Abstract:
In a method and device for automatic determination of a flow of a bodily fluid within vessels of an organism by a magnetic resonance, a magnetic resonance angiography to procedure is implemented generate magnetic resonance angiography images, a of magnetic resonance flow measurement is implemented to generate magnetic resonance flow images, and the magnetic resonance angiography images are applied to the magnetic resonance flow images as a mask to produce a resulting image depicting vessels with flow therein.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention concerns a method for automatic determination of a flow of a bodily fluid within vessels of an organism (in particular a person) by means of magnetic resonance and a correspondingly designed device, particularly for allowing stenoses and aneurysms to be localized and depicted through an analysis of the flow. 
         [0003]    2. Description of the Prior Art 
         [0004]    Magnetic resonance systems are increasingly used for image-based examination of patients since they enable a relatively stress-free examination of the patient as well as an appraisal of many different body regions of the patient. The manner of operation of such magnetic resonance systems is well known. 
         [0005]    Magnetic resonance angiography and magnetic resonance flow measurement can be undertaken with a magnetic resonance system. In magnetic resonance angiography, lumens (in particular blood vessels) within an organism are localized by magnetic resonance tomography and one depicted in images for a physician to interpret. In magnetic resonance flow measurement, moving or flowing elements within the organism are determined and depicted in images for a physician to interpret. Both magnetic resonance angiography and magnetic resonance flow measurement (two-dimensional as well as three-dimensional) are well known to those skilled in the art, so they need not be explained in further detail herein. 
         [0006]    Magnetic resonance angiography has conventionally been used, for example, to assist a physician searching for lesions (for example stenoses and aneurysms) by using the corresponding magnetic resonance angiography images. Moreover, with the magnetic resonance flow measurement the physician can check whether the lesions detected with the magnetic resonance angiography are hemodynamically relevant. 
         [0007]    In conventional investigation of this type, the physician must manually evaluate magnetic resonance angiography images and magnetic resonance flow images separately from one another in order to identify lesions (such as, for example, stenoses or aneurysms) in a patient. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is to provide a method and a device with which lesions (such as, for example, stenoses or aneurysms) in an organism can be identified more simply than is presently possible. 
         [0009]    According to the invention, this object is achieved by a method for automatic determination of a flow of a bodily fluid within vessels of an organism by magnetic resonance that includes the steps of generating of magnetic resonance angiography images of an examination subject in a magnetic resonance angiography procedure, generating magnetic resonance flow images by magnetic resonance flow measurements (two-dimensional or three-dimensional), and masking the magnetic resonance flow images through the magnetic resonance angiography images, such that after the masking, vessels with corresponding flow information are identified in the organism. 
         [0010]    The superimposition of the magnetic resonance angiography images and the magnetic resonance flow images in the inventive method results in the vessels with a flow being able to determined or identified. Essential information from the magnetic resonance angiography images and the magnetic resonance flow images in combination thus is presented to a physician. For example, the physician can thereby determine stenoses and/or aneurysms in the vessels with less effort than is possible with conventional methods. It should be noted that it is not significant in the inventive method whether the magnetic resonance angiography images are generated before the magnetic resonance flow images or vice versa. 
         [0011]    Conventional magnetic resonance images that depict flow information and are used for flow measurement, show information of the entire acquired body region, which includes tissue and vessels at rest. For the physician who analyzes the flow images for diagnosis, it is difficult to optically (mentally) filter out the flow information from the flow images. By the use of magnetic resonance angiography images as a mask, the regions in the flow images that correspond to vessels can be automatically identified according to the invention. Moreover, the regions in the flow image that contain no vessel information can be automatically masked out by means of the angiography information. 
         [0012]    Through registration and the subsequent superimposition or masking of the magnetic resonance flow images with the magnetic resonance angiography images, in particular only the flow of bodily fluids that flow through the vessels of the organism is determined. In other words, any flow information outside of the vessels is removed so that only the flow through the vessels can be presented to the physician. This offers the advantage that, in the analysis of the flow, the physician is not distracted by flow movements outside of the vessels. 
         [0013]    As used herein, “registration” means that the magnetic resonance flow images are fused or synchronized with the magnetic resonance angiography images so they are aligned exactly relative to one another in the subsequent superimposition such that, given a superimposition of a magnetic resonance flow image with an associated magnetic resonance angiography image, overlapping regions of the two images of the same body regions correspond. 
         [0014]    In the inventive embodiment the flow in the vessels is analyzed automatically in order to identify regions within the vessels in which the flow exhibits irregularities. For example, an analysis can identify areas within the vessels in which a speed gradient (a change of a flow speed dependent on the location) is greater in terms of magnitude than a predetermined threshold. Moreover, the analysis can identify regions within the vessels in which a non-laminar flow is present or, respectively, in which the flow exhibits turbulences. 
