Method and device for determination of a magnetic resonance control sequence

Abstract

In a method and device for the determination of a magnetic resonance control sequence that includes at least one first pulse arrangement that acts in a spatially selective manner in a first selection direction and a subsequent second pulse arrangement that acts in a spatially selective manner in a second selection direction, viewing volume dimension parameter values are registered that define the spatial extent of a viewing volume to be excited. The first selection direction and the second selection direction are established automatically depending on a length ratio of the spatial extent of the viewing volume to be excited in the different selection directions.

Claims

1. A computerized method to determine a magnetic resonance control sequence comprising at least one first pulse arrangement that spatially selectively excites nuclear spins in an examination subject in a first selection direction, and a subsequent second pulse arrangement that spatially selectively excites said nuclear spins in said examination subject in a second selection direction, said method comprising: providing a computerized processor with viewing volume dimension parameter values that define a spatial extent of a viewing volume within the examination subject in which said nuclear spins are to be excited; in said computerized processor, establishing said first selection direction and said second selection direction in said magnetic resonance control sequence automatically depending on a length ratio of a spatial extent of said viewing volume in the respective first selection direction and the second selection direction; and via an output interface of said computerized processor, making the magnetic resonance control sequence, with the established first and second selection directions, available in an electronic format configured to operate a magnetic resonance apparatus to acquire magnetic resonance data according to said magnetic resonance control sequence.

2. A method as claimed in claim 1 comprising, in said processor, generating said first pulse arrangement in said magnetic resonance control sequence as a slab excitation radio-frequency pulse, and generating said second pulse arrangement as a refocusing radio-frequency pulse, with a target flip angle of said slab selection radio-frequency pulse being smaller than a target flip angle of said refocusing radio-frequency pulse.

3. A method as claimed in claim 1 wherein the step of providing said computerized processor with said viewing volume dimension parameter values comprises providing said computerized processor with a first selection direction parameter that defines said first selection direction and a second selection direction parameter that defines said second selection direction, and, in said computerized processor, automatically modifying said first selection direction parameter and said selection direction parameter if said first selection direction defined by said first selection direction parameter and said second selection direction defined by said second selection direction parameter do not satisfy a predetermined condition that is dependent on said length ratio.

4. A method as claimed in claim 3 wherein said viewing volume comprises respectively different spatial extents along different spatial directions of said viewing volume, and wherein said predetermined condition is that said second selection direction coincide with a spatial direction of said viewing volume that has a smallest extent.

5. A method as claimed in claim 4 comprising, in said processor, automatically exchanging the first slice direction defined by said first selection direction parameter and the second selection direction defined by said second selection direction parameter if the second selection direction defined by said second selection direction parameter does not coincide with said spatial direction of said viewing volume having said smallest extent.

6. A method to operate a magnetic resonance apparatus comprising: providing a computerized processor with viewing volume dimension parameter values that define a spatial extent of a viewing volume within the examination subject in which said nuclear spins are to be excited; in said computerized processor, establishing said first selection direction and said second selection direction in said magnetic resonance control sequence automatically depending on a length ratio of a spatial extent of said viewing volume in the respective first selection direction and the second selection direction; and via an output interface of said computerized processor, transferring the magnetic resonance control sequence, with the established first and second selection directions, to a magnetic resonance apparatus, and operating the magnetic resonance apparatus to acquire magnetic resonance data according to said magnetic resonance control sequence.

7. A computerized control sequence determination device to determine a magnetic resonance control sequence comprising at least one first pulse arrangement that spatially selectively excites nuclear spins in an examination subject in a first selection direction, and a subsequent second pulse arrangement that spatially selectively excites said nuclear spins in said examination subject in a second selection direction, said device comprising: an input interface configured to provide said computerized processor with viewing volume dimension parameter values that define a spatial extent of a viewing volume within the examination subject in which said nuclear spins are to be excited; said computerized processor being configured to establish said first selection direction and said second selection direction in said magnetic resonance control sequence automatically depending on a length ratio of a spatial extent of said viewing volume in the respective first selection direction and the second selection direction; and an output interface of said computerized processor configured to make the magnetic resonance control sequence, with the established first and second selection directions, available in an electronic format configured to operate a magnetic resonance apparatus to acquire magnetic resonance data according to said magnetic resonance control sequence.

