Method and device for identifying a faulty detuned circuit in a magnetic resonance tomography device

Abstract

The invention relates to a method for checking a detuning device of an antenna coil of a magnetic resonance tomography device, and to a magnetic resonance tomography device according to the invention for carrying out the method. In one step of the method, the detuning device of the antenna coil is activated. In a further step, a first received signal and a second received signal are received. The received signals are compared and a warning signal is output depending on the result.

Description

Technical Field

[0001] The invention relates to a method for checking a detuning arrangement of an antenna coil of a magnetic resonance tomography system. In the method, a receive signal is received by means of a receiver via the antenna coil. Background Art

[0002] A magnetic resonance tomography system is an imaging device that uses a strong external magnetic field to align the nuclear spins of the object under examination for imaging, and excites the nuclear spins to precess about the alignment by means of an alternating magnetic field. The precession or return of the spins from the excited state to a state with lower energy in turn generates an alternating magnetic field in response, which is received by an antenna.

[0003] By means of the gradient magnetic field, a spatial encoding is applied to the signal, which subsequently enables the received signal to be associated with a volume element. The received signal is then analyzed and a three-dimensional imaging display of the examination object is provided.

[0004] In order to achieve the best possible signal-to-noise ratio (SNR), attempts are made to arrange the antenna coils used for reception as close as possible to the patient. This is achieved by so-called local coils, which are usually connected to the magnetic resonance tomography system using a cable connection. However, due to the high magnetic fields when exciting nuclear spins, a defective local coil can also pose a risk to the patient if the safety device fails. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to make the application of local coils more reliable.

[0006] The above technical problem is solved by the method according to the present invention.

[0007] The method according to the invention is provided for checking a detuning device of an antenna coil of a magnetic resonance tomography device. For the detuning device, there is the possibility of targeted activation of the detuning device by a control signal. This can be, for example, a DC voltage or a DC current applied to the detuning device, as is common in PIN diodes or switches. However, the control signal can also be another analog or digital signal, which in the control device of the detuning device causes the antenna coil to be detuned.

[0008] However, if a signal, in particular a high-frequency signal induced in the antenna coil, which can itself lead to harm to the patient by means of an induced voltage, activates the detuning device, as is the case, for example, for a passive fuse or a Zener diode, this is not considered in particular as an activation of the detuning device in the sense of the present invention. Preferably, the detuning device leads to a shift in the resonant frequency of the antenna coil, wherein reception of the high-frequency signal can also be achieved by a connected receiver. The detuning device can be realized, for example, by a diode with a variable capacitance or a switchable inductor or capacitor in a parallel or series resonant circuit of the antenna coil. However, it is conceivable that the detuning device also has passive components, which perform a limitation of the induced voltage or current. For example, detuning diodes are conceivable, which are detuned by an induced, rectified voltage without an external control signal, or cross-connected diodes or Zener diodes are conceivable, which short-circuit induced voltages that are greater than a limit value.

[0009] In one step of the method, a detuning device of the antenna coil is activated, for example by applying a current, a voltage or another control signal to a control device of the antenna coil.

[0010] In a further step, the receiver receives a first received signal of the antenna coil with the activated detuning device. In this case, the high-frequency current signal and / or voltage signal is regarded as a received signal, which is processed analogously or in an analog manner and / or arrives at the receiver digitally. In particular, the received signal has information about the amplitude, phase and / or spectral distribution. In this case, the receiver can be a special receiver for testing the detuning device, but is preferably a receiver of a magnetic resonance tomography device, which is also used to receive magnetic resonance signals from the magnetic resonance tomography device for imaging.

[0011] In a further step, a second receive signal of the antenna coil is received by means of a receiver. In this case, depending on the embodiment of the method, as will be described later in the present invention, the detuning device can be activated or not activated. What has already been mentioned applies to the receive signal and the receiver.

