Patent Description:
With the advance of science and technology, medical imaging has obtained great development, and more imaging modes have become available, such as X-Ray photography, magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET) and so on, each of which with its strengths may complement each other.

PET is a fairly advanced clinical imaging technique in the field of nuclear medicine. In PET, a positron generated by the decay of a radionuclide gets in collision with a negatron in vivo, then the positron and the negatron are annihilated with each other, two gamma photons are emitted in almost opposite directions. Functional information relating to metabolic activities may be obtained by way of detectable gamma rays to diagnose a disease. A PET image may show the functional information and identify a tumor. However, the resolution of the PET image may be low.

CT is another clinical imaging technique in which a specific part of a body with a certain thickness may be scanned. For instance, when X rays pass through human tissues, a portion of the X rays may be absorbed by the tissues, and a portion passing through the body may be detected by a detector on the basis of which a corresponding signal may be generated. Corresponding to the differences in densities of various tissues and the differences in the x-ray penetration abilities, the detected rays may be different. The signal corresponding to the detected rays may be converted to a digital signal. The digital signal may be processed by a computer, and then an image may be generated and displayed. A minor lesion in vivo may be identified based on the image. The CT may generate an anatomical image with a high resolution and a high sensitivity in identifying the morphology of a tissue. However, CT may lack the capacity to determine other characteristics of the lesion.

PET/CT is a technology combining CT with PET. It may provide the information of CT and PET with only one diagnostic examination using a same table and a same image processing workstation. Fused images may be obtained by image reconstruction and image fusion. The fused images may show both functional and anatomical information. The fused images with more complementary information and higher resolution may improve diagnostic accuracy. For instance, the fused images may provide more information for making a treatment plan for tumor.

A PET/CT fused image may be obtained by superimposing one image on another of a same anatomical location or level. In this case, the vertical position of the table on which a patient may be placed for examination may need to be controlled to facilitate the image fusion.

Usually, a plate of the table supported at only one end may be displaced relative to the CT scanner in an axial direction during a CT scanning. When the plate extends out, because of the weight of a patient placed on the plate, the plate may bend within a scanning cross-section. The scanning cross-section may be a plane perpendicular to the rotation axis and through an iso-center of the CT scanner. The plate may also bend during a PET scanning. The CT image and the PET image at a same anatomical location or level may need to be matched so that the CT image and the PET image may be fused. Hence, the bending of the plate may need to be corrected in order to match a CT image with a corresponding PET image.

Besides, in the PET/CT system as illustrated in <FIG>, a table unit <NUM> includes a base <NUM>, a bracket <NUM> and a plate <NUM>. Plate <NUM> may move relatively to the bracket <NUM> along the axial direction. There is a position <NUM> for a CT scan (shown as a dotted line in <FIG>) and a position <NUM> for a PET scan (shown as a dotted line in <FIG>) on the base <NUM> along the z axis parallel to the rotation axis of the CT scanner <NUM> (i.e., the length direction of the plate <NUM>). When the bracket <NUM> is placed at position <NUM> for a CT scan, a patient may be placed onto or removed from the table unit <NUM> (e.g., the plate <NUM> of the table unit <NUM>). The plate <NUM> may exit from the bore of CT scanner <NUM> completely to avoid collision with CT scanner <NUM> when the plate <NUM> is moved up or down. In this case, the distance between one end of the plate <NUM> close to CT scanner <NUM> and the scanning cross-section is large. CT scan may not be performed before the plate <NUM> arrives at the scanning cross-section. In the case of a fixed maximum moving distance of the plate <NUM>, the further an initial position of the plate <NUM> is away from the scanning cross-section, the smaller the scanning range of CT scanner <NUM> is.

The present invention is directed to a PET/CT system according to independent claim <NUM> and a method according to claim <NUM>. Preferred embodiments of the presently claimed invention are set out in the dependent claims.

A first aspect of the present disclosure relates to a table. The table includes a base, a bracket, and a plate. The plate is configured to move relatively to the bracket. There are various positions on the base along a length direction of the plate including a position at which a patient may be placed onto or removed from the table (or referred to as a releasing position), a position for CT scan (or referred to as a CT scan position), and a position for PET scan (or referred to as a PET scan position). When the bracket is placed at the releasing position, the position of the plate is adjustable (e.g., by moving the plate up or down) and the distance between the floor and the plate may be in the range from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. When the bracket is placed at the CT scan position, the position of the plate is adjustable (e.g., by moving the plate up or down) and the distance between the floor and the plate may be in the range from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. The plate is movable (e.g., by moving the plate up or down) for a first distance from the floor when the bracket is placed at the PET scan position of the base and the plate is movable (e.g., by moving the plate up or down) for a second distance from the floor when the bracket is placed at the CT scan position, wherein the first distance is the same as the second distance.

A second aspect of the present disclosure relates to a PET/CT system. The PET/CT system includes a CT scanner configured to perform CT scanning, a PET scanner configured to perform PET scanning, and a table unit. The table unit includes a base, a bracket, and a plate. The plate is configured to move relatively to the bracket. There is a releasing position, a CT scan position, and a PET scan position on the base of the table unit. When the bracket is placed at the releasing position, the position of the plate is adjustable (e.g., by moving the plate up or down) and the distance between the floor and the plate may be in a range from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. When the bracket is placed at the CT scan position, the position of the plate is adjustable (e.g., by moving the plate up or down) and the distance between the floor and the plate may be in a range from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. The plate is movable (e.g., by moving the plate up or down) for a first distance from the floor when the bracket is placed at the PET scan position of the base and the plate is movable (e.g., by moving the plate up or down) for a second distance from the floor when the bracket is placed at the CT scan position, wherein the first distance is the same as the second distance. A maximum scan range of the CT scanner may be from <NUM> to <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. The PET scanner may achieve a whole body scan with one scan. A field of view of the PET scanner may be from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

The PET/CT system further includes a measuring unit and a height adjustment unit. The measuring unit is configured to measure the distance of the plate from the floor (or referred to as the height of the plate) at the scanning cross-section during the CT scanning. The height adjustment unit is e configured to adjust the height of the plate according to the height of the plate measured by the measuring unit during the CT scanning.

