Inverse geometry tetrahedral beam computed tomography (CT)

Abstract

The present disclosure relates generally to CT x-ray imaging systems and methods, and in particular to inverse geometries with tetrahedral beams. In particular, a dose efficient and controllable inverse geometry tetrahedral beam CT imaging is disclosed. The disclosed CT geometry includes a linear array of x-ray sources perpendicular to an axis of rotation of the CT system and rotating with a linear array of detectors extending parallel to the axis of rotation. The x-ray emission from each of the plurality of sources is collimated to be projected to the linear detector array as a fanned beam. The intensity of each beam is dynamically adjusted and controlled during rotation of the source array and the detector array. Such a configuration provides control of x-ray intensity over a selected region of interest in the target object during rotation with efficient dose control even if the region of interest is offset from the axis of rotation.

Description

[0001] Inventor

[0002] Jiang Hao

[0003] Emre Toker

[0004] Zhang Tiezhi

[0005] Zhou Shuang

[0006] Jonathan Hefner

[0007] Shen Liuxing

[0008] Shu Ziyu

[0009] Government support

[0010] This invention was made with government support under Grant Nos. R41DE029727 and R42EB026401 awarded by the National Institute of Health. The U.S. Government has certain rights in this invention.

[0011] Cross-references

[0012] This application is based on and claims priority to U.S. Provisional Patent Application No. 63 / 380,121 filed on October 19, 2022 and U.S. Provisional Patent Application No. 63 / 507,151 filed on June 9, 2023, both of which are incorporated herein by reference in their entirety. background Technical Field

[0014] The present disclosure relates generally to computed tomography (CT) x-ray imaging systems and methods, and more particularly to inverse geometry with tetrahedral beams for CT x-ray imaging. Background Art

[0015] X-ray sources and x-ray detectors can be configured and arranged in various geometries for CT x-ray imaging. With the advent of new x-ray sources and x-ray detectors, new geometries can be designed to better control the x-ray dosage while enhancing the CT image resolution and contrast of the region of interest in the target object. Summary of the invention

[0016] The present disclosure relates generally to CT x-ray imaging systems and methods, and more particularly to inverse geometry with tetrahedral beams. Specifically, a dosage-efficient and controllable inverse geometry tetrahedral beam CT imaging is disclosed. The disclosed CT geometry includes a linear array of x-ray sources that is perpendicular to the rotation axis of the CT system and rotates with a linear detector array that extends parallel to the rotation axis. The x-ray emissions from each of the multiple sources are collimated into a fan beam that is projected onto the linear detector array. During rotation of the source array and the detector array, the intensity of each beam is dynamically adjusted and controlled. Such a configuration provides control of the x-ray intensity on a selected region of interest in a target object during rotation, with efficient dosage control even if the region of interest is offset from the rotation axis.

[0017] In some example embodiments, a computer tomography x-ray imaging system for imaging a target object is disclosed. The system may include: a gantry configured to rotate around the target object about a rotation axis; an x-ray source array disposed on the gantry, the x-ray source array including a plurality of x-ray sources, the plurality of x-ray sources being aligned in a direction perpendicular to the rotation axis; an elongated linear detector array disposed on the gantry, opposite to the x-ray source array relative to the rotation axis, the elongated linear detector array including a plurality of x-ray detectors extending linearly along the rotation axis; a multi-slot collimator disposed on the gantry, between the x-ray source array and the target object; and a circuit configured to control activation of the plurality of x-ray sources to generate an x-ray emission sequence, the x-ray emission sequence being further collimated by the multi-slot collimator into a fan-shaped beam sequence, the fan-shaped beam sequence passing through the target object is projected into the elongated linear detector array for measurement, and the fan-shaped beam sequence intersects the target object to form a tetrahedral imaging volume.

[0018] In the above example embodiments, the circuit is further configured to dynamically adjust the intensity of the x-ray emission sequence individually.

[0019] In any of the above example embodiments, the intensity of the x-ray emission sequence is dynamically adjusted to cumulatively benefit the amount of x-rays projected through the region of interest in the target object.

[0020] In any of the above example embodiments, the control signal for adjusting the intensity of the x-ray emission sequence is based on a pre-calculation performed according to a region of interest in the target object.

[0021] In any of the above example embodiments, the intensity of the x-ray emission sequence is dynamically adjusted based on attenuation of the fan beam sequence by the target object.

[0022] In any of the above example embodiments, the system further comprises an elongated butterfly filter covering the plurality of x-ray sources to generate a predefined intensity distribution along the axis of rotation in each fan beam in the sequence of fan beams.

[0023] In any of the above example embodiments, the system further comprises an elongated butterfly filter covering the plurality of x-ray sources to generate a predefined intensity distribution along the axis of rotation in each fan beam in the sequence of fan beams.

[0024] In any of the above example embodiments, the gantry together with the x-ray source array, the elongated linear detector array and the multi-slot collimator are configured to rotate about a rotation axis to detect projections of a plurality of fan-beam sequences passing through a target object; and the circuit is further configured to reconstruct a computed tomography x-ray image of the target object based on the detected projections.

[0025] In any of the above example embodiments, the plurality of x-ray sources may be arranged to form a curve in a plane perpendicular to the axis of rotation, the center of the curve being located at the elongated linear detector array.

