Abstract:
Certain embodiments include a system and method for positioning a patient with a patient positioning system. The system includes a patient positioning surface for supporting a patient. The system also includes a lift subsystem for adjusting elevation of the patient positioning surface, a longitudinal subsystem for moving the patient positioning surface in a longitudinal direction, a lateral subsystem for moving the patient positioning surface in a lateral direction, a tilt subsystem for tilting the patient positioning surface, and a rotation subsystem for rotating the patient positioning surface. The system further includes a control subsystem for controlling operation of the patient positioning system and a base affixed to a floor for securing the patient positioning system. The control subsystem may perform iso-center tracking to maintain a region of interest of the patient in an image area during tilt. The control subsystem may also avoid collision with the ground and/or predetermined objects.

Description:
Background of Invention  
         [0001]    The present invention generally relates to a patient positioning platform. In particular, the present invention relates to a patient positioning platform with particular use in vascular applications.  
           [0002]    Patient positioner platforms allow a medical practitioner, such as a doctor, nurse or technician, to position a patient during a medical procedure, such as XR, CT, EBT, nuclear, and PET procedures. Patient positioner platforms, such as tables or other supports, allow a patient to be elevated, moved in lateral &amp; longitudinal directions, rotated and/or tilted during a procedure. Patient positioning platforms improve a medical practitioner&#39;s ability to examine and/or perform a medical procedure on a patient.  
           [0003]    There is a need for an improved patient positioning platform that may be used in angiography, neurology, and cardiac procedures. Current patient positioner platforms may introduce limitations in obtaining images of blood flow in arteries, heart, lungs, or brain, for example. Thus, a patient positioning system that improves stability and reliable positioning for blood flow imaging in angiography, neurology, cardiac and other such procedures would be highly desirable.  
           [0004]    Additionally, there is a need for an improved patient positioning platform that may be used for emerging vascular procedures, such as emergent situations, venous access, and CO 2  studies. Emergent situations include emergency, life-threatening or serious situations, such as falling artery pressure or a blood vessel rupture, that prompt immediate medical attention. Proper and easy positioning of a patient may help a medical practitioner provide treatment to correct the emergent situation. Venous access relates to insertion of a catheter into a patient for introduction or retrieval of fluids in a patient&#39;s veins. Proper and easy positioning of a patient may aid insertion of the catheter as well as introduction or extraction of materials through the catheter. CO 2  studies involve injecting carbon dioxide as a contrast agent in patient veins. While CO 2  is excreted on the first pass of the blood through the lungs, it is desirable to limit the possibility of contamination or toxicity in certain areas of the body, such as the brain. Proper and reliable positioning of a patient may help reduce the chance of CO 2  contamination during CO 2  studies of the patient.  
           [0005]    Currently, patient positioner platforms possess limitations in properly positioning a patient for vascular applications, such as emergent situations, venous access, and CO 2  studies. Additionally, many current patient positioner platforms lack flexibility to accommodate emergent situations, venous access, and CO 2  studies of a patient. Therefore, a patient positioning system that provides reliable and easy positioning of a patient with flexibility to accommodate a variety of vascular applications, such as emergent situations, venous access, and CO 2  studies, would be highly desirable.  
           [0006]    Thus, a need exists for a patient positioning system that provides a reliable, flexible and complete solution for vascular and other medical applications.  
         SUMMARY OF INVENTION  
         [0007]    Certain embodiments include a system and method for positioning a patient with a patient positioning system. The system includes a patient positioning surface for supporting a patient. The system also includes a lift subsystem for adjusting elevation of the patient positioning surface, a longitudinal subsystem for moving the patient positioning surface in a longitudinal direction, a lateral subsystem for moving the patient positioning surface in a lateral direction, a tilt subsystem for tilting the patient positioning surface, and a rotation subsystem for rotating the patient positioning surface. The system further includes a control subsystem for controlling operation of the patient positioning system. The control subsystem may also avoid collision with the ground and/or predetermined objects.  
