Apparatus and method for transmitting a clock signal from an imaging apparatus to a peripheral device

Abstract

The present invention relates to a peripheral device for a magnetic resonance tomography apparatus, a system comprising the magnetic resonance tomography apparatus and the peripheral device, and an operating method. The peripheral device includes a first sensor for receiving an electromagnetic data signal from an environment surrounding the peripheral device. The peripheral device is configured to perform signal processing based on the electromagnetic data signal, wherein the frequency of the electromagnetic data signal is greater than the Larmor frequency of the magnetic resonance tomography apparatus.

Description

Technical Field

[0001] The invention relates to a device for transmitting clock signals and / or control signals from a magnetic resonance tomography device to a peripheral device. Background Art

[0002] Magnetic resonance tomography (MRI) devices are imaging devices that, to image an object under examination, align the object's nuclear spins using a strong external magnetic field and excite these nuclear spins to precess about this orientation using an alternating magnetic field. The precession of the nuclear spins from this excited state, or their return to a state with lower energy, in turn generates an alternating magnetic field, which is received by an antenna.

[0003] Gradient magnetic fields spatially encode the signals, which then allows the received signals to be assigned to volume elements. The received signals are then evaluated to provide a three-dimensional image of the examination object. Local receiving antennas, so-called local coils, are preferably used to receive the signals. These are positioned directly above the examination object to achieve a better signal-to-noise ratio.

[0004] Peripheral or accessory devices that do not directly interface with the MR system are increasingly operating within the shielded rooms of MR systems. These devices include communications equipment, music / video entertainment devices, patient monitors for vital signs, cameras, and motorized mobile furniture. Signal processing within these devices is often timed using signals from free-running oscillators. These clock signals do not operate synchronously with the MR system's system clock.

[0005] Because MRT systems have very sensitive receiver systems that, due to their use of multidimensional Fourier analysis techniques, are particularly sensitive to continuous interference signals, artifacts can easily appear in the imaging. These interferences can occur when harmonics of the clock signal either fall directly into the MRT system's reception area or, through cross-modulation with other, at least occasionally continuously running, signals, appear in the reception area or in the alias band of the analog-to-digital conversion. Furthermore, methods for generating motion information, such as pilot tone methods, can be disrupted by harmonics of the clock signal.

[0006] Another problem is that these additional devices cannot be controlled from outside the shielded room, for example via the user interface of the magnetic resonance tomography apparatus. Summary of the Invention

[0007] It is therefore an object of the present invention to provide a peripheral device and a magnetic resonance tomography apparatus which enable improved image acquisition.

[0008] This object is achieved by the peripheral device according to the invention, the magnetic resonance tomography apparatus according to the invention, and the method according to the invention.

[0009] The peripheral device according to the invention has a first sensor for receiving electromagnetic data signals from the environment of the magnetic resonance tomography device. The electromagnetic data signals are considered to be electromagnetic waves, including electromagnetic waves in the wavelength range up to visible light.

[0010] In this context, the term "environment" is understood to mean the free space surrounding the MRI device, particularly at locations depending on the application, such as near the opening of a patient access where an operator is working, or even within a patient access where a patient is present. Preferably, the distance within this environment is less than 10 m, 5 m, or 2 m from the MRI device. The environment is within a shielded room, if such a room exists. This does not include, in particular, wired connections, such as cables or optical fibers, between peripheral equipment and the MRI device, but rather open transmissions.

[0011] The first sensor converts the electromagnetic data signal into an electrical signal, which is further used in a peripheral device for signal processing based on the electromagnetic data signal. The electromagnetic data signal transmits information from the magnetic resonance tomography device to the peripheral device. For example, the electromagnetic data signal may transmit a clock signal, which serves as the basis for signal processing in the peripheral device. The electromagnetic data signal has a frequency greater than the Larmor frequency of the magnetic resonance tomography device for nuclear spins detected during image acquisition by the magnetic resonance tomography device. This is preferably the Larmor frequency of hydrogen nuclei in the static magnetic field B0 of the magnetic resonance tomography device. "Greater than" here preferably means a frequency greater than two, three, or ten times the Larmor frequency. The electromagnetic data signal may, for example, be visible light or infrared light, or radio waves, preferably in the license-free ISM bands such as 2.4 GHz, 5.8 GHz, 24 GHz, or 61 GHz as the transmission medium. The information is modulated onto the transmission medium, preferably by amplitude modulation. It is also conceivable that a carrier wave, onto which control signals or other information to be transmitted is modulated, may also be modulated. In a preferred embodiment, the clock signal is modulated onto a transmission medium, for example, light or radio waves, wherein the clock signal is in turn modulated into a carrier wave with control commands or other information to be transmitted.

[0012] The sensor can, for example, have an antenna for radio signals or a photodiode, phototransistor or other electronic component as detector element for light signals, or it can be a combination of electronic components, for example with an amplifier, which converts the electromagnetic data signal into an electrical signal or sensor signal.

[0013] Advantageously, the peripheral device according to the invention allows information for controlling the peripheral device to be transmitted via the sensor without interfering with the magnetic resonance reception or requiring cables that interfere with operation. In particular, the fact that the frequency of the electromagnetic data signal is greater than the Larmor frequency ensures that no harmonic frequencies interfere with the reception of the magnetic resonance signals.

[0014] The magnetic resonance tomography system according to the present invention includes a transmitter that is configured to wirelessly transmit clock signals and / or control signals to peripheral devices in the environment of the magnetic resonance tomography system using electromagnetic data signals. The transmitter may, for example, include an oscillator and an antenna for the radio signal, as well as a light source, such as an LED or a semiconductor laser, for the optical data signal. The frequency of the electromagnetic data signal is greater than the Larmor frequency of the magnetic resonance tomography system.

