the x-ray source emits radiation over a large angle through the subject, which is captured by the array of detectors. The source and the array of detectors are moved slightly with respect to the subject and the x-ray source emits radiation again over a large angle through the subject, which is captured by the array of detectors. This process is repeated until the necessary data is collected. Since the second generation CT scanner is able to capture multiple projections of radiation for each emission, the second generation CT scanner is significantly more efficient and faster than the first generation CT scanner.  
         [0010]     Third generation CT scanners have an x-ray source which is rigidly fixed to an array of x-ray detectors and the source and detectors are mounted for rotational movement about an axis. The array of detectors is large enough to allow the simultaneous measurement of an x-ray projection of the entire cross-section of the subject. To collect one slice of imaging data, the source and the array of detectors are rotated about the subject taking projection data throughout each revolution.  
         [0011]     Fourth generation CT scanners have an x-ray source mounted for rotational movement about an axis and a stationary ring of detectors so there is a detector opposing the rotating x-ray source at each angle. To collect one slice of imaging data, the source is rotated about the subject and radiation emitted from the source throughout each revolution is captured by the ring of detectors.  
         [0012]     There are some variations for each of the generations of CT scanners discussed above. For example, the CT scanners discussed above may use a half a rotation or several rotations about the subject to obtain one slice of imaging data. As another example, the CT scanners discussed above may have multiple arrays of detectors or multiple x-ray sources to acquire multiple slices of imaging data simultaneously.  
         [0013]     In each of the generations of CT scanners discussed above, in order to obtain an image of the entire subject or a section of the subject, the subject is translated axially through the patient aperture by a motorized platform resembling a couch or bed. The translation may be in discrete steps (“step and shoot” mode) or in a continuous motion (spiral mode).  
         [0014]     Since the subject needs to be moved through the aperture of these CT scanners, all of the components of the CT scanners are built around the aperture for the subject. These components include (1) the main bearing or other mechanical rotor support system, (2) the rotor drive system utilizing a motor or a belt, (3) cables, slip rings, and data links that transfer power and data to and from the rotor, and (4) rotational encoders or resolvers used to measure the angular position of the rotor.  
         [0015]     To permit a subject to pass into these CT scanners a large diameter opening is required, but this larger opening complicates the design of the components for the CT scanners, making them more expensive. Additionally, for a given angular rotation velocity, the linear velocity of some interfacing components, particularly the bearing and slip rings, is large, limiting the scanner speed and resulting in noise and rapid wear. Further, because it is difficult and expensive to transfer the high voltages required by the x-ray source through large diameter slip rings, modern CT scanners have the high voltage generator mounted directly on the rotor, further complicating the design. Also, because it is difficult to transfer cooling liquid to and from the rotor, removal of heat generated on the rotor is accomplished by air flow, which is less efficient than liquid cooling.  
         [0016]     Most of these large diameter CT scanners generate scattered radiation during operation. Therefore, they need to be installed in special radiation shielded rooms or otherwise provide suitable radiation shielding to onlookers, operators, and patients during operation. Personnel need to be located outside of the scan room during the scan or must wear radiation protective clothing. Further, personnel must be continuously monitored for exposure to ionizing radiation from the CT scanner as cumulative effects may be harmful as well.  
         [0017]     Prior CT scanners have also failed to address the inability to perform CT scans on critically ill patients in intensive care units or operating rooms who are too sick to transport to Radiology for a CT scan. The movement of critically ill patients for imaging studies can endanger the patient since such patients are often physiologically unstable, require accurate and on-going monitoring of their physiologic functions, may be receiving precisely controlled intravenous medications, such as vasopressors, and may have spinal injuries that could be aggravated by movement.  
         [0018]     Additionally, in cases of patients with known or suspected major craniocerebral injury, there is often no time to transfer the patient from the trauma bed to the CT scanner couch to perform the CT scan. Often, the minutes required to transfer the patient would result in diminished outcomes or even death. Further, time is often wasted in disconnecting and re-connecting life support equipment, intravenous hydration solutions and medications, and physiological monitoring equipment, as part of the transfer to the CT scanner bed. Some intensive care unit patients, such as those receiving continuous hemofiltration, jet-ventilation, extra-corporeal lung assist, aortic balloon counterpulsation or other invasive support, cannot be transported. Movement of any intensive care unit patient requires physicians, nurses, respiratory therapists, and other support staff, all at increased cost and with increased risk to the patient. Similar challenges exist when attempting to assess diagnostic results in a surgical setting such as in the operating room or in the management of acute cerebral trauma cases requiring surgery.  
         [0019]     A CT scanner with a gantry structure that overcomes some of the disadvantages discussed above is made by Analogic Corp. of Peabody, Mass. Some versions of this CT scanner have a gantry body that has a range of tilting motion of up to sixty degrees, so a patient&#39;s head may be scanned by altering the angle of the gantry to cover an anatomical area of interest. However, for patients with relatively smaller necks, and for those patients who suffer from head or neck trauma that make accurate positioning of the head and neck impossible, adjusting the gantry tilt angle may not sufficiently cover the entire area of interest. With this CT scanner, no movement of the subject is needed to image a volume of the subject. The CT scanner is connected to an external power source, but is also provided with a rechargeable battery to boost the power during scan. The battery is mounted on the rotor, requiring the rotor to go to a “park” position for re-charging. Some versions of this CT scanner have wheels that make it portable.  