           [0008]    In a certain embodiment, the control subsystem performs iso-center tracking to maintain a region of interest of the patient in an image area during tilt. The lift subsystem adjusts elevation of the patient positioning surface using a two-stage synchronized telescopic lift system. The longitudinal subsystem moves the patient positioning surface in a longitudinal direction using a two-stage synchronized telescopic longitudinal system. The longitudinal and lateral subsystems allow manual or motorized movement of the patient positioning surface in lateral direction and/or longitudinal direction.  
           [0009]    The system may also include a base affixed to a floor for securing the patient positioning system. The system may also include patient restraints for securing the patient to the patient positioning surface. The system may also include a power-on brake for braking when a voltage is supplied to the power-on brake and a power-off brake for braking when a voltage is removed from the power-off brake. The system may further include at least one encoder for determining the position of the patient positioning surface. The encoder may allow the patient positioning surface to return to a recorded position.  
           [0010]    The method includes vertically positioning a patient positioning surface to a desired height to allow a patient to be loaded onto the patient positioning surface, rotating the patient positioning surface to a position to allow a patient to be loaded onto the patient positioning surface, and loading a patient on the patient positioning surface. The method further includes positioning the patient for a medical procedure by rotating, lifting, lateral motion, longitudinal motion, and/or longitudinal tilting of the patient positioning surface. The method also includes maintaining a region of interest of the patient during movement of the patient positioning surface.  
           [0011]    The method may also include unloading the patient from the patient positioning surface. The method may also include returning the patient positioning surface to a horizontal starting position for emergency situations. The method may further include securing the patient to the patient positioning surface. Additionally, the method may include locking the patient positioning surface during the medical procedure. Also, the method may include manually moving the patient positioning surface in at least one of the lateral and longitudinal directions.  
           [0012]    Certain embodiments of the present invention include a patient positioning system. The patient positioning system includes a table for positioning a patient, a base attaching the table to a floor, and a user interface for controlling movement of the table. The table is capable of rotation, lift, and longitudinal motions. The table is also capable of longitudinal tilt. A region of interest of the patient is maintained in an image area during tilt. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 illustrates a patient positioning system that is used in accordance with an embodiment of the present invention.  
         [0014]    [0014]FIG. 2 illustrates a telescopic lift system used in accordance with an embodiment of the present invention.  
         [0015]    [0015]FIG. 3 illustrates a longitudinal system used in accordance with an embodiment of the present invention.  
         [0016]    [0016]FIG. 4 depicts a tilt system used in accordance with an embodiment of the present invention.  
         [0017]    [0017]FIG. 5 depicts a lateral system used in accordance with an embodiment of the present invention.  
         [0018]    [0018]FIG. 6 depicts a rotation system used in accordance with an embodiment of the present invention.  
         [0019]    [0019]FIG. 7 depicts positions of the patient positioning surface used in accordance with an embodiment of the present invention.  
         [0020]    [0020]FIG. 8 shows positions of the patient positioning surface used in accordance with an embodiment of the present invention.  
         [0021]    [0021]FIG. 9 depicts a tilting of the patient positioning surface with and without iso-center tracking used in accordance with an embodiment of the present invention.  
         [0022]    [0022]FIG. 10 illustrates a flow diagram for a method for positioning a patient in a medical imaging system used in accordance with an embodiment of the present invention. 
     
    
       [0023]    The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, certain embodiments are shown in the drawings. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings.  
       DETAILED DESCRIPTION  
       [0024]    [0024]FIG. 1 illustrates a patient positioning system  100  that is used in accordance with an embodiment of the present invention. The patient positioning system  100  includes a patient positioning surface  105 , a base  10 , a telescopic lift system  120 , a longitudinal system  130 , a tilt system  140 , a lateral system  150  and a rotation system  160 . The patient positioning system  100  is grouted, or fixed to the floor at the table base  110 .  
         [0025]    To enhance loading and unloading of a patient, the patient positioning surface  105  may rotate around a vertical axis using the rotation system  160 . The patient positioning surface  105  may also be manually rotated about the rotation system  160 . To move the patient to an image area, the patient positioning surface  105  may move vertically using the telescopic lift system  120  from a height at which the patient may be conveniently loaded to a height where imaging may occur (780 mm to 1080 mm, for example). To move a portion of the patient&#39;s body into the image area, the patient positioning surface  105  may move in a lateral direction (+/−140 mm from a normal imaging position, for example) using the lateral system  150 .  
