MRI WITH MATCHING STATES OF VIBRATION

Abstract

The invention relates to a magnetic resonance system (100) configured for acquiring magnetic resonance data from a GC subject (118). Execution of the machine executable instructions (140) stored in a memory (134) causes a processor (130) to control the magnetic resonance system (100) using a set of waveform and pulse sequence commands (142, 152) to prepare a first state of vibration (211) of the one or more hardware elements and/or the subject (118). The preparing comprises generating the vibration matching gradient (200) inducing the first vibrations (210) of the one or more hardware elements and/or the subject (118), while the net magnetization vector of the subject (118) is aligned along the longitudinal axis of the main magnetic field. The magnetic resonance system (100) is further controlled to acquire the magnetic resonance data (144, 154) according to a magnetic resonance protocol. The acquiring comprises generating in sequence at least two spin manipulating gradients (202, 204) for manipulating phases of nuclear spins within the subject (118), while the net magnetization vector of the subject (118) comprises a non-vanishing component in a transverse plane perpendicular to the longitudinal axis of the main magnetic field. A first one of the at least two spin manipulating gradients (202) is generated during the first state of vibration (211) and a second one of the at least two spin manipulating gradients (204) is generated during a second state of vibration (213) of the one or more hardware elements and/or the subject (118). The vibration matching gradient (200) is used for matching with the first state of vibration (211) the second state of vibration (213).

Claims

1. A magnetic resonance system configured to acquire magnetic resonance data from a subject in a data acquisition volume of the magnetic resonance system, comprising: a memory configured to store machine executable instructions and a set of waveform and pulse sequence commands, wherein the set of waveform and pulse sequence commands is configured to generate a vibration matching gradient for inducing first vibrations of one or more hardware elements of the magnetic resonance system and/or the subject, while a net magnetization vector of the subject is aligned along a longitudinal axis of a main magnetic field generated by the magnetic resonance system, wherein the set of waveform and pulse sequence commands is further configured to acquire magnetic resonance data from the subject according to a magnetic resonance protocol, wherein the acquiring of the magnetic resonance data comprises generating in sequence at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject, while the net magnetization vector of the subject comprises a non-vanishing component of net magnetization in a transverse plane perpendicular to the longitudinal axis of the main magnetic field, a processor configured to control the magnetic resonance system, wherein execution of the machine executable instructions causes the processor to control the magnetic resonance system using the set of waveform and pulse sequence commands to prepare a first state of vibration of the one or more hardware elements and/or the subject, the preparing comprises generating the vibration matching gradient inducing the first vibrations the one or more hardware elements and/or the subject, while the net magnetization vector of the subject is aligned along the longitudinal axis of the main magnetic field, acquire the magnetic resonance data according to the magnetic resonance protocol, wherein the acquiring comprises generating in sequence the at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject, while the net magnetization vector of the subject comprises a non-vanishing component in the transverse plane perpendicular to the longitudinal axis of the main magnetic field, wherein a first one of the at least two spin manipulating gradients is generated during the first state of vibration and a second one of the at least two spin manipulating gradients is generated during a second state of vibration of the one or more hardware elements and/or the subject, wherein the vibration matching gradient is used for matching with the first state of vibration the second state of vibration.

2. The magnetic resonance system of claim 1, wherein the second state of vibration results from second vibrations induced by the first one of the at least two spin manipulating gradients.

3. The magnetic resonance system of claim 1, wherein the magnetic resonance protocol is sensitive to an accumulation of spin displacement-induced phases with the at least two spin manipulating gradients being used for accumulating spin displacement-induced phases and the acquired magnetic resonance data encoding effects of the accumulated spin displacement-induced phases.

4. The magnetic resonance system of claim 3, wherein the magnetic resonance protocol is one of the following: a diffusion-weighted protocol, an apparent diffusion coefficient protocol, a diffusion tensor imaging protocol, a diffusion-weighted spectroscopy protocol, a diffusion weighted preparation protocol, a higher-order diffusion model protocol, a phase contrast velocimetry protocol, a displacement encoding protocol and an magnetic resonance elastography protocol.

5. The magnetic resonance system of claim 1, wherein the execution of the machine executable instructions further causes the processor to control the magnetic resonance system to compute a representation of the acquired magnetic resonance data.

6. The magnetic resonance system of claim 5, wherein the computing of the representation comprises computing one or more of the following using the acquired magnetic resonance data a diffusion-weighted magnetic resonance image, an apparent diffusion coefficient map, a diffusion tensor image, an exponential apparent diffusion coefficient map, a fractional anisotropy image, a principal diffusion direction map, a fiber tracking map, a velocity map, a magnetic resonance spectrum, an elastogram and a modeled parameter extracted using a signal model in-cooperating diffusion-weighting, velocity encoding and/or displacement encoding.

7. The magnetic resonance system of claim 1, wherein the one or more hardware elements comprise a supporting element for supporting the subject in the data acquisition volume of the magnetic resonance system.

8. The magnetic resonance system of claim 1, wherein a first time interval between generating the vibration matching gradient and the first one of the at least two spin manipulating gradients equals a second time interval between generating the first one and the second one -of the at least two spin manipulating gradients.

9. The magnetic resonance system of claim 1, wherein an amplitude of the vibration matching gradient equals an amplitude of the first one of the at least two spin manipulating gradients.

10. The magnetic resonance system of claim 1, wherein the vibration matching gradient comprises a first waveform and first one of the at least two spin manipulating gradients comprises a second waveform, wherein a slope of a flank of the first waveform equals a slope of a flank of the second waveform.

11. The magnetic resonance system of claim 10, wherein the first waveform equals the second waveform.

12. A computer program product comprising machine executable instructions stored on a non-transitory computer readable medium for execution by a processor controlling a magnetic resonance system configured for acquiring magnetic resonance data from a subject in a data acquisition volume of the magnetic resonance system, wherein the computer program product further comprises a set of waveform and pulse sequence commands, wherein the set of waveform and pulse sequence commands is configured for generating a vibration matching gradient for inducing first vibrations of one or more hardware elements of the magnetic resonance system and/or the subject, while a net magnetization vector of the subject is aligned along a longitudinal axis of a main magnetic field generated by the magnetic resonance system, wherein the set of waveform and pulse sequence commands is further configured for acquiring magnetic resonance data from the subject according to a magnetic resonance protocol, wherein the acquiring of the magnetic resonance data comprises generating in sequence at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject, while the net magnetization vector of the subject comprises a non-vanishing component of net magnetization in a transverse plane perpendicular to the longitudinal axis of the main magnetic field, and wherein execution of the machine executable instructions the processor to control the magnetic resonance system using the set of waveform and pulse sequence commands to prepare a first state of vibration of the one or more hardware elements and/or the subject, the preparing comprises generating the vibration matching gradient inducing the first vibrations of the one or more hardware elements and/or the subject, while the net magnetization vector of the subject is aligned along the longitudinal axis of the main magnetic field, acquire the magnetic resonance data according to the magnetic resonance protocol, wherein the acquiring comprises generating in sequence the at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject, while the net magnetization vector of the subject comprises a non-vanishing component along the transverse plane perpendicular to the longitudinal axis of the main magnetic field, wherein a first one of the at least two spin manipulating gradients is generated during the first state of vibration and a second one of the at least two spin manipulating gradients is generated during a second state of vibration of the one or more hardware elements and/or the subject wherein the vibration matching gradient used for matching with the first state of vibration the second state of vibration.

13. A method for operating a magnetic resonance system configured for acquiring magnetic resonance data from a subject in a data acquisition volume of the magnetic resonance system, the magnetic resonance system comprising: a memory configured to store machine executable instructions and a set of waveform and pulse sequence commands, wherein the set of waveform and pulse sequence commands configured for generating a vibration matching gradient for inducing first vibrations one or more hardware elements of the magnetic resonance system and/or the subject, while a net magnetization vector of the subject is aligned along a longitudinal axis of a main magnetic field generated by the magnetic resonance system, wherein the set of waveform and pulse sequence commands is further configured for acquiring magnetic resonance data from the subjects according to a magnetic resonance protocol, wherein the acquiring of the magnetic resonance data comprises generating in sequence at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject, while the net magnetization vector of the subject comprises a non-vanishing component of net magnetization in a transverse plane perpendicular to the longitudinal axis of the main magnetic field, and a processor for controlling the magnetic resonance system, wherein execution of the machine executable instructions causes the processor to control the magnetic resonance system according to the method using the set of waveform and pulse sequence commands, wherein the method comprises: preparing a first state of vibration of the one or more hardware elements and/or the subject, the preparing comprises generating the vibration matching gradient inducing the first vibrations of the one or more hardware elements and/or the subject, while the net magnetization vector of the subject is aligned along the longitudinal axis of the main magnetic field, acquiring the magnetic resonance data according to the magnetic resonance protocol, wherein the acquiring comprises generating in sequence the at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject, while the net magnetization vector of the subject comprises a non-vanishing component in the transverse plane perpendicular to the longitudinal axis of the main magnetic field, wherein a first one of the at least two spin manipulating gradients is generated during the first state of vibration and a second one of the at least two spin manipulating gradients is generated during a second state of vibration of the one or more hardware elements and/or the subject, wherein the vibration matching gradient is used for matching with the first state of vibration the second state of vibration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In the following preferred embodiments of the invention will be described, by way of example only, and with reference to the drawings in which:

[0062] FIG. 1 illustrates an example of a magnetic resonance system;

[0063] FIG. 2 illustrates an example of a magnetic resonance system;

[0064] FIG. 3 illustrates an exemplary pulse sequence;

[0065] FIG. 4 illustrates an exemplary dependency of the vibration compensation on

[0066] T.sub.vibration;

[0067] FIG. 5 illustrate exemplary dependencies of the vibration compensation on b-value;

[0068] FIG. 6 shows a flow chart which illustrates a method of operating the magnetic resonance system of FIG. 1 and FIG. 2;

[0069] FIG. 7 illustrate exemplary dependencies of the vibration compensation on T.sub.vibration;

[0070] FIGS. 8 illustrate an exemplary vibration compensation;

[0071] FIGS. 9 illustrate an exemplary vibration compensation.

[0072] FIG. 10 shows the results from the phantom scans.

[0073] FIG. 11 shows the mean obtained ADC value in the tibia bone marrow.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] Like numbered elements in these figures are either equivalent elements or perform the same function. Elements which have been discussed previously will not necessarily be discussed in later figures if the function is equivalent.

[0075] FIG. 1 illustrates an example of a magnetic resonance system 100. The magnetic resonance system 100 comprises a magnet 104. The magnet 104 is a superconducting cylindrical type magnet with a bore 106 through it. The use of different types of magnets is also possible. For instance, it is also possible to use both a split cylindrical magnet and a so-called open magnet. A split cylindrical magnet is similar to a standard cylindrical magnet, except that the cryostat has been split into two sections to allow access to the iso-plane of the magnet. Such magnets may for instance be used in conjunction with charged particle beam therapy. An open magnet has two magnet sections, one above the other with a space in-between that is large enough to receive a subject 118 to be imaged, the arrangement of the two sections area similar to that of a Helmholtz coil. Open magnets are popular, because the subject is less confined. Inside the cryostat of the cylindrical magnet there is a collection of superconducting coils. Within the bore 106 of the cylindrical magnet 104 there is a data acquisition volume 108, also referred to as an imaging zone, where the magnetic field is strong and uniform enough to perform magnetic resonance imaging. A region of interest 109 is shown within the imaging zone 108. The magnetic resonance data is typically acquired for the region of interest. A subject 118 is shown as being supported by a subject support element 120 such that at least a portion of the subject 118 is within the imaging zone 108 and the region of interest 109. In this example, the support element 120 is a support table. In other examples, other designs and/or combinations of support elements may be used for supporting and positioning the subject 118 within the imaging zone 108 and the region of interest 109.

[0076] Within the bore 106 of the magnet there is also a set of magnetic field gradient coils 110 which is used for generating magnetic field gradients, e.g. pulsed magnetic field gradients. The set of magnetic field gradient coils 110 is, e.g., used for acquisition of magnetic resonance data to spatially encode magnetic spins within the imaging zone 108 of the magnet 104. The magnetic field gradient coils 110 are connected to a magnetic field gradient coil power supply 112. The magnetic field gradient coils 110 are intended to be representative. Typically, magnetic field gradient coils 110 contain three separate sets of coils for spatially encoding in three orthogonal spatial directions. A magnetic field gradient power supply supplies current to the magnetic field gradient coils. The current supplied to the magnetic field gradient coils 110 is controlled as a function of time and may be ramped or pulsed.

[0077] Adjacent to the imaging zone 108 is a radio-frequency coil 114 for manipulating the orientations of magnetic spins within the imaging zone 108 and for receiving radio transmissions from spins also within the imaging zone 108. The radio frequency antenna may contain multiple coil elements. The radio frequency antenna may also be referred to as a channel or antenna. The radio-frequency coil 114 is connected to a radio frequency transceiver 116. The radio-frequency coil 114 and radio frequency transceiver 116 may be replaced by separate transmit and receive coils and a separate transmitter and receiver. It is understood that the radio-frequency coil 114 and the radio frequency transceiver 116 are representative. The radio-frequency coil 114 is intended to also represent a dedicated transmit antenna and a dedicated receive antenna. Likewise, the transceiver 116 may also represent a separate transmitter and separate receivers. The radio-frequency coil 114 may also have multiple receive/transmit elements and the radio frequency transceiver 116 may have multiple receive/transmit channels. For example, if a parallel imaging technique such as SENSE is performed, the radio-frequency coil 114 will have multiple coil elements.

