JP2010094509A - Method and system for x-ray imaging - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve high spatial and temporal resolution, good image quality and good coverage of a visual field by using a standard detector or a smaller detector. <P>SOLUTION: There is provided a technique for imaging a field (72) of view using an X-ray source (12) including two or more emission points (70). The two or more emission points (70) may be independently operated. Independent operation of the two or more emission points (70) is performed in accordance with a list of commands that specifies the operation of the emission points (70). According to one embodiment, the list of commands is stored in a sequence buffer (32). According to another embodiment, the list of commands is generated for a given usage without being stored in a sequence buffer (32). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present disclosure relates generally to the field of non-invasive imaging, and more specifically to the field of computed tomography (CT) imaging. Specifically, the present disclosure relates to scanner configurations and instruction sequences useful for CT imaging.

  CT scanners operate by projecting a fan-shaped (fan-shaped) or cone-shaped (conical) x-ray beam from an x-ray source. An x-ray source emits x-rays at a number of view angle positions around an imaging target, such as a patient, and the object attenuates the x-ray beam as it passes through the object. The attenuated beam is detected by a set of detector elements that generate a signal representative of the intensity of the incident x-ray beam. These signals are processed to generate data representing the line integral of the attenuation coefficient of interest along the X-ray path. These signals are typically referred to as “projection data” or simply “projection”. By using a reconstruction technique such as filtered back projection, a useful image can be constructed from the projection. Further, volume rendering of the region of interest can be formed by associating these images. The medical environment can then locate or identify the affected area or other structure of interest from the reconstructed image or rendered volume. In other environments, items or structures inside baggage or parcels, or defects in manufactured goods can be identified.

  In general, it is desirable to develop a CT scanner with high spatial and temporal resolution, good image quality, and sufficient field of view (coverage) along the z-axis, the longitudinal axis of the CT scanner. In order to meet some or all of these objectives, it is desirable to expand the field of view provided by the detector, thereby enabling an expanded scanning field of view in one or more dimensions. For example, the longitudinal field of view of the detector can be improved by increasing the number of rows of detector elements of the detector.

  This approach has led to the development of CT systems with larger detectors. However, larger detectors may not be desirable for a variety of reasons. For example, as can be expected, both the larger detector and the associated acquisition electronics are expensive and difficult to manufacture. In addition, the mechanical subsystem for supporting and / or rotating the enlarged detector also needs to be enlarged and complicated and / or subject to greater mechanical stress. In addition, large detectors are accompanied by an increase in cone angle, i.e., the angle at which the source focal spot looks at the outer detector rows. As the cone angle formed by both detector longitudinal boundaries increases, the cone beam artifact of the reconstructed image increases accordingly. If the cone angle increases beyond some limit, image quality degradation can be significant in axial or stepwise scanning. For this reason, it may be difficult to expand the scan field range by simply increasing the longitudinal dimension of the detector. Therefore, it would be desirable to have a technique that achieves high spatial and temporal resolution, good image quality, and a sufficient field of view using standard detectors or even smaller detectors.

  The approach of the present invention can be applied to two or more discrete X-ray emissions, ie, X-ray emission points that are laterally offset, i.e., have different xy coordinates, and / or X-ray emission points that are longitudinally offset, i.e., have different z coordinates. A novel method and apparatus for providing points or focal spots is provided. For example, these sources can be offset in the azimuth direction, and after rotation each source identifies the projection line needed to reconstruct the imaged object inside the field of view. A subset of is given. These sources may be activated alternately, but not necessarily at equal intervals, i.e. some of the sources may be activated more frequently or for a longer time than others. One or more detectors can be used with these two or more sources. In one embodiment, one detector can have a relatively small in-plane extent, and in some implementations the detector can be a flat panel detector.

  In some embodiments, the behavior of individual focal spots can be specified by a list of instructions or instructions for activation timing, energy, duration, focal spot size, etc. Similarly, activation and operation of one or more detectors or other aspects of the CT system can be specified by a list of instructions or instructions. Such a list of instructions for controlling focal spot operation, detector operation, or other aspects of the CT system is also referred to as an instruction sequence. Such a command sequence may be stored in a sequence buffer of the CT system, or may be transmitted to the CT system simultaneously with the operation of the CT system. There may be a single command associated with each single X-ray pulse and / or each single detector frame.

  According to one embodiment, a CT imaging system is provided. The CT imaging system includes a plurality of discrete x-ray emission focal spots and one or more detectors configured to detect x-rays emitted by the plurality of x-ray emission focal spots. . The CT imaging system is also configured to read signals from one or more detectors and an X-ray controller configured to operate a plurality of discrete X-ray emission focal spots independently. Data acquisition system. The CT imaging system also includes a sequence buffer configured to store a list of instructions that control the operation of the x-ray controller.

  According to another embodiment, a sequence buffer is provided. The sequence buffer includes a data storage structure. An instruction sequence is physically encoded in the data storage structure. The command sequence includes instructions for independently operating a plurality of X-ray emission focal spots of the distributed X-ray source.

  According to yet another embodiment, a method is provided. The method includes an operation for processing a list of instructions related to operation of the imaging system. Multiple X-ray focal spots of the distributed X-ray source are individually operated according to the list of instructions.

  According to another embodiment, a method is provided. The method includes the act of providing a distributed x-ray source including a plurality of discrete and separately operable x-ray emission focal spots. There is also provided one or more detectors configured to generate signals in response to X-rays emitted by the distributed X-ray source. Also provided is a sequence buffer capable of storing a list of instructions for operating a plurality of X-ray emission focal spots. An x-ray controller is electrically connected to the distributed x-ray source and the series buffer. The X-ray controller can operate multiple X-ray emission focal spots independently according to the list of instructions. A data acquisition system is electrically connected to the one or more detectors. The data acquisition system can read the signal generated by one or more detectors.

These and other advantages and features of the present invention will become apparent upon reading the following detailed description with reference to the drawings.
1 is a diagram of an exemplary imaging system in the form of a CT imaging system used to form a processed image according to this embodiment. FIG. FIG. 6 is a timing diagram of an exemplary instruction sequence according to the present embodiment. 2 is a diagram of one possible configuration of a distributed X-ray source and detector according to this embodiment. FIG. FIG. 6 is a diagram of another possible configuration of a distributed X-ray source and detector according to another embodiment. It is an in-plane view of a pair of X-ray emission points in the complete visual field configuration according to the present embodiment. It is an in-plane view of a pair of X-ray emission points in the half field configuration according to the present embodiment. It is an in-plane view of a pair of X-ray emission points in an arbitrary visual field configuration according to the present embodiment. FIG. 6 is an in-plane view of four X-ray emission points in the complete visual field configuration according to the present embodiment. It is an in-plane view of four X-ray emission points in the half field configuration according to the present embodiment. It is an in-plane view of four X-ray emission points in an arbitrary visual field configuration according to the present embodiment. 2 is a perspective view of a CT scanner having a plurality of emission point configurations offset along a longitudinal axis according to the present embodiment. FIG. FIG. 3 is a side view of a number of axial X-ray emission points and detectors according to this embodiment. FIG. 6 is a perspective view of a CT scanner having a dual emission point configuration along the longitudinal axis according to this embodiment. It is a figure which shows the array of the focal spot of the dispersive X-ray source by this embodiment. It is r-theta figure of the prior art of a half scan overscan acquisition system. It is a r-theta figure of the half scan overscan acquisition system performed according to this embodiment.

  FIG. 1 shows diagrammatically an imaging system 10 that acquires and processes image data. In the illustrated embodiment, the system 10 is a computer designed to acquire X-ray projection data according to the techniques of the present invention, reconstruct the projection data as an image, and process the image data for display and analysis. Is a computed tomography (CT) system. Although the imaging system 10 is discussed in a medical imaging environment, the techniques and configurations discussed herein may be used in other non-invasive CT imaging environments such as baggage or parcel inspection and / or manufacturing quality control. Applicable.

  In the embodiment shown in FIG. 1, the CT imaging system 10 includes an x-ray radiation source 12. As discussed in detail herein, the X-ray radiation source 12 may consist of two or more discrete or separate emission points or focal points for X-ray emission. For example, a conventional x-ray tube is considered equivalent to a single emission point. Alternatively, an X-ray source such as a solid state X-ray source having a field emitter or a thermionic X-ray source may include multiple emission points. Such a solid X-ray source or a thermionic X-ray source can be configured such that each emission point forms a stationary or rotating array, or a stationary ring.

  Although the description herein may discuss rotation of the x-ray source 12 as found in conventional third generation CT systems, such discussion of rotating the x-ray source 12 also includes functionally equivalent configurations. . For example, in a solid X-ray source 12 configured as a ring, the source 12 and each emission point need not be physically rotated. Alternatively, multiple emission points along the annulus can be activated in a sequential or non-sequential manner that is effectively equivalent to rotating the x-ray source 12 about the imaging volume. Thus, if the X-ray source 12 or emission point is described as rotating, then such rotation may result from the physical rotation of the source 12 or elements of the source 12, or such a functional equivalent configuration. I want you to understand.

  As described above, in some embodiments, the x-ray source 12 may be a distributed x-ray source that allows x-rays to be generated over a wide range of focal spot (ie emission point) positions. For example, in an embodiment of a distributed X-ray source, the respective emission points may be separated by tens of centimeters, such as 10 cm, 15 cm, 20 cm, 25 cm, and 30 cm. Such distributed x-ray sources generate x-rays that traverse substantially different portions of the patient or object being imaged and / or are being imaged at substantially different azimuth angles. Can be useful for generating X-rays that traverse.

  An example of such a distributed X-ray source is an electron beam CT scanner that generates X-rays by sweeping one or more target rings surrounding the scanner field of view with an electron beam. Such a configuration can generate X-rays from different azimuth angles in a high-speed scanning sequence. Some other scanning beam X-ray sources can be understood to be distributed X-ray sources. In addition, in some embodiments, the distributed x-ray source is stationary so that it does not use mechanical motion to generate x-rays in various views around the patient or object being imaged. It may be a thing. In such a stationary embodiment, the distributed source may be based on one or more swept electron beams, a plurality of discrete electron emitters, or a combination of the two approaches. In addition, in some embodiments, the distributed source architecture may be rotated. For example, in one such embodiment, the distributed x-ray source may be based on a 2D array of discrete electron emitters.

  In some embodiments, the x-ray source 12 may be located proximate to the collimator 14. The collimator 14 may comprise a collimating region such as a lead or tungsten shutter provided for each emission point of the radiation source 12. The collimator 14 typically defines the size and shape of one or more radiation streams 16 that flow into an area where a subject such as a patient 18 is located. The radiation stream 16 may be generally conical depending on the detector array configuration described below and the desired data acquisition method. The attenuated portion of the radiation 20 passes through the subject to be attenuated and impinges on the detector array, generally designated by reference numeral 22.

  The detector 22 is generally formed by a plurality of detector elements, and these detector elements detect X-rays that have passed through the subject of interest and passed adjacent to the subject. The detector 22 may include a number of rows of detector elements. When using such a multi-row detector, the radiation stream 16 has a non-zero cone angle associated with the radiation stream 16 for detector rows that are not in the same plane as the active emission point. It becomes. The following example abstracts this z-range to simplify the representation, i.e., by limiting the discussion to detector elements that lie in the same plane as the active emission point. Do. However, the following geometric discussion and examples are equally applicable to multi-row detectors.

  As each detector element is struck by x-rays, it generates an electrical signal representative of the intensity of the x-ray beam at the position of that element at the time the beam is incident on the detector. Typically, the signals are acquired at various view angular positions around the subject of interest so that multiple radiographic views can be acquired. These signals are acquired and processed to reconstruct an image of various features in the body of the subject, as will be described later.

  The X-ray source 12 is controlled by a system controller 24, which supplies power signals, focal spot position signals, control signals, etc. for CT examination sequences. A detector 22 is also coupled to the system controller 24, which commands acquisition of signals generated at the detector 22. The system controller 24 can also perform various signal processing and filtering operations, such as initial adjustment of dynamic range and interleaving processing of digital image data. In general, the system controller 24 commands the operation of the imaging system 10, executes the examination protocol, and processes the acquired data. In the context of this document, the system controller 24 also includes a signal processing circuit, typically a general purpose or application specific digital computer, and an associated memory circuit. The attached memory circuitry can store programs and routines (such as programs, routines and / or algorithms that embody the subject matter disclosed herein), configuration parameters, and image data.

  In the embodiment shown in FIG. 1, the system controller 24 can control the movement of the rotating subsystem 26 and the linear arrangement subsystem 28 via the motor controller 34. In the imaging system 10 in which the source 12 and / or detector 22 may rotate, the rotation subsystem 26 may include the X-ray source 12, collimator 14, and / or detector 22 around the patient 18 once or multiple times. Can be rotated. It should be noted that the rotation subsystem 26 can include a gantry. The linear placement subsystem 28 can linearly displace the patient 18, or more specifically the patient table. In this way, the patient table can be moved linearly within the gantry to form an image of a particular area of the patient 18.

  The radiation source 12 can be controlled by an x-ray controller 30 disposed within the system controller 24. The X-ray controller 30 may be configured to supply a power signal and a timing signal to the X-ray source 12. In addition, the X-ray controller may provide a focal spot position or emission point if the X-ray source 12 is a distributed source such as a solid X-ray source or a thermionic X-ray source configured as an array or ring. May be configured to provide activation of the. For example, the X-ray controller 30 may be embodied as a high voltage switching circuit that turns on and off individual focal spots or emission points of the distributed X-ray source. Such circuitry may include or be in communication with a logic controller that controls the various high voltage stages.

  In one embodiment, the x-ray controller 30 includes a sequence buffer 32 that stores various commands or instructions, such as a command sequence to operate various focal spots of the x-ray source 12, or as discussed herein. This series buffer 32 can be communicated. Specifically, different X-ray focal spot command sequences are used to change image quality, noise, scatter, X-ray source thermal, patient dose, or other parameters related to the operation of the imaging system 10. Can be made. For example, the command sequence may be a list of commands in which each command has the number of the focal spot that it wishes to activate, as well as the mA, kVp, focal spot size and / or integration time (dwell) at each focal spot activation. time, pulse duration). The sequence buffer 32 may also store a hard-coded or programmable “dead time” between focal spot activations to help reduce crosstalk. In addition, the instruction sequence stored in the sequence buffer 32 may be used in a detector mode (photon counting mode versus energy integration mode and high flux mode mode) that may be used by the X-ray controller 30 and / or data acquisition system 36 during operation. A low flux mode or the like). In practice, sequence buffer 32 may be embodied as a memory device or other storage structure suitable for storing instructions embodied in a computer. For example, the series buffer 32 is a solid-state memory device (such as a memory chip used as a ROM or RAM in a processor type system or a solid-state hard drive), an optical storage device (such as an optical disk), a magnetic storage device (conventional memory) Hard drive) or any other suitable for storing instruction scripts for the operation of individual focal spots of a distributed X-ray source and / or the operation of one or more detectors 22 of the imaging system 10 It can be embodied as a suitable data storage structure.

  The size of sequence buffer 32 may be based on the length and number of instructions stored in sequence buffer 32. In one embodiment, each indication line is a 2-byte field for a sample period number (eg, sample periods 1, 5, 15 etc.), an action code or indication (eg, code “7” is an indication to trigger the focal spot 7 3 byte fields for qualifiers or variables that determine, modify or supplement one byte field, action code, or some other aspect of the instruction system (eg “27”, “30”, etc.) ”And“ 45 ”may include that the source spot to be activated should be operated at 27 mA for 30 μs 45 μs after receiving the trigger, etc.). This indicator system can be added to the 6 bytes of a typical sub-view. In one such embodiment, therefore, the sequence buffer size is 42 kB + 1 kB per second of scan assuming a sampling rate of 7 kHz. In other implementations, the size of the sequence buffer may be about 50 kB to about 60 kB per second.

  In some embodiments, the sequence buffer 32 may not be present in the system controller or may not be used. For example, in some embodiments, the processor and appropriate memory in communication with the processor (which may or may not be the sequence buffer 32 or memory 40) may be used for immediate use as described above. Instruction sequences can be generated, i.e., instruction sequences are generated ad hoc or "on-the-fly" without resorting to pre-stored or pre-generated sequences Can be done. Such a processor and suitable memory may be associated with the system controller 24, computer 38, or other suitable processor type system in communication with or forming the CT system 10. Thus, in such an embodiment, the sequence buffer 32 or other memory structure, such as the memory 40, is not used as a storage buffer even if it exists, but for immediate use of generated and generated instruction sequences. It can be used as a scaffold area.

  In embodiments where the sequence buffer 32 is not present or provided as part of the system controller 24, the instructions may alternatively be sent to the system controller 24 in real time and the link data payload is sequenced. It can be less than the raw contents of the buffer. In an embodiment having a distributed x-ray source with 50 focal spots and 20 possible grating levels (ie, mA levels), 3 per typical sample period if the sample period number need not be transmitted. A byte is sufficient, and 6 bytes if two focal spots are activated simultaneously. Assuming a sampling rate of 7 kHz, a baud rate of 500 kilobaud or more is sufficient.

  In some embodiments, the delay in μs between focal spot activations may be encoded using only 5 bits (ie, 0-4). In one such embodiment, two focal spots can be activated during the same sample period, but the time after triggering can be different. For example, the first focal spot may be instructed to be activated 55 μs after the trigger, and the second focal spot may be instructed to be activated 60 μs after the trigger. In such an implementation, 5 bits may not be enough to transmit these delays, but instead the logic to instruct the sequence buffer, in this example, until the remaining time is less than 31 μs, etc. As such, the transmission of instructions can be delayed for an appropriate amount of time to effectively achieve the desired delay. A representation of such a packing scheme provided with a fixed waiting time of 40 μs is given in FIG.

  The system controller 24 may also include a data acquisition system (DAS) 36 such as detector electronics that collects and amplifies the respective signals from each cell of the detector 22. In this example embodiment, detector 22 is coupled to system controller 24, and more specifically, is coupled to data acquisition system 36. Data acquisition system 36 receives the data collected by the readout electronics of detector 22. Specifically, the data acquisition system 36 typically receives a sampled analog signal from the detector 22 and converts the data to a digital signal for subsequent processing by the computer 38.

  Computer 38 is typically coupled to system controller 24. Data collected by the data acquisition system 36 can be sent to a computer 38 for subsequent processing and reconstruction. For example, data collected from detector 22 may be pre-processed and calibrated at data acquisition system 36 and / or computer 38 to adjust the data to represent the line integral of the attenuation coefficient to be scanned. The processed data is commonly referred to as a projection, which can then be rearranged, filtered and backprojected to construct an image of the scanned area. Once reconstructed, the image formed by the system of FIG. 1 represents a region of interest within the patient 18 that may be used for diagnosis, evaluation, and the like.

  The computer 38 can include or be in communication with a memory 40 that can store data processed by the computer 38 or data to be processed by the computer 38. Any form of computer-accessible memory device (eg, solid state memory device, hard drive, optical disk, etc.) capable of storing a desired amount of data and / or code can be used by such example system 10. I want you to understand. The memory 40 may also include one or more memory devices, such as similar or different types of solid state devices, magnetic devices or optical devices that may be located locally and / or remotely with respect to the system 10. Memory 40 may store data, processing parameters, and / or computer programs that include one or more routines that perform the processes described herein.

  The computer 38 may also be configured to control features enabled by the system controller 24, such as scanning operations and data acquisition. Further, the computer 38 may be configured to receive commands and scanning parameters from an operator via an operator workstation 42 that may be equipped with a keyboard and / or other input device. The operator can thereby control the system 10 via the operator workstation 42. In this manner, the operator can observe the reconstructed image and other data from the computer 38 related to the system, start imaging, and the like.

  A reconstructed image can be viewed using a display 44 coupled to the operator workstation 42. In addition, the scanned image can be printed by a printer 46 that can be coupled to an operator workstation 42. The display 44 and the printer 46 may be directly connected to the computer 38 or may be connected via the operator workstation 42. In addition, operator workstation 42 may also be coupled to an image storage and communication system (PACS) 48. Note that the PACS 48 is a remote system 50, a radiology information system (RIS), a hospital information system (HIS), or a local or external network so that third parties at different locations can gain access to the image data. Note that it may be coupled to

  One or more operator workstations 42 may be coupled to the system for outputting system parameters, requesting examinations, displaying images, and the like. In general, displays, printers, workstations, and similar devices provided within the system may be located locally with respect to the data acquisition components, or for these components. One or more such as the Internet and a virtual private network, such as being located remotely in a facility or hospital premises, or in a completely different location, etc. It may be coupled to the image acquisition system via a network.

  The CT imaging system 10 described above can be configured in a variety of ways to increase spatial and temporal resolution, increase image quality, reduce patient radiation dose, and / or improve longitudinal field of view. . Indeed, various source 12 and detector 22 configurations can be implemented that improve one or more of these parameters. For example, as discussed herein, an X-ray source 12 using multiple emission points or focal spots can be used. The activation of each discharge point can be coordinated such that only one is activated at a time, such as by using an alternate activation scheme, or can be coordinated to allow simultaneous activation. In this manner, each emission point may provide a subset of the projection lines needed to reconstruct the object within a given field of view when activated. However, when these subsets are combined, the field of view can be reconstructed. In addition, in embodiments where only a subset of the projection lines associated with the field of view are acquired at a time, the in-plane spread of the detector 22 can be reduced. Indeed, the in-plane extent of the detector 22 can be reduced to such an extent that a flat panel detector or radiographic detector panel can be used.

  According to the method of the present invention, various configurations and activation methods of the X-ray source 12 can be executed. This document discusses some exemplary configurations and schemes. However, it should be understood that the illustrated examples do not limit the scope of the present technique. Instead, the approach of the present invention can be broadly understood to encompass any x-ray source configuration that allows for a large number of discrete emission points, and any activation scheme for such emission points.

  For example, referring to FIGS. 3 and 4, examples of different distributed X-ray source 12 configurations are described. In the example shown in FIG. 3, a standard array-source inverted geometry CT architecture is illustrated. In this example, an X-ray source 12 consisting of 20 × 3 focal spots or emission points 70 respectively dispersed in the x direction (azimuth angle direction) and the z direction (longitudinal direction) is shown. As will be appreciated, 1, 2, 3, 4, 5, ..., 100 or more emission points in the z direction, and 2, 3, 4, ..., 1,000 or more emission points in the x direction, etc. A similar geometric configuration using a different number of emission points 70 may be used. The illustrated architecture includes a detector 22, such as a flat panel detector. In one embodiment, detector 22 is approximately 10 cm x 10 cm. The emission point 70 emits X-rays 16 incident on the detector 22 through the field of view 72.

  In the example shown in FIG. 4, an inverted geometry CT architecture for cardiac applications is shown. In this example, the distributed X-ray source 12 has about 30 × 3 emission points dispersed in the x direction (azimuth angle direction) and z direction (longitudinal direction), respectively, and two detectors 22. is doing. In one embodiment, the detectors 22 are each about 10 cm × 10 cm. In other embodiments, more than two detectors 22 may be used. As will be appreciated, 1, 2, 3, 4, 5, ..., 100 or more emission points in the z direction, and 2, 3, 4, ..., 1,000 or more emission points in the x direction, etc. A similar geometric configuration using a different number of emission points 70 may be used.

  With the above discussion of the distributed X-ray source example in mind, the following simplified example describes several embodiments of the present technique with respect to an x-direction emission point configuration. For example, as shown in FIG. 5, a pair of discrete emission points 70 offset in the azimuthal direction are illustrated as radiation source 12 in the xy plane. The emission point 70 may be configured to be at the same vertical distance from a detector 22 such as a flat panel detector 60, or may be located at a different distance. Each emission point 70 is either a focal spot of a distributed X-ray source based on an X-ray tube, a solid electron emitter or a thermionic electron emitter, or some other focus that can emit X-rays upon activation. Also good. The X-ray source 12 and its respective emission points 70 may be arranged in a grid. The emission point 70 may also be offset in the z direction as discussed herein.

  The emission points 70 can be rotated around the desired field of view 72 to allow each emission point 70 to emit the radiation stream 16 from the desired view angle. As the emission points 70 rotate, only one emission point 70 can be alternately activated at a given time to emit X-rays. Each emission point 70, when activated, may be configured to emit a fan-shaped radiation stream that bounds a portion of the field 72, such as one half of the field 72, as shown in FIG. The radiation stream 16 passes through the field of view 72 and passes through any attenuating material within the field of view 72 before entering the detector 22 such as the flat panel detector 60. At each activation of the emission point 70, the data acquisition system 36 (FIG. 1) can read the signals generated by the detector 22 and process these signals to generate projection data. As the emission point 70 rotates about the field 72, the combined or accumulated acquired projection data describes the entire field.

  For example, as shown in FIG. 5, a first emission point 74 can emit X-rays within a fan that surrounds a portion of the field 72, such as one half of the field 72, in operation. Thus, projection data can be acquired for this portion by a detector 22, such as a flat panel detector 60, when the first emission point 74 is activated. When the first emission point 74 is inactive, the second emission point 76 is activated to provide projection data for the portion of the field 72 surrounded by the X-ray fan emitted by the second emission point 76. Can be made available. The emission point 70 can be rotated around the field 72 while being alternately activated at each desired view angle until the desired projection data for reconstructing the field 72 is obtained.

  As will be appreciated by those skilled in the art, sufficient projection data to reconstruct the field 72 can be acquired with less than a full rotation of the emission point 70 around the field 72. In fact, a half rotation plus angle (β) between two emission points 70, ie 180 ° + β, may be sufficient to provide projection data to reconstruct the field of view 72.

  In addition, multiple emission points 70 can be configured such that the combined fan at emission point 70 borders only one-half of the field of view 72 or only some other portion in operation, ie, a half-field configuration. For example, referring to FIG. 6, there are shown two emission points 70 that emit X-rays inside a fan that encloses only one-half of the field of view 72 in operation. As shown, the combined fan at the first and second emission points 74, 76 bounds only one half of the field of view 72. By limiting the fan angle α associated with each emission point 70, a small portion of the field of view 72 is imaged when the emission point 70 is operating, so that the detector 22, here a flat panel detector 60. It is possible to further reduce the spread in the plane. As will be appreciated by those skilled in the art, sufficient projection data to reconstruct the field of view 72 using a half-field configuration as shown in FIG. 6 is obtained by full rotation of the emission point 70 around the field of view 72. obtain.

  In addition, it should be appreciated that the X-rays emitted by the first emission point 74 and the second emission point 76 do not pass through the same region of the field of view 72. Specifically, the X-rays emitted by the first emission point 74 pass through the central region of the field of view 72 where the object or patient being imaged is typically centered. Conversely, the X-rays emitted by the second emission point 76 pass through an empty space and a peripheral region of the field of view 72 that may include a relatively unfocused region of the patient or object being imaged. This relationship remains true as the first and second emission points 74, 76 rotate around the field of view 72, ie, the first emission point 74 continuously images the central region of the field of view 72. The second emission point 76 continuously images the periphery of the image field 72.

  Because of this distinction between the first and second emission points 74, 76, the first and second emission points 74, 76 may be used when the peripheral edge of the field of view 72 is relatively or not noticed, etc. It does not need to be operated equivalently. For example, if desired, a relatively small number of views can be acquired using the second emission point 76, i.e., the second emission point 76 is activated less frequently than the first emission point 74. be able to. For example, the second emission point 76 can be activated in alternate views or less, as desired. Similarly, the second emission point 76 may be operated for a reduced duration or duty cycle relative to the first emission point 74, or at low energy.

  Similarly, if the peripheral area imaged by the second emission point 76 is relatively unimportant, the second emission point 76 is of lower quality than the first emission point 74, i.e. less flux and lower spatial resolution, etc. You may have. Specifically, if the attenuation of the periphery of the region of interest 72 is tolerable for small attenuation, low resolution and / or large noise, a second emission point 76 with a small bundle or low spatial resolution may be acceptable. . Different doses at the center and periphery of the region of interest 72 can be administered to the patient 18 by differential activation of the first and second release points 74, 76 and / or the use of the second release point 76 with a small bundle of rays. become. In this manner, the dose received by the patient 18 can be individually adjusted based on the situation.

  These concepts can be extended to any configuration between a half-field configuration and a full-field configuration, or any configuration where there can be a clear central region of interest 80 such as a cardiac field. For example, as shown in FIG. 7, the first and second emission points 74 and 76 may respectively border different portions of the visual field 72, that is, the central region of interest 80 and the peripheral region 82, respectively. As will be appreciated by those skilled in the art, the discussion of the central region of interest 80 and the peripheral region 82 with respect to FIG. 7 is similar to the related discussion with respect to FIG.

  Specifically, referring to FIG. 7, the first emission point 74 is capable of emitting X-rays within the fan that surrounds the central region of interest 80 within the field of view 72 during operation. In this manner, the first emission point 74 can generate a projection line associated with the central region of interest 80. In operation, the second emission point 76 can emit X-rays within the fan surrounding the radial or peripheral portion 82 of the region of interest 72 outside the central region of interest 80. For example, one edge of the X-ray fan emitted by the second emission point 76 can touch the center region of interest 80 and the other edge can touch the edge of the field of view 72. In this manner, the second emission point 76 can generate projection lines for the supplemental portion of the field of view 72 that is not contained within the central region of interest 80.

  As in the previous example, the entire field of view 72 is not covered by a single emission point 70 and detector 22, so that the in-plane dimensions of detector 22 are greater than with a single emission point 70. It can be small. For example, the detector 22 may have a relatively small in-plane extent and may actually be substantially flat like the flat panel detector 60. For example, if the radius of the central region of interest 80 is 15 cm and the radius of the field of view 72 is 50 cm, the detector 22 is no more than 30% of the size of each detector associated with the same field of view and a single emission point 70. It may be.

  Using half-scan data acquisition, data for reconstructing the center region of interest 80, that is, data for a rotation of (180 ° + α) degrees can be acquired. In addition, since the fan angle α is smaller than when a single emission point 70 is employed, a half scan can be performed faster, thereby imaging a dynamic organ such as the heart. Provide increased time resolution. For example, when using the second emission point 76, α can be equal to 15 ° instead of 50 °, and half-scan data acquisition is 195 for the first emission point 74 instead of a rotation of 230 °. Rotation of ° can be included. However, full rotation of the first and second emission points 74, 76, ie 360 °, may be required to reconstruct the complete field of view 72, ie, to fully reconstruct the peripheral region 82.

  gotogoto As described above with respect to the half-field configuration of FIG. 6, a relatively small number using the second emission point 76, such as when the peripheral view provided by the second emission point 76 is relatively unimportant. Can be obtained as desired. Similarly, the second release point 76 can be activated less frequently or for a shorter duration than the first release point 74 as discussed in the example above. Similarly, as described above, if the peripheral area 82 imaged by the second emission point 76 is relatively unimportant, the second emission point 76 is of lower quality or less than the first emission point 74. It may have a wire bundle or the like.

  Differential activation of the first and second emission points 74, 76 and / or the use of the second emission point 76 with a small bundle allows different doses to be administered to the patient 18 inside and outside the central region of interest 80. can do. In fact, in some examples, such as when the imaging object or organ is within the central region of interest 80, the second emission point 76 can be left inactive when acquiring image data. There is a case. In such an embodiment, the data acquired corresponding to the peripheral region 82 is incomplete, but if some part of the imaging target is located within the range of the peripheral region 82, etc., as desired It can still be reconstructed using special reconstruction techniques. In this manner, the dose received by the patient 18 can be individually adjusted based on the situation.

  While the above example discusses an implementation that includes two emission points 70, this approach can be extended to more than two emission points 70. For example, three or more X-ray tubes may be used, or a solid X-ray source or thermionic X-ray source 12 including three or more addressable emission points 70 configured as an array or ring. It may be used. Other x-ray sources 12 including emission points 70 that are discrete and addressable may also be suitable for use with the techniques of the present invention.

  For example, FIG. 8 shows four emission points 70 in a full field configuration similar to that shown in FIG. The emission points 70 may be configured to be located at the same vertical distance from the flat panel detector 60, or may be located at different distances. As discussed with respect to FIG. 5, the emission points 70 can be rotated around a desired field of view 72 such that each emission point 70 can emit a stream of radiation 16 from a desired view angle.

  The emission points 70 can be alternately activated so that only one emission point 70 emits X-rays at a given time when rotating. Each emission point 70, when activated, may be configured to emit a fan-shaped radiation stream that bounds a portion of the field of view 72. The radiation stream 16 passes through the field of view 72 and passes through any attenuating material within the field of view 72 before entering the flat panel detector 60. At each activation of the emission point 70, the data acquisition system 36 (FIG. 1) can read the signals generated by the detector 22 and process these signals to generate projection data. As the emission point 70 rotates about the field 72, the combined or accumulated acquired projection data describes the entire field. As described above, with such a full field configuration, sufficient projection to reconstruct the field 72 can be acquired with a half-scan acquisition, ie 180 ° + some summing angle, depending on the geometric configuration.

  Similarly, a half-field configuration can be implemented using more than two emission points 70. For example, referring to FIG. 9, four emission points 70 are shown, and the fan-shaped radiation stream 16 from these emission points 70 is a half of the field of view 72 or some other portion. Is bounded globally. Each discharge point 70 can be alternately activated, as described above, so that only one discharge point 70 is activated at a time. Due to the limited fan angle α associated with each emission point 70, the detector 22 may have a reduced in-plane extent. In such a half-field configuration, sufficient projection data to reconstruct the field 72 can be obtained by full rotation of the emission point 70 around the field 72.

  Further, as described above, each emission point bounds a different radial region of the field of view 72. For example, the first emission point 74 defines a central region and the second emission point 76 borders the next outer radial region. Similarly, the third emission point 86 borders the next radial region, and the fourth emission point 88 borders the peripheral region or the outer radial region. Since each emission point 70 borders different radial regions of the field of view 72, different emission points 70 are deactivated during the imaging sequence if no or little attention is paid to the radial region bounded by the emission points 70. I can keep it. For example, the fourth emission point 88 may be left inactive if the peripheral area of the field of view 72 includes empty space or otherwise is not of interest at all. As in the case of the discussion above the half-field configuration, as shown in FIG. 9, sufficient projection data to reconstruct the field 72 using the half-field configuration provides a complete view of the emission point 70 around the field 72. Can be obtained by rotation.

  Similarly, as discussed with respect to FIGS. 6 and 7, the first, second, third and fourth emission points 74, 76, 86, 88 differ in the different radial regions that each emission point bounds. Thus, it is not necessary to operate equivalently to the extent that attention or importance is given. For example, each emission point 70 may be activated for a different number of views. For example, the first and second emission points 74, 76 are activated for every view, the third emission point 86 is activated for every other view, and the fourth emission point 88 is for any view. It can be disabled. Such an implementation may allow the image to be built with good quality towards the center of the field of view, with a lower quality outside the center, and no image of the peripheral region of the field of view 72 being generated. Similarly, different emission points, such as the fourth emission point 88, may be operated at lower energy for a reduced duration relative to the first emission point 74. Similarly, the quality, i.e., flux, of each emission point 70 may vary based on the radial region that each emission point 70 bounds. For example, in an x-ray tube implementation, the third and / or fourth emission points 86, 88 may be low quality or low flux x-ray tubes.

  Thus, as the number of x-ray emission points 70 increases, the ability to adaptively adjust the x-ray dose to the patient 18 or the object being imaged can also be enhanced. Specifically, the number of possible radial regions increases as the number of emission points 70 increases. As the number of radial regions increases, so does the opportunity to use differential operations such as activation and / or duration, or different hardware configurations such as low flux x-ray tubes. In this manner, the dose received by the patient 18 and the image quality of different parts of the image can also be individually adjusted based on the situation.

  Similarly, the use of this additional emission point 70 can be extended to any configuration or configuration with a clear central region of interest 80, such as the cardiac field 80, as discussed with respect to FIG. For example, referring to FIG. 10, the first and second emission points 74, 76 can bound the central region of interest 80 of the field of view 72. Conversely, the third and fourth emission points 86, 88 can bound the peripheral region 82 of the field of view 72. As discussed with respect to FIGS. 7 and 9, each release point 70 can be operated or configured in a differential manner such that the dose to patient can be adaptively adjusted or adjusted based on the situation. For example, the third and / or fourth emission points 86, 88 may not be activated when the peripheral region 82 is relatively or not of interest, or only for a subset of possible view angles. Also good. Similarly, if the peripheral region 82 is relatively unfocused, the third and fourth emission points 86, 88 may be activated with low quality using low flux or large focal spot size or the like.

  As in the previous example, the in-plane dimensions of a detector 22 such as a flat panel detector 60 are single because the entire field of view 72 is not covered by a single emission point 70 and detector 22. It may be smaller than when the discharge point 70 is used. Similarly, using half-scan data acquisition using the first and second emission points 74 and 76, data for reconstructing the center region of interest 80, that is, 180 ° + some additional rotation angle is acquired. be able to. However, in order to acquire data for reconstructing the complete field of view 72, i.e. to completely reconstruct the peripheral region 82, the first, second, third and fourth emission points 74, 76, 86, 88 Full rotation or 360 ° may be required.

  Although the above example shows a configuration using two or four emission points 70 to simplify the illustration of the concept of the present invention, the disclosed technique is more than one emission point 70. Can be extended to other configurations such as Similarly, field configurations other than those shown are not excluded from the approach of the present invention and may benefit from the use of multiple emission points 70 as discussed herein.

  Further, with the distributed X-ray source configuration of FIGS. 3 and 4 in mind, it is often desirable to offset the emission point 70 in the z direction. For example, as shown in FIG. 11, when a z-offset is applied to successive emission points 70, an array of emission points 70 that are slightly inclined with respect to the main axis of the CT scanner 100 can be obtained. This can be particularly useful for helical cone beam acquisition. This is because the resulting data set can be reorganized to simulate the acquisition obtained by a single emission point. In order to achieve such results, the z offset, and thus the resulting array pitch, depends on the helical pitch used during image acquisition. The z offset can be adjusted to accommodate the desired helical pitch.

  In addition, for cone beam and volumetric CT geometries it may be desirable to include each additional emission point 70 along the longitudinal axis. Specifically, the use of multiple emission points 70 along the longitudinal axis allows the axial extent of the detector 22 to be reduced instead of or in addition to the aforementioned in-plane extent reduction of the detector. Can be. For example, FIG. 12 shows three emission points 70 that are diffused along the longitudinal axis of the CT scanner 100. Each discharge point 70 can be fired alternately, such as sequentially, so that only one discharge point 70 is activated at a time. A detector 22, such as a flat panel detector 60 having a reduced axial extent, can be used with multiple longitudinal emission points in a manner similar to that discussed in the previous example. As in the previous example, an implementation of the inventive approach allows the use of a small cone angle in the longitudinal direction and thus the use of a detector 22 that is small in the longitudinal direction.

  For example, FIG. 13 illustrates three sets of dual emission points 94, 96, 98 along the longitudinal axis of the CT scanner 100. In the illustrated example, each set of dual emission points 94, 96, 98 shares coordinates in the xy plane, but differs in position in the z-axis or longitudinal direction.

  As described in the above example of in-plane offset and longitudinal offset, the techniques disclosed herein can provide a variety of benefits. For example, since the in-plane and / or longitudinal extent of the detector 22 is reduced, a small and inexpensive detector such as the flat panel detector 60 can be used (FIGS. 5 to 10 and FIG. 12). In general, it is relatively easy and inexpensive to manufacture small detectors, particularly flat panel detectors.

  In addition, the technique of the present invention can provide even higher spatial resolution, especially when separated from the isocenter. Specifically, a single emission point may involve a large fan angle and correspondingly a large detector. The focal spot associated with the emission point appears larger at the edge of the detector due to the increase in the so-called “apparent” focal spot size. As the apparent focal spot size increases, the spatial resolution at the edge of the detector may be degraded compared to the center of the detector. In the detector 22 used together with the method of the present invention (FIGS. 5 to 10 and 12), the fan angle is reduced, the in-plane spread is reduced, and the apparent focal size of each emission point 70 is reduced. Thus, it may be possible to increase the spatial resolution over the remainder of the field of view.

  Furthermore, since the multiple emission point 70 (FIGS. 5 to 10) is used, dynamic line bundle control at the time of image acquisition can be enabled. For example, the multiple emission point 70 can be used to maintain signal uniformity at the detector 22, thereby increasing efficiency and limiting the dynamic range at the detector, or optimizing dose or image quality. It can be activated with a differential equation based on the angle. Specifically, in a medical imaging environment, patient 18 (FIG. 1) is typically elliptical in cross section, resulting in a varying path length through patient 18, ie, X-rays traverse patient 18. The path length to be changed depends on the view angle position with respect to the patient 18. Conventional CT techniques can compensate for these varying path lengths using a bowtie filter that is adaptively configured to the overall cross-section of the body region being imaged.

  However, the technique of the present invention allows for real-time flux modulation or virtual dynamic bowtie based on the anatomy of the patient 18. Specifically, at a view angle corresponding to a short path length through the patient 18 such as through the chest and back, an emission point 70 emitting X-rays with a low flux can be activated. Conversely, at view angles corresponding to long path lengths, such as through both shoulders, an emission point 70 that emits X-rays with high flux can be activated. Similarly, in the case of an intermediate path length, the emitted X-ray flux can be appropriately adjusted. Further, as the patient is linearly displaced through the CT scanner, the flux associated with a certain view angle position may be dynamically adjusted. In this manner, the effect of the bow tie filter can be reproduced while allowing dynamic adjustment to maintain signal uniformity at the detector 22. Furthermore, the X-ray focal spot and view flux can be adjusted to minimize the radiation dose to sensitive organs and to optimize the image noise in the region of interest.

  The techniques of the present invention may also consider the use of various detector technologies such as energy discriminating detectors so that CT techniques such as energy discriminating CT may be performed. Due to the small detector spread in the in-plane direction and / or longitudinal direction, such a new technology can be implemented at a reasonable cost. Similarly, such detectors can also be more easily manufactured to accommodate the reduced detector dimensions associated with the present technique. In addition, the fan angle and cone angle associated with the method of the present invention are reduced, which reduces the scattering of X-ray intensity measurements and allows the anti-scatter grid to be omitted from the detector, thereby Efficiency can be increased.

  The above discussion describes various physical configurations of the source emission point 70 and detector 22 in the x and z dimensions suitable for use in an imaging system. In some embodiments, each emission point 70 and / or detector (s) 22 has instructions or instructions that separately define each emission point or focal spot and / or some operating parameters of the detector. May operate according to one or more sequences of For example, the command sequence relates to the order in which the focal spots are fired or fired, the duration for which each focal spot is fired, the energy at which each emission point 70 is fired, the focal spot firing. mA, focal spot activation duration, etc. can be defined. Thus, a given command sequence has a focal spot firing pattern in which no focal spot is fired at the same time, a focal spot firing pattern in which several focal spots are fired simultaneously, and several focal spots. Can be defined such that the focal spot firing pattern is fired more or less than the other focal spots, and / or the sequential or non-sequential firing order of each focal spot. In this manner, cardiac overscan is minimized, helical overscan is minimized, image quality is increased, noise is reduced, scatter is reduced, x-ray source heat flow is reduced, and patient dose is reduced An instruction sequence that achieves several goals, such as limiting, can be selected. A suitable command sequence for a given patient may be calculated based on an initial scout scan, such as a scan acquired using a conventional command sequence with a standard bowtie filter in some embodiments. . As will be appreciated, instructions for the various instruction sequences discussed herein may be stored in and obtained from such sequence buffers 32 as discussed with respect to FIG. Alternatively, the instruction sequence may be calculated ad hoc or “on the fly”, for example using closed loop feedback based on detector measurements.

  With reference to FIG. 14 for the following discussion of the command sequence, the focal spot column in the z direction is labeled alphabetically, ie, A, B, C, etc., and the focal spot column in the x direction is numbered from 1 or Number up to 20. In the illustrated example, the outer focal spot 64 may correspond to an outer radial field in some embodiments, as will be described in detail later. Similarly, the inner focal spot 66 may correspond to an inner circular field, such as a cardiac field in some embodiments.

  With the above naming convention in mind, a standard sequential activation sequence for a distributed source with discrete focus at x and z will be described. In this example, the distributed x-ray source is a 3 × 20 array of focal points as shown in FIG. Such a distributed X-ray source can be activated one after the other via a sequence of instructions stored in a sequence buffer such as the sequence buffer 32 of FIG. Such sequential instruction sequences include A1-A2-A3-. | A20-B1-B2-B3 -...- B20-C1-C2-C3 -...- C20-A1-A2-A3 -...- A20-. It is possible to correspond to such an activation order. Alternatively, another example of a sequential instruction sequence is A1-B1-C1-A2-B2-C2-A3 -...- A20-B20-C20-A1-B1-C1-A2 -... etc. obtain. Thus, in these examples, emission point activation may proceed sequentially from row to row or column to column. In other examples, alternative patterns such as spiral patterns, zigzag patterns and pseudo-random patterns can be used. In these sequential examples, there is a fixed or predetermined order, and activation proceeds sequentially based on this fixed predetermined order.

  In other embodiments, the instruction sequence may be non-uniform. In some such embodiments, some focal spots can be fired or activated more frequently than others. For example, a focal spot that ignites through a highly attenuated part of a patient or object and / or a focal spot that ignites through a region of interest that requires good image quality can be ignited with a high frequency (larger mA, kW and / or Instead of or in addition to firing at the total time). Conversely, focal spots that ignite through reduced weakness of the patient or object and / or focal spots that ignite through sensitive organs can be ignited less frequently (with smaller mA, kW and / or integration time). Instead of or in addition to ignition). As an example of such a non-uniform command sequence, all the focal spots of the distributed X-ray source are activated one after another (A1 → C20), and then the inner focal spot 66 (A6 → A15, B6 → B15, C6 → C15). Only one after the other and repeating each of these instruction sequences. Thus, in this example, the inner focal spot 66 is activated twice as often as the outer focal spot 64. In another example, some focal spots may not be activated at all. For example, in an implementation that focuses only on a small part of the patient or object, only the inner focal spot 66 need be activated (A6 → A15, B6 → B15, C6 → C15). As will be appreciated, different focal spots or different subsets of focal spots fire (or do not ignite) focal spots that are activated more frequently or less frequently than other focal spots or subsets of focal spots. ) Other combinations may be used.

  In another embodiment, two or more focal spots may be activated simultaneously. Such an embodiment may be useful when focal spots that are activated simultaneously generate X-rays that are incident on different parts of the detector 22 or on different detectors 22. For example, the focal spots associated with rows A and C are such that each row of focal spots has a detector such that little or no overlap occurs in detector 22 when the focal spots of rows A and C are activated simultaneously. It can be collimated in the z direction to ignite in 22 different longitudinal portions. In this example, the focal spots in rows A and C can be activated simultaneously according to a command sequence such as A1C1-B1-A2C2-B2-A3C3-B3-... -A20C20-B20-A1C1-B1-.

  In implementations using more than one detector 22 as shown in FIG. 4, the focal spot may be collimated so that it is detected by only one of the available detectors 22. In such an implementation, a focal spot collimated to illuminate one detector 22 may be activated simultaneously with a focal spot collimated to illuminate a different detector 22. By using two or more small detectors in this manner, the resulting increase in scatter can be managed and mitigated in a manner that is adaptively configured for the anatomy or object being scanned. A large bundle of single large area detectors can be achieved.

  In such an embodiment using simultaneous activation of focal spots, additional cross-scatter can be generated. Thus, the decision as to whether or not to simultaneously activate the focal spot is based on the object being imaged, the predicted path length through the object for each focal spot (in general, the larger the path length, the greater the potential for scattering Position of each focal spot (optionally to avoid simultaneously launching a focal spot having X-rays incident on one detector or multiple detectors too close to each other) , Based on the detectable signal predicted for each focal spot (to optionally avoid simultaneously activating a focal spot having a large difference in the predicted detectable signal). In some embodiments, the focal spot may be selected for simultaneous activation such that the predicted path length is substantially equivalent. If there is a substantial difference in path length, have a small path length (and therefore less attenuation) to equalize the received primary flux and reduce cross-scatter incident on the detector that receives less signal The focal spot may be activated by a small mA.

  Further, in some embodiments, in a given “sample period” or activation interval, one focal spot is activated over some portion of the period and the other focal spots overlap in time with the initial period. It can be activated for different periods that may or may not be present, i.e. each focal spot may have a complementary integration time. To the extent that net cross scatter exists, cross scatter can be measured directly by turning on the source from time to time rather than simultaneously with others.

  In addition, in some embodiments, a sequence of instructions that mitigate motion artifacts can be constructed. For example, in coronary vessels that move in the xy plane along the y-axis in most cases, the focal point aligned with the direction of motion observes minimal motion. Thus, by increasing either the frequency of activation or the integration time, the motion sequence artifacts in the reconstructed image are minimized by using a sequence of instructions that focuses on the activation of the focus aligned with the moving structure. Can do.

  Further, in some embodiments, different sized or scaled focal spots can be used so that different sized focal spots are more suitable for imaging different sized structures. For example, an embodiment of the heart can use a command sequence that focuses on the activation of a small focal spot that covers a small structure in a region of interest such as a coronary blood vessel.

  In general, in terms of the order in which the individual focal spots can be activated, in terms of whether the focal spots are activated simultaneously, in terms of absolute mA associated with the individual focal spots, in relation to the focal spots activated simultaneously There is flexibility in terms of relative mA and the complementary integration time provided for each focal spot. Alternatively, these various factors assume that no confusion can occur at the detector or readout level as to which focal spot the detected x-rays originate from, i.e. the detector (s). As long as there is no overlap in, it may vary at individual focal spot levels or for some or all of the focal spots. Indeed, in some embodiments, an exhaustive evaluation of possible subsequences or sequences can be performed, and a command sequence that provides the desired tradeoff between sampling, dose efficiency, scatter, image noise, temporal resolution and spatial resolution. Is selected.

  In addition to the focus non-uniform instruction sequence, other instruction sequences suitable for addressing the cardiac half-scan / over-scan problem may be used. In conventional third generation CT systems, the “half scan” consists of a 180 ° + α rotation section, where α is the fan angle, which may be the physical fan angle of the X-ray beam. However, the fan angle corresponding to the visual field of interest may be used. The data set obtained in a half-rotation scan is typically rebinned to correspond to the set acquired by the parallel beam, or reconstructed as is using Parker's weighting scheme. Extra rotation across the fan angle results in an additional dose to the patient or object being scanned compared to parallel beam acquisition. For example, referring to FIG. 15, a prior art diagram showing useful projection data 80 and useless dose 82 acquired using a half-scan acquisition scheme is shown, where r is the ray distance to the isocenter. , Θ is expressed in r-θ coordinates with the angle of the ray with respect to the vertical axis.

  Using a distributed X-ray source and a suitable activation scheme as discussed herein can reduce the wasted dose associated with half-scan acquisition. For example, in one embodiment, the working focal spot or emission range is such that the focal spot is 180 ° parallel beam range (or 90 ° for a dual detector implementation, and for a triple detector implementation). 60 °, etc.) can be gradually enlarged. As the X-ray source rotates out of the parallel beam range of interest, the focal spot can be progressively deactivated. Referring to FIG. 16, there is shown an r-θ coordinate diagram illustrating useful data and wasted dose associated with this approach. As can be seen in FIGS. 15 and 16, the wasted dose associated with this example technique is reduced relative to the conventional half-scan acquisition technique.

  Similarly, in the helical scan mode, some X-ray dose may be wasted at the end of the helix. When the spatial arrangement of the distributed source is controlled by an activation scheme that gradually activates and deactivates the focal spot, it avoids such a useless dose as the focal spot enters and exits the longitudinal region of interest. Can be (along z for x). In this manner, the helical overscan problem can be addressed.

  In addition, the instructions stored in the sequence buffer may include respective X-ray pulses and so that the corresponding measurements are well aligned in r-theta space (Radon space) for efficient data reordering or image reconstruction. The timing of detector readout can be optimized.

  When the instruction sequence stored in the sequence buffer 32 is implemented, external information such as an ECG sequence may be taken into consideration. For example, in prospective cardiac synchronization acquisition, the ECG signal can be used to determine when the heart is in the desired time phase for imaging. In such an embodiment, the gantry angle dependency may be imparted to the sequence, such as when the virtual bowtie filter is embodied as part of the command sequence. Thus, in such an embodiment, X-rays may not be generated halfway through the buffer, i.e., the sequence buffer instruction is such that any instruction cannot be embodied until the desired condition is first met. Conditions for position and ECG trigger can be imposed. Similarly, the related embodiments provide a set of instructions using a stored sequence of “JUMP” or “GOTO” instructions once it is determined that the ECG trigger and / or gantry position is appropriate. Can proceed to execute.

  Alternatively, a similar approach can be implemented in the form of an indication to the DAS stored in the sequence buffer 32. For example, sequence buffer instructions can operate in a loop mode and can be passed through without executing until the desired gantry angle and / or ECG trigger occurs. At this time, that is, when the acquisition condition is satisfied, an “exposure” command can be issued, and when the next superview starts, the logic stored in the series buffer starts normal execution.

  As described above, the instruction or instruction stored as the instruction sequence may be related to the operation of the distributed X-ray source and the control of the X-ray controller 30 or may be related to the operation of the DAS 36. . For example, a scheduled adjustment of data acquisition can be provided as part of the list of instructions for the sequence buffer. In one example, when the flux is low, there may be a benefit of electronic noise for longer sub-views (DAS sampling interval). Thus, when a sequence buffer instruction to the X-ray controller 30 produces a low flux, the corresponding instruction can be placed in the sequence buffer to extend the sampling period of the DAS 36 over the duration of the low flux. Similarly, when double kVp scanning is being executed, an instruction to switch kV can be stored in the series buffer 32.

  The technical effects of the present invention include the use of two or more discrete emission points and one or more corresponding detectors to image the field of view. The operation of two or more discrete emission points may be independent of each other. The operation of each emission point and / or the reading of the detector can be carried out according to the instructions stored in the sequence buffer.

  This written description discloses the invention, including the best mode, and any person skilled in the art can make and use the invention, including making and using any device or system and performing any incorporated methods. Use examples to make it possible. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. If such other examples have structural elements that do not differ from the written language of the claims, or include equivalent structural elements that are only slightly different from the written language of the claims, Be within range.

DESCRIPTION OF SYMBOLS 10 Imaging system 12 X-ray source 14 Collimator 16 Radiation flow 18 Patient 20 Radiation attenuation part 22 Detector 24 System controller 26 Rotation subsystem 28 Linear arrangement subsystem 30 X-ray controller 32 Sequence buffer 34 Motor controller 36 Data Acquisition system (DAS)
38 Computer 40 Memory 42 Operator workstation 44 Display 46 Printer 48 PACS
60 Flat Panel Detector 64 Outer Focus Spot 66 Inner Focus Spot 70 Emission Point 72 Field of View 74 First Emission Point 76 Second Emission Point 80 Center Area of Interest 82 Peripheral Area 86 Third Emission Point 88 Fourth Emission Point 94, 96, 98 Release point 100 CT scanner

Claims (9)

A plurality of discrete X-ray emission focal spots (70);
One or more detectors (22) configured to detect X-rays (16, 20) emitted by the plurality of X-ray emission focal spots (70);
An X-ray controller (30) configured to operate the plurality of discrete X-ray emission focal spots (70) independently;
A data acquisition system (36) configured to read signals from the one or more detectors (22);
A computed tomography (CT) imaging system (10) comprising a sequence buffer (32) configured to store a list of instructions for controlling operation of the x-ray controller (30).   The CT imaging system (10) of claim 1, wherein the sequence buffer (32) is further configured to store a list of second instructions that control operation of the data acquisition system (36). .   The second list of instructions includes one or more instructions that instruct the data acquisition system (36) to adjust the sampling period, to start reading data, or to stop reading data. A CT imaging system (10) according to claim 2.   The CT imaging system (10) of claim 1, wherein the plurality of discrete x-ray emission focal spots (70) are part of a distributed x-ray source (12).   The list of instructions is sent to the X-ray controller (30) at a predetermined interval from a trigger at a predetermined time, in a predetermined sequence, at a predetermined mA, for a predetermined duration, at a predetermined focal spot size. A CT imaging system (10) according to claim 1 including one or more instructions that direct to activate each X-ray emission focal spot at a predetermined energy or at a predetermined kVp. ).   The CT imaging system (10) of claim 1, wherein each instruction in the list of instructions corresponds to operation of an x-ray emission focal spot in a respective view.   The CT imaging system (10) of claim 1, wherein each x-ray emission from the plurality of discrete x-ray emission focal spots (70) is defined by a different instruction in the list of instructions. Providing a distributed x-ray source (12) comprising a plurality of discrete and separately operable x-ray emission focal spots (70);
Providing one or more detectors (22) configured to generate signals in response to X-rays (16, 20) emitted by the distributed X-ray source (12);
Providing a sequence buffer (32) capable of storing a list of instructions for operating the plurality of X-ray emission focal spots (70);
Electrically connecting an X-ray controller (30) to the distributed X-ray source (12) and the sequence buffer (32), the X-ray controller (30) being in accordance with the list of instructions Electrically connecting a plurality of X-ray emitting focal spots (70) independently operable;
Electrically connecting a data acquisition system (36) to the one or more detectors (22), the data acquisition system (36) being generated by the one or more detectors (22); Electrically connecting the signal, wherein the signal can be read out.   The method of claim 8, wherein the data acquisition system (36) operates according to the list of instructions.

Images