[0015] The optical transmitter is configured to transmit a clock signal and / or a control signal to a local coil in an examination region of a magnetic resonance tomography apparatus by optically transmitting a light signal. For example, a multiplier can be used as a modulator to amplitude-modulate a clock signal, serving as a carrier signal, with a data signal. The amplified clock signal is then applied to an LED, which then emits an intensity-modulated optical signal containing the clock signal and the control signal as the data signal for the local coil. However, digital modulation by switching the light source, and thus the light signal, on and off is also conceivable.

[0016] The explanations given above regarding signals and frequencies for the peripheral devices apply analogously here.

[0017] The terms "first modulation frequency" and "second modulation frequency" are used below. In the case of analog modulation, for example, using a multiplier, the carrier signal to be modulated, or the carrier frequency to be modulated, corresponds to the first modulation frequency, which preferably corresponds to the frequency of the clock signal to be transmitted. In the preferred embodiment explained below, frequency shift keying occurs between two widely separated frequencies. These two widely separated frequencies are therefore referred to as the first modulation frequency and the second modulation frequency and do not represent a modulated carrier signal in the narrow sense. Here, the signals having the corresponding frequencies may also be referred to as the first modulation frequency or the second modulation frequency.

[0018] Advantageously, in this way, data signals can be transmitted from the magnetic resonance tomography apparatus to the peripheral device without disrupting the magnetic resonance reception.

[0019] Further advantageous embodiments are explained in the following description.

[0020] In one possible embodiment of the peripheral device according to the present invention, the electromagnetic data signal is an optical data signal. Optical data signals include signals within the wavelength range of 380 nm to 750 nm, which is visible to the human eye, and also within adjacent wavelength ranges, such as the ultraviolet range of 150 nm to 380 nm or the near-infrared range of 750 nm to 2000 nm. The energy of the photons is preferably greater than 0.8 eV.

[0021] Advantageously, optical signals are easy to generate and receive and are not regulated in the intensities used, so no additional licensing standards need to be considered.

[0022] In one conceivable embodiment of the peripheral device according to the present invention, the peripheral device includes a second sensor adjacent to a first sensor. "Adjacent" in this context is understood to be a distance between the first and second sensors at which the electric and / or magnetic fields generated by the magnetic resonance tomography device have substantially the same strength, so that the interference caused by these fields in the first and second sensors is substantially the same. This distance can, for example, be less than 2 mm, 5 mm, 1 cm, or 5 cm. The sensors are preferably arranged or aligned such that a light signal source in the environment of the peripheral device produces substantially the same effect in the detector elements of the first and second sensors, particularly in terms of intensity or value, e.g., generating approximately the same number of electron-hole pairs in both sensors.

[0023] The first sensor is configured to generate a first output signal from an optical data signal, and the second sensor is configured to generate a second output signal from the same optical data signal. The first output signal has an amplitude that is inverted relative to the second output signal; in other words, the amplitude is substantially the same, but the sign is different. The output signals are considered to be offset relative to or relative to a static level generated by the first and second sensors, for example, when not affected by the optical signal, or to be AC ​​components of the signals generated by the sensors with frequency components greater than 1 Hz, 100 Hz, 1 kHz, 100 kHz, or 1 MHz. Opposite signs can be achieved, for example, by connecting the photodiode in the first sensor to a positive supply voltage and, via a resistor, to a negative supply voltage, while the photodiode in the second sensor is connected to a negative supply voltage and, via a resistor, to a positive supply voltage. The output signals with different signs appear at the connection points between the photodiodes and the resistors, respectively.

[0024] The peripheral device includes an inverter for inverting the output signal of the first sensor and a summing element configured to add the inverted output signal of the first sensor and the output signal of the second sensor to form a sensor signal. Signal inversion can be achieved, for example, by an emitter circuit having a transistor.

[0025] Advantageously, the output signals generated by the optical signals are summed with the same sign by inversion and subsequent phase inversion and are thus amplified, while electrically and / or magnetically induced interferences are ideally cancelled out during the summation by simple phase inversion, so that interference components in the sensor signal are significantly reduced.

[0026] In one possible embodiment of the peripheral device according to the present invention, the peripheral device includes a filter configured to select the carrier signal frequency or the first modulation frequency of the sensor signal. In other words, the filter has a local or preferably even global minimum of passband attenuation for the predetermined carrier signal frequency. The filter preferably attenuates the sensor signal by more than 24 dB, 30 dB, or 36 dB relative to the attenuation at the modulation frequency at frequencies that are one octave apart or equal to half or twice the carrier signal frequency. The filter can preferably be a bandpass filter, but can also be a lowpass filter, for example, depending on the spectrum of the optical signal.

[0027] Furthermore, the peripheral device comprises a narrowband phase-locked loop circuit (PLL circuit) which is configured to stabilize a stable oscillator, preferably a quartz oscillator, in accordance with the frequency of a carrier signal. Within the meaning of the present invention, a narrowband PLL circuit is considered to be a PLL circuit which locks to a frequency deviation of less than 100 ppm, 10 ppm or 1 ppm from the natural frequency of the oscillator.

[0028] Advantageously, the narrowband PLL circuit is immune to interference and can provide an accurate clock signal even if the sensor signal is briefly lost.

