Local coil with energy-saving device

Abstract

The invention relates to a local coil for a magnetic resonance imaging (MRI) scanner and a MRI scanner with a local coil. The local coil has a detuning device with a signal path for activation. The local coil has a further functional unit with two operating states with different energy consumption. The local coil also has an energy consumption control configured to control the operating states of the functional unit depending on image acquisition.

Description

[0001] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0002] The invention relates to a local coil for a magnetic resonance imaging scanner and a magnetic resonance imaging scanner with a local coil. The local coil has a detuning device with a signal path for activation. The local coil has a further functional unit with two operating states with different energy consumption.

[0003] Magnetic resonance imaging scanners are imaging devices that, to create an image of a subject, align the nuclear spins of the subject with a strong external magnetic field and then excite them to precess around this alignment using an alternating magnetic field. The precession, or return, of the spins from this excited state to a lower-energy state, in turn generates a response alternating magnetic field, which is received via antennas.

[0004] Using magnetic gradient fields, a spatial coding is imprinted on the signals, which subsequently allows the received signal to be assigned to a volume element. The received signal is then evaluated, and a three-dimensional image of the object under examination is provided. Local receiving antennas, so-called local coils, are preferably used to receive the signal. These antennas are positioned directly on the object under examination to achieve a better signal-to-noise ratio.

[0005] These local coils are usually connected to the MRI scanner's receivers via coaxial cables. However, handling the cables is difficult due to their thickness and the required sheath wave filters, and the multi-pin connectors are prone to failure.

[0006] Another approach is to transmit the magnetic resonance signals wirelessly from the local coil to the receiver. However, this requires that the local coil's power supply is also wireless or via energy storage devices such as batteries within the local coil. In particular, essential loads such as analog preamplifiers consume considerable energy due to the required dynamic range.

[0007] Regardless of the energy consumption, the waste heat generated by a wired local coil is also a problem for the patient

[0008] It is therefore an object of the present invention to improve the operation of a local coil.

[0009] This object is achieved by a wireless local coil according to claim 1 and a magnetic resonance imaging device according to claim 7.

[0010] The local coil according to the invention is intended for use with a magnetic resonance imaging scanner. The invention is particularly advantageous in conjunction with a wireless local coil. A wireless local coil is a local coil that has no connection to the magnetic resonance imaging scanner via a cable, be it an electrical connection cable or an optical connection cable. This significantly simplifies handling of the local coil. A wireless local coil necessarily has a wireless power supply, such as a battery or a supercapacitor, to enable uninterrupted operation. A wireless local coil benefits from lower energy consumption, explained below, due to a longer uninterrupted service life. However, local coils according to the invention with a wired connection to the magnetic resonance imaging scanner also benefit, for example, from less heating.

[0011] The local coil has a detuning device with a signal path for activation. A detuning device is a device designed to protect an antenna coil for receiving a magnetic resonance signal from the local coil in an activated state from damage caused by an excitation pulse for the nuclear spins. To generate the magnetic resonance signal in a patient's body, the nuclear spins must first be excited. This is achieved by a radio-frequency signal which, due to the constant static magnetic field B0, also contains significant signal components at the Larmor frequency, which are also present in the magnetic resonance signals to be received by the antenna coil. The excitation pulse can have powers of several hundred watts or several kilowatts, so that in a resonantly tuned antenna coil, the induced currents and voltages would damage the antenna coil and endanger the patient.To prevent this, the detuning device is activated before the excitation pulse is transmitted via the signal path, so that the antenna coil is no longer resonant at the Larmor frequency and the induced currents and voltages are orders of magnitude smaller.

[0012] In the local coil according to the invention, the signal path for activating the detuning device is either wired or, in particular in the wireless embodiment, wireless.

[0013] In the case of a wired local coil, a separate line can be provided for transmitting a detune signal to activate the detuning device. For example, a signal line that transmits a current and / or a voltage that activates or directly operates the detuning device is conceivable. However, a line that transmits an activation command is also conceivable.