[0026] In any of the above example embodiments, the plurality of x-ray sources may comprise a linear array of x-ray sources.

[0027] In any of the above example embodiments, the multi-slot collimator comprises a plurality of slot openings, each slot opening being associated with one x-ray source of the plurality of x-ray sources for generating one fan beam of the fan beam sequence.

[0028] In any of the above example embodiments, activation of the plurality of x-ray sources is repeated at a repetition rate that matches a frame rate of the elongated linear detector array.

[0029] In some other example embodiments, a method for generating a computed tomography x-ray image of a target object is disclosed. The method may include: sequentially controlling activation of a plurality of x-ray sources to generate an x-ray emission sequence while rotating a gantry around the target object about a rotation axis, the plurality of x-ray sources being disposed on the gantry and aligned in a direction perpendicular to the rotation axis; collimating the x-ray emission sequence into a fan beam sequence; projecting the fan beam sequence through the target object into an elongated linear detector array, the elongated linear detector array being disposed on the gantry, opposite to the plurality of x-ray sources relative to the rotation axis, and including a plurality of x-ray detectors, the plurality of x-ray detectors extending linearly along the rotation axis, and the fan beam sequence intersecting the target object to form a tetrahedral imaging volume; and measuring the quantities of the plurality of fan beam sequences while rotating the gantry to generate a computed tomography x-ray image of the target object. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 An example CT system is shown.

[0031] Figure 2 A generalized inverse geometry CT with tetrahedral bundles is shown.

[0032] Figure 3 A perspective view of an inverse geometry tetrahedral beam CT with a linear array of x-ray sources, a linear detector array, a multi-slot collimator, and a butterfly filter is shown.

[0033] Figure 4 Shows Figure 3 Top view of the inverse geometry of tetrahedral beam CT.

[0034] Figure 5 Shows Figure 1 Side view of the inverse geometry of tetrahedral beam CT.

[0035] Figure 6 An example of sequentially scanning x-ray sources in a source array is shown.

[0036] Fig. 7A and Figure 7B Selection of an off-axis region of interest by dynamic control of the intensity distribution of an x-ray source is shown.

[0037] Figure 8 An example of a CT image reconstructed using uniform x-ray fluence and using intensity modulation based on a selected region of interest is shown.

[0038] Fig. 9 An inverse geometry tetrahedral beam CT configuration with a stacked x-ray source array is shown.

[0039] Fig.10 An inverse geometry tetrahedral beam CT configuration with an axial offset between the x-ray source array and the detector array is shown.

[0040] Fig.11 An example multipixelthermionic emission x-ray (MPTEX) source with control circuitry is shown.

[0041] Fig.12 An example relationship between the driving voltage of the thermionic filament cathode and the emission current of electrons at an example negative bias is shown. DETAILED DESCRIPTION

[0042] Various aspects of CT imaging will now be described in detail below with reference to the accompanying drawings, which form a part of the present disclosure and illustrate various example implementations and embodiments by way of illustration. However, as disclosed herein, the systems, devices, and methods for configuring an x-ray source array and a detector array in an inverse geometry to achieve a tetrahedral volumetric field of view with a dynamically adjustable x-ray intensity distribution may be embodied in a variety of different forms, and therefore, the disclosure herein is intended to be interpreted as not being limited to the embodiments set forth below. Furthermore, in addition to the disclosed devices and systems, the present disclosure may also be embodied as methods, components, and / or platforms. Therefore, the embodiments of the present disclosure may, for example, take the form of hardware, software, firmware, or any combination thereof.

[0043] In general, terms can be understood at least in part according to their use in context. For example, terms such as "and", "or", or "and / or" used herein can include multiple meanings, which can depend at least in part on the context in which these terms are used. Generally, if the term "or" is used to associate lists such as A, B, or C, it is intended to mean A, B, and C (here for inclusive meanings), and A, B, or C (here for exclusive meanings). In addition, at least in part depending on the context, the terms "one or more" or "at least one" used herein can be used to describe any feature, structure, or characteristic in a singular sense, or can be used to describe a combination of features, structures, or characteristics in a plural sense. Similarly, at least in part depending on the context, terms such as "one", "one", or "the" can be understood to convey singular usage or convey plural usage equally. In addition, also at least in part depending on the context, the term "based on" or "determined by..." can be understood to not necessarily be intended to convey an exclusive set of factors, but can allow the presence of additional factors that are not necessarily explicitly described.

[0044] Many other modifications may be made to the above embodiments to adapt a particular situation or material to the teachings without departing from the scope of the present disclosure. Therefore, it is intended that the present methods and systems are not limited to the specific embodiments explicitly disclosed. The disclosed methods and systems include all embodiments that fall within the scope of the appended claims.

[0045] As an introduction, computed tomography (CT) is an important tool in medical imaging diagnosis. Figure 1 An example CT system 100 is shown in . The example CT system 100 may include a gantry 106 that is configured to rotate about an axis 108 (also labeled "z") in an example direction shown by arrow 109. The example CT system 100 also includes a lying platform 110 that is used to support a target object 150 during CT image acquisition. The example CT system 100 also includes an x-ray source assembly 104 disposed on or in the gantry 106, and an x-ray detector assembly 102 disposed on or in the gantry 106, the x-ray detector assembly being located on an opposite side of the x-ray source assembly relative to the rotation axis 108 such that an x-ray beam emitted from the x-ray source assembly 104 passes through the target object 150 and is projected onto the x-ray detector assembly 102. Figure 1 In the configuration of , the gantry and the x-ray source assembly 104 and the x-ray detector assembly 102 disposed therein / on it can be configured to rotate about the fixed lying platform 110 and the axis 108.

