Method for Simultaneous Recording of Scan Data From at Least Two Slices of an Examination Object by Means of Magnetic Resonance

Abstract

The disclosure relates to techniques for an improved recording of scan data, which can be recorded from at least two slices of an examination object simultaneously by means of a magnetic resonance system. The technique includes selecting a desired simultaneous recording of scan data from at least two slices (S1, Sn), determining an artifact-preventing minimum RF pulse duration (dRF) for a desired recording, considering desired recording parameters (PA), and performing the desired recording using the determined minimum RF pulse duration.

Claims

1. A method for recording scan data simultaneously from at least two slices of an examination object via a magnetic resonance system, comprising: selecting a simultaneous recording of scan data from the at least two slices; determining an artifact-preventing radio frequency (RF) pulse duration for the selected simultaneous recording based upon one or more recording parameters; and executing the selected simultaneous recording using the determined artifact-preventing RF pulse duration.

2. The method of claim 1, wherein the artifact-preventing RF pulse duration is a minimum RF pulse duration that is determined based upon the one or more recording parameters.

3. The method as claimed in claim 1, wherein the artifact-preventing RF pulse duration is determined for a multi-band RF pulse.

4. The method as claimed in claim 1, wherein the artifact-preventing RF pulse duration is determined for a Variable Rate Selective Excitation (VERSE) pulse.

5. The method as claimed in claim 2, wherein the determination of the artifact-preventing RF pulse duration is based upon values for the minimum RF pulse duration and a maximum RF pulse duration.

6. The method as claimed in claim 5, wherein the minimum RF pulse duration and the maximum RF pulse duration are determined based upon extreme values of at least one of the recording parameters of the magnetic resonance system.

7. The method as claimed in claim 6, wherein the extreme values of at least one of the recording parameters of the magnetic resonance system include at least one of a maximum RF transmitting power, a maximum gradient strength, and a minimum slice thickness.

8. The method as claimed in claim 1, wherein the artifact-preventing RF pulse duration is determined based upon a recording parameter including at least one of a slice thickness and a gradient strength.

9. The method as claimed in claim 1, wherein the artifact-preventing RF pulse duration is determined based upon a bandwidth and/or a pulse shape of an RF pulse to be used.

10. The method as claimed in claim 1, wherein the artifact-preventing RF pulse duration is determined based upon a relationship between the one or more recording parameters and an RF pulse duration that is achievable via the magnetic resonance system.

11. The method as claimed in claim 5, wherein the determined artifact-preventing RF pulse duration occupies a region delimited by the minimum RF pulse duration and the maximum RF pulse duration.

12. A magnetic resonance system for recording scan data simultaneously from at least two slices of an examination object via a magnetic resonance system, comprising: a main magnet; and control circuitry configured to: select a simultaneous recording of scan data from the at least two slices; determine an artifact-preventing radio frequency (RF) pulse duration for the selected simultaneous recording based upon one or more recording parameters; and execute the selected simultaneous recording using the determined artifact-preventing RF pulse duration.

13. A non-transitory computer-readable medium having information stored thereon that, when executed by control circuitry of a magnetic resonance system, cause the magnetic resonance system to record scan data simultaneously from at least two slices of an examination object via a magnetic resonance system by: selecting a simultaneous recording of scan data from the at least two slices; determining an artifact-preventing radio frequency (RF) pulse duration for the selected simultaneous recording based upon one or more recording parameters; and executing the selected simultaneous recording using the determined artifact-preventing RF pulse duration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

[0029] Further advantages and details of the present disclosure are disclosed in the following description of exemplary embodiments and by reference to the drawings. The examples given do not represent restrictions of the disclosure. In the drawings:

[0030] FIG. 1 illustrates an example schematic flow diagram of a method according to one or more embodiments of the disclosure,

[0031] FIG. 2 illustrates an example a schematically represented magnetic resonance system according to one or more embodiments of the disclosure.

DETAILED DESCRIPTION

[0032] FIG. 1 shows a schematic flow diagram of a method according to the disclosure for improved recording of scan data MD, which can be recorded simultaneously from at least two slices S1, Sn of an examination object by means of a magnetic resonance system.

[0033] Therein, values dependent upon a magnetic resonance system that is used can be loaded for a minimum RF pulse duration dmin and for a maximum RF pulse duration dmax (block 101). For this purpose, information relating to the hardware HW of the magnetic resonance system used can be requested (block 101′).

[0034] A loaded minimum RF pulse duration dmin and a loaded maximum RF pulse duration dmax can be determined dependent upon applicable hardware-specific extreme values for parameters of the magnetic resonance system used.

[0035] For example, for the determination of the loaded minimum RF pulse duration dmin and the loaded maximum RF pulse duration dmax, extreme values of at least one of the parameters of the magnetic resonance system used from the group comprising a maximum RF transmitting power (B1max), a maximum gradient strength (Gmax) and a minimum slice thickness (thmin) can be considered.