[0014] In the wireless embodiment of the local coil, it can be provided, for example, that a high-frequency magnetic or electromagnetic alternating field is induced by the magnetic resonance imaging scanner at a frequency different from the Larmor frequency as a detune signal, which is received by an antenna or antenna coil of the local coil and activates the detuning device. It is also conceivable that the detune signal itself transmits sufficient energy to supply the detuning device with power. For example, the detune signal received by the antenna can be rectified and thus itself supply and activate the detuning device. However, it is also conceivable that the detune signal merely serves as a message on the basis of which the detuning device actively carries out the activation itself using a power source of the local coil, such as a battery. In this case, the signal can also be transmitted optically, for example.

[0015] The local coil according to the invention has at least one further functional unit that has two operating states with different energy consumption. These can be, for example, low-noise preamplifiers (LNAs) or mixers for downmixing the received magnetic resonance signals. In the simplest case, the operating states can be an on state when magnetic resonance signals are to be processed and an off state during pauses in between. Magnetic resonance signals for imaging only occur during specific periods of an image acquisition sequence, for example, when the nuclear spins in a volume to be acquired are in phase.It is also conceivable that signals with particularly large amplitude occur in these rephased sections, so that LNA and / or mixers must be operated with particularly high currents for linear processing with high dynamics, while in sections with small amplitude even smaller currents are sufficient, which is a further operating state within the meaning of the invention.

[0016] Furthermore, it is conceivable that in a digital local coil, for example, digital units such as multiplexers, A / D converters, memories and / or processors are only activated in the corresponding phases with evaluable magnetic resonance signals, while they remain in an energy-saving sleep mode in between.

[0017] The local coil according to the invention has a power consumption controller. This is understood to mean a circuit, analog or digital, or even a processor, designed to control the operating states of the functional unit(s) depending on an image acquisition. In other words, the power consumption controller places the functional unit into different operating states with different power consumption depending on the image acquisition, in particular on the sequence of an image acquisition sequence. Preferably, the power consumption controller places the functional unit into the operating state with the lowest energy consumption possible in the respective section of the image acquisition sequence.

[0018] In an advantageous manner, the local coil according to the invention achieves a reduced energy consumption and thus an extended operating time with the available energy through the energy consumption control.

[0019] Further advantageous embodiments are explained in the subclaims.

[0020] In one possible embodiment of the local coil according to the invention, the energy consumption controller is designed to detect a detune signal for the detuning device on the signal path. In the simplest case, the energy consumption controller can be in direct signal connection with the signal path, for example, it can have a signal input that also receives the detune signal for the detuning device via an electrical connection. However, processing of the detune signal, such as voltage conversion, filtering, or level limiting, is also conceivable.

[0021] The energy consumption control then controls the operating states of the functional unit depending on the detune signal. In the simplest case, the energy consumption control can, for example, interrupt the power supply to the preamplifier and / or mixer if the detune signal specifies activation of the detuning device. This is because no magnetic resonance signal can be received during the excitation pulse and these can be deactivated. However, it is also conceivable for the energy consumption control to detect and take into account additional signals containing information about the image acquisition, such as signals from a sensor for detecting the gradient fields, as explained below. It is also possible for the energy consumption control to take into account additional information about the passage of time, so that the change in the operating states is indirectly caused by the detune signal but does not necessarily occur synchronously with it.

[0022] Advantageously, energy savings can be easily achieved simply by coupling the detune signal and the operating state. Furthermore, the energy consumption controller can also further reduce energy consumption with knowledge of the image acquisition sequence, e.g., over sections without a magnetic resonance signal, by setting an operating state with reduced energy consumption beyond the immediate duration of the detune signal, but triggered by it. For example, it is conceivable that the energy consumption controller sets a predetermined operating state for a predetermined time using the detune signal, e.g., for receiving the magnetic resonance signals generated by the associated excitation pulse.

