Local coil with energy-saving device

Abstract

The invention relates to a local coil for a magnetic resonance tomography apparatus and a magnetic resonance tomography apparatus having a local coil. The local coil has a detuning device with a signal path for activation. The local coil has a further functional unit which has two operating states, which have different energy consumptions. The local coil also has an energy consumption controller which is designed to control the operating state of the functional unit as a function of the image capture.

Description

Technical Field

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

[0002] The invention relates to a local coil for a magnetic resonance tomography system and a magnetic resonance tomography system having 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 having different energy consumptions. Background Art

[0003] A magnetic resonance tomography system is an imaging device that uses a strong external magnetic field to align the nuclear spins of the object under examination for imaging and excites the nuclear spins to precess about the alignment by means of an alternating magnetic field. The precession or return of the spins from this excited state to a state of lower energy in turn generates an alternating magnetic field in response, which is received by an antenna.

[0004] The signals are subjected to a position encoding by means of a gradient magnetic field, which subsequently enables the received signals to be associated with a volume element. The received signals are then evaluated and a three-dimensional imaging display of the examination object is provided. For receiving the signals, local receiving antennas, so-called local coils, are preferably used, which are arranged directly on the examination object to achieve a better signal-to-noise ratio.

[0005] These local coils are usually connected to the receiver of the magnetic resonance tomography system via a coaxial cable. However, due to the thickness of the cable and the required external sheath filter, the cable is difficult to implement and the multi-pole plug connection is prone to errors.

[0006] Another approach is to transmit the magnetic resonance signals wirelessly from the local coil to the receiver. However, this presupposes that the energy supply to the local coil is also wireless or via an energy storage device, such as a battery in the local coil. In this case, especially the mandatory electrical consumers, such as analog preamplifiers, have a significant energy consumption due to the required dynamic range.

[0007] Independently of the energy consumption, in the case of wired local coils the waste heat thereby generated in the patient is also a problem. Summary of the invention

[0008] SUMMARY OF THE INVENTION The object of the present invention is therefore to improve the operation of a local coil.

[0009] The above-mentioned technical problem is solved by a wireless local coil according to the invention and a magnetic resonance tomography system according to the invention.

[0010] The local coil according to the invention is designed for use with a magnetic resonance tomography system. The invention is particularly advantageous in combination with a wireless local coil. A wireless local coil is a local coil that is not connected to the magnetic resonance tomography system via a wire, either an electrical or an optical connection wire. This significantly simplifies the implementation of the local coil. A wireless local coil necessarily has a wireless power supply, such as a battery or a supercapacitor, to allow uninterrupted operation. A wireless local coil benefits from a lower energy consumption, explained below, due to a longer uninterrupted operating time. However, a local coil according to the invention with a wired connection to the magnetic resonance tomography system also benefits, for example, from less heating.

[0011] The local coil has a detuning device, which has a signal path for activation. The detuning device refers to a device that is designed to protect the antenna coil for receiving the magnetic resonance signal of the local coil from being damaged by the excitation pulse used for nuclear spins in the activated state. In order to generate magnetic resonance signals in the patient, it is first necessary to excite the nuclear spins. This is achieved by a high-frequency signal, which, due to the constant static magnetic field B0, also has a main signal component, which has the Larmor frequency and also has the magnetic resonance signal to be received by the antenna coil. In this case, the excitation pulse can have a power of several hundred watts or several kilowatts, so that in the case of a resonantly tuned antenna coil, the induced current and voltage can damage the antenna coil and endanger the patient. In order to prevent this, the detuning device is activated through the signal path before the excitation pulse is emitted, so that the antenna coil no longer resonates at the Larmor frequency and the induced current and voltage are several 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 a wireless embodiment, wireless.

[0013] In the case of wired local coils, separate lines can be provided for transmitting a detuning signal for activating the detuning device. For example, signal lines are conceivable, which transmit a current and / or a voltage, which activates or directly operates the detuning device. However, lines for transmitting activation commands are also conceivable.

[0014] In a wireless embodiment of the local coil, it can be provided, for example, that as a detuning signal, a high-frequency magnetic alternating field or a high-frequency electromagnetic alternating field is induced by the magnetic resonance tomography device at a frequency not equal to the Larmor frequency, which high-frequency magnetic alternating field or high-frequency electromagnetic alternating field is received by the antenna or antenna coil of the local coil and activates the detuning device. It is also conceivable that the detuning signal itself transmits sufficient energy to supply energy to the detuning device. For example, the detuning signal received by the antenna can be rectified and thus the detuning device itself can be powered and activated. However, it is also conceivable that the detuning signal is used only as a message, based on which the detuning device itself is activated actively using the energy source of the local coil, such as a battery. The signal can then also be transmitted optically, for example.

[0015] The local coil according to the invention has at least one further functional unit which has two operating states with different energy consumption. This can be, for example, a low noise preamplifier (LNA) or a mixer for down-mixing received magnetic resonance signals. In the simplest case, the operating state can be an on state when the magnetic resonance signals are to be processed and an off state in the intervals therebetween. The magnetic resonance signals used for imaging appear only in certain time periods within the scope of an image acquisition sequence, for example when the nuclear spins are in phase in the volume to be acquired. It is also conceivable that signals with particularly large amplitudes appear in these re-phasing sections, so that for linear processing with high dynamics, the LNA and / or the mixer must be operated with particularly high currents, while in sections with small amplitudes, smaller currents are also sufficient, which are further operating states within the meaning of the invention.

[0016] Furthermore, it is conceivable that in digital local coils, for example, digital units such as multiplexers, A / D converters, memories and / or processors are activated only in corresponding phases with analyzable magnetic resonance signals, while they remain in an energy-saving quiescent mode during this period.

[0017] The local coil according to the invention has an energy consumption controller. This can be understood as an analog or digital circuit or also as a processor, which is designed to control the operating state of one or more functional units depending on the image acquisition. In other words, the energy consumption controller puts the functional units into different operating states with different energy consumption depending on the image acquisition, in particular the process of the image acquisition sequence. In this case, the energy consumption controller preferably puts the functional units into the operating state with the lowest energy consumption, which is possible in the corresponding section of the image acquisition sequence.

[0018] The local coil according to the invention advantageously enables reduced energy consumption by means of an energy consumption control and thus a prolonged operating time using the available energy.

[0019] Further advantageous embodiments are described in the present invention.

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

[0021] The energy consumption controller then controls the operating state of the functional unit as a function of the detuning signal. In the simplest case, the energy consumption controller can, for example, interrupt the energy supply to the preamplifier and / or mixer when the detuning signal predetermines the activation of the detuning device, since no magnetic resonance signals can be received during the excitation pulse and the amplifier and / or mixer can be deactivated. However, it is also conceivable that the energy consumption controller acquires and takes into account other signals with information about the image acquisition, such as the signals of the sensors for acquiring gradient fields explained below. It is also possible that the energy consumption controller takes into account additional information about the time course, so that the change in the operating state is indirectly caused by the detuning signal, but does not necessarily take place synchronously with the detuning signal.

[0022] In an advantageous manner, energy savings can already be achieved in a simple manner by coupling the detuning signal to the operating state. Furthermore, the energy consumption controller can also further reduce the energy consumption with knowledge of the image acquisition sequence, for example in sections without magnetic resonance signals, by setting an operating state with reduced energy consumption, also outside the direct duration of the detuning signal, but triggered by the detuning signal. For example, it is conceivable that a predetermined operating state is set by the energy consumption controller within a predetermined time by means of the detuning signal, for example for receiving magnetic resonance signals generated by the excitation pulses associated therewith.

[0023] In a conceivable embodiment of the local coil according to the invention, the energy consumption controller has a decoder. The decoder is configured to decode a plurality of messages encoded in the detuning signal. In this case, a large number of messages are considered as a plurality, which messages exceed the binary on / off information of the detuning signal for controlling the detuning device. For example, it is conceivable to encode further information in the detuning signal by one or more short interruptions of the detuning signal. In this case, the interruption is preferably so short that it does not lead to a change in the detuning state, for example by a low-pass filter in the detuning device, or the interruption is also eliminated in the decoder by a holding link before the detuning signal is forwarded from the decoder to the detuning device.

[0024] In this context, a detuning signal can also be understood in a broad sense to mean a signal which is transmitted on the same line or signal path as the actual signal which triggers the detuning state of the detuning device. In particular, it is conceivable that a message is transmitted by the detuning signal or a signal on the signal path for the actual detuning signal at a time when there is no excitation pulse. Preferably, this coded message differs from the actual detuning signal in that it does not trigger or activate the detuning device, for example by virtue of the fact that it consists of a pulse which is short in comparison to the actual detuning duration, which pulse can also be emitted by the magnetic resonance tomography device before the excitation pulse.

[0025] The energy saving device receives the message and sets a plurality of operating states of the functional unit as a function of the message. For example, additional operating states with different energy saving levels are conceivable. In addition, this can be a message about the expected amplitude of the magnetic resonance signal or a bias current in the LNA in order to be able to process the signal in the linear range. However, a message about the duration of an energy saving state, which differs from the duration of the detuning signal, is also conceivable.

[0026] In a magnetic resonance tomography system according to the invention having a corresponding local coil according to the invention, the magnetic resonance tomography system has a corresponding or complementary encoding unit in order to encode information about the operating state in the detuning signal and subsequently transmit it to the local coil.

[0027] Advantageously, a magnetic resonance tomography system with a coding unit can transmit further energy-saving measures to the local coils by means of a detuning signal with the aid of a coded message and a decoder in the local coils, thereby further improving the operating time. The use of the detuning signal saves additional communication channels or lines and, in particular in the case of wireless local coils, simplifies both the licensing of the system and the design of the local coils, which means further energy savings.

[0028] In a possible embodiment of the local coil according to the invention, the energy consumption controller is designed to place one or more functional units in a predetermined operating state when a predetermined event for image acquisition is not present. The absence of a predetermined event for image acquisition can be considered, for example, as the absence of a detuning signal, such as the gradient field explained below for the magnetic field sensor, or other signals that can be acquired by the local coil in a predetermined interval. If, for example, no excitation pulses are emitted for a longer period of time, i.e., within a period of several seconds to several minutes, and the local coil does not acquire the detuning signal associated therewith, then there are no longer excited nuclear spins in the sample or patient, and magnetic resonance signals can no longer be received. Then, for example, the LNA and / or the mixer can be placed in a quiescent state or switched to no current by the energy consumption controller. It is conceivable that the energy consumption controller ends the energy-saving state again by a new detuning signal. However, it is also conceivable that the energy-saving operating state is maintained for a predetermined time.

[0029] The detection of the operating pause by the absence of the signal makes it possible to achieve further energy-saving time periods for the local coil according to the invention.

[0030] In a conceivable embodiment of the local coil according to the invention, the local coil has a magnetic field sensor which is signal-connected to the energy consumption controller. The magnetic field sensor is designed to detect gradient fields. Exemplary magnetic field sensors are induction coils or Hall sensors.

[0031] In principle, the induction coils only detect changing magnetic fields, while the static B0 field is already blanked. If the signals of the induction coils are sent through a low-pass filter, only the signals induced by the gradient fields remain, which can be easily detected. The Hall sensors can be saturated by the B0 field, which makes the detection of the gradient fields difficult. This problem can be solved by suitable alignment and / or design, wherein the B0 detection can then also be used to put the local coils into an energy-saving operating state outside the patient channel, for example, by means of an energy consumption controller.

[0032] In this case, the energy consumption control is designed to set the operating state as a function of the signal of the magnetic field sensor. Thus, for example, it is conceivable that in the case of no detuning signal in a certain time section of an image acquisition sequence, which can be defined by the time relationship with the switching process of the gradient fields, no magnetic resonance signal is also present and an energy-saving operating state is activated by the energy consumption control for the functional unit. It is also conceivable that when gradient fields are activated, an operating state with increased energy consumption and the associated reception readiness is established, since these gradient fields are required for reading in the corresponding sequence. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above-described characteristics, features and advantages of the present invention and the manner in which these characteristics, features and advantages are achieved will become clearer and more clearly understood in conjunction with the following description of embodiments, which are explained in detail in conjunction with the accompanying drawings.

[0034] In the attached figure:

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

[0036] Figure 2 A schematic diagram showing the time course of an exemplary image acquisition sequence;

[0037] Figure 3 shows a schematic detail view of an embodiment of a local coil according to the invention;

[0038] Figure 4 A schematic diagram showing the time course of an exemplary image acquisition sequence;

[0039] Figure 5 A schematic detail view of an embodiment of a local coil according to the invention is shown. DETAILED DESCRIPTION

[0040] Figure 1 A schematic diagram of an exemplary embodiment of a magnetic resonance tomography system 1 according to the invention is shown.

[0041] The magnet unit 10 has a field magnet 11 which generates a static magnetic field B0 which is used to align the nuclear spins of the sample or the patient 100 in the recording area. The recording area is arranged in a patient channel 16 which extends through the magnet unit 10 in the longitudinal direction 2. The patient 100 can be moved into the recording area by means of a patient couch 30 and a moving unit 36 ​​of the patient couch 30. Typically, the field magnet 11 is a superconducting magnet which is able to provide a magnetic field with a magnetic flux density of up to 3 T, and even higher in the latest devices. However, for smaller field strengths, permanent magnets or electromagnets with normally conducting coils can also be used.

[0042] The magnet unit 10 also has gradient coils 12, which are designed to superimpose variable magnetic fields on the magnetic field B0 in three spatial directions in order to spatially differentiate the acquired imaging regions in the examination volume. The gradient coils 12 are usually coils made of normally conducting wires, which are able to generate mutually orthogonal fields in the examination volume.

[0043] The magnet unit 10 also has a body coil 14, which is designed to transmit high-frequency signals conveyed via a signal line 33 into the examination volume and to receive resonance signals emitted by the patient 100 and output them via the signal line. However, the body coil 14 for transmitting high-frequency signals and / or receiving is preferably replaced by a local coil 50, which is arranged in the patient channel 16 close to the patient 100. However, it is also conceivable that the local coil 50 is designed for transmission and reception and the body coil 14 can therefore be omitted.

[0044] 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. In this case, a magnetic resonance tomography controller 23 coordinates the subunits.

[0045] The control unit 20 therefore has a gradient controller 21 which is designed to supply the gradient coils 12 via input lines with variable currents which provide the desired gradient fields in the examination volume in a time-coordinated manner.

[0046] The control unit 20 also has a radio-frequency unit 22, which is designed to generate radio-frequency pulses with a predetermined time curve, amplitude and spectral power distribution for exciting nuclear spin magnetic resonance in the patient 100. Pulse powers in the kilowatt range can be achieved. The individual units are connected to one another via a signal bus 25.

[0047] The high-frequency signal generated by the high-frequency unit 22 is supplied via a signal connection to the body coil 14 and emitted into the body of the patient 100 in order to excite the nuclear spins there. However, it is also conceivable to emit the high-frequency signal via one or more local coils 50 .

[0048] The local coil 50 then preferably receives magnetic resonance signals from the body of the patient 100, since the signal-to-noise ratio (SNR) of the local coil 50 is better than when receiving via the body coil 14 due to the short distance. The MR signals received by the local coil 50 are conditioned in the local coil 50 and transmitted to the high-frequency unit 22 of the magnetic resonance tomography system 1 for evaluation and image acquisition. In the local coil according to the invention, the transmission takes place wirelessly or also by wire. Likewise, control signals, in particular detuning signals for detuning the local coil 50, must be transmitted to the local coil 50 during the excitation pulse. In the case of a wired local coil 50, this can be achieved via a control line, while in the case of a wireless local coil 50, this can be achieved, for example, by an alternating magnetic field generated by the magnetic resonance tomography system 1 and received by the induction coil in the local coil 50. Transmission via electromagnetic waves, for example in the ISM frequency band or using commercial radio technologies such as Bluetooth or WLAN is also conceivable.

