DE102009058267A1 - Method for detecting contrast agent in lung tissue in air path of lungs of patient, involves detecting presence or absence of agent based on computer tomography values of pixels in tomographic images and/or voxels in volume datasets - Google Patents

Abstract

The method involves providing two-dimensional (2D) X-ray projections with two different X-ray energies by an X-ray computer tomography (CT) device (1). The projections are absorbed by a region of lungs whose tissue supplies a contrast agent over a blood vessel. Two tomographic images with two pixels and/or two volume datasets with two voxels of the region of the lungs are reconstructed based on the projections, respectively. CT values of the pixels and/or voxels are set in relation to each other, and presence or absence of the contrast agent is detected based on the values. Independent claims are also included for the following: (1) a computer tomography device comprising a processing unit (2) a data carrier comprising instructions to perform a method for detecting a contrast agent in a lung tissue in an air path of lungs of a patient.

Description

The invention relates to a method for detecting a contrast agent in lung tissue, in particular to be able to determine to what extent at least one lung tissue section or at least one wall of an airway of the lung is perfused. The invention also relates to a computed tomography device and to a data carrier having a computer program in order to be able to make a statement about the perfusion of at least one lung tissue section or at least one wall of an airway of the lung.

In some diseases of the airways of the lungs, it is not only of interest whether z. B. the walls of the airways are thickened or verschleimt, but also to what extent the walls of the airways perfused, d. H. flowed through by blood.

In principle, it is conceivable to carry out an examination of the lung by means of X-ray computer tomography after administration of a contrast agent in order to determine the perfusion of the lung tissue, in particular of the airways. In order to be able to differentiate perfused tissue from non-perfused tissue, it would be conceivable to use a constant threshold value for the CT values, so that all CT values which are above the threshold point to perfused tissue.

In practice, however, this encounters difficulties. While the uptake of contrast agent in the relatively thick wall of the trachea is still reasonably well detectable over the CT values, detection of contrast in the fine major or lobar bronchi of the lung is difficult on the basis of CT values, since these are relatively high have low wall thickness. In addition, the density of the walls of the airways varies in the different parts of the lung tissue. Even without the presence of contrast agent in the fine lung tissue sections, therefore, the measured CT values already fluctuate. With a constant threshold value for the CT values, it is therefore difficult to make a statement as to whether the fine lung tissue, in particular of the airways, has absorbed contrast media and is thus perfused. Due to the small wall thickness of the fine bronchi and the comparatively low resolution of X-ray computed tomography or the comparatively excessive layer thickness of a reconstructed slice image, the measured CT values of the slice image are additionally falsified by partial volume artefacts.

The invention is therefore based on the object of specifying a method, a computed tomography device and a data carrier of the type mentioned above such that the detection of contrast agent in lung tissue, in particular in an airway of the lung in an improved form is possible.

According to the invention, this object is achieved by a method for detecting a contrast agent in lung tissue, in particular in an airway of the lung in which at least from a region of the lung, the lung tissue via blood vessels a contrast agent was supplied with a computed tomography device X-ray projections with a first and with a second, from the first different X-ray energy are recorded. Based on the X-ray projections obtained with the first X-ray energy, at least one first pixel-containing slice image and / or one first voxel-containing volume data set of at least the region of the lung is reconstructed. Based on the x-ray projections obtained with the second x-ray energy, at least a second slice image corresponding to the first slice image and / or a second volume set corresponding to the first volume data set and voxel-containing volume data set are reconstructed from at least the region of the lung. Subsequently, the CT value of at least one pixel of the at least one first slice image and the CT value of a pixel corresponding to the at least one pixel of the at least one first slice image of the at least one second slice image corresponding to the first slice image and / or the CT value at least one voxel of the first volume data set and the CT value of a voxel of the second volume data set corresponding to the at least one voxel of the first volume data set of the first volume data set in relation to each other. Based on the value of each ratio, the presence or absence of contrast agent is detected in the lung tissue area represented by the two CT values of corresponding pixels or voxels.

