Receiving useful signals in the magnetic resonance frequency band

Abstract

A method for determining an item of evaluation information from a reception signal received by a magnetic resonance apparatus, a computer program product for carrying out such a method, and a magnetic resonance apparatus generate a useful signal having a first frequency band. The magnetic resonance apparatus is configured to generate a magnetic resonance signal in a second frequency band. The first frequency band lies at least partially, (e.g., completely), within the second frequency band. A reception signal is received by a receiving unit of the magnetic resonance apparatus. From the reception signal, an item of evaluation information is determined which characterizes the useful signal.

Claims

1. A method for determining an item of evaluation information from a reception signal received by a magnetic resonance apparatus, the method comprising: generating a useful signal in a first frequency band; generating a magnetic resonance signal in a second frequency band, wherein the first frequency band lies at least partially within the second frequency band; receiving a reception signal by a receiving unit of the magnetic resonance apparatus, wherein the reception signal comprises the useful signal and the magnetic resonance signal; and determining an item of evaluation information characterizing the useful signal from the reception signal, wherein the item of evaluation information comprises information regarding a movement of a patient.

2. The method of claim 1, wherein the first frequency band lies completely within the second frequency band.

3. The method of claim 1, further comprising: generating a magnetic resonance signal in the first frequency band, wherein the reception signal has an overlaying of the magnetic resonance signal in the first frequency band with the useful signal.

4. The method of claim 3, wherein the magnetic resonance signal is reconstructed from the reception signal based on the evaluation information.

5. The method of claim 4, wherein at least one magnetic resonance image is calculated from the reconstructed magnetic resonance signal.

6. The method of claim 1, wherein the generating of the useful signal comprises: generating a useful excitation signal; and changing the useful excitation signal into the useful signal by interaction with an examination object.

7. The method of claim 6, wherein the examination object is the patient.

8. The method of claim 6, wherein the useful excitation signal is used for determining the evaluation information.

9. The method of claim 8, wherein a portion of the useful excitation signal is decoupled by a coupler.

10. The method of claim 6, wherein the reception signal comprises a plurality of reception signal portions which are each received by a receiving channel, and wherein the magnetic resonance signal is reconstructed for each receiving channel by subtraction of the useful excitation signal from a respective reception signal portion weighted with a respectively determined weighting factor.

11. The method of claim 1, wherein the receiving unit comprises a plurality of receiving channels, and wherein, for each receiving channel, a weighting factor is determined as the evaluation information.

12. The method of claim 11, wherein the weighting factors are determined by reconstruction of the magnetic resonance signal from the reception signal.

13. The method of claim 11, further comprising: determining a temporal change in at least one weighting factor, comparing the at least one weighting factor with at least one pre-determined reference value, comparing the at least one weighting factor of a receiving channel with at least one weighting factor of another receiving channel, or a combination thereof.

14. A magnetic resonance apparatus comprising: a radio frequency transmitter configured to generate a useful signal in a first frequency band; and a radio frequency transmitting coil configured to generate a magnetic resonance signal in a second frequency band, wherein the first frequency band lies at least partially within the second frequency band; a receiving unit configured to receive a reception signal comprising both the useful signal and the magnetic resonance signal; and an evaluating unit configured to determine an item of evaluation information characterizing the useful signal from the reception signal, wherein the item of evaluation information comprises information regarding a movement of a patient.

15. The magnetic resonance apparatus of claim 14, wherein the first frequency band lies completely within the second frequency band.

16. A computer program product which comprises a program and is directly loadable into a memory store of a programmable system control unit of a magnetic resonance apparatus, wherein the program, when executed in a system control unit of the magnetic resonance apparatus, is configured to: generate a useful signal in a first frequency band; generate a magnetic resonance signal in a second frequency band, wherein the first frequency band lies at least partially within the second frequency band; receive a reception signal comprising both the useful signal and the magnetic resonance signal; and determine an item of evaluation information characterizing the useful signal from the reception signal, wherein the item of evaluation information comprises information regarding a movement of a patient.

