Abstract:
The present invention provides a rheology module ( 200 ) for use in a magnetic resonance (MR) rheology imaging system ( 110 ), whereby the rheology module ( 200 ) is adapted to introduce mechanical oscillations into a subject of interest ( 120 ), comprising a housing ( 202 ), a mechanical oscillator unit ( 204 ), which extends at least partially outside the housing ( 202 ) and is movable relative to the housing ( 202 ), and a transducer ( 206 ) for moving the oscillator unit ( 204 ), whereby the rheology module ( 200 ) comprises at least one radio frequency (RF) antenna unit ( 210, 212 ), which comprises at least one RF coil ( 214, 216 ). With the RF antenna device integrated into the rheology module, an antenna placement close to a region of interest (ROI) can be achieved to improve the MR imaging capabilities of a MR rheology imaging system. Thus, imaging of the ROI can be performed more efficiently. Furthermore, connection and cabling can be facilitated, since only one module has to be connected to generate the oscillation and to operate the RF antenna device.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to the field of magnetic resonance (MR) rheology imaging. In particular, the invention relates to the field of rheology modules for use in a MR rheology imaging system, whereby the rheology module is adapted to introduce mechanical oscillations into a subject of interest. Furthermore, the invention relates to the field of rheology arrangements for use in a MR rheology imaging system, comprising at least one RF antenna module comprising at least one RF antenna unit, and at least one rheology module as specified above. Still further, the invention relates to the field of MR rheology imaging systems comprising a rheology module as specified above. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the area of magnetic resonance (MR) imaging, MR rheology is a technique for gathering additional information on tissue properties, which is not accessible with MR imaging alone. Parameters like tissue viscosity or elasticity can otherwise only be determined using biopsy and/or histology. On the other hand it has been demonstrated, that these tissue properties can help in the detection of cirrhotic or cancerous changes, e.g. in liver, breast or brain tissue. In particular, MR rheology has been proven to be especially useful for determining and staging liver cirrhosis as well as breast cancer. Initial applications to degenerative brain diseases have also been proposed. 
         [0003]    Typically a MR rheology setup contains a rheology module for introducing mechanical oscillations into a subject of interest and an MR imaging system. In order to determine tissue properties of a particular region of interest (ROI) of the subject of interest, the rheology module is placed close to this area to introduce the oscillations. Appropriate radio frequency (RF) antenna units comprising one or more RF coils are provided for generating the anatomical ‘background’ images. These RF antenna units can be part of the MR imaging system, or additional RF antenna units can be provided in RF antenna modules to improve the imaging in respect to the ROI of the subject of interest. Particularly, the RF antenna modules are provided close to the ROI. 
         [0004]    For some MR measurements, a rheology arrangement is used. The arrangement comprises a rheology module and typically at least one RF antenna module comprising at least one RF antenna unit. These modules are combined and interconnected, so that the rheology arrangement can be placed at the subject of interest or close to the subject of interest. In general, the closer a RF antenna unit is located to the ROI, the better are the results of the MR rheology imaging process. Due to the size of the modules, placement of the RF antenna units is usually not as close to the ROI as desired. The optimum size of the RF-coil to the ROI is determined by this distance. Thus, large coils can image with good results even from a larger distance. A field-of-view (FOV) of such coils on the other hand is relatively large and may not be appropriate for the MR rheology imaging process. If the ROI is rather small and/or close to the surface of the subject of interest, small receive coils perform better due to reduced noise pickup from the surroundings outside the ROI. Moreover a larger number of coil elements allows for speeding up the imaging process using algorithms like SENSE. With few coil elements such an acceleration in imaging is not possible. 
         [0005]    Furthermore, cabling of the rheology module and the RF antenna modules is rather complicated. Apart from signaling lines, also a supply line is a required for providing power to the rheology module as well as the RF antenna module. Cabling needs increase the setup time for performing MR rheology measurements, and can even reduce the imaging performance of the MR rheology system. Accordingly, improvements are desired. 