[0029] In one conceivable embodiment of the peripheral device according to the invention, the peripheral device comprises an amplitude demodulator with a compensation circuit. The compensation circuit is configured to compensate for signal components of the sensor signal that have a lower frequency than the modulation frequency of the modulation signal. For the purposes of the present invention, low-frequency components are considered to be spectral components of the signal demodulated by the amplitude demodulator, the frequencies of which are less than 10%, 1%, or one thousandth of the modulation frequency. In particular, components in the range below 200 Hz, 120 Hz, or 60 Hz, caused by movement of the peripheral device during use or by external light sources, are considered to be low-frequency components. Possible embodiments are detailed in the following description.

[0030] Intensity changes caused by movements or interruptions are slow signal changes which, due to this frequency difference, can advantageously be separated from the clock frequency or the data signal by a compensation circuit and suppressed.

[0031] In one possible embodiment of the peripheral device according to the present invention, the compensation circuit comprises a differential amplifier with a reference voltage input connected as a comparator. This reference voltage input is in a first signal connection to the sensor signal via an attenuator, preferably in the form of a resistive voltage divider, in a series circuit with a low-pass filter. A comparator is considered a circuit that compares two input signals and provides a comparison result in the form of a controlled output voltage, even when there are only slight differences between the input signals. In this sense, a comparator corresponds to a differential amplifier with high amplification. For example, it is conceivable that the reference voltage input is non-inverting, and the sensor signal or a signal proportional thereto is applied to the inverting input of the differential amplifier.

[0032] Therefore, a low-pass filter filters only the low-frequency components of the sensor signal as the comparator reference signal, which is applied to the non-inverting input of the differential amplifier. This allows the comparator reference signal to advantageously follow slow changes, such as those caused by movement or blocking. Preferably, an upstream voltage divider reduces the voltage of the low-pass filtered reference signal to below the sensor voltage in the absence of a control signal, so that the comparator output signal responds exclusively to the components of the sensor signal caused by the rapidly changing modulation signal.

[0033] In one conceivable embodiment of the peripheral device according to the invention, the first signal connection has a track and hold element that is actuated as a function of the differential voltage between the sensor signal and the reference voltage. For example, an electronic switch can be provided between the sensor signal source and the low-pass filter.

[0034] Advantageously, when the sensor signal voltage falls below the reference voltage due to rapid modulation, the switch disconnects the sensor signal path to the low-pass filter, thereby keeping the reference voltage constant until the sensor signal voltage again exceeds the reference voltage due to the modulation content.

[0035] The magnetic resonance tomography apparatus according to the present invention has an optical transmitter with amplitude modulation. The optical transmitter is configured to transmit clock signals and / or control signals by optically transmitting the optical signal to a peripheral device according to the present invention in the environment or examination area of ​​the magnetic resonance tomography apparatus. For example, the clock signal can be used as a carrier signal, amplitude-modulated with a data signal using a multiplier as an amplitude modulator, and then amplified and applied to an LED. The LED then emits an intensity-modulated optical signal with the clock and control signals as a data signal for the peripheral device. However, digital modulation by switching the light source, and therefore the optical signal, on and off, is also conceivable. The description provided for the corresponding peripheral device applies analogously to the optical signal.

[0036] Advantageously, optical signals are easy to generate and receive and are not regulated in the intensities used, so no additional licensing standards need to be considered.

[0037] In one possible embodiment of the magnetic resonance tomography apparatus according to the present invention, the optical transmitter includes an amplitude modulator. The amplitude modulator is configured to synchronously change the light intensity to modulate the optical signal in order to transmit the clock signal and the control signal. For example, the amplitude modulator may include a sample-and-hold element or a flip-flop that switches the change in the control signal to the multiplier of the amplitude modulator using only the edges of the clock signal. In particular, the amplitude modulator here should be understood as a device that is configured to also set an intermediate level in the optical signal between the non-luminous "off" state and the maximum intensity "on" state, and is therefore different from the digital modulation switch described below in the sense of the present invention.

[0038] Advantageously, the synchronous modulation of the control signal results in that the phase of the modulated clock signal is not changed in this way and the PLL on the receiving side is not disturbed.

[0039] In a conceivable embodiment of the magnetic resonance tomography apparatus according to the invention, the transmitter is configured to switch the optical signal on and off at a modulation frequency (amplitude shift keying or amplitude shift keying or amplitude on / off keying) in order to transmit a control signal and a clock signal, wherein the magnetic resonance tomography apparatus is configured to change the frequency of the modulation signal from a first modulation frequency to a second modulation frequency that is not equal to the first modulation frequency in order to transmit the control signal.

[0040] Since the intensity of the light signal is switched sharply in time as a function of the modulation frequency, the optical sensor provides a square-wave sensor signal having a fundamental frequency corresponding to the first or second modulation frequency. In conjunction with a bandpass filter according to claim 3 or with another filter having frequency-dependent attenuation as part of the signal path of the sensor signal, spectral components (harmonics or fundamental frequency) of the square-wave signal are selected for further processing.

[0041] For nonlinear light sources, such as LEDs or semiconductor lasers, changing the modulation frequency is much easier and more accurate than directly controlling the brightness. Preferably, only the modulation frequency at which the switch switches the light source on and off is changed.

[0042] In one conceivable embodiment of the magnetic resonance tomography apparatus according to the invention, the frequency of the clock signal is an odd-integer multiple of the modulation frequency. For example, the clock signal can have a frequency of 10 MHz. The modulation frequency is then preferably switched between a first modulation frequency and a second modulation frequency, wherein the first modulation frequency in the example is 10 MHz and the second modulation frequency is one-third thereof, i.e., the frequency of the clock signal is equal to the first modulation frequency multiplied by 1 and equal to the second modulation frequency multiplied by 3. The modulation frequency is switched in a phase-neutral manner, i.e., within the time range of the clock frequency or the first modulation frequency.