       SUMMARY OF THE INVENTION  
       [0020]     A scanner in accordance with embodiments of the present invention includes a base system and a rotor system. The rotor system has an axle that is rotationally mounted to the base system. At least one x-ray source is mounted to the rotor system. A power interface system at least partially disposed about the axle couples power to the x-ray source.  
         [0021]     A scanning system in accordance with embodiments of the present invention includes a base system, a rotor system, and a power source. The rotor system has an axle that is rotationally mounted to the base system. At least one x-ray source is mounted to the rotor system. A power interface system at least partially disposed about the axle couples power from the power source to the x-ray source.  
         [0022]     A method for making a scanner in accordance with embodiments of the present invention includes providing a base system and a rotor system. The rotor is provided with an axle that is mounted to the base system for rotational movement. At least one x-ray source is mounted to the rotor system. A power interface system is provided that is at least partially disposed about the axle and that couples power to the x-ray source.  
         [0023]     A method for making a scanner in accordance with embodiments of the present invention includes providing a base system, a rotor system, and a power source. The rotor is provided with an axle that is mounted to the base system for rotational movement. At least one x-ray source is mounted to the rotor system. A power interface system is provided that is at least partially disposed about the axle and that power from the power system to the x-ray source.  
         [0024]     The present invention provides a portable CT scanner which can be brought directly to the patient, enabling CT scanning without moving the patient from their hospital bed. As a result, with the present invention critical CT scans can be performed more quickly and with less risk to the patient resulting from unnecessary movement of the patient. Further, critically ill patients who previously were not candidates for CT scans can now have images generated of anatomical regions, such as the head and neck areas, to aid in rapid diagnosis.  
         [0025]     The reduced size of the CT scanner in accordance with the present invention also makes it truly portable, affording a mobile CT system that may be moved from room to room or from bed to bed as the diagnostic imaging needs of patients are assessed. The reduced size of the CT system further reduces the radiation shielding requirements which enables the scanner to be operated in areas without traditional radiation shielding.  
         [0026]     The present invention also incorporates a head and neck support system for the patient which establishes known reference points between the CT system and the patient support to enable precise and repeatable scans as may be necessary in an operating room environment to repeatedly monitor on-going surgical procedures and assess the results of emergency craniotomies in head trauma cases, for example.  
         [0027]     Further, the system and method of the present invention allows the display and manipulation of the captured images, presenting clinically useful images for use in immediate patient diagnosis and treatment decisions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]      FIG. 1A  is a side, cross-sectional view of a CT scanner of the present invention;  
         [0029]      FIG. 1B  is a front, cross-sectional view of the CT scanner of  FIG. 1A ;  
         [0030]      FIG. 2A  is a side, cross-sectional view of a CT scanner of the present invention utilizing an alternate detector assembly embodiment;  
         [0031]      FIG. 2B  is a front, cross-sectional view of the CT scanner of  FIG. 2A ;  
         [0032]      FIG. 3  is a side, cross-sectional view illustrating an alternate embodiment of a CT scanner of the present invention;  
         [0033]      FIG. 4  is a block diagram of a CT scanner system of the present invention;  
         [0034]      FIG. 5  illustrates an alternate slip ring apparatus for transferring high voltage power to the rotor in a CT scanner of the present invention;  
         [0035]      FIGS. 6A and 6B  are diagrams of a cable alternative to the slip ring apparatus of  FIG. 5 ;  
         [0036]      FIGS. 7A, 7B , and  7 C show several configurations of the subject head support platform for use with the CT scanner system of the present invention; and  
         [0037]      FIG. 8  shows a configuration of the radiation shield for use with the CT scanner of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]     A CT scanner  200 ( 1 ) in accordance with embodiments of the present invention is illustrated in  FIGS. 1A and 1B . The CT scanner  200 ( 1 ) includes a base  202 , carriage system  204 ( 1 ), and rotor system  206 ( 1 ) with an x-ray source  248  and a detector assembly  252 ( 1 ), although the CT scanner  200 ( 1 ) can comprise other numbers and types of components, devices, and systems, such as power conditioning assemblies and x-ray tube cooling assemblies, in other configurations. The present invention provides a portable CT scanner  200 ( 1 ) which can be brought directly to the patient, enabling CT scanning without moving the patient from their hospital bed.  
         [0039]     Referring to  FIGS. 1A and 1B , an embodiment of the portable CT scanner  200 ( 1 ) is illustrated. Since the standard components of CT scanners along with their connections and operation are well known, only the major components of the CT scanner  200 ( 1 ) that are related to the present invention are described in detail herein.  
         [0040]     The base  202  is a cart-shaped structure which supports the carriage system  204 ( 1 ), rotor system  206 , and other components, both required and optional, of the CT scanner  200 ( 1 ), such as batteries  212 , power conditioning and control systems, and cooling system, although the base  202  could have other shapes and configurations and could support and house other devices.  
