阅读说明：本技术 双分辨率Dixon磁共振成像 (Dual resolution Dixon magnetic resonance imaging ) 是由 H·埃格斯 于 2019-01-09 设计创作，主要内容包括：本发明提供了一种磁共振成像系统(100)。机器可执行指令(140)使控制所述磁共振成像系统的处理器：利用脉冲序列命令控制(200)所述磁共振成像系统采集两点Dixon磁共振数据和单点Dixon磁共振数据；使用所述两点Dixon磁共振数据来计算(202)第一分辨率磁场不均匀性图(148)；通过将所述第一分辨率磁性不均匀性图内插到所述第二分辨率来计算(204)第二分辨率磁场不均匀性图(154)；并且使用所述单点Dixon磁共振成像数据和所述第二分辨率磁场不均匀性图来计算(206)第二分辨率水图像(156)和第二分辨率脂肪图像(158)。所述第一分辨率低于所述第二分辨率。(The invention provides a magnetic resonance imaging system (100). Machine executable instructions (140) cause a processor controlling the magnetic resonance imaging system to: controlling (200) the magnetic resonance imaging system with pulse sequence commands to acquire two-point Dixon magnetic resonance data and single-point Dixon magnetic resonance data; calculating (202) a first resolution magnetic field inhomogeneity map (148) using the two-point Dixon magnetic resonance data; calculating (204) a second resolution magnetic field inhomogeneity map (154) by interpolating the first resolution magnetic inhomogeneity map to the second resolution; and calculating (206) a second resolution water image (156) and a second resolution fat image (158) using the single point Dixon magnetic resonance imaging data and the second resolution magnetic field inhomogeneity map. The first resolution is lower than the second resolution.)

1. A magnetic resonance imaging system (100), comprising:

a memory (134) for storing machine executable instructions (140) and pulse sequence commands (142), wherein the pulse sequence commands are configured to acquire two-point Dixon magnetic resonance data from a region of interest according to a two-point Dixon magnetic resonance imaging protocol (300, 700, 1000), wherein the pulse sequence commands are configured to acquire a single-point Dixon magnetic resonance data (146) from the region of interest according to a single-point Dixon magnetic resonance imaging protocol (500, 900, 1000), wherein the two-point Dixon magnetic resonance imaging protocol is configured to sample (324, 326) the two-point Dixon magnetic resonance data (144) from a central k-space region (402), wherein the single-point Dixon magnetic resonance imaging protocol is configured to sample (326, 508) the single-point Dixon magnetic resonance data from an extended k-space region (404) and the central k-space region, the extended k-space region is larger than the central k-space region, wherein the extended k-space region at least partially surrounds the central k-space region, wherein the two-point Dixon magnetic resonance imaging protocol is configured for acquiring images of the region of interest at a first resolution, wherein the single-point Dixon magnetic resonance imaging protocol is configured for acquiring images of the region of interest at a second resolution, wherein the second resolution is higher than the first resolution; and

a processor (130) for controlling the magnetic resonance imaging system, wherein execution of the machine executable instructions causes the processor to:

controlling (200) the magnetic resonance imaging system to acquire the two-point Dixon magnetic resonance data and the single-point Dixon magnetic resonance data with the pulse sequence commands;

calculating (202) a first resolution magnetic field inhomogeneity map (148) at the first resolution using the two-point Dixon magnetic resonance data;

calculating (204) a second resolution magnetic field inhomogeneity map (154) by interpolating the first resolution magnetic inhomogeneity map to the second resolution; and is

Calculating (206) a second resolution water image (156) at the second resolution and a second resolution fat image (158) at the second resolution using the single point Dixon magnetic resonance imaging data and the second resolution magnetic field inhomogeneity map.

2. The magnetic resonance imaging system of claim 1, wherein the pulse sequence commands are configured to sample the two-point Dixon magnetic resonance data from a central k-space region using a bipolar dual-echo pulse sequence (300, 700, 1000), wherein the first echo is generated with first readout gradient side lobes (310) having a first polarity and the second echo is generated with second readout gradient side lobes (316) having a second polarity.

3. The magnetic resonance imaging system of claim 2, wherein the first readout gradient sidelobe has a first amplitude (312) and a first duration (314), wherein the second readout gradient sidelobe has a second amplitude (318) and a second duration (320), and wherein the first duration times the first amplitude is less than the second duration times the second amplitude.

4. The magnetic resonance imaging system of claim 3, wherein the pulse sequence commands are further configured to asymmetrically sample the second echo.