[0012] In another step, the test controller compares the first received signal with the second received signal. Here, the test controller can be, for example, a controller of a magnetic resonance tomography device or an image analysis or a dedicated processor. As a comparison of the first and second received signals, for example, it can be to find a difference or a quotient and to compare with a predetermined difference or quotient, or to a relationship with an average or maximum amplitude or energy. Here, the comparison is preferably not limited to an exact value, but can also be defined by a value range, which, for example, has a maximum of 5%, 10%, 20% or 50% width of one of the two values ​​of the first or second received signal, or in the case of a quotient, deviates from the value 1 by a factor less than 0.1, 0.2 or 0.5. In the framework of the comparison, it is also conceivable to further mathematically calculate these relationships. For this reason, an exemplary embodiment is provided below.

[0013] If the result of the comparison does not agree with the predetermined value range, the controller outputs a warning signal to the user via an output device and / or interrupts further image acquisition.

[0014] For example, it is conceivable that a change in the input signal over time, such as a decay, depends on the activated detuning device and that the function of the detuning device can therefore be inferred by comparing the two received signals. Advantageously, the method according to the invention allows a rapid check of the detuning device by means of components of a magnetic resonance tomography system.

[0015] The magnetic resonance tomography device according to the invention has a test device for testing the detuning device of the antenna coil of the magnetic resonance tomography device using a test controller. The test controller can be a dedicated processor or logic module, but can also be a processor of the magnetic resonance tomography device, which, through a program, also performs the tasks described in addition to image acquisition. The test controller is designed to activate the detuning device of the antenna coil, receive a first received signal using a receiver, receive a second received signal using a receiver, compare the first received signal with the second received signal, and output a warning signal when the result of the comparison is inconsistent with a predetermined relationship between the first received signal and the second received signal. The warning signal can be output to a user on a display or to the controller of the magnetic resonance tomography device, for example, in order to stop further image acquisition.

[0016] The magnetic resonance tomography device according to the invention shares the advantages of the method according to the invention.

[0017] The present invention also provides other advantageous embodiments.

[0018] In a possible embodiment of the method according to the invention, the method has a step of disabling the detuning device. The step of receiving the first received signal is carried out with the detuning device activated, and the step of receiving the second received signal is carried out with the detuning device switched off. In the comparison step, the noise level of the first received signal is compared with the noise level of the second received signal. For example, the amplitude or energy of the noise can be compared by taking a difference or a quotient. It is also conceivable to display the result by taking a logarithm over a larger dynamic range. It is also conceivable to take into account the spectral distribution of the noise energy caused by the detuning device through the change of the resonant frequency.

[0019] Comparing the two received signals with activated detuning device and with deactivated detuning device makes it possible in a simple manner to check the functionality of the active part of the detuning device.

[0020] In a conceivable embodiment of the method according to the invention, the transmitter of the magnetic resonance tomography device transmits a small signal during the step of receiving the first received signal and the second received signal. If the amplitude of the test pulse is low enough to avoid damage to the local coil or danger to the patient in the event of a local coil failure and not to overcontrol the receiver, it is considered a small signal. Therefore, the small signal or test pulse must have a low power or a reduced power. In this case, a power of less than 0.1 Watt, 1 Watt or 5 Watt is considered to be a reduced power. In this case, the reduced power can also be represented by the amplitude of the test pulse formed at the transmission antenna, wherein the effective voltage is usually less than 0.5V, 1V, 5V or 15V.

[0021] For example, a separate signal source may be provided as a transmitter for generating a small signal.

[0022] By controlling the receiver only with a small signal, the method according to the invention advantageously also makes it possible to detect small differences, for example slight attenuations or changes in the spectral distribution, when comparing the first received signal with the second received signal.

[0023] In a possible embodiment of the method according to the invention, a transmitter is provided, which is used to generate an excitation pulse of a magnetic resonance tomography device to generate a small signal. For this purpose, the transmitter has a switchable attenuation device between the signal generator and the power output stage, and the attenuation device is designed to attenuate the input signal of the power output stage in the receiving step so that the transmitter does not over-control the receiver. For this purpose, the transmitter must have a corresponding linear circuit technology so that it can generate a correspondingly small signal strength proportionally and with sufficiently small distortion and noise. For example, a switchable attenuation device can be provided to reduce the input signal by 40dB, 60dB, 80dB, 100dB or more, so that the transmitter also generates a correspondingly reduced output signal. However, a corresponding attenuation element can also be provided on the output side, so that the requirements for the linearity of the power output stage are reduced.