The method is based on the consideration that a particular lung tissue area is considered, whether it is represented by a pixel or that it is represented by a voxel, for the first CT value based on the first x-ray energy and for the one based on the second, from the first different X-ray energy, a second CT value can be determined. If there is no difference between the first and second CT values, then there is no contrast agent in the lung tissue region under consideration, as the presence of contrast agent in the lung tissue area would have resulted in a higher CT value at the lower of the two X-ray energies used. True density differences in a considered larger section of lung tissue would also become one However, these changes are independent of the X-ray energy used so that the ratio of the CT values of corresponding pixels and / or voxels of a lung tissue area does not change.

According to a variant of the invention, therefore, contrast agent is present in the lung tissue region represented by two pixels or voxels corresponding to two CT values, for example an airway, if the ratio of the two CT values within the determination accuracy is smaller or greater than one. For example, if the second X-ray energy is higher than the first X-ray energy, then it is determined that the CT value of a pixel or voxel obtained with the second, higher X-ray energy corresponds to the CT value of a corresponding pixel or voxel obtained with the first, lower X-ray energy Relationship is established, contrast medium is always present in the lung tissue area belonging to the two CT values, if the ratio of the CT values is less than one. Conversely, if the ratio is reversed, contrast media will be present in the lung tissue area associated with the two CT scans whenever the ratio of CT scores is greater than one.

According to a further variant of the invention, consequently, no contrast agent is present in the lung tissue region represented by two pixels or voxels corresponding to two CT values, for example an airway, if the ratio of the two CT values within the determination accuracy is one. If a determination within the scope of the determination accuracy is mentioned above, this means that, for example due to rounding errors, etc., a tolerance range of one has to be established for the computational determination of the CT values and the values of the ratios. If the value of the ratio is in this tolerance range, the value is assumed to be one.

According to one embodiment of the invention, the CT values of preferably all mutually corresponding pixels of corresponding first and second slice images and / or the CT values of preferably all voxels of the first and second volume data set corresponding to one another are set in relation to one another for the detection of the contrast agent. In this way, for a larger area of the lung or for the entire lung, the detection of contrast agents can be carried out or the perfusion of the lung tissue can be determined.

According to a further embodiment of the invention, the images of the X-ray projections with the first X-ray energy and the images of the X-ray projections with the second X-ray energy of at least the region of the lung take place simultaneously. Preferably, the images of the X-ray projections with the first X-ray energy and the images of the X-ray projections with the second X-ray energy of at least the region of the lung with a two, each having an X-ray source and X-ray receiver comprehensive X-ray systems having computer tomography device. As an example, the SOMATOM definition of Siemens AG is mentioned here.

Due to the polychromatic X-ray spectrums commonly used in X-ray computer tomography, in each case an effective X-ray energy is assumed for the first and the second X-ray energy. According to a variant of the invention, the first X-ray energy is effectively about 60 keV and the second X-ray energy is effectively about 90 keV. In the case of the use of X-ray tubes as X-ray sources is to generate X-rays of the first X-ray energy of effectively about 60 keV, a voltage of about 80 kV at the first X-ray tube and for generating X-rays of the second X-ray energy of effectively about 90 keV a voltage of 140 kV at the second x-ray tube.

The contrast agent according to one embodiment of the invention is preferably iodine.

According to a further embodiment of the invention, the presence or absence of contrast agent, in particular of iodine in lung tissue, in particular in the fine walls of the airways of the lungs with the computed tomography device below the resolution limit of the computed tomography device for imaging takes place. The detection of contrast agent according to the method of the invention is therefore possible even if the resolution of the computed tomography device is insufficient, d. h., That, for example, the minimum achievable layer thickness of a layer image is too large to represent a fine lung structure, in particular the fine wall of an airway can. Even in this case contrast agent in the lung structure and thus the perfusion of the lung structure can be detected with the method according to the invention.

The object of the present invention is also achieved by a computed tomography device which has two X-ray systems each comprising an X-ray source and an X-ray receiver, and also a computing unit which is set up to carry out one of the methods described above.

Furthermore, the object of the present invention is achieved by a data carrier which has a computer program implementing one of the methods described above, which is stored on the data carrier and can be loaded from the data carrier by an arithmetic unit in order to carry out a method as described above the arithmetic unit is loaded.

