Monitoring architecture for magnetic resonance transmission systems and method for operating same

Abstract

A magnetic resonance tomography unit includes a transmitter, a transmission monitoring device for monitoring an excitation signal from the transmitter, and a plurality of transmit antennas. The magnetic resonance tomography unit also includes a switching device configured to bring the transmission monitoring device selectively into a signal connection to one transmit antenna of the plurality of transmit antennas. A method for operating the magnetic resonance tomography unit is also provided.

Claims

1. A magnetic resonance tomography unit comprises: a transmitter; a transmission monitoring device configured to monitor an excitation signal from the transmitter; a plurality of transmit antennas; and a switching device configured to bring the transmission monitoring device selectively into a signal connection to one transmit antenna of the plurality of transmit antennas.

2. The magnetic resonance tomography unit of claim 1, wherein the transmission monitoring device comprises a plurality of sensors configured to detect a radiofrequency power, the plurality of sensors being respectively arranged in a transmit path of the plurality of transmit antennas.

3. The magnetic resonance tomography unit of claim 2, wherein the switching device is further configured to bring, controlled by the transmission monitoring device, at least one predetermined sensor of the plurality of sensors into a signal connection to the transmission monitoring device.

4. The magnetic resonance tomography unit of claim 3, wherein the transmission monitoring device is further configured to scale a signal from the at least one predetermined sensor by a predetermined weighting.

5. The magnetic resonance tomography unit of claim 1, further comprising a sensor with a signal connection to the transmission monitoring device, wherein the sensor is arranged in a transmit path, and wherein the switching device is further configured to bring, controlled by the transmission monitoring device, the transmit path into a signal connection to a predetermined transmit antenna for emitting a signal.

6. The magnetic resonance tomography unit of claim 5, wherein the transmit path has a hybrid coupler having at least two signal outputs, and wherein the switching device is further configured to connect a signal output of the hybrid coupler selectively to two different transmit antennas.

7. The magnetic resonance tomography unit of claim 5, wherein the transmit path has a hybrid coupler having at least two signal outputs, and wherein the switching device is further configured to connect the transmit path to the predetermined transmit antenna, bypassing the hybrid coupler.

8. A method for operating a magnetic resonance tomography unit including a transmitter, a transmission monitoring device for monitoring an excitation signal from the transmitter, a plurality of transmit antennas, and a switching device configured to bring the transmission monitoring device selectively into a signal connection to one transmit antenna of the plurality of transmit antennas, the method comprising: connecting a transmit local coil to the magnetic resonance tomography unit; making a signal connection between the transmission monitoring device and the transmit local coil using the switching device; emitting an excitation signal from the transmitter via the transmit local coil; receiving a monitoring signal from the transmit local coil via the signal connection to the transmission monitoring device; comparing the monitoring signal with a reference value; and interrupting the emission depending on the comparison.

9. The method of claim 8, wherein the magnetic resonance tomography unit further includes a hybrid coupler, wherein the connecting comprises connecting the transmit local coil to a first signal output of the hybrid coupler.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic diagram of one embodiment of a magnetic resonance tomography unit;

(2) FIG. 2 shows a schematic diagram of components specific to an exemplary embodiment;

(3) FIG. 3 shows a schematic diagram of components specific to an exemplary embodiment;

(4) FIG. 4 shows a schematic diagram of components specific to an exemplary embodiment; and

(5) FIG. 5 shows a schematic flow diagram showing a method according to an embodiment.

DETAILED DESCRIPTION

(6) FIG. 1 shows a schematic diagram of an embodiment of a magnetic resonance tomography unit 1.

(7) The magnet unit 10 has a field magnet 11 that produces a static magnetic field B0 for aligning nuclear spins of samples or of the patient 100 in an acquisition region. The acquisition region is characterized by an extremely homogeneous static magnetic field B0. The homogeneity relates, for example, to the magnetic field strength or magnitude. The acquisition region is approximately spherical and located in a patient tunnel 16 that extends through the magnet unit 10 in a longitudinal direction 2. A patient couch 30 may be moved inside the patient tunnel 16 by the travel unit 36. The field magnet 11 is usually a superconducting magnet that may provide magnetic fields having a magnetic flux density of up to 3 T or even higher in the latest equipment. For lower magnetic field strengths, however, permanent magnets or electromagnets having normal-conducting coils may also be used.

(8) The magnet unit 10 also has gradient coils 12 that are configured to superimpose time-varying and spatially varying magnetic fields in three spatial dimensions on the magnetic field B0 for the purpose of spatial discrimination of the acquired mapping regions in the volume of interest. The gradient coils 12 are usually coils made of normal-conducting wires that may generate mutually orthogonal fields in the volume of interest.

(9) The magnet unit 10 also has a body coil 14 that is configured to radiate into the volume of interest a radiofrequency signal supplied via a signal line, and to receive resonance signals emitted by the patient 100 and to output the resonance signals via a signal line.

(10) A control unit 20 supplies the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14, and analyzes the received signals.