In some embodiments, the PET/CT system may further include an obtaining unit configured to obtain images, a determining unit configured to determine a relationship between the heights of the plate from a floor in the images and the distances of the plate moving along the length direction of the plate (or referred to as the axial direction), wherein the height adjustment unit is configured to adjust the height of the plate according to the relationship such that the movement (including, for example, the movement along the length direction, the height adjustment, and the bending) of the adjusted plate fits the relationship. The images may be CT images or topograms. In some embodiments, the relationship may be linear or essentially linear. In some embodiments, the relationship may be non-linear.

The PET/CT system may further include a correcting unit configured to correct a position error of the plate during the PET scanning compared to the CT scanning.

In some embodiments, the PET/CT system may further include a correcting unit configured to correct data acquired in the PET scanning.

A third aspect of the present disclosure relates to a method for PET/CT imaging. The method may include loading a patient when the bracket is placed at a releasing position, performing a CT scan when the bracket is placed at the position for CT scan and performing a PET scan when the bracket is placed at the position for PET scan.

The method includes adjusting a first height of the plate from the floor according to a second height of the plate from the floor at the scanning cross-section during the CT scanning so that a changing trend of the first height of the adjusted plate from the floor is consistent with a changing trend of the second height of the plate from the floor during the CT scanning. In some embodiments, the adjustment may be made before performing a PET scan.

In some embodiments, the method may include obtaining CT images or topograms, determining the relationship between the heights of the plate from the floor in the CT images or topograms and the distances of the plate moving in the length direction of the plate, and adjusting the plate according to the relationship to make the movement of the adjusted plate fitting the relationship. In some embodiments, the relationship may be linear or essentially linear.

In some embodiments, the method may include correcting the PET data after performing a PET scan.

In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant disclosure. However, it should be apparent to those skilled in the art that the present disclosure may be practiced without such details. In other instances, well known methods, procedures, systems, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present disclosure. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is not limited to the embodiments shown, but to be accorded the widest scope consistent with the claims.

It will be understood that the term "system," "unit," "module," and/or "block" used herein are one method to distinguish different components, elements, parts, section or assembly of different level in ascending order. However, the terms may be displaced by other expression if they may achieve the same purpose.

It will be understood that when a unit, engine, module or block is referred to as being "on," "connected to" or "coupled to" another unit, engine, module, or block, it may be directly on, connected or coupled to, or communicate with the other unit, engine, module, or block, or an intervening unit, engine, module, or block may be present, unless the context clearly indicates otherwise.

The terminology used herein is for the purposes of describing particular examples and embodiments only, and is not intended to be limiting. It will be further understood that the terms "include," and/or "comprise," when used in this disclosure, specify the presence of integers, devices, behaviors, stated features, steps, elements, operations, and/or components, but do not exclude the presence or addition of one or more other integers, devices, behaviors, features, steps, elements, operations, components, and/or groups thereof.

In an imaging system or a method according to the present disclosure, a relationship between the heights of the plate from a floor and the distances of the plate moving in an axial direction (or a length direction) of the plate is determined from images in advance. The plate may be adjusted so that the movement of the plate (including, for example, the movement along the axial direction, the height adjustment, and the bending of the plate) may conform to the relationship. At this point, an image of a patient may be obtained. Scan data may be corrected according to the position error between a height of the plate from the floor in previously acquired images and a height of the plate from the floor during imaging. The previously acquired images and the current images may be matched to facilitate image fusion. The imaging system or method according to the present disclosure may compensate a difference of the bending of the plate between different imaging modes. Consequently, the image matching or fusion may be simplified and the quality of image fusion may be improved. The system in the present disclosure may be CT, MRI, PET or any combination thereof. In the following embodiments of the present disclosure, a PET/CT system combining CT with PET described below is merely provided for illustration purposes, and not intended to limit the scope of the present disclosure.

<FIG> is a diagram of a prior art PET/CT system in which a CT scan is being performed; <FIG> is a diagram illustrating the bending of the plate of a table in a CT scan; <FIG> is a diagram of a prior art PET/CT system in which a PET scan is being performed; <FIG> is a diagram illustrating the bending of the plate of a table in a PET scan.

With reference to <FIG>, a PET/CT system includes a CT scanner <NUM>, a PET scanner <NUM>, and a table unit <NUM>. The CT scanner <NUM> is configured to run a CT scan and the PET scanner <NUM> is configured to run a PET scan. The table unit <NUM> includes a base <NUM>, a bracket <NUM> and a plate <NUM>. The plate <NUM> is configured to move relatively to the bracket <NUM> in an axial direction. There is a position <NUM> for CT scan (shown as dotted line) and a position <NUM> for PET scan (shown as dotted line) on the base <NUM> along z axis which is parallel to a rotation axis of the CT scanner <NUM> (i.e., length direction of the plate <NUM>). The bracket <NUM> at position <NUM> may be used for CT scan, and the bracket <NUM> at position <NUM> may be used for PET scan. The table <NUM> is configured to support and transport the patient from a region to be imaged to a scanning cross-section of CT scanner <NUM> or a field of view (FOV) of PET scanner <NUM>. Wherein the scanning cross-section is a plane perpendicular to the rotation axis and through an iso-center of the CT scanner <NUM>. Usually, the distance between position <NUM> and position <NUM> along z axis may be equal to the distance between the iso-center of the CT scanner <NUM> and the center of FOV of the PET scanner <NUM>.

As shown in <FIG>, during the CT scanning, the bracket <NUM> may be placed at position <NUM>, and the plate <NUM> supporting the patient moves along the positive direction of the z axis t, and transfer the region to be imaged (e.g., head of the patient) to the scanning cross-section of the CT scanner <NUM>. An x-ray tube of the CT scanner <NUM> may be configured to emit radiation rays and a detector of the CT scanner <NUM> may be configured to detect radiation rays traverses the region to be imaged. And then a reconstruction unit may be configured to reconstruct CT images based on a processed detected signal.

