U.S. Philips Corporation

Josephus J In Den Kleef

Johannes Petrus Groen

Rudolf G De Graaf

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.

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Eindhoven, Netherlands

Josephus J In Den Kleef