Patent Description:
A computed tomography (CT) scanner is a common piece of equipment in modern medical imaging. Generally, a CT scanner is formed of a generally stationary portion and a rotating portion. The rotating portion supports a radiation outputting system such as an X-ray tube and an opposing radiation measurement system that generates raw data that can be used to reconstruct the CT image(s). A subject support supports an object/subject in an examination region around which the rotating portion rotates. During a scanning procedure, the subject support moves linearly to facilitate imaging of different sections of the supported subject/object.

One mode of operation for a CT scanner is a helical or spiral mode, in which the subject support is accelerated to move at a predefined (and constant) speed relative to the gantry rotation speed to acquire the needed raw data to reconstruct CT images.

This relationship between the moving speed (V) of the subject support and the gantry rotation speed is defined by CT scan pitch, which is the table distance travelled in one <NUM>° (2π) gantry rotation divided by the total thickness of all simultaneously acquired slices during that rotation.

When performing a helical/spiral mode scan (or simply "helical CT scan"), there is a period of time during which the subject support accelerates or decelerates, e.g. to reach the predefined speed or to reach standstill after travelling at the predefined speed. Conventionally, no imaging is performed during this acceleration/deceleration phase, such that part of the subject/object, which could be theoretically imaged, are not imaged in practice. In current CT scanners, an over-scan region is added before the prescribed scan region and another over-scan region is added after the prescribed scan region for reconstruction of the helical scan images. The additional pre and post regions increase the region of the subject exposed to x-ray radiation. Also in current CT scanners, while the collimator is open, the x-ray tube is turned on before raw data acquisition starts to ensure the tube stabilizes when data acquisition starts, which also introduces extra radiation to the subject being scanned.

Document <CIT> discloses scanning imaging systems having an x-ray beam width with a dynamically changeable width.

According to examples in accordance with an aspect of the invention, there is provided a computer-implemented method of operating a computed tomography scanner comprising a subject support configured to move linearly and a rotating portion that mounts a radiation outputting system and controllably rotates around the subject support.

The computer-implemented method comprises performing a scanning procedure comprising: controlling the radiation outputting system to output radiation during/throughout an imaging phase of the scanning procedure; controlling the subject support to move linearly, the linear movement of the subject support during/throughout the imaging phase of the scanning procedure including at least one acceleration or deceleration phase; and controlling one or more parameters of the computed tomography scanner responsive to the speed of the subject support, wherein the one or more parameters comprises at least a beam width of the radiation output by the radiation outputting system.

The present disclosure thereby provides a mechanism for controlling the operation of a CT scanner, e.g. during a helical scanning procedure. During a helical scanning procedure, a rotating portion rotates as the subject support is moved linearly.

The present invention proposes to control beam width of radiation provided by a radiation outputting system out of the collimator responsive to the speed of the (linearly moving) subject support. This facilitates control over the amount of radiation exposed (dose) on/to a subject positioned on the subject support. In particular, it is recognized that appropriate control over this characteristic of the radiation facilitates provision of a constant dose of radiation to all parts of a subject positioned on the subject support.

Conceptually, a prescribed image region is divisible into one or more acceleration regions, constant speed regions, and deceleration regions, the sum of which equals the total prescribed image region. By controlling the beam width responsive to patient table speed, imaging can be performed during each of these regions without needing to add extra pre and post scan regions on top of the prescribed image region. The beam width is preferably controlled in such a way that a dose provided to the subject will remain constant throughout these regions.

The skilled person will appreciate that the CT scanner may comprise a number of other features or elements, e.g. a radiation measurement system, a control panel, a console and so on. These are not specified in the claim set for the sake of conciseness, and because they are well known elements of a standard CT scanner.

The step of controlling one or more parameters of the computed tomography scanner responsive to the speed of the subject support comprises controlling the beam width proportionally to the speed of the subject support.

The radiation output by the radiation outputting system is the radiation incident within an examination region, e.g. the radiation that will interact with the subject support. In particular, if a patient/subject occupies an entire surface of the subject support, then radiation output by the radiation outputting system will interact with the subject support.

In some examples, the radiation outputting system comprises a radiation source configured to generate radiation and a collimator configured to control the beam width of radiation generated by the radiation source; and the step of controlling the one or more parameters of the computed tomography scanner comprises controlling the beam width by controlling an operation of the collimator.

Using a collimator to control a beam width provides a highly sensitive and accurate mechanism to control the beam width of the radiation output by the radiation outputting system. This approach facilitates direct control over the area of radiation incident upon a subject positioned on the subject support.

The collimator may comprise a collimator opening having a controllable width, and the step of controlling the beam width comprises controlling a width of the collimator opening responsive to the speed of the subject support.

In some examples, the width of the collimator opening is defined by a distance between a front blade and a rear blade aligned in a direction of travel of the subject support, and the step of controlling a width of the collimator opening comprises controlling the distance between the front blade and the rear blade.