[0078] In this example the subject 118 is positioned such that the subject's thorax region is located within the region of interest 109. In other examples, other parts of the subject's 118 body may be positioned in the region of interest 109. In other examples, the subject 118 may be some other object, like, e.g., a sample container comprising a sample 119 as shown in FIG. 2.

[0079] The transceiver 116 and the gradient controller 112 are shown as being connected to a hardware interface 128 of a computer system 126. The computer system further comprises a processor 130 that is in communication with the hardware interface 128, a memory 134, and a user interface 132. The memory 134 may be any combination of memory which is accessible to the processor 130. This may include such things as main memory, cached memory, and also non-volatile memory such as flash RAM, hard drives, or other storage devices. In some examples the memory 134 may be considered to be a non-transitory computer-readable medium. The user interface 132 may enable the processor 104 to display or render images and other information which may be provided to a user or operator. The user interface 132 may also be used to receive control or input data from a user or operator. The user interface 132 may comprise a display for selecting and/or configuring pulse sequences as well as displaying results of magnetic resonance data acquisition and/or processing executed by the magnetic resonance system 100.

[0080] The memory 134 is shown as containing machine-executable instructions 140. The machine-executable instructions 140 enable the processor 130 to control the operation and function of the magnetic resonance system 100 to execute a magnetic resonance imaging procedure. The machine-executable instructions 140 may also enable the processor 130 to perform various data analysis and calculation functions, e.g., data processing and image processing tasks. The memory 134 is further shown as containing a set of waveform and pulse sequence commands 142. The waveform and pulse sequence commands 142 are either instructions or data which can be converted into instructions which enable the processor 104 to control the magnetic resonance system 100 to acquire magnetic resonance imaging data 144. The set of waveform and pulse sequence commands 142 may be configured for generating a vibration matching gradient for inducing first vibrations of one or more hardware elements of the magnetic resonance system 100 and/or the subject 118. The vibration matching gradient while a net magnetization vector of the subject 118 is aligned along, i.e., parallel or antiparallel to, a longitudinal axis of the main magnetic field generated by the magnetic resonance system 100. The set of waveform and pulse sequence commands 142 may further be configured for acquiring magnetic resonance data from the subject according to a magnetic resonance protocol. The acquiring of magnetic resonance data 144 comprises generating in sequence at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject 118 in the imaging volume 108 according to a magnetic resonance imaging protocol. The least two spin manipulating gradients are generated while the net magnetization vector of the subject comprises a non-vanishing component of net magnetization in a transverse plane perpendicular to the longitudinal axis of the main magnetic field. The magnetic resonance imaging protocol may be any of the magnetic resonance imaging protocol described herein. The magnetic resonance imaging protocol may, e.g., be sensitive to an accumulation of spin displacement-induced phases. The at least two spin manipulating gradients may be used for accumulating spin displacement-induced phases and the acquired magnetic resonance data may comprise effects of the accumulated spin displacement-induced phases encoded therein. The memory 134 is further shown as containing the magnetic resonance imaging data 144 acquired by controlling the magnetic resonance system 100 with the waveform and pulse sequence commands 142. Furthermore, the memory 110 may comprise one or more representations 146 of the acquired magnetic resonance data 144, e.g., graphical representations in form of magnetic resonance images reconstructed using the acquired magnetic resonance imaging data 144. The one or more representations 146 may comprise any representation described herein.

[0081] FIG. 2 shows a further exemplary embodiment of the magnetic resonance system 100 of FIG. 1. In the data acquisition volume 108 a subject 118 in form of sample container providing a sample 119 is located. Alternatively, the subject 118 may be some other object or a human person, like shown in FIG. 1, at least a portion of which is located within the data acquisition volume 108 and the region of interest 109. The machine-executable instructions 140 stored in memory 134 may enable the processor 130 to control the operation and function of the magnetic resonance system 100 to perform magnetic resonance imaging/spectroscopy using waveform and pulse sequence commands 152. The waveform and pulse sequence commands 152 are either instructions or data which can be converted into instructions enabling the processor 104 to control the magnetic resonance system 100 to acquire magnetic resonance imaging/spectroscopy data 154. The set of waveform and pulse sequence commands 152 may be configured for generating a vibration matching gradient for inducing first vibrations, while the net magnetization is oriented longitudinal without any transverse net magnetization present. The set of waveform and pulse sequence commands 152 may further be configured for acquiring of the magnetic resonance imaging/spectroscopy data 154 from the subject 118 in the data acquisition volume 108 according to a magnetic resonance imaging/spectroscopy protocol. The magnetic resonance imaging/spectroscopy protocol may be any magnetic resonance imaging/spectroscopy protocol described herein, according to which the data acquisition comprises generating in sequence at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject 118 in the data acquisition volume 108, while at least some transverse net magnetization is present. The memory 110 is further shown as containing magnetic resonance imaging/spectroscopy data 154, that has been acquired by controlling the magnetic resonance system 100 with the waveform and pulse sequence commands 152. Furthermore, the memory 110 may comprise one or more representations 156 of the acquired magnetic resonance data 154, like a magnetic resonance spectrum, a magnetic resonance image or some parameters computed using the acquired magnetic resonance imaging/spectroscopy data 154.