         [0026]    Additionally, the telescopic lift system  120  may provide a stroke or lift motion for iso-center tracking. Iso-center is the point at which three axes of an x-ray imaging system gantry meet (not shown). Iso-center tracking maintains a patient region of interest at the iso-center during tilt or other movement of the patient positioning system  100 . The intersection of the longitudinal and transverse axes (the iso-center) does not shift when the patient positioning surface  105  is tilted or rotated. Additional stroke for iso-center tracking is provided by the telescopic lift system  120  supported by a telescopic guide mechanism to accommodate a moment resulting from overhanging load.  
         [0027]    For head to toe coverage of the patient, the patient positioning system  100  may use longitudinal motion from the longitudinal system  130 . For bolus chasing (following a bolus or contrast agent through a patient&#39;s blood vessels), the longitudinal motion may be motorized with a variable speed motor (2 to 15 cm/sec, for example) using the longitudinal system  130  and a guide mechanism. In a certain embodiment, in addition to motorized motion, lateral and longitudinal axes include a clutch to support manual panning of the patient positioning surface  105 . That is, the clutch may be released to allow the patient positioning surface  105  to be positioned manually by an operator.  
         [0028]    For emerging vascular procedures, such as emergent situations (falling artery pressure, for example), venous access and CO 2  studies, the patient positioning surface  105  may tilt head up and head down in the longitudinal direction (12 degrees up and 20 degrees down, for example). A region of interest of the patient may remain at the iso-center or the image area when the patient positioning surface  105  is tilted. In an embodiment, the region of interest remains in the iso-center or the image area using synchronized motion of the telescopic lift system  120 , the longitudinal system  130  and the tilt system  140  as defined by the Inverse Kinematics Formula.  
         [0029]    In an embodiment, mechanical and electrical interlocks and position feedback from the patient positioning system  100  help to ensure patient safety. Patient restraints may be provided to keep the patient on the patient positioning surface  105  and to help ensure patient safety. Certain embodiments of the patient positioning system  100  help to ensure a high level of patient safety through effective safety interlock systems and redundant systems for avoiding single point failures.  
         [0030]    [0030]FIG. 2 illustrates a telescopic lift system  200  used in accordance with an embodiment of the present invention. The telescopic lift system  200  is similar to the telescopic lift system  120  described above in relation to FIG. 1 and the patient positioning system  100 . The telescopic lift system  200  provides a stroke for lift motion to move the patient positioning surface  105  from a height where the patient may be conveniently loaded to a position where imaging occurs. In addition, the telescopic lift system  200  may also provide a stroke for vertical compensation during iso-center tracking.  
         [0031]    The telescopic lift system  200  provides a stroke higher than that of the collapsed height of the patient positioning surface  105 . In an embodiment, the telescopic lift system  200  includes a single motor  213  that drives a two-stage ball screw  203 ,  216 . The telescopic lift system  200  has two-stage linear motion (“LM”) guides (first stage LM guides  214  and second stage LM guides  220 ) to compensate for moments. The LM guides  214 ,  220  help provide accurate, consistent and smooth linear motion along the guides (rails, for example). Both stages of the telescopic lift system  200  are synchronized. Synchronizing the stages and driving both stages with a single motor  213  allows the telescopic lift system  200  to be compact, have a high load-carrying capacity, and maintain a high degree of precision. Thus, the telescopic lift system  200  addresses and improves deficiencies in stroke, load-carrying capacity, and high moment-carrying capacity that are constraints in current off-the-shelf lifting systems.  
         [0032]    The telescopic lift system  200  includes a guidance system. The guidance system includes a main structure  202 , a first stage structure  218 , and a second stage structure  221 . The main structure  202  of the lift system is fixed to a base  230 . The main structure  202  houses first stage LM guide blocks  204  for the first stage of the telescopic lift system  200 . The first stage LM guides  214  are fixed to the first stage structure  218 . The first stage LM guides  214  slide through first stage LM guide blocks  204  and second stage LM guide blocks  217 . In an embodiment, the first stage structure  218  has a stroke of 305 mm. The second stage structure  221  houses the second stage LM guides  220 . The second stage LM guides  220  slide through the second stage LM guide blocks  217 . In an embodiment, the second stage structure  221  has additional stroke (305 mm for example). In an embodiment, the combined stroke of the first stage structure  218  and the second stage structure  221  is 610 mm.  