In at least one embodiment, wherein the step of controlling one or more parameters of the computed tomography scanner comprises setting and maintaining the beam width to be equal to <NUM> until the radiation generated by the radiation source has stabilized. In other words, the beam width may be set and maintained at zero whilst the radiation source is turned on and/or is stabilizing. Thus, the step of controlling the radiation outputting system to output radiation may comprise a step of controlling the radiation source to begin generating radiation (whilst the controlling of the parameters keeps the beam width at <NUM>, i.e. the collimator shut). Once the radiation source has stabilized, allowing the beam width to have a width greater than <NUM> (i.e. allow the collimator to open) for raw data acquisition.

In some examples, the subject support does not begin moving until the radiation source has stabilized and the beam width is permitted to have a width greater than <NUM>. Thus, the step of controlling the subject support to move linearly may comprise controlling the subject support to move linearly only after the radiation source has stabilized.

Mechanisms for identifying when the radiation source has stabilized will be readily apparent to the skilled person, e.g. by waiting a predetermined period of time after powering the radiation source (e.g. according to known times for the radiation source to stabilize).

The present invention facilitates control over the beam width during the stabilization of the source of the scanning procedure. The proposed approach of maintain the beam width at <NUM> until the radiation source has stabilized reduces (unnecessary) radiation exposure or dosage of a subject positioned on the subject support. In particular, beam width will be kept at <NUM> and imaging (i.e. measuring of output radiation) will not take place whilst the source is stabilizing.

In some examples, the step of controlling the one or more parameters of the computed tomography scanner comprises controlling the one or more parameters such that a total radiation dosage per volume of a subject positioned on the subject support remains substantially constant throughout the scanning procedure.

Optionally, the step of controlling 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.

In at least one embodiment, the step of controlling one or more parameters of the computed tomography scanner comprises controlling the beam width to be equal to the product of the speed of the subject support and the time taken for the rotating portion to perform a 2π rotation, divided by a desired CT scan pitch.

The one or more parameters of the computed tomography scanner may further comprise an intensity of the radiation output by the radiation outputting system. In some examples, the radiation outputting system comprises an X-ray tube and the step of controlling an amount of radiation intensity output by the radiation outputting system comprises controlling an emission current supplied to the X-ray tube.

The one or more parameters of the computed tomography scanner may further comprise a rotation speed of the rotating portion of the computed tomography scanner.

The step of controlling the subject support to move linearly may comprise controlling the subject support to have a linear movement including a single acceleration and/or a single deceleration phase.

The scanning procedure may comprise obtaining (during/throughout the imaging phase of the scanning procedure) using a radiation measurement system mounted on the rotating portion, raw signal data responsive to the absorption of radiation output by the radiation outputting system by a subject positioned on the subject support.

There is also proposed a computer program product comprising computer program code means which, when executed on a computing device having a processing system, cause the processing system to perform all of the steps of any herein described method. The computer program product may be formed of a (non-transitory) computer-readable medium.

There is also proposed a processing system configured to operate a computed tomography scanner comprising a subject support configured to move linearly and a rotating portion that mounts a radiation outputting system and controllably rotates around the subject support, the processing system being configured to control a scanning procedure comprising: controlling the radiation outputting system to output radiation during/throughout an imaging phase of the scanning procedure; controlling the subject support to move linearly, the linear movement of the subject support during/throughout the imaging phase of the scanning procedure including at least one acceleration or deceleration phase; and controlling one or more parameters of the computed tomography scanner responsive to the speed of the subject support, wherein the one or more parameters comprises at least a beam width of the radiation output by the radiation outputting system.

There is also proposed an image generating system comprising the processing system and an image reconstruction system that is configured to process projection data, generated by a radiation measurement system of the computed tomography scanner, to reconstruct one or more 2D and/or 3D images.

There is also proposed an imaging system comprising: the projection system or the image generation system and the computed tomography scanner comprising the subject support configured to move linearly and the rotating portion that mounts the radiation outputting system and controllably rotates around the subject support. The computed tomography scanner may further comprise a radiation measurement system configured to generate projection data responsive to radiation incident on the radiation measurement system.

The invention provides a mechanism for controlling the operation of a CT scanner during a scanning procedure. A radiation outputting system is configured to output radiation during an imaging phase of the scanning procedure. The subject support (patient table) of the CT scanner is controlled to move linearly, e.g. according to some predetermined linear pattern, during this imaging phase. The linear movement includes at least one acceleration and/or deceleration phase. At least a beam width of radiation output by the CT scanner is controlled throughout the imaging phase responsive to the speed of the subject support.

Embodiments are based on a realization that a CT scan pitch and/or amount of irradiation per unit volume of an examination region can be controlled by controlling a beam width. This facilitates maintenance of a constant pitch or irradiation per unit volume, or maintaining a pitch or irradiation per unit volume below some predetermined threshold, to control radiation exposure of the subject. This enables an imaging phase of the scanning procedure to include periods during which the subject support is accelerating and/or decelerating, increasing a size of an available region for imaging.