During the CT scanning, the plate <NUM> may bend when moving towards the CT scanner <NUM> because of the weight of the patient and/or the weight of the plate itself. The further the plate <NUM> extends out, the more the plate <NUM> may bend. For different positions of the plate <NUM> at the scanning cross-section, the height of the plate <NUM> at the scanning cross-section may be different. The height of the plate <NUM> may be the distance between the plate <NUM> and the floor on which the table (e.g., the base of the table) is placed. In the CT images so acquired, the bending of the plate <NUM> may increase along an inverse direction of the z axis, as shown in <FIG>. Please note that the bending of the plate <NUM> shown in <FIG> is exaggerated for illustration purposes.

As shown in <FIG>, during a PET scanning, the bracket <NUM> at position <NUM> and the plate <NUM> may operate in concert to transfer the region to be imaged of the patient to the FOV of the PET scanner <NUM>. The plate <NUM> may bend due to the weight of the patient and/or the weight of the plate <NUM> itself. During a PET scanning, the plate <NUM> may be stationary. In the PET images so acquired, the bending of the plate <NUM> may increase along a positive direction of the z axis, as shown in <FIG>. Please note that the bending of the plate <NUM> shown in <FIG> is exaggerated for illustration purposes.

Comparing CT images in <FIG> with PET images in <FIG>, the trends of the bending of the plate <NUM> in these two imaging modes are different. Because the distance between position <NUM> and position <NUM> is equal to the distance between the iso-center of the CT scanner <NUM> and the center of FOV of the PET scanner <NUM>, the bending of the plate <NUM> at or around the portion corresponding to the middle of the region to be imaged in a CT image may be approximately equal to the bending of plate <NUM> in a corresponding PET image. The bending of other portions of the plate <NUM> in the CT image may be different from the bending of the plate in the corresponding PET image.

As described in background, for PET/CT, an image showing both functional and anatomical information may be obtained by fusing a CT image and a PET image.

To improve the accuracy of fused images, an imaging system compensates a difference in the bending of the plate <NUM> between different imaging modes. With reference to <FIG>, a diagram illustrates an exemplary PET/CT system. The PET/CT system <NUM> includes a CT scanner <NUM>, a PET scanner <NUM>, and a table unit <NUM>. In some embodiments, the CT scanner <NUM> and the PET scanner <NUM> may be coaxial. In some embodiments, the CT scanner <NUM> and the PET scanner <NUM> may be non-coaxial. The table unit <NUM> includes base <NUM>, a bracket <NUM>, and a plate <NUM>. The plate <NUM> is configured to move relatively to the bracket <NUM> along a length direction of the plate <NUM>. There is a position <NUM> for CT scan (indicated by a dotted line) and a position <NUM> for PET scan (indicated by a dotted line) on the base <NUM> along the z axis. The z direction may be parallel to the rotation axis of the CT scanner <NUM> (also the length direction of the plate <NUM>). When the bracket <NUM> placed at position <NUM>, a CT scan may be performed. When the bracket <NUM> placed at position <NUM>, a PET scan may be performed. The plate <NUM> is configured to support and/or transport the patient so that the region to be imaged may be moved to the scanning cross-section of the CT scanner <NUM> or a field of view (FOV) of the PET scanner <NUM>. As used herein, the scanning cross-section is a plane through the iso-center and perpendicular to the rotation axis of the CT scanner <NUM>. There is a height adjustment unit <NUM> on one side of the PET scanner <NUM> away from the CT scanner <NUM>. By adjusting the plate <NUM> according to the height of the plate <NUM> at the scanning cross-section during the CT scanning, a changing trend of the height of the plate <NUM> during the CT scanning may be reproduced or mimicked.

To control the height adjustment unit <NUM> to drive the plate <NUM> and to compensate a difference in the bending of the plate <NUM> between the CT imaging mode and the PET imaging mode, the PET/CT system <NUM> may further include an obtaining unit <NUM> and a determining unit <NUM>.

The obtaining unit <NUM> may be configured to obtain images. In <FIG>, the obtaining unit <NUM> may be connected to the CT scanner <NUM>. In some embodiments, the obtaining unit <NUM> may acquire a CT image, instead of CT scan data. The CT scan data may be sent to a data acquisition unit and then reconstructed in an image reconstruction unit to generate the CT image provided to the obtaining unit <NUM>. In some embodiments, obtaining CT images is merely provided for illustration purposes, and not intended to limit the scope of the present disclosure. As used herein, CT images may be computed tomographic images.

In some embodiments, the images obtained by the obtaining unit <NUM> may be topograms. As used herein, a topogram may be a photograph acquired by setting the radiation source at a certain projection angle. In some embodiments, CT images and topograms may be obtained through the CT unit <NUM> of the PET/CT system <NUM>, or through one or more stand-alone CT apparatuses. In some embodiments, the CT images or topograms may be images retrieved from a storage.

The determining unit <NUM> may be configured to determine a relationship between the heights of the plate in the images (e.g., CT images, topograms, etc.) and the distances of the plate moving in the axial direction of the plate.

In some embodiments, a coordinate system may have its origin set at the iso-center of the CT scanner <NUM>. Every pixel in a CT image may have a coordinate value. A minimal coordinate value in the x axis of the pixels corresponding to the plate <NUM> of CT images may be designated as a lowest point of the plate <NUM>. The coordinate value in the x axis of the lowest point may represent a height of the plate <NUM>. The height of the plate <NUM> may be the distance of the plate <NUM> from the floor on which the table unit <NUM> is placed. Thus, the height of the plate <NUM> in a CT image may be obtained by analyzing CT images. Coordinate values of the other pixels may be selected to represent the height of the plate <NUM>. The height of the plate <NUM> of CT images is obtained by measuring the height of the plate <NUM> when the different portions of the plate <NUM> pass through the scanning cross-section. As another example, a distance measuring unit may measure the distance along the x axis between the portion of the plate <NUM> at the scanning cross-section and the distance measuring unit. The distance measuring unit may be a sonar or a laser rangefinder. Other devices that may measure the height of the plate <NUM> are within the scope of present disclosure.

