LOCAL COIL DEVICE FOR A HEAD OF A PATIENT, SHIM COIL DEVICE AND METHOD FOR COMPENSATING BASIC FIELD INHOMOGENEITIES IN A REGION OF INTEREST OF THE PREFRONTAL CORTEX OF THE PATIENT

Abstract

A local coil device for a head of a patient for use in a magnetic resonance device includes a local coil with at least one local coil element and a receiver for the head of the patient in which the head may be received in a desired pose. The local coil device also includes a shim coil device with at least one shim coil element for compensating basic field inhomogeneities in a region of interest of the prefrontal cortex of the patient. With respect to the desired pose, the shim coil element of the shim coil device integrated in the local coil or received in a receiver for the shim coil device is arranged anterior to the head.

Claims

1. A local coil device for a head of a patient for use in a magnetic resonance device, the local coil device comprising: a local coil including at least one local coil element and a receiver for the head of the patient in which the head is receivable in a desired pose; and a shim coil device including at least one shim coil element for compensating basic field inhomogeneities in a region of interest of the prefrontal cortex of the patient, wherein with respect to the desired pose, the at least one shim coil element of the shim coil device integrated in the local coil or received in a receiver for the shim coil device is arranged anterior to the head.

2. The local coil device of claim 1, wherein the at least one shim coil element and the at least one local coil element are metallically isolated, the at least one shim coil element has a radio frequency choke for decoupling from the at least one local coil element, or the at least one shim coil element and the at least one local coil element are metallically isolated and the at least one shim coil element has a radio frequency choke for decoupling from the at least one local coil element.

3. The local coil device of claim 1, wherein one or more shim coil elements of the at least one shim coil element has just one winding, one or more shim coil elements of the at least one shim coil element has a plurality of windings, or one or more shim coil elements of the at least one shim coil element has just one winding and one or more shim coil elements of the at least one shim coil element has a plurality of windings.

4. The local coil device of claim 2, wherein with respect to the desired pose, the at least one shim coil element extends in a plane parallel to a frontal plane of the head.

5. The local coil device of claim 4, wherein one or more shim coil elements of the at least one shim coil element is configured as a connected or separated butterfly coil having current loops that follow each other in a cranial-caudal direction in relation to the desired pose.

6. The local coil device of claim 5, wherein two metallically isolated coil sections of the separated butterfly coil that are supplied with current in opposite directions and follow each other in the cranial-caudal direction in relation to the desired pose are suppliable with current independently but essentially in opposite directions.

7. The local coil device of claim 1, wherein the at least one shim coil element is arranged on a support moveably guided in at least one direction by a guide device.

8. The local coil device of claim 7, wherein the support is moveably guided in a cranial-caudal direction relative to the desired pose.

9. The local coil device of claim 1, wherein the at least one shim coil element includes a plurality of shim coil elements offset in at least one direction.

10. The local coil device of claim 9, wherein for one or more shim coil elements of the at least one shim coil element extending in a plane parallel to a frontal plane of the head with respect to the desired pose, at least one further shim coil element of the at least one shim coil element is provided that is offset only in an anterior-posterior direction of the head defined with respect to the desired pose, an array of shim coil elements of the at least one shim coil element that extends in a plane is provided, or a combination thereof.

11. The local coil device of claim 10, wherein the array of shim coil elements of the at least one shim coil element extends in a plane with respect to the desired pose in a plane parallel to a frontal plane of the head.

12. The local coil device of claim 8, wherein the shim coil device further includes at least one switching device for choosing shim coil elements of the at least one shim coil element to be supplied with current, for distributing a basic current among a plurality of shim currents to be fed to different shim coil elements of the at least one shim coil element, or for a combination thereof, at least two shim coil elements of the at least one shim coil element are connected in parallel, at least two shim coil elements of the at least one shim coil element are connected in series, or any combination thereof.

13. The local coil device of claim 7, further comprising a controller configured to: choose a position of the moveable support; choose one or more shim coil elements of the at least one shim coil element to be supplied with current; determine and apply a shim current to one or more shim coil elements of the at least one shim coil element as a function of an item of patient information describing anatomy, the pose of the head of the patient for current recording, or the anatomy and the pose of the head; or any combination thereof.

14. The local coil device of claim 13, wherein the shim coil device further includes a switching device, and wherein the controller is configured to choose one or more shim coil elements of the at least one shim coil element to be supplied with current by controlling the switching device.

15. A shim coil device for compensating basic field inhomogeneities in a region of interest of the prefrontal cortex of a patient in a magnetic resonance device, the shim coil device comprising: at least one shim coil element, wherein the at least one shim coil element is arrangeable anterior to the head of the patient.

16. The shim coil device of claim 15, wherein the shim coil device is configured for arrangement in a receiver for the shim coil device of a local coil device, