WO2008120121A1

WO2008120121A1 - Centerpoint of interest controlled relative positioning of table and imaging unit

Info

Publication number: WO2008120121A1
Application number: PCT/IB2008/050964
Authority: WO
Inventors: Nicolaas H. Bakker
Original assignee: Koninklijke Philips Electronics N. V.
Priority date: 2007-03-29
Filing date: 2008-03-14
Publication date: 2008-10-09

Abstract

An imaging system (2) comprises a table (4) for receiving a patient (6) and an imaging unit (8) for generating an image of at least a portion of said patient received on said table (4) wherein said imaging unit (8) defines an axis of rotation (14, 16) about which said imaging unit (8) is rotatable. At least when an region (44) of interest of the patient is spaced from the axis of rotation (14, 16), in response to a rotation of said imaging unit (8) about said axis of rotation a spatial relationship between the imaging unit (8) and the table (4) is changed by a control system (32) so as to maintain a region of interest (44) of the patient within an image region of said imaging unit (8). This has the advantage that no image has to be acquired in order to check whether the region of interest (44) is within an image area of the imaging unit (8) after rotation of the imaging unit. According to embodiments of the invention, the change in spatial relationship can be performed either by moving the imaging unit (8) or by moving the table (4).

Description

CENTERPOINT OF INTEREST CONTROLLED RELATIVE POSITIONING OF TABLE AND IMAGING UNIT

FIELD OF THE INVENTION

The invention relates to the field of imaging, and more specifically to an imaging system which includes an imaging unit that is rotatable about an axis of rotation.

BACKGROUND OF THE INVENTION

US 6,986,179 B2 relates to a patient positioning system for medical applications. The system includes a patient positioning surface for supporting a patient. The system further includes a lift subsystem for adjusting elevation of the patient positioning surface, a longitudinal subsystem for moving the patient positioning surface in a longitudinal direction, a lateral subsystem for moving the patient in a lateral direction, a tilt subsystem for tilting the patient positioning system and a rotation subsystem for rotating the patient positioning system. The system further includes a control subsystem for controlling operation of the patient positioning system and a base affixed to a floor for securing the patient positioning system. The control subsystem may perform iso-center tracking to maintain a region of interest of the patient at an iso- center during tilt or other movement of the patient positioning system. In an embodiment, the control subsystem performs iso-center tracking to maintain a region of interest of the patient in an image area during tilt. SUMMARY OF THE INVENTION

It would be advantageous to achieve a method or an imaging system which provides a good working comfort for the operator as well as a low radiation dose. To better address this concern, in a first aspect of the invention an imaging system is presented which comprises a table for receiving a patient, and an imaging unit for generating an image of at least a portion of the patient received on the table, wherein the imaging unit defines an axis of rotation about which the imaging unit is rotatable. Further a drive system is provided for controllably changing a spatial relationship between the table and the imaging unit. Further, the imaging system comprises a control system for providing control signals to the drive system in response to a rotation of the imaging unit about the axis of rotation, at least when a center of the region of interest is located at a distance from the axis of rotation, to thereby maintain the region of interest within an image region of the imaging unit.

An advantage thereof is that upon rotating the imaging system, even when the centerpoint of a region of interest of the patient is spaced from an axis of rotation of the imaging unit, the centerpoint of the region of interest is maintained within the imaging area without the necessity to acquire any additional image to check whether the region of interest is within the imaging area of the imaging unit. Accordingly, in an embodiment of the invention, the change of the spatial relation between the table and the imaging unit is performed without taking images, i.e. without subjecting the patient to radiation.

An embodiment of an imaging system of this kind has the advantage that the table on which the patient is received can be adjusted to an arbitrary height that provides a good working height for the physician. While maintaining the table height and rotating the imaging system, even when the centerpoint of a region of interest is spaced from an axis of rotation of the imaging unit, the centerpoint of the region of interest of the patient is maintained within the imaging area without the necessity to acquire any additional image to check whether the region of interest is within the imaging area of the imaging unit. According to an embodiment, the control signals are provided to the drive system irrespective whether the centerpoint of the region of interest is spaced from the axis of rotation or not.

