Abstract:
A system for performing medical imaging in a mobile environment. The system includes a sensing array, a controller, and a mobile frame. The sensing array is configured to image a subject. The controller is in communication with the sensing array to control and process the acquisition performed by the sensing array. The sensing array is attached to the mobile frame, and the mobile frame includes wheels to facilitate movement of the system. At least one of the wheels of the base interacts with a wheel lock, such that the wheel lock prevents motion of the wheel when activated by the controller.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to a system and method for locking the wheels of a portable medical imaging device. 
         [0003]    2. Description of Related Art 
         [0004]    In a typical x-ray computed tomography system, an x-ray source projects an x-ray beam through an object and onto a detector. However, more recently portable computed tomography systems have been introduced into the market. These systems generally include an x-ray source, a detector, and a gantry system mounted to a movable base. The base may include wheels allowing the system to be taken into the room of the patient rather than moving the patient to the computed tomography system. This can reduce the possibility of injury to the patient and allow for better utilization of hospital space. While the mobility of a portable computed tomography system is very desirable, computed tomography systems take many scans of a patient at a number of angles. As such, the gantry must move, for example rotate around the patient, during the measurement scan. However, any change in the position of the system relative to the patient may introduce significant error and reduce the resolution of the measurements made by the computed tomography system. Therefore, it is important to maintain a fixed relationship between the base and the patient during scanning. 
         [0005]    In view of the above, it is apparent that there exists a need for a system and method for locking the wheels of a portable medical imaging device. 
       SUMMARY 
       [0006]    In overcoming the drawbacks and other limitations of the related art, the present invention provides a system and method for locking the wheels of a portable medical imaging device. 
         [0007]    The system includes a sensing array, a controller, and a mobile base. The sensing array is configured to image a subject. A controller is in communication with the sensing array to control and process the acquisition performed by the sensing array. The sensing array is attached to the mobile base and the mobile base includes wheels to facilitate movement of the system. At least one of the wheels of the base interacts with a wheel lock, such that the wheel lock prevents motion of the wheel when activated by the controller. 
         [0008]    In another aspect of the system, the wheel lock may prevent the wheel from rolling, swiveling, or both. In addition, the system may alert the user if the wheel lock is faulty. The controller may also prevent acquisition by the sensing array or suppress motion by a motion device if the wheel is not locked. 
         [0009]    In another aspect of the system, the system defaults to a transportation mode where at least one wheel is swivel locked when the system is powered off. 
         [0010]    In another aspect of the system, the system defaults to a free motion mode where each of the wheel locks is deactivated when the system is powered on or an alignment tool is activated. 
         [0011]    In yet another aspect of the system, the system defaults to a free motion mode where each of the wheel locks is deactivated when an emergency stop control is activated allowing the operator to quickly move the system away from the subject. 
         [0012]    Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic view of a system for performing computed tomography; 
           [0014]      FIG. 2  is a perspective view of an x-ray source and detector; 
           [0015]      FIG. 3  is a perspective view of x-ray paths projected through a voxel; 
           [0016]      FIG. 4  is a perspective view of x-ray paths and combinations of voxels through which the x-ray paths pass; 
           [0017]      FIG. 5  is a schematic view of a system for controlling wheel lock mechanisms; 
           [0018]      FIG. 6  is a perspective view of a motor assembly for locking wheels; and 
           [0019]      FIG. 7  is a flowchart illustrating a method for controlling wheel lock mechanisms. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  illustrates a portable flat panel x-ray tomography system  10  embodying the principles of the present invention. The system  10  includes an x-ray source  112  and a detector  114 . The x-ray source  112  projects x-rays, denoted by reference number  115  through an object  116  and toward the detector  114 . The detector  114 , may be a two-dimensional detector array, such as an amorphous silicon flat panel (coupled with a scintillation crystal), a traditional multi row computed tomography detector, or other similar imaging detectors. The object  116  may for example, be the head of a patient and the system  110  may be configured to image a sinus cavity within the patient. The x-ray source  112  and the detector  114  may be mounted to a structure  118 . The structure  118  maintains the position and orientation of the x-ray source  112  with respect to the detector  114 . The structure  118  includes a recess  119  that allows various objects, for example, a patient&#39;s head to be located between the x-ray source  112  and the detector  114 . 
