Patent Publication Number: US-9892810-B2

Title: Collimator shutter drive mechanism

Description:
BACKGROUND 
     Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this disclosure and are not admitted to be prior art by inclusion in this section. 
     An x-ray system typically includes an x-ray tube and a detector. The power and signals for the x-ray tube can be provided by a tube generator. The x-ray tube emits radiation, such as x-rays, toward an object. The object is positioned between the x-ray tube and the detector. The radiation typically passes through the object and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then generates data based on the detected radiation, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object, such as a patient in a medical imaging procedure or an inanimate object in an inspection scan. 
     The radiation detector (e.g., x-ray detector) can include a conversion element that converts an incoming radiation beam into electrical signals, which can be used to generate data about the radiation beam, which in turn can be used to characterize an object being inspected (e.g., the patient or inanimate object). In one example, the conversion element includes a scintillator that converts a radiation beam into light, and a sensor that generates electrical signals in response to the light. The detector can also include processing circuitry that processes the electrical signals to generate data about the radiation beam. 
     In some configurations, a collimator can be positioned between the x-ray tube and the object. The collimator can adjustably narrow the radiation beam to a specific area of interest on the object. The technology (devices, systems, and methods) described herein provides collimator solutions to adjust the radiation beam from a radiation source. 
     BRIEF SUMMARY OF SOME EXAMPLE EMBODIMENTS 
     A collimator is a device that narrows a beam of particles or waves (e.g., x-ray radiation) so the directions of motion becomes more aligned in a specific direction or the spatial cross section of the beam becomes smaller (i.e., a beam limiting device). Collimators used to limit x-ray radiation can have features that include materials (e.g., lead [Pb]) to absorb or block radiation. Collimators can include various structures, shapes, sizes, and mechanisms for different application. Collimators can limit the x-ray beam to a specific region of interest (e.g., examination area or a treatment area) or improve image quality by reducing x-ray scattering. Collimator can be used to reduce exposure of patient tissue from x-ray radiation that is outside the target area, which can be beneficial to the patient by reducing the total x-ray dose to the patient (or operator). Collimators can be used in various applications, such as radiological imaging and therapy, computed tomography (CT), fluoroscopy, and mammography. 
     A collimator can have a drive mechanism that uses ramps and control pins to pivot shutter pairs in a collimator assembly. The use of the drive mechanism can provide a compact design (e.g., in height) of the shutters. In an example, a collimator assembly includes a base and a shutter assembly. The shutter assembly includes a lower shutter and a shutter control. The lower shutter includes a yoke, a control pin, and an inner extension extending from a first end of the yoke and supports the control pin. The shutter control includes a ramp feature that is slidably engaged with the control pin. The yoke rotates or tilts as the control pin slides along the ramp feature and the shutter control is slidably engaged with the base. 
     In another example, the shutter assembly further includes a first shutter bracket attached to the base and a second shutter bracket attached to the base. The lower shutter further includes an outer extension extending from a second end of the yoke, an outer hinge pin supported by the outer extension and the second shutter bracket, and an inner hinge pin supported by the inner extension and the first shutter bracket. The outer hinge pin is hingedly engaged with the outer extension or the second shutter bracket. The inner hinge pin is hingedly engaged with the inner extension or the first shutter bracket. 
     In another configuration, the base includes an opening (i.e., a hole) and the shutter assembly further includes an upper shutter with a lower end that is in communication with the lower shutter. Communication refers to being coupled to, adjacent to, or in close proximity to a component (e.g., lower shutter) through direct contact or attached via another medium (e.g., shutter base). A majority of the upper shutter has a substantially planar shape. The upper shutter rotates or tilts with the rotation of the yoke of the lower shutter and the rotation of the upper shutter is configured to variably block radiation from passing through the opening. The upper shutter can include a circular segment extending from an end of the upper shutter furthest from the lower shutter and the chord of the circular segment is a furthest end of the upper shutter. 
     In another example, the shutter assembly further includes a shutter base coupling the lower shutter to the upper shutter. The lower shutter and the upper shutter can include a radiation shielding material (e.g., lead [Pb]). The shutter assembly further includes a cantilever spring with a first end and a second end. The first end is fixed in position by a middle bracket. The second end applies a resilient force on the upper shutter or a shutter base coupling the lower shutter to the upper shutter. The lower shutter can include a notch in the yoke. The notch in the yoke allows rotation of the lower shutter without applying a direct force on the cantilever spring by the lower shutter. 
     In another configuration, the shutter assembly further includes a second lower shutter. The second lower shutter includes a second yoke, a second control pin, an inner extension extending from a first end of the second yoke and supports the second control pin, a second inner hinge pin supported by the inner extension of the second yoke and the first shutter bracket, an outer extension extending from a second end of the second yoke, and a second outer hinge pin supported by the outer extension of the second yoke and the second shutter bracket. The second inner hinge pin is hingedly engaged with the inner extension of the second yoke or the first shutter bracket. The second outer hinge pin is hingedly engaged with the outer extension of the second yoke or the second shutter bracket. A length of the yoke is substantially parallel to a length of the second yoke. The shutter control further includes a second ramp feature that is slidably engaged with the second control pin. The second yoke rotates or tilts as the second control pin slides along the second ramp feature. The rotation of the yoke is in an opposite direction as the rotation of the second yoke. 
