Operation of a transmission device of a magnetic resonance device

Abstract

A method for operating a transmission device of a magnetic resonance device is provided. In order to actuate coil elements of a radiofrequency coil with different phases, phase differences in a reference plane are taken into consideration. In a first calibration measurement to be performed once for each transmission path, a first phase of a transmitted radiofrequency signal is measured by an internal measuring device installed permanently in the transmission device spaced apart from the reference plane. A second phase of the transmitted radiofrequency signal is measured by a second, external measuring device to be connected to the reference plane for the first calibration measurement. At least one phase of the first phase and the second phase is taken into consideration in the phase-accurate actuating of the coil elements and/or for correcting further measurements with the internal measuring device.

Claims

1. A method for operating a transmission device of a magnetic resonance device, the transmission device being configured to independently actuate a plurality of coil elements of a radiofrequency coil over different transmission paths, wherein phase differences in a reference plane are taken into consideration to actuate the plurality of coil elements with different phases, the method comprising: measuring, by an internal measuring device installed permanently in the transmission device spaced apart from the reference plane, a first phase of a transmitted radiofrequency signal in a first calibration measurement performed once for each transmission path; measuring, by an external measuring device to be connected to the reference plane, a second phase of the transmitted radiofrequency signal for the first calibration measurement; and determining, for each transmission path, a correction value from a difference between the first phase and the second phase and subtracting the determined correction value from following measurements with the internal measuring device in order to determine a present phase at the reference plane, subtracting, for each transmission path, the second phase from a target phase for determining an actuation phase, with which a radiofrequency signal is generated in order to obtain the target phase at the reference plane, or a combination thereof, wherein at least one phase of the first phase and the second phase is taken into consideration in the phase-accurate actuating of the plurality of coil elements, for correcting further measurements with the internal measuring device, or a combination thereof.

2. The method of claim 1, wherein the reference plane is at plug-in location for the plurality of coil elements.

3. The method of claim 1, further comprising using, in each case, one directional coupler that is connected to a receiver having an analog-to-digital converter as the internal measuring device and the external measuring device.

4. The method of claim 3, wherein the receiver that is associated with the external measuring device and is installed permanently in the transmission device is used exclusively for the external measuring device.

5. The method of claim 3, wherein the receivers for the internal measuring devices are also used for receiving magnetic resonance signals with the radiofrequency coil.

6. The method of claim 3, further comprising: generating signals on the transmission paths using one modulator in each case, wherein the internal measuring devices each include one of the modulators or the receiver; during the first calibration measurement, comparing the phases of all of the receivers with a phase of a predetermined reference modulator of the modulators and storing discrepancies as receiver reference phases, comparing the phases of all of the modulators with a phase of a predetermined reference receiver of the receivers and storing discrepancies as modulator reference phases, or a combination thereof; during a second calibration measurement following restarting of the transmission device, comparing the phases of all of the receivers with the phase of the predetermined reference modulator, and storing discrepancies as present receiver phases, comparing the phases of all of the modulators with the phase of the predetermined reference receiver and storing discrepancies as present modulator phases, or a combination thereof, wherein, after every second calibration measurement, in the case of phase-accurate actuating, correction, or phase-accurate actuating and correction, for each transmission path, at least one of the differences between the present receiver phase and the receiver reference phase and between the present modulator phase and the modulator reference phase is taken into consideration.

7. The method of claim 1, further comprising: transmitting a clearly defined test signal on each transmission path as part of the first calibration measurement; measuring, for each test signal using the internal measuring device, an amplitude and a phase of a forward test signal and a return test signal, and storing the amplitude and the phase of the forward test signal and the return test signal as check values, wherein at at least one later point in time in a check measurement with the same configuration, for each transmission path, the test signal is transmitted again and, for each test signal, the amplitude and the phase of the forward and the return test signal are measured by the internal measuring device; and establishing and outputting a cable fault when there is a discrepancy in the check values for a transmission path.

8. The method of claim 6, wherein the at least one difference is taken into consideration such that the difference between the present receiver phase and the receiver reference phase is added to the correction value determined as the difference between the first phase and the second phase, after every second calibration measurement, the difference between the present modulator phase and the modulator reference phase is subtracted from the target phase for determining the actuation phase, or a combination thereof.

9. The method of claim 6, wherein the second calibration measurement is performed automatically every time the transmission device is restarted.

10. The method of claim 6, further comprising determining the receiver reference phases and the present receiver phases, the determining comprising distributing a comparison signal of the determined reference modulator among the receivers using a splitter.

11. The method of claim 10, further comprising determining the modulator reference phases and the present modulator phases, the determining comprising passing the comparison signal of the modulators on to the specific reference receiver via a combiner.

