Patent Description:
In computed tomography (CT), instability of focal positions of an X-ray tube may lead to a decrease in image quality and even result in image artifacts. Focus shifts are mainly caused by the thermal conditions of an X-ray tube.

It is well known that during a scan, the anode plate of the X-ray tube expands when heated, and the focal position moves in one direction along the Z-axis; when the scan has stopped, as the temperature decreases, the anode plate of the X-ray tube will be turned around and move in the opposite direction. This phenomenon is particularly evident in the Z-direction of the tube, and if no corrective measures are taken, an X-ray having passed through the collimator (TCO) will deviate from an effective detector area, which will result in a decrease in image quality. As shown in <FIG>, the CT machine comprises an anode plate <NUM> for generating X-rays. The collimator used for the CT machine comprises a slot plate <NUM> and a controller <NUM>. When the anode plate expands due to heat, the focal position <NUM> will move in one direction along the Z-axis to <NUM>', so when the scan target <NUM> on the scanning table <NUM> is scanned, the X-ray will have displacements.

<CIT> discloses an X-ray tube that is heated under an X-ray scan condition and thus a focal point is shifted. Artifact occurs in a reconstructed image due to the focal point shift. The invention has an object to enable correction of the focal point shift caused by heating the tube. The applicant and inventor of this application has confirmed that the focal point shift amount of the tube varies in accordance with whether it is in a heating direction or cooling direction when viewed from a past sequence. Therefore, the sequence record and the focal point shift amount based on the heating and cooling directions are stored as data in a storage device. A just near past sequence record when viewed from now is stored in a storage unit, and the tube temperature is detected by a tube temperature detector. On the basis of this temperature and the data in the storage unit, heating or cooling and the present accumulated heat capacity are determined in a determining unit, and the storage device is accessed to determine a focal point shift amount. The position of the tube is corrected on the basis of this shift amount.

To address this problem, thermal Z-control is the most commonly used to compensate for focus shift. With this method, real-time data obtained by the detector are used, and the distance to be covered by the slot plate is calculated to ensure that the X-ray remains within an effective area of the scan target <NUM>.

As shown in <FIG>, the Z-direction displacement of segment P represents the Z-direction displacement of the slot plate during a scan, and since no X-ray is emitted during the scan stop period from the closing of the previous scan till the start of the next scan, thermal Z-control cannot be performed. Therefore, when a scan has stopped, the Z-direction displacement of the slot plate is within the scan stop period, and the slot plate has no displacement. When the next scan starts, the actual focus position has substantially deviated from the slot plate position, which results in a decrease in image quality at the beginning of the scan.

An objective of the present invention is to provide a tuning method for a collimator of a CT machine, which makes it possible to control the displacement of the slot plate during the scan stop stage, thereby improving the image scan quality of the CT machine.

The present invention provides a collimator for a CT machine. The CT machine comprises an anode plate. The collimator comprises a slot plate and a controller. The tuning method for a collimator of a CT machine, which, in each cycle of an X-ray scan operation and a stop, comprises: a detection step of determining whether an X-ray is generated from the anode plate; if an X-ray is detected in the detection step, the controller calculates the Z-direction heating displacement <MAT> of the slot plate during the current scan, wherein a indicates the current cycle; the controller drives the slot plate to move by the heating displacement in the Z-direction; if no X-ray is detected in the detection step, the controller calculates the total Z-direction heating displacement <MAT> of the slot plate at the end of the current scan; the controller, on the basis of the stop time of the X-ray, calculates the cooling displacement <MAT> of the slot plate during the current stop; and the controller drives the slot plate to move.

With the tuning method for a collimator of a CT machine provided by the present invention, by "learning control", the slot plate can, on the basis of the total displacement of the previous scan and the stop time, control the displacement of the slot plate during the scan stop stage, thereby minimizing the substantial jitter of the slot plate at the beginning and at the end of a scan, which, in turn, reduces risks of image quality degradation.

In an illustrated embodiment of the tuning method for a collimator of a CT machine, the cooling displacement <MAT> at the time of the current stop is the difference between the total heating displacement <MAT> of the current scan and f (ΔTα), a function of the current stop time ΔTα, namely <MAT> ΔTα). Thus, a linear model may be used to estimate the cooling displacement generated at the time when a scan is performed again after cooling following a scan stop.

In another schematic embodiment of the tuning method for a collimator of a CT machine, f (ΔTα) , a function of the current stop time, is a linear function, namely f (ΔTα) = κ· ΔTα, wherein κ is the thermal coefficient of the anode plate. During the scan stop ΔT, the X-ray tube cools down because no scan is performed. Therefore, the focal position keeps drifting in a direction opposite to a heating direction. Therefore, a linear equation in units of time ΔT is established to estimate the required slot plate position before the next scan.

In another illustrated embodiment of the tuning method for a collimator of a CT machine, the method, in each cycle of an X-ray scan operation and a stop, further comprises a step of comparing the cooling displacement <MAT> at the current stop with a predetermined cooling position Zmin of the slot plate; if the cooling displacement <MAT> is not smaller than the predetermined cooling position Zmin, the controller drives the slot plate to move by the cooling displacement <MAT>; if the cooling displacement <MAT> is smaller than the predetermined cooling position Zmin, the controller drives the slot plate to move by the predetermined cooling position Zmin. When the calculated slot plate displacement exceeds a predetermined value, the displacement is a linear change, and when the calculated slot plate displacement is smaller than a predetermined value, the slot plate is displaced by the predetermined value.

In another illustrated embodiment of the tuning method for a collimator of a CT machine, the total heating displacement <MAT> of the current scan is the sum of the total cooling displacement <MAT> of the previous scan and the heating displacement <MAT> of the current scan, namely <MAT>.

