METHOD AND APPARATUS FOR TAKING INTO ACCOUNT SUSCEPTIBILITY DEVIATIONS IN MR-BASED THERAPY PLANNING

Abstract

Systems and methods for taking into account susceptibility deviations in magnetic-resonance-based therapy planning by a magnetic resonance tomography unit. A B0 field map is determined by the magnetic resonance tomography unit. A location blur distribution is determined from the B0 field map and from the location blur distribution in turn, a parameter of an image acquisition as a function of the location blur distribution, in such a way that an image acquisition brings about a reduced location blur with the determined parameter.

Claims

1. A method for taking into account susceptibility deviations in magnetic-resonance-based therapy planning by a magnetic resonance tomography unit, the method comprising: acquiring a B0 field map by the magnetic resonance tomography unit; determining a location blur distribution from the B0 field map; and determining at least one parameter of an image acquisition as a function of the location blur distribution in such a way that an image acquisition with this determined parameter brings about a reduced location blur.

2. The method of claim 1, further comprising: executing an image acquisition with the determined parameter; executing an image reconstruction with data of the image acquisition; and outputting the reconstructed image on an output device.

3. The method of claim 1, wherein acquiring the B0 field map comprises a Dixon gradient echo sequence.

4. The method of claim 1, wherein a parameter set is predetermined for the image acquisition, and for determining the location blur distribution, the location blur distribution is carried out as a function of a parameter of the parameter set.

5. The method of claim 1, wherein determining the location blur distribution comprises a weighted location deviation.

6. The method of claim 1, wherein the magnetic resonance tomography unit includes an image acquisition region, and the determination of the location blur distribution only takes place for a genuine subset of the image acquisition region.

7. The method of claim 6, wherein for determining at least one parameter of the image acquisition, the at least one parameter is set in such a way that a location blur is reduced in a predetermined subset of the image acquisition region.

8. The method of claim 1, wherein the at least one parameter is at least one of readout bandwidth, readout direction, type of sequence, or trajectory.

9. The method of claim 1, further comprising: executing the image reconstruction as a function of the location blur distribution.

10. The method of claim 1, further comprising: performing an image acquisition with a computed tomography unit as a function of the location blur distribution.

11. A magnetic resonance tomography unit comprising: a control unit; a field magnet; one or more gradient coils; a transmitting antenna; and a receiving antenna; wherein the magnetic resonance tomography unit is configured to: acquire a B0 field map with the control unit, the field magnet, the one or more gradient coils, the transmitting antenna, and the receiving antenna; determine a location blur distribution with the control unit from the B0 field map; and determine, with the control unit, at least one parameter of an image acquisition as a function of the location blur distribution which leads to a reduction in the location blur.

12. The magnetic resonance tomography unit of claim 11, wherein the magnetic resonance tomography unit is further configured to: perform an image acquisition using the determined parameter with the control unit, the field magnet, the one or more gradient coils, the transmitting antenna, and the receiving antenna; perform an image reconstruction with the control unit using data from the image acquisition; and output the reconstructed image on an output device.

13. The magnetic resonance tomography unit of claim 11, wherein acquiring the B0 field map comprises a Dixon gradient echo sequence.

14. The magnetic resonance tomography unit of claim 11, wherein a parameter set is predetermined for the image acquisition, and for determining the location blur distribution, the location blur distribution is carried out as a function of a parameter of the parameter set.

15. The magnetic resonance tomography unit of claim 11, wherein determining the location blur distribution comprises a weighted location deviation.

16. The magnetic resonance tomography unit of claim 11, wherein the magnetic resonance tomography unit includes an image acquisition region, and the determination of the location blur distribution only takes place for a genuine subset of the image acquisition region.

17. The magnetic resonance tomography unit of claim 16, wherein for determining at least one parameter of the image acquisition, the at least one parameter is set in such a way that a location blur is reduced in a predetermined subset of the image acquisition region.

