Patent Description:
During a patient imaging operation, a moveable support of a couch assembly may move a patient to a specified position so that an imaging apparatus such as a computed tomography (CT) scanner may obtain imaging data at an imaging plane corresponding to a specified part of the patient's body. However, the accuracy of positioning of the patient with respect to the imaging plane may affect the outcome of the imaging operation. For example, if there is an error in the position of the patient relative to the imaging plane, the imaging data may not correspond to the specified part of the patient. In some cases, the patient may need to be moved again so that the specified part of the patient is imaged, which may unnecessarily increase patient exposure to radiation and/or increase the time spent performing the imaging operation. In some cases, the error may not be recognized, which may lead to an incorrect analysis of the imaging data. The error of patient position relative to imaging plane in a vertical direction has been discussed in <CIT> and <CIT>, and the error of patient position relative to imaging plane in a horizontal direction has been discussed in <CIT> and <CIT>.

Aspects or embodiments described herein may relate to improving the accuracy of positioning a subject such as a patient relative to an imaging apparatus. Aspects or embodiments described herein may obviate one or more problems associated with or arising from inaccurate positioning of a subject during an imaging operation.

In a first aspect, a method is described. The method is a computer-implemented method. The method comprises receiving an indication of a weight on a moveable support of a couch assembly. The moveable support is moveable relative to a couch frame of the couch assembly. The method further comprises determining a horizontal shift of the couch frame relative to an imaging apparatus associated with the couch assembly based on a shift model indicative of the horizontal shift as a function of: the indicated weight on the moveable support; and a horizontal position of the moveable support relative to the couch frame.

Some embodiments relating to the first and other aspects are described below.

In some embodiments, the method comprises receiving an indication of an expected position for the moveable support to move to relative to the couch frame to provide the moveable support at a specified position relative to the imaging apparatus. The method further comprises determining the horizontal shift for the expected position.

In some embodiments, the method comprises causing the moveable support to move to a modified position determined based on a difference between the expected position and the horizontal shift, such that the moveable support is provided at the specified position.

In some embodiments, causing the moveable support to move to the modified position comprises causing a moveable support actuator of the couch assembly to move the moveable support to the modified position.

In some embodiments, causing the moveable support to move to the modified position comprises: generating a command configured to cause the moveable support actuator to move the moveable support to the modified position; and sending the command to the moveable support actuator to cause actuation of the moveable support actuator according to the command.

In some embodiments, the moveable support actuator is configured to move the moveable support in a horizontal direction relative to a surface supporting the couch assembly, such that the moveable support is provided at the specified position.

In some embodiments, the indication of the weight comprises an indication of electrical current supplied to a couch frame actuator of the couch assembly. The couch frame actuator may be configured to control a height of the moveable support relative to a surface supporting the couch assembly.

In some embodiments, the couch frame actuator is configured to maintain the moveable support at a specified height during horizontal movement of the moveable support relative to the couch frame.

In some embodiments, the method comprises receiving the indication of the weight by receiving the indication of the electrical current. The method may further comprise estimating the weight by using a vertical force balancing model of the electrical current needed to provide the moveable support at a specified height. The method may further comprise receiving a command specifying an expected position to which the moveable support is to move to relative to the couch frame. The method may further comprise determining an expected shift of the couch frame according to the shift model based on the estimated weight and the expected position. The method may further comprise generating a revised, or 'modified', command specifying a modified position to which the moveable support is to move to relative to the couch frame based on a difference between the expected position and the expected shift for the expected position.

In some embodiments, the shift model is determined from a set of measured values for the horizontal shift and a corresponding set of indicated values for the horizontal position of the moveable support where the horizontal shift is measured.

In some embodiments, the shift model is based on a linear function fitted to the set of measured values for the horizontal shift and the corresponding set of indicated values for the horizontal position of the moveable support.

In some embodiments, the shift model is determined from the set of indicated values for the horizontal position of the moveable support at each of a set of indicated values for the weight on the moveable support.

In a second aspect, a tangible machine-readable medium is described. The tangible machine-readable medium comprises instructions which, when executed by at least one processor, cause the at least one processor to perform the method of the first aspect or any related embodiment.

