Abstract:
A method of using a medical instrument (300, 400) comprising a magnetic resonance imaging (MRI) system (302). The MRI system acquires (100, 202) first magnetic resonance data (342) and reconstructs (102, 204) a first magnetic resonance image (344, 502). A registration (352) of multiple graphical objects (346, 510, 512) to the first magnetic resonance image is received which defines spatial positions of the multiple graphical objects in the first magnetic resonance image. The method further comprises repeatedly: acquiring (106, 210) second magnetic resonance data (354); reconstructing (108, 212) a second magnetic resonance image (356, 502′); receiving (110, 214) repositioning coordinates (358, 700) in the second magnetic resonance image for a first group (348, 510) selected from the multiple graphical objects; and determining (112, 216) a coordinate transformation (359, 702) of a second group (350, 512) selected from the multiple graphical objects by applying a coordinate transformation model (364) to the repositioning coordinates.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to magnetic resonance imaging, in particular to the registration of graphical objects to the magnetic resonance image. 
       BACKGROUND OF THE INVENTION 
       [0002]    In High Intensity Focused Ultrasound (HIFU), a volume of interest is detected during the planning stages and may be marked on medical images, such as magnetic resonance images. For example, an ellipsoid can be quickly drawn over a uterine fibroid. Volumes to be destroyed, so called treatment cells, can be planned in advance and may landmark vessels or other structures to be destroyed. Regions of interest can be drawn to highlight organs at risk and safety margins to organ structures. Once sonications have been carried out, the produced temperature map overlays and thermal doses correspond to signal changes in images where the tissue has been altered with thermal energy. These form the basic HIFU graphical objects. The international application WO2010/113050 discloses delineating anatomical features in images used for image-guided therapy planning. This known delineation makes use of a comparison of the position of anatomical landmarks in the image to reference landmarks. 
         [0003]    However, subjects may have external and/or internal motion during a course of sonication. Automatic re-registration algorithms are susceptible to errors when the input image data does not provide sufficient/correct contrast or signal to noise ratio. Landmark-based manual methods need extensive user interaction to define suitable anatomical landmarks and slow down the therapy session. The ISMRM abstract in Proc. ISMRM(2009)443 mentions that a 2D selective navigator is employed to compensate out-of-plane motion. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides for a medical instrument, a computer program product, and a method of controlling the medical instrument in the independent claims. Embodiments are given in the dependent claims. 
         [0005]    A ‘computer-readable storage medium’ as used herein encompasses any tangible storage medium which may store instructions which are executable by a processor of a computing device. The computer-readable storage medium may be referred to as a computer-readable non-transitory storage medium. The computer-readable storage medium may also be referred to as a tangible computer readable medium. In some embodiments, a computer-readable storage medium may also be able to store data which is able to be accessed by the processor of the computing device. Examples of computer-readable storage media include, but are not limited to: a floppy disk, a magnetic hard disk drive, a solid state hard disk, flash memory, a USB thumb drive, Random Access Memory (RAM), Read Only Memory (ROM), an optical disk, a magneto-optical disk, and the register file of the processor. Examples of optical disks include Compact Disks (CD) and Digital Versatile Disks (DVD), for example CD-ROM, CD-RW, CD-R, DVD-ROM, DVD-RW, or DVD-R disks. The term computer readable-storage medium also refers to various types of recording media capable of being accessed by the computer device via a network or communication link. For example a data may be retrieved over a modem, over the internet, or over a local area network. 
         [0006]    ‘Computer memory’ or ‘memory’ is an example of a computer-readable storage medium. Computer memory is any memory which is directly accessible to a processor. Examples of computer memory include, but are not limited to: RAM memory, registers, and register files. 
         [0007]    ‘Computer storage’ or ‘storage’ is an example of a computer-readable storage medium. Computer storage is any non-volatile computer-readable storage medium. Examples of computer storage include, but are not limited to: a hard disk drive, a USB thumb drive, a floppy drive, a smart card, a DVD, a CD-ROM, and a solid state hard drive. In some embodiments computer storage may also be computer memory or vice versa. 
         [0008]    A ‘processor’ as used herein encompasses an electronic component which is able to execute a program or machine executable instruction. References to the computing device comprising “a processor” should be interpreted as possibly containing more than one processor or processing core. The processor may for instance be a multi-core processor. A processor may also refer to a collection of processors within a single computer system or distributed amongst multiple computer systems. The term computing device should also be interpreted to possibly refer to a collection or network of computing devices each comprising a processor or processors. Many programs have their instructions performed by multiple processors that may be within the same computing device or which may even be distributed across multiple computing devices. 
