Control of computed tomography procedures

Abstract

A mechanism for controlling the operation of a CT scanner during a scanning procedure is provided. The radiation output system is configured to output radiation during an imaging phase of the scanning procedure. A subject support of the CT scanner is controlled to move linearly during the imaging phase, e.g. according to a predefined linear pattern. The linear movement of the subject support includes at least one acceleration and / or deceleration phase. At least a beam width of the radiation output from the CT scanner is controlled as a function of the velocity of the subject support throughout the imaging phase.

Description

[Technical Field]

[0001] The present invention relates to the field of medical imaging, and in particular to the field of computed tomography imaging. [Background technology]

[0002] Computed tomography (CT) scanners are common instruments in modern medical imaging. CT scanners are generally made up of a stationary portion and a rotating portion. The rotating portion supports a radiation output system, such as an x-ray tube, and a radiation measurement system opposite the radiation output system, which generates raw data that can be used to reconstruct a CT image. A subject support supports an object / subject within an examination region as the rotating portion rotates around the object / subject. The subject support moves linearly during the scanning procedure, facilitating imaging of various cross-sections of the supported subject / object.

[0003] One operating mode of a CT scanner is the helical or spiral mode, in which the subject support is accelerated to move at a predetermined (and constant) velocity relative to the rotational speed of the gantry to acquire the raw data needed to reconstruct a CT image.

[0004] This relationship between the subject support movement speed (V) and the gantry rotation speed is defined by the CT scan pitch, which is the distance the support moves during one 360° (2π) rotation of the gantry divided by the total thickness of all slices acquired simultaneously during that rotation. Summary of the Invention [Problem to be solved by the invention]

[0005] When performing a helical / spiral mode scan (or simply a "helical CT scan"), there is a period during which the subject support is accelerated or decelerated, for example, to reach a predetermined speed or to reach a stop after moving at a predetermined speed. Traditionally, no imaging is performed during this acceleration / deceleration phase, and therefore, a portion of the subject / object that could theoretically be imaged is not actually imaged. In current CT scanners, an overscan region is added before the predetermined scan region and another overscan region is added after the predetermined scan region to reconstruct a helical scan image. The addition of the pre-region and post-region increases the area to which the subject is exposed to X-ray radiation. Furthermore, in current CT scanners, the X-ray tube is turned on before raw data collection begins while the collimator is open to ensure the tube is stable when data collection begins, which also results in extra radiation to the subject being scanned. [Means for solving the problem]

[0006] The invention is defined by the claims.

[0007] According to an example in accordance with one aspect of the present invention, a computer-implemented method is provided for operating a computed tomography scanner comprising a subject support configured to move linearly and a rotating portion carrying a radiation output system and controllably rotating around the subject support.

[0008] The computer-implemented method includes steps of performing a scanning procedure, the scanning procedure including steps of controlling a radiation output system to output radiation during / throughout an imaging phase of the scanning procedure, controlling a subject support to move linearly, wherein the linear movement of the subject support during / throughout the imaging phase of the scanning procedure includes at least one acceleration or deceleration phase, and controlling one or more parameters of a computed tomography scanner in response to the velocity of the subject support, wherein the one or more parameters include at least the beam width of the radiation output from the radiation output system.

[0009] The present disclosure therefore provides a mechanism for controlling the operation of a CT scanner, for example, during a helical scanning procedure, in which the rotating portion rotates as the subject support moves linearly during the helical scanning procedure.

[0010] The present invention proposes controlling the beam width of the radiation delivered by the radiation output system from the collimator depending on the speed of the (linearly moving) subject support. This facilitates control over the amount of radiation (dose) exposed to / on a subject positioned on the subject support. In particular, it will be appreciated that appropriate control over this property of the radiation facilitates delivery of a constant dose of radiation to all parts of a subject positioned on the subject support.

[0011] Conceptually, a predetermined image region can be divided into one or more acceleration, constant velocity, and deceleration regions, the sum of which equals the total predetermined image region. By controlling the beam width in response to the velocity of the patient support table, imaging can be performed during each of these regions without the need for additional pre-scan and post-scan regions above the predetermined image region. The beam width is preferably controlled so that the dose delivered to the subject remains constant throughout these regions.

[0012] Those skilled in the art will understand that a CT scanner may comprise several other functions or elements, such as a radiation measurement system, a control panel, a console, etc. These are well-known elements of a standard CT scanner and are not specified in the claim set for the sake of brevity.

[0013] Controlling one or more parameters of the computed tomography scanner in response to the velocity of the subject support optionally comprises controlling the beam width in proportion to the velocity of the subject support.

[0014] The radiation output from the radiation output system is radiation incident within the examination region, e.g., radiation that will interact with the subject support. Specifically, the radiation output from the radiation output system will interact with the subject support if the patient / subject occupies the entire surface of the subject support.

[0015] In some examples, the radiation output system includes a radiation source configured to generate radiation and a collimator configured to control a beam width of the radiation generated by the radiation source, and controlling one or more parameters of the computed tomography scanner includes controlling the beam width by controlling operation of the collimator.

[0016] The use of a collimator to control the beam width provides a highly accurate and precise mechanism for controlling the beam width of the radiation output from the radiation output system, facilitating direct control over the area of ​​radiation incident on a subject positioned on a subject support.

[0017] The collimator comprises a collimator opening with a controllable width, and controlling the beam width comprises controlling the width of the collimator opening in response to a velocity of the subject support.

[0018] In some examples, the width of the collimator opening is defined by the distance between a front blade and a rear blade aligned in the direction of movement of the subject support, and controlling the width of the collimator opening includes controlling the distance between the front blade and the rear blade.

