Patent Description:
The x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam from a focal point. X-ray detectors typically include an anti-scatter grid or collimator for rejecting scattered x-rays at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom. The x-ray source is supplied power through a power system. Optionally, a portion of the generator rotates with the x-ray source and the detector array about the object.

CT systems may be configured to operate in different scanning modes. In a multi-energy acquisition mode, for example, the x-ray source is supplied with different operating voltages (or energy levels). Various CT system configurations use a variable operating voltage of the x-ray source including: (<NUM>) acquisition of low-energy and high-energy projection data from two sequential scans of the object using different operating voltages of the x-ray tube, (<NUM>) acquisition of projection data utilizing rapid switching of the operating voltage of the x-ray tube to acquire low-energy and high-energy information for an alternating subset of projection views, or (<NUM>) concurrent acquisition of energy-sensitive information using multiple imaging systems with different operating voltages of the x-ray tube.

Although such multi-energy acquisition modes can provide images that enable material density differentiation, other acquisition modes with one more improved characteristics (e.g., image quality, resolution, or sampling) are generally desired.

<CIT> describes a CT system including a rotatable gantry having an opening for receiving an object to be scanned, at least one x-ray source coupled to the gantry and configured to project x-rays toward the object, a detector coupled to the gantry and having a scintillator therein and configured to receive x-rays that pass through the object, and a generator configured to energize the at least one x-ray source. The system includes a controller configured to energize the generator to project a first beam of x-rays toward the object from a first focal spot position of an anode, the first beam of x-rays having a ray traversing a path through the object, acquire imaging data from the first beam of x-rays, position the at least one x-ray source such that a second beam of x-rays projected from a second focal spot position of the anode has a ray directed to traverse the path through the object, the second anode focal spot position different than the first anode focal spot position, energize the generator to project the second beam of x-rays toward the object, and acquire imaging data from the second beam of x-rays.

<CIT> describes anode targets for an x-ray tube and methods for controlling x-ray tubes for x-ray systems are provided. One x-ray system includes a field-generator configured to generate a field, an electron beam generator configured to generate an electron beam directed towards a target and a voltage controller configured to control the electron beam generator to produce an electron beam at a first energy level and an electron beam at a second energy level. The x-ray system also includes a field-generator controller configured to control a field to deflect at least one of the electron beams, wherein the electron beam, at the first energy level, impinges on the target at a first contact position and the electron beam, at the second energy level, impinges on the target at a second contact position.

In accordance with embodiments herein, a computed tomography (CT) imaging system is provided. The system comprises an x-ray source that is configured to be powered by a power system at different operating voltages. The x-ray source is operable to emit a beam of x-rays from a focal spot toward an object. The x-ray source is operable to move a spot position of the focal spot. A detector is configured to detect the x-rays attenuated by the object. At least one processing unit is configured to execute programmed instructions stored in memory. While executing the programmed instructions, the at least one processing unit is configured to direct the x-ray source to emit different beams of the x-rays at different energy levels and to receive data from the detector that are representative of detection of the x-rays emitted at the different energy levels. The at least one processing unit is also configured to direct the x-ray source to move the focal spot between different spot positions such that the focal spot is at different spot positions while the beams are emitted at the different energy levels. The x-ray source, at each of a first spot position and a second spot position, is configured to emit at least a first beam at a first energy level and a second beam at a second energy level.

The at least one processing unit may be configured to direct the x-ray source to, repeatedly, emit a first beam at a higher-energy level from a first spot position, move the focal spot toward a second spot position after emitting the first beam from the first spot position, emit a second beam at a lower-energy level from the second spot position, and move the focal spot toward the first spot position after emitting the second beam from the second spot position. The beams may be emitted along an XY plane that may be perpendicular to a Z axis. The x-ray source may move the focal spot relative to the Z axis and relative to the XY plane. The x-ray source may include electrodes that may be spaced apart and positioned such that the beams of the x-rays may pass between the electrodes. The electrodes may be operable to adjust a strength of the electric field to move the spot position of the focal spot.

Optionally, the electrodes may be configured to move the spot position between first and second spot positions. The electric field may be operable to deflect the different beams by differing amounts. The x-ray source may include an electromagnet configured to generate a magnetic field. The electromagnet may be operable to adjust a strength of the magnetic field to move the spot position of the focal spot.

In some aspects, the at least one processing unit may be configured to receive higher-energy data from the detector while the focal spot is in a first position and may be configured to receive lower-energy data while the focal spot is in a second position. The at least one processing unit may be configured to interpolate the higher-energy data at the second position and the lower-energy data at the first position.

Optionally, the at least one processing unit is configured to generate material density projections for two different materials for the first position of the focal spot using (a) a material decomposition process and (b) the lower-energy data for the first position of the focal spot and the higher-energy data for the first position of the focal spot. The at least one processing unit may be configured to generate material density projections for the two different materials for the second position of the focal spot using (a) the material decomposition process and (b) the lower-energy data for the second position and the higher-energy data for the second position. After generating the material density projections for the two different materials from the first and second positions, the at least one processing unit may be configured to reconstruct high-resolution material-density images using the material density projections for the two different materials from the first and second positions.

Optionally, the at least one processing unit may be configured to generate higher-energy high-resolution images using the higher-energy data for the first focal position and the higher-energy data for the second focal position. The at least one processing unit may be configured to generate lower-energy high-resolution images using the lower-energy data for the first focal position and the lower-energy data for the second focal position. The at least one processing unit may be configured to then reconstruct high-resolution material-density images using the higher-energy and lower-energy high-resolution images.

In accordance with embodiments herein, a method is provided. The method directs an x-ray source to emit different beams of x-rays at different energy levels and directs the x-ray source to move a focal spot of the x-ray source between different spot positions such that the focal spot is at different spot positions while the beams are emitted at the different energy levels. The x-ray source, at each of a first spot position and a second spot position, is configured to emit at least a first beam at a first energy level and a second beam at a second energy level. The method receives data that is representative of detection of the x-rays emitted at the different energy levels.

Optionally, the method may direct the x-ray source to emit the different beams and to move the focal spot includes directing the x-ray source to repeatedly emit a first beam at a first energy level while the focal spot is in the first spot position, move the focal spot toward a different second spot position, emit a second beam having a different second energy level while the focal spot is in the second spot position and move the focal spot toward the first spot position. The beams may be emitted along an XY plane that may be perpendicular to a Z axis. The x-ray source may move the focal spot relative to the Z axis and relative to the XY plane while moving the focal spot between the different spot positions.