         [0009]    A ‘user interface’ as used herein is an interface which allows a user or operator to interact with a computer or computer system. A ‘user interface’ may also be referred to as a ‘human interface device.’ A user interface may provide information or data to the operator and/or receive information or data from the operator. A user interface may enable input from an operator to be received by the computer and may provide output to the user from the computer. In other words, the user interface may allow an operator to control or manipulate a computer and the interface may allow the computer indicate the effects of the operator&#39;s control or manipulation. The display of data or information on a display or a graphical user interface is an example of providing information to an operator. The receiving of data through a keyboard, mouse, trackball, touchpad, pointing stick, graphics tablet, joystick, gamepad, webcam, headset, gear sticks, steering wheel, pedals, wired glove, dance pad, remote control, and accelerometer are all examples of user interface components which enable the receiving of information or data from an operator. 
         [0010]    A ‘hardware interface’ as used herein encompasses an interface which enables the processor of a computer system to interact with and/or control an external computing device and/or apparatus. A hardware interface may allow a processor to send control signals or instructions to an external computing device and/or apparatus. A hardware interface may also enable a processor to exchange data with an external computing device and/or apparatus. 
         [0011]    Examples of a hardware interface include, but are not limited to: a universal serial bus, IEEE 1394 port, parallel port, IEEE 1284 port, serial port, RS-232 port, IEEE-488 port, Bluetooth connection, Wireless local area network connection, TCPIP connection, Ethernet connection, control voltage interface, MIDI interface, analog input interface, and digital input interface. 
         [0012]    A ‘display’ or ‘display device’ as used herein encompasses an output device or a user interface adapted for displaying images or data. A display may output visual, audio, and or tactile data. Examples of a display include, but are not limited to: a computer monitor, a television screen, a touch screen, tactile electronic display, Braille screen, Cathode ray tube (CRT), Storage tube, Bistable display, Electronic paper, Vector display, Flat panel display, Vacuum fluorescent display (VF), Light-emitting diode (LED) displays, Electroluminescent display (ELD), Plasma display panels (PDP), Liquid crystal display (LCD), Organic light-emitting diode displays (OLED), a projector, and Head-mounted display. 
         [0013]    Magnetic Resonance (MR) data is defined herein as being the recorded measurements of radio frequency signals emitted by atomic spins by the antenna of a Magnetic resonance apparatus during a magnetic resonance imaging scan. A Magnetic Resonance Imaging (MRI) image is defined herein as being the reconstructed two or three dimensional visualization of anatomic data contained within the magnetic resonance imaging data. This visualization can be performed using a computer. 
         [0014]    An ‘ultrasound window’ as used herein encompasses a window which is able to transmit ultrasonic waves or energy. Typically a thin film or membrane is used as an ultrasound window. The ultrasound window may for example be made of a thin membrane of BoPET (Biaxially-oriented polyethylene terephthalate). 
         [0015]    In one aspect the invention provides for a medical instrument comprising a magnetic resonance imaging system for acquiring magnetic resonance data from an imaging zone. The medical instrument further comprises a processor for controlling the medical instrument. The medical instrument further comprises a memory containing machine-readable instructions for execution by the processor. Execution of the instructions causes the processor to acquire first magnetic resonance data with the magnetic resonance imaging system. The first magnetic resonance data is magnetic resonance data. Execution of the instructions further causes the processor to reconstruct a first magnetic resonance image using the first magnetic resonance data. The first magnetic resonance image is a magnetic resonance image. 
         [0016]    A magnetic resonance image as used herein encompasses data which may be used to render or display an image on a display. For instance the magnetic resonance image may comprise data which represents a slice, a single voxel, or even a three-dimensional volume. Execution of the instructions further causes the processor to receive a registration of multiple graphical objects to the first magnetic resonance image. The registration defines spatial positions of the multiple graphical objects with respect to the first magnetic resonance image. Execution of the instructions further causes the processor to repeatedly acquire second magnetic resonance data using the magnetic resonance imaging system. 
         [0017]    The second magnetic resonance data is magnetic resonance data. Execution of the instructions further causes the processor to repeatedly reconstruct a second magnetic resonance image using the second magnetic resonance data. The second magnetic resonance image is also a magnetic resonance image. Execution of the instructions further cause the processor to receive positioning coordinates in the second magnetic resonance image for a first group selected from the multiple graphical objects. The repositioning coordinates describe a repositioning of the first group in the second magnetic resonance image with respect to the first magnetic resonance image. It is in other words to say that the position of the multiple graphical objects is defined in the first magnetic resonance image. 
