Method for image reconstruction in a computed tomography device
AssigneeSiemens Aktiengesellschaft
InventorsThomas Flohr, Bernd Ohnesorge, Karl Schwarz
Life of this patent
Estimating the term…
Abstract
In a method for image reconstruction in a computed tomography (CT) device, which picks up projections of a region located in a measuring field of an examination subject having an extent which exceeds this measuring field, the projections are identified in which the measuring field was exceeded, and extrapolated measurement points representing the detected cut-off projections, are added to the series of “actual” measurement points in such a way that each series of measurement points representing a detected projection is completed in an optimally realistic manner, and begins and ends with a measurement point whose measurement value is substantially zero.
Claims15
A method for image reconstruction in a computed tomography device comprising the steps of:
- rotating a focus of a radiation source around a system axis and an examination subject disposed in a measuring field, said subject also exceeding said measuring field, to irradiate said examination subject from a plurality of different projection angles and detecting attenuated radiation from said examination subject at said different angles to form a plurality of projections, with each projection being represented by a series of measurement points, each measurement point being characterized by a channel number and a measurement value;
- detecting projections in which said examination subject exceeded said measuring field;
- for said projections in which said examination subject exceeded said measuring field, adding extrapolated measurement points to said series of measurement points representing the detected projection so that each series of measurement points representing a detected projection begins and ends with respective measurement points having respective measurement values substantially equal to zero;
- and
- obtaining said extrapolated measurement points by at least one of:
- for each detected projection, mapping the measurement points representing the detected projection in a rectangular coordinate system having a measurement value axis and a channel number axis, and reflecting a number of consecutive measurement points at at least one of a beginning and an end of the series of measurement points representing the projection, at a first line proceeding through a first measurement point of said series of measurement points when reflecting at said beginning of said series of measurement points and proceeding through a last measurement point of said series of measurement points when reflecting at said end of said series of measurement points, said first line being parallel to said measurement value axis, and subsequently reflecting said number of consecutive measurement points at said at least one of said beginning and said end of said series of measurement points representing the projection, at a second line proceeding through said first measurement point of said series of measurement points when reflecting at said beginning of said series of measurement points and proceeding through said last measurement point of said series of measurement points when reflecting at said end of said series of measurement points, said second line being parallel to said channel number axis, and
- obtaining reference data measured for a measuring field which exists without gating of radiation from said x-ray source, and employing said reference data to generate said extrapolated measurement points.
Dependencies are inferred from the claim text.