8. A computerized control sequence determination device as claimed in claim 7: wherein said input interface is configured to provide said computerized processor with a first selection direction parameter that defines said first selection direction and a second selection direction parameter that defines said second selection direction; and said computerized processor comprises a direction parameter modification unit configured to automatically modify said first selection direction parameter and said selection direction parameter if said first selection direction defined by said first selection direction parameter and said second selection direction defined by said second selection direction parameter do not satisfy a predetermined condition that is dependent on said length ratio.

9. A magnetic resonance apparatus comprising: a magnetic resonance data acquisition unit comprising a radio-frequency transmitter, a gradient system, and a control unit; a computerized processor provided with viewing volume dimension parameter values that define a spatial extent of a viewing volume within the examination subject in which said nuclear spins are to be excited; said computerized processor being configured to establish said first selection direction and said second selection direction in said magnetic resonance control sequence automatically depending on a length ratio of a spatial extent of said viewing volume in the respective first selection direction and the second selection direction; said computerized processor comprising an output interface in communication with said control unit, and being configured to transfer the magnetic resonance control sequence, with the established first and second selection directions, in an electronic format to said control unit; and said control unit being configured to operate the radio-frequency transmitter and the gradient system of the magnetic resonance data acquisition unit to acquire magnetic resonance data according to said magnetic resonance control sequence.

10. A non-transitory, computer-readable data storage medium encoded with programming instructions, said storage medium being loaded into a computerized processor, and said programming instructions causing said processor to: generate a magnetic resonance control sequence comprising at least one first pulse arrangement that spatially selectively excites nuclear spins in a first slice selection direction of an examination subject, and a subsequent second pulse arrangement that spatially selectively excites said nuclear spins in said examination subject in a second selection direction; receive volume dimension parameter values that define a spatial extent of a viewing volume within the examination subject in which said nuclear spins are to be excited; establish said first selection direction and said second selection direction in said magnetic resonance control sequence automatically depending on a length ratio of a spatial extent of said viewing volume in the respective first selection direction and the second selection direction; and via an output interface of said computerized processor, make the magnetic resonance control sequence, with the established first and second selection directions, available in an electronic format configured to operate a magnetic resonance apparatus to acquire magnetic resonance data according to said magnetic resonance control sequence.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic depiction of an exemplary embodiment of a magnetic resonance system according to the invention.

(2) FIG. 2 is a schematic depiction of an example of a field of view that can be selected by means of an inner volume refocusing sequence.

(3) FIG. 3 is a schematic depiction to explain the typical selection of a viewing volume given a 3D excitation in an examination subject in a plan view of said examination subject.

(4) FIG. 4 is a schematic depiction of a viewing volume as in FIG. 3, however now in a section view through the examination subject.

(5) FIG. 5 is a sequence diagram for an example of an inner volume refocusing sequence given a typical selection of the selection directions.

(6) FIG. 6 is a flowchart of an exemplary embodiment of the method according to the invention for the determination of a control sequence,

(7) FIG. 7 is a sequence diagram for an example of an inner volume refocusing sequence given a selection of the selection direction that is optimized according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) A magnetic resonance system 1 according to the invention is schematically depicted in FIG. 1. The system includes the actual magnetic resonance scanner 2 with an examination space 8 or patient tunnel 8 therein. A bed 7 can be driven into this patient tunnel 8, such that a patient O or test subject lying on said bed 7 can be supported at a defined position within the magnetic resonance scanner 2 (relative to the magnet system and radio-frequency system arranged therein) during an examination, or so that the patient O or test subject on said bed 7 can also be moved between different positions during a measurement (data acquisition).

