The invention relates to a new process for graphic visualization and diagnosis of thrombi as well as the use of particle suspensions for the production of contrast media for the visualization of thrombi by means of nuclear spin tomography.
A thrombus is a circumscribed blood solidification that forms in arteries or veins by intravascular clotting. A thrombosis, i.e., a partial or complete obstruction of arteries or veins by a thrombus, can result in anemia and tissue death of an organ (infarction). A typical example of an arterial thrombosis is that of the coronary arteries (coronary thrombosis). If a thrombus detaches from the vessel wall, it is borne away by the blood stream. In terms of a thromboembolism, this thrombus can obstruct a downstream smaller vessel. The brain-supplying arteries are a typical example of thromboembolisms in arteries. The very common thromboses of the pelvic veins and leg veins typically result in a thromboembolism of the lung arteries. The lung artery embolism is especially feared since it is difficult to detect and often leads to a fatal outcome.
Thrombi are currently diagnosed with the aid of various processes. The most frequently used processes are catheter-radiologic angiography, radiologic phlebography and various ultrasound processes.
Angiography is increasingly performed with the aid of nuclear spin tomography (nuclear spin angiography), whereby the blood flow into the vessels is visualized. An example of this process is described by Siewert et al, Fortschr. Rxc3x6ntgenstr. 156 (1992), pp. 549-554. This process visualizes thrombi as areas with deficient flow into the vessel. Possible errors arise in smaller veins with slow or deficient flow. Such vessels are not visualized. The nuclear spin angiography with use of contrast media is an improvement relative to flow-dependent processes. An example of such a process is described by Schmitz et al. in Fortschr. Rxc3x6ntgenstr. 170 (1999), pp. 316-321. Intravenously-injected contrast media are mixed with the blood and selectively visualize those vessels in which the contrast medium-mixed blood is dispersed. Thrombi are indirectly visible as recesses (filling defects) in the vessels.
Not all vessels are reached in the case of radiologic phlebography. Of the ultrasound processes, that of the duplex-sonography FKDS, which, however, can visualize only surface veins and is ineffective in the pelvic area, is a frequently used process. All of these diagnostic processes provide results that are ambiguous and can result in misdiagnoses.
In International Patent Application WO 98/16256, a process for visualizing thrombi by means of nuclear spin tomography is proposed, in which contrast media that consist of chelating agents and integrin-binding molecules coupled thereto are administered to the patient. The chelating agents complex paramagnetic metal ions, such as, e.g., gadolinium ions.
Similar contrast media are also proposed in International Application WO 95/20603. The agents that are described there are peptides, to which one complexing agent in each case is coupled. The complexing agent can complex a metal ion, which can either release radioactive radiation and can be detected with a gamma camera or is a gadolinium ion or other paramagnetic metal ion that is suitable for use as a contrast medium in nuclear spin tomography.
These patent applications, however, describe only the synthesis of contrast media and first in-vitro tests. No in-vivo experiments or nuclear spin tomograms, with which the action of the agents could be demonstrated unambiguously, are shown. To date, such contrast media also have not been developed by pharmaceutical companies or cannot be purchased as usable contrast media.
There is therefore a need for new, unambiguous and reliable diagnostic processes for arterial and venous thrombi and for contrast media that are suitable for such a process.
The object of this invention is therefore to develop a new process for the diagnosis of arterial and venous thrombi and to find suitable contrast media for such a process.
This object is achieved with the new process according to claim 1 and the use of particle suspensions for the production of contrast media according to claim 6.
It was found, surprisingly enough, that MR blood pool-contrast media, such as superparamagnetic iron oxide (SPIO), especially in a formulation with small particles (ultrasmall superparamagnetic iron oxide, USPIO), accumulate in an animal model in experimental thrombi and are visible after a time interval of several blood half-lives in nuclear spin tomograms and can be used diagnostically. It was found that the contrast medium preferably accumulates in the thrombi but also frequently in the adjoining vessel wall and surrounding area.
In the process according to the invention, first a particulate MR-contrast medium is accordingly administered to the patient, and a nuclear spin tomogram is recorded after the contrast medium accumulates in the thrombus and/or the adjoining vessel wall and surrounding area (i.e., after a time interval of several blood half-lives). An especially good visualization is achieved with T1-weighted nuclear spin tomograms. After an intracellular recording of the contrast medium in the macrophages (phagocytes) of thrombi, an effect can also be produced in T2-weighted images.
The ultrasmall superparamagnetic iron oxide particles (USPIO) that are used in the experiment that is described in more detail below consist of an iron oxide nucleus and a carboxydextran shell. The mean diameter of the particles is preferably less than 50 nm, especially preferably approximately 25 nm. The production of such particles is described in, e.g., Patents EP 656 368 and WO 98/05430. A contrast medium that contains such particles is at present being developed by the Schering AG Company.
The iron-containing contrast media are used at, for example, a dosage of 200 xcexcmol of Fe/kg of body weight.
After a waiting time of several blood half-lives, in which the contrast medium accumulates in the thrombi, images are recorded with a nuclear spin tomograph. The thrombi are clearly visible in the images that are obtained in such a way.
If the contrast medium accumulates extracellularly, then its T1-effect can make the thrombus visible by producing a strong signal in T1-weighted images. If the contrast medium of macrophages (phagocytes), which within the limits of thrombus degradation (thrombus organization) regularly migrate into the vessel wall or the edge of the thrombus, is recorded, the T2-effect of the contrast medium can predominate, by which the labeled tissue appears to produce little or no signal in T2- or T2*-weighted images.
Below, an animal experiment is described in detail, in which thrombi were produced in 25 rabbits by catheter embolization and thrombin injection into the external jugular vein. After 1, 3, 5, 7 and 9 days (each n=5), measurements were taken using T1w-MP-RAGE and T2*w-FLASH nuclear spin tomograms at 1.5 Tesla before and 24 hours after intravenous administration of ultrasmall superparamagnetic iron oxide (USPIO, particle size about 25 nm) at a dose of 200 xcexcmol of Fe/kg of body weight. The radiologic phlebography and histology were used as a gold standard. The length of the thrombus visible in 3D-reconstructions of the T1w-MP-RAGE sequence was expressed in a ratio to true thrombus length. The structure, the signal intensity and the extent of contrast of the thrombus in the T2*w-technology were subjected to a subjective analysis with a defined scaling. 25 rabbits with age-appropriate thrombi were used as controls.
This experiment is to illustrate the invention without intending to be limited to this experiment.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.
The entire disclosure[s] of all applications, patents and publications, cited above [or below], and of corresponding German application No. DE 100 46 514.5, filed Sep. 15, 2000, and U.S. Provisional Application Serial No. 60/235,553, filed Sep. 27, 2000, are hereby incorporated by reference.
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