JPS61154656A - Generation of motion signal and mri tomography apparatus forperforming the same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for generating a motion signal in an MHI tomography device in dependence on the motion of a subject.

The invention also relates to an intermittent tomography apparatus implementing such a method, comprising a first radio-frequency coil system serving to generate a radio-frequency magnetic field having the Larmor frequency and to receive a spin resonance signal.

MHI tomography devices of this type are known.

And generally, the same high-frequency coil system is used both for generating the high-frequency magnetic field and for receiving the spin resonance signal. Although the term "high-frequency coil system" is used here, it should be interpreted broadly. For example, a resonator such as that described in German Patent Application No. P3347597 must also be understood. In this way, a high frequency magnetic field is generated, the frequency of which falls within the so-called Larmor frequency range. Larmor frequency is M
It is proportional to the strength of the static magnetic field generated in the RI tomography device, reaching approximately 42.5 MHz/T for hydrogen. The high frequency magnetic field excites each spin within the subject. Therefore, after this magnetic field disappears, a spin resonance signal is induced in the high frequency coil system as a quasi-echo. This signal is further processed by a computer to determine the nuclear spin density and relaxation time Tl, T2, or both within the subject.

When an object is examined many times by such an MHI tomography device, a high frequency magnetic field is generated during the nuclear cycle and resonance signals are received. - A relatively long time elapses after the resonance signals are received before the high-frequency magnetic field is generated again (on the order of magnitude of several 100 m5)
. The total inspection time is therefore also relatively long. Generally it takes more than 1 minute. Obviously, it is unavoidable that the patient moves during such a long period of time, especially respiratory and swallowing movements.

However, these movements tend to falsify test results. To avoid this phenomenon, known MHI tomography devices are also equipped with motion detectors to detect patient motion, but such motion detectors can be thermal, pneumatic, mechanical, electrical or optical. The device must be attached to the patient. The motion signals thus generated must then be transmitted via separate channels. Nevertheless, the motion signal thus generated can considerably reduce the moving artifacts caused by patient motion.

One way to take this into account is to start each cycle only when the movement signal indicates that the patient's body will again assume a defined position (so-called triggering). Another method is to complete the cycle regardless of the motion signal from the motion detector, preferably at regular time intervals, which eliminates spin resonance signals from the reconstructed image that occur when the object is in motion (so-called gating). The cycle that has been messed with must now be repeated in the same manner.

It is also possible to combine both methods, ie gating and triggering.

An object of the present invention is to provide a simple method for detecting motion and an MHI tomography device for implementing this method.

To achieve this, we extend the method of the type mentioned at the beginning, so that during an examination, a magnetic field acts on the subject and causes the impedance of a high-frequency coil system to resonate, which is tuned to a predetermined resonant frequency. It is characterized in that it measures in a frequency range and derives the motion signal from the measurement signal thus formed.

The present invention utilizes the fact that the Q and stray capacitance of a radio frequency coil system changes in response to all movements of a patient located within the magnetic field of the radio frequency coil system, such as breathing, coughing, heartbeat, and jerking movements. . Thus, the impedance of this coil system changes in magnitude and phase. According to the invention,
This impedance is measured at least at intervals during the test, and a movement signal is derived from the resulting measurement signal, for example by rectification. Each value of impedance is associated with a given phase of motion.

Two methods exist to implement this method. 1st
The method is based on an MHI tomography device equipped with an impedance measurement unit for measuring the impedance of a high-frequency coil system used to generate a high-frequency magnetic field and to receive spin resonance signals. This method is characterized in that the impedance measuring unit is activated during the examination of the subject and the measuring signal thus generated is used as a motion signal.

It should be noted that it is necessary to measure the impedance of the high frequency coil system of the MHI tomography device. This is because placing a patient in the magnetic field of the high-frequency coil system affects the Q or conformity and resonance frequency of the high-frequency coil system. Therefore, an impedance measuring unit is provided which acts on the adjustment member for automatically adapting or readjusting the high-frequency coil system. After actually starting the test, the impedance measuring unit is no longer activated. This can also be used to generate motion signals.