         [0021]    The structure  118  is connected to a number of motion control devices configured to manipulate the position of the x-ray source  112  and detector  114  relative to the object  116  during scanning. The x-ray beam is projected along each path to the detector  114 . Each path generates a different intensity on the detector  114  based on the density of the object along that path, as shown in  FIG. 2 . As such, the intensity at each pixel  252  in the detector  114  corresponds to an accumulated density at each point along the line representing the x-ray path  254 . Therefore, it is helpful to represent the object  116  as a model that is made up of small cube-type elements called voxels  256 . The intensity seen at the two-dimensional detector  114  is a function of the density accumulation through each voxel  256  that the x-ray path  254  travels through. To calculate the density at a particular voxel  262 , a number of x-ray path lines  260  through each voxel  256  may be utilized to isolate the density contribution for that particular voxel  262  as shown in  FIG. 3  and  FIG. 4 . This serves as the basis for various computed tomography systems and many methods and adaptations are well known in the art. Since a computed tomography image is constructed based on many scans in various poses, the reference for each pose must be consistent. As such, it is important to maintain a known relationship between the system and the object being scanned. As such the system should closely track planned motion and constrain unwanted motion between the object and the system. 
         [0022]    Being a portable system, the system  10  includes wheels  152 ,  153 ,  154 , and  155 . To allow easy motion of the system  10 , the wheels are generally allowed to swivel as well as roll. For the purposes of this application, wheel rolling is generally considered rotation about a central axis of the wheel that is substantially parallel to the outer surface of the wheel that contacts the ground. Swiveling is generally considered rotation of the wheel about an axis that is substantially perpendicular to the central axis of the wheel and the ground. To provide maximum portability, each wheel  152 - 155  may be allowed to freely roll and swivel. However, it is contemplated herein that each or any combination of the wheels may be controlled to allow or prevent rolling and/or swiveling selectively based on the mode of the system. 
         [0023]    While the wheels  152 - 155  are important for the portability of the system  10 , it is equally important to constrain undesired motion of the system  10  during scanning. As such, the system  10  includes wheel locking mechanisms  162 ,  163 ,  164 ,  165 . As discussed above, each wheel locking mechanism  162 - 165  may selectively prevent rolling, swiveling, or both swiveling and rolling for its corresponding wheel  152 - 162 . For example, a control such as a button on the machine or a selection on a graphical user interface may be activated to initiate scanning of the object. Accordingly, the system  10  may be configured to automatically actuate one or more of the locking mechanisms  162 - 165  to prevent rolling and/or swiveling of the corresponding wheels  152 - 155 . The locking of rolling and swiveling of the wheels may be optimal during scanning. Although, locking either rolling or swiveling of a subset of the wheels may be sufficient for maintaining the relationship between the system  10  and object  116  in a more cost-effective manner. 
         [0024]    For example, two of the wheels in opposite corners of the system  10  may be locked to prevent undesired system movement. In one implementation, the front right wheel  152  may be swivel locked while the rear left wheel  155  may be full (rotation and swivel) locked. As such, translation of the system  10  is constrained by the full locking of the rear left wheel  155 , and rotation of the system  10  about the rear left wheel  155  is prevented by the swivel locking of the front right wheel  152 . Similarly, both the front right wheel  152  and the rear left wheel  155  may be full (rotation and swivel) locked to fully constrain motion of the system. In this case, the front left wheel  153  may be swivel locked during transportation of the system. 
         [0025]    Generally, the front of the system  10  is defined by the recess  119  for receiving the object  116 . As such, wheels  152  and  153  are generally defined as front wheels and wheels  154  and  155  are generally defined as rear wheels. Accordingly, wheels  152  and  154  are designated as right wheels, while wheels  153  and  155  are designated as left wheels. 
