Nuclear spin resonance apparatus with a regulating unit for matching or adjusting the resonator.

The invention relates to a magnetic resonance apparatus with a magnet for generating a uniform static main magnetic field and a Resonantoranordnung for generating a high-frequency, to the main magnetic field at least approximately perpendicular magnetic field, with at least one actuator, which for an actuator for the adjustment of the resonator to an RF generator and / or acts tuning the resonator.

A magnetic resonance imaging apparatus of this kind is shown in FIG. 1. It comprises a four-coil electromagnet, which generates a static homogeneous extending in the direction of the common horizontal axis magnetic field coils. A bearing supported on a tabletop 2 in the interior of the electromagnet Patient 3 is enclosed by a high frequency coil 4 which generates a perpendicular to the main magnetic field generated by the electromagnet directional high frequency magnetic field in a pulsed manner. The frequency of the high frequency magnetic field is the flux density of the main magnetic field, which can be, depending on the design of the electromagnet between 0.1 T and T 2, proportional; the constant of proportionality is equal to the gyromagnetic ratio. Therefore, nuclear magnetic resonance can be generated within the area enclosed by the RF coil volume. Four so-called gradient coils 5 that generate a extending in the direction of the main magnetic field and linearly in this direction changing magnetic field, however, ensure that this suggestion is limited to a vertical layer. 6

It is important in such devices, that the frequency of vibrations generated by the high frequency coil corresponds exactly predetermined by the gyromagnetic ratio, and the flux density of the main magnetic nuclear spin resonance frequency, and that the resonator, the RF coil 4 containing is always adapted to the high frequency vibrations providing high frequency generator.

However, when introducing the patient to be examined results depending on body size and body area detuning the resonant frequency and a reduction in the quality of the resonator. This effect is caused by the dielectric properties and electrical conductivity of the body tissue. As a result, are the high-frequency generator or high-frequency receiver, which is then connected to the resonator, and receives the resulting in the examined body portion nuclear magnetic resonance signal, no longer adapted in the so-called magnetic resonance frequency to the resonator.

It is therefore necessary, the high frequency generator after the introduction of the patient and before starting the actual magnetic resonance examination, exactly retune to the predetermined magnetic resonance frequency and adapted to the high-frequency generator. This can be done with the aid of the circuit shown in Fig. 2. The resonator includes the coil 5 and the capacitor 9 and the tuning capacitor 7, which are connected in parallel to the coil 5. The capacitor 9 can also be omitted with suitable dimensioning. This resonator is connected via a variable capacitor 8 to a high frequency generator 10th The adjustment is made by means of the variable capacitor 8 and the vote by means of the variable capacitor 7, which influence both processes mutually.

Difficult is the adjustment of the variable capacitors. These are arranged outside the high-frequency coil in the interior of the electromagnet and can not be adjusted by stepping motors or the like, because the ferromagnetic parts would interfere with the homogeneity of the magnetic field. The stepper motors have to be arranged outside the electromagnet in such a distance that they do not interfere with the homogeneity of the main magnetic field and not be affected by the stray fields of the electromagnet in its function, and they need to be coupled via a long drive rods with the arranged in the interior of the solenoid actuators , It is not possible to arrange the actuators outside the electromagnet, because they would then be connected to the resonator inside via electrical lines, the length of which - especially at high magnetic flux densities and high magnetic resonance frequencies - no longer small compared to the wavelength, which interference would result.

It is an object of the present invention to provide a magnetic resonance apparatus of the kind set forth so that the drive for adjusting the actuators in the interior of the electromagnet can be arranged, without thereby affecting the homogeneity of the main magnetic field is deteriorated.

This object is achieved in that the actuator includes a main magnetic field exposed and movably mounted coil, the coil is connected to an electrical pulse generator for generating current pulses of either polarity, through the coil in one direction or the other from its rest position is deflected, and in that the deflection movement is transmitted to the actuator via a drive step, which converts the reciprocating movement of the coil into a stepwise movement of the actuator, the direction associated with the direction of the deflection clearly.

