DE102011084023A1 - Method for representing blood vessels in body part of human or animal body by blood vessel representing device, involves enriching blood with X-ray contrast agent, acquiring projection images of body part, and generating combination image - Google Patents

Abstract

The method involves enriching the blood in the blood vessels with an X-ray contrast agent, acquiring a projection image of the body part at primary cathode voltage of an X-ray tube (12), and acquiring another projection image of the body part at secondary cathode voltage of the X-ray tube. The pixels of the former and latter projection images are calculated, or three-dimensional images are reconstructed from each of the projection images with each other by an arithmetic operation, and a combination image is generated. The blood vessels are represented using the combination image. An independent claim is included for a device for representing blood vessels in a body part of a human or animal body.

Description

The invention relates to a method for the representation of blood vessels in a body part of a human or animal body with an X-ray apparatus having an image acquisition unit with an X-ray tube and an X-ray detector, wherein the blood is enriched in the blood vessels with an X-ray contrast agent. The invention further relates to a corresponding device for carrying out the method. The invention preferably finds application in angiographic X-ray devices, for example C-arm angiographs.

Subtraction angiography is a well-known method by which blood vessels in the body can be displayed by X-ray images, for example by means of digital subtraction angiography (DSA). In this case, the patient is injected with a bolus of X-ray contrast medium which has a high absorption coefficient for X-radiation and thus strongly contrasts the vessels on a simultaneously recorded X-ray image. With DSA, a so-called mask image without contrast agent is taken before the injection of the contrast agent. This is stored and subtracted from the images taken after the contrast agent. This eliminates background structures and, ideally, only the blood vessels are visible on the difference images.

In addition, fluoroscopic roadmapping is a well known angiographic imaging technique. In this case, a mask image is recorded and stored after contrast agent administration. Later, so-called fluoroscopy images of the same body part, but without contrast media, are taken. Fluoroscopy images are taken to mean low-radiation but high-temporal resolution projection or fluoroscopic images with which typically minimally invasive interventions, e.g. advancing a catheter into a vascular tree. In roadmapping, the contrast mask image is subtracted from such a series of real-time fluoroscopy images. The result is a static rendering of the vascular structures, typically shown in white, while the catheter is visible in black.

Angiographic procedures can provide both two-dimensional (2-D) projection images as well as three-dimensional (3-D) images. 3-D plots can be obtained using computer-aided rotational angiography, in which a 3-D image is reconstructed from a series of projection x-ray images taken from different projection angles. The state of the art for this purpose are so-called C-arm angiographs, in which an X-ray source and an X-ray detector arranged opposite to it are rotated in an approximately 200 ° arc around the body part of a patient to be examined, thereby taking between 50 and 500 X-ray projection images and digital get saved. This is called a rotation run. From this series of X-ray projection images, a three-dimensional image of the X-rayed body part can then be calculated.

In the 3-D angiography method, a so-called mask run and a filling run are usually recorded. During the mask run, the C-arm is rotated around the body part without contrast medium. Thereafter, contrast agent is injected into the blood vessel of interest, and a second set of X-ray projection images, which form the so-called filling run, are recorded during a renewed C-arm rotation. The two image sequences can now be reconstructed separately to each of a 3-D image, which in turn can be subtracted from each other so that in the result only the contrasted vessels can be seen. Alternatively, the respectively corresponding projection images in the mask and filling run can be subtracted directly from each other.

In X-ray angiography an iodine-containing contrast agent is used in most cases, which provides excellent contrast, but also represents a strong health burden for the patient. To keep the dose as low as possible, X-ray contrast agents were developed that are not rapidly eliminated but remain in the vascular system for many hours. It is iodine, which is specifically encapsulated by certain membranes. Corresponding contrast agents are disclosed in, for example "Tumor Vascular Permeability to a Nanoprobe Correlates to Tumor-Specific Expression Levels of Angiogenic Markers", E. Karathanasis et al., PLoS ONE, June 2009, Vol. 4, Issue 6, e5843 , available at www.plosone.org and in "Imaging of Pulmonary Embolism and t-PA Therapy Effect Using MDCT and Liposomal Iohexol Blood Pool Agent: Preliminary Results in a Rabbit Model" by Steven J. Burke et al., Acad. Radiol. 2007; 14: 355-362 ,