     In another example, the shutter assembly further includes a first upper shutter with a lower end that is in communication with the lower shutter, and a second upper shutter with a lower end that is in communication with the second lower shutter. A majority of the first upper shutter has a substantially planar shape. The first upper shutter rotates or tilts with the rotation of the lower shutter and the rotation of the first upper shutter is configured to variably block radiation from passing through an opening (i.e., hole) in the base. A majority of the second upper shutter has a substantially planar shape. The second upper shutter rotates or tilts with a rotation of the second lower shutter, and the rotation of the second upper shutter is configured to variably block radiation from passing through the opening. The slideable movement of the shutter control changes the distance between an upper end of the first upper shutter and an upper end of the second upper shutter. 
     In another configuration, the lower shutter, the second lower shutter, and the shutter control form a first shutter assembly pair. The collimator assembly further includes a second shutter assembly pair that includes a third lower shutter, a fourth lower shutter, and a second shutter control. The third lower shutter includes a third yoke and a third control pin. The fourth lower shutter that includes a fourth yoke and a fourth control pin. The a second shutter control that includes a third ramp feature that is slidably engaged with the third control pin and a fourth ramp feature that is slidably engaged with the fourth control pin. The second shutter control is slidably engaged with the base. The third yoke rotates or tilts as the third control pin slides along the third ramp feature and the fourth yoke rotates or tilts as the fourth control pin slides along the fourth ramp feature. The rotation of the third yoke is in an opposite direction as the rotation of the fourth yoke. In another example, the length of the lower shutter and the second lower shutter are substantially perpendicular to a length of the third lower shutter and the fourth lower shutter. A length of the shutter control is substantially perpendicular to a length of the second shutter control. The lower shutter, the second lower shutter, the third lower shutter, and the fourth lower shutter form sides of a substantially rectangular shape with overlapping ends. A portion of the lower shutter and the second lower shutter overlap a portion of the third lower shutter and the fourth lower shutter. 
     In another example, the shutter assembly further includes a control guide attached to the base that substantially confines movement of the shutter control to a single axis. The control guide can include an elongated slot and the shutter control can include at least one protrusion slidably engaged in the elongated slot. The at least one protrusion limits movement of the shutter control in the single axis. 
     Another example provides a method of collimating radiation. The method includes the operation of sliding a shutter control that includes a ramp feature along a base of a collimator assembly. The next operation of the method can include sliding a control pin along the ramp feature when the shutter control slides along the base. The method can further include rotating or tilting a yoke of a lower shutter about an axis of an inner hinge pin when the control pin slides along the ramp feature. The yoke includes an inner extension extending from a first end of the yoke that supports the control pin and the inner hinge pin. The yoke also includes an outer extension extending from a second end of the yoke that supports an outer hinge pin. The next operation of the method can variably block radiation based on the rotation of the lower shutter. 
     In a configuration, rotating the yoke of the lower shutter rotates or tilts an upper shutter extending from the lower shutter. The upper shutter includes a radiation shielding material and provides greater variation in blocking radiation than the lower shutter alone. 
     In another example, the method can further include applying a resilient force from the base to the upper shutter via a cantilever spring. The next operation of the method includes forcing the control pin down onto the ramp feature when the resilient force is applied to the upper shutter. 
     In another example, a collimator assembly includes a base including an opening (i.e., a hole), two shutter controls, four shutter brackets, and four shutter assemblies. Each shutter assembly is located on one of four sides of the opening and each shutter assembly includes a lower shutter. The lower shutters includes a yoke, a control pin, an inner hinge pin, an inner extension extending from a first end of the yoke and supports the control pin and the inner hinge pin, an outer hinge pin, and an outer extension extending from a second end of the yoke and supports the outer hinge pin. Two opposing shutter assemblies provide a shutter assembly pair, and one shutter assembly pair is substantially perpendicular to another shutter assembly pair. The control pins of the lower shutters of each shutter assembly pair are slidably engaged with separate ramp features of one of the two shutter controls. Each yoke rotates or tilts as the corresponding control pin slides along the corresponding ramp feature. The inner hinge pins of the lower shutters of each shutter assembly pair are supported by an inner shutter bracket that is one of the four shutter brackets. The outer hinge pins of the lower shutters of each shutter assembly pair are supported by an outer shutter bracket that is one of the four shutter brackets. Each inner hinge pin is hingedly engaged with the inner extension or the inner shutter bracket, and each outer hinge pin is hingedly engaged with the outer extension or the outer shutter bracket. 
     In another configuration, each shutter assembly further includes an upper shutter that is in communication with the lower shutter, wherein the upper shutter rotates or tilts with the rotation of the lower shutter, and the rotation of the upper shutter is configured to variably block radiation from passing through the opening. 
     The summary provided above is illustrative and is not intended to be in any way limiting. In addition to the examples described above, further aspects, features, and advantages of the invention will be made apparent by reference to the drawings, the following detailed description, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of an example x-ray tube. 
         FIG. 2  illustrates a perspective view of an example x-ray system that includes a collimator. 
         FIG. 3  illustrates a perspective view of an example collimator. 
         FIG. 4  illustrates a perspective top view of an example collimator assembly. 
         FIG. 5  illustrates a perspective top view of an example collimator assembly on a base radiation shield. 
         FIG. 6  illustrates a perspective bottom view of an example collimator assembly. 
         FIG. 7  illustrates a perspective bottom view of an example collimator assembly on a base radiation shield. 