[0046] In some example embodiments, the gantry 106 and the x-ray source assembly 104 and the x-ray detector assembly 102 disposed therein / thereon may also be configured to translate in the z-direction to project coverage of a target object in the z-direction.

[0047] In some example embodiments, the CT system 100 may also include one or more x-ray beam shapers 105 disposed in front of the x-ray source assembly 104 to shape the x-ray emissions from the x-ray source assembly 104. The shaping of the x-ray emissions may include, but is not limited to, collimation, fanning, orientation, and intensity profiling. Examples such as butterfly filters and slot collimators are described in more detail below.

[0048] The example CT system 100 also includes an x-ray drive circuit 120 for activating and controlling the emission of one or more x-ray beams in the x-ray source assembly 104. The example CT system 100 also includes a detector circuit 130 for controlling the detection of the projected x-ray beam and for collecting the detected x-ray amount. The example CT system 100 also includes a gantry drive 160 for controlling the rotation and / or translation of the gantry 106. The detector circuit 130, the x-ray drive circuit 120, and the gantry drive 160 can communicate with one or more central computers or distributed computers 140, which provide operational control of the x-ray source assembly 104, the x-ray detector assembly 102, and the gantry, as well as the computational and reconstruction requirements of the CT system 100.

[0049] During operation of the example CT system 100, the one or more computers 140 can be configured to control the x-ray source assembly 104 to emit one or more x-ray beams, which can be shaped by the beam shaper 105 and projected through the target object 150 to the x-ray detector assembly 102 for measurement. As the gantry rotates about the rotation axis 108 and / or translates along the rotation axis 108, multiple projections can be detected. The multiple projections cumulatively cover a volumetric region of the target object and are then reconstructed by the one or more computers to form a CT image.

[0050] In the above example CT system 100, the design / control of the x-ray source assembly 104 and the x-ray detector assembly 102 may greatly affect the required x-ray flux, image acquisition speed, and quality of the reconstructed images.

[0051] For example, in a conventional CT system, a point x-ray source may be employed in the x-ray source assembly 104. The x-ray beam shaper 105 may be configured to shape the emissions from the point x-ray source into a unidirectional beam. Thus, each projection from the x-ray source assembly 104 to the detector 102 covers only one linear direction through the target object. In order to obtain projections covering the imaging volume in a reasonable amount of time, the gantry 106 may be rotated at a relatively high speed and translated along the axis of rotation when the x-ray source assembly 104 is fired or activated, wherein each activation produces one projection. Such a system may be referred to as a spiral CT scanner. A spiral CT scanner may produce high quality images, but may be too cumbersome for many applications that are not solely for diagnostic purposes, such as CT systems that also incorporate treatment, such as point-of-care imaging systems and image-guided intervention systems.

[0052] In some other example embodiments of a point x-ray source, the x-ray beam shaper 105 may be configured to generate a planar fan beam that is projected through the target object to the x-ray detector assembly 102. The x-ray detector assembly 102 will then accordingly include a detector array, such as a linear detector array, having a plurality of detectors linearly aligned in a single row or multiple rows in the plane of the fan beam for pixelated detection. In this way, each projection of the fan beam will pass through a plane (rather than a line) in the target object to allow for simultaneous detection of multiple projection lines in the fan beam, thereby significantly increasing the speed of data acquisition or reducing the requirement for the rotation speed of the gantry 106.

[0053] A collimator can be used as an x-ray beam shaper to shape the emission from a point x-ray source into a fan-shaped beam. For example, a collimator can be made based on slots in a piece of radiopaque material, such as brass.

[0054] The fan beam can be further processed by a butterfly filter to produce a predefined intensity distribution within the fan plane of the fan beam. As described in further detail below, such an intensity distribution can facilitate focusing the x-ray flux to a more interesting area of ​​the target object. An example of using a butterfly filter is provided in more detail below.

[0055] In some other example embodiments of a point x-ray source, the x-ray beam shaper 105 may be configured to generate a cone beam that is projected through the target object 150 to the x-ray detector assembly 102. The x-ray detector assembly 106 will accordingly include a detector array, such as a two-dimensional (2D) detector array or a flat panel having a plurality of detectors arranged in two dimensions to receive the projected cone beam. In this way, each projection of the cone beam will cover a conical volume in the target object (rather than a plane or a line as described above) to allow simultaneous detection of multiple projection lines in the cone beam, thereby significantly increasing the speed of data acquisition or reducing the requirement for the rotation speed of the gantry. The terms "detector array" or "array detector" or "multiple array detectors" are used interchangeably to refer to an assembly or collection containing multiple x-ray detectors.

[0056] CT systems based on point sources and cone beams may have compact geometries and can scan large volumes with a single system rotation by requiring a 2D detector. However, cone beam CT systems may not produce high image quality due to excessive x-ray scatter and poor performance of typical flat panel 2D x-ray detectors.