These contrast agents have many advantages but also provide some limitations in X-ray angiographic imaging. Since the contrast medium lingers in the vessels for a long time, the traditional DSA is no longer feasible, with each of which a new mask image is included, if for the other images a new projection geometry is selected or the patient has moved. Also a roadmapping, in particular with new mask, is only clearly limited feasible. In addition, the visibility of possibly introduced into the blood vessels medical instruments, such as catheters and thin guide wires in the fluoroscopic image is no longer given, as they are covered by the high and quasi-permanent vessel contrast.

The object of the invention is therefore to provide a method with which the known and proven subtraction angiographic methods, such as DSA and roadmapping, can also be realized with a contrast agent which, once applied, can be used for the entire duration of the imaging or intervention in the vascular system remains.

The object is achieved by a method according to claim 1 and an apparatus according to claim 10.

The invention proposes to carry out the transillumination in dual-energy mode. In doing so, the X-ray tube is alternately operated at low and high high voltages to produce lower and higher energy X-rays. By calculating image pairs recorded with the different energies, a new image, the so-called combination image, can be generated in each case, in which e.g. certain structures have been eliminated or the visibility (contrast) of certain structures has been increased.

The invention makes use of the fact that the absorption coefficient of tissue, on the one hand, and iodine-containing contrast agent, on the other hand, does not depend in the same way on the energy of the X-rays. 1 shows the mass absorption coefficients of iodine as well as various tissues as a function of the X-ray radiation energy. The dashed lines show the dependency for fat (F) and muscle tissue (M), while the solid line (B) represents the mass absorption coefficient of bone. As can be seen from the figure, the absorption coefficients between the bones and the soft tissues are the same as the radiation energy increases, so that the contrast decreases. The absorption coefficient of iodine behaves differently.

The steps (a) to (c) according to claim 1 are preferably carried out successively, in particular without further intermediate steps.

The steps (a) and (b) of acquiring the first and second projection images at the first and second cathode voltages are preferably carried out in succession, so that e.g. a fluoroscopic or projection image from the same projection angle is taken shortly after one another with different radiant energy. The x-ray tube is therefore preferably designed to quickly switch the tube voltage, here called the cathode voltage, for example within a period of 1-100 ms.

Alternatively, it is also possible to take in each case a plurality of projection images at the same cathode voltage, in particular if this is done during a movement of the image acquisition unit about the body part, e.g. a rotation run, takes place, and from the sequence of recorded thereby projection images, a 3-D image is to be reconstructed. Preferably, however, alternately with different cathode voltages is also acquired in such a rotation run, so that after a rotation run from each projection geometry, there is a pair of projection images with different radiant energy.

The cathode voltage used for the acquisition of the first and second projection images is preferably in a range of 50-99 kV for the lower voltage and 100-180 kV for the higher voltage, respectively.

The projection images acquired with different cathode voltages are then offset from one another by an arithmetic operation, corresponding pixels of the first and second projection images being offset in the same way in each case. If necessary, the images are previously superimposed or registered with each other so that corresponding structures are superimposed. However, since the first and the second projection image are preferably recorded directly one after the other, registration is usually unnecessary.

The arithmetic operation is preferably a linear combination, in particular a weighted subtraction. As a result, a so-called combination image is generated, which can be configured in various ways. In one embodiment, a subtraction is weighted such that the pixel intensities of the contrast agent-enriched blood vessels at least substantially cancel, but the background and any medical instrument that may be present in the blood vessel are visible in the combination image. This image can thus be used as a native (non-contrasted) mask image.

Alternatively, the subtraction may also be weighted such that the pixel intensities of the background cancel, but the blood vessels in the combination image are visible. By "background" is meant all parts of the body or tissue structures which are not blood vessels, eg bone, fat and muscle tissue. Such Combination image can be used for roadmapping procedures.