         [0015]    Since blood speed is average before and after a stenosis (constriction) but is high within the stenosis (thus higher than in the flow direction before or after the stenosis), the stenosis can be identified by an analysis of the speed gradients. By contrast, given an aneurysm the flow speed before and after the aneurysm is average and is low within the aneurysm (lower than in the flow direction before or after the aneurysm), such that an aneurysm also can be identified by analysis of the speed gradients. A further indicator of a lesion is the degree of turbulence within the flow, wherein it can lead to flow diminution or eddies in the magnetic resonance flow images in areas in which corresponding turbulences occur, such that turbulences and therewith a lesion can be extrapolated using these diminutions or eddies or, respectively, inhomogeneities. 
         [0016]    The regions in which an irregularity of the flow has been determined can be presented in an advantageous manner so that they are differentiable by a physician from other regions in which the current flows regularly or homogeneously. For example, for this purpose the magnetic resonance angiography images can be presented as a shaded surface display or by means of the volume rendering technique, wherein areas of a suspected lesion are characterized by a color overlay. The color intensity of the color overlay can be used in order to represent the risk potential of the corresponding lesion with differing color intensity. For example, the color intensity of a high-grade stenosis could be greater than that of a lower-grade stenosis. Moreover, it is possible to characterize the type of the lesion by means of a corresponding color tone, such that stenoses are characterized with a different color tone than aneurysms, for example. 
         [0017]    Moreover, it is possible to present the magnetic resonance angiography images by means of two-dimensional or three-dimensional maximum intensity projection, wherein regions of a possible lesion are marked in color. 
         [0018]    According to an inventive embodiment, the flow within the vessels can be simulated by moving particles, so the magnetic resonance angiography images can be presented as semi-transparent. The particles thereby move corresponding to the speeds and directions of the flow measurement. The density of the particles at one point can also be adjusted or simulated such that the density is increased as the current speed of the flow, which has been previously determined or calculated at this point, increases. The density and the color of the particles thus vary correspondingly given passage through a lesion (for example a stenosis) and thus, as an animation, serve as an optical aid for analysis of the corresponding lesion by a physician. 
         [0019]    The inventive method can ensue either “online”, (meaning simultaneously with the generation of the corresponding magnetic resonance angiography images and magnetic resonance flow images directly after an acquisition of a last data set), or “offline” (meaning the superimposition of the magnetic resonance flow images by the magnetic resonance angiography images ensues subsequently on magnetic resonance angiography images and magnetic resonance flow images already determined previously), for example by operating personnel (for example a physician) activating the appropriate (desired) image processing. 
         [0020]    Two groups of magnetic resonance angiography images and magnetic resonance flow images can also be evaluated to determine lesions. For this purpose, a group of images is generated before an administration of a medicine (for example a vasodilator to expand the vessels or a blood thinner) while the other group of images is generated after the administration of the medicine. For medicines (such as, for example, a vasodilator) which act virtually immediately, according to the invention only the magnetic resonance flow images need be generated after the administration of the medicine. Since in this case the patient remains in the magnetic resonance system, the magnetic resonance angiography images generated before the administration of the medicine (which magnetic resonance angiography images can be stored in a memory of the magnetic resonance system) can also be used as the magnetic resonance flow images generated after the medicine administration, as discussed below. In other words, generation of the magnetic resonance angiography images after the administration of the medicine is foregone, so the inventive method is advantageously accelerated since the generation of the magnetic resonance angiography images normally takes multiple minutes. 
         [0021]    In this embodiment, registration of the magnetic resonance angiography images with the generated magnetic resonance flow images and masking of the magnetic resonance angiography images with the magnetic resonance flow images generated after the administration of the medicine are implemented after the administration of the medicine. Differences with regard to the flow before and after the administration of the medicine are thereby determined by comparing the results of the flow measurement with regard to the magnetic resonance flow images generated before the administration with the results of the flow measurement with regard to the magnetic resonance flow images generated after the administration, and regions in which these results are clearly different are depicted by a corresponding color superimposition, for example. 
         [0022]    For example, regions within the vessels can be determined in which a difference (with regard to the speed measured by the flow measurement) between the results before the administration and the results after the administration lies above a predetermined threshold. Regions in which a difference that is representative of turbulence in the flow between the results before the administration and the results after the administration lies above a further predetermined threshold can be determined in a similar manner. 
         [0023]    In cause of administration of a blood thinner, which normally only becomes active after many hours, stenoses (for example), which were formed due coagulation of blood components before the administration of the blood thinner, may have been eliminated by the blood thinning, such that a corresponding stenosis is no longer detected given an analysis of the results after the administration of the blood thinner. By presenting a region to the physician that corresponds to the location of a stenosis due to blood coagulation before administration of the blood thinner, the inventive comparison between the results before and after the administration allows the physician to differentiate between stenoses which occur due to a blood coagulation and stenoses that arise due to some other cause. 
