Siemens Aktiengesellschaft

Siemens Aktiengesell Schaft

Stefan Nowak

Franz Schmitt

Hubertus Fischer

Robert Bleisteiner

Ludwig Kreischer

Aleksandar Juloski

Arthur Kaindl

Siegfried Hofler

Hossein Borsi

Karl-Heniz Ideler

Gunter Petzold

Wieland Portisch

In method for operating a magnetic resonance apparatus that has a gradient power amplifier that supplies a voltage to a gradient coil, and a gradient power amplifier control processor that provides control a control signal thereto that predetermines the aforementioned voltage, and a simulation computer that models an operational characteristic of each of the gradient coil the gradient power amplifier, an actual current value of a current fed into the gradient coil by the gradient power amplifier is measured and a target current value of the current fed into the gradient coil by the gradient power amplifier is determined by the simulation computer, using the control signal as an input variable. A fault signal is generated as a function of a determined deviation in the actual current value from the target current value.

Magnetic resonance apparatus and method for the operation thereof

An arrangement to generate a basic magnetic field and a gradient magnetic field in a magnetic resonance tomography system include at least one basic electromagnet without an iron core that generates the basic magnetic field, at least three gradient field electromagnets that generate the gradient magnetic field, with the basic field electromagnet situated within the gradient field electromagnets such that during acquisition of magnetic resonance data from a subject, the basic field electromagnet is closer to the subject than the gradient field electromagnets. Because the basic electromagnet is situated within the gradient field electromagnets, an active shielding of the gradient field electromagnets can be foregone, and since the basic field electromagnet is situated near the subject, it can be a water-cooled air coil.

Arrangement to generate the basic magnetic field and a gradient magnetic field of a magnetic resonance tomography system, and method to operate a magnetic resonance tomography system

An inverter is proposed for providing an inverter output signal scalable in frequency. The inverter has a controller for controlling frequency of the inverter output signal according to a predefinable value. In order to generate a signal having a frequency value prescribed for the inverter output signal, the controller initiates a time delay of signals and superimposes the signals onto the signal having the frequency value prescribed for the inverter output signal. A low-complexity inverter concept for high voltages or high power is thus provided.

Inverter scalable in power and frequency

A connection system that couples a contact of a flat block of components to an apparatus is provided. The connection system comprises a conductive connecting element electrically coupled to the contact of the flat block of components, and a clamping device electrically coupled to the apparatus. The clamping device receives the connecting element. The connecting element is a rigid conductor. The rigid conductor is a screw fastened conductively to the contact. The screw penetrates a bore in the flat block of components and is locked by a nut on a second side of the flat block of components, which is opposite a first side of the flat block of components.

Connection system for connecting a flat block of components to an apparatus

A transistor module formed on a substrate comprises a first transistor, a first recovery diode, a second transistor and a second recovery diode. A first transistor chip associated with the first transistor and a second diode chip associated with the second recovery diode are disposed adjacently on a positive potential area. The first transistor chip and the second diode chip are disposed on an output potential area. A second transistor chip associated with the second transistor and a first diode chip associated with the first recovery diode are adjacently disposed on the output potential area. At least two sides of the output potential area are adjacent to a negative potential area. Both the second transistor chip and the first diode chip are connected to the negative potential area, and one of the first and second transistor chips is disposed opposite one of the first and second diode chips located on a different potential area.

Transistor module

A gradient coil for use in magnetic resonance tomography is assembled from electrically conductive elements that each define a plane and that are arranged such that these planes lie parallel to one another. These elements are connected in a coil-forming fashion to electrically conductive spacers and in a stabilizing fashion to electrically insulating spacers.

Gradient coil for a magnetic resonance tomography apparatus, and method for producing same

A method for determining sources of interference that cause partial discharges in an encapsulated conductor structure of a magnetic resonance apparatus, particularly in a gradient coil. Under the method, a low-frequency high voltage is applied to a conductor, and signals resulting from an adjacent high voltage are measured within a frequency range located in the kHz range, particularly from 40 to 400 kHz. The signals are analyzed in order to determine partial discharges. The conductor is again charged with a low-frequency high voltage and additional signals are measured within a frequency range located in the MHz range, particularly from 10 to 300 MHz. The additional signals are analyzed in order to determine partial discharges.