         [0006]    A magnetic resonance elastography (MRE) scan is known from U.S. Pat. No. 7,307,423 B2. The scan is performed using an array of transducers for applying a strain wave to tissues in a region of interest. A calibration process is performed prior to the scan in which the strain wave produced by each transducer in the array is imaged using an MRE pulse sequence so that information may be acquired that enables each transducer to be properly driven during a subsequent MRE scan. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the invention to provide a rheology module, a rheology arrangement comprising such a module, and a MR rheology imaging system, which enable improved MR rheology imaging, and which facilitate and improve a workflow for performing MR rheology imaging. 
         [0008]    In one aspect of the present invention, the object is achieved by a rheology module for use in a magnetic resonance (MR) rheology imaging system, whereby the rheology module is adapted to introduce mechanical oscillations into a subject of interest, comprising a housing, a mechanical oscillator unit, which extends at least partially outside the housing and is movable relative to the housing, and a transducer for moving the oscillator unit, whereby the rheology module comprises at least one radio frequency (RF) antenna unit, which comprises at least one RF coil. 
         [0009]    With the RF antenna device integrated into the rheology module, an antenna placement close to a region of interest (ROI) can be achieved to improve the MR imaging capabilities of a MR rheology imaging system. Thus, imaging of the ROI can be performed more efficiently. Furthermore, connection and cabling can be facilitated, since only one module has to be connected to generate the oscillation and to operate the RF antenna device. The RF antenna device can be used as transmit/receive or receive only device, where each coil can be a receive coil only or a local transmit/receive coil. The MR rheology module overcomes disadvantages of the separate placement of the mechanical oscillator unit and the RF antenna device. Accordingly, also cable routing can be improved and interaction between mechanical oscillator unit and MR imaging equipment can be reduced. The geometry of the module can be freely chosen. Also the geometry of the RF antenna units and RF coils can be chosen as required. Typically, the RF coils have an essentially circular or rectangular shape. Further preferred, the essentially circular shape can be formed by six to eight linear segments, e.g. in the form of a stop sign or octagon. Preferably, the RF antenna unit is provided at the side of the rheology module, where the mechanical oscillator comes into contact with the subject of interest. Any suitable kind of transducer can be used to generate the oscillation of the mechanical oscillator unit, including an electrical, a pneumatic, or a hydraulic transducer. The electrical transducer is preferably a piezoelectric transducer, which converts electric energy into mechanical energy or an electromechanical transducer making use of the movement of a current driven coil within the static magnetic field of the MR imaging device. Piezoelectric transducers can respond very rapidly to drive voltage changes. In a preferred embodiment, the rheology module is provided with a thin housing, which facilitates its placement. The transducer can be provided as a backpack with a local, heavy mass to provide sufficient mechanical inertia to keep amplitude of the oscillations high. The local mass can be exchanged with respect to a desired application, e.g. for different organs or depending on the thickness of fatty tissue layer. The local mass is chosen to be MR compatible. 
         [0010]    According to a preferred embodiment at least one RF antenna unit is located at the housing. Different placements of the RF antenna unit at the housing are possible. The RF antenna unit is preferably arranged to surround the oscillator unit. The RF antenna unit can be provided at an upper surface of the housing, integrated into the housing, or at an inner surface thereof. Preferably, the RF antenna unit is provided over an entire face of the housing, e.g. the face facing the subject of interest in operation. 
         [0011]    According to a preferred embodiment at least one RF antenna unit is located at the oscillator unit. The RF antenna unit can be provided at an upper surface of the oscillator unit, so that the RF antenna unit is in direct contact with the subject of interest. Alternatively, the RF antenna unit can be integrated into the oscillator unit, or the RF antenna unit can be located at a lower surface thereof facing the housing. 
