High-frequency antenna device in apparatus for nuclear spin tomography and method for operating this device

Claim 1

An antenna device for generating a high-frequency magnetic field in an apparatus for nuclear spin tomography, comprising: (a) an energy source; (b) at least two conductor sections of predetermined length which extend on an imaginary cylinder surface parallel to the direction of the axis of the imaginary cylinder and are arranged for current flow in opposite directions when one end of each of said sections is connected to said energy source; (c) a tubular enclosure arranged at a predetermined distance concentrically with respect to the imaginary cylinder surface, surrounding the conductor sections, said enclosure being at least largely permeable to low frequencies for magnetic gradient fields, containing electrically highly conductive material and connected to said energy source, said tubular enclosure extending in the axial direction beyond the end of the conductor sections by a predetermined amount to form a circular waveguide antenna with aperiodic wave propagation in a cut-off mode at the axial ends of said enclosure, the coupling elements of which are said conductor sections; and (d) means for reflecting the waves of the high-frequency field terminating the other ends of said conductors so that a high-frequency field oscillating in phase is formed by the tubular enclosure and the conductor sections which field is attenuated axially beyond said conductor sections.

Claim 21

A method of operating an antenna device which antenna comprises: (a) at least two conductor sections of predetermined length which extend on an imaginary cylinder surface parallel to the direction of the axis of the imaginary cylinder and are arranged for current flow in opposite directions when one end of each of said sections is connected to an external current source; (b) a tubular enclosure arranged at a predetermined distance concentrically with respect to the imaginary cylinder surface, surrounding the conductor sections, said enclosure being at least largely permeable to low frequencies for magnetic gradient fields, containing electrically highly conductive material and connected to said current source, said tubular enclosure extending in the axial direction beyond the end of the conductor sections by a predetermined amount so as to form a circular waveguide antenna with a periodic wave propogation and operating in a cut-off mode at the axial ends of said enclosures, the coupling elements of which are said conductor sections; (c) mcans for reflecting the waves of the high-frequency field terminating the other ends of said conductors so that a high-frequency field oscillating in phase is formed by the tubular enclosure and the conductor sections; and (d) a further system of coupling elements disposed at at least two parallel cross-sectional planes which are symmetrical to the central cross-sectional plane passing through said tubular enclosure forming a circular waveguid antenna, said method comprising the steps of: adjusting the phase and amplitude conditions at the additional coupling systems by means of an energy feeding device connected thereto in such a manner that the field strengths caused by these coupling systems together with the field strength by the conductor sections alone are superimposed to form a total field strength which is practically zero outside of the region bounded by the parallel cross-sectional planes of the two additional coupling systems.

Claim 22

A method of operating an antenna device which antenna comprises: (a) at least two conductor sections of predetermined length which extend on an imaginary cylinder surface parallel to the direction of the axis of the imaginary cylinder and are arranged for current flow in opposite directions when one end of each of said sections is connected to an external current source; (b) a tubular enclosure arranged at a predetermined distance concentrically with respect to the imaginary cylinder surface, surrounding the conductor sections, said enclosure being at least largely permeable to low frequencies for magnetic gradient fields, containing electrically highly conductive material and connected to said current source, said tubular enclosure extending in the axial direction beyond the end of the conductor sections by a predetermined amount so as to form a circular waveguide antenna with a periodic wave propogation and operating in a cut-off mode at the axial ends of said enclosures, the coupling elements of which are said conductor sections; (c) mcans for reflecting the waves of the high-frequency field terminating the other ends of said conductors so that a high-frequency field oscillating in phase is formed by the tubular enclosure and the conductor sections; and (d) a further system of coupling elements disposed at at least two parallel cross-sectional planes which are symmetrical to the central cross-sectional plane passing through said tubular enclosure forming a circular waveguid antenna, said method comprising the steps of: adjusting the phase and amplitude conditions at the additional coupling systems by means of an energy feeding device connected thereto in such a manner that the field strengths caused by these coupling systems together with the field strength by the conductor sections alone are superimposed to form a total field strength which is practically zero outside of the region bounded by the parallel cross-sectional planes of the two additional coupling systems.