In a second method, the MHI tomography device comprises a second high-frequency coil system for generating motion signals, and this second
The impedance of the high-frequency coil system is measured using an impedance measurement unit.

The first method is simpler. This is because only one high-frequency coil system is required and it performs a dual function. That is, it serves on the one hand to generate high-frequency magnetic fields and to receive spin resonance signals, and on the other hand to generate motion signals. However, a second method provides a second coil system and is structured to respond much better to the motion of the object. In addition, this allows continuous measurement during the entire inspection. The examination is not adversely affected by the formation of motion signals, especially if the frequency is shifted considerably from the Larmor frequency.

The invention will be explained in detail with reference to the drawings.

As shown in Figure 1, the MRI tomography device has four
It comprises an electromagnet consisting of several coils 1, generating a strong, uniform static magnetic field extending in the direction of a common horizontal coil axis. A patient 3 on a bed 2 inside an electromagnet is surrounded by a high-frequency coil 4. This high frequency coil 4 generates a pulsed high frequency magnetic field that extends perpendicularly to the main magnetic field generated by the electromagnet. The frequency of the high-frequency magnetic field is proportional to the magnetic flux density of the main magnetic field and ranges from 0.1T to 4T depending on the structure of the electromagnet. This proportionality constant corresponds to the gyromagnetic ratio (approximately 42.5 M
)Iz/T).

In this way, nuclear spins are resonantly excited by the high-frequency magnetic field in the space surrounded by the high-frequency coil.

The MHI tomography device also has four gradient coils 5
Equipped with. These gradient coils 5 generate a magnetic field that extends in the direction of the main magnetic field and varies linearly in this direction. M.H.
The I tomography device also comprises further gradient coils which generate magnetic fields varying in two directions, again extending in the direction of the main magnetic field, but perpendicular to this direction. When these gradient coils are energized, the phase of the signal induced in the radio-frequency coil system 4 following the generation of the radio-frequency magnetic field is changed depending on the nuclear spin density in the object region being examined. Therefore, the nuclear spin density within a two-dimensional or three-dimensional region of an object can in principle be determined by such an MHI tomography device.

FIG. 2 shows a block diagram of a first embodiment according to the invention. This high frequency coil system 4 is accompanied by a variable capacitor 7 to form a parallel resonant circuit. This parallel resonant circuit is connected to ground on the one hand and to a switch 9 via another variable capacitor 8 on the other hand.

When switch 9 is in the position shown, network 4°7.
8 receives the power of a high power radio frequency transmitter 10 whose carrier frequency corresponds to the spin resonance frequency.

When switch 9 is in a position not shown, the receiver (
A preamplifier 11 (not shown) is connected to the network formed by the variable capacitors 7 and 8 and the high-frequency coil 4, and the preamplifier 11 receives the signal induced in the high-frequency coil 4 by spin resonance.

At the spin resonance frequency, the input impedance of the preamplifier 11 and the output impedance of the high frequency transmitter IO,
The impedance of network 4.1.8 is equal, for example 50Ω. After introducing the patient 3 and before actually starting the test, capacitors 7 and 8 are adjusted, i.e. preferably automatically using an impedance measuring device (not shown) to adjust this matching condition. . However, as the patient moves within the coil, ie, breathes, clap, beats, and jerks, this alignment changes depending on the position of the coil.

This is because the Q and stray capacitance of the coil 4 are affected. The instantaneous value of the impedance of network 4.7.8 is therefore a measure of the current phase of the motion of the object being examined, and a motion signal can therefore be derived from this.

For this purpose, a reflectometer 12 is connected between the transmitter 10 and the switch 9 and the output signal of the reflectometer 12 is processed in a reflection measurement receiver 13 . A motion signal appears at the output terminal 14 of the receiver 13. High frequency transmitter 10 and circuitry 4.7.
As long as 8 is matched, the output signal of reflectometer 12 will be approximately zero. However, if they are not matched, a portion of the applied high frequency power will be reflected. The output of the reflectometer then carries a high-frequency signal whose amplitude depends on the reflection factor, ie the degree of mismatch. This high frequency signal is reflected and amplified by the receiver 13 and then appears at the output terminal 14.