         [0041]     The base  202  includes wheels  208  which are connected to the cart-shaped structure which can be used to move the scanner  200 ( 1 ) into position to scan a portion of the anatomy, such as the head H of subject S, although other types of devices for making the base  202  mobile can be used or the base  202  may be not have any type of mobility system. The base  202  may also include other components to enhance the mobility and control of positioning the CT scanner  200 ( 1 ), such as a motor to drive the wheels, a steering system, and a braking system.  
         [0042]     The base  202  is also provided with jacks  210  which are used to stabilizing the CT scanner  200 ( 1 ) during a scanning operation when the jacks  210  are extended, although other types of stabilizing devices could be used or could be left off of the base  202 .  
         [0043]     The batteries  212  are coupled to and can be used to supply power to one or more devices of the CT scanner  200 ( 1 ), such as the x-ray source  248  and a detector assembly  252 ( 1 ). For example, the batteries may provide additional power to one or more devices of the CT scanner  200 ( 1 ) when demand increases during a scan operation. In another example, the scanner  200 ( 1 ) may be unplugged from a remote external power supply altogether and operated for a limited time using only batteries  212 . This feature further improves the portability of the scanner  200 ( 1 ) as used in a clinical setting. The batteries  212  can be recharged during breaks between scans.  
         [0044]     The base  202  also includes a scanner cover  266  that provides a protective external shell for the scanner  200 . The cover  266  is mounted on a frame supported by base  202 . The cover  266  forms a cavity  267  that extends into the scanning region within the rotor system  206 . As shown in  FIGS. 1A and 1B , the cavity  267  is 30 cm in diameter and 30 cm deep beyond slice plane  256  when carriage system  204  is in the front-most position. A depth of 30 cm provides a 20 cm scanning range plus a 10 cm free space beyond the limits of the subject S, accommodating patients with attached surgical devices such as stereotactic surgical appliances, intravenous medication delivery equipment, and other devices that may lie near the anatomical region of interest. The cover  266  may be made of any rigid material such as fiberglass or a polycarbonate composite. The cylindrical section  268  intersecting slice plane  256  in the entire range of the carriage translation is made of an x-ray transparent material, such as polycarbonate, so that the cover  266  does not attenuate the x-ray beam, create image artifacts, or otherwise negatively affects the imaging process.  
         [0045]     CT scanners generate heat, particularly during operation of the x-ray tube. A common solution to removing heat from the x-ray tube is to provide it with a heat exchanger. Accordingly, an oil to air heat exchanger is mounted on the rotor system  206  to remove heat from the x-ray source  248 . The resultant hot air is vented from within the cover  266 . Further, the x-ray source  248  may be cooled by an oil to water heat exchanger and the heat removed by circulating cold water to and from the rotor system  206 . Suitable rotating fluid joints may be used to facilitate the heat exchange.  
         [0046]     The carriage system  204 ( 1 ) includes a carriage structure  203  and a linear motion system  205 , although the carriage system  204 ( 1 ) can comprise other numbers and types of devices and systems in other configurations. The carriage structure  203  has a bearing housing  222  located at one end. Two sets of rotational bearings  224  are mounted in the bearing housing  222  to provide the rotor system  206  with stability during rotation and comprise a pair of single row angular contact ball bearings, although other types and numbers of bearings in other arrangements can be used. The bearings  224  in the bearing housing  222  support an axle  226  for rotational movement about a rotation axis A-A.  
         [0047]     The bearings  224  employed by the present invention are substantially smaller, easier to manufacture at the required precision, and less expensive than the main rotational bearing used in previous CT scanners because of the reduced size of the portable CT scanner  200 ( 1 ). In previous CT scanners, the main bearing is installed around the large diameter gantry aperture, which is normally 60 cm, whereas in the present invention the bearings  224  are installed around a small diameter axle  226 . Therefore, for a given angular velocity of the rotor system  206 , for example, one revolution per second, the linear velocity of the bearing components is substantially less than the linear velocity in the bearings of previous CT scanners. Consequently, the acoustic noise generated by the rotation is smaller, and the wear of the components is reduced in the CT scanner  200 ( 1 ).  
         [0048]     The axle  226  extends from the outer surface of the closed end  225  of drum  247 ( 1 ) coaxial with the rotation axis A-A. Generally, the diameter of the axle  226  is smaller than the outer diameter of the drum  247 ( 1 ). Another end of the carriage structure  203  is connected to a linear motion system  205  that moves the carriage system  204 ( 1 ) and the rotor system  206  linearly along a linear axis B-B. The rotation axis A-A and the linear axis B-B are substantially parallel to each other, although other configurations can be used, such as having the rotation axis A-A at an angle with respect to the direction of the linear axis B-B.  
         [0049]     The linear motion system  205  includes linear sliding rails  214  and a carriage drive system  215 , although the linear motion system  205  can comprise other numbers and types of devices and systems in other configurations. The linear sliding rails  214  are mounted on the base  202  and allow the carriage structure  203  of the carriage system  204 ( 1 ) to travel linearly relative to the base  202 . The range of travel depends upon the linear range over which the scanner  200 ( 1 ) is intended to operate. By way of example, the linear range may be about 20 cm.  
