Dynamic magnetic resonance imaging with variable contrast
In a method for computing MR images of an examination object that performs a cyclic movement, MR signals are detected over at least two cycles of the cyclic movement. In each of these cycles, data for multiple MR images are recorded. Over these cycles, a magnetization of the examination object that influences the MR images approaches a state of equilibrium in a second of these cycles is closer to the state of equilibrium than in a first of these cycles. Movement information for various movement phases of the cyclic movement of the examination object is determined using the MR images from the second cycle, with movement information of the examination object determined for each of the various movement phases. Movement correction of the examination object is carried out in the MR images of the first cycle using the movement information determined in the second cycle.
1. A method for generating magnetic resonance (MR) images of an examination object that performs a cyclic cardiac movement, with each cycle in said cyclic cardiac movement being divisible into successive movement phases, said movement phases being comparable from cycle-to-cycle, said method comprising:
from a control computer, operating an MR scanner, while the examination object is situated therein, to acquire MR signals from the examination object over at least two cycles of said cyclic movement by acquiring, in each of said at least two cycles, a plurality of MR data sets respectively for a plurality of MR images wherein, over said at least two cycles, a magnetization given to nuclear spins of the examination object, that influences said MR data sets, is changing toward a state of equilibrium of said nuclear spins and wherein, in a second data set of said at least two cycles, said magnetization is closer to said state of equilibrium than in a first of said at least two cycles;
in said control computer, determining movement information representing the respective movement phases in the second of said cycles, using the MR data sets acquired during said second of said cycles, with said movement information of the examination object being determined individually for each of said respective movement phases in the second of said cycles;
in said control computer, executing a movement correction for correcting for said cyclic movement of said examination object in said first of said cycles by applying said movement information individually for the respective movement phases of the cyclic movement in said first of said cycles using the movement information determined individually for the respective movement phases in the second of said cycles;
in said control computer, reconstructing MR images of the respective movement phases of said first of said cycles by executing a movement-corrected reconstruction wherein movement of the examination object in each of said movement phases of said first cycle is corrected using said movement information determined for said movement phases of said first of said cycles; and
providing the reconstructed MR images available at an output of said control computer in electronic form, as an image data file.
2. A method as claimed in claim 1 comprising, in said control computer, for each of said respective movement phases of the examination object in said second of said cycles, determining a movement change relative to each of the other respective movement phases in said second of said cycles, and executing said movement correction algorithm for said MR data sets of said first of said cycles to produce a movement corrected MR image for each of the respective movement phases in said first of said cycles.
3. A method as claimed in claim 1 comprising:
at a display in communication with said control computer, displaying each of said MR images with a contrast value; and
reconstructing said MR images to produce a contrast change between temporally adjacent MR images of said first of said cycles that is greater than for temporally adjacent MR images of said second of said cycles.
4. A method as claimed in claim 1 comprising, in said control computer:
executing said reconstruction to give each MR image of said first of said cycles a different contrast value, and to assign a respective movement phase of said first of said cycles to each reconstructed MR image of said first of said cycles;
for the respective contrast values, reconstructing at least one initial MR image acquired with the respective contrast value and using the movement information for said initial reconstructed MR image to reconstruct movement-corrected MR images for the other movement phases of said first of said cycles, with the same contrast value as the associated initial MR image.
5. A method as claimed in claim 4 comprising after reconstructing said movement-corrected MR images, MR images for all contrast values of said first of said cycles and for all movement phases of said cyclic movement are present as reconstructed MR images.
6. A method as claimed in claim 1 comprising using the acquired MR images and the reconstructed movement-corrected MR images for reconstructing spatially-resolved T1 and T2 relaxation times of said examination object.
7. A method as claimed in claim 6 wherein said examination object is the heart of a patient, and comprising acquiring said MR data sets over a plurality of cardiac cycles between three and six.
8. A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner to prepare said magnetization by applying a preparation pulse, that starts said changing of said magnetization toward said equilibrium state, before acquiring said MR data sets.
9. A method as claimed in claim 8 comprising applying said preparation pulse as an inversion pulse that inverts said magnetization.
10. A method as claimed in claim 8 wherein said first of said cycles is the first-occurring cycle in time after said preparation pulse, and wherein said second of said cycles follows said first of said cycles.
11. A method as claimed in claim 1 comprising, from said control computer, operating said MR scanner to cause said magnetization to approach said state of equilibrium by radiating a plurality of radio-frequency (RF) pulses at an interval that is smaller than the T1 time of the examination object.
12. A method as claimed in claim 1 wherein said first of said cycles is a first-occurring cycle in said cyclic movement during which said MR data sets are acquired, and wherein said second of said cycles is a last cycle in said cyclic movement in which said MR data sets are acquired.
13. A method as claimed in claim 1 comprising generating said movement information to comprise first movement information dependent on movement of an organ as said examination object, and second movement information accounting for movement of said organ by movement of an environment of said organ, and determining said second movement information by registering a reconstructed MR image of said first of said cycles with a reconstructed MR image of a second of said cycles, both in a same movement phase.
14. A magnetic resonance (MR) apparatus comprising:
an MR scanner adapted to receive an examination object that performs a cyclic cardiac movement, with each cycle in said cyclic respiratory movement, with each cycle in cyclic cardiac movement being divisible into successive movement phases, said movement phases being comparable from cycle-to-cycle;
a control computer configured to operate said MR scanner, while the examination object is situated in the MR scanner, to acquire MR signals from the examination object over at least two cycles of said cyclic movement by acquiring, in each of said at least two cycles, a plurality of MR data sets respectively for a plurality of MR images wherein, over said at least two cycles, a magnetization given to nuclear spins of the examination object, that influences said MR data sets, is changing toward a state of equilibrium of said nuclear spins and wherein, in a second data set of said at least two cycles, said magnetization is closer to said state of equilibrium than in a first of said at least two cycles;
said control computer being configured to determine movement representing the respective movement phases in the second of said cycles, using the MR data sets acquired during said second of said cycles, with said movement information of the examination object being determined individually for each of said respective movement phases in the second of said cycles;
said control computer being configured to execute a movement correction for correcting for said cyclic movement of said examination object in said first of said cycles by applying said movement information individually for the respective movement phases of the cyclic movement in said first of said cycles using the movement information determined individually for the respective movement phases in the second of said cycles;
said control computer being configured to reconstruct MR images of the respective movement phases of said first of said cycles by executing a movement-corrected reconstruction wherein movement of the examination object in each of said movement phases of said first cycle is corrected using said movement information determined for said movement phases of said first of said cycles; and
said control computer being configured to provide the reconstructed MR images at an output of said control computer in electronic form, as an image data file.