Method and magnetic resonance system to generate multiple magnetic resonance images

1. A method to generate multiple magnetic resonance (MR) images of an examination subject, comprising:

operating an MR data acquisition unit, in which said examination is situated, according to a multi-echo MR data acquisition sequence to acquire raw MR data from the examination subject;

entering said raw MR data acquired from the examination subject into an electronic memory organized as k-space comprising a plurality of rectangular k-space segments each comprising a plurality of k-space lines along which said raw MR data are entered;

by operating said MR data acquisition unit with said multi-echo MR data acquisition sequence, producing, for each k-space line, a first gradient echo at a first echo point in time and a second gradient echo at a later second echo point in time;

operating said data acquisition unit with said multi-echo MR data acquisition sequence by, for each k-space line, radiating a radio-frequency pulse that manipulates a transverse magnetization of nuclear spins in the examination subject, activating a phase encoding gradient field that phase codes the raw MR data of the respective k-space line, activating a first readout gradient field and a second readout gradient field that, in combination with the manipulation of the transverse magnetization produced by said radio-frequency pulse, respectively produce said first gradient echo and said second gradient echo, and reading out raw MR data, for the respective k-space line, of said first gradient echo during activation of said first readout gradient field in a time interval around said first echo point in time, and reading out raw MR data, for the respective k-space line, of said second gradient echo during activation of said second readout gradient field in a time interval around said second echo point in time;

orienting said rectangular k-space segments in k-space with a longer side of each k-space segment oriented along a direction in the respective k-space segment that is defined by said phase encoding gradient field;

orienting said rectangular k-space segments in k-space with a short side of each k-space segment oriented along a direction of the respective k-space segment that is defined by said readout gradient fields; and

in a processor having access to said memory, reconstructing individual MR images from raw data in said k-space acquired at identical echo times, respectively.

2. A method as claimed in claim 1 comprising:

entering said raw data into said k-space segments with said k-space lines oriented parallel to each other;

orienting said long side of said k-space segments orthogonally to said k-space lines; and

orienting said short side of said k-space segments along said k-space lines.

3. A method as claimed in claim 2 , comprising:

in said multi-echo MR data acquisition sequence, activating a slice selection gradient field during the radiation of said radiofrequency pulse; and

shifting said k-space segments essentially parallel to said short side of said k-space segments in a plane defined by said slice selection gradient field.

4. A method as claimed in claim 1 wherein k-space comprises a k-space center, and comprising:

organizing said k-space segments to all include said k-space center; and

in said multi-echo MR data acquisition sequence, activating a slice selection gradient field during the radiation of said radiofrequency pulse, and rotating said k-space segments in a plane defined by said slice selection gradient field around said k-space center.

5. A method as claimed in claim 4 said k-space comprising exactly two of said k-space segments; and

rotating said k-space segments to each other by an angle of approximately 90° around said k-space center in said plane defined by said slice selection gradient field.

6. A method as claimed in claim 1 wherein k-space comprises a k-space center, said method comprising:

organizing said k-space segments in k-space to all include said k-space center; and

rotating said k-space segments to each other around said k-space center in order to enter said raw data into a sphere in k-space.

7. A method as claimed in claim 1 comprising:

organizing said k-space segments in three-dimensional k-space as cuboid k-space segments that each comprise a plurality of rectangular sub-segments;

in said multi-echo MR data acquisition sequence, activating a slice selection gradient field during the radiation of said radiofrequency pulse, and activating an additional phase encoding gradient field that shifts said plurality of rectangular sub-segments to each other along a direction defined by said slice selection gradient field;

orienting a long side of the plurality of sub-segments along a direction defined by the phase encoding gradient field or by the additional phase encoding gradient field; and

orienting a short side of the plurality of sub-segments along a direction of the respective k-space segment defined by said first and second readout gradient fields.

8. A method as claimed in claim 7 wherein k-space comprises a k-space center, said method comprising:

orienting said k-space segments in k-space so as to all include said k-space center; and

rotating said k-space segments to each other in a plane defined by the readout gradient field and a plane defined by the phase encoding gradient field or the additional phase encoding gradient field.