Method for determining sources of interference

A switching amplifier operable in a switched mode has a common-mode charging current which arises due to charge reversals in the conductor to ground and coupling capacitances. In order to make this charging current easily filterable, in a switching amplifier and a method for operating a switching amplifier, n successively connected cascade elements are provided n being odd and greater than equal to three, and a control unit drives comparable switch elements in the individual cascade elements so that these comparable switch elements are driven offset from cascade element-to-cascade element by 1/n times the switching period.

Switching amplifier and method for operating same

The current supply of a gradient coil in a magnetic resonance tomography apparatus with a gradient amplifier and a connectable capacitor that can be interconnected with the gradient coil to form a series resonant circuit. The gradient amplifier produces at least a part of the voltage needed for driving a predetermined gradient current through the gradient coil. The resonant frequency of the capacitor in combination with the gradient coil is lower than 1/4 T.sub.r, whereby T.sub.r is the duration of a leading or trailing edge of the gradient current.

NMR gradient power supply including a resonant circuit having a

A gradient coil is connected to a controllable gradient amplifier via a first diagonal of a bridge circuit having four switches and unbiased diodes respectively connected parallel thereto. A capacitor that forms a resonant circuit together with the gradient coil is connected into the second bridge diagonal of the bridge circuit. A sinusoidal current is supplied through the gradient coil. Due to intentionally incomplete discharging of the capacitor at every other half-wave, an offset current can be superimposed on the sinusoidal current through the gradient coil.

Method and apparatus for gradient power supply for a nuclear magnetic

A gradient coil for generating a periodically changing read-out gradient in a magnetic resonance imaging apparatus is operated in a series resonant circuit having a capacitor. One of the elements of the series resonant circuit is charged before the beginning of each read-out gradient. The gradient coil can be charged with current, or the capacitor can be charged with voltage. Such operation either avoids or significantly shortens the transient effect which occurs after excitation of the nuclear spins. The use of a series resonant circuit instead of a parallel resonant circuit significantly reduces the voltage load on the gradient amplifier, so that the gradient amplifier can be constructed simpler and more inexpensively.

Magnetic resonance imaging apparatus having a resonant circuit for

A nuclear magnetic resonance tomography apparatus has at least one gradient coil interconnected with a capacitor to form a resonant circuit. Before the beginning of each read-out sequence, the capacitor is charged to a higher voltage than would be necessary to produce a pure sine oscillation during the read-out sequence. The rise time of the gradient pulse thus produced is less than one-fourth of the duration of the sinusoidal oscillation before the zero-axis crossing, and the decay time is less than one-fourth of the duration of the sinusoidal oscillation after the zero-axis crossing. Additionally, a constant part of each gradient pulse is non-resonantly generated by a gradient amplifier. Only the steep parts of the oscillation of the resonant circuit are used for the rising and trailing edges, whereas the flattened part of the sine oscillation is cut off. The rising and trailing edges can thus be noticeably shortened, so that a greater range for the constant gradient value, which can be equidistantly sampled in the k-space is available for the signal evaluation.

Nuclear magnetic resonance tomography apparatus having a resonant

Switched transistors (T1 . . . through T4 . . .) are arranged in a bridge circuit such that a plurality of transistors (T1 . . . through T4 . . .) are connected in parallel in every bridge branch. These transistors are secured on a thermally and electrically conductive ring (R, R'), are symmetrically distributed over this ring (R1, R1'), and have a respective terminal electrically connected thereto. The connection to further terminals of the transistors (T1 . . . through T4 . . .) occurs essentially in rotationally-symmetrical fashion via large-area printed circuit boards (LE1 through LE6). Short connecting paths with low values of inductance are achieved with this arrangement. Furthermore, the waste heat from all transistors (T1 . . . through T4 . . .) is uniformly carried off via the rings (R1, R1'), so that all transistors (T1 . . . through T4 . . .) work at the same temperature. A uniform current division onto all transistors (T1 . . . through T4 . . .) connected in parallel is assured with this arrangement, even in a dynamic case.

Power amplifier for feeding an inductance with switched transistors

A DC chopper converter including four switching elements arranged in a four-arm or an H-bridge configuration between power supply terminals and on opposite sides of a load, each switching element having a free-wheeling diode connected parallel thereto, whereby at every load current direction, the two switching elements positioned diagonally opposite in the bridge are cyclically clocked such that the means value of the load current is defined by the overlap of the open times of the switching elements, while the two switching elements lying in series are clocked out of phase. Since all the switching elements are clocked, there is a steady transition during load current reversals such that the zero axis crossings of the load current need not be separately acquired for each reversal in the drive current.

Growing community of inventors

Hessdorf, Germany

Stefan Nowak