[0057] In some other example embodiments, the above CT system may use an inverse geometry. The term "inverse" may be used to refer to the reversal of the projection between the x-ray source and the x-ray detector, particularly in the context of the above fan beam geometry or cone beam geometry. For example, in the context of fan beam geometry, rather than having a single x-ray source generate a fan beam and using a linear detector array to detect different portions of the fan beam, an array of x-ray beams may be generated by the x-ray source assembly 104 and projected into a single pixel detector in the x-ray detector assembly 102. Nevertheless, this inverse geometry still covers the same projection plane in the target object, except that the multiple x-ray sources in the source array will be activated in time sequence, each activation providing a line projection, and the measurements made by the single detector for each line projection are time-resolved from the other projection lines.

[0058] This inverse geometry allows the use of highly sensitive single-pixel x-ray detectors (e.g., photon counters) and would be beneficial if compact linear arrays of x-ray sources were readily available.

[0059] In the above example inverse geometry implementation, the x-ray source can be extended to two dimensions. In this way, the projection volume from the detector array to a single pixel detector can be covered by sequentially activating each x-ray source in the array and time-resolving the detection of these x-ray sources in the single pixel detector after projection.

[0060] In some other example embodiments of volume CT, both the x-ray source assembly 104 and the x-ray detector assembly 102 may include arrays of separate components. For example, the x-ray source assembly 104 may include a plurality of individually activatable and controllable x-ray sources, and the x-ray detector assembly 1024 may include a plurality of pixelated x-ray detectors. Specifically, both arrays may be arranged linearly: the x-ray detector assembly may include an extended row of x-ray detectors, and the x-ray source assembly may include an extended row of x-ray sources.

[0061] In some example embodiments, Figure 2 As shown, the two linear assemblies can be arranged or set on the frame so that they are perpendicular to each other. Specifically, Figure 2 A linear detector array 202 and a linear source array 204 are shown. The x-ray emission of each of these sources (e.g., source 210) can be shaped into a planar fan beam that projects through the target object ( Figure 2 (not shown) to cover the detector array 202. Similar to other systems based on source arrays, Figure 2Each x-ray source in the x-ray source array 204 can be activated and controlled individually. These x-ray sources can be activated in sequence so that their fan beams are projected in sequence and detected by the detector array 202, and are therefore time-resolved. The N detectors (N is an integer) in the detector array 202 further spatially resolve the N lines in each of the fan beams. In this way, each of these fan beams covers a line in the target sample, and the activation sequence of all sources in the x-ray source array 204 cumulatively covers the volumetric region of the target object. The volumetric region of the target object is defined by the intersection of all fan beams with the target object. From Figure 2 As can be seen from the figure, such a volume region is essentially a tetrahedron in the z and x directions, and is represented by Figure 2 Therefore, this geometric structure is called a tetrahedral geometric structure, and a CT system using this geometric structure can be called a tetrahedral beam CT system.

[0062] The example geometry of the linear detector array and the linear source array is also an inverse geometry because all x-ray sources in the source array 204 project to each detector element in the detector array 202, such as the detector 220. Figure 2 The CT system of the geometry shown may alternatively be referred to as an inverse geometry tetrahedron CT system. Tetrahedron beam CT may advantageously produce high quality images similar to the above spiral CT in a compact geometry similar to the above cone beam CT. The terms detector unit, detector pixel, and individual detectors, etc. may be used interchangeably.

[0063] exist Figure 2 In a specific example implementation, the source array 204 may be arranged at Figure 1 The gantry 106 in the embodiment of the present invention is arranged to extend parallel to the rotation axis 108, and the detector array 202 is arranged in the gantry 106 to extend perpendicular to the rotation axis 108. The gantry 106 can be rotated slowly so that motion blur during activation or scanning of each x-ray beam sequence in the source array is negligible. In one gantry rotation, multiple sequences can be scanned in the source array, thereby correspondingly forming multiple tetrahedral volume projections. The time-resolved and spatially-resolved measurements of these projections can then be reconstructed into a CT image by one or more computers 140.

[0064] exist Figure 2 In another specific example embodiment, the source array 204 may be arranged at Figure 1 The rack 106 in the embodiment extends perpendicular to the rotation axis 108, and the detector array 202 is arranged in the rack 106 to extend parallel to the rotation axis 108, such as Figure 3 As shown. Figure 3In FIG. 1 , the inverse geometry tetrahedral beam CT system 300 includes a linear array x-ray source 304, a linear array detector 302, a butterfly filter 320, and a multi-slot collimator 310. The butterfly filter 320 and the multi-slot collimator 310 are used together as Figure 1 300 is a beam shaper 105 in the embodiment of the present invention. The system 300 rotates about a central axis 306. The linear source array 304 is aligned perpendicular to the rotation axis 306, and the linear array detector 302 is aligned parallel to the rotation axis 306 and perpendicular to the rotation plane. The x-ray sources in the linear source array 304 produce divergent x-ray emissions at the focal position. The emissions from each of the x-ray sources are collimated into a fan-shaped x-ray beam by a multi-slot collimator 310.

[0065] Figure 4 Shows Figure 3 A top view of an example embodiment of FIG. Figure 4 As shown, similarly, the x-ray beam generated by the linear x-ray source is collimated by the multi-slot collimator 310 into a stack of fan beams 402 , passes through or projects through the imaging object or target object 350 , and is then received by the linear array detector 302 .