This signal is then compared with two presettable thresholds corresponding to a predetermined impedance and thus to a predetermined phase of motion. The opening of these two thresholds can be used to initialize the control procedure.

FIG. 5 is a typical time diagram of an examination performed by such an MRI tomography apparatus. In the period Ta, a so-called 90″ pulse is generated, i.e. the high-frequency transmitter 10 is connected to the high-frequency coil 4 via the switch 9 so that the nuclear magnetization of the object being examined is exactly 90″ with respect to the direction of the main magnetic field. “It can be tilted.

Next, usually one or more so-called 180° pulses Tb are applied, after which the signal induced in the coil is received (period Tc). At this time, the switch 9 assumes a position different from that shown. The typical duration of this procedure is approximately 100 m
It is 5. 60 long compared to the duration of the procedure itself
This procedure is repeated regularly with a period of 0 m5. The magnetic field of the gradient coil is then switched in a defined manner during each repetition.

In the device shown in FIG. 2, the coil 4 is connected to the high frequency transmitter 10
Impedance measurement can be performed only during the period when the power is received. Therefore, in FIG. 5 these are the periods Ta and T
It is b. Relatively closely following periods Ta, 01. Assuming that the patient's body is in approximately the same phase at Tc, so-called gating can be performed using the derived motion signal. When the motion signal is within a predetermined amplitude range, that is, when the patient's body is in a substantially constant position, the spin resonance signal attracted to the coil 4 is evaluated during the period Tc. If this is not the case, the induced signal is not evaluated and the measurement has to be repeated (with the same gradient field).

In the embodiment shown in FIG. 2, when the bird also has to perform a ring process, the time elapses between the reception of the last pulse Tc of one measurement and the sending of the first pulse Ta of the next measurement. Impedance must be measured over a relatively long period of time. Therefore, the high frequency transmitter 10 must also apply a signal to the coil 4 during this period. However, in order to avoid these measurements from influencing the spin relaxation that occurs during the period between Tc and Ta, the lever signal must be powered down considerably or within well-defined time intervals within this period. You must add it as you would do in . In the latter case, if measurement is not performed at a frequency other than the Larmor frequency, the measurement is performed in a considerably shorter period than the periods Ta and Tb. However, in this case it is more difficult to generate a motion signal. However, the reflected signal must have a relatively small amplitude or be formed within a relatively short time interval.

As previously discussed, patient movement affects the coil's Q and inductance. This shifts the resonance curve of the network 7.8.9 towards higher or lower frequencies. but,
There is no clear relationship between impedance and the associated phase of motion. This can be avoided by slightly detuning the network 4.7.8 with respect to the measurement frequency (usually the spin resonance frequency). This detuning must be small relative to the 3 dB bandwidth of the network. However, it must be large so that the resonant frequency of the network 4.7.8 always remains below or above the measurement frequency during any phase of motion. A suitable detuning value is 20 KHz if the 3 dB bandwidth is 300 KHz and the spin resonance frequency is approximately 85 MHz.
It is.

FIG. 3 shows another embodiment of the invention. Corresponding parts are given corresponding symbols. Switch 9 connects directly to high frequency transmitter IO. In contrast to the switch shown in FIG. 2, this switch has three positions. In one position, the power of the radio frequency transmitter 10 is applied to the network 4.7.8. In the second switch position, the preamplifier 11 is connected to this network, and in the third switch position the impedance measuring unit is connected to this network. The impedance measuring unit consists of another high frequency generator 15 and an impedance measuring bridge 16 which is supplied with power from this high frequency generator 15.

The impedance measuring bridge 16 is configured, for example, as a Wheatstone bridge and has a predetermined reference impedance, for example 50Ω, which is necessary for matching the impedance of the network 4°7.8 at the frequency of the high-frequency generator 15.
It is designed to be balanced when High frequency generator 1
The power of 5 is considerably lower than that of high frequency transmitter 10.