During the CT scanning, a displacement of the plate <NUM> along the z axis may be recorded. According to the height of the plate <NUM> in CT images and the displacement of the plate <NUM>, a relationship between the heights and the displacements of the plate <NUM> may be determined. In some embodiments, the relationship between the heights and the displacements of the plate <NUM> may be approximately linear. In some embodiments, the relationship between the heights and the displacements of the plate <NUM> may be determined by linear fitting. The displacements of the plate <NUM> may be the same as or relate to the distances of the plate moving in the axial direction. The shorter the scanning range is, the closer to being linear the relationship between the bending or the heights and the displacement of the plate <NUM> may be. In some embodiments, the gradient of the linear relationship may be the ratio of a change in the bending to the corresponding change in the displacement of the plate <NUM> based on a geometric relationship. For example, the ratio of the maximum change in the bending to the maximum relative displacement of the plate <NUM> may be calculated to obtain the gradient of the linear relationship. As used herein, the maximum change in the bending of the plate <NUM> may refer to the maximum difference between the height of a first portion of the plate <NUM> in a first CT image and the height of a second portion of the plate <NUM> in a last CT image. As used herein, the maximum relative displacement may refer to the difference between the position of the plate <NUM> in the z axis corresponding to the first CT image and the position of the plate <NUM> in the z axis corresponding to the last CT image. The gradient of the linear relationship may be symbolized by a parameter k. In some embodiments, the linear relationship may be symbolized by one or more other parameters, for example, an angle with respect to the z axis.

The plate <NUM> may be adjusted by the height adjustment unit <NUM> to conform to the linear relationship.

As shown in <FIG>, the plate <NUM> may be supported by the bracket <NUM>. When the height adjustment unit <NUM> drives one end away from the bracket <NUM> of the plate <NUM> to move in a positive direction of the x axis, the plate <NUM> may not be separated from the bracket <NUM> completely. One unsupported end of the plate <NUM> may be raised by the height adjustment unit <NUM> to tilt the plate <NUM>, such that a surface of the plate <NUM> may rise in a positive direction of the z axis.

For example, the height adjustment unit <NUM> may be installed underneath the plate <NUM>. The height adjustment unit <NUM> may include a drive element configured to provide a driving force, a transform element configured to transform a rotation movement to a linear movement, and a transfer element connected to the transform element. The drive element may be, for example, a motor, etc. The transform element may include a lead screw and a nut. When the motor operates, the lead screw driven by the motor may rotate, and the nut may move in a straight line along the x axis. Meanwhile, the transfer element may move in a straight line together with the nut. The transfer element may drive one end of the plate <NUM> to rise together, as shown in <FIG>.

The height adjustment unit <NUM> may adjust the height of the plate <NUM> to be level first, and then continue to raise one end of the plate <NUM>. The distance between the bracket <NUM> and the height adjustment unit <NUM> in the z axis is symbolized by a parameter d. The distance of one end of the plate <NUM> away from the bracket <NUM> raised from the level is symbolized by a parameter h. The distance h may be monitored while the plate rises. A determination may be made as to whether the relationship among k, h, and d satisfies the following formula (<NUM>). If the formula (<NUM>) is satisfied, the plate <NUM> may have been adjusted in place. Otherwise, the plate <NUM> the plate <NUM> may continue to be adjusted as to the height of the plate <NUM>.

There are many ways of monitoring the distance h in real time. For example, an encoder may monitor the rotation of the motor in order to monitor the distance h in real time. As another example, a distance measuring unit installed on the floor may monitor the distance h in real time by monitoring the distance between one end of the plate <NUM> and the distance measuring unit. Other devices for measuring the distance h are within the scope of the present disclosure and won't be enumerated here.

The height adjustment unit <NUM> may include a device configured to drive one end of the plate <NUM> to rise and are not enumerated here. The height adjustment unit <NUM> may be installed on the floor, or on the gantry of the PET scanner <NUM>. The height adjustment unit <NUM> may drive the plate <NUM> to move in the x axis and not affect imaging. The method and the location of installment of the height adjustment unit <NUM> are not limited to those exemplified in the present disclosure.

If the relationship among k, d, and h satisfies the formula (<NUM>), the shape of the plate <NUM> may be kept and a PET scan may be performed. PET images may be obtained by reconstructing the PET scan data. The changing trend of the height of the plate <NUM> in the PET images may conform to the linear relationship. The relationship may be linear or essentially linear. The relationship may represent the changing trend of the height of the plate <NUM> in the CT images or topograms. Accordingly, the PET/CT system in the some embodiments may obtain CT images and PET images with the same or essentially the same changing trends of the height of the plate <NUM>. The problem of different changing trends of the height of the plate <NUM> in different imaging modes may be solved. The fusion or matching of the images obtained in different imaging modes may be simplified.

<FIG> illustrates an exemplary PET/CT system. The PET/CT system is similar to the PET/CT system illustrated in <FIG>. The PET/CT system in <FIG> may include a computing unit <NUM> configured to compute a distance of the plate <NUM> that needs to be raised according to the relationship determined by the determining unit <NUM> described above.

For example, the gradient k may be obtained by the determining unit <NUM>. The distance d between the bracket <NUM> and the height adjustment unit <NUM> in the z axis may be obtained as described elsewhere in the present disclosure. The distance h<NUM> of one end of the plate <NUM> away from the bracket <NUM> that needs to be raised from the horizontal level may be computed by the computing unit <NUM> according to the above formula (<NUM>). Then the height adjustment unit <NUM> may raise the end of the plate <NUM> by h<NUM> from the horizontal level. Similar with the description with reference to <FIG>, the height adjustment unit <NUM> may drive the plate <NUM> to a horizontal level, and then continue to drive the end of the plate <NUM> away from the bracket <NUM> to be raised by h<NUM> in the positive direction of the x axis so that the surface of the plate may fit the relationship described above. A PET scan may be performed. The problem of the different changing trends of the height of the plate in the CT imaging mode and the PET imaging mode may be solved. More descriptions may be found elsewhere in the present disclosure. See, for example, <FIG> and the description thereof.