[0066] like Figure 4 As shown, the multi-slot collimator 310 may include angled slots that focus the x-ray beam onto the detector 302. The multi-slot collimator may be made by machining the angled slots in a piece of radiopaque material (e.g., brass) or by machining the angled slots in a piece of radiolucent material with a radiopaque plate inserted therein.

[0067] Figure 5 Shows Figure 3 310 to more clearly illustrate the function of the butterfly filter 320. The x-ray emission from the source passes through the butterfly filter 320 before reaching the multi-slot collimator 310. Figure 5 As shown in the example transmission profile indicated in 320, the butterfly filter 320 allows more x-ray flux to pass through the emission center. Thus, each fan beam can carry such an intensity distribution in its fan plane parallel to the rotation axis 306. Thus, the x-ray flux can be more concentrated in the portion projected through the region of interest in the target object 350 in the axial direction.

[0068] The butterfly filter 320 may be constructed of a semi-transparent x-ray material (i.e., aluminum or polytetrafluoroethylene (Teflon)). The butterfly filter may be constructed to be thinner in the middle and thicker on the sides, like a bow tie. The butterfly filter may be removably disposed in or on the gantry, in front of one or more x-ray sources, so that it may be replaceable. The butterfly filter may have a shape that allows for the z direction ( Figure 5Different shapes of different lengths / ranges in the axial direction in the middle) are used to receive higher x-ray flux. Different butterfly filters or no butterfly filter can be selected according to different requirements.

[0069] like Figure 6 As further shown, a fan beam 602 from one of the x-ray sources in the x-ray source array 304 can be activated while all other x-ray sources are turned off. As described above, each x-ray source can be turned on or activated in sequence to produce a fan beam sequence. The activation or scanning of the fan beam sequence is repeated as the gantry slowly rotates about the rotation axis 306. The linear detector array 302 acquires a frame of projection data with each x-ray fan beam.

[0070] exist Figure 3 In an example inverse geometry tetrahedron embodiment, the intensity of the fan beam 305 can be individually controlled during activation and scanning of each x-ray source of the x-ray source array 304. Fig.11 Further shown is an example of an array of x-ray sources 304 and the control / adjustment of the emission intensity of each individual source.

[0071] In some example embodiments, Figure 1 The intensity of each of the fan beams 305 in the image can be programmed, with the center beam having a higher intensity and the off-center beam having a lower intensity. This programmed intensity profile can be configured to emulate the butterfly filter described above and can be repeated (or reprogrammed) between scans of each x-ray source during gantry rotation.

[0072] Compared to conventional fixed physical butterfly filters, the x-ray source can be further dynamically reprogrammed from beam sequence to beam sequence, and the intensity distribution between sequences can be dynamically changed. One advantage of this capability is that the intensity distribution of the beam projection can be kept close to the region of interest (ROI) in the target object during gantry rotation, even if the ROI is offset from the rotation axis, as shown in FIG7. Specifically, as shown in FIG7, the ROI 702 can be offset from the rotation axis 108 of the gantry. When the gantry rotates about the rotation axis 108 with the x-ray source, collimator, and butterfly filter and detector array (304, 320, 310, and 302), the activated beam from each specific x-ray source in the source array 304 passes through different slices in the target object 350 during the rotation. If the intensity distribution of the beam is repeated from beam sequence to beam sequence during the rotation, the off-axis ROI 702 will not receive the same intensity because the target object does not rotate. In order to keep the ROI 702 illuminated at a higher intensity during gantry rotation, the distribution within each beam sequence can be dynamically adjusted (or reprogrammed). Fig. 7AAs shown, at a first angular position of the rotation axis 108, the x-ray beam from the portion A of the x-ray source and projected through the ROI 702 can be adjusted to have a higher intensity. Figure 7B As shown, when the gantry rotates to a second angular position of the rotation axis 108, the x-ray source at position B will instead be adjusted to have a higher intensity. In this way, the intensity distribution can be dynamically adjusted or reprogrammed during the gantry rotation to maintain a higher x-ray intensity at or near the ROI 702. In the absence of such dynamic adjustability (e.g., in a fixed butterfly filter), the ROI must be placed at the rotation axis so that it always receives the desired higher intensity during the gantry rotation.

[0073] In some other example embodiments, the intensity of each sequence of fan beams can be dynamically programmed based on the maximum reading of the detector 102 or 302 during the scan of the beam in the x-ray source array, thereby producing a variable intensity distribution similar to a virtual butterfly filter for each scan sequence of the x-ray sources in the source array. Thus, the dynamic control of the intensity distribution between the fan beams effectively creates a virtual butterfly filter, whose intensity distribution can change as programmed when the gantry rotates around the target object. For example, the beam intensity can be modulated or adjusted according to the thickness of the slice through which the beam in the target is projected at a specific time of the gantry rotation.

[0074] In some example embodiments, a dynamically adjusted intensity distribution may be pre-calculated and programmed for an entire rotation of the gantry (including multiple scan sequences of the x-ray source). Such pre-calculation may be based, for example, on the location of the ROI in the target object, and the rotation speed of the gantry. Such pre-calculation may be converted to a program for driving the gantry. Figure 1 7 to sequentially activate the x-ray sources in the x-ray source array 304.

