U.S. Philips Corporation

Koninklijke Philips Corporation N.v.

Johannes Petrus Groen

Miha Fuderer

Cornelis Leonardus Gerardus Ham

Johannes J Cuppen

Peter Van Der Meulen

Josephus J In Den Kleef

Johannes J Van Vaals

Marinus Johannes Adrianus Maria Van Helvoort

Robert Paul Kleihorst

Jouke Smink

Gerrit H Van Yperen

Michel Paul Jurriaan Jurrissen

Arianne M C Van Muiswinkel

Antoon F Mehlkopf

Wilhelmus Reinerius Maria Mens

Gerrit Hendrik Van Yperen

Hans Gerard Jenniskens

Rudolf G De Graaf

Gerald Van Ensbergen

Ljouke Smink

An object positioned in an examination volume of a magnetic resonance (MR) device () is T-weighted MR imaged such that the MR image is essentially free from interfering contributions from MR signals without Tweighting. The object () is subject to a first Tpreparation sequence (TPREP) including an excitation RF pulse (), one or more refocusing RF pulses (), and a tip-up RF pulse (). The object () is subject to a first readout sequence (RO) including at least one excitation RF pulse and switched magnetic field gradients for acquiring a first set of MR signals. The object () is subject to a second Tpreparation sequence (TPREP) including an excitation RF pulse ('), one or more refocusing RF pulses (&#x2032;), and a tip-up RF pulse (&#x2032;). At least one of the RF pulses (&#x2032;) of the second Tpreparation sequence (TPREP) has a different phase than the corresponding RF pulse () of the first Tpreparation sequence (TPREP). The object () is subject to a second readout sequence (RO) including at least one excitation RF pulse and switched magnetic field gradients for acquiring a second set of MR signals. The MR image is reconstructed from the first and second sets of MR signals.

T2-weighted MR imaging with elimination of non-T2-weighted signal contributions

The invention relates to a method of MR imaging of an object positioned in an examination volume of a MR device (). It is an object of the invention to enable 'silent' ZTE imaging with improved sampling of k-space center. According to the invention, the object () is subjected to an imaging sequence of RF pulses () and switched magnetic field gradients, which imaging sequence is a zero echo time sequence comprising: i) setting a readout magnetic field gradient having a readout direction and a readout strength (G, G); ii) radiating a RF pulse () in the presence of the readout magnetic field gradient; iii) acquiring a FID signal in the presence of the readout magnetic field gradient, wherein the FID signal represents a radial k-space sample (), wherein the acquisition of the FID signal is started at an acquisition time at which a receiver gain of the MR device () has not yet stabilized after the radiation of the RF pulse (); iv) incrementally varying the readout direction; v) sampling a spherical volume in k-space by repeating steps i) through iv) a number of times. Finally, a MR image is reconstructed from the acquired FID signals. Moreover, the invention relates to a MR device and to a computer program for a MR device.

Zero echo time MR imaging

In an EPI acquisition sequence for magnetic resonance signals k-space is scanned along sets of lines in k-space along opposite propagation directions, e.g. odd and even lines in k-space. Phase errors that occur due to the opposite propagation directions are corrected for in a SENSE-type parallel imaging reconstruction. The phase error distribution in image space may be initially estimated, calculated form the phase difference between images reconstructed from magnetic resonance signals acquired from the respective sets of k-space lines, or from an earlier dynamic.

EPI ghost correction involving sense

The invention relates to a device () for magnetic resonance imaging of a body (), comprising a main magnet () for generation of a stationary and substantially homogeneous main magnetic field within the examination zone, a plurality of wireless receiving units () placed in or near the examination zone, and sampling means () operating at a variable sampling frequency for sampling the received MR signals and for converting them into digital signal samples. The invention proposes to make provision for energizing means () generating an RF energizing field within the examination zone for inductively supplying electric power to the wireless receiving units (), wherein the frequency of the RF energizing field is an integer multiple of the sampling frequency.

Magnetic resonance device and method for energizing receiving units

A magnetic resonance imaging (MRI) system includes an examination volume (), a main magnet system () for generating a main magnetic field (B) in the examination volume, a gradient magnet system () for generating gradients of the main magnetic field, and a control system () for compensating disturbances of the magnetic field caused by mechanical vibrations of the MRI system. The control system is a feed-forward control system which determines a necessary compensation for said disturbances in dependence on an electric current in the gradient magnet system according to a predetermined response relation. Since in most MRI systems the mechanical vibrations are predominantly caused by the altering electric currents in the gradient magnet system and by eddy currents induced thereby, an accurate and reliable compensation for said disturbances is provided, so that artifacts and other distortions of the reconstructed image caused by said disturbances are considerably reduced.

Compensation of magnetic field disturbances due to vibrations in an MRI system

A magnetic resonance imaging method which involves a pulse sequence for generating magnetic resonance signals and in which diffusion weighting is applied, for example, by way of a pair of gradient pulses which are separated by a 180&#xb0; refocusing RF pulse. The magnetic resonance signals are generated as spin echo signals due to refocusing pulses. The refocusing pulses are flanked by compensation gradient pulses and the gradient strengths of the compensation gradient pulses are alternated according to a periodic pattern.

Diffusion weighted multiple spin echo (rare) sequence with periodically amplitude-modulated crusher gradients

According to the known method, a reference measurement is performed by measurement of magnetic resonance signals, without application of a magnetic gradient field to introduce phase encoding in the magnetic resonance signals. According to the invention, two measurements are performed with a read-out gradient of opposite polarity at substantially corresponding instants, relative to an instant at which the contributions to the phase error due to frequency deviations are zero. The advantage of the novel method resides in the fact that a higher insensitivity to field inhomogeneities and chemical shifts is achieved.