According to an embodiment, the imaging unit is rotatable about only one axis. According to other embodiments, the imaging unit is rotatable about two or more axes. According to still another embodiment, the imaging unit is rotatable about three axes. In an exemplary embodiment, the imaging unit is a x-ray imaging unit comprising a x-ray source and a x-ray detector. For example, the imaging unit may be a C-arc x-ray imaging unit wherein two axes of rotation, about which the C-arm is rotatable, and one longitudinal axis, defined by the x-ray source and the x-ray detector, intersect at an iso-center of the C-arc. According to an embodiment, the control system provides control signals to the drive system in response to a rotation of the imaging unit about any of its axes of rotation, at least when a centerpoint of the region of interest is located at a distance from the axis of rotation, to thereby maintain the region of interest within an image region of the imaging unit. According to an embodiment of the invention, an imaging system is presented wherein the control system provides the control signals to the drive system automatically upon a rotation of the imaging unit about the axis of rotation. This provides for an automatic positioning of the region of interest of the patient in the imaging area of the imaging unit without the necessity of a user interaction. For example, according to an embodiment, the table follows C-arc in real time. According to another embodiment, the table is panned after C-arc movement stops.

According to another embodiment of the invention, an imaging system is provided wherein the control system provides a status signal indicative of a planned activation of the drive system in response to the rotation of the imaging unit. The imaging system further comprises a user interface for approving the planned activation of the drive system and the control system provides the control signals to the drive system automatically upon approval of the planned activation of the drive system by the user interface. Thereby, the table is only moved when the physician approves the movement which may be desirable in some cases. According to still another embodiment of the invention, the imaging system further comprises a user interface for effecting a rotation of the imaging unit about the axis of rotation into a desired angular position. The user interface allows the user, e.g. the physician, to adjust the rotational position of the imaging unit while the control system in conjunction with the drive system maintains the region of interest within the imaging area of the imaging system. According to still another embodiment of the invention, an imaging system is provided wherein the drive system includes a table related drive system for changing a spatial position of the table. For example, the position of the at least one rotational axis of the imaging unit may be fixed in space, whereas the table is moveable with respect to the axes of rotation.

According to still another embodiment of the invention, an imaging system is presented wherein the drive system includes an imaging unit related drive system for changing a spatial position of the imaging system. According to an embodiment, the imaging related drive system is operable to move the imaging unit in at least one direction, e.g. parallel to an axis of rotation of the imaging unit. For example the imaging related drive system may be operable to move the imaging unit in at least one horizontal direction.

According to a second aspect of the invention, a method of operating an imaging system comprising a table for receiving a patient and an imaging unit for imaging of at least a portion of the patient is presented, wherein the method comprises receiving input data specifying a region of interest of the patient, rotating the imaging unit about an axis of rotation while a centerpoint of a region of interest is spaced from the axis of rotation and controllably changing a spatial relationship between the table and the imaging unit in response to the rotation of the imaging unit to thereby maintain the region of interest within an image region of the imaging unit.

According to another embodiment of the invention, controllably changing a spatial relationship between the table and the imaging unit comprises changing a horizontal distance between the table and the imaging unit. Accordingly, the table may be provided at a fixed height or at a variable height. According to an embodiment, the table is moved to a desired height and the change in spatial relationship is a change in horizontal distance between the imaging unit and the table, e.g. between an iso-center of the imaging unit and the table. According to an embodiment, the change in spatial relationship comprises or consists of at least one longitudinal relative motion of the table and the imaging unit. According to another embodiment, the change in spatial relationship comprises or consists of at least one rotational relative movement of the table and the imaging unit. The method according to the second aspect of the invention may be adapted so as to operate an imaging system according to the first aspect of the invention or an embodiment thereof.

According to a third aspect of the invention, a computer program product is presented which enables a processor to carry out the method according to the second aspect or an embodiment thereof.

According to a fourth aspect of the invention, a computer program product is presented which enables a processor to provide the functionality of the control system of the imaging system according to the first aspect of the invention or an embodiment thereof.