5. The magnetic resonance imaging system of claim 2, 3 or 4, wherein the second resolution is as high as twice the first resolution in a readout direction and/or a phase encoding direction.

6. The magnetic resonance imaging system of claim 2, 3 or 4, wherein the pulse sequence commands are further configured to sample the single point Dixon magnetic resonance data from the central k-space region and the extended k-space region using the bipolar dual echo pulse sequence.

7. The magnetic resonance imaging system of claim 6, wherein the pulse sequence commands are configured to obtain the single point Dixon magnetic resonance data from the second echoes (326) of the bipolar dual echo pulse sequence.

8. The magnetic resonance imaging system of claim 2, wherein the pulse sequence commands are configured to sample the single point Dixon magnetic resonance data partially from the extended k-space region using a unipolar single echo pulse sequence (500, 900), wherein the pulse sequence commands are further configured to sample the single point Dixon magnetic resonance data partially from the central k-space region using the bipolar dual echo pulse sequence and to sample the single point Dixon magnetic resonance data partially from the extended k-space region.

9. The magnetic resonance imaging system of claim 8, wherein the first readout gradient sidelobe (310) has a first amplitude (312) and a first duration (314), wherein the second readout gradient sidelobe (316) has a second amplitude (318) and a second duration (320), wherein the first duration multiplied by the first amplitude is less than the second duration multiplied by the second amplitude.

10. The magnetic resonance imaging system of claim 9, wherein the unipolar single-echo pulse sequence has third readout gradient sidelobes (502), wherein the third readout gradient sidelobes have a third amplitude (504) and a third duration (506), wherein the third duration multiplied by the third amplitude is greater than the second duration multiplied by the second amplitude.

11. The magnetic resonance imaging system of claim 8, 9 or 10, wherein the bipolar dual-echo pulse sequence and the unipolar single-echo pulse sequence have identical repetition times and flip angles.

12. The magnetic resonance imaging system of claim 1, 2 or 3, wherein the pulse sequence commands are configured to acquire the two-point Dixon magnetic resonance imaging data and the single-point Dixon magnetic resonance data interleaved in time.

13. The magnetic resonance imaging system of any one of the preceding claims, wherein the calculation of the second resolution water image and the second resolution fat image is calculated at least in part using the two point Dixon magnetic resonance imaging data.

14. A method of operating a magnetic resonance imaging system (100), wherein the method comprises:

controlling (200) the magnetic resonance imaging system to acquire two-point Dixon magnetic resonance data (144) and single-point Dixon magnetic resonance data (146) with pulse sequence commands (142), wherein the pulse sequence commands are configured to acquire the two-point Dixon magnetic resonance data from a region of interest (109) according to a two-point Dixon magnetic resonance imaging protocol (300, 700, 1000), wherein the pulse sequence commands are configured to acquire the single-point Dixon magnetic resonance data from the region of interest according to a single-point Dixon magnetic resonance imaging protocol (500, 900, 1000), wherein the two-point Dixon magnetic resonance imaging protocol is configured to sample the two-point Dixon magnetic resonance data from a central k-space region (402), wherein the single-point Dixon magnetic resonance imaging protocol is configured to sample the Dixon magnetic resonance data from an extended k-space region (404) and the central k-space region, wherein the extended k-space region is larger than the central k-space region, wherein the extended k-space region at least partially surrounds the central k-space region, wherein the two-point Dixon magnetic resonance imaging protocol is configured for acquiring images of the region of interest at a first resolution, wherein the single-point Dixon magnetic resonance imaging protocol is configured for acquiring images of the region of interest at a second resolution, wherein the second resolution is higher than the first resolution;

calculating (202) a first resolution magnetic field inhomogeneity map (148) at the first resolution using the two-point Dixon magnetic resonance data;

calculating (204) a second resolution magnetic field inhomogeneity map (154) by interpolating the first resolution magnetic inhomogeneity map to the second resolution; and

calculating (206) a second resolution water image (156) at the second resolution and a second resolution fat image (158) at the second resolution using the single point Dixon magnetic resonance imaging data and the second resolution magnetic field inhomogeneity map.

