US20150257717A1 - Extremity imaging apparatus for cone beam computed tomography - Google Patents

Abstract

An apparatus for cone beam computed tomography can include a support structure, a scanner assembly coupled to the support structure for controlled movement in at least x, y and z orientations, the scanner assembly can include a DR detector configured to move along at least a portion of a detector path that extends at least partially around a scan volume with a distance D1 that is sufficiently long to allow the scan volume to be positioned within the detector path; a radiation source configured to move along at least a portion of a source path outside the detector path, the source path having a distance D2 greater than the distance D1, the distance D2 being sufficiently long to allow adequate radiation exposure of the scan volume for an image capture by the detector; and a first gap in the detector path.

Description

FIELD OF THE INVENTION
• The invention relates generally to diagnostic imaging and in particular to cone beam imaging systems used for obtaining volume images of extremities.
BACKGROUND OF THE INVENTION
• 3-D volume imaging has proved to be a valuable diagnostic tool that offers significant advantages over earlier 2-D radiographic imaging techniques for evaluating the condition of internal structures and organs. 3-D imaging of a patient or other subject has been made possible by a number of advancements, including the development of high-speed imaging detectors, such as digital radiography (DR) detectors that enable multiple images to be taken in rapid succession.
• Cone beam computed tomography (CBCT) or cone beam CT technology offers considerable promise as one type of diagnostic tool for providing 3-D volume images. Cone beam CT systems capture volumetric data sets by using a high frame rate digital radiography (DR) detector and an x-ray source, typically affixed to a gantry that rotates about the object to be imaged, directing, from various points along its orbit around the subject, a divergent cone beam of x-rays toward the subject. The CBCT system captures projections throughout the rotation, for example, one 2-D projection image at every degree of rotation. The projections are then reconstructed into a 3D volume image using various techniques. Among well known methods for reconstructing the 3-D volume image from the 2-D image data are filtered back projection approaches.
• Although 3-D images of diagnostic quality can be generated using CBCT systems and technology, a number of technical challenges remain. In some cases, for example, there can be a limited range of angular rotation of the x-ray source and detector with respect to the subject. CBCT Imaging of legs, arms, and other extremities can be hampered by physical obstruction from a paired extremity. This is an obstacle that is encountered in obtaining CBCT image projections for the human leg or knee, for example. Not all imaging positions around the knee are accessible; the patient's own anatomy often prevents the radiation source and image detector from being positioned over a portion of the scan circumference.
• To illustrate the problem faced in CBCT imaging of the knee, the top view ofFIG. 1 shows the circular scan paths for aradiation source22 anddetector24 when imaging the right knee R of a patient as asubject20. Various positions ofradiation source22 anddetector24 are shown in dashed line form.Source22, placed at some distance from the knee, can be positioned at different points over an arc of about 200 degrees; with any larger arc the paired extremity, left knee L, blocks the way.Detector24, smaller thansource22 and typically placed very nearsubject20, can be positioned between the patient's right and left knees and is thus capable of positioning over the full circular orbit.
• A full 360 degree orbit of the source and detector is not needed for conventional CBCT imaging; instead, sufficient information for image reconstruction can be obtained with an orbital scan range that just exceeds 180 degrees by the angle of the cone beam itself, for example. However, in some cases it can be difficult to obtain much more than about 180 degree revolution for imaging the knee or other joints and other applications. Moreover, there can be diagnostic situations in which obtaining projection images over a certain range of angles has advantages, but patient anatomy blocks the source, detector, or both from imaging over that range. Some of the proposed solutions for obtaining images of extremities under these conditions require the patient to assume a position that is awkward or uncomfortable. The position of the extremity, as imaged, is not representative of how the limb or other extremity serves the patient in movement or under weight-bearing conditions. It can be helpful, for example, to examine the condition of a knee or ankle joint under the normal weight load exerted on that joint by the patient as well as in a relaxed position. But, if the patient is required to assume a position that is not usually encountered in typical movement or posture, there may be excessive strain, or insufficient strain, or poorly directed strain or tension, on the joint. The knee or ankle joint, under some artificially applied load and at an angle not taken when standing, may not behave exactly as it does when bearing the patient's weight in a standing position. Images of extremities under these conditions may fail to accurately represent how an extremity or joint is used and may not provide sufficient information for assessment and treatment planning.
• Still other difficulties with conventional solutions for extremity imaging relate to poor image quality. For image quality, the CBCT sequence requires that the detector be positioned close to the subject and that the source of the cone beam radiation be at a sufficient distance from the subject. This provides the best image and reduces image truncation and consequent lost data. Positioning the subject midway between the detector and the source, as some conventional systems have done, not only noticeably compromises image quality, but also places the patient too near the radiation source, so that radiation levels are considerably higher.
• CBCT imaging represents a number of challenges that also affect other types of volume imaging that employ a radiation source and detector orbiting an extremity over a range of angles. There are various tomographic imaging modes that can be used to obtain depth information for a scanned extremity.
• In summary, for extremity imaging, particularly for imaging the lower paired extremities, a number of improvements are needed, including the following:
• • (i) improved placement of the radiation source and detector relative to the imaged subject to provide acceptable radiation levels and image quality throughout the scanning sequence, with the capability for at least coarse automated setup for examining an extremity under favorable conditions;
  • (ii) system flexibility for imaging at different heights with respect to the rotational axis of the source and detector, including the flexibility to allow imaging with the patient standing or seated comfortably, such as with a foot in an elevated position, for example;
  • (iii) capability to adjust the angle of the rotational axis to suit patient positioning requirements;
  • (iv) improved patient accessibility, so that the patient does not need to contort, twist, or unduly stress limbs or joints that may have been injured in order to provide images of those body parts;
  • (v) improved ergonomics for obtaining the CBCT image, allowing the patient to stand or sit with normal posture, for example. This would also allow load-bearing extremities, such as legs, knees, and ankles, to be imaged under the normal load exerted by the patient's weight, rather than under simulated loading conditions and provide options for supporting the patient; and
  • (vi) adaptability for multi-use imaging, allowing a single imaging apparatus to be configurable for imaging any of a number of extremities, including knee, ankle, toe, hand, elbow, and other extremities. This also includes the capability to operate the imaging system in different imaging modes, including CBCT, two-dimensional (2-D) projection radiography, fluoroscopy, and other tomography modes.
• In summary, the capability for straightforward configuration and positioning of the imaging apparatus allows the advantages of CBCT imaging to be adaptable for use with a range of extremities, to obtain volume images under a suitable imaging modality, with the image extremity presented at a suitable orientation under both load-bearing and non-load-bearing conditions, and with the patient appropriately standing or seated.
SUMMARY OF THE INVENTION
• An aspect of this application is to advance the art of medical digital radiography.
• Another aspect of this application is to address, in whole or in part, at least the foregoing and other deficiencies in the related art.
• It is another aspect of this application to provide, in whole or in part, at least the advantages described herein.
• It is another aspect of this application to advance the art of diagnostic imaging of extremity body parts, particularly jointed or load-bearing, paired extremities such as knees, legs, ankles, fingers, hands, wrists, elbows, arms, and shoulders.
• It is another aspect of this application to provide apparatus and/or method embodiments that adapt to imaging conditions suitable for a range of extremities and/or allows the patient to be in a number of positions for suitable imaging of the extremity.
• It is another aspect of this application to provide apparatus and/or method embodiments that provide a first set of indicia formed along one or more curved surfaces of the housing and indicating at least a first position along the longitudinal length of a scan volume for positioning and a second set of indicia formed along one or more substantially flat surfaces of the cylindrical housing and indicating the location of a scan volume center for a CBCT imaging apparatus.
• It is another aspect of this application to provide apparatus and/or method embodiments that provide a progress indicator oriented to face the scan volume to indicate time remaining in the image capture for a CBCT imaging apparatus.