In summary, an aspect of the invention relates to an imaging system comprising a table for receiving a patient and an imaging unit for generating an image of at least a portion of the patient received on the table wherein the imaging unit defines an axis of rotation about which the imaging unit is rotatable. According to a basic idea of the invention, in response to a rotation of the imaging unit about the axis of rotation, a spatial relationship between the imaging unit and the table is changed by a control system so as to maintain a region of interest of the patient within an image region of the imaging unit. In other words, by a coordinated relative movement of the table and the imaging unit in response to a rotation of the imaging unit, the movement of the region of interest due to the rotation of the imaging unit is compensated. This has the advantage that no image has to be acquired in order to check whether the region of interest is still within an image area of the imaging unit after rotation of the imaging unit. According to embodiments of the invention, the change in spatial relationship can be performed either by moving the imaging unit or by moving the table. According to embodiments of the invention, the relative movement of the table and the imaging unit is performed in a horizontal direction.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed description, reference is made to the drawings in which Fig. 1 shows a schematic side view of an embodiment of an imaging system according to the invention; Fig. 2 shows in part a schematic front view of the imaging system of Fig. 1, wherein a region of interest is illustrated by a schematic heart;

Fig. 3 shows the front view of the imaging system of Fig. 2 with the imaging unit in a rotated position;

Fig. 4 shows the front view of the imaging system of Fig. 3 with the imaging unit in the rotated position and the table in an offset position wherein the region of interest is maintained in an image region of the imaging unit;

Fig. 5 shows a schematic side view of another embodiment of an imaging system according to the invention;

Fig. 6 shows in part a schematic side view of the imaging system of Fig. 5, wherein a region of interest is illustrated by a schematic heart and an imaging unit is in a rotated position;

Fig. 7 shows the side view of Fig. 6 with the imaging unit in an offset position in which the region of interest is maintained in an image region of the imaging unit.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference to the drawings, illustrative embodiments of the present invention will now be described in more detail. Throughout the detailed description of the embodiments, the illustrated imaging units are C-arc x-ray imaging systems.

However, it should be understood that other imaging systems are contemplated. For example, instead of x-ray radiation sources other radiation sources may be used. Further, other geometries are possible.

Fig. 1 shows an embodiment of an imaging system 2 which comprises a table 4 for receiving a patient 6. An imaging unit 8 for generating an image of at least a portion of the patient 6 is provided. In the illustrated embodiment, the imaging unit 8 comprises an x-ray source 10 and an x-ray detector 12. The imaging unit 8, i.e. the x-ray source 10 and the x-ray detector 12 are rotatable about a first axis of rotation 14 and a second axis of rotation 16 (perpendicular to the drawing plane). The x-ray source 10 and the x-ray detector 12 define a third axis 18 which extends through both, the source 10 and the detector 12. The third axis 18 corresponds to an x-ray trajectory 19 of undisturbed x-rays travelling from the x-ray source 10 to the x-ray detector 12. The x-ray imaging unit 8 in Fig. 1 is a so-called C-arc imaging unit, wherein the x-ray source 10 and the x-ray-detector 12 are mounted on a C-arc 20 in diametrically opposed positions. The C-arc is mounted in a curved guide 22 in which the C-arc 20 can be moved by appropriate drive systems (not shown), resulting in a rotational movement about the axis 16. The guide 22 itself is rotatably mounted about the axis 14 at an imager support 24.

