Imaging apparatus

#The invention relates to an imaging apparatus, an imaging method and an imaging computer program for imaging an object. The invention relates further to a weighted base function generation apparatus, a weighted base function generation method and a corresponding computer program for generating weighted base functions, which are usable by the imaging apparatus for imaging an object.

#The article “Empirical dual energy calibration (EDEC) for cone-beam computed tomography” by Philip Stenner et al., Medical Physics, Vol. 34, No. 9, p. 3630-3641 (September 2007) discloses a dual-energy computed tomography system, which generates energy projection data values corresponding to rays after having traversed an object to be imaged, wherein for each ray energy projection data values for two different energies are generated. A decomposition function, which depends on the generated energy projection data values, is used for decomposing the generated energy projection data values into base material projection data values such that for each ray two base material projection data values are determined, which correspond to two different base materials of the object to be imaged. The decomposed base material projection data values are then used for reconstructing a first base material image, which corresponds to a first base material of the object, and a second base material image, which corresponds to a second base material of the object. The decomposition function is a polynomial function, wherein the polynomial's coefficients are determined using a least squares fit based on thresholded images of a calibration phantom.

#The decomposition of the initially generated energy projection data values into the base material projection data values can produce artifacts in the determined base material projection data values and, thus, in the finally reconstructed base material images. The quality of the finally reconstructed base material images can therefore be reduced.

#These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

#In the drawings:

#FIG. 1 shows schematically and exemplarily an embodiment of an imaging apparatus for imaging an object,

#FIG. 1 shows schematically and exemplarily an imaging apparatus for imaging an object. In this embodiment, the imaging apparatus 31 is a computed tomography apparatus for imaging an object within an examination zone 5. The computed tomography apparatus 31 includes a gantry 1 which is capable of rotation about a rotational axis R which extends parallel to the z direction. A radiation source 2 generates a conical radiation beam 4 for traversing the examination zone 5. The radiation source 2 comprises an x-ray tube 17 and a collimator 3 which forms the conical radiation beam 4 from the radiation generated by the x-ray tube 12. The radiation 4 traverses an object (not shown) such as a patient, which is located within the examination zone 5 being, in this embodiment, cylindrical. After having traversed the object the radiation beam 4 is incident on a detector 6 comprising a two-dimensional detection surface 21. The detector 6 is mounted on the gantry 1.

#The computed tomography apparatus 31 comprises two motors 7, 8. The gantry 1 is driven at a preferably constant but adjustable angular speed by the motor 7. The motor 8 is provided for displacing the object, for instance, a patient, who is arranged on a patient table in the examination zone 5, parallel to the direction of the rotational axis R or the z axis. The motors 7, 8 are controlled by a control unit 9 such that the radiation source 2 and the object within the examination zone 5 are moved relative to each other along a helical trajectory. However, the motors 7, 8 can also be controlled such that the radiation source 2 and the object within the examination zone 5 are moved relative to each other along another trajectory. For instance, the motor 7 can drive the gantry 1 such that the radiation source 2 rotates around the object within the examination zone 5, while the motor 8 does not move the object parallel to the direction of the rotational axis R or the z axis. In this case, the radiation source 2 and the object within the examination zone 5 are moved relative to each other along a circular trajectory. During the relative movement of the radiation source 2 and the object within the examination zone 5 the detector 6 generates energy projection data values being indicative of the radiation beam 4 after having traversed the object.

#The motors 7, 8, the radiation source 2, the detector 6, the gantry 1 and the control unit 9 form a computed tomography acquisition unit 30 being the projection data providing unit for providing energy projection data values, which are energy-dependent and which correspond to rays of the radiation beam 4 after having traversed the object.