DE102017107590A1 - System for generating a magnetic resonance image - Google Patents

Abstract

The invention relates to a system 1 for generating a magnetic resonance image of an object 6, in particular a human head. The system 1 comprises a recording unit 4 for recording magnetic resonance tomograms of the object 6 in a plurality of recording steps, wherein the recording unit 4 is adapted to record magnetic resonance tomograms with different magnetic resonance contrast in a same recording step at different slice positions. The system 1 further comprises an imaging unit 5 for generating a magnetic resonance volume image on the basis of the acquired magnetic resonance tomographic images.

Description

The invention relates to a system, a method and a computer program for generating a magnetic resonance image.

Magnetresonanzschichtbildern aufgenommen werden. Dieses Aufnehmen der Magnetresonanzschichtbilder mit unterschiedlichem Magnetresonanzkontrast in unterschiedlichen Aufnahmevorgängen ist relativ zeitaufwendig.It is known to generate different sets of magnetic resonance tomograms in different imaging processes, which have a different magnetic resonance contrast. For example, in a first acquisition procedure, a set of diffusion-weighted magnetic resonance tomographic images and in a second acquisition process a set of ${\text{<figure-callout id="2" label="T" filenames="DE102017107590A1\_0012.png" state="{{state}}">T</figure-callout>}}_2^{*}-\text{Weighted}$

Magnetic resonance images are recorded. This acquisition of the magnetic resonance tomograms with different magnetic resonance contrast in different acquisition processes is relatively time-consuming.

It is therefore an object of the present invention to provide a system, a method and a computer program for generating a magnetic resonance image of an object, which allow a faster acquisition of magnetic resonance tomograms with different magnetic resonance contrast.

• - eine Aufnahmeeinheit zum Aufnehmen von Magnetresonanzschichtbildern des Objekts in mehreren Aufnahmeschritten, wobei die Aufnahmeeinheit angepasst ist, in jedem Aufnahmeschritt an unterschiedlichen Schichtpositionen Magnetresonanzschichtbilder mit unterschiedlichem Magnetresonanzkontrast aufzunehmen, und
• - eine Bilderzeugungseinheit zum Erzeugen eines Magnetresonanzvolumenbildes auf Basis der aufgenommenen Magnetresonanzschichtbilder.

The object is achieved by a system for generating a magnetic resonance image of an object, the system comprising:

• a recording unit for recording magnetic resonance tomograms of the object in a plurality of recording steps, the recording unit being adapted to record magnetic resonance tomograms with different magnetic resonance contrast in each imaging step at different slice positions, and
• an image generation unit for generating a magnetic resonance volume image on the basis of the acquired magnetic resonance layer images.

Since layers with different magnetic resonance contrast are recorded at the different slice positions in a same acquisition step, ie, for example, not all of the first magnetic resonance contrast images and then all the second magnetic resonance contrast layers are captured, the acquisition time can be reduced. It is possible to acquire magnetic resonance tomograms with different magnetic resonance contrast in a recording operation or in a measurement that has the multiple recording steps. In each acquisition step, magnetic resonance tomograms having different magnetic resonance contrast are recorded at different slice positions, the magnetic resonance tomograms being arranged at different slice positions, based on a same magnetic resonance contrast in different acquisition steps.

ein Diffusions-Wichtungskontrast et cetera.In magnetic resonance imaging, different magnetic resonance contrasts result from a manipulation, that is, modification, of different sequence parameters, such as, for example, a manipulation of the temporal and / or spatial sequence of gradient circuits and excitation pulses. The resulting different magnetic resonance sequences can then be used to produce, for example, differently high, measured signal strengths or gray values in a magnetic resonance image for a same material. By way of example, a same liquid or a same tissue in different magnetic resonance tomograms with different magnetic resonance contrast, that is to say in magnetic resonance tomograms which have been recorded with different magnetic resonance sequences, can have different gray values. The system for generating the magnetic resonance images can be used, for example, to achieve a desired magnetic resonance contrast by measuring a low magnetic resonance signal from water and a strong magnetic resonance signal from fat. In the magnetic resonance images, areas of water may appear dark and areas of fat may appear bright. By contrast, another magnetic resonance contrast can be the other way round. Due to the many degrees of freedom of the recording unit countless different magnetic resonance contrasts are possible, for example, a T ₁ - weighting contrast, a ${\text{<figure-callout id="2" label="T" filenames="DE102017107590A1\_0012.png" state="{{state}}">T</figure-callout>}}_2^{*}-\text{Weighting contrast}\text{.}$

a diffusion weighting contrast et cetera.

Preferably, the recording unit is adapted so that the magnetic resonance tomograms with the different magnetic resonance contrast are recorded simultaneously in a recording step at the different slice positions. By simultaneously recording the magnetic resonance tomograms with different magnetic resonance contrast at different slice positions, the acquisition time for the acquisition of all magnetic resonance tomograms having a different magnetic resonance contrast can be further reduced.

It is further preferred that the recording unit comprises a) gradient coils for generating gradient magnetic fields, b) an excitation coil for magnetic resonance excitation of the object, c) receiver coils for receiving magnetic resonance signals from the magnetic resonance excitation object, d) a control unit for Controlling the coils; and e) a magnetic resonance tomographic image generating unit for generating the magnetic resonance tomograms based on the received magnetic resonance signals, wherein the control unit is adapted to control the excitation coil and the gradient coils such that magnetic resonance excitations with different magnetic resonance contrast occur in a recording step at different slice positions Reception coils are to be controlled in such a way that magnetic resonance signals are received by the different slice positions, and wherein the magnetic resonance tomographic image generating unit is adapted to generate the magnetic resonance tomograms with different magnetic resonance contrast at the different slice positions on the basis of the magnetic resonance signals received in a recording step. In one embodiment, the magnetic resonance tomograms with the different magnetic resonance contrast are recorded simultaneously in a recording step at the different slice positions and the receiver coils have spatially dependent coil sensitivities, wherein the magnetic resonance tomograph generating unit is adapted, at the different slice positions the magnetic resonance tomograms with different magnetic resonance contrast based on the spatially dependent Coil sensitivities and the magnetic resonance signals simultaneously received in one acquisition step. Since magnetic resonance signals are received simultaneously by the layers of the object stimulated with different magnetic resonance contrast, the magnetic resonance signals received by the different layers can not be distinguished on the basis of different reception times. Instead, this distinction is preferably made taking into account the spatially dependent coil sensitivities of the receiving coils.