15. A computer program product comprising machine executable instructions (140) for execution by a processor (130) controlling a magnetic resonance imaging system (100), wherein execution of the machine executable instructions causes the processor to:

controlling (200) the magnetic resonance imaging system to acquire two-point Dixon magnetic resonance data (144) and a single-point Dixon magnetic resonance data (146) with pulse sequence commands (142), wherein the pulse sequence commands are configured to acquire the two-point Dixon magnetic resonance data from a region of interest according to a two-point Dixon magnetic resonance imaging protocol, wherein the pulse sequence commands are configured to acquire the single-point Dixon magnetic resonance data from the region of interest according to a single-point Dixon magnetic resonance imaging protocol, wherein the two-point Dixon magnetic resonance imaging protocol is configured to sample the single-point Dixon magnetic resonance data from a central k-space region (402), wherein the single-point Dixon magnetic resonance imaging protocol is configured to sample the single-point Dixon magnetic resonance data from an extended k-space region (404) and the central k-space region, wherein the extended k-space region is larger than the central k-space region, wherein the extended k-space region at least partially surrounds the central k-space region, wherein the two-point Dixon magnetic resonance imaging protocol is configured for acquiring images of the region of interest at a first resolution, wherein the single-point Dixon magnetic resonance imaging protocol is configured for acquiring images of the region of interest at a second resolution, wherein the second resolution is higher than the first resolution;

calculating (202) a first resolution magnetic field inhomogeneity map (148) at the first resolution using the two-point Dixon magnetic resonance data;

calculating (204) a second resolution magnetic field inhomogeneity map (154) by interpolating the first resolution magnetic inhomogeneity map to the second resolution; and is

Calculating (206) a second resolution water image (156) at the second resolution and a second resolution fat image (158) at the second resolution using the single point Dixon magnetic resonance imaging data and the second resolution magnetic field inhomogeneity map.

Technical Field

The present invention relates to magnetic resonance imaging, in particular to Dixon magnetic resonance imaging.

Background

Magnetic Resonance Imaging (MRI) scanners use large static magnetic fields to align the nuclear spins of atoms as part of a procedure for generating images within a patient. This large static magnetic field is referred to as the B0 field.

During an MRI scan, Radio Frequency (RF) pulses generated by the transmitter coil cause perturbations to the local magnetic field, and RF signals emitted by the nuclear spins are detected by the receiver coil. These RF signals are used to construct MRI images. These coils can also be referred to as antennas. In addition, the transmitter coil and the receiver coil can also be integrated into a single transceiver coil that performs both functions. It should be understood that the use of the term transceiver coil also refers to systems that use separate transmitter and receiver coils. The transmitted RF field is referred to as the B1 field.

MRI scanners are capable of constructing images of slices or volumes. A slice is a thin volume that is only one voxel thick. A voxel is a small volume over which the MRI signal is averaged and represents the resolution of the MRI image. Voxels may also be referred to herein as pixels.

The Dixon method of magnetic resonance imaging includes a series of techniques for producing separate water and lipid (fat) images. Various Dixon techniques (e.g., without limitation, two-point Dixon methods, three-point Dixon methods, and six-point Dixon methods) are collectively referred to herein as Dixon techniques or methods. Reconstruction of water and fat images relies on accurate determination of phase errors due largely to B0 inhomogeneity to prevent exchange of water and fat signals.

The journal article "Single Acquisition Water-FatSeparation: FeasitilityStudyfor dynamic imaging" (magnetic resonance in medicine55: 413-422 (2006)) by Yu et al discloses a single echo Dixon method that assumes a priori knowledge of B0 inhomogeneities.

Disclosure of Invention

The invention provides a magnetic resonance imaging system, a computer program product and a method in the independent claims. Embodiments are given in the dependent claims.

Gradient echo Dixon imaging is typically associated with high sound pressure levels due to scan time, spatial resolution, echo time, and receiver bandwidth constraints.

Drawings

In the following, preferred embodiments of the invention will be described by way of example only and with reference to the accompanying drawings, in which:

figure 1 illustrates an example of a magnetic resonance imaging system;

figure 2 shows a flow chart illustrating a method of operating the magnetic resonance imaging system of claim 1;

fig. 3 illustrates an example of a pulse sequence;

figure 4 shows an example of a sampling pattern in k-space;

fig. 5 illustrates another example of a pulse sequence;

fig. 6 shows another example of a sampling pattern in k-space;

fig. 7 illustrates another example of a pulse sequence;

fig. 8 shows another example of a sampling pattern in k-space;

fig. 9 illustrates another example of a pulse sequence;

fig. 10 illustrates another example of a pulse sequence;

fig. 11 shows another example of a sampling pattern in k-space; and

fig. 12 shows another example of a sampling pattern in k-space.

