Koninklijke Philips Corporation N.V.

Thomas Köhler

Michael Grass

Roland Proksa

Claas Bontus

Tim Nielsen

Michael Harald Kuhn

Robert Manzke

Peter Forthmann

Peter Koken

Udo Van Stevendaal

A method for processing polychromatic attenuation values, wherein the polychromatic attenuation values are acquired by means of a polychromatic source of radiation generating a cone beam and radiation detector array with a plurality of detector rows, wherein the plurality of detector rows are arranged adjacent to each other in a first direction perpendicular to a second direction, wherein the second direction is parallel to the plurality of detector rows, the method comprising the step of: assigning the monochromatic attenuation values to polychromatic attenuation values, wherein the polychromatic attenuation values depend on the first direction and a three-dimensional look-up table is used for assigning the monochromatic attenuation values to the polychromatic attenuation values.

Correction of artifacts caused by the heel effect

Motion is one of the most critical sources of artifacts in helical conebeam CT. By comparing opposite rays corresponding to projection data, the amount of motion may be estimated and, in the following suppression of corresponding motion artifacts may be performed according to an exemplary embodiment of the present invention. The method of motion artifact compensation may be implemented in both approximate reconstruction algorithms and exact reconstruction algorithms. Advantageously, motion during the data acquisition is detected automatically and related motion artifacts may be suppressed adaptively.

Motion artifacts compensation

Using only projection data in one temporal gating window around a certain target phase point may lead to motion artifacts such as blurred images. By using projection data corresponding to three temporal gating windows, which are slightly shifted with respect to each other but at least partially overlap, motion within the gating window may be estimated and, according to an exemplary embodiment of the present invention, this estimation may be used for improving the image quality. Advantageously, only the projection data inside the at least partially overlapping gating windows are used for reconstruction and motion compensation.

Motion compensation

Image quality is an important feature for CT scanning, in particular for helical cone-beam CT scanning. By using projection data acquired at two different positions of the focal spot of the radiation beam and rebinning that projection data from a first geometry to a second geometry the two sub-sets of projection data are combined to one rebinned projection data set, thereby improving the radial resolution of the data set. Advantageously, according to an aspect of the present invention, a further rebinning may be performed, from the second geometry back to the first geometry, therefore resulting in a projection data set in the initial geometry with a higher radial resolution.

Multiple focus acquisition

The invention relates to a computed tomography method in which an examination zone is irradiated along a helical trajectory by a conical radiation beam. The radiation transmitted by the examination zone is measured by means of a detector unit and therefrom the absorption distribution in the examination zone is reconstructed without approximations. The reconstruction comprises a derivation of the measuring values of parallel rays of different projections, an integration of these values along K lines, a weighting of these values and a back projection.

Method and apparatus for exact cone beam computed tomography

In the CT imaging of non-homogeneously moving objects such as the heart or the coronary vessel tree, there is a problem that different parts of the objects are at rest at different points in time. Thus, a gated reconstruction with a globally selected time point does not yield a sharp image of such objects. According to the present invention, a motion of the objects is estimated, describing the motion of selected regions of these objects. Then, on the basis of the estimated motion, time points are determined, where these areas have minimal motion. Then, an image is reconstructed, wherein the data from which the respective regions are reconstructed, correspond to the respective time points, where the regions have minimal motion. Due to this, an improved image qualify maybe provided.

Reconstruction of an image of a moving object from volumetric data

The invention relates to a computer tomograph, in which data from a rotor, which during operation of the computer tomograph rotates about an axis of rotation, is transferred optoelectronically. For that purpose, on the rotor there is located at least one transmitter, which transmits light towards a receiver mounted on the axis of rotation, the light being modulated with the data to be transferred.

Computer tomograph with optoelectronic data transfer

The invention relates to a computerized tomography method, wherein a radiation source executes an nPi relative movement along a helix with respect to an object. Acquired measured values are partially derived according to the angular position of the radiation source on the helix and intermediate filter values are generated by filtering the derived measured values along the filter lines with a k filter. Each intermediate filter value is multiplied by a filter factor, where the filter factor for intermediate filter values that have been generated by filtering the derived measured values along filter lines, which run exclusively within the Pi window, is greater than or equal to those filter factors by which the intermediate filter values are multiplied, which have been generated by filtering the derived measured values along filter lines, which run inside as well as outside the Pi window. The intermediate filter values assigned to a measured value are added to a filter value and the filter values are back-projected for reconstruction of a CT image.