Magnetresonanzschichtbilder aufzunehmen. Die Kombination dieser beiden Magnetresonanzkontraste ist insbesondere vorteilhaft bei einer Schlaganfalldiagnose.The recording unit is preferably adapted, diffusion-weighted magnetic resonance tomograms and ${\text{<figure-callout id="2" label="T" filenames="DE102017107590A1\_0012.png" state="{{state}}">T</figure-callout>}}_2^{*}-\text{weighted}$

Record magnetic resonance images. The combination of these two magnetic resonance contrasts is particularly advantageous in a stroke diagnosis.

The acquisition unit may be adapted to receive magnetic resonance tomograms with two different magnetic resonance contrast. However, the acquisition unit can also be adapted to record more than two magnetic resonance tomograms with more than two different magnetic resonance contrasts. It is preferred that the image generation unit is adapted to generate a respective magnetic resonance volume image for the respective magnetic resonance contrast on the basis of the magnetic resonance tomograms recorded with the respective magnetic resonance contrast. Therefore, different sets of magnetic resonance tomograms having different magnetic resonance contrast, that is, corresponding different magnetic resonance volume images having different magnetic resonance contrast, may be taken in a photographing operation having a plurality of recording steps, whereby, as explained above, the recording time can be significantly reduced.

The image generation unit may be adapted to generate a corrected magnetic resonance image for a magnetic resonance contrast on the basis of the magnetic resonance contrast recorded magnetic resonance tomograms, wherein the acquisition unit and / or the image generation unit are adapted to perform a correction by means of the magnetic resonance tomograms recorded with a different magnetic resonance contrast. The acquisition unit and / or the image generation unit may in particular be adapted to perform a movement correction and / or a phase correction. That is, in a recording process, first magnetic resonance tomograms having a first magnetic resonance contrast and second magnetic resonance tomograms having a second magnetic resonance contrast can be recorded, wherein the first magnetic resonance tomograms can be used to correct the second magnetic resonance tomograms. This correction can take place during the acquisition of the second magnetic resonance tomograms and / or after the acquisition of the two magnetic resonance tomograms. The correction can improve the quality of a finally reconstructed magnetic resonance volume image. If the first magnetic resonance slice images are used only for the correction, the image generation unit could generate only a magnetic resonance volume image based on the acquired and corrected second magnetic resonance slice images.

The expression "A and / or B" preferably comprises the following options: a) A without B, b) B without A and c) A and B. If, for example, it is defined that "the recording unit and / or the image-forming unit can be adapted ", This expression preferably includes the following options: a) the acquisition unit may be adapted, but not the image generation unit, b) the image generation unit may be adapted, but not the acquisition unit, and c) the image generation unit and the acquisition unit may be adapted.

In principle, the image generation unit may be adapted, at least on the basis of a set of magnetic resonance tomograms having a same magnetic resonance contrast, to generate a corresponding magnetic resonance volume image. The image forming unit is preferred adapted to combine the magnetic resonance tomograms of a same magnetic resonance contrast to produce a corresponding magnetic resonance volume image.

• - Aufnehmen von Magnetresonanzschichtbildern des Objekts in mehreren Aufnahmeschritten mittels einer Aufnahmeeinheit, wobei in einem selben Aufnahmeschritt an unterschiedlichen Schichtpositionen Magnetresonanzschichtbilder mit unterschiedlichem Magnetresonanzkontrast aufgenommen werden, und
• - Erzeugen eines Magnetresonanzvolumenbildes auf Basis der aufgenommenen Magnetresonanzschichtbilder mittels einer Bilderzeugungseinheit.

The invention also relates to a method for generating a magnetic resonance image of an object, the method comprising:

• - Recording magnetic resonance tomograms of the object in a plurality of recording steps by means of a recording unit, wherein in a same recording step at different layer positions magnetic resonance tomograms are recorded with different magnetic resonance contrast, and
• Generating a magnetic resonance volume image on the basis of the recorded magnetic resonance tomographic images by means of an imaging unit.

The invention also relates to a computer program for generating a magnetic resonance image of an object, the computer program having program code means adapted to control a system for generating a magnetic resonance image of an object according to claim 1 such that the method for generating a magnetic resonance image of an object according to Claim 11 is performed when the computer program is executed on a controller that controls the system.

It should be understood that the system of claim 1, the method of claim 11 and the computer program of claim 12 have similar and / or identical preferred embodiments as defined in particular in the dependent claims.

• 1 eine Ausführungsform eines Systems zum Erzeugen eines Magnetresonanzbildes eines Objekts schematisch und beispielhaft darstellt,
• 2 Empfangsspulen zum Empfangen von Magnetresonanzsignalen von dem Kopf eines Patienten schematisch und beispielhaft darstellt,
• 3 ein Erzeugen separater Magnetresonanzschichtbilder mit unterschiedlichem Magnetresonanzkontrast illustriert,
• 4 ein Flussdiagramm zeigt, dass Ausführungsform ein Verfahren zum Erzeugen eines Magnetresonanzbildes eines Objekts beispielhaft darstellt, und
• 5 ein beispielhaftes Pulssequenzdiagramm zeigt.