The three axes 14, 16 and 18 define an iso-center 26 of the imaging unit. An region of interest which lies in the iso-center 26 of the imaging unit 8 does not move out of the image region of the imaging unit 8 when the imaging unit 8 is rotated about one of the axes of rotation 14, 16. However, it might be desirable to image a region of interest, a centerpoint 28 of which is outside the iso-center 26, as illustrated in Fig. 1. As illustrated in detail below, such a configuration causes the centerpoint 28 of the region of interest to move out of the image region of the imaging unit. Hence, after a rotation of the imaging unit 8 about an axis 14, 16 of rotation, the centerpoint 28 of the region of interest would lie outside the image taken by the imaging unit 8 or would be at least offset from the center of the image, which may be displayed on a display device 29, as exemplarily shown in Fig. 1. In order to avoid the centerpoint 28 of the region of interest to move out of the image region of the imaging unit 8, the imaging system 2 shown in Fig 1 further comprises a drive system 30 for controllably changing a spatial relationship between the table 4 and the imaging unit 8. In the illustrated embodiment, the drive system 30 is a table related drive system which provides for a controlled movement of the table 4 with respect to the imaging unit 8. The table related drive system 30 shown in Fig. 1 is capable of moving the table 4 in a horizontal plane parallel to the floor 33 i.e. in x and y directions, wherein in the illustrated embodiment the x direction is parallel to the axis 14 and the y direction is parallel to the axis 16, i.e. perpendicular to the paper plane. Further, the table related drive system 30 is capable of moving the table 4 in z direction, i.e. in the direction of a table height. The table related drive system 30 is used for changing the spatial relationship between the table 4 and the imaging unit 8. Further, the table related drive system 30 may be used to initially position the patient in the imaging unit, i.e. between the x-ray source 10 and the x-ray detector 12. The table related drive system may be capable of rotating the table in a horizontal plane, either in addition to the movability in x direction and y direction, or instead of the movability in the x direction and the y direction. It should be understood that the exemplary orientation of the x direction and the y direction is not essential for the function of the invention. Rather any coordinate system may be used that enables the drive system to perform the movements necessary to maintain the region of interest within an image region of the imaging unit 8. In the illustrated embodiment, the table related drive system 30 is mounted between a table support 31 and the table 4. In other embodiments, the drive system 30 is mounted between the table support 31 and the floor 33. Further any other configuration of the drive system is possible as long as it provides for the desired relative movement of the table 4 and the imaging unit 8.

The imaging system 2 further comprises a control system 32 for providing control signals 34 to the drive system 30 in response to a rotation of the imaging unit 8 about one of the axes 14, 16 of rotation to thereby maintain the region of interest within an image region of the imaging unit 8. The control system 32 provides these control signals 34 at least when a centerpoint 28 of the region of interest is located at a distance from the axis 14, 16 of rotation, as shown in Fig. 1. In the illustrated embodiment, the control system 32 provides the control signals 34 irrespective whether the centerpoint 28 of the region of interest is located at a distance from the axis 14, 16 of rotation or not. However, it should be understood that in the case that the centerpoint 28 of the region of interest coincides with the iso-center 26, the control signals would effect no or only a negligible change of the spatial relationship between imaging unit 8 and the table 4. In the other case, when the centerpoint 28 of the region of interest is located at a distance from the axis 14, 16 of rotation, the control system 32 provides appropriate control signals 34 in order to maintain the region of interest within the image region of the imaging unit 8. The imaging system 2 further comprises a user interface 36 for effecting a rotation of the imaging unit 8 about the axis 14, 16 of rotation into a desired angular position. To this end, the user interface 36 transmits respective control signals 38 to the control system 32. The control system 32 communicates with the drive systems (not shown) of the imaging unit 8 via imaging communication signals 40 in order to effect the commanded rotation of the imaging unit 8. In the illustrated embodiment, the control system 32 takes the control signals 38 from the user interface 36 into account to generate the control signals 34 to the drive system 30 in order to maintain the region of interest within an image region of the imaging unit 8. In other embodiments, the control system 32 may use other signals to take the rotational movement of the imaging unit 8 into account. Imaging communication signals 40 may include signals for commanding desired settings of the x-ray source 10 and the x-ray detector 12. The imaging communication signals 39 may further include detector signals of the image acquired by the x-ray detector 12. The control system 32 provides in response hereto image signals 42 to the display unit 29.

The control system 32 may provide the control signals to the drive system automatically upon a rotation of the imaging unit 8 about the axis 14, 16 of rotation. For example, in the illustrated implementation the table panning directly follows the movements of the C-arc in real-time. In an alternative implementation the table panning is activated automatically after movement of the C-arc has stopped. In still further embodiments, the table panning may be activated by indication of the user. Hence the embodiment illustrated in Fig. 1 allows physicians to work at their own desired working height and table panning is automatically executed by the system 2 without using fluoroscopy. Based on knowledge of the 3D location of the centerpoint of the region of interest (centerpoint-of- interest), the table is automatically panned to keep this point in the center of the image during any rotation of the C-arc. The centerpoint of the region of interest for cardiology procedures lies within the heart. The physician controls the rotations of the C-arc as he would do currently, typically with some form of joystick, and the control system 32 continuously calculates the required table panning needed to keep the centerpoint of the region of interest in the center of the image and automatically pans the table 4 by motorized movement. No fluoroscopy or user action is needed to pan the table 4 thus saving X-ray dose and improving the workflow.