List of reference numerals

100 magnetic resonance imaging system

104 magnet

106 magnet bore

108 imaging zone

109 region of interest

110 magnetic field gradient coil

112 magnetic field gradient coil power supply

114 radio frequency coil

116 transceiver

118 object

120 object support

126 computer system

128 hardware interface

130 processor

132 user interface

134 computer memory

140 machine-executable instructions

142 pulse sequence commands

144 two point Dixon magnetic resonance data

146 single point Dixon magnetic resonance data

148 first resolution magnetic field inhomogeneity map

150 first resolution water image

152 first resolution fat image

154 second resolution magnetic field inhomogeneity map

156 second resolution water image

158 second resolution fat image

200 controlling a magnetic resonance imaging system to acquire two-point Dixon magnetic resonance data and single-point Dixon magnetic resonance data using pulse sequence commands

202 use two-point Dixon magnetic resonance data to compute a first resolution magnetic field inhomogeneity map

204 calculate a second resolution magnetic field inhomogeneity map by interpolating the first resolution magnetic inhomogeneity map to the second resolution

206 using single point Dixon magnetic resonance imaging data and a second resolution magnetic field inhomogeneity map; calculating a second resolution water image and a second resolution fat image

300 bipolar dual echo pulse sequence

302 readout gradient

304 phase encoding gradient

306 slice selection gradient

308 radio frequency transmission and reception

310 first readout gradient sidelobe

312 first amplitude

314 first duration

316 second readout gradient sidelobe

318 second amplitude

320 second duration

322 RF pulses

324 first sample

326 second sample

400 sampled k-space

402 central k-space region

404 expanded k-space region

406 magnetic resonance data sampled during 324

408 magnetic resonance data sampled during 326

500 unipolar single echo pulse sequence

502 third readout gradient sidelobe

504 third amplitude

506 third duration

508 third sample

600 magnetic resonance data sampled during 508

700 bipolar dual echo pulse sequence

900 unipolar single echo pulse sequence

1000 Bipolar double echo pulse sequence

1100 magnetic resonance data sampled during 324

1102 magnetic resonance data sampled during 326

1104 non-sampled region

1200 magnetic resonance data sampled during 508

1202 k-space region with a modified pulse sequence 900 applied

1204 k-space region with the pulse sequence 1000 applied

Embodiments may reduce the amount of acoustic noise generated by combining a lower resolution (first resolution) two-point Dixon magnetic resonance imaging protocol with a higher resolution (second resolution) single-point Dixon magnetic resonance imaging protocol. A two-point Dixon magnetic resonance imaging protocol is used to determine the first resolution magnetic field inhomogeneity map. The first resolution magnetic field inhomogeneity map is then interpolated to the second resolution to create a second resolution magnetic field inhomogeneity map. The second resolution magnetic field inhomogeneity map then enables the use of a single point Dixon magnetic resonance imaging protocol.

In one aspect, the invention provides a magnetic resonance imaging system comprising a memory for storing machine executable instructions and pulse sequence commands. Pulse sequence commands as used herein contain commands or data that can be converted into such commands that can be used to control a magnetic resonance imaging system to acquire magnetic resonance imaging data. For example, the pulse sequence commands may take the form of timing diagrams that illustrate when various actions are performed by various components of the magnetic resonance imaging system. The pulse sequence commands are configured to acquire two-point Dixon magnetic resonance data from a region of interest according to a two-point Dixon magnetic resonance imaging protocol. The pulse sequence commands are configured to acquire single point Dixon magnetic resonance data from the region of interest according to a single point Dixon magnetic resonance imaging protocol. The two-point Dixon magnetic resonance imaging protocol is configured to sample the two-point Dixon magnetic resonance data from a central k-space region.

The single point Dixon magnetic resonance imaging protocol is configured to sample the single point Dixon magnetic resonance data from an extended k-space region and the central k-space region. In some cases, a particular data point may belong to both single point Dixon magnetic resonance data and two point Dixon magnetic resonance data.

The expanded k-space region is larger than the central k-space region. The combination of the extended k-space region and the central k-space region can be regarded as the complete k-space being sampled. The expanded k-space region at least partially surrounds the central k-space region. The two-point Dixon magnetic resonance imaging protocol is configured to generate an image of the region of interest at a first resolution. The single point Dixon magnetic resonance imaging protocol is configured to generate an image of the region of interest at a second resolution. The second resolution is higher than the first resolution.