Embodiments of the invention will be described below with reference to the following figures, wherein

• 1 schematically and by way of example represents an embodiment of a system for generating a magnetic resonance image of an object,
• 2 Shows receiving coils for receiving magnetic resonance signals from the head of a patient schematically and by way of example,
• 3 illustrating generation of separate magnetic resonance tomograms with different magnetic resonance contrast,
• 4 a flowchart shows that embodiment exemplifies a method for generating a magnetic resonance image of an object, and
• 5 an exemplary pulse sequence diagram shows.

An embodiment of a system for generating a magnetic resonance image of an object is schematic and exemplary in FIG 1 shown. The system 1 includes a known coil system 9 with gradient coils 12 for generating gradient magnetic fields, with an excitation coil 13 for magnetic resonance excitation of a patient 3 on a patient table 2 and receiving coils for receiving magnetic resonance signals from the magnetic resonance-excited patient. The receiver coils are for clarity in 1 not shown. They will be discussed below with particular reference to 2 explained in more detail. The system 1 further comprises a control unit 7 for controlling the coils, that is the coil system 9 , and a magnetic resonance film formation unit 8th for generating magnetic resonance tomograms based on the received magnetic resonance signals.

The control unit 7 is adapted to control the excitation coil and the gradient coils such that magnetic resonance excitations of layers of the patient 3 with different magnetic resonance contrast, and to control the receiving coils so that received from the layers of the patient magnetic resonance signals. The magnetic resonance tomographic imaging unit 8th is adapted to generate the magnetic resonance tomograms with different magnetic resonance contrast based on the received magnetic resonance signals. The coil system 9 , the control unit 7 and the magnetic resonance tomographic imaging unit 8th can therefore as components of a recording unit 4 for taking magnetic resonance images of the patient 3 be understood.

The recording unit 4 is adapted to record the magnetic resonance tomograms with different magnetic resonance contrast during a recording process, wherein the recording process has a plurality of recording steps and magnetic resonance tomograms with different magnetic resonance contrast are recorded in a same recording step at different slice positions. In this embodiment, the receiving unit 4 adapted to simultaneously record the magnetic resonance tomograms with the different magnetic resonance contrast at different slice positions.

Magnetresonanzschichtbilder zum Erzeugen eines ${\text{T}}_2^{\ast }-\text{gewichteten}$

Magnetresonanzvolumenbildes verwendet werden.The system 1 further comprises an image forming unit 5 for generating a magnetic resonance volume image on the basis of recorded magnetic resonance layer images. In this embodiment, the image forming unit is 5 adapted to generate a respective magnetic resonance volume image on the basis of the recorded with the respective magnetic resonance contrast magnetic resonance layer images for a respective magnetic resonance contrast. For example, diffusion-weighted magnetic resonance tomograms can be used to generate a diffusion-weighted magnetic resonance volume image and ${\text{<figure-callout id="2" label="T" filenames="DE102017107590A1\_0012.png" state="{{state}}">T</figure-callout>}}_2^{*}-\text{weighted}$

Magnetic resonance images for generating a ${\text{<figure-callout id="2" label="T" filenames="DE102017107590A1\_0012.png" state="{{state}}">T</figure-callout>}}_2^{*}-\text{Weighted}$

Magnetic resonance volume image can be used.

The receiver coils of the coil system 9 For example, they can be used to scan magnetic resonance images of the head 6 of the patient 3 to create. This is schematic and exemplary in 2 shown.

In 2 are the receiving coils 20 around the head 6 arranged by the patient. A first shift 21 was excited with a first magnetic resonance contrast and a second layer 22 was excited with a second magnetic resonance contrast, wherein in this embodiment, the magnetic resonance signals resulting from the excitation of the layers 21 . 22 at the same time from the receiver coils 20 be received.

Magnetresonanzkontrast und der zweite Magnetresonanzkontrast ein diffusionsgewichteter Magnetresonanzkontrast ist. Es ist allerdings das Ziel, für die erste Schicht 21 ein erstes Magnetresonanzschichtbild mit dem ersten Magnetresonanzkontrast und für die zweite Schicht 22 ein zweites Magnetresonanzschichtbild mit dem zweiten Magnetresonanzkontrast zu erzeugen. In 3 sind diese gewünschten Magnetresonanzschichtbilder mit dem Bezugszeichen 31 und 32 versehen. Die Magnetresonanzschichtbilder-Erzeugungseinheit 8 ist daher angepasst, auf Basis von räumlich abhängigen Spulensensitivitäten der Empfangsspulen 20 und der gleichzeitig von den Schichten 21, 22 empfangenen Magnetresonanzsignale die unterschiedlichen Magnetresonanzschichtbilder 31, 32 an den unterschiedlichen Schichtpositionen 21, 22 zu erzeugen.On the basis of the received magnetic resonance signals, the magnetic resonance tomographic image generating unit 8th a combined magnetic resonance layer image 30 generate that in 3 is shown schematically and exemplified and that the first layer 21 with the first magnetic resonance contrast as well as the second layer 22 with the second magnetic resonance contrast, in this example the first magnetic resonance contrast ${\text{T}}_{}^{}$${}_2^{*}-\text{weighted}$

Magnetic resonance contrast and the second magnetic resonance contrast is a diffusion-weighted magnetic resonance contrast. However, it is the goal for the first shift 21 a first magnetic resonance layer image with the first magnetic resonance contrast and for the second layer 22 to generate a second magnetic resonance tomographic image with the second magnetic resonance contrast. In 3 These are the desired magnetic resonance tomograms with the reference numeral 31 and 32 Mistake. The magnetic resonance tomographic imaging unit 8th is therefore adapted on the basis of spatially dependent coil sensitivities of the receiving coils 20 and at the same time of the layers 21 . 22 received magnetic resonance signals, the different magnetic resonance layer images 31 . 32 at the different layer positions 21 . 22 to create.