[0075] Dynamic intensity distribution adjustment / programming is performed in the projection plane parallel to the rotation axis as described above, and by Figure 3 The combination of the butterfly filter 320 in FIG. 7 (if included) with additional intensity distribution adjustments within each fan beam in the direction along the axis of rotation advantageously provides ROI control in all three spatial dimensions in the target object.

[0076] In other inverse geometry tetrahedral beam embodiments where the detector array extends in the plane of rotation and the x-ray source array extends along the axis of rotation, the intensity of the beam can be similarly controlled in a dynamic manner. However, this intensity distribution control will be along the axis of rotation. When coupled with a similar but fixed distribution bow-tie filter to generate the intensity distribution of each beam, only off-axis cylindrical regions with higher intensity can be achieved. Therefore, Figure 3 The geometry to that in FIG. 7 provides a more selective off-axis ROI in the target object.

[0077] and Figure 8 Compared with the image in the left panel where the X-ray energy density distribution is kept uniform, Figure 8 The right panel shows the Figure 3 The simulated results of the image reconstructed by the dynamically modulated energy density are shown in Figure 7 for the ROI position generated by the inverse geometry tetrahedron implementation. Due to the concentrated x-ray energy density, the image area such as Figure 8 The ROI indicated by the arrow in the figure is used Figure 3 The case of the geometry of Figure 7 has better visibility than the case using uniform x-ray energy density.

[0078] Fig. 9 Another inverse geometry tetrahedral beam CT system 900 is shown. Figure 3 Compared to the embodiment in FIG. 7 , the system 900 includes multiple (e.g., two) x-ray source arrays 304 and 904. Accordingly, the system 900 also includes, for example, two butterfly filters 320 and 920, and two tilted multi-slot collimators 310 and 910. Therefore, the two x-ray source arrays generate two sets of x-ray emissions, which are filtered by the butterfly filters 320 and 920 and then collimated by the multi-slot collimators 310 and 910 to generate a sequence of two x-ray fan beams 305 and 905. The two linear source arrays help increase the imaging field of view in the axial direction, and can additionally or alternatively provide a stereoscopic view of the anatomical structure at the center of the target object.

[0079] Fig.10 Further shown is another inverse geometry tetrahedral beam CT system 1000, which follows Figure 3 7, but the linear array x-ray source 1004 and the linear array detector 1002 are in offset positions relative to the rotation axis 1008. The offset of the source and detector positions allows a larger field of view to be reconstructed using a source array of similar size. A larger reconstructed field of view can be achieved by offsetting only the source array, only the detector array, or both.

[0080] In any of the above embodiments, Figure 1 To Figure 7 and Fig. 9 and Fig.10 The linear x-ray source arrays 104, 304, 904, and 1004 in FIG. 1 may also be curved, for example, a partial arc centered at the detector location. The detector arrays 102, 302, and 1002 may also be curved, for example, a partial arc centered at the source array location.

[0081] The linear array detector 104 may be implemented as a multi-row x-ray detector array. In some example embodiments, the detector pixel size may be very small, such as 0.1 millimeter (mm) to 1 mm, but the x-ray fan beam cannot be so thin. A multi-row detector that is not too wide may be used to detect the fan beam. For example, the detector 104 may be a 6 mm wide, 15 centimeters (cm) long detector containing 60×1500 detector pixels.

[0082] An anti-scatter grid may be used to further suppress scattered x-ray photons. The anti-scatter grid may be one-dimensional (1D) or 2D and is positioned in front of the detector 104 to suppress scattered photons from the object 150.

[0083] above Figure 1 To Figure 7 and Fig. 9 and Fig.10 The linear x-ray source arrays 102, 304, 904, and 1004 in FIG. 1 may be implemented in various ways to facilitate dynamic control of the emission intensity of each individual x-ray source in the array on a sufficiently fast time scale during gantry rotation, as well as rapid control of the on / off of x-ray emission to sequentially activate and scan the sources as described above. For example, Fig.11 As shown, such an x-ray source array can be implemented as a multi-pixel thermionic emission x-ray (MPTEX) source including multiple thermal electron (thermionicelectron) sources. For example, such an MPTEX can include 20 to 100 (e.g., 50) thermal electron sources 1110. The x-ray flux generation from each thermal electron source 1110 can be controlled by changing the heating power of the filament 1124 of the thermal electron source 1110 and changing the bias voltage 1170 between the electron source 1110 and the gate 1140. The x-ray emission can turn on and off the current in the filament. The emission flux or intensity can be controlled by changing the heating / driving current or power 1130 of the heating filament and / or by pulse width modulation of the driving current of the electron source (by changing the duty cycle). When one source is controlled to emit x-rays, the switch 1150 controls the closing of other sources in the array.