Computerized tomography method with helical relative movement and conical beam

Iterative algorithms, which may be used for image reconstruction, include alternating projections and backprojections usually have a slow convergence, due to correlations between simultaneously processed data. Consequently, a low image quality results. A filtering step is introduced before backprojection, allowing parallel processing without the loss of convergence speed or image quality. Advantageously, this allows several projections/backprojections to be performed simultaneously.

Iterative data reconstruction

The invention relates to a computer tomography method in which a periodically moving object, in particular an organ of the body, is irradiated by a cone-shaped beam cluster () along a trajectory which runs on a cylindrical surface. The radiation transmitted through the object is measured by means of a detector unit (), and at the same time the periodic movement of the object is recorded. In order to reconstruct the absorption distribution of the object, the measured values or the corresponding beams are rebinned to form a number of parallel projections, where for each of these projections a measured value is determined whose beam irradiates the object. The point in time at which this measured value was acquired is allocated to the respective projection. For the reconstruction, which may for example be carried out using a filtered back-projection, only projections whose allocated points in time lie within a predefined, specific time range (H) within a period of the object movement are used.

Computer tomography method for a periodically moving object

The invention relates to a computer tomography method in which an examination area is passed through by a cone-shaped bundle of rays. The bundle of rays comes from a radiation source location which moves around the examination area on an overall trajectory. The overall trajectory consists of a first, closed partial trajectory, at least one second, closed partial trajectory and at least one third partial trajectory which connects the first and the at least one second partial trajectories to one another. Measured values which depend on the intensity in the bundle of rays on the other side of the examination area are acquired by means of a detector unit while the radiation source location is moving on the overall trajectory, and a CT image of the examination area is reconstructed from these measured values.

Computer tomography method using a cone-shaped bundle of rays

An iterative method determines a spatial distribution of values of a property of an object, and particularly values of its absorption, in an examination region, on the basis of measured values that values are acquired with a measuring device, and particularly with a computer tomograph. The reliability of each measured value is taken into account when this is done. The measured values can each be represented as a sum of values of the property that have each been multiplied by a proportional factor, the proportional factor being a measure of the proportion that a value of the property forms of the measured value. Each value of the property is approached by one iteration value at a time by setting each iteration value to a starting value and, in an iteration step, generating for each measured value a reference measured value, forming the difference between each reference measured value and the corresponding measured value, and multiplying this difference by a reliability parameter and projecting it backward into the examination region.

Iterative method of determining a spatial distribution of values of a property

The invention relates to a method of computed tomography wherein a radiation source moves relative to an examination zone along a helical trajectory and wherein the movement involves a rotation around a rotational axis and a shifting parallel to the rotational axis. During the movement, a detector unit acquires real measured values. Fictitious measured values are determined from the real measured values by solving John's equation for a virtual movement of the radiation source along an intersection ellipse. The intersection ellipse intersects the helical trajectory at an intersection point and is the intersection of a virtual cylindrical surface, on which the helical trajectory is situated, with an intersection plane that is defined by a tangent vector of the helical trajectory at the intersection point and a vector that is oriented perpendicular to the rotational axis. Finally, an image of the examination zone is reconstructed using the real and fictitious measured values.

Computed tomography method for the reconstruction of object images from real and fictitious measured values

The reconstruction of computer tomography data is very often based on a parallel rebinning step of the projection data prior to the filtered back projection. In case of cardiac reconstruction, a gating technique is applied to select appropriate projections for a time-dependent image reconstruction. Usually, the gating window is a function of the fan-beam/cone-beam projection only. According to the present invention, a function corresponding to the location on the detector surface, where the respective projection was detected is used to further verify whether the respective projection is truly within the selected gating window or not.

Method and device for volumetric image reconstruction

The invention relates to a method of reconstructing the current flow, or the bolus arrival times, in a vessel system. For the sections (i) of the vessel tree, bolus arrival times (m) are measured, for example in connection with an injection of contrast medium. Based on this measured data, linear programming is then used to calculate model bolus arrival times (t), which, on the one hand, through minimization of the function E=&#x3a3;|m&#x2212;t|, are as close as possible to the measured data, and, on the other, by adherence to the boundary condition &#x394;=t&#x2212;t&#x2267;0, ensure the monotony of the propagation, wherein p(i) is the index of the vessel section in front of vessel section (i). Preferably, as smooth as possible a progression is compelled by means of an additional minimization of E=&#x3a3;|t&#x2033;|.

Growing community of inventors

Norderstedt, Germany

Thomas Köhler