In 2 are the individual receiver coils 20 for receiving the magnetic resonance signal. Each individual receiver coil 20 , here exemplarily six pieces, receives signal from, here two, excited layers 21 . 22 , A receiver coil is more sensitive in regions where it is closer to space. The picture of a single receiver coil 20 Thus, a higher signal is received from areas that are close to the element than from areas that are further away. The receiver coils 20 therefore have a "spatially dependent sensitivity" on. Different receiver coils 20 measure different signal intensities at the same X, Y position 24, 25 and at different Z positions. Here, the X, Y directions are perpendicular to the longitudinal axis of the patient or to the longitudinal axis of the coil system, that is the magnetic resonance system, and the Z direction parallel to the longitudinal axis of the patient or to the longitudinal axis of the coil system. The distance between two different Z positions is in 2 with the double arrow 26 characterized. For the simultaneous recording of several excited layers, this means that the individual receiving coils 20 have recorded different signal intensities from the object points that appear "collapsed" in the simultaneously captured image. In 3 is based on the picture 30 represented the "collapsed" signal of the two simultaneously recorded layers with different magnetic resonance contrast. The simultaneously recorded images / layers can then be due to the spatially different sensitivities of the individual receiving coils 20 be separated by various known algorithmic methods, so that both layers their respective signal can be assigned. A well-known algorithmic method is, for example, in the article "Use of Multicoil Arrays for Separation of Signal from Multiple Slices Simultaneously Excited" of DJ Larkman et al., Journal of Magnetic Resonance Imaging, Vol. 13, pp. 313-31 (2001) disclosed herein by this reference. Another known algorithmic method is the so-called slice GRAPPA method, which is described, for example, in the article "Blipped-Controlled Aliasing in Parallel Imaging for Simultaneous Multislice Echo Planar Imaging With Reduced G-Factor Penalty" K. Setsompop et al., Magnetic Resonance in Medicine, Vol. 67, pp. 1210-1224 (2012). which is also incorporated herein by reference. In this method, so-called reference data of the layers which are to be separated are recorded with a low resolution, which represent the spatially different sensitivities of the receiving coils. The reference layers are used to calculate so-called "kernels" or "weights", which in turn are used to separate the "collapsed" signal of the two layers. Appropriate separate layers are in the pictures 31 . 32 shown with different magnetic resonance contrast.

The recording unit 4 and / or the image forming unit 5 may be adapted to generate a corrected magnetic resonance image based on the magnetic resonance contrast recorded magnetic resonance tomographic images for a magnetic resonance contrast, wherein a correction can be performed by means of the magnetic resonance tomograms recorded with a different magnetic resonance contrast. This correction can be, for example, a movement correction and / or a phase correction.

For example, magnetic resonance tomograms of a magnetic resonance contrast or multiple magnetic resonance contrasts can be used as so-called navigator data for correction methods, such as motion correction or phase correction. Motion correction is exemplified in the article "Volumetry Navigators for Prospective Motion Correction and Selective Reacquisition in Neuroanatomical MRI" by MD Tisdall et al., Magnetic Resonance in Medicine, vol. 68, pp. 389-399 (2012) disclosed by this reference in this specification. A phase correction is exemplary in the article "Nonlinear Phase Correction for Navigated Diffusion Imaging, Magnetic Resonance in Medicine, 2003, pp. 343-353 described, which is also incorporated by reference in this description.

Magnetresonanzkontrast sein und der zweite Magnetresonanzkontrast kann ein diffusionsgewichteter Magnetresonanzkontrast mit variablen Diffusionskodierrichtungen sein. Zu Beginn der Messung kann ein Referenz-Magnetresonanzvolumen oder ein Teilsatz von Referenz-Magnetresonanzschichten mit dem ersten Magnetresonanzkontrast akquiriert werden. Diese Referenzdaten können während der Messung mit aktuell aufgenommen ersten Magnetresonanzschichtbilder verglichen werden, um während der Messung Bewegungsinformationen zu bestimmen. Diese bestimmten Bewegungsinformationen können dann während der Messung dazu verwendet werden, Aufnahmeparameter, die auch als Scanparameter bezeichnet werden könnten, für die Aufnahme der zweiten Magnetresonanzschichtbilder so zu verändern, dass Bewegungsartefakte in den zweiten Magnetresonanzschichtbildern reduziert werden. Es kann demnach eine Echtzeitbewegungskompensation während der Aufnahme der zweiten Magnetresonanzschichtdaten erfolgen. Die Adaption der Aufnahmeparameter bzw. der Scanparameter in Abhängigkeit von einer bestimmen Bewegung kann beispielsweise so durchgeführt werden, wie es in dem Artikel „Prospective acquisition correction for head motion with image-based tracking for realtime fMRI“ von S. Thesen et al., Magentifc Resonance in Medicine, Band 44, Seiten 457 bis 465 (2000) offenbart ist, wobei diese hiermit in die Beschreibung aufgenommen worden ist.In one embodiment, first magnetic resonance tomograms having a first magnetic resonance contrast and second magnetic resonance tomograms having a second magnetic resonance contrast are acquired in a plurality of acquisition steps, wherein the first magnetic resonance contrast in each acquisition step is the same and the second magnetic resonance contrast can vary from acquisition step to acquisition step. The first magnetic resonance contrast may be, for example ${\text{T}}_{}^{}$${}_2^{*}-\text{weighted}$

Magnetic resonance contrast and the second magnetic resonance contrast may be a diffusion-weighted magnetic resonance contrast with variable diffusion encoding directions. At the beginning of the measurement, a reference magnetic resonance volume or a subset of reference magnetic resonance layers with the first magnetic resonance contrast can be acquired. These reference data can be compared during the measurement with currently recorded first magnetic resonance slice images in order to determine motion information during the measurement. This particular motion information may then be used during the measurement to modify acquisition parameters, which could also be referred to as scan parameters, for acquisition of the second magnetic resonance slices so as to reduce motion artifacts in the second magnetic resonance slices. Accordingly, a real-time motion compensation during the recording of the second magnetic resonance layer data can take place. The adaptation of the acquisition parameters or the scan parameters as a function of a certain movement can be carried out, for example, as described in the article "Prospective acquisition correction for head motion with image-based tracking for realtime fMRI" by S. Thesen et al., Magentifc Resonance in Medicine, Vol. 44, pages 457 to 465 (2000). is disclosed, which has been incorporated herein by reference.