         [0018]    When the second magnetic resonance image is reconstructed the multiple graphical objects may not be properly registered with the second magnetic resonance image. 
         [0019]    The repositioning coordinates describe the new position of the first group of multiple graphical objects. The first group may for instance contain one or more of the multiple graphical objects. Execution of the instructions further cause the processor to repeatedly determine a coordinate transformation of a second group selected from the multiple graphical objects by applying a coordinate transformation model to the repositioning coordinates. 
         [0020]    An insight of the invention is that in the treatment plan formed from the first magnetic resonance image contains suitable graphical objects that can be employed to derive motion. The graphical objects in the treatment plan per se could for example be delineated in the first magnetic resonance image by way of the approach in the international application WO2010/113050. That known approach, however , limits its application to automatic delineation of anatomy in image guided therapy planning That is, the known approach is applied only in the original generation of the therapy plan. The present invention is based on the insight that the same graphical objects can be employed to detect movement and accordingly correct the treatment plan. By registering the corresponding graphical objects in the first magnetic resonance image to those in the second magnetic resonance image a coordinate transformation is found that represents the motion that occurred between the first magnetic resonance image that forms the basis of the treatment plan and the subsequent second magnetic resonance image. This coordinate transformation is then employed to modify or update the treatment plan to account for the motion that has occurred. The high-instensity focused ultrasound system is continued to be controlled on the basis of the modified treatment plan. For example the adjustable focus is moved so as to account for the motion that has occurred. In this way even if motion occurs, the high-intensity focused ultrasound radiation remains focused into a target zone that is to be treated and deposition of energy surrounding healthy tissue is avoided. Thus, hyperthermia is accurately applied to the tissue in the target region even if motion occurs. Because the graphical objects contained in the treatment plan are used, there is no need to separately select graphical objects. Notably, the graphical objects in the treatment plan represent relevant anatomical structures of which the motion is taken into account in the update of the treatment plan. 
         [0021]    This embodiment may be beneficial because it provides for a means of properly positioning the multiple graphical objects on the second magnetic resonance image. One or more of the multiple graphical objects are first repositioned and then a coordinate transformation model is used to reposition one or more of the remaining multiple graphical objects based on the way the first repositioning was performed. This may provide for a means of repositioning the multiple graphical objects in the second magnetic resonance image for instance when a subject moves. For instance, the first and second magnetic resonance data may be acquired from a subject. 
         [0022]    In another embodiment execution of the instructions further causes the processor to receive a treatment plan for controlling a high-intensity focused ultrasound system with an adjustable focus. A treatment plan as used herein encompasses a set of instructions or data which may be used for generating a set of instructions for operating the high-intensity focused ultrasound system. In some embodiments the treatment plan may contain anatomical or other data descriptive of the subject. 
         [0023]    Execution of the instructions further causes the processor to repeatedly modify the treatment plan using the repositioning coordinates and the coordinate transformation. This embodiment may be beneficial because it provides for a means of correcting the position of the multiple graphical objects which specify a location such as regions to sonicate and/or protect from heating. 
         [0024]    In another embodiment the medical instrument further comprises the high-intensity focused ultrasound system. Execution of the instructions further cause the processor to control the high-intensity focused ultrasound system in accordance with the treatment plan. This embodiment may be beneficial because the treatment plan used to control the high-intensity focused ultrasound system is updated using the repositioning coordinates and the coordinate transformation. 
         [0025]    In another embodiment execution of the instructions further cause the processor to perform a reduced intensity sonication before acquisition of the first magnetic resonance data. Execution of the instructions causes the processor to check the registration using the first magnetic resonance image. This embodiment may be beneficial because the reduced intensity sonication may be a test shot for determining if the registration between the image and the high-intensity focused ultrasound system is correct or not. 
         [0026]    In another embodiment the coordinate transformation model is a deformable shape model. A deformable shape model as used herein encompasses a model descriptive of a subject&#39;s internal structure which uses a least energy or other algorithm to fit the model to the actual geometry in a magnetic resonance image. 