17. The computer program product of claim 16, wherein the first frequency band lies completely within the second frequency band.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, features, and details of the disclosure are disclosed in the exemplary embodiments described below and the drawings. Parts which correspond to one another are provided with the same reference signs in all the drawings.

(2) In the drawings:

(3) FIG. 1 is a schematic representation of an example of a magnetic resonance apparatus.

(4) FIG. 2 is an exemplary method shown as a flow diagram.

(5) FIG. 3 is an example of a frequency graph with the frequency bands of a magnetic resonance signal and of a useful signal.

(6) FIG. 4 is an extended exemplary method shown as a flow diagram.

(7) FIG. 5 is a schematic representation of an example of a signal processing.

DETAILED DESCRIPTION

(8) FIG. 1 shows schematically a magnetic resonance apparatus 10. The magnetic resonance apparatus 10 includes a magnet unit 11 which has a main magnet 12 for generating a strong and, particularly, temporally constant main magnetic field. In addition, the magnetic resonance apparatus 10 includes a patient receiving region 14 to accommodate a patient 15. In the present exemplary embodiment, the patient receiving region 14 is configured cylindrical and is surrounded cylindrically in a peripheral direction by the magnet unit 11. In principle, however, an embodiment of the patient receiving region 14 deviating therefrom is readily conceivable. The patient 15 may be pushed by a patient positioning apparatus 16 of the magnetic resonance apparatus 10 into the patient receiving region 14. For this purpose, the patient positioning apparatus 16 has a patient table 17 configured to be movable within the patient receiving region 14.

(9) The magnet unit 11 also has a gradient coil unit 18 for generating magnetic field gradients that are used for position encoding during an imaging process. The gradient coil unit 18 is controlled by a gradient control unit 19 of the magnetic resonance apparatus 10. The magnetic resonance apparatus 10 further includes an RF transmitting coil 20 configured in the present exemplary embodiment as a body coil which is firmly integrated into the magnetic resonance apparatus 10. The radio frequency transmitting coil 20 is configured for an excitation of atomic nuclei, which arises in the main magnetic field generated by the main magnet 12. The radio frequency antenna unit 20 is controlled by an RF control unit 21 of the magnetic resonance apparatus 10 and radiates radio frequency magnetic resonance sequences into an examination space which is substantially formed by a patient receiving region 14 of the magnetic resonance apparatus 10. The RF transmitting coil 20 is also configured for the reception of magnetic resonance signals.

(10) For control of the main magnet 12, the gradient control unit 19 and, for control of the RF control unit 21, the magnetic resonance apparatus 10 has a system control unit 22. The system control unit 22 centrally controls the magnetic resonance apparatus 10, for example, the execution of a pre-determined imaging gradient echo sequence. Furthermore, the system control unit 22 includes an image reconstruction unit (not disclosed in detail) for calculating magnetic resonance images from magnetic resonance signals acquired during the magnetic resonance examination. Furthermore, the magnetic resonance apparatus 10 includes a user interface 23 which is connected to the system control unit 22. Control information such as, for example, imaging parameters and calculated magnetic resonance images may be displayed on a display unit 24, for example, on at least one monitor, of the user interface 23 for medical operating personnel. In addition, the user interface 23 has an input unit 25 by which information and/or parameters may be input by the operating medical personnel during a scanning procedure.

(11) In addition, the magnetic resonance unit has a local coil 27 which is arranged on the patient 15. In this example, for reasons of clear representation, the local coil 27 is shown with only three coil elements A.sub.1, A.sub.2, A.sub.3. The number of coil elements may also, however, be larger or smaller. Each of these coil elements A.sub.1, A.sub.2, A.sub.3 is designed for the reception of RF signals within the frequency band of magnetic resonance signals.