In a further embodiment, first magnetic resonance tomograms may be acquired at a relatively high temporal resolution to detect phase and frequency errors that may result from dynamic changes in the magnetic field, for example due to respiration. These data can then be used to correct second magnetic resonance tomograms with a second magnetic resonance contrast. For the actual correction, known methods can be used. For example, in the article "Correction of physiologically induced global off-resonance effects in dynamic echo-planar and spiral functional imaging" of J. Pfeuffer, Magnetic Resonance in Medicine, Vol. 47, pp. 344-353 (2002) disclosed methods which has been incorporated herein.

The system further includes an input unit 10 such as a keyboard, a computer mouse, a touchpad, etc., and a display 11 to show the generated magnetic resonance volume images. The generated magnetic resonance tomograms can also be displayed 11 to be shown.

The following is an embodiment of a method for generating a magnetic resonance image of the patient 3 described with the help of a flowchart which is in 4 is shown.

Magnetresonanzkontrast und ein zweites Magnetresonanzschichtbild einen diffusionsgewichteten Magnetresonanzkontrast auf. Bevorzugt werden die zwei Magnetresonanzschichtbilder gleichzeitig aufgenommen. Der Schritt 101 kann als ein Aufnahmeschritt aufgefasst werden.In step 101 Two magnetic resonance tomograms are taken at different slice positions of the patient 3 recorded, wherein these magnetic resonance layer images have a different magnetic resonance contrast. For example, a first magnetic resonance layer image has a ${\text{<figure-callout id="2" label="T" filenames="DE102017107590A1\_0012.png" state="{{state}}">T</figure-callout>}}_2^{*}-\text{Weighted}$

Magnetic resonance contrast and a second magnetic resonance layer image on a diffusion-weighted magnetic resonance contrast. The two magnetic resonance layer images are preferred recorded simultaneously. The step 101 can be considered as a pickup step.

In step 102 it is decided whether a next recording step should be performed. In a next acquisition step, two magnetic resonance tomograms with different magnetic resonance contrast would again be recorded, this time based on the respective magnetic resonance contrast the magnetic resonance tomogram would be recorded at a different slice position. The number of slice positions at which the magnetic resonance tomograms are to be recorded is preferably defined by a predetermined thickness of the magnetic resonance tomograms to be recorded and by the length of the magnetic resonance volume image to be finally generated in the slice thickness direction. In the step 102 it is preferably checked whether a magnetic resonance tomographic image with a first magnetic resonance contrast and a magnetic resonance tomographic image with a second magnetic resonance contrast has been generated for each of these layer positions. If this is not the case, two further magnetic resonance tomograms with different magnetic resonance contrast are recorded at slice positions in a further recording step, for which no magnetic resonance tomogram has yet been recorded with the respective magnetic resonance contrast.

That is, the steps 101 and 102 may be performed in a loop until a respective magnetic resonance tomographic image has been acquired for each slice position and for each magnetic resonance contrast. When magnetic resonance tomograms of both magnetic resonance contrasts have been recorded for each slice position, in step 103 generates at least one magnetic resonance volume image on the basis of the acquired magnetic resonance tomograms. Preferably, a first magnetic resonance volume image is generated on the basis of the magnetic resonance tomograms having a first magnetic resonance contrast, and a second magnetic resonance volume image is generated on the basis of the magnetic resonance tomograms having a second magnetic resonance contrast. In step 104 The generated magnetic resonance volume images are displayed 11 shown.

It is known to generate magnetic resonance volume images of a same patient with different magnetic resonance contrast in independent acquisition procedures. That is, normally, first a first magnetic resonance volume is generated with a first magnetic resonance contrast, after which a second magnetic resonance volume is generated with a second magnetic resonance contrast. The acquisition time for a single magnetic resonance volume of a single magnetic resonance contrast could be reduced by using so-called "simultaneous multi-slice" (SMS) imaging, in which nuclear spins are excited at different slice positions and the resulting magnetic resonance signal is received by receive coils. For example, the SMS imaging is in the article "Simultaneous Multislice Acquisition of MR Images" by JB Weaver, Magnetic Resonance in Medicine, Volume 8, pages 275 to 284 (1988) , which has been incorporated by reference into this specification. On the basis of the received magnetic resonance signals, layer-specific signals can be generated by using spatially-dependent coil sensitivities of the receiving coils. This determination of layer-specific signals is for example in the article "Use of Multicoil Arrays for Separation of Signal from Multiple Slices Simultaneously Excited" by DJ Larkman et al., Journal of Magnetic Resonance Imaging, Volume 13, pages 313 to 317 (2001). which has also been incorporated herein by this reference. In order to improve this signal separation, a layer-specific phase development during the data acquisition can be generated in order to shift the resulting magnetic resonance layer images differently in a phase coding direction. This phase evolution can be generated either by modulating the phase of high frequency excitation pulses or by using a magnetic field gradient in a slice selection direction. The modeling of the phase of the high-frequency excitation pulse is, for example, in the article "Controlled Aliasing in Parallel Imaging Results in Higher Acceleration (CAIPIRINHA) for Multi-Slice Imaging" by FA Breuer et al., Magnetic Resonance in Medicine, Vol. 53, pages 684 to 691 (2005). which is also incorporated into this specification by this reference. The use of the magnetic field gradient in the slice-selecting direction is, for example, in the article "Blipped-Controlled Aliasing in Parallel Imaging for Simultaneous Multislice Echo Planar Imaging With Reduced G-Factor Penalty", by K. Setsompop et al., Magnetic Resonance in Medicine, Volume 67, pages 1210 to 1224 (2012). which is also incorporated herein by this reference. Since SMS imaging captures magnetic resonance signals from different layers simultaneously, the number of layer excitations is reduced. This in turn makes it possible to reduce the repetition time (TR) for a given number of layers, which can reduce the total acquisition time. For this reason, the technique is only effective for acquisition protocols with large TR values that can be reduced without significant impact on image contrast or signal-to-noise ratio. However, many clinical recording protocols use TR values that can not be downsized without degrading image quality.