The coil is when it is traversed by a current pulse, deflected in the main magnetic field from its rest position and returns to the current pulse - eg by means of restoring springs - in its rest position. Be supplied to the coil a plurality of current pulses of the same polarity, this therefore carries out a reciprocating movement. This is implemented by means of the plant in step a gradual (rotational or thrust) movement of the actuator, the direction of the direction of the deflection and thus the polarity of the current pulses is clearly assigned. Such actuator requires no ferromagnetic parts. Therefore, and because the wires from the current pulse to the coil during the actual measurement can remain de-energized, does not impair such an actuator the field homogeneity.

The invention is explained hereinafter with reference to the drawing. Show it<ul><li>_Fig. 1, a magnetic resonance imaging apparatus in which the invention is applicable,</li><li>Fig. 2 shows the circuit diagram of the resonator and the high frequency generator,</li><li>Fig. 3 shows a first embodiment,</li><li>Fig. 4 is a plan view of the arrangement of FIG. 3 taken along the lines AB,</li><li>Fig. 5 shows another embodiment of the invention, and</li><li>Fig. 6 is a side view of the embodiment of FIG. 5. In FIG. 3, an elongated solenoid coil 11 is connected to a support body 12 which is mounted in a housing frame 13 at its lower end pivotable about a horizontal axis 14. The upper end of the holder body 12 is connected to a control member 15, that a tilting movement of the bobbin 12 is converted into a thrust movement of the control member 15, which is guided in a horizontally extending guide rail sixteenth bring two attached to the two ends of the control member 15 springs that the bracket body and with it the solenoid coil in the rest position, ie when no further external forces act on it, taking a vertical position. The coil axis so then extends perpendicularly to the main magnetic field whose direction is indicated in Fig. 3 by the arrows 18 horizontally extending.</li></ul>

With the terminals of the coil 11 a current pulse generator 19 is connected, which may contain a DC power source, for example, which can be connected via a controllable multi-pole changeover switch with terminals that either current in one direction, no power or current in the opposite direction through the coil 11 can flow.

When a current pulse flows through the coil 11, in this, a magnetic field is built up, which extends in the direction of the coil axis and thus perpendicular to the main magnetic field. As a result, then acts on the coil a force, which seeks this about axis 14 to tilt in the direction of the main magnetic field, that is, depending on the polarity of the current through the coil either to the left or to the right. This tilting movement of the spool is transmitted through the bracket body 12 to a control member 15 which is thereby displaced to the left or to the right in the horizontal --- extending guide rail 16, this movement which by the stops 20 on the ends of the guide rail, with the control member 15 is connected via the springs 17 is limited. If a plurality of current pulses of the same polarity of the coil 11 are supplied, supplies the control member 12 a from the center to the left (or right) and walk-back movement from. This reciprocating motion is converted by the plant in step a stepwise rotary motion of the rotor of the variable capacitor 7 and 8, so that the polarity of which gradually increases with current pulses of one polarity, and gradually decreases with current pulses of the other polarity.

As this, in FIG. 4 can be seen, the control member 15 is provided with two pawls 21 and 22 which are arranged symmetrically to the central position of the control member 15 and pivotable about vertical pivot pins 23 and 24 respectively. Springs not shown in detail, make it sure that the opposite ends of the control handles are pressed against two ratchet gears 25 and 26, which are offset from one another in the direction of the magnetic field and stored symmetrically to the rest position of the control member 15 about a vertical axis. there is a control pin 27, which is fixedly connected to the housing frame 13 between the facing ends of the control pawls 21 and 22nd

If the coil is energized by a current pulse, through which the control member 15 is displaced to the right (Fig. 3) or top (Fig. 4), then the following occurs:<ul><li>The _Sexpensive pawl 21 follows, as you come an end in this movement of the control pin 27 free, the contour of the ratchet gear, until it abuts against one of the flanks of the ratchet teeth and the ratchet gear 25 rotates by one tooth in the counterclockwise direction. The other control pawl 22 is pushed by this movement of the control member 15 against the control pin 27, wherein this control pawl simultaneously performs a pivotal movement counter-clockwise about the bearing pin 24 because of the banana-shaped curvature of the control pin 27 facing outer contour, whereby the other end of the control latch 22, the ratchet gear 26 releases. The step movement of the ratchet gear 25 is transmitted via a transmission gear 28 which is about the same axis is fixedly connected to the ratchet gear 25 and rotatable like this on a gear 30, which is connected to the rotor of the variable capacitor 7 and 8 (Fig. 3 ). The gear 30 is in mesh with a gear 29 which is connected to the ratchet gear 26 in the same manner as the gear 28 with the ratchet gear 25th</li></ul>