• From one aspect, the present invention provides an imaging apparatus for cone beam computed tomography imaging that can include a scanner including (i) a detector for acquiring image data according to received radiation, wherein the detector is translatable to orbit the extremity along a detector path that lies at a first radius R1 about a β axis; (ii) a radiation source that is energizable to direct radiation through the extremity being imaged and toward the detector, wherein the radiation source is translatable to orbit the extremity along a radiation source path at a second radius R2 about the β axis and opposite the detector; (iii) a housing with an opening and having a door that is movable to enclose a portion of the opening to define a scan volume for patient extremity positioning, wherein sides of the scan volume are substantially symmetrical about the β axis; (iv) a first set of indicia formed along one or more curved surfaces of the housing and indicating at least a first position along the length of the β axis for extremity positioning; and (v) a second set of indicia formed along one or more substantially flat surfaces of the cylindrical housing and indicating the location of the β axis.
• These objects are given only by way of illustrative example, and such objects may be exemplary of one or more embodiments of the invention. Other desirable objectives and advantages inherently achieved by the disclosed invention may occur or become apparent to those skilled in the art. The invention is defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the embodiments of the invention, as illustrated in the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other.
• FIG. 1 is a schematic view showing the geometry and limitations of CBCT scanning for portions of the lower leg.
• FIG. 2 shows a top and perspective view of the scanning pattern for an imaging apparatus according to an embodiment of the application.
• FIG. 3A is a perspective view showing patient access to an imaging apparatus according to an embodiment of the application.
• FIG. 3B is a top view showing a sequence of steps for enclosing the extremity to be imaged within the path of the detector transport.
• FIG. 4 show portions of the operational sequence for obtaining CBCT projections of a portion of a patient's leg at a number of angular positions when using the imaging apparatus according to an embodiment of the application.
• FIG. 5 is a perspective view that shows a CBCT imaging apparatus for extremity imaging according to an embodiment of the application.
• FIG. 6A shows internal components used for imaging ring translation and positioning.
• FIG. 6B shows reference axes for rotation and translation.
• FIG. 6C is a schematic diagram that shows components of the positioning system for the imaging scanner.
• FIG. 6D is a perspective view showing some of the components of a vertical translation apparatus.
• FIG. 6E shows the CBCT imaging apparatus with covers installed.
• FIG. 7A shows translation of the imaging ring with respect to a vertical or z-axis.
• FIG. 7B shows rotation of the imaging ring about an α-axis that is orthogonal to the z-axis.
• FIG. 7C shows rotation of the imaging ring about a γ-axis that is orthogonal to the α-axis.
• FIG. 7D shows the position of operator controls for fine-tune position of the imaging scanner.
• FIG. 7E shows an enlarged view of the positioning controls.
• FIG. 8 is a perspective view that shows the extremity imaging apparatus configured for knee imaging with a standing patient.
• FIG. 9 is a perspective view that shows the extremity imaging apparatus configured for foot or ankle imaging with a standing patient.
• FIG. 10 is a perspective view that shows the extremity imaging apparatus configured for knee imaging with a seated patient.
• FIG. 11 is a perspective view that shows the extremity imaging apparatus configured for foot or ankle imaging with a seated patient.
• FIG. 12 is a perspective view that shows the extremity imaging apparatus configured for toe imaging with a seated patient.
• FIG. 13 is a perspective view that shows the extremity imaging apparatus configured for hand imaging with a seated patient.
• FIG. 14 is a perspective view that shows the extremity imaging apparatus configured for elbow imaging with a seated patient.
• FIG. 15A is a top view of the scanner components of an extremity imaging apparatus according to an embodiment of the application.
• FIG. 15B is a perspective view of a frame that supports scanner components of an extremity imaging apparatus according to an embodiment of the application.
• FIG. 15C is a perspective view of a frame that supports scanner components of an extremity imaging apparatus with added counterweight according to an embodiment of the application.
• FIG. 16A is a top view of the imaging scanner showing the door open position.
• FIG. 16B is a perspective view of the imaging scanner showing a door closing position.
• FIG. 16C is a top view of the imaging scanner showing the door closed position.
• FIG. 16D is a perspective view showing the door in closed position.
• FIG. 17A is a top view of the imaging scanner with a number of its internal imaging components shown, at one extreme end of the imaging scan.
• FIG. 17B is a top view of the imaging scanner with a number of its internal imaging components shown, at the opposite extreme end of the imaging scan from that shown inFIG. 17A.
• FIG. 17C is a top view of the imaging scanner with its housing shown.
• FIG. 17D is a top view of the imaging scanner with internal imaging components and central arc angles shown.
• FIG. 18A shows the cylindrical shape of the scan volume and a plane of orbit for a central axis of the x-ray radiation source, with fiducial marks on the side of the scanner.
• FIG. 18B is a top view of the scanner showing the circular shape of the scan volume and fiducial marks on the top of the scanner.
• FIG. 19 is a perspective view that shows using a light pattern as a fiducial mark.
• FIG. 20A is a side view that shows a patient in position for imaging a portion of the arm.
• FIG. 20B shows a stabilizing member for the arm and having a fiducial mark for extremity placement.
• FIG. 21A is a side view in cross section that shows a stabilizing member fitted into the scan volume of the scanner.
• FIG. 21B is an enlarged view of the stabilizing member ofFIG. 4A.
• FIG. 22 is a perspective view of an alternate stabilizing member.
• FIG. 23 is a perspective view that shows a foot rest for extremity imaging.
• FIG. 24 is a diagram that shows an exemplary progress indicator embodiment for a CBCT imaging apparatus according to the application.
• FIG. 25 is a diagram that shows another exemplary progress indicator embodiment for a CBCT imaging apparatus according to the application.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
• The following is a description of exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
• For illustrative purposes, principles of the invention are described herein by referring mainly to exemplary embodiments thereof. However, one of ordinary skill in the art would readily recognize that the same principles are equally applicable to, and can be implemented in, all types of radiographic imaging arrays, various types of radiographic imaging apparatus and/or methods for using the same and that any such variations do not depart from the true spirit and scope of the application. Moreover, in the following description, references are made to the accompanying figures, which illustrate specific exemplary embodiments. Electrical, mechanical, logical and structural changes can be made to the embodiments without departing from the spirit and scope of the invention.
• In the context of the application, the term “extremity” has its meaning as conventionally understood in diagnostic imaging parlance, referring to knees, legs, ankles, fingers, hands, wrists, elbows, arms, and shoulders and any other anatomical extremity. The term “subject” is used to describe the extremity of the patient that is imaged, such as the “subject leg”, for example. The term “paired extremity” is used in general to refer to any anatomical extremity wherein normally two or more are present on the same patient. In the context of the application, the paired extremity is not imaged unless necessary; only the subject extremity is imaged. In one embodiment, a paired extremity is not imaged to reduce patient dose.
• A number of the examples given herein for extemporary embodiments of the application focus on imaging of the load-bearing lower extremities of the human anatomy, such as the leg, the knee, the ankle, and the foot, for example. However, these examples are considered to be illustrative and non-limiting.
• In the context of the application, the term “arc” or, alternately, or arcuate has a meaning of a portion of a curve, spline or non-linear path, for example as being a portion of a curve of less than 360 degrees or, considered alternately, of less than 2π radians for a given radius or distance from a central bore.
• The term “actuable” has its conventional meaning, relating to a device or component that is capable of effecting an action in response to a stimulus, such as in response to an electrical signal, for example.
• As used herein, the term “energizable” relates to a device or set of components that perform an indicated function upon receiving power and, optionally, upon receiving an enabling signal.
• In the context of the application, two elements are considered to be substantially orthogonal if their angular orientations differ from each other by 90 degrees, +/−no more than about 10 degrees.
• It is instructive to observe that the mathematical definition of a cylinder includes not only the familiar “can-shaped” right circular cylinder, but also any number of other shapes. The outer surface of a cylinder is generated by moving a first straight line element along a closed curve or other path along a base plane, while maintaining the first straight line element parallel to a second, fixed straight line that extends out from the base plane, wherein the moving first straight line intersects a fixed closed curve or base in the base plane. A cube, for example, is considered to have a cylindrical shape according to this definition. A can-shaped cylinder of revolution, for example, is generated when the moving first straight line intersects a circle in the base plane at a right angle. An object is considered to be substantially cylindrical when its overall surface shape is approximated by a cylinder shape according to this definition, with allowance for standard edge rounding, protruding or recessed mechanical and electrical fasteners, and external mounting features.