The above with reference to the 1 to 4 The described system and method for generating a magnetic resonance image of an object, such as a patient, is based on a different approach to reduce the total acquisition time of magnetic resonance examinations. The technique described may use techniques known from SMS imaging to simultaneously receive magnetic resonance signals from different layers. However, SMS imaging captures multiple magnetic resonance slices with a same contrast, whereas those discussed above with reference to FIGS 1 to 4 described system and method receives a plurality of magnetic resonance tomograms with different magnetic resonance contrast. This leads to a reduced total acquisition time for the desired magnetic resonance volumes with different magnetic resonance contrast. For example, two magnetic resonance measurements for the generation of two magnetic resonance volumes with two different magnetic resonance contrast can be combined into a single magnetic resonance measurement, so that the total acquisition time or the overall examination time can be reduced since fewer individual magnetic resonance measurements are required. The above with reference to the 1 to 4 In contrast to SMS imaging, the technique described does not result in a reduction of the repetition time (TR), so that there are not the same losses in image contrast and signal-to-noise ratio. Compared to the SMS technique, magnetic resonance volume images with different magnetic resonance contrast are generated by means of a modified combination of slice excitation and sequence timing that has less effect on signal-to-noise ratio and image contrast.

Magnetresonanzkontrast in einer selben Magnetresonanzmessung zu erzeugen. Diese beiden Magnetresonanzkontraste können insbesondere nützlich sein, um einen akuten Schlaganfall klinisch zu untersuchen, wobei die neue Technik zu sehr schnellen Diagnosen führen kann, was im Falle eines Schlaganfalls dringend benötigt werden. Die US-Patentanmeldung 2013/0033262 A1 und der Artikel „Diffusion-Weighted, Readout-Segmented EPI with Synthesized T2- and T2*-Weighted Images“ von D. A. Porter, Proceedings of the 22^nd Annual Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM), Montreal, Canada, 2014:798 offenbaren andere Techniken, Magnetresonanzvolumenbilder mit unterschiedlichem Magnetresonanzkontrast aufzunehmen. Diese anderen Techniken sind weniger effizient und ermöglichen nicht die flexible Kontrolle des Bildkontrastes, die durch das oben beschriebene System und das oben beschriebene Verfahren ermöglicht wird. Das rs-EPI-Verfahren ist beispielhaft in dem soeben genannten Artikel von D. A. Porter offenbart, wobei dieser Artikel durch diese Referenz ebenfalls in diese Beschreibung aufgenommen worden ist.In one embodiment, read-out segmented echo planar imaging (EPI), rs-EPI, is used to generate magnetic resonance tomograms and, finally, magnetic resonance volume images with diffusion-weighted MRI ${\text{T}}_{}^{}$${}_2^{*}-\text{weighted}$

To produce magnetic resonance contrast in a same magnetic resonance measurement. These two magnetic resonance contrasts may be particularly useful for clinically evaluating an acute stroke, and the new technique may lead to very rapid diagnoses, which are urgently needed in the event of a stroke. The US Patent Application 2013/0033262 A1 and the article "Diffusion-Weighted, Readout-Segmented EPI with Synthesized T2 and T2 * Whiteed Images" by DA Porter, Proceedings of the 22 ^nd Annual Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM), Montreal, Canada, 2014: 798 disclose other techniques for acquiring magnetic resonance volume images with different magnetic resonance contrast. These other techniques are less efficient and do not allow the flexible control of the image contrast enabled by the system and method described above. The rs-EPI process is exemplified in the just-mentioned article by DA Porter, which article has also been incorporated into this specification by this reference.