[0082] FIG. 3 illustrates an exemplary pulse sequence 201 generated according to a set of waveform and pulse sequence commands. The pulse sequence 201 is supplemented by a vibration matching gradient 200 generated, while the net magnetization vector of the subject is aligned longitudinal, i.e., before any RF-pulses have been applied or after their effect on the net magnetization has dissipated. The pulse sequence 201 further comprises a pair of spin manipulating gradients 202, 204 for manipulating phases of nuclear spins, generated while the net magnetization vector comprises a non-vanishing transverse component, i.e., a non-vanishing component in a transverse plane perpendicular to the longitudinal axis of the net magnetic field, due to the RF-pulses. The pulse sequence 201 may, e.g., be implemented in form of a vibration-compensated DW spin echo (diffusion-weighted spin echo) sequence, i.e., a DW spin echo sequence which has been extended by a vibration compensating gradient in form of a vibration matching gradient 200. The DW spin echo sequence 201 comprises a 90° RF-pulse and a 180° RF-pulse. Symmetrically distributed around the 180° RF-pulse are the two spin manipulating gradients 202, 204 in form of diffusion gradients temporally spaced apart from each other by a time interval Δ. The vibration matching gradient 200 may have the same waveform, i.e., shape, and amplitude as the diffusion gradients 202, 204. A time interval T.sub.vibration between the vibration matching gradient 200 and the first diffusion gradient 202 may be equal to Δ.

[0083] The gradients 200, 202, 204 of sequence 201 may each induce tissue displacements, i.e., vibrations of the subject. Without the vibration matching gradient 200, the first diffusion gradient 202 may be generated in a state of vibration of the subject with negligible vibrations. The first diffusion gradient 202, however, may induce mechanical vibrations in hardware components of the MR system as well as in the subject resulting in the tissue displacements 212. Tissue displacements 212 may be damped with time, i.e., during time interval A, resulting in a state of vibration 213 during which the second diffusion gradient 202 is generated that differs significantly from the state of vibration during which the first diffusion gradient 202 was generated. Any magnetic resonance protocol that is sensitive to an accumulation of spin displacement-induced phases will be negatively affected by such differences between states of vibrations. When the vibration matching gradient 200 is added, the vibration matching gradient 200 induces additional vibrations resulting in tissue displacements 210 that are damped with time, i.e., during time interval T.sub.vibration. The damped tissue displacements 210 result in a state of vibration 211 during which the first diffusion gradient 202 is generated that matches the subsequent state of vibration 213. In other words, the displacements 210, 212 are similar for both diffusion gradients 202, 204. Thus, negative influences on the accumulation of spin displacement-induced phases due to differences between the states of vibration 211, 213 may be efficiently prevented.

[0084] FIG. 4 illustrates an exemplary dependency of the vibration compensation on the time interval T.sub.vibration between a vibration matching gradient and a first spin manipulating gradient. For the analysis shown in FIG. 4, a high b-value DW TSE sequence has been used for measuring lipids ADC in a water-fat-phantom. The high b-value DW TSE sequence comprises of a DW stimulated echo preparation with four 90° RF pulses and mono-polar diffusion sensitizing gradients, followed by a 2D-TSE readout. A vibration matching gradient matching the diffusion sensitizing gradients is generated before the diffusion preparation.

[0085] The water-fat-phantom is an 80% fat fraction water-fat-phantom. The water-fat-phantom comprises 800 ml oil, 200 ml water, 4 ml Tween80 and 1 g of sodium benzoate. Emulsification is carried out with a colloid mill at 6000 revolutions per minute. The phantom is scanned with a 3T-MR-system using an 8-channel wrist coil on a supporting table of the MR-system.

[0086] The time interval T.sub.vibration is varied under strong diffusion weighting with a b-value of 50,000 s/mm.sup.2 within a range from 40 ms to 525 ms in order to determine an optimal T.sub.vibration. Further parameters used comprise a field of view (FOV) of (120 mm).sup.2, a voxel size of 2×2×10 mm.sup.3, a repetition time (TR) of 2000 ms, an echo time (TE) of 23 ms, a TM.sub.Prep of 220 ms and a TE.sub.Prep of 61 ms.

