Patent Application
20240395491
The present disclosure pertains to the field of high-energy electron beams, specifically to scanning electron-beam X-ray sources enabling fast scans for imaging and/or treatment devices, including computed tomography (CT) imaging systems.
X-ray imaging and treatment are extensively utilized in medical and other fields. X-ray generation in an X-ray tube is well known in the art, which includes an electron source and an anode, both enclosed in a vacuum-sealed envelope. The electron source, or electron gun, comprises a cathode to emit electrons. The anode is kept at a large positive potential relative to the cathode. The electrons are accelerated from the electron source toward the anode, forming a high-energy beam directed towards a high-atomic-number anode, such as tungsten. As electrons impinge on the anode, they decelerate rapidly, converting their kinetic energy to X-rays via the Bremsstrahlung process. The impingement point is referred to as focal spot. The resulting X-rays are transmitted out of the tube through an X-ray exit window for use in various medical and other applications.
Computed tomography (CT) is an important imaging modality. CT imaging requires the measurement of X-ray projections from multiple angles through an object, achieved either by physically moving the X-ray tube, together with a detector on a rotating gantry(the 3rd generation CT) or with stationary detector (the 4th generation CT), or by scanning the electron beam along an anode ring, as in Electron Beam (EB) CT with a stationary detector (the 5th generation CT as disclosed in U.S. Pat. No. 4,352,021A, its derivatives and its variations).
Many CT systems today are the 3rd generation CT, where the X-ray tube together with the detector array are mounted on the CT gantry, physically rotating around the object. However, the speed of rotation in the 3rd generation CT is limited by the centripetal forces due to the physical rotation of heavy X-ray tube with a larger moment of inertia. This limitation in rotation speed may lead to degradation (in terms of blur and errors) of the CT image caused by patient motion, such as cardiac, respiratory, and/or other organ movements. While some motion-induced blur and errors may be mitigated by reducing patient motion, such as decreasing the patient's heart rate, this often requires additional medical preparation and may include medication (such as P-blockers), resulting in significant overhead in terms of time and resources. Moreover, patients may experience side effects from the medication.
The 5th generation CT systems, as disclosed by U.S. Pat. No. 4,352,021A, its derivatives and its variations could eliminate the need to physically rotate an X-ray tube around the object. The 5th generation CT typically uses Electron Beam (EB) scan technology, namely circular anode(s) and a single electron gun with a magnetic deflection system that deflects the electron beam onto one or multiple anodes ring around the patient. Consequently, X-ray can be generated around the object by magnetically scan at a much faster rate than a mechanically rotated X-ray tube. Therefore, EB CT is less susceptible to motion-induced degradation. EB CT presents significant market potential as it eliminates the need for administering costly and potentially adverse medication. However, prior art EB CT suffers certain deficiencies. For example, U.S. Pat. No. 4,352,021A contains a large and heavy cone-shaped scan tube enclosure, which is complex to manufacture, operate, and maintain. Further, the cone-shape scan tube enclosure closes one end of the CT bore opening, greatly limiting the patient comfort, maneuverability, and accessibility, especially, limiting axial and helical (also referred to as spiral) scan. The helical scan is a standard scanning method in modern CT imaging where the patient lies on a movable table that passes through the bore opening while imaging.
U.S. Pat. No. 7,639,785B2 discloses an alternative EB scan tube design featuring a linear drift tube substantially parallel to the direction of the electron beam emitted by the electron gun and a linear anode mounted along the sidewall of the drift tube. The electrons move in a straight line until they encounter a magnetic deflection field that changes their direction. By changing the locations of the applied deflection magnetic fields at various locations along the drift tube, X-rays are generated at various focal spot positions along the linear anode. This scan tube design results in a much more compact scan tube enclosure. However, U.S. Pat. No. 7,639,785B2 suffers from the deficiency that it limits to a linear anode and is not adequately suited for CT application because the X-ray projections from a linear anode does not provide sufficient directions for adequate CT reconstruction.
There have been efforts to address the deficiencies in both prior arts by using multiple X-ray tubes with multiple electron guns, which add to complexity, inefficiency and impracticality of such CT system. These prior arts are impracticable because the electron gun is typically the least reliable part in the EB CT, thus using multiple electron guns leads to lower overall system reliability.
The current disclosure discloses a new EB scan tube design and examples of its applications, including CT application, to address the deficiencies of existing devices.
The present disclosure discloses a novel charged particle scan device, including a new electron beam (EB) scan tube design suitable for CT imaging using a single electron gun and featuring a compact, lightweight, reliable, and cost-effective construction. The examples include a compact curvilinear X-ray electron beam scan tube for rapid computed tomography (CT) and other applications.