• Certain exemplary embodiments according to the application address the difficulties of extremity imaging by providing an imaging apparatus that defines coordinated non-linear source and detector paths (e.g., orbital, curved, concentric about a center point), wherein components that provide the source and detector paths are configured to allow patient access prior to and following imaging and configured to allow the patient to sit or stand with normal posture during the CBCT image capture series. Certain exemplary embodiments provide this capability by using a detector transport device that has a circumferential access opening allowing positioning of the extremity, wherein the detector transport device is revolved about the positioned extremity once it is in place, enclosing (e.g., partially, substantially, fully) the extremity as it is revolved through at least a portion of the scan.
• It is instructive to consider dimensional attributes of the human frame that can be considerations for design of CBCT equipment for scanning extremities. For example, an adult human patient of average height in a comfortable standing position has left and right knees generally anywhere from about 10 to about 35 cm apart. For an adult of average height, exceeding about 35-40 cm (14-15.7 inches) between the knees becomes increasing less comfortable and out of the range of normal standing posture. It is instructive to note that this constraint makes it impractical to use conventional gantry solutions for obtaining the needed 2-D image sequence. For certain exemplary embodiments, either the source or the detector must be able to pass between the legs of a standing patient for knee CBCT imaging, a capability not available with gantry or other conventional solutions.
• The perspective and corresponding top views ofFIG. 2 show how the scanning pattern is provided for components ofCBCT imaging apparatus10 according to an embodiment of the application. Adetector path28 of a suitable radius R1 from a central axis β is provided for a detector device by adetector transport34. Asource path26 of a second, larger radius R2 is provided for a radiation source by asource transport32. In one embodiment, anon-linear source path26 is greater in length than anon-linear detector path24. According to an embodiment of the application, described in more detail subsequently, the same transport system provides bothdetector transport34 andsource transport32. The extremity, subject20, is preferably substantially centered along central axis β so that central axis β can be considered as a line through points insubject20. In one embodiment, an imaging bore or the CBCT apparatus can include or encompass the central axis β. The limiting geometry for image capture is due to the arc ofsource transport32, blocked by gap38 (e.g., for patient anatomy, such as by a paired limb), and thus limited typically to less than about 220 degrees, as noted previously. The circumferential gap oropening38 can occupy the space between the endpoints of the arc ofsource path26. Gap or opening38 gives space for the patient a place to stand, for example, while one leg is being imaged.
• Detector path28 can extend throughcircumferential gap38 to allow scanning, since the detector is not necessarily blocked by patient anatomy but can have a travel path at least partially around an imaged extremity that can extend between the standing patient's legs. Embodiments of the present invention allow temporary restriction of thedetector path28 to allow access for the patient as part of initial patient positioning. The perspective view inFIG. 2, for example, showsdetector transport34 rotated to open upcircumferential gap38 so that it extends from the axis β (e.g., beyond a source path or housing). Withdetector transport34 translated to the open position shown inFIG. 3A, the patient can freely move in and out of position for imaging. When the patient is properly in position,detector transport34 is revolved about axis β by more than 180 degrees; according to an embodiment of the application,detector transport34 is revolved about axis β by substantially 200 degrees. This patient access and subsequent adjustment ofdetector transport34 is shown in successive stages inFIG. 3B. This orbital movement confines the extremity to be imaged more effectively and placesdetector24, not visible inFIGS. 2-3B due to thedetector transport34 housing, in position nearsubject20 for obtaining the first projection image in sequence. In one embodiment, adetector transport34 can include shielding or a door over part of the detector path, and/or thegap38.
• Circumferential gap or opening38 not only allows access for positioning of the subject leg or other extremity, but also allows sufficient space for the patient to stand in normal posture during imaging, placing the subject leg for imaging in the central position along axis β (FIG. 2) and the non-imaged paired leg within the space defined bycircumferential gap38. Circumferential gap oropening38 extends approximately 180 degrees minus the fan angle (e.g., between ends of th source path), which is determined by source-detector geometry and distance. Circumferential gap or opening38 permits access of the extremity so that it can be centered in position along central axis β. Once the patient's leg or other extremity is in place,detector transport34, or a hooded cover or hollow door or other member that defines this transport path, can be revolved into position, closing the detector portion of circumferential gap oropening38.
• By way of example, the top views ofFIG. 4 show portions of the operational sequence for obtaining CBCT projections of a portion of a patient's leg at a number of angular positions when using a CBCT imaging apparatus. The relative positions ofradiation source22 anddetector24, which may be concealed under a hood or chassis, as noted earlier, are shown inFIG. 4. Thesource22 anddetector24 can be aligned so theradiation source22 can direct radiation toward the detector24 (e.g., diametrically opposite) at each position during the CBCT scan and projection imaging. The sequence begins at abegin scan position50, withradiation source22 anddetector24 at initial positions to obtain an image at a first angle. Then, bothradiation source22 anddetector24 revolve about axis13 as represented in interim scan positions52,54,56, and58. Imaging terminates at anend scan position60. As this sequence shows,source22 anddetector24 are in opposing positions relative to subject20 at each imaging angle. Throughout the scanning cycle,detector24 is within a short distance D1 ofsubject20.Source22 is positioned beyond a longer distance D2 ofsubject20. The positioning ofsource22 anddetector24 components on each path can be carried out by separate actuators, one for each transport path, or by a single rotatable member, as described in more detail subsequently. It should be noted that scanning motion in the opposite direction, that is, clockwise with respect to the example shown inFIG. 4, is also possible, with the corresponding changes in initial and terminal scan positions.
• Given this basic operation sequence in which thesource22 anddetector24 orbit the extremity, the usefulness of an imaging system that is adaptable for imaging patient extremities with the patient sitting or standing and in load-bearing or non load-bearing postures can be appreciated. The perspective view ofFIG. 5 shows aCBCT imaging apparatus100 for extremity imaging according to an embodiment of the application.Imaging apparatus100 has a gimballed imaging ring orscanner110 that houses and concealssource22 anddetector24 within ahousing78.FIG. 5 shows their supporting transport mechanisms.Scanner110 is adjustable in height and rotatable in gimbaled fashion about non-parallel axes, such as about substantially orthogonal axes as described in subsequent figures, to adapt to various patient postures and extremity imaging conditions. Asupport column120 supportsscanner110 on a yoke, or bifurcated or forkedsupport arm130, a rigid supporting element that has adjustable height and further provides rotation ofscanner110 as described subsequently.Support column120 can be fixed in position, such as mounted to a floor, wall, or ceiling. According to portable CBCT embodiments such as shown inFIG. 6A and elsewhere,support column120 mounts to asupport base121 that also includes optional wheels orcasters122 for transporting andmaneuvering imaging apparatus100 into position. Acontrol panel124 can provide an operator interface, such as a display monitor, for entering instructions forapparatus100 adjustment and operation.Support column120 can be of fixed height or may have telescoping operation, such as for improved visibility whenapparatus100 is moved.
Vertical and Rotational Movement
• FIG. 6A shows portions of exemplary internal imaging and positioning mechanisms (with covers removed) forscanner110 that allowimaging apparatus100 the capability for imaging extremities with a variety of configurations.FIG. 6B shows rotation axes definitions forscanner110 positioning. The α-axis and the γ-axis are non-parallel, to allow gimbaled action. According to an embodiment of the application as shown inFIG. 6A, the α-axis and the γ-axis are mutually orthogonal. The α-axis is substantially orthogonal to the z-axis. The intersection of the α-axis and the γ-axis can be offset fromsupport column120 by some non-zero distance.
• First considering the z-axis,FIG. 6A shows an exemplary embodiment to achieve vertical motion. Withinsupport column120, a verticalcarriage translation element128 is actuated in order to travel upwards or downwards alongcolumn120 within atrack112 in a vertical direction.Carriage translation element128 has asupport shaft132 that is coupled to anactuator136 for providing α-axis rotation to forked or C-shapedsupport arm130. Forkedsupport arm130, shown only partially inFIG. 6A to allow a better view of underlying components, is coupled to supportshaft132. X-raysource22 andreceiver24 are mounted on arotatable gantry36 for rotation about a scan or central axis, designated as the β axis. Axis β is orthogonal to the α-axis and the γ-axis.