         [0050]     The carriage drive system  215  includes a motor  216  mounted on the base  202 , a lead screw  218  coupled to the motor  216 , and a nut  220  mounted on the lead screw  18 , although the carriage drive system  215  can comprise other numbers and types of devices and systems in other configurations. The motor  216  is a DC electrical motor, although other types of motors, such as an AC electrical motor or any other type of rotational motor, could be used. The motor  216  is directly coupled to the lead screw  218  or via a gear assembly. As the motor  216  rotates the lead screw  218 , the screw threads cause the nut  220 , the carriage system  204 ( 1 ), and the rotor system  206  to move linearly on the rails  214 . By way of example, an alternative embodiment for the carriage drive system  215  could have a linear motor, a position encoder, sensors which signal the two end positions or the position of carriage system  204 ( 1 ) relative to base  202 .  
         [0051]     The rotor system  206  includes a circular drum  247 ( 1 ), a rotor drive system  227 , a rotational encoder  236 , a collimator  262 , the x-ray source  248 , and the x-ray detector assembly  252 ( 1 ), although the rotor system  206  can comprise other numbers and types of devices and systems in other configurations.  
         [0052]     The circular drum  247 ( 1 ) has a hollow interior  265  with an open end  223  and a closed end  225 . The wall of the closed end  225  is generally perpendicular to the rotation axis A-A. This structure is rigid and helps to minimize radiation exposure to others in the room when the CT scanner  200 ( 1 ) is in operation. Although a circular drum  247 ( 1 ) is shown, other types of structures that can support the x-ray source  248  and the x-ray detector assembly  252 ( 1 ) relative to the rotation axis A-A may also be used, including closed or opened-end structures with other cross-sectional shapes, such as circular, triangular, hexagonal, and octagonal. Additionally, the closed end  225  of the drum does not have to be completely closed. It may consist merely of struts up to a completely solid surface as long as it provides a rigid foundation for the axle  226 . Additionally, the wall of the drum  247 ( 1 ) does not have to completely encircle the interior. A section of the drum  247 ( 1 ) opposite the x-ray source  248  may be open.  
         [0053]     In order to allow a subject S to lay in a more comfortable and convenient position, the rotation axis A-A may be adjusted to a tilted position, typically about 70 to 100 above horizontal, although other angles could be used. This tilt can be achieved in a number of ways. For example, the rotor system  206  can be mounted at a fixed angle relative to the carriage system  204 ( 1 ) or can include an angular position adjustment system, such as an adjustable bracket system or and electromechanical adjustment system, that allows the angle of the rotor system  206  to be adjusted to one position or to a continuously changing angular position. In an alternative example, the entire carriage system  204 ( 1 ) may be mounted at an angle relative to the floor F.  
         [0054]     The rotor drive system  227  includes a motor  228  mounted to the carriage system  204 ( 1 ), a motor pulley  232  driven by the motor  228 , an axle pulley  234  mounted to the axle  226 , and a belt  230  between the motor pulley  232  and the axle pulley  234 . The motor  228  is a DC electrical motor, although other types of motors such as an AC electrical motor or an other type of rotational motor, could be used. The motor  228  is directly coupled to the motor pulley  232 , although other manners for coupling the motor  228  to the pulley  232  could be used, such as via a gear assembly. In an alternative example, the rotor drive system  227  may comprise a ring motor mounted on carriage system  204 ( 1 ) and which is directly coupled to axle  226 .  
         [0055]     The rotational encoder  236  is connected to the carriage system  204 ( 1 ) and measures the angular position of the rotor system  206 . The rotational encoder  236  provides an absolute angle reading with a precision of at least 0.50 and a relative angle reading with precision of at least 0.005°. Within these limits, accuracy of rotor movement and positioning is ensured, and likewise image quality and repeatability of scans.  
         [0056]     A collimator  262  is connected to the drum  247 ( 1 ) and is used to adjust the x-ray beam from the x-ray source  248  to a fan shape with the desired fan angle and width, although other types of devices for adjusting the x-ray beam could be used. Collimation is achieved in the collimator  262  by metal blades made of highly-x-ray absorbent materials. Optionally, the collimator  262  includes a bowtie filter and other radiation filters depending upon the slice profile desired.  
         [0057]     The x-ray source  248  and the detector assembly  252 ( 1 ) are connected to the drum and are spaced from each other and from the rotation axis A-A. A plane perpendicular to the rotation axis A-A is formed along the line of an x-ray beam extending from a focal spot  254  in the x-ray source  248  to an arc of detector elements  253  in the detector assembly  252 ( 1 ). This plane is referred to as slice plane  256 . The center of rotation  258  is the point of intersection between the slice plane  256  and rotation axis A-A.  
         [0058]     The x-ray source  248  and the detector assembly  252 ( 1 ) are mounted on the rotor system  206  and rotated about subject S. In  FIG. 1A , the CT scanner is in the process of being positioned about the head H of subject S so the slice plane  256  extends through the region of interest in the subject. A single image slice or multiple image slices, depending upon the structure of the detector assembly  252 ( 1 ), are obtained in one revolution of the rotor system  206 . In order to image the entire subject S, the subject S and the rotor system  206  are translated axially relative to each other.  