As a result of the displacement of the control member so that gear 28 is rotated by a gear pitch in a counterclockwise direction, which has a value dependent on the transmission ratio rotating step in the clockwise direction of the gear 30 result, which causes a rotation of the gear 29 and thus the ratchet gear 26, which is the same size and in the same direction as that of the ratchet gear 25. After the end of the current pulse, the control member returns to its rest position shown in figures 3 and 4, without thereby alter the position of the gears a bit. A new current pulse of the same polarity then causes a further rotation step of the gear wheels in the same direction.

As indicated by dashed lines, and a broken line in FIG. 4, indicated rack, instead of the gear 30, which is connected to the rotor of the variable capacitor, can be used 31, which communicates with the gears 28 and 29 into engagement and is connected to a dielectric which - will be moved inside a acting as a stub coaxial line, so that its reactance changes gradually - as known from DE-OS 33 47 597th In this case, therefore, the translatory reciprocating movement of the control member 15 is converted into a thrust movement of the rack gradually 31st

In the figures 5 and 6 an embodiment is shown, wherein the swivel movement of the coil is converted directly and not via the detour of a translatory movement. The coil, which comprises one or more turns with for example rectangular cross section, is in this case mounted rotatably about its to the main magnetic field perpendicular axis of symmetry 33 and disposed in the rest position so that the magnetic field lines of the main magnetic field parallel to the coil plane.

With the top of the coil, a driving lever 34 is fixedly connected, which is provided in the vicinity of its end by drive lugs 35 which embrace one arm of a three arm armature 36, the two other arms are provided with latches 37, of which one each with a gear wheel 38 can engage. The armature 36 is rotatably mounted about an axis of rotation of the coil 32 parallel axis 39 on a further lever 40 and its two the ratchets 37 bearing arms are connected by springs with this lever, which they are in the rest position symmetrical to this lever. The lever 40 itself is in turn held by springs 41 in a resting position. The lever 34 and the coil 32, the gear 38 and the further lever 40 are mounted independently rotatably about the same axis.

When the coil 32 is traversed by a current pulse, it performs as a result of the force action of the magnetic field to its current-carrying conductor, a rotational movement whose direction depends on the polarity of the current in the .Spule. In this case, the driving lever 34 is deflected, in turn, first the armature 36 pivots about the driving pin 35 about the axis 39 until die.eine of the two pawls 37 comes with the teeth of the gear wheel 38 into, engagement. Thereafter, it is pivoted about the armature 36 of the lever 40 against the forces of the springs 41 in the same direction, so that the gear 38 executes a rotation step. After the decay of the current pulse of the lever 40, the armature 36 and thus the drive lever 34 are again returned to the rest position, a locking mechanism 42 ensures that the gear 38 maintains its reached after shooting step position. The next current pulse the gear 38 is shifted again by one tooth further in the same direction.

In this way, the reciprocating pivoting movement of the drive lever 34 and the coil 32 is converted by current pulses of a certain polarity in a gradual rotation of the gear 38 when the coil is energized. This can be transmitted directly to the rotor of a variable capacitor or implemented on a rack in a linear step motor and be used for adjusting a stub.

Thus, the invention uses to produce a displacement of the actuator from the forces which are exerted by the main magnetic field on a current-carrying coil. The actuator of the invention comprises only non-magnetic material and after the adjustment or retuning the current no longer flows through the coil, so that in the subsequent nuclear magnetic resonance measurements no disturbing fields can occur that might affect the homogeneity of the main magnetic field. This actuator which the RF coil 4 (FIG. 1) can be structurally combined and replaced with this for another high-frequency coil with a corresponding actuator, is very suitable for automatic adjustment or retuning using a computer because the drive only current pulses in the required number to be generated.