Method for reducing motion artifacts
View Patent ↗Artifacts result from unrecorded, stochastically distributed relative movements of a radiation source, radiation detector, and/or the object during a scanning process. The artifacts occur when a three-dimensional image dataset is reconstructed from two-dimensional projection images acquired from different projection directions. Geometric parameters describing an acquisition geometry for each projection image are taken into account during the reconstruction. The correction includes filtering the projection images to obtain a set of filtered first intermediate images. A set of second intermediate images are formed by filtering the projection images with a second filter. A three-dimensional reconstruction dataset is constructed from the filtered projection images filtered by way of the second filter, and forward projection is applied in the projection directions. Displacement information is determined for each projection direction by comparing the respective first intermediate image with the second intermediate image, and the geometric parameters are adjusted as a function of the displacement information.
1. A method of reducing artifacts resulting from unrecorded, stochastically distributed movements of a radiation source and/or a radiation detector and/or an object during a scanning of the object, wherein the artifacts occur when a three-dimensional image dataset is reconstructed from two-dimensional projection images acquired from mutually different projection directions by way of an image acquisition arrangement having the radiation source and the radiation detector, and wherein geometric parameters describing an acquisition geometry for each projection image are taken into account during the reconstruction of the three-dimensional image dataset, the method which comprises performing the following correction steps:
subjecting the projection images to a first filter for determining a set of filtered first intermediate images;
subjecting the projection images to a second filter combining a ramp filter and the first filter, reconstructing a three-dimensional reconstruction dataset from the projection images after filtering by the second filter, and applying a forward projection in the projection directions and determining a set of second intermediate images;
comparing a respective first intermediate image with a second intermediate image, for determining displacement information for each projection direction; and
adjusting the geometric parameters in dependence on the displacement information.
2. The method according to claim 1 , wherein the first filter is a ramp filter.
3. The method according to claim 1 , wherein the second filter is a second derivative.
4. The method according to claim 1 , which comprises determining the displacement information based on a rigid registration between the respective first and second intermediate images.
5. The method according to claim 1 , which comprises repeating the correction steps iteratively until a quality value describing the deviation of the geometric parameters from the real geometry falls below a limit value.
6. The method according to claim 1 , which comprises repeating the correction steps iteratively until a quality value describing the deviation of the geometric parameters from the real geometry reaching a minimum.
7. The method according to claim 5 , wherein the quality value is a value describing a sharpness of the second intermediate image.
8. The method according to claim 7 , wherein the quality value is a value describing a sharpness of the second intermediate image in comparison with the first intermediate image.
9. The method according to claim 5 , which comprises assuming every other second intermediate image as a corresponding first intermediate image convoluted with a two-dimensional Gaussian core and determining a displacement between the intermediate images and the standard deviations as parameters of the Gaussian core, and using the displacements as displacement information and deriving the quality value from the standard deviations.
10. The method according to claim 5 , which comprises performing a plurality of iteration processes for mutually different levels of detail increasing in a course of the correction, in that before the correction steps are performed, applying a lowpass filter to the projection images for all iteration processes preceding a most recent iteration process, and reducing a lowpass filtering as a number of iteration processes increases.
11. The method according to claim 1 , which comprises adjusting only geometric parameters of the radiation detector.
12. The method according to claim 11 , which comprises adjusting only geometric parameters describing a movement of the radiation detector in a radiation detector plane.