Output of high frequency generator 15.

The force frequency is shifted from the output frequency of the high-frequency transmitter 10, but the shift is small in proportion to the 3 dB bandwidth of the network 4, 7.8, and to the extent that nuclear spins in the region of the object are not excited thereby. Enlarge.

In this way, the actual test is not influenced by the impedance measurement. It is also advantageous to offset the resonant frequency of the network 4.7.8 from the measuring frequency of the high-frequency generator 15.

When such a circuit is used, between periods Ta and Tb, Tb
Impedance measurement can be performed at any time between Tc and Tc, and between Tc and Ta. That is, impedance measurements can be carried out whenever the high frequency coil 4 does not generate a magnetic field or a resonant signal is induced therein. For this reason, the motion signal generated by the impedance measuring unit can be used not only for gating (but also for triggering).

The signal appearing at the output of the impedance measuring bridge usually requires further processing (amplification, rectification). Appropriate processing equipment is required for this purpose. However, as shown by the dashed line, the output signal of the impedance measuring bridge 16 can also be amplified by the preamplifier 11 or a part thereof instead. In that case, a preamplifier, an impedance measuring unit 15.16 (for balancing the network 4.7.8 before the test and for generating the motion signal during the test) and a high-frequency coil (for motion detection and spin resonance (excitation and reception of signals) serves a dual function.

Figure 4 shows the impedance measurement unit shown in Figure 3.
An easy-to-make example of 15.16 will be shown. High frequency generator 1
5 (one is grounded) is 4 inductances 17.1
8. Power an inductive RF bridge circuit comprising iaa and 19. Inductances 17 and 19 are equal, and inductances 18 and 18a are also equal. The two inductances 17 and 19 are also permanently magnetically coupled. A transmitter is thus obtained. A resistor 20 is connected to the connection point between the inductances 17 and 18. The other terminal of resistor 20 is grounded. The resistance value of the resistor 20 is made to correspond to the reference impedance (50Ω) of the RP coil 4.

The connection point between the inductances 19 and 181 is connected to the circuit network 4, 7° via the switch 9 when measuring the impedance when the impedance is exactly the value required to match the frequency of the high frequency generator 15 (50Ω). Connect to 8.

At this time, both connection points of the inductance have the same size,
A voltage of opposite phase appears. Therefore, no voltage is generated at the center tap 21 of the inductance. In the unmatched condition, the voltages appearing at both junctions of the inductance are not equal and therefore a voltage different from essentially zero appears at the center tap 21. This voltage is a measure of mismatch.

So far, we have assumed that the coil that generates the high-frequency magnetic field to excite the nuclear spins also receives the spin resonance signal. However, the present invention can also be applied to a case where the excitation of the magnetic field and the reception of the resonance signal are performed using separate coils. At this time, the embodiment shown in Fig. 2 is used in combination with a coil necessary to generate a high-frequency magnetic field, and the embodiment shown in Fig. 3 is used in combination with a coil whose purpose is to receive a spin resonance signal. be able to.

It has also been assumed up to now that the impedance measurement is performed at a frequency that is at least close to the frequency of the spin resonance signal. However, this measurement can also be carried out at a frequency of the second order of the resonant frequency of the network 4.7.8. However, the impedance of this network varies significantly in magnitude and phase even at the secondary resonant frequency. This gives the advantage that impedance measurements do not affect the excitation of nuclear spins.

In the embodiments described so far, it has been assumed that the radio-frequency coil system serves on the one hand to excite the nuclear spins and on the other hand to form a motion signal. In the following, an embodiment will be described in which a separate high-frequency coil system is provided for generating the motion signal.

Figure 6 shows an MH equipped with such a separate high-frequency coil system.
I is a cross-sectional view of a part of the tomography device.