(12) The coil elements A.sub.1, A.sub.2, A.sub.3 are each part of a receiving channel, e.g., 3 receiving channels are represented here. By the receiving channels, the signals received by the coil elements A.sub.1, A.sub.2, A.sub.3 are transferred to an evaluating unit 26.

(13) Furthermore, the magnetic resonance apparatus includes an RF transmitter 13 configured to emit a useful excitation signal. The useful excitation signal may enter into interaction with an examination object, for example, the patient 15. By the interaction, the useful excitation signal may change into a useful signal. The frequency portions of the useful signal lie at least partially within the frequency band of the magnetic resonance signals and may thus also be received by the coil elements A.sub.1, A.sub.2, A.sub.3 of the local coil 27.

(14) It is conceivable that the magnetic resonance apparatus 10, (e.g., the RF transmitter 13), has a coupler (not shown here) configured to feed a portion of the useful excitation signal to the evaluating unit 26.

(15) In FIG. 2, a method for determining an item of evaluation information from a reception signal received by the magnetic resonance apparatus 10 is shown. The magnetic resonance apparatus 10 is herein configured to generate a magnetic resonance signal in a second frequency band. In act 130, a useful signal is generated in a first frequency band, wherein the first frequency band lies at least partially, (e.g., completely), within the second frequency band. In act 140, the useful signal is received or recorded by a receiving unit of the magnetic resonance apparatus 10. The receiving unit may include coil elements A.sub.1, A.sub.2, A.sub.3. In act 150, an item of evaluation information characterizing a useful signal is determined from the reception signal.

(16) In FIG. 3, for example, a first frequency band FB.sub.1 of the useful signal and a second frequency band FB.sub.2 of the magnetic resonance signal is shown. Entered on the horizontal axis of the graph is the frequency f. Herein, the first frequency band FB.sub.1 is situated completely within the second frequency band FB.sub.2. Thus, the receiving unit, which naturally is configured to cover the first frequency band FB.sub.2 in order to be able to receive magnetic resonance signals is also capable of receiving signals in the second frequency band. Thereby, useful signals may be sent along as well on the second frequency band FB.sub.2, the magnetic resonance frequency band. An additional, separate receiving unit is thus not necessary.

(17) In FIG. 4, an extended method for determining an item of evaluation information from a reception signal received by the magnetic resonance apparatus 10 is shown. Herein, a useful excitation signal is generated in act 110. By an interaction with an examination object, for example, a patient 15 or a receiver chain, in act 120, the useful excitation signal is changed into the useful signal so that in act 130, the useful signal is generated. There follow the acts 140 and 150 already disclosed in FIG. 2. In act 160, the evaluation information determined in act 150 is further processed. If, for example, in act 120 an interaction with a receiver chain takes place, in act 160, a property of the receiver chain may be determined. This may be advantageous, for example, during a monitoring of a receiving unit for service purposes and/or for delimiting an error cause in the receiver chain.

(18) The method may also include further acts. Thus, in act 210, a magnetic resonance excitation signal may be generated, the frequency portions of which lie within the second frequency band FB.sub.2. By an interaction with the patient 15 in act 220, magnetic resonance signals may be generated in act 230. The useful signal generated in act 130 and the magnetic resonance signal generated in act 230 may become overlaid to a reception signal and be received in act 140. In act 150, an item of evaluation information characterizing a useful signal is determined from the reception signal. Associated therewith, in act 240, the magnetic resonance signal is reconstructed. Finally in act 250, one or more magnetic resonance images are calculated from the magnetic resonance signal. Evaluation information from act 160 may also be included in this calculation. If, for example, in act 120, an interaction with a patient 15 has taken place, then, in act 160, a movement of the patient may be determined. This information may be considered in the context of a movement correction in the calculation of the magnetic resonance images in act 250.

(19) Possible aspects of the proposed method are now to be described in detail making reference to FIG. 5 together with FIGS. 3 and 4.