         [0026]    In addition, other combinations of wheel locking may be implemented based on the current mode of use of the system  10 . For example, in a transportation mode, one or more of the wheels may be swivel locked while all the wheels are allowed to roll freely. In one example, the front left wheel  153  may be swivel locked. 
         [0027]    In another example, the rear left wheel  155  and optionally the rear right wheel  154  may be swivel locked to aid in steering the system  10  as it is transported from room to room. In this scenario, the system will have the feel of a shopping cart where the system  10  is not allowed spin freely about any axis. Rotation is allowed only about a certain wheel base defined by the swivel locked wheel(s). The system  10  may be designed to default to the transportation mode when the system power is off, as the system will typically be shut down and unplugged prior to transportation. 
         [0028]    In alignment mode, the system  10  may allow all wheels to rotate and swivel freely. Allowing full flexibility when aligning the system, provides the flexibility to adjust the translation and rotation of the system without constraints. The system  10  may automatically enter the alignment mode upon power up of the system. As the system  10  will likely be in the proximity of the patient when it is plugged in and/or powered on. From that position, the free rotation and swivel flexibility can be used to translate or rotate the system  10  aligning it with the object  16  to be scanned. 
         [0029]    In another embodiment, the system  10  may include an alignment tool  170 . The alignment tool  170  may, for example include a laser projector indicating the optimal position of the object  16  relative to the system  10 . As such, the system  10  may be configured to automatically enter the alignment mode upon activation of the alignment tool  170 . Accordingly, a control may be provided activate the alignment tool  170  and the control may be monitored for a change in state indicative of activating the alignment tool  170 . Accordingly, the system  10  may enter the alignment mode and unlock all wheels upon sensing the change of state in the control. In another aspect of the invention, an emergency stop button may immediately change the state of the system to a free wheel mode allowing all wheels to roll and swivel freely. Based on this description one can recognize variations on the wheel locking modes discussed may be implemented without deviating from the scope of this application. As such, additional methods for utilizing the wheel locking mechanisms are provided later. 
         [0030]    The motion control devices described above may manipulate the position and orientation of the structure  118 , thus the x-ray source  112  and detector  114 , with regard to the object  116 . As such, the system may include a linear gantry  120  configured to translate the structure  118  longitudinally along an axis  126 , as denoted by arrow  122 . Similarly, a second gantry  130  may be configured to translate the structure  118  laterally with respect to the axis  126 , as denoted by arrow  132 . As such, gantry  120  and gantry  130  may be oriented with their axis of translation perpendicular to one another providing a simple two-dimensional translation function between the gantries  120 ,  130 . Further, a rotational stage  124  may be provided and connected to the structure  118  through a shaft  125 . As such, the rotational stage  124  may be configured to rotate the structure  118  about the axis  126 , as denoted by arrow  128 . In one example, the linear gantries  120  and  130  may be used for fine alignment of the source  112  and detector  114  relative to the object  116  prior to scanning. 
         [0031]    The motion devices  120 ,  124 ,  130  are connected to a controller  135 , as denoted by line  134 . The connection may be through a cable or a wireless connection, or other standard means of system communication. The motion devices  120 ,  124 ,  130  are in communication with a motion control processor  136  of the controller  135 . The motion control processor  136  generates electrical control signals to manipulate the motors of each of the motion control devices  120 ,  124 ,  130 . Similarly, the wheel lock mechanisms  162 ,  163 ,  164  and  165  are in communication with an I/O processor  182  of the controller  135  to actuate or released the wheel lock mechanisms as described elsewhere in the specification. The I/O processor  182  may communicate via a simple digital or analog output, or alternatively may communicate with smarter wheel lock mechanisms via a serial communication link or similar connection. 