Circular area 30 corresponding to the free aperture of electromagnet 1 (FIG. 1)
Inside is provided a high frequency coil system 4 suitable for high frequencies as described in German Patent Application No. P3347597. This two-part coil system supplies current in the conductors of the upper loop (which extends perpendicular to the plane of the drawing) in the opposite direction to the corresponding conductors of the lower loop. In this way, the high frequency magnetic field generated by this coil extends perpendicularly to the static magnetic field in the X direction.

The high frequency coil system 4 is attached in a manner not shown to a hollow cylindrical plastic body 31 which is rigidly connected to the bed on which the patient rests. High frequency coil 3 that helps generate motion signals
3 is connected to the plastic body 31 via a support 32. This coil can also be displaced in the y or two directions. It can also be connected to the plastic body in a manner that is invisible to the patient. For example, it is provided on the outside of the plastic body.

This coil has one turn or a plurality of turns, and is arranged so that the magnetic field generated thereby extends in the X direction. Plastic body 31 with high frequency coil system 4
in the area of the patient's head, the coil 33 is arranged in such a way that the magnetic field generated by it extends in two directions, namely in the longitudinal direction of the patient's bed, in other words perpendicular to the plane of the drawing. Place it in

It is only important that the magnetic field generated by the high-frequency coil 33 extends essentially perpendicular to the magnetic field generated by the high-frequency coil system 4.

In this way, the high frequency coil system 4 and the high frequency coil 33
are not highly magnetically coupled to each other, and therefore, on the one hand, the magnetic field generated by the high-frequency coil system 4 becomes small due to the presence of the high-frequency coil 33, and on the other hand, the magnetic field generated by the high-frequency coil system 4 becomes small due to the presence of the high-frequency coil 33. This is because the induced signal also becomes smaller.

Reference numeral 34 schematically represents another, preferably flat, coil. This coil is placed on the patient's body 3 and its magnetic field is also oriented essentially in the X direction. This coil is made in the same way as the surface coil used in the MHI tomography device only for the reception of spin resonance signals (rather than for the excitation of nuclear spins). In contrast to coils 33 that are fixed to the plastic body, the structure of such surface coils can be adapted to the relevant application. This fact, and the fact that the coil can move in close proximity to the area whose motion is to be monitored, provides an inherently high sensitivity. Such a coil is therefore able to extract useful motion signals even from relatively small movements, such as, for example, respiratory movements. On the other hand, these coils need to be attached to the patient's body before the examination.

FIG. 7 shows a circuit for deriving the motion signal.

This circuit comprises an impedance measuring unit, for example an impedance measuring bridge 35, to which a high-frequency generator 46 is connected to one branch and a high-frequency coil 33 connected to the other branch via a conversion network. Or connect 34. The frequency of the radio frequency transmitter is significantly higher than the Larmor frequency, which is derived from the strength of the magnetic field of the magnet in the case of hydrogen. If the strength of the magnetic field of the magnet is, for example, 2T, the Larmor frequency is approximately 85Mz), and the frequency of the high-frequency transmitter must be between 100MHz and 200MHz, and the high frequency of the Larmor frequency and Must not match. If this MHI tomography device is also used to investigate the distribution of elements other than hydrogen, such as sodium, phosphorus, or fluorine, the Larmor frequencies for sodium, phosphorus, and fluorine at 2T (approximately 68 MHz, respectively) 35M)lz and 80MHz)
It must not coincide with the high frequency of

On the one hand, converting the impedance of the high-frequency coil into a real resistance of 50 Ω as desired, the high-frequency coil 33
(34) on the other hand by a tuning capacitor 36 connected in series with a parallel resonant circuit 37 in parallel, and on the other hand by a trimmer capacitor 38. Coil 33 (34)
One end is connected to one branch of the impedance measuring bridge 35 via this trimmer 38 and a parallel resonant circuit 39 connected in series thereto. Parallel resonant circuits 37 and 39
are tuned to the Larmor frequency and designed such that their capacitive impedance at the frequency of radio frequency transmitter 36 is lower (at least not substantially higher) than the capacitance of capacitors 36 and 38. Therefore, the capacitive impedance of the series or parallel branches can be varied by varying the capacitance of capacitors 36 and 38.