[0036] For instance, a loaded minimum RF pulse duration dmin can be determined as a function F1 of the inverse values of the maximum gradient strength Gmax and the maximum RF transmitting power B1max, where dmin=F1(1/B1max, 1/Gmax) applies. A procedure of this type reflects that shorter RF pulse durations require higher RF transmitting power levels and higher gradient strengths.

[0037] A maximum RF pulse duration dmax can be determined, for example, as a function F2 of the maximum gradient strength Gmax and the inverse minimum slice thickness thmin, where dmax=F2(1/thmin, Gmax) applies. A procedure of this type reflects that longer RF pulse durations increase an achievable minimum slice thickness, but reduce a required gradient strength.

[0038] Herein, the values of the loaded minimum and maximum RF pulse duration dmin and dmax can be adopted, for example, from manufacturer specifications of the magnetic resonance system, or determined uniquely for a specific magnetic resonance system. However, it is also conceivable to determine the values for the minimum and maximum RF pulse duration dmin and dmax of a magnetic resonance system before carrying out a recording of scan data, at least in predetermined time intervals, always or anew after a corresponding user input, whereby possibly occurring changes to the extreme values can be considered.

[0039] A desired simultaneously recording of scan data from at least two slices S1, Sn of, for example, a total of N slices to be recorded N (N>n) of the examination object, is selected (block 103). By way of the selection of the desired recording, associated recording parameters PA and possible RF pulses usable in the desired recording are also stipulated together with their associated RF parameters PRF.

[0040] As a desired recording, for example a simultaneous recording of n slices by means of a slice multiplexing method, e.g. using gradient blips for impressing a phase difference, for example, a blipped CAIPIRINHA method can be selected.

[0041] The minimum RF pulse duration can herein be determined for a multi-band RF pulse and/or for a VERSE (Variable Rate Selective Excitation) pulse if the desired recording permits. Multi-band RF pulses are readily used as described above for slice multiplexing methods. VERSE pulses can advantageously also be used, due to their inherently low required RF transmitting power levels. This is because, due to the fundamentally lower RF transmitting power levels required as compared with other RF pulses, an achievable minimum RF pulse duration can be reduced further than is the case with other RF pulses and/or an achievable minimum slice thickness smaller than with other RF pulses can be achieved.

[0042] Taking account of desired recording parameters PA, a minimum artifact-reducing RF pulse duration d.sub.RF is determined for the desired recording (block 105).

[0043] Advantageously, in the determination of the minimum RF pulse duration d.sub.RF, loaded values of the minimum and maximum RF pulse duration dmin and dmax for the magnetic resonance system used are also considered. For instance, it can be required that a determined minimum RF pulse duration d.sub.RF lies in a region delimited by the loaded minimum RF pulse duration dmin and the loaded maximum RF pulse duration dmax. In this way, it is ensured that the determined minimum RF pulse duration is achievable with the magnetic resonance system.

[0044] A desired recording parameter PA considered in the determination of the minimum RF pulse duration d.sub.RF can be a recording parameter PA from the group comprising a desired slice thickness ths1 and an intended gradient strength G. In this way, it can be ensured for example, that no (excessive) deviation from the desired slice thickness takes place.

[0045] In the determination of the minimum RF pulse duration d.sub.RF, at least one characteristic RF pulse parameter PRF for an RF pulse to be used, the minimum RF pulse duration of which is determined, such as for example, a bandwidth and/or a pulse shape of the RF pulse can be considered. The minimizing can thus be carried out in a pulse-specific manner.

[0046] A determination of the minimum RF pulse duration d.sub.RF can comprise a use of a relationship between desired recording parameters and an achievable RF pulse duration. If such a relationship between desired recording parameters and an achievable RF pulse duration is known, this can be used to determine the minimum RF pulse duration.

[0047] For example, a minimum RF pulse duration d.sub.RF can be determined as a function F3 dependent upon a desired slice thickness ths1 and a gradient strength G that is provided, as follows:

d.sub.RF=F3(/(ths1*G)),

[0048] where /(ths1*G) reflects a relationship between the desired recording parameters and the RF pulse duration, and the function F3 can further depend upon at least one RF pulse parameter, for example, the selected pulse shape.

[0049] In order to ensure, as mentioned above, that the determined minimum RF pulse duration d.sub.RF lies within the loaded values of minimum and maximum RF pulse durations dmin and dmax for a magnetic resonance system, the determination can further comprise a maximum function that reflects the largest of the elements input to it and a minimum function which reflects the smallest of the elements input into it.

[0050] For example, a minimum RF pulse duration d.sub.RF with the minimum RF pulse duration dmin initially determined, for example, by means of a function F3 can be subjected to a maximum function to obtain as the result a first tested minimum RF pulse duration, d.sub.RF1=max(d.sub.RF, dmin).

[0051] The first tested minimum RF pulse duration d.sub.RF1 can be subjected with the maximum RF pulse duration dmax to a minimum function in order to obtain as the result a finally tested minimum RF pulse duration, d.sub.RF2=min(d.sub.RF1, dmax) as the final result of the determination of the minimum RF pulse duration.