An embodiment of the invention is illustrated in the accompanying schematic drawings. Show it:

1 an X-ray computer tomography device having two X-ray systems,

2 a schematic representation of two rows of mutually corresponding slice images,

3 a schematic representation of the lung of a human,

4 a schematic cross-section through a tubular airway of the lung of a person with registered profile line and

5 the trajectories of CT values based on two X-ray energies over the in 4 registered profile line.

In the figures, identical or functionally identical elements, components, fabrics, etc. are provided with the same reference numerals throughout. The illustrations in the figures are schematic and not necessarily to scale, scales may vary between the figures. On the in 1 illustrated X-ray computer tomography device 1 is in the following and without restriction of generality only to the extent that it is considered necessary for the understanding of the invention.

This in 1 X-ray computer tomography device shown 1 points in a housing 2 one relative to the housing 2 around a system axis 8th rotatable gantry 3 on, offset by about 90 ° relative to each other two X-ray systems are arranged. The first X-ray system has, opposite to each other, an X-ray source in the form of an X-ray tube 4 and an X-ray detector 5 and the second X-ray system has, opposite to each other, an X-ray source in the form of an X-ray tube 6 and an X-ray detector 7 on. The central ray of the first X-ray tube 4 outgoing X-ray beam and the central beam of the second X-ray tube 6 Outgoing X-ray beam intersect approximately at a 90 ° angle on the system axis 8th of the X-ray computer tomography device 1 , In operation go from the X-ray tube 4 X-radiation in the direction of the X-ray detector 5 and from the x-ray tube 6 X-radiation in the direction of the X-ray detector 7 from each of the X-ray detector 5 respectively. 7 is detected.

On the patient support plate 9 a patient couch 10 of the X-ray computer tomography device 1 is a patient P stored. With the X-ray computer tomography device 1 should in the case of the present embodiment of the invention, the perfusion of the lung tissue, in particular the airways of the lung so the circulation of the lung tissue or the airways of the lungs of the patient P are determined, including with the two X-ray systems of the X-ray computer tomography device 1 In each case a large number of 2D X-ray projections must be recorded. The control of the recording of the 2D X-ray projections as well as the computational processing of the 2D X-ray projections or the reconstruction of slice images or volume data sets of the lungs having body region of the patient P based on the 2D X-ray projections is performed with a mathematical unit shown schematically 11 of the X-ray computer tomography device 1 ,

The arithmetic unit 11 of the X-ray computer tomography device 1 is with a corresponding computer program 12 provided, in the present case by means of a portable storage medium 13 , For example, a CD in the arithmetic unit 11 was loaded.

First, the patient P is administered a contrast agent in at least one leading to the lung blood vessel. In the case of the present embodiment of the invention, the contrast agent is iodine. The iodine should be taken up via the bloodstream in the walls of the airways of the lungs or in the lung tissue in general, so that on the detection or detection of iodine, a statement about the perfusion or perfusion of the walls of the airways and the lung tissue can be taken.

Controlled by the computer program 12 For this purpose, from the lungs-containing body portion of the iodinated patient P simultaneously with the first and the second X-ray system 2D X-ray projections by rotation of the gantry 3 from different projection directions, z. B. in a spiral scan, obtained in which the patient support plate 9 simultaneously in the direction of the system axis 8th in the opening 14 the gantry 3 is adjusted or moved.

In this case, in the case of the present embodiment of the invention to the X-ray tube 4 a tube voltage of about 80 kV, so that of the x-ray tube 4 generated polychromatic X-ray radiation has an effective X-ray energy of about 60 keV. At the x-ray tube 6 In contrast, a tube voltage of about 140 kV, so that of the X-ray tube 6 generated polychromatic X-ray has an effective X-ray energy of about 90 keV. The two X-ray energies simultaneously record a large number of 2D X-ray projections.