         [0012]    According to a preferred embodiment at least one RF antenna unit comprises a set of multiple RF coils. Multiple RF coils can be used for image generation with increased speed for dynamic processes. The RF coils of the RF antenna unit can be arranged in different ways, e.g. in an array. The RF coils can also be arranged to overlap with adjacent coils and hence being geometrically decoupled from each other. The RF antenna unit can also comprise at least one local, separate transmit coil and a separate receive coil array. For more than one transmit channel, the integrated transmit coil has a nearby RF power combiner to distribute RF power to different transmit coil elements. Accordingly, the MR rheology unit can be used independent from the presence of a large integrated body transmit coil. The receive coil array is detuned during the transmit pulse and the transmit coil is detuned during reception of MRI signals. 
         [0013]    According to a preferred embodiment the transducer converts electrical energy into mechanical oscillations, and the rheology module comprises an electrical connector, whereby the electrical connector is provided as a single harness to provide electrical power and a signaling connection to the transducer and the at least one RF antenna unit. With the single harness, connection of the MR rheology module can easily be performed. The harness can comprise individual lines for power and signaling for the transducer and the RF antenna unit. The signaling line can be provided as bi-directional line for sending signals to the transducer and/or the RF antenna unit and receiving signals from the transducer and/or the RF antenna unit. Nevertheless, also independent signaling lines can be provided. Furthermore, multiple signaling lines can be provided for transmitting different kinds of signals. The harness can be further provided with a power line for the transducer and/or the RF antenna unit. A typical rheology module has four types of lines for the RF Antenna device, which are DC feed, RF signal, detune, and malfunction detection, and two lines for the transducer, which are a driving signal and a sensing line to monitor the performance of the transducer. Only one supply line for RF coils and transducer can be realized using a local semiconductor FET switch or amplifier inside the oscillator unit. A local amplifier can directly drive the transducer. Accordingly, B 0 -compensation for the power line has to be performed only once. 
         [0014]    According to a preferred embodiment the harness comprises at least one line, which is connected to the transducer and the at least one RF antenna unit, and a filter unit provided in the line for splitting signals received from the line according to their frequency, whereby electrical signals on the line are provided from the filter unit to the transducer and the RF antenna unit depending on their frequency. The line can be a signaling line. Preferably, the line is a combined signaling and power line. A typical MR signal has a frequency of some 10 MHz, power supply for the RF antenna device, in particular for preamplifiers associated to the RF antenna device, is a DC signal, and the transducer is driven by a signal having some 10 Hz. 
         [0015]    According to a preferred embodiment the harness comprises at least one digital signaling line, the rheology module comprises an AD/DA converter unit, which is connected to the digital signaling line, the transducer and the at least one RF antenna unit, and the AD/DA converter unit is adapted to perform a conversion and allocation of signals between the digital signaling line and the transducer and the at least one RF antenna unit. The signal conversion refers to AD/DA conversion. The allocation of the signals to the transducer and the RF antenna unit refers to multiplexing of signals from different RF coils to be transmitted, or to a separation of received signals, so that they can be provided to the correct recipient, i.e. the corresponding RF coil or the transducer. The digital line can be a bi-directional line, or a unidirectional line. The AD/DA converter is adapted to perform the required conversion. The AD conversion of the RF signal is preferably done on the RF antenna device, further preferred in the RF coil of the RF antenna device. 
         [0016]    According to a preferred embodiment the digital signaling line is an optical signaling line. The optical signaling line enables high data transmission rates. Furthermore, the influence on the magnetic fields of the MR rheology imaging system is reduced compared to an electrical line, which generates a magnetic field when electrical signals are transmitted. The optical line is preferably a standard optical high-speed data connection. 
         [0017]    According to a preferred embodiment the housing is flexible. The flexible housing facilitates the positioning of the rheology module. Furthermore, the rheology module can adapt to the form of the subject of interest, so that the RF antenna device can be in close contact thereto. 
