Wilhelm Duerr

Arrangement for operating a symmetrical radio-frequency antenna in a nuclear magnetic resonance tomography apparatus

For operating the radio-frequency antenna of a nuclear magnetic resonance tomography apparatus, the antenna being connected to an asymmetrical line, a sheath wave trap is provided between the antenna and the line, with the inductor of the sheath wave trap being a toroid. A low-scatter sheath wave trap is obtained in this manner, particularly suitable for circularly polarized resonators. The trap suppresses difference currents caused by asymmetries, and thus simultaneously functions as a balanced-to-unbalanced transformer (balun).

Diagnostic magnetic resonance apparatus having a radio frequency shield between the radio frequency antenna and the gradient coil system

In a diagnostic magnetic resonance apparatus having an examination space, a radio-frequency antenna and a gradient coil system, the radio-frequency antenna is arranged closer to the examination space than is the gradient coil system. A radio-frequency shield arranged between the radio-frequency antenna and the gradient coil system, and has a first electrically conductive layer arrangement and a second electrically conductive layer arrangement arranged lying opposite the first arrangement, these being separated from one another by a dielectric. The layer arrangements have interconnects arranged side-by-side that are separated from one another by electrically insulating slots. The slots of the first layer arrangement are arranged offset relative to the slots in the second layer arrangement. Neighboring interconnects in at least one layer arrangement are connected to one another via bridges that conduct high-frequency currents, the bridges being arranged such that currents induced in the layer arrangement by the radio-frequency antenna can essentially flow only between the neighboring interconnects via the bridges.

Adaptable antenna for a magnetic resonance apparatus including a wiper contact for varying the size of the antenna without frequency change

An antenna for a magnetic resonance apparatus has an antenna conductor that can be adapted to examination regions of different sizes, with one region of the antenna conductor divided into conductor sections. The conductor sections are connected to one another via capacitive elements, with the conductor sections and the capacitive elements connected alternating in series. The conductor sections are connectable to the remaining antenna conductor via releasable electrical connections.

Antenna structure for exciting and/or receiving RF fields in an NMR tomography apparatus

An antenna structure for exciting a substantially homogeneous magnetic RF field and/or for receiving RF signals in a nuclear magnetic resonance tomography apparatus includes a hollow cylindrical conductor sheath which is substantially transmissive at low frequencies for gradient magnetic fields, a number of conductor units within the conductor sheath, each conductor unit including at least one conductor element, and RF reflector disposed at the end faces of the antenna structure and an external energy feed or reception device. In this antenna structure, the current drop which increasingly occurs toward the end faces of the antenna structure is largely compensatable by shaping the electrically conductive cross-section of the conductor units so as to decrease symmetrically from an axial center of the antenna structure moving toward the end faces of the structure. The conductor units thus have a largest cross-section at a center of the antenna structure, and a smallest cross-section at the end faces.