Optionally, the x-ray source may include electrodes that may be spaced apart and positioned such that the beams of the x-rays pass between the electrodes. Moving the focal spot may include adjusting a strength of an electric field between the electrodes. Adjusting the strength of the electric field may cause the different beams to be deflected by differing amounts. The x-ray source may include an electromagnet that may be configured to generate a magnetic field. Moving the focal spot may include adjusting a strength of a magnetic field of the electromagnet. Detecting the x-rays may include detecting higher-energy data and detecting lower-energy data. The method may further comprise interpolating the higher-energy data and interpolating the lower-energy data.

In accordance with embodiments herein, a computed tomography (CT) imaging system is provided. An x-ray source is configured to be powered by a power system at different operating voltages. The x-ray source is operable to emit a beam of x-rays from a focal spot toward an object. The x-ray source is operable to move a spot position of the focal spot. A detector is configured to detect the x-rays attenuated by the object. At least one processing unit is configured to execute programmed instructions stored in memory. The at least one processing unit, while executing the programmed instructions, is configured to direct the x-ray source to, repeatedly emit a first beam at a higher-energy level from a first spot position, move the focal spot toward a second spot position after emitting the first beam from the first spot position, emit a second beam at a lower-energy level from the second spot position and move the focal spot toward the first spot position after emitting the second beam from the second spot position.

Optionally, the beams may be emitted along an XY plane that may be perpendicular to a Z axis. The x-ray source may move the focal spot relative to the Z axis and relative to the XY plane. The x-ray source may include electrodes that may be spaced apart and may be positioned such that the beams of the x-rays pass between the electrodes. The electrodes may be operable to adjust a strength of the electric field to move the spot position of the focal spot.

The detector may include a plurality of detector pixel elements in which each detector pixel element of said plurality may detect the x-rays emitted at higher energy levels and the x-rays emitted at lower energy levels.

The inventive subject matter described herein will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:.

Embodiments set forth herein may increase spatial sampling in a CT imaging system by dynamically adjusting a position of a focal spot of the imaging system with respect to a detector assembly of the imaging system. Image data acquired from different locations of the focal spot may be interlaced together to form higher sampling data (relative to the image data acquired with a single focal spot position) before going through an image reconstruction process. As described herein, the CT system also can acquire image data at different energy levels. For example, the CT system may use fast kV switching in which a generator of the imaging system oscillates an energy level supplied to an x-ray source. This allows for both spectral information and high-resolution sampling to be achieved concurrently as the x-ray source and the detector assembly are moved relative to a body being imaged by the imaging system.

As used herein, the terms "high energy" and "low energy" do not require specific values or ranges. Instead, the terms "high" and "low" are labels that identify an energy level relative to another energy level. For example, a high-energy level has an energy that is greater than a low-energy level, and the low-energy level has an energy that is less than the high-energy level. The high-energy and low-energy levels may be, for example, <NUM> kV and <NUM> kV, respectively. Optionally, high-energy levels can be energy levels above or in excess of 80kV, while low-energy levels may be energy levels that are no greater than 80kV.

Embodiments set forth herein are described with respect to a multislice CT system capable of spectral imaging in which the CT system acquires data sets at different energy levels. For example, the CT system may be configured to cycle or switch energy (kV) from high to low at a switching rate (e.g., up to <NUM>) and utilize the detector assembly to capture two data sets that are temporally registered. In some embodiments, the beam energy is non-static such that the beam energy cycles in a sinusoidal manner during image acquisition. As such, energy levels may be characterized as a mean-high energy level and a mean-low energy level. The mean-high energy level may have, for example, a maximum of about <NUM> kV, and the mean-low energy level may have a minimum of about <NUM> kV.

CT systems set forth herein may also be configured to dynamically control a position of a focal spot of the x-ray beam during data acquisition. For example, the focal spot may move between a first position and a second position as the x-ray source and the detector move relative to the person (e.g., helically or axially). A sample is acquired while the focal spot is at the first focal position, and another sample is acquired while the focal spot is at the second focal position. The different focal positions effectively provide different view angles or beam orientations with respect to the detector assembly. The position of the focal spot may be dynamically controlled through electrostatic deflection of the beam and/or magnetic deflection of the beam.

In some embodiments, an x-ray source may emit a first beam at a first energy level while the focal spot is in the first spot position and emit a second beam having a different second energy level while the focal spot is in the second spot position. It should be understood that the phrase "while the focal spot is in [a designated] spot position" does not require that the focal spot be completely stationary as the beam is emitted or that the energy level be uniform throughout emission. The focal spot may be constantly moving and the energy level may be constantly changing. However, the amount of movement and/or the amount of change in energy during emission may be relatively small or may offset one another such that useful data may be acquired for generating image data at different energy levels and/or from different focal spots. For example, the average spot position during emission of the first beam and the average spot position during emission of the second beam may be sufficiently spaced apart such that useful data (e.g., data representing samples from different spot positions) may be obtained. Likewise, the average energy level during emission of the first beam and the average energy level during emission of the second beam may be sufficiently different such that useful data (e.g., data representing samples from different energy levels) may be obtained.

The CT system may be configured for axial scanning, helical scanning, and cine scanning. Embodiments can also be used to detect, measure, and characterize materials that may be injected into the subject such as contrast agents and other specialized materials using energy weighting to boost the contrast of iodine and calcium (and other high atomic or materials). Contrast agents can, for example, include iodine that is injected into the blood stream for better visualization. For baggage scanning, the effective atomic number generated from energy sensitive CT principles allows reduction in image artifacts, such as beam hardening, as well as provides addition discriminatory information for false alarm reduction.

In some embodiments, at least one technical effect of the subject matter described herein includes the ability to generate spectral image data that has a higher spatial resolution with fewer aliasing artifacts compared to spectral image data generated by some known systems. In some embodiments, at least one technical effect of the subject matter described herein includes the ability to generate high-resolution image data having an improved overall image quality compared to high-resolution image data generated by known systems. In some embodiments, at least one technical effect of the subject matter described herein includes enabling a spectral imaging mode for clinical applications that have heretofore not used spectral imaging (e.g., due to a lack of spatial resolution).