[0043] When the optical signal is modulated by switching on and off, a square wave signal is generated with harmonics that are odd-integer multiples of the modulation frequency. Therefore, if the second modulation frequency is one-third of the clock signal's frequency, the third harmonic is at three times the modulation frequency, or exactly at the clock signal's frequency. A bandpass filter can be used to select the spectral component at the clock signal's frequency and suppress or attenuate all further harmonics, for example, by more than 24 dB, 30 dB, or 36 dB. Thus, a clock signal of, for example, 10 MHz is provided at both the first and second modulation frequencies. Due to the phase-neutral switching between the two modulation frequencies, the phase of the transmitted clock signal also remains unchanged, allowing, for example, a downstream PLL circuit to provide a phase-stable output signal to peripheral devices. However, in the case of a symmetrical square wave signal without a direct component, the amplitude of the third harmonic is only one-third of the amplitude of the fundamental (first harmonic). This results in the amplitude modulation of the bandpass-filtered received signal being between one-third and full amplitude during frequency shift keying. This amplitude modulation of selected spectral components enables the transmission of control signals, for example, to activate peripheral devices or output messages to an operator. In the digital code transmitted using this amplitude modulation, correspondingly different control commands can be transmitted while simultaneously providing a phase-stable clock signal, wherein the modulation can preferably be provided by simple switches.

[0044] However, it is also conceivable that the first sensor 51 is not an optical sensor, but rather a radio wave receiver for receiving the electromagnetic data signal. In this case, the radio wave assumes the function of the light wave, serving as the carrier signal for the first and second modulation frequencies. The sensor output signal can then be generated by rectifying the received radio wave or an intermediate frequency derived therefrom. The frequency of the electromagnetic data signal, the intermediate frequency, or the radio wave is preferably significantly higher than the first and second modulation frequencies, for example, by a factor of 10, 100, or 1000.

[0045] The method according to the present invention is provided for wirelessly transmitting clock and control signals using a system comprising an MRI apparatus according to the present invention and a peripheral device according to claim 4. The method comprises the following steps: modulating an electromagnetic data signal at a first modulation frequency and emitting the first modulated electromagnetic data signal. For example, an LED or semiconductor laser can be switched on and off temporally in accordance with the first modulation frequency by an electronic switch, thereby generating and emitting a light signal having the first modulation frequency. However, it is also conceivable that a high-frequency signal having a frequency in the radio wave range is switched on and off in the transmitter or switched between two amplitude values ​​and radiated as a radio wave via an antenna into the environment of the peripheral device.

[0046] In a further step, the electromagnetic data signal having the first modulation frequency is received by the first sensor and converted into an electrical signal.

[0047] The first sensor can be, for example, a photodiode that receives a light signal and converts it into an electrical signal, also referred to below as a first output signal. It is also conceivable to amplify the electrical signal and / or combine it with electrical signals from other sensors.

[0048] However, the first sensor can also be a receiver of radio waves and output a first output signal which is preferably proportionally dependent on the field strength of the radio signal.

[0049] In a further step, the first output signal of the first sensor is then filtered by a bandpass filter.

[0050] Similarly, in a further step, the electromagnetic data signal is modulated at a second modulation frequency different from the first modulation frequency, transmitted and received by the first sensor, and bandpass filtered.

[0051] The output signal of the first sensor for the second modulation frequency is referred to as the third output signal here, since the term "second output signal" is already used for the output signal of the second sensor. Generally, the method can also use the output signal of the second sensor or a combination of the two output signals of two sensors according to the present invention to suppress interference.

[0052] Here, preferably, the change between the first modulation frequency and the second modulation frequency is performed in a phase-synchronized manner.

[0053] In a further step, the first output signal and the third output signal of the first sensor are used to stabilize the clock frequency of the oscillator.In another step, a control signal is obtained from the first output signal and the third output signal by demodulation using an amplitude modulator.

[0054] A key feature of these steps is the characteristic that the frequency of the clock signal is an odd-integer multiple of the modulation frequency. For example, the first modulation frequency can correspond to the clock frequency, which corresponds to a simple multiple. The second modulation frequency can correspond to one-third of the clock signal frequency, so that the clock signal frequency corresponds to three times the second modulation frequency. The switching on and off during modulation generates a square wave signal with harmonics whose frequencies correspond to odd-integer multiples of the fundamental frequency. Therefore, both the first modulation frequency, which is equal to the clock signal frequency, and the second modulation frequency, which is one-third of the clock signal frequency, generate a frequency component equal to the clock signal frequency. In this case, the bandpass filter always allows for the frequency range of the clock signal and suppresses other harmonics or lower fundamental frequencies. Therefore, a signal with the clock signal frequency is always available as the sensor output signal, for example, to stabilize the oscillator using a PLL.

[0055] However, the output signal has different amplitudes depending on the frequency of the modulator signal, as the harmonics have lower amplitudes than the fundamental. Shift keying between two modulation frequencies allows amplitude modulation of selected spectral components, which can then be demodulated and decoded using an amplitude demodulator. Phase-synchronized keying between the modulation frequencies prevents interference with the transmitted clock signal.

[0056] The above-mentioned characteristics, features and advantages of the present invention and the manner in which they are achieved will become more clear and easily understood with reference to the following description of exemplary embodiments, which are explained in more detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a schematic diagram of a magnetic resonance tomography apparatus according to the present invention;

[0058] Figure 2 is a schematic diagram of a magnetic resonance tomography apparatus according to the present invention;

[0059] Figure 3 is a schematic diagram of an exemplary embodiment of an optical transmitter of a magnetic resonance tomography apparatus according to the present invention;

[0060] Figure 4 is a schematic diagram of components for recovering a clock signal of a peripheral device according to the present invention;

[0061] Figure 5 is a schematic diagram of an exemplary embodiment of an optical transmitter of a magnetic resonance tomography apparatus according to the present invention;

[0062] Figure 6 is a schematic diagram of a sensor combination of a peripheral device according to the present invention;

[0063] Figure 7 is a schematic diagram of a compensation circuit of a possible embodiment of a peripheral device according to the present invention.