         FIG. 8A  illustrates a perspective top view of cross shutters and control assembly in an open position. 
         FIG. 8B  illustrates a perspective top view of cross shutters and control assembly in a closed position. 
         FIG. 9A  illustrates a side view of cross shutters and control assembly in an open position. 
         FIG. 9B  illustrates a side view of cross shutters and control assembly in a closed position. 
         FIG. 10A  illustrates a perspective top view of long shutters and control assembly in an open position. 
         FIG. 10B  illustrates a perspective top view of long shutters and control assembly in a closed position. 
         FIG. 11A  illustrates a side view of long shutters and control assembly in an open position. 
         FIG. 11B  illustrates a side view of long shutters and control assembly in a closed position. 
         FIG. 12A  illustrates a perspective bottom view of an example collimator assembly in an open position. 
         FIG. 12B  illustrates a perspective bottom view of an example collimator assembly in a closed position. 
         FIG. 13A  illustrates a perspective top view of an example collimator assembly in an open position. 
         FIG. 13B  illustrates a perspective top view of an example collimator assembly in a closed position. 
         FIG. 14  illustrates a perspective cross-sectional bottom view of an example collimator. 
         FIG. 15  illustrates a perspective cross-sectional side view of an example collimator. 
         FIG. 16  is flowchart illustrating an example of a method of collimating radiation. 
     
    
    
     DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Numbers provided in flow charts and processes are provided for clarity in illustrating steps and operations and do not necessarily indicate a particular order or sequence. Unless otherwise defined, the term “or” can refer to a choice of alternatives e.g., a disjunction operator, or an exclusive or) or a combination of the alternatives (e.g., a conjunction operator, and/or, a logical or, or a Boolean OR). 
     Disclosed embodiments relate generally to x-ray collimator and, more particularly, to drive mechanism for shutters of a collimator and methods to operate shutters for a collimator. 
     Reference will now be made to the drawings to describe various aspects of example embodiments of the invention. It is to be understood that the drawings are diagrammatic and schematic representations of such example embodiments, and are not limiting of the present invention, nor are they necessarily drawn to scale. 
       FIG. 1  is a block diagram of an example rotary or rotating anode type x-ray tube  100  with a rotatable disc-shaped anode  122 . The x-ray tube  100  includes a housing  102  and an x-ray insert  110  within the housing  102 . The housing  102  encloses the insert  110 . A coolant or air may fill the space or cavity between the housing  102  and the insert  110 . A cathode  112  and an anode assembly  120  are positioned within an evacuated enclosure, also referred to as the insert  110 . The anode assembly  120  includes the anode  122 , a bearing assembly  130 , and a rotor  128  mechanically coupled to the bearing assembly  130 . The anode  122  is spaced apart from and oppositely disposed to the cathode  112 . The anode  122  and cathode  112  are connected in an electrical circuit that allows for the application of a high voltage potential between the anode  122  and the cathode  112 . The cathode  112  includes an electron emitter  116  that is connected to an appropriate power source (not shown). 
     As disclosed in  FIG. 1 , prior to operation of the example x-ray tube  100 , the insert  110  is evacuated to create a vacuum. The insert  110  encloses the vacuum. Then, during operation of the example x-ray tube  100 , an electrical current is passed through the electron emitter  116  of the cathode  112  to cause electrons “e” to be emitted from the cathode  112  by thermionic emission. The application of a high voltage differential between the anode  122  and the cathode  112  then causes the electrons “e” to accelerate from the cathode electron emitter toward a focal spot on a focal track  124  that is positioned on the anode  122 . The focal track  124  may be composed for example of tungsten (W) and rhenium (Re) or other materials having a high atomic (“high Z”) number. As the electrons “e” accelerate, they gain a substantial amount of kinetic energy, and upon striking the rotating focal track  124  some of this kinetic energy is converted into x-rays “x”. 
     The focal track  124  is oriented so that emitted x-rays “x” are visible to an x-ray tube window  104 . The x-ray tube window  104  includes an x-ray transmissive material, such as beryllium (Be), so the x-ray&#39;s “x” emitted from the focal track  124  pass through the x-ray tube window  104  in order to strike an intended object (not shown) and then the detector to produce an x-ray image (not shown).  FIG. 1  illustrates a single window  104  on the housing  102  (e.g., with a glass insert that allows radiation to pass through the glass of the insert). In other examples, a separate window may be included on both the insert  110  (e.g., a metal insert) and the housing  102 , or a window may be included on just the insert  110 . 
     As the electrons “e” strike the focal track  124 , a significant amount of the kinetic energy of the electrons “e” is transferred to the focal track  124  as heat. To reduce the heat at a specific focal spot on the focal track  124 , a disc-shaped anode target is rotated at high speeds, typically using an induction motor that includes a rotor  128  and a stator  106 . The induction motor is an alternating current (AC) electric motor in which the electric current in the rotor  128  needed to produce torque is obtained by electromagnetic induction from a magnetic field of stator winding. Then, the rotor  128  rotates a hub of the bearing assembly  130  that is mechanically coupled to the anode  122 , which rotates the anode  122 . In other examples (not shown), the x-ray tube uses a stationary′ track. 