The magnetic resonance imaging system further comprises a processor for controlling the magnetic resonance imaging system. Execution of the machine-executable instructions causes the processor to control the magnetic resonance imaging system to acquire the two-point Dixon magnetic resonance data and the single-point Dixon magnetic resonance data with the pulse sequence commands. Execution of the machine-executable instructions further causes the processor to calculate a first magnetic field inhomogeneity map using the two-point Dixon magnetic resonance data. Execution of the machine-executable instructions further cause the processor to calculate a second magnetic field inhomogeneity map by interpolating the first resolution magnetic inhomogeneity map to the second resolution. Execution of the machine-executable instructions further cause the processor to calculate a second resolution water image and a second resolution fat image using the single point Dixon magnetic resonance data and the second resolution magnetic field inhomogeneity map.

This embodiment may be beneficial because acquiring two-point Dixon magnetic resonance data at a lower resolution may have the effect of reducing the amount of acoustic noise that occurs when two-point Dixon magnetic resonance data is acquired as compared to acquiring two-point Dixon magnetic resonance data at the second resolution. A priority for performing the two-point Dixon magnetic resonance imaging protocol is that the magnetic field inhomogeneity map can be determined more reliably. Thus, in this embodiment, the two-point Dixon magnetic resonance imaging protocol is performed at a lower resolution to reduce noise and obtain the magnetic field inhomogeneity map at the first resolution. This is then interpolated and used as an input for processing single point Dixon magnetic resonance data. The use of the second magnetic field inhomogeneity map reduces the likelihood that voxels are incorrectly identified as containing mainly water or fat.

In another embodiment, the pulse sequence commands are configured to sample the two-point Dixon magnetic resonance data from a central k-space region using a bipolar dual echo pulse sequence. The first echo is generated with first readout gradient side lobes having a first polarity and the second echo is generated with second readout gradient side lobes having a second polarity.

In another embodiment, the first readout gradient sidelobe has a first amplitude and a first duration. The second readout gradient sidelobe has a second amplitude and a second duration. The first duration times the first amplitude is less than the second duration times the second amplitude. This embodiment has the effect that the first resolution is smaller than the second resolution. This may be beneficial, for example, because it may reduce the amount of noise generated when the magnetic resonance data is acquired.

As used herein, the terms "first readout gradient side lobe" and "second readout gradient side lobe" are labels for a particular readout gradient side lobe. The "first readout gradient side lobe" may be performed before or after the "second readout gradient side lobe" depending on the embodiment.

In another embodiment, the first amplitude and the second amplitude are the same, which may be beneficial because it may enable minimization of gradient amplitude, which may reduce the generation of acoustic noise.

In another embodiment, for example, the first amplitude and the second amplitude are equal.

In another embodiment, the first amplitude is less than the second amplitude. This may be beneficial because it may reduce the amount of acoustic noise generated during the acquisition of two-point Dixon magnetic resonance data.

In another embodiment, the first duration times the first amplitude times X is less than or equal to the second duration times the second amplitude, where X is a numerical value having any one of the following values: 1.5, 2, 2.5, 3, 4 and 5.

In another embodiment, the first readout gradient sidelobe has a first amplitude and a first duration. The second readout gradient sidelobe has a second amplitude and a second duration. The first duration times the first amplitude times 2 equals the second duration times the second amplitude. The advantages of this embodiment have been discussed previously.

In another embodiment, the pulse sequence commands are further configured to asymmetrically sample the second echo. This again may have the benefit of reducing the amount of acoustic noise.

In another embodiment, the second resolution is as high as twice the first resolution in the readout direction and/or the phase encoding direction. This embodiment may be beneficial because it may reduce the amount of acoustic noise generated during acquisition of the magnetic resonance data.

In another embodiment, the pulse sequence commands are further configured to sample the single point Dixon magnetic resonance data from the central k-space region and the extended k-space region using the bipolar dual echo pulse sequence. In this embodiment, a bipolar dual echo pulse sequence is used to acquire all the magnetic resonance data. Again, this may have the benefit of reducing the amount of acoustic noise generated.

In another embodiment, the pulse sequence commands are configured to obtain the single point Dixon magnetic resonance data from the second echoes of the bipolar dual echo pulse sequence. For example, data acquired from both the first and second echoes may be used for a two-point Dixon magnetic resonance protocol, and data acquired from only the second echo may be used as input for a single-point Dixon magnetic resonance imaging protocol.