In a third aspect, apparatus is described. The apparatus comprises at least one processor communicatively coupled to an interface configured to receive an indication of a weight on a moveable support of a couch assembly. The moveable support is moveable relative to a couch frame of the couch assembly. The apparatus further comprises a tangible machine-readable medium storing instructions readable and executable by the at least one processor to perform a method. The method comprises receiving the indication of the weight. The method further comprises determining a horizontal shift of the couch frame relative to an imaging apparatus associated with the couch assembly based on a shift model indicative of the horizontal shift as a function of: the indicated weight on the moveable support; and a horizontal position of the moveable support relative to the couch frame.

An embodiment relating to the third aspect and other aspects is described below.

In some embodiments, the interface is further configured to receive an indication of an expected position for the moveable support to move to relative to the couch frame to provide the moveable support at a specified position relative to the imaging apparatus. The interface may further be configured to send a command to a moveable support actuator of the couch assembly. The command may be configured to actuate the moveable support actuator. The instructions may further comprise instructions readable and executable by the at least one processor to perform a method. The method comprises receiving the indication of the expected position. The method may further comprise determining the horizontal shift for the expected position. The method may further comprise causing the moveable support to move to a modified position determined based on a difference between the expected position and the horizontal shift, such that the moveable support is provided at the specified position, by: generating the command configured to cause the moveable support actuator to move the moveable support to the modified position; and sending the command, via the interface, to the moveable support actuator to cause actuation of the moveable support actuator according to the command.

Exemplary embodiments of the invention will now be described, by way of example only, with reference to the following drawings, in which:.

<FIG> is a schematic drawing of an example couch assembly <NUM> associated with an imaging apparatus <NUM> such as a computed tomography (CT) scanner. The couch assembly <NUM> is used to support a subject <NUM> such as a patient. Two configurations, (a) and (b), of the couch assembly <NUM> are shown. For ease of illustration, certain reference signs or connecting elements are not shown in both configurations.

As shown by configuration (a), the subject <NUM> is positioned on a moveable support <NUM> of the couch assembly <NUM>. The moveable support <NUM> may sometimes be referred to as a 'table', 'table top' or 'couch'. As shown by configuration (b), movement of the moveable support <NUM> from the position shown in configuration (a) has positioned the subject <NUM> in an imaging plane <NUM> associated with the imaging apparatus <NUM>. Thus, by moving the moveable support <NUM> relative to the imaging plane <NUM>, different parts of the subject <NUM> may be imaged. For example, multiple imaging 'slices' may be obtained at different axial positions along the subject <NUM> by moving the subject <NUM> relative to the imaging plane <NUM> and acquiring an image at each of the axial positions.

The couch assembly <NUM> also comprises a couch frame <NUM> for supporting the moveable support <NUM> and facilitating movement (e.g., horizontal movement) of the moveable support <NUM> relative to the imaging apparatus <NUM>. The couch frame <NUM> is configured to balance the weight, W, of the subject <NUM> (and any other equipment supported by the moveable support <NUM>) so that the subject <NUM> can be positioned at a specified distance (e.g., height) above a surface <NUM> such as the floor upon which the couch assembly <NUM> is positioned.

In this example couch assembly <NUM>, the couch frame <NUM> comprises a scissor mechanism <NUM> for supporting a base member <NUM> upon which the moveable support <NUM> is mounted. Other mechanisms are possible as described below. In this example, the scissor mechanism <NUM> comprises two ('lever') members <NUM> which are configured to lever relative to each other via a pivot <NUM> at the center of each member <NUM>.

One end of each member <NUM> is pivotably connected to the base member <NUM> while another end of each member <NUM> is pivotably mounted on the surface <NUM>. The ends of the two members <NUM> pivotably connected to the base member <NUM> are moveably spaced apart from each other so that the base member <NUM> is appropriately supported by the scissor mechanism <NUM> (e.g., so that the base member <NUM> is parallel to the surface <NUM>). Similarly, the other ends of the two members <NUM> pivotably mounted on the surface <NUM> are moveably spaced apart from each other. The couch assembly <NUM> comprises a couch frame actuator <NUM> (e.g., an electric motor) configured to control/adjust the height of the subject <NUM> by causing the members <NUM> to lever relative to each other (while also causing relative movement between the ends of the members <NUM> connected to the base member <NUM>). In this embodiment, the couch frame actuator <NUM> is mounted on the surface <NUM> and is configured to apply a force to the end of one of the members <NUM> mounted on the surface <NUM>. The end of the other member <NUM> mounted on the surface <NUM> is fixed in place, as indicated by fixed mount <NUM>.