Embodiments can be employed in any suitable CT scanning system, which can be used in a wide variety of industries such as the healthcare industry, anthropology industries and/or archeological industries.

<FIG> schematically illustrates a computed tomography scanner system <NUM> including a computed tomography scanner. The computed tomography scanner <NUM> includes a generally stationary portion <NUM> and a rotating portion <NUM>, which is rotatably supported by the stationary portion <NUM> and rotates around an examination region <NUM> about a z-axis. A subject support <NUM>, such as a couch, supports an object or subject (e.g. a patient) in the examination region <NUM>.

A radiation outputting system <NUM>, comprising a radiation source (such as an x-ray tube) and a collimator, is rotatably supported by the rotating portion <NUM>, rotates with the rotating portion <NUM>, and outputs radiation that traverses the examination region <NUM>.

A radiation measurement system <NUM>, e.g. a radiation sensitive detector array, subtends an angular arc opposite the radiation source <NUM> across the examination region <NUM>. The radiation measurement system ("radiation detector") detects radiation traversing the examination region <NUM> and generates an electrical signal(s) (projection data) indicative thereof.

The radiation measurement system <NUM> can include single layer detectors, direct conversion photon counting detectors, and/or multi-layer detectors. The direct conversion photon counting detectors may include a conversion material such as CdTe, CdZnTe, Si, Ge, GaAs, or other direct conversion material. An example of multi-layer detector includes a double decker detector such as the double decker detector described in <CIT>, and entitled "Double Decker Detector for Spectral CT,".

A reconstructor <NUM> receives projection data from the radiation measurement system <NUM> and reconstructs one or more CT images from the projection data. The reconstructed CT images may comprise one or more 2D or 3D images. Mechanisms for reconstructing one or more CT images from projection data are well-established in the art.

A processing system <NUM> is configured to control an operation of the computed tomography scanner, and in particular to control the operation of the computed tomography scanner during a scanning procedure. Approaches for controlling the operation of the computed tomography scanner according to embodiments form the subject of this disclosure.

During a scanning procedure, the processing system <NUM> controls the subject support <NUM> to move linearly along the z-axis. The processing system <NUM> also controls the rotating portion <NUM> to rotate about the examination region <NUM> and the radiation outputting system <NUM> to output radiation into the examination region. As previously explained, the radiation measurement system <NUM> collects radiation traversing the examination region and generates projection data (e.g. as an electrical signal) indicative to radiation that has traversed the examination region. The reconstructor <NUM> then reconstructs a CT image from the projection data.

The processing system <NUM> may include a processor <NUM> (e.g., a microprocessor, a controller, a central processing unit, etc.) and a computer readable storage medium <NUM>, which excludes non-transitory medium, and includes transitory medium such as a physical memory device, etc..

The computer readable storage medium <NUM> may include instructions <NUM> for controlling the operation of the computed tomography scanner. The processor <NUM> is configured to execute the instructions <NUM>. The processor <NUM> may additionally be configured to execute one or more computer readable instructions carried by a carrier wave, a signal and/or other transitory medium. However, instead of a processor <NUM> executing instructions to perform a herein described method, the processor may instead comprise fixed-function circuitry (e.g. appropriately programmed field-programmable gate arrays (FPGAs) or the like) to carry out the described methods.

In some examples, the processing system may also serve as an operator console. The processing system <NUM> includes a human readable output device such as a monitor and an input device such as a keyboard, mouse, etc. Software resident on the processing system <NUM> allows the operator to interact with and/or operate the scanner <NUM> via a graphical user interface (GUI) or otherwise.

A processing system <NUM> may be configured to process CT images generated by the computed tomography scanner <NUM>. This may, for instance, comprise controlling a user interface to display or provide a visual representation of reconstructed CT images.

As previously mentioned, the present disclosure proposes approaches for controlling the operation of the computed tomography scanner <NUM>. In particular, the present disclosure proposes approaches for controlling the operation of the computed tomography scanner during the scanning procedure. These approaches may be carried out by the processing system <NUM>.

<FIG> is a flowchart illustrating a (computed-implemented) method <NUM> according to an embodiment. The computer-implemented method may be carried out by the processing system <NUM> of <FIG>.

The method <NUM> is for operating a computed tomography (CT) scanner comprising a subject support configured to move linearly and a rotating portion (that mounts a radiation outputting system) and controllably rotates around the subject support. The CT scanner may further comprise a radiation measurement system configured to detect radiation output by the radiation outputting system (which may be at least partially absorbed by a subject positioned on the subject support).