[0023] In one conceivable embodiment of the local coil according to the invention, the energy consumption controller comprises a decoder. The decoder is designed to decode a plurality of messages encoded in the detune signal. A plurality is considered to be a set of messages that goes beyond the binary on / off information of the detune signal for controlling the detuning device. For example, it is conceivable that further information is encoded in the detune signal through one or more short interruptions in the detune signal. Preferably, the interruptions are so short that they do not lead to a change in the detuned state, for example, due to a low-pass filter in the detuning device, or are eliminated by a holding element in the decoder before the detune signal is passed from the decoder to the detuning device.

[0024] The detune signal is to be understood in a broader sense here as a signal that is transmitted on the same line or signal path as the actual signal that triggers the detuned state of the detuning device. In particular, it is conceivable that a detune signal or a signal on the signal path for the actual detune signals could transmit a message at a time without an excitation pulse. This coded message preferably differs from the actual detune signal in that it does not trigger or activate the detuning device, for example, by consisting of pulses that are short compared to the actual detune duration, which can also be sent by the magnetic resonance imaging scanner before the excitation pulse.

[0025] The energy-saving device receives the message and sets a number of operating states of the functional unit depending on the messages. For example, additional operating states with different energy-saving levels are conceivable. This could include, among other things, a message regarding an expected amplitude of the magnetic resonance signal or a bias current in the LNA to allow the signal to be processed in the linear range. A message regarding a duration of the energy-saving state that differs from the duration of the detune signal would also be conceivable.

[0026] In the magnetic resonance tomograph according to the invention with a corresponding local coil according to the invention, the magnetic resonance tomograph has a corresponding or complementary coding unit in order to encode the message relating to the operating state into the detune signal and subsequently transmit it to the local coil.

[0027] Advantageously, the magnetic resonance imaging scanner with the coding unit can transmit additional energy-saving measures to the local coil via the detune signal using a coded message and a decoder in the local coil, thus further improving the runtime. Using the detune signal eliminates the need for additional communication channels or cables and, especially with a wireless local coil, simplifies both the system approval and the construction of the local coil, resulting in further energy savings.

[0028] In one possible embodiment of the local coil according to the invention, the energy consumption controller is designed to place the functional unit or functional units into a predetermined operating state in the absence of a predetermined image acquisition event. The absence of a predetermined image acquisition event can be considered, for example, the absence of the detune signal, of gradient fields as explained below with regard to the magnetic field sensor, or of other signals detectable by the local coil within a predetermined interval. If, for example, no excitation pulse has been emitted for a prolonged period, i.e., within a period of several seconds to minutes, and the local coil has not detected a correlated detune signal, then no excited nuclear spins are present in the sample or the patient, and a magnetic resonance signal can no longer be received.For example, the LNA and / or mixer can then be put into a standby state or de-energized by the power consumption controller. It is conceivable that the power-saving mode will be terminated by the power consumption controller with another detune signal. It is also conceivable that the power-saving operating mode will remain for a predetermined period of time.

[0029] The detection of operating breaks due to the absence of signals enables further energy-saving periods for the local coil according to the invention.

[0030] In one conceivable embodiment of the local coil according to the invention, the local coil has a magnetic field sensor in signal communication with the energy consumption controller. The magnetic field sensor is designed to detect a gradient field. Examples of magnetic field sensors are induction coils or Hall sensors.

[0031] Induction coils, in principle, only detect changing magnetic fields, while the static B0 field is already filtered out. If the induction coil signal is passed through a low-pass filter, only signals induced by the gradient fields remain, making them easy to detect. Hall sensors can saturate due to the B0 field, making gradient field detection difficult. This problem can be solved through appropriate alignment and / or design. B0 detection can then also be used, for example, to set the local coil outside the patient tunnel to an energy-saving operating state through energy consumption control.

[0032] The energy consumption controller is designed to adjust the operating states depending on a signal from the magnetic field sensor. For example, it is conceivable that in the absence of the detune signal, no magnetic resonance signals are present at certain time periods of an image acquisition sequence, which can be defined by a temporal relationship to the switching processes of the gradient fields, and an energy-saving operating state is activated by the energy consumption controller for the functional unit. It would also be conceivable to establish an operating state with increased energy consumption and the associated readiness to receive when gradient fields are active, because these are required for readout in the corresponding sequence.