<FIG> illustrates a computed tomography (CT) imaging system <NUM> (referred to herein as a CT system), and <FIG> illustrates a schematic diagram of the CT system <NUM>. As shown, the CT system <NUM> includes a gantry <NUM> having an x-ray source <NUM> (e.g., x-ray tube) that projects a beam of x-rays toward an opposing detector assembly <NUM> of the gantry <NUM>. Optionally, the gantry <NUM> and the components mounted thereon may rotate about a center of rotation <NUM> during a scan. In some embodiments, the detector assembly <NUM> may include a layer for conversion of x-ray to light (e.g., scintillator layer), a layer for converting light to current (e.g., photodiode layer), and a substrate layer to support electronics for communicating data. The detector assembly <NUM> includes a plurality of detector cells or modules <NUM> and a data acquisition system (DAS) <NUM>. Each detector cell <NUM> may include a group or array of pixel elements in which each pixel element is configured to sense x-rays. The plurality of detector cells <NUM> sense the projected x-rays <NUM>, including those that pass through and are attenuated by an object or body <NUM>. The detector cells <NUM> may communicate data that is representative of the detection of the x-rays by the detector cells <NUM> or, more specifically, the pixel elements of the respective detector cells <NUM>. The object <NUM> is hereinafter referred to as a person, but it should be understood that the object may be, for example, luggage or another inanimate object.

<FIG> and <FIG> illustrate a coordinate system relative to rotatable components of the gantry <NUM>, such as the detector assembly <NUM> and the x-ray source <NUM>. The x-ray source <NUM> is supplied power through a generator <NUM>. In some embodiments, at least a portion of the generator <NUM> (e.g., second stage) rotates with the x-ray source <NUM>. The coordinate system includes mutually perpendicular X, Y, and Z-axes. The Z-axis extends generally along an axial length of the person <NUM> and extends parallel to the axis of rotation <NUM>. The Z-axis defines a slice direction of the CT system <NUM>. The X- and Y-axes define a plane that is perpendicular to the Z-axis. The x-ray source <NUM> and the detector assembly <NUM> coincide with and face in a direction along the XY plane. The direction may be a vector that, depending upon the rotational orientation of the x-ray source <NUM> and the detector assembly <NUM>, has an X component and a Y component. The generator <NUM>, the x-ray source <NUM>, and the detector assembly <NUM> may rotate circumferentially about the axis of rotation <NUM> (<FIG>) as a group.

The generator <NUM> supplies the power and, optionally, timing signals to the x-ray source <NUM>. The generator <NUM> may output a first voltage and output a second voltage to the x-ray source <NUM>. In some embodiments, the first and second voltages may be outputted in a fast-switching pattern such that the voltage increases and decreases in a sinusoidal manner between a maximum first voltage and a minimum second voltage (e.g., <NUM> kVp and <NUM> kVp). Optionally, the generator <NUM> may cause the first voltage and the second voltage to be effectively switched at a frequency of up to <NUM> or more. In other embodiments, the generator <NUM> causes the first voltage and the second voltage to be switched at frequencies of <NUM> or more. By rapidly switching the voltage supplied to the x-ray source <NUM>, samples may be obtained at low energy levels (<NUM> kVp) and high energy levels (<NUM> kVp).

Operation of the x-ray source <NUM> may be controlled, in part, by a deflection-control module <NUM>. The deflection-control module <NUM> is configured to control an electrical and/or magnetic field that deflects electrons from the x-ray source <NUM> prior to the electrons reaching a focal spot from which the beam <NUM> projects. As described herein, the deflection-control module <NUM> may control an electrical field formed by electrodes or may control a magnetic field formed by an electromagnet (e.g., solenoid). More specifically, the deflection-control module <NUM> may increase or decrease a strength of the respective field, thereby increasing or decreasing an amount of deflection. Optionally, the deflection-control module <NUM> is operably coupled to the generator <NUM> such that a change in power level causes a change in a strength of the respective field.

The deflection-control module <NUM> may form part of the at least one processing unit that controls operation of the CT system. For example, the deflection-control module <NUM> may form part of the computing system <NUM> and/or part of the x-ray controller. Alternatively, at least a portion of the deflection-control module may be separate circuitry (e.g., hardwired electronics) that directly connects the voltage source and the x-ray source.

In certain embodiments, the CT system <NUM> is configured to traverse different angular positions around the person <NUM> for acquiring desired projection data. Accordingly, the gantry <NUM> and the components mounted thereon may be configured to rotate about a center of rotation <NUM> for acquiring the projection data. The table <NUM> may be moved along the axis of rotation <NUM> as the gantry <NUM> is rotated or, alternatively, as the gantry <NUM> remains in a fixed position.

The detector cells <NUM> may communicate data that is representative of the detection of the x-rays by the pixel elements. For example, each detector cell <NUM> may communicate an analog electrical signal that represents the intensity of impinging x-rays attenuated by the person <NUM>. The detector cells <NUM> provide the analog electrical signals (or data) to the DAS <NUM>. The DAS <NUM> samples the analog data received from the detector cells <NUM> and converts the analog data to digital signals (or digital data) for subsequent processing. The DAS <NUM> may communicate the data that is representative of the detection of the x-rays to a computing system <NUM>.

The computing system <NUM> may include or be represented by at least one processing unit. For example, the computing system <NUM> may include multiple processing units (e.g., a combination of processors, hardwired circuitry, or other logic-based devices) distributed throughout the CT system <NUM>. The at least one processing unit, which may be referred to generally as <NUM>, is configured to execute programmed instructions stored in memory <NUM>. While executing the programmed instructions, the at least one processing unit is configured to control operation of the x-ray source <NUM> and the generator <NUM>, among other things.

In one example, the computing system <NUM> stores the data in a memory <NUM>, which is labeled as a "storage device" in <FIG>. The memory <NUM>, for example, may include a hard disk drive, a floppy disk drive, a compact disk-read/write (CD-R/W) drive, a Digital Versatile Disc (DVD) drive, a flash drive, and/or a solid-state storage device. The computing system <NUM> may also process the data to generate images.