[0024] Advantageously, the use of a transmitter for generating excitation pulses when testing a detuned arrangement allows simple integration of the test into existing hardware.

[0025] In a conceivable embodiment of the method according to the invention, a transmitter is also provided, which is used to generate the excitation pulse of the magnetic resonance tomography device and also to generate a small signal. In this case, during the steps of receiving the first received signal and receiving the second received signal, no input signal is fed to the power output stage. In other words, the generation of the excitation signal is interrupted, or a signal with a constant output value is generated. For example, it is also conceivable to interrupt the connection between the signal generator and the power output stage or to connect the input of the power output stage to a constant potential. The power output stage then generates noise at the output, which is transmitted as a small signal during the test.

[0026] According to the invention, the use of the noise of the power output stage makes it possible to generate and transmit small signals using the transmitter without changing the transmitter, and thereby facilitates the implementation of the test procedure according to the invention.

[0027] In a possible embodiment of the method according to the invention, during the step of receiving the first receive signal and the second receive signal, a signal source is arranged in the patient channel as a transmitter of a small signal. The signal source transmits the small signal, wherein the power of the small signal changes by a predetermined magnitude between the step of receiving the first receive signal and the step of receiving the second receive signal. Preferably, the frequency of the high-frequency alternating field is equal to the Larmor frequency or is in a range close to the Larmor frequency.

[0028] The predetermined change in the size of the small signal advantageously provides the possibility of identifying the small signal and / or eliminating the background signal. Furthermore, the effectiveness of the passive elements of the detuning device can also be checked, for example, by means of the nonlinear behavior of the received signal.

[0029] In a conceivable embodiment of the method according to the invention, an active transmitter of the magnetic resonance tomography device generates a signal. Here, a transmitter or oscillator is considered to be an active transmitter: the transmitter or oscillator not only reflects the incident high frequency or temporarily stores it as a high-frequency current in a resonant circuit or temporarily stores it in an excited quantum state and then transmits it, but also generates a high-frequency signal based on the current fed from the energy source via the electrical conductor. This signal is a small signal that does not over-control the receiver. The test controller controls the transmitter in one step to change the power. For example, the test controller can increase or decrease the gain in the transmitter between receiving a first reception signal and receiving a second reception signal. It is also conceivable that the test controller changes the amplitude of the input signal of the transmitter.

[0030] By means of the test controller, the signal can be varied in a predetermined manner so that an amplitude can be advantageously set at which the detuning device and its correct functioning can be detected in different ways, for example by nonlinearity or a predetermined attenuation or energy absorption.

[0031] In a possible embodiment of the method according to the invention, the transmitter is a passive signal source, for example a resonator or an object with nuclear spins, which is temporarily excited by the high-frequency excitation signal of the magnetic resonance tomography device to emit an alternating magnetic field, which then decreases exponentially over time in a predetermined manner by decay. In this way, a high-frequency signal or a magnetic resonance signal that decreases over time is generated as a small signal between the step of receiving the first reception signal and the step of receiving the second reception signal.

[0032] Advantageously, a passive signal source as a transmitter requires no or only minimal changes to the magnetic resonance tomography system and nevertheless can provide a test signal in the frequency range of the desired Larmor frequency and with a small amplitude suitable for the receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The characteristics, features and advantages of the present invention described above and the implementation methods thereof will be more clearly understood with reference to the following description of the embodiments described in detail with reference to the accompanying drawings.

