Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1996-06-20
1998-07-07
O'Shea, Sandra L.
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
G01R 3336
Patent
active
057774757
DESCRIPTION:
BRIEF SUMMARY
This is a 371 of application Ser. No. PCT/DE94/01449 filed on Dec. 6, 1994.
FIELD OF THE INVENTION
The present invention relates to a device in a nuclear spin tomography installation for automatic impedance matching of a high-frequency (HF) transmitter or receiver to a coupled transmitting or, respectively, receiving antenna, and to a method of operating same.
BACKGROUND INFORMATION
German Published Patent Application No. 40 35 994 describes a matching device for use in a nuclear spin tomography installation for providing automatic impedance matching for HF systems and antennas.
In a nuclear spin tomography installation, the required high-frequency (HF) (or radio frequency, RF) transmitter or receiver must be connected respectively to a transmitting or receiving antenna representing a load or source. However, the impedance of this antenna is not constant. The reason for this change in impedance is the interaction (loading) of the latter with different test objects, in particular patients. On the other hand, however, the transmitter or receiver is to be operated at a specific impedance, optimum for them, of 50.OMEGA., for example, in order to have power matching in the transmitting case and noise matching in the receiving case. Consequently, it is usual to provide between the transmitter or receiver and the receiving or transmitting antenna, respectively, a variable matching circuit which, however, must be preset for each load impedance. Typically provided in the matching circuit for this purpose are two actuators, for example variable capacitors, which permit the active component and reactive component of impedance to be influenced. Depending on different test objects, however, the settings of these actuators have to be determined anew in each case.
For the purpose of this determination of the optimum setting points, the absolute value of the reflection factor into the matching network is continuously measured during a tuning procedure on the line between the transmitter or receiver and the network of the matching circuit. In this case, the actuators are adjusted systematically by hand or with an automatic device until the absolute value of the reflection factor is sufficiently small, for example below 5%. The optimum setting is then approximately achieved (compare the above named German Offenlegungsschrift).
During the search, many settings of the actuators must be thoroughly tested and a corresponding number of measurements must be carried out. This is bound up with a correspondingly high outlay on time, in particular when mechanically operated actuators are used. Again, the relationship between the setting points and the absolute value of the reflection factor is frequently not easy to predict, since it depends not only on the selected circuit and design of the network of the matching circuits, but also on the unknown antenna impedance. This complicates the systematic search for the optimum setting.
SUMMARY OF THE INVENTION
The present invention is directed to a device in a nuclear spin tomography installation for automatic impedance matching of a high-frequency (HF) (or radio frequency, RF) transmitter or receiver to a coupled transmitting or, respectively, receiving antenna, via a variable matching circuit which contains a matching network and two adjustable actuators connected thereto. The device has means for detecting the reflection factor at the input, facing the transmitter or receiver, of the matching circuit while the antenna interacts with a test object, and an electronic control device having means for calculating and adjusting the setting points of the actuators.
An object of the present invention is to provide such a matching device which overcomes the above-discussed shortcomings in the prior art. In particular, the aim is to make quick semi or fully automatic impedance matching possible for arbitrary test objects. In addition, a method is to be specified for operating such a matching device.
The following features are provided in the matching device according to the present inven
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Eisenberg Michael
O'Shea Sandra L.
Siemens Aktiengesellschaft
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