阅读说明：本技术 并行多切片mr成像 (Parallel multi-slice MR imaging ) 是由 M·P·J·于里森 A·F·N·格里戈莱托博尔戈诺维 T·H·罗济杰恩 于 2018-06-08 设计创作，主要内容包括：本发明涉及一种对放置在MR设备(1)的检查体积中的对象(10)进行MR成像的方法。所述方法包括以下步骤：通过使所述对象(10)经受包括多切片RF脉冲(21)的多回波成像序列的N次击发来生成MR信号,以同时激发两个或更多个空间上分离的图像切片,其中,切片方向上的相位偏移被赋予给MR信号,其中,所述相位偏移在击发之间变化,采集所述MR信号,其中,所述MR信号是经由在检查体积内具有不同空间灵敏度概况的至少两个RF线圈(11、12、13)的集合并行接收的,并且使用并行重建算法针对每个图像切片从采集的MR信号重建MR图像,其中,基于根据所述RF线圈(11、12、13)的空间灵敏度概况的MR信号的空间编码,并且基于归属于各图像切片和击发的所述相位偏移,分离来自不同图像切片的MR信号贡献。此外,本发明涉及用于执行该方法的MR设备以及要在MR设备上运行的计算机程序。(The invention relates to a method of MR imaging of an object (10) placed in an examination volume of a MR device (1). The method comprises the following steps: generating MR signals by subjecting the object (10) to N firings of a multi-echo imaging sequence comprising multi-slice RF pulses (21) to simultaneously excite two or more spatially separated image slices, wherein a phase offset in a slice direction is imparted to the MR signals, wherein the phase offset varies between firings, the MR signals being acquired, wherein the MR signals are received in parallel via a set of at least two RF coils (11, 12, 13) having different spatial sensitivity profiles within the examination volume, and reconstructing a MR image from the acquired MR signals for each image slice using a parallel reconstruction algorithm, wherein the spatial encoding of the MR signals is based on a spatial sensitivity profile of the RF coils (11, 12, 13), and separating MR signal contributions from different image slices based on the phase offsets attributed to each image slice and shot. Furthermore, the invention relates to an MR device for carrying out the method and to a computer program to be run on an MR device.)

1. Method of MR imaging of an object (10) placed in an examination volume of a MR device (1), the method comprising the steps of:

generating MR signals by subjecting the object (10) to N firings of a multi-echo imaging sequence comprising multi-slice RF pulses (21) to simultaneously excite two or more spatially separated image slices, wherein a phase offset is imparted to the MR signals of each image slice, wherein the phase offset varies between firings,

-acquiring the MR signals, wherein the MR signals are received in parallel via a set of at least two RF coils (11, 12, 13) having different spatial sensitivity profiles within the examination volume, and

-reconstructing an MR image from the acquired MR signals for each image slice using a parallel reconstruction algorithm, wherein MR signal contributions from different image slices are separated based on a spatial encoding of the MR signals according to a spatial sensitivity profile of the RF coils (11, 12, 13) and on the phase offsets attributed to the respective image slice and firing.

2. The method of claim 1, wherein in each shot of the imaging sequence, undersampled k-space data in a phase encoding direction is acquired.

3. The method of claim 1 or 2, wherein in each shot of the imaging sequence undersampled k-space data in a phase encoding direction imparted by a varying phase offset is acquired.

4. The method according to any of claims 1-3, wherein the phase offset is imparted by means of phase modulation of the RF pulses.

5. The method according to any one of claims 1-3, wherein the phase shift is imparted by means of a magnetic field gradient (25) applied in a slice selection direction.

6. Method of any one of claims 1-5, wherein the inverse problem of MR image reconstruction is solved by using an encoding matrix, wherein matrix elements of the encoding matrix are determined by the spatial sensitivity profiles of the RF coils (11, 12, 13), the k-space samples of each shot of the imaging sequence, and the phase shifts attributed to the image slices and shots.

7. Method of claim 6, wherein a priori known phase errors of the MR signals are taken into account by incorporating corresponding phase error values into the encoding matrix.

8. Method of any one of claims 1-7, wherein motion weighting based on motion information is applied in the MR image reconstruction.

9. The method of claim 8, wherein navigator signals are generated by subjecting the subject (10) to a navigator sequence between the firings of the imaging sequence, wherein the motion information is derived from the navigator signals.

10. The method of claim 6 or 7, wherein navigator signals are generated by subjecting the object (10) to a navigator sequence, wherein motion-induced phase errors are taken into account by incorporating phase information derived from the navigator signals into the encoding matrix.