18. A non-transitory computer implemented storage medium that stores machine-readable instructions executable by at least one processor, the machine-readable instructions comprising: acquiring a B0 field map by a magnetic resonance tomography unit; determining a location blur distribution from the B0 field map; and determining at least one parameter of an image acquisition as a function of the location blur distribution in such a way that an image acquisition with this determined parameter brings about a reduced location blur.

19. The non-transitory computer implemented storage medium of claim 18, wherein the machine-readable instructions further comprise: executing an image acquisition with the determined parameter; executing an image reconstruction with data of the image acquisition; and outputting the reconstructed image on an output device.

20. The non-transitory computer implemented storage medium of claim 18, wherein acquiring the B0 field map comprises a Dixon gradient echo sequence.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0036] FIG. 1 depicts a diagrammatic view of a magnetic resonance tomography unit for performing the method according to an embodiment.

[0037] FIG. 2 depicts a diagrammatic flow chart of the method according to an embodiment.

DETAILED DESCRIPTION

[0038] FIG. 1 depicts a diagrammatic view of an embodiment of a magnetic resonance tomography unit 1 for carrying out the method according to an embodiment.

[0039] The magnet unit 10 includes a field magnet 11 that generates a static magnetic field B0 for aligning nuclear spins of samples or of the patient 100 in a receiving area. The receiving area is characterized by an extremely homogenous static magnetic field B0, the homogeneity relating to the magnetic field strength or the magnitude. The receiving area is almost spherical and arranged in a patient tunnel 16 that extends in a longitudinal direction 2 through the magnet unit 10. A patient couch 30 may be moved in the patient tunnel 16 by the positioning unit 36. The field magnet 11 may be a superconducting magnet that may provide magnetic fields with a magnetic flux density of up to 3T, and in the case of the latest devices even higher. However, permanent magnets or electromagnets with normally conducting coils may also be used for lower field strengths.

[0040] Furthermore, the magnet unit 10 includes gradient coils 12 that are configured to superimpose variable magnetic fields on the magnetic field B0 in three spatial directions to spatially differentiate the acquired imaging regions in the examination volume. The gradient coils 12 may be coils of normally conducting wires that may generate fields in the examination volume that are orthogonal to one another.

[0041] The magnet unit 10 includes a body coil 14 that is configured to radiate a radio frequency signal supplied via a signal line into the examination volume and to receive resonance signals emitted by the patient 100 and to output them via a signal line. Hereinafter, the term transmitting antenna denotes an antenna via which the radio frequency signal for exciting the nuclear spins is emitted. This may be the body coil 14, but also a local coil 50 with a transmission function.

[0042] A control unit 20 supplies the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14 and evaluates the received signals.

[0043] The control unit 20 includes a gradient control 21 that is configured to supply the gradient coils 12 via supply lines with variable currents that provide the desired gradient fields in the examination volume in a time-coordinated manner.

[0044] The control unit 20 includes a radio frequency unit 22 that is configured to generate a radio frequency pulse with a predetermined time profile, amplitude, and spectral power distribution for excitation of a magnetic resonance of the nuclear spins in the patient 100. Pulse outputs in the range of kilowatts may be achieved. The excitation signals may be emitted into the patient 100 via the body coil 14 or also via a local transmitting antenna.

[0045] A controller 23 communicates via a signal bus 25 with the gradient controller 21 and the radio frequency unit 22.

[0046] A local coil 50 is arranged on the patient 100 and is connected to the radio frequency unit 22 and the receiver thereof via a connecting line 33. The body coil 14 may be a receiving antenna.

[0047] FIG. 2 depicts an embodiment of the method.

[0048] In a step S10, the magnetic resonance tomography unit detects a B0 field map with the control unit 20, the field magnet 10, the gradient coils 12, the transmitting antenna, and the receiving antenna. For example, information relating to B0 deviations may be determined by single or dual gradient echo sequences. B0 field deviations may be determined from the phase of interleaved dual-echo EPI sequences. In an embodiment, a Dixon gradient echo sequence is used.