[0087] FIG. 4 depicts a mean signal evolution in DWI raw images of the water-fat-phantom for different length of the time interval T.sub.vibration. The signal depicted is a relative signal, i.e., the signal with vibration compensation over the signal without vibration compensation. A single global maximum of the relative signal amplitude of 117% of the signal value without vibration compensation can be observed for the time interval T.sub.vibration equaling the time interval Δ between the first and a second sensitizing gradient, also referred to as diffusion time. Further local maxima are shown with relative signal amplitude of more than 100%, but less than 117%. These local maxima resemble the eigenfrequencies of the subject being analyzed. Thus, alternative to T.sub.vibration=Δ, the time interval T.sub.vibration of one of the local maxima may be determined and used for a vibration compensation. However, the most efficient and thus preferable choice may be T.sub.vibration=Δ.

[0088] FIG. 5 illustrate exemplary dependencies of the vibration compensation on b-value. As in FIG. 4, a high b-value DW TSE sequence is used for measuring lipids ADC in the water-fat-phantom. The ADC is measured with a b-value in a range from 5,000 s/mm.sup.2 to 50,000 s/mm.sup.2 using steps of 5,000 s/mm.sup.2 without and with using a vibration matching gradient. Further parameters used comprise a field of view (FOV) of (120 mm).sup.2, a voxel size of 2×2×10 mm.sup.3, a TR of 2000 ms, a TE of 23 ms, a TM.sub.Prep of 220 ms and a TE.sub.Prep of 61 ms. The frequency of the observed signal oscillation is of the order of 11 Hz.

[0089] In FIG. 5A, a log of a measured signal decay curve and a mean ADC value without using the vibration matching gradient are shown. The fit of the ADC value yields 1.1 e.sup.−0.5 mm.sup.2/s. In FIG. 5B, a log of a measured signal decay curve and mean ADC value using the vibration matching gradient are shown. In this case, the fit of the ADC value yields 7.8 e.sup.0.6 mm.sup.2/s. For the measurements shown in FIG. 5C and FIG. 5D, a standard scanner table comprised by the MR system and used for the measurements of FIGS. 5A and 5B has been replaced by a wooden support structure. This wooden support structure decouples the subject located thereon from vibrations introduced by the MR system, e.g., introduced due to gradients generated by the MR system. In FIG. 5C, a log of a measured signal decay curve and a mean ADC value for the wooden support structure without using the vibration matching gradient are shown. The fit of the ADC value yields 6.2 e.sup.Δ0.6 mm.sup.2/s. In FIG. 5B, a log of a measured signal decay curve and mean ADC value for the wooden support structure using the vibration matching gradient are shown. In this case, the fit of the ADC value yields 6.1 e.sup.−0.6 mm.sup.2/s. Thus, the ADC value is 70% higher when comparing the measurements performed on the standard scanner table in FIG. 5A with the wooden support structure in FIG. 5C, each without any vibration compensation using a vibration matching gradient. When the vibration matching gradient is employed a 25% higher ADC value is measured in FIG. 5B compared with FIG. 5D. Only minor differences of about 2% are observable for using the wooden support structure without and with vibration-compensation gradient in FIGS. 5C and 5D. This illustrates the effectiveness of vibration compensation using the method proposed herein. The ADC value determined using the standard scanner table with the proposed vibration compensation method matches the ADC values determined using the wooden support structure, i.e., the ADC values determined for a subject decoupled from vibrations introduced by the MR system, significantly better than the ADC value determined using the standard scanner table without the proposed vibration compensation method.

[0090] FIG. 6 shows a flow chart which illustrates a method of operating the MR systems of FIG. 1 and FIG. 2. In step 600, a first state of vibration of the one or more hardware elements of the MR system and/or the subject in the data acquisition volume of the MR system is prepared. For this purpose, a vibration matching gradient is generated. The vibration matching gradient is generated, while a net magnetization vector of the subject is aligned parallel or antiparallel to a longitudinal axis of a main magnetic field generated by the magnetic resonance system. The generation of the vibration matching gradient induces first vibrations of one or more hardware elements and/or the subject resulting in the first state of vibration. In step 602, magnetic resonance data is acquired from the subject according to a magnetic resonance protocol, e.g., a magnetic resonance protocol sensitive to an accumulation of spin displacement-induced phases. According to the magnetic resonance protocol at least two spin manipulating gradients for manipulating phases of nuclear spins within the subject are generated in sequence, while the net magnetization vector of the subject comprises a non-vanishing component of net magnetization in the transverse plane perpendicular to the longitudinal axis of the main magnetic field. The first spin manipulating gradient is generated during the first state of vibration prepared using the vibration matching gradient. Since the first spin manipulating gradient itself as well induces vibrations, i.e., second vibrations, of the one or more hardware elements and/or the subject, a second state of vibration results from the second vibrations, during which the second spin manipulating gradient is generated. The vibration matching gradient of step 600 is configured for mimicking with the first state of vibration the second state of vibration resulting in a matching of both states. In addition, one or more representations of the acquired magnetic resonance data may be computed. The computed representation may comprise a graphical representation, such as an image, a map, a spectrum, or a graph, and/or the computed representation may comprise a parameter of interest, like, e.g., a scaler, vector or matrix.

