Abstract:
A contrast agent system for X-ray and computed tomography diagnostics has a dissolvable microcapsule in which a substance or substance mixture that releases CO 2  upon contact with a bodily fluid is enclosed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention concerns a contrast agent for X-ray diagnostics, such as radiographic imaging and computed tomography.  
         [0003]     2. Description of the Prior Art  
         [0004]     X-ray-positive substances (such as, for instance, iodine or barium compounds) are primarily used as a contrast agent for imaging with X-rays. Such contrast agents (in particular iodine compounds) can cause side effects, such as allergic reactions and impairments of the kidney function. By contrast, CO 2  causes no problems in this regard. In the form of finely distributed small bubbles, it is an X-ray-negative contrast agent, by being more permeable to X-ray radiation than body tissue. It can be applied arterially (angiography) since it is quickly resorbed and does not, like air or nitrogen, lead to embolisms. Due to the fast resorption of CO 2 , the contrast-increasing effect decreases rapidly with increasing distance from the injection point. Transport, for instance to internal organs, is therefore hardly possible. A further disadvantage is that special injectors are required for application of CO 2 .  
       SUMMARY OF THE INVENTION  
       [0005]     An object of the present invention to provide a contrast agent based on the release of CO 2  that can be applied in a simple manner and that offers a greater application spectrum than is the case for a conventional CO 2  injection.  
         [0006]     This object is achieved in accordance with the invention by a contrast agent system having a substance or substance mixture that releases CO 2  upon contact with body fluid, which is enclosed in a microcapsule with a dissolving casing. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0007]     Dissolvable microcapsules can be produced with modern techniques on the order of some micrometers and can even pass the smallest venules without the danger of a blockage or destruction. In accordance with the invention, such a microcapsule contains a substance or a substance mixture that releases CO 2  upon contrast with a body fluid. The duration up to the CO 2  release can be controlled by selection of the casing material, such that organs far removed from the application location can be reached. It is also for the casing material to be selected that concentrates in the tissue to be examined, such that this tissue can be clearly differentiated (primarily in a CT examination) from neighboring tissues after release of the carbon dioxide. In a preferred embodiment, such a tissue specificity is achieved by coupling at least one microcapsule to tissue-specific antibodies. The parenterally-administered contrast agent is initially transported to the target tissue and there couples to corresponding antigens. After resolution or resorption of the capsule casing, the capsule content comes in contact with blood or a different bodily fluid, whereby the CO 2  release is initiated. It is also possible for the substances of a substance mixture to be respectively enclosed by separate microcapsules. This variant could be advantageous when a common encapsulation of the substances poses problems, for example in production engineering.  
         [0008]     Advantageously contained in the capsule is a substance mixture composed of an acid and a carbonate which dissolve into aqueous bodily fluid in the manner of an effervescent powder, with CO 2  generation. A gas bubble greater by the factor 10 3  arises from a capsule only a few micrometers in size. A voxel size (at minimum 0.4 3  mm 3 ) that can be shown in CT is thereby achieved. If a conventional contrast agent were to be encased with a capsule, this would have to be fashioned correspondingly voluminous so that the cited voxel size is achieved after its dissolution. Such a capsule would, however, not be able to pass smaller vessels and would block these, such that a specific contrasting of a tissue would not be possible.  
         [0009]     Tartaric acid and sodium bicarbonate are advantageously used as a CO 2 -releasing substance mixture that is harmless in terms of toxicity. Given context with aqueous bodily fluid, disodium tartrate, water and CO 2  form. Disodium tartrate (CAS number: 6106-24-7) is a food additive (E335) that dissolves well and exhibits no harmful effects. A value of 30 mg/kg of body weight is specified by the European Union as an acceptable daily allowance (ADI). Toxic doses (LD50) are not known.  
         [0010]     Fructose, glucose, mannose, galactose, sucrose, raffinose, polysaccharide or a mixture of these substances are, for example, considered as casing materials. The cited sugars dissolve in aqueous bodily fluid with a delay suitable for the purposes being discussed. Known techniques can be resorted to for the coupling of a capsule casing comprising the cited sugars to an antibody or recombinant antibody fragments or, respectively, antibody variants acquired through bioengineering.  
         [0011]     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.