9. A method as claimed in claim 7 wherein k-space comprises a k-space center, and said method comprising:

organizing said k-space segments to all include said k-space center; and

rotating said k-space segments to each other around said k-space center to enter said raw data into a sphere or a cylinder in k-space.

10. A method as claimed in claim 1 comprising forming said gradient echoes by operating said MR data acquisition unit with a spin echo/gradient echo hybrid sequence, as said multi-echo MR data acquisition sequence.

11. A method as claimed in claim 10 comprising, in said spin echo/gradient echo hybrid sequence, radiating said radio-frequency pulse as a refocusing pulse to generate a spin echo of said transverse magnetization, with said first echo point in time and said second echo point in time being within a time duration of said spin echo.

12. A method as claimed in claim 11 comprising:

radiating said refocusing pulse as one of a series of multiple refocusing pulses that follow a radio-frequency excitation pulse to excite said transverse magnetization; and

after one of said refocusing pulses in said series of multiple refocusing pulses, acquiring raw data for at least one of the k-space lines of at least one of said k-space segments such that all k-space data required for said at least one particular segment is acquired by this series of multiple refocusing pulses.

13. A method as claimed in claim 1 comprising, in said multi-echo MR data acquisition sequence, acquiring raw data from successive gradient echoes during activation of respective readout gradient fields with different polarity.

14. A method as claimed in claim 1 comprising reconstructing said MR images from raw data in said k-space segments acquired at identical echo times using a reconstruction technique selected from the group consisting of regridding in k-space, density compensation in k-space, successive shear operation in k-space, parallel imaging techniques, combining, for each echo time, multiple intermediate MR images respectively reconstructed from each k-space segment, or combining, for each echo time, MR data of multiple k-space segments and reconstructing images from the combined MR data.

15. A method as claimed in claim 1 comprising reconstructing said MR images from raw data of gradient echoes of said k-space segments acquired at identical echo times, according to a GRAPPA (Generalized Autocalibrating Partially Parallel Acquisition) technique.

16. A method as claimed in claim 1 comprising:

operating said MR data acquisition unit with said multi-echo MR data acquisition sequence to produce a third gradient echo at a third echo point in time, which follows said first echo point in time and said second echo point in time; and

acquiring raw data for a respective k-space line by activating a third readout gradient during a time interval around said third echo point in time.

17. A magnetic resonance (MR) apparatus, comprising:

an MR data acquisition unit;

a control unit configured to operate said MR data acquisition unit, in which an examination subject is situated, according to a multi-echo MR data acquisition sequence to acquire raw MR data from the examination subject;

said control unit being configured to enter said raw MR data acquired from the examination subject into an electronic memory organized as k-space comprising a plurality of rectangular k-space segments each comprising a plurality of k-space lines along which said raw MR data are entered;

said operation of said MR data acquisition unit with said multi-echo MR data acquisition sequence, producing, for each k-space line, a first gradient echo at a first echo point in time and a second gradient echo at a later second echo point in time;

said control unit being configured to operate said data acquisition unit with said multi-echo MR data acquisition sequence by, for each k-space line, radiating a radio-frequency pulse that manipulates a transverse magnetization of nuclear spins in the examination subject, activating a phase encoding gradient field that phase codes the raw MR data of the respective k-space line, activating a first readout gradient field and a second readout gradient field that, in combination with the manipulation of the transverse magnetization produced by said radio-frequency pulse, respectively produce said first gradient echo and said second gradient echo, and reading out raw MR data, for the respective k-space line, of said first gradient echo during activation of said first readout gradient field in a time interval around said first echo point in time, and reading out raw MR data, for the respective k-space line, of said second gradient echo during activation of said second readout gradient field in a time interval around said second echo point in time;

said control unit being configured to enter said raw data into said electronic memory with said rectangular k-space segments oriented in k-space with a longer side of each k-space segment oriented along a direction in the respective k-space segment that is defined by said phase encoding gradient field;

said control unit being configured to enter said raw data into said electronic memory with said rectangular k-space segments oriented in k-space with a short side of each k-space segment oriented along a direction of the respective k-space segment that is defined by said readout gradient fields; and

a processor having access to said memory, said processor being configured to reconstruct individual MRI images from said raw data in said k-space acquired at identical echo times, respectively.