         [0033]    The telescopic lift system  200  also includes a drive system. Elements of the drive system are connected to the first stage structure  218  through a drive plate  210 . A motor/gearbox  213  is fixed to the drive plate  210 . The motor/gearbox  213  provides torque to drive stages one and two of the telescopic lift system  200 . The motor/gearbox  213  includes a gear-A  209 . The gear-A  209  drives a gear-B  208 . The gear-B  208  is fixed to a rotary nut  215  for a stationary ball screw  203 . The stationary ball screw  203  is fixed to the base  230 . Rotation of the gear-A  209  and the gearB  208  translates the first stage structure  218  with the drive plate  210  through the stationary ball screw  203 . The gear-B  208  also meshes a gear-C  207 . The gear-C  207  rotates a second stage rotating ball screw  216 . The second stage rotating ball screw  216  is housed in a bearing in the drive plate  210 . The second stage rotating ball screw  216  translates a normal nut  219  in the same direction as the first stage. The normal nut  219  is fixed to the second stage structure  221 . Simultaneous movement of elements of the drive system facilitates a lift stroke of, for example, 610 mm. The gear-C  207  also meshes with a gear-D  205  that is fixed to an absolute encoder  212  for motion control applications. A fail-safe electromagnetic brake  211  is located on the load side of the drive system and is fixed to a gear-E  206 , which is driven by gear-D  205 . The feedback from the encoder  212  sends signals to the brake  211  through a motion control system  170  (not pictured) in case of failure of any drive elements.  
         [0034]    [0034]FIG. 3 illustrates a longitudinal system  300  used in accordance with an embodiment of the present invention. The longitudinal system  300  is similar to the longitudinal system  130  described above in relation to FIG. 1 and the patient positioning system  100 . The patient positioning system  100  allows longitudinal motion for imaging in the forward direction (1700 mm, for example). For iso-center tracking during tilting of the patient positioning surface  105 , the patient positioning surface  105  may move longitudinally in the reverse direction (25 mm, for example).  
         [0035]    Longitudinal motion is produced by the longitudinal system  300 . The longitudinal system  300  includes two-stage telescopic rails with LM guides  380 . Longitudinal motion is produced through a rack and pinion mechanism driven by a motor  310 . Motion of the two telescopic rails is synchronized through an additional rack and pinion mechanism. The longitudinal system  300  also includes a clutch  360  that disengages the motor  310  of the longitudinal system  300  from drive to aid in manual panning of the patient positioning surface  105 . An absolute encoder  350  is used to determine the position of the patient positioning surface  105  in the longitudinal direction.  
         [0036]    The two-stage telescopic longitudinal system  300  is divided into a top section and a bottom section. The motor  310  drives the top section. The top and bottom sections are synchronized to aid in low and uniform panning of the patient positioning surface  105  and to help avoid slippage of the bottom section during tilt of the patient positioning surface  105 .  
         [0037]    The first stage, or top c-channel, of the telescopic longitudinal system  300  is driven by a main drive pinion  320  and a main rack  325  through the motor  310 . The main rack  325  drives the brake pinion  330  of the brake axis  335 . The drive from the brake pinion  330  is transmitted to a synchronization pinion  340  through a drive gear and a driven gear. The drive and driven gear from a gearbox  370  determine the direction of movement of a synchronization rack  345 . The synchronization pinion  340  drives the synchronization rack  345 , which is mounted on to the second stage or bottom c-channel of the telescopic longitudinal system  300 . The relative motion and mechanical advantage for manual panning are achieved by the gear ratio of the brake pinion  330  and synchronization pinion  340 .  
         [0038]    [0038]FIG. 4 illustrates a tilt system  400  used in accordance with an embodiment of the present invention. The tilt system  400  is similar to the tilt system  140  described above in relation to FIG. 1 and the patient positioning system  100 . The tilt system  400  is capable of tilting the patient positioning surface  105  head up and head down in the longitudinal direction (+/−20 degrees, for example). The tilt system  400  also supports iso-center tracking during a tilt (head down at −16 degrees, for example).  