11. The method of any of claims 1-10, wherein M < N shots of an imaging sequence are performed two or more times for the purpose of improving signal-to-noise ratio.

12. MR device for performing the method according to any one of claims 1-11, the MR device (1) comprising: at least one main magnet coil (2) for generating a homogeneous static magnetic field within an examination volume; a number of gradient coils (4, 5, 6) for generating switched magnetic field gradients in different spatial directions within the examination volume; a set of at least two RF coils (11, 12, 13) having different spatial sensitivity profiles; a control unit (15) for controlling the temporal sequence of the RF pulses and the switched magnetic field gradients; and a reconstruction unit (17), wherein the MR device (1) is configured to perform the steps of:

generating MR signals by subjecting the object (10) to N firings of a multi-echo imaging sequence comprising multi-slice RF pulses (21) to simultaneously excite two or more spatially separated image slices, wherein a phase offset is imparted to the MR signals of each image slice, wherein the phase offset varies between firings,

-acquiring the MR signals, wherein the MR signals are received in parallel via the set of RF coils (11, 12, 13), and

-reconstructing an MR image from the acquired MR signals for each image slice using a parallel reconstruction algorithm, wherein MR signal contributions from different image slices are separated based on a spatial encoding of MR signals according to a spatial sensitivity profile of the RF coil (11, 12, 13) and on the phase offsets attributed to the respective image slice and firing.

13. Computer program to be run on a MR device, the computer program comprising instructions for:

generating N firings of a multi-echo imaging sequence comprising multi-slice RF pulses (21) to simultaneously excite two or more spatially separated image slices, imparting a phase offset to the MR signal of each image slice, wherein the phase offset varies between firings,

-acquiring the MR signals, and

-reconstructing an MR image from the acquired MR signals for each image slice using a parallel reconstruction algorithm, wherein MR signal contributions from different image slices are separated based on a spatial encoding of spatial sensitivity profiles from a set of at least two RF coils (11, 12, 13) and on phase offsets attributed to the respective image slice and firing.

Technical Field

The present invention relates to the field of Magnetic Resonance (MR) imaging. It relates to a method of MR imaging of an object. The invention also relates to an MR device and to a computer program to be run on an MR device.

Background

Image-forming MR methods, which utilize the interaction between magnetic fields and nuclear spins to form two-or three-dimensional images, are widely used today, in particular in the field of medical diagnostics, because they are advantageous over other methods for imaging soft tissue in many respects, do not require ionizing radiation and are generally non-invasive.

According to a general MR method, an object, for example a body of a patient to be examined, is arranged in a strong, homogeneous magnetic field whose direction simultaneously defines the axis (usually the z-axis) of a coordinate system on which the measurement is based. The magnetic field produces energy levels that differ for the individual nuclear spins depending on the magnetic field strength, which energy levels can be excited (spin resonance) by applying an electromagnetic alternating field (RF field) with a defined frequency (the so-called larmor frequency, or MR frequency). From a macroscopic point of view, the distribution of the individual nuclear spins produces an overall magnetization which can be deflected out of the equilibrium state by applying electromagnetic pulses (RF pulses) of suitable frequency, so that the spins perform a precession about the z-axis. Precession describes a tapered surface, the aperture angle of which is called the flip angle. The magnitude of the flip angle depends on the strength and duration of the applied electromagnetic pulse. In the case of a so-called 90 ° pulse, the spins are deflected from the z-axis into the transverse plane (flip angle 90 °).

After the RF pulse has ended, the magnetization relaxes back to the initial equilibrium state, in which the magnetization in the z direction has a first time constant T₁(spin lattice relaxation or longitudinal relaxation time) and the magnetization in the direction perpendicular to the z-direction with a second time constant T₂(spin-spin or transverse relaxation time) relaxation. The change in magnetization can be detected by means of a receiving RF coil, which is arranged and oriented within the examination volume of the MR device in the following manner: so that the change in magnetization is measured in a direction perpendicular to the z-axis. The decay of the transverse magnetization is accompanied, for example, by a transition of the nuclear spins (caused by the inhomogeneity of the magnetic field) from an ordered state with the same phase to a state in which all phase angles are uniformly distributed (dephasing) after the application of a 90 ° pulse. The phase loss can be compensated by means of a refocusing pulse (e.g. a 180 ° pulse). This produces an echo signal (spin echo) in the receive coil.