         [0027]    In another embodiment each of the graphical objects has a tag. The coordinate transformation of the second group is determined at least partially using the tag of each of the second group. For instance the graphical objects may have a type or tag which may be used to identify the type of graphical objects or some of its properties. For instance considering the case of a subject who is breathing within the abdominal cavity the organs may move around considerably during the process of the subject breathing or working. By using a tag the particular graphical object may be classified as to an anatomical region it is nearby and this may aid in choosing a model to predict its motion or for instance points on a subject&#39;s skin could be selected and in this case the motion of the tags may be limited. 
         [0028]    In another embodiment the graphical objects are any one of the following: treatment cells, regions of interest, measured doses, planned target volumes, and combinations thereof. 
         [0029]    In another embodiment the memory further contains an image selection module containing machine-readable instructions for execution by the processor for segmenting the magnetic resonance image to determine the repositioning coordinates. Execution of the instructions further causes the processor to receive the repositioning coordinates from the segmentation module. In this embodiment the position of the first group is determined automatically using the segmentation module. In some embodiments, the segmentation module can be used to identify and/or tag objects. Tagging an object may be equivalent to classifying the objects. The classification may then be used by a particular coordinate transformation model the new coordinates in response to the repositioning coordinates. This may provide for more accurate and timely updating of the treatment plan. 
         [0030]    In another embodiment execution of the instructions further causes the processor to repeatedly display the second magnetic resonance image on a display. The repositioning coordinates are received from a user interface in response to displaying the second magnetic resonance data. 
         [0031]    In another embodiment execution of the instructions further causes the processor to display the first magnetic resonance image on the display. The registration is received from the user interface and responds to displaying the first magnetic resonance data. 
         [0032]    In another aspect the invention provides for a computer program product comprising machine-executable instructions for execution by a processor controlling the medical instrument. The medical instrument comprises a magnetic resonance imaging system for acquiring magnetic resonance data from an imaging zone. Execution of the instructions further causes the processor to acquire first magnetic resonance data with the magnetic resonance imaging system. Execution of the instructions further causes the processor to reconstruct a first magnetic resonance image using the first magnetic resonance data. Execution of the instructions further causes the processor to receive a registration of multiple graphical objects to the first magnetic resonance image. The registration defines spatial positions of the multiple graphical objects with respect to the first magnetic resonance image. Execution of the instructions further causes the processor to repeatedly acquire second magnetic resonance data using the magnetic resonance imaging system. 
         [0033]    Execution of the instructions further causes the processor to repeatedly reconstruct a second magnetic resonance image using the second magnetic resonance data. Execution of the instructions further causes the processor to repeatedly receive repositioning coordinates in the second magnetic resonance image for a first group selected from the multiple graphical objects. The repositioning coordinates describe a repositioning of the first group in the second magnetic resonance image with respect to the first magnetic resonance image. Execution of the instructions further cause the processor to repeatedly determine a coordinate transformation of a second group selected from the multiple graphical objects by applying a coordinate transformation model to the repositioning coordinates. 
         [0034]    In another embodiment execution of the instructions causes the processor to receive a treatment plan for controlling a high-intensity focused ultrasound system with an adjustable focus. Execution of the instructions further causes the processor to repeatedly modify the treatment plan using the repositioning coordinates and the coordinate transformation. 
         [0035]    In another embodiment the medical instrument further comprises the high-intensity focused ultrasound system. Execution of the instructions further causes the processor to control the high-intensity focused ultrasound system in accordance with the treatment plan. 
         [0036]    In another aspect the invention provides for a method of controlling the medical instrument. The medical instrument comprises a magnetic resonance imaging system for acquiring magnetic resonance data from and imaging zone. The method comprises the steps of acquiring first magnetic resonance data with the magnetic resonance imaging system. The method further comprises the step of reconstructing a first magnetic resonance image using the first magnetic resonance data. The method further comprises the step of receiving a registration of multiple graphical objects to the first magnetic resonance image. The registration defines spatial positions of the multiple graphical objects with respect to the first magnetic resonance image. 
         [0037]    The method further comprises repeatedly performing the step of acquiring second magnetic resonance data using the magnetic resonance imaging system. The method further comprises repeatedly performing the step of reconstructing a second magnetic resonance image using the second magnetic resonance data. The method further comprises the step of repeatedly receiving repositioning coordinates in a second magnetic resonance image for a first group selected from the multiple graphical objects. The repositioning coordinates describe a repositioning of the first group in the second magnetic resonance image with respect to the first magnetic resonance image. The method further comprises the step of repeatedly determining a coordinate transformation of a second group selected from the multiple graphical objects by applying a coordinate transformation model to the repositioning coordinates. 
