Peripheral equipment for magnetic resonance imaging system and system with peripheral equipment

Abstract

The invention relates to a peripheral device for a magnetic resonance imaging system, and a system formed by the magnetic resonance imaging system and the peripheral device. The peripheral device has a sensor for receiving a control signal in an environment of the peripheral device. The peripheral device is designed to obtain a reference clock for signal processing in the peripheral device and control information of the peripheral device from the control signal. The control information is modulated into the control signal by means of phase modulation.

Description

Technical Field

[0001] The present invention relates to a peripheral device for a magnetic resonance imaging system and a system having the peripheral device. Background Art

[0002] The magnetic resonance imaging system is an imaging device that uses an external strong magnetic field to align the nuclear spins of the subject, and excites the nuclear spins to precess around this alignment through an alternating magnetic field, so as to image the subject. The precession or return of the spins from this excited state to a state with less energy generates an alternating magnetic field in response, which is received via an antenna.

[0003] The signals are subjected to positional encodings by means of gradient magnetic fields, which subsequently allow the received signals to be assigned to volume elements. The received signals are then evaluated and a three-dimensional image of the object under examination is provided. The signals are preferably received using local receiving antennas, so-called local coils, which are arranged directly on the object under examination to achieve a better signal-to-noise ratio.

[0004] These local coils are usually connected to the magnetic resonance imaging system via cables, through which received signals are transmitted for image reconstruction and energy and control signals are provided for the local coils.

[0005] Since magnetic resonance imaging for image generation also relies on accurate phase information, the local coils need to have an accurate and uniform phase reference.

[0006] However, other wireless peripherals for magnetic resonance imaging systems can also be used, and these wireless peripherals must be provided with frequency and phase stable clocks and control information, which is only to reduce the interference of the peripherals with the image acquisition. They may be sensors for detecting physiological values ​​of patients, or operating or communication devices.

[0007] Publication DE 10 2021 206 483 A1 discloses a local coil and a magnetic resonance imaging system, wherein the magnetic resonance imaging system transmits a reference clock optically to the local coil, wherein control information is transmitted between two modulation frequencies by means of keying. The modulation frequency is modulated into an optical signal by amplitude modulation. Summary of the invention

[0008] In view of the above, an object of the present invention is to provide a peripheral device with lower cost and better performance, in particular a wireless local coil.

[0009] In an embodiment of the peripheral device of the invention, the peripheral device has a sensor for receiving an electrical and / or magnetic control signal in the surroundings of the peripheral device, wherein the peripheral device is designed to obtain a reference clock for signal processing in the peripheral device and control information of the peripheral device from the control signal, and the control information is modulated into the control signal by means of phase modulation. In other words, the peripheral device is designed to obtain the control information from the control signal by means of a phase modulator.

[0010] Advantageously, the reference clock can be used to stabilize the frequency of the peripheral device, thereby reducing interference. Phase modulation can reliably transmit control information without reference clock interference, which will be explained below.

[0011] In a possible implementation of the peripheral device of the present invention, the peripheral device is adapted to obtain phase modulation by phase shift keying of 360 / n degrees to obtain control information, wherein the natural number is greater than 1.

[0012] Advantageously, the information density of the transmission can be increased by phase shift keying with a plurality of steps.

[0013] In one possible embodiment of the peripheral device, the peripheral device has a frequency multiplier with a factor of n, wherein the reference clock is obtained by frequency multiplication.

[0014] Advantageously, the frequency multiplication by a factor of n results in a phase jump of 360 degrees / n of the modulation becoming a phase jump of 360 degrees at the doubled frequency, and thus having phase stability as a reference frequency.

[0015] In a possible embodiment of the peripheral device according to the invention, the value n of the divisor in the frequency multiplication and phase modulation is equal to 2. In other words, the phase modulation is implemented by a phase jump of 180 degrees, and the reference frequency corresponds to twice the frequency of the control signal.

[0016] In a possible embodiment of the invention, the peripheral device is a local coil of a magnetic resonance imaging system. The local coil has an antenna coil for receiving magnetic resonance signals for image acquisition with a magnetic resonance imaging system. Interference-free image acquisition requires a well-defined frequency and phase relationship, which is ensured by a reference clock. The magnetic resonance signals for image acquisition are processed using the reference clock, for example, for frequency conversion and / or as a clock for digitization.

[0017] The peripheral device of the invention is suitable for use with a magnetic resonance imaging system. The peripheral device does not cause interference or causes as little interference as possible during image acquisition. The peripheral device is preferably wireless, that is, it is not connected to the magnetic resonance imaging system by wire, but a wired embodiment is also possible. In a preferred embodiment described below in conjunction with the dependent claims, the peripheral device is a local coil.