Thus, in use, the couch frame actuator <NUM> may apply a force on the member <NUM> to cause the ends of the members <NUM> mounted on the surface <NUM> to move closer together. Due to the lever motion about the pivot <NUM>, this movement of the members <NUM> raises the base member <NUM>, hence also raising the subject <NUM>. The weight, W, may be balanced using a specified force applied by the couch frame actuator <NUM>. By varying this force, the subject <NUM> may be raised or lowered relative to the surface <NUM>. In the case that the couch frame actuator <NUM> comprises an electric motor, the electrical current supplied to the electric motor may be varied to controllably adjust the height of the subject <NUM>.

As highlighted above, the configuration of the scissor mechanism <NUM> and associated parts of the couch assembly <NUM> may differ to that shown and described in relation to <FIG>. For example, the two members <NUM> may not be configured in a scissor-like arrangement as shown by <FIG> but instead may move independently of each other (e.g., the members <NUM> may not be connected to each other via a pivot <NUM>). Further, the number of members <NUM> may differ (e.g., more than two members <NUM> may be used or one member may be used). Further, the configuration of the couch frame actuator <NUM> may be different (e.g., the couch frame actuator <NUM> may be connected to a different part of the member <NUM>, etc.).

Therefore, in terms of function, the couch assembly <NUM> is configured to facilitate adjustment/control of the height of the subject <NUM> while balancing the weight, W, so that the subject <NUM> can be provided at the specified height. Any configuration of couch assembly <NUM> that facilitates such a function may be relevant to this disclosure.

It shall be appreciated that the configuration shown in <FIG> is schematic to better illustrate possible components of the couch assembly <NUM> and therefore the configuration and design of the components may differ to that shown by <FIG>.

As will now be described, the configuration of the couch assembly <NUM> may lead to an error in terms of the positioning of the subject <NUM> relative to the imaging apparatus <NUM>.

The couch assembly <NUM> comprises a moveable support actuator <NUM> for moving the moveable support <NUM> relative to the couch frame <NUM>. In this example, the moveable support actuator <NUM> is mounted between the base member <NUM> and the moveable support <NUM>. In use, the moveable support actuator <NUM> (such as an electric motor, hydraulic system, etc.) applies a force between the base member <NUM> and the moveable support <NUM> to cause relative movement therebetween. The moveable support <NUM> is mounted on a sliding mechanism <NUM> (e.g., at least one roller) mounted on the base member <NUM> to facilitate movement (e.g., sliding movement) between the moveable support <NUM> and the base member <NUM>.

In order to move between the configurations, (a) and (b), a command ('L1_cmd') is sent by a controller <NUM> communicatively coupled to the moveable support actuator <NUM> to cause the moveable support <NUM> to move a distance 'L1' so that the end of the moveable support <NUM> overhanding the couch frame <NUM> is at a specified position <NUM> (which means that the subject <NUM> is provided at a specified position defined by the command, L1_cmd). There may be an error, 'err1', in the actual distance moved. Therefore, a correcting mechanism such as a servo motor (not shown) may correct for this error, err1.

The controller <NUM> (or a different controller) may also be communicatively coupled to the couch frame actuator <NUM>. Therefore, in use, the controller <NUM> may send commands to the couch frame actuator <NUM> to control/adjust the vertical position (e.g., height) of the subject <NUM> and/or the moveable support actuator <NUM> to control/adjust the position (e.g., horizontal position) of the subject <NUM> relative to the imaging apparatus <NUM>. The controller <NUM> may receive feedback from the couch frame actuator <NUM> and/or moveable support actuator <NUM> such as an indication of electrical current supplied and/or an indication of the configuration of the couch frame actuator <NUM> and/or moveable support actuator <NUM>.

Between the two configurations, (a) and (b), a position of the center of gravity is shifted when the subject <NUM> is moved, by the moveable support <NUM>, towards and into the imaging plane <NUM> so that the end of the moveable support <NUM> overhanging the couch frame <NUM> is provided at the specified position <NUM>.

In configuration (a), a force F1 acts on the couch frame <NUM> at the point indicated in <FIG> (i.e., where the ends of the members <NUM> are connected to the base member <NUM>).

In configuration (b), a larger force F2 acts on the couch frame <NUM> at the same point since the center of gravity has shifted to a position that is no longer acting over the center of the couch frame <NUM>, as depicted by configuration (a).