In another embodiment, the pulse sequence commands are configured to partially sample the single point Dixon magnetic resonance data from the extended k-space region using a unipolar single echo pulse sequence. The pulse sequence commands are further configured to sample the single point Dixon magnetic resonance data from the central k-space region and partially sample the extended k-space region using the bipolar dual echo pulse sequence. In this example, a combination of a single-polarity single-echo pulse sequence and a dual-echo pulse sequence is used to acquire magnetic resonance data. This may provide a more complete sampling of k-space than using a bipolar dual echo pulse sequence alone. This may provide better image quality.

In another embodiment, the first readout gradient sidelobe has a first amplitude and a first duration. The second readout gradient sidelobe has a second amplitude and a second duration. The first duration times the first amplitude is less than the second duration times the second amplitude. This embodiment has the effect that the first resolution is smaller than the second resolution. This may be beneficial, for example, because it may reduce the amount of noise generated when the magnetic resonance data is acquired.

In another embodiment, the first amplitude and the second amplitude are the same, which may be beneficial because it may enable minimization of gradient amplitude, which may reduce the generation of acoustic noise.

In another embodiment, for example, the first amplitude and the second amplitude may be the same. The value of the first amplitude can then be selected to reduce noise.

In another embodiment, the first amplitude is less than the second amplitude. This may be beneficial because it may reduce the amount of acoustic noise generated during the acquisition of two-point Dixon magnetic resonance data.

In another embodiment, the first duration times the first amplitude times X is less than or equal to the second duration times the second amplitude. Wherein X is a numerical value having any one of the following values: 1.5, 2, 2.5, 3, 4 and 5.

In another embodiment, the first readout gradient sidelobe has a first amplitude and a first duration. The second readout gradient sidelobe has a second amplitude and a second duration. The multiplication of 2 times the first duration times the first amplitude equals the second duration x the second amplitude. The advantages of this embodiment have been discussed previously.

In another embodiment, the unipolar single-echo pulse sequence has third readout gradient side lobes having a third amplitude and a third duration. The third duration times the third amplitude is greater than the second duration times the second amplitude. In this case, a unipolar single-echo pulse sequence is used to sample k-space regions which have not yet been sampled by a bipolar dual-echo pulse sequence. When a bipolar dual echo pulse sequence is used, the part of the extended k-space region adjacent to the central k-space region is not sampled. This embodiment can be used to sample lines of k-space that are completely outside the central k-space region. For the single point Dixon protocol, it provides sampling k-space at the same resolution.

In another embodiment, the third amplitude is equal to or less than the second amplitude.

In another embodiment, the unipolar single-echo pulse sequence has third readout gradient side lobes having a third amplitude and a third duration. The third duration times the third amplitude equals the second duration times the second amplitude times 1.5. In this case, a unipolar single-echo pulse sequence is used to sample k-space regions which have not yet been sampled by a bipolar dual-echo pulse sequence. When a bipolar dual echo pulse sequence is used, the part of the extended k-space region adjacent to the central k-space region is not sampled. This embodiment can be used to sample lines of k-space that are completely outside the central k-space region. For the single point Dixon protocol, it provides sampling k-space at the same resolution.

In another embodiment, the third amplitude and the second amplitude are the same. This may be beneficial because the amplitude of the gradient pulses may be minimized, which may reduce acoustic noise generation.

In another embodiment, the bipolar dual-echo pulse sequence and the unipolar single-echo pulse sequence have exactly the same repetition time and flip angle. This embodiment may be beneficial because the use of exactly the same repetition time and flip angle means that the data acquired from the two pulse sequences can be combined and the contrast and other quality of the image will be the same.

In another embodiment, the pulse sequence commands are configured to acquire the two-point Dixon magnetic resonance imaging data and the single-point Dixon magnetic resonance imaging data interleaved in time. For example, a bipolar dual-echo pulse sequence may be used to sample only the central k-space region, and a unipolar single-echo pulse sequence may be used to sample the complete k-space including both the extended k-space region and the central k-space region. The two sequences may then be interleaved. In this case, the bipolar dual-echo pulse sequence and the unipolar single-echo pulse sequence have exactly the same repetition time and flip angle, which is not, however, strictly necessary.

In another embodiment, the calculation of the second resolution water image and the second resolution fat image is calculated at least in part using the two point Dixon magnetic resonance imaging data. In this way, the two-point Dixon magnetic resonance imaging data is used not only to calculate the magnetic field inhomogeneity map, but also to improve the signal-to-noise ratio in, for example, the resulting water and fat images.