         [0059]     The x-ray source  248  is an x-ray tube mounted and aligned on the drum  247 ( 1 ) with brackets  260 . The x-ray source  248  may be a single-ended tube, for example with the anode at ground potential and the cathode at −120 KV, or the x-ray source  248  may be a dual-ended tube, with the anode at +60 KV and the cathode at −60 KV, although other types of x-ray sources  248  can be used, such as a rotating anode tube or a fixed target tube. The focal spot  254  is positioned asymmetrically with respect to the length of the x-ray source  248  so that the slice plane  256  is positioned as near to the scanner front surface  259  as practical when the carriage system  204 ( 1 ) is in the front-most position.  
         [0060]     As shown in  FIGS. 1A and 1B , the x-ray detector assembly  252 ( 1 ) comprises an arc of x-ray detector elements  253  that is mounted and aligned on the rotor system  206  with a support structure  264 . The detector assembly  252 ( 1 ) includes a single arc of detector elements  253  that acquires a single slice of data per x-ray exposure, although other types of detector assemblies can be used, such as one with two or more parallel arcs of detector elements that acquire two or more slices of data per x-ray exposure. The detector assembly  252 ( 1 ) may be made of scintillator crystals coupled to silicon photodiodes or any other appropriate detector assembly type, for example, photomultiplier tubes. Further, the detector assembly  252 ( 1 ) may include an anti-scatter grid collimator.  
         [0061]     Due to the unique size and manner of practicing the present invention, the approach to signal and power transfer methods is also unique to the present invention. To facilitate signal transfer both to and from the rotor system  206 , there are a number of interfaces that may be employed. Power interface systems include, for example, slip rings and cables, while interface systems for transferring control and data signals include, for example, wired interfaces such as slip rings and cables, as well as wireless interfaces such as optical coupling, radio frequency transmission, and inductive and capacitive coupling, all of which are well-known as methods for transferring information.  
         [0062]     A power interface system is shown in  FIG. 1A , and includes a bracket  238  is mounted on the carriage system  204 ( 1 ) to support a contact array  244  which is coupled to a disc-like slip ring  246  mounted to the outer surface  225  of the rotor system  206 . Also, the slip ring assembly may be cylindrical and built around the axle  226 .  
         [0063]     The slip ring assembly  243  is used to transfer high-voltage power from the high-voltage power source  194  mounted on the base  202  to the x-ray source  248 . Alternatively, a high-voltage generator may be mounted on the rotor system  206  as a separate unit or in a “monoblock” configuration as a combined unit with the x-ray source  248 . In this fashion, power at low voltage (up to several hundred volts) is transferred to the rotor system  206  and converted to high voltage directly on the rotor system  206 .  
         [0064]     If the x-ray source  248  is a single-ended x-ray tube, only one voltage relative to ground is necessary. Correspondingly, the high-voltage slip ring assembly  243  may be designed for a single voltage transfer. A typical single-ended tube voltage for scanning a human head is approximately 120 KV, the polarity depending on the structure of x-ray tube. However, if the x-ray source  248  is a dual-ended x-ray tube, requiring both negative and positive voltages, the high voltage slip ring must be designed to provide both positive and negative voltages. Typical dual-ended x-ray tube voltages for scanning a human head are approximately +60 KV and −60 KV.  
         [0065]     While the present invention permits the use of substantially smaller diameter and lower cost rotational encoder  236  and slip ring assemblies  243  than previously used in CT scanners, an alternate power interface system is illustrated in  FIG. 5 . The high-voltage connection is constructed at the center of rotation, as opposed to previous designs built around the gantry aperture. In the high-voltage connection of  FIG. 5 , the x-ray source  248  is a single ended x-ray tube. Three leads  702  are provided, one for a reference high voltage and two for carrying the filament current. While many similar designs may support other voltage and lead configurations depending upon the type of x-ray tube and manner of supplying high voltage and filament current, for illustrative purposes as shown in  FIG. 5 , and for brevity, a single ended x-ray tube with a three lead configuration is shown.  
         [0066]     The axle  226  is used to support the rotor system  206  as described previously with reference to  FIG. 1A . An electrical multiconductor plug  706  at the end of a cable  708  carrying three leads  702  is mounted on the axle  226 . The plug  706  is extended by an insulator  710  made of a high dielectric material such as a dielectric ceramic. The insulator  710  is mounted within the cavity  726  in the axle  226 . At the end of the insulator  710  is a set of slip rings  712 , one ring for each of three leads  702 , made of conductive material and connected to the appropriate contacts of the plug  706 . Mating spring-loaded brushes  714  are mounted in a brush block  716 , which is mounted to the axle  226 . The brush block  716  is connected to a cable  718 , which transfers the three signals to the x-ray source. Alternatively, the rings may be mounted on the axle while the brushes may be mounted on the insulator. Likewise, the slip rings may be positioned on the face  719  of the insulator  710  around the center of rotation rather than on the side of the insulator  710 .  