This larger force F2 leads to additional compression of the couch frame <NUM> with a corresponding horizontal shift of the couch frame <NUM>. This leads to movement of the couch frame <NUM>, relative to the surface <NUM>, towards the imaging apparatus <NUM>. In some cases, this compression may also result in a (relatively small) reduction in the height of the couch frame <NUM>. As shown by configuration (b), the position of the couch frame <NUM> is shifted by a distance, L2, from the previous position of the couch frame <NUM>. In particular, the end the base member <NUM> in configuration (a) is indicated by line <NUM> in configuration (b). The distance between the end of the base member <NUM> and the line <NUM> corresponds to the shift, L2. Thus, the larger the distance, L1, the larger the distance, L2, since more force acts on the couch frame <NUM> due to shifted center of gravity causing an increase in the lever effect acting on the scissor mechanism <NUM>.

However, it may not be possible for the correcting mechanism for correcting the error, err1, associated with L1 to correct for the shift, L2.

While in configuration (a), the motion control reference frame of the moveable support <NUM> is based on the couch frame <NUM> (i.e., the movement of the moveable support <NUM> is defined with respect to a frame of reference defined by the couch frame <NUM>). However, the reference frame of the couch frame <NUM> itself is defined in relation to the surface <NUM> (e.g., a 'ground' reference frame). Similarly, the imaging apparatus <NUM> is fixed in relation to the surface <NUM>. Thus, if it is assumed that the couch frame <NUM> and imaging apparatus <NUM> are fixed relative to each other, then movement of the moveable support <NUM> is relative to the surface <NUM> itself. For example, when the couch frame <NUM> is not shifted, as indicated by configuration (a), the frame of reference of the moveable support <NUM> and couch frame <NUM> is the same.

However, when the couch frame <NUM> is shifted as indicated by configuration (b), a deviation/offset is introduced which means that the assumption about the frames of reference cannot be relied upon to ensure accurate positioning of the subject <NUM> relative to the imaging apparatus <NUM>. The deviation/offset may affect the quality and/or outcome of the imaging operation. In some cases, the deviation may be such that additional images need to be acquired, which may unnecessarily increase patient exposure to radiation and/or increase the time spent performing the imaging operation. In some cases, the error may not be recognized, which may lead to an incorrect analysis of the imaging data.

At present, the deviation/offset of the couch frame <NUM> is not considered and therefore a systematic error may be introduced that is proportional to the movement distance, L1. Embodiments described herein may facilitate correction of this deviation/offset. For example, certain embodiments described herein may determine the couch frame shift. Certain embodiments may take action to correct for the determined couch frame shift.

<FIG> shows a method <NUM> (e.g., a computer-implemented method) of determining couch frame shift according to an embodiment. In the discussion of method <NUM>, reference is made to <FIG> depicts a controller <NUM> which may implement the method <NUM>. The controller <NUM> may be implemented by a computer such as a user computer communicatively coupled to a user interface, or a server or cloud-based service (e.g., communicatively coupled to the user computer and/or user interface). Thus, the method <NUM> may be implemented in situ (e.g., on a user computer in the locality of the couch assembly <NUM>) or in another location (e.g., on a server or in the cloud). Commands and/or feedback may be communicated between the controller <NUM> and the couch frame actuator <NUM> and/or moveable support actuator <NUM> to facilitate the implementation of certain methods described herein (e.g., method <NUM>).

The method <NUM> comprises, at block <NUM>, receiving an indication of a weight on a moveable support <NUM> of a couch assembly <NUM>. The moveable support <NUM> is moveable relative to a couch frame <NUM> of the couch assembly <NUM>. Further discussion on the indication of the weight is provided below.

The method <NUM> further comprises, at block <NUM>, determining a shift, L2, of the couch frame <NUM> relative to an imaging apparatus <NUM> associated with the couch assembly <NUM>. The determination of the shift, L2, is based on a shift model (a description of which is given below) indicative of the shift as a function of: the indicated weight on the moveable support <NUM>; and a position of the moveable support <NUM> relative to the couch frame <NUM>. The position of the moveable support <NUM> may be defined in relation to the distance L1 moved. For example, the end of the moveable support <NUM> is at the specified position <NUM> according to the distance L1 moved.

The method <NUM> may allow the couch frame shift to be determined. Accordingly, as will be described in more detail below, a correction can be applied to the command, L1_cmd, to ensure that the subject <NUM> is provided at a specified position. For example, during an imaging operation, an operator may command the moveable support <NUM> to move to a specified position (e.g., defined by a fixed point such as the end of the moveable support <NUM> being provided at the specified position <NUM>). However, to correct for the couch frame shift which may otherwise lead to the subject <NUM> being moved to an incorrect (e.g., unexpected) position, the command may be modified to take into account the (expected) couch frame shift so that the subject <NUM> is moved to a correct (e.g., expected or specified) position.