         [0024]    The above object is achieved in accordance with the present invention by a device for automatic identification of a flow of a bodily fluid within vessels of an organism. The device has a unit for generation of magnetic resonance angiography images and a further unit for generation of magnetic resonance flow images. The device is fashioned to mask the magnetic resonance flow images with the magnetic resonance angiography images such that the vessels with flow are determined. 
         [0025]    The advantages of the inventive device correspond to the advantages of the inventive method as described above, so these advantages need not be repeated. 
         [0026]    The present invention is advantageously suited for evaluation of results that have been generated with a magnetic resonance system, but the present invention is naturally not limited to this known application field but rather can be used anywhere where images of any fluid conducting conduit system exist and images or results of elements moving through this system exist as well, such that a superimposition of these images of the fluid conducting conduit system can be analyzed, for example with regard to bottlenecks. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  schematically illustrates an embodiment of an inventive device. 
           [0028]      FIG. 2  is a flowchart of an inventive method. 
           [0029]      FIG. 3  is a depiction of a pictorial result of a preferred exemplary embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    An inventive device  1  for automatic determination and presentation of flow irregularities of a bodily fluid within vessels  11  of an organism is shown in  FIG. 1 . The device  1  includes a unit  3  for generation of magnetic resonance flow images, a unit  6  for generation of magnetic resonance angiography images, a processor  4  and a monitor  5  in order to be able to present results determined from the generated images. The device  1  also includes a memory  2  in order to be able to store the magnetic resonance flow images and the magnetic resonance angiography images for specific inventive methods. 
         [0031]    A program workflow diagram of an inventive method is shown in  FIG. 2 . In a first step of the method, magnetic resonance angiography images of a patient are generated in a magnetic resonance system. In a second step magnetic resonance flow images of the same body regions from which the magnetic resonance angiography images were generated in the first step are generated from the same patient. In a further step of the inventive method the magnetic resonance angiography images and the magnetic resonance flow images are subsequently registered, meaning that the same body regions of corresponding magnetic resonance angiography images and magnetic resonance flow images are respectively aligned on one another such that they overlap one another virtually exactly with regard to the corresponding body regions. After this registration step the magnetic resonance flow images are masked with the magnetic resonance angiography images such that the images resulting from this shown only vessels, wherein information about the flow in these vessels exists within the vessels due to the magnetic resonance flow images. In a further step of the inventive method the flow in the vessels can now be analyzed in order to identify regions in which flow irregularities exist in the vessels. Regions within the vessels in which lesions (for example stenoses or aneurysms) exist can then be determined from these flow irregularities in this step. The identified lesions are then marked (for example by color) in a further step and presented (for example to a treating physician) on a display unit in the last step of the inventive method. 
         [0032]    It is noted that the two steps “generation of magnetic resonance angiography images” and “generation of magnetic resonance flow images” can also be executed in a reversed order relative to the order shown in  FIG. 2 . 
         [0033]    A preferred exemplary embodiment for presentation of flow irregularities is presented in  FIG. 3 . A blood vessel  11  with a stenosis  14  is shown on a monitor image  10 . This stenosis is identified in that the inventive method analyzes the flow within the blood vessel  11  and determined a region  14  with increased speed gradients. This means that, given an analysis of the speed of individual blood particles,  12 , the inventive method detects that in the region  14  there are different speeds for the individual particles  12  dependent on the location. The speed of the blood particles  12  is highest at a point in which the blood vessel  11  is most constricted while the speed of the blood particles  12  decreases both in the flow direction  15  and counter to the flow direction from this point. 
         [0034]    The flow speed of the particles  12  is already average in a region identified with a reference character  13 , wherein a laminar flow occurs in the region  13 . In addition to the increased speed gradients the region  14  is also characterized in that here turbulences occur in the current, which is also inventively detected and contributes to the inventive method identifying a stenosis at this point. 
         [0035]    The flow through the blood vessel  11  is inventively presented on the monitor image  10  in that individual particles  12  are shown within the vessel  11 . These particles  12  thereby exhibit a flow speed of the current at the corresponding point or, respectively, the inventive method simulates the particles  12  with the corresponding flow speed so that, in the case presented in  FIG. 3 , the particles  12  move faster in the region  14  (due to the narrow point or, respectively, stenosis located there) than in the region  13 . Moreover, the number of the particles per volume unit is higher in the region  14  (due to the constriction there) than in the region  13  (the inventive method simulates more particles  12  in the region  14  than in the region  13 ), wherein it is additionally depicted that the speed in this region  14  is increased in comparison to the speed in the region  13 . The region  14  is marked in color such that it differs from other regions (such as, for example, the region  13 ) such that it is indicated to an observer of the monitor image  10  that the inventive method has detected or identified a suspected lesion in the region  14 . 
         [0036]    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.