The combination image is then used in the further course of the diagnostic examination or intervention on the human or animal body, which is preferably a patient or a subject, in order to achieve an improved representation of the blood vessels and / or of a medical instrument located in the blood vessels , The generated images, in particular combination images or subtraction images, are preferably displayed on a screen directly after their generation, particularly preferably in real time, and thus allow the control of the further process, e.g. the navigation of a guidewire or catheter through a blood vessel.

According to a preferred embodiment, after the generation of the combination image further projection images of the body part are acquired, preferably either with the first or the second cathode voltage, or else alternately with both. In this embodiment, the combination image is then offset with each further projection image, in particular subtracted in a pixel-wise manner from each weighted image in order to generate subtraction images. Depending on the properties of the combination image, the subtraction images are then comparable to conventional DSA or roadmapping images.

Alternatively, the combination image can also be used directly to display the blood vessels, for example, displayed immediately after generation on a screen. In this case, the steps (a) - (c) are preferably repeated continuously in order to always generate new combination images, possibly also from different projection angles.

The angiographic procedure of the present invention may be used for diagnosis, but is preferably performed during a surgical or angiographic procedure, including in the blood vessels also a medical instrument, such as a catheter, a guide wire, an instrument for balloon dilation, a stent, The instrument is preferably at least partially made of metal, and therefore has such high X-ray absorption that, in some embodiments, it absorbs all of the radiation in image acquisition at both the first and second cathode voltages , that is, each having the same pixel intensity. This effect makes it possible to select an arithmetic operation that particularly emphasizes the medical instrument, even if it is surrounded by contrast-enhanced blood. The invention therefore allows to avoid the disadvantages of roadmapping processes with contrast agents that are not rapidly eliminated.

In yet another embodiment, it is possible to follow step (a) with a multiple pass of steps (b) and (c), respectively. Therefore, only one image is taken with the first cathode voltage, and then several images with the second cathode voltage. These are each offset with the same first projection image, in particular weighted by this subtracted (or vice versa). This variant has the advantage that the cathode voltage does not have to be switched quickly, and yet allows, by suitable linear combinations between a first projection image and further second projection images, which are preferably recorded as fluoroscopic images, a selective representation of either blood vessels or medical instruments.

All variants described here are possible both in 2-D and in 3-D. In other words, the combination image and any subsequently generated subtraction images can each be generated directly in the two-dimensional variant by offsetting the fluoroscopic images and optionally displayed directly on a screen. Each 2-D image then shows a projection (or possibly a linear combination of different projection images) through the body part.

In the three-dimensional embodiment not only a first or second projection image is recorded, but in each case a sequence, e.g. a rotation run of first and second projection images from different projection angles. These are then either immediately offset against each other, and then reconstructed from the images computed together a 3-D combination image. Alternatively, the sequence of first and second projection images can also be reconstructed separately and the resulting 3-D images can then be converted into a 3-D combination image. Also, any post-rotation rotations taken can then be e.g. to 3-D images, of which, if necessary, the 3-D combination image is subtracted weighted to produce 3-D subtraction images.

According to a preferred embodiment, the X-ray tube is operated not only with different cathode voltages for the first and second projection image. In addition, in the first and / or the second projection image, the X-ray radiation for the acquisition of the projection image is filtered with a beam filter. As a result, the radiation energies and bandwidths can be optimized.

The invention is also directed to an apparatus according to claim 10 which is a specially configured x-ray machine. Preferably, this is a C-arm angiograph, wherein the invention with any other digital angiographic X-ray device is feasible.