[0049] Figure 2 A schematic diagram of the time course of an exemplary image acquisition sequence is shown. The abscissa represents the time in arbitrary time units. The main signals of the image acquisition sequence are plotted along the ordinate. From top to bottom:

[0050] Excitation pulse 60, wherein the numbers in the figure indicate in degrees the spin deflection to be achieved by the excitation pulse 60. In this case, 90 degrees corresponds to the maximum deflection as an excitation pulse and 180 degrees to the spin flip for generating a spin echo;

[0051] 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 a time constant T1 due to dephasing until it is re-phased again by spin flipping. The amplitude of the spin echo decreases exponentially with the time constant T2, so that no useful magnetic resonance signal can be acquired after a multiple of T2.

[0052] A detuning signal 62 , wherein the detuning signal 62 is a signal transmitted from the magnetic resonance tomography system 1 to the local coil 50 and indicates when the local coil 1 should be detuned so that the excitation pulse 60 does not damage the local coil 50 or endanger the patient 100 .

[0053] The energy control signal 63 indicates a signal which the energy consumption controller 56 of the local coil 50 outputs to the functional units of the local coil 50 in order to place these functional units into an energy-saving operating state.

[0054] exist Figure 2 In the embodiment shown, before the functional unit is placed in the energy-saving operating state, the energy control signal 63 predetermines an operating state with increased energy consumption for acquiring magnetic resonance signals, the duration of which is substantially determined by T2. The energy-saving operating state ends with the next detuning signal 62 accompanying the next excitation pulse 60.

[0055] exist Figure 3 The main units involved in the wireless local coil 50 according to the present invention are shown in the figure as an example, and the units are used to convert Figure 2 The details of energy storage devices such as batteries or wireless transmission are not shown in detail here.

[0056] In the case of 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.

[0057] The local coil 50 has an antenna coil 51 for receiving magnetic resonance signals. The antenna coil 51 can be placed in a non-resonant state by a detuning device 52 coupled thereto, so that the excitation pulses of the magnetic resonance tomography apparatus 1 do not cause damage. The detuning device 52 receives a detuning signal from a wireless transmission unit 55, which is responsible for wireless signal transmission from and to the magnetic resonance tomography apparatus 1.

[0058] The received magnetic resonance signal is amplified by the preamplifier / LNA 53 , converted to an intermediate frequency by the mixer 54 , and transmitted to the magnetic resonance tomography apparatus 1 by the wireless transmission unit 55 .

[0059] Preferably, the mixing frequency for the frequency conversion is provided by the magnetic resonance tomography scanner 1 via the transmission unit 55 .

[0060] The transmission unit 55 can also have different functional groups for different signals. For example, the transmission of magnetic resonance signals can similarly take place at an intermediate frequency. Detuned signals can be induced into the receiving coils of the transmission unit 55 by means of an alternating magnetic field, and the same is conceivable for mixed signals. However, digital transmission of all signals is also conceivable.

[0061] The energy consumption controller 56 also receives the detuning signal and forwards the energy control signal to the functional units, namely the mixer 54 and the LNA 53, according to the detuning signal. Figure 2 As shown, the energy consumption controller 56 has a timing element, such as a monostable trigger or a timer, in order to provide the energy control signal not only for the duration of the detuning signal but also for a predetermined time in the order of magnitude of T2.

[0062] The energy control signal is converted by the functional unit in such a way that, in the absence of the energy control signal, the functional unit assumes an energy-saving operating state. There are corresponding modules, such as amplifiers from Texas Instruments, which have a power-off mode. However, it is also conceivable that the energy consumption controller 56 directly interrupts the energy supply to one or more functional units.