         [0038]    In another embodiment the method further comprises the step of receiving a treatment plan for controlling a high-intensity focused ultrasound system with an adjustable focus. The method further comprises the step of modifying the treatment plan using the repositioning coordinates and the coordinate transformation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    In the following preferred embodiments of the invention will be described, by way of example only, and with reference to the drawings in which: 
           [0040]      FIG. 1  shows a flow diagram which illustrates an example of a method; 
           [0041]      FIG. 2  shows a flow diagram which illustrates a further example of a method; 
           [0042]      FIG. 3  illustrates an example of a medical apparatus; 
           [0043]      FIG. 4  illustrates a further example of a medical apparatus; 
           [0044]      FIG. 5  illustrates an example of a user interface; 
           [0045]      FIG. 6  illustrates a further example of a user interface; 
           [0046]      FIG. 7  illustrates a further example of a user interface; 
           [0047]      FIG. 8  illustrates a further example of a user interface; and 
           [0048]      FIG. 9  illustrates a further example of a user interface. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0049]    Like numbered elements in these figures are either equivalent elements or perform the same function. Elements which have been discussed previously will not necessarily be discussed in later figures if the function is equivalent. 
         [0050]      FIG. 1  shows a flow diagram which illustrates an example of a method. First in step  100  first magnetic resonance data is acquired using a magnetic resonance imaging system. Next in step  102  a first magnetic resonance image is reconstructed using the first magnetic resonance data. Next in step  104  a registration of multiple graphical objects is received for the first magnetic resonance image. The registration may for instance come from an automatic segmentation module or it may also be received from a user interface. For instance the first magnetic resonance image may be displayed and a user may manually place the multiple graphical objects on the first magnetic resonance image thereby registering them. Next in step  106  second magnetic resonance data is acquired using the magnetic resonance imaging system. Then in step  108  a second magnetic resonance image is reconstructed using the second magnetic resonance data. Next in step  110  repositioning coordinates are received for a first group of objects selected from the multiple graphical objects. The repositioning coordinates identifies the position of the first group in the second magnetic resonance image. Next in step  112  a coordinate transformation of a second group selected from the multiple graphical objects is determined by applying a coordinate transformation model to the repositioning coordinates. Next box  114  is a decision box, is the data acquisition finished. If the answer is yes then the method ends in step  116 . If it is no then the method returns to step  106  where second magnetic resonance data is acquired. The method then proceeds as previously described and repeats until the decision in step  114  is yes. 
         [0051]      FIG. 2  shows a flow diagram which illustrates a further example of a method. First in step  200  a treatment plan is received. The treatment plan may contain data useful for constructing control commands for a high-intensity focused ultrasound system or itself may contain commands for controlling a high-intensity focused ultrasound system. Next in step  202  first magnetic resonance data is acquired using a magnetic resonance imaging system. Then in step  204  a first magnetic resonance image is reconstructed using the first magnetic resonance data. Next in step  206  a registration is received of multiple graphical objects in the first magnetic resonance image. Next in step  208  the high-intensity focused ultrasound system is controlled in accordance with the treatment plan. Then in step  210  second magnetic resonance data is acquired using the magnetic resonance imaging system. Next in step  212  a second magnetic resonance image is reconstructed using the second magnetic resonance data. Next in step  214  repositioning coordinates are received in the second magnetic resonance image for a first group selected from the multiple graphical objects. 
         [0052]    Next in step  216  a coordinate transformation is determined for a second group selected from the multiple graphical objects by applying a coordinate transformation model to the repositioning coordinates. Next step  218  is a decision box. The question is sonication finished. If the answer is yes then the method ends in step  220 . If the answer is no then in step  222  the treatment plan is modified using the repositioning coordinates and the coordinate transformation. The method then proceeds back to step  208  where the high-intensity focused ultrasound system is controlled in accordance with the treatment plan. The method then proceeds as described previously and repeats until in step  218  it is indicated that the sonication is finished and the method ends at step  220 . The method described in  FIG. 2  forms a closed control loop for control of the high-intensity focused ultrasound system. 