         [0018]    In another aspect of the present invention, the object is achieved by a rheology arrangement for use in a magnetic resonance (MR) rheology imaging system, comprising at least one RF antenna module comprising at least one RF antenna unit, and at least one rheology module as specified above, whereby the at least one RF antenna module and the at least one rheology module are interconnected. The modules can be arranged in any suitable way, e.g. as an array with multiple modules arranged in two directions, or as chain, where the modules are arranged in only one direction. Preferably, also an electrical connection between the modules is provided, so that the rheology arrangement can be easily connected. Further preferred, the rheology arrangement is provided with a single connector for electrically connecting all modules. The modules can be combined, i.e. attached to each other, outside the MR rheology imaging system. Preferably, a reversible connecting method is used for interconnecting the modules, e.g. zip or Velcro fastener. This allows easily adapting the applicator and coil array to the subject of interest and furthermore the ROI. The rheology arrangement can be tailored to fit the desired imaging/rheology measurement depending on the application, thus providing superior images. 
         [0019]    According to a preferred embodiment the rheology arrangement is provided as a belt for application to the subject of interest. A belt can easily be positioned at the subject of interest and cover its entire circumference. 
         [0020]    In a further aspect of the present invention, the object is achieved by a magnetic resonance (MR) rheology imaging system, comprising a main magnet for generating a static magnetic field, a magnetic gradient coil system for generating gradient magnetic fields superimposed to the static magnetic field, an examination space provided to position a subject of interest within, at least one radio frequency (RF) antenna device for applying an RF field to the examination space to excite nuclei of the subject of interest, a control unit for controlling the at least one RF antenna device, and at least one rheology module as specified above. The control unit is connected to the at least one rheology module and adapted to control the at least one rheology module, so that the MR rheology imaging system can autonomously introduce oscillations into the subject of interest and perform the required MR measurements. Preferably, information from RF antenna units installed on the MR imaging system is combined with information received from the rheology module. 
         [0021]    According to a preferred embodiment the magnetic resonance (MR) rheology imaging system comprises a rheology arrangement as specified above, whereby the rheology arrangement comprises the at least one rheology module. Preferably, information from RF antenna units installed on the MR imaging system are combined with information received from the rheology module(s) and the RF antenna module(s). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Such an embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention. 
           [0023]    In the drawings: 
           [0024]      FIG. 1  is a schematic illustration of a part of an embodiment of a magnetic resonance (MR) imaging system in accordance with the invention, 
           [0025]      FIG. 2  is a perspective view of a rheology module according to a first embodiment in accordance with the invention, 
           [0026]      FIG. 3  is a top view of the rheology module according to  FIG. 2 , 
           [0027]      FIG. 4  is a perspective view of a rheology module according to a second embodiment in accordance with the invention, 
           [0028]      FIG. 5  is a schematic illustration of a rheology module according to a third embodiment in accordance with the invention, 
           [0029]      FIG. 6  is a schematic illustration of a rheology module according to a fourth embodiment in accordance with the invention, 
           [0030]      FIG. 7  is a schematic illustration of a rheology module according to a fifth embodiment in accordance with the invention, and 
           [0031]      FIG. 8  is a schematic illustration of a rheology arrangement comprising a rheology module in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0032]      FIG. 1  shows a schematic illustration of a part of an embodiment of a magnetic resonance (MR) imaging system  110  comprising an MR scanner  112 . The MR imaging system  110  includes a main magnet  114  provided for generating a static magnetic field. The main magnet  114  has a central bore that provides an examination space  116  around a center axis  118  for a subject of interest  120 , usually a patient, to be positioned within. In this embodiment, the central bore and therefore the static magnetic field of the main magnet  114  has a horizontal orientation in accordance with the center axis  118 . In an alternative embodiment, the orientation of the main magnet  114  can be different, e.g. to provide the static magnetic field with a vertical orientation. Further, the MR imaging system  110  comprises a magnetic gradient coil system  122  provided for generating gradient magnetic fields superimposed to the static magnetic field. The magnetic gradient coil system  122  is concentrically arranged within the bore of the main magnet  114 , as known in the art. 