• It can be appreciated that z-axis translation can be effected in a number of ways. Challenges that must be addressed by the type of system that is used include handling the weight of forkedsupport arm130 and theimaging scanner110 that arm130 supports. This can easily weigh a few hundred pounds. In addition, precautions must be provided for handling conditions such as power loss, contact with the patient, or mechanical problems that hamper positioning movement or operation. According to an embodiment of the application, as shown schematically inFIG. 6C and in the perspective view ofFIG. 6D, avertical actuator129 rotates a threadedshaft123. Verticalcarriage translation element128 employs a ballscrew mount apparatus125 to translate rotational motion to the needed linear (e.g., z-direction) motion, thus urging verticalcarriage translation element128 upward or allowing verticalcarriage translation element128 to move downward. Ball screw translation devices are advantaged for handling high weight loads and are typically more efficient than other types of translators using threaded devices. The use of a ball screw arrangement also allows a small motor to drive the shaft that liftsscanner110 into position and can help to eliminate the need for a complex and bulky counterweight system for allowing control of vertical movement. Anencoder145, such as a linear encoder element, can provide feedback signals that are used to indicate the vertical position of verticalcarriage translation element128.
• Verticalcarriage translation element128 travelsinside track112 formed in support column120 (FIG. 6A);wheels138 help to guidetranslation element128 within the slots. Pairedwheels138 can be orthogonal to each other to provide centering withincolumn120.
• A braking system can also be provided forsupport column120. Spring-loaded brakes142 (FIG. 6D) are positioned to actuate andgrip shaft123 or other mechanical support when mechanical difficulties, power failure, or other conditions are detected. Asensor144, such as a load cell, is configured to sense rapid movement or interference conditions that are undesirable and to causebrake142 actuation.
• Other features ofsupport column120 for vertical translation include built-in redundancy, with springs to absorb weight and impact, the load cell to sense a mechanical problem including obstruction by the patient, and manually operable brake mechanisms.
• It should be noted that other types of translation apparatus could be used for providing vertical movement of verticalcarriage translation element128. One conventional method for vertical movement control uses a system of pulleys and counterweights to provide lifting force, with motorized assistance. Such an arrangement, however, can be disadvantageous because it can add considerable weight to thecolumn120 and supporting structure. In spite of its weight-related drawbacks, use of a pulley mechanism can be advantageous for allowing a retractable ortelescoping column120 arrangement, for example, to simplify transport ofimaging apparatus100 between rooms.
Gimbaled Arrangement for Scanner
• Forkedsupport arm130 can supportscanner110 in a gimbaled arrangement.Source22 anddetector24 are shown ongantry36 for reference inFIG. 6A and covered in the alternate view ofFIG. 6E. Verticalcarriage translation element128 is configured to ride within a track112 (FIG. 6A) withinsupport column120.
• For certain exemplary embodiments, some level of manual operability can be provided, such as for power loss situations. In one embodiment, forkedsupport arm130 can be lifted upwards in position by one or more persons, for example, raising verticalcarriage translation element128 even whenbrakes142 are set. Shiftingsupport arm130 upwards does not release thebrakes142, but simply sets thebrakes142 to holdelement128 position at new levels.
• According to an alternate embodiment of the application, verticalcarriage translation element128 can be a motor that moves vertically along supporting threadedshaft132; alternately, verticalcarriage translation element128 can be driven using a chain, pulley, or other intermediate mechanism that has considerable counterweights for manually raising and lowering verticalcarriage translation element128 and its connected forkedsupport arm130 and components withinsupport column120. Additional supporting components include a more complex braking system, such as a pneumatic braking system for providing a force opposing gravity in order to prevent sudden movement of forkedsupport arm130 as a precaution against damage or injury. Verticalcarriage translation element128 can be automated or may be a manually operated positioning device that uses one or more springs or counterweight devices to allow ease of manual movement of forkedsupport arm130 into position.
• Next, considering the α-axis movement of forkedsupport arm130, in one embodiment arotational actuator136 can be energizable to allow rotation of shaft132 (FIG. 6A). This rotational actuation can be concurrent with z-axis translation as well as with rotation with respect to the γ-axis.
• Forkedsupport arm130 allows movement relative to the γ-axis according to the position and angle of forkedsupport arm130. In the example ofFIG. 6A, the γ-axis is oriented vertically, substantially in parallel with the z-axis.FIG. 6E shows the γ-axis oriented horizontally. A pivotingmount140 with arotational actuator146, provided by forkedsupport arm130, allows rotation along the γ-axis. The gimbaled combination of α-axis and γ-axis rotation can allow the imaging apparatus to be set up for imaging in a number of possible positions, with the patient standing, seated, or prone.
• An exemplary positioning capability of theimaging apparatus100 is shown nFIGS. 7A-7C.FIG. 7A shows movement of forkedsupport arm130 onsupport column120 to provide z-axis (vertical) translation ofscanner110.FIG. 7B shows rotation of forkedsupport arm130 about the horizontal α-axis.FIG. 7C shows rotation about the γ-axis as defined by the C-arm arrangement of forkedsupport arm130.
Sequence and Controls forPositioning Support Arm130
• According to an embodiment of the present invention, an initial set of operator commands automatically configureCBCT imaging apparatus100 to one of a well-defined set of default positions for imaging, such as those described subsequently. The patient waits until this initial setup is completed. Then, the patient is positioned atCBCT imaging apparatus100 and any needed adjustments in height (z-axis) or rotation about the α or γ axes can be made by the technician. This type of fine-tuning adjustment is at slow speeds for increased patient comfort and because only incremental changes to position are needed in most cases.
• FIG. 7D and the enlarged view ofFIG. 7E showuser control stations156,158 that are provided on arm130 (withscanner110 removed for improved visibility) for operator adjustment of z-axis translation and α- and γ-axis rotation as described inFIGS. 7A-7C. Bothcontrol stations156 and158 are essentially the same, duplicated to allow easier access for the operator for different extremity imaging arrangements. By way of example,FIG. 7E shows an enlarged view ofcontrol station158. Anenablement switch159 is pressed to activate acontrol160 and an associated indicator illuminates whencontrol160 is active or enabled. As a patient safety feature to protect from inadvertent patient contact with the controls in some imaging configurations, one or bothcontrol stations156,158 are disabled. One or bothcontrol stations156,158 can also be disabled following a time-out period afterswitch159 has been pressed. Anemergency stop control162 can stop all motion of the imaging apparatus including downward motion ofsupport arm130.
• Still referring toFIG. 7E,control160 can activate any of the appropriate actuators for z-axis translation, α-axis rotation and/or γ-axis rotation. Exemplary responses of the system can be based on operator action, as follows:
• • (i) z-axis vertical movement is effected by pressingcontrol160 in a vertical upward or downward direction. The control logic adjusts for the angular position of thesupport arm130, so that pressing the control upward provides z-axis movement regardless ofsupport arm130 orientation.
  • (ii) α-axis rotation is effected by rotatingcontrol160. Circular motion ofcontrol60 in an either clockwise (CW) or counterclockwise (CCW) direction causes corresponding rotation about the α axis.
  • (iii) γ-axis rotation is effected by horizontal left-to-right or right-to-left movement ofcontrol60. As with z-axis movement, control logic adjusts for the angular position of thesupport arm130, so that left-right or right-left movement is relative to the operator regardless ofsupport arm130 orientation.
• It should be noted thatCBCT imaging apparatus100 as shown inFIG. 6E provides three degrees of freedom (DOF) forscanner110 positioning. In addition to the z-axis translation and rotation about α- and γ-axes previously described,casters122 allow rotation ofscanner110 position with respect to the z-axis as well as translation along the floor.
Configurations for Imaging Various Extremities
• Given the basic structure described with reference toFIGS. 6A-7D, the positioning versatility ofscanner110 for various purposes can be appreciated. SubsequentFIGS. 8-14 show, by way of example, how this arrangement serves different configurations for extremity imaging.