(9) Among the components of the magnetic resonance scanner 2 are a basic field magnet 3, a gradient system 4 with magnetic field gradient coils to generate magnetic field gradients in the x-, y- and z-directions, and a whole-body radio-frequency coil 5. The magnetic field gradient coils in the x-, y- and z-direction are controllable independently of one another so thatvia a predetermined combinationgradients can be applied in arbitrary logical spatial directions (for example in a slice selection direction, in a phase encoding direction or in a readout direction) that are not situated in parallel to the axes of the spatial coordinate system. The acquisition of magnetic resonance signals induced in the examination subject O can take place via the whole-body coil 5 with which the radio-frequency signals for induction of the magnetic resonance signals are also normally emitted. However, these signals are typically received with a local coil arrangement 6 with local coils (of which only one is shown here) placed on or below the patient O, for example. All of these components are known in principle to those skilled in the art, and therefore are only roughly schematically depicted in FIG. 1.

(10) The components of the magnetic resonance scanner 2 are controllable from a control device 10. This can be a control computer which can also comprise a plurality of individual computers (which possibly are also spatially separated and connected among one another via suitable cables or the like). This control device 10 is connected via a terminal interface 17 with a terminal 20 via which an operator can control the entire system 1. In the present case, this terminal 20 has a computer 21 with keyboard, one or more monitors and additional input devices (for example mouse or the like), or is designed as such a computer 21, such that a graphical user interface is provided to the operator.

(11) Among other things, the control device 10 has a gradient control unit 11 that can in turn comprise multiple sub-components. The individual gradient coils can be fed with control signals according to a gradient pulse sequence GS via this gradient control unit 11. As described above, these are hereby gradient pulses that are set at precisely provided temporal positions and with a precisely predetermined time curve during a measurement.

(12) Moreover, the control device 10 has a radio-frequency transmission unit 12 in order to feed respective radio-frequency pulses into the whole-body radio-frequency coil 5 according to a predetermined radio-frequency pulse sequence RFS of the control sequence AS. The radio-frequency pulse sequence RFS includes the aforementioned excitation and refocusing pulses. The receipt of the magnetic resonance signals then occurs with the aid of the local coil arrangement 6, and the raw data RD acquired by this are read out and processed by an RF reception unit 13. The magnetic resonance signals in digital form are passed as raw data RD to a reconstruction unit 14, which reconstructs the image data BD from these and stores them in a memory 16 and/or passes them via the interface 17 to the terminal 20 so that the operator can view them. The image data BD can also be stored and/or displayed and evaluated at other locations via a network NW. Alternatively, a radio-frequency pulse sequence can also be emitted via the local coil arrangement and/or the magnetic resonance signals can be received by the whole-body radio-frequency coil (not shown).

(13) Via an additional interface 18, control commands are transmitted to other components of the magnetic resonance scanner 2 (for example the bed 7 or the basic field magnet 3) or measurement values or, respectively, other information are received.

(14) The gradient control unit 11, the RF transmission unit 12 and the RF reception unit 13 are respectively controlled in coordination by a measurement control unit 15. Via corresponding commands, this ensures that the desired gradient pulse sequence GS (i.e. the series of gradient pulses) and radio-frequency pulse sequence RFS of the pulse sequence are emitted. Moreover, it must therefore be ensured that the magnetic resonance signals at the local coils of the local coil arrangement 6 are read out by the RF reception unit 13 at the matching point in time and are processed further, meaning that readout windows must be set in that the ADCs of the RF reception unit 13 are switched to receive, for example. The measurement control unit 15 likewise controls the interface 18.

(15) However, the basic workflow of such a magnetic resonance measurement and the cited components for control are known to those skilled in the art, such that here they do not need to be discussed further in detail. Moreover, such a magnetic resonance scanner 2 and the associated control device can furthermore have a plurality of additional components, which here are likewise not explained in detail. At this point, it is noted that the magnetic resonance scanner 2 can also be designed differentlyfor example with a laterally open patient spaceor as a smaller scanner in which only one body part can be positioned.

(16) In order to start a measurement, via the terminal 20 an operator typically selects a control protocol P provided for this measurement from a memory 16 in which are stored a plurality of control protocols P for different measurements. This control protocol P includes, among other things, various control parameter values SP for the respective measurement. Counting among these control parameter values SP are, for example: the sequence type; the target magnetization for the individual radio-frequency pulses; echo times; repetition times; the various selection directions etc. Slice thicknesses, resolution, number of slices or, respectivelyin the case of a 3D excitation, in particular an inner volume methodthe slab thickness or additional dimensions of the viewing volume (i.e. the aforementioned viewing volume dimension parameters can likewise already be provided here. All of these parameter values can be offered to the operator for adoption upon retrieval of this protocol, and said operator can also arbitrarily vary the values and adapt them to the current examination job with the aid of the user interface.