         [0033]    Further, the MR imaging system  110  includes a radio frequency (RF) antenna device  140  designed as a whole-body coil having a tubular body. The RF antenna device  140  is provided for applying an RF magnetic field to the examination space  116  during RF transmit phases to excite nuclei of the subject of interest  120 . The RF antenna device  140  is also provided to receive MR signal from the excited nuclei during RF receive phases. In a state of operation of the MR imaging system  110 , RF transmit phases and RF receive phases are taking place in a consecutive manner. The RF antenna device  140  is arranged concentrically within the bore of the main magnet  114 . As is known in the art, a cylindrical metal RF screen  124  is arranged concentrically between the magnetic gradient coil system  122  and the RF antenna device  140 . 
         [0034]    Moreover, the MR imaging system  110  comprises an MR image reconstruction unit  130  provided for reconstructing MR images from the acquired MR signals and an MR imaging system control unit  126  with a monitor unit  128  provided to control functions of the MR scanner  112 , as is commonly known in the art. Control lines  132  are installed between the MR imaging system control unit  126  and an RF transmitter unit  134  that is provided to feed RF power of an MR radio frequency to the RF antenna device  140  via an RF switching unit  136  during the RF transmit phases. The RF switching unit  136  in turn is also controlled by the MR imaging system control unit  126 , and another control line  138  is installed between the MR imaging system control unit  126  and the RF switching unit  136  to serve that purpose. During RF receive phase, the RF switching unit  136  directs the MR signals from the RF antenna device  140  to the MR image reconstruction unit  130  after pre-amplification. 
         [0035]    The MR imaging system  110  is provided as a MR rheology system comprising a rheology module  200 , which is shown in  FIGS. 2 and 3 , and which is adapted to introduce mechanical oscillations into the subject of interest  120 . 
         [0036]    The rheology module  200  comprises a thin and flexible housing  202  and a mechanical oscillator unit  204 , which is provided to be in contact with the subject of interest  120  in use. The oscillator unit  204  in this embodiment extends partially outside the housing  202  and is movable relative thereto. The rheology module  200  further comprises a transducer  206 , which is indicated schematically in  FIGS. 5 to 7 , for moving the oscillator unit  204 . The transducer  206  in this embodiment is an electromechanical transducer, which converts electric energy into mechanical energy, i.e. into mechanical oscillations. The rheology module  200  further comprises a local, heavy mass, which is not shown in the figures and which is MR compatible, to provide mechanical inertia to keep the amplitude of the mechanical oscillations high. The local mass is exchangeable with respect to a desired application. In an alternative embodiment, the mass can be omitted in case the subject of interest is placed in such a manner that a table, on which the subject of interest can be placed, counters the rheology unit. Also, the MR rheology unit can be fixed to the patient bed or an inner wall of a bore of the MR rheology imaging system. 
         [0037]    The rheology module  200  of this embodiment is provided with two RF antenna units  210 ,  212 , which are respectively located at the housing  202  and the oscillator unit  204 . Each RF antenna unit  210 ,  212  in this embodiment comprises one RF coil  214 ,  216 , respectively. The RF coil  214  of the RF antenna unit  210  located at the housing  202  is provided at an upper face  218  of the housing  202 , through which the oscillator unit  204  is connected to the transducer  206 . The RF coil  214  is provided at an upper surface of the housing  202 , i.e. at an upper surface of the upper face  218 , and has a rectangular shape extending along the sides of the upper face  218 . Accordingly, the RF coil  214  surrounds the oscillator unit  204 . The RF coil  216  of the RF antenna unit  212  located at the oscillator unit  204  has a circular shape and is provided at an upper surface of the oscillator unit  204 . The rheology module  200  also comprises pre-amplifiers  220 , which are provided within the housing  202  for driving the RF coils  214 ,  216 , as indicated in  FIGS. 5 and 6 . 
         [0038]    The control unit  126  of the MR rheology imaging system  110  is connected to the rheology module  200  and adapted to control the rheology module  200 , so that the MR rheology imaging system  110  can autonomously introduce mechanical oscillations into the subject of interest  120  and perform MR rheology imaging operations. A physical connection between the rheology module  200  and the control unit  126  is described in detail below. 