To achieve spatial resolution in the body, a constant magnetic field gradient extending along the main axis is superimposed on the uniform magnetic field, resulting in a linear spatial dependence of the spin resonance frequency. The signals picked up in the receiving antennas then comprise components of different frequencies, which may be associated with different locations in the body/object.

The signal data obtained via the receive coils correspond to the spatial frequency domain and are referred to as k-space data. The k-space data typically comprises a plurality of lines acquired with different phase encodings. Each line is digitized by collecting several samples. The set of k-space data is converted into an MR image by means of an image reconstruction algorithm.

Parallel acquisition techniques are commonly used to accelerate MR acquisition. The methods in this category are SENSE (sensitivity encoding), SMASH (spatial harmonic simultaneous acquisition) and GRAPPA (generalized auto-calibration partial parallel acquisition). SENSE, SMASH and GRAPPA and other parallel acquisition techniques use undersampled k-space data acquisition obtained from multiple parallel RF receive coils. In a corresponding reconstruction algorithm, the (complex) signal data from the multiple coils are combined with complex weights in a way that suppresses undersampling artifacts (aliasing) in the final reconstructed MR image. This type of complex array signal combination is sometimes referred to as spatial filtering and includes combining performed in the k-space domain (e.g., SMASH and GRAPPA) or image domain (e.g., SENSE), as well as hybrid approaches.

Larkman et al (Journal of Magnetic Resonance Imaging,13,313-317,2001) propose to apply sensitivity encoding also in the slice direction in the case of multi-slice Imaging to improve scanning efficiency. A method called "controlling in parallel imaging results in high probability access" (CAIPIRINHA) proposed by Breuer et al (Magnetic Resonance in Medicine,53, 684) 691,2005 improves this basic idea. The technique improves the subsequent parallel image reconstruction process by imparting a phase shift to the MR signal of each image slice, thereby modifying the occurrence of aliasing artifacts in each individual slice during the multi-slice acquisition. Therefore, CAIPIRINHA is a parallel multi-slice imaging technique that is more efficient than other multi-slice parallel imaging concepts that use only pure post-processing methods. In CAIPIRINHA, multiple slices of arbitrary thickness and distance are excited simultaneously using a phase-modulated multi-slice RF pulse (similar to the known Hadamard pulse). The acquired MR signal data is undersampled, generating superimposed slice images that appear offset with respect to each other, corresponding to different phase offsets. The shift of the aliased slice images is controlled by the phase offset applied by the phase modulation scheme of the RF pulses according to the fourier shift theorem. By using this shift, the numerical adjustment of the inverse reconstruction problem, which separates the individual signal contributions of the separated segments, can be improved.

US2014/0225612a1 discloses a method of MR imaging using a segmented Echo Planar Imaging (EPI) pulse sequence. The pulse sequence includes a plurality of multi-slice RF pulses for simultaneously exciting two or more spatially separated image slices. A particular gradient encoding scheme is applied along the slice encoding direction to impart a controlled phase shift to the different slices. Acquired MR signal data is reconstructed into MR images using a parallel imaging reconstruction method that separates overlapping slices in the imaging data to provide a series of MR images for each slice across the imaging subject.

US 2016/0018499 a1 solves the problem of the CAIPIRINHA using a fixed phase modulation scheme of RF pulses such that the relative displacement of adjacent slices is, for example, half the field of view (FOV) size or other integer fraction of the FOV size. The disadvantage of this fixed scheme is that it does not take into account a priori information. Therefore, the encoding capabilities of the array of receive RF coils and the basic structure of the imaging problem are not fully considered, which may result in a sub-optimal phase modulation and thus a sub-optimal reconstruction performance. As a solution to this problem, US 2016/0018499 a1 suggests using available coil sensitivity information to derive an adjusted slice-specific phase offset to further optimize the encoding process and hence the unfolding problem, thereby improving the final image quality.

Disclosure of Invention

In accordance with the invention, a method of MR imaging of an object placed in an examination volume of a MR device is disclosed. The method comprises the following steps:

generating MR signals by subjecting the object to N firings of a multi-echo imaging sequence comprising multi-slice RF pulses to simultaneously excite two or more spatially separated image slices, wherein a phase offset in slice direction is imparted to the MR signals of each image slice, wherein the phase offset varies from firing to firing,

acquiring MR signals, wherein the MR signals are received in parallel via a set of at least two RF coils having different spatial sensitivity profiles within an examination volume, and

reconstructing an MR image from the acquired MR signals for each image slice using a parallel reconstruction algorithm, wherein MR signal contributions from different image slices are separated based on spatial encoding of the MR signals according to the spatial sensitivity profile of the RF coil and on the phase offsets due to the respective image slice and firing.