Such a correction may improve the quality and/or outcome of the imaging operation. In some cases, the correction may avoid the need to acquire additional images. In some cases, the correction may improve the quality and/or outcome of analysis of the imaging data.

<FIG> shows a method <NUM> (e.g., a computer-implemented method) of determining and correcting for couch frame shift according to various embodiments. The method <NUM> may be implemented in the same way as method <NUM> (e.g., using the controller <NUM>). For example, the method <NUM> may comprise the same or similar functionality as the method <NUM>. Reference is made to <FIG> and <FIG>, where appropriate. Certain blocks of the method <NUM> may not need to be implemented and/or certain blocks of the method <NUM> may be performed in a different order to that shown by <FIG>.

In some embodiments, the method <NUM> comprises, at block <NUM>, receiving <NUM> an indication of an expected position for the moveable support <NUM> to move to relative to the couch frame <NUM> to provide the moveable support <NUM> at a specified position <NUM> relative to the imaging apparatus <NUM>. The `expected position' may refer to a position to which the moveable support <NUM> is to move (i.e., after the command, L1_cmd, has been executed). The `expected position' is based on the assumption that the frame of reference of the couch frame <NUM> does not shift upon moving the moveable support <NUM> to the specified position <NUM>. However, the command, L1_cmd, may not lead to the moveable support <NUM> being moved to the specified position <NUM>. Rather, the command L1_cmd does not take into account the shift described above. Thus, the method <NUM> further comprises, at block <NUM>, determining the shift for the expected position (e.g., in accordance with the method <NUM>).

In some embodiments, the method <NUM> comprises, at block <NUM>, causing the moveable support <NUM> to move to a modified position determined based on a difference between the expected position and the shift, such that the moveable support <NUM> is provided at the specified position <NUM> (i.e., as expected). Thus, the `modified position' takes into account the shift, L2. In other words, if the couch frame is shifted by L2 then the command, L1_cmd, may be modified to take this into account. For example, if the shift is a distance L2, then the command may specify that the moveable support <NUM> is to move by a distance L1-L2. As a result of this modified command, the subject <NUM> may be positioned correctly, or as expected (since the modified position, L1-L2, of the moveable support <NUM> relative to the couch frame <NUM> results in the moveable support <NUM> being correctly provided at the specified position <NUM>).

In some embodiments, causing the moveable support <NUM> to move to the modified position comprises, at block <NUM>, causing the moveable support actuator <NUM> of the couch assembly <NUM> to move the moveable support <NUM> to the modified position.

In some embodiments, the method <NUM> of causing the moveable support to move to the modified position according to block <NUM> comprises, at block <NUM>, generating a command configured to cause the moveable support actuator <NUM> to move the moveable support <NUM> to the modified position (e.g., with respect to the frame of reference defined by the couch frame <NUM>). Block <NUM> further comprises, at block <NUM>, sending the command to the moveable support actuator <NUM> to cause actuation of the moveable support actuator <NUM> according to the command.

In some embodiments, the moveable support actuator <NUM> is configured to move the moveable support <NUM> in a horizontal direction relative to the surface <NUM> supporting the couch assembly <NUM>, such that the moveable support <NUM> (e.g., the end of the moveable support <NUM> overhanging the couch frame <NUM>) is provided at the specified position <NUM>.

In some embodiments, the couch frame actuator <NUM> is configured to control a height of the moveable support <NUM> relative to the surface <NUM>.

In some embodiments, the indication of the weight comprises an indication of electrical current supplied to the couch frame actuator <NUM>.

In some embodiments, the couch frame actuator <NUM> is configured to maintain the moveable support <NUM> at a specified height during horizontal movement of the moveable support <NUM> relative to the couch frame <NUM>.

An embodiment describing estimation of the weight (used to provide the indication of the weight) is described in more detail below.

<FIG> shows a simplified illustration of a couch assembly <NUM> similar to the couch assembly <NUM> depicted by <FIG>. Reference signs for features of the couch assembly <NUM> that are the same as or similar to corresponding features of the couch assembly <NUM> are incremented by <NUM>. Some features are not shown or described for ease of illustration and reference is made to <FIG>, where appropriate.