Working at a desired table height is advantageous, since physicians working with imaging systems, e.g. interventional radiologists and cardiologists, need to wear heavy lead coats during diagnostic and interventional procedures, e.g. cardiovascular X-ray procedures. Working with the patient table at an ergonomic height is capable of reducing the load on the back during procedures. However, the preferred table height often does not correspond to a height where a region of interest of the patient lies in the iso-center of rotation of the C-arc of the x-ray system, but often lies well below this iso-center depending on the physician's length and the geometry of the system, as shown in Fig. 1. This would mean that without the functionality according to the invention, every time the C-arc is rotated, the centerpoint of the region of interest would move out of the center of the image. As a result, an imaging system without the functionality of according to the invention, working at a desired table height would require frequent panning by hand under fluoroscopy in order to change views during cardiac procedure. This would require additional fluoroscopy and disturbs the workflow by adding additional time, actions required and distraction to the procedure. Further, by additional fluoroscopy the patient would be subjected to an additional radiation dose besides the dose required for interventional imaging. Fig. 2 to Fig. 4 illustrate an embodiment of a method according to the invention. The method is carried out using the imaging system of Fig. 1. Fig. 2 shows a partial front view of the imaging system 2 of Fig. 1, wherein a region of interest 44 is depicted as a schematic heart with the centerpoint 28. In Fig. 2 to Fig. 4 some elements of the imaging system 2 of Fig. 1 have been omitted. In Fig. 3, the imaging unit 8 has been rotated about the axis 14, wherein the direction of rotation is indicated by an arrow 46. Since the centerpoint 28 of the region of interest 44 is spaced from the iso-center 26 and the axis 14, upon rotation of the imaging unit 8 the region of interest 44 moves out of the center of the image region of the imaging unit 8. In accordance with an embodiment of the invention, this is compensated by the movement, i.e. the panning of the table with the patient and hence by panning the region of interest 44 of the patient in a horizontal direction substantially perpendicular to the axis 14 of rotation. In the illustrated embodiment, upon rotation of the whole C-arc about axis 14, about which the C-arc is supported by the imager support 24, the table 4 is moved in a lateral direction, following the movement of the C-arc. By this compensating movement of the table 4, indicated at 48 in Fig. 4, the centerpoint 28 of the region of interest 44 is mainained in the center of the image region of the imaging unit 8 and hence in the center of the image acquired by the imaging unit 8. In other words, the centerpoint 28 of the region of interest 44 is maintained on the axis 18 extending through the x-ray source 10 and the x- ray detector 12.

Compared to the embodiment described with respect to Fig. 1, the embodiment illustrated by Fig. 2 to Fig. 4 differs in that the table does not follow the rotation of the imaging unit 8 in real time, but is automatically moved after the rotation of the imaging unit 8 has stopped. That is, first the imaging unit 8 is rotated about the axis of rotation 14, indicated at 46 in Fig. 3. Subsequently, after the rotation of the imaging unit 8 has stopped, the table 4 together with the region of interest 44 is panned to maintain the region of interest within the image region of the imaging unit 8 (Fig. 4).

Fig. 5 illustrates another embodiment of an imaging system 102 according to the invention. Compared to Fig. 1, like reference numbers indicate like elements in Fig. 5, the description of which is not repeated with regard to Fig. 5. Rather the differences between the embodiment of Fig. 5 compared to the embodiment of Fig. 1 are emphasized. The control system 132 of the embodiment of Fig. 5 is similar to the control system 32 of the embodiment of Fig. 1, except for the differences emphasized in the following.

Different from Fig. 1, Fig. 5 comprises a imaging unit related drive system 130 which is capable of moving the imaging unit in at least one of the x direction, y direction and z direction as defined with regard to Fig. 1, in order to change the spatial relationship between the imaging unit 8 and the table 4. Further, according to another embodiment, the drive system 130 is capable of rotating the imager support 24, at which the C-arc is rotatably mounted, in a horizontal plane. The imaging unit related drive system 130 is provided between the floor 33 and the imager support 24. In the illustrated embodiment of Fig. 5, the table 4 is also equipped with a table related drive system 30. The table related drive system in Fig. 5 may be used only for initially positioning the patient and in particular the region of interest 44 in the imaging unit 8. According to another embodiment, the table related drive system 30 and the imaging unit related drive system 130 are both commanded by the control system 132 so as to change the spatial relationship between the imaging unit 8 and the table 4. This has the advantage of a shorter travel of each of the drive systems 30, 130 in order to compensate for the rotation of the imaging unit 8. Further, according to another embodiment, the imaging related drive system 130 is used with a different priority than the table related drive system 30.