         [0067]     The axle cavity  726  is fitted with an insert  720  made of a high-dielectric material as well. The insert  720  has one or more spark barriers  722  and the insulator  710  has one or more spark barriers  724 . Optionally, the cavity  726  between the insulator  710  and the insert  720  is filled with an insulating liquid or gas. A retainer ring  727  and seal  728  retain liquid or gas within the cavity  726 . A bearing  730  is provided between the carriage system  204  and the rotor axle  226  in order to maintain accurate positioning of the insulator  710  at the center of rotation. Without the bearing  730 , the insulator  710  may wobble, causing the brushes  714  to intermittently lose contact with the slip rings  712  during rotation. Additionally, the seal  728  may not retain the insulating liquid or gas and the system wear will be high. The bearing  730  may be used in any combination of the high-voltage connections as well as signal connections. Additional bearing sets may also be used to support the rotor system  206  relative to the carriage system  204 . Similarly, the insulator  710  may be mounted to the axle  226  and the brush block  716  may be mounted to the carriage system  204  with similar results.  
         [0068]     Additionally, power and, optionally, control and/or data signals may be transferred by one or more cables in a bundle rather than by slip ring assemblies. As shown in  FIGS. 6A and 6B , the rotor system  206 ( 1 ) is permitted only a limited range of rotation, for example 540 degrees. The cables  506  are sufficiently long that when the rotor system  206 ( 1 ) rotates in one direction, the cables  506  wrap around the axle  226 . When the rotor system  206 ( 1 ) rotates in the opposite direction, the cables  506  unwrap. Additionally, the cables  506  may be supported by a cable carrier assembly  508 .  
         [0069]     Referring to  FIGS. 6A and 6B , the cables  506  are shown in a completely wound state and a completely unwound state, respectively. The cables  506  are supported by a carrier assembly  508  and are anchored on one side to a block  510  mounted on the carriage  204 . The opposite end of the cables  506  is anchored to the block  512  mounted on the rotor system  206 ( 1 ) adjacent to the axle  226 . As a lower cost alternative to slip ring technology, the design illustrated in  FIGS. 6A and 6B  is advantageous over previous methods of providing signal and power terminations by cables since the cables  506  in the present invention need not wrap around a large diameter ring build around a gantry bore, but rather only around the small diameter axle  226 , thereby simplifying construction and manufacture. Regardless of the manner in which power, signal, data, and control signals are distributed, it is imperative that a robust manner of furnishing these signals to the rotor is provided.  
         [0070]     In addition to the unique configuration of the CT scanner system of the present invention, the ability to provide stable, comfortable, and repeatable positioning of a patient is essential in exploiting the inventive features of the present invention. Proper positioning of the head and neck of critically ill patients is crucial to realizing the efficacy of the present invention.  
         [0071]      FIGS. 7A, 7B , and  7 C illustrate several configurations of a platform  300  used in connection with the scanner  200  to provide a rigid and stable support for the head of the subject S during scanning. With adequate head and neck support, the subject S may be scanned in the scanner  200  without the need to transfer the subject S to a special CT bed/couch prior to performing the scan. Without the need for transferring the subject S to a special bed, CT scans may be performed on critically ill patients who were previously not candidates for CT scanning.  
         [0072]     Referring to  FIGS. 7A, 7B , and  7 C, a head section  302  is structured to fit into scanner cavity  267  and is composed of an x-ray transparent material such as polycarbonate or a composite material reinforced by carbon fiber to minimize the effect on the imaging process. The head section  302  may be supplemented with cushions and straps for stabilizing the subject&#39;s head H during scanning. As shown in  FIG. 7A , poles  304  are used to mount the platform  300  on a hospital bed using the mounts for IV poles. In  FIG. 7B , a flat section  306  is inserted underneath the subject S, so the platform  300  is balanced by the subject&#39;s weight. Additionally, the flat section  306  may be lined with radiation absorbing material to help reduce scatter radiation in the vicinity. In  FIG. 7C , a hinge  310  between the head section  302  and the flat section  308  provides for a variety of tilt angles of the head section  302  relative to the slice plane  256 . A knob  312  is used to lock the head section  302  at the desired angle. In this fashion, the subject S may be scanned without being transferred to a special bed.  
         [0073]     While a shielding platform  300  will help reduce scatter radiation, the outer surface  271  and inner surface  269  of the drum  247  may also be coated with a 2 mm to 3 mm thick layer of lead or other x-ray absorbent material of the appropriate thickness to absorb scatter radiation from the scanned subject S and from the assemblies on rotor system  206 . Due to the closed design of the scanner  200 , scatter radiation is greatly reduced over previous CT scanners with the majority of it occurring forward of the slice plane  256  since the back of the scanner is closed and shielded. However, even with the cup design of the present invention, scatter radiation may be further reduced by employing a radiation shield  400  as shown in  FIG. 8 .  