[0064] Figure 8 is a schematic diagram of a transmitter of a possible embodiment of a magnetic resonance tomography apparatus according to the present invention;

[0065] Figure 9 is a schematic flow chart of an exemplary method according to the present invention. DETAILED DESCRIPTION

[0066] Figure 1 A schematic diagram of an embodiment of a magnetic resonance tomography apparatus 1 according to the present invention is shown.

[0067] The magnet unit 10 has a field magnet 11 that generates a static magnetic field B0 for orienting the nuclear spins of a sample or patient 100 in an acquisition region. The acquisition region is characterized by a highly uniform static magnetic field B0, where the uniformity is particularly dependent on the magnetic field strength or magnitude. The acquisition region is nearly spherical and is arranged in a patient tunnel 16 that extends through the magnet unit 10 in the longitudinal direction 2. A patient couch 30 can be moved in the patient tunnel 16 via an actuator 36. The field magnet 11 is typically a superconducting magnet capable of generating magnetic fields with flux densities up to 3 T, and even higher in the latest equipment. However, for lower magnetic field strengths, permanent magnets or electromagnets with normally conductive coils can also be used.

[0068] The magnet unit 10 also includes gradient coils 12 configured to superimpose temporally and spatially variable magnetic fields in three spatial directions on the magnetic field B0 in order to spatially distinguish an imaging region to be examined in the examination volume. The gradient coils 12 are typically coils made of normal conductive wires capable of generating mutually orthogonal fields in the examination volume.

[0069] The magnet unit 10 further comprises a body coil 14 , which is provided 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.

[0070] The control unit 20 provides the magnet unit 10 with the different signals for the gradient coils 12 and the body coil 14 and evaluates the received signals.

[0071] The control unit 20 therefore has a gradient controller 21 which is configured 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.

[0072] The control unit 20 also includes a radio-frequency unit 22, which is configured to generate radio-frequency pulses having a predetermined time distribution, amplitude, and spectral power distribution for exciting magnetic resonance of nuclear spins in the patient 100. Pulse powers in the kilowatt range can be achieved. The excitation signal can be radiated into the patient 100 via the body coil 14 or via local transmitting antennas.

[0073] The controller 23 communicates with the gradient controller 21 and the high-frequency unit 22 via a signal bus 25 .

[0074] The surroundings of the magnetic resonance tomography apparatus 1 contain a plurality of peripheral devices 80 or accessories that can participate in the acquisition of magnetic resonance images. These can be operating elements, devices for communicating with or entertaining the patient, or even sensors that acquire (or detect) physiological parameters of the patient 100. For example, the peripheral device 80 shown here is a tablet computer for a user interface. It is also conceivable that the peripheral device 80 is a local coil 50.

[0075] Many of these peripheral devices 80 contain digital circuits or processors, whose clock signals and signals derived from them can generate interference. In particular, frequencies below the clock frequency, often with frequencies that are integer fractions of the clock frequency, and thus with harmonics, are also generated during signal processing. However, with a suitable choice of the clock frequency, it can be ensured that these interfering signals lie between the useful frequencies of the signal or the subsequent signal processing path and do not cause interference. However, the clock frequency must be sufficiently stable to ensure that it does not migrate into the interfering frequency range, for example due to temperature changes. Therefore, the magnetic resonance tomography device 1 according to the invention has a transmission device for wirelessly transmitting the clock signal, for example, Figure 1 The optical transmitter 70 shown or Figure 7 The transmitter 73 for radio waves is shown. The clock signal preferably originates from a stable master clock of the magnetic resonance tomography apparatus 1 and is provided by the control unit 20 to the optical transmitter 70 or the transmitter 73.

[0076] For transmission to a peripheral device 80, the control unit 20 includes an optical transmitter 70, wherein light-emitting luminous devices 71 are arranged in the environment of the magnetic resonance tomography apparatus such that they directly or indirectly illuminate the peripheral device 80. The magnetic resonance tomography apparatus preferably includes a plurality of luminous devices 71 that are spatially distributed or illuminate light-scattering surfaces, thereby preventing the light signals emitted by the luminous devices 71 from being blocked in the peripheral device 80. The luminous devices 71 can be LEDs or semiconductor lasers that receive the electrical signal fed by the optical transmitter 70, convert it into an optical signal, and emit it into the environment. However, it is also conceivable that the LED emitter or semiconductor laser in the optical transmitter 70 already performs the conversion into light, and that this signal is guided to the radiation point in the environment via a glass fiber and, optionally, a beam splitter.

[0077] Figure 2 A schematic diagram of an embodiment of a magnetic resonance tomography apparatus 1 according to the present invention is shown, wherein the peripheral device is a local coil (50).

[0078] In this embodiment, the magnetic resonance tomography apparatus 1 includes a plurality of light-emitting devices 71, which are distributed over the inner surface of the patient channel 16 or illuminate the light-scattering inner surface from the outside, thereby preventing the light signal emitted by the light-emitting devices 71 from being blocked at the local coil 50. The light-emitting devices 71 may be LEDs or semiconductor lasers, which receive the electrical signal fed by the optical transmitter 70, convert it into an optical signal, and emit it into the patient channel 16. However, it is also conceivable that the LED radiator or semiconductor laser in the optical transmitter 70 already performs the conversion into light and guides it to the patient channel 16 via a glass fiber and an optional beam splitter, wherein the glass fiber end is arranged in the patient channel 16 as the light-emitting device 71.