• FIG. 8 shows anexemplary scanner110 positioning for a knee exam, where subject20 is a standing patient. An optionalpatient support bar150 can be attached to supportcolumn120. In one embodiment,support bar150 is mounted to verticalcarriage translation element128. Accordingly, as the verticalcarriage translation element128 moves, a corresponding position of thesupport bar150 can be moved. According to an alternate embodiment of the application, thesupport bar150 can be mounted to thescanner110, such as to the cover ofscanner110 or to the forkedsupport arm130. In contrast, embodiments ofsupport bar150 can be motionless during imaging or during a scan by thescanner110. For this embodiment, vertical adjustment along the z-axis sets the knee of the patient at the center of thescanner110. Forkedsupport arm130 is arranged so that the plane that contains both the α-axis and the γ-axis is substantially horizontal. Patient access is through an opening, circumferential gap or opening38 inscanner110. Adoor160 is pivoted into place acrossgap38 to enclose an inner portion of circumferential gap oropening38.Door160 fits between the legs of the patient once the knee of the patient is positioned.
• Certain exemplary embodiments of optionalpatient support bar150 can be mounted to movable portions of theCBCT apparatus100, preferably to have a prescribed spatial relationship to an imaging volume. For such embodiments, a presence detector151 can be configured to detect when thesupport bar150 is mounted to theCBCT system100. When detected, a controller or the like, for example, in thecontrol panel124, can calculatescanner110, and/or forkedsupport arm130 movements to prevent collisions therebetween with the affixedsupport bar150. Thus, when attachedsupport bar150 can limit motion of thescanner110. Exemplary presence detectors151 can include but are not limited to magnetic detectors, optical detectors, electro-mechanical detectors or the like. As shown inFIG. 9, a pair of optional orremovable support arms150 can be affixed to the verticalcarriage translation element128 and have their attachment reported by a pair of presence detectors151.
• ForFIG. 8 and selected subsequent embodiments,door160, once pivoted into its closed position, can effectively extend the imaging path by protecting and/or providing thecurved detector transport34 path as shown inFIG. 4. With this arrangement, whendoor160 is closed to protect the transport path, the knee can be examined under weight-bearing or non-weight-bearing conditions. By enclosing the portion ofdetector transport34 path that crossesopening38,door160 enables the extremity to be positioned suitably for 3D imaging and to be maintained in position between the source and detector as these imaging components orbit the extremity in the CBCT image capture sequence.
• FIG. 9 showsscanner110 positioning for a foot or ankle exam wherein subject20 is a standing patient. With this configuration,scanner110 is lowered to more effectively scan the area of interest. The plane that contains both the α-axis and the γ-axis is approximately 10 degrees offset from horizontal, rotated about the γ axis. A step116 is provided across circumferential gap oropening38 for patient access.
• FIG. 10 showsscanner110 positioning for a knee exam with the patient seated. For this configuration, forkedsupport arm130 is elevated with respect to the z-axis. Rotation about the α-axis orients the γ-axis so that it is vertical or nearly vertical. Circumferential gap oropening38 is positioned to allow easy patient access for imaging the right knee. It should be noted that 180 degree rotation about the γ-axis would position circumferential gap or opening38 on the other side ofscanner110 and allow imaging of the other (left) knee.
• FIG. 11 showsscanner110 positioning for a foot or ankle exam with the patient seated. For this configuration, forkedsupport arm130 is elevated with respect to the z-axis. Some slight rotation about the α-axis may be useful. Rotation about the γ-axis orientsscanner110 at a suitable angle for imaging. Circumferential gap oropening38 is positioned for comfortable patient access.
• FIG. 12 showsscanner110 positioning for a toe exam with the patient seated. For this configuration, forkedsupport arm130 is elevated with respect to the z-axis. Rotation about the γ-axis positionscircumferential gap38 at the top of the unit for patient access.
• FIG. 13 showsscanner110 positioning for a hand exam, with the patient seated. For this configuration, forkedsupport arm130 is elevated with respect to the z-axis. Rotation about the γ-axis positionscircumferential gap38 suitably for patient access. Rotation about the α-axis may be provided to orientscanner110 for patient comfort.
• FIG. 14 showsscanner110 positioning for an elbow exam, with the patient seated. For this configuration, forkedsupport arm130 is again elevated with respect to the z-axis. Rotation about the γ-axis positionscircumferential gap38 suitably for patient access. Further rotation about the α-axis may be provided for patient comfort.
• In one embodiment ofCBCT imaging apparatus100, the operator can first enter an instruction at the control console orcontrol panel124 that specifies the exam type (e.g., for the configurations shown inFIGS. 8-14). The system then automatically adapts the chosen configuration, prior to positioning the patient. Once the patient is in place, manually controlled adjustments to z-axis and α- and γ-axes rotations can be made, as described previously.
Scanner Configuration and Operation
• As previously described with reference toFIGS. 1-4,scanner110 is configured to provide suitable travel paths forradiation source22 anddetector24 about the extremity that is to be imaged, such as those shown inFIGS. 8-14.Scanner110 operation in such various exemplary configurations can present a number of requirements that can be at least somewhat in conflict, including the following:
• • (i) Imaging over a large range of angles, preferably over an arc exceeding 180 degrees plus the fan angle of the radiation source.
  • (ii) Ease of patient access and extremity positioning for a wide range of limbs.
  • (iii) Capability to allow both weight-bearing and non-weight-bearing postures that allow imaging with minimized strain on the patient.
  • (iii) Enclosure to prevent inadvertent patient contact with moving parts.
  • (iv) Fixed registration of source to detector throughout the scan cycle.
• The top view ofFIG. 15A shows a configuration of components ofscanner110 that orbit subject20 according to an embodiment of the application. One ormore sources22 anddetector24 are mounted in a cantilevered C-shapedgantry36 that is part of atransport assembly170 that can be controllably revolved (e.g., rotatable over an arc about central axis β).Source22 anddetector24 are thus fixed relative to each other throughout their movement cycle. Anactuator172 is mounted to aframe174 ofassembly170 and provides a moving hinge for gantry pivoting.Actuator172 is energizable to movegantry36 andframe174 with clockwise (CW) or counterclockwise (CCW) rotation as needed for the scan sequence. Housing184 can reduce or keeps out dust and debris and/or better protect the operator and patient from contact with moving parts.
• The perspective view ofFIG. 15B showsframe174 andgantry36 oftransport assembly170 in added detail.Actuator172 cooperates with abelt178 to pivotframe174 for movingsource22 anddetector24 about axis β. The perspective view ofFIG. 15C showsframe174 with addedcounterweights182 for improved balance of the cantilevered arrangement.
• Because a portion of the scan arc that is detector path28 (FIG. 2) passes through the circumferential gap or opening38 that allows patient access, this portion of the scan path should be isolated from the patient.FIG. 16A,16B, and16C show, in successive positions for closing over gap oropening38, aslidable door176 that is stored in a retracted position within a housing180 for providing a covering over thedetector path28 once the patient is in proper position. In one embodiment,door176 can be substantially a hollow structure that, when closed, allows passage of thedetector24 around the patient's extremity. Referring toFIG. 15B, the portion offrame174 ofgantry36 that supportsdetector24 can pass through the hollow inner chamber provided bydoor176 during the imaging scan. At the conclusion of the imaging sequence,frame174 ofgantry36 rotates back into its home position anddoor176 is retracted to its original position for patient access or egress within housing180. In one embodiment, thedoor176 is manually opened and closed by the operator. In one embodiment, interlocks are provided so that movement of scanning transport components (rotation of cantilevered frame174) is only possible while full closure of thedoor176 is sensed.
• FIG. 16B also shows top andbottom surfaces190 and192, respectively, of housing180. An outercircumferential surface194 extends between and connects top andbottom surfaces190 and192. An innercircumferential surface196 is configured to connect the top andbottom surfaces190 and192 to form acentral opening198 extending from the first surface to the second surface, where thecentral opening198 surrounds the β axis.
• As shown with respect toFIGS. 2 and 4, in oneembodiment radiation source22 anddetector24 each can orbit the subject along an arc with radii R2 and R1, respectively. According to an alternate embodiment, withinsource transport32, a source actuator could be used, cooperating with a separate, complementary detector actuator that is part ofdetector transport34. Thus, two independent actuator devices, one in each transport assembly, can be separately controlled and coordinated by an external logic controller to movesource22 anddetector24 along their respective arcs, in unison, aboutsubject20.
• In the context of the present disclosure, a surface is considered to be “substantially” flat if it has a radius of curvature that exceeds about 10 feet.
• The perspective view ofFIG. 10 shows the extremityCBCT imaging apparatus100 configured for knee imaging with a seated patient. FromFIG. 10, it can be seen that the patient needs room outside of the scan volume for comfortable placement of the leg that is not being imaged. For this purpose,housing78 is shaped to provide additional clearance.
• As is readily visible fromFIGS. 8-14 and16A-16D,imaging scanner110 has ahousing78. According to one embodiment of the application,housing78 is substantially cylindrical; however, a cylindrical surface shape forhousing78 is not required. By substantially cylindrical is meant that, to at least a first approximation, thehousing78 surface shape closely approximates a cylinder, with some divergence from strict geometric definition of a cylinder and with a peripherally gap and some additional features for attachment and component interface that are not in themselves cylindrical.
