Abstract:
A device for the investigation of an object uses a microwave transmitter, a microwave receiver, a control device and a contrast medium. The microwave transmitter and the microwave receiver are controlled by the control device. In one embodiment, the following steps may be implemented:
       introduction of the contrast medium into the object under investigation;   transmission of a microwave signal into the object under investigation by the microwave transmitter;   scattering of the microwave signal by the object under investigation and by the contrast medium; and/or   reception of the scattered microwave signal by the microwave receiver.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method, a contrast medium and the use of a contrast medium for microwave-based investigation. 
     BACKGROUND 
     In some cases, the dielectric constants of objects under investigation, especially living tissue, are very homogeneous, and reliable results which can be presented with a clear contrast cannot always be attained with conventional microwave-based investigations. 
     Magnetic-resonance tomographies are prepared as an alternative. With the help of contrast media, more accurate results can be obtained. However, the preparation of magnetic-resonance tomographies is associated with high costs. Furthermore, in the case of patients in intensive care, an investigation of this kind is possible only with difficulty. 
     Accordingly, DE 44 33 572 A1 discloses the use of gadolinium-diethylene-triamino-penta-acetate (Gd-DPTA) as a contrast medium for magnetic-resonance investigations. 
     SUMMARY 
     A measuring device according to the invention comprises a microwave transmitter, a microwave receiver, a control device, a contrast medium and an electromagnet. The control device controls the microwave transmitter, the microwave receiver and the electromagnet. The contrast medium is introduced into an object under investigation. The electromagnet provides the object under investigation with a magnetic field. The contrast medium changes its polarisation properties dependent upon the field strength of the magnetic field. The microwave transmitter transmits a microwave signal. The object under investigation and the contrast medium scatter the microwave signal. The contrast medium changes a polarisation of the microwave signal. The microwave receiver receives the scattered microwave signal changed in its polarisation. Accordingly, a low-stress investigation of the object can be implemented at low cost. 
     The microwave transmitter and/or the microwave receiver preferably focus successively on several locations within the object under investigation. In this manner, a good local resolution can be achieved. 
     The control device preferably determines a microwave topography from the received microwave signal. In this manner, a detailed, three-dimensional image is achieved. 
     According to the invention, a contrast medium is used in the microwave-based investigation of an object. The contrast medium is introduced into the object under investigation. By comparison with its surroundings in the object under investigation, the contrast medium provides a different permittivity and/or conductivity and/or polarisation effect. Accordingly, an increase in the accuracy of the microwave-based investigation is achieved. 
     The contrast medium preferably comprises a paramagnetic metal ion, preferably a gadolinium ion (Gd3+) or an iron ion (Fe3+) or aluminium ion (Al3+) or a technetium ion (Tc3+). A particularly good improvement in accuracy can be achieved in this manner. Although the use of technetium ions brings about a clear increase in accuracy, it is disadvantageous that technetium is slightly radioactive and therefore causes radiation stress in the object under investigation. A cost-benefit assessment must therefore be implemented before a use of technetium. 
     The contrast medium preferably contains a coordinative bond. In this manner, a very stable structure of the contrast medium can be achieved. In particular, a good biocompatibility is achieved in this manner. 
     The contrast medium advantageously comprises gadolinium and/or a gadolinium compound and/or gadolinium-diethylene-triamino-penta-acetate (Gd-DTPA). Readily available contrast media can therefore be used. 
     The polarising effect of the contrast medium is preferably intensified or attenuated by an applied magnetic field. Polarising effects of the object under investigation can therefore be compensated. 
     A method according to the invention for investigating an object uses a microwave transmitter, a microwave receiver, a control device and a contrast medium. The microwave transmitter and the microwave receiver are controlled by the control device. The following steps are implemented:
         introduction of the contrast medium into the object under investigation;   transmission of a microwave signal into the object under investigation;   scattering of the microwave signal by the object under investigation and by the contrast medium; and   reception of the scattered microwave signal by the microwave receiver. A good accuracy of the investigation is achieved in this manner with low stress on the object under investigation.       

     The object under investigation is preferably a tissue of a patient. The contrast medium is preferably injected or swallowed. The contrast medium is preferably enriched in given regions of the tissue. The given regions of the tissue are preferably tumours. Accordingly, a high-precision investigation and detection of tumours is possible. 
     By preference, an external magnetic field is applied. The external magnetic field intensifies or attenuates a polarising effect of the contrast medium. A further increase in the contrast and accordingly of the measurement accuracy is achieved. 
     During the investigation, the external magnetic field preferably successively adopts at least two different field strengths. In this manner, a comparative measurement can be implemented. Polarising effects of the tissue can thus be eliminated. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention is described in an exemplary manner below on the basis of the drawings, in which an advantageous exemplary embodiment of the invention is illustrated. The drawings are as follows: 
         FIG. 1  shows an exemplary embodiment of the measuring device according to the invention; 
         FIG. 2  shows a structural formula of an exemplary contrast medium; and 
         FIG. 3  shows a flow diagram of an exemplary embodiment of the method according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The structure and functioning of the measuring device are initially explained on the basis of  FIG. 1 . With reference to  FIG. 2 , the structure of an exemplary contrast medium is illustrated. Finally, on the basis of  FIG. 3 , the functioning of the method according to the invention is shown. The presentation and description of identical elements in similar drawings has in some cases not been repeated. 
       FIG. 1  shows an exemplary embodiment of the measuring device according to the invention. A patient  1  lies on a patient support  7 . Electromagnets  8  are arranged alongside the patient  1 . A housing  5  is arranged below the patient  1 . The housing  5  contains a microwave transmitter  2 , a microwave receiver  3 , an antenna array  6  and a control device  4 . The microwave transmitter  2  and the microwave receiver  3  in this context are each connected to the antenna array  6  and to the control device  4 . The control device  4  controls the microwave transmitter  2 , the microwave receiver  3  and the electromagnets  8 . 