(17) Moreover, the user can also retrieve control protocols via a network NW (instead of from the memory 16)for example from a manufacturer of the magnetic resonance systemwith corresponding control parameter values SP, and then use these as described in the following.

(18) Based on the control parameter values SP (including the selected viewing volume dimension parameters), a control sequence AS is then determined according to which the control of the remaining components via the measurement control unit 15 ultimately takes place. The control sequence AS here is calculated in a control sequence determination device 22 that is depicted as part of the terminal 20, and is passed to the control device 10 of the magnetic resonance scanner 2 via a control sequence output interface 25. The detailed functioning of the control sequence determination device 22 and its individual components are explained further in the following.

(19) As explained above, in an inner volume refocusing method a viewing volume V.sub.in that is limited in the two selection directions is excited via clever selection of a slab excitation radio-frequency pulse with a gradient switched to match this, as well as a subsequent refocusing radio-frequency pulse, likewise with an associated gradient in a direction situated orthogonal to the first direction. This is presented as an example in FIG. 2. The viewing volume V.sub.in (also designated as an inner volume, or more frequently as a field of view or shortened to FoV) thereby results by the slice region between the volume ES being selectively excited by the slab excitation radio-frequency pulse and the refocusing slice RS being selectively excited by the refocusing radio-frequency pulse. In the third direction, this inner volume V.sub.in is limited by the readout coding.

(20) Strictly speaking, the first slice selection direction SR.sub.1 and the second slice selection direction SR.sub.2 can be placed arbitrarily. However, these directions are typically established by the protocol, wherein most often the first selection direction SR.sub.1 in which the slice selection takes place via the slab excitation radio-frequency pulse travels in the z-direction, and the second selection direction SR.sub.2 travels orthogonal to this in the y-direction. The corresponding slice selection direction parameter SRP (as a first selection direction parameter) and the refocusing direction parameter RRP (as a second selection direction parameter) which establish these selection directions SR.sub.1, SR.sub.2 are typically accepted from the control sequence determination device 22 together with the other control parameters SP, for example (as shown in FIG. 1) via an interface 24, which inasmuch also forms a selection direction parameter interface 24. Moreover, via the computer 21 of the terminal 20 with the associated graphical user interface the operator can establish viewing volume dimension parameter values dx, dy, dz, i.e. the length, width and height of the viewing volume V.sub.in. Corresponding parameters have also possibly already been defined by the control parameter SP in the protocol P, and the operator can modify the viewing volume dimension parameter values dx, dy, dz. Via a suitable interface arrangement 23, the control sequence determination device 22 can accept these viewing volume dimension parameter values dx, dy, dz.

(21) An example of a typical viewing volume V.sub.in within a roughly schematically depicted torso of a patient O is depicted in FIGS. 3 and 4. The torso typically extends in the z-direction, i.e. in the direction of the longitudinal axis of the tomograph. FIG. 3 thereby shows a plan view of the upper body from above, and FIG. 4 shows a slice orthogonal to the z-direction. With the aid of the user interface, the operator can enter inputs designating the dimensions of the viewing volume V.sub.in, i.e. a width in the z-direction dz, a width in the y-direction dy and a width in the x-direction dx. For this purpose, overview images are typically presented to him on the monitor of the computer 21, and with the aid of the graphical user interface he can plot the viewing volume V.sub.in so that the matching viewing volume dimension parameter values dx, dy, dz that correspond to the region selected in the overview presentations are generated automatically. As this is also shown in FIGS. 3 and 4, for historical reasons most operators select the viewing volume V.sub.in so that it is relatively narrow in the z-direction and is significantly longer in the y-direction and x-direction. This is due to the fact that the operator classically selects individual, thin slices with the conventional multislice applications, wherein he is accustomed to generating slice images orthogonal to the z-axis. However, given a three-dimensional excitation such a selection of the dimensions of the viewing volume V.sub.in is not actually necessary at all; rather, the slab could just as well be situated parallel to the z-direction, i.e. have the shortest width in the y-direction.