[0049] In order to record the B0 field map, a predetermined set of parameters is used that is determined by the sequence used or, conversely, defines it. Parameters may be, for example, frequency, spectral distribution and amplitude of excitation pulses, strength, and direction of gradient fields as well as their temporal course and temporal arrangement with respect to one another, and the B0 field strength of the field magnet 11.

[0050] In a further step S20, the control unit 20 determines a location blur distribution from the B0 field map. The control unit may have its own computing unit or use a computing unit for image reconstruction or also use the controller 23 for image acquisition. In the simplest case, it may be assumed that the location blur is proportional to a deviation in the B0 field strength. However, the location blur may also include a directional dependence that differs in a direction perpendicular to a boundary between two regions of different susceptibility from the direction parallel to the interface.

[0051] The determined location blur may depend on the predetermined set of parameters in the acquisition of the B0 field map, as will be explained hereinafter with regard to the selection of the parameter for image acquisition.

[0052] For a simpler assessment of adequate image quality with regard to geometric distortions, the location blur distribution may be reduced to a smaller amount of data. For example, relevant image regions and irrelevant image regions may be weighted differently in the assessment. Regions that include, for example, the tissue to be examined or treated or, conversely, sensitive organs that must not be damaged, may be regarded as relevant image regions. The data may thus also be reduced, for example, to a single measure that is formed by a sum of the location blur amounts multiplied by the weighting factor for all voxels. Histograms with an optionally weighted number of voxels in a predetermined location blur region may be used.

[0053] The location blur distribution may be determined only for a subset of the voxels, for example, in relevant image regions. Conversely, the location blur for voxels in irrelevant regions could also be given a correspondingly low weighting or multiplied by a weighting factor of zero.

[0054] In a step S30, the control unit 20 determines a parameter of an image acquisition from the location blur distribution, or as a function of the location blur distribution. As already explained above with regard to step S20, the location blur may depend on the direction relative to a susceptibility limit. Thus, for example, by selecting the readout direction as a parameter of the image acquisition relative to the susceptibility limit, the location blur may be reduced.

[0055] Further parameters of the image acquisition with which the location blur may be influenced in the case of image acquisition for given susceptibility discontinuities are, for example, also readout bandwidth, type of sequence, and/or trajectory.

[0056] However, the location blur in the case of a predetermined susceptibility jump also depends on the absolute magnetic field strength used. In order to limit the location blur to a required maximum, the control unit 20 may, for example, determine a maximum magnetic field strength B0 for which this is fulfilled as a parameter. This value may be output to an operator on an output unit. The operator may then, for example, execute an image acquisition of the patient 100 with another magnetic resonance system of suitable field strength B0 in a step S40.

[0057] In the case of extreme susceptibility jumps, the parameter may also indicate in a broader sense that the imaging cannot be carried out with an available magnetic resonance tomography unit 1 with sufficient accuracy and therefore the image acquisition must take place on a different modality, for example a computed tomography unit. An instruction as a corresponding parameter is then output by the magnetic resonance tomography unit 1 to the operator.

[0058] The same magnetic resonance tomography unit 1 may carry out an image acquisition with the determined parameter in step S40. This may, for example, be an image acquisition with a changed readout direction. In suitable magnetic resonance systems 1 with conventional field magnets 11 and broadband reception technology, however, it may be possible to reduce the magnetic field strength B0 to a maximum value determined as a parameter.

[0059] In a step S50, the magnetic resonance tomography unit 1 performs an image reconstruction with the acquired magnetic resonance signals. In the image reconstruction, the parameters may be modified in the direction of a lower location deviation, or a suitable image reconstruction algorithm may be selected as a function of the parameter.

[0060] In step S60, the control unit 20 outputs the pictorial representation on an output device, for example, a display.

[0061] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

[0062] While the present invention has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.