In the embodiments illustrated in <FIG>, the position of the plate <NUM> in a CT image may be below the horizontal level, while the position of the plate <NUM> in a PET image may be above the horizontal level. The position error, symbolized by a parameter Δ, may exist between the CT image and the PET image for a same slice. A changing trend of a position of the plate in the CT image mode and a changing trend of the same position of the plate in the PET imaging mode may be essentially the same. Thus the position error Δ between each slice of a CT image and a corresponding portion of a PET image in the x axis may be approximately equal. As used herein, a portion of a PET image may be referred to as corresponding to a slice of a CT image when the portion of the PET image and the slice of the CT image represent or depict a same portion of an object that is scanned. The position error Δ may be corrected to compensate the difference of the height of the plate between the CT imaging mode and the PET imaging mode and to match a CT image with a corresponding PET image.

<FIG> is a diagram illustrating an exemplary PET/CT system. With reference to <FIG>, the PET/CT system may include a correcting unit <NUM> configured to correct the position error of the plate between the CT imaging mode and the PET imaging mode. Position errors in different systems may be different and may be obtained by experiments.

Experiments may be conducted using a water phantom and loads of different weights in the PET/CT system. CT images may be obtained by performing CT scans. The relationship between the heights of the plate and the distances of the plate moving in the axial direction may be determined based on CT images. Then the plate may be adjusted so that the heights of the plate conform to the relationship. PET images may be obtained by performing a PET scan at a height.

Each position error of the plate between the CT image and the PET image in the x axis for each slice may be determined, and the mean value of all position errors may be used as the final position error Δ.

To assess the position error Δ more accurately, the experiment may be repeated for multiple times using a water phantom and loads of different weights (e.g., wedges of different weights, etc.). For each load, multiple position errors Δ<NUM>, Δ<NUM>,. , Δn may be obtained, in which n≥<NUM> and n represents the times of the experiments. The times of the experiments for at least two loads of different weights may be the same or different. For each load, the mean value of Δ<NUM>, Δ<NUM>. Δn may be determined and used as the final position error Δ.

The position errors Δ for loads of different weights may be obtained by experiments and may be stored for future use. The position errors Δ may be acquired directly based on the weight of a patient during a scan when needed. In some embodiments, after a PET scan, the correcting unit <NUM> may acquire the position error Δ corresponding to the patient and correct the data acquired in the PET scanning. The reconstruction unit of the PET scanner <NUM> may reconstruct the corrected data to obtain the PET images in which the positions of the plate of PET images may match the positions of the plate in the CT images. Because such experiments may be performed for a limited number of times, the number of position errors that may be obtained by experiments is limited. The weight of a patient may vary widely. When the weight of a patient is not already determined by experiment, the position error may be obtained by interpolation or extrapolation.

As illustrated in <FIG>, the region to be examined is the head of a patient. In this case, the scanning range is short and the position error may be minor, for example, about a few millimeters. In some embodiments, the correcting unit <NUM> may correct the position error as follows.

The obtaining unit <NUM> may be configured to obtain images. The images may be CT images or topograms. The determining unit <NUM> may be configured to determine the relationship between the heights of the plate in the images and the distances of the plate moving in the axial direction. The height adjustment unit <NUM> may be configured to adjust the height of the plate based on the relationship, in order to make the movement of the adjusted plate fit the relationship. The correcting unit <NUM> may be configured to acquire the position error Δ based on the patient and send it to the controller of the table unit <NUM> and the height adjustment unit <NUM> such that the entire plate may be lowered by Δ in the x axis. In this case, the PET images in which the positions of the plate match the positions in CT images may be obtained by performing a PET scan. In some embodiments, the distance Δ may be short, and thus the region to be examined may be still substantially within the center of FOV of the PET scanner <NUM>.

The PET/CT system may operate as follows. The obtaining unit <NUM> may be configured to obtain images. The images may be CT images or topograms. The determining unit <NUM> may be configured to determine the relationship between the heights of the plate in the images and the distances of the plate moving in the axial direction. The relationship may be linear or approximately linear. The correcting unit <NUM> may be configured to acquire the position error Δ corresponding to a patient and send the position error Δ to the controller of the table unit <NUM>. The controller may make the plate <NUM> lower by Δ in the x axis. The height adjustment unit <NUM> may be configured to adjust the height of the plate according to the relationship such that the movement of the adjusted plate (including, for example, the movement along the axial direction, the height adjustment, and the bending of the plate) may fit the relationship. In this case, the PET images where the positions of the plate match the positions of the plate in the CT images may be obtained by performing a PET scan.

In the PET/CT system, the changing trends of the positions of the plate in CT images and in the PET images are adjusted to be substantially the same. Then the position error between a CT image and a PET image may be corrected based on the experimental data in the PET image in which the spatial positions and/or spatial coordinates of the PET image may match those in the CT image, thereby facilitating image fusion. In some examples an exemplary PET/CT system has been described. It is understood that in embodiments not forming part of the present invention the imaging system may be a single-mode system or a multi-mode system, such as a separated PET system, an MRI system, and so on, in which the difference of the bending of the plate compared with another imaging system (for example, a CT system) may be compensated.

Merely by way of example, the region to be examined is the head of the patient. When the scanning range is long, for example, in a whole body scan, at least a portion of the plate may bend greatly, and thus the need to compensate the height of the plate may be great.

Usually, the scan range of the PET unit <NUM> is about <NUM> in a single scan. The plate <NUM> may be moved in the z axis for many times to perform multiple PET scans if a whole body scan is to be performed on a patient. In the case, the height of the plate is adjusted according to the process described elsewhere in the present disclosure, so that the changing trend of the height of the plate during a PET scan is the same or substantially the same as that in a CT scan. Because the height adjustment unit <NUM> is installed at a fixed position, the positions of the plate <NUM> in the FOV may be constant for multiple PET scans. The position error between the height of the plate during a PET scan and the height of the plate in a corresponding CT scan may change. Thus the PET scan data may be corrected separately to compensate the difference of the heights of the plate between the CT imaging mode and the PET imaging mode, in order to make a CT image and a corresponding PET image match. The correction data may be obtained by experiments conducted in advance and stored for future use. In some embodiments, the height of the plate may be adjusted to compensate the difference of the heights of the plate between the CT imaging mode and the PET imaging mode so as to make a CT image and a corresponding PET image match.