[0018] The peripheral device of the present invention has a sensor for receiving an electric control signal, a magnetic control signal or an electromagnetic control signal in the surroundings of the peripheral device. That is, the control signal is transmitted via an electric alternating field, a magnetic alternating field or an electromagnetic alternating field. The frequency of the alternating field is preferably greater than 1 MHz, 10 MHz, 100 MHz or 1 GHz. The reception can be implemented by capacitive, inductive means or by free field transmission. The signal can also be an optical signal. The sensor can be, for example, an electric antenna, a magnetic antenna, an induction coil or a photodetector. Preferably, the space in which the magnetic resonance imaging system, in particular the patient tunnel of the magnetic resonance imaging system, is provided is regarded as the surroundings.

[0019] The peripheral device is designed to obtain a reference clock for signal processing in the peripheral device and control information of the peripheral device from the control signal. The periodic signal is called a reference clock, which defines a frequency and can achieve a stable time reference to the reference clock through a phase. The following will describe a solution in which, for example, a reference clock can be obtained from a control signal in conjunction with the dependent claims and the accompanying drawings.

[0020] Control information refers to all information that can be used by the magnetic resonance imaging system to control peripheral devices to change the operating state. This operating state can be, for example, a static state of the operating device or a so-called detuned state of the local coil. Amplification can also be set or input channels can be selected.

[0021] The above object is also achieved by a system of the present invention, which has a magnetic resonance imaging system and a peripheral device of the present invention. The magnetic resonance imaging system has a reference clock generator, a modulator and a control signal transmitter. The reference clock generator is suitable for providing a reference clock with stable frequency and phase. Preferably, the reference clock is derived from a central clock of the magnetic resonance imaging system, which is also preset as a clock for detecting and analyzing magnetic resonance data. The magnetic resonance imaging system also has a modulator. The modulator is in signal connection with the reference clock generator and obtains the reference clock from this reference clock generator. The modulator is suitable for modulating the reference clock with control information by means of phase modulation. The control information is preferably provided by a controller of the magnetic resonance imaging system and is related to the execution of the sequence. The magnetic resonance imaging system also has a control signal transmitter for wirelessly transmitting a control signal. The control signal transmitter is in signal connection with the modulator, thereby receiving the reference clock modulated with the control signal, and transmitting the control signal to the surrounding environment of the peripheral device in the magnetic resonance imaging system. This can be implemented, for example, by an antenna, an induction coil or an optical transmitter, such as an LED or a laser.

[0022] Advantageously, the system of the present invention is capable of controlling operations in peripheral devices within a sequence for a magnetic resonance imaging system, thereby providing reliable and optimized image acquisition.

[0023] In a possible embodiment of the system according to the invention, the modulator is adapted to implement phase modulation at the zero crossing of the reference clock. In particular, in phase modulation with a phase shift of 180 degrees, the shift is implemented at the zero crossing by switching the polarity of the output signal at the zero crossing, that is, the output signal of the modulator is inverted until the next modulation step. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the above and other features and advantages of the present invention will be more apparent to those skilled in the art. In the accompanying drawings:

[0025] Figure 1 is a schematic diagram of a system of the present invention consisting of a magnetic resonance imaging system and an electronic peripheral device of the present invention;

[0026] Figure 2 A block diagram of a transmission system for transmitting a clock signal and a control signal according to the present invention;

[0027] Figure 3 is a schematic diagram of an exemplary embodiment of a modulator of the system of the present invention;

[0028] Figure 4 FIG. 1 is a schematic diagram of an exemplary embodiment of a demodulator of the system of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail with reference to the following embodiments.

[0030] Figure 1 A schematic diagram of an embodiment of the system according to the invention is shown, consisting of a magnetic resonance imaging system 1 and electronic peripherals according to the invention.

[0031] 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 is particularly related to the magnetic field strength or the absolute value. The recording area is approximately spherical and is arranged in a patient tunnel 16 which extends through the magnet unit 10 in the longitudinal direction 2. The patient examination table 30 is moved in the patient tunnel 16 by a displacement unit 36. The field magnet 11 is usually a superconducting magnet capable of providing a magnetic field with a magnetic flux density of up to 3 T, and in the latest devices even higher magnetic fields can be provided. However, smaller magnetic field strengths can also be achieved using permanent magnets or electromagnets with constant conductive coils.

[0032] In addition, the magnet unit 10 has gradient coils 12, which are designed to superimpose temporally and spatially variable magnetic fields in three spatial directions on the magnetic field B0 to spatially distinguish the imaging regions acquired in the volume to be examined. The gradient coils 12 usually have coils made of constant wires, which can generate mutually orthogonal fields in the volume to be examined.