After putting the patient in, and maybe the high frequency coil 34.

After fixing and before starting the test, adjust the capacitors 36 and 38 (preferably automatically) and close the high frequency coil 33.
(34) and element 36. ,,． The input resistance of the network formed by 39 is such that it has a predetermined value at the frequency of the high-frequency transmitter 46, for example 50Ω. The human resistance is thus matched with the impedance measuring bridge.

Throughout the subsequent test, the output terminal 21 of the impedance measuring bridge 35 carries a measuring signal whose amplitude has the value zero or a minimum value in the matching state.

In response to patient movements, e.g. respiration, coughing, heartbeat and gag movements, the Q and stray capacitance of the coil 33 or 34 will change, thus changing the impedance of the network connected to the impedance measuring bridge 35. and the amplitude of the output signal increases according to the phase of the associated motion. The signal at the output terminal 21 can be used as a motion signal after being preferably rectified by a circuit with a small time constant.

In general, it is not possible to sufficiently prevent the magnetic field generated by the high-frequency coil system 4 from inducing voltages in the high-frequency coils 33 and 34 for generating motion signals. this is,
This is particularly the case when the position relative to the high-frequency coil system 4 can change, as in the case of the high-frequency coil 34. As a result, current flows through the circuit connected to the high frequency coil 33 or 34,
A load is applied to the high frequency coil system 4, and the magnetic field generated by the high frequency coil system 4 is distorted. In addition, the output terminal 21
The signals that appear on the surface are error-prone. This fact must be taken into account when the power applied to the high-frequency coil system 4 is considerably greater than the power applied to the high-frequency coils 33 or 34. These two effects are reduced by the resonant circuits 37 and 39, which have high impedance at the frequency of the high frequency coil system 4.

Elements 36 and 37 cause the high frequency coil 33 or 34 to operate in parallel resonance at the frequency of the high frequency generator 46. However, when the high frequency coil 33 (34) operates in a series resonance state due to the trimmer 38 in series,
The series branch connected in parallel with the parallel resonant circuit) 7 can be omitted. This is because the series resonant circuit already formed at this time has high impedance at frequencies far from the series resonant frequency, such as the 40 frequency of the high frequency coil system.

An advantage of the embodiment with a separate high-frequency coil system for generating the movement signal is that the state of movement of the patient is determined continuously during or almost during the entire examination. Further, the magnetic field generated by the high frequency coil 33 or 34 does not excite nuclear spins. This is because the frequency of the high-frequency transmitter deviates considerably from the Larmor frequency.

[Brief explanation of the drawing]

Figure 1 is a schematic longitudinal cross-sectional view of an MHI tomography device; Figures 2 and 3 are a type of MHI in which a high-frequency coil system that excites nuclear spins and also receives resonance signals is used to generate motion signals. Block diagrams of two embodiments of the tomography apparatus; FIG. 4 is a circuit diagram of an impedance measurement circuit used in the embodiment shown in FIG. 3; FIG. 5 is a time diagram showing the operation of the high-frequency coil system; FIG. 6 is a cross-sectional view of an MHI tomography device with a separate high-frequency coil system for generating the motion signal, and FIG. 7 is a circuit diagram of an impedance measuring circuit for such an MHI tomography device. ■ Coil 2 Bed 3 Patient 4 High frequency coil 5 Gradient coil 7 Variable capacitor 8 Variable capacitor 9 Switch 10 Transmitter
11... Preamplifier 12... Reflectance meter
13... Reflection measurement receiver 14... Output terminal
15...High frequency generator 16...Impedance measurement bridge 17-19...Inductance 20...Resistance 21...Center tap 3
0...Circular area 31...Hollow cylindrical plastic body 32...Support 33...High frequency coil (for motion signal) 34...Another coil 35...Impedance measurement bridge 36...Tuning Capacitor 37...Parallel resonant circuit 38...Trimmer 39...Parallel resonant circuit 46...High frequency generator patent applicant N.B.Philips Fluiranpenfabriken