Compared to (single shot) EPI scans, the method of the present invention uses a multi-shot multi-echo imaging sequence to improve image resolution and/or reduce geometric distortion and/or increase signal-to-noise ratio (SNR). According to the present invention, the multi-slice phase offset is varied on a shot-by-shot basis. In this way, additional phase encoding can be applied in a flexible way in the slice direction, which improves the stability of the separation of the slice images in the reconstruction step.

The invention uses a parallel imaging reconstruction algorithm (e.g. SENSE or SMASH reconstruction) to separate MR signal contributions from different image slices. The imaging signal data acquired in each shot of the multi-echo imaging sequence is a subset of the complete k-space modulated according to the different phase shifts applied in the slice direction. Parallel image reconstruction algorithms are used to generate complete (unfolded) slice images from the signal data. The MR signals are acquired in parallel via different RF coils ("channels"), preferably with undersampling in the phase encoding direction to speed up the acquisition speed. This is taken into account in a conventional manner by a parallel reconstruction algorithm during the image reconstruction. By additionally incorporating corresponding phase information into the encoding matrix on which the parallel reconstruction algorithm is based, phase offsets applied in the slice direction between shots may be taken into account. In other words, according to the invention, the inverse problem of image reconstruction is solved using an encoding matrix whose matrix elements are determined not only by the spatial sensitivity profiles of the RF coils and the k-space sampling pattern of each shot of the imaging sequence but also by the different phase offsets attributed to the image slices and shots. This approach is comparable to the known IRIS (image reconstruction using image space sampling) reconstruction schemes that perform efficient image reconstruction in multi-shot multi-echo SENSE imaging (see Jeoung et al, Magnetic Resonance in Medicine 2013, volume 69, page 793 and 802), except that not only a single MR image is considered, but also multiple image slices are considered and the concept is extended to multi-slice imaging by merging the corresponding phase information into the encoding matrix.

The imaging sequence of the method of the invention is a multi-shot sequence which requires the sampling of k-space in a segmented manner. In other words, only a subset of k-space is sampled in each shot of the imaging sequence. Notably, there is acquired k-space data that is undersampled in the phase encoding direction imparted by the varying phase offset.

In one possible embodiment, the variable phase offset may be imparted by means of phase modulation of the RF pulses (like, for example, in the known POMP technique, see Glover et al, Journal of Magnetic Resonance Imaging, 1991, p.457-). Alternatively, a magnetic field gradient applied in the slice selection direction may be used to impart a phase shift (as in US2014/0225612a1 cited above).

The MR signals acquired in different firings of the imaging sequence may contain different phase errors, for example due to heating of the gradient coils or due to motion of the imaged object in the presence of a diffusion gradient. If these phase errors are known a priori, the method of the present invention can take them into account by incorporating the corresponding phase error values into the coding matrix. Similarly, odd and even echo signals (obtained in the presence of readout magnetic field gradients of opposite polarity) may contain systematic phase errors, e.g. due to different delays of the opposite gradients. By dividing the queue of echo signals in each complete shot into two MR signal data sets, one comprising odd echo signals and the other comprising even echo signals, the number of shots is actually doubled from the point of view of the reconstruction algorithm. By incorporating the respective phase error values into the encoding matrix, odd/even echo phase errors can be corrected.

In order to take into account the motion of the imaging subject, motion information may be collected from the imaging subject, for example using a respiration belt during acquisition, wherein motion weighting based on the motion information is applied in the MR image reconstruction. The MR signal data obtained in the presence of strong motion have a reduced weighting compared to MR signal data obtained with less motion.

The navigator signal can be generated by subjecting the subject to a navigator sequence between firings of the imaging sequence. The motion weights derived from the navigator signals can then be applied in the MR image reconstruction. Alternatively, similar to the known IRIS method, motion-induced shot-to-shot phase errors may be accounted for by directly incorporating the respective phase information derived from the navigation signal into the encoding matrix.

In another preferred embodiment of the method of the invention, M < N shots of the imaging sequence may be performed two or more times in order to improve the SNR. Instead of repeating the full acquisition via averaging to improve SNR, only a subset of the total number of N shots may be repeated. The corresponding MR signals can then be added to the parallel reconstruction scheme of the invention. These additional firings may employ different phase offsets than other firings of the imaging sequence to further improve the stability of the reconstruction algorithm.