• FIGS. 17A-17D show a number of features that are of interest for an understanding of howscanner110 is configured and operated (e.g., scans).FIG. 17A shows howperipheral gap38 is formed byhousing78, according to an embodiment of the application.Scan volume228, outlined with a dashed line, is defined by the source anddetector paths26 and28, as described previously, and typically includes at least a portion of the β axis. An innercentral volume230 can be defined by surface S2 ofhousing78 and can typically enclosescan volume228. Innercentral volume230 can also be defined bydoor176 when closed, as shown inFIG. 17C.Peripheral gap38 is contiguous with innercentral volume230 whendoor176 is in open position (e.g., fully or partially opened).
• FIG. 17A showssource transport32 anddetector transport34 at one extreme end of the scan path, which may be at either the beginning or the end of the scan.FIG. 17B showssource transport32 anddetector transport34 at the other extreme end of the scan path. It should be noted thatsource22 is offset alongsource transport32. With this asymmetry, the extent of travel ofsource22 relative to surface S3 ofhousing78 differs from its extent of travel relative to surface S4. At the extreme travel position shown inFIG. 17B,source22 is more than twice the distance from surface S4 assource22 is from surface S3 at the other extreme travel position shown inFIG. 17A. In one embodiment, the inventors use this difference to gain additional clearance for patient positioning with the patient seated.
• FIG. 17C shows the configuration ofhousing78. In the context of the present disclosure,top surface190 is considered to be aligned with the top of, at least partially above, or abovescan volume228;bottom surface192 is aligned with the bottom of, at least partially below, or belowscan volume228. In one embodiment, thetop surface190 or thebottom surface192 can intersect a portion of thescan volume228. As shown inFIG. 17C,scan volume228 can be cylindrical or circularly cylindrical. However, exemplary embodiments of the application are intended to be used with other known 2D scan areas and/or 3D scan volumes. The cover ofhousing78 can be metal, fiberglass, plastic, or other suitable material. According to an embodiment, at least portions of top andbottom surfaces190 and192 are substantially flat.
• As shown inFIGS. 17A-17C, thescanner110 has a number of surfaces that define its shape and the shape of peripheral gap or opening38:
• • (i) an outer connecting surface S1 extends between a portion oftop surface190 and a portion ofbottom surface192 to at least partially encompass the source and detector; at least a portion of the outer connecting surface extends outside the path the source travels while scanning; embodiments of the outer connecting surface S1 shown inFIGS. 17A-17C provide an arcuate surface that is generally circular at a radius R5 about center13 and that extends, between edges E1 and E2 of the housing;
  • (ii) an inner connecting surface S2 extends between a portion of the first surface and a portion of the second surface to define an innercentral volume230 that includes a portion ofscan volume228; in the embodiment shown inFIG. 17D, inner connecting surface S2 is approximately at a radius R4 from the β axis. At least portions of inner connecting surface S2 can be cylindrical.
  • (iii) other connecting surfaces can optionally include a surface S3 that corresponds to a first endpoint of the travel path for source transport32 (FIGS. 17A-17B) and is adjacent to curved surface S1 along an edge E1, wherein surface S3 extends inward toward curved inner surface S2; and a surface S4 that corresponds to a second endpoint at the extreme opposite end of the travel path from the first endpoint forsource transport32 and is adjacent to curved surface S1 along an edge E2 wherein surface S4 extends inward toward curved inner surface S2. According to an embodiment, surfaces S3 and S4 are substantially flat and the angle between surfaces S3 and S4 is greater than about 90 degrees. In general, other additional surface segments (e.g., short linear or curved surface segments) may extend between or comprise any of surfaces S1-S4.
• Inner and outer connecting surfaces S1, S2, and, optionally, other surfaces, define peripheral gap or opening38 that is contiguous with the innercentral volume230 and extends outward to intersect the outer connecting surface S1 to formgap38 as an angular recess extending from beyond or toward where the outer connecting surface S1 would, if extended, cross theopening38. As shown inFIG. 17D, a central angle of a first arc A1 that is defined with a center located within the scan volume and between edges of theperipheral gap38 determined at a first radial distance R4 outside the scan volume is less than a central angle of a second arc A2 that is defined with the first arc center and between the edges of theperipheral gap38 at a second radial distance R3 outside the scan volume, where the second radial distance R3 is greater than the first radial distance R4. In one embodiment, as shown inFIG. 17D, a first distance that is defined between edges of theperipheral gap38 determined at a first radial distance R4 outside the scan volume is less than a second distance between the edges of theperipheral gap38 at a second radial distance R3 outside the scan volume, where the second radial distance R3 is greater than the first radial distance R4. According to one embodiment, arcs A1 and A2 are centered about the β axis, as shown inFIG. 17D and edges ofgap38 are defined, in part, by surfaces S3 and S4 ofhousing78.
• The needed room for patient anatomy, such as that described with reference toFIG. 10, can be provided when the central angle for arc A2 is large enough to accommodate the extremity that is to be imaged. According to one embodiment, the central angle for arc A2 between edges ofgap38 exceeds the central angle for arc A1 by at least about 5 degrees; more advantageously, the central angle for arc A2 exceeds the central angle for arc A1 by at least about 10 or 15 degrees.
• The perspective views ofFIGS. 8-14 show various configurations of extremityCBCT imaging apparatus100 for imaging limbs of a patient. For each of these configurations, the limb or other extremity of the patient must be positioned at the center ofscanner110 and space must be provided for the paired extremity. As described herein, peripheral gap oropening38 is provided to allow access space for the patient and room for other parts of the patient anatomy.Door176 is withdrawn into thehousing78 until the patient is positioned; then,door176 is pivoted into place in order to provide a suitable transport path for the imaging receiver,detector24, isolated from the patient being imaged.
• FIG. 16A showsscanner110 withdoor176 in open position, not obstructingopening38, that is, keepingopening38 clear, allowing patient access for extremity placement withinopening38.FIG. 16C is a top view that showsscanner110 withdoor176 in closed position, held by a latch92.Door176 thus extends into theopening38, enclosing a portion of opening38 for imaging of the patient's extremity. Asensor82 provides an interlock signal that indicates at least whetherdoor176 is in closed position or in some other position. Movement ofinternal scanner110 components such as c-shapedgantry36 is prevented unless thedoor176 is latched shut. Arelease90 unlatchesdoor176 from its latched position. As shown inFIGS. 16C and 16D, handle76 can be positioned outside of opening38, such as along surface S1 as shown, for opening or closingdoor176. Placement ofhandle76, or other type of door closure device, outside of opening38 is advantageous for patient comfort when closing or openingdoor176. As shown in the exemplary embodiment ofFIGS. 16C and 16D, handle76 is operatively coupled withdoor176 so that movement ofhandle76 in a prescribed direction, such as along the circumference ofscanner110 housing78 (e.g., a corresponding direction, or in the clockwise direction shown), causesdoor176 corresponding movement (e.g., in the same direction). In one embodiment, clockwise movement ofhandle76 causes clockwise movement ofdoor176, extendsdoor176 into the opening, and closesdoor176; counterclockwise movement ofhandle76 causes counterclockwise movement ofdoor176 and opensdoor176, so that it does not obstruct the opening or moves to a position that is clear of the opening.
• According to one embodiment, thedoor176 is manually pivoted, closed, and opened by the operator. This allows the operator to more carefully support the patient and the extremity that is to be imaged. According to an alternate embodiment, an actuator is provided to close or open the door automatically.
• The schematic ofFIG. 18A shows, not to scale, the cylindrical shape of ascan volume228 within which the imaged extremity is positioned.Scan volume228 is defined within the orbital radius of thedetector22 and its height along the β axis is constrained by the corresponding height ofdetector22. Assource24 orbits scanvolume228, there is defined a plane of orbit P that includes the optical axis of the emitted x-ray beam. As a preferred practice, the subject to be imaged is generally centered along plane P. Thus, for example, when imaging the knee, scanning works effectively when the region of interest of the knee is at least approximately centered with the optical axis and also approximately centered along the β axis.
• Embodiments of the present invention providefiducial marks260 as indicia for alignment of the knee or other subject with the optical axis of the radiation beam. These indicia can be stripes, indentations, or other markings. This allows the patient and operator to position the extremity at a suitable depth of thescanner housing78 for imaging. The operator can use controls to reposition thescanner housing78 until the appropriate alignment is achieved.
• Alignment with respect to the β axis is also desirable for most extremity imaging. The top view ofFIG. 18B shows the circular shape of thescan volume228 withinhousing78. Fiducial marks262 are formed onhousing78 as indicia to help guide alignment of the extremity to be imaged along the β axis.