[0019] Controlling one or more parameters of the computed tomography scanner, in at least one embodiment, comprises setting and maintaining the beam width equal to zero until the radiation generated by the radiation source is stable. In other words, the beam width is set to and maintained at zero while the radiation source is powered on and / or stabilizing. Controlling the radiation output system to output radiation therefore comprises controlling the radiation source to start generating radiation (while maintaining the beam width at zero, i.e., closing the collimator, by controlling the parameters). Once the radiation source is stable, the beam width can be made greater than zero (i.e., the collimator can be opened) in order to acquire raw data.

[0020] In some examples, the subject support does not begin to move until the radiation source has stabilized and the beam width can be made greater than 0. Controlling the subject support to move linearly therefore includes controlling the subject support to move linearly only after the radiation source has stabilized.

[0021] Mechanisms for identifying when the radiation source has stabilized will be readily apparent to those skilled in the art, for example, by waiting a predetermined period of time (e.g., according to a known time for the radiation source to stabilize) after powering the radiation source.

[0022] The present invention facilitates control over beam width during source stabilization of a scanning procedure. The proposed technique of maintaining the beam width at zero until the radiation source is stabilized reduces (unnecessary) radiation exposure or dosage to a subject positioned on a subject support. Specifically, during source stabilization, the beam width will be kept at zero and no imaging (i.e., measurement of output radiation) will occur.

[0023] In some examples, controlling one or more parameters of the computed tomography scanner includes controlling one or more parameters such that the total radiation dose per volume of the subject positioned on the subject support remains approximately constant throughout the scanning procedure.

[0024] Controlling one or more parameters of the computed tomography scanner optionally comprises controlling one or more parameters of the computed tomography scanner such that the CT scan pitch is constant throughout the scanning procedure.

[0025] In at least one embodiment, controlling one or more parameters of the computed tomography scanner includes controlling the beam width to be equal to the product of the speed of the subject support and the time it takes for the rotating part to perform a 2π rotation, divided by the desired CT scan pitch.

[0026] The one or more parameters of the computed tomography scanner further include an intensity of radiation output from a radiation output system, which in some examples comprises an x-ray tube, and controlling the amount of radiation intensity output from the radiation output system comprises controlling an emission current supplied to the x-ray tube.

[0027] The one or more parameters of the computed tomography scanner further include a rotational speed of a rotating part of the computed tomography scanner.

[0028] Controlling the subject support to move linearly may include controlling the subject support to perform linear movement that includes a single acceleration phase and / or a single deceleration phase.

[0029] The scanning procedure includes a step of using a radiation measurement system mounted on the rotating part (during / throughout the imaging phase of the scanning procedure) to obtain raw signal data corresponding to the absorption of radiation output from the radiation output system by a subject positioned on the subject support.

[0030] It is also proposed a computer program product comprising computer program code means which, when executed on a computing device comprising a processing system, causes the processing system to perform all the steps of any of the methods described herein. The computer program product is formed on a (non-transitory) computer readable medium.

[0031] A processing system configured to operate a computed tomography scanner has also been proposed, the processing system being configured to control a scanning procedure comprising: a subject support configured to move linearly; and a rotating part carrying a radiation output system and controllably rotating around the subject support; the processing system being configured to control a scanning procedure comprising: a step of controlling the radiation output system to output radiation during / throughout the imaging phase of the scanning procedure; a step of controlling the subject support to move linearly, wherein the linear movement of the subject support during / throughout the imaging phase of the scanning procedure includes at least one acceleration or deceleration phase; and a step of controlling one or more parameters of the computed tomography scanner depending on the speed of the subject support, the one or more parameters including at least the beam width of the radiation output from the radiation output system.

[0032] An image generation system has also been proposed, comprising a processing system and an image reconstruction system configured to process projection data generated by a radiation measurement system of a computed tomography scanner to reconstruct one or more 2D and / or 3D images.

[0033] An imaging system has also been proposed that includes a projection system or image generation system, a subject support configured to move linearly, and a computed tomography scanner having a rotating portion carrying the radiation output system and controllably rotating around the subject support, The computed tomography scanner further includes a radiation measurement system configured to generate projection data in response to radiation incident on the radiation measurement system.

[0034] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0035] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 illustrates a computed tomography scanner system. [Figure 2] FIG. 1 illustrates a method according to one embodiment. [Figure 3] 10A-10C illustrate exemplary movements of a subject support during the imaging phase of a scanning procedure, as used in one embodiment. [Figure 4] FIG. 1 illustrates a radiation output system. [Figure 5] FIG. 10 is a diagram showing the relationship between the difference in beam edge and the rotation of the rotating part. [Figure 6] FIG. 1 illustrates a method according to one embodiment. [Figure 7] FIG. 1 illustrates a processing system according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention will be described with reference to the drawings.

[0038] It should be understood that the detailed description and specific examples, while indicating representative embodiments of the devices, systems, and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will be better understood from the following description, the appended claims, and the accompanying drawings. It should be understood that the figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to indicate the same or similar parts.

[0039] The present invention provides a mechanism for controlling the operation of a CT scanner during a scanning procedure. A radiation output system is configured to output radiation during an imaging phase of the scanning procedure. A subject support (patient support table) of the CT scanner is controlled to move linearly during the imaging phase, for example, according to a predetermined linear pattern. The linear movement includes at least one acceleration and / or deceleration phase. At least the beam width of the radiation output from the CT scanner is controlled in response to the velocity of the subject support throughout the imaging phase.

[0040] Embodiments are based on the recognition that controlling the beam width can control the CT scan pitch and / or the exposure per unit volume of the examination region. This facilitates maintaining a constant pitch or exposure per unit volume, or maintaining the pitch or exposure per unit volume below some predefined threshold, in order to control the radiation exposure of the subject. This allows the imaging phase of the scanning procedure to include periods of acceleration and / or deceleration of the subject support, thereby increasing the size of the region available for imaging.