(22) However, if the viewing volume dimension parameter values dz, dy in the z-direction and y-direction are conventionally selected so that the width in the z-direction is smaller than the width in the y-direction, and at the same time (as this is provided in the previous protocols) the first selection direction SR.sub.1 is placed in the z-direction and the second selection direction SR.sub.2 is placed in the y-direction, this most often leads to the situation that the gradient amplitude in the second selection direction SR.sub.2 must be chosen to be extremely low upon emission of the refocusing radio-frequency pulse in order to achieve a sufficient sampling over the entire width dy of the viewing volume V.sub.in.

(23) A sequence diagram for a corresponding 3D turbo spin echo sequence (TSE sequence) AS with an inner volume refocusing is presented in FIG. 5. In this pulse diagram, the radio-frequency pulses and the readout windows, as well as gradients to be switched in coordination with these on various overlapping time axes, are typically shown over time t. FIG. 5 shows only the start of the pulse sequence AS.

(24) Here the radio-frequency pulses RF.sub.S, RF.sub.R and the readout windows W.sub.1, W.sub.2: W.sub.3 are shown on the upper time axis; the gradient pulses GR.sub.1, GR.sub.2, GR.sub.3, GR.sub.4 in the readout direction are shown on the time axis lying below this; the gradient pulses GP.sub.1, GP.sub.2, GP.sub.3, GP.sub.4, GP.sub.5, GP.sub.6, GP.sub.7, GP.sub.8, GP.sub.9, GP.sub.10 in the classical phase encoding direction are shown on the third time axis; and the gradient pulses GS.sub.1, GS.sub.2, GS.sub.3, GS.sub.4, GS.sub.5, GS.sub.6, GS.sub.7, GS.sub.8, GS.sub.9, GS.sub.10, GS.sub.11 in the slice selection direction (here z) are shown on the lowermost time axis.

(25) As is apparent in this pulse diagram, a first pulse arrangement PA.sub.1 (consisting of the slab excitation radio-frequency pulse RF.sub.S and the gradient GS.sub.2 switched in parallel with this in the slice selection direction) ensures a selective excitation of a slice in the slice selection direction, i.e. here in the z-direction. The gradient pulse GS.sub.1 switched before this gradient pulse GS.sub.2 is a spoiler in order to dephase the residual signal of the previous excitation. The gradient pulses GS.sub.3, GS.sub.4 are rephasers. The signal is dephased by the slice selection gradient GS.sub.2 (as it would be by any gradient) and must be rephased again after the slice selection. It is normally the case that the gradient pulses GS.sub.3, GS.sub.4 together have half the area of the gradient pulse GS.sub.2. Since the gradient pulse GS.sub.4 comes after the refocusing radio-frequency pulse, it has a different polarity than the gradient pulse GS.sub.3.

(26) A second pulse arrangement PA.sub.2 is subsequently emitted with a refocusing radio-frequency pulse RF.sub.R that is accompanied by a parallel gradient pulse GP.sub.2 in the phase encoding direction (i.e. here in the y-direction). This gradient GP.sub.2 in the phase encoding direction ensures that the refocusing radio-frequency pulse also acts selectively. As is shown in FIG. 2, the additional coding can thus be limited to the inner volume V.sub.n. The first pulse arrangement PA.sub.1 and the second pulse arrangement PA.sub.2in particular the gradient pulses GS.sub.2, GP.sub.2are thereby selected so that the dimensions of the field of view or, respectively, of the inner volume V.sub.in correspond precisely to the dimensions in the respective directions as predetermined by the user.

(27) The additional gradient pulses GR.sub.1, GR.sub.2, GR.sub.3, GR.sub.4 in the readout direction have the following functions: the gradient pulse GR.sub.1 is a dephaser. Via this pulse, the signal is initially dephased in order to then be rephased during the readout window (readout). The signal maximum thereby arises precisely in the middle of the readout. The gradient pulses GR.sub.2, GR.sub.3, GR.sub.4 are normal readout gradients.