[0034] In the attached figure:

[0035] Figure 1 A schematic diagram of a magnetic resonance tomography apparatus having a local coil according to the present invention is shown;

[0036] Figure 2 A schematic diagram showing a testing device for a magnetic resonance tomography apparatus according to the present invention is shown;

[0037] Figure 3 A schematic flow chart of an exemplary method according to the invention is shown. DETAILED DESCRIPTION

[0038] Figure 1 A schematic diagram of an embodiment of a magnetic resonance tomography system 1 having a local coil 50 according to the invention is shown.

[0039] The magnet unit 10 has a field magnet 11, which generates a static magnetic field B0 for aligning the nuclear spins of a sample or patient 100 in a recording area. The recording area is characterized by an extremely uniform static magnetic field B0, wherein the uniformity particularly relates to the magnetic field strength or the amount of magnetic field strength. The recording area is almost spherical and is arranged in a patient channel 16, which extends through the magnet unit 10 in the longitudinal direction 2. The patient couch 30 can be moved in the patient channel 16 by a moving unit 36. The field magnet 11 is usually a superconducting magnet, which can provide a magnetic field with a magnetic flux density of up to 3T, or even higher for the latest equipment. However, for smaller field strengths, permanent magnets or electromagnets with normally conductive coils can also be used.

[0040] Furthermore, the magnet unit 10 has gradient coils 12 which are designed to superimpose variable magnetic fields in three spatial directions on the magnetic field B0 in order to spatially differentiate the acquired imaging regions in the examination volume. The gradient coils 12 are usually coils made of normally conducting wires which can generate mutually orthogonal fields in the examination volume.

[0041] The magnet unit 10 likewise has a body coil 14 which is designed to radiate high-frequency signals fed via signal lines into an examination volume and to receive resonance signals emitted by the patient 100 and output them via signal lines.

[0042] The control unit 20 supplies the magnet unit 10 with various signals for the gradient coil 12 and the body coil 14 , and analyzes the received signals.

[0043] The control unit 20 therefore has a gradient controller 21 which is designed to supply the gradient coils 12 via feed lines with variable currents which provide the desired gradient fields in the examination volume in a time-coordinated manner.

[0044] The control unit 20 also has a radio-frequency unit 22, which is designed to generate radio-frequency pulses with a predetermined time course, amplitude and spectral power distribution to excite nuclear spin magnetic resonance in the patient 100. Pulse powers in the kilowatt range can be achieved. The excitation pulses can be radiated into the patient 100 via the body coil 14 or via local transmission antennas.

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

[0046] A local coil 50 is arranged on the patient 100 and is connected to the high-frequency unit 22 and its receiver 65 via a connecting line 33 .

[0047] A defective local coil 50 poses a particular risk due to the direct proximity to the patient, for example, if a detuning device for detuning the local coil 50 fails and excessively high voltages and / or currents are induced in the local coil during an excitation pulse. The local coil 50 is particularly susceptible to failures due to long-term movement, plugging and unplugging of connections. It is therefore advantageous to test the basic functionality of the local coil 50 with the magnetic resonance tomography system in the configuration provided for image acquisition, at least before each image acquisition.

[0048] exist Figure 2 Schematically depicted are the elements of a test device that are relevant for the method according to the invention in different embodiments.

[0049] The local coil 50 has a detuning device 51 to prevent an excessive current from flowing and / or an excessive voltage from being induced in the antenna coil of the local coil 50 during an excitation pulse for nuclear spins, which could damage the local coil and in particular endanger the patient due to voltage or heat. Preferably, the detuning device 50 has a passive detuner 53 and an active detuner 52 for this purpose.

[0050] The passive detuner is implemented, for example, by two diodes connected in anti-parallel, so that when the induced AC voltage exceeds the threshold voltage of the diode, the diode becomes conductive and an additional LC element is connected in series to the antenna coil, thereby changing the resonant frequency and limiting the induced voltage.

[0051] The active detuner 52 is implemented by a PIN diode. The controller can apply a cutoff voltage and / or a forward current to the PIN diode, so that detuning can be performed through a changed junction capacitance or through a switching action combining a capacitor and / or an inductor connected in series or in parallel.

