1. Field of the Invention
The present invention concerns an apparatus to control an antenna arrangement in a magnetic resonance apparatus.
2. Description of the Prior Art
Magnetic resonance apparatuses with a transmission antenna for multi-channel measurements are increasingly gaining importance.
FIG. 1 shows a first activation of an antenna arrangement ANT1 according to the prior art.
The antenna arrangement ANT1 here is fashioned as a cylindrical birdcage antenna and serves for acquisition of a patient in a magnetic resonance examination.
The antenna arrangement ANT1 has eight longitudinal rods LS11 through LS18. Both ends of the longitudinal rods LS11 through LS18 are connected with one another by respective circular termination rings AR11 and AR12. Each termination ring has capacitors in the circumferential direction as needed.
The shown antenna arrangement ANT1 is designed for a multi-channel system so that each longitudinal rod LS11 through LS18 has an associated infeed point AP11 through AP18. Amplified transmission signals for emission are respectively connected at each of the infeed points AP11 through AP18. The transmission signals differ from one another.
Only one infeed situation at a first infeed point AP11 of a first longitudinal rod LS11 is described in the following as an example.
The infeed situation at the infeed points AP12 through AP18 is correspondingly designed.
The first longitudinal rod LS11 serves as an antenna element and has the first infeed point AP11 with two connections AS11 and AS12. An amplified transmission signal SV11 for emission is connected at the two connections AS11 and AS12.
The amplified transmission signal SV11 is formed by an amplifier RFPA1 at whose input a radio-frequency signal SS11 arrives via a signal line SL11.
The amplifier RFPA1 is connected at the output side via two feed lines ZL11 and ZL12 with the two connections AS11 and AS12 of the infeed point AP11.
As an alternative (not shown), it is possible for a number of the infeed points to be arranged on one of the termination rings at which transmission signals of different amplification are connected for a multi-channel system for emission.
The type of antenna excitation shown here is designated as a “single rod excitation”.
FIG. 2 shows a second control of an antenna arrangement ANT2 according to the prior art.
The antenna arrangement ANT2 here is fashioned in an arc and has a curved antenna element SE21 with an infeed point AP21.
The infeed point AP21 has two connections AS21 and AS22 at which an amplified transmission signal SV21 is connected for emission.
The amplified transmission signal SV21 is formed by an amplifier RFPA2 at whose input a radio-frequency signal SS21 arrives via a signal line SL21.
The amplifier RFPA2 is connected at the output side via two feed lines ZL21 and ZL22 with the two connections AS21 and AS22 of the infeed point AP21.
However, the two embodiments described have disadvantages, as follows.
The amplified transmission signals are presently directed from the amplifier outputs to the infeed points via relatively thick, low-attenuation coaxial lines of specific capacity. Due to the unwieldy coaxial cables, this solution is difficult to manage and is also error-prone, depending on the wiring arrangement.
The transmission signals to be amplified are correspondingly also directed via coaxial lines to the associated amplifiers.
It should be noted that additional signal attenuations are caused even given use of low-attenuation coaxial cables.