[0091] FIGS. 7 illustrate exemplary dependencies of the vibration compensation on T.sub.vibration for the setup of FIG. 4. In FIG. 7A, a DW image of the fat-water-phantom is shown using a high b-value DW TSE sequence without applying a vibration matching gradient. FIG. 7B shows a DW image of the fat-water-phantom using a high b-value DW TSE sequence with a vibration matching gradient. The time interval T.sub.vibration is chosen to be T.sub.vibration=205 ms. T.sub.vibration=205 ms corresponds to a global minimum of the relative signal amplitude depicted in FIG. 4, where the signal with vibration compensation is about on half of the signal without vibration compensation. FIG. 7C as well shows a DWI image of the fat-water-phantom using a high b-value DW TSE sequence with a vibration matching gradient. In FIG. 7C, the time interval T.sub.vibration is chosen to be T.sub.vibration=255 ms. T.sub.vibration=255 ms corresponds to Δ, i.e., the global maximum of the relative signal amplitude of 117% depicted in FIG. 4.

[0092] FIG. 8 illustrate an exemplary vibration compensation in case of an analysis of lipids ADCs in vivo in a human leg. FIG. 8A shows the location of a 2D imaging slice 300 through a lower leg. FIG. 8B shows a corresponding fat fraction map acquired at this location. FIGS. 8C and 8D show ADC maps obtained without applying a vibration matching gradient (FIG. 8C) and with applying a vibration matching gradient (FIG. 8D). The measurements are performed using an 8-channel extremity coil with the following parameters: FOV of (140 mm).sup.2, voxel size of (2.2 mm).sup.3, TR of 1800 ms, TE of 10 ms, TM.sub.Prep of 220 ms, and TE.sub.Prep of 61 ms. The b-values are identical with the water-fat-phantom experiment shown in FIG. 4, FIG. 5, and FIG. 7. The scan time is 4:32 min. A comparison of FIG. 8C with FIG. 8D illustrates that the subcutaneous fat ADC is qualitatively more heterogeneous, especially in the region indicated by the ellipse 302, without vibration matching gradient. A more homogenous ADC value in the subcutaneous fat is observed with the vibration matching gradient, especially in region 302 of FIG. 8D. In FIG. 8E, a mean ADC value and in FIG. 8F a corresponding standard deviation are shown for different segmented regions of the lower leg. On the left frame axis of FIG. 8E and FIG. 8F, values determined without vibration compensation are plotted, while on the right frame axis of FIG. 8E and FIG. 8F, values determined with vibration compensation are plotted. In the subcutaneous fat, a total decrease of 5% and a local decrease of 12% are observed in the ADC according to FIG. 8E. Furthermore, a decrease of 16% in total and 43% locally are observed in the ADC standard deviation with the vibration matching gradient according to FIG. 8F. In the tibia and fibula bone marrow, only minor differences are observed. In summary, in the subcutaneous fat, a global and local (cf region 302 in FIG. 8C and FIG. 8D) decrease in the ADC value and standard deviation are observed, whereas the values stay nearly constant for the more rigid region of the bone marrow in the tibia and fibula.

[0093] FIGS. 9 illustrate an exemplary vibration compensation for an in vivo high b-value DWI in a human brain. FIG. 9A shows an iso DWI of the brain without applying a vibration matching gradient, while FIG. 9B shows an iso DWI of the brain with applying a vibration matching gradient. The measurements are performed using a 32-channel head coil, an DW EPI (echo-planar imaging) with a FOV of 230×230×114 mm.sup.3, a voxel size of 1.5×1.5×4 mm.sup.3, a TR of 6070 ms, a TE of 124 ms, and a halfscan factor of 0.7 at a b-value of 10,000 s/mm.sup.2. It is possible to use the same shortest TE and TR with and without vibration compensation gradient, while the time penalty of the compensation is not severe, i.e., the time increases from 3:20 min to 3:27 min. The effect of applying the vibration matching gradient is visible in particular in the indicated regions 304.