• FIG. 19 is a perspective view that shows using alight pattern264 as a type of indicium or fiducial marking.Light pattern264, emitted toward the subject from a conventional incandescent or a solid-state light source, such as an LED or laser. This projected light indicates lines along which an extremity is positioned for obtaining an image.
• Various types of indicia are also used on devices that support and accommodate the patient for imaging.FIG. 20A is a side view that shows a patient in position for imaging a portion of the arm.FIG. 20B shows a stabilizingmember266 for the arm and having a fiducial mark for extremity placement. As shown inFIG. 20A, stabilizingmember266 is inserted into the bore opening inhousing78 for imaging the extremity. Fiducial marks268 are formed onmember266 as indicia for placement of the extremity to be imaged at the proper depth ofscanner110.
• FIG. 21A is a side view in cross section that shows a compressible stabilizingmember272 fitted into the scan volume of the scanner. This uses the shape ofhousing78 to register the foot or other extremity to be imaged.FIG. 21B is an enlarged view of the stabilizing member ofFIG. 21A.Compressible stabilizing member272 can be foam, for example, such as a foam with shape memory that substantially restores its original shape when compression force is released.
• FIG. 22 is a perspective view of an alternate stabilizingmember274 that has a foam core and abinding strap276, such as a hook-and-loop fastener, for example.
• FIG. 23 is a perspective view that shows a foot rest280 for extremity imaging. Foot rest280 can be of a compressible or non-compressible material and can be fitted to the opening inhousing78 to register the foot for imaging.
• Certain exemplary system and/or method CBCT embodiments according to the application can provide a “keep still” patient indicator. In one embodiment, a progress indicator can be oriented to face thescan volume228 to indicate time remaining in the image capture. Generally, embodiments of a progress indicator can show how long the CBCT scan has remaining to complete, which can be useful to inform the patient to keep still while the scan is in progress because patient motion during the scan leads to image artifacts. In addition, the technician also can use the progress indicator embodiments to know how long till the CBCT scan ends.
• FIG. 24 is a diagram that shows an exemplary progress indicator embodiment for a CBCT imaging apparatus according to the application. As shown inFIG. 24, an exemplary progress indicator2410 (e.g., visual) can indicate aninterval2412 representing a temporal range of thescanner110 image capture scan and aprogress mark2414 to show a current temporal position in theinterval2412.
• Embodiments of progress indicators according to the application can include indicators that can provide various indications of total scan time, scan time elapsed and/or scan time remaining.FIG. 25 is a diagram that shows another exemplary progress indicator embodiment for a CBCT imaging apparatus according to the application. As shown inFIG. 25, aprogress indicator2520 can include a changing indicator such as agraphical representation2520A or a time (e.g., second countdown)count2520B to show relative time or actual time elapsed for the image capture or remaining in the image capture. In alternative embodiments, the progress indicator can include but is not limited to a visual alarm, audible alarm, a moving indicators showing relative/actual time, a scan bar or flashing light. Certain exemplary progress indicator embodiments can be mounted to theCBCT apparatus100, for example, mounted on a scanner assembly or the support structure. In one embodiment, progress indicator embodiments can be mounted at one or more of a base support, a wall, the ground, a ceiling, a second elongated support or a mobile cart to be visible during the image capture. Certain exemplary progress indicator embodiments are provided independent of and as a supplement to thecontrol panel124.
• Consistent with at least one embodiment, exemplary methods/apparatus can use a computer program with stored instructions that perform on image data that is accessed from an electronic memory. As can be appreciated by those skilled in the image processing arts, a computer program of an embodiment herein can be utilized by a suitable, general-purpose computer system, such as a personal computer or workstation. However, many other types of computer systems can be used to execute the computer program of described exemplary embodiments, including an arrangement of networked processors, for example.
• The computer program for performing methods of certain exemplary embodiments described herein may be stored in a computer readable storage medium. This medium may comprise, for example; magnetic storage media such as a magnetic disk such as a hard drive or removable device or magnetic tape; optical storage media such as an optical disc, optical tape, or machine readable optical encoding; solid state electronic storage devices such as random access memory (RAM), or read only memory (ROM); or any other physical device or medium employed to store a computer program. Computer programs for performing exemplary methods of described embodiments may also be stored on computer readable storage medium that is connected to the image processor by way of the internet or other network or communication medium. Those skilled in the art will further readily recognize that the equivalent of such a computer program product may also be constructed in hardware.
• It should be noted that the term “memory”, equivalent to “computer-accessible memory” in the context of the present disclosure, can refer to any type of temporary or more enduring data storage workspace used for storing and operating upon image data and accessible to a computer system, including a database, for example. The memory could be non-volatile, using, for example, a long-term storage medium such as magnetic or optical storage. Alternately, the memory could be of a more volatile nature, using an electronic circuit, such as random-access memory (RAM) that is used as a temporary buffer or workspace by a microprocessor or other control logic processor device. Display data, for example, is typically stored in a temporary storage buffer that can be directly associated with a display device and is periodically refreshed as needed in order to provide displayed data. This temporary storage buffer can also be considered to be a memory, as the term is used in the present disclosure. Memory is also used as the data workspace for executing and storing intermediate and final results of calculations and other processing. Computer-accessible memory can be volatile, non-volatile, or a hybrid combination of volatile and non-volatile types.
• It will be understood that computer program products for exemplary embodiments herein may make use of various image manipulation algorithms and processes that are well known. It will be further understood that exemplary computer program product embodiments herein may embody algorithms and processes not specifically shown or described herein that are useful for implementation. Such algorithms and processes may include conventional utilities that are within the ordinary skill of the image processing arts. Additional aspects of such algorithms and systems, and hardware and/or software for producing and otherwise processing the images or co-operating with the computer program product of the application, are not specifically shown or described herein and may be selected from such algorithms, systems, hardware, components and elements known in the art.
• It should be noted that while the present description and examples are primarily directed to radiographic medical imaging of a human or other subject, embodiments of apparatus and methods of the present application can also be applied to other radiographic imaging applications. This includes applications such as non-destructive testing (NDT), for which radiographic images may be obtained and provided with different processing treatments in order to accentuate different features of the imaged subject.
• Although sometimes described herein with respect to CBCT digital radiography systems, embodiments of the application are not intended to be so limited. For example, other DR imaging system such as dental DR imaging systems, mobile DR imaging systems or room-based DR imaging systems can utilize method and apparatus embodiments according to the application. As described herein, an exemplary flat panel DR detector/imager is capable of both single shot (radiographic) and continuous (fluoroscopic) image acquisition. Further, a fan beam CT DR imaging system can be used.
• Exemplary DR detectors can be classified into the “direct conversion type” one for directly converting the radiation to an electronic signal and the “indirect conversion type” one for converting the radiation to fluorescence to convert the fluorescence to an electronic signal. An indirect conversion type radiographic detector generally includes a scintillator for receiving the radiation to generate fluorescence with the strength in accordance with the amount of the radiation.
• Exemplary embodiments according to the application can include various features described herein (individually or in combination). Priority is claimed from commonly assigned, copending U.S. provisional patent application Ser. No. 61/710,832, filed Oct. 8, 2012, entitled “Extremity Scanner and Methods For Using The Same”, in the name of John Yorkston et al., the disclosure of which is incorporated by reference.
• While the invention has been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the invention can have been disclosed with respect to one of several implementations, such feature can be combined with one or more other features of the other implementations as can be desired and advantageous for any given or particular function. The term “at least one of” is used to mean one or more of the listed items can be selected. The term “about” indicates that the value listed can be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the illustrated embodiment. Finally, “exemplary” indicates the description is used as an example, rather than implying that it is an ideal. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims (21)