[0079] Figure 3 An exemplary embodiment of an optical transmitter 70 of a magnetic resonance tomography apparatus 1 according to the present invention is shown.

[0080] Optical transmitter 70 includes an amplitude modulator 72 that modulates a high-frequency clock signal with a low-frequency control signal. For example, the amplitude modulator can include a multiplier that multiplies the clock signal by the low-frequency control signal. The modulation of the clock signal is preferably performed in phase synchronization, i.e., with the rising or falling edge of the clock signal. This can be achieved, for example, by switching the control signal to the multiplier via a sample-and-hold element, where the sample-and-hold element is controlled by the clock signal, for example, switching at a low level of the clock signal.

[0081] The output signal of the amplitude modulator is output directly or via an output stage to one or more LEDs or LED radiators or semiconductor lasers for conversion into an optical signal.

[0082] Figure 4 An exemplary embodiment is shown with components of a peripheral device 80 according to the invention, which are involved in the transmission or recovery of clock signals and control signals. For the sake of clarity, other elements of the peripheral device 80 are not shown.

[0083] A first optical sensor 51, such as a photodiode with a preamplifier, converts an optical signal (or optical signal) into an electrical signal. A filter 53, such as a bandpass filter or a low-pass filter, preferably allows signals having the clock signal frequency to pass through and attenuates signals having other frequencies, for example, by more than 24 dB, 30 dB, or 36 dB.

[0084] The filtered signal is fed to the amplitude demodulator 54 in the demodulation branch to recover the control signal modulated onto the clock signal. In the simplest case, the amplitude demodulator 54 can be composed of a diode as a rectifier and a low-pass filter or a buffer capacitor.

[0085] The demodulated signal still has fluctuations, which are caused by, for example, changing blockages on the propagation path. These fluctuations are compensated by the compensation circuit 55. Figure 7 Explain it.

[0086] The filtered signal is also fed in parallel to a branch of the circuit that generates a stable master clock for the peripheral device 80. Here, the filtered signal from the first sensor 51 is first amplified in a limiting amplifier 56 so that amplitude fluctuations are eliminated by amplitude limitation, leaving only the carrier phase information. In the PLL circuit (phase-locked loop control circuit), the frequency and phase of the VCO 58 (voltage-controlled oscillator), which is preferably a quartz-stabilized VCO, are thereby stabilized. The output signal of the VCO 58, or a signal derived therefrom, serves as the master clock for the peripheral device 80.

[0087] Figure 5 Another conceivable embodiment of an optical transmitter 70 is shown. This embodiment is based on the concept that a square wave signal has harmonic components whose frequencies correspond to odd multiples of the fundamental frequency. Here, exemplarily represented as input signals for the optical transmitter are a square wave signal with a high frequency, also referred to as a first modulation frequency, for example 10 MHz, and a square wave signal with a lower frequency or second modulation frequency of (10 / 3) MHz, i.e., approximately 3.33 MHz. The control unit 20 provides these signals with high precision derived from a stable master clock. In other words, even when the optical transmitter 70 transmits an optical signal with the second modulation frequency, it also has a frequency component of the first modulation frequency of 10 MHz.

[0088] Using the first or second modulation signal as a clock, the optical transmitter switches the power supply for the LED or semiconductor laser serving as the light source, or light emitting device 71, on and off via an electronic switch, thereby generating a light signal modulated with a square wave signal. Preferably, multiple light emitting devices 71 are simultaneously switched on to avoid blocking the sensor 51. Alternatively, walls or reflectors on the magnetic resonance tomography apparatus 1 can advantageously be designed to scatter light and illuminated by one or more light emitting devices 71. Modulation using a square wave signal via a switch is advantageously easy to implement and more efficient than linear intensity modulation.

[0089] By changing between the first modulation frequency and the second modulation frequency, a signal component with the first modulation frequency is always available here due to the harmonics, which signal component is selected by the filter 53 in the peripheral device 80. Since the harmonic components always have a lower amplitude than the fundamental frequency, the change between the modulation frequencies results in an amplitude modulation in the spectral range of the first modulation frequency, which amplitude modulation can be used, for example, Figure 4 The peripheral device 80 according to the present invention is evaluated. If the first modulation frequency and the second modulation frequency are in a phase-stable relationship, preferably with the edges of the signal at the second modulation frequency synchronized with the edges of the signal at the first modulation frequency, the clock signal generated by the PLL will not be affected by frequency shift keying. This can be achieved, for example, by deriving the second modulation frequency from the first modulation frequency through phase-synchronous frequency division.

[0090] Figure 6 The diagram schematically shows an advantageous combination of a first sensor 51 and a second sensor 52 for detecting light signals. This combination reduces, in particular, electromagnetic interference with the light signal reception caused by the operation of the magnetic resonance tomography apparatus.

[0091] For this purpose, the first sensor 51 and the second sensor 52 are arranged adjacent to each other to minimize induction in the connecting lines and to expose both sensors 51, 52 to as identical an electromagnetic field as possible. This distance is preferably less than 2 cm, 1 cm or 5 mm.

[0092] The first sensor 51, here a photodiode, is Figure 6 The positive supply voltage is connected directly in the reverse direction, while the connection to ground potential is made via a resistor.

[0093] For the second sensor 52, the roles of the resistor and sensor are reversed, i.e. the resistor is connected directly to the positive supply voltage, while the second sensor 52 is connected to ground potential. By the reversed arrangement, the same optical signal in the two sensors 51, 52 generates electrical signals with comparable amplitudes but opposite signs.