The couch assembly <NUM> has a scissor mechanism, which can be modeled to determine the weight, W. The weight, W, of the components of the couch assembly <NUM> such as the base member <NUM> and moveable support (not shown) are fixed. However, the weight may vary depending on the weight of the subject and any other equipment (not shown) provided on the moveable support <NUM>.

The couch frame actuator <NUM> is used to balance the vertical force applied due to the weight of the components and the subject, etc. In case the couch frame actuator <NUM> comprises an electric motor for applying a force to balance the vertical force, the electrical current supplied to the electric motor may be varied accordingly. Based on the electrical current feedback, the weight, W, can be estimated using the following vertical force balancing model: <MAT> <MAT> <MAT> <MAT> <MAT>.

Where: theta 'θ' is the internal angle between the member <NUM> and the surface <NUM>; g is the gravitational force coefficient (a constant); H is the couch frame <NUM> height; h1 is the base member <NUM> (sub-pallet) height; h2 is the couch base <NUM> (not shown previously but the top of the couch base <NUM> represents the surface <NUM>) height; F is the force applied by the couch frame actuator <NUM> on the member <NUM>; p is the screw lead associated with a screw (connecting the member <NUM> to the couch frame actuator <NUM>) driven by the couch frame actuator <NUM>; T is the motor torque associated with the couch frame actuator <NUM>; i is the transmission ratio; ηT is the transmission efficiency; ηe is the motor efficiency; KT is the motor torque coefficient; I is the electrical current supplied to the couch frame actuator <NUM>; R is the half-length of the member <NUM>; r is the radius of the pivot <NUM>.

In the above expressions, the height of H and motor current of I are variables, and the other parameters are constant. In order to simplify the weight estimation, the height H of couch is assumed to be fixed during estimation of the weight. It is also assumed that the relationship between weight, W, and electrical current, I, is linear. A linear curve may therefore be fitted to actual measurement data of the electrical current. In other words, the electrical current, I, may linearly depend on the weight, W.

Accordingly, the weight may be estimated such that an indication of this weight may be used to determine the shift in accordance with certain methods described herein. Rather than having a separate sensor for measuring the weight, certain embodiments may facilitate a simple way to estimate the weight.

<FIG> shows a method <NUM> (e.g., a computer-implemented method) of determining and correcting for couch frame shift according to an embodiment. In this embodiment, the method <NUM> uses the weight estimation determined according to the model described in relation to <FIG>, although in other embodiments the weight estimation may be provided by a separate weight sensor (not shown). The method <NUM> may be implemented in the same way as methods <NUM>, <NUM> (e.g., using the controller <NUM>). For example, the method <NUM> may comprise the same or similar functionality as the methods <NUM> and/or <NUM>. Reference is made to the previous Figures, where appropriate. Certain blocks of the method <NUM> may not need to be implemented and/or certain blocks of the method <NUM> may be performed in a different order to that shown by <FIG>.

The method <NUM> comprises, at block <NUM>, receiving the indication of the weight by receiving the indication of the electrical current (e.g., the electrical current referred to in <FIG>).

The method <NUM> further comprises, at block <NUM>, estimating the weight by using a vertical force balancing model (e.g., as described in relation to <FIG>) of the electrical current needed to provide the moveable support <NUM> at a specified height.

The method <NUM> further comprises, at block <NUM>, receiving a command (e.g., 'L1_cmd') specifying an expected position to which the moveable support <NUM> is to move to relative to the couch frame <NUM>.

The method <NUM> further comprises, at block <NUM>, determining an expected shift (e.g., 'L2') of the couch frame according to the shift model (referred to in <FIG> and described in more detail below) based on the estimated weight and the expected position (e.g., defined by 'L1').

The method <NUM> further comprises, at block <NUM>, generating a revised command specifying a modified position to which the moveable support <NUM> is to move to relative to the couch frame <NUM> based on a difference between the expected position and the expected shift for the expected position (e.g., 'L1-L2').

A description of how to determine the `shift model' for determining the couch frame shift is now given.

The shift model is determined by taking measurements of the actual position of the couch frame <NUM> relative to the imaging apparatus <NUM> (e.g., a ground reference frame) for a set of (horizontal) positions (in the range <NUM> to <NUM>) of the moveable support <NUM> for each of a set of different weights (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) on the moveable support <NUM>. The `actual position' may be measured using an independent measurement of the distance between a fixed point on the moveable support <NUM> (e.g., the end of the moveable support <NUM> overhanging the couch frame <NUM> or another appropriate point) and a fixed point defined in relation to the surface <NUM> (e.g., on the imaging apparatus <NUM> itself or another appropriate point). Such an independent measurement may be performed by a laser-based position encoder, e.g., using laser-based interferometry.