         [0039]    The tilt system  400  includes a tilt drive system. The tilt drive system includes a ball screw  402  and a rotary nut  405  driven by a motor  409 . In an embodiment, the tilt drive system is hinged at the rear side of the patient positioning surface  105 . The tilt system  400  includes a LM guide  401  to compensate for moments. In an embodiment, the tilt system  400  is hinged  413  at the front side of the patient positioning surface  105 . The motor  409  drives the rotary nut  405 . The rotary nut  405  linearly translates the ball screw  402  for tilt about the tilt axis hinge  413  at the front of the patient positioning surface  105 .  
         [0040]    The tilt system  400  is fixed to the main structure  202  of the lift system  200 . A tilt plate  412  is hinged to the main structure  202  through a tilt axis hinge  413  at the front side of the main structure  202 . The tilt plate  412  is supported at the rear by an LM guide  401  and the non-rotating ball screw  402  through a hinge  414 . The rotary nut  405  of the ball screw  402  and LM guide blocks  403  are housed on a plate  407  which is mounted to the main structure  202  through a hinge  415 . The motor  409 , as well as a brake and an incremental encoder, is mounted to the plate  407 . A drive gear  406  on the motor  409  meshes with a driven gear  404  on the rotary nut  405  of the ball screw  402 . The driven gear  404  also meshes with a brake gear  408 . A fail-safe electromagnetic brake  410  and an absolute encoder  411  are mounted on the shaft of the brake gear  408 .  
         [0041]    The motor  409  drives the rotary nut  405  of the ball screw  402  through the drive gear  406  and the driven gear  404 . The rotary nut  405  translates rotary motion into linear motion of the non-rotating ball screw  402  which may push/pull the tilt plate  412  with respect to the tilt axis hinge  413 . The driven gear  404  meshes with the brake gear  408 . The fail-safe electromagnetic brake  410  is mounted on to the brake gear  408  shaft. The fail-safe brake  410  may prevent the tilt system  400  from collapsing even if the drive gear  406 , motor  409 , and/or motor brake fails. The fail-safe electromagnetic brake  410  prevents collapse by sensing signals from the incremental encoder in the motor and the absolute encoder  411  connected to the brake gear  408  shaft through the motion control system  170 .  
         [0042]    [0042]FIG. 5 illustrates a lateral system  500  used in accordance with an embodiment of the present invention. The lateral system  500  is similar to the lateral system  150  described above in relation to FIG. 1 and the patient positioning system  100 . The lateral system  500  moves the patient positioning surface  105  in the lateral direction (+/−140 mm, for example). The lateral system  500  includes a motor  510 , a timing belt drive  520 , LM guides  530 , brake  540 , and an encoder  550  for lateral movement. The lateral system  500  produces motion through the timing belt drive  520 . The timing belt drive  520  is driven by the motor  510  and is guided by the LM guides  530 . The lateral system  500  also includes a clutch  560  that disengages the lateral system  500  from drive by the motor  510  to aid in manual panning of the patient positioning surface  105 .  
         [0043]    The lateral system  500  and the longitudinal system  300  support both motorized and manual panning of the patient positioning surface  105 . In an embodiment, a user interface (not pictured) controls the motor  310  of the longitudinal system  300  and the motor  510  of the lateral system  500  to facilitate motorized panning. For example, a joystick in the user interface may control the motors  310 ,  510  for motorized panning of the patient positioning surface  105 . The clutches  360 ,  560  in the longitudinal system  300  and the lateral system  500  disengage the motors  310 ,  510  to facilitate manual panning.  
         [0044]    A panning operation is carried out to move the patient to the image area in the longitudinal and/or lateral direction. Manual panning is possible when the patient positioning surface  105  is positioned horizontally. When manual panning mode is selected, the longitudinal and lateral clutches  360 ,  560  disengage the patient positioning surface  105  from the lateral and longitudinal motors  310 ,  510 . Then the patient positioning surface  105  floats on the anti-friction LM guides, which allow movement of the patient positioning surface  105  in the lateral and/or longitudinal directions. The patient positioning surface  105  may be locked at any position.  