All drawings are for clarity; not all components or spatial relationships are illustrated to scale.
In some embodiments, an Electron Beam (EB) X-ray tube includes two primary components: 1) an electron gun generating and emitting electrons from a cathode in the gun, and 2) a scan tube projecting electrons onto a sequence of impingement points on an anode to generate X-rays from various directions. This trajectory of points of impingement is referred to as the anode trajectory (or the target trajectory, or the focal spots trajectory). The scan tube enclosure generally comprises three sections: 1) the entry end through which electrons from the electron gun enter, 2) the sidewall section along the centerline or length of the scan tube; 3) the opposite (or exit) end. The centerline of the scan tube is defined as the trajectory of the center points of the scan tube's cross-sections moving from one end to the other end.
The axis of curvature of the anode trajectory (i.e., the anode ring) is illustrated as Z and labeled as 130 in
In certain embodiments, the configuration further ensures a compact placement of the scan tube and the electron gun into a toroidal shape enclosure similar to a conventional CT gantry so that the central opening of the toroidal shape enclosure (commonly referred to as the imaging bore of the CT) can be fully open and accessible at both ends, as shown in
In certain embodiments, the configuration further ensures a placement of the electron gun close to the anode, with the closest distance to the anode trajectory being less than 20 cm in some examples, as shown in
In some embodiments, the configuration further ensures the direction of the electron gun (i.e., the direction of entry electrons) and initial anode trajectory to be aligned within an angle of typically less than, for example, 20, 10, or 5 degrees, as shown in
The alignment of the anode trajectory with the centerline of the scan tube and with the electron gun enables X-ray tube in certain embodiments more compact, which can fit into a toroidal-shaped enclosure, resulting in a fully open central opening of the toroidal shape enclosure (or the imaging bore in CT application) that is accessible at both ends. Such open access is difficult, if not impossible, to attain in systems similar to that disclosed in U.S. Pat. No. 4,352,021A and its derivatives.
In some embodiments, an additional control, or guiding, component, referred to in this disclosure as the scanning control component, is used in generating X-rays disclosed herein. In some embodiments, separate control components, namely, the scanning and aiming components are used. In an example shown in
In one embodiment, the scanning control component employs one or more magnets, referred to as the scanning magnet, to guide the electrons within certain distance of the anode trajectory 105 without impinging on it. Under this embodiment, in one embodiment, such a distance is within 50 cm. In one embodiment, the trajectory of electrons is substantially perpendicular to the axis of curvature 130 of the anode trajectory 105. In another embodiment, the trajectory of electrons is substantially parallel to the anode trajectory 105. The scanning magnets may be placed outside, proximal to, Scan Tube 104.
In one embodiment the scanning magnet is exemplified by a Helmholtz coil illustrated by two windings, Winding 122A and Winding 122B in
Thus, the scanning control component guides the electrons to travel in an orbit in the vicinity of the anode trajectory 105 without impinging on it.
In one embodiment, the aiming control component utilizes a series of magnets, referred to as the aiming magnets, to direct the electrons to target at a specific focal spot on the anode trajectory 105, generating X-rays. The aiming magnets may be implemented using a series of Helmholtz coils with windings wrapped around a set of non-magnetic yokes. As an example, two such yokes, Winding Form 124A and Winding Form 124B, are illustrated and labeled in
The separation of two control components of electron beam control system, namely, scanning and aiming, where aiming is distributed along the anode trajectory and occurred at a close distance to the impinging point, stands in contrast to U.S. Pat. No. 4,352,021A and its derivatives where aiming occurs at roughly single point near the entry end of the scan tube (the apex of the cone), which is far (around 200 cm) from the focal spot to be targeted (on the base of the cone). Distributing the aiming points along the anode trajectory brings them closer to the impinging point thus shortening the portion of the trajectory outside of the magnetic fields. This results in a more compact design and a tighter electron beam.
One important application of EB X-ray tube is its CT application. CT application requirements include 1) to use an adequate anode trajectory, preferably a ring trajectory to achieve the required angular coverage of 180 degrees plus the fan beam angle around the Region of Interest (ROI), to collect X-ray projections from sufficient angles for adequate CT reconstruction; 2) to use a simple X-ray source with, preferably, a single electron gun, because using multiple electron guns add to complexity, inefficiency and impracticality of such CT system.