und diffusionsgewichtetem Magnetresonanzkontrast mit rs-EPI Auslese und zusätzlicher 2D-Navigatorkorrektur. In dieser Sequenz erfolgt zunächst ein Anregungspuls der Schicht, die später diffusionsgewichteten Magnetresonanzkontrast aufweisen wird (Bezugszeichen 51). Anschließend erfolgt eine Re-Fokussierung des Signals dieser Schicht mit einem 180° Radiofrequenz (RF) - Pulses (Bezugszeichen 52). Danach wird die zweite Schicht mit einem RF-Puls angeregt, welche später einen T2*-Kontrast aufweisen wird (Bezugszeichen 53). Ein weiterer Re-Fokussierungspuls für die erste Schicht erfolgt für die Aufnahme der Navigatordaten (Bezugszeichen 54). In der zweiten Zeile des Sequenzdiagrammes sind die beiden Diffusionsgradienten abgebildet, die für die Diffusionsgewichtung in der ersten Schicht verantwortlich sind (Bezugszeichen 55). In der dritten Zeile sind die Gradienten eingezeichnet, die darüber entscheiden, welche Schicht des Objektes/Patienten zu welchem Zeitpunkt mit den RF-Pulsen angeregt wird (Bezugszeichen 56). Während der Signalaufnahme/Auslese erhält in diesem Ausführungsbeispiel die T2*-gewichtete Schicht eine Phasenverschiebung durch entsprechend geschaltete Gradienten in Schichtrichtung, die zu einer Verschiebung des Objektes im Bildraum führt (Bezugszeichen 57). In der vierten Zeile ist der zeitliche Verlauf der Auslesegradienten dargestellt. Da es sich um eine segementierte Auslese handelt, ist die Amplitude der sogenannten Pre-Phasierung variabel (Bezugszeichen 58). Die Amplitude variiert, damit unterschiedliche Segmente ausgelesen werden. Die Auslese selbst erfolgt mit einer sinusodialen Trajektorie (Bezugszeichen 59). Die fünfte Zeile des Sequenzdiagramms zeigt die Phasenkodierungsgradienten (Bezugszeichen 60). In der sechsten Zeile ist die Phase der Ausleseeinheit (engl. „receiver“) während der Signalaufnahme dargestellt (Bezugszeichen 61). In der letzten Zeile ist der zeitliche Ablauf der Signalaufnahme zu sehen, wobei das erste sogenannte Echo Signal aus der ersten und zweiten Schicht beinhaltet (Bezugszeichen 62) und das zweite Echo das Signal des Navigatorbildes, welches für eine Phasenkorrektur der diffusionsgwichteten Schicht verwendet wird (Bezugszeichen 63). 5 shows an exemplary sequence diagram for the combination of ${\text{<figure-callout id="2" label="T" filenames="DE102017107590A1\_0012.png" state="{{state}}">T</figure-callout>}}_2^{*}-\text{weighted}$

and diffusion-weighted magnetic resonance contrast with rs-EPI readout and additional 2D navigator correction. In this sequence, first an excitation pulse of the layer, which will later have diffusion-weighted magnetic resonance contrast (reference symbol 51 ). Subsequently, the signal of this layer is re-focused with a 180 ° radiofrequency (RF) pulse (reference numeral 52 ). Thereafter, the second layer is excited with an RF pulse, which will later have a T2 * contrast (reference numeral 53 ). Another re-focusing pulse for the first layer takes place for recording the navigator data (reference numerals 54 ). In the second line of the sequence diagram, the two diffusion gradients are shown, which are responsible for the diffusion weighting in the first layer (reference numerals 55 ). In the third line, the gradients are plotted, which decide which layer of the object / patient at which time with the RF pulses is excited (reference numeral 56 ). During the signal recording / readout, the T2 * -weighted layer in this embodiment receives a phase shift by appropriately switched gradients in the slice direction, which leads to a displacement of the object in the image space (reference numeral 57 ). The fourth line shows the time course of the readout gradients. Since it is a segementierte Auslese, the amplitude of the so-called pre-phasing is variable (reference numeral 58 ). The amplitude varies so that different segments are read out. The readout itself is carried out with a sinusoidal trajectory (reference numeral 59 ). The fifth line of the sequence diagram shows the phase encoding gradients (reference numerals 60 ). In the sixth line, the phase of the readout unit ("receiver") during the signal recording is shown (reference numeral 61 ). In the last line, the timing of the signal recording can be seen, wherein the first so-called echo signal from the first and second layer includes (reference numerals 62 ) and the second echo the signal of the Navigatorbildes, which is used for a phase correction of the diffusion-weighted layer (reference numeral 63 ).

Although certain magnetic resonance sequences have been mentioned above, the invention is not limited to particular magnetic resonance sequences. For example, the type of high-frequency excitation pulses used at the different slice positions, and / or the times of the high-frequency excitation pulses, in particular the times between these high-frequency excitation pulses, may be varied to produce a wide range of possible combinations of magnetic resonance contrasts. For example, slice-selective 2D sequences or layer-sensitive 3D magnetic sequences ("slab-selective 3D sequences") can be used to generate magnetic resonance tomograms.

Although two magnetic resonance contrasts have been used in the embodiments described above, more than two magnetic resonance contrasts may also be used.

Although magnetic resonance tomograms with different magnetic resonance contrast are recorded simultaneously in different slice positions in one recording step in the above-described embodiments, in a recording step these magnetic resonance slices can also be recorded one after the other.

Although magnetic resonance images of a patient, in particular a head of the patient, have been generated in embodiments described above, magnetic resonance images of other "objects" can also be generated. For example, magnetic resonance images of other parts of the body, of healthy persons or animals or magnetic resonance images of technical, that is, non-living objects, can be generated.

In the claims, the words "comprising" and "comprising" do not exclude other elements or steps, and the indefinite article "a" does not exclude a plurality.

A single unit or device can perform the functions of several elements listed in the claims. The fact that individual functions and elements are listed in different dependent claims does not mean that a combination of these functions or elements could not be used to advantage.

Procedures, such as the generation of a magnetic resonance tomogram based on received magnetic resonance signals, the generation of a magnetic resonance volume image on the basis of a plurality of magnetic resonance tomograms, the control of the coil system, the control of the overall system 1 in particular, according to the above-described method, etc., which are performed by one or more units, may also be performed by a different number of units. These procedures can also be implemented as program code of a computer program and / or as corresponding hardware.

A computer program may be stored and / or distributed on a suitable medium, such as an optical storage medium or a solid state storage medium, distributed along with or as part of other hardware. The computer program can also be distributed in other forms, for example via the Internet or other telecommunication systems.