     After the x-rays are emitted from the x-ray tube, the x-rays strike an intended object (e.g., the patent or inanimate object) and then the radiation detector to produce an x-ray image. The radiation detector includes a matrix or array of pixel detector elements. The pixel detector elements (e.g., x-ray detector element or detector element) refer to an element in a matrix or array that converts x-ray photons to electrical charges. A detector element may include a photoconductor material which can convert x-ray photons directly to electrical charges (electron-hole pairs) in a direct detection scheme. Suitable photoconductor material include and are not limited to mercuric iodide (HgI 2 ), lead iodide (PbI 2 ), bismuth iodide (BiI 3 ), cadmium zinc telluride (CdZnTe), or amorphous selenium (a-Se). In some embodiments, a detector element may comprise a scintillator material which converts x-ray photons to light and a photosensitive element coupled to the scintillator material to convert the light to electrical charges (i.e., indirect detection scheme). Suitable scintillator materials include and are not limited to gadolinium oxisulfide (Gd 2 O 2 S:Tb), cadmium tungstate (CdWO 4 ), bismuth germinate (Bi 4 Ge 3 O 12  or BGO), cesium iodide (CsI), or cesium iodide thallium (CsI:Tl)). Suitable photosensitive element may include a photodiode, a photogate, or phototransistors. Other circuitry for pixel detector elements may also be used. 
     The x-ray tube and radiation detector can be components in an imaging system that are located in an x-ray room.  FIG. 2  illustrates an imaging or x-ray system  200  that includes an x-ray-tube  220 , a tube generator  222  to provide power and signals to the x-ray tube, a collimator  210  to shape the x-ray beam from the x-ray tube, an x-ray tube support  202  to support the x-ray tube and collimator, a radiation or x-ray detector  230  to capture the emitted x-ray, a table  204  to support a patient or object, and a table pedestal  206  to support the table. The x-ray tube or x-ray tube support can include a mechanism to rotate the x-ray tube in both the horizontal and axial direction relative to the x-ray tube support. The collimator can be coupled near the x-ray tube window  104  ( FIG. 1 ). In a fully open position, the collimator can allow a maximum field size  216  of the x-ray beam, which area or size can change based on the distance of the x-ray detector from the x-ray tube. The maximum field size is the largest effective area that radiation can strike for an x-ray tube-collimator combination. Effective area is the area with radiation strong enough that the radiation can be detected by pixel detector elements of an x-ray detector. As illustrated, the maximum field size is smaller than the area of the x-ray detector. In other examples, the maximum field size of the collimator is larger, equal to, or smaller than the x-ray detector. The operation of the collimator can reduce the effective area of the x-ray radiation down to a minimum collimated field size  218 . The minimum collimated field size is the effective area of the x-ray radiation with the collimator in a fully closed position. With adjustment to the collimator, the x-ray radiation can have various sizes or shapes (e.g., rectangles) between the maximum field size and the minimum collimated field size. Although the collimator is shown with an x-ray tube, the collimator  210  may also be used with another radiation source. 
       FIG. 3  illustrates a perspective view of the collimator  210  shown in  FIG. 2 . The collimator  210  include a collimator assembly  300  (i.e., a first collimator assembly) and dials  311  and  321  to adjust shutters of the collimator assembly. The cross control dial  311  adjust the shutters in the cross shutter control assembly  310  ( FIGS. 8A-9B ), which adjusts the x-ray radiation exposure in a front to back direction, if viewed from the control dials. The long control dial  321  adjust the shutters in the long shutter control assembly  320  ( FIGS. 10A-11B ), which adjusts the x-ray radiation exposure in a side to side direction, if viewed from the control dials. The collimator may include a light or laser (not shown) that is illuminated through the collimator window  208  ( FIG. 14 ) to help position the x-ray tube and collimator relative to the object, patient, or x-ray detector  230  ( FIG. 2 ). In another example (not shown), the laser may use a different opening from the collimator window. A mirror may be used to center the collimator light with the collimator assembly. The collimator can include components that include metals (e.g., stainless steel or lead), polymers (e.g., plastics and rubber), paints, or other rigid or resilient materials. The collimator assembly  300  provides one set of shutters for the collimator  210 . In another example, the collimator may include another set of shutters (i.e., cross shutters  240  and long shutters  242  in a second collimator assembly in  FIG. 15 ) located within a housing of the collimator. The shutters  240  and  242  of the second collimator assembly can include a radiation shielding or absorbing material and provide additional collimating functionality. The dials  311  and  321  can adjust shutters of the first collimator assembly  300  along with the shutters  240  and  242  of the second collimator assembly. 
       FIGS. 4-13B  illustrate various views of the collimator assembly  300 .  FIG. 4  shows a perspective top view of the collimator assembly. The collimator assembly  300  can include a base  302  (collimator base) with an opening, a source alignment flange  306  that can be used to couple the collimator to the x-ray tube (or tube assembly), and shutters to variably block electromagnetic waves (e.g., light and x-ray radiation) passing through the opening. The source alignment flange  306  is shown as a protrusion and a ring. In other examples, the source alignment flange can have another shape that can mate or couple to the x-ray tube. The source alignment flange includes flange lock assemblies  308  that include a flange lock housing  308 A, a flange lock  308 B, and a set screw  308 G. The flange lock  308 B adjustably applies a force on a mating feature of the x-ray tube. The adjustment is provided by a set screw  308 G. The set screw head can be a hexagonal, slot, Phillips, Torx head, or other type of head that allows a torque to be applied to the screw. 