The scan range of the PET unit <NUM> may be long. For example, a whole body scan may be performed in a single scan.

In the imaging system <NUM>, there is a position <NUM> for a CT scan and a position <NUM> for PET scan on the base <NUM> along the z axis. When the bracket <NUM> is placed at the position <NUM> for CT scan, a patient may be placed onto or removed from the table unit <NUM>. In some embodiments, the plate may need to exit from the bore of the CT scanner <NUM> completely to avoid collision with the CT scanner <NUM> when the plate <NUM> is moved up or down. In this case, the distance between one end of the plate <NUM> close to CT scanner <NUM> and the scanning cross-section along the z axis may be at least half of the size of the CT scanner <NUM> in the z axis, for example, about <NUM>. The maximum moving distance of the plate may be <NUM> or so. The CT scan may not be performed for the patient if the range of the plate <NUM> movement is within <NUM> as it needs to leave enough distance for the plate <NUM> to slow down. Thus the maximum scan range of the CT scanner <NUM> is less than <NUM>. For a patient who is taller than <NUM>, the CT scanner <NUM> may not provide a whole body scan.

PET/CT system <NUM> according to some embodiments of the present disclosure, may extend the scan range of the CT scanner without changing the size of the imaging system.

<FIG>, <FIG>, and <FIG> are diagrams illustrating different states of an exemplary PET/CT system. With reference to <FIG>, The PET/CT system <NUM> includes a CT scanner <NUM>, a PET scanner <NUM>, and a table unit <NUM>. In some embodiments, the CT scanner <NUM> and the PET scanner <NUM> may be coaxial. The CT scanner <NUM> and the PET scanner <NUM> may be non-coaxial. The table unit <NUM> includes a base <NUM>, a bracket <NUM>, and a plate <NUM>. The plate <NUM> is configured to move relatively to the bracket <NUM> along a length direction of the plate <NUM>. The PET/CT system of <FIG> includes a releasing position <NUM>, a CT scan position <NUM>, and a PET scan position <NUM> on the base <NUM> along the z axis that is parallel to a rotation axis of the CT scanner <NUM> (i.e., a length direction of the plate <NUM>).

When the bracket <NUM> is placed at the position <NUM>, the distance of the plate <NUM> to move up or down is larger and the plate <NUM> may move to the position below the bore of the CT scanner <NUM> for the patient to be placed onto or removed from the table unit <NUM>. When the bracket <NUM> is placed at the position <NUM> (or the position <NUM>), the distance of the plate <NUM> to move up or down is shorter than the diameter of the bore of the CT scanner <NUM> (or the PET scanner <NUM>) to avoid collision.

With reference to <FIG>, when the bracket <NUM> is placed at the position <NUM>, the plate <NUM> may exit from the bore of CT scanner <NUM> completely to avoid collision with CT scanner <NUM> when the plate <NUM> is moved up or down. At this time, the distance of the plate <NUM> for moving in the x axis is larger, and may be the range from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>, wherein the distance may be the distance from the floor in the x axis. The plate <NUM> may move to a position about <NUM> above the floor, which is convenient for a short patient to get or be placed onto or removed from the table unit <NUM>.

Optionally, when the bracket <NUM> is placed at the position <NUM>, if the plate <NUM> moves in the x axis with a displacement relative to the bracket <NUM>, the alarm may be triggered; optionally, when the bracket <NUM> is placed at the position <NUM>, the plate <NUM> may be unable to move in the x axis with a displacement relative to the bracket <NUM>; optionally, when the bracket <NUM> is placed at the position <NUM>, if the distance from the plate <NUM> to the floor is outside a given range, the plate <NUM> may move up or down in the x axis but not in the z axis; if the distance from the plate <NUM> to the floor is within the given range, the plate <NUM> may move in the z axis; optionally, when the bracket <NUM> is placed at the position <NUM>, the plate <NUM> may move up or down in the x axis but not in the z axis without a displacement relative to the bracket <NUM>. It may improve the safety to avoid the collision due to misoperation at the position <NUM>.

With reference to <FIG>, when the CT scan is to be performed for a patient, the bracket <NUM> may be placed at the position <NUM>, and the distance between one end of the plate <NUM> close to CT scanner <NUM> and the scanning cross-section in the z axis is short. The speed of the plate <NUM>, referred to as the scan speed, may be low when a CT scan is performed in the CT scanner <NUM>. In <FIG>, the distance between one end of the plate <NUM> close to CT scanner <NUM> and the scanning cross-section in the z axis is long enough to allow the plate <NUM> to accelerate to the scan speed. The distance between one end of the plate <NUM> close to CT scanner <NUM> and the scanning cross-section in the z axis may be in the range from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>, etc..

Merely by way of example, the maximum distance for the plate <NUM> to move in the z axis is about <NUM>; the maximum distance is assumed to be <NUM>; the distance between one end of the plate <NUM> close to CT scanner <NUM> and the scanning cross-section in the z axis is <NUM> when the bracket <NUM> is placed at the position <NUM>. That is, the distance for the plate <NUM> to accelerate from <NUM> to the scan speed is <NUM>. The distance for the plate <NUM> to slow down from the scan speed to <NUM> is <NUM> when the scan ends. If the scan range is <NUM>, the distance for the plate <NUM> to move corresponding to the scan range is <NUM>+<NUM>+<NUM>=<NUM>, which is less than the maximum distance <NUM>. So the PET/CT system <NUM> may extend the scan range of the CT scanner <NUM> compared with the PET/CT system <NUM> in <FIG>.

