TECHNIQUES FOR DETERMINING A FUNCTIONAL MAGNETIC RESONANCE DATA SET

Abstract

Techniques for determining a functional magnetic resonance data set of an imaging region of a brain of a patient are disclosed in which blood oxygenation level dependent functional magnetic resonance imaging is used. The techniques include using a plurality of reception coils, and acquiring magnetic resonance signals using parallel imaging and a magnetic resonance sequence defining a k-space trajectory, wherein undersampling in at least two k-space directions is performed. The techniques further include reconstructing the functional magnetic resonance data set from the magnetic resonance signals and sensitivity information regarding the plurality of reception coils using a reconstruction technique for undersampled magnetic resonance data, wherein the k-space trajectory is chosen to allow controlled aliasing in all three spatial dimensions including the readout direction.

Claims

1. A method for determining a functional magnetic resonance (MR) data set of an imaging region of a brain of a patient in which blood oxygenation level dependent functional MR imaging is used, the method comprising: acquiring, using a plurality of reception coils, (i) MR signals using parallel imaging, and (ii) a MR sequence defining a k-space trajectory in which undersampling in at least two k-space directions is performed; and reconstructing, using a reconstruction technique for undersampled MR data, the functional MR data set from (i) the MR signals, and (ii) sensitivity information regarding the plurality of reception coils, wherein the k-space trajectory is selected to enable a controlled aliasing in each one of three spatial dimensions, including a readout direction.

2. The method according to claim 1, wherein the k-space trajectory is selected as a wave-controlled aliasing in parallel imaging (CAIPI) echo planar imaging (EPI) trajectory using sinusoidal gradient pulses having a quarter-cycle phase shift in a phase encoding direction and a slice select direction combined with interslice shifts and an EPI readout.

3. The method according to claim 1, wherein the act of reconstructing the functional MR data set comprises reconstructing the functional MR data set using a low rank plus sparse reconstruction technique in which dynamic MR data as a space-time matrix is used as a linear superposition of a spatially- and temporally-correlated image background matrix and a sparse dynamic information matrix.

4. The method according to claim 1, wherein the undersampling is performed with a first undersampling factor of 2 to 6 regarding a phase encoding direction, and a second undersampling factor of 2 to 6 regarding a slice select direction.

5. The method according to claim 1, wherein a three-dimensional sensitivity distribution of the plurality of reception coils is used as the sensitivity information.

6. A magnetic resonance (MR) imaging device for determining a functional MR data set of an imaging region of a brain of a patient in which blood oxygenation level dependent functional MR imaging is used, the MR imaging comprising: control device circuitry configured to control operation of the MR imaging device; sequence circuitry configured to acquire, using a plurality of reception coils, (i) MR signals using parallel imaging, and (ii) a MR sequence defining a k-space trajectory in which undersampling in at least two k-space directions is performed; and reconstruction circuitry configured to reconstruct, using a reconstruction technique for undersampled MR data, the functional MR data set from (i) the MR signals, and (ii) sensitivity information regarding the plurality of reception coils, wherein the k-space trajectory is selected to enable a controlled aliasing in each one of three spatial dimensions, including a readout direction

7. The MR imaging device according to claim 6, wherein the k-space trajectory is selected as a wave-controlled aliasing in parallel imaging (CAIPI) echo planar imaging (EPI) trajectory using sinusoidal gradient pulses having a quarter-cycle phase shift in a phase encoding direction and a slice select direction combined with interslice shifts and an EPI readout.

8. The MR imaging device according to claim 6, wherein the reconstruction circuitry is configured to reconstruct the functional magnetic resonance data set using a low rank plus sparse reconstruction technique in which dynamic magnetic resonance data as a space-time matrix is used as a linear superposition of a spatially- and temporally-correlated image background matrix and a sparse dynamic information matrix.

9. The MR imaging device according to claim 6, wherein the undersampling is performed with a first undersampling factor of 2 to 6 regarding a phase encoding direction, and a second undersampling factor of 2 to 6 regarding a slice select direction.

10. The MR imaging device according to claim 6, wherein a three-dimensional sensitivity distribution of the plurality of reception coils is used as the sensitivity information.

11. A non-transitory computer-readable medium having instructions stored thereon that, when executed by control circuitry identified with a magnetic resonance (MR) imaging device, cause the MR imaging device to determine a functional MR data set of an imaging region of a brain of a patient in which blood oxygenation level dependent functional MR imaging is used by: acquiring, using a plurality of reception coils, (i) MR signals using parallel imaging, and (ii) a MR sequence defining a k-space trajectory in which undersampling in at least two k-space directions is performed; and reconstructing, using a reconstruction technique for undersampled MR data, the functional MR data set from (i) the MR signals, and (ii) sensitivity information regarding the plurality of reception coils, wherein the k-space trajectory is selected to enable a controlled aliasing in each one of three spatial dimensions, including a readout direction.

12. The non-transitory computer-readable medium according to claim 11, wherein the instructions, when executed by the control circuitry, cause the MR imaging device to select the k-space trajectory as a wave-controlled aliasing in parallel imaging (CAIPI) echo planar imaging (EPI) trajectory using sinusoidal gradient pulses having a quarter-cycle phase shift in a phase encoding direction and a slice select direction combined with interslice shifts and an EPI readout.