[0052] Other circuit and component combinations of the detuning device 51 are also conceivable. For example, the active detuner 52 and the passive detuner 53 can also be implemented separately without common paths or components. In particular, the object of the method according to the invention and the magnetic resonance tomography device according to the invention is to be able to check the function of as many components as possible or all components.

[0053] exist Figure 3 In the figure, the method according to the invention is schematically shown in a flow chart.

[0054] The method according to the invention provides that in step S10 a detuning device of an antenna coil, for example a local coil 50, is activated by a test controller. In this case, the test controller can be a controller 23 of the magnetic resonance tomography device 1, which is implemented by a corresponding program or program module. However, a dedicated processor or logic circuit, such as an FPGA, is also conceivable. In the case of activation, the active detuner 52 is controlled so that the local coil 50 or, for example, the body coil electrically connected to the active detuner 52 no longer resonates at a frequency that is optimal for the reception situation in the activated state. Typically, the optimal frequency is the Larmor frequency of the nuclear spins to be examined in the static magnetic field B0 of the magnetic resonance tomography device 1. In different embodiments of the method according to the invention, the activation of the active detuner 52 can be carried out at different points in time and not only at one time. Figure 3 As shown in the beginning.

[0055] The common point for different embodiments of the method according to the invention is that in step S20 and step S50, the second received signal is received by the receiver S50 at two different time points. For example, if further steps of the method are carried out between steps S20 and S50, or at least the received signal changes due to physical conditions between steps S20 and S50, for example due to attenuation or reduced excitation, these can be regarded as different time points. Therefore, the two times of steps S20 and S50 differ by, for example, more than 1 ms, 5 ms, 10 ms, 50 ms or 100 ms.

[0056] In step S60, the test controller compares the first received signal with the second received signal. For example, the difference of the amplitude or the square of the amplitude of the two received signals can be regarded as the comparison. It is also conceivable to find the phase difference or to perform a spectral analysis of the energy distribution at a plurality of or a plurality of frequencies. Functions applied thereto, such as finding the logarithm, can also be part of the comparison.

[0057] Finally, in step S70, if the result of the comparison is inconsistent with the predetermined relationship between the first received signal and the second received signal, a warning signal is output. Various examples of signals and expected predetermined relationships are given below. The warning signal can be output to the operator via an output terminal or can also be output directly to the control unit 20, so that this, for example, interrupts further image acquisition so that the patient 100 is not endangered due to a faulty detuning device 51.

[0058] In an embodiment of the method according to the invention, it is provided that the detuning device is disabled by the test controller in step S30. One of the two receive signals is received when the active detuner 52 is activated, and the other receive signal is received when the active detuner 52 is disabled. Step S10 can be performed, for example, before step S20, and step S30 can be performed between step S20 and step S50. It is provided that the magnetic resonance tomography device 1 does not send a useful signal during steps S20 and S50, in other words, does not control the high-frequency unit 22 and / or the test transmitter 60 with an input signal. The receive signal is therefore characterized, for example, by a noise signal of the output stage of the transmitter. Therefore, in the comparison step S60, the noise level of the first receive signal is compared with the noise level of the second receive signal. It is conceivable, for example, that the level and energy of the receive signal received by the receiver 65 changes in a characteristic manner by the active detuner 52. This can be associated with or caused by a changed resonance frequency of the antenna or the local coil 50. It is therefore also conceivable to examine, for example by means of FFT, the changes in the spectral distribution of the noise signal, which is produced by convolving the spectrum of the noise source with the resonance frequency of the antenna and which is in turn modified by the active detuner, for comparison. Advantageously, the noise signal is small in amplitude, so that the passive detuner 53 does not occur, so that only the function of the active detuner 52 can be checked.

[0059] However, it is also conceivable in embodiments of the method according to the invention that during the receiving steps S20 , S50 , the transmitter of the magnetic resonance tomography system transmits a small signal which is designed not to overcontrol the receiver.