Thus, in this example, there are six datasets - one for each weight, where the shift (i.e., the difference between the actual position and the expected position of the moveable support <NUM>) is measured for a set of positions in the range <NUM> to <NUM>.

<FIG> depicts a graph of the shift (in mm) as a function of the (expected) position (in mm) of the moveable support <NUM> (relative to the couch frame <NUM>) for each of the six datasets. The steepest curve corresponds to the heaviest weight, <NUM>, while the gentlest curve corresponds to the lightest weight, <NUM>.

As will be recognized, the shift curve is linear and can be fitted with linear function, such as: Y=K(W)*P+D(W), where Y is the measured shift; K(W) is the proportion coefficient (corresponding to the slope of the dataset as a function of the weight, W); P is the expected position of the moveable support <NUM>, D(W) is the offset (corresponding to where the fitted curve intercepts the y-axis). The curve may be fitted with any appropriate algorithm such as a linear regression algorithm. For the depicted datasets, the curve is fitted with confidence bounds of <NUM>%.

In order to obtain a linear function of K(W) and D(W) with respect to the weight, W, K(W) and D(W) are plotted for each weight, as described below.

<FIG> depicts a graph plotting K(W) and D(W) as a function of the weight, W, as well as linear curves fitted to each variable. The confidence bounds are <NUM>%. The positive slope shown in <FIG> represents K(W), while the negative slope represents D(W). Accordingly, if the weight, W, is estimated as described above, the couch frame shift curve can be determined (as function of the expected position of the moveable support <NUM>) by obtaining K(W) and D(W) for the estimated weight. The values K(W) and D(W) therefore represent a `shift model' as referred to above.

In other words, the `shift model' may be represented by a proportion coefficient and an offset fitted to a set of measurement data, where the measurement data comprises an actual measurement of the position of the moveable support <NUM> (relative to the imaging apparatus <NUM> or 'ground' reference frame) at each of a set of expected positions of the moveable support <NUM> (to determine the 'actual' shift). The measurement data can be scaled by weight so that the shift model depends on the weight, e.g., as indicated by the electrical current described above.

Some embodiments relating to the shift model are described below.

In some embodiments, the shift model is determined from a set of measured values for the shift and a corresponding set of indicated values for the position of the moveable support <NUM> where the shift is measured.

In some embodiments, the shift model is based on a linear function fitted to the set of measured values for the shift and the corresponding set of indicated values for the position of the moveable support <NUM>.

In some embodiments, the shift model is determined from the set of indicated values for the position of the moveable support at each of a set of indicated values for the weight on the moveable support <NUM>.

In order to correct for the shift as determined in accordance with the shift model, the command (e.g., 'L1_cmd') may be modified based on the (expected) position of the moveable support <NUM>. For example, if the command is configured to cause the moveable support <NUM> to move by a distance `D1', the shift `S1' may be estimated using the shift model according to S1=K(W)*D1 (e.g., if the offset is relatively small). Thus, the command may be modified as 'D1-S1', or '(<NUM>-K(W))*D1'. In use, the shift model may be used to modify the commands that are otherwise generated and sent to the moveable support actuator <NUM>.

In other words, a command received by the controller <NUM> to move the moveable support <NUM> by an (expected) distance, D1, may be modified by the difference between D1 and the (estimated) shift, i.e., D1-S1.

Accordingly, certain embodiments described herein may compensate for motion error introduced by the shift without adding any additional sensors to the set-up. In some embodiments, a force balancing model may be used to estimate the load, or weight, on the moveable support <NUM>. A shift model may be generated based on a set of measurements. The shift model may be used to estimate the couch frame shift for a given position of the moveable support <NUM> at the estimated weight. Accordingly, certain embodiments may facilitate correction of the motion commands used to drive the moveable support <NUM> to a specified position such that the subject <NUM> is more accurately positioned with respect to the imaging apparatus <NUM> (compared with if the shift is not taken into account).

<FIG> shows a tangible machine-readable medium <NUM> according to an embodiment. The tangible machine-readable medium <NUM> comprises instructions <NUM> which, when executed on at least one processor <NUM>, cause the at least one processor <NUM> to implement certain methods described herein (e.g., methods <NUM>, <NUM>, <NUM>). Any of the methods described herein may be implemented by virtue of the tangible machine-readable medium <NUM> causing the at least one processor <NUM> to implement such methods.