From the 2D x-ray projections taken with the first x-ray system with the x-ray energy of effectively about 60 keV, several first, in the direction of the system axis 8th reconstructed pixel images of the lung, which are numbered consecutively with S1.1, S1.2, S1.3, etc., which is shown in FIG 2 is shown. In the same way, from the 2D x-ray projections taken with the second x-ray system with the x-ray energy of effectively about 90 keV, several second, in the direction of the system axis 8th reconstructed pixel images of the lung, which are numbered consecutively with S2.1, S2.2, S2.3, etc., which is described in US Pat 2 is also shown. The slice images S1.1 and S2.1, S1.2 and S2.2, S1.3 and S2.3 etc. correspond to one another in each case, which means that they each represent the same body layer of the patient P. Due to the defined arrangement of the two X-ray systems in a recording plane at the gantry 3 of the X-ray computer tomography device 1 and the corresponding reconstruction of the slices this correspondence is given.

In accordance with the method according to the invention, the CT values of corresponding pixels are set in relation to each other beginning with the slice images S1.1 and S2.1. In the case of the present embodiment of the invention, the CT value of the pixel P1.1S1.1 of the slice S1.1 and the CT value of the pixel P1.1S2.1 of the slice S2.1 are set in relation to one another as follows: CT value (P1.1S2.1) / CT value (P1.1S1.1) ,

If the value of this ratio is equal to one within the determination accuracy, then there is no iodine in the lung tissue area of the lung of the patient P represented by these two CT values of corresponding pixels P1.1S1.1 and P1.1S2.1. Namely, in the presence of iodine, the CT value of the pixel P1.1S1.1 of the slice image S1.1 based on the lower X-ray energy would have to be larger than the CT value of the pixel P1.1S2.1 of the slice image S2.1 based on the higher X-ray energy be. Accordingly, the presence of iodine in the lung tissue region of the patient's lung represented by these two CT values corresponding pixels P1.1S1.1 and P1.1S2.1 is detected when the value of the ratio is less than one.

In the same way, the CT values of all further mutually corresponding pixels of the slice images S1.1 and S2.1 are set in relation to each other, eg. Eg P1.2S2.1 / P1.2S1.1, P1.3S2.1 / P1.3S1.1 or P2.1S2.1 / P2.1S1.1, P3.1S2.1 / P3.1S1.1 etc .. This procedure is finally continued for the corresponding slices S1.2 and S2.2, S1.3 and S2.3, etc. In this way, the presence or absence of iodine in the lung tissue and thus the perfusion of the lung tissue, in particular the airways of the lung, can be detected on the basis of the corresponding slice images of the lung of the patient P body layer.

Alternatively, the detection can also take place in such a way that, based on the 2D X-ray projections obtained with the X-ray energy of approximately 60 keV, a voxel-containing first volume data set and a voxel based on the 2D X-ray projections obtained with the X-ray energy of effectively approximately 90 keV second volume data set is reconstructed with the arithmetic unit.

In this case, the detection of iodine takes place in such a way that the CT values of mutually corresponding voxels of the first and of the second volume data set are set in relation to one another.

In 3 is to further illustrate the method, the lung 19 of the patient P with the trachea 20 , the main bronchus 21 , a secondary bronchus 21 , a tertiary bronchus 22 and small bronchi 24 and the axial arrangement of the layer image pairs shown schematically.

In 4 is an example of the cross section of a tubular airway 25 the lung of the patient P shown schematically, as it is present in two reconstructed, corresponding to each other slice images or in a tomographic image pair. In the cross section is arbitrarily a profile line 26 entered, which cuts several pixels. In 5 the curves of the CT values along the profile line for the two X-ray energies used are shown. The upper course 27 The CT scores are based on X-ray projections taken with the lower X-ray energy of effectively about 60 keV, and the lower trace 28 The CT values are based on X-ray projections taken with the higher X-ray energy of effectively about 90 keV. Out of the progressions 27 and 28 it can be seen that in the left wall section of the airway 25 which is defined by the first maxima 29 . 30 is detected, due to the different CT values iodine, while in the right wall section of the airway 25 , which by the second maxima 31 . 32 No iodine is present, which is expressed in the quasi-identical CT values for both X-ray energies. Left of the maxima 29 . 30 as well as to the right of the maxima 31 . 32 there is more tissue. The area between the maxima 29 . 30 and 31 . 32 has air.