Additionally, the computing system <NUM> provides commands and parameters to one or more of the DAS <NUM>, the x-ray controller <NUM>, and the gantry-motor controller <NUM> for controlling system operations. In certain embodiments, the computing system <NUM> controls system operations based on operator input. Although <FIG> illustrates only one operator console <NUM>, more than one operator console may be coupled to the CT system <NUM>, for example, for inputting or outputting system parameters, requesting examinations, and/or viewing images. Further, in certain embodiments, the CT system may be coupled to multiple displays, printers, workstations, and/or similar devices located either locally or remotely, for example, within an institution or hospital, or in an entirely different location via one or more configurable wired and/or wireless networks such as the Internet and/or virtual private networks.

In one embodiment, for example, the CT system <NUM> either includes, or is coupled to, a picture archiving and communications system (PACS) <NUM>. In one example implementation, the PACS <NUM> is further coupled to a remote system, such as a radiology department information system, hospital information system, or an internal or external network (e.g., cloud-computing network). The remote system allows operators at different locations to supply commands and parameters and/or gain access to the image data. In particular embodiments, the remote system enables users to retrieve, update, and store designated protocols.

The computing system <NUM> uses the operator-supplied and/or system-defined commands and parameters to operate a table motor controller <NUM>, which in turn, may control a motorized table <NUM>. Particularly, the table motor controller <NUM> moves the table <NUM> to appropriately position the person <NUM> in the gantry <NUM> for acquiring projection data corresponding to the target volume of the person <NUM>.

As described above, the DAS <NUM> samples and digitizes the projection data acquired by the detector cells <NUM>. Subsequently, an image reconstructor <NUM> uses the sampled and digitized x-ray data to perform high-speed reconstruction. Although <FIG> illustrates the image reconstructor <NUM> as a separate entity, in certain embodiments, the image reconstructor <NUM> may form part of the computing system <NUM>. Alternatively, the image reconstructor <NUM> may be located locally or remotely, and may be operatively connected to the CT system <NUM> using a wired or wireless network. Particularly, one exemplary embodiment may use computing resources in a cloud-computing network for the image reconstructor <NUM>.

In one embodiment, the image reconstructor <NUM> reconstructs the images stored in the storage device <NUM>. Alternatively, the image reconstructor <NUM> transmits the reconstructed images to the computing system <NUM> for generating useful person information for diagnosis and evaluation. In certain embodiments, the computing system <NUM> transmits the reconstructed images and/or the person information to the display <NUM> communicatively coupled to the computing system <NUM> and/or the image reconstructor <NUM>.

The various methods and processes described further herein may be stored as executable instructions in non-transitory memory in the CT system <NUM>. For example, the computing system <NUM>, the x-ray controller <NUM>, the detector assembly <NUM>, the table-motor controller <NUM>, and the gantry-motor controller <NUM> may include instructions in non-transitory memory, and may apply the methods described herein to scan the person <NUM>.

As used herein, the phrase "at least one processing unit" or the phrase "the computing system" includes the possibility of multiple processing units (e.g., processors, hardwired circuitry, or other logic-based devices) distributed throughout the CT system <NUM>. For example, the phrase "at least one processing unit" may include a combination of one or more processing units of the computing system <NUM>, one or more processing units of the x-ray controller <NUM>, and one or more processing units of the gantry-motor controller <NUM>, one or more processing units of the table-motor controller <NUM>, and one or more processing units of the image reconstructor <NUM>. The at least one processing unit may executed programmed instructions stored in memory to direct components of the CT imaging system to operate as described herein. For example, the at least one processing unit may direct the x-ray source, the detector, or the generator to operate as set forth herein. The at least one processing unit may also process (e.g., reconstruct) the data acquired during the CT scan to generate image data.

The computing system <NUM> also receives commands and scanning parameters from an operator via console <NUM> that has an operator interface. The operator interface may include, for example, a keyboard, mouse, voice-activated controller, touch-sensitive screen or pad, or any other suitable input apparatus. An associated display <NUM> allows the operator to observe the reconstructed image and other data from computing system <NUM>. Optionally, the display <NUM> forms part of the operator interface and includes a touch-sensitive screen.

Optionally, a filter (not shown) may be positioned between the person <NUM> and the x-ray source <NUM>. For example, bowtie filters may be used to modulate the output of the radiation source. Bowtie filters can compensate for the difference in beam path length through the axial plane of the object such that a more uniform fluence can be delivered to the detector. Bowtie filters can also reduce scatter and radiation dosage at the periphery of the imaging field of view (FOV).

As described herein, embodiments of the subject matter are capable of acquiring data sets at different energy levels. For example, the CT system may be configured to cycle or switch energy (kV) from high to low and utilize the detector assembly to capture two data sets that are temporally registered. A previously proposed design for acquiring data sets having different energy levels included positioning a grating collimator between the person and the x-ray tube. If the bowtie filter was used, the grating collimator could be positioned on either side of a bowtie filter. The proposed grating collimator included alternating regions in which each region has the same material (e.g., air and tungsten), which differs from the material of the other region. The different materials have a different attenuation of the x-rays. In particular embodiments, the CT system is devoid of a grating collimator that includes alternating regions in which at least one of these regions attenuates the x-rays prior to reaching the person.

As part of the previously proposed design, an alternating pattern of x-rays would be incident upon the detector. X-rays for either energy level (high or low) would be incident upon the pixel elements of the detector in an alternating manner. The x-ray source and the detector are designed to achieve the alternating pattern. In particular embodiments, the CT system is not designed to achieve an alternating pattern of incident x-rays on the detector surface and the x-rays are not attenuated based on energy level.

<FIG> illustrates one embodiment of the detector assembly <NUM> in greater detail. It should be understood, however, that other embodiments may include detector assemblies with other designs and configurations. The detector assembly <NUM> includes rails <NUM> having collimating plates <NUM> placed therebetween. The collimating plates <NUM> are positioned to collimate x-rays <NUM> before the x-rays <NUM> impinge upon, for instance, the detector cells <NUM> (<FIG>) of the detector assembly <NUM>. Each of the detector cells <NUM> may include a number of detector pixel elements, which may be referred to as pixel elements, detector pixels, or detector elements. The detector pixel elements may be optically coupled to backlit diode array (not shown) that is, in turn, electrically coupled to the DAS <NUM> (<FIG>). In operation, x-rays <NUM> pass through and are attenuated by the person <NUM> and then impinge upon the detector pixel elements of each detector cell <NUM>, thereby generating an analog signal that is communicated to the DAS <NUM>. The DAS <NUM> converts the analog signal to a digital signal.