The invention will now be explained in more detail by means of embodiments with reference to the accompanying drawings. In the drawings show:

1 the function of mass absorption coefficient of various tissues and iodine as a function of the X-ray radiation energy;

2 a schematic representation of an apparatus according to an embodiment of the invention;

3 a schematic representation of a projection image;

4 the pixel intensities of the projection image of the 3 along the line AA;

5 the pixel intensities along the same line through a projection image with the same image detail as 3 , but recorded with a different radiant energy;

6 the pixel intensities along the line AA of a first combination image from the projection images of 4 and 5 ;

7 the pixel intensities along the line AA of a second combination image from the projection images of 4 and 5 ;

2 schematically shows a C-arm device, which is preferably used to carry out the method according to the invention and configured for this purpose. The C-arm angiograph 10 has a C-arm 11 on whose arms an x-ray tube 12 and a digital, planar x-ray detector 13 are attached. The x-ray tube 12 can deliver a cone of x-rays with different radiant energy. The rays penetrate one on the patient couch 15 bedded body or patient 14 and the unabsorbed radiation is from the planar detector 13 detected as a fluoroscopic or projection image. The C-arm 11 is with many degrees of freedom around the patient bed 15 rotatable and movable to take pictures from as many different projection angles as possible. The images are sent via a data cable to the control and evaluation unit 16 transfer. This performs the calculation steps of the method according to the invention. For this purpose, it usually has at least one storage unit 17 on, for example, a hard disk or optical disk, and a computing unit 18 , eg a processor, in particular a CPU together with main memory (RAM), optionally a GPU and network connection. At the S control and evaluation unit 16 It can be a normal computer, especially a PC. This is preferably still with a screen 19 which preferably displays the combination or subtraction images immediately after their generation, thereby allowing the physician to control the diagnostic or surgical intervention. Furthermore, an input device such as a mouse 20 or a keyboard may be provided.

3 shows by way of example and greatly simplified a projection image P through a body part in which a blood vessel 1 located. A background structure, eg a bone, is with 3 designated. Into the blood vessel 1 becomes a catheter 2 introduced. This should continue to be advanced along the dashed line until it reaches the point 9 reached, where, for example, a balloon dilatation to take place. During this procedure, it is essential that, while the catheter 2 through the vascular tree 1 is advanced, continuously further projection images are acquired to the direction of the catheter 2 to be able to control. These should be contrasted in accordance with the needs of the physician using the present invention.

The 4 and 5 should demonstrate the contrast difference that results from the acquisition of the same image detail with different cathode voltages. For this purpose, the pixel intensities are plotted on the ordinate, while the abscissa is a line along AA in 3 represents. 4 shows by way of example the pixel intensities of a first projection image P ₁ , which was recorded with a first cathode voltage. The catheter 2 has essentially completely absorbed the X-ray radiation and therefore has the highest image intensity. Still high in intensity but well below that is the blood vessel filled with contrast medium. The background structure 3 on the other hand has an even lower intensity.

The same picture line is in 5 taken in the projection image P ₂ with a lower radiation energy, because the contrast medium-filled blood vessel 1 has absorbed more X-rays and therefore has a higher intensity. The catheter 2 has unchanged absorbed the entire X-ray radiation and therefore has the greatest intensity. The background structure 3 has a slightly higher intensity, but is essentially unchanged.

The projection images P ₁ and P ₂ can now be combined or calculated in different ways, resulting in different Combination images K can lead. This is in the 6 and 7 exemplified.

In 6 For example, the projection image P _{2 was} scaled by a factor of about 0.7 and then subtracted from the first projection image P ₁ . The scaling factor was chosen so that the pixel intensities in the area filled with iodine-containing contrast agent vessels 1 is exactly the same, so that these extinguish in the subtraction. Accordingly, the vessel is in 6 not shown, the medical instrument contained therein 2 however, already. Also the background structure 3 is faintly visible. This image can therefore be used as a native mask image for a DSA.

An alternative form of combination shows the 7 , In this combination image K ', the scaling factor for the weighted subtraction was chosen so that the background structure 3 is not visible from soft tissue. The container 1 contrast has a good contrast, with the catheter 2 turn off well in the vessel.

