U.S. Philips Corporation

Wilhelmus R Mens

Rudolf Kemner

Peter Hanzen Wardenier

Johannes A Overweg

Eddy B Boskamp

Jan Konijn

Cornelis L Ham

Hilco T Kalmijn

In a magnetic resonance apparatus, a coil system is added to a gradient coil system, as a result of which a measuring field range is adapted to the geometry of an object to be examined. For example, by addition of a Bo coil system to be activated simultaneously with the z-gradient system, an asymmetry is realized in the z-gradient field, as a result of which return of disturbing resonance signals from an object part located outside the gradient field operating range is avoided. Further, by addition of additional arc conductors, the z-gradient linearity range is displaced in the z-direction.

Magnetic resonance apparatus

In an rf coil of a magnetic resonance apparatus steps are taken to optimize a uniform rf measuring field. To this end, axially extending current conductors are provided with means for generating a non-constant effective current intensity in current paths extending across a cylindrical surface so as to be parallel with a symmetry axis of the coil. This can be realized by deflecting axial conductors away from the cylindrical surface, by partly shielding them, by adding auxiliary coils to be individually controlled, or by connecting L-C circuits across the current conductors.

Magnetic resonance apparatus with an optimized detection field

An r.f. transmitter coil is coupled to individually or group-wise independently drivable antenna wire elements, each independently drivable element being driven by its own power amplifier via a sliding contact. An r.f. supply source is coupled to the inputs of the power amplifiers via an input network which provides a phase distribution among the r.f. signals supplied to the amplifiers for the coil to transmit with a circularly polarized r.f. field.

Magnetic resonance apparatus having an improved RF coil

In a magnetic resonance apparatus with an rf detection coil system constructed from overlapping coils the extent of overlap has been chosen to be so that the mutual inductance between overlapping coils is restricted to a non-disturbing minimum by flux compensation. As a result of this the coils of the cascade can be operated simultaneously for the measurement of coronal and sagittal slices without detrimental mutual influence.

Magnetic resonance apparatus with uncoupled rf coils

In a magnetic resonance apparatus a gradient coil system and an r.f. coil are combined so as to form a magnetically, electrically and structurally integrated coil system with current conductors in substantially the same cylinder. Thus, a substantial saving is realized as regards the activation energy required for generating gradient fields as well as for generating r.f. fields and notably r.f. stray-fields are also reduced.

Magnetic resonance apparatus comprising integrated gradient r.f. coils

A so-called birdcage coil must be quickly deactivated after having generated an RF magnetic field, so as not to disturb the detection of the generated spin resonance signals by the surface coil (or another coil). To this end, semiconductor switches are included in some of the rod conductors of the birdcage coil. The switches are arranged substantially halfway along the rod conductors, because the RF voltage exhibits a zero crossing at that area. As a result, the semiconductor switches can operate with a low voltage. It has been found that the interruption of the rod conductors which are situated in one symmetry half of the birdcage coil and which carry most current in that half suffices for substantial deactivation.

Magnetic resonance imaging apparatus comprising an activatable birdcage

Disclosed is a magnetic resonance imaging apparatus, with an r.f. coil which is designed on the basis of the sinusoidal current distribution across a circular-cylindrical surface about a central coil axis and which is, subject to a generally applicable looping-through condition z.sub.1 =-K z.sub.2, when K is a positive constant which depends on the number of bars and geometrical deviations, z.sub.1 is the impedance of the bar conductors, and z.sub.2 is the impedance of ring conductor elements between each two pair of bar conductors. The coil based on the above condition is particularly adapted to parasitic capacitances of the bar conductors and to the general shape of objects to be examined.

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Eindhoven, Netherlands

Wilhelmus R Mens