         [0039]    A second embodiment of the rheology module  200  is shown in  FIG. 4 . The rheology module  200  is similar to the rheology module  200  of the first embodiment, so that only the differences will be described in detail. 
         [0040]    The rheology module  200  of the second embodiment differs from that of the first embodiment in the structure of the RF antenna units  210 ,  212 . According to the second embodiment, the RF antenna unit  210  located at the housing  202  comprises two rectangular RF coils  214 , which are provided at an upper face  218  of the housing  202  as described above. Each RF coil  214  extends over half the area of the upper face  218 . The RF antenna unit  212  located at the oscillator unit  204  comprises a set of seven individual RF coils  216 , each of which has an essentially circular shape formed by six linear segments  220 . The RF coils  216  of the RF antenna unit  216  are arranged in an array overlapping with adjacent RF coils  216 . The rheology module  200  also comprises pre-amplifiers  222 , which are provided within the housing  202  for driving the RF coils  214 ,  216 , as indicated in  FIGS. 5 and 6 . Although the pre-amplifiers  222  are indicated in  FIGS. 5 and 6  as a single box, each RF coil  214 ,  216  has one pre-amplifier  222  associated thereto. 
         [0041]    The control unit  126  of the MR rheology imaging system  110  is connected to the rheology module  200  and adapted to control the rheology module  200 , so that the MR rheology imaging system  110  can autonomously introduce oscillations into the subject of interest  120  and perform MR rheology imaging operations. The physical connection between the rheology module  200  and the control unit  126  is described in detail below. 
         [0042]      FIG. 5  shows a rheology module  200  according to a third embodiment with a physical connection. By way of example, the physical connection is illustrated based on the rheology module  200  of the second embodiment, as indicated by the RF antenna device  212  located in the oscillator unit  204  having multiple RF coils  216 . Nevertheless, the connection can be realized without general modifications for other rheology modules  200 , e.g. that of the first embodiment. 
         [0043]    The rheology module  200  according to the third embodiment comprises an electrical connector  300 , which is provided as a single harness  300 . The electrical connector  300  provides electrical power and a signaling connection to the transducer  206  and the RF coils  214 ,  216  of the RF antenna units  210 ,  212 . The electrical connector  300  comprises an individual power line  302  and signaling lines  304  for the transducer  206  and the RF antenna units  210 ,  212 . The power line  302  and the signaling lines  304  are indicated by a single line in  FIG. 5 . In particular, the pre-amplifiers  222  are connected by four lines  302 ,  304 , which are DC feed as power line  302 , as well as RF signal, detune, and malfunction detection as signaling lines  304 . The transducer  206  is connected by two lines  302 ,  304 , which are a driving signal and a sensing line to monitor the performance of the transducer  206 . The signaling lines  304  are provided as bi-directional lines for sending signals to the transducer  206  and the RF antenna units  210 ,  212  and receiving signals from the transducer  206  and the RF antenna units  210 ,  212 . The power lines  302  are B 0 -compensated. 
         [0044]      FIG. 6  shows a rheology module  200  according to a fourth embodiment with a physical connection. The rheology module  200  of the fourth embodiment only differs in the connection of its RF antenna units  210 ,  212  and transducer  206  to a harness  300  from the rheology module  200  of the third embodiment. Accordingly, only the differences between these rheology modules  200  will be discussed. 
         [0045]    The rheology module  200  according to the fourth embodiment comprises an electrical connector  300 , which is provided as a single harness  300 . The harness  300  comprises power lines  304 , which are directly connected to the transducer  206  and pre-amplifiers  222  of the RF antenna units  210 ,  212 . The harness  300  further comprises a signaling line  304 , which is connected to a filter unit  306  of the rheology module  200 . The filter unit  306  is adapted for splitting signals received from the signaling line  304  according to their frequency. 