[0094] The electrical signals generated by sensors 51 and 52 are amplified and fed to the inverting or non-inverting input of differential amplifier 49. Advantageously, the electrical signals induced by the optical signals at sensors 51 and 52 are summed at the output of differential amplifier 59 due to their different signs. Conversely, electromagnetic interference preferably induces interference signals of the same sign in both branches, so they essentially cancel each other out in the differential amplifier. At the same time, the signal-to-noise ratio of the sum signal is 3 dB higher than that of the individual signals because the noise contributions of the electrical components are uncorrelated and therefore sum in power, while correlated received signals sum in voltage.

[0095] Figure 7 is a schematic diagram of a possible embodiment of compensation circuit 55. The filtered and demodulated sensor signal is fed to the inverting input of comparator 60. Simultaneously, the sensor signal is reduced by a resistor divider, low-pass filtered by an RC element, and fed to the non-inverting input of comparator 60. The capacitor of the RC element also serves as a charging capacitor for the track-and-hold element, whose electrical switch is implemented here as a MOS-FET. The track-and-hold element is driven by the output of comparator 60, so that the switch of the track-and-hold element is closed when the sensor signal becomes less than a reference signal.

[0096] Figure 8 An exemplary magnetic resonance tomography apparatus 1 and peripheral device 80 according to the present invention are shown, which use radio waves rather than optical signals to transmit electromagnetic data signals or a first modulation frequency. To this end, the control unit 20 includes a transmitter 73 for transmitting radio waves. An oscillator generates a high-frequency signal having a frequency higher than the Larmor frequency when imaging nuclear spins to be detected by the magnetic resonance imaging unit 1 in the static magnetic field of the magnetic resonance tomography apparatus 1. For example, the frequency of the high-frequency signal can be greater than two, five, or ten times the Larmor frequency. This frequency is preferably less than 100 GHz, 50 GHz, or 10 GHz.

[0097] The transmitter 73 modulates a high-frequency signal for the peripheral device using the clock signal and / or the control signal and transmits it as a radio wave via an antenna in the environment of the magnetic resonance tomography apparatus 1 in which the peripheral device 80 is located. It is also conceivable that the frequency corresponds to a multiple of the clock frequency to be transmitted, which is obtained from the clock signal by a frequency multiplier.

[0098] The peripheral device receives the radio waves via the receiver 81. Here, the clock signal and / or control signal to be transmitted can be obtained by the peripheral device 80 through demodulation of the radio waves, as has been described with respect to Figure 3 and 4As described for the output signals of sensors 51, 52. If the frequency of the radio wave or high-frequency signal is a multiple of the clock signal to be transmitted, it is also conceivable to recover (or re-obtain) the clock signal by frequency division.

[0099] The peripheral device 80 according to the invention uses the recovered clock signal as a master clock for internal signal processing. This also ensures that, as already described, interference frequencies and their harmonics generated by the signal processing do not lie at the signal frequency of the magnetic resonance signal.

[0100] Figure 9 A schematic flow chart of a method according to the present invention for wirelessly transmitting clock signals and control signals using a magnetic resonance tomography device is shown.

[0101] In step S10, an electromagnetic data signal is modulated at a first modulation frequency. For example, control unit 20 can switch an electronic switch connecting one or more LEDs to a power supply voltage on and off at the first modulation frequency. The LEDs then emit a light signal modulated at the first modulation frequency. However, it is also conceivable that a high-frequency signal with a frequency in the radio wave range is switched on and off, or switched between two amplitude values, in transmitter 73 and radiated as radio waves via an antenna into the environment of peripheral device 80.

[0102] In a further step S20, a first sensor 51, such as a photodiode, receives the light signal and converts it into an electrical signal, also referred to as a first output signal. It is also conceivable to amplify the electrical signal and / or combine it with electrical signals from other sensors. However, the first sensor can also be a receiver for radio waves and output a first output signal which preferably depends proportionally on the field strength of the radio signal. This can be achieved, for example, by rectifying the received radio signal or the intermediate frequency generated therefrom with a diode and filtering it with a buffer filter. In this case, the buffer filter, such as an RC element, has a frequency response which is set to keep the output voltage essentially constant between two half-waves of the high-frequency signal or the intermediate-frequency signal and has essentially the same pass-through attenuation for the two modulation frequencies mentioned below. For example, the attenuation difference is less than 1 dB.

[0103] In a further step S30, the first output signal of the first sensor is filtered by a bandpass filter. The bandpass filter preferably has a minimum passband attenuation at the frequency of the clock signal.

[0104] In a further step S40, the electromagnetic data signal is modulated as in step S10, but at a second modulation frequency that is different from the first modulation frequency. Here, the frequency of the clock signal is an odd-integer multiple of the first modulation frequency and the second modulation frequency, wherein the multiplier differs at the first and second modulation frequencies. For example, the multiplier at the first modulation frequency is equal to 1, so that the first modulation frequency corresponds to the frequency of the clock signal. The multiplier for the second modulation frequency can be, for example, 3, so that the second modulation frequency is one-third the frequency of the clock signal. The electromagnetic data signal having the second modulation frequency is also transmitted by transmitter 73 as described above.

[0105] In step S50, as already described with respect to step S20, an electromagnetic data signal having a second modulation frequency is received by first sensor 51 and converted into a third electrical output signal. Here, the term "second output signal" is used and predefined for the output signal of second sensor 52. However, in principle, interference suppression can also be performed using the previously described method of combining first sensor 51 and second sensor 52, wherein the term "first output signal" applies accordingly to the combined output signal of these sensors at the first modulation frequency, similarly to the third output signal at the second modulation frequency.