The method <NUM> comprises a scanning procedure, which may be a helical scanning procedure. Generally, a scanning procedure can be divided into an "imaging phase" (during which projection data used to reconstruct image data, e.g. one or more 2D and/or 3D images, is generated) and a "non-imaging phase" (during which no projection data used to reconstruct image data, e.g. one or more 2D and/or 3D images, is generated). In a helical scanning procedure, the rotating portion rotates as the subject support moves linearly (e.g. so that the radiation output element and/or the radiation measurement system appear(s) to move in a spiral with respect to the subject support).

Steps for carrying out a scanning procedure are well known in the prior art, and may include additional steps that are not explicitly described in this disclosure for the sake of brevity. These steps include, but are not limited to, those previously described with reference to <FIG>, e.g. using a radiation measurement system for detecting radiation output by the radiation outputting system and/or reconstructing images from projection data generated by a radiation measurement system.

The method <NUM> comprises a step <NUM> of controlling the radiation outputting system to output radiation during an imaging phase of the scanning procedure. In particular, the radiation outputting system outputs a non-zero radiation (to the examination region) throughout the imaging phase. Methods for controlling a radiation output system to output radiation are widely known and readily apparent to the skilled person, e.g. by supplying a current to an X-ray tube or the like.

As previously explained, an imaging phase is a phase during which radiation detected by a radiation measurement system of the CT scanner contributes to the generation of image data, e.g. one or more (2D or 3D) CT images, produced by the CT scanner. Thus, the scanning procedure (e.g. as part of step <NUM>) may further comprise controlling the radiation measurement system to detect radiation output by the radiation outputting system.

The method <NUM> comprises a step <NUM> of controlling a linear motion of the subject support during the imaging phase of the computed tomography scanner to include at least one acceleration and/or a deceleration phase.

Thus, the linear motion may be controlled to have a single acceleration phase and/or a single deceleration phase. In another example, the linear motion may be controlled to have a plurality of acceleration phases and/or a plurality of deceleration phases. In some examples, the number of acceleration phases and the number of deceleration phases are equal. This later approach increases the overall size of the imaging area, as explained below.

Thus, the linear motion of the subject support is controlled according to some predetermined linear motion pattern, which defines a speed and direction of the linear motion. One example of a linear motion pattern would include (i.e. consist of) an acceleration phase, a steady state phase and a deceleration phase. However, other examples may include a plurality of different acceleration, steady state and/or deceleration phases. For instance, one linear motion pattern may comprise X acceleration phases, Y steady state phases and Z deceleration phases, e.g. where X = Z and Y = X - <NUM>.

It will be appreciated that the linear position of the subject support defines an area or volume of the examination region that is being irradiated by the radiation outputting system (when it is outputting radiation), and thereby a region of the examination area that is imaged (by detection of radiated radiation). Thus, there is a total imaging region, which is the entire region irradiated and imaged during the scanning procedure.

<FIG> illustrates one example of a linear motion pattern <NUM> for the subject support. In particular, <FIG> illustrates a position (z) and a speed (v) of the subject support according to a linear motion pattern. <FIG> also illustrates a subject <NUM> positioned on a subject support <NUM>, to demonstrate how the speed of the subject support can change with respect to a current position (of the rotating portion) with respect to the subject support.

The linear motion pattern comprises an acceleration phase ta, a steady state phase tss and a deceleration phase td. During the acceleration phase ta, from time t<NUM> to time t<NUM>, a speed of the subject support increases (from <NUM>) to a maximum speed vmax. During the steady state phase tss, from time t<NUM> to time t<NUM>, the speed of the subject support is held at the maximum speed vmax. During the deceleration phase, from time t<NUM> to time t<NUM>, a speed of the subject support decreases to <NUM>.

The maximum speed vmax is not necessarily the maximum possible speed of the subject support, but rather the maximum speed for that linear motion pattern. This may be defined by a clinician, e.g. providing a user input, and will be bounded by the maximum possible speed of the subject support.

For the subject support being controlled according to the linear pattern illustrated by <FIG>, and for linear acceleration (a) and deceleration (d), the subject support speed v(t) can be calculated as: <MAT> where:.

Turning back to <FIG>, the method <NUM> also comprises a step <NUM> of controlling one or more (other) parameters of the computed tomography scanner responsive to the speed of the subject support. The one or more other parameters includes at least a beam width of radiation output by the radiation outputting element.

Thus, step <NUM> comprises controlling at least a beam width of radiation output by the radiation outputting element responsive to the speed of the subject support. Step <NUM> may also be performed throughout at least the imaging phase.

Other suitable parameters that might also be controlled in step <NUM> include a speed of rotation of the rotating portion and/or an intensity of radiation output by the radiation outputting element (and in particular, an intensity of radiation output by a radiation source of the radiation outputting element).

It is herein recognized that, for a conventional helical scanning procedure in which a speed of the rotating portion is constant, if radiation were output by the radiation outputting element during any acceleration and/or deceleration phases of the linear motion of the subject support, then the total amount of radiation per volume of the examination region during such phases would be greater than during the steady state phase. This is because the slower movement of the subject support during these phases causes a smaller gap or potentially a (greater) overlap between areas radiated between a 2π rotation of the rotating portion.