The maximum scan range of the CT scanner <NUM> may be determined by the maximum distance for the plate to move, the scan speed and the acceleration of the plate, or the like, or a combination thereof. Suppose the maximum distance for the plate <NUM> to move is L, the distance for the plate <NUM> to accelerate from <NUM> to the scan speed is S<NUM> and the distance for the plate <NUM> to slow down from the scan speed to <NUM> is S<NUM>, and the maximum scan range of the CT scanner <NUM> is: <MAT>.

In some embodiments, suppose the maximum distance for the plate <NUM> to move is <NUM> and the distance for the plate <NUM> to accelerate or decelerate is <NUM>, the maximum scan range of the CT scanner <NUM> is <NUM>-<NUM>-<NUM>=<NUM>. If the maximum distance for plate <NUM> to move is <NUM>, the maximum scan range of the CT scanner <NUM> is <NUM>. The maximum scan range of the CT scanner <NUM> may also be other values, for example, <NUM>. Without increasing the size of the table unit <NUM>, the maximum scan range of the CT scanner <NUM> is from <NUM> to <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, and so the CT scanner <NUM> may substantially perform a whole body scan for many patients.

When the bracket <NUM> at the position <NUM>, the distance for the plate <NUM> to move in the x axis is shorter and may be the range from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. As used herein, the distance for the plate <NUM> to move in the x axis is the distance from the floor in the x axis. The motion range of the plate <NUM> in the x axis may be limited. When the plate <NUM> moves in the positive direction of the x axis, the patient may need to be protected from collision with the CT scanner <NUM>; when the plate <NUM> moves in the negative direction of the x axis, the plate <NUM> may need to be protected from collision with the CT scanner <NUM>.

With reference to <FIG>, when the PET scan is to be performed for a patient, the bracket <NUM> is placed at the position <NUM> and the whole body of the patient is in the FOV of the PET scanner <NUM> such that the PET scanner <NUM> may perform a whole body scan in a single scan. The FOV may be related to the size of the PET scanner <NUM> in the z axis and may be the range from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>, etc..

When the bracket <NUM> is at the position <NUM>, the distance for the plate <NUM> to move in the x axis may be the same as that during the CT scanning or not, provided that the plate <NUM> or the patient does not collide with the PET scanner <NUM>.

In some embodiments, the distance between one side of the CT scanner <NUM> and the scanning cross-section in the z axis may be about <NUM> long, and the FOV of the PET scanner <NUM> may be about <NUM> long. The distance between the scanning cross-section and the center of the FOV is about <NUM>. If the distance between position <NUM> and position <NUM> is <NUM>, the structure and size of the table unit <NUM> may need to be changed, which may cause an increase in not only the size of the imaging system but also the cost. So the distance between position <NUM> and position <NUM> may be different from the distance between the scanning cross-section and the center of FOV of the PET scanner <NUM>.

Compared with the embodiments in <FIG> in which the distance between one end of the plate <NUM> close to CT scanner <NUM> and the scanning cross-section is about <NUM> when the bracket <NUM> is placed at the position <NUM>, the distance between one end of the plate <NUM> close to CT scanner <NUM> and the scanning cross-section is only about <NUM> when the bracket <NUM> is placed at the position <NUM>. If the maximum distance for the plate to move in <FIG>, <FIG>, or <FIG> is the same as that in <FIG>, the longer distance for the plate <NUM> of the table unit <NUM> to move may be used for the CT scan in the embodiments illustrated in <FIG>, <FIG>, and <FIG>. That is, the embodiments illustrated in <FIG>, <FIG>, and <FIG> may extend the scan range of the CT scanner <NUM> without increasing the size of the table unit <NUM>.

When the scan range is longer, one unsupported end of the plate <NUM> may bend with the movement of the plate <NUM> in the z axis during a CT scan. The farther the plate <NUM> moves in the z axis, the more seriously the plate <NUM> bends. The unsupported end of the plate <NUM> may also bend during a PET scan. From the description of <FIG> and <FIG>, the trends of the bending of the plate in a CT image and a corresponding PET image may be opposite. Thus, the bending of the plate may be compensated by combining the embodiments described with reference to <FIG>, <FIG>, and <FIG> with the embodiments described with reference to <FIG>, in order to compensate the difference of the bending of the plate between the CT imaging mode and the PET imaging mode.

The PET/CT system <NUM> includes a height adjustment unit <NUM> configured to adjust the height of the plate <NUM> based on the height of the plate <NUM> at the scanning cross-section during the CT scan so that the changing trend of the height of the adjusted plate <NUM> during a PET scan is consistent with the changing trend of the height of the plate during the CT scan. To compensate the difference of the bending between the CT imaging mode and the PET imaging mode, the height adjustment unit <NUM> may be controlled to drive the plate <NUM>. The PET/CT system <NUM> may further include an obtaining unit <NUM> and a determining unit <NUM>.

The obtaining unit <NUM> may be configured to obtain images. The images may be CT images or topograms.

The determining unit <NUM> may be configured to determine the relationship between the heights of the plate in the images and the distances of the plate moving in the axial direction. In some embodiments, the relationship may be linear or substantially linear. In some embodiments, the relationship may be non-linear.

The height adjustment unit <NUM> may be configured to adjust the height of the plate based on the relationship to make the movement of the adjusted plate (including, for example, the movement of the plate along the axial direction, the height adjustment, the bending of the plate) fit the relationship. In this case, PET scan data may be obtained by a PET scan. PET images may be obtained by reconstructing the PET scan data. The changing trend of the height of the plate <NUM> in a PET image may be consistent with the changing trend of the height of the plate in a CT image. There may be a position error of the plate between the CT image and the corresponding PET image for a same slice. The position error may be corrected to compensate the difference of the height of the plate between the CT imaging mode and the PET imaging mode and to make the CT image and the corresponding PET image match.

The PET/CT system <NUM> may further include a correcting unit <NUM> configured to correct the position error of the plate during a PET scan compared to a CT scan.

The position error with respect to loads of different weights may be obtained by experiments and stored. The position error may be acquired directly based on the weight of a patient when needed. Specifically, after a PET scan, the correcting unit <NUM> may obtain the position error relating to the patient and correct data acquired in the PET scanning. The reconstruction unit of the PET scanner <NUM> may reconstruct the corrected data to obtain the PET images in which the positions of the plate may match the positions of the plate in CT images. The matching may be obtained by performing a PET scan after the entire plate <NUM> is adjusted for the position error.