As an example of one or more embodiments, the detector assembly <NUM> may include an array of collimating plates <NUM> that are positioned for fifty-seven detector cells <NUM> in which each of the detector cells <NUM> has <NUM>×<NUM> detector pixel elements. As such, the detector assembly <NUM> of <FIG> may have sixty-four rows and nine hundred twelve columns (sixteen by fifty-seven detector cells), which enables sixty four simultaneous slices of data to be collected with each rotation of the gantry <NUM> (<FIG>).

During operation, multiple sets of measurements (or sets of attenuation data) may be acquired at different respective energy levels (e.g., mean energy levels) and at different focal spots. The measurements (IL and IH) at two different energy spectra SL(E) and SH(E) can be given by: <MAT> <MAT> where µ is the linear attenuation coefficient at energy E and location r.

Typically, the linear attenuation coefficient µ can be decomposed into two (or more) basis materials: <MAT> where a(r) and b(r) are the spatially varying coefficient, and A(E) and B(E) are the energy dependencies of the respective basis materials.

Similarly, the line integral of the linear attenuation coefficient can be decomposed as: <MAT> where pa and pb are the basis material line integrals.

The set of current measurements (IL and IH) may thus be re-written as: <MAT> <MAT> where the functions fL and fH can be determined empirically, based on calibration measurements of different material combinations with spectra SL and SH, after which pa and pb can be computed.

In some embodiments, the inverse functions ga and gb may be directly defined from calibration experiments, resulting in the following material decomposition (MD) step: <MAT> <MAT>.

A reconstruction algorithm may be used to reconstruct a(r) and b(r) based on sinograms pa and pb, respectively. The reconstruction algorithm can be a direct algorithm (such as filtered backprojection) or an iterative algorithm (such as penalized weighted least squares with ordered subsets or iterative coordinate descent). In such cases, the input to the reconstruction algorithm are sinograms pa and pb obtained. In other embodiments, an iterative reconstruction process may be performed with unknowns a(r) and b(r) and using the measurements IL and IH as inputs. Embodiments may start from a first reconstruction of the basis materials and improve the reconstructed images by incorporating knowledge of the noise in the measurements and prior knowledge on the images.

<FIG> is a schematic diagram of a power system <NUM> that is operable to supply power to an x-ray source <NUM>. The power system <NUM> includes a voltage source <NUM> (e.g., high frequency, high voltage power generator). Optionally, the power system <NUM> includes an interposer circuit <NUM>. The interposer circuit <NUM> is operable to rapidly switch or assist in switching between a first voltage level and a second voltage level. In some embodiments, the power system <NUM> is communicatively coupled to a deflection-control module <NUM>. As described above, a deflection-control module may form a part of the computing system <NUM> and/or a part of the x-ray controller <NUM>. In some embodiments, the deflection-control module <NUM> may be communicatively coupled to the interposer circuit <NUM> and/or communicatively coupled to the voltage source <NUM>. In some embodiments, the deflection-control module <NUM> may be integrated with interposer circuit <NUM>.

The interposer circuit <NUM> may include, for example, a voltage divider and a plurality of switching stages coupled in series. Each switching stage may have a pair of switches, a diode operable to block reverse current flow, and a capacitor. Under operation, the interposer circuit <NUM> may receive a voltage from a high-voltage generator, such as the voltage source <NUM>. The series of switching stages enables rapid switching of the input voltage between a pair of voltage levels at an output. The total number of switching stages depends upon the magnitude of voltage increase.

The power system <NUM> is configured to supply an x-ray source <NUM> with electrical power at an operating voltage for generating an x-ray beam at a designated energy level. In some embodiments, the voltage source <NUM> and the interposer circuit <NUM> may be configured as an active resonant module. In some embodiments, the voltage source <NUM> and the interposer circuit <NUM> may be configured as a passive resonant module. The interposer circuit <NUM> may include switching component(s) that facilitate switching of the voltage generated from the voltage source <NUM> and applied to an X-ray tube <NUM>. For example, in operation, the interposer circuit <NUM> provides switching between a high kV level (e.g., <NUM> kV) and a low kV level (e.g., <NUM> kV). However, it should be noted that other high and low voltage levels may be provided and the various embodiments are not limited to a particular voltage level. As another example, the high kV level can range from a few tens of kV (e.g., about <NUM> kV for mammography) to hundreds of kV (e.g., about <NUM> kV for industrial inspection applications). The energy may be reused and recirculated when switching between the voltage levels. In some embodiments, switching between the voltage levels can occur in about ten to one hundred microseconds or less.

In a resonant configuration of one or more embodiments, the electronics of the CT system can transmit power to the X-ray source <NUM> to charge or continue to provide power to the load (e.g., vacuum tube) at high voltage operation at different voltage levels. As shown, the interposer circuit <NUM> is secured to the x-ray source <NUM> and electrically coupled to the voltage source <NUM> through cabling <NUM>. The cabling <NUM> may be rated for high voltages (e.g., <NUM> kV or more). In particular embodiments, the interposer circuit <NUM> may be integrated with the voltage source <NUM> such that the interposer circuit <NUM> forms part of the voltage source. In such embodiments, the voltage source <NUM> and the interposer circuit can be communicatively coupled to the x-ray source <NUM> through the cabling <NUM>.

In particular embodiments, the voltage source <NUM> is a high voltage generator capable of generating voltages corresponding to low levels, for example, <NUM> kV, and the interposer circuit <NUM> is configured to provide additional energy/power to operate the load (e.g., vacuum chamber) at a high voltage level, for example, <NUM> kV. The interposer circuit <NUM> may operate to store energy when switching from a high voltage level to a low voltage level, and use the stored energy when transitioning to the next high voltage cycle. The interposer circuit <NUM> may store energy in, for example, one or more capacitors.

The deflection-control module <NUM> may be separate from or integrated with the interposer circuit <NUM>. As described herein, the deflection-control module <NUM> is configured to dynamically control a position of the focal spot. In some embodiments, the deflection-control module <NUM> controls the position of the focal spot in response to a change in the power supplied to the x-ray source <NUM>.