(20) A, particularly digital, control signal E is emitted to the RF transmitter 13, whereupon the RF transmitter 13 emits in act 110, a useful excitation signal within the bandwidth of the magnetic resonance experiment FB.sub.2. By an interaction with the patient 15 in act 130, the useful excitation signal is converted in act 120 into a useful signal. Useful excitation signals and the useful signal arising therefrom may differ insignificantly in their frequency spectrum, so that the useful excitation signal lies in the first frequency band FB.sub.1.

(21) In act 140, the useful signal is recorded by the coil elements A.sub.1, A.sub.2, A.sub.3 and the receiving components lying behind them, each of which, together with the respective coil element, forms a receiving channel. This may take place temporally together with the recording of magnetic resonance signals or separately from them.

(22) In the case that magnetic resonance signals are recorded simultaneously, in act 210 the RF transmitting coil 20, controlled by the RF control unit, emits magnetic resonance excitation signals which interact in act 220 with the patient, so that in act 230, magnetic resonance signals are generated. The magnetic resonance signals would then be received in act 140, overlaid with the useful signal as a reception signal by the coil elements A.sub.1, A.sub.2, A.sub.3. Each coil element A.sub.1, A.sub.2, A.sub.3 thereby receives a reception signal portion of the reception signal.

(23) The useful excitation signal is known, (e.g., exactly), in amplitude and phase. This is provided, for example, in that the control signal E is known exactly and the RF transmitter 13 is very precisely calibrated. A further possibility lies therein that a coupler (not shown here) decouples a small part C of the useful excitation signal and feeds it to the evaluating unit 26. As a result, the useful excitation signal may be used for determining the weighting factor w.sub.kn.

(24) A subsequent signal processing in act 150 subtracts the useful signal from each individual receiving channel. Before the subtraction, the weighting factors w.sub.kn (n=1, 2 or 3), with which the useful signal is extracted from the respective reception signal portion, are determined. The weighting factors w.sub.kn are therein determined such that the useful signal is minimized following the subtraction into corrected reception signal portions S.sub.kn (n=1, 2 or 3). An elimination of such “disturbance signals” by suitable subtraction may be carried out, for example, with a sidelobe canceler method. Disturbance suppression of more than 60 dB may be achieved thereby. In the event of a simultaneous reception of magnetic resonance signals, therefore, on the basis of the weighting factors w.sub.kn, the magnetic resonance signal is reconstructed from the reception signal.

(25) The corrected reception signal portions S.sub.kn may be combined in act 240, weighted in a known manner with coil sensitivities w.sub.n (n=1, 2 or 3), to an image data set Σ. Therefrom, in act 250, one or more magnetic resonance images are calculated.

(26) Rather than evaluating the levels (amplitude and phase) of the useful signal itself, in act 160 in particular, the weighting factors w.sub.kn may be used as evaluation information. The weighting factors w.sub.kn may be used, in particular, to determine a movement of the patient 15 or a property of the receiver chain. For this purpose, for example, the temporal sequence w.sub.kn(t) may be determined. Furthermore, the weighting factors w.sub.kn, may be compared with previously known values or with values of adjacent coil elements. For example, an altered coupling between the useful signal and the coil element may affect the weighting factor accordingly, on the basis of the patient movement, and this complex-valued number may be used directly to observe patient movement.

(27) Finally, it should again be noted that the method described above in detail and the magnetic resonance apparatus disclosed are merely exemplary embodiments which may be modified by a person skilled in the art in a broad variety of ways without departing from the scope of the disclosure. Further, the use of the indefinite article “a” or “an” does not preclude the possibility that the relevant features are also present plurally. Similarly, the expression “unit” does not preclude the relevant components consisting of a plurality of cooperating subcomponents which may also be spatially distributed if necessary.

(28) 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 disclosure. 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.

(29) While the present disclosure 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.