In another aspect, the invention provides a method of operating a magnetic resonance imaging system. The method comprises controlling the magnetic resonance imaging system to acquire two-point Dixon magnetic resonance data and single-point Dixon magnetic resonance data using pulse sequence commands. The pulse sequence commands are configured to acquire two-point Dixon magnetic resonance data from a region of interest according to a two-point Dixon magnetic resonance imaging protocol. The pulse sequence commands are configured to acquire the single point Dixon magnetic resonance data from the region of interest according to a single point Dixon magnetic resonance imaging protocol. The two-point Dixon magnetic resonance imaging protocol is configured to sample the two-point Dixon magnetic resonance data from a central k-space region.

The single point Dixon magnetic resonance imaging protocol is configured to sample the single point Dixon magnetic resonance data from an extended k-space region. The expanded k-space region is larger than the central k-space region. The expanded k-space region at least partially surrounds the central k-space region. The two-point Dixon magnetic resonance imaging protocol is configured to generate an image of the region of interest at a first resolution. The single point Dixon magnetic resonance imaging protocol is configured to generate an image of the region of interest at a second resolution. The second resolution is higher than the first resolution. The method further includes calculating a first magnetic field inhomogeneity map using the two-point Dixon magnetic resonance data. The method further comprises calculating a second magnetic field inhomogeneity map by interpolating the first resolution magnetic field inhomogeneity map to the second resolution. The method further includes calculating a second resolution water image and a second resolution fat image using the single point Dixon magnetic resonance imaging data and the second resolution magnetic field inhomogeneity map. The advantages of this embodiment have been discussed previously.

In another aspect, the invention provides a computer program product comprising machine executable instructions for execution by a processor controlling a magnetic resonance imaging system. Execution of the machine-executable instructions causes the processor to control the magnetic resonance imaging system to acquire two-point Dixon magnetic resonance data and single-point Dixon magnetic resonance data with pulse sequence commands. The pulse sequence commands are configured to acquire two-point Dixon magnetic resonance data from a region of interest according to a two-point Dixon magnetic resonance imaging protocol. The pulse sequence commands are configured to acquire the single point Dixon magnetic resonance data from the region of interest according to a single point Dixon magnetic resonance imaging protocol.

The two-point Dixon magnetic resonance imaging protocol is configured to sample the two-point Dixon magnetic resonance data from a central k-space region. The single point Dixon magnetic resonance imaging protocol is configured to sample the single point Dixon magnetic resonance data from an extended k-space region. The expanded k-space region is larger than the central k-space region. The expanded k-space region at least partially surrounds the central k-space region. The two-point Dixon magnetic resonance imaging protocol is configured to generate an image of the region of interest at a first resolution. The single point Dixon magnetic resonance imaging protocol is configured to generate an image of the region of interest at a second resolution. The second resolution is higher than the first resolution.

Execution of the machine-executable instructions further causes the processor to calculate a first resolution magnetic field inhomogeneity map using the two-point Dixon magnetic resonance data. Execution of the machine-executable instructions further cause the processor to calculate a second resolution magnetic field inhomogeneity map by interpolating the first resolution magnetic field inhomogeneity map to the second resolution. Execution of the machine-executable instructions further cause the processor to calculate a second resolution water image and a second resolution fat image using the single point Dixon magnetic resonance data and the second resolution magnetic field inhomogeneity map. The advantages of this embodiment have been discussed previously.

It is to be understood that one or more of the aforementioned embodiments of the invention may be combined, as long as the combined embodiments are not mutually exclusive.

As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as an apparatus, method or computer program product. Accordingly, aspects of the present invention may take the form of: an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit," module "or" system. Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer-readable media having computer-executable code embodied thereon.

Any combination of one or more computer-readable media may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. As used herein, a "computer-readable storage medium" includes any tangible storage medium that can store instructions executable by a processor of a computing device. The computer-readable storage medium may be referred to as a computer-readable non-transitory storage medium. The computer readable storage medium may also be referred to as a tangible computer readable medium. In some embodiments, the computer-readable storage medium is also capable of storing data that is accessible by a processor of the computing device. Examples of computer-readable storage media include, but are not limited to: a floppy disk, a magnetic hard drive, a solid state disk, flash memory, a USB thumb drive, Random Access Memory (RAM), Read Only Memory (ROM), an optical disk, a magneto-optical disk, and a register file for a processor. Examples of optical disks include Compact Disks (CDs) and Digital Versatile Disks (DVDs), e.g., CD-ROMs, CD-RWs, CD-R, DVD-ROMs, DVD-RWs, or DVD-R disks. The term computer readable storage medium also refers to various types of recording media that can be accessed by a computer device via a network or a communication link. For example, data may be retrieved over a modem, over the internet, or over a local area network. Computer executable code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to: wireless, wired, fiber optic cable, RF, etc., or any suitable combination of the foregoing.