[0106] In step S60, the third output signal of the first sensor is filtered by a bandpass filter. Because the bandpass filter has minimum attenuation at the frequency of the clock signal, the bandpass filter preferably allows the harmonics of the second modulation signal at the frequency of the clock signal to pass.

[0107] In step S70, the receiver 81 of the peripheral device 80 uses the first and third output signals of the first sensor to stabilize the clock frequency of the oscillator, for example, by means of a PLL circuit. This can be achieved by: the first modulated signal also has a signal component at the frequency of the clock signal and preferably passed by a bandpass filter.

[0108] In another step S80, the control signal is demodulated from the first output signal and the third output signal by an amplitude demodulator. The difference in amplitude between the first and third electrical output signals is caused by the fact that the signal component of the harmonics decreases with increasing order.

[0109] Although the present invention has been illustrated and described in more detail by means of preferred exemplary embodiments, the present invention is not limited to the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of protection of the present invention.

Claims

1. A peripheral device for a magnetic resonance tomography apparatus (1), wherein: The peripheral device (80) has: a first sensor (51) for receiving an optical data signal from an environment of said peripheral device (80), a second sensor (52) adjacent to the first sensor (51), wherein the first sensor (51) is arranged to generate a first output signal from the optical data signal and the second sensor (52) is arranged to generate a second output signal from the optical data signal, wherein the first output signal has an opposite amplitude to the second output signal; An inverter for inverting the first output signal of the first sensor (51); and a summing element arranged to add the inverted first output signal of the first sensor (51) and the second output signal of the second sensor (52) to form a sensor signal, wherein the peripheral device (80) is configured to perform signal processing based on the optical data signal; The frequency of the optical data signal is greater than the Larmor frequency of the magnetic resonance tomography device (1).

2. The peripheral device according to claim 1, wherein The peripheral device is a local coil (50).

3. The peripheral device according to claim 1, wherein The peripheral device (80) further comprises a filter (53) configured to select a modulation frequency of the sensor signal and a narrowband phase-locked loop circuit (57) configured to stabilize an oscillator according to the modulation frequency and modulation phase.

4. The peripheral device according to claim 1, wherein The peripheral device (80) further comprises an amplitude demodulator (54) having a compensation circuit (55) which is arranged to compensate for signal components of the sensor signal which have a low frequency compared to the modulation frequency of the modulation signal.

5. The peripheral device according to claim 4, wherein: The compensation circuit (55) has a comparator (60) with a reference voltage input, which is in a first signal connection to the sensor signal via a low-pass filter.

6. The peripheral device according to claim 5, wherein: The first signal connection has a track and hold element that is actuated according to a differential voltage between the sensor signal and the reference voltage.

7. A magnetic resonance tomography apparatus, wherein: The magnetic resonance tomography apparatus (1) has an optical transmitter, wherein the optical transmitter is configured to transmit a clock signal and / or a control signal to a peripheral device (80) in the environment of the magnetic resonance tomography apparatus by means of optically open transmission of an optical signal, wherein the optical transmitter is configured to modulate the optical signal at a modulation frequency in order to transmit the control signal and the clock signal, wherein the magnetic resonance tomography apparatus (1) is configured to change the modulation frequency from a first modulation frequency to a second modulation frequency that is not equal to the first modulation frequency in order to transmit the control signal, The frequency of the optical signal is greater than the Larmor frequency of the magnetic resonance tomography device (1).

8. The magnetic resonance tomography apparatus according to claim 7, wherein: The optical transmitter (70) has an amplitude modulator (72) configured to synchronously perform amplitude changes to modulate the optical signal in order to transmit a clock signal and a control signal.

9. The magnetic resonance tomography apparatus according to claim 7, wherein: The frequency of the clock signal is an odd multiple of the modulation frequency.

10. The magnetic resonance tomography apparatus according to claim 7, wherein: The optical transmitter (70) is configured to radiate the optical signal into the environment of the magnetic resonance tomography device (1) and distribute the optical signal on a surface by scattering.

11. A method for wirelessly transmitting clock signals and control signals using a magnetic resonance tomography apparatus (1) according to one of claims 7 to 10 and a peripheral device (80) according to claim 3, wherein: The method comprises the following steps: (S10) modulating the electromagnetic data signal at a first modulation frequency, and transmitting the first modulated electromagnetic data signal using a transmitter (73); (S20) receiving the electromagnetic data signal using a first sensor (51); (S30) filtering the first output signal of the first sensor (51) using a filter (53); (S40) modulating the electromagnetic data signal at a second modulation frequency, and transmitting the second modulated electromagnetic data signal using the transmitter (73); (S50) using the first sensor (51) to receive an optical signal; (S60) filtering the third output signal of the first sensor (51) using the filter (53); (S70) stabilizing a clock frequency of an oscillator using the first output signal and the third output signal of the first sensor (51); (S80) demodulating a control signal from the first output signal and the third output signal using an amplitude demodulator (54), The frequency of the clock signal is an odd multiple of the first modulation frequency and the second modulation frequency.

12. A magnetic resonance tomography apparatus, wherein: The magnetic resonance tomography apparatus (1) comprises: an optical transmitter, wherein the optical transmitter (70) is configured to transmit clock signals and / or control signals to a peripheral device (80) in the environment of the magnetic resonance tomography apparatus by means of optically open transmission of light signals; The optical transmitter has an amplitude modulator, which is configured to synchronously perform amplitude changes to modulate the optical signal so as to transmit a clock signal and a control signal, wherein the modulation of the clock signal is synchronized with the phase of a rising edge or a falling edge of the clock signal; The frequency of the optical signal is greater than the Larmor frequency of the magnetic resonance tomography device (1).

Images