(28) The gradient pulses GP.sub.1, GP.sub.3 in the phase encoding direction are spoilers and rephasers arranged around the refocusing pulse RF.sub.R in order to avoid FID artifacts.

(29) The additional gradient pulses in the phase encoding direction GP.sub.4, GP.sub.10 are normal phase encoding gradients. The additional gradient pulses in the slice selection direction GS.sub.5, GS.sub.11 are likewise normal phase encoding gradients in the slice selection direction.

(30) As is apparent from FIG. 5, the refocusing radio-frequency pulse RF.sub.R is significantly longer than the slab selection radio-frequency pulse RF.sub.S. This is due to the fact that, given the refocusing, a significantly greater target flip angle is used (namely from 145 to 180) than given the slab excitation (in which a target flip angle of 90 is sufficient). However, since the amplitude of the refocusing radio-frequency pulse RF.sub.R cannot be arbitrarily increased for various reasons (for example a system-dependent B.sub.1 limit and/or SAR reasons), this pulse must be extended accordingly. For the aforementioned reasons, this extension together with the significantly wider dimension of the inner volume or field of view V.sub.in in the y-direction (as is most often predetermined by the operator, as explained using FIG. 4), also leads to the situation that the gradient pulse GP.sub.2 in the phase encoding direction (i.e. in the y-direction) must be chosen to be extremely short. This in turn leads to a high sensitivity to B.sub.0 inhomogeneities and effects due to the chemical shift, such that the probability of aliasing artifacts due to adipose tissue is increased.

(31) In order to avoid this problem, in the method according to the invention it is ensured that the first selection direction SR.sub.1 and the second selection direction SR.sub.2 are selected automatically depending on a length ratio of the dimensions of the viewing volume V.sub.in to be excited. For this purpose, it is sufficient to introduce an additional method step into the typical method to create a control sequence AS on the basis of the control parameters SP that are predetermined by the protocol, and on the basis of the viewing volume dimension parameter values dx, dy, dz, as they are confirmed or predetermined by the user.

(32) This is explained using FIG. 6. In a first method step I, the slice selection direction parameter SRP (i.e. here a slab selection direction parameter) and a refocusing direction parameter RRP are typically registered (for example are adopted from the protocol) and moreover the viewing volume dimension parameter values dx, dy, dz are registered. In the exemplary embodiment according to FIG. 1, this takes placed as was already mentioned with the aid of the interfaces 23 and 24.

(33) These data are then passed to a direction definition unit 26. This direction definition unit 26 has a direction parameter testing unit 27 that checks whether the first selection direction SR.sub.1 and the second selection direction SR.sub.2 correspond to the predetermined conditions with regard to the viewing volume dimensions. Specifically, a check is made as to whether the width or the viewing volume dimension parameter value dy is greater in the classical phase encoding direction (here, the y-direction) than the width or the viewing volume dimension parameter value dz in the classical slab selection direction (i.e. the z-direction). Moreover, a check is made as to whether the slice selection direction parameter SRP is selected so that it likewise lies in the z-direction. If this classical combination is providedmeaning that the dimensions of the viewing volume V.sub.in are selected by the user and the first selection direction SR.sub.1 and the second selection direction SR.sub.2 are defined by the protocol so that the refocusing radio-frequency pulse RF.sub.R must act selectively in the direction of a longer extent of the viewing volume V.sub.in as the slab excitation radio-frequency pulse RF.sub.S (branch y)in Step III it is ensured that the slice selection direction parameter SRP and the refocusing direction parameter RRP are changed so that now the slice selection travels in the y-direction and the refocusing direction travels in the z-direction. It is automatically ensured that the slab selection radio-frequency pulse RF.sub.S must then act selectively in the y-direction (i.e. in the classical phase encoding direction) and the refocusing radio-frequency pulse RF.sub.R must only still act selectively in the slice selection direction (i.e. in the z-direction). This swapping of the selection direction parameters SRP and the refocusing direction parameter RRP can, for example, be implemented in a direction parameter modification unit 28 of the direction definition unit 26 which receives the result from the direction parameter testing unit 27.

(34) If, in the check in Step II, it turns out that one of the two conditions is not satisfied, it is to be assumed that (by chance) the operator has chosen the viewing volume V.sub.in so that the dimension in the z-direction is greater anyway than in the y-direction. In this case (branch n), no change or swapping of the selection direction parameter SRP and of the refocusing direction parameter RRP must take place.