ADC Measurements in Phantoms

[0094] To evaluate the performance of the proposed scheme, the lipid ADC value was estimated within the WF phantoms (6,000 and 11,000 rpm). Three different phantoms were utilized in the phantom measurements. For the lipid diffusion property measurements, two WF phantoms with 80% fat fraction were produced (content: 800 ml sun flower oil, 200 ml water, 4 ml Tween80 and 1 g of sodium benzoate). Emulsification was carried out with a colloid mill at 6,000 and 11,000 revolutions per minute (rpm). The obtained phantoms yield different lipid droplet sizes and consequently different viscosities. The experiments were performed on the scanner table and on a decoupling table made of wood that decoupled the sample and the vibrating scanner table. The following two interferometer experiments were performed with the interferometer setup to quantify the effects under investigation. The voxel of interest was placed in the middle of the WF phantom material. The experiment was repeated for the same three different measurement scenarios as performed in the interferometer measurements and with the same scanning parameters. The utilized additional sequence parameters were: 16 averages per b-value (half of the averages with positive and the other half with negative polarity), 1 start-up cycle, b-values: 10,000-20,000-40,000-60,000 s/mm2, 2:48 min scan time per phantom. Diffusion gradients were applied simultaneously in all three axes to minimize TE.

[0095] FIG. 10 shows the results from the phantom scans. Assuming that the phantoms on the decoupling table are not affected by vibration artefacts, the ADC value on the decoupling table represents the real lipid ADC value. In the 6,000 rpm phantom, the DW MRS experiment on the scanner table yields to a 119.0% overestimation of the ADC value whereas only a relative error of 5.5% is observed on the scanner table with the VMG. In the 11,000 rpm phantom, the obtained lipid ADC value is very similar between the different measurement scenarios and only relative differences below 1% are observed.

ADC Measurements In Vivo

[0096] The bone marrow in the tibia of three healthy volunteers (volunteer 1: 24 years/85 kg; volunteer 2: 29 years/57 kg; volunteer 3: 28 years/80 kg) was scanned using an 8-channel extremity coil without and with the VMG and with different additional weight placed on the scanner table (0/10/20 kg). By changing the loading of the scanner table, the mechanical vibrations were altered and the influence of the vibrations on the DW measurement could be investigated. Each scan was repeated three times to access the reproducibility of the ADC measurement. The DW MRS voxel was placed approximately 1 cm below the growth plate in the tibia bone marrow and was performed with the same parameters as the phantom scans (including the same diffusion directions and b-values). Afterwards, the lipid ADC was extracted for each loading without and with the VMG.

[0097] FIG. 11 shows the mean obtained ADC value in the tibia bone marrow with corresponding standard deviation of the three repeated measurements with different loading of the scanner table. Without the VMG, a dependency of the measured ADC value on the additional loading of the scanner table is observed and a larger standard deviation of the lipid ADC estimation is observed. The ADC value combined from the different measurement is comparable with and without VMG. However, the coefficient of variation is reduced by 34.9% (volunteer 1), 18.9% (volunteer 2) and 24.0% (volunteer 3) in the three volunteers, comparing the measurement without the VMG to the measurement with the VMG.

[0098] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0099] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. Ordinal numbers, like e.g. ‘first’ and ‘second’, may be used herein to indicate a relative temporal ordering, but not to indicate any absolute temporal ordering. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

LIST OF REFERENCE NUMERALS

[0100] 100 magnetic resonance system [0101] 104 magnet [0102] 106 bore of magnet [0103] 108 data acquisition volume [0104] 109 region of interest [0105] 110 magnetic field gradient coils [0106] 112 magnetic field gradient coil power supply [0107] 114 radio-frequency coil [0108] 116 transceiver [0109] 118 subject [0110] 119 sample [0111] 120 subject support [0112] 126 computer system [0113] 128 hardware interface [0114] 130 processor [0115] 132 user interface [0116] 134 computer memory [0117] 140 machine executable instructions [0118] 142 waveform and pulse sequence commands [0119] 144 magnetic resonance imaging data [0120] 146 magnetic resonance images [0121] 152 waveform and pulse sequence commands [0122] 154 magnetic resonance imaging/spectroscopy data [0123] 156 magnetic resonance image/spectrum [0124] 200 vibration matching gradient [0125] 201 pulse sequence [0126] 203 pulse sequence [0127] 202 spin manipulating gradient [0128] 204 spin manipulating gradient [0129] 206 radio frequency pulse [0130] 208 radio frequency pulse [0131] 210 first vibrations [0132] 211 first state of vibration [0133] 212 second vibrations [0134] 213 second state of vibration [0135] 300 2D imaging slice [0136] 302 indicated region [0137] 304 indicated region [0138] 600 generate a vibration matching gradient [0139] 602 acquire magnetic resonance data using at least two spin manipulating gradients