[0033] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0034] They show: Fig. 1 a schematic representation of a magnetic resonance imaging apparatus according to the invention; Fig. 2 is a schematic representation of a timing diagram of an exemplary image acquisition sequence; Fig. 3 a schematic detailed representation of an embodiment of a local coil according to the invention; Fig. 4 is a schematic representation of a timing diagram of an exemplary image acquisition sequence; Fig. 5 a schematic detailed representation of an embodiment of a local coil according to the invention.

[0035] Fig. 1 shows a schematic representation of an exemplary embodiment of a magnetic resonance imaging device 1 according to the invention.

[0036] The magnet unit 10 has a field magnet 11 that generates a static magnetic field B0 for aligning nuclear spins of samples or patients 100 in a recording area. The recording area is arranged in a patient tunnel 16 that extends in a longitudinal direction 2 through the magnet unit 10. A patient 100 can be moved into the recording area by means of the patient bed 30 and the movement unit 36 ​​of the patient bed 30. The field magnet 11 is typically a superconducting magnet that can generate magnetic fields with a magnetic flux density of up to 3T, and even higher in the latest devices. However, permanent magnets or electromagnets with normally conducting coils can also be used for lower field strengths.

[0037] 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 for spatial differentiation of the acquired imaging regions in the examination volume. The gradient coils 12 are typically coils made of normally conducting wires that can generate mutually orthogonal fields in the examination volume.

[0038] The magnet unit 10 also has a body coil 14, which is designed to emit a high-frequency signal supplied via a signal line 33 into the examination volume and to receive resonance signals emitted by the patient 100 and transmit them via a signal line. Preferably, however, the body coil 14 for transmitting and / or receiving the high-frequency signal is replaced by local coils 50, which are arranged in the patient tunnel 16 close to the patient 100. However, it is also conceivable that the local coil 50 is designed for both transmitting and receiving, and therefore a body coil 14 can be omitted.

[0039] A control unit 20 supplies the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14 and evaluates the received signals. A magnetic resonance imaging controller 23 coordinates the subunits.

[0040] Thus, the control unit 20 has a gradient control 21 which is designed to supply the gradient coils 12 with variable currents via supply lines, which provide the desired gradient fields in the examination volume in a time-coordinated manner.

[0041] Furthermore, the control unit 20 has a radio-frequency unit 22, which is designed to generate a radio-frequency pulse with a predetermined temporal profile, amplitude, and spectral power distribution for exciting a magnetic resonance of the nuclear spins in the patient 100. Pulse powers in the kilowatt range can be achieved. The individual units are interconnected via a signal bus 25.

[0042] The radio-frequency signal generated by the radio-frequency unit 22 is fed to the body coil 14 via a signal connection and transmitted into the body of the patient 100 to stimulate the nuclear spins there. However, it is also conceivable to transmit the radio-frequency signal via one or more local coils 50.

[0043] The local coil 50 then preferably receives a magnetic resonance signal from the body of the patient 100. Due to the short distance, the signal-to-noise ratio (SNR) of the local coil 50 is better than when received by the body coil 14. The MR signal received by the local coil 50 is processed in the local coil 50 and forwarded to the radio-frequency unit 22 of the magnetic resonance imaging scanner 1 for evaluation and image acquisition. With the local coil according to the invention, transmission occurs wirelessly or via a wired connection. Control signals, in particular a detune signal for detuning the local coil 50 during the excitation pulse, must also be transmitted to the local coil 50.In the case of a wired local coil 50, this can be done via a control line; in the case of a wireless local coil 50, for example, it can be done via an alternating magnetic field generated by the magnetic resonance imaging scanner 1 and received by an induction coil in the local coil 50. Transmission via an electromagnetic wave is also conceivable, for example, transmission in an ISM band or using commercial radio technologies such as Bluetooth or WLAN.