[0041] Embodiments may be used with any suitable CT scanning system, which may be used in a wide variety of industries, such as the medical, anthropological, and / or archaeological industries.

[0042] 1 illustrates a schematic representation of a computed tomography scanner system 100 comprising a computed tomography scanner. The computed tomography scanner 102 generally comprises a stationary portion 104 and a rotating portion 106 rotatably supported by the stationary portion 104 and configured to rotate about a z-axis around an examination region 108. A subject support 110, such as a couch, supports an object or subject (e.g., a patient) within the examination region 108.

[0043] The radiation output system 112 includes a radiation source (such as an X-ray tube) and a collimator, is rotatably supported by the rotating portion 106 , rotates with the rotating portion 106 , and outputs radiation that traverses the examination region 108 .

[0044] A radiation measurement system 114, e.g., a radiation sensitive detector array, spans an angled arc across the examination region 108 on the opposite side of the radiation source 112. The radiation measurement system ("radiation detector") detects radiation traversing the examination region 108 and generates electrical signals (projection data) indicative of the traversing radiation.

[0045] The radiation measurement system 114 can include single-layer detectors, direct conversion photon counting detectors, and / or multi-layer detectors. Direct conversion photon counting detectors include a conversion material such as CdTe, CdZnTe, Si, Ge, GaAs, or other direct conversion materials. Examples of multi-layer detectors include double-decker detectors, such as the double-decker detector described in U.S. Patent No. 7,968,853 B2, filed April 10, 2006, entitled "Double-Decker Detector for Spectral CT."

[0046] The reconstructor 116 receives the projection data from the radiation measurement system 114 and reconstructs one or more CT images from the projection data. The reconstructed CT images may include one or more 2D or 3D images. Mechanisms for reconstructing one or more CT images from the projection data are well established in the art.

[0047] The processing system 118 is configured to control the operation of the computed tomography scanner, and in particular to control the operation of the computed tomography scanner during a scanning procedure. Techniques for controlling the operation of the computed tomography scanner, according to embodiments, form the subject of this disclosure.

[0048] The processing system 118 controls the subject support 110 to move linearly along the Z-axis during the scanning procedure. The processing system 118 also controls the rotating portion 106 to rotate around the examination region 108 and the radiation output system 112 to output radiation to the examination region. The radiation measurement system 114, as previously described, collects radiation traversing the examination region and generates projection data (e.g., electrical signals) indicative of the radiation traversing the examination region. The reconstructor 116 then reconstructs a CT image from the projection data.

[0049] The processing system 118 comprises a processor 120 (e.g., a microprocessor, controller, central processing unit, etc.) and a computer-readable storage medium 122, which includes transitory media such as physical memory devices but not non-transitory media.

[0050] The computer-readable storage medium 122 includes instructions 124 for controlling the operation of the computed tomography scanner. The processor 120 is configured to execute the instructions 124. The processor 120 is further configured to execute one or more computer-readable instructions carried by a carrier wave, signal, and / or other transitory medium. However, the processor is not the processor 120 that executes instructions to perform the methods described herein; instead, the processor may include fixed-function circuitry (e.g., a suitably programmed field-programmable gate array (FPGA) or the like) for performing the methods described.

[0051] The processing system also functions as an operator console in some examples. The processing system 118 includes a human-readable output device, such as a monitor, and input devices, such as a keyboard, mouse, etc. Software resident on the processing system 118 allows an operator to interact with and / or operate the scanner 102 via a graphical user interface (GUI) or otherwise.

[0052] The processing system 118 is configured to process the CT images produced by the computed tomography scanner 102, including, for example, controlling a user interface that displays or provides a visual representation of the reconstructed CT images.

[0053] As previously mentioned, this disclosure proposes techniques for controlling the operation of the computed tomography scanner 102. Specifically, this disclosure proposes techniques for controlling the operation of the computed tomography scanner during a scanning procedure. These techniques are executed by the processing system 118.

[0054] 2 is a flow diagram illustrating a computer-implemented method 200 according to one embodiment. The computer-implemented method is performed by the processing system 118 of FIG.

[0055] Method 200 is a method of operating a computed tomography (CT) scanner comprising a subject support configured to move linearly and a rotating portion (carrying a radiation output system) that controllably rotates around the subject support. The CT scanner further comprises a radiation measurement system configured to detect radiation output from the radiation output system (which is at least partially absorbed by a subject positioned on the subject support).

[0056] Method 200 includes a scanning procedure that is a helical scanning procedure. The scanning procedure can generally be divided into an "imaging phase" (during which image data, e.g., projection data used to reconstruct one or more 2D and / or 3D images, is generated) and a "non-imaging phase" (during which image data, e.g., projection data used to reconstruct one or more 2D and / or 3D images, is not generated). In a helical scanning procedure, the rotating part rotates as the subject support moves linearly (so that, for example, the radiation output element and / or radiation measurement system appear to move helically relative to the subject support).

[0057] The steps of performing a scanning procedure are well known in the art and, for the sake of brevity, include additional steps not explicitly described in this disclosure, including, but not limited to, steps previously described with reference to FIG. 1 , such as using a radiation measurement system to detect radiation output from a radiation output system and / or reconstructing an image from projection data generated by the radiation measurement system.

[0058] The method 200 comprises controlling 210 a radiation output system to output radiation during the imaging phase of the scanning procedure. The radiation output system specifically outputs non-zero radiation (to the examination region) throughout the imaging phase. Methods for controlling a radiation output system to output radiation are well known and will be readily apparent to those skilled in the art, for example by supplying current to an X-ray tube or the like.

[0059] The imaging stage, as previously explained, is the stage in which radiation detected by a radiation measurement system of the CT scanner contributes to the generation of image data produced by the CT scanner, e.g., one or more (2D or 3D) CT images. Thus, the scanning procedure (e.g., part of step 210) further comprises the step of controlling a radiation measurement system to detect radiation output from the radiation output system.