<FIG> is a schematic view of an x-ray source <NUM> illustrating one mechanism for dynamic focal spot control. The x-ray source <NUM> is configured to emit different beams at different energy levels. As shown, the x-ray source <NUM> includes a cathode <NUM> having a filament <NUM>. A beam <NUM> of electrons is emitted from filament <NUM>. The beam <NUM> may be directed to a focal spot <NUM> at a first focal position <NUM> on an anode <NUM>, and the beam <NUM> may be directed to the focal spot <NUM> at a second focal position <NUM> on the anode <NUM>. The anode <NUM> includes a beveled surface <NUM> positioned on a base <NUM> of the anode <NUM>.

The beam <NUM> is electrostatically deflected by an electrode assembly having electrodes <NUM>, <NUM> (e.g., electrode plates) as the electrons pass therethrough. Optionally, the x-ray source <NUM> may include additional electrodes to facilitate deflection, steering, or focusing the beam <NUM>. The electrodes may be configured to deflect, steer, or focus the beam <NUM> in either direction along the page (as shown in <FIG>) or in a perpendicular direction into and out of the page. The beam <NUM> of electrons may be directed along a path <NUM> to the focal spot <NUM> at the first focal position <NUM> or directed along a second path <NUM> to the focal spot <NUM> at the second focal position <NUM> by applying an electric field between the electrodes <NUM>, <NUM>. This electric field may change (in magnitude and/or direction) with respect to time. Accordingly, a beam of electrons emitted from a single filament <NUM> may be rapidly oscillated (or wobbled) between by varying the electrostatic field. A distance <NUM> exists between the first and second focal positions <NUM>, <NUM>.

In some embodiments, the beam <NUM> may oscillate the distance <NUM> along a path in the XY plane, wherein the path is generally transverse to the beam direction. In other embodiments, the beam <NUM> may oscillate the distance <NUM> along a path that extends along the Z-axis. The beam <NUM> may oscillate up to several kHz or more. For example, the beam may oscillate at approximately <NUM>. As such, x-rays can be caused to emit from the first and second focal positions <NUM>, <NUM> such that a beam <NUM> is projected toward the detector assembly <NUM> (<FIG>).

In addition to moving the focal spot <NUM> between the first and second positions <NUM>, <NUM>, the x-ray controller <NUM> (<FIG>) may cause the energy level to change. For example, the x-ray controller <NUM> may cause the energy level to change by fast kV switching.

Also shown, the x-ray source <NUM> may include or be controlled by a deflection-control module <NUM> that is operably coupled to the electrodes <NUM>, <NUM>. The deflection-control module <NUM> may control a potential difference between the pair of electrodes <NUM>, <NUM> so that the different beams may be deflected by differing amounts. As the electrons pass between the electrodes <NUM>, <NUM>, the electrons are deflected. The amount of deflection is a function of the strength of the electric field, which is determined by the deflection-control module <NUM>.

When the focal positions are controlled electrostatically using, for example, the mechanism shown in <FIG>, the deflection is approximately proportional to <NUM>/kV. Optionally, the deflection-control module <NUM> may be communicatively coupled to the generator, such as the generator <NUM>, such that the strength of the electric field between the electrodes <NUM>, <NUM> changes with a change in the power level supplied to the x-ray source. It is noted that for any given electric field, both a high energy level (e.g., <NUM> kVp) beam and a low energy level (e.g., <NUM> kVp) beam will be deflected in a common direction, but the high energy level beam will be deflected more than the low energy level beam. For example, a lower-energy beam may be deflected by a first amount, and the higher-energy beam may be deflected by a second amount that is greater than the first amount.

Optionally, the position of the focal spot and the energy level of the electron beam may be synchronized. For example, the generator may be directly connected to the electrodes (e.g., hardwired) and function as the deflection-control module. In such embodiments, the generator may independently and quickly switch the voltages applied to the deflection electrodes <NUM>, <NUM>.

<FIG> illustrates a cross-sectional view of an x-ray source <NUM> according to an embodiment that is configured to emit different beams at different energy levels. The x-ray source <NUM> includes a vacuum chamber or frame <NUM> having a cathode assembly <NUM> and a target or rotating anode <NUM> positioned therein. The cathode assembly <NUM> includes several elements, including a cathode cup (not shown) that supports a filament (not shown) and serves as an electrostatic lens that focuses a beam <NUM> of electrons emitted from the heated filament toward a surface <NUM> of the target <NUM>.

An electromagnet assembly <NUM> (e.g., deflection coil) of the x-ray source <NUM> is mounted at a location near the path of the electron beam <NUM>. According to one embodiment, the electromagnet assembly <NUM> may include a coil that is wound as a solenoid and is positioned over and around vacuum chamber <NUM> such that the magnetic field created is in the path of electron beam <NUM>. The electromagnet assembly <NUM> generates a magnetic field that acts on electron beam <NUM>, causing the electron beam <NUM> to deflect and move between a pair of focal spots or positions <NUM>, <NUM>. The direction of movement of the electron beam <NUM> is determined by the direction of current flow though coil of the electromagnet assembly <NUM>.

In some embodiments, the electromagnetic assembly <NUM> includes one or more quadrupoles or a plurality of dipoles. For example, the electromagnet assembly <NUM> may include two sets of quadrupole coils and yokes in which the yokes of each are distributed around the path of the beam. The quadrupoles may be configured for focusing, and the dipoles may be configured for deflection. However, the quadrupoles may have second-order effects with respect to deflection, and the dipoles may have second-order effects with respect to focusing.

A direction and magnitude of current flow may be controlled via a deflection-control module <NUM> that is coupled to electromagnet <NUM>. The deflection-control module <NUM> may be hardwired circuitry that is controlled by, for example, the x-ray controller <NUM> (<FIG>) and/or the power system. The deflection-control module <NUM> may include a current source (e.g., real current source or ideal current source), voltage sources (e.g., low voltage source, high voltage source), switches, and a resonant circuit.

Dynamic magnetic focusing may be achieved for multi-energy acquisition modes when the voltage between the cathode and the anode (target) is rapidly changed between different values. The current through the focusing coil may be adjusted between a value for the lower-energy voltage and a value for the higher-energy voltage to maintain the geometry of the focal spot. In such embodiments, the electromagnet may be synchronized to the kV setting of the accelerating voltage to effectively maintain the geometry of the focal spot. The electromagnet may be controlled to determine the position of the focal spot.