The prior art disclosed in U.S. Pat. No. 4,352,021A and its derivatives meets the above CT application requirements. In contrast, an alternative EB scan tube design disclosed in U.S. Pat. No. 7,639,785B2 does not meet the requirements because it is designed only for a linear anode, whereas X-ray projections from a straight line is insufficient for adequate CT reconstruction. Furthermore, other prior arts proposing to reduce the deficiencies of U.S. Pat. No. 4,352,021 or U.S. Pat. No. 7,639,785B2 by using multiple X-ray sources with multiple election guns fail to meet the above requirements. These prior art systems are impracticable because the electron gun is typically the least reliable part in the EB CT, thus using multiple electron guns leads to lower overall system reliability. Thus, the various embodiments can be more directly compared with U.S. Pat. No. 4,352,021A.
The devices and systems in certain embodiments address the deficiencies in prior arts by using a single electron gun with a curvilinear anode trajectory (e.g. an anode ring trajectory). Thus, the devices and systems meet the above CT application requirements more fully. Furthermore, the embodiments include the scanning component of the electron beam control system, which is lacking in prior arts, to track the curvature of the anode trajectory.
In certain additional embodiments in CT application, as shown in
In medical CT scanners, these other key components are mounted on a gantry (commonly referred to as CT gantry) together with an X-ray tube to rotate around the Region of Interest 50. This case is referred to as the 3rd generation CT.
In one embodiment, the rotation of an X-ray tube around ROI 50 can be achieved by EB scanning along the anode ring 105 inside X-ray Tube 100, thus physical rotation of a X-ray tube 100 around ROI 50 is no longer necessary. This embodiment is referred to as the stationary X-ray tube. In this embodiment, the other key components, such as X-ray detector, can be mounted stationary (without rotation).
In some embodiments, while X-ray Tube 100 is stationary, at least one set of other components, for example, X-ray detector 156, X-ray filter 151, or X-ray collimator 152 or 154, or any combination is mounted on a rotational gantry. The rotating components rotate in synchronization with, i.e., being fixed relative to, the sequential movement of the focal spot (one shown as 150) along the target ring 105.
In some embodiments, coordination, or synchronization, of the movement of focal spots 150 in the stationary tube 100 with the rotating gantry is achieved by dynamically adjusting and timing the field in the aiming magnets based on the rotational position signal of the gantry received optically or other way. In other embodiments, the rotational speed of the gantry can be continuously adjusted based on the electron beam sensor information.
In some other embodiments, the X-ray filter 151 is equipped with an adjustable aperture. The aperture is dynamically adjusted to modulate the X-ray dose delivered at each angle based on predetermined delivery scheme that minimized dose while maintaining suitable level of image noise. The aperture in some embodiments is adjusted by means of a rotating disk with a slit cut into it, where the width of the slit varies along the perimeter of disk. Rotating the disk changes the width of the opening in the disk thus varying the amount of X-ray radiation going into the patient. In some embodiments, the rotating disk with a slit is paired with a stationary disk with another aperture for improved collimation efficiency.
In some embodiments the detector 156 is also rotated with the gantry. This allows to reduce the length of the detector arc, thus reducing the count of detector pixels. In one embodiment the detector is powered using slip ring mechanism, which is also used to read out the detector data to the reconstruction computer. In another embodiment, the detector is powered autonomously through an energy storage device, such as a battery. In this embodiment, the detector signals can be read out from the detector using wireless communication technology.
The combination of stationary (for at least X-ray Tube 100) and rotational components described above has multiple advantages over both the 3rd and 5th CT generations. The CT apparatus disclosed in the present disclosure can achieve faster scan speeds compared to the 3rd generation CT (roughly, 50 ms or faster vs 200 ms) due to a much smaller moment of inertia to be rotated, because the X-ray source, which accounts for a majority of the inertia in the 3rd generation CT, is stationary. At the same time, the CT apparatus disclosed in the present disclosure inherits the advantages of the 3rd generation CT in dose efficiency, dynamic range and reduced detector count.
Certain embodiments disclosed herein pertains to general EB scan technology that may be used in a multiview imaging, a tomosynthesis imaging, a CT imaging, or any combined imaging. For the embodiment of CT imaging with a rotating detector, it differs from 3rd generation CT because of using a stationary x-ray tube. It also differs from 5th generation CT because of using a rotating detector. Even for the embodiment of CT imaging with a stationary detector, it still differs from the 5th generation CT as disclosed in U.S. Pat. No. 4,352,021A and its variations and derivatives because the new EB scan technology disclosed herein has a designed alignment between the anode trajectory and the direction of the electron beam until deflected toward the anode, with an angle of the two directions being less than, say, 20 degrees. In contrast, the EB technology in 5th generation CT (namely U.S. Pat. No. 4,352,021A and its variations and derivatives) lacks such a designed alignment, thus the alignment is almost 90 degrees off.