     The collimator assembly  300  can include four shutter assemblies for the four sides of the opening. Each shutter assembly can include an upper shutter  352 ,  354 ,  356 , and  358 ; a lower shutter  332 ,  334 ,  336 , and  338 ; and a shutter base  342 ,  344 ,  346 , and  348  that couples the lower shutter to the upper shutter. Upper refers to a relative position closer to (e.g., in the y-axis) an x-ray source or x-ray tube. Lower refers to a relative position further away from (e.g., in the y-axis) the x-ray source or x-ray tube. The shutter base can have a substantially planar form that follows the form of the upper shutter or lower shutter. Upper and lower can refer to relative positions along a y-axis. The upper shutter can be coupled to one side of the shutter base and the lower shutter can be coupled to another side of the shutter base. The coupling may include screws. In another example (not shown), the upper shutter and lower shutter can be coupled to the same side of the shutter base.  FIGS. 4-13B  illustrate the upper shutter, lower shutter, and shutter base as three separate components. In another example, the upper shutter, lower shutter, and shutter base may be integrated as one or two components. The upper shutter, lower shutter, or shutter base can include a radiation shielding or absorbing material, such as lead (Pb). As illustrated in  FIG. 5 , the base ( 302  of  FIG. 4 ) of the collimator assembly can include a base radiation shield  304  that includes radiation shielding or absorbing material, such as lead (Pb). Thus, the radiation emitted from the x-ray tube can be blocked by the radiation shielding or absorbing material except through the opening of the base and the area not blocked by shutters of the shutter assemblies. 
       FIG. 6  illustrates a perspective bottom view of the collimator assembly  300 . The collimator assembly includes two sets of shutters: cross shutters  332 ,  334 ,  342 ,  344 ,  352 , and  354  controlled by a cross shutter control  312  that is moved, driven, or adjusted (e.g., in the x-axis) by the cross control dial  311  ( FIG. 3 ) for front and back adjustment; and long shutters  336 ,  338 ,  346 ,  348 ,  356 , and  358  controlled by a long shutter control  322  that is moved, driven, or adjusted (e.g., in the y-axis) by the long control dial  321  ( FIG. 3 ) for side to side adjustment. In another example (not shown), the cross shutter control and the long shutter control is operated by a motorized mechanism and electronic controls (with or without feedback and sensors). 
     Referring back to  FIG. 6 , the cross shutter control  312  operates on the cross shutters via the cross lower shutters  332  and  334 . The long shutter control  322  operates on the long shutters via the long lower shutters  336  and  338 . Cross refers to components associated with or near the cross shutter control  312 . Long refers to components associated with or near the long shutter control  322 . Each lower shutter includes an inner extension  332 A,  334 A,  336 A, and  338 A; an outer extension  332 C,  334 C,  336 C, and  338 C; and a yoke  334 B,  336 B, and  338 B that couples the inner extension to the outer extension. Inner refers to a relative position of a component closer to a shutter control (e.g., cross shutter control  312  and long shutter control  322 ). Outer refers to a relative position of a component farther away from the shutter control. For example, a cross inner lower shutter (CILS)  332  is closer to the long shutter control  322  than a cross outer lower shutter (COLS)  334 . A long inner lower shutter (LILS)  336  is closer to the cross shutter control  312  than a long outer lower shutter (LOLS)  338 . Similarly, the COLS inner extension  334 A is closer to the cross shutter control  312  than the COLS outer extension  334 C. From a top or bottom view, the ends (e.g., yoke or extension) of the lower shutter can overlap with the ends of an adjacent lower shutter. For example, the ends of CILS  332  overlaps with ends of LILS  336  and LOLS  338 , and the ends of COLS  334  overlaps with the other ends of LILS  336  and LOLS  338 . 
     The extensions of the lower shutters support control pins and hinge pins, which is also illustrated in  FIG. 7 . The inner extension  332 A,  334 A,  336 A, and  338 A supports a control pin  362 ,  364 ,  366 , and  368  and an inner hinge pin  361 A,  363 A,  365 A, and  367 A. The outer extension  332 C,  334 C,  336 C, and  338 C supports an outer hinge pin  361 B,  363 B,  365 B, and  367 B. The lower shutters are hingedly engaged or connected to the base  302  through the hinge pins supported by brackets  382 ,  384 ,  386 , and  388 . For example, the CILS inner hinge pin  361 A and the COLS inner hinge pin  363 A are supported by the LILS bracket  386 , and the CILS outer hinge pin  361 B and the COLS outer hinge pin  363 B are supported by the LOLS bracket  388 . The LILS inner hinge pin  365 A and the LOLS inner hinge pin  367 A are supported by the CILS bracket  382 , and the LILS outer hinge pin  365 B and the LOLS outer hinge pin  367 B are supported by the COLS bracket  384 . The brackets are coupled to the base using screws, bolts, semi-permanent attachment mechanism, or permanent attachment mechanism. A semi-permanent attachment mechanism includes a screw, a bolt, or other mechanism that can be attached or unattached through manipulation of a component of the attachment mechanism. A permanent attachment includes a weld, an adhesive, heat or chemical treatment to combine two component together, which requires more than manipulation of the components to remove the components from each other without damage to the components. Unless otherwise stated, the attachments for the collimator assembly can be provide by the semi-permanent attachment mechanism or the permanent attachment. The bracket  386  and  388  may include a notch (e.g., LILS bracket notch  387  or LOLS bracket notch  389 ). For example, the LILS bracket  386  includes a LILS bracket notch  387  to allow downward movement of the CILS control pin  362  on a cross control inner ramp  314  (also seen in  FIG. 9B ). 