[0052] The desired recording is carried out (i.e. executed or otherwise performed) using the determined minimum RF pulse duration d.sub.RF (block 107) in order to obtain the desired scan data. The use of the minimum pulse duration DRF according to the disclosure, a displacement in the slice direction of spins bound in different tissue types is adjusted, so that artifacts, in particular artifacts caused by a chemical shift, are reduced.

[0053] FIG. 2 shows schematically a magnetic resonance system 1 according to the disclosure.

[0054] This system comprises a magnet unit 3 (e.g. a main magnet) for generating the main magnetic field, a gradient unit (e.g. gradient generation circuitry) 5 for generating the gradient fields, a radio-frequency unit (e.g. an RF signal circuitry, which may be referred to herein as an RF transmitter, receiver, or transceiver) 7 for radiating in and receiving radio-frequency signals, and a control apparatus (e.g. control circuitry) 9 configured for carrying out (i.e. executing or otherwise performing) any of the methods according to the disclosure.

[0055] In FIG. 2, these subunits of the magnetic resonance system 1 are shown only roughly schematically. In particular, the radio-frequency unit 7 can consist of a plurality of subunits, for example, a plurality of coils such as the schematically shown coils 7.1 and 7.2 or more coils, which can be configured either only to transmit radio-frequency signals (e.g. when implemented or otherwise configured as an RF transmitter) or only to receive the triggered radio-frequency signals (e.g. when implemented or otherwise configured as an RF receiver), or for both (e.g. when implemented or otherwise configured as an RF transceiver).

[0056] In order to examine an examination object U, for example, a patient or a phantom, the object U may be introduced on a support L into the magnetic resonance system 1, in the scanning volume thereof. The slices Sa and Sb represent slices of the examination object that are to be recorded simultaneously in the example and from which echo signals are to be recorded and captured as scan data.

[0057] The control apparatus 9 (e.g. a computing device, one or more processors, processing circuitry, a controller, computer, etc.) serves to control the magnetic resonance system 1 and may e.g. control the gradient unit 5 by means of a gradient controller (e.g. gradient controller circuitry) 5′ and the radio-frequency unit 7 by means of a radio-frequency transmitting/receiving controller (e.g. RF controller circuitry) 7′. The radio-frequency unit 7 can herein comprise a plurality of channels on which signals can be transmitted or received.

[0058] The radio-frequency unit 7 is configured, together with its radio-frequency transmitting/receiving controller 7′, to generate and radiate-in (e.g. transmit) a radio-frequency alternating field for manipulation of the spins in a region to be manipulated (for example, in slices S to be scanned) of the examination object U. Herein, the center frequency of the radio-frequency alternating field, also designated the B1 field, is typically adjusted so that, as far as possible, it lies close to the resonance frequency of the spin to be manipulated. Deviations of the center frequency from the resonance frequency are referred to as off-resonance. In order to generate the B1 field, in the radio-frequency unit 7, currents controlled by means of the radio-frequency transmitting/receiving controller 7′ are applied to the RF coils.

[0059] Furthermore, the control apparatus 9 comprises a pulse duration determining unit (e.g. pulse duration determination circuitry) 15 with which minimum RF pulse durations can be determined. The control apparatus 9 is configured overall to carry out a method according to the disclosure.

[0060] A computing unit (e.g. also referred to herein as a computing device, computer, controller, computing circuitry, etc.) 13 included in the control apparatus 9 is configured to carry out all the computation operations necessary for the required scans and determinations. Intermediate results and results needed for this or determined herein can be stored in a storage unit (e.g. volatile and/or non-volatile memory) S of the control apparatus 9. The units shown are herein not necessarily to be understood as physically separate units, but represent merely a subdivision into units of purpose which, however, can also be implemented, for example, in fewer, alternate, or even only in one single, physical unit.

[0061] By means of an input/output apparatus (E/A or I/O) of the magnetic resonance system 1, for example, control commands can be passed by a user to the magnetic resonance system and/or results from the control apparatus 9 such as, for example, image data can be displayed via a suitable display device, which may be part of the input/output apparatus.

[0062] A method described herein may also be implemented in the form of a computer program product, which comprises a program and implements the described method on a control apparatus 9 when said program is executed on the control apparatus 9. An electronically readable data carrier 26 with electronically readable control information stored thereon can also be provided, said control information comprising at least one computer program product as described above and being configured to carry out any of the methods described when the data carrier 26 is used in a control apparatus 9 of a magnetic resonance system 1.

[0063] The various components described herein may be referred to as “units.” As noted above, such components may be implemented via any suitable combination of hardware and/or software components as applicable and/or known to achieve the intended respective functionality. This may include mechanical and/or electrical components, FPGAs, processors, processing circuitry, or other suitable hardware components configured to execute instructions or computer programs that are stored on a suitable computer readable medium. Regardless of the particular implementation, such units, as applicable and relevant, may alternatively be referred to herein as “circuitry,” “processors,” or “processing circuitry.”