A computer readable signal medium may include a propagated data signal with computer executable code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to: electromagnetic, optical, or any suitable combination thereof. The computer readable signal medium may be any computer readable medium: the computer readable medium is not a computer readable storage medium and can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

"computer memory" or "memory" is an example of computer-readable storage media. Computer memory is any memory that can be directly accessed by a processor. A "computer storage device" or "storage device" is another example of a computer-readable storage medium. The computer storage device may be any non-volatile computer-readable storage medium. In some embodiments, the computer storage device may also be computer memory or vice versa.

A "processor," as used herein, includes an electronic component capable of executing a program or machine-executable instructions or computer-executable code. References to a computing device that includes a "processor" should be interpreted as potentially containing more than one processor or processing core. The processor may be, for example, a multi-core processor. A processor may also refer to a collection of processors within a single computer system or distributed among multiple computer systems. The term computing device should also be read to possibly refer to a collection or network of computing devices, each of which includes a processor or processors. The computer executable code may be executed by multiple processors, which may be within the same computing device, or even distributed across multiple computing devices.

The computer executable code may include machine executable instructions or programs that cause a processor to perform an aspect of the present invention. Computer executable code for performing operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language (e.g., Java, Smalltalk, C + + or the like) and conventional procedural programming languages, such as the "C" programming language or similar programming languages, and compiled as machine executable instructions. In some instances, the computer executable code may be in a high level language form or in a pre-compiled form, and may be used in conjunction with an interpreter that generates machine executable instructions on the fly.

The computer executable code may run entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the last scenario, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider).

Aspects of the present invention are described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block, or portion of a block, of the flowchart, illustrations and/or block diagrams, can be implemented by computer program instructions in computer-executable code, where applicable. It will also be understood that combinations of blocks in the different flowcharts, diagrams and/or block diagrams may be combined, when not mutually exclusive. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

A "user interface" as used herein is an interface that allows a user or operator to interact with a computer or computer system. The "user interface" may also be referred to as a "human interface device". The user interface may provide information or data to and/or receive information or data from an operator. The user interface may enable input from an operator to be received by the computer and may provide output from the computer to the user. In other words, the user interface may allow an operator to control or manipulate the computer, and the interface may allow the computer to indicate the effect of the operator's control or manipulation. The display of data or information on a display or graphical user interface is an example of providing information to an operator. Receiving data through a keyboard, mouse, trackball, trackpad, pointing stick, tablet, joystick, gamepad, web camera, head-mounted device, foot pedal, wired glove, remote control, and accelerometer are all examples of user interface components that enable receiving information or data from an operator.

As used herein, "hardware interface" encompasses an interface that enables a processor of a computer system to interact with and/or control an external computing device and/or apparatus. The hardware interface may allow the processor to send control signals or instructions to an external computing device and/or apparatus. The hardware interface may also enable the processor to exchange data with external computing devices and/or apparatus. Examples of hardware interfaces include, but are not limited to: a universal serial bus, an IEEE1394 port, a parallel port, an IEEE1284 port, a serial port, an RS-232 port, an IEEE-488 port, a Bluetooth connection, a wireless local area network connection, a TCP/IP connection, an Ethernet connection, a control voltage interface, a MIDI interface, an analog input interface, and a digital input interface.

"display" or "display device" as used herein encompasses an output device or user interface suitable for displaying images or data. The display may output visual, auditory, and or tactile data. Examples of displays include, but are not limited to: computer monitors, television screens, touch screens, tactile electronic displays, braille screens, Cathode Ray Tubes (CRTs), memory tubes, bi-stable displays, electronic paper, vector displays, flat panel displays, vacuum fluorescent displays (VFs), Light Emitting Diode (LED) displays, electroluminescent displays (ELDs), Plasma Display Panels (PDPs), Liquid Crystal Displays (LCDs), organic light emitting diode displays (OLEDs), projectors, and head mounted displays.

Magnetic Resonance (MR) data is defined herein as being the recorded measurements of radio frequency signals emitted by atomic spins by an antenna of a magnetic resonance apparatus during a magnetic resonance imaging scan. A Magnetic Resonance Imaging (MRI) image or MR image is defined herein as being a two-dimensional visualization or a three-dimensional visualization reconstructed of anatomical data contained within the magnetic resonance imaging data. Such visualization can be performed using a computer.