         [0053]      FIG. 3  illustrates a medical apparatus  300  according to an embodiment of the invention. The medical apparatus  300  comprises a magnetic resonance imaging system  602 . The magnetic resonance imaging system  302  is shown as comprising a magnet  304 . The magnet  304  is a cylindrical type superconducting magnet with a bore  306  through the center of it. The magnet  304  has a liquid helium cooled cryostat with superconducting coils. It is also possible to use permanent or resistive magnets. The use of different types of magnets is also possible for instance it is also possible to use both a split cylindrical magnet and a so called open magnet. A split cylindrical magnet is similar to a standard cylindrical magnet, except that the cryostat has been split into two sections to allow access to the iso-plane of the magnet, such magnets may for instance be used in conjunction with charged particle beam therapy. An open magnet has two magnet sections, one above the other with a space in-between that is large enough to receive a subject: the arrangement of the two sections area similar to that of a Helmholtz coil. Open magnets are popular, because the subject is less confined. Inside the cryostat of the cylindrical magnet there is a collection of superconducting coils. Within the bore  306  of the cylindrical magnet  304  there is an imaging zone  308  where the magnetic field is strong and uniform enough to perform magnetic resonance imaging. 
         [0054]    Also within the bore  306  of the magnet is a magnetic field gradient coil  310  which is used for acquisition of magnetic resonance data to spatially encode magnetic spins within an imaging zone of the magnet. The magnetic field gradient coil  310  is connected to a magnetic field gradient coil power supply  312 . The magnetic field gradient coil is representative. Typically magnetic field gradient coils contain three separate sets of coils for spatially encoding in three orthogonal spatial directions. A magnetic field gradient power supply  312  supplies current to the magnetic field gradient coils. The current supplied to the magnetic field coils is controlled as a function of time and may be ramped and/or pulsed. 
         [0055]    Adjacent the imaging zone  308  is a radio-frequency coil  314 . The radio-frequency coil  314  is connected to a radio-frequency transceiver  316 . Also within the bore of the magnet  304  is a subject  318  that is reposing on a subject support  320  and is partially within the imaging zone  308 . 
         [0056]    Adjacent to the imaging zone  308  is a radio-frequency coil  314  for manipulating the orientations of magnetic spins within the imaging zone  308  and for receiving radio transmissions from spins also within the imaging zone  308 . The radio-frequency coil  314  may contain multiple coil elements. The radio-frequency coil  314  may also be referred to as a channel or an antenna. The radio-frequency coil is connected to a radio frequency transceiver  316 . The radio-frequency coil  314  and radio frequency transceiver  316  may be replaced by separate transmit and receive coils and a separate transmitter and receiver. It is understood that the radio-frequency coil  314  and the radio-frequency transceiver  316  are representative. The radio-frequency coil  314  is intended to also represent a dedicated transmit antenna and a dedicated receive antenna. Likewise the transceiver  316  may also represent a separate transmitter and a separate receiver. 
         [0057]    The magnetic field gradient coil power supply  312  and the radio-frequency transceiver  316  are connected to a hardware interface  324  of a computer system  322 . The computer system  322  further comprises a processor  326 . The processor  326  is connected to the hardware interface  324 . The hardware interface  324  enables the processor  326  to send and receive data and commands to the magnetic resonance imaging system  302 . The computer system  322  further comprises a user interface  328 , computer storage  330  and computer memory  332 . 
         [0058]    The computer storage  330  is shown as containing a pulse sequence  340 . The pulse sequence  340  contains instructions or data which may be used for generating instructions for controlling the operation and function of the magnetic resonance imaging system  302 . The computer storage  330  is shown as further containing first magnetic resonance data that was acquired using the pulse sequence  340 . The computer storage  330  is shown as further containing a first magnetic resonance image  344  which was reconstructed from the first magnetic resonance data  342 . The computer storage  330  is further shown as containing multiple graphical objects. The computer storage  330  is further shown as containing a first group or an identification of a first group  348  within the multiple graphical objects  346 . 
         [0059]    The computer storage  330  is further shown as containing a second group  350  or an identification of a second group  350  chosen from the multiple graphical objects  346 . The computer storage  330  is shown as further containing an image registration  352  of the multiple graphical objects  346  in the first magnetic resonance image  344 . The computer storage  330  is further shown as containing a second magnetic resonance data  354 . The computer storage  330  is shown as further containing a second magnetic resonance image  356  reconstructed from the second magnetic resonance data  354 . The computer storage  330  is further shown as containing repositioning coordinates  358  which identify the location of the first group  348  within the second magnetic resonance image  356 . The computer storage  330  is shown as further containing a coordinate transformation  358  which identifies the location of the second group  350  within the second magnetic resonance image  356 . 