         [0032]    In addition, the x-ray source  112  and the detector  114  are in communication with the controller  135 , as denoted by line  140 . As such, the detector  114  is in communication with an image acquisition and processing module  142 . The image acquisition and processing module  142  receives data from the detector  114  and calculates the density for each voxel  256 . 
         [0033]    The density for each voxel  256  is calculated by storing the intensity projection for multiple x-ray path lines  260  through the object  116 , as can be seen from  FIG. 4 . As described above, each x-ray path line  260  includes a different combination of voxels  254 . The density of the object  116  within each voxel  256  may be isolated by solving each voxel&#39;s contribution to the accumulated density along each x-ray path line  260 . Since the total density along each x-ray path  260  is known from the pixel intensity, the unknown voxel densities can be solved for utilizing the series of equations representing the voxel combinations along each x-ray path  260 . In addition, the image processing module  142  may account for any difference in intensity response for each pixel  252  of the detector  114  in reconstructing each voxel  256  in the model. As such, the intensity profile or image for each position may be stored in memory  146 . In addition, the memory  146  may also store the resulting density at each voxel and the relationship between each pixel on the detector  114 . The relationship between the intensity response for each pixel on the detector  114  may be stored as parameters of an equation or in a look-up table format. Note that multiple x-ray paths are recorded at each position of the structure (i.e., one for each pixel on the detector). 
         [0034]    In addition, the controller  135  may include a display and planning module  148  that determines the series of positions and orientations of the structure  118  that will be necessary for constructing the model of the object  116 . Such position planning may be stored in the memory  150  and transferred to or accessed by memory  138  of the motion control module  136 . In addition, the planning and display module  148  may access or transfer the voxel model information from memory  150  to memory  146  of the image processing module  142 . 
         [0035]    One embodiment of the system for locking one or more of the wheels of a medical imaging system is provided in  FIG. 5  and as denoted by reference numeral  270 . In one embodiment, locking of the wheels may occur automatically during initiation of a scan sequence. In other embodiments manipulation of the wheel locks can occur upon changing modes of the system between an acquisition mode, a transport mode, or a free motion mode. The modes may be changed through a graphical user interface denoted by reference number  272  or by a physical interface (i.e. buttons) as denoted by reference numeral  274 . The graphical user interface  272  is generated and interpreted by a general purpose or industrial computer  276 . The computer  276  may transmit commands received through the graphical user interface  272  to a programmable logic controller  278 . In a similar manner, the programmable logic programmer  278  may receive commands from the physical interface  274  (i.e. buttons) directly through a PLC I/O interface. The programmable logic controller  278  is in communication with a circuit board  280  specially designed to interface with the wheel locking mechanisms. The interface board  280  receives power supply signals from the logic power supply and power supply signals from a motor power supply. The interface board  280  is in communication with a motor  284  in each wheel assembly  282 . As described above, each wheel assembly may be swivel locked, rotation locked, or both. The motor  284  interfaces with a caster assembly  288  such that the motor  284  may rotate in one direction to swivel lock the caster assembly  288 . Similarly, the motor  284  may rotate in a second direction to both swivel lock and roll lock the caster assembly  288 . Alternatively, the motor  284  may move to in intermediate position such that the caster assembly  288  is neither swivel locked nor roll locked. In addition, the wheel assembly  282  includes a limit switch  286  that physically determines the position of the motor  284  and thereby the locking status of the corresponding caster assembly  288 . The limit switch  286  may be a three position switch, thereby indicating if the wheel is in a full lock mode, a swivel lock mode, or a free motion mode. 
         [0036]    One specific embodiment of the wheel assembly  282  is shown in  FIG. 6 . The motor  284  is connected to a mounting plate  290  for example, using bolts. A sleeve  298  with a hexagonal end portion extends over the shaft of the motor  284 . A first collar  292  is tightened over the sleeve  298  thereby attaching sleeve  298  to the shaft of the motor  284 . In addition, the switch  286  is attached to the mounting plate  290  and interacts with a second collar  294  fastened over the sleeve  298  and configured to rotate along with the sleeve  294  and motor shaft. The collar  294  includes a channel  296 . The channel  296  receives an arm extending from the limit switch  286 , such that the motor  284  causes the collar  294  to rotate in a first direction such that the channel  296  moves the limit switch  286  to a first position. The limit switch being in the first position can provide a wheel status signal to the programmable logic controller. 
