Method and device for controlling a magnetic resonance imaging system
View Patent ↗In a magnetic resonance apparatus and a method for the operation thereof, a pulse sequence is employed that is composed of a number of pulse sequence segments, each including an excitation procedure and a readout procedure. For each of a number of slices of an examination subject that are to be simultaneously excited, the pulse sequence segment is repeated, as a pulse sequence segment pair, with a prephasing gradient pulse being generated between the respective excitations in the respective segments of the pair. The prephasing gradient is configured to cause a gradient moment for all gradients between the respective centers of the respective excitations to be zero. The respective rephasing gradient pulses in each pair of segments are similar, and the respective excitation pulses have different phases.
1. A method for acquiring magnetic resonance image data from an examination subject, comprising:
from a control computer, operating a magnetic resonance data acquisition unit, while an examination subject is situated therein, said examination unit comprising gradient coils and at least one radio-frequency (RF) antenna, with a pulse sequence comprising a plurality of pulse sequence segments, each pulse sequence segment comprising an excitation procedure and a subsequent readout procedure;
from said control computer, in each excitation procedure, operating said gradient coils to generate a first slice selection gradient pulse in a slice selection direction and operating said at least one RF antenna to generate an RE excitation pulse comprising N excitation frequencies that simultaneously excite N slices of said examination subject;
from said control computer, in each readout procedure, operating said gradient coils to generate a rephasing pulse in said slice selection direction and operating said at least one RE antenna to receive RF signals comprising magnetic resonance raw data;
from said control computer, after receiving said RF signals for a respective pulse sequence segment, and before generating the RF excitation pulse in a pulse sequence segment that immediately follows said respective pulse sequence segment, operating said gradient coils to generate a prephasing gradient pulse in said slice selection direction, and configuring said prephasing gradient pulse to make a zeroth gradient moment thereof, which is integrated over all of said gradient pulses in said slice selection direction, from a center of said RF excitation pulse in said respective pulse sequence segment to a center of said RF excitation pulse in said immediately following pulse sequence segment, have a value of zero;
from said control computer, for each of said N slices that are simultaneously excited, repeating said pulse sequence segment, as a plurality of immediately subsequent pulse sequence segment pairs with the rephasing gradient pulse differing from pair-to-pair, and within each pair, generating said respective rephasing pulses as similar rephasing pulses that differ from each other by less than 180°, and generating respective RF excitation pulses with different phases; and
from said control computer, entering said raw magnetic resonance data for each slice into a memory organized as k-space, and making the data entered into k-space available at an output of said control computer in electronic form as a data file for further processing.
2. A method as claimed in claim 1 comprising generating said similar rephasing gradient pulses in each pair of pulse sequence segments as equal rephasing gradient pulses.
3. A method as claimed in claim 1 comprising operating said gradient coils to generate a gradient pulse in a plane that is transverse to said slice selection direction simultaneously with said rephasing gradient pulse, and generating said gradient pulse in said plane that is transverse to said slice selection direction as a balanced gradient pulse.
4. A method as claimed in claim 1 comprising, in each pair of pulse sequence segments, operating said gradient coils to generate different gradient pulses in a plane that is transverse to said slice selection direction, and generating each of said different gradient pulses as a balanced gradient pulse.
5. A method as claimed in claim 1 comprising entering said raw magnetic resonance data into said memory organized as k-space by undersampling k-space.
6. A method as claimed in claim 1 comprising entering said magnetic resonance raw data into said memory organized as k-space by Cartesian sampling of k-space.
7. A method as claimed in claim 1 comprising entering said magnetic resonance raw data into said memory organized as k-space by radial sampling of k-space.
8. A method as claimed in claim 1 comprising entering said magnetic resonance raw data into said memory organized as k-space by randomly controlled sampling of k-space.
9. A method as claimed in claim 1 comprising operating said magnetic resonance data acquisition unit according to said pulse sequence for sine acquisition of said magnetic resonance raw data.