(11) Thus, the control unit 20 has a gradient controller 21 that is configured to supply the gradient coils 12 via supply lines with variable currents that provide, coordinated in time, the desired gradient fields in the volume of interest.

(12) In addition, the control unit 20 has a radiofrequency unit 22 that is configured to produce a radiofrequency pulse having a defined variation over time, amplitude, and spectral power distribution for the purpose of exciting magnetic resonance of the nuclear spins in the patient 100. Pulse powers may reach in the region of kilowatts here. The excitation signals may be radiated via the body coil 14 or via a local transmit antenna into the patient 100.

(13) A controller 23 communicates via a signal bus 25 with the gradient controller 21 and the radiofrequency unit 22.

(14) Arranged on the patient 100 is a local coil 50 that may be connected via a connecting line 33 to the radiofrequency unit 22 and a receiver of the radiofrequency unit 22.

(15) The local coil 50 as the local transmit coil has a transmit function and is arranged on or against the patient 100 when only a subregion is to be examined Examples of local transmit coils are knee, chest, or head coils, for example.

(16) A transmission monitoring device 60 of the radiofrequency unit 22, which is described in greater detail with reference to FIGS. 2 to 4, monitors the transmit function.

(17) FIG. 2 shows components of the magnetic resonance tomography unit according to the present embodiments, which in one embodiment, are involved in the transmission process and the monitoring thereof.

(18) A radiofrequency signal to be emitted (e.g., an excitation signal) is produced in the radiofrequency unit 22. The control unit 20 coordinates the emission with the other components such as the gradient controller 21 as part of an image acquisition sequence. For example, control signals are transferred for this purpose via a signal bus 25.

(19) The radiofrequency unit has two signal outputs that have a signal connection to two transmit antennas (e.g., a body coil 14 and a local coil 50 as the local transmit antenna). In one embodiment, there are further signal outputs of the radiofrequency unit 22 (e.g., a further output with a signal connection to the body coil 14 in order to produce a circularly polarized alternating magnetic field) or for further local transmit coils.

(20) In the radiofrequency unit 22, the radiofrequency signals are provided, for example, by oscillators and radiofrequency power amplifiers, which are not shown in detail here for the sake of clarity.

(21) A sensor 61 for detecting information about the excitation signal is arranged in each of the signal connections between the radiofrequency unit and the transmit antennas, referred to below as the transmit path, via which transmit antennas the excitation signal is emitted. For example, the sensors may be one or more directional couplers in order to detect a forward and/or reverse radiofrequency amplitude and/or radiofrequency power. In one embodiment, a pickup coil that may be used to directly detect a radiofrequency alternating magnetic field produced by the excitation signal may be provided. The sensor 61 may also include initial parts of a signal conditioner (e.g., pre-amplifiers, matching elements, filters, or analog-to-digital converters).

(22) A switching device 62 has a signal connection to the sensors 61, from which the switching device 62 receives the produced signals containing information about the radiofrequency signals on the transmit paths. The switching device 62 also has a signal connection to the transmission monitoring device 60 and is configured to select and transfer to the transmission monitoring device, under the control of the magnetic resonance tomography unit 1, at least one of the signals from the sensors 61. In an embodiment that is not shown in FIG. 2 having a plurality of signal connections between the switching device 62 and the transmission monitoring device 60, however, there may also be a plurality of sensors 61 connected at one time to the transmission monitoring device 60 (e.g., in the case of a local coil array such as a spine coil). The signal connection between the sensor 61 and the transmission monitoring device 60 may be a low-power connection that may be switched and multiplexed using small and inexpensive switches (e.g., even by semiconductor switches).

(23) In one embodiment, additional transmit antennas are present beyond the transmit antennas shown in FIG. 2, with the sensors 61 of some transmit paths to these transmit antennas being permanently connected to the transmission monitoring device 60, and, for example, only the sensors 61 of transmit paths to local transmit antennas being switchably connected via the switching device 62.

(24) The transmission interference suppression device 60 may be configured to assess the signal according to the sensor 61 connected by the switching device 62. For example, the transmission monitoring device 60 may have a calibration memory, in which calibration data for each of the sensors 61 is stored. For example, these may be parameters for a weighting function that are used as multipliers of signal values. A table containing corresponding value pairs, with the transmission monitoring device 60 interpolating between the table values, may also be provided. Differences in the sensitivity, the characteristic, and/or offset of the sensors 61 may thereby be taken into account.

(25) FIG. 3 shows another embodiment. FIG. 3 differs in subject matter in that the sensor 61 is permanently arranged in the transmit path between the radiofrequency unit 22 and the switching device. The sensor 61 also has a permanent signal connection to the transmission monitoring device 60. In this embodiment, the switching device 62 does not switch the signal connection between different sensors 61 and the transmission monitoring device 60, but switches the transmit path after the switching device 62 to different transmit antennas. A plurality of transmit antennas may thereby be monitored by a single sensor 61.