[0084] For further details, Fig.11 An example MPTEX vacuum tube (1104) and a control unit (dashed box 1102) are shown. The MPTEX vacuum tube 1104 may include, for example, 50 cathodes 1110 ( Fig.11Only three of them are shown as representatives in the figure, and for experimental purposes, the 50 cathodes correspond to 50 focal electron points on an elongated fixed anode 1120 for generating 50 x-ray point sources. The anode voltage 1122 is provided, for example, by a commercial 6 kilowatt (kW), 120 kilovolt (kV) high voltage power supply (e.g., Model STR120 from Spellman High Voltage Electronics). Each heating filament 1124 acts as a cathode and is powered by an isolated and therefore individually controllable direct current (DC) power supply 1130. Using the ground grid 1140 in the MPTEX tube 1104, the beam can be controlled to be turned on and off by switching in or out of the negative bias voltage between the cathode heating filament 1124 and the ground grid. For example, to turn on electron emission, the switch 1150 is controlled using a control signal 1160 to connect the negative bias voltage 1170 from the line to pass the bias voltage 1170 to the heating filament. When a negative bias is applied (source is on), the electron flux is controlled by a DC voltage from power supply 1130. To shut off the current in the filament, switch 1150 can be gated by control signal 1160 to disconnect the negative bias voltage 1170 from the heating filament. In this way, MPTEX can achieve at least two different controls on the emission of x-rays. For example, the on / off of electron emission can be controlled by controlling the bias voltage via switch 1150, and the electron emission flux can be controlled by the drive voltage from power supply 1130 when the bias is applied.

[0085] Specifically, in Fig.11 In the example of , the power to each cathode can be provided by a variable power supply. The output parameters of the variable power supply can be controlled by a microcontroller unit (MCU). By programming the MCU, the heating power or current of each channel can be dynamically adjusted when the channel (cathode) is biased to open during inverse geometry CT scanning.

[0086] Such as Fig.11 Burning out of the 1124 filament cathode in the MPTEX source can be a possible failure mode of the MPTEX source. Therefore, it is important to minimize the operating temperature of the cathode during a CT scan. The heating power can be controlled by an MCU, which communicates with the controller of the variable power supplies. The voltage of each variable power supply can be adjusted in a few milliseconds, enough for dynamic intensity control during gantry rotation. On the other hand, the bias control for switching the cathode current on / off can be as short as a few microseconds, thus fast enough to scan from cathode to cathode. This can even be fast enough to implement pulse width modulation, thereby achieving additional or alternative flux / intensity control by adjusting the pulse width duty cycle of a specific source in the array during a time slot.

[0087] Regarding dynamic intensity control by adjusting the drive power to the wire, Fig.12 An example measured relationship between the emission current and the wire voltage of a typical wire is shown. With the bias voltage between the wire and the ground grid fixed at -200 volts (V), the emission current begins to rise at a wire voltage of 9V, with an emission current of 1.05 milliamperes (mA). The corresponding wire current (not shown) is 2.11 amperes (A), and the wire power is about 18 watts (W). As the wire voltage further increases, the emission current increases rapidly, gradually reaching 144mA at 14V. During the inverse geometry CT scan, the MPTEX source operates between 5mA and 30mA. Therefore, during the inverse geometry CT scan, the wire voltage varies between 9V and 11V as programmed by the MCU.

[0088] In the above inverse geometry tetrahedral beam CT embodiments, the rotation of the gantry can be from a few seconds per rotation to tens of seconds per rotation. The source scan of each source in the source array can be on a time scale of microseconds to milliseconds. There can be tens to hundreds of sources in the array, so it takes tens of microseconds to hundreds of milliseconds to complete a sequence. Therefore, there can be many source scans or sequences during one gantry rotation. For example, there can be between tens to thousands of scans or sequences during one rotation.

[0089] Finally, the above inverse geometry tetrahedral beam CT implementations (especially Figure 3 To Figure 7 and Fig. 9 and Fig.10 Advantages of the inverse geometry tetrahedral beam CT embodiment shown in ) include, for example, a significant reduction in radiation dose to peripheral tissues and organs outside the region of interest due to dynamic intensity distribution control of each individual source. The above embodiment allows off-axis ROI selection, which is not possible using conventional butterfly filters. The intensity of the beam can also be adjusted based on the thickness of the target object along the slice associated with a particular beam at a particular time. The above embodiment achieves a more efficient utilization of the x-range usage.

[0090] It will be understood that the various embodiments above are not limited in their application to the details of construction and arrangement of the components set forth above or in the drawings. The present disclosure is intended to encompass other embodiments that may be practiced or performed in various ways following the basic principles disclosed herein.

[0091] It should also be noted that multiple hardware- and software-based devices and multiple different structural components can be used to implement various embodiments of the present disclosure. In addition, it should be understood that the various embodiments of the present disclosure may include hardware, software, and electronic components or modules, and for the purpose of discussion, these hardware, software, and electronic components or modules can be shown and described as if most components are implemented only in hardware. However, those of ordinary skill in the art will recognize that, based on reading the present disclosure, in at least one embodiment, the electronic-based aspects of the present invention can be implemented with software that can be executed by one or more processors (e.g., stored on a non-transient computer-readable medium). Therefore, it should be noted that multiple hardware- and software-based devices and multiple different structural components can be used to implement the present invention. In addition, as described in subsequent paragraphs, the specific mechanical configurations shown in the accompanying drawings are intended to illustrate embodiments of the present invention, and other alternative mechanical configurations are also possible. For example, the "controller" described in the specification may include standard processing components, such as one or more processors, one or more computer-readable medium modules, one or more input / output interfaces, and various connections (e.g., system buses) connecting various components. These controllers can be implemented as dedicated processing circuits or general-purpose processors, as well as as a combination of various software and / or firmware, and as a combination of other wired or wireless communication interfaces.