         [0037]    Similarly, if the motor rotates in the opposite direction, the collar  294  rotates in a second direction causing the channel  296  to move the limit switch  286  to a second position indicating a full lock mode. Accordingly, the limit switch being in the second position can provide another wheel status signal to the programmable logic controller indicating the wheel is fully locked. Alternatively, when the switch  286  is between the first and second positions the switch may for example, provide an open contact indicating that the wheel is in a free motion mode and the wheel is neither swivel locked or fully locked. 
         [0038]    Now referring to  FIG. 7 , a flow chart illustrating a method  300  for locking the wheels of a medical imaging device is provided. The method  300  starts in block  310 , where a scan, such as a computed tomography scan is initiated. The scan may be initiated through a physical button on a machine or a graphical user interface. In block  312 , the system controller activates one or more wheel lock mechanisms. In one exemplary embodiment, the system fully locks the rear left wheel and the front right wheel to prevent movement of the system during the scanning process. In block  314 , the system determines whether the wheels are locked. The system may determine that the wheels are locked based on a status flag in the controller indicating that the wheel lock mechanisms have been activated or alternatively, may check a sensor, such as a switch, in the wheel lock mechanisms to determine if the wheel has physically been locked. 
         [0039]    If the system determines the wheels are locked, the method  300  proceeds along line  316  to block  326 . If the system determines the wheels are not locked, the method  300  follows line  318  to block  320 . In block  320 , a system may request the operator to manually lock the wheels. In addition, the system may inform the operator that the wheels are not locked, as denoted in block  322 . The system may also be connected to a network, for example the Internet over a wired or wireless connection, to send a service message indicating that the wheel locking mechanism has malfunctioned, as denoted by block  324 . The message may indicate information including but not limited to the time, the date, system identification, the lock mechanism that malfunctioned, and the type of malfunction. 
         [0040]    In block  326 , the system may enable and start the gantry motors to manipulate the system into various poses required to produce a scan. The system acquires the scans, as denoted by block to  328 . In block  330 , the system saves the scan data and may also save the status of the wheel lock mechanisms. Saving the status of the wheel lock mechanisms may provide for better analysis of unexpected perturbations the data. The method  300  ends in block  332 , where the wheel lock mechanisms are deactivated. 
         [0041]    In an alternative embodiment, dedicated hardware implementations, such as application specific integrated circuits, programmable logic arrays and other hardware devices, can be constructed to implement one or more of the methods described herein. Applications that may include the apparatus and systems of various embodiments can broadly include a variety of electronic and computer systems. One or more embodiments described herein may implement functions using two or more specific interconnected hardware modules or devices with related control and data signals that can be communicated between and through the modules, or as portions of an application-specific integrated circuit. Accordingly, the present system encompasses software, firmware, and hardware implementations. 
         [0042]    In accordance with various embodiments of the present disclosure, the methods described herein may be implemented by software programs executable by a computer system. Further, in an exemplary, non-limited embodiment, implementations can include distributed processing, component/object distributed processing, and parallel processing. Alternatively, virtual computer system processing can be constructed to implement one or more of the methods or functionality as described herein. 
         [0043]    Further the methods described herein may be embodied in a computer-readable medium. The term “computer-readable medium” includes a single medium or multiple media, such as a centralized or distributed database, and/or associated caches and servers that store one or more sets of instructions. The term “computer-readable medium” shall also include any medium that is capable of storing, encoding or carrying a set of instructions for execution by a processor or that cause a computer system to perform any one or more of the methods or operations disclosed herein. 
         [0044]    As a person skilled in the art will readily appreciate, the above description is meant as an illustration of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.