(35) With the selection direction parameter SRP and refocusing direction parameter RRP that are automatically optimized in such a manner, the control sequence AS can be calculated in Step IV with a conventional method.

(36) The calculation of the control sequence thereby takes place in a pulse arrangement determination unit 29.

(37) FIG. 7 shows a corresponding pulse diagram with a control sequence AS analogous to the control sequence AS in FIG. 5, wherein here however the first pulse arrangement PA.sub.1 and the second pulse arrangement PA.sub.2 have been optimized with the method according to the invention to the effect that the first selection direction SR.sub.1 and the second selection direction SR.sub.2 have been selected under consideration of the dimensions of the viewing volume V.sub.in chosen by the user. This has led to the situation that now a gradient is no longer emitted in the slice selection direction (i.e. in the z-direction), parallel to the slab excitation radio-frequency pulse RF.sub.S, but rather instead of this a gradient pulse GP.sub.1 is emitted in the classical phase encoding direction (i.e. in the y-direction). Here the slab excitation radio-frequency pulse RF.sub.Swhich must only achieve a significantly smaller target flip anglemust thus act selectively in the longer extent direction of the viewing volume V.sub.in (see FIG. 4, the extent in the y-direction in relation to the extent of the viewing volume V.sub.in in the z-direction in FIG. 3). However, this is unproblematical since the slab excitation radio-frequency pulse RF.sub.S must only achieve a target flip angle of 90. In contrast to this, the second pulse arrangement PA.sub.2 of the control sequence AS is selected so that now a gradient pulse GS.sub.3 in the slice selection direction (i.e. in the z-direction) is emitted in parallel with the refocusing radio-frequency pulse RF.sub.R. The refocusing radio-frequency pulse RF.sub.R only needs to still act selectively over the smaller extent dz. This leads to the situation that the corresponding gradient pulse GS.sub.3 can be chosen to be greater in the slice selection direction z than given the conventional gradient pulse GP.sub.2 (see FIG. 5) to be switched in the phase encoding direction. Overall, it is thus ensured that the control device AS is insensitive to B.sub.0 inhomogeneities, and in particular to the chemical shift, such that aliasing artifacts can be avoided with a greater probability.

(38) In FIG. 7, the gradient pulses GR.sub.1, GR.sub.2, GR.sub.3, GR.sub.4 in the readout direction again have the same function as was described above regarding FIG. 5. The gradient pulses GP.sub.2, GP.sub.3 in the phase encoding direction and the gradient pulses GS.sub.1, GS.sub.3, GS.sub.4 likewise again serve as spoilers or, respectively, rephasers, analogous to the explanations above. The additional gradient pulses GP.sub.4, . . . , GP.sub.10 in the phase encoding direction, as well as the additional gradient pulses in the slice selection direction GS.sub.5, . . . , GS.sub.11, are again normal phase encoding gradients.

(39) At this point it is noted that an optimization can also take place under consideration of the third direction (i.e. the readout direction). For this, only the method steps II and III must be modified accordingly, wherein care is then advantageously taken that the readout direction is always placed so that it corresponds to the longest dimension of the viewing volume selected by the user, since it costs nearly no time to accordingly increase the sampling in the readout direction.

(40) A particular advantage of this method is that the previous methods must merely be supplemented by the method steps II and III depicted in FIG. 6, and otherwise no additional changes need to be made in the method or in the existing protocols. Furthermore, the method also has the advantage that no additional hardware is required. In principle, it can be applied at all previously known MR systems, thus both at systems with only one transmission channel and at pTX systems.

(41) In conclusion, it is noted that the methods and designs described in detail in the preceding are exemplary embodiments, and that the basic principle can also be varied by those skilled in the art without departing the scope of the invention. For example, the control sequence determination device 22 can also be realized as part of the control device 10 itself instead of at the terminal, in particular also as a component of the measurement control unit 15. The control sequence determination device could likewise also be realized at a separate computer system which, for example, is connected with the magnetic resonance system 1 via the network NW.

(42) Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.