Method and magnetic resonance apparatus for image reconstruction with multiple virtual coils
An MR image is produced from data acquired by radiating an RF pulse and switching multiple bipolar magnetic field gradients to generate multiple gradient echoes that are acquired in a raw data set with multiple raw data lines by a reception coil, the multiple gradient echoes being acquired with bipolar magnetic field gradients of different polarity. Due to the bipolar magnetic field gradients of different polarity, in the raw data set first raw data lines are filled with MR signals in one direction in raw data space, and second raw data lines are filled with MR signals in the opposite direction. The MR image is reconstructed from MR signals that have simultaneously been acquired with at least two different reception coils, by generating a first coil raw data set from the raw data set in the image reconstruction, which coil raw data set has only the raw data lines of the raw data set that were filled with MR signals in one direction, and by selecting a second coil raw data set that has only the raw data lines of the raw data set that were filled with MR signals in the other set direction. The MR image is reconstructed from the two coil raw data sets using a parallel imaging reconstruction algorithm, under the assumption that the two coil raw data sets have been acquired by different reception coils.
1. The method to produce a magnetic resonance (MR) image, comprising
operating an MR data acquisition unit, in which a subject is situated, by radiating a radio frequency (RF) pulse and activating multiple bipolar magnetic field gradients to excite nuclear spins in the subject and to generate multiple gradient echoes resulting from the excited nuclear spins;
operating the MR data acquisition unit to acquire raw data representing said multiple gradient echoes with a single reception coil of the MR data acquisition unit, and entering said raw data into respective raw data lines in an electronic memory organized as raw data space, with multiple raw data sets being acquired respectively for said multiple gradient echoes during activation of said bipolar magnetic field gradients with first raw data lines in raw data space being filled, in each raw data set, in a first direction by said bipolar magnetic field gradient having a first polarity and second raw data lines in each raw data set being filled in an opposite direction by said bipolar magnetic field gradient having a second polarity;
in a computer, reconstructing an MR image from the raw data in said electronic memory, using a reconstruction algorithm designed to reconstruct said MR image from raw data simultaneously acquired with at least two different reception coils and, in said reconstruction algorithm, generating a first coil raw data set comprised only of raw data lines that were filled with raw data in said one direction, and generating a second coil raw data set comprising only raw data lines that were filled with raw data in said other direction, and reconstructing said MR image using said generated first and second coil raw data sets in said algorithm as if the raw data in said generated first and second coil raw data sets were acquired by different reception coils, and
making the reconstructed MR image available at an output of said computer in electronic form as a data file.
2. A method as claimed in claim 1 comprising, in said computer, reconstructing said MR image by automatically determining any raw data in raw data lines that are missing in said first coil raw data sets from raw data in raw data lines of said second coil raw data set.
3. A method as claimed in claim 2 comprising reconstructing said MR image using, as said algorithm, a reconstruction algorithm selected from the group consisting of GRAPPA, SENSE, and SMASH.
4. A method as claimed in claim 2 comprising, in said computer, generating a coil-dependent calibration raw data set comprising only data from raw data lines that are filled with raw data only in one direction, and using said coil-dependent calibration data to form a calibration raw data set, and using said calibration raw data set to reconstruct raw data from said missing lines.
5. A method as claimed in claim 4 comprising filling missing raw data lines with said calibration raw data set in one of said first or second coil raw data sets, and reconstructing said MR image using said one of said first and second raw data sets, and the other of said first and second coils raw data sets.
6. A method as claimed in claim 5 comprising filling said missing raw data lines with said calibration raw data set only in portions thereof around a center of raw data space.
7. A magnetic resonance (MR) apparatus comprising:
an MR data acquisition unit comprising a radio-frequency (RF) system and a gradient system;
a control unit configured to operate the MR data acquisition unit, in which a subject is situated, by radiating a radio frequency pulse with said RF system and activating multiple bipolar magnetic field gradients with said gradient system, to excite nuclear spins in the subject and to generate multiple gradient echoes resulting from the excited nuclear spins;
an electronic memory;
said control unit being configured to operate the MR data acquisition unit to acquire raw data representing said multiple gradient echoes with a single reception coil of the MR data acquisition unit, and to enter said raw data into respective raw data lines in said electronic memory organized as raw data space, with multiple raw data sets being acquired respectively for said multiple gradient echoes during activation of said bipolar magnetic field gradients with first raw data lines in raw data space being filled, in each raw data set, in a first direction by said bipolar magnetic field gradient having a first polarity and second raw data lines in each raw data set being filled in an opposite direction by said bipolar magnetic field gradient having a second polarity;
a computer configured to reconstruct an MR image from the raw data in said electronic memory, using a reconstruction algorithm designed to reconstruct said MR image from raw data simultaneously acquired with at least two different reception coils and, in said reconstruction algorithm, said computer being configured to generate a first coil raw data set comprised only of raw data lines that were filled with raw data in said one direction, and generating a second coil raw data set comprising only raw data lines that were filled with raw data in said other direction, and to reconstruct said MR image using said generated first and second coil raw data sets in said algorithm as if the raw data in said generated first and second coil raw data sets were acquired by different reception coils, and
said computer being configured to make the reconstructed MR image available at an output of said computer in electronic form as a data file.