1. An imaging apparatus for cone beam computed tomography imaging of an extremity of a patient, the apparatus comprising:

a detector for acquiring image data according to received radiation, wherein the detector is translatable to orbit the extremity along a detector path that lies at a first radius R1 about a β axis;

a radiation source that is energizable to direct radiation through the extremity being imaged and toward the detector, wherein the radiation source is translatable to orbit the extremity along a radiation source path at a second radius R2 about the β axis and opposite the detector;

a housing with an opening and having a door that is pivotable to enclose a portion of the opening to define a scan volume for patient extremity positioning, wherein sides of the scan volume are substantially symmetrical about the β axis;

a first set of indicia formed along one or more curved surfaces of the housing and indicating at least a first position along the length of the β axis for extremity positioning; and

a second set of indicia formed along one or more substantially flat surfaces of the cylindrical housing and indicating the location of the β axis.

2. The imaging apparatus ofclaim 1, further comprising a progress indicator oriented to face the scan volume to indicate time remaining in the image capture, where the progress indicator to indicate an interval representing a temporal range of the image capture, where the progress indicator is configured to provide a changing indicator showing relative time or actual time elapsed for the image capture or remaining in the image capture.

3. The imaging apparatus ofclaim 1 wherein the first set of indicia are stripes, comprise one or more light patterns, or comprise indentations formed in the housing, wherein members of the first set of indicia are formed along the sides of the scan volume.

4. The imaging apparatus ofclaim 1 further comprising a third set of indicia for guiding alignment of patient extremities within the scan volume.

5. The imaging apparatus ofclaim 1 further comprising a light pattern formed within the scan volume and projected onto the patient's extremity, where the light pattern comprises a plurality of different light sources to generate a plurality of different patterns corresponding to different exams, where the different exams comprise at least two of a hand exposure, a wrist exposure, an elbow exposure, a knee exposure, and an ankle exposure.

6. The imaging apparatus ofclaim 1 further comprising a stabilizing member that seats within the scan volume and that at least partially encloses the extremity to be imaged, where the stabilizing member has a third set of indicia for extremity placement.

7. The imaging apparatus ofclaim 6 wherein the stabilizing member seats in a defined position within the scan volume.

8. The imaging apparatus ofclaim 1 further comprising a stabilizing member that seats beyond the scan volume and that at least partially encloses a distal end of the extremity to be imaged, where the stabilizing member stabilizes the distal end of the extremity to be imaged.

9. An imaging apparatus for cone beam computed tomography imaging of an extremity of a patient, the apparatus comprising:

a gantry that is configured to pivot about a β axis;

a detector that is coupled to the gantry for acquiring image data according to received radiation, wherein the detector is translatable to orbit the extremity along a detector path that lies at a first radius R1 about the β axis;

a radiation source that is energizable to direct radiation through the extremity being imaged and toward the detector, wherein the radiation source is coupled to the gantry and is translatable to orbit the extremity along a radiation source path at a second radius R2 about the β axis and opposite the detector;

a housing that encloses the detector and radiation source, with an opening and having a door that is movable to enclose a portion of the opening to define a scan volume for patient extremity positioning; and

a stabilizing member that seats within the scan volume and that at least partially encloses the extremity to be imaged, wherein the stabilizing member has one or more indicia indicative of positioning of the extremity.

10. The apparatus ofclaim 9, wherein the seat includes at least one of axially locating feature and depth into the bore locating feature, wherein the stabilizing member is formed of a compressible material that has shape memory.

11.-15. (canceled)

16. An apparatus for cone beam computed tomographic imaging of one extremity of a patient, the apparatus comprising:

a digital radiation detector;

a detector mechanism attached to the detector and configured to move the detector along a detector path, a shape of the detector path comprising a first circular arc, the detector path defining a detector axis whereat at least a portion of the one extremity of the patient is positioned to be imaged by the apparatus;

a radiation source;

a source mechanism attached to the source and configured to move the source along a source path, a shape of the source path comprising a second circular arc, the source path defining a source plane and a source axis, the source axis coaxial with the detector axis, wherein a distance from the detector path to the detector axis is shorter than a distance from the source path to the source axis; and

a C-shaped housing to enclose the source, the source mechanism, the detector, and the detector mechanism, the C-shaped housing comprising a first set of indicia formed along one or more curved surfaces of the housing to indicate at least a first position of the detector axis for extremity positioning.

17. The apparatus ofclaim 16, further comprising a second set of indicia formed along one or more substantially flat surfaces of the housing to indicate a location of the detector axis.

18. The apparatus ofclaim 16, further comprising a housing gap configured to allow the one extremity of the patient to be positioned at the detector axis by moving the at least a portion of the one extremity of the patient through the housing gap in a direction substantially perpendicular to the detector axis.

19. The apparatus ofclaim 18, further comprising a housing extension attached to the housing and configured to controllably extend from the housing across the housing gap to enclose the detector as the detector moves along the detector path across the housing gap.

20. The apparatus ofclaim 18, wherein the apparatus is configured to allow the one extremity of the patient to be positioned at the detector axis by moving at least the portion of the one extremity of the patient through the gap in a direction substantially perpendicular to the detector axis and parallel to the source plane.

21. The apparatus ofclaim 16, wherein the source mechanism includes a rigid C-shaped assembly to provide mechanical support for the source as the source is moved along the source path.

22. The apparatus ofclaim 21, wherein the detector mechanism includes the rigid C-shaped assembly to provide mechanical support for the detector as the detector is moved along the detector path.

23. The apparatus ofclaim 22, further comprising a gap in the C-shaped assembly configured to allow the one extremity of the patient to be positioned at the detector axis by moving said at least a portion of the one extremity of the patient through the gap in the C-shaped assembly.

24. The apparatus ofclaim 21, wherein the source mechanism further includes a source support arm, a proximate end of the source support arm attached to the C-shaped assembly and a distal end of the source support arm attached to the source to provide mechanical support for the source as the source is moved along the source path.

25. The apparatus ofclaim 23, wherein the detector path includes a gap in the first circular arc, and wherein at least a portion of the gap in the first circular arc is diametrically opposite at least a portion of the gap in the second circular arc.

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