Method for recording a complete projection data set in the central layer for CT reconstruction using a C-arm X-ray apparatus with a limited rotation range
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Publication Number
US-9655568-B2
Publication Date
2017-05-23
Expiration Date
Abstract
A method for recording a scan from a series of 2D X-ray projections using a C-arm X-ray apparatus allows an analytical volume reconstruction of a disk-shaped region of interest. The C-arm X-ray apparatus has a coherent, flat focus trajectory comprising three sections on which the focus of the X-ray source is moved with recording of X-ray projection views. The X-ray source emits a cone beam in the direction of an imaging X-ray detector, such as in particular a flat panel detector FPD. In some implementations, the cone beam is configured as a fan beam with a fan angle in the plane of the focus trajectory, which contains the ROI with the virtual scan center in its center, wherein the central ray of the fan beam is located on the bisector of the fan angle, and stands vertically on the ray inlet window. Before the beginning of the scan, the C-arm is positioned in the orbital movement axis in a first extreme position in which the holder engages at one end of the C-arm with the X-ray source, and the adjustable holder of the C-arm is positioned in such a manner that the ROI is located outside of the circle segment formed by the C-arm and the central ray, and a first limiting beam of the fan beam, which starts from the focus point and which is located on the side of the central ray facing away from the C-arm, is tangential to the ROI. During the recording of the scan, the plane of the C-arm remains fixed in space.
Core Innovation
The invention relates to a method for recording a scan of a region of interest using a C-arm X-ray apparatus with a virtual scan center located in the center of the region of interest. The scan comprises a series of X-ray projection views recorded as a complete set of X-ray projection data of the region of interest in the plane of the C-arm X-ray apparatus for 3D reconstruction.
The C-arm has a space-fixed plane and is mounted so that it can be moved parallel with a multiply adjustable holder and can also be moved by a motor along an orbital movement axis between a first and a second extreme position. The focus is moved along a flat coherent focus trajectory during recording of the projection views, with a three-section focus trajectory and boundary conditions on the fan beam to keep the region of interest fully within the relevant beam region.
At the start point, the C-arm is positioned in the first extreme position and a first limiting fan beam is tangential to the region of interest. In a first section, the holder is moved parallel in the plane of the C-arm until the central ray vector extends through the virtual scan center and the region of interest is located completely within the fan beam. In a second section, the C-arm is moved along the orbital movement axis into a second extreme position, with the orbital movement angle area between the first and second extreme position at least 180° minus fan angle, and the holder is moved parallel such that the central ray vector extends through the virtual scan center and the region of interest is entirely within the fan beam.
In a third section, the C-arm is maintained in the second extreme position while the holder is moved parallel in the plane of the C-arm until a second limiting fan beam is tangential to the region of interest. The invention addresses projection completeness for 3D reconstruction of a disk-shaped region of interest despite a limited orbital rotation range by shaping the trajectory and, when needed, removing fan-beam portions outside the region of interest, while maintaining the central ray vector through the virtual scan center and avoiding abrupt direction changes in detector trajectory directions.
Claims Coverage
The independent claim is clm-00001, which recites 9 inventive features centered on a C-arm CT recording method using a virtual scan center and a three-section flat coherent focus trajectory to obtain a complete set of projection data for 3D reconstruction in the plane of the C-arm. Dependent claims clm-00002 to clm-00005 further define detector trajectory smoothness, an oscillating focus trajectory shape, and motor-driven primary radiation diaphragm use synchronized with holder movement control to remove fan-beam portions outside the ROI.
Virtual scan center for complete ROI projection data in C-arm plane
A method for recording a scan of a region of interest using a C-arm X-ray apparatus with a virtual scan center located in the center of the region of interest, wherein the series of X-ray projection views provides a complete set of X-ray projection data of the region of interest in the plane of the C-arm X-ray apparatus for 3D reconstruction.
Three-section flat coherent focus trajectory with tangential fan-beam limits
Recording the series of X-ray projection views using a focus trajectory with a first section, a second section, and a third section in which, at the start point, a first limiting fan beam is tangential to the region of interest, in the first section the central ray vector extends through the virtual scan center while the region of interest is completely within the fan beam, in the second section the orbital movement angle area between first and second extreme position is at least 180° minus fan angle while the central ray vector extends through the virtual scan center and the region of interest is entirely within the fan beam, and in the third section a second limiting fan beam is tangential to the region of interest.
Space-fixed C-arm plane with parallel holder movement and orbital movement axis
Using a C-arm with a space-fixed plane, mounted so that it can be moved parallel with a holder which is multiply adjustable by means of a motor, and mounted so that it can be moved by means of a motor in the holder along an orbital movement axis between a first and a second extreme position.
Central ray vector passes through virtual scan center with fan-beam inclusion
Controlling movement so that the central ray vector extends through the virtual scan center and the region of interest is located completely within the fan beam in the first section, and the region of interest is located entirely within the fan beam in the second section.
Flat coherent focus trajectory movement of focus during recording
Moving the focus of the X-ray source, while the X-ray projection views are recorded, along a flat coherent focus trajectory between a start point and an end point in any direction.
Motor-driven primary radiation diaphragm synchronized with movement control
Employing an X-ray source disposed at a first end of the C-arm comprising a primary radiation diaphragm controlled by means of a motor, wherein movements of the holder and of the C-arm in the orbital movement axis are controlled by a movement control, and generating a cone beam containing, in the plane of the C-arm, a fan beam having a fan angle.
Detector trajectory with no abrupt direction changes
Selecting first, second, and third sections of the focus trajectory such that the detector trajectory describing movement of the center of the radiation inlet window has no abrupt direction changes.
Oscillating focus trajectory around circular arc with radial extensions
Defining the focus trajectory such that it has three oscillating sections about a circular arc centered on the virtual scan center, with radial extensions at the junctions between the first section and the second section and between the second section and the third section.
Removing fan-beam portions outside the ROI with synchronized diaphragm movement
Removing fan-beam portions outside the region of interest in the first and third sections using a primary radiation diaphragm that is motor-driven and moved synchronously with movement of the holder.
Across the independent claim and its dependents, the claim set centers on using a virtual scan center and a three-section flat coherent focus trajectory with fan-beam tangency and fan-beam inclusion of the region of interest, while using a space-fixed C-arm plane and combined parallel holder movement with orbital movement. Refinements specify a detector trajectory without abrupt direction changes, an oscillating focus trajectory about a circular arc with radial extensions, and motor-driven primary radiation diaphragm beam shaping synchronized with holder movement to remove fan-beam portions outside the region of interest.
Stated Advantages
Not explicitly described in patent.
Documented Applications
Not explicitly described in patent.
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