While the scan tubes disclosed in the examples above have a ring anode, scan tubes with anodes of other shapes can be used. For example, curvilinear anodes, i.e., an anode inside the sidewall section of the scan tube and extending over the length (or centerline) of the section of the scan tube to form (or arrange) the anode trajectory, containing at least a curved anode trajectory. A curvilinear anode trajectory may include 1) a ring (segment) as discussed previously, 2) multiple curves; 3) a curve with either or both ends attached to a line; 4) two curves connected by a line, 5) and others.
In some embodiments, the X-rays generated by X-ray Tube 100 exit the tube through an X-ray Window, illustrated and labeled as 109 in
Furthermore, multiple anodes may be used on the same sidewall section (say at the bottom) of the X-ray Tube 100, but at different radial distance r to the Z axis. Specifically, by selecting different strengths of the scanning magnetic field {right arrow over (B)} 131, the electrons rotate in different circular orbit with different radial distance r according to the above equation. Once the aiming magnetic field {right arrow over (b)} 132 is applied, the electrons will impinge upon the anode at different radial distance r to the Z axis. Anodes at different radial distance may be offset in z (for example, by amounting on different stand-off structures), thus generating X-ray at different z locations for the benefit described above.
In one embodiment, modulating the scanning magnetic field {right arrow over (B)} 131, and/or the aiming magnetic field {right arrow over (b)} 132, to control the focal spots positions can also be used to achieve increased sampling rate along the anode and/or in z direction, resulting in the increased image spatial resolution.
In some embodiments, aiming magnetic field is contained within field region of Scan Tube 104 by placing permalloy or other magnetic material with ultra-low hysteresis characteristics around magnets so that the magnets share the continuous magnetic return. A common form of the material used for such applications is called mu-metal. In the embodiments of
For simplicity of illustration,
The embodiments described above may contain magnetic Lens, 106, and a quadrupole magnetic lens, Quadrupole Lens 108, positioned about a Coupling Tube 110 illustrated in
In some embodiments, Lens 106 and quadrupole 108 comprises dynamically and separately adjusted (driven) coils resulting dynamically focused and shaped electron beam emitted by Electron Gun 102. As the location of the electron beam impact on the anode changes, the electron travel distance changes and therefore the focal distance changes. Dynamical adjustment of the Lens 106 and quadrupole 108 accounts for these changes.
In some embodiments, the magnets are electromagnets, i.e., windings or sets of windings forming electromagnets with or without magnetic returns. For example, a magnet may be an electromagnet comprising turns of wire about Scan Tube 104. In some embodiments, the magnet comprises a Helmholtz coil, including two sets of windings separated by a sufficient distance. In other embodiments, permanent magnets, or a combination of permanent magnet(s) and electromagnets, are used. For example, one or more permanent magnets or electromagnets may be positioned adjacent to the scan tube and moved along the scan tube to move the focal spot along the anode trajectory. In some embodiments, one or more permanent magnets or electromagnets and an X-ray detector can be mounted at opposing ends of the rotating bracket.
The aiming magnets are energized in such order as to target electrons toward various positions along the anode trajectory 105. Each aiming magnet may be independently energized or driven, so that any number of aiming magnets may at any time be independently energized to generate a magnetic field.
For clarity of illustration,
Energizing one or more aiming magnets deflects an electron beam to the anode trajectory 105. The positions on the anode trajectory 105 to which electrons are targeted (i.e., the focal spots) depend upon the superposition of magnetic fields from these magnets. One or more drivers coupled to the aiming magnets may be used to provide dynamically adjusted values of current to the aiming magnets to target an electron beam to various positions on the anode trajectory 105.
Some embodiments energize the aiming magnets in sequential fashion so that groups of aiming magnets are energized at a time to target an electron beam impact point along the anode trajectory 105 so that a focal spot is essentially swept/scanned along the anode trajectory 105. In this way, an embodiment may find application in a tomosynthesis or CT X-ray scanner, where X-rays are generated along a curve surrounding a patient. Furthermore, the aiming magnets may be broken into more than one subgroup energized in sequential fashion within each subgroup so that the movement of focal spot due to each subgroup is essentially swept/scanned along the anode trajectory.
Because only one or a few subsets of aiming magnets are energized at any moment during the operation, the controller in some embodiments include a multiplexing circuit that connects the output of the power supply to the particular subsets of magnets to be energized at the moment.