     The lower shutters  332 ,  334 ,  336 , and  338  (e.g., the yoke  334 B,  336 B, and  338 B) rotate or pivot around or about the hinge pins  361 A-B,  363 A-B,  365 A-B, and  367 A-B with the inner extensions  332 A,  334 A,  336 A, and  338 A along with the control pins  362 ,  364 ,  366 , and  368  acting as a lever arms. The control pin moves in a nearly vertical (e.g., up and down with a slight angle) based on lateral movement (along the x-axis or the z-axis) of the shutter control  312  and  322  along the base  302 . The shutter control can have a substantially rectangular cuboid with various features. Each shutter control  312  and  322  includes at least one ramp feature  314 ,  315 ,  324 , and  325  (i.e., incline/decline portion or wedge in the shutter control) that is slidably engaged with the control pins. The cross shutter control  312  includes two ramp features (i.e., cross control inner ramp  314  and cross control outer ramp  315 ) on opposite sides of the shutter control. The cross control inner ramp  314  slidably engages with CILS control pin  362 , and the cross control outer ramp  315  slidably engages with COLS control pin  364 . The long shutter control  322  includes two ramp features (i.e., long control inner ramp  324  and long control outer ramp  325 ) on a same side of the shutter control. The long control inner ramp  324  slidably engages with LILS control pin  366 , and the long control outer ramp  325  slidably engages with LOLS control pin  368 . As the shutter control slides along a single axis (e.g., x-axis or the z-axis), the control pin slides along the ramp and moves the control pin up or down (in the y-axis) a ramp, which in turn rotates or pivots the lower shutter. The lower shutter then rotates or tilts the shutter base  342 ,  344 ,  346 , and  348  and the upper shutter  352 ,  354 ,  356 , and  358 , which moves opposing upper shutters closer together or farther apart to collimate the radiation (or electromagnetic wave). A large movement of the control pin along the ramp can generate a relatively small rotation of the lower shutter, which can provide a relative small movement of a circular flange segment  352 C,  354 C,  356 C, and  358 C of the upper shutter. The slope (or angle) of the ramp can determine the amount (or degree) of rotation or tilt of the lower shutter relative to the linear motion of the shutter control. A length of the lever arm of the inner extension of the lower shutter can also determine the amount (or degree) of rotation or tilt of the lower shutter relative to the linear motion of the shutter control. For example, a steep slope increases the rotation or tilt of the lower shutter with a linear motion to the shutter control compared to a shallow slope. The slope of multiple ramps can be similar to each or differ from each other. For example, the cross shutter control can have ramp slopes that are similar and the long shutter control can have ramp slopes that are similar, but the ramp slopes of the cross shutter control can have different angles from the ramp slopes of the long shutter control. 
     The control pins  362 ,  364 ,  366 , and  368  can have a cylindrical shape with various diameters in the same control pin. The different diameter can be used various reasons, such as avoiding contact with other components. For example, the LOLS control pin  368  can have a narrow diameter near the long control ramps  324  and  325  to avoid contact with the long control inner ramp  324 . 
     As illustrated by  FIG. 7 , a flat spring or cantilever spring  372 ,  374 ,  376 , and  378  applies a resilient force on the shutter base  342 ,  344 ,  346 , and  348  (or upper shutter). A resilient force is a force provided by a resilient or elastic component, such as a spring, which changes as the resilient or elastic component deflects. In an example, the shutter base may allow some deflection of the shutter. One end of the spring can be held or fixed in position by the bracket  382 ,  384 ,  386 , and  388 . The  372  CILS spring is secured by the CILS bracket  382 , the COLS spring  374  is secured by the COLS bracket  384 , the LILS spring  376  is secured by the LILS bracket  386 , and the LOLS spring  378  is secured by the LILS bracket  386 . The other end of the spring slides along the shutter base. The resilient force of the spring is translated as a force on the control pin  362 ,  364 ,  366 , and  368  onto the ramp feature  314 ,  315 ,  324 , and  325 , which can keep the control pin engaged on the ramp features. The yoke  334 B,  336 B, and  338 B of the lower shutter  332 ,  334 ,  336 , and  338  can include a lower shutter notch  333 ,  335 ,  337 , and  339  above the lower shutter, as with CILS notch  333  and COLS notch  335 , or below or laterally to the lower shutter, as with LILS notch  337  and LOLS notch  339  to allow free movement of the spring without interference from the lower shutter or having the spring touch the lower shutter. The shutter base (e.g., cross inner shutter base [CISB]  342  and cross outer shutter base [COSB]  344 ) may include a slot or opening for the spring to cross the plane of shutter base from the bracket to an opposite side of the shutter base. 