Claims (1)

[Claims] 1. In a method of generating a motion signal depending on the motion of a subject in an MRI tomography apparatus, during an examination, a magnetic field acts on the subject (3) and generates a predetermined resonance. A method for generating a motion signal, characterized in that the impedance of a high-frequency coil system (33; 34) tuned to the frequency is measured in a resonant frequency range, and a motion signal is derived from the measurement signal thus formed. 2. MRI tomography apparatus for implementing the method according to claim 1, comprising a first high-frequency coil system (4) for generating a high-frequency magnetic field having the Larmor frequency and for receiving spin resonance signals. In order to generate a motion signal, a second high frequency coil system (33; 34) is installed.
An MRI tomography apparatus characterized in that an MRI tomography apparatus is provided with an impedance measuring unit (35; 41) to measure the impedance thereof. 3. Claims characterized in that the second high-frequency coil system (33; 34) is tuned to a resonant frequency essentially offset from the resonant frequency of the protons, preferably considerably higher than the resonant frequency of the protons. MRI tomography apparatus according to item 2. 4. The second high-frequency coil system (33; 34) is arranged such that the magnetic field generated thereby extends at least approximately perpendicular to the magnetic field of the first high-frequency coil system (4). An MRI tomography apparatus according to claim 2 or 3. 5. Place the second high-frequency coil system (33; 34) in the filter device (36...39) so that this second high-frequency coil system takes as little energy as possible from the first high-frequency coil system. An MRI tomography apparatus according to any one of claims 2 to 4, characterized in that the MRI tomography apparatus is configured as follows. 6. A switching device (43) is provided, which suppresses the motion signal when the first high-frequency coil system generates a magnetic field. MRI tomography apparatus according to item 1. 7. Claim 2, characterized in that the second high-frequency coil system (33) is mechanically and rigidly connected to the first high-frequency coil system, or is capable of sliding within at most one plane.
MRI tomography apparatus according to any one of Items 6 to 6. 8. The second high-frequency coil system (34) can be positioned independently of the first high-frequency coil system, as set forth in any one of claims 2 to 6. MRI tomography device. 9. An MRI tomography apparatus that implements the method according to claim 1, comprising an impedance measurement unit that measures the impedance of a high-frequency coil system used to generate a high-frequency magnetic field and receive a spin resonance signal. , impedance measurement unit (12, 15
, 16; 15, 23) is activated during the examination of the subject (3), and the measurement signal thus generated is used as a motion signal. 10. The MRI tomography apparatus according to claim 9, wherein the impedance measuring unit is activated when a high frequency magnetic field is generated by the high frequency coil system (4). 11. Claims characterized in that the impedance measuring unit (12) is a reflectance meter connected between a high frequency coil system (4) and a high frequency generator (10) that supplies power to this high frequency coil system. 11. MRI tomography apparatus according to item 10. 12. Connect the high frequency coil system (4) to the switching device (9).
), and in the first switch position the high-frequency generator (1
0), in the second switch position it is connected to the receiver preamplifier (11) which receives the spin resonance signal, and in the third
In the switch position, the impedance measuring device (15, 1
6), the switching device is in the third switch position even during inspection, and the impedance measuring device (15, 1
10. The MRI tomography apparatus according to claim 9, wherein 6) is activated when coupled to the high frequency coil system. 13. The MRI tomography apparatus according to claim 12 or any one of claims 2 to 8, characterized in that impedance measurement is performed at a frequency that deviates from the spin resonance signal. . 14. The MRI tomography according to claim 9, wherein the impedance measurement unit measures impedance at a second resonance frequency of a high-frequency coil system that is considerably higher than the frequency of the spin resonance signal. Device. 15. The impedance measurement unit is a high frequency coil system (
4; 33, 34), wherein the measurement frequency for measuring the impedance is slightly shifted from the resonance frequency of the high frequency coil system. MRI tomography apparatus according to section 1.