Optionally, the focal spot may be moved using deflection magnets in addition to the electromagnet <NUM>. The deflection magnets may also be electromagnets that are, for example, similarly positioned as the electrodes <NUM>, <NUM> (<FIG>). Current flowing through a coil that is wrapped about each deflection magnet may be controlled to modulate deflection of the electron beam. Compared to using focusing magnets alone, adjusting the position of the focal spot with deflection magnets may be easier to achieve, as the magnetic fields required for deflection are generally lower and do not need to be as accurate compared to those used for the focusing the beam. After focusing electronics are designed to maintain a focal spot geometry in kV switching using electromagnetic focusing, similar technology may be used to change the position of the focal spot as kV is switched.

<FIG> illustrates how embodiments of the subject matter described herein may move a focal spot FS between different spot positions SP. As described herein, the x-ray source may be operable to deflect (e.g., magnetically or electrostatically) by adjusting a strength of the respective field. For example, the focal spot FS may be moved in-plane (e.g., along the XY plane) between the spot position SPA and the spot position SPB. The focal spot FS may be moved axially along the Z axis between the spot position SPA and the spot position SPc. In certain embodiments, the focal spot FS may be moved diagonally such that the focal spot FS moves partially along the Z axis and partially along the XY plane between the spot position SPA and the spot position SPD.

For embodiments that move the focal spot FS axially or in-plane, a distance between the different spot positions (e.g., SPA and SPB or SPA and SPC) may be about half the corresponding dimension of a detector pixel element. If the focal spot FS is moved in-plane along a width of the detector pixel elements, the distance between the spot positions SPA and SPB may be about half the width of a detector pixel element. If the focal spot FS is moved axially along a length of the detector pixel elements, the distance between the spot positions SPA and SPC may be about half the length of a detector pixel element. If the focal spot FS is moved diagonally, the distance between the spot positions SPA and SPD may be the length of a diagonal for a rectangle having one-half the length (L) of the detector pixel element and one-half the width (W) of the detector pixel element, which is the square root of ((<NUM>)<NUM> + (<NUM>. By way of example, a length and width of a detector pixel element may be <NUM> millimeter (mm) X <NUM>. As another example, the length and width may be <NUM> X <NUM> the length and width may be <NUM> X <NUM>. The length and width may be <NUM> X <NUM>, or the length and width may be <NUM> X <NUM>. Although the above examples have the lengths and widths being equal, the lengths and widths may not be equal in other embodiments.

Pixel elements typically have a rectangular detection area. As used herein the phrase, "wherein the pixel elements have an area that is at least L mm X W mm" means that the length is at least L mm and the width is at least W mm. For example, the phrase "wherein the pixel elements have an area that is at least <NUM> X <NUM>" means that the length is at least <NUM> and the width is at least <NUM>. In some embodiments, the pixel elements have an area that is at least <NUM> X <NUM>. In certain embodiments, the pixel elements have an area that is at least <NUM> X <NUM>. In particular embodiments, the pixel elements have an area that is at least <NUM> X <NUM>.

As such, the spot position may move a greater distance when moving diagonally. Optionally, the diagonal movement may include unequal Z and XY components. For instance, the bi-directional arrow representing diagonal movement in <FIG> is about <NUM>° with respect to the bi-directional arrows representing axial movement and in-plane movement. Optionally, the diagonal movement may be less than <NUM>° or more than <NUM>°.

<FIG> and <FIG> illustrate different acquisition modes that may utilize data acquired at different energy levels and different positions of the focal spot. In <FIG>, the focal spot of the beam and the voltage of the power system may be controlled so that samples acquired at one energy level are acquired at the same position of the focal spot and samples acquired at another energy level are acquired at another position of the focal spot. As shown in the graph <NUM>, each sample acquired at a low energy level (LE) is acquired at a first focal position (pt1) and each sample acquired at a high energy level (HE) is acquired at a second focal position (pt2). In such embodiments, the data may undergo interpolation to provide useful image data.

In <FIG>, the focal spot of the beam and the voltage of the power system may be controlled so that subsequent samples acquired at one position of the focal spot are acquired at two energy levels. As shown in the graph <NUM>, two samples are acquired at a first focal position (pt1), low energy (LE) followed by high energy (HE). Two following samples are then acquired at a second focal position (pt2), low energy (LE) followed by high energy (HE). Optionally, the two following samples may be acquired at the second focal position (pt2), high energy (HE) followed by low energy (LE). In other embodiments, the focal spot of the beam and the voltage of the power system may be controlled so that subsequent samples acquired at one energy level are acquired at different focal positions. For example, two samples are acquired at a high energy (HE), the first focal position (pt1) followed by the second focal position (pt2). Two following samples are then acquired at a low energy (LE), the first focal position (pt1) followed by the second focal position (pt2). Optionally, the two following samples may be acquired at a low energy (LE), the second focal position (pt2) followed by the first focal position (pt1).

Data acquired at different energy levels and focal positions may be processed to generate image data. A middle row <NUM> illustrates the acquired data, which includes low-energy data (hereinafter referred to as "lower-energy data") acquired at the focal spot having the first focal position and high-energy data (hereinafter referred to as "higher-energy data") acquired at the focal spot having the second focal position. The acquired data may then be separated to generate two sets of projections, a higher-energy projection and a lower-energy projection. The data is interpolated to provide the missing data, specifically, lower-energy data acquired at the focal spot having the second focal position and higher-energy data acquired at the focal spot having the first focal position. Interpolation may be performed in the projection-space or image-space.

In <FIG>, the data referenced as (LE' pt2) and (HE' pt1) refer to interpolated data. With acquired lower-energy data and interpolated higher-energy data corresponding to the first focal position, material density projections can be achieved through a material decomposition process to provide a first projection data set. Material decomposition is a process that is used to map projection data acquired at different energy levels to projection data that represents equivalent densities of the basis-material. Material decomposition differentiates materials (e.g., bone and tissue) in a person by decomposing the energy-dependent linear attenuation coefficients into a linear combination of energy-dependent basis functions and the corresponding basis set coefficients. Material density images may provide qualitative and quantitative information regarding tissue composition and contrast media distribution. Materials that may be imaged include, for example, iodine, water, calcium, hydroxyapatite (HAP), uric acid, and fat.