12. A transmission device for a magnetic resonance device, the transmission device being configured for independently actuating a plurality of coil elements of a radiofrequency coil, the transmission device comprising: a plurality of transmission paths, each transmission path of the plurality of transmission paths comprising: a modulator; an amplifier device; an internal measuring device connected downstream of the amplifier device, the internal measuring device configured for measuring a first phase of a transmitted radiofrequency signal; a plug-in location considered as reference plane for a coil element of the plurality of coil elements; an external measuring device that is connectable to the plug-in location, the external measuring device configured for measuring a second phase of a transmitted radiofrequency signal; and a control device configured to: operate the transmission device; measure, using the internal measuring device, which is installed permanently in the transmission device spaced apart from the reference plane, the first phase of the transmitted radiofrequency signal in a first calibration measurement performed once for each transmission path of the plurality of transmission paths; and measure, using the external measuring device connected to the reference plane, the second phase of the transmitted radiofrequency signal for the first calibration measurement; and take at least one phase of the first phase and the second phase into consideration in the phase-accurate actuating of the plurality of coil elements, for correcting further measurements with the internal measuring device, or a combination thereof, wherein the transmission device is further configured to independently actuate the plurality of coil elements of the radiofrequency coil over the plurality of transmission paths, and wherein the control device is configured to actuate the plurality of coil elements with different phases taking phase differences in the reference plane into consideration.

13. A method for operating a transmission device of a magnetic resonance device, the transmission device being configured to independently actuate a plurality of coil elements of a radiofrequency coil over different transmission paths, wherein phase differences in a reference plane are taken into consideration to actuate the plurality of coil elements with different phases, the method comprising: measuring, by an internal measuring device installed permanently in the transmission device spaced apart from the reference plane, a first phase of a transmitted radiofrequency signal in a first calibration measurement performed once for each transmission path; measuring, by an external measuring device to be connected to the reference plane, a second phase of the transmitted radiofrequency signal for the first calibration measurement; transmitting a clearly defined test signal on each transmission path as part of the first calibration measurement; measuring, for each test signal using the internal measuring device, an amplitude and a phase of a forward test signal and a return test signal, and storing the amplitude and the phase of the forward test signal and the return test signal as check values, wherein at at least one later point in time in a check measurement with the same configuration, for each transmission path, the test signal is transmitted again and, for each test signal, the amplitude and the phase of the forward and the return test signal are measured by the internal measuring device; and establishing and outputting a cable fault when there is a discrepancy in the check values for a transmission path, wherein at least one phase of the first phase and the second phase is taken into consideration in the phase-accurate actuating of the plurality of coil elements, for correcting further measurements with the internal measuring device, or a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows one embodiment of a magnetic resonance device including a transmission device; and

(2) FIG. 2 shows one embodiment of a transmission device.

DETAILED DESCRIPTION

(3) FIG. 1 shows one embodiment of a magnetic resonance device 1 that, as is not illustrated in more detail here for reasons of clarity, includes components that are conventional in the prior art. For example, a main magnet unit includes a superconducting main magnet. The main magnet unit defines a patient area, into which a patient couch may be inserted. In addition, a gradient coil arrangement is provided surrounding the patient area.

(4) Radiofrequency signals for exciting the nuclear spins are generated by a radiofrequency multichannel transmission system 2 in the magnetic resonance device 1. The radiofrequency multichannel transmission system includes a radiofrequency coil 3 (e.g., a body coil that includes a plurality of independently actuatable coil elements 4). In one embodiment, with knowledge of the magnetic fields (e.g., may be measured and stored as B1 maps) produced by the individual coil elements 4, any desired excitations may be produced (e.g., the coil elements 4 are actuated with different phases with the result that a phase difference is formed and results in intentional interference in specific regions). Since the phase response of the coil elements 4 and corresponding cables 5 is already known in principle and may be supplied by the manufacturer of the coil elements 4 in the form of a model, this is not necessarily the case for the transmission device 6, which provides the radiofrequency signals to be transmitted via the coil elements 4. In order to allow phase-accurate actuation and checking of the correct phase differences, the phase differences at a reference plane 7, which, for example, is defined by the plug-in locations 8 of the transmission device 6, are to be known. One or more of the present embodiments deal with the calibration of the transmission device 6 with respect to possible phase differences during transmission and during the check measurement of transmitted radiofrequency signals and during use of the calibration information during conventional operation of the transmission device 6.

(5) For this purpose, the structure of the transmission device 6 is illustrated in more detail with reference to FIG. 2. FIG. 2 shows the principle working relationships of different components, but does not reproduce a precise circuit diagram. The specific realization of this is possible for a person skilled in the art.