For example,
At some point during the ramped down of current 7001, its corresponding magnet is switched from 7101 to 7104. This can be done when the current is close zero or at point 7013 to reduce the current in the switched associated with the stored energy in coil 7101.
After time point 7013 current 7001 is increased again. However, it is now coils 7102, 7103, and 7104, with currents 7002, 7003, and 7001, respectively, that affect aiming of the electron beam. The process of switching currents to successive aiming coils continues until all magnets along tube 701 are addressed and the beam covers the full anode trajectory.
In other embodiments, current waveforms 7001, 7002 and 7003 can be chosen differently to conform to such factors as desired motion profile and speed of the focal spot, shape and size of the anode and other geometrical considerations.
Some embodiments may have fewer than three current waveforms, whereas other embodiments may have more than three waveforms, for each focal spot.
The dynamic switching of the current driver output can be achieved using any suitable circuit. For example, in the example shown in
In some embodiments only one switch from the set connected to a single output of 8000 is closed. In other embodiments, each output may be split into multiple coils by closing multiple switches simultaneously.
Some embodiments may employ solid state switches, while others may use electro-mechanical switches. Some embodiments may use a combination of two.
Some embodiments may use a digital or analog control device 8010.
Some embodiments may use multiple control devices 8010.
It should be noted that embodiments may include anodes positioned differently than that illustrated in the several drawings, and it is only a matter of orienting the aiming magnets (or adding additional aiming magnets) so that their respective magnetic fields as experienced by the electrons have the proper magnitude and direction to target the electrons to the desired positions on the anode to generate X-rays.
In the embodiments of
Similarly, two winding pairs, such as 124A and 124B in
In the drawings, the aiming magnetic field {right arrow over (b)} provided by aiming magnets at various positions along anode trajectory 105, for example, are in a direction parallel to the axis of curvature or in a radial direction orthogonal to the axis of curvature. However, the orientations of the aiming magnets may vary from embodiment to embodiment, as well as within an embodiment. For example, for some embodiments there may be multiple aiming magnets with varying orientations.
For aiming magnets that are of the Helmholtz coil type, aiming magnetic field {right arrow over (b)} at an interior region where the electron beam is expected may be taken to be parallel to its axis of symmetry. Accordingly, some embodiments may be described as comprising a set of aiming magnets where each aiming magnet has an axis of symmetry along a radial direction from some point (the same point for each aiming magnet) on the axis of curvature.
The term Helmholtz coil is generalized herein to include magnets having two sets of windings parallel to each other, but where the relationship of their diameters to their separation distance need not satisfy the classical definition of a Helmholtz coil. Furthermore, a set of windings need not be circular in form but may take any arbitrary planar shape.
The magnets do not need to be comprised of Helmholtz coils. Any suitable combination of winding may be used. For example, any combination of windings that provide uniform dipole magnetic field may be used to accomplish described electron beam guiding.
In a case where X-ray Tube 100 is powered but no X-ray exposure is desired, for example during the pause of a patient x-ray scan, the electrons travel through the entire length of Scan Tube 104 without impinging on the focal spots 105 and are absorbed and terminated at Collector labeled as 114 in
The heat created by the anode or Collector 114 may be removed by running water or other cooling liquid through them, or air cooled if sufficient time between irradiations is provided.
An ultra-high vacuum (UHV) pump, Pump 116, is coupled to X-ray Tube 100, and is coupled directly to Electron Gun 102 in the embodiments of
An anode, also referred to as an anode, may comprise a mixture of tungsten and other materials, and in some embodiments is held at ground electrical potential. Electron emits electrons with the kinetic energy in the range from few keV up to several MeV depending on applications.
While the foregoing examples involve X-ray sources, with an electron gun and anode, other radiation sources can be similarly devised. In general, a radiation source can have a similar configuration as the X-ray tubes described above, but with an emitter of a different type of charge particles than electrons and a scan tube enclosing a target that is appropriate for generating the desired radiation upon impingement of the charged particles. Similar scanning and aiming components as described above can be used.
The phrases “or” is used in accordance with formal mathematical logic. Relating a measurable aspect of an embodiment (e.g., length, angle, time, magnetic field) to a numerical value or vector, relating by an equality or equivalence a measurable aspect of an embodiment to another measurable aspect (e.g., that a set of focal spots on an anode are in a curvilinear geometry), or describing an aspect as constant or uniform (e.g., a uniform magnetic field over some interior region of the tube) is accurate to within accepted tolerances as practiced in the relevant art; accordingly, the qualifiers “substantially” or “substantially constant” or the like for a numerical quantity, vector, or relationship are not needed when describing embodiments or reciting a claim element.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
