Abstract:
In a magnetic resonance apparatus and a method for the operation of a magnetic resonance apparatus, the measured data generating unit sends additional control information to the measured data evaluation unit, and the measured data evaluation unit sends feedback information to the measured data acquisition unit. The feedback information influences the generation of measured data in the measured data generation unit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is directed to a magnetic resonance apparatus and to a method for the operation of a magnetic resonance apparatus of the type having a unit for generating measured data and a unit for evaluating the measured data, wherein the measured data generating unit sends magnetic resonance raw data to the measured data evaluation unit.  
           [0003]    2. Description of the Prior Art  
           [0004]    For generating images with nuclear magnetic resonance, magnetic resonance signals are location-encoded with magnetic gradient fields before and during their reception. Such location encoding means that a mathematical domain known as k space is occupied with signals k space is defined by the time integral of the gradient fields. The signals in k space are then subjected to a Fourier transformation, the result of which is supplied to an image display.  
           [0005]    The sampling of k space and the reconstruction of the images defined therewith on the basis of the acquired measured data ensue according to a fixed strategy that is defined and set before the beginning of the measurement.  
           [0006]    In physiologically controlled measurements (for example, controlled by ECG, respiration or pulse), a time profile or template is transmitted from the measured data generating unit to the measured data evaluation unit in addition to the digitized magnetic resonance data. This information indicates the time reference of the generation of the magnetic resonance data with respect to a selected reference point of the physiological signal. The magnetic resonance data registered over many cycles of the physiological signal thus can be allocated to identical time intervals of the physiological signal in the measured data evaluation unit. This also enables the acquisition of magnetic resonance images of predominantly periodically moving subjects, which is also referred to as retrogating.  
           [0007]    There are also methods wherein further magnetic resonance data are generated at previously defined intervals in addition to the k space data in order to control the image reconstruction therewith. Parallel to the sampling of k space for the actual image generation, thus, the data of one or more further k spaces can be acquired in timedivision multiplex so that, for example, the position of the diaphragm of a patient can be recognized on the basis of the existing supplementary data. The respiration can in turn be tracked therefrom and motion artifacts can be compensated.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the invention is to provide a magnetic resonance apparatus and a method for the operation of a magnetic resonance apparatus with improved measured data or image data pickup.  
           [0009]    This object is achieved in a method and apparatus wherein the measured data generating unit sends additional control information to the measured data evaluation unit, the measured data evaluation unit sends feedback information to the measured data acquisition unit, and the feedback information influences the generation of measured data in the measured data generation unit. It is thus possible for the unit that evaluates the measured data to influence the k space sampling during the acquisition of the measured data. With such a fast feedback, having a dead time preferably below the repetition time of the sampling of the k-space rows, flexible control loops can be constructed for improving image quality. For example, a repetition of the sampling of k-space rows can be prescribed by modification of parameters until a desired quality feature such as, for example, the signal-to-noise ratio of the measured data is achieved. Another exemplary application is to control the k-space sampling in abdomen imaging or functional imaging so that motion artifacts are reduced. In another application, the measurement field is automatically shifted by an image-controlled tracking of a catheter or a biopsy needle, so that these subjects are always imaged in the middle of a graphic presentation of the examination region despite their change in position in this region.  
           [0010]    In an embodiment, the control information is generated from a predetermined magnetic resonance measurement sequence. This measurement sequence specifies individual control information for every sampled k-space row. The additional row information is transmitted to the measured data evaluation synchronously with the measured raw data.  
           [0011]    In a further embodiment, the control information controls the processing of the raw data of the k-space rows in the evaluation of the measured data. The raw data are supplied to an image reconstruction stage and/or to a specific data evaluation stage.  
           [0012]    The measurement sequence can react to feedback information from the measured data evaluation at any time during the run time of the measurement. The reaction is thereby predetermined at the sequence side. In an embodiment, the feedback information is employed for the generation of the gradient control signals and/or the transmission system control signals and/or the reception system control signals. The reaction time thereby preferably lies below the typical repetition time of the sampling of the k-space row, i.e. the time that is required for generating the data for a k-space row.  
