Method for production of tomographic section images of a periodically moving object with a number of focus detector combinations

#The present application hereby claims priority under 35 U.S.C. §119 on German patent application number DE 103 54 900.5 filed Nov. 24, 2003, the entire contents of which are hereby incorporated herein by reference.

#The invention generally relates to a method for production of tomographic section images. In particular, it relates to a method for production of X-ray CT images, of a periodically moving object with periodically changing movement and rest phases, with a number of focus detector combinations being moved on coaxially running paths around the examination object in order to scan the periodically moving examination object, and movement signals from the examination object at the same time being measured in order to determine movement and rest phases, and being stored correlated with the detector output signals. Tomography images can then be created with the aid of back-projections by spiral reconstruction and reformatting, on the basis of the stored detector output signals.

#Computer tomography methods for creation of section images with the aid of multiple focus detector combinations are known, for, example, from the patent specifications U.S. Pat. No. 4,196,352, U.S. Pat. No. 4,384,359, U.S. Pat. No. 5,966,422, U.S. Pat. No. 4,991,190 and U.S. Pat. No. 6,421,412 B1. The Laid-Open Specification DE 199 57 082 A1 discloses the recording of movement signals of the heart by the use of an EKG in order to display a beating heart in parallel with the scanning process. As such, the rest phases of the heart can be determined and exclusively images from the rest phase can be assessed. The X-ray source may additionally be active only during the rest phase in the cited document.

#The invention will be explained in more detail in the following text with reference to a preferred exemplary embodiment and with the aid of figures, in which the following reference symbols and variables are used: 1 CT scanner; 2 first tube; 3 first detector; 4 second tube; 5 second detector; 6 housing; 7 opening; 8 couch; 9 system axis/z axis; 10 control/evaluation unit; 11 first beam; 12 second beam; 13 first/small section field; 14 second/large section field; 15 shutter for the second beam; 16 shutter for the first beam; 17 R peak in the EKG; 18 EKG line; 19 reconstructable volume element with data from one heart cycle; 20 reconstructable volume element with data from two heart cycles; 21 time back to the start of the rest phase; 22 detector lines; 23 virtual detector; D1 first detector; D2 second detector; d pitch; k the number of the half revolution of the gantry; L1 length of the first detector; L2 length of the second detector; P patient; p parallel positions on a parallel projection; Prgn n-th program module; Pn π/2 partial data record; Pn,max maximum position of the detector n; q number of lines; Rf focus path radius; S layer thickness; Sn n-th spiral data record; Trev time delay with respect to the R peak; TR time of the R peak; TRR duration of one heart cycle from one R peak to the next; Trot revolution time of the gantry; z z axis; zn z position of the n-th detector; zimg z position of the image; α rotation angle of the gantry/projection angle; αn start angle; αjs start projections of the segment elements; αje final projections of the segment elements; αnms m-th start angle of the n-th focus; β1 fan angle of the first beam; β2 fan angle of the second beam; Δtima time image resolution; Θn n-th segment element; Θtrans length of the transition area.

#In detail, in the figures:

#FIG. 1: shows a 3D illustration of a CT scanner with two focus detector combinations including an evaluation unit;

#FIG. 1 shows a 3D illustration of one preferred exemplary embodiment of a CT scanner 1 with two focus detector combinations 2, 3 and 4, 5, which can be rotated within the housing 6 on a gantry, which is not illustrated. However, the illustration shows only X-ray tubes 2 and 4, since the actual focus is located within the tubes. Controlled by the control and evaluation unit 10, the patient P is moved along the z axis 9 with the aid of the movable patient couch 8 through the opening 7 in the CT scanner 1 while, at the same time, the gantry rotates with the two focus detector combinations 2, 3 and 4, 5 about the z axis 9. With respect to the patient as the reference system, this results in spiral movement paths of the focus detector combinations. If the focus detector combinations are arranged on one plane, then each focus detector combination runs on its own spiral path, which is shifted with respect to the other spiral path corresponding to its angle offset.

#At the same time as the scanning of the patient P with the focus detector combinations, the movement signals of the heart are scanned by means of an EKG which is integrated in the control/evaluation unit 10, from which it is possible to retrospectively determine the previous rest phase in time with respect to the currently measured heart cycle, on the basis of the R peak detected in the EKG.

#In order to assist understanding, FIG. 2 shows the scanning system of the two focus detector combinations once again in the form of a schematic section illustration, although the X-ray tubes forming the respective foci F1 and F2 are not illustrated here. This illustration thus shows the two focus detector combinations from FIG. 1, respectively with a first focus F1 and a second focus F2, and the respective multiple line detectors D1 and D2 arranged opposite them. A beam 11 with a smaller fan angle β1, which is set in a fixed manner by the shutter 16, extends from the focus F1 to the opposite detector D1, which has a length L1 in the direction of the fan angle β1 and has a number of detector lines in the z direction.