Claims

1. A computer tomography x-ray imaging system for imaging a target object, include: a frame configured to rotate about the target object about a rotation axis; an x-ray source array, the x-ray source array being disposed on the gantry, the x-ray source array comprising a plurality of x-ray sources, the plurality of x-ray sources being aligned in a direction perpendicular to the rotation axis; an elongated linear detector array disposed on the gantry opposite the x-ray source array relative to the rotation axis, the elongated linear detector array comprising a plurality of x-ray detectors extending linearly along the rotation axis; a multi-slot collimator, the multi-slot collimator being disposed on the frame and between the x-ray source array and the target object; as well as circuitry configured to control activation of the plurality of x-ray sources to produce an x-ray emission sequence, the x-ray emission sequence being further collimated by the multi-slot collimator into a fan-beam sequence, the fan-beam sequence being projected through the target object into the elongated linear detector array for measurement, and the fan-beam sequence intersecting the target object to form a tetrahedral imaging volume.

2. The computer tomography x-ray imaging system according to claim 1, in, The circuit is also configured to dynamically adjust the intensity of the x-ray emission sequence individually.

3. The computer tomography x-ray imaging system according to claim 2, in, The intensity of the x-ray emission sequence is dynamically adjusted to cumulatively facilitate the delivery of x-rays through a region of interest in the target object.

4. The computer tomography x-ray imaging system according to claim 3, in, A control signal for adjusting the intensity of the x-ray emission sequence is based on a pre-calculation performed according to the region of interest in the target object.

5. The computer tomography x-ray imaging system according to claim 2, in, The intensity of the x-ray emission sequence is dynamically adjusted based on attenuation of the fan beam sequence by the target object.

6. The computer tomography x-ray imaging system according to claim 2, further comprising: include: An elongated butterfly filter covers the plurality of x-ray sources to generate a predefined intensity distribution along the rotation axis in each fan beam in the sequence of fan beams.

7. The computer tomography x-ray imaging system according to claim 1, further comprising: include: An elongated butterfly filter covers the plurality of x-ray sources to generate a predefined intensity distribution along the rotation axis in each fan beam in the sequence of fan beams.

8. The computer tomography x-ray imaging system according to claim 1, in: The gantry, together with the x-ray source array, the elongated linear detector array, and the multi-slot collimator, is configured to rotate about the rotation axis to detect projections of a plurality of fan-beam sequences through the target object; and The circuit is also configured to reconstruct a computed tomography x-ray image of the target object based on the detected projections.

9. The computer tomography x-ray imaging system according to claim 1, in, The plurality of x-ray sources are arranged to form a curve in a plane perpendicular to the rotation axis, the center of the curve being located at the elongated linear detector array.

10. The computer tomography x-ray imaging system according to claim 1, in, The plurality of x-ray sources comprises a linear array of x-ray sources.

11. The computer tomography x-ray imaging system according to claim 1, in, The multi-slot collimator includes a plurality of slot openings, each slot opening being associated with one of the plurality of x-ray sources for generating one fan beam in the fan beam sequence.

12. The computer tomography x-ray imaging system according to claim 1, in, Activation of the plurality of x-ray sources is repeated at a repetition rate that matches a frame rate of the elongated linear detector array.

13. A method for generating a computed tomography x-ray image of a target object, the method include: sequentially controlling activation of a plurality of x-ray sources to generate an x-ray emission sequence while rotating a gantry about the target object about a rotation axis, the plurality of x-ray sources being disposed on the gantry and aligned in a direction perpendicular to the rotation axis; collimating the x-ray emission sequence into a fan beam sequence; projecting the fan beam sequence through the target object into an elongated linear detector array disposed on the gantry, opposite the plurality of x-ray sources relative to the rotation axis, and comprising a plurality of x-ray detectors extending linearly along the rotation axis, and the fan beam sequence intersects the target object to form a tetrahedral imaging volume; as well as While the gantry is rotated, quantities of a plurality of fan beam sequences are measured to generate a computed tomography x-ray image of the target object.

14. The method according to claim 13, further comprising: include: The intensity of the x-ray emission sequence is individually and dynamically adjusted.

15. The method according to claim 14, in, The intensity of the x-ray emission sequence is dynamically adjusted to cumulatively facilitate the delivery of x-rays through a region of interest in the target object.

16. The method according to claim 15, in, A control signal for adjusting the intensity of the x-ray emission sequence is based on a pre-calculation performed according to the region of interest in the target object.

17. The method according to claim 14, further comprising: include: A predefined intensity distribution along the rotation axis is generated in each fan beam in the sequence of fan beams using an elongated butterfly filter arranged to cover the plurality of x-ray sources.

18. The method according to claim 13, further comprising: include: A predefined intensity distribution along the rotation axis is generated in each fan beam in the sequence of fan beams using an elongated butterfly filter arranged to cover the plurality of x-ray sources.

19. The method according to claim 13, in, The plurality of x-ray sources are arranged to form a curve in a plane perpendicular to the rotation axis, the center of the curve being located at the elongated linear detector array.

20. The method according to claim 13, in, Activation of the plurality of x-ray sources is repeated at a repetition rate that matches a frame rate of the elongated linear detector array.

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