US 5,208,537 AGranted

Method for matching antennas in a nuclear magnetic resonance imaging apparatus

AssigneeSiemens Aktiengesellschaft

InventorsNorbert Rietsch, Markus Vester, Horst Kroeckel

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Abstract

In a method for matching a transmission/reception antenna in a nuclear magnetic resonance imaging apparatus to the impedance of a high-frequency system which feeds the antenna, a directional coupler is used for acquiring respective signals corresponding to a forward voltage wave supplied to the antenna, and the associated return voltage wave. The amplitudes of the forward and return waves are calculated in a controller for all matching conditions of a transformation network, the transformation network being interconnected between the high frequency system and the antenna. When a tomogram is to be produced, the transformation network is set so that the antenna is matched as best as is possible to the high-frequency system. The same method can be used for matching an antenna which is only used for reception when producing tomograms.

Claims16

Dependent claims

A method for matching a transmission/reception antenna in a magnetic resonance imaging apparatus to the impedance of a high-frequency system connected to said transmission/reception antenna via a transformation network, said transformation network being settable at a plurality of settings, each setting defining a different impedance for said transmission/reception antenna, said method comprising the steps:

(a) for a setting of said transmission network, generating a high-frequency pulse in said high-frequency system having a pulse length between 1 ms and 50 ms and a power of substantially 100 W and thereby causing a forward voltage wave to be supplied to said transmission/reception antenna resulting, in the event of mismatching, in an associated return voltage wave reflected by said transmission/reception antenna;
(b) demodulating each forward voltage wave and its associated return voltage wave;
(c) detecting a peak amplitude value of the each demodulated forward voltage wave and its associated demodulated return voltage wave;
(d) forming a ratio of the peak amplitude values of each forward voltage wave and its associated return voltage wave and storing said ratio;
(e) repeating steps (a), (b), (c) and (d) for each impedance of said transmission/reception antenna which can be respectively defined by said settings of said transmission network and thereby obtaining a plurality of stored ratios respectively corresponding to said different impedances of said transmission/reception antenna, said plurality of stored ratios including an extreme ratio;
and
(f) during generation of a tomogram of a subject, setting said transformation network at a setting which defines an impedance of said transmission/reception antenna corresponding to said extreme ratio.

4 more elements

A method for matching a transmission/reception antenna in magnetic resonance imaging apparatus to the impedance of a high-frequency system connected to said transmission/reception antenna via a transformation network, said transformation network being settable at a plurality of settings, each setting defining a different impedance for said transmission/reception antenna, said method comprising the steps of:

(a) for a setting of said transmission network, generating a high-frequency pulse in said high-frequency system and thereby causing a forward voltage wave to be supplied to said transmission/reception antenna, said forward voltage wave having an associated return voltage wave reflected by said transmission/reception antenna associated therewith;
(b) demodulating said return voltage wave;
(c) detecting a peak amplitude value of the demodulated return voltage wave and storing said peak amplitude value;
(d) repeating steps (a), (b) and (c) at a substantially constant HF pulse power for each impedance of said transmission/reception antenna which can be respectively defined by said settings of said transformation network and thereby obtaining a plurality of stored peak amplitude values respectively corresponding to different impedances of said transmission/reception antenna, and including a minimum stored peak amplitude value;
and
(e) during obtaining a tomogram of a subject, setting said transformation work at a setting which defines an impedance of said transmission/reception antenna corresponding to said minimum stored peak amplitude value.

3 more elements

A method for matching a reception antenna in a magnetic resonance imaging apparatus to the impedance of a high-frequency system connected to said reception antenna via a transformation network, said transformation network being settable at a plurality of settings, each setting defining a different impedance for said reception antenna, said method comprising the steps of:

(a) for a setting of said transformation network, generating a high-frequency signal in said high-frequency system having a power below -10 dBm and thereby causing a forward voltage wave to be supplied to said reception antenna, said forward voltage wave having an associated return voltage wave reflected by said reception antenna;
(b) demodulating said return voltage wave;
(c) detecting a peak amplitude value of the demodulated return voltage wave and storing said peak amplitude value;
(d) repeating steps (a), (b) and (c) for each impedance of said reception antenna which can be respectively defined by said settings of said transformation network and thereby obtaining a plurality of stored peak amplitude values respectively corresponding to different impedances of said reception antenna, and including a minimum value;
and
(e) during obtaining a tomogram of a subject, setting said transformation network at a setting which defines an impedance of said reception antenna corresponding to said minimum value.

3 more elements

Dependencies are inferred from the claim text.