Method for reconstruction of an image of a moving object
View Patent ↗A very fast reconstruction is undertaken in an image reconstruction process by tomography, by dividing measurements through the subject into a series of subsequent sets that are inverted by back projections giving partial result blocks used to search for the change law for the subject. Partial contents of the image can then be predicted at a reference time and their accumulation gives the image. The law for how the subject changes with time is evaluated and is used to compensate for partial results before their accumulation.
1. Process for reconstruction of an image of a moving subject, including taking a set of successive measurements of the subject on projection rays passing through the subject, through a network ( 4 ) of detectors ( 5 ) at corresponding incidences around the subject, a measurement back projection step and a correction step following a subject change law, characterised in that the back projection step is made in several steps to give corresponding blocks (f b ) of back projection results, each of the blocks grouping projection rays taken only for an angular sector of a turn of the detectors network using measurement quantities that are insufficient to genuinely express the required image; the subject change law is estimated based on the first images obtained by accumulating back projection blocks on at least half a turn of incidences of the detectors network; and the back projection result blocks are combined after they have been corrected using the subject change law to give the image at a reference time (t r ).
2. Process for reconstruction of a three-dimensional image according to claim 1 , characterised in that the change law includes variations of the appearance of the subject with time.
3. Process for reconstruction of a three-dimensional image according to claim 2 , characterised in that the said variations are estimated by regression calculations between the corresponding portions in the first images derived from the results of back projection blocks.
4. Process for reconstruction of a three-dimensional image according to any one of claims 1 to 3 , characterised in that the change law includes displacements D(x,y,z) of portions of the subject.
5. Process for reconstruction of a three-dimensional image according to claim 4 , characterised in that the said displacements are estimated by distance searches between similar portions of the said first images of the subject obtained by accumulating successive back projection blocks.
6. Process for reconstruction of a three-dimensional image according to any one of claims 1 to 5 , characterised in that the subject change law is obtained within groups of back projection result blocks, the back projection result blocks are combined firstly within groups to give a fragment of the content of the image at the reference instant, and the image is obtained by adding the said fragments, the angular sectors of the blocks in the same group being separated either by a half-turn or a complete turn.
7. Process for reconstruction of a three-dimensional image according to any one of claims 1 to 6 , characterised in that the subject change law is estimated from undersampling of the projections.
8. Process for reconstruction of a three-dimensional image according to any one of claims 1 to 6 , characterised in that the subject change law is estimated from a complete sampling of the projections.
9. Process for reconstruction of a three-dimensional image according to claim 5 , characterised in that the first images are submitted to undersampling before the said displacements are estimated.
10. Process for reconstruction of a three-dimensional image according to claim 6 , characterised in that the subject change law is updated while measurements sets are taken.
11. Process for reconstruction of a three-dimensional image according to any one of claims 1 to 10 , characterised in that confidence factors C ij are calculated for each block (F bi, j ) once the subject change law has been obtained, and blocks are weighted as a function of the said factors, before being combined.