Method of and device for imaging by means of magnetic resonance

An MR system for interventional procedures, includes an MR device and an invasive device. The MR device is arranged to acquire images of a part of an object. A part of the invasive device can be imaged in an MR image by providing a coil or a conductor loop which has two non-magnetic conductors which are situated at some distance from one another underneath the surface of the invasive device. A reduction of artefacts due to the movement of a patient or the invasive device can be obtained by sampling an MR signal, whereby an auxiliary magnetic field is periodically applied during the time in which the plurality of lines in k-space are scanned.

MR system and invasive device for interventional procedures

In a magnetic resonance method for imaging a part of a body which is arranged in a steady magnetic field, magnetic resonance signals are measured utilizing an initial read gradient and an alternating read gradient. The method can be used, for example for phase contrast angiography and for flow velocity measurements in a body of a patient. In order to counteract artifacts in the image due to inhomogeneities of the steady magnetic field, the time elapsing between an excitation RF pulse exciting spins in the part of the body and the initial read gradient is varied in successive pulse sequences. However, this causes artifacts in the fluid flow images due to the phase error which itself is caused by the spins flowing in the direction of the gradient field. In order to counteract these artifacts, the first-order moment of the initial read gradient and a first order lobe of the alternating read gradient is kept substantially constant in each pulse sequence.

Method of and device for the imaging of objects by means of magnetic

In an EPI or GRASE magnetic resonance method, phase errors caused by the alternation of the read gradient polarity (G.sub.x) are corrected by obtaining a set of reference measurements with both polarities at low values in the phase encoding (k.sub.y) direction. From these reference measurements the phase errors are estimated. Subsequently, the measurements covering the whole of k-space are corrected and a magnetic resonance image obtained in which artefacts due to the alternating polarity of the read gradient are suppressed.

Correction of read-gradient polarity in EPI and grase MRI

In an MRI device operating according to a spin-echo method, switched gradient magnetic fields are applied in the form of slice selection, phase encoding and read gradients. The switching of the gradients causes eddy currents in metal parts of the apparatus. The eddy currents disturb the applied magnetic fields, thereby changing the phases of the precessing nuclear spins of a body to be examined and causing artefacts in a reconstructed image. The disturbing effects of the eddy currents is compensated for by supplementing a sequence of switched gradient magnetic fields with additional gradient fields. These additional fields have zero net effect but induce further eddy currents which compensate for the disturbing effects of the eddy currents generated by the regular switched gradient magnetic fields. The additional gradient fields are chosen such that the total time-integrated strength of a gradient in any interval between two RF-pulses is substantially equal to the desired value.

Eddy current compensation in magnetic resonance imaging

An MR angiography method in which an angiogram is formed from the difference between amplitude and/or phase information contained in first and second complex images produced by different gradient waveforms in respective first and second types of excitation sequences. The gradient waveforms are chosen so that in the angiogram obtained from the first and second complex images, ideally, signals orginating from excited stationary spin nuclei are not present while the signals orginating from moving spin nuclei, due to flow in blood vessels, are present. However, stationary spin nuclei can be somewhat differently excited in the first and second sequence due to the different gradient waveforms used which cause different eddy currents to flow in metal parts of the apparatus. In the absence of correction, these eddy currents would exert their influence magnetically by causing a smoothly varying phase error in the difference between the first and second complex images resulting in erroneous signal contribution to the angiogram from stationary spin nuclei. This erroneous signal is eliminated by estimating the smoothly varying phase difference before forming the angiogram from the first and second complex images and by thus carrying out a non-linear phase correction.

Method and apparatus for carrying out a phase correction in MR

During known MRI measurements, for example spin echo and inversion recovery measurements, phase errors occur in pixels, inter alia due to eddy currents caused by the application or interruption of magnetic field gradients during a measurement. There is proposed an inversion recovery method combined with a method where the magnetization is not inverted in advance in order to determine for each pixel the phase error in an image obtained by means of an inversion recovery method, so that inversion recovery images can be obtained which do not contain phase errors.

Method for the phase correction of MR inversion recovery images

In known spin echo imaging examination a waiting period is customarily observed between two successive spin echo measurements in order to allow for the magnetic moment to relax in the direction of the uniform magnetic field Bo. In addition to this waiting period, the use of 180.degree. pulses also leads to a comparatively long examination time which increases the risk of image artefacts due to motions of, for example a patient to be examined. This comparatively long examination time is also unfavorable in view of the radiation load. In order to avoid these drawbacks, a method is proposed in which the electromagnetic pulses used are exclusively excitation pulses in the form of .alpha..degree. pulses, where 0&lt;.alpha.&lt;90.

Magnetic resonance imaging method utilizing small excitation pulses

The invention relates to the determination of an NMR distribution in which an alternating gradient field is applied while sampling the NMR signal (FID signal, nuclear spin echo signal). The frequency of the alternating gradient field is comparatively low (order of magnitude of 100 Hz) and the field has from a few to some tens of cycles during each measurement period. While an FID signal is being sampled, the image frequency field matrix is scanned using a zig-zag (oscillating) line pattern during each line when data is provided for elements in from a few to some tens of rows in the image frequency matrix. By applying preparation gradient fields, the image frequency matrix can be filled by means of successive zig-zag line patterns which have been shifted with respect to one another and which thus enable a uniform sampling density to be provided in the image frequency space. The filling of the image frequency matrix with signal samples is thus speeded up by a factor of a few to some tens of times by the invention, the energy required for controlling the gradient field coils being substantially reduced at the same time.

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Eindhoven, Netherlands

Johannes Petrus Groen