[0060] On the one hand, the transmitter can be a transmitter used by a magnetic resonance tomography device to generate excitation pulses for nuclear spins during image acquisition. However, the transmitter is usually designed to generate extremely strong high-frequency pulses in the range of several hundred watts to several kilowatts with high efficiency. In order to generate a small signal that does not over-control the receiver 65, the magnetic resonance tomography device can have a linear output stage and a switchable attenuation device between the signal generator and the linear output stage, which is sufficient to attenuate the input signal of the linear output stage during the receiving steps S20, S50 to generate a corresponding small signal at the output end of the linear output stage. In principle, it is also conceivable to attenuate the output signal of a conventional power output stage, but the high power as a power loss of the attenuation element must be conducted.

[0061] The generated small signal can be transmitted, for example, via the body coil 14 as a transmitting antenna into the patient channel 16 having the local coil 50 as a receiving antenna.

[0062] However, a separate test transmitter 60 is also conceivable as part of the magnetic resonance tomography apparatus 1 according to the invention, which generates a small signal under control by a test controller and transmits it via a transmission antenna 70 into the patient channel 16 having the local coil 50 .

[0063] In the method according to the invention, by changing the power and / or spectrum between step S20 and step S50, actively generating a small signal provides greater freedom when comparing the first received signal and the second received signal. For example, the power of the small signal can be changed between steps S20 and S50 so that the passive detuner 53 intervenes already at a larger power and limits the level of the received signal. The functionality of the passive detuner 53 can be checked based on this limitation or the nonlinearity of three or more measured values.

[0064] It is also conceivable to change the spectral distribution of the small signal between the steps in order to check the function of the active detuner 52 and / or the passive detuner 53. It is conceivable here to check the overall function of the detuning device 51 with different combinations of different small signals and the settings of the active detuner.

[0065] It is also conceivable to use the nuclear spins as a small signal source even after excitation. For example, measured values ​​from a previous image acquisition sequence are used to estimate the expected magnetic resonance signal in terms of intensity and its time course. In the case of known spin density and excitation signal, a Bloch simulation of the expected magnetic resonance signal is conceivable. Here, a typical course is an exponential decrease in the magnetic resonance signal. The steps already described, in particular the check of the active detuner 53, can also be implemented by a small signal with a known time course, and compared to a passive detuner, the check of the active detuner 53 does not require a minimum amplitude of the small signal for responding to the detuning.

[0066] In this case, the nuclear spins can also be provided by the phantom. For lower signal intensities, it is also conceivable to use the patient as a source of magnetic resonance signals. However, passive resonators such as oscillating circuits or dipoles are also conceivable, which are excited by the excitation pulses of the high-frequency unit 22 and have a signal drop of an exponent predetermined by the quality of the oscillating circuit or dipole.

[0067] Although the present invention has been illustrated and described in detail through preferred embodiments, the present invention is not limited to the disclosed examples and those skilled in the art may derive other variations therefrom without departing from the scope of protection of the present invention.

Claims

1. A method for checking a detuning device (51) of an antenna coil of a magnetic resonance tomography device (1), the method comprising the following steps: (S10) activating a detuning device (51) of the antenna coil; (S20) receiving a first reception signal using a receiver (65); (S50) receiving a second reception signal using the receiver (65); (S60) comparing the first received signal with the second received signal by a test controller; (S70) if the comparison result is inconsistent with the predetermined relationship between the first received signal and the second received signal, outputting a warning signal, The method comprises a step (S30) of disabling the detuning device (51), wherein the step (S50) of receiving the second received signal is performed with the detuning device (51) switched off, and in a comparison step (S60) the noise level of the first received signal is compared with the noise level of the second received signal, It is characterized in that the first received signal and the second received signal are each a high-frequency current signal and / or voltage signal which arrives at the receiver in analog or digital form and has information about the amplitude, phase and / or spectral distribution.

2. The method according to claim 1, wherein: During a receiving step (S20, S50), the transmitter of the magnetic resonance tomography system transmits a small signal which is designed to control the receiver (65).