With the invention, the visibility of medical instruments in the blood vessel can be restored or even enhanced.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• "Tumor Vascular Permeability to a Nanoprobe Correlates to Tumor-Specific Expression Levels of Angiogenic Markers", E. Karathanasis et al., PLoS ONE, June 2009, Vol. 4, Issue 6, e5843 [0006]
• "Imaging of Pulmonary Embolism and t-PA Therapy Effect Using MDCT and Liposomal Iohexol Blood Pool Agent: Preliminary Results in a Rabbit Model" by Steven J. Burke et al., Acad. Radiol. 2007; 14: 355-362 [0006]

Claims (10)

Method for displaying blood vessels ( 1 ) in a body part of a human or animal body ( 14 ) with an X-ray machine ( 10 ), which is an image acquisition unit ( 11 ) comprising an x-ray tube ( 12 ) and an x-ray detector ( 13 ), wherein the blood in the blood vessels ( 1 ) is enriched with an X-ray contrast agent, comprising the following steps: (a) acquisition of at least one first projection image (P ₁ ) of the body part by the image acquisition unit ( 11 ) at a first cathode voltage of the x-ray tube ( 12 ); (b) acquisition of at least one second projection image (P ₂ ) of the body part by the image acquisition unit ( 11 ) at a second cathode voltage of the x-ray tube ( 12 ); (C) Compute each corresponding pixels of the first and second projection image (P ₁ , P ₂ ), or of each of a plurality of first and second projection images reconstructed 3D images, together by an arithmetic operation, and thereby generating a combination image (K, K '); (d) using the combination image (K, K ') for an improved representation of the blood vessels and / or of a blood vessel located in the medical instrument. Method according to Claim 1, in which further projection images of the body part are acquired in step (d), the combination image (K, K ') being offset with each further projection image, in particular weighted subtracted therefrom, in order to produce subtraction images. Method according to one of the preceding claims, which is carried out during a surgical or angiographic procedure, whereby in the blood vessels also a medical instrument ( 2 ) is located. Method according to one of the preceding claims, in which a step (a) is followed in each case directly by a multiple pass of steps (b) and (c), the billing of the pixels of the second projection image (P ₂ ) in step (c) respectively with the same first projection image (P ₁ ). Method according to one of the preceding claims, in which the arithmetic operation is a linear combination. Method according to one of the preceding claims, in particular according to claim 2, in which the arithmetic operation is a weighted subtraction, in which the pixel intensities (I _a , I _b ) of the contrast agent-enriched blood vessels ( 1 ), the background and, if applicable, the medical instrument ( 2 ) are visible in the combination image (K), Method according to one of the preceding claims, wherein the arithmetic operation is a weighted subtraction, in which the pixel intensities of the background ( 3 ), the blood vessels ( 1 ) are visible in the combination image. Method according to one of the preceding claims, wherein in step (a) and / or step (b) the X-ray radiation for the acquisition of the projection image (P ₁ , P ₂ ) is filtered with a beam filter. Method according to one of the preceding claims, in which the image acquisition unit ( 11 ) during steps (a) and (b) around the body ( 14 In this case, a series of projection images (P ₁ ) is acquired from different projection geometries, a series of first projection images (P ₁ ) being reconstructed into a first 3D image and a series of second projection images being reconstructed into a second 3D image, and in which the first and second 3D images are computed to produce a 3-D combination image. Device for the representation of blood vessels ( 1 ) in a body part of the human or animal body ( 14 ) which is configured to carry out the method according to any one of the preceding claims, comprising - an X-ray machine ( 10 ) with an image acquisition unit ( 11 ) comprising an x-ray tube ( 12 ) and an x-ray detector ( 13 ), wherein the x-ray tube is adapted to be operated in alternation between at least two different cathode voltages. A storage unit ( 17 ) for storing at least one first projection image (P ₁ ) of the body part which is detected by the image acquisition unit at a first cathode voltage of the x-ray tube ( 12 ) and at least one second projection image (P ₂ ) of the body part which is detected by the image acquisition unit at a second cathode voltage of the x-ray tube ( 12 ) and a combination image (K, K '). A computing unit ( 18 ), which is configured to respectively offset respective pixels of the first and second projection images (P ₁ , P ₂ ), or three-dimensional images reconstructed from a plurality of first and second projection images, by an arithmetic operation, thereby generating a combination image (K To produce, K ').

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