10. A method as claimed in claim 1 wherein N=2.
11. A method as claimed in claim 1 wherein N=3.
12. A magnetic resonance apparatus comprising:
a magnetic resonance data acquisition unit comprising gradient coils and at least one radio-frequency (RF) antenna;
a control computer configured to operate the magnetic resonance data acquisition unit, while an examination subject is situated therein, with a pulse sequence comprising a plurality of pulse sequence segments, each pulse sequence segment comprising an excitation procedure and a subsequent readout procedure;
said control computer being configured, in each excitation procedure, to operate said gradient coils to generate a first slice selection gradient pulse in a slice selection direction and to operate said at least one RF antenna to generate an RF excitation pulse comprising N excitation frequencies that simultaneously excite N slices of said examination subject;
said control computer being configured, in each readout procedure, to operate said gradient coils to generate a rephasing pulse in said slice selection direction and to operate said at least one RF antenna to receive RF signals comprising magnetic resonance raw data;
said control computer being configured, after receiving said RF signals for a respective pulse sequence segment, and before generating the RF excitation pulse in a pulse sequence segment that immediately follows said respective pulse sequence segment, operate said gradient coils to generate a prephasing gradient pulse in said slice selection direction, and to configure said prephasing gradient pulse to make a zeroth gradient moment thereof, which is integrated over all of said gradient pulses in said slice selection direction, from a center of said RF excitation pulse in said respective pulse sequence segment to a center of said RF excitation pulse in said immediately following pulse sequence segment, have a value of zero;
said control computer being configured, for each of said N slices that are simultaneously excited, to repeat said pulse sequence segment, as a plurality of immediately subsequent pulse sequence segment pairs with the rephasing gradient pulse differing from pair-to-pair, and within each pair, to generate said respective rephasing pulses as similar rephasing pulses that differ from each other by less than 180°, and to generate respective RF excitation pulses with different phases; and
said control computer being configured to enter said raw magnetic resonance data for each slice into a memory organized as k-space, and to make the data entered into k-space available at an output of said control computer in electronic form as a data file for further processing.
13. A non-transitory, computer-readable data storage medium encoded with programming instructions, said data storage medium being loaded into a control computer of a magnetic resonance apparatus that comprises a magnetic resonance data acquisition unit comprising gradient coils and at least one radio-frequency (RF) antenna, said programming instructions causing said control computer to:
operate the magnetic resonance data acquisition unit, while an examination subject is situated therein, with a pulse sequence comprising a plurality of pulse sequence segments, each pulse sequence segment comprising an excitation procedure and a subsequent readout procedure;
in each excitation procedure, operate said gradient coils to generate a first slice selection gradient pulse in a slice selection direction and operate said at least one RF antenna to generate an RF excitation pulse comprising N excitation frequencies that simultaneously excite N slices of said examination subject;
in each readout procedure, operate said gradient coils to generate a rephasing pulse in said slice selection direction and operate said at least one RF antenna to receive RF signals comprising magnetic resonance raw data;
after receiving said RF signals for a respective pulse sequence segment, and before generating the RF excitation pulse in a pulse sequence segment that immediately follows said respective pulse sequence segment, operate said gradient coils to generate a prephasing gradient pulse in said slice selection direction, and configure said prephasing gradient pulse to make a zeroth gradient moment thereof, which is integrated over all of said gradient pulses in said slice selection direction, from a center of said RF excitation pulse in said respective pulse sequence segment to a center of said RF excitation pulse in said immediately following pulse sequence segment, have a value of zero;
for each of said N slices that are simultaneously excited, repeat said pulse sequence segment, as a plurality of immediately subsequent pulse sequence segment pairs with the rephasing gradient pulse differing from pair-to-pair, and within each pair, generate said respective rephasing pulses as similar rephasing pulses that differ from each other by less than 180°, and generate respective RF excitation pulses with different phases; and
enter said raw magnetic resonance data for each slice into a memory organized as k-space, and make the data entered into k-space available at an output of said control computer in electronic form as a data file for further processing.