           [0013]    The data channel from the measured data evaluation to the measured data generating unit is fashioned such that, in addition to a high bandwidth, for example 100 MB/s, a slight and deterministic dwell or delay time, is guaranteed in the data transmission, for example on the order of magnitude of 4 through 4 Ms. 
       
    
    
     DESCRIPTION OF THE DRAWING  
       [0014]    The single figure is a block diagram of a magnetic resonance apparatus constructed and operating in accordance with the principles of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    In the form of a block circuit diagram, the Figure shows those function units of a conventional diagnostic magnetic resonance apparatus that must be modified for implementing the inventive fast feedback method. The diagnostic magnetic resonance apparatus has a measured data generating unit  2  that contains all components required for the excitation and reception of magnetic resonance signals as well as for the location encoding of these signals.  
         [0016]    The measured data generating unit includes a measurement sequence control  4  that generates control signals from a magnetic resonance measurement sequence while it is being run. The magnetic resonance measurement sequence is implemented, for example, as C++ program that sequences within the measured data generating unit  2  under a real-time operating system, for example VxWorks. First control signals  6  are generated for controlling a gradient system  8 , which comprises amplifiers and magnetic coils. The measurement sequence control  4  also generates second control signals for a radio frequency transmission system  12 . The radio frequency transmission system  12  has a radio frequency power amplifier and an antenna. Finally, third control signals  14  are generated from the magnetic resonance measurement sequence  4  for a radio frequency reception system  16  that comprises a reception antenna with following pre-amplifiers as well as a digitalization unit. The received magnetic resonance signals are thus present in digital form as magnetic resonance raw data  18  for further-processing.  
         [0017]    The measured data generating unit  2  having the above-described conventional components of the magnetic resonance apparatus is modified by a multiplexer  20 . The multiplexer  20  likewise receives control signals  22  that the measurement sequence control  4  generates from the magnetic resonance measurement sequence. Controlled by the control signals  22 , the multiplexer  20  attaches k-space row-specific control information  24  for a subsequent measured data evaluation to the digitized magnetic resonance raw data  18 .  
         [0018]    The magnetic resonance raw data  18  are synchronously transmitted to a measured data evaluation unit  26  as packet with the appertaining control information  24 . To that end, a data connection  28 , for example in the form of a light waveguide link, is provided between the measured data generating unit  2  and the measured data evaluation unit  2 , the magnetic resonance raw data  18  together with the row-specific control information  24 , this transmission ensuing with a serial protocol. The measured data evaluation also ensues program-controlled, for example under the operating system Windows NT. The measured data evaluation unit  26  has a decoder wherein a control signal  32  for the control of a demultiplexer  34  is generated. The incoming magnetic resonance raw data are then supplied by the demultiplexer  34  either to a raw data analysis unit  36  and/or to an image reconstruction unit  38  dependent on the control signal  32 . The raw data analysis unit  36  generates first feedback information  40 , and the image reconstruction unit  38  generates second feedback information  42 , both of which are supplied via a feedback channel  44  to the measurement sequence control  4  in order to intervene in the running of the sequence. The feedback channel  44  is, for example, designed as a standard Ethernet connection with TCP/IP protocol. For adhering to the real-time demands made of the dead time of the feedback, the raw data evaluation unit  36  runs as a real-time process given employment of Windows NT.  
         [0019]    For example, the feedback information can cause a repetition of the sampling of k-space rows, whereby the parameters are modified at the excitation side until a desired quality feature such as, for example, a minimum signal-to-noise ratio of the measured data is achieved. Another application is the control of the k-space sampling such that motion artifacts are reduced, for example in abdomen imaging or in functional imaging. A further control can ensue using the feedback information to cause a catheter or a biopsy needle always to be displayed in the middle of an image despite a positional change in the examination region.  
         [0020]    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 contributions to the art.