The method of the invention described so far can be performed by means of an MR device comprising: at least one main magnet coil for generating a uniform static magnetic field within an examination volume; a plurality of gradient coils for generating switched magnetic field gradients in different spatial directions within the examination volume; a set of RF coils for receiving MR signals from a body in parallel, the RF coils having different spatial sensitivity profiles; a control unit for controlling the time sequence of RF pulses and the switched magnetic field gradients; and a reconstruction unit. The method of the invention can be implemented, for example, by a corresponding programming of the reconstruction unit and/or a control unit of the MR device.

The method of the invention can advantageously be implemented in most MR apparatuses currently used in clinics. For this purpose, it is only necessary to use a computer program controlling the MR device such that it executes the above explained method of the invention. The computer program may be present on a data carrier or may be present on a data network so as to be downloadable for installation in a control unit of the MR device.

Drawings

The accompanying drawings disclose preferred embodiments of the present invention. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and description and not as a definition of the limits of the disclosure. In the drawings:

fig. 1 shows an MR device for carrying out the method of the invention;

FIG. 2 illustrates one shot of a multi-shot, multi-echo imaging sequence employed in accordance with the present invention;

fig. 3 schematically shows a k-space encoding scheme applied according to the present invention.

Detailed Description

Referring to fig. 1, an MR device 1 is shown. The device comprises superconducting or normally conductive main magnet coils 2 such that a substantially uniform, spatially constant main magnetic field is created along a z-axis through the examination volume.

The magnetic resonance generation and manipulation system applies a series of RF pulses and switched magnetic field gradients to invert or excite nuclear magnetic spins, induce magnetic resonance, refocus magnetic resonance, manipulate magnetic resonance, spatially or otherwise encode magnetic resonance, saturate spins, etc. to perform MR imaging.

More specifically, the gradient amplifier 3 applies current pulses to selected ones of the whole-body gradient coils 4, 5 and 6 along the x, y and z axes of the examination volume. A digital RF frequency transmitter 7 transmits RF pulses or pulse packets via a transmit/receive switch 8 to a whole-body volume RF coil 9 to transmit RF pulses to the examination volume. A typical MR imaging sequence includes a packet of short duration RF pulse segments that, along with any applied magnetic field gradients, achieve a selected manipulation of nuclear magnetic resonance. The RF pulses are used to saturate, excite resonance, invert magnetization, refocus resonance, or manipulate resonance and select the portion of the body 10 positioned in the examination volume.

To generate MR images of a limited region of the body 10 by means of parallel imaging, a set of local RF coils 11, 12, 13 is placed adjacent to the region selected for imaging.

The resulting MR signals are picked up by the RF coils 11, 12, 13 and demodulated by a receiver 14 which preferably comprises a preamplifier (not shown). The receiver 14 is connected to the RF coils 9, 11, 12, and 13 via the transmission/reception switch 8.

The host computer 15 controls the gradient pulse amplifier 3 and the transmitter 7 to generate any one of a plurality of MR imaging sequences, such as Echo Planar Imaging (EPI), echo volume imaging, gradient and spin echo imaging, fast spin echo imaging, and so forth. The receiver 14 receives a single or multiple MR data lines in rapid succession after each RF excitation pulse for a selected sequence. The data acquisition system 16 performs analog-to-digital conversion of the received signals and converts each MR data line to a digital format suitable for further processing. In modern MR devices, the data acquisition system 16 is a separate computer, which is dedicated to acquiring raw image data.

Finally, the digital raw image data is reconstructed into an image representation by a reconstruction processor 17 applying a fourier transform or other suitable reconstruction algorithm. The MR images may represent planar slices through the patient, an array of parallel planar slices, a three-dimensional volume, and so forth. The image is then stored in an image memory where it can be accessed for converting the slices, projections or other portions of the image representation into an appropriate format for visualization, for example via a video monitor 18 that provides a human-readable display of the resulting MR image.

The host computer 15 and the reconstruction processor 17 are programmed to run the method of the present invention described above and below.

With continuing reference to FIGURE 1 and with further reference to FIGURES 2 and 3, an embodiment of the imaging technique of the present invention is explained.