         [0060]    The computer memory  332  is shown as containing a control module  360 . The control module  360  comprises computer-executable code which enables the processor  326  to control the operation and function of the magnetic resonance imaging system  302 . For instance it may use the pulse sequence  340  for acquiring the magnetic resonance data  342 ,  354 . The computer memory  332  is further shown as containing an image reconstruction module  362 . The image reconstruction module  362  enables the processor to reconstruct the first magnetic resonance image  344  from the first magnetic resonance data  342 . The image reconstruction module  362  also enables the reconstruction of the second magnetic resonance image  356  from the second magnetic resonance data  354 . The computer memory  332  is further shown as containing a coordinate transformation module  364  which enables the processor  362  to calculate the coordinate transformation  359  using the repositioning coordinates  358 . 
         [0061]      FIG. 4  shows a further embodiment of the medical apparatus  400  according to the invention. In this embodiment the heating system is a high-intensity focused ultrasound system  402 . The high-intensity focused ultrasound system comprises a fluid-filled chamber  404 . Within the fluid-filled chamber  404  is an ultrasound transducer  406 . Although it is not shown in this Fig. the ultrasound transducer  406  may comprise multiple ultrasound transducer elements each capable of generating an individual beam of ultrasound. This may be used to steer the location of a sonication point  418  electronically by controlling the phase and/or amplitude of alternating electrical current supplied to each of the ultrasound transducer elements. The sonication point  418  is operable to be controlled to sonicate the target zone  417 . 
         [0062]    The ultrasound transducer  406  is connected to a mechanism  408  which allows the ultrasound transducer  406  to be repositioned mechanically. The mechanism  408  is connected to a mechanical actuator  410  which is adapted for actuating the mechanism  408 . 
         [0063]    The mechanical actuator  410  also represents a power supply for supplying electrical power to the ultrasound transducer  406 . In some embodiments the power supply may control the phase and/or amplitude of electrical power to individual ultrasound transducer elements. In some embodiments the mechanical actuator/power supply  410  is located outside of the bore  306  of the magnet  304 . 
         [0064]    The ultrasound transducer  406  generates ultrasound which is shown as following the path  412 . The ultrasound  412  goes through the fluid-filled chamber  404  and through an ultrasound window  414 . In this embodiment the ultrasound then passes through a gel pad  416 . The gel pad is not necessarily present in all embodiments but in this embodiment there is a recess in the subject support  320  for receiving a gel pad  416 . The gel pad  416  helps couple ultrasonic power between the transducer  406  and the subject  318 . After passing through the gel pad  416  the ultrasound  412  passes through the subject  318  and is focused to a sonication point  418 . The sonication point  418  is being focused within a target zone  418 . The sonication point  418  may be moved through a combination of mechanically positioning the ultrasonic transducer  406  and electronically steering the position of the sonication point  418  to treat the entire target zone  418 . 
         [0065]    The high-intensity focused ultrasound system  402  is shown as being also connected to the hardware interference  324  of the computer system  322 . The computer system  322  and the contents of its storage  330  and memory  332  are equivalent to that as shown in  FIG. 3 . 
         [0066]    In this example the computer storage  330  is shown as additionally containing a treatment plan  440 . The computer memory  332  is shown as additionally containing a high-intensity focused ultrasound system control module  450 . The high-intensity focused ultrasound system control module  450  contains computer-executable code which enables the processor  326  to control the high-intensity focused ultrasound system  402  using the treatment plan  440 . The computer memory  332  is shown as further containing a treatment plan modification module  452 . The treatment plan modification module  452  contains computer-executable code which enables the processor  326  to modify the treatment plan  440  using the repositioning coordinates  358  and the coordinate transformation  359 . 
         [0067]    The computer memory  332  is shown as further containing an image segmentation module  454 . The image segmentation module  454  is not present in all examples and enables the processor  326  to generate the image registration  352  using the first magnetic resonance image  344 . The computer memory  332  is further shown as containing a user interface control module  456 . The user interface control module  456  may or may not be present in all examples. The user interface control module  456  contains computer executable code which enables the processor  326  to display the second magnetic resonance image  356  on a display and receive repositioning coordinates  358  from a user interface, for example a graphical user interface. 
         [0068]      FIG. 5  shows a portion of a graphical user interface  500 . The graphical user interface  500  displays a number of first magnetic resonance images  502 . On some of these images a model of a high-intensity focused ultrasound transducer  504  can be observed. The path of the ultrasound  506  is also indicated on some of these Figs. There are a number of sonication volumes  508  indicated on the various Figs. A first graphical object  510  and a second graphical object  512  are also indicated. 