[0044] Fig. Figure 2 shows a schematic representation of the timing of an exemplary image acquisition sequence. The abscissa indicates time in arbitrary time units. The key signals of an image acquisition sequence are plotted along the ordinate. From top to bottom, these are: The excitation pulses 60, where the numbers in the figure indicate the deflection of the spins to be achieved by the excitation pulses 60 in degrees. Here, 90 degrees corresponds to a maximum deflection as an excitation pulse, and 180 degrees to a spin flip to generate a spin echo;

[0045] The magnetic resonance signal 61 to be acquired by the local coil has a maximum amplitude after the 90-degree excitation pulse and then decreases with the time constant T1 due to dephasing until it is rephased again by the spin flip. The amplitude of the spin echoes decreases exponentially with the time constant T2, so that after a multiple of T2, no usable magnetic resonance signal can be acquired.

[0046] The detune signal 62, where the detune signal 62 is the signal transmitted from the magnetic resonance tomograph 1 to the local coil 50 and indicates when the local coil 1 should be detuned so that the excitation pulses 60 do not cause damage to the local coil 50 or endanger the patient 100.

[0047] The energy control signal 63 indicates the signal that an energy consumption controller 56 of the local coil 50 outputs to functional units of the local coil 50 in order to put them into an energy-saving operating state.

[0048] In the Fig. In the embodiment illustrated in Figure 2, the energy control signal 63 specifies an operating state with increased energy consumption for acquiring the magnetic resonance signals for a duration substantially determined by T2 before the functional units are placed in an energy-saving operating state. The energy-saving operating state is terminated with the next detune signal 62, which accompanies the next excitation pulse 60.

[0049] In Fig. 3 are shown by way of example the essential units involved in a wireless local coil 50 according to the invention, which are required to ensure a time sequence of the Fig. 2. Energy storage devices such as batteries or details of wireless transmission are not described in detail here.

[0050] In a wired embodiment of the local coil according to the invention, the wireless transmission unit 55 can be replaced by a wired transmission, in the simplest case by a cable / plug connection for the individual signals to be transmitted.

[0051] The local coil 50 has an antenna coil 51 for receiving magnetic resonance signals. The antenna coil 51 can be brought into a non-resonant state by a detuning device 52 coupled thereto, so that excitation pulses from the magnetic resonance imaging scanner 1 do not cause damage. The detuning device 52 receives the detune signal from the wireless transmission unit 55, which ensures wireless signal transmission to and from the magnetic resonance imaging scanner 1.

[0052] Received magnetic resonance signals are amplified by a preamplifier / LNA 53, converted to an intermediate frequency by a mixer 54 and transmitted by the wireless transmission unit 55 to the magnetic resonance tomograph 1.

[0053] Preferably, a mixed frequency for the frequency conversion is provided by the magnetic resonance imaging device 1 via the transmission unit 55.

[0054] The transmission unit 55 can also consist of different functional groups for the different signals. For example, the magnetic resonance signals can be transmitted analogously at the intermediate frequency. The detune signal can be induced into a receiving coil of the transmission unit 55 using an alternating magnetic field; the same is conceivable for the mixed signal. Digital transmission of all signals is also conceivable.

[0055] A power consumption controller 56 also receives the detune signal and, depending on the detune signal, forwards a power control signal to the functional units mixer 54 and LNA 53. To control the power control signal, as in Fig. 2, not only for the duration of the detune signal, but for a predetermined time in the order of magnitude of T2, the energy consumption controller 56 has a timing element, for example a mono-flop or timer.

[0056] The power control signal is implemented by the functional units in such a way that, when the power control signal is not present, the functional units enter a power-saving operating state. There are corresponding components, such as amplifiers from Texas Instruments, that feature a power-down mode. However, it is also conceivable that the power consumption controller 56 directly interrupts the power supply to one or more functional units.