[0033] The magnet unit 10 also has a body coil 14 , which is designed to radiate a high-frequency signal provided through a signal line to a volume to be examined, and to receive a resonance signal emitted by the patient 100 and output it through the signal line.

[0034] The control unit 20 provides the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14 and evaluates the received signals.

[0035] 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.

[0036] The control unit 20 also has a high-frequency unit 22, which is designed to generate high-frequency pulses with a predetermined time curve, amplitude and spectral power distribution to stimulate magnetic resonance of nuclear spins of the patient 100. Pulse frequencies in the kilowatt range can be achieved. The excitation signal can be radiated to the patient 100 via the body coil 14 or via a local transmission antenna.

[0037] The controller 23 communicates with the gradient controller 21 and the high-frequency unit 22 via a signal bus 25 .

[0038] There are a large number of peripheral devices or auxiliary devices in the environment of the magnetic resonance imaging system 1, which can participate in the detection of magnetic resonance images. These devices can be operating elements, devices for communicating or talking with the patient, or physiological sensors for detecting physiological parameters of the patient 100. Examples of peripheral devices of the present invention are local coils 50 or tablet computers 80.

[0039] Many of these peripheral devices contain digital circuits or processors, whose clock signals and derived signals may generate interference. When processing signals, frequency components lower than the clock frequency are generated, whose frequencies are usually integer fractions of the clock frequency, and harmonics are generated. However, when the clock frequency is appropriately selected, it can be ensured that these interference signals are between the effective frequencies of the magnetic resonance signal or the subsequent signal processing path and do not cause interference. However, the clock frequency must be stable enough so that it will not migrate to the interference frequency range due to, for example, temperature changes. Therefore, the magnetic resonance imaging system 1 of the present invention has a transmission device for wirelessly transmitting the clock signal, such as a control signal transmitter 60. The clock signal is preferably derived from a stable master clock of the magnetic resonance imaging system 1, and the control unit 20 provides the master clock to the control signal transmitter 60. When optical transmission is performed, the clock signal can be modulated into an optical carrier. When the transmission is performed by means of an electric and / or magnetic alternating field in the radio frequency range, the clock signal can be directly transmitted by the frequency of the alternating field.

[0040] The peripheral devices of the present invention also require control signals. The control signals may involve simple switching on and off or enabling / disabling functions, for example to prevent the peripheral devices from interfering with image acquisition. The control signals may also enable protection functions, such as detuning of the local coil 50, to prevent the local coil 50 from being damaged or the patient 100 from being exposed to hazards associated with the excitation pulses.

[0041] Figure 2 A schematic block diagram of a transmission path for clock and control signals is shown. The transmission path has a control signal transmitter 60 including a modulator 61. The control unit 20 inputs the clock signal and the control information to the modulator 61. The control information is modulated into a clock signal in the modulator 61. Details and different embodiments are explained in conjunction with the figures. Subsequently, the transmitter 62 emits the modulated control signal for transmission.

[0042] In wired transmission, the transmitter 62 can be, for example, a small power amplifier or a power driver adapted to the transmission line. In wireless transmission by means of electric, magnetic or electromagnetic fields, the transmitter 62 can be, for example, an electric antenna or a magnetic induction coil, which can also have an amplifier. In optical transmission, an LED or a laser can be used as the transmitter 62.

[0043] A complementary sensor 71 for receiving the control signal is provided on the peripheral device side. It can also be an antenna or an induction coil, or an optical receiver, such as a photoelectric tube or a photodiode. The sensor 71 can also have an amplifying element for amplifying the received control signal to adjust this control signal to a predetermined level.

[0044] Subsequently, the received control signal is input to the demodulator 73, which extracts the clock signal and control information by demodulation. Among them, the frequency multiplier 72 also outputs the control signal whose frequency is multiplied by the integer coefficient n to the demodulator 73. For example, the frequency multiplication can be achieved by bidirectional rectification of the control signal. For example, an odd multiple can be achieved by converting it into a square wave signal or by filtering out the desired harmonics afterwards. For example, other multiplication factors can also be achieved by using a PLL circuit.

[0045] Figure 3 An exemplary embodiment of a modulator 61 of the system of the present invention is shown. The modulator 61 is supplied with a clock signal C and control information D to be modulated.

[0046] The clock signal C is mostly a square wave signal, so it is first filtered by a first low-pass filter 611 to generate an approximately sinusoidal signal with fewer interfering harmonics. Subsequently, an adjustable phase shift is implemented by a phase shifter 613, and the function of the phase shifter will be described below.

[0047] The control information D or data signal is edge synchronized with the clock signal C by flip-flop 612 and then multiplied as a bipolar signal with the low pass filtered clock signal in analog multiplier 614 or mixer. The product is low pass filtered and provided as a BPSK modulated control signal for transmission.