As shown in fig. 2, the body 10 is subjected to multiple shots of a multi-echo imaging sequence. The imaging sequence is a modified multi-shot EPI sequence. The sequence comprises a slice-selective multi-slice RF pulse 21 for simultaneously exciting two or more spatially separated image slices. The RF pulses 21 are radiated in the presence of corresponding slice-selection magnetic field gradients 22 in order to generate transverse nuclear magnetization in several imaging slices. After the excitation RF pulse 21, MR signals are acquired by sampling a series of gradient, called echo, signals in the presence of alternating readout magnetic field gradients 23. Phase encoding of the MR signals is performed by a series of phase encoding magnetic field gradients "blip" 24. During the application of each phase encoding gradient blip 24, a further magnetic field gradient blip25 is also applied in the slice encoding direction. According to the invention, a slice encoding gradient blip25 is used to impart a phase shift to the MR signal of each image slice. Although a gradient blip25 may be used to apply different phase shifts, successive shots may be usedThe respective phases of the transmitted slice-select RF pulses 21 impart a phase shift. The acquisition of the MR signals is accelerated by SENSE encoding. The MR signals are acquired in parallel via RF receive coils 11, 12, 13 with different spatial sensitivities and are acquired by undersampling in the phase encoding direction. One firing of the imaging sequence is shown in fig. 2. Multiple (N) shots of the multi-echo sequence are used to fully sample k-space to enable reconstruction of a complete MR slice image from the acquired imaging echo signal data using SENSE reconstruction, wherein, according to the invention, the phase offset of the MR signals assigned to the different signals varies from shot to shot. In other words, k_zThe phase encoding varies between firing and for each k_zThe phase encoding performs various ky phase encodings. Each (k) in k-space_z，k_y) Position, for the whole k in the frequency encoding direction_xThe line is sampled.

The MR image of each image slice is reconstructed from the acquired MR signal data using a parallel reconstruction algorithm, wherein the MR signal contributions from the different image slices are separated based on the spatial encoding of the MR signals according to the spatial sensitivity profile of the RF coil and on the phase offsets attributed to the respective image slice and firing. This will be explained in detail below:

in a multi-shot sequence with N shots, where each shot represents a conventional undersampling of the table k-space, the set of SENSE equations may be set to:

wherein the vector

Including image pixel values that need to be calculated from aliased pixel values measured via a separate RF coil ("channel"). Aliasing pixel value by vector

A description is given. S is a coil sensitivity matrix, which is formed by the spatial sensitivity of the RF coil usedAnd determining the sensitivity profile. The size of the sensitivity matrix S depends on the undersampling of the firing, the number of RF coils used, and the number of slices excited by the multi-slice RF pulse. The phase shift applied in each shot of the imaging sequence according to the invention may be determined by the matrix Φ_shConsidered, it is a diagonal matrix describing the extra phase resulting from encoding in the slice direction. The SENSE equation can be written on this basis as:

here,. phi.,. phi._shIs a diagonal matrix that contains the phase encoding for each position:

not only must the slice direction (k) be considered_z) And also the phase encoding direction (k) must be taken into account_y) Different phase encoding of (1). Therefore, the temperature of the molten metal is controlled,by encoding in the conventional phase encoding direction (k) is described_y) Phase encoding in (c) and in the slice direction (k)_z) Both of the above phase offsets are assigned to the phase of each pixel value. The coil sensitivity encoding and phase encoding (y and z) can be combined into an encoding matrix E_sh：

SΦ_sh＝E_sh

Finally, the equations for all N shots may be combined in one generalized SENSE reconstruction kernel:

wherein the content of the first and second substances,

including all pixel values of the final slice images consisting of slicesPhase encoded multi-slice SENSE reconstruction in the direction.The least squares solution (noise-free decorrelation and regularization) of (a) is:

the multi-slice acquisition method according to the invention can be regarded as a three-dimensional scan, in which k is encoded by the corresponding phase pairs_y-k_zSpace is sampled, where k_zThe number of lines is equal to the number of slices excited simultaneously. With the multi-strike method of the present invention, it becomes possible to use different k_zEncoding multiple acquisitions of a given k_yAnd (5) encoding. This allows optimal sampling of the three-dimensional k-space (using undersampling). FIG. 3 shows k according to the invention_y-k_zAn example of sampling, where eight slices are excited simultaneously. Four different phase shifts applied along the slice direction are applied to the four shots a, B, C and D of the EPI sequence. Undersampling is at the k-th_yAnd k_zIn both directions, in

The directions have alternating samples. In the depicted embodiment, each firing applies a constant k_zEncoding such that no additional gradient blip in slice direction needs to be applied within a single shot EPI sequence.