[0057] Fig. Figure 4 shows a schematic representation of a timing diagram of an exemplary image acquisition sequence. The timing diagram of the Fig. 2 and Fig. 4 differs in that several different operating states are set at different times, which is represented by two energy control signals 63. However, it is also conceivable that the energy supply controller 56 has a common line or bus via which the energy consumption controller 56 can communicate different operating states to the functional units.

[0058] In order to transmit different states independently or in addition to the detune signal from the magnetic resonance imaging device 1 to the local coil 50, as in Fig. 4, the detune signal can be encoded with a message, for example, by short interruptions. As shown below, the power consumption controller 56 produces a detune output signal 64 without interruptions for the detuning device 52.

[0059] In Fig. 5 is a schematic detailed representation of an embodiment of a local coil 50 according to the invention, which shows the timing of the Fig. 4 uses and implements.

[0060] The design of the Fig. 5 differs from the design of the Fig. 3, the energy consumption controller 56 not only receives the coded detune signal from the magnetic resonance imaging scanner 1, but also transmits it in the same form to the detuning device 52. Instead, the energy consumption controller 56 has a decoder that recognizes the coding and captures the coded message. Depending on the message, the energy consumption controller 56 sends energy control signals 63 to one or more functional units via one or more signal connections.

[0061] Furthermore, the decoder again produces a detune output signal 64 without the short interruptions and forwards it to the detuning device 52. This ensures that the antenna coil 51 is detuned without interruption.

[0062] In the concrete example of Fig. 4 and Fig.5, the LNA is used for reception in two different operating modes. In an initial phase immediately after the 90-degree excitation pulse, the magnetic resonance signals have a high amplitude, which requires a high bias current from the LNA for linear processing. When the magnetic resonance signals have fallen below a threshold due to the reduction of the excitation, optimal processing can be ensured with a lower bias current and thus lower energy consumption. The magnetic resonance tomograph 1 or its controller 23 signals this by a brief interruption in the detune signal 62, which can be detected, for example, by a high-pass filter, a logic circuit, or a processor. The energy consumption controller 56 generates a separate control signal for the LNA 53 from this to set this operating state with reduced bias.This can be generated, for example, by a monostable flip-flop or a bistable flip-flop, which is then reset by the detune signal ANDed with the inverted second power control signal. This implementation using simple logic circuits advantageously features low power consumption, generates minimal interference, and can be integrated into an existing environment without major changes, particularly in a wireless local coil 50 with analog transmission.

[0063] However, more complex variants are also conceivable, for example with digital transmission, in which the magnetic resonance imaging device 1 transmits the operating states separately to the local coil 50 without changing the detune signal.

[0064] Although the invention has been illustrated and described in detail by the preferred embodiment, the 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 the invention.

Claims

[1] Local coil for a magnetic resonance imaging device, wherein the local coil (50) has a detuning device (52) with a signal path for activation and a further functional unit which has two operating states with different energy consumption and an energy consumption controller (56) which is designed to control the operating states of the functional unit as a function of an image acquisition. [2] Local coil according to claim 1, wherein the energy consumption controller (56) is designed to detect a detune signal for the detuning device (52) on the signal path and to control the operating states of the functional unit in dependence on the detune signal. [3] Local coil according to claim 2, wherein the energy consumption controller (56) comprises a decoder configured to decode a plurality of messages encoded in the detune signal and to set a plurality of operating states of the functional unit in dependence on the messages. [4] Local coil according to one of the preceding claims, wherein the energy consumption control (56) is designed to place the functional unit into a predetermined operating state in the absence of a predetermined image acquisition event. [5] Local coil according to one of the preceding claims, wherein the local coil (50) has a magnetic field sensor in signal connection with the energy consumption controller (56) and the magnetic field sensor is designed to detect a gradient field, wherein the energy consumption controller (56) is designed to adjust the operating states in dependence on a signal from the magnetic field sensor. [6] Magnetic resonance tomograph with a local coil (50) according to one of claims 3 or 4, wherein the magnetic resonance tomograph (1) has a coding unit which is designed to encode a message relating to an operating state of the functional unit in the detuning signal.

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