(26) FIG. 4 shows a development of the embodiment from FIG. 3. In this embodiment, a hybrid coupler 63 is arranged between the radiofrequency unit 22 on the transmitter side and the sensors 61 and the switching device 62 on the antenna side. The excitation signal from the transmitter of the radiofrequency unit 22 to the transmit antenna is fed to one port. In an embodiment, the hybrid coupler produces therefrom two output signals offset in phase by 90 degrees. The output signals may be connected via the switching device 62, for example, to two connection points of a body coil 14 in order to produce a circularly polarized alternating magnetic field for exciting the nuclear spins. In another switch setting, the switching device connects a first signal output of the hybrid coupler 63 to a local transmit antenna. The signal outputs of the hybrid coupler 63 are selected in this case such that, given a second signal output that remains unconnected, a radiofrequency power present there is reflected to a terminating resistor 64 at a third signal output, and converted there into heat. In one embodiment, however, the switching device connects a further transmit antenna to the second signal output.

(27) The hybrid coupler 63 may reduce the number of required transmit output stages in the radiofrequency unit 22 while protecting by the terminating resistor 64 the output stage from reflected power if only one local transmit coil is connected to the first signal output.

(28) The invention is not restricted to the presented embodiments. For example, hybrid forms may also be provided. For example, only some of the antennas may be switchable (e.g., local transmit coils), and therefore, because of the lower transmit power that must be switched compared with the body coil 14, the switches may be simpler and less costly. In one embodiment, only some of the sensors 61 and/or the transmit paths may be switchable. For example, the body coil 14 or its sensors 61 may be permanently connected.

(29) FIG. 5 shows a flow diagram of an embodiment of a method.

(30) The method according to the present embodiments is performed on a magnetic resonance tomography unit according to the present embodiments.

(31) In act S10 of the method, a transmit local coil is connected to the magnetic resonance tomography unit 1. This may take place by an operator, for example, who plugs a transmit local coil 50 into a plug-in slot of the magnetic resonance tomography unit 1, thereby making an electrical connection. In one embodiment, the transmit local coil is part of an antenna array (e.g., part of a spine coil) that the controller 23 connects to the radiofrequency unit using a switching matrix.

(32) In an embodiment, the magnetic resonance tomography unit 1 has a hybrid coupler 63, and the transmit local coil is connected to a first signal output of the hybrid coupler 63. In one embodiment, given a second signal output that is unassigned, the power is reflected there and may be guided to a fourth signal output of the hybrid coupler 63 that is terminated by a terminating resistor 64.

(33) In another act of the method, the control unit 20 of the magnetic resonance tomography unit 1 makes a signal connection between the transmission monitoring device 60 and the transmit local coil using the switching device 62.

(34) This may take place by the sensor 61 having a fixed signal connection to the transmit local coil, or to the plug-in slot of the transmit local coil 50, and the switching device 62 making a feedback connection for the sensor signal from the sensor 61 to the transmission monitoring device 60 via the switching device 62. In this case, the number of signal inputs for sensor signals for the transmission monitoring device 60 may be less than the number of sensors 61.

(35) In another embodiment of the magnetic resonance tomography unit 1, the sensor 61 may be arranged in a fixed manner in a transmit path between radiofrequency unit 22 and the switching device 62, and a continuous signal connection may exist between the sensor 61 and the transmission monitoring device. The control unit 20 then makes the signal connection to the transmit local coil, by the switching device 62 switching the transmit path through to the transmission monitoring device 60.

(36) In a further act S30, the transmitter of the radiofrequency unit 22 emits the excitation signal via the transmit local coil.

(37) In another act S40, the transmission monitoring device 60 receives a monitoring signal from the transmit local coil via the signal connection. The monitoring signal has information about the excitation signal that the sensor 61 has obtained via the excitation signal. The monitoring signal may be produced, for example, by a directional coupler as the sensor 61, and may be a voltage that is proportional to a forward and/or reverse power. In the case of a pickup coil as the sensor 61, the voltage may also be proportional to a field strength produced by the transmit antenna. The signal may also be filtered, rectified, or even digitized.

(38) In a further act S50, the transmission monitoring device 60 compares the monitoring signal, or the information about the excitation signal, with a reference value. For example, the reference value may be a peak value that is not be exceeded. Also conceivable, for example, is a weighted average.

(39) The transmission interference suppression device 60 uses, for example, a different weighting, characteristic, or threshold value according to the connected sensor 61 or transmit antenna.

(40) In another act S60, depending on the comparison, the transmission monitoring device 60 interrupts the emission of the excitation signal by the radiofrequency unit 22. For example, the transmission monitoring device 60 may ascertain in the comparison that the excitation signal is exceeding a threshold value, and may send via the signal bus 25 an interrupt signal to the radiofrequency controller.

(41) Although the invention has been illustrated and described in detail using the exemplary embodiments, the invention is not limited by the disclosed examples, and a person skilled in the art may derive other variations therefrom without departing from the scope of protection of the invention.

(42) 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. Such new combinations are to be understood as forming a part of the present specification.

(43) 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.