     The object under investigation in this exemplary embodiment is a tissue of the patient  1 . In order to implement an investigation, a contrast medium is first injected into the object under investigation. In this exemplary embodiment, the contrast medium is introduced into the tissue or into a blood vessel by injection. The microwave transmitter  2  transmits a microwave signal into the tissue of the patient  1  by means of the antenna array  6 . The microwave signal is scattered by the tissue and/or by the contrast medium. A repolarisation of the microwave signal can be additionally implemented by the contrast medium. The possibly repolarised and scattered microwave signal is received by the microwave receiver  3  by means of the antenna array  6 . 
     An alignment of the contrast medium within the magnetic field is achieved by activating the electromagnets  8 . Through this alignment, the polarisation properties of the contrast medium change. The method presented above is repeated for at least one field strength of the magnetic field. The accuracy can be further increased through additional repetitions with different field strengths of the magnetic field. 
     The control device  4  determines a microwave tomography from the received microwave signals. Since the contrast medium is not distributed homogeneously in the object under investigation but is enriched in an intensified manner in given regions, an improvement in accuracy is achieved especially in these regions. In this exemplary embodiment, the regions are regions with a particularly strong blood circulation, which indicates the presence of tumours. The detection of other pathologically altered tissue changes is achieved in this manner. 
     The contrast medium is a substance, which provides a different conductivity and/or dielectric constant and/or polarisation effect by comparison with the object under investigation, here, the human tissue. Biocompatibility is especially necessary in this exemplary embodiment. 
     The use of the contrast medium to improve the measurement accuracy in microwave-based investigations is also possible without the participation of a magnetic field; repolarisation does not then take place. 
       FIG. 2  illustrates the structural formula of an exemplary contrast medium. The contrast medium is gadolinium-diethylene-triamino-penta-acetate (Gd-DTPA). That is to say, a trivalent gadolinium cation (Gd3+) is disposed in a coordinative bond with diethylene-triamino-penta-acetate (DTPA). This provides a very stable, biocompatible contrast medium. A coordinative bond of diethylene-triamino-penta-acetate (DTPA) with another paramagnetic metal ion is also possible. 
     In this context, a first carbon atom is bound via a single bond to a central nitrogen atom. Two hydrogen atoms and a second carbon atom are bound to the first carbon atom. A first oxygen atom is bound to the second carbon atom by means of a double bond. A second oxygen atom is also bound to the second carbon atom by means of a single bond. The second oxygen atom accordingly provides a negative charge. 
     Furthermore, two identical structures are bound to the central nitrogen atom. One of these structures is described below. A third carbon atom is bound to the central nitrogen atom by means of a single bond. The third carbon atom is bound to two hydrogen atoms and by means of a single bond to a fourth carbon atom. The fourth carbon atom is bound to two hydrogen atoms and by means of a single bond to a second nitrogen atom. 
     The second nitrogen atom is bound by means of a single bond to a fifth carbon atom. The fifth carbon atom is bound to two hydrogen atoms and by means of a single bond to a sixth carbon atom. The sixth carbon atom is bound by means of a double bond to a third oxygen atom. The sixth carbon atom is a further bound by means of a single bond to a fourth oxygen atom. The fourth oxygen atom accordingly provides a negative charge. 
     The second nitrogen atom is further bound to a seventh carbon atom. The seventh carbon atom is bound to two hydrogen atoms and an eighth carbon atom. The eighth carbon atom is bound by means of a single bond to a fifth oxygen atom. The fifth oxygen atom is bound to a hydrogen atom. Furthermore, the eighth carbon atom is bound by means of a double bond to a sixth oxygen atom. 
     The negative charges of the oxygen atoms form a coordinative bond with a trivalent gadolinium cation. As an alternative, other trivalent paramagnetic cations can be used instead of the gadolinium ion. For example, iron ions, aluminium ions or technetium ions can be used. However, the use of technetium is disadvantageous because technetium is slightly radioactive and accordingly causes a radiation stress on the object under investigation. 
       FIG. 3  shows a flow chart of an exemplary embodiment of the method according to the invention. In a first step  30 , the contrast medium is introduced into the object under investigation. For example, if the object under investigation is human tissue, as illustrated in  FIG. 1 , the introduction is implemented by injection or orally by swallowing. In an optional second step  31 , the object under investigation is positioned opposite to an antenna. Different locations within the object under investigation can be investigated in this manner. As an alternative, different locations within the object under investigation can be investigated through the use of an antenna array, as illustrated in  FIG. 1 . In a third step  32 , the object under investigation or respectively given locations within the object under investigation is/are supplied with microwave signals. 
     In a fourth step  33 , the microwave signal is scattered by the object under investigation or respectively by the contrast medium and possibly repolarised. In a fifth step  34 , the scattered, possibly repolarised microwave signal is received. The optional second step  31  is repeated for different locations within the object under investigation up to step  34 . In a sixth step  35 , a microwave tomography is determined from the received microwave signal or the received microwave signals. 
     A further increase in accuracy can be achieved by the application of a magnetic field with the use of a corresponding contrast medium. This is illustrated in greater detail on the basis of  FIG. 1 . 
     The invention is not restricted to the exemplary embodiment illustrated. As already mentioned, different contrast media can be used. An investigation of an extremely diverse range of objects is also possible. For example, material testing is one conceivable area of application. All of the features described above or illustrated in drawings can be advantageously combined with one another as required within the framework of the invention.