Coordinate transformation of graphical objects registered to a magnetic resonance image

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.

TECHNICAL FIELD

The invention relates to magnetic resonance imaging, in particular to the registration of graphical objects to the magnetic resonance image.

BACKGROUND OF THE INVENTION

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.

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

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.

‘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.

‘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.

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.

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.

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).

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.

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.

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.

When the second magnetic resonance image is reconstructed the multiple graphical objects may not be properly registered with the second magnetic resonance image. 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. 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.

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.

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.

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.

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.

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.

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's internal structure which uses a least energy or other algorithm to fit the model to the actual geometry in a magnetic resonance image.

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's skin could be selected and in this case the motion of the tags may be limited.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1shows a flow diagram which illustrates an example of a method. First in step100first magnetic resonance data is acquired using a magnetic resonance imaging system. Next in step102a first magnetic resonance image is reconstructed using the first magnetic resonance data. Next in step104a 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 step106second magnetic resonance data is acquired using the magnetic resonance imaging system. Then in step108a second magnetic resonance image is reconstructed using the second magnetic resonance data. Next in step110repositioning 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 step112a 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 box114is a decision box, is the data acquisition finished. If the answer is yes then the method ends in step116. If it is no then the method returns to step106where second magnetic resonance data is acquired. The method then proceeds as previously described and repeats until the decision in step114is yes.

FIG. 2shows a flow diagram which illustrates a further example of a method. First in step200a 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 step202first magnetic resonance data is acquired using a magnetic resonance imaging system. Then in step204a first magnetic resonance image is reconstructed using the first magnetic resonance data. Next in step206a registration is received of multiple graphical objects in the first magnetic resonance image. Next in step208the high-intensity focused ultrasound system is controlled in accordance with the treatment plan. Then in step210second magnetic resonance data is acquired using the magnetic resonance imaging system. Next in step212a second magnetic resonance image is reconstructed using the second magnetic resonance data. Next in step214repositioning coordinates are received in the second magnetic resonance image for a first group selected from the multiple graphical objects.

Next in step216a 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 step218is a decision box. The question is sonication finished. If the answer is yes then the method ends in step220. If the answer is no then in step222the treatment plan is modified using the repositioning coordinates and the coordinate transformation. The method then proceeds back to step208where 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 step218it is indicated that the sonication is finished and the method ends at step220. The method described inFIG. 2forms a closed control loop for control of the high-intensity focused ultrasound system.

FIG. 3illustrates a medical apparatus300according to an embodiment of the invention. The medical apparatus300comprises a magnetic resonance imaging system602. The magnetic resonance imaging system302is shown as comprising a magnet304. The magnet304is a cylindrical type superconducting magnet with a bore306through the center of it. The magnet304has 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 bore306of the cylindrical magnet304there is an imaging zone308where the magnetic field is strong and uniform enough to perform magnetic resonance imaging.

Also within the bore306of the magnet is a magnetic field gradient coil310which is used for acquisition of magnetic resonance data to spatially encode magnetic spins within an imaging zone of the magnet. The magnetic field gradient coil310is connected to a magnetic field gradient coil power supply312. 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 supply312supplies 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.

Adjacent the imaging zone308is a radio-frequency coil314. The radio-frequency coil314is connected to a radio-frequency transceiver316. Also within the bore of the magnet304is a subject318that is reposing on a subject support320and is partially within the imaging zone308.

Adjacent to the imaging zone308is a radio-frequency coil314for manipulating the orientations of magnetic spins within the imaging zone308and for receiving radio transmissions from spins also within the imaging zone308. The radio-frequency coil314may contain multiple coil elements. The radio-frequency coil314may also be referred to as a channel or an antenna. The radio-frequency coil is connected to a radio frequency transceiver316. The radio-frequency coil314and radio frequency transceiver316may be replaced by separate transmit and receive coils and a separate transmitter and receiver. It is understood that the radio-frequency coil314and the radio-frequency transceiver316are representative. The radio-frequency coil314is intended to also represent a dedicated transmit antenna and a dedicated receive antenna. Likewise the transceiver316may also represent a separate transmitter and a separate receiver.

The magnetic field gradient coil power supply312and the radio-frequency transceiver316are connected to a hardware interface324of a computer system322. The computer system322further comprises a processor326. The processor326is connected to the hardware interface324. The hardware interface324enables the processor326to send and receive data and commands to the magnetic resonance imaging system302. The computer system322further comprises a user interface328, computer storage330and computer memory332.

The computer storage330is shown as containing a pulse sequence340. The pulse sequence340contains instructions or data which may be used for generating instructions for controlling the operation and function of the magnetic resonance imaging system302. The computer storage330is shown as further containing first magnetic resonance data that was acquired using the pulse sequence340. The computer storage330is shown as further containing a first magnetic resonance image344which was reconstructed from the first magnetic resonance data342. The computer storage330is further shown as containing multiple graphical objects. The computer storage330is further shown as containing a first group or an identification of a first group348within the multiple graphical objects346.