(6) In the transmission device 6, a transmission path is provided for each channel (e.g., each coil element 4). In the transmission path, the radiofrequency signal is generated as a low-level signal by a modulator 9. The low-level signal is passed on to a radiofrequency amplifier device 10 and amplified at the radiofrequency amplifier device 10 to the desired amplitude. The radiofrequency signal thus amplified may be passed on to the plug-in location 8. In this case, the components are not shown for each of the n transmission paths but, for reasons of clarity, only for the first transmission path, i=1, and the last transmission path, i=n. The other components are indicated by corresponding dots.

(7) Owing to the spatial and electromagnetic field conditions, in a magnetic resonance device 1, an internal measuring device that picks up the phase and amplitude of the radiofrequency signal may not be arranged directly at the plug-in location 8 (e.g., the reference plane 7). Therefore, a cable length between an internal measuring device and the plug-in location 8 that may be different from transmission channel to transmission channel is present, and in addition, there may be differences between the internal measuring devices themselves. In this case, the internal measuring devices connected downstream of the amplifier device 10 are realized in each case by a directional coupler 11 and a receiver 12. The receiver 12 contains a demodulator and an analog-to-digital converter.

(8) The operation of the transmission device 6 is controlled via a control device 22 that also implements the method according to one or more of the present embodiments.

(9) The method according to one or more of the present embodiments enables operation of the transmission device 6, which allows phase-accurate transmission and detection of radiofrequency pulses (e.g., radiofrequency signals) in a radiofrequency coil 3 including n coil elements 4. For this purpose, a series of calibration measurements is performed. These calibration measurements may be divided into a first calibration measurement (e.g., tune-up) that only is to be performed once, and second calibration measurements that are to be performed each time the transmission device 6 is restarted and will overall be illustrated in more detail below.

(10) When the transmission device 6 is first connected, after wiring between the components of the transmission device 6, the following measurements are performed once. Prior to completion of the measurements, no system restart of the transmission device 6 is performed in order to avoid sudden changes in phase of the modulators 9 and the receivers 12.

(11) An external measuring device that has a directional coupler 13 and a receiver 14, which is, for example, installed permanently in the transmission device 6, is used for a first submeasurement of the first calibration measurement performed at the beginning. The component with the directional coupler 13 may be connected directly in the plug-in locations 8, with the result that the phase may actually be measured in the reference plane 7. In this case, a 50 termination 15 (dummy load) is used, which defines an ideal coil. In one embodiment, via the external measuring device, the phases may be measured for all transmission paths at the reference plane 7 since the external measuring device may be connected successively to all plug-in locations 8. Since the measurements are performed with the same external measuring device, the phases are comparable. The modulators 9 are actuated with the same phase (e.g., a predetermined radiofrequency signal (test pulse) for each measurement).

(12) The measurement procedure is as follows. The external directional coupler is connected to the plug-in location 8 of the i-th transmission path. A predetermined radiofrequency signal is transmitted, and the phase .sub.i is measured at the external directional coupler 13 via the receiver 14 and thus via the signal path 16. The phase .sub.i will be referred to below as the second phase. The second phases .sub.i are stored and may be used afterwards in order to calculate a corrected actuation phase .sub.c,i, with which the i-th modulator 9 is to be actuated in order to obtain the target phase .sub.z,i in the reference plane 7. The target phase .sub.z,i results from desired phase differences. This provides that when the target phases .sub.t,i are known, the control device 22 may first calculate the actuation phase for each transmission path i, as long as still no system restart has been performed:
.sub.c,i=.sub.t,i.sub.i

(13) In the first submeasurement, however, a first phase .sub.i is also measured at the internal directional coupler 11 of the internal measuring device for the predetermined radiofrequency signal (e.g., test pulse). The first phase and the second phase are measured for all n transmission channels. In this case, user support may be implemented by actuation of an output device by the control device 22, which may give instruction, for example, to connect the external measuring device (e.g., the directional coupler 13) to a specific plug-in location and then to actuate an operating element in order to indicate measurement readiness.

(14) If the first and second phases are known, further measurements at the directional couplers 10 (e.g., at least up to a system restart) may also be converted such that the phase is obtained at the reference plane 7. If the phase measured at the i-th directional coupler 11 is denoted by .sub.m,i, a correction is to be made by the control device 22 in order to obtain the phase .sub.s,i at the associated plug-in location 8, as follows:
.sub.s,i=.sub.i(.sub.i.sub.m,i)=.sub.m,i(.sub.i.sub.i)

(15) The value (.sub.i.sub.i) is therefore a correction value, which is likewise stored in the control device 22.