In another illustrated embodiment of the tuning method for a collimator of a CT machine, the heating displacement <MAT> of the current scan is the sum of the displacements in the successive movements made by the slot plate during the current scan, namely <MAT>, wherein n is the total number of slot plate movements during the current scan. Therefore, <MAT> may also be expressed as <MAT> <MAT>. Therefore, the heating displacement during a scan may change by a gradient.

In another illustrated embodiment of the tuning method for a collimator of a CT machine, f (ΔTα), a function of the current stop time, is a linear function, namely f (ΔTα), = κ· ΔTα, wherein κ is the thermal coefficient of the anode plate. Therefore, the heating displacement during a scan may change linearly.

In another illustrated embodiment of the tuning method for a collimator of a CT machine, the method, in each cycle of an X-ray scan operation and a stop, further comprises a step of comparing the calculated heating displacement <MAT> of the current scanning with a predetermined heating displacement Zmax of the slot plate; if the calculated heating displacement <MAT> is not greater than the predetermined heating displacement Zmax, the controller drives the slot plate to move by the heating displacement <MAT>; if the calculated heating displacement <MAT> is greater than the predetermined heating displacement Zmax, the controller drives the slot plate to move by the predetermined heating displacement Zmax. During a scan, the anode plate is heated, wherein, when the calculated slot plate displacement does not exceed a predetermined value, the displacement changes linearly, and when the calculated slot plate displacement is greater than a predetermined value, the slot plate is displaced by the predetermined value.

The present invention further provides a controller for a collimator of a CT machine, the controller comprising a control module for executing the above steps.

The present invention provides a collimator of a CT machine, the collimator comprising a slot plate and a controller as described above.

The present invention further provides a CT machine, which comprises a collimator as described above.

A controller, a collimator, and a CT machine provided by the present invention make it possible to, on the basis of the total displacement and stop time of the previous scan, control the displacement of the slot plate during the scan stop stage or simultaneously control the displacement of the slot plate during the scan stage, so that possibility of the slot plate undergoing any substantial jitter when the CT machine performs a scan or stops is minimized, thereby keeping the image quality stable.

The present invention is explained in detail below in conjunction with the accompanying drawings and particular embodiments.

To enable clearer understanding of the technical features, objectives and effects of the invention, particular embodiments of the present invention are now explained with reference to the accompanying drawings, in which identical labels indicate structurally identical components or components with similar structures but identical functions.

As used herein, "schematic" means "serving as an instance, example or illustration". No drawing or embodiment described herein as "schematic" should be interpreted as being a more preferred or more advantageous technical solution.

The various numbers used herein, instead of being strict mathematical and/or geometric limitations, also contain errors that are comprehensible to those skilled in the art and are allowable in manufacture or use.

<FIG> is an illustrated embodiment of the tuning method for a collimator of a CT machine. As shown in <FIG>, the tuning method for a collimator of a CT machine, in each cycle of an X-ray scan operation and a stop, comprises the steps of:.

<FIG> show the changes in the Z-direction displacement over time according to the tuning method for a collimator of a CT machine shown in <FIG>. As shown in <FIG>, part (a) shows the time of an X-ray scan or a stop. Part (b) is a graph of the changes in the Z-direction displacement over time. As shown in <FIG>, during a scan stop, the controller, on the basis of the X-ray stop time, calculates the cooling displacement <MAT> of the slot plate during the current stop, which is a linear displacement during the stop period ΔT.

<FIG> show the changes in the Z-direction displacement over time according to the tuning method for a collimator of a CT machine shown in <FIG>. In step S30, the heating displacement <MAT> of the current scan may be calculated by the controller on the basis of the thermal coefficient κHα of the current scan and the time ΔTHα of the current scan: <MAT>, wherein κHα is determined by a lookup table stored in the controller. <FIG> shows the changes in the Z-direction displacement over time according to the tuning method of this embodiment, wherein part (a) shows the time of an X-ray scan or a stop. Part (b) is a graph of the changes in the Z-direction displacement over time. As shown in <FIG>, during a scan, the heating displacement <MAT> is a linear displacement. During a scan stop, the controller, on the basis of the X-ray stop time, calculates the cooling displacement <MAT> of the slot plate at the time of the current stop, which is a linear displacement during the stop period ΔT.

The present invention further provides a controller for a collimator for a CT machine, the controller comprising a control module for executing the above steps.

The present invention provides a collimator for a CT machine, which comprises a slot plate for a collimator and a controller as described above.

It should be understood that although the description herein is based on various embodiments, it is by no means the case that each embodiment contains just one independent technical solution. Such a method of presentation is adopted herein purely for the sake of clarity. Those skilled in the art should consider the description in its entirety. The technical solutions in the various embodiments could also be suitably combined to form other embodiments understandable to those skilled in the art.

Claim 1:
A tuning method for a collimator of a CT machine, the CT machine comprising an anode plate (<NUM>), the collimator comprising a slot plate (<NUM>) and a controller (<NUM>), wherein the tuning method, in each cycle of an X-ray scan operation and a stop, comprises:
a detection step (S10) of determining whether an X-ray is generated from the anode plate;
if an X-ray is detected in the detection step (S10), the controller calculates a Z-direction heating displacement <MAT> of the slot plate during the current scan (S20), wherein a indicates the current cycle;
the controller drives the slot plate to move by the heating displacement in the Z-direction (S22);
if no X-ray is detected in the detection step (S10), the controller calculates a total Z-direction heating displacement <MAT> of the slot plate at the end of the current scan (S30);
the controller, on the basis of the stop time of the X-ray, calculates a cooling displacement <MAT> of the slot plate during the current stop (S32); and the controller drives the slot plate to move (S34).