For example, the imaging unit related drive system may be used, i.e. commanded by the control system 132, with a higher priority than the table related drive system 30. This means that the required change in spatial relationship between the imaging unit 8 and the table 4 is carried out by the imaging unit related drive system 130 as long as the travel of this drive system 130 is sufficient. This has the advantage, that the physician is not confronted with a table movement, i.e. with a spatial movement of the object of interest. In the case that the travel of the imaging unit related drive system 130 is not sufficient to carry out the required change in spatial relationship, the control system 132 may be adapted to command a movement of table by the table related drive system 30 in addition. In other embodiments, only a table related drive system 130 is provided while the table position is fixed or is only adjustable in height (z direction).

Different from the control system 32 of the imaging system of Fig. 1, the control system 132 of the imaging system 102 shown in Fig. 5 does not automatically command a change of the spatial relationship between the imaging unit 8 and the table 4. Rather, the control system 132 provides a status signal 150 indicative of a planned activation of the drive system 30, 130 in response to the rotation of the imaging unit 8. In the illustrated embodiment, the status signal 150 is provided to the display device 29 which in response hereto provides a visible signal 152 to the user. In other embodiments, an audio signalling device is provided which provides an audible signal to the user in response to the status signal. The imaging system 102 further comprises a user interface 154 for approving the planned activation of the drive system 30, 130. In the illustrated embodiment, the user interface 154 is provided by a touch screen function of the display device. In response to the approval of the planned activation by the user via the user interface, the user interface 154 provides an approval signal 156 to the control system 132. The control system 132 provides the control signals 34, 134 to the drive system 30, 130 automatically upon approval of the planned activation of the drive system 30, 130 via the user interface 154.

Fig. 6 and Fig. 7 illustrate a rotation of the imaging unit 8 about the axis 16, i.e. a rotation of the imaging unit 8 which is performed by a relative movement of the C-arm 20 in the guide 22. This rotation of the imaging unit 8 is indicated at 146 in Fig. 6. For comparison, the x, y and z directions are indicated in Fig. 6 as well as in Fig. 2. Since the centerpoint 28 of the region of interest 44 is spaced from the iso-center 26 and the axis of rotation 16, the region of interest moves out of the center of the image region of the imaging unit 8 upon its rotation about the axis 16. This is compensated by a change in the spatial relationship between the imaging unit 8 and the table 4 by a respective movement 148 of the imaging unit 8 which is effected by the drive system 130.

For the operation of the imaging system according to the invention, the control system 32, 132 needs the specification of the centerpoint of the region of interest in space with respect to the imaging system. This 3D location of the centerpoint of interest with respect to the imaging system can be obtained in various ways, for instance:

^■ The user isocenters the system at the start of the procedure and stores this location, meaning that the physician positions the centerpoint 28 of the region of interest 44 in the iso-center 26 by adjusting table height and panning while checking in different views under fluoroscopy to make sure the centerpoint 28 of the region of interest 44 is positioned in the center of the image, after which the physician stores the iso-center location. After this the physician adjusts the table 4 to ergonomic working height and the panning can be automatically controlled by calculation from the C-arm movements for the remainder of the procedure or until the centerpoint 28 of the region of interest 44 changes. ■ In a second option the user starts working as normal, with the table 4 set at ergonomic working height, acquiring images, e.g. cine images, at different views, panning the table 4 under fluoroscopy. After the first two image acquisitions are made in two different views, the control system 32,132 can calculate the 3D location of the centerpoint 28 of the region of interest 44 from the geometric setup of the imaging system 2 in the first two image acquisitions (intersection of the projection lines of the two X-ray projection). From this moment on, the panning can be automatically controlled by calculation from the C-arm movements for the remainder of the procedure or until the centerpoint 28 of the region of interest 44 changes.