It thus becomes clear that with the invention the perfusion of lung tissue can be determined by detecting a contrast agent, in particular iodine. One advantage of the method is, inter alia, that the presence of contrast agent in lung tissue areas or lung tissue structures can be detected, even if the size of individual lung tissue areas or lung tissue structures, especially of fine airways is far below the resolution of the computed tomography device. In the absence of resolution, the affected lung tissue structures can not be displayed correctly with respect to the absolute CT values with the computed tomography device. Nevertheless, the invention can provide evidence that in the corresponding lung tissue area or the corresponding lung tissue structure, in particular in the case of iodine, an element with a high atomic number must be present. A quantification of the iodine content is usually not.

Claims (11)

Method for detecting a contrast agent in lung tissue, in which - at least from one area of the lung ( 19 ), whose lung tissue was supplied with contrast agent via blood vessels, with a computed tomography device ( 1 X-ray projections are recorded with a first and with a second, different from the first different X-ray energy, based on the X-ray energy obtained with the first X-ray at least a first pixelized layer image (S1.1, S1.2, S1.3) and / or a voxel-containing volume data set of at least the area of the lung ( 19 ) are reconstructed, based on the X-ray projections obtained with the second X-ray energy, at least one second slice image (S2.1, S2.2, S2) corresponding to the first slice image (S1.1, S1.2, S1.3) has pixels .3) and / or a second voxel-containing volume data set corresponding to the first volume data set is reconstructed from at least the region of the lung, - the CT value of at least one pixel (P1.1S1.1) of the at least one first slice image (S1. 1) and the CT value of a pixel (P1.1S2.1) corresponding to the at least one pixel (P1.1S1.1) of the at least one first layer image (S1.1) of the at least one pixel and the first layer image (S1. 1) and / or the CT value of at least one voxel of the first volume data set and the CT value of a voxel corresponding to the at least one voxel of the first volume data set corresponding to the first volume data set in the second volume data set, and in which the presence or absence of contrast agent is detected based on the value of the respective ratio. The method of claim 1, wherein contrast agent is present in the lung tissue region represented by two CT values corresponding pixels (P1.1S1.1, (P1.1S2.1) or voxels, when the ratio of the two CT values within the detection accuracy is smaller or greater than one. The method of claim 1 or 2, wherein there is no contrast agent in the lung tissue region represented by two CT values corresponding pixels (P1.1S1.1, (P1.1S2.1) or voxel, if the ratio of the two CT values in the frame the determination accuracy is one. Method according to one of Claims 1 to 3, in which the CT values of all mutually corresponding pixels (P1.1S1.1, (P1.1S2.1) of first and second slice images (S1.1, S2. 1) and / or the CT values of all mutually corresponding voxels of the first and second volume data sets are related to each other. Method according to one of Claims 1 to 4, in which the images of the X-ray projections with the first X-ray energy and the images of the X-ray projections with the second X-ray energy of at least the region of the lung ( 19 ) at the same time. Method according to one of Claims 1 to 5, in which the images of the X-ray projections with the first X-ray energy and the images of the X-ray projections with the second X-ray energy of at least the region of the lung ( 19 ) with a computed tomography device having two x-ray systems ( 1 ) respectively. Method according to one of claims 1 to 6, wherein the first X-ray energy effectively about 60 keV and the second X-ray energy is effectively about 90 keV. Method according to one of claims 1 to 7, wherein the contrast agent is iodine. A method according to any one of claims 1 to 8, wherein the detection of the presence or absence of contrast agent in lung tissue with the computed tomography device ( 1 ) below the resolution of the computed tomography device ( 1 ) for imaging. Computed tomography device comprising two each an X-ray source ( 4 . 6 ) and an X-ray receiver ( 5 . 7 ) comprehensive X-ray systems and a computing unit ( 11 ) for carrying out a method according to one of claims 1 to 9. Disk ( 13 ), comprising a computer program implementing a method according to one of claims 1 to 9 ( 12 ), which on the disk ( 13 ) and stored by a computing unit ( 11 ) from the disk ( 13 ) in order to carry out a method according to one of claims 1 to 9, when the computer program ( 12 ) in the arithmetic unit ( 11 ) is loaded.

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