         [0074]      FIG. 8  shows a radiation shield  400  for use with the scanner  200 . The shield body  402  is made of an x-ray absorbing material, such as lead acrylic. The shield  400  is placed over the subject S during scanning to reduce scatter radiation from reaching subject S. Additionally, the shield  400  may have flexible flaps  404  to adjoin the scanner face  259  and flexible flaps  406  to further shield the subject S. The flaps  404 ,  406  may be composed of a synthetic rubber or polyvinyl chloride mixed with lead powder. Handles  408  are provided on shield  400  to facilitate moving and positioning.  
         [0075]     With the above-described configuration of the present invention, the subject S remains on a non-specialized CT bed while the scanner is operated. An image capture assembly comprises the carriage system  204 ( 1 ) and the rotor system  206 ( 1 ) and is sized to make the CT scanner  200 ( 1 ) portable. In particular, the image capture assembly is sized to be less than about one meter wide by one meter high by one meter in depth, although other dimensions for the image capture assembly can be used.  
         [0076]     A fourth generation CT scanner  200 ( 2 ) according to the present invention is illustrated in  FIGS. 2A and 2B . The fourth generation CT scanner  200 ( 2 ) is identical to the third generation CT scanner  200 ( 1 ) as described with reference to  FIGS. 1A and 1B , except as described below. Elements in  FIGS. 2A and 2B  which are like those in  FIGS. 1A and 1B  will have like reference numerals.  
         [0077]     In the embodiment shown in  FIGS. 2A and 2B , a fourth generation CT scanner is shown where the detector assembly  252 ( 2 ) is a complete ring  604  of detector elements  605  mounted outside of the rotor system  206 . At any angle of the rotor system  206 ( 2 ), there is an arc of opposing detector elements  605  responsive to radiation from the x-ray source  248 . The detector ring  604  is supported by a circular frame  606  mounted to the carriage system  204 ( 1 ) by support  608 . Additionally, the wall of the drum  247 ( 2 ) of the rotor system  206  does not completely encircle the interior and has a open-ended, partial hexagon shape. In particular, the section  610  of the drum  247 ( 2 ) of the rotor system  206  opposite the x-ray source  248  is open.  
         [0078]     Referring to  FIG. 3 , a CT scanner  200 ( 3 ) in accordance with other embodiments of the present invention is shown. The CT scanner  200 ( 3 ) is identical to the CT scanner  200 ( 1 ) described with reference to  FIGS. 1A and 1B , except as described below. Elements in  FIG. 3  which are like those in  FIGS. 1A and 1B  will have like reference numerals. The carriage system  204 ( 2 ) in the CT scanner  200 ( 3 ) does not have the linear motion system  205 . The base  202  and carriage system  204 ( 2 ) are combined into a single stationary pedestal  802 . The CT scanner  200 ( 3 ) may be used when the subject S is on a bed which translates the subject relative to the scanner  200 ( 3 ). Like the CT scanner  200 ( 1 ) of  FIGS. 1A and 1B , the rotor system  206  ( 1 ) has a position adjustment system, such as adjustable brackets or a motorized electromechanical system, for adjusting the angle of the rotor system  206 ( 1 ) with respect to the carriage system  204 ( 2 ) and the base  202 .  
         [0079]     Referring to  FIG. 4 , a scanning system  190  in accordance with embodiments of the present invention is illustrated. Elements in  FIG. 4  which are like those in  FIGS. 1A and 1B  will have like reference numerals. The scanning system  190  includes a controller  192  which is coupled to the CT scanner  200 ( 1 ), high-voltage power source  194 , mass storage or memory  196 , and video display  198 , although the scanning system  190  can comprise other numbers and types of systems, devices, and components, such as the CT scanner  200 ( 2 ) or the CT scanner  200 ( 3 ), which are coupled together in other configurations. The controller  192  includes one or more processors for executing programmed instructions for one or more aspects of the present invention as described herein, including programmed instructions for controlling the operation of a CT scanner and processing data to generate images from captured radiation in manners well known to those of ordinary skill in the art. The programmed instructions are stored in mass storage device  196  for execution by the processor in controller  192 , although the instructions could be stored in other locations. A variety of different types of memory storage devices can be used for mass storage  196  and mass storage  196  may be located in the controller  192 . The display  198  is a monitor for displaying an image reconstructed from the image data from the x-ray detector assembly  252 ( 1 ), although other types of display devices can be used. The image data or reconstructed image may also be communicated by the controller  192  to other systems.  
         [0080]     The controller  192  transmits carriage control signals to the carriage drive system  215  and receives carriage position signals which identify the position of the carriage system  204 ( 1 ) and the rotor system  206 ( 1 ), although other configurations for controlling the carriage drive system  215  can be used. Additionally, the controller  192  transmits rotor control signals to the rotor drive system  227  and receives rotor position signals which identify the position and rotational speed of the rotor system  206 ( 1 ), although other configurations for controlling the rotor drive system  227  can be used. The controller  192  also receives image data for reconstruction, storage, and display from the x-ray detector assembly  252 ( 1 ), although other configurations can be used, such as having the controller  192  transmit detector control signals to the detector assembly  252 ( 1 ).  
         [0081]     The controller  192  transmits x-ray source control signals to the power source  194  which is coupled to supply high-voltage power to the x-ray source  248  in response to these control signals. The controller  192  also receives x-ray source status signals regarding the status of power being supplied to the x-ray source  248 , although other configurations for controlling the power source  194  and the x-ray source  248  can be used.  