<FIG> shows apparatus <NUM> for determining couch frame shift according to various embodiments. The apparatus <NUM> comprises at least one processor <NUM> (e.g., implemented by the controller <NUM> depicted by <FIG>). The at least one processor <NUM> is communicatively coupled to an interface <NUM> for communicating with the couch frame actuator <NUM> and/or the moveable support actuator <NUM> (e.g., for receiving information such as electrical current indications and/or sending commands to control the respective actuator <NUM>, <NUM>). In this embodiment, the interface <NUM> is configured to receive an indication of a weight on the moveable support <NUM>. As indicated previously, the moveable support <NUM> is moveable relative to the couch frame <NUM> of the couch assembly <NUM>. The interface <NUM> may be part of the controller <NUM> referred to in <FIG>. Reference is made to certain features of the previous Figures in the description of the apparatus <NUM>.

The apparatus <NUM> further comprises a tangible machine-readable medium <NUM> storing instructions <NUM> readable and executable by the at least one processor <NUM> to perform a method corresponding to certain methods described herein (e.g., any of the methods <NUM>, <NUM> and/or <NUM>).

In an embodiment, the instructions <NUM> are configured to cause the at least one processor <NUM> to perform the method <NUM>.

In some embodiments relating to the above embodiment, the interface <NUM> is further configured to receive an indication of an expected position for the moveable support <NUM> to move to relative to the couch frame <NUM> to provide the moveable support <NUM> at a specified position <NUM> relative to the imaging apparatus <NUM>. The interface <NUM> may further be configured to send a command to a moveable support actuator <NUM> of the couch assembly <NUM>. Such a command may be configured to actuate the moveable support actuator <NUM>. In such embodiments, the instructions <NUM> may be configured to cause the at least one processor <NUM> to perform the method <NUM>. In the context of the apparatus <NUM>, the method <NUM> comprises receiving the indication of the expected position; determining the shift for the expected position; and causing the moveable support <NUM> to move to a modified position determined based on a difference between the expected position and the shift, such that the moveable support <NUM> is provided at the specified position <NUM>. A 'modified' command generated to cause the moveable support <NUM> to move is configured to cause the moveable support actuator <NUM> to move the moveable support <NUM> to the modified position. The modified command is sent, via the interface <NUM>, to the moveable support actuator <NUM> to cause actuation of the moveable support actuator <NUM> according to the command.

In some embodiments, any other method or combination of methods according to the various embodiments described herein may be implemented by storing instructions (e.g., instructions <NUM>, <NUM>) which, when executed by at least one processor <NUM>, <NUM> cause the method to be implemented.

One or more features described in one embodiment may be combined with or replace features described in another embodiment.

Embodiments in the present disclosure can be provided as methods, systems or as a combination of machine-readable instructions and processing circuitry. Such machine-readable instructions may be included on a non-transitory machine (for example, computer) readable storage medium (including but not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

The present disclosure is described with reference to flow charts and block diagrams of the method, devices, and systems according to embodiments of the present disclosure. Although the flow charts described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. It shall be understood that each block in the flow charts and/or block diagrams, as well as combinations of the blocks in the flow charts and/or block diagrams can be realized by machine readable instructions.

The machine-readable instructions may, for example, be executed by a general-purpose computer, a special purpose computer, an embedded processor, or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing circuitry, or a module thereof, may execute the machine-readable instructions. Thus, functional modules of apparatus and other devices described herein may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term 'processor' is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc. The methods and functional modules may all be performed by a single processor or divided amongst several processors.

Such machine-readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode.

Such machine-readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer-implemented processing, thus the instructions executed on the computer or other programmable devices realize functions specified by block(s) in the flow charts and/or in the block diagrams.

Further, the teachings herein may be implemented in the form of a computer program product, the computer program product being stored in a storage medium and comprising a plurality of instructions for making a computer device implement the methods recited in the embodiments of the present disclosure.

Claim 1:
A computer-implemented method (<NUM>), comprising:
receiving (<NUM>) an indication of a weight on a moveable support (<NUM>) of a couch assembly (<NUM>), the moveable support being moveable relative to a couch frame (<NUM>) of the couch assembly;
determining (<NUM>) a horizontal shift of the couch frame relative to an imaging apparatus (<NUM>) associated with the couch assembly based on a shift model indicative of the horizontal shift as a function of:
the indicated weight on the moveable support; and
a horizontal position of the moveable support relative to the couch frame.