(16) The operating method according to one or more of the present embodiments does, however, also take into consideration further effects (e.g., the fact that the phase relationships between different modulators 9 and different receivers 12 no longer need to be the same as in the case of the first calibration measurement after restarting of the transmission device 6, and the possibility of cable breakages, with the result that further submeasurements in the context of the first calibration measurement are performed). Once, therefore, the first phase .sub.i has been measured over the signal path 17 and the second phase .sub.i has been measured over the signal path 16, the external measuring device is again removed from the coil plug-in locations 8, and the phases of all of the receivers 12 are compared, as second submeasurement, with a uniform reference signal always from the same modulator 9. The discrepancies are stored as receiver reference phases .sub.i. For this purpose, the transmission device 6 has a splitter 18 that may be connected via a corresponding switching device 19 for the purpose of the second submeasurement by the control device 22. The splitter 18 distributes the signal of the fixed, predetermined reference modulator 9 amongst the receivers 12, with the result that the determination of .sub.i may take place. The receiver reference phases .sub.i are stored.

(17) In a third submeasurement, the phases of all of the modulators 9 are compared with the phase of a fixed, predetermined reference receiver 12. The discrepancies are stored as modulator reference phases .sub.i. For this purpose, a combiner 20 that also has an associated corresponding switching device 21 actuatable by the control device 22 is used. The actual measurement then takes place in the reference receiver 12. The stored values .sub.i and .sub.i are used later, after a restart of the transmission device 6 and the second calibration measurement, in order to be able to establish sudden changes in phase of the individual modulators 9 or receivers 12.

(18) A fourth submeasurement that is performed by the internal measuring device (e.g., at the directional couplers 11) also takes place. In this case, the above-described correction value (.sub.i.sub.i) is already used. In order to be able to establish, at a later point in time, cable breakages or other cable damage, a clearly defined test signal is transmitted on each transmission path. A clearly defined load situation according to the plug-in location 8 is also provided, however, whether it be an open end or the already connected coil elements 4 of the radiofrequency coil 3. For this test signal, the amplitude and the phase of the forward and return test signal are measured by the internal measuring device. Correspondingly, the receivers 12 symbolize devices for the forward and return waves. The amplitudes and phases of the forward and return test signal are stored as check values for each transmission path.

(19) Thus, the first calibration measurement is completed during tune-up, and the operation of the transmission device 6 may be resumed. In accordance with the two formulae above, actuation phases and corrected measured values relating to the reference plane 7 are obtained.

(20) A second calibration measurement is performed after restarting of the transmission device 6. This is because, after a restart, the phases .sub.i of the modulators 9 and the phases .sub.i of the receivers 12 may change. Therefore, in the second calibration measurement, the second and third submeasurements of the first calibration measurement are repeated automatically (e.g., without the intervention of operating personnel being required), with the result that values *.sub.i and *.sub.i result. The automated implementation of the measurements is produced by the use of the actuatable or programmable switching devices 19, 21. Such a switching device may also be provided for the signal path 17.

(21) If the present receiver phases *.sub.i and the present modulator phases *.sub.i are known first, the sudden changes in phase that may be present at the modulators 9 and the receivers 12 may also be taken into consideration, and the following results for the correct actuation phase .sub.c,i:
.sub.c,i=.sub.t,i.sub.i(*.sub.i.sub.i).

(22) Correspondingly, the formula with which the phases in the reference plane 7 may be determined from the phases at the directional couplers 11 is updated as follows:
.sub.s,i=.sub.m,i(.sub.i.sub.i)(*.sub.i.sub.i).

(23) In addition, after a restart of the transmission device 6, the system 2 is tested for broken transmission cables. While producing the same circumstances as in the fourth submeasurement of the first calibration measurement (e.g., similar to the tune-up measurement), the clearly defined test signal in a check measurement is transmitted on all transmission paths in order. The phases and amplitudes of the forward and return test signal are measured again after application of the corrections for all transmission paths and compared with the check values. If there is a cable breakage or cable damage between the amplifier device 10 and the directional coupler 11, the amplitude and the phase of the forward wave are changed. If there is a cable breakage or cable damage between the directional coupler 11 and the coil plug-in location 8 in the case of an open end or the coil element 4 in the case of a connected radiofrequency coil 3, the amplitude and the phase of the return wave are changed. Cable length changes are easily identifiable from the phase. If a fault is established, the operation of the transmission device 6 and therefore of the entire radiofrequency multichannel transmission system 2 is interrupted.

(24) Whether a radiofrequency coil 3 and/or which radiofrequency coil 3 is connected to the plug-in locations may be established using detection apparatuses that are known in principle from the prior art. Submeasurements of the two calibration measurements that relate to the check values may be implemented a plurality of times for different load or connection states. Thus, it is possible to distinguish, for example, whether there is a problem in the cable from the plug-in location to the coil element 4 or within the transmission device 6.

(25) Although the invention has been illustrated and described in detail by the exemplary embodiments, the invention is not restricted by the disclosed examples, and other variations may be derived from this by a person skilled in the art without departing from the scope of protection of the invention.

(26) 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 can, 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.

(27) While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can 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.