^■ In a third option the centerpoint 28 of the region of interest 44 is determined by the user with the aid of laser crosshairs projected on the patient 6 of which the intersection indicates the iso-center 26.

^■ In a fourth option, a default height of the centerpoint 28 of the region of interest 44 is proposed by the control system based on patient data, e.g. patient weight, patient size, etc. According to this option, only one image acquisition for determining the horizontal position of the centerpoint 28 of the region of interest 44 is necessary, to determine the location of this centerpoint 28 in space.

The present invention is applicable for acquiring one or more individual images as well as for rotational scans. For rotational scans in which a predefined trajectory of rotations is completed by the C-arc, the features of the invention or embodiments thereof can also be used either by pre-calculating the trajectory or by calculating and following the C-arc movement with table panning in real-time.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclose embodiments.

For example, the invention is not limited to a C-arc x-ray imaging system. Rather, it is possible to use the change in spatial relationship between the imaging unit and the table in response to a rotation of the imaging unit about the axis of rotation in any imaging system which is rotatable about an axis of rotation. In this sense, an imaging system which is rotatable about an axis of rotation includes an imaging system wherein only a radiation detector or only a radiation source is rotatable about an axis of rotation.

Other variations to the discussed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. For example, instead of a floor mounted imaging unit 8, a ceiling mounted imaging unit may be used. In other embodiments, the imaging unit may be a mobile imaging unit. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. Further, each of the functions of the control system might be carried out by an individual processor or other unit. The mere fact that certain measures are recited in mutually different dependent claims does no indicate that a combination of these measures cannot be used to advantage. A computer program product may be stored/distributed on a suitable medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. A computer program product may be a complete release or may be an update which enables a processor to carry out the desired method. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An imaging system (2, 102) comprising: a table (4) for receiving a patient (6); an imaging unit (8) for generating an image of at least a portion of said patient (6) received on said table (4), said imaging unit (8) defining an axis of rotation (14, 16) about which said imaging unit (8) is rotatable; a drive system (30, 130) for controllably changing a spatial relationship between said table (4) and said imaging unit (8); a control system (32, 132) for providing control signals (34, 134) to said drive system (30, 130) in response to a rotation of said imaging unit (8) about said axis of rotation (14, 16), at least when a center (28) of said region of interest (44) is located at a distance from said axis of rotation (14, 16), to thereby maintain said region of interest (44) within an image region of said imaging unit (8).

2. The imaging system of claim 1, wherein said control system (32, 132) provides said control signals (34, 134) to said drive system automatically upon a rotation of said imaging unit (8) about said axis of rotation (14, 16).

3. The imaging system of claim 1, wherein: said control system (32, 132) provides a status signal (150) indicative of a planned activation of said drive system (30, 130) in response to said rotation of said imaging unit (8); said imaging system (2, 102) further comprises a user interface (154) for approving said planned activation of said drive system (30, 130); and said control system (30, 130) provides said control signals (34, 134) to said drive system automatically upon approval of said planned activation of said drive system by said user interface.

4. The imaging system of claim 1, further comprising a user interface (36) for effecting a rotation of said imaging unit (8) about said axis of rotation (14, 16) into a desired angular position.

5. The imaging system of claim 1 wherein said drive system includes a table related drive system (30) for changing a spatial position of said table (4).

6. The imaging system of claim 1 wherein said drive system includes an imaging unit related drive system (130) for changing a spatial position of the imaging system (8).

7. Method of operating an imaging system (2, 102) comprising a table (4) for receiving a patient (6) and an imaging unit (8) for imaging of at least a portion of said patient, the method comprising: receiving input data specifying a region of interest (44) of said patient

(6); rotating said imaging unit (8) about an axis of rotation (14, 16) while a centerpoint (28) of a region of interest (44) is spaced from said axis of rotation; controllably changing a spatial relationship between said table (4) and said imaging unit (8) in response to said rotation of said imaging unit (8) to thereby maintain said region of interest within an image region of said imaging unit (8).

8. Method according to claim 7, wherein controllably changing a spatial relationship between said table (4) and said imaging unit (8) comprises changing a horizontal distance between said table and said imaging unit.

9. Computer program product which enables a processor to carry out the method according to claim 7. o

10. Computer program product which enables a processor to provide the functionality of the control system of the imaging system according to claim 1.