Magnetic resonance method and system to correct phase information in MR images

摘要

In a magnetic resonance (MR) method and system for correction of phase information in MR images of a predetermined volume segment of an examination subject, a basic magnetic field is applied and MR data of the predetermined volume segment are acquired and evaluated such that phase information is calculated for each image element of the predetermined volume segment. A navigator signal is acquired that detects an unintentional change of the basic magnetic field that is caused by movements of the examination subject or by the magnetic resonance system itself. The phase information is corrected with this navigator signal.

主权项

1. A method to correct phase information in magnetic resonance (MR) images of a volume segment of an examination subject, comprising;
placing an examination subject in an MR data acquisition unit and operating the MR data acquisition unit to apply a basic magnetic field at least to a predetermined volume segment of the examination subject and to acquire MR data from the predetermined volume segment, said MR data representing image elements of said predetermined volume segment; detecting a navigator signal originating within said MR data acquisition unit during acquisition of said MR data; in a processor, evaluating said MR data to calculate phase information for each of said image elements of said predetermined volume segment; in said processor, using said navigator signal to determine a change in said basic magnetic field caused by a source selected from the group consisting of movement of the examination subject, and said MR data acquisition unit itself; determining a first reference phase value by detecting transverse magnetization in said examination subject in a reference measurement in which said navigator signal is not phase coded, using free induction decay, during a first time interval after said RF excitation; determining a second reference phase value by transverse magnetization of an echo signal resulting from said navigator signal being detected in a center of k-space in said reference measurement at a second time interval after said RF excitation; determining a first phase value by detecting the transverse magnetization in a measurement with a measurement signal that is not phase coded using the free induction decay after said first time interval after said RF excitation; determining a second phase value by detecting the transverse magnetization of an echo signal resulting from the measurement signal during said measurement in the center of k-space after a second time interval after the RF excitation; correcting said MR data during entry thereof into k-space dependent on said first reference phase value, said second reference phase value, said first phase value and said second phase value; determining a factor F dependent on time t according to
F(t)=e−i(Δφ+Δω·t), wherein Δφ and Δω are calculated according to
Δφ=(T2·(φn,1−φR,1)−T1·(φn,2−φR,2))/(T2−T1),Δω=((φn,2−φR,2)−(φn,1−φR,1))/(T2−T1),wherein φR,1 is the first reference phase value, φR,2 is the second reference phase value, φn,1 is the first phase value, φr,2 is the second phase value, T1 is the first time interval and T2 is the second time interval;
correcting the MR data by multiplying the MR data with the factor F at time t; and from said processor, making said MR data with the corrected phase information available in electronic form at an output of said processor, as a data file.