Ralph Oppelt

Duplexer including a field-effect transistor for use in an ultrasound imaging system

A duplexer for an ultrasound imaging system is capable of selectively coupling a transducer element to either a transmitter or a receiver, depending on whether the imaging system is in the transmit mode or receive mode. The duplexer contains a field-effect transistor whose source and drain are connected between the transducer element and the receiver. The gate of the field effect transistor may either be driven with a control voltage or short-circuited to the source. In this manner, one obtains an improved duplexer that operates with virtually no power loss, without drive circuits, without leakage currents, and with low noise.

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).

Detuning circuit for resonators in a nuclear magnetic resonance imaging apparatus

A circuit for detuning a resonator in a nuclear magnetic resonance imaging apparatus has an output connected to a terminal of the resonator via a high-frequency line composed of two conductors. The resonator is shortened at this terminal with a shorting capacitor that can be short-circuited for detuning the resonator. The length of the high-frequency line is shorter than one-fourth of the wavelength of a high-frequency signal having the operating frequency of the nuclear magnetic resonance imaging apparatus on the high-frequency line. For detuning the resonator the high-frequency line can be terminated at the output with a further capacitor, so that the high-frequency line acts as a short-circuit at the terminal.

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.

Duplexer including a variable capacitance diode for an ultrasound imaging system

A duplexer for an ultrasound imaging-system capable of selectively coupling a transducer element to either a transmitter or a receiver, depending on whether the imaging system is in the transmit mode or receive mode, contains a variable capacitance diode which is connected in a direction opposite that of transmit pulses emitted by the transmitter between the transducer element and the receiver. In this manner, one obtains an improved duplexer that operates with virtually no power loss, without drive circuits, without leakage currents, and with low noise.

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.

Neue Impulse für die Ultraschall-Transmissionskamera

The ultrasonic transmission procedure is presented and compared to the B-Scan method. As a diagnosis tool ultrasound transmission cameras show excellent real-time images of tendons and ligaments with their skeleton connection during their natural movement. The picture is orthographic with good lateral resolution in both dimensions and easy to interprete. Clinical studies in surgery, orthopedics and rheumatology exhibit the good application for specific clinical questions. A novel ultrasonic transmission system will be presented. It consists of two crosswise arranged 1-D ultrasound arrays with focusing means. 2-D resolution in the object plane is achieved by exciting only a line with the transmit array while reading out only a perpendicular row with the receive array. This results in an advantageous combination of a large field of view and a low-cost technology. Für die Dokumentation Ultraschall / Transmission / Kamera / Abbildung / Diagnose / Rheuma