By way of further explanation, for the purposes of this disclosure, during a helical scanning procedures (for CT scanners), a "pitch" or CT scan pitch is defined as the total distance travelled by the subject support (along the z-axis) during one 2π rotation of the rotating portion, divided by the total thickness (along the z-axis) that is irradiated with radiation (i.e. the beam width of radiation output by the radiation outputting system).

In conventional imaging practices, if the subject were imaged throughout the entire movement of the subject support, the CT scan pitch would change over the course of the scanning procedure due to acceleration and deceleration of the subject support. This would affect the relative amount of radiation incident per volume of the examination region, and could lead to undesirable radiation dosing of a subject on the subject support.

To avoid this issue, conventional scanning procedures simply avoid imaging (e.g. avoid or minimize emitting radiation) during any acceleration or deceleration phases. This means that the total imaging area is limited to only the areas that can be irradiated whilst the linear motion of the subject support is in the steady state phase. In other words, the imaging phases of conventional scanning procedures do not include an acceleration or deceleration phases for the linear motion of the subject support.

The present disclosure proposes a different approach in which at least a beam width is controlled responsive to the speed of movement. This facilitates control over the size of the area/volume irradiated with radiation and therefore the total amount of radiation for each phase of the linear motion.

By adopting approaches according to the present disclosure, the size of the total imaging region can be effectively increased without impacting on the total amount of radiation (per volume irradiated area). In particular, the total imaging area can be increased to also include areas that can be irradiated whilst the linear motion of the subject support is in an acceleration and/or deceleration phase.

In other words, the imaging phase of a scanning procedure may be extended to include periods of acceleration/deceleration of the subject support, e.g. so that an imaging phase may occupy the entirety of the scanning procedure.

The relationship between pitch P(t), subject support speed v(t), rotation speed r(t) and beam width w(t) can be calculated as: <MAT>.

The pitch P(t) is dimensionless, the subject support speed v(t) is in m/s (or mm/s), the rotation speed r(t) is in revolutions per second (RPS) and the beam width is in m (or mm). Generally, a beam width is a width of the beam of radiation at the isocenter of the rotating portion. The isocenter is an axis parallel with the z-axis and which passes through a center of the circle/cylinder around which the rotating portion rotates.

Thus, by controlling a beam width responsive to a change in subject support speed, a pitch of the scanning procedure can be controlled. In particular, by controlling a change in beam width to be proportional to a change in subject support speed, a maximum change in pitch during an acceleration/deceleration phase of the linear motion of the subject support can be reduced.

In particular examples, step <NUM> may be configured to comprise controlling only a beam width responsive to the speed of the subject support. In particular, step <NUM> may comprise controlling a beam width to maintain a constant pitch P (which may be predetermined, e.g. according to a user-input or scanning procedure). Suitable examples for a desired pitch value P are <NUM>, <NUM>, <NUM>. Other pitch values are possible and known by those who are skilled in the art. By way of example, the pitch may be maintained to be a constant pitch having a value of between <NUM> and <NUM>, e.g. between <NUM> and <NUM>.

In this way, the step of controlling one or more parameters of the computed tomography scanner may comprise controlling the beam width to be equal to the product of the speed of the subject support and the time taken for the rotating portion to perform a 2π rotation (at its current speed), divided by a desired (CT scan) pitch.

This is equivalent to controlling the beam width to be equal to the speed of the subject support divided by the product of the desired (CT scan) pitch and the speed (in rotations per second) of the rotating portion of the CT scanner.

By way of example only, consider a scenario in which a desired pitch value P is <NUM>, a rotation speed r is fixed at <NUM> rotations per second, a maximum speed vmax for the subject support (i.e. a speed during the steady state phase of the linear motion) is <NUM>/s and an acceleration a is a constant value of <NUM>/s<NUM>.

In this scenario, the acceleration phase will be <NUM> seconds long, in which the speed linearly increases from <NUM> to <NUM>/s. If step <NUM> comprises controlling a beam width to maintain a constant pitch (following equation (<NUM>)), then the beam width will also linearly increase from <NUM> to <NUM>. It will be apparent that, in this example, the magnitude of the beam width is thereby controlled to be proportional to the subject support speed.

In other examples, step <NUM> may be configured to comprise controlling a plurality of parameters of the computed tomography scanner, wherein the parameters include at least a beam width. The parameters may also include a rotation speed of the rotating portion and/or an intensity of radiation output by the radiation outputting element.

Equation (<NUM>) demonstrates how a pitch is also dependent upon the time taken for the rotating portion to perform a rotation, i.e. the speed of rotation. By controlling the speed of the rotating portion, a time taken for the rotating portion to perform a rotation can be changed, and therefore provides a further possible controllable variable for controlling the pitch of the scanning procedure.