With interpolated lower-energy data and acquired higher-energy data corresponding to the second focal position, material density projections can also be achieved through a material decomposition process to provide a second projection data set. The first and second projection data sets may be reconstructed to provide high-resolution material-density (or spectral) image data.

In other embodiments, a lower-energy projection data set may be generated using the acquired lower-energy data corresponding to the first focal position and interpolated lower-energy data corresponding to the second focal position. A higher-energy projection data set may be generated using the acquired higher-energy data corresponding to the second focal position and interpolated higher-energy data corresponding to the first focal position. The higher-energy and lower-energy projection data sets may be reconstructed to provide higher-energy, high-resolution images and lower-energy, high-resolution images, respectively. With the high-resolution images at different energy levels, high-resolution material-density image data can be generated using image space material decomposition methods.

High-resolution monochromatic images at different energy levels can further be derived from the high-resolution material-density images. Accordingly, high-resolution material-density images may be generated in the projection domain or in the image domain.

<FIG> is a flowchart illustrating a method <NUM> in accordance with an embodiment. The method <NUM> may be, for example, a method of obtaining high-resolution material-density image data. The method <NUM> employ structures or aspects of various embodiments (e.g., systems and/or methods) discussed herein. In various embodiments, certain steps may be omitted or added, certain steps may be combined, certain steps may be performed simultaneously, certain steps may be performed concurrently, certain steps may be split into multiple steps, certain steps may be performed in a different order, or certain steps or series of steps may be re-performed in an iterative fashion. The method <NUM> may be carried out, at least in part, by the at least one processing unit <NUM> (<FIG>).

The method <NUM> may include receiving operator inputs, at <NUM>, to select an acquisition mode. The acquisition mode may be, for example, a high-resolution spectral imaging mode. In some embodiments, the operator inputs designated energy levels, such as a lower-energy level and a higher-energy level. Optionally, the operator inputs may designate one or more intermediate energy levels. In other embodiments, the acquisition mode selected by the operator may automatically populate or assign the energy levels.

At <NUM>, the method <NUM> may include receiving operator inputs to initiate the scan. The scan may repeatedly execute an acquisition sub-sequence <NUM>. The acquisition sub-sequence <NUM> includes emitting, at <NUM>, a first beam of x-rays from a focal spot at a first designated energy level and detecting, at <NUM>, the x-rays from the first beam after passing through the person. At <NUM>, the focal spot may be moved to a different focal position (e.g., second focal position). The method <NUM> also includes emitting, at <NUM>, a second beam of x-rays from a focal spot at a second designated energy level and detecting, at <NUM>, the x-rays from the second beam after passing through the person. At <NUM>, the focal spot may be moved to a different focal position (e.g., returned to the first focal position). The method <NUM> may repeat the acquisition sub-sequence <NUM> several times.

Accordingly, emission of the first and second beams may be synchronized with the first and second focal positions. In particular, the first beam may be provided when the focal spot is in the first focal position, and the second beam may be provided when the focal spot is in the second focal position. The CT system may not acquire attenuation data when the focal spot is in the first focal position and the beam has the second designated energy level. The CT system may not acquire attenuation data when the focal spot is in the second focal position and the beam has the first designated energy level.

In other embodiments, however, the acquisition sub-sequence <NUM> may have a different order of steps. For example, the sub-sequence may move the focal position prior to the second beam so that the acquired data for each view includes both energy levels. Alternatively, the sub-sequence may change the energy level while maintaining the focal position so that the acquired data for each view may include both energy levels.

At <NUM>, data processing may be initiated. The data processing may be conducted in the projection domain and/or the image domain. At <NUM>, the data may be interpolated, as described above, to fill in missing data points to complete data sets. For example, using the interpolated data, a higher-energy data set and a lower-energy data set for the first focal position may be formed and a higher-energy data set and a lower-energy data set for the second focal position may be formed. At <NUM>, the high energy data set and low energy data set for each focal position may be processed to provide material density projections that may be used, in turn, to generate high-resolution material-density image data, at <NUM>. Optionally, the high-resolution material-density image data may be processed, at <NUM>, to generate high-resolution monochromatic images at different energy levels.

Alternatively, the data sets from step <NUM> may be used to generate higher-energy image data for each of the first and second focal positions and lower-energy image data for each of the first and second focal positions. The higher-energy data and lower-energy data may be reconstructed, at <NUM>, to provide higher-energy high-resolution image data and lower-energy high-resolution image data, respectively. The image data from step <NUM> may be combined or fused, at <NUM>, to generate high-resolution material-density image data. Optionally, the high-resolution material-density image data may be processed, at <NUM>, to generate high-resolution monochromatic images at different energy levels.

Furthermore, references to "one embodiment" are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising," "including," or "having" an element or a plurality of elements having a particular property may include additional such elements that do not have that property.

Claim 1:
A computed tomography, CT, imaging system (<NUM>) comprising:
an x-ray source (<NUM>) configured to be powered by a power system at different operating voltages, the x-ray source (<NUM>) operable to emit a beam (<NUM>) of x-rays (<NUM>) from a focal spot toward an object, the x-ray source (<NUM>) operable to move a spot position, SP, of the focal spot, FS;
a detector assembly (<NUM>) configured to detect the x-rays (<NUM>) attenuated by the object; and
at least one processing unit (<NUM>) configured to execute programmed instructions stored in memory (<NUM>), wherein the at least one processing unit (<NUM>), while executing the programmed instructions, is configured to direct the x-ray source (<NUM>) to emit different beams (<NUM>) of the x-rays (<NUM>) at different energy levels and to receive data from the detector assembly that are representative of detection of the x-rays (<NUM>) emitted at the different energy levels;
wherein the at least one processing unit (<NUM>) is also configured to direct the x-ray source (<NUM>) to move the focal spot, FS, between different spot positions, SP, such that the focal spot is at different spot positions while the beams (<NUM>) are emitted at the different energy levels, wherein the x-ray source (<NUM>), at each of a first spot position and a second spot position, is configured to emit at least a first beam at a first energy level and a second beam at a second energy level.