Methods for acquiring a magnetic resonance image dataset and for generating a motion-corrected image dataset
A method for acquiring a magnetic resonance image dataset of an object includes using an imaging protocol in which a number of k-space lines are acquired in one shot. The imaging protocol includes a plurality of shots. A plurality of additional k-space lines are acquired in at least a subset of the shots, such that movement of the object is detected throughout the imaging protocol. A method for generating a motion-corrected magnetic resonance image dataset from the dataset thus acquired, a magnetic resonance imaging apparatus, and a computer program are also provided.
1 . A method for acquiring a magnetic resonance image dataset of an object, the method comprising:
using an imaging protocol in which spatial encoding is performed using phase encoding gradients along at least one spatial dimension, and frequency encoding gradients along another spatial dimension,
wherein k-space is sampled during an acquisition in a plurality of k-space lines oriented along a frequency encoding direction,
wherein a number of k-space lines of the plurality of k-space lines are acquired in one shot, the imaging protocol comprising a plurality of shots,
wherein a plurality of additional k-space lines are acquired in at least a subset of shots of the plurality of shots, such that movement of the object is detected throughout the imaging protocol, and
wherein the k-space is sampled in a sampling order in which one more of the phase encoding gradients are changed incrementally from one k-space line to the next, with the exception of the plurality of additional k-space lines.
2 . The method of claim 1 , wherein a position in k-space of the plurality of additional k-space lines acquired in each shot of the plurality of shots or in each of the subset of shots is constant or is varied over the shots or the subset of shots.
3 . The method of claim 1 , wherein the plurality of additional k-space lines are acquired in each shot of the plurality of shots.
4 . The method of claim 1 , wherein 2 to 16 additional k-space lines are acquired in each shot of the plurality of shots or in each of the subset of shots.
5 . The method of claim 4 , wherein 4 to 8 additional k-space lines are acquired in each shot of the plurality of shots or in each of the subset of shots.
6 . The method of claim 1 , wherein the acquisition of the plurality of additional k-space lines takes up 0.5% to 5% of a total acquisition time of the imaging protocol.
7 . The method of claim 6 , wherein the acquisition of the plurality of additional k-space lines takes up 1% to 3% of the total acquisition time of the imaging protocol.
8 . The method of claim 1 , wherein the plurality of additional k-space lines are disposed in a central region of the k-space, which is equivalent to a magnetic resonance image of low resolution.
9 . The method of claim 8 , wherein the magnetic resonance image of low resolution has a pixel size of ≥3 mm.
10 . The method of claim 9 , wherein the magnetic resonance image of low resolution has a pixel size of ≥4 mm.
11 . The method of claim 1 , further comprising acquiring a low-resolution scout image of the object.
12 . The method of claim 1 , wherein the imaging protocol uses a parallel imaging technique, in which one or all phase encoding directions are subsampled by a predetermined acceleration factor, and the magnetic resonance image dataset is acquired using a multi-channel coil array.
13 . The method of claim 1 , further comprising:
generating a motion-corrected magnetic resonance image dataset of the object, the generating comprising:
receiving k-space data acquired using the imaging protocol; and
estimating the motion-corrected magnetic resonance image dataset and rigid-body motion parameters for each shot of the plurality of shots or each of a subset of shots, the estimating comprising minimizing a data consistency error between the k-space data acquired in the imaging protocol and a forward model,
wherein the forward model includes effects of rigid-body motion for each shot and Fourier encoding.
14 . The method of claim 13 , wherein the forward model further includes subsampling, coil sensitivities, or subsampling and coil sensitivities of a multi-channel coil array.
15 . The method of claim 14 , further comprising receiving a low-resolution scout image of the object,
wherein minimizing the data consistency error comprises:
estimating the rigid-body motion parameters for each shot using the low-resolution scout image and k-space lines acquired in at least a subset of shots; and
estimating the motion-corrected image using the estimated rigid-body motion parameters.
16 . The method of claim 15 , wherein the k-space lines are not used in the estimating of the motion-corrected image.
17 . A magnetic resonance imaging apparatus comprising:
a radio frequency controller configured to drive a radio frequency (RF) coil comprising a multi-channel coil array;
a gradient controller configured to control gradient coils;
a controller configured to control the radio frequency controller and the gradient controller to execute an imaging protocol, the execution of the imaging protocol comprising:
use of the imaging protocol, in which spatial encoding is performed using phase encoding gradients along at least one spatial dimension, and frequency encoding gradients along another spatial dimension,
wherein k-space is sampled during an acquisition in a plurality of k-space lines oriented along a frequency encoding direction,
wherein a number of k-space lines of the plurality of k-space lines are acquired in one shot, the imaging protocol comprising a plurality of shots,
wherein a plurality of additional k-space lines are acquired in at least a subset of shots of the plurality of shots, such that movement of the object is detected throughout the imaging protocol, and
wherein the k-space is sampled in a sampling order in which one more of the phase encoding gradients are changed incrementally from one k-space line to the next, with the exception of the plurality of additional k-space lines.
18 . A non-transitory computer-readable storage medium that stores instructions executable by one or more processor to acquire a magnetic resonance image dataset of an object, the instructions comprising:
using an imaging protocol in which spatial encoding is performed using phase encoding gradients along at least one spatial dimension, and frequency encoding gradients along another spatial dimension,
wherein k-space is sampled during an acquisition in a plurality of k-space lines oriented along a frequency encoding direction,
wherein a number of k-space lines of the plurality of k-space lines are acquired in one shot, the imaging protocol comprising a plurality of shots,
wherein a plurality of additional k-space lines are acquired in at least a subset of shots of the plurality of shots, such that movement of the object is detected throughout the imaging protocol, and
wherein the k-space is sampled in a sampling order in which one more of the phase encoding gradients are changed incrementally from one k-space line to the next, with the exception of the plurality of additional k-space lines.