1. Field of the Invention The present invention is directed to a method for the presentation of an examination subject by means of tomograms of the type wherein a number of tomograms are produced which differ in position with respect to one dimension such as, for example, each tomogram being allocated to a different time center of gravity or each tomogram being allocated to a different position of a location axis.
2. Description of the Prior Art
Such methods are known, for example, from computed tomography (CT) and serve the purpose of illustrating modifications within the examination subject as a function of time and/or location. A disadvantage of such known methods is that a number of tomograms must be viewed in order to be able to acquire the information with respect to the time or position change.
There is the possibility of presenting the modifications by producing three-dimensional images or with dynamic, cinematic-like presentation of the tomograms; however, the evaluation of such presentations is not always simple since, in particular, the users of CT apparatuses are accustomed to interpreting static, two-dimensional tomograms.
U.S. Pat. No. 5,216,602 discloses showing the blood flow in an examination subject in CT images with the use of an x-ray contrast agent, with the individual pixels of a diagnostically relevant image being compared to the pixels of a reference image, and those pixels of the diagnostically relevant image that deviate in terms of their CT number from the corresponding pixels of the reference image are presented in color, the color corresponding to the extent of the respective deviation.
An object of the present invention is to provide a method of the type initially described that allows information with respect to a third dimension to be presented in a static tomogram.
This object is inventively achieved by a method for the presentation of an examination subject upon employment of tomograms including the steps of generating a number (series) of tomograms that differ from one another in position with respect to one dimension, coloring some of tomograms in the series of tomograms, with respective colors, whose respective positions on a color scale correspond to the positions of the respective tomograms with respect to the dimension, being allocated to the respective tomograms, and superimposing a number of the color tomograms to form a resultant image.
When three tomograms are colored with the colors red, green and blue, a black-and-white image would arise by superimposition of the colored tomograms if there are no differences whatsoever with respect to the dimension among the tomograms. When, by contrast, differences are present in the three tomograms with respect to the dimension, then an image arises as resultant image that is colored in those regions wherein differences are present with respect to the dimensions, but is a black-and-white image in those regions wherein there are no differences with respect to the dimension.
Thus information with respect to an additional dimension can be presented and recognized in the inventive method in a static tomogram.
The procedure of coloring a tomogram is to be understood as meaning that this operation relates to the tomogram overall, for example by converting all gray-scale values of a black/white image into corresponding red values. In the case of a tomogram that is composed of pixels arranged matrix-like in a manner known from computed tomography, this means that all pixels of the tomogram are affected by the operation of coloring by, for example, the original gray scale value of the respective pixel being replaced by an analogous red value.
In a further version of the invention, the tomograms respectively have substantially the same section plane, and the dimension with respect to which the tomograms differ is the position of the time center of gravity on a time axis, and each tomogram is allocated to a different time center of gravity, and a color is allocated to the respective tomogram to be colored whose position on a color scale corresponds to the position of the time center of gravity of the respective tomogram on the time axis. In this case, all time changes are shown on the basis of color changes.
The term xe2x80x9ctime center of gravityxe2x80x9d means that point in time within the time interval from which the data underlying the tomogram are derived at which half of the data underlying the tomogram are acquired.
Continuous, chronologically successive tomograms, can be produced with the most recently produced tomogram being added at successive points in time to the series of tomograms and inserted, with a tomogram produced earlier from the series of tomograms being removed from the series, and with a number of colored tomograms being superimposed to form a resultant image at each of the following points in time. In this case, the resultant image represents a time window of defined length that is continuously updated. To make the resultant image easily interpretable, the colored tomograms that are superimposed to form a resultant image at each of the successive points include the most recently generated tomogram. Therefore, the point in time (among the aforementioned successive points in time) at which the superimposition takes place occurs after the point in time at which the most recently generated tomogram in the superimposed tomograms was generated.
The resultant images have particular diagnostic effect when the time centers of gravity of successive tomograms superimposed to form a resultant image have identical spacings from one another on the time axis.
The interpretation of a resultant image has a simple form when tomograms are produced that substantially correspond to parallel planes of section.
In a further, preferred embodiment of the invention, the tomograms are of different section planes, with the dimension with respect to which the tomograms differ being the position of the section plane on a location axis, and a color is allocated to the respective tomogram to be colored whose position on a color scale corresponds to the position of the section plane of the respective tomogram on the location axis. In this case, the position of the section planes on the location axis is presented as an additional dimension. This means that those regions that do not coincide in the superimposed tomograms are displayed colored in the resultant image. In contrast thereto, those regions that coincide in the superimposed tomograms are presented in the manner of a black-and-white image.
The term xe2x80x9csection planexe2x80x9d means the plane that represents the center plane of the slice of the examination subject scanned in the acquisition of the data underlying the tomogram.
As described above tomograms can be continuously produced, namely for positions following one another along the location axis, with the most recently produced tomogram at successive points in time being added to the series of tomograms and inserted, and the tomogram produced earliest is removed from the series of tomograms, and with the colored tomograms of the series being superimposed to form a resultant image at each of the successive points in time. In this case, the resultant image represents a section on the location axis having a defined length that is continuously updated. As above, for good interpretation of the resultant image a tomogram is used in the superimposition to form a resultant image at each of the successive points in time that is generated for a position along the location axis that lies following the position for which the most recently produced tomogram of the tomograms superimposed to form a resultant image was generated at the preceding point in time.
When the dimension for which the tomograms differ is the position of the section planes on the location axis, in a further embodiment of the invention sets of tomograms are produced in continuous succession for a number of different section planes that respectively have substantially the same time center of gravity as the respective tomograms of a set be colored and superimposed to form a resultant image, whereby a new, resultant image is respectively generated as soon as a new set of tomograms is present. This method is particularly suited for implementation on a CT apparatus having a multi-line detector, whereby each line of the detector can simultaneously generate one tomogram. The slice or slices in which a medical instrument, for example a punction needle, is located in the implementation of an intervention under CT monitoring can then be recognized on the basis of the color in the resultant image.
In order to be able to optimally utilize the information available in the form of tomograms, all tomograms in accordance with the invention are colored in the number of tomograms and all colored tomograms are superimposed.
The tomograms need not be directly produced but, in an embodiment of the invention, can be produced by scanning a volume of the examination subject, and the tomograms are determined from measured data acquired in the scanning, being determined with known methods of multi-planar reconstruction (MPR). This offers the advantage that arbitrary tomograms within the scope of the scanned volume can be utilized for the superimposition.
In a preferred embodiment of the invention, the tomograms are acquired with a CT apparatus, for example a spiral CT apparatus known from German OS 198 00 946, with the location axis corresponding to the system axis of the CT apparatus in the case where the additional dimension is the position of the section planes with respect to a location axis.
The CT apparatus as disclosed by U.S. Pat. No. 5,377,250, can have a detector system with a number of lines of detector elements. In this case in another, preferred embodiment of the invention that the tomograms are acquired with different lines of detector elements, with the positions of the section planes respectively corresponding to the tomograms on the location axis corresponding to the position of the respective line of detector elements with respect to the system axis of the CT apparatus. In this case, the tomograms to be superimposed can be simultaneously generated, i.e. with the same time center of gravity, even though they exhibit differently positioned section planes with respect to the system axis of the CT apparatus.