13. The non-transitory computer-readable medium according to claim 11, wherein the instructions, when executed by the control circuitry, cause the MR imaging device to perform the reconstructing of the functional magnetic resonance data set using a low rank plus sparse reconstruction technique in which dynamic magnetic resonance data as a space-time matrix is used as a linear superposition of a spatially- and temporally-correlated image background matrix and a sparse dynamic information matrix.

14. The non-transitory computer-readable medium according to claim 11, wherein the instructions, when executed by the control circuitry, cause the MR imaging device to perform the undersampling with a first undersampling factor of 2 to 6 regarding a phase encoding direction, and a second undersampling factor of 2 to 6 regarding a slice select direction.

15. The non-transitory computer-readable medium according to claim 11, wherein a three-dimensional sensitivity distribution of the plurality of reception coils is used as the sensitivity information.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other objects and features of the present disclosure will become apparent from the following detailed description considered in conjunction with the accompanying drawings. The drawings, however, are intended for the purpose of illustration and do not limit the disclosure. The drawings show:

[0024] FIG. 1 illustrates an example flow chart of a method according to one or more embodiments of the disclosure;

[0025] FIG. 2 illustrates an example pulse sequence diagram of a magnetic resonance sequence for 3D EPI with wave-CAIPI sampling, according to one or more embodiments of the disclosure;

[0026] FIG. 3 illustrates an example undersampling pattern, according to one or more embodiments of the disclosure; and

[0027] FIG. 4 illustrates an example magnetic resonance imaging device, according to one or more embodiments of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0028] FIG. 1 shows a flow chart of an example method according to the disclosure. In the method, BOLD fMRI is performed in an imaging region of a brain of a patient. In step S1, magnetic resonance signals (raw data) are acquired. The acquisition is performed undersampled along a 3D wave-CAIPI EPI trajectory, such that controlled aliasing in three dimensions is achieved.

[0029] FIG. 1 shows a magnetic resonance sequence diagram for the used multi-shot 3D EPI readout with wave-CAIPI sampling. As can be seen, the usual gradient pulses 1 are used after the excitation pulse 2. However, during the readout intervals 3, sinusoidal gradient pulses 4 are used in both the phase encoding direction (Gy) and the slice select direction (Gz). The triangular gradient pulses between the sinusoidal gradient pulses advance the current acquisition line from one phase encoding step to the next, providing the interslice shifts. The shown scheme results in a staggered corkscrew-like trajectory set.

[0030] As already mentioned, undersampling is applied when acquiring the magnetic resonance signals in step S1. Here, undersampling is applied in the phase encoding direction (Gy) and in the slice select direction (Gz). As can be seen from the exemplary undersampling pattern of FIG. 3, showing the ky-kz-plane, this exemplary undersampling scheme uses an undersampling factor of two in the phase encoding direction and an undersampling factor of five in the slice select direction, resulting in an acceleration factor of 5*2=10. Of course, other undersampling schemes may also be applied.

[0031] In a step S2 of FIG. 1, a magnetic resonance data set of the BOLD fMRI is reconstructed using a reconstruction technique. Since aliasing is controlled in all three dimensions, the full three-dimensional coil sensitivity distribution is used as the sensitivity information during reconstruction, increasing the amount of total information used.

[0032] In this embodiment, an L+S reconstruction technique is combined with the multi-shot 3D wave-CAIPI EPI k-space trajectory. This combination is particularly advantageous, since temporal and/or spatial resolution may be significantly increased. Since wave-CAIPI has been proven to lead to minimal noise enhancement (g-factor) and the wave-CAIPI k-space trajectory could be readily implemented in 3D EPI resonance sequences, as shown in FIG. 2, high acceleration factors are possible, as explained with respect to FIG. 3. Due to the reduced acquisition time, temporal resolution, spatial resolution, and/or both may be increased. Since the 3D wave-CAIPI technique has a negligible G-factor penalty, high SNR is maintained.

[0033] FIG. 4 is a principle drawing of a magnetic resonance imaging device 5 according to the disclosure. The magnetic resonance imaging device 5 comprises a main magnet unit 6 having a cylindrical bore 7 into which a patient may be introduced using a patient table 8. Surrounding the bore 7, a radio frequency coil arrangement and a gradient coil arrangement (not shown) may be provided. In this case, the magnetic resonance signals are acquired using a local head coil 9 comprising a plurality of reception coils 10 whose three-dimensional coil sensitivity distribution is known as sensitivity information to be used in reconstruction step S2, as explained above.

[0034] The operation of the magnetic resonance imaging device 5 is controlled by a control device 11, which comprises a sequence unit 12 for controlling the acquisition of magnetic resonance signals, e.g. also according to step S1, and a reconstruction unit 13 for reconstructing magnetic resonance data sets from the acquired magnetic resonance signals, e.g. also according to step S2 as explained above. The control device 11 further comprises a storage means 14, where, for example, the sensitivity information may be stored.

[0035] Although the present disclosure has been described in detail with reference to the preferred embodiment, the present disclosure is not limited by the disclosed examples from which the skilled person is able to derive other variations without departing from the scope of the disclosure.

[0036] The various components described herein may be referred to as “devices” or “units.” Such components may be implemented via any suitable combination of hardware and/or software components as applicable and/or known to achieve the intended respective functionality. This may include mechanical and/or electrical components, processors, processing circuitry, or other suitable hardware components configured to execute instructions or computer programs that are stored on a suitable computer readable medium. Regardless of the particular implementation, such devices and units, as applicable and relevant, may alternatively be referred to herein as “circuitry,” “processors,” or “processing circuitry.”