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

In some examples, rather than controlling the one or more parameters of the computed tomography scanner responsive to subject support speed to maintain a constant pitch (as previously described), the one or more parameters may be controlled to maintain a constant irradiation per unit volume of the examination region (i.e. a constant dose). An irradiation per unit volume of the examination region is functionally equivalent to a total radiation dosage per volume of a subject positioned on the subject support.

A measure of total irradiation per unit volume Ir(t) may be defined by the following equation: <MAT> where In(t) is radiation (intensity) output by the radiation outputting system and P(t) is the pitch.

Thus, by controlling a pitch (using the beam width and optionally the rotation speed) and optionally an intensity of radiation output by the radiation outputting system, a total irradiation per unit volume of the examination region can be controlled. In particular examples, a total irradiation per unit volume of the examination region can be kept constant for different speeds of the subject support.

The desired value for Ir(t) may be predetermined, e.g. according to some medical protocol or clinical/environmental recommendation (such as those set out in guidelines for CT scanning). In another example, the desired value for Ir(t) may be chosen by a clinician, e.g. employing their experience to choose a suitable level for Ir(t).

Thus, in some embodiments, step <NUM> comprises controlling the beam width and either the intensity of radiation output by the radiation outputting system or the rotation speed of the rotating portion or both. Thus, a hybrid system for delivering constant dose during a scanning procedure (including an acceleration and/or deceleration phase) may be employed.

In embodiments in which the pitch is kept constant, the radiation output by the radiation outputting system may also be kept constant (i.e. there is no need to change the magnitude of radiation output by the radiation outputting system).

Of course, it will be appreciated that hardware or software limitations may be unable to maintain a constant pitch and/or dosage using approaches previously described. However, a change in pitch and/or dosage could be minimized by controlling the aforementioned parameters to the best of the systems capabilities to reduce an impact on a subject.

Thus, rather than attempting to maintain a constant pitch, controlling the one or more parameters of the computer tomography scanner (including at least a beam width) may be used to reduce a range of (i.e. reduce a change in) pitch and/or total/average irradiation per unit volume of the examination region.

For the sake of completeness, it is noted that other parameters and functions of the scanning procedure may be controlled according to well-known CT scanning protocols, e.g. control of sampling speeds, operation of radiation measurement system functionality and so on. The present disclosure proposes approaches for modifying some (i.e. not necessarily all) aspects of the scanning procedure.

In some examples, the step <NUM> of controlling one or more parameters of the computed tomography scanner comprises setting and maintaining the beam width to be equal to <NUM> until the radiation generated by the radiation source has stabilized.

Thus, step <NUM> may comprise controlling a radiation source to begin emitting radiation, and step <NUM> may comprise controlling the beam width to remain at <NUM> until the radiation source has stabilized (i.e. emitted radiation is near-constant). This reduces unnecessary irradiation of the subject, thereby reducing radiation dosage. Once the radiation source has stabilized, the beam width may be controlled accordingly to previously described approaches, i.e. responsive to the speed of the subject support.

In some further examples, step <NUM> may comprise not beginning a linear movement of the subject support, i.e. keeping the subject support stationary, until the radiation source has stabilized. This ensures that the size of an imaging area of the subject is maintained or increased.

Thus, there may effectively be a delay between steps <NUM> and the performance of steps <NUM> and <NUM> (during which time the beam width is maintained or kept at <NUM> or near-zero), to allow the radiation source to stabilize.

Previous embodiments have described how a beam width is controlled, during a scanning procedure, responsive to a speed of a subject support. One method of controlling a beam width is to control the operation of the radiation outputting system.

In particular, where the radiation outputting system comprises a radiation source and a collimator, an operation of the collimator may be controlled to define the beam width. For instance, a size of a collimator opening may be controlled to control the beam width, e.g. a width of a collimator opening.

<FIG> illustrates one example of a radiation outputting system <NUM> for use with an embodiment of the invention.

The radiation outputting system <NUM> comprises a radiation source <NUM> that outputs a beam X of radiation (e.g. an X-ray source such as an X-ray tube) and a collimator <NUM>. The collimator <NUM> is formed of a front blade <NUM> and a rear blade <NUM>. The front <NUM> and rear <NUM> blades are aligned in a direction of travel of the subject support (i.e. along a z-axis). In particular, during a positive travel direction of the subject support, the front blade leads the rear blade, i.e. is positioned ahead of the rear blade. The collimator opening <NUM> is the gap formed between the front <NUM> and rear <NUM> blades. Any radiation output by the radiation source <NUM> that falls on the front or rear blades (i.e. and not in the collimator opening) is blocked (and not illustrated for the sake of clarity). The position of the front <NUM> and rear <NUM> blades can be individually controlled in order to control the size of the collimator opening (and therefore the size of the beam width).