The computer storage330is further shown as containing a second group350or an identification of a second group350chosen from the multiple graphical objects346. The computer storage330is shown as further containing an image registration352of the multiple graphical objects346in the first magnetic resonance image344. The computer storage330is further shown as containing a second magnetic resonance data354. The computer storage330is shown as further containing a second magnetic resonance image356reconstructed from the second magnetic resonance data354. The computer storage330is further shown as containing repositioning coordinates358which identify the location of the first group348within the second magnetic resonance image356. The computer storage330is shown as further containing a coordinate transformation358which identifies the location of the second group350within the second magnetic resonance image356.

The computer memory332is shown as containing a control module360. The control module360comprises computer-executable code which enables the processor326to control the operation and function of the magnetic resonance imaging system302. For instance it may use the pulse sequence340for acquiring the magnetic resonance data342,354. The computer memory332is further shown as containing an image reconstruction module362. The image reconstruction module362enables the processor to reconstruct the first magnetic resonance image344from the first magnetic resonance data342. The image reconstruction module362also enables the reconstruction of the second magnetic resonance image356from the second magnetic resonance data354. The computer memory332is further shown as containing a coordinate transformation module364which enables the processor362to calculate the coordinate transformation359using the repositioning coordinates358.

FIG. 4shows a further embodiment of the medical apparatus400according to the invention. In this embodiment the heating system is a high-intensity focused ultrasound system402. The high-intensity focused ultrasound system comprises a fluid-filled chamber404. Within the fluid-filled chamber404is an ultrasound transducer406. Although it is not shown in this Fig. the ultrasound transducer406may 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 point418electronically by controlling the phase and/or amplitude of alternating electrical current supplied to each of the ultrasound transducer elements. The sonication point418is operable to be controlled to sonicate the target zone417.

The ultrasound transducer406is connected to a mechanism408which allows the ultrasound transducer406to be repositioned mechanically. The mechanism408is connected to a mechanical actuator410which is adapted for actuating the mechanism408. The mechanical actuator410also represents a power supply for supplying electrical power to the ultrasound transducer406. 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 supply410is located outside of the bore306of the magnet304.

The ultrasound transducer406generates ultrasound which is shown as following the path412. The ultrasound412goes through the fluid-filled chamber404and through an ultrasound window414. In this embodiment the ultrasound then passes through a gel pad416. The gel pad is not necessarily present in all embodiments but in this embodiment there is a recess in the subject support320for receiving a gel pad416. The gel pad416helps couple ultrasonic power between the transducer406and the subject318. After passing through the gel pad416the ultrasound412passes through the subject318and is focused to a sonication point418. The sonication point418is being focused within a target zone418. The sonication point418may be moved through a combination of mechanically positioning the ultrasonic transducer406and electronically steering the position of the sonication point418to treat the entire target zone418.

The high-intensity focused ultrasound system402is shown as being also connected to the hardware interference324of the computer system322. The computer system322and the contents of its storage330and memory332are equivalent to that as shown inFIG. 3.

In this example the computer storage330is shown as additionally containing a treatment plan440. The computer memory332is shown as additionally containing a high-intensity focused ultrasound system control module450. The high-intensity focused ultrasound system control module450contains computer-executable code which enables the processor326to control the high-intensity focused ultrasound system402using the treatment plan440. The computer memory332is shown as further containing a treatment plan modification module452. The treatment plan modification module452contains computer-executable code which enables the processor326to modify the treatment plan440using the repositioning coordinates358and the coordinate transformation359.

The computer memory332is shown as further containing an image segmentation module454. The image segmentation module454is not present in all examples and enables the processor326to generate the image registration352using the first magnetic resonance image344. The computer memory332is further shown as containing a user interface control module456. The user interface control module456may or may not be present in all examples. The user interface control module456contains computer executable code which enables the processor326to display the second magnetic resonance image356on a display and receive repositioning coordinates358from a user interface, for example a graphical user interface.

FIG. 5shows a portion of a graphical user interface500. The graphical user interface500displays a number of first magnetic resonance images502. On some of these images a model of a high-intensity focused ultrasound transducer504can be observed. The path of the ultrasound506is also indicated on some of these Figs. There are a number of sonication volumes508indicated on the various Figs. A first graphical object510and a second graphical object512are also indicated.

FIG. 6shows 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 by502′. It can be seen that the first graphical object510and the second graphical object512have shifted with respect to the magnetic resonance image502′. This may be representative of a subject moving during or between sonications. If the sonication volumes508are sonicated they will be performed in a location that is different from the original anatomical position shown inFIG. 5.

InFIG. 7the graphical user interface500is again displayed. In this example the first graphical object510is selected and is repositioned in the magnetic resonance image502′. The first graphical object510is therefore the first group. The second graphical object512forms the second group. A transformation700correcting the position of the first graphical object510is indicated inFIG. 7and is equivalent to the repositioning coordinates. A transformation702correcting the position of the second graphical object512is also indicated inFIG. 7and is equivalent to the coordinate transformation. Some of the images shown inFIG. 7are shown from a different plane with respect to images inFIGS. 5, 6, 8, and 9and with different orientations.

InFIG. 8the first graphical object510has been moved back into its correct position and is properly registered to the magnetic resonance image502′. The first graphical object510is moved to the position set in three different images. The position of the second graphical object512has been updated automatically by applying a coordinate transformation model.

FIG. 9indicates how the sonication volumes508have been repositioned using the new positions of the first graphical object510and the second graphical object512.

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.

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.

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.

LIST OF REFERENCE NUMERALS