[0060] The method 200 includes controlling 220 the linear motion of the subject support such that the imaging phase of the computed tomography scanner includes at least one acceleration and / or deceleration phase.

[0061] The linear motion may therefore be controlled to have a single acceleration phase and / or a single deceleration phase. In other instances, the linear motion may be controlled to have multiple acceleration phases and / or multiple deceleration phases. In some instances, the number of acceleration phases and the number of deceleration phases are equal. This equal number of acceleration phases and deceleration phases approach increases the overall size of the imaging area, as explained below.

[0062] The linear motion of the subject support is therefore controlled according to a predetermined linear motion pattern that defines the speed and direction of the linear motion. One example of a linear motion pattern includes (i.e., consists of) an acceleration phase, a steady-state phase, and a deceleration phase. However, other examples include multiple distinct acceleration phases, steady-state phases, and / or deceleration phases. One linear motion pattern, for example, has X acceleration phases, Y steady-state phases, and Z deceleration phases, where, for example, X=Z and Y=X-1.

[0063] It will be appreciated that the linear position of the subject support defines the area or volume of the examination region that is illuminated by the radiation output system (when the radiation output system is outputting radiation), and thus defines the region of the examination region that is imaged (by detecting the emitted radiation). Thus, there is a total imaging region, which is the total region that is illuminated and imaged during the scanning procedure.

[0064] Figure 3 shows an example of a linear motion pattern 301 of a subject support. Specifically, Figure 3 shows the position (z) and velocity (v) of the subject support according to the linear motion pattern. Figure 3 also shows a subject 305 positioned on a subject support 310, and illustrates how the velocity of the subject support may change relative to the current position (of the rotating part) relative to the subject support.

[0065] The linear motion pattern begins with an acceleration phase t a , steady-state stage t ss , and the deceleration phase t d The velocity of the subject support is determined by an acceleration step t from time t0 to time t1. a to the maximum speed v (from 0) max The velocity of the subject support increases from time t1 to time t2 during the steady-state phase t ss , the maximum speed v max The velocity of the subject support decreases to 0 during the deceleration phase from time t2 to time t3.

[0066] maximum speed vmax is not necessarily the maximum possible velocity of the subject support, but the maximum velocity of its linear motion pattern. max is defined by the clinician, for example by providing user input, and will be limited by the maximum possible speed of the subject support.

[0067] If the subject support is controlled according to the linear pattern shown in Figure 3, and for linear acceleration (a) and linear deceleration (d), the velocity v(t) of the subject support can be calculated as follows:

number

[0068] 2, the method 200 also includes controlling 230 one or more (other) parameters of the computed tomography scanner in response to the velocity of the subject support, including at least the beam width of the radiation output from the radiation output elements.

[0069] Step 230 therefore comprises at least controlling the beam width of the radiation output from the radiation output element in response to the velocity of the subject support, and is also performed at least throughout the imaging phase.

[0070] Other suitable parameters that may also be controlled in step 230 include the rotational speed of the rotating portion and / or the intensity of the radiation output from the radiation output element (specifically, the intensity of the radiation output from the radiation source of the radiation output element).

[0071] It is to be appreciated herein that during a conventional helical scanning procedure in which the speed of the rotating part is constant, when radiation is output from the radiation output elements during any acceleration and / or deceleration phases of the linear motion of the subject support, the total radiation dose per volume of the examination region during such phases will be greater than the total radiation dose per volume during the steady-state phases, because the slower the subject support moves during the acceleration and / or deceleration phases, the smaller the gap or, in some cases, the (larger) overlap of the areas irradiated during 2π rotations of the rotating part.

[0072] For further explanation, in this disclosure, the "pitch" or CT scan pitch during a helical scanning procedure (of a CT scanner) is defined as the total distance traveled by the subject support (along the z-axis) during 2π rotations of the rotating part, divided by the total thickness (along the z-axis) irradiated (i.e., the beam width of the radiation output from the radiation output system).

[0073] In actual conventional imaging, when a subject is imaged across a subject support movement, the CT scan pitch changes over the course of the scanning procedure due to acceleration and deceleration of the subject support, which affects the relative amount of radiation per volume incident on the examination region and can lead to undesirable radiation dosage to the subject on the subject support.

[0074] To avoid this problem, conventional scanning procedures simply avoid imaging (e.g., avoid or minimize radiation emissions) any acceleration or deceleration phases. This means that the total imaging area is limited to only the area that can be irradiated during the steady-state phase of linear motion of the subject support. In other words, the imaging phase of a conventional scanning procedure does not include either the acceleration or deceleration phases of linear motion of the subject support.

[0075] The present disclosure proposes a different approach where at least the beam width is controlled as a function of the movement speed, which facilitates control of the size of the area / volume to be irradiated and therefore the total radiation dose for each linear movement step.

[0076] By employing the techniques of the present disclosure, the overall size of the imaging region can be effectively increased without affecting the total amount of radiation (per volume of irradiated area). Specifically, the total imaging area can be increased to include areas that can be irradiated during acceleration and / or deceleration phases of linear motion of the subject support.

[0077] In other words, the imaging phase of the scanning procedure is extended to include periods of acceleration / deceleration of the subject support, eg, so that the imaging phase occupies the entire scanning procedure.

[0078] The relationship between pitch P(t), subject support velocity v(t), rotational velocity r(t), and beam width w(t) can be calculated as follows:

number

[0079] The pitch P(t) is dimensionless, the subject support velocity v(t) is in m / sec (or mm / sec), the rotational speed r(t) is in revolutions per second (RPS), and the beamwidth is in m (or mm). The beamwidth is generally the width of the radiation beam at the isocenter of the rotating part. The isocenter is the axis parallel to the z-axis and passing through the center of the circle / cylinder around which the rotating part rotates.