         [0045]    [0045]FIG. 6 illustrates a rotation system  600  used in accordance with an embodiment of the present invention. The rotation system  600  is similar to the rotation system  160  described above in relation to FIG. 1 and the patient positioning system  100 . The rotation system  600  includes a bull gear  610 , a bearing clamping plate  620 , pinions  630 ,  635 , a power-off brake  640 , and a power-on brake  645 . In an embodiment, the patient positioning surface  105  rotates manually. The rotation system  600  rotates the patient positioning surface  105  about the vertical axis (+/−90 degrees, for example). The rotation system  600  may include a docking mechanism for locating the zero position (0 degrees in the rotation axis) easily.  
         [0046]    The bull gear  610  is machined onto the bearing clamping plate  620 . The bull gear  610  is stationary. Two pinions  630 ,  635  are mounted at 90 degrees on the bearing housing  625 . The pinions  630 ,  635  mesh with the bull gear  610  and rotate along with the main structure  202 . The power-off brake  640  is mounted directly on the pinion  630  and the power-on brake  645  is mounted on the pinion  635 . When the brake  640 ,  645  is applied the pinion  630 ,  635  holds the main structure  202  against the stationary bull gear  610 . The use of a gear drive with the rotation system  600  allows torque multiplication.  
         [0047]    In an embodiment, the patient positioning system  100  includes power-on brakes that are active when power is supplied and power-off brakes that are active when power is shut off. The rotation system  600  has a power-on brake  645  and a power-off brake  640 . During medical procedures, the rotation system  600  activates both power-on and power-off brakes  640 ,  645  to help ensure stability and rigidity of the patient positioning surface  105 . When power is off, only the power-off brake  640  may be activated for ease in removing the patient from the patient positioning surface  105 .  
         [0048]    In an embodiment, the combination of the power-on and power-off brakes  640 ,  645  results in three states. In the first state, power is supplied to the power-on brake  645 , and no power is supplied to the power-off brake  640  (100% capacity). Both brakes  640 ,  645  hold the table through pinions  630 ,  635  and provide a rigid connection. During procedures (i.e., during imaging and while loading the patient on to the patient positioning surface  105 ), power is supplied only to the power-on brake  645 , and both brakes  640 ,  645  hold the patient positioning surface  105 .  
         [0049]    In the second state, no power is supplied to both the power-on brake  645  and the power-off brake  640  (50% capacity). In a power fail condition, the power-off (failsafe) brake  640  engages, but the power-on brake  645  is released. Thus, the patient positioning surface  105  may be rotated with less effort to, for example, unload a patient in case of emergency.  
         [0050]    In the third state, power is supplied to the power-off brake  640  and not to the power-on brake  645  (0% capacity). Thus, both brakes  640 ,  645  are released, and the patient positioning surface  105  is free to rotate. The free patient positioning surface  105  may be used for repeating the scans at an angle. The free patient positioning surface  105  may also be used after loading the patient to bring the patient positioning surface  105  to the zero position.  
         [0051]    The motion control system  170  (not shown) for the patient positioning system  100  includes three major parts: a user interface, an I/O board, and servo nodes (not shown). A user may move the patient positioning surface  105  using the user interface. User interface commands are processed by the I/O board (CPU). Commands are then sent to corresponding servo nodes that control the respective axis movements. In an embodiment, a power PC-based micro controller is used as the CPU. An application program, which is running on a real-time operating system, may control the patient positioning system  100 .  
         [0052]    The patient positioning surface  105  may be prevented from tilting at the lowest position of the patient positioning surface  105 , since the lowest position of the patient positioning surface  105  is used for easy loading and unloading of the patient. Each axis is provided with a power-off brake to lock the motion during a power failure and/or any malfunction of the motors and servo drives. Each axis is provided with a software limit, a hardware limit, and mechanical hard stops. An example of a software limit is the following: during normal operations, the patient positioning surface  105  shall not move beyond a certain point. An example of a hard limit is the following: the patient positioning surface  105  is controlled by a limit switch. The limit switch stops the motion of the patient positioning surface  105  if a software malfunction occurs. An example of a mechanical hard stop is as follows: an end stop is provided as backup if both software and hardware limits fail. The coordinates of all axes may be continuously monitored to avoid a collision with the ground and/or predetermined objects.  