3. The method according to claim 2, wherein: The transmitter is configured to generate excitation pulses for the magnetic resonance tomography device and has a switchable attenuation device between the signal generator and the power output stage, wherein the attenuation device is designed to attenuate the input signal of the power output stage during the receiving step (S20, S50) so that the transmitter does not control the receiver (65).

4. The method according to claim 2, wherein: The transmitter is configured to generate excitation pulses for a magnetic resonance tomography device (1) and, during a receiving step (S20, S50), no input signal is fed to the power output stage.

5. A method for checking a detuning device (51) of an antenna coil of a magnetic resonance tomography device (1), the method comprising the following steps: (S10) activating a detuning device (51) of the antenna coil; (S20) receiving a first reception signal using a receiver (65); (S50) receiving a second reception signal using the receiver (65); (S60) comparing the first received signal with the second received signal by a test controller; (S70) if the comparison result is inconsistent with the predetermined relationship between the first received signal and the second received signal, outputting a warning signal, wherein during the receiving step (S20, S50), a signal source is arranged in the patient channel (16) and transmits a signal, wherein between the step of receiving the first received signal (S20) and the step of receiving the second received signal, the power of the signal changes by a predetermined amount, It is characterized in that the first received signal and the second received signal are each a high-frequency current signal and / or voltage signal which arrives at the receiver in analog or digital form and has information about the amplitude, phase and / or spectral distribution.

6. The method according to claim 5, wherein: The transmitter of the magnetic resonance tomography device (1) generates a signal as a signal source, and the signal is a small signal that does not over-control the receiver (65), and the test controller controls the transmitter to change the power in step (S40).

7. The method according to claim 5, wherein: The signal source is a passive signal source, which is excited by the magnetic resonance tomography device (1) to send a small signal, wherein between the step (S20) of receiving the first reception signal and the step (S50) of receiving the second reception signal, the amplitude of the small signal emitted by the signal source decreases over time in a predetermined manner.

8. A magnetic resonance tomography apparatus having a testing device for testing a detuning device (51) of an antenna coil of the magnetic resonance tomography apparatus (1), wherein: The test device has a test controller, and the test controller is designed to activate a detuning device (51) of the antenna coil; Receiving a first reception signal using a receiver (65); Receiving a second reception signal using the receiver (65); comparing the first received signal with the second received signal, and outputting a warning signal if a result of the comparison is inconsistent with a predetermined relationship between the first received signal and the second received signal, The magnetic resonance tomography device (1) has a transmitter for generating an excitation pulse, the transmitter has a switchable attenuation device, and the test controller is designed to transmit a small signal by means of the transmitter and the attenuation device during the step (S20, S50) of receiving the first reception signal and / or the second reception signal, wherein the small signal is designed not to overcontrol the receiver (65). wherein the test controller is configured to disable the detuning device (51), wherein the test controller is configured to perform the step (S50) of receiving the second received signal when the detuning device (51) is turned off, and to compare the noise level of the first received signal with the noise level of the second received signal in the comparison step (S60), It is characterized in that the first received signal and the second received signal are each a high-frequency current signal and / or voltage signal which arrives at the receiver in analog or digital form and has information about the amplitude, phase and / or spectral distribution.

9. A magnetic resonance tomography device having a testing device for testing a detuning device (51) of an antenna coil of the magnetic resonance tomography device (1), wherein: The test device has a test controller, and the test controller is designed to activate a detuning device (51) of the antenna coil; Receiving a first reception signal using a receiver (65); Receiving a second reception signal using the receiver (65); comparing the first received signal with the second received signal, and outputting a warning signal if a result of the comparison is inconsistent with a predetermined relationship between the first received signal and the second received signal, The magnetic resonance tomography device (1) has an active signal source, which is arranged in the patient channel (16) and sends a signal during the receiving step (S20, S50), wherein the test controller is designed to change the power of the signal by a predetermined amount between the step of receiving the first received signal (S20) and the step of receiving the second received signal (S50), It is characterized in that the first received signal and the second received signal are each a high-frequency current signal and / or voltage signal which arrives at the receiver in analog or digital form and has information about the amplitude, phase and / or spectral distribution.

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