[0063] Figure 4 A schematic diagram showing the time course of an exemplary image acquisition sequence. Figure 2 and Figure 4 The time sequence of the energy consumption controller 56 differs in that a plurality of different operating states are set at different times, which is indicated by the two energy control signals 63. However, it is also conceivable that the energy consumption controller 56 has a common line or bus via which the energy consumption controller 56 can transmit the different operating states to the functional units.

[0064] In order to transmit different states from the magnetic resonance tomography system 1 to the local coil 50 independently or in addition to the detuning signal, such as Figure 4 As shown, the detuning signal can be encoded, for example, by a short interruption using a message. As shown below, the energy consumption controller 56 generates a detuning output signal 64 for the detuning device 52 without an interruption.

[0065] exist Figure 5 A schematic detail view of an embodiment of a local coil 50 according to the present invention is shown in FIG. Figure 4 time process.

[0066] Figure 5 The implementation method and Figure 3 The embodiment of the invention differs in that the energy consumption controller 56 not only receives the coded detuning signal of the magnetic resonance tomography system 1, but also transmits it in the same form to the detuning device 52. Instead, the energy consumption controller 56 has a decoder which recognizes the code and receives the coded message. Depending on the message, the energy consumption controller 56 sends an energy control signal 63 to one or more functional units via one or more signal connections.

[0067] Furthermore, the decoder generates the detuned output signal 64 again without a short interruption and passes it on to the detuning device 52. This ensures that the antenna coil 51 is detuned without interruption.

[0068] exist Figure 4 and Figure 5 In the specific example of , the LNA is used for reception in two different operating modes. In the initial phase immediately after the 90-degree excitation pulse, the magnetic resonance signal has a high amplitude, which requires a high bias current of the LNA for linear processing. When the magnetic resonance signal drops below the threshold due to the disappearance of the excitation, optimal processing can be ensured with a smaller bias current and therefore also with a smaller energy consumption. The magnetic resonance tomography device 1 or its controller 23 issues a signal by a short interruption in the detuning 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 to set this operating state with a reduced bias. This can be generated, for example, by a monostable trigger or a bistable trigger, which is then reset again by an AND operation of the detuning signal with the inverted second energy control signal. This implementation by a simple logic circuit has a low energy consumption in itself in an advantageous manner, generates almost no interference emission, and can be integrated into existing environments, especially also in wireless local coils 50 with analog transmission, without major changes.

[0069] However, more complex variants are also conceivable, for example using digital transmission, in which the magnetic resonance tomography system 1 transmits the operating state individually to the local coil 50 , even without changing the detuning signal.

[0070] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited to the disclosed examples, and those skilled in the art may derive other variations therefrom without departing from the scope of protection of the present invention.

Claims

1. A local coil for a magnetic resonance tomography device, wherein: The local coil (50) has a detuning device (52) having a signal path for activation and a further functional unit having two operating states with different energy consumptions, the local coil also having an energy consumption controller (56) which is designed to control the operating state of the functional unit as a function of image acquisition.

2. The local coil according to claim 1, wherein: The energy consumption controller (56) is designed to detect a detuning signal for the detuning device (52) on the signal path and to control an operating state of the functional unit as a function of the detuning signal.

3. The local coil according to claim 2, wherein: The energy consumption controller (56) has a decoder which is designed to decode a plurality of messages encoded in the detuning signal and to set a plurality of operating states of the functional units as a function of the messages.

4. The local coil according to claim 1, wherein: The energy consumption controller (56) is designed to place the functional unit in a predetermined operating state in the absence of a predetermined event for image acquisition.

5. The local coil according to claim 1, wherein: The local coil (50) has a magnetic field sensor which is signal-connected to 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 set the operating state as a function of a signal from the magnetic field sensor.

6. A magnetic resonance tomography apparatus having a local coil (50) according to claim 3 or 4, wherein: The magnetic resonance tomography system (1) has an encoding unit which is designed to encode a message about an operating state of a functional unit in a detuning signal.

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