         [0053]    In operation, the patient positioning system  100  may tilt the patient positioning surface  105  head down or head up and/or rotate the patient positioning surface  105 . FIGS. 7 and 8 illustrate some exemplary positions of the patient positioning surface  105  in an imaging system. For iso-center tracking, the telescopic lift system  200 , tilt system  400 , and longitudinal system  300  are simultaneously activated in an inverse kinematic relationship to keep the patient region of interest at the iso-center or image area during tilt of the patient positioning surface  105 . FIG. 9 depicts a tilting of the patient positioning surface with and without iso-center tracking used in accordance with an embodiment of the present invention.  
         [0054]    Kinematics defines relationships between positions, velocities, and accelerations of axes of motion (transverse, longitudinal, etc.) in the patient positioning system  100 . Direct kinematics involves determining the position of the patient positioning surface  105  in the patient positioning system  100  in terms of angles and displacements between the axes. Inverse kinematics involves determining relationships between the axes (and the telescopic lift system  200 , longitudinal system  300 , and tilt system  400 ) based on the location of the patient positioning surface  105  and/or the patient in the patient positioning system  100 .  
         [0055]    Safety interlocks and redundant safety systems are provided to help ensure patient safety in the patient positioning system  100 . In an embodiment, all axes in the patient positioning system  100  are designed to have position encoders to read the coordinates of the patient positioning surface  105  at any position at any time. Ground clearance of the patient positioning surface  105  is calculated, and motion of the patient positioning surface  105  stops if the ground clearance is less than or equal to a specified safe limit. Thus, collisions may be avoided.  
         [0056]    In a certain embodiment, all axes are designed with redundant safety systems to avoid single point failures and to help ensure patient safety. Each motorized axis of the patient positioning system  100  may include an incremental encoder and brake (on the drive or motor side). Each motorized axis may also include an absolute encoder and brake at the load side. During normal operation, the brake at the drive side operates to stop any axis of motion. If a problem arises in the driveline, a difference in incremental encoder (drive side) and absolute encoder (load side) readings operates the brake at the load side to stop the axis. Additionally, as described above, both power-on and power-off brakes may be activated during procedures to ensure stability and rigidity of the patient positioning surface  105 . During power-off conditions, only the power-off brake is activated to allow easy removal of the patient by rotating the patient positioning surface  105 .  
         [0057]    The following are some examples of operations involving the patient positioning system  100 . The examples are provided to illustrate the use of components and systems in the patient positioning system  100  and are not intended to be a comprehensive list.  
         [0058]    For example, a patient may be loaded on the patient positioning surface  105 . First, the patient positioning surface  105  is positioned at 780 mm from the ground using the telescopic lift system  200 . Then, the patient positioning surface  105  is rotated to the right-hand or left-hand side using the rotation system  600 . Next, the patient is loaded onto the patient positioning surface  105 . Patient restraints may be used to secure the patient on the patient positioning surface  105 . To unload the patient, the patient positioning surface  105  is rotated to the right-hand or left-hand side using the rotation system  600 . The patient positioning surface  105  is repositioned to a height of 780 mm from ground level by the lift system  200 . The patient restraints are unlocked, and the patient is removed from the patient positioning surface  105 .  
         [0059]    Also, for example, the patient may be moved into the image area. First, the rotation system  600  rotates the patient positioning surface  105  to zero degrees. Next, the patient positioning surface  105  is moved vertically to the image area using the telescopic lift system  200 . Then, the patient positioning surface  105  is adjusted laterally in the image area with the lateral system  500 . The patient positioning surface  105  may also be adjusted longitudinally by the longitudinal system  300  to reach a desired position in the image area.  