[0080] Therefore, by controlling the beam width in response to changes in the velocity of the subject support, the pitch of the scanning procedure can be controlled. Specifically, by controlling the change in beam width to be proportional to the change in velocity of the subject support, the maximum change in pitch during the acceleration / deceleration phase of the linear motion of the subject support can be reduced.

[0081] In a particular example, step 230 is configured to include controlling only the beam width in response to the velocity of the subject support. Step 230 specifically includes controlling the beam width to maintain a constant pitch P (e.g., determined in advance by user input or according to the scanning procedure). Suitable examples of the desired pitch value P are 0.5, 1, and 2. Other pitch values ​​are possible and known to those skilled in the art. The pitch is maintained at a constant pitch, for example, between 0.5 and 2, e.g., between 0.5 and 1.5.

[0082] In this manner, the step of controlling one or more parameters of the computed tomography scanner includes controlling the beam width to be equal to the product of the speed of the subject support and the time it takes for the rotating part to perform a 2π rotation (at the current speed of the rotating part), divided by the desired (CT scan) pitch.

[0083] This is equivalent to controlling the beam width to be equal to the velocity of the subject support divided by the product of the desired (CT scan) pitch and the velocity of the rotating part of the CT scanner (in revolutions per second).

[0084] By way of example only, suppose the desired pitch value P is 1, the rotational speed r is fixed at 5 revolutions per second, and the maximum speed of the subject support (i.e., the speed of the steady-state phase of linear motion) v max Consider a scenario where the velocity is 400 mm / s and the acceleration a is a constant value of 200 mm / s per second.

[0085] In this scenario, the acceleration phase will be 2 seconds long, with the velocity increasing linearly from 0 to 400 mm / sec. If step 230 includes controlling the beam width to maintain a constant pitch (according to equation (2)), the beam width will also increase linearly from 0 to 80 mm. In this example, it will be apparent that the magnitude of the beam width is therefore controlled to be proportional to the velocity of the subject support.

[0086] In another example, step 230 may comprise controlling a plurality of parameters of the computed tomography scanner, including at least the beam width, the rotation speed of the rotating part, and / or the intensity of the radiation output from the radiation output elements.

[0087] Equation (2) shows how pitch also depends on the time it takes the rotating part to make a rotation, i.e., the rotation speed. By controlling the speed of the rotating part, the time it takes the rotating part to make a rotation can be changed, which provides a further possible controllable variable for controlling the pitch of the scanning procedure.

[0088] In some examples, as the velocity of the subject support varies according to a linear motion pattern, the velocity and beam width of the rotating portion are controlled to maintain a constant pitch P. Suitable methods for determining pitch P, and suitable values ​​for P, have been previously described.

[0089] In some examples, rather than controlling one or more parameters of the computed tomography scanner in response to the velocity of the subject support to maintain a constant pitch (as previously described), one or more parameters are controlled to maintain a constant exposure (i.e., a constant dose) per unit volume of the examination region, which exposure per unit volume of the examination region is functionally equivalent to the total radiation dose per volume of the subject positioned on the subject support.

[0090] The measure of total radiation dose per unit volume, Ir(t), is defined as:

number

[0091] Thus, by controlling the pitch (using the beam width and optionally the rotation speed), and optionally controlling the intensity of the radiation output from the radiation output system, the total dose per unit volume of the examination region can be controlled. In certain examples, the total dose per unit volume of the examination region can be kept constant for different speeds of the subject support.

[0092] The desired value of Ir(t) may be predetermined, for example, according to some medical practice guidelines or clinical / environmental recommendations (such as those set forth in CT scan guidelines). The desired value of Ir(t) may alternatively be selected by a clinician, for example, using the clinician's experience to select a suitable level of Ir(t).

[0093] Step 230 thus, in some embodiments, comprises controlling the beam width and the intensity of the radiation output from the radiation output system or the rotational speed of the rotating portion, or both, such that a hybrid system for delivering a constant dose during a scanning procedure (including acceleration and / or deceleration phases) is used.

[0094] In embodiments in which the pitch is kept constant, the radiation output from the radiation output system is also kept constant (ie, the magnitude of the radiation output from the radiation output system does not need to be changed).

[0095] Of course, it will be appreciated that hardware or software limitations may prevent a constant pitch and / or dosage from being maintained using the previously described techniques, but by controlling the aforementioned parameters to the best of the system's capabilities, variations in pitch and / or dosage may be minimized to reduce the impact on the subject.

[0096] Therefore, rather than attempting to maintain a constant pitch, steps are used to control one or more parameters of the computed tomography scanner (including at least the beam width) to reduce the range of pitch (i.e., reduce pitch variation) and / or reduce the total / average irradiation dose per unit volume of the examination region.

[0097] For completeness, it is noted that other parameters and functions of the scanning procedure are controlled according to well-known CT scanning practices, e.g., controlling sampling rates, operating radiation measurement system functions, etc. This disclosure proposes techniques for modifying some (i.e., not necessarily all) aspects of the scanning procedure.

[0098] Controlling 230 one or more parameters of the computed tomography scanner may, in some examples, include setting and maintaining the beam width equal to zero until the radiation produced by the radiation source stabilizes.

[0099] Thus, step 210 comprises controlling the radiation source to begin emitting radiation, and step 230 comprises controlling the radiation source to maintain the beam width at zero until it stabilizes (i.e., the emitted radiation is approximately constant). This reduces unnecessary exposure to the subject and therefore reduces the radiation dose. Once the radiation source stabilizes, the beam width is controlled according to the techniques previously described, i.e., as a function of the velocity of the subject support.

[0100] Step 220, in some further examples, includes not commencing linear motion of the subject support, i.e., keeping the subject support stationary, until the radiation source has stabilized, thereby ensuring that the size of the imaging area of ​​the subject is maintained or increased.