     Referring back to  FIG. 6 , each shutter control  312  and  322  is slidably engaged with a control guide or control guide assembly  316  and  326  that is attached (e.g., using screws) to the base  302 . In an example, the control guide components or structure  316  and  326  can have similar features. The control guide includes a guide channel (e.g., cross guide channel  317  or long guide channel  327 ) in the control guide that supports a portion of the shutter control. The guide channel can be a void (i.e., space) in the control guide. The control guide assembly can include a single component or multiple components.  FIG. 6  illustrates the control guide assembly as two components that are mirror images of each other (e.g., lower cross control guide  316 A and upper cross control guide  316 B for the cross shutter control assembly  310 ; and lower long control guide  326 A and upper long control guide  326 B for the long shutter control assembly  320 ). The control guide includes a guide slot (e.g., lower cross guide slot  318  and upper cross guide slot [not shown]; and lower long guide slot  328  and upper long guide slot [not shown]) that slidably engages with control protrusions (e.g., cross control protrusions  313 A-D and long control protrusions  323 A-D) extending from the shutter control. The control protrusions can extend above a substantial surface or plane of the shutter control and below a substantial surface or plane of the control guide. The guide channel and the control protrusions substantially confine, restrict, or limit the movement of the shutter control to a single axis (e.g., x-axis for the cross shutter control  312  and z-axis for the long shutter control  322 ). The cross shutter control slides along the cross control guide  316  in the x-axis. The long shutter control slides along the long control guide  326  in the z-axis. The length of the guide slot and the position of the control protrusions can confine, restrict, or limit the distance or movement of the shutter control within the single axis. The control guide and guide channel interfaces with one edge of the shutter control (opposite to the edge or side with the ramp features), which can reduce tilting, lifting, twisting, or torque of the shutter control. 
     Another guide on the opposite edge of the shutter control (on the same edge or side with the ramp features), such as a long anti-tilting block or bracket  329 , can provide additional stability against tilting, lifting, twisting, or torque of the shutter control. The long anti-tilting block  329  can hold the long shutter control  322  in a substantially parallel position relative to the base or control guide when the LILS control pin  366  and LOLS control pin  368  apply a force on the long control ramps  324  and  325 . 
     The cross shutter control  312  may also include a cross shutter control notch  309  that can receive a cross collimator guide  212  ( FIG. 14 ) that couples the cross shutter control to the cross control dial  311  via a geared mechanism. The long shutter control  322  may also include a long shutter control notch  319  that can receive a long collimator guide  214  ( FIG. 14 ) that couples the long shutter control to the long control dial  321  via another geared mechanism. 
       FIGS. 8A-9B  illustrate various views of cross shutters (including a cross inner upper shutter [CIUS]  352  and a cross outer upper shutter [COUS]  354 ) relative to the cross shutter control  312  in open and closed positions.  FIGS. 10A-11B  illustrate various views of long shutters (including a long inner upper shutter [LIUS]  356  and a long outer upper shutter [LOUS]  358 ) and the long shutter control  322  in open and closed positions.  FIGS. 12A-B  illustrate perspective bottom views of the collimator assembly in open and closed positions.  FIGS. 13A-B  illustrate perspective top views of the collimator assembly in open and closed positions. As shown in  FIGS. 8A-8B and 10A-10B , the upper shutter can have substantially folded planar shape (or folded plate) of an “I” with one elongated flange (or substantially planar flange segment  352 A,  354 A,  356 A, and  358 A) and another circular segment flange (or circular flange segment  3520 ,  354 C,  356 C, and  358 C) with a web  352 B and  358 B joining the elongate flange with the circular segment flange. A void between the planar flange segment and the circular flange segment can be referred to as the web notch  353  and  359 A. The web and web notch can facilitate overlapping circular segment flanges in adjacent shutters (upper shutters and shutter base) when the shutters are in a closed position. For example, the LIUS circular flange segment  586 C and the LOUS circular flange segment  358 C can be on the same plane in the vertical (y-axis) as the CIUS web  352 B. CIUS web notch  353 , COUS web, and COUS web notch, as shown in  FIG. 13B . The circular flange segment may also include a circular segment notch  359 B to accommodate the web of an adjacent shutter in a closed position. For example, the LOUS circular segment notch  359 A and LIUS circular segment notch can be notched (e.g., substantially rectangular cuboid void) to accommodate the CIUS web  352 B and COUS web in a closed position, as shown in  FIG. 13B . The planar surface of the circular flange segment can be at angle between 60° and 120° angle with the planar flange segment, as shown in  FIGS. 9A-9B and 11A-11B . In another example, the planar surface of the circular flange segment can be at angle between 70° and 110° angle with the planar flange segment. In another example, the planar surface of the circular flange segment can be at angle between 80° and 100° angle with the planar flange segment. In an example the upper shutter can have a substantially uniform width. Each circular flange segment includes a chord edge  352 D,  354 D,  356 D, and  358 D. The CIUS chord edge  352 D is substantially parallel to the COUS chord edge  354 D from the open position to the closed position. The LIUS chord edge  356 D is substantially parallel to the LOUS chord edge  358 D from the open position to the closed position. Open refers to a substantially maximum distance between the chord edges of opposite facing upper shutters. Closed refers to a substantially minimum distance between the chord edges of opposite facing upper shutters. The upper shutters can be in multiple positions between the open and closed position. The upper shutters can vary in position between the open and closed position. The opening and closing of the shutters (including the lower shutters, the shutter bases, and the upper shutters) collimates the radiation (or other electromagnetic wave, such as visible light). The chord edges of the upper shutters can define the shape of the collimated area.  FIG. 13A  illustrates an open collimated area  392  with both the cross and long shutters in a fully open position, which can produce a maximum field size  216  ( FIG. 2 ) of an emitted x-ray beam.  FIG. 13B  illustrates a closed collimated area  394  with both the cross and long shutters in a fully closed position, which can produce a minimum collimated field size  218  ( FIG. 2 ) of an emitted x-ray beam or visible light. 