More descriptions may be found elsewhere in the present disclosure. See, for example, the description with reference to <FIG>.

<FIG> is a flowchart illustrating an imaging process according to some embodiments of the present disclosure.

The images may be CT images or topograms. In some embodiments, CT images are provided merely for illustration purposes, and not intended to limit the scope of the present disclosure.

In step <NUM>, a relationship between the heights of the plate in the images and the distances of the plate moving in the axial direction may be determined. In some embodiments, the relationship may be linear or substantially linear. In some embodiments, the relationship may be non-linear.

In step <NUM>, the plate may be adjusted according to the relationship, in order to make the movement of the adjusted plate fitting the linear relationship.

The plate may be adjusted according to the linear relationship determined in step <NUM>, in order to make the surface of the plate (including, for example, the movement of the plate along the axial direction, the height adjustment, the bending of the plate) fit the relationship. The distance may be monitored when the plate rises to assess the movement of the plate based on the relationship. The distance by which the plate needs to rise based on the relationship may be determined in advance and then one end of the plate may be raised to make the movement of the plate fit the relationship.

In step <NUM>, an imaging scan may be performed.

In this case, a PET scan may be performed. The problem that the changing trend of the height of the plate in the CT imaging mode is different from that in the PET imaging mode may be solved. PET images may be obtained by reconstructing the PET scan data, in which the changing trend of the height of the plate in the PET images may be consistent with that in the CT images. Image fusion that matches the images obtained in different imaging modes may be simplified.

In some embodiments, there may be a position error of the plate between the PET images and the CT images. The position error may be corrected to compensate the difference of the height of the plate between the CT imaging mode and the PET imaging mode and to make a CT image and a corresponding PET image match. In some embodiments, the imaging process may further include step <NUM>.

In step <NUM>, the scan data may be corrected.

The position error may be corrected by lowering the plate directly, as shown in <FIG>. More descriptions may be found elsewhere in the present disclosure. See, for example, the description with reference to <FIG>.

In step <NUM>, the images may be obtained.

In step <NUM>, the relationship between the heights of the plate in the images and the distances of the plate moving in the axial direction may be determined. In some embodiments, the relationship may be linear or substantially linear. In some embodiments, the relationship may be non-linear.

In step <NUM>, the plate may be adjusted according to the relationship, in order to make the movement of the adjusted plate fit the relationship. The movement of the plate may include, for example, the movement of the plate along the axial direction, the height adjustment, the bending of the plate.

In step <NUM>, the position error may be obtained.

In step <NUM>, the plate may be adjusted according to the position error to make the height of the adjusted plate constant in various images.

In some embodiments, the position error in step <NUM> may be obtained before the step <NUM>, which is a variation within the scope of the present disclosure.

More description may be found elsewhere in the present disclosure. See, for example, the description with reference to <FIG>.

Having thus described the basic concepts, it may be rather apparent to those skilled in the art after reading this detailed disclosure that the foregoing detailed disclosure is intended to be presented by way of example only and is not limiting. Various alterations, improvements, and modifications may occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested by this disclosure, and are within the scope of the exemplary embodiments of this disclosure.

Accordingly, aspects of the present disclosure may be implemented entirely hardware, entirely software (including firmware, resident software, micro-code, etc.) or combining software and hardware implementation that may all generally be referred to herein as a "block," "module," "engine," "unit," "component," or "system.

The program code may execute entirely on the operator's computer, partly on the operator's computer, as a stand-alone software package, partly on the operator's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the operator's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider) or in a cloud computing environment or offered as a service such as a Software as a Service (SaaS).

Furthermore, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes and methods to any order except as may be specified in the claims. Although the above disclosure discusses through various examples what is currently considered to be a variety of useful embodiments of the disclosure, it is to be understood that such detail is solely for that purpose, and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover modifications and equivalent arrangements that are within the spirit and scope of the disclosed embodiments. For example, although the implementation of various components described above may be embodied in a hardware device, it may also be implemented as a software only solution-e.g., an installation on an existing server or mobile device.

Similarly, it should be appreciated that in the foregoing description of embodiments of the present disclosure, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive embodiments. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, inventive embodiments lie in less than all features of a single foregoing disclosed embodiment.

In some embodiments, the numbers expressing quantities of ingredients, properties, and so forth, used to describe and claim certain embodiments of the application are to be understood as being modified in some instances by the term "about," "approximate," or "substantially. " For example, "about," "approximate," or "substantially" may indicate ±<NUM>% variation of the value it describes, unless otherwise stated. Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.

Claim 1:
A PET/CT system (<NUM>) comprising:
a CT scanner (<NUM>) configured to perform CT scanning,
a PET scanner (<NUM>) configured to perform PET scanning,
a table unit (<NUM>) comprising a base (<NUM>), a bracket (<NUM>), and a plate (<NUM>) movable relative to the bracket (<NUM>), wherein
the base (<NUM>) has a releasing position (<NUM>), a CT scan position (<NUM>), and a PET scan position (<NUM>) along a length direction of the plate (<NUM>), and the bracket (<NUM>) is adapted to be placed at each of the positions; and
the PET/CT system (<NUM>) further comprises a height adjustment unit (<NUM>, <NUM>) configured to adjust a height of the plate (<NUM>) to compensate a difference of a height of the plate (<NUM>) between a CT imaging mode and a PET imaging mode,
characterized in that the system further comprises:
a measuring unit configured to measure a height of the plate at the scanning cross-section during the CT scanning,
wherein the height adjustment unit (<NUM>, <NUM>) is further configured to adjust the height of the plate (<NUM>) based on the height of the plate (<NUM>) at a scanning cross-section during the CT scanning so that a changing trend of the height of the adjusted plate (<NUM>) during the PET scanning is consistent with the changing trend of the height of the plate (<NUM>) during the CT scanning.