The size C of the collimator opening <NUM> at time t can be calculated using the following equation: <MAT> where w(t) is the (desired) beam width at time t, SCD is the distance from the radiation source <NUM> to the collimator opening and SID is the distance from the radiation source <NUM> to the isocenter <NUM> of the computed tomography scanner. SCD and SID can be predetermined or known values (e.g. according to the structure of the computed tomography scanner).

The position of the front and rear blade edges can be defined based on a position ZX(t) of the center of the X-ray beam during the course of the scanning procedure. The position (Zcf) of the collimator edge of the front blade <NUM> will be equal to ZX(t) + <NUM>. The position (Zcr) of the collimator edge of the rear blade <NUM> will be equal to ZX(t) -<NUM>.

In one scenario, a linear motion of the table follows a linear motion pattern being a sequence of an acceleration phase (of constant acceleration), a steady state phase, and a deceleration phase (of constant deceleration). In this scenario, for any time t, the center of the X-ray beam ZX(t) (along the z-axis) relative to the starting point of the subject support position (along the z-axis) can be defined as. <MAT> where:.

ZX(<NUM>) or ZX(t<NUM>) is defined as the starting position of the center of the X-ray beam, which here defines a point <NUM> on the z-axis.

Other approaches for determining the position of the center of the X-ray beam will be apparent to the skilled person, e.g. depending upon the linear motion pattern employed when moving the subject support. In particular, the skilled person would be readily capable of combining various equations of motion (as illustrated with equation (<NUM>)) in order to predict or determine the position ZX(t) of the center of the X-ray beam with respect to time.

<FIG> illustrates an example beam edge difference (BED) with respect to rotation angle (R) at a transition between an acceleration phase ta and a steady state phase tss - in which the collimator opening size alone is controlled to maintain a pitch at a constant value of <NUM>. Vertical dashed lines represent completion of one full rotation (i.e. there is a 2π rad difference between each vertical dashed line).

The beam edge difference BED is a difference between the instant position of the beam front edge (i.e. after a rotation of N radians of the rotating portion) and the instant position of the beam rear edge at the same rotation angle in the next full rotation (i.e. after a rotation of N+2π radians of the rotating portion). The beam edge difference BED therefore effectively represents a measure of overlap between a first beam after N rotations and a second beam after N + <NUM> rotations of the rotating portion.

It can be seen that there is a non-zero BED in the last rotation RLA during the acceleration phase, in which the size of the collimator opening is still increasing during this last rotation, but is kept constant in the next rotation RFSS (the first rotation in the steady state phase). However, it is noted that the BED is small compared to the collimator opening size, so can be considered negligible.

A similar BED can also be found for the rear edge of the beam in the first rotation. In the first rotation, ideally the rear edge of the beam shall be at position <NUM> but, in practice, there is small (≤<NUM>) difference to <NUM>. This is due to errors that can arise when trying to match a fixed position for the starting edge using a moving blade.

If desired, the non-zero BEDs can be compensated. To compensate the first identified non-zero BED (illustrated in <FIG>), the front beam edge of the last rotation in the acceleration phase can be set as the corresponding rear beam edge of the first rotation of the steady state phase.

To compensate the second identified non-zero BED (not illustrated) the rear beam edge position can be set at <NUM> in the first rotation.

<FIG> illustrates a method <NUM> according to an embodiment.

The method <NUM> comprises the method <NUM> (previously described) as well as a step <NUM> of obtaining, using a radiation measurement system mounted on the rotating portion, raw signal data (i.e. projection data) responsive to the absorption of radiation output by the radiation outputting system by a subject positioned on the subject support.

A typical radiation measurement system may be formed of an array of discrete radiation detection elements, each of which contributes to the raw signal data generated by the radiation measurement system. These discrete radiation detection elements may be arranged in a grid of rows (aligned in the direction of the z-axis, i.e. the direction of travel of the subject support) and columns.

The method may further comprise a step <NUM> of processing the raw signal data (projection data) to reconstruct one or more CT images from the raw signal data. The CT image(s) may comprise one or more 2D CT images and/or one or more 3D CT images.

Mechanisms for obtaining raw signal data (projection data) and reconstructing CT images from raw signal data are well known in the art.

Processes for performing steps <NUM> and <NUM> typically comprise iteratively sampling an amount of radiation incident on the radiation measurement system.

By way of further example, <FIG> illustrates an example of a processing system <NUM> within which one or more parts of an embodiment may be employed. The processing system <NUM> provides one example of a processing system <NUM> described with reference to <FIG>.

Various operations discussed above may utilize the capabilities of the processing system <NUM>. For example, one or more parts of a mechanism for controlling the operation of a computed tomography scanner may be incorporated in any element, module, application, and/or component discussed herein. In this regard, it is to be understood that system functional blocks can run on a single computer or may be distributed over several computers and locations (e.g. connected via Ethernet and/or fieldbus or the internet).