[0048] In order to keep the interference caused by the conversion process at an extremely low level, the phase conversion time is set at the zero crossing point of the clock signal by a statically settable phase shifter 613. The limit frequency of the subsequent output low-pass filter 615 is greater than twice the signal frequency, so that the conversion process is as smooth as possible. In the example, a 25MHz 7th-order Chebyshev low-pass filter is applied as the output low-pass filter 615 at a clock frequency of 10MHz.

[0049] Figure 4An exemplary embodiment of a demodulator 73 is schematically shown. The demodulator 73 is supplied with control signals, which are output by a sensor 71 and provided by a frequency multiplier 72, and with control signals whose frequency is multiplied by a factor n. In the simplest case, the factor n is equal to two.

[0050] The bandpass filter 731 filters the frequency-multiplied control signal and outputs it to the simple PLL 732 as a reference frequency. The PLL 732 works as a "Jitter Cleaner" with a smaller loop bandwidth (e.g., 50 Hz). The PLL 732 removes the interference effect of data modulation and the noise caused by the insufficient amplitude dynamics of the transmission channel. In addition to the loop bandwidth, the signal quality is mainly determined by the quality of the VCXO inside the PLL. Subsequently, after being divided by n in the frequency divider 733, a clock signal C is provided at the output. There is no modulation on this signal anymore.

[0051] BPSK demodulation of the control information D is performed by simply multiplying the modulated control signal S with the clean output clock signal C in a multiplier 741. The mixed product is filtered in a low pass filter 742, for example, with a 5th order Butterworth low pass filter, and then output as a data signal D.

[0052] The combination of Schmitt trigger 735 and RC low-pass filter 734 ensures that the "lock detection" signal of PLL 732 is further processed only when PLL 732 has been reliably locked. The trigger 736, which is clocked with the received signal S, generates a switching signal synchronized with the clock signal from the output signal of Schmitt trigger 735. This switching signal is logically connected to the unfiltered "lock detection" signal through an AND operation in AND gate 737. This ensures that the output signal or clock signal C is cut off immediately after the received signal is interrupted. Only when the PFD has a stable "lock detection" signal, the output signal C is sent synchronously with the 10MHz received signal. The signal edge at the clock input of the trigger 736 is set in cooperation with the clearing function of the frequency divider 733 by means of a static phase shifter 738 and a threshold switch 739. The triggered clearing function ensures that the data signal has a defined logic state after switching on. The signal phase of the maximum detector sensitivity is set by means of a static phase shifter 740. The control signal or data signal D can then either be used directly as a switching signal or first decoded as a serial data signal in order to control a plurality of control functions.

[0053] exist Figure 4 In the implementation of the additional functions shown (such as synchronization of data and clock signals or jitter and amplitude stabilization of clock signals), although it is beneficial to the operation, the transmission of clock signals and control information and modulated control signals according to the present invention can also be achieved without such additional functions.

[0054] Although the present invention has been illustrated and described in detail by means of preferred embodiments, the present invention is not limited to these 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.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A peripheral device for a magnetic resonance imaging system (1), characterized in that The peripheral device has a sensor (71) for receiving electrical and / or magnetic control signals in the surroundings of the peripheral device, wherein the peripheral device is designed to obtain a reference clock for signal processing in the peripheral device and control information of the peripheral device from the control signal, and the control information is modulated into the control signal by means of phase modulation. 2 . The peripheral device according to claim 1 , wherein the peripheral device is adapted to demodulate the phase modulation by 360 / n degree phase shift keying to obtain the control information, wherein n is a natural number greater than 1. 3 .

3. The peripheral device according to claim 2, wherein the peripheral device has a frequency multiplier (72) for multiplying the frequency of the control signal by the factor n, wherein the peripheral device is designed to obtain the reference clock from the frequency multiplication of the control signal.

4. The peripheral device according to any of the preceding claims, wherein n is equal to 2.

5. The peripheral device according to any one of the preceding claims, wherein the peripheral device is a local coil (50) of the magnetic resonance imaging system (1), and the local coil (50) is suitable for processing magnetic resonance signals for image acquisition using the reference clock.

6. A system, comprising a peripheral device according to any one of the preceding claims and a magnetic resonance imaging system (1), wherein the magnetic resonance imaging system (1) has a reference clock generator, a modulator (61) and a control signal transmitter (60), wherein the reference clock generator is adapted to provide a reference clock to the modulator (61), the modulator (61) is adapted to modulate the reference clock with control information by means of phase modulation, and the control signal transmitter (60) is adapted to transmit the control signal to the surrounding environment of the peripheral device in the magnetic resonance imaging system (1).

7. A system having a peripheral device according to claim 4 or 5, wherein the modulator (61) is adapted to implement the phase modulation in zero crossings of the reference clock.

Images