[0101] Mechanisms for identifying when the radiation source has stabilized will be readily apparent to those skilled in the art, for example, by waiting a predetermined period of time (e.g., according to a known time for the radiation source to stabilize) after powering the radiation source.

[0102] Therefore, it is advantageous to provide a delay between the execution of step 210 and the execution of steps 220 and 230 to allow the radiation source to stabilize (during which time the beam width is maintained, i.e., kept, at zero or near zero).

[0103] In the previous embodiments, we have described how the beam width is controlled depending on the velocity of the subject support during the scanning procedure. One way to control the beam width is to control the operation of the radiation output system.

[0104] In particular, when the radiation output system comprises a radiation source and a collimator, the operation of the collimator is controlled to define the beam width, e.g., by controlling the size of the collimator opening, the beam width, e.g., the width of the collimator opening, is controlled.

[0105] FIG. 4 illustrates an example of a radiation output system 400 for use in one embodiment of the present invention.

[0106] The radiation output system 400 includes a radiation source 410 (e.g., an X-ray source such as an X-ray tube) that outputs a beam of radiation X, and a collimator 420. The collimator 420 is formed by a front blade 421 and a rear blade 422. The front blade 421 and the rear blade 422 are aligned in the direction of movement of the subject support (i.e., along the Z axis). Specifically, during positive movement of the subject support, the front blade leads the rear blade, i.e., is located in front of the rear blade. The collimator opening 423 is a gap formed between the front blade 421 and the rear blade 422. All radiation output from the radiation source 410 that strikes the front or rear blade (i.e., does not enter the collimator opening) is blocked (not shown for clarity). The positions of the front blade 421 and the rear blade 422 can be individually controlled to control the size of the collimator opening (and therefore the size of the beam width).

[0107] The size C of the collimator opening 423 at time t can be calculated using the following formula:

number

[0108] The positions of the leading and trailing blade edges are determined by the position Z of the center of the X-ray beam during the scanning procedure. X The collimator edge position (Z cf ) is Z X(t) + 0.5C(t). The collimator edge position (Z cr ) is Z X (t) - 0.5C(t).

[0109] In one scenario, the linear motion of the support stage follows a linear motion pattern that is a series of acceleration (constant acceleration), steady-state, and deceleration (constant deceleration) stages. In this scenario, the position of the center Z of the X-ray beam (along the z-axis) relative to the starting point of the subject support position (along the z-axis) at any time t is X (t) can be defined as follows:

number

[0110] Other techniques for determining the position of the center of the X-ray beam will be apparent to those skilled in the art, depending, for example, on the linear motion pattern used in moving the subject support. Specifically, those skilled in the art can determine the position Z of the center of the X-ray beam versus time. X Various equations of motion (such as those shown in equation (5)) could be easily combined to predict or determine (t).

[0111] Figure 5 shows the acceleration phase t a and steady-state stage t ss1 shows an exemplary beam edge difference (BED) versus rotation angle (R) at the transition from 0 to 1, where only the collimator aperture size is controlled to maintain a constant pitch of 1. The vertical dashed lines represent the completion of one full rotation (i.e., there is a difference of 2π radians between each vertical dashed line).

[0112] The beam edge difference BED is the difference between the instantaneous position of the leading beam edge (i.e., after the rotating portion has rotated N radians) and the instantaneous position of the trailing beam edge at the same rotation angle in the next full rotation (i.e., after the rotating portion has rotated N+2π radians). The beam edge difference BED therefore effectively represents the degree of overlap of the rotating portion between a first beam after N rotations and a second beam after N+1 rotations.

[0113] Final rotation R in the acceleration phase LA , there is a non-zero BED and the collimator aperture size is still increasing during this last rotation, but FSS It can be seen that the BED remains constant (first rotation in the steady state phase). Note, however, that the BED is small compared to the size of the collimator aperture and can therefore be considered negligible.

[0114] A similar BED can be seen at the trailing edge of the beam in the first rotation. Ideally, the trailing edge of the beam should be at position 0 in the first rotation, but in reality it is slightly different (≤1.0 mm) from 0. This is due to potential errors when using a moving blade to match a fixed position relative to the starting edge.

[0115] If necessary, a non-zero BED can be compensated for. To compensate for the initially identified non-zero BED (shown in Figure 5), the leading edge of the beam for the last rotation in the acceleration phase can be set to the corresponding trailing edge of the beam for the first rotation in the steady-state phase.

[0116] To compensate for the second specified non-zero BED (not shown), the position of the trailing beam edge in the first rotation can be set to zero.

[0117] FIG. 6 illustrates a method 600 according to one embodiment.

[0118] Method 600 includes method 200 (previously described) as well as step 610 of using a radiation measurement system mounted on the rotating part to obtain raw signal data (i.e., projection data) corresponding to the absorption of radiation output from the radiation output system by a subject positioned on a subject support.

[0119] A typical radiation measurement system is formed of an array of individual radiation detector elements, each of which contributes to the raw signal data generated by the radiation measurement system, arranged in a grid of rows and columns (aligned in the z-axis direction, i.e., the direction of movement of the subject support).

[0120] The method further comprises processing 620 the raw signal data (projection data) to reconstruct one or more CT images from the raw signal data, including one or more 2D CT images and / or one or more 3D CT images.

[0121] The mechanisms for obtaining raw signal data (projection data) and reconstructing CT images from the raw signal data are well known in the art.

[0122] The process of performing steps 610 and 620 typically involves repeatedly sampling the radiation dose incident on the radiation measurement system.

[0123] 7 further illustrates an example processor system 700 within which one or more components of the embodiments may be used. Processing system 700 provides an example of processing system 118, as described with reference to FIG.