         [0082]     The controller  192  is also coupled to the collimator  262  (shown in  FIG. 1A ) in CT scanner  200 ( 1 ) and provides control signals for adjusting the size of the opening in the collimator  262  is so that the thickness and profile of the scanned slice can be varied according to the type of scan to be performed. The controller  192  is also coupled to the rotational encoder  236  (shown in  FIG. 1A ) which measures the angular position of the rotor system  206  and transfers that position information to the controller  192  for use in generating the rotor control signals.  
         [0083]     The operation of the CT scanner  200 ( 1 ) in the scanning system  190  will be described with reference to  FIGS. 1A, 1B , and  4 . To operate the CT scanner  200 ( 1 ), the subject S remains on a hospital bed with the subject&#39;s head H supported on the platform  300 . The subject S or scanner  200 ( 1 ) is moved so as to position the subject&#39;s head H within the scanner cavity  267 , such that the slice plane  256  coincides with the position of the first desired slice. If necessary, the height of the bed is adjusted to bring the subject&#39;s head H to the height of the scanner cavity  267 . Positioning may be facilitated by light markers or other alignment device or techniques. A radiation shield  400  may be placed over the subject S prior to initiating the scan.  
         [0084]     Once the subject S and radiation shield  400  are properly positioned, the x-ray source  248  is energized and rotation of rotor system  206  is initiated. As the x-ray exposure proceeds, projection data is acquired from the detector assembly  252 ( 1 ) and is transferred to the controller  192  as previously discussed with regard to  FIG. 4 . Once the desired rotation angle of the rotor system  206 ( 1 ) is traversed about the rotation axis A-A, image data collection for that particular slice is complete.  
         [0085]     Once data collection for a particular slice is complete, the carriage system  204 ( 1 ) is translated to a new position along the linear axis B-B and image data corresponding to the next slice (or multiple slices) is acquired. The process repeats until the entire volume of interest is scanned. As image data is received by the controller  192 , it may be stored in the mass storage  196  and cross sectional slice images may be reconstructed and viewed on the display  198 . The images may then be stored, displayed, communicated to remote computer stations, and processed to form volumetric images.  
         [0086]     The operation described above applies to scanning in “step and shoot” mode. The CT scanner  200 ( 1 ) may also be operated in spiral mode yielding similar results. Additionally, the scanner can be used in “scanogram” mode, also called “scout” or “pilot” views, where data is acquired while the slice plane  256  is moved relative to the subject S without rotation of the rotor assembly  206 , yielding a projected image. This type of projection operation is especially convenient for verifying proper positioning of the subject S prior to beginning transverse slice acquisitions.  
         [0087]     Persons skilled in the art will appreciate that the CT scanner  200 ( 1 ) can be used for scanning extremities (hands and legs), folded elbows and knees, entire bodies of babies, small size pets, and various articles of appropriately small dimensions. CT scanner  200 ( 1 ) may also be used to scan the female breast since the slice plane  256  is at or near the front surface  259  of the CT scanner  200 ( 1 ).  
         [0088]     The operation of the CT scanner  200 ( 2 ) in the scanning system  190  is identical to the operation of CT scanner  200 ( 1 ) in the scanning system  190 , except as described below. In the operation of the CT scanner  200 ( 1 ), as the carriage system  204 ( 1 ) moves the rotor system  206 ( 2 ) along the linear axis B-B from slice position to slice position, so does the entire detector ring  604 . This embodiment can be used in “step and shoot” mode where the carriage system  204 ( 1 ) is moved incrementally between slice acquisitions and in spiral mode where there is continuous data acquisition in a spiraling pattern as the carriage moves continuously during x-ray exposure. This fourth generation scanner system is a simpler design than the previous third generation system because less hardware is required to be mounted on the rotor system  206 . Therefore fewer signals and less power must be transferred to and from the rotor system  206 .  
         [0089]     The operation of the CT scanner  200 ( 3 ) in the scanning system  190  is identical to the operation of the CT scanner  200 ( 1 ) in the scanning system  190 , except as described below. After an image slice is obtained, CT scanner  200 ( 3 ) does not move the carriage system  204 ( 2 ) along the linear axis B-B because carriage system  204 ( 2 ) is fixed to base  202 . Instead, the CT scanner  200 ( 3 ) may incrementally adjust the angle of the rotor system  206 ( 1 ) with respect to the carriage system  204 ( 2 ) and periodically capture an image slice of the head H or other region being examined. The entire head H of the subject S can be imaged by tilting the rotor system  206 ( 1 ) through a range of motion where the position of the scan plane  256  is altered using the angular position adjustment system to move the rotor system  206 ( 1 ) with respect to the carriage system  204 ( 2 ) as described earlier. In this fashion, head scans may be completed without the need for an additional transverse carriage system.  
         [0090]     Having thus described the basic concept of the invention, it will be readily apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These modifications, alterations and improvements are intended to be suggested hereby, and are within the spirit and scope of the invention. Accordingly, the invention is limited only by the following claims and equivalents thereto.