The reference signs in the claims are not to be understood as limiting the subject matter and the scope of the claims to these references.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2013/0033262 A1 [0037]

Cited non-patent literature

• D.J. Larkman et al., Journal of Magnetic Resonance Imaging, Vol. 13, pp. 313-31 (2001) [0025]
• K. Setsompop et al., Magnetic Resonance in Medicine, Vol. 67, pp. 1210-1224 (2012). [0025]
• Tisdall, MD, et al., Magnetic Resonance in Medicine, Vol. 68, pp. 389-399 (2012). [0027]
• "Nonlinear Phase Correction for Navigated Diffusion Imaging, Magnetic Resonance in Medicine, 2003, pp. 343-353 [0027]
• S. Thesen et al., Magentifc Resonance in Medicine, Vol. 44, pp. 457-465 (2000) [0028]
• J. Pfeuffer, Magnetic Resonance in Medicine, Vol. 47, pp. 344-353 (2002) [0029]
• "Simultaneous Multislice Acquisition of MR Images" by J.B. Weaver, Magnetic Resonance in Medicine, Vol. 8, pp. 275 to 284 (1988) [0035]
• Larkman et al., Journal of Magnetic Resonance Imaging, Vol. 13, pp. 313-31 (2001)
• "Controlled Aliasing in Parallel Imaging Results in Higher Acceleration (CAIPIRINHA) for Multi-Slice Imaging" by F.A. Breuer et al., Magnetic Resonance in Medicine, Vol. 53, pages 684 to 691 (2005). [0035]
• "Blipped-Controlled Aliasing in Parallel Imaging for Simultaneous Multislice Echo Planar Imaging With Reduced G-Factor Penalty", by K. Setsompop et al., Magnetic Resonance in Medicine, Vol. 67, pp. 1210-1224 (2012) [0035]
• "Diffusion-Weighted, Readout-Segmented EPI with Synthesized T2 and T2 * Whiteed Images" by DA Porter, Proceedings of the 22 ^nd Annual Meeting of the International Society of Magnetic Resonance in Medicine (ISMRM), Montreal, Canada, 2014: 798 [0037]

Claims (12)

A system for generating a magnetic resonance image of an object, the system (1) comprising: a recording unit (4) for recording magnetic resonance tomograms of the object (6) in a plurality of recording steps, the recording unit (4) being adapted to record magnetic resonance tomograms with different magnetic resonance contrast in a same recording step at different slice positions, and - An image generating unit (5) for generating a magnetic resonance volume image based on the recorded magnetic resonance layer images. System after Claim 1 , characterized in that the recording unit (4) is adapted to simultaneously record the magnetic resonance tomograms with the different magnetic resonance contrast in a recording step at the different slice positions. System according to one of the preceding claims, characterized in that the recording unit (4) comprises: - gradient coils for generating gradient magnetic fields, - an excitation coil for magnetic resonance excitation of the object (6), - receiving coils for receiving magnetic resonance signals from the magnetic resonance-excited object (6 ), - a control unit (7) for controlling the coils and - a magnetic resonance tomographic image generating unit (8) for generating the magnetic resonance tomograms based on the received magnetic resonance signals, wherein: - the control unit (7) is adapted to control the excitation coil and the gradient coils in this way in that magnetic resonance excitations with different magnetic resonance contrast take place in a recording step at different slice positions, and the receiving coils are controlled in such a way that magnetic resonance signals are received by the different slice positions, and - the magnetic resonance tomographic image generating unit (8) is adapted It is possible to generate the magnetic resonance tomograms with different magnetic resonance contrast at the different slice positions on the basis of the magnetic resonance signals received in one acquisition step. System after the Claims 2 and 3 , characterized in that the receiving coils have spatially dependent coil sensitivities and that the magnetic resonance tomographic image generating unit (8) is adapted to generate the magnetic resonance tomograms with different magnetic resonance contrast at the different slice positions on the basis of the spatially dependent coil sensitivities and the magnetic resonance signals simultaneously received in a recording step. System according to one of the preceding claims, characterized in that the recording unit (4) is adapted, diffusion-weighted magnetic resonance layer images and ${\text{T}}_2^{*}-\text{weighted}$

Record magnetic resonance images. System according to one of the preceding claims, characterized in that the recording unit (4) is adapted to receive magnetic resonance tomograms with two different magnetic resonance contrast. System according to one of Claims 1 to 5 , characterized in that the recording unit (4) is adapted to receive more than two magnetic resonance tomograms with more than two different magnetic resonance contrast. System according to one of the preceding claims, characterized in that the image-generating unit (5) is adapted to generate a respective magnetic resonance volume image for the respective magnetic resonance contrast on the basis of the magnetic resonance tomograms recorded with the respective magnetic resonance contrast. System according to one of the preceding claims, characterized in that the image generating unit (5) is adapted to generate a corrected magnetic resonance image for a magnetic resonance contrast on the basis of the magnetic resonance contrast recorded magnetic resonance layer images, wherein the recording unit (4) and / or the image generating unit (5) are adapted to perform a correction by means of the recorded with a different magnetic resonance contrast magnetic resonance tomographic images. System after Claim 9 , characterized in that the recording unit (4) and / or the image generating unit (5) are adapted to perform a movement correction and / or a phase correction. Method for generating a magnetic resonance image of an object (6), the method comprising: recording magnetic resonance tomograms of the object (6) in a plurality of imaging steps by means of a recording unit (4), wherein magnetic resonance tomograms with different magnetic resonance contrast are recorded in a same acquisition step at different slice positions, and - Generating a magnetic resonance volume image on the basis of the recorded magnetic resonance tomographic images by means of an imaging unit (5). Computer program for generating a magnetic resonance image of an object, the computer program having program code means adapted to a system (1) for generating a magnetic resonance image of an object according to Claim 1 in such a way that the method for generating a magnetic resonance image of an object according to Claim 11 is performed when the computer program is executed on a controller that controls the system (1).

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