         [0069]      FIG. 6  shows a view of the same graphical interface except a later magnetic resonance image has been acquired. The new magnetic resonance images are second magnetic resonance and are indicated by  502 ′. It can be seen that the first graphical object  510  and the second graphical object  512  have shifted with respect to the magnetic resonance image  502 ′. This may be representative of a subject moving during or between sonications. If the sonication volumes  508  are sonicated they will be performed in a location that is different from the original anatomical position shown in  FIG. 5 . 
         [0070]    In  FIG. 7  the graphical user interface  500  is again displayed. In this example the first graphical object  510  is selected and is repositioned in the magnetic resonance image  502 ′. The first graphical object  510  is therefore the first group. The second graphical object  512  forms the second group. A transformation  700  correcting the position of the first graphical object  510  is indicated in  FIG. 7  and is equivalent to the repositioning coordinates. A transformation  702  correcting the position of the second graphical object  512  is also indicated in  FIG. 7  and is equivalent to the coordinate transformation. Some of the images shown in  FIG. 7  are shown from a different plane with respect to images in  FIGS. 5 ,  6 ,  8 , and  9  and with different orientations. 
         [0071]    In  FIG. 8  the first graphical object  510  has been moved back into its correct position and is properly registered to the magnetic resonance image  502 ′. The first graphical object  510  is moved to the position set in three different images. The position of the second graphical object  512  has been updated automatically by applying a coordinate transformation model. 
         [0072]      FIG. 9  indicates how the sonication volumes  508  have been repositioned using the new positions of the first graphical object  510  and the second graphical object  512 . 
         [0073]    In High Intensity Focused Ultrasound (HIFU), patient or organ movement can cause misregistration between already acquired images and the physical patient position. The misregistration can be corrected by the acquisition of new images from the patient and by comparison of the old and new images. Embodiment of the invention may use the already existing graphical HIFU objects, such as the planned target volume, to perform the registration: one of the HIFU planning object is re-positioned on the new image set without a need to first define landmarks or other registration-specific regions of interests. 
         [0074]    Registering of image sets acquired at different times with possible patient motion in-between is conventionally arranged with automatic re-registration algorithms or with a landmark-based manual method. These tools typically produce displacement vector field mappings or affine transformations to describe the change in patient position. 
         [0075]    Embodiments of the invention may re-use the HIFU planning and treatment graphics to re-register patient position: When new images have been acquired, the positions of HIFU graphical objects on the new images are visually inspected. If discrepancies are found, for example, the fibroid border no longer matches the original planned target volume ellipsoid, the HIFU graphical object is repositioned on one or more 2D slices to register the HIFU plan and possible sonications data to new images. The other HIFU graphical objects are updated and act as verification for the registration. 
         [0076]    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. 
         [0077]    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. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           300  medical apparatus 
           302  magnetic resonance imaging system 
           304  magnet 
           306  bore of magnet 
           308  imaging zone 
           310  magnetic field gradient coil 
           312  magnetic field gradient coil power supply 
           314  radio frequency coil 
           316  radio frequency transceiver 
           318  subject 
           320  subject support 
           322  computer system 
           324  hardware interface 
           326  processor 
           328  user interface 
           330  computer storage 
           332  computer memory 
           340  pulse sequence 
           342  first magnetic resonance data 
           344  first magnetic resonance image 
           346  multiple graphical objects 
           348  first group 
           350  second group 
           352  image registration 
           354  second magnetic resonance data 
           356  second magnetic resonance image 
           358  repositioning coordinates 
           359  coordinate transformation 
           360  control module 
           362  image reconstruction module 
           364  coordinate transformation module 
           400  medical apparatus 
           402  high intensity focused ultrasound system 
           404  fluid filled chamber 
           406  ultrasound transducer 
           408  mechanism 
           410  mechanical actuator/power supply 
           412  path of ultrasound 
           414  ultrasound window 
           416  gel pad 
           417  target zone 
           418  sonication point 
           440  treatment plan 
           450  high intensity focused ultrasound system control module 
           452  treatment plan modification module 
           454  image segmentation module 
           456  user interface control module 
           500  graphical user interface 
           502  magnetic resonance image 
           502 ′ magnetic resonance image 
           504  high intensity focused ultrasound transducer 
           506  path of ultrasound 
           508  sonication volumes 
           510  first graphical object 
           512  second graphical object 
           700  transformation 
           702  transformation