The processing system <NUM> includes, but is not limited to, PCs, workstations, laptops, PDAs, palm devices, servers, storages, and the like. Generally, in terms of hardware architecture, the processing system <NUM> may include one or more processors <NUM>, memory <NUM>, and one or more I/O devices <NUM> that are communicatively coupled via a local interface (not shown). The local interface can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface may have additional elements, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components.

The processor <NUM> is a hardware device for executing software that can be stored in the memory <NUM>. The processor <NUM> can be virtually any custom made or commercially available processor, a central processing unit (CPU), a digital signal processor (DSP), or an auxiliary processor among several processors associated with the processing system <NUM>, and the processor <NUM> may be a semiconductor based microprocessor (in the form of a microchip) or a microprocessor.

The software in the memory <NUM> may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. The software in the memory <NUM> includes a suitable operating system (O/S) <NUM>, compiler <NUM>, source code <NUM>, and one or more applications <NUM> in accordance with exemplary embodiments. As illustrated, the application <NUM> comprises numerous functional components for implementing the features and operations of the exemplary embodiments. The application <NUM> of the processing system <NUM> may represent various applications, computational units, logic, functional units, processes, operations, virtual entities, and/or modules in accordance with exemplary embodiments, but the application <NUM> is not meant to be a limitation.

When the application <NUM> is a source program, then the program is usually translated via a compiler (such as the compiler <NUM>), assembler, interpreter, or the like, which may or may not be included within the memory <NUM>, so as to operate properly in connection with the O/S <NUM>. NET, and the like.

The I/O devices <NUM> may include input devices such as, for example but not limited to, a mouse, keyboard, scanner, microphone, camera, etc. Furthermore, the I/O devices <NUM> may also include output devices, for example but not limited to a printer, display, etc. Finally, the I/O devices <NUM> may further include devices that communicate both inputs and outputs, for instance but not limited to, a network interface card (NIC) or modulator/demodulator (for accessing remote devices, other files, devices, systems, or a network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. The I/O devices <NUM> also include components for communicating over various networks, such as the Internet or intranet.

If the processing system <NUM> is a PC, workstation, intelligent device or the like, the software in the memory <NUM> may further include a basic input output system (BIOS) (omitted for simplicity). The BIOS is a set of essential software routines that initialize and test hardware at startup, start the O/S <NUM>, and support the transfer of data among the hardware devices. The BIOS is stored in some type of read-only-memory, such as ROM, PROM, EPROM, EEPROM or the like, so that the BIOS can be executed when the processing system <NUM> is activated.

When the processing system <NUM> is in operation, the processor <NUM> is configured to execute software stored within the memory <NUM>, to communicate data to and from the memory <NUM>, and to generally control operations of the processing system <NUM> pursuant to the software. The application <NUM> and the O/S <NUM> are read, in whole or in part, by the processor <NUM>, perhaps buffered within the processor <NUM>, and then executed.

The skilled person would be readily capable of developing a processing system for carrying out any herein described method. Thus, each step of the flow chart may represent a different action performed by a processing system, and may be performed by a respective module of the processing system.

Embodiments may therefore make use of a processing system. The processing system can be implemented in numerous ways, with software and/or hardware, to perform the various functions required. A processor is one example of a processing system which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the required functions. A processing system may however be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

Examples of processing system components that may be employed 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).

In various implementations, a processor or processing system may be associated with one or more storage media such as volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on one or more processors and/or processing systems, perform the required functions. Various storage media may be fixed within a processor or processing system or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or processing system.

It will be understood that disclosed methods are preferably computer-implemented methods. As such, there is also proposed the concept of a computer program comprising code means for implementing any described method when said program is run on a processing system, such as a computer. Thus, different portions, lines or blocks of code of a computer program according to an embodiment may be executed by a processing system or computer to perform any herein described method. In some alternative implementations, the functions noted in the block diagram(s) or flow chart(s) may occur out of the order noted in the figures.

Claim 1:
A computer-implemented method (<NUM>, <NUM>) of operating a computed tomography scanner (<NUM>) comprising a subject support (<NUM>) configured to move linearly and a rotating portion (<NUM>) that mounts a radiation outputting system (<NUM>, <NUM>) and controllably rotates around the subject support, the computer-implemented method comprising performing a scanning procedure comprising:
controlling (<NUM>) the radiation outputting system to output radiation during an imaging phase of the scanning procedure;
controlling (<NUM>) the subject support to move linearly, the linear movement of the subject support during the imaging phase of the scanning procedure including at least one acceleration (ta) or deceleration phase (td); and
controlling (<NUM>) one or more parameters of the computed tomography scanner responsive to the speed of the subject support, wherein the one or more parameters comprises at least a beam width (w) of the radiation output by the radiation outputting system, and
characterized in that
the step of controlling one or more parameters comprises controlling the beam width proportionally to the speed of the subject support.