         [0060]    A patient may be positioned on the patient positioning surface  105  for several medical procedures and examinations. For example, in angiography, a patient&#39;s height may be adjusted by raising and lowering the patient positioning surface  105  using the telescopic lift system  200 . Additionally, four-way panning may be accomplished using the lateral system  500  and the longitudinal system  300 . For peripheral angiography, the patient positioning surface  105  may also be rotated into proper position using the rotation system  500  and tilted using the tilt system  400 .  
         [0061]    For bolus chasing, patient restraints may be used to secure the patient on the patient positioning surface  105 . The longitudinal system  300  advances the patient positioning surface  105  in the longitudinal direction in bolus mode (015 cm/sec). For venous access and CO 2  studies, for example, patient restraints may keep the patient in touch with the patient positioning surface  105 , and the lift  200 , longitudinal  300 , and tilt  400  systems may be used for iso-center tracking to maintain a desired image area during movement. In emergent situations, restraints secure the patient on the patient positioning surface  105 , and the tilt system  400  tilts the patient to a desired position.  
         [0062]    Cardiac pulmonary resuscitation (CPR) is a procedure performed for patients who suffer from cardiac arrest, for example. In order to bring a patient to a CPR position if the patient positioning surface  105  is in a horizontal position, the patient positioning surface  105  is moved longitudinally in a backward direction using the longitudinal system  300 . Then, the patient positioning surface  105  is lowered using the lift system  200 . If the patient positioning surface  105  is titled, the tilt system  400  returns the patient positioning surface  105  to a horizontal position. Then, the longitudinal system  300  moves the patient positioning surface  105  backward, and the lift system  200  lowers the patient positioning surface  105  to enable CPR to be performed on the patient.  
         [0063]    [0063]FIG. 10 illustrates a flow diagram  1000  for a method for positioning a patient in a medical imaging system used in accordance with an embodiment of the present invention. First, at step  1010 , the patient positioning surface  105  is positioned vertically at a desired distance from the ground, such as 780 mm. Then, at step  1020 , the patient positioning surface  105  is rotated to allow the patient to be loaded on the patient positioning surface  105 . Then, at step  1030 , the patient may be secured on the patient positioning surface  105 .  
         [0064]    At step  1040 , the patient is positioned in the image area. The patient positioning surface  105  is rotated, moved vertically, moved laterally, and/or moved longitudinally to position the patient or a region of interest in the patient in the image area. At step  1050 , during imaging or other medical examination or procedure, the patient positioning surface  105  may be moved laterally or longitudinally, lifted, rotated, and/or tilted to accommodate the procedure. Iso-center tracking may be used to maintain the position of a patient region of interest inside the image area.  
         [0065]    Then, at step  1060 , in the event of difficulties requiring CPR or other emergency procedure, the patient positioning surface  105  may be repositioned to a horizontal position. The patient positioning surface  105  may also be moved backward and lowered to a starting position for easy access to the patient.  
         [0066]    Finally, at step  1070 , the patient may be unloaded from the patient positioning surface  105 . The patient positioning surface  105  may be rotated to allow access to the patient. The patient positioning surface  105  is adjusted to a height that will allow the patient to easily be removed. After patient restraints are removed, the patient is removed from the patient positioning surface  105 .  
         [0067]    Thus, certain embodiments of the present invention provide a fixed table that may be used for vascular and other applications. The patient positioning system  100  may rotate the patient positioning surface  105  about the vertical axis for loading and unloading patients. The rotation system  600  is equipped to adjust holding torque under power-off and power-on conditions.  
         [0068]    The telescopic lift system  200  is used by the patient positioning system  100  to accommodate high load, moments, and lift motion or stroke to position a patient in the image area. The tilt system  300  allows the patient positioning system  100  to tilt head up or head down and maintain a desired image through iso-center tracking. The patient positioning system  100  includes a lateral system  500  to move the patient positioning surface  105  laterally using motorized and/or manual panning.  
         [0069]    The patient positioning system supports motorized bolus chasing with head to toe coverage so that an image may be traced as the contrast agent travels through the patient. The patient positioning system  100  tracks the coordinates of the patient positioning surface  105 . Positioning tracking facilitates collision avoidance with the ground and/or other predetermined objects. Tracking also allows the patient positioning system  100  to return the patient positioning surface  105  to a previously recorded and/or memorized position.  
         [0070]    While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.