     The shutter base can have a similar outline and shape to the upper shutter in the area that overlaps with the upper shutter. The shutter base can include features to support the upper shutter, such as tabs in the web notch  353  and  359 A. In an example, the upper shutter can include a radiation shielding or absorbing material and the shutter base includes a non-radiation shielding or absorbing material. In another example, both the upper shutter and shutter base include a radiation shielding or absorbing material. 
     In another example, the upper shutter can have a different shape or outline (as shown in  FIGS. 3-15 ) so long at the cross upper shutters can overlap with the long upper shutters and the upper shutter provide a variable collimated area. 
     As illustrated in  FIGS. 8A-9B , the CILS  332  is attached to the CISB  342 , which is attached to the CIUS  352 , and the COLS  334  is attached to the COSB  344 , which is attached to the COUS  354 . The sliding movement of the CILS control pin  362  on the cross control inner ramp  314  rotates or tilts the cross inner shutter about the CILS hinge pins  361 A-B, which moves the CIUS chord edge  352 D toward or away from the COUS chord edge  354 D. Similarly, the sliding movement of the COLS control pin  364  on the cross control outer ramp  315  rotates or tilts the cross outer shutter about the COLS hinge pins  363 A-B, which moves the COUS chord edge  354 D toward or away from the CIUS chord edge  352 D. The CIUS chord edge  352 D can move toward or away from the COUS chord edge  354 D simultaneously with movement of the cross shutter control  312 . 
     As illustrated in  FIGS. 10A-11B , the LILS  336  is attached to the long inner shutter base (LISB)  346 , which is attached to the LIUS  356 , and the LOLS  338  is attached to the long outer shutter base (LOSB)  348 , which is attached to the LOUS  358 . The sliding movement of the LILS control pin  366  on the long control inner ramp  324  rotates or tilts the long inner shutter about the LILS hinge pins  365 A-B, which moves the LIUS chord edge  356 D toward or away from the LOUS chord edge  358 D. Similarly, the sliding movement of the LOLS control pin  368  on the long control outer ramp  325  rotates and tilts the cross outer shutter about the LOLS hinge pins  367 A-B, which moves the LOUS chord edge  358 D toward or away from the LIUS chord edge  356 D. The LIUS chord edge  356 D can move toward or away from the LOUS chord edge  358 D simultaneously with movement of the long shutter control  322 . 
     Adjacent upper shutters can have different heights (in the y-axis) to allow the shutters to overlap with each other. For example, the cross upper shutters  352  and  354  have a greater height than the long upper shutters  356  and  358 , as shown in  FIG. 13B . 
       FIGS. 14-15  illustrates perspective cross-sectional views of the mechanical features (e.g., gears, belts, and springs) that couples the collimator assembly  300  to the control dials or knobs  311  and  321 . The mechanical features shown in  FIGS. 14-15  are manually operated. In another example (not shown), the mechanical features are electrically driven. Various mechanism can be used to convert or translate the rotary movement of the control knobs into the linear motion for the shutter controls  312  and  322 .  FIGS. 2-3 and 14-15  illustrates control dials or knobs to adjust or move the shutter controls  312  and  322 . In other examples, the controls for the shutter control can include sliding controls or slide controls (instead of control dials or knobs) or electronic controls to adjust or move the shutter controls  312  and  322  or other control device that allows multiple positions of the control. 
     The flowchart shown in  FIG. 16  illustrates a method  400  of collimating radiation. The method includes the step of sliding a shutter control that includes a ramp feature along a base of a collimator assembly, as in step  410 . The step of sliding a control pin along the ramp feature when the shutter control slides along the base follows, as in step  420 . The next step of the method includes rotating a yoke of a lower shutter about an axis of an inner hinge pin when the control pin slides along the ramp feature, where the yoke includes an inner extension extending from a first end of the yoke that supports the control pin and the inner hinge pin, and the yoke includes an outer extension extending from a second end of the yoke that supports the outer hinge pin, as in step  430 . The method further includes the step of variably blocking radiation based on the rotation of the lower shutter, as in step  440 . 
     The technology (systems, devices, assemblies, components, and methods) described herein can provide a collimator drive mechanism that includes a ramp with a specified slope or angle, which can be used to pivot a control pin up and down, where the control pin is coupled to a spring-loaded top shutter. The relatively long path of the control pin of the lower shutter on the ramp can be transformed to a small movement for the top shutter without using gears or similar mechanism in the collimator assembly. The collimator assembly allows simultaneous movement of the shutter pairs (including the upper shutter along with the lower shutter). The collimator assembly has a very compact design and profile, such as the height of the shutters, which provides a relatively small end product. 
     Reference throughout this specification to an “example” or an “embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one embodiment of the invention. Thus, appearances of the words an “example” or an “embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. 
     Furthermore, the described features, structures, or characteristics may be combined in a suitable manner in one or more embodiments. In the following description, numerous specific details are provided (e.g., examples of layouts and designs) to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, layouts, etc. In other instances, well-known structures, components, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
     While the forgoing examples are illustrative of the principles of the invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited. Various features and advantages of the invention are set forth in the following claims.