         [0046]    Electrical signals on the signaling line  304  are provided from the filter unit  306  to the transducer  206  and the RF antenna units  210 ,  212  depending on their frequency. MR signals having a typical frequency of some 10 MHz are provided to the RF antenna units  210 ,  212 , and a driving signal having some 10 Hz is provided to the transducer  206 . A threshold for splitting the signals is defined between these frequencies. 
         [0047]      FIG. 7  shows a rheology module  200  according to a fifth embodiment with a physical connection. The rheology module  200  of the fifth embodiment only differs in the connection of its RF antenna units  210 ,  212  and transducer  206  to a harness  300  from the rheology module  200  of the third embodiment. Accordingly, only the differences between these rheology modules  200  will be discussed. 
         [0048]    The rheology module  200  according to the fifth embodiment comprises an electrical connector  300 , which is provided as a single harness. The rheology module  200  comprises an AD/DA converter unit  308 , which is in this embodiment integrally provided with pre-amplifiers  222  in a driving box  308 . The driving box  308  is connected to a digital signaling line  310  and a power line  302 , whereby the power line  302  provides power for the pre-amplifiers  222 . A transducer  206  is connected with a separate power line  302  of the harness  300 . The signaling line  310  is used for signaling to/and from the transducer  206  and the preamplifiers  222  in the driving box  308 . An analog signaling line  304  is provided between the transducer  206  and the AD/DA converter unit  308 . The AD/DA converter unit  308  performs an AD/DA conversion. Additionally, an allocation of signals between the digital signaling line and the transducer  206  and the RF antenna unit, i.e. the pre-amplifiers  222  is performed, so that all signals are multiplexed on the digital signaling line  310 . The digital signaling line  310  is a bi-directional line. 
         [0049]    In an alternative embodiment the digital signaling line  310  in the harness  300  is an optical digital signaling line. 
         [0050]    A sixth embodiment refers to a rheology arrangement  400  for use in a magnetic resonance (MR) rheology imaging system  110 , which is shown in  FIG. 8 . The rheology arrangement  400  comprises three RF antenna modules  402 , which comprises a RF antenna unit as described above in respect to the rheology modules  200 , and one rheology module  200  as specified above. The modules  200 ,  402  are interconnected and arranged in a chain, so that the rheology arrangement  400  can be used as a belt for application to the subject of interest  120 . The modules  200 ,  402  are attached to each other by Velcro fasteners, which are not explicitly shown in  FIG. 8 . In an alternative embodiment, the modules  200 ,  402  comprise electrical connectors for connecting to adjacent modules  200 ,  402 , and the rheology arrangement  400  comprises a single connector for electrically connecting all modules  200 ,  402  to the MR rheology imaging system  110 . 
         [0051]    According to a modified embodiment, the magnetic resonance (MR) rheology imaging system  110  comprises a rheology arrangement  400 , whereby the rheology arrangement  400  comprises the at least one rheology module  200 . 
         [0052]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. 
       REFERENCE SYMBOL LIST 
       [0000]    
       
           110  magnetic resonance (MR) imaging system 
           112  magnetic resonance (MR) scanner 
           114  main magnet 
           116  RF examination space 
           118  center axis 
           120  subject of interest 
           122  magnetic gradient coil system 
           124  RF screen 
           126  MR imaging system control unit 
           128  monitor unit 
           130  MR image reconstruction unit 
           132  control line 
           134  RF transmitter unit 
           136  RF switching unit 
           138  control line 
           140  radio frequency (RF) antenna device 
           200  rheology module 
           202  housing 
           204  oscillator unit 
           206  transducer 
           210  RF antenna unit (at housing) 
           212  RF antenna unit (at oscillator) 
           214  RF coil (at housing) 
           216  RF coil (at oscillator) 
           218  upper face 
           220  linear segment 
           222  pre-amplifier 
           300  electrical connector, harness 
           302  power line 
           304  signaling line 
           306  filter unit 
           308  AD/DA converter unit 
           310  digital signaling line 
           400  rheology arrangement 
           402  RF antenna module