[0124] The various operations discussed above utilize the capabilities of processor system 700. For example, one or more parts of the mechanisms for controlling the operation of a computed tomography scanner may be incorporated into any of the elements, modules, applications, and / or components discussed herein. In this regard, it should be understood that the functional blocks of the system may be executed on a single computer or may be distributed across multiple computers and locations (e.g., connected via Ethernet and / or fieldbus or the Internet).

[0125] The processor system 700 may include, but is not limited to, a PC, a workstation, a laptop, a PDA, a palm device, a server, a storage device, etc. From a hardware architecture perspective, the processor system 700 generally comprises one or more processors 701, a memory 702, and one or more I / O devices 707 communicatively coupled via an internal interface (not shown). The internal interface may be, for example, but not limited to, one or more buses or other wired or wireless connections known in the art. The internal interface may comprise additional elements such as controllers, buffers (caches), drivers, repeaters, and receivers to enable communication. The internal interface may further comprise address, control, and / or data connections to enable appropriate communication between the aforementioned components.

[0126] Processor 701 is a hardware device that executes software that may be stored in memory 702. Processor 701 may in fact be any custom or commercially available processor, central processing unit (CPU), digital signal processor (DSP), or co-processor among multiple processors associated with processor system 700. Processor 701 may also be a semiconductor-based microprocessor (in the form of a microchip) or microprocessor.

[0127] The memory 702 may include any one or combination of volatile memory elements (e.g., random access memory (RAM), such as dynamic random access memory (DRAM), static random access memory (SRAM)), and non-volatile memory elements (e.g., ROM, erasable programmable read-only memory (EPROM), electronically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), tape, compact disc read-only memory (CD-ROM), disk, diskette, cartridge, cassette, etc.). The memory 702 may further incorporate electronic, magnetic, optical, and / or other types of storage media. It should be noted that the memory 702 may have a distributed architecture in which various components are located remotely from each other but are accessible by the processor 701.

[0128] The software in memory 702 includes one or more separate programs, each having an ordered list of executable instructions for implementing logical functions. The software in memory 702 includes, according to an exemplary embodiment, a suitable operating system (O / S) 705, a compiler 704, source code 703, and one or more applications 706. The applications 706, as illustrated, have a number of functional components for implementing the features and operations of the exemplary embodiments. The applications 706 of the processor system 700 represent various applications, computing units, logic, functional units, processes, operations, virtual entities, and / or modules according to an exemplary embodiment, but the applications 706 are not intended to be limiting.

[0129] Operating system 705 controls the execution of other computer programs and provides scheduling, input / output control, file and data management, memory management, and communication control and related services. The inventors believe that application 706 implementing the exemplary embodiment is applicable to all commercially available operating systems.

[0130] The application 706 may be a source program, an executable program (object code), a script, or any other entity that includes a set of instructions to be executed. If the application 706 is a source program, the program is typically translated by a compiler (such as compiler 704), assembler, interpreter, etc., whether in memory 702 or not, to operate properly with the O / S 705. The application 706 may also be written in an object-oriented programming language with classes of data and methods, or a procedural programming language with routines, subroutines, and / or functions, such as, but not limited to, C, C++, C#, Pascal, BASIC, API calls, HTML, XHTML, XML, ASP script, JavaScript, FORTRAN, COBOL, Perl, Java, ADA, .NET, etc.

[0131] The I / O devices 707 include input devices such as, for example, but not limited to, a mouse, keyboard, scanner, microphone, camera, etc. The I / O devices 707 also include output devices such as, for example, but not limited to, a printer, display, etc. Finally, the I / O devices 707 further include devices that communicate both input and output, such as, but not limited to, a network interface card (NIC) or modulator / demodulator (for accessing remote devices, other files, devices, systems, or networks), a radio frequency (RF) or other transceiver, a telephone interface, a bridge, a router, etc. The I / O devices 707 also include components that communicate over various networks, such as the Internet or an intranet.

[0132] If processor system 700 is a PC, workstation, intelligent device, etc., the software in memory 702 further includes (omitted for simplicity) a basic input / output system (BIOS). The BIOS is a set of basic software routines that initializes and tests hardware at power-on, starts O / S 705, and assists in transferring data between hardware devices. The BIOS is stored in some type of read-only memory, such as ROM, PROM, EPROM, EEPROM, etc., so that the BIOS can be executed when processor system 700 is powered on.

[0133] Processor 701 is configured, during operation of processor system 700, to execute software stored in memory 702, to communicate data to and from memory 702, and to generally control the operation of processor system 700 in accordance with the software. Applications 706 and O / S 705 are read, in whole or in part, by processor 701, typically buffered within processor 701, and then executed.

[0134] It should be noted that application 706, when implemented in software, may in fact be stored on any computer-readable medium for use by or in conjunction with any computer-related system or method, a computer-readable medium, in the context of this document, being any electronic, magnetic, optical, or other physical device or means capable of containing or storing a computer program for use by or in conjunction with a computer-related system or method.

[0135] The application 706 may be embodied in any computer-readable medium for use by or in conjunction with an instruction execution system, apparatus, or device, such as a computer-based system, a processor-embedded system, or other system capable of fetching instructions from and executing instructions from an instruction execution system, apparatus, or device. A "computer-readable medium," in the context of this document, may be any means that can store, transmit, propagate, or transfer a program for use by or in conjunction with an instruction execution system, apparatus, or device. A computer-readable medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium.

[0136] Those skilled in the art will be able to readily develop a processing system that performs any of the methods described herein, i.e., each step in the flow chart represents a different action performed by the processing system and is performed by a respective module of the processing system.

[0137] The embodiments therefore employ a processing system. A processing system can be implemented in many ways using software and / or hardware to perform the various functions required. The processor is one example of a processing system that employs one or more microprocessors that are programmed using software (e.g., microcode) to perform the necessary functions. However, a processing system may be implemented with or without the use of a processor, and may further be implemented with a combination of dedicated hardware to perform some functions and processors (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

[0138] Examples of processing system components used in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0139] In various embodiments, a processor or processing system is associated with one or more storage media, such as volatile and non-volatile computer memory, including RAM, PROM, EPROM, and EEPROM. The storage media are encoded with one or more programs that, when executed on the one or more processors and / or processing systems, perform the necessary functions. The various storage media may be fixed within the processor or processing system, or may be portable, such that one or more programs stored on the storage media can be loaded into the processor or processing system.

[0140] It will be understood that the disclosed methods are preferably computer-implemented methods. Accordingly, the concept of a computer program product including code means, which, when executed on a processing system such as a computer, performs any of the described methods, is also proposed. Accordingly, various portions, lines, or blocks of code of a computer program product according to one embodiment are executed by a processing system or computer to perform all of the methods described herein. In some alternative implementations, functions depicted in block diagrams or flow diagrams may occur out of the order depicted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may be executed in the reverse order, depending on the functionality required.

[0141] Those skilled in the art will understand and produce variations to the disclosed embodiments in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the singular form of an element does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in a claim. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used to advantage. Where computer programs are discussed above, the computer programs may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided integrally with or as part of other hardware, or may be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. It should be noted that where the term "adapted to" is used in the claims or the description, the term "adapted to" is intended to be synonymous with the term "configured to." Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. A computer-implemented method for operating a computed tomography scanner comprising a linearly moving subject support and a rotating portion carrying a radiation output system and controllably rotating around the subject support, the computer-implemented method comprising the steps of performing a scanning procedure, the scanning procedure comprising: controlling the radiation output system to output radiation during an imaging phase of the scanning procedure; controlling the subject support to move linearly, wherein the linear movement of the subject support during the imaging phase of the scanning procedure includes at least one acceleration phase before reaching a predetermined speed or a deceleration phase after moving at the predetermined speed; controlling one or more parameters of the computed tomography scanner in response to a velocity of the subject support, the one or more parameters including at least a beam width of the radiation output from the radiation output system; 1. A computer-implemented method having:

10. A computer-implemented method, wherein controlling the one or more parameters comprises controlling the beam width in proportion to the velocity of the subject support.

2. the radiation output system comprising a radiation source for generating radiation and a collimator for controlling the beam width of the radiation generated by the radiation source; 2. The computer-implemented method of claim 1, wherein controlling the one or more parameters of the computed tomography scanner comprises controlling the operation of the collimator, thereby controlling the beam width.

3. 3. The computer-implemented method of claim 2, wherein the collimator comprises a collimator opening with a controllable width, and wherein controlling the beam width comprises controlling the width of the collimator opening in response to the velocity of the subject support.

4. 4. The computer-implemented method of claim 3, wherein the width of the collimator opening is defined by the distance between a front blade and a rear blade aligned in the direction of movement of the subject support, and wherein controlling the width of the collimator opening comprises controlling the distance between the front blade and the rear blade.

5. 5. The computer-implemented method of claim 1, wherein controlling the one or more parameters of the computed tomography scanner comprises setting and maintaining the beam width equal to 0 until radiation produced by a radiation source stabilizes.

6. 2. The computer-implemented method of claim 1, wherein controlling the one or more parameters of the computed tomography scanner comprises controlling the one or more parameters such that a total radiation dose per volume of the subject positioned on the subject support remains substantially constant throughout the scanning procedure.

7. Controlling the one or more parameters of the computed tomography scanner comprises: controlling the one or more parameters of the computed tomography scanner so that a CT scan pitch is constant throughout the scanning procedure; and / or controlling the beam width to be equal to the product of the velocity of the subject support and the time it takes for the rotating portion to perform a 2π rotation, divided by a desired CT scan pitch.

2. The computer-implemented method of claim 1, comprising:

8. The computer-implemented method of claim 1 , wherein the one or more parameters of the computed tomography scanner further include an intensity of the radiation output from the radiation output system.

9. The computer-implemented method of claim 1 , wherein the one or more parameters of the computed tomography scanner further comprise a rotational speed of the rotating portion of the computed tomography scanner.

10. 2. The computer-implemented method of claim 1, wherein the step of controlling the subject support to move linearly comprises controlling the subject support to perform linear movement including a single acceleration step and / or a single deceleration step during the imaging step.

11. 2. The computer-implemented method of claim 1, wherein the scanning procedure includes a step of using a radiation measurement system mounted on the rotating portion to obtain raw signal data corresponding to the absorption of the radiation output from the radiation output system by the subject positioned on the subject support.

12. 10. A computer program comprising computer program code means which, when executed on a computing device comprising a processing system, causes said processing system to perform all the steps of the method of claim 1.

13. 1. A processing system configured to operate a computed tomography scanner comprising a linearly moving subject support and a rotating portion carrying a radiation output system and controllably rotating around the subject support, the processing system controlling a scanning procedure, the scanning procedure comprising: controlling the radiation output system to output radiation during an imaging phase of the scanning procedure; controlling the subject support to move linearly, wherein the linear movement of the subject support during the imaging phase of the scanning procedure includes at least one acceleration phase before reaching a predetermined speed or a deceleration phase after moving at the predetermined speed; controlling one or more parameters of the computed tomography scanner in response to a velocity of the subject support, the one or more parameters including at least a beam width of the radiation output from the radiation output system; 1. A processing system having:

10. A processing system, wherein controlling the one or more parameters comprises controlling the beam width in proportion to the velocity of the subject support.

14. A processing system according to claim 13, and the computed tomography scanner comprising: a subject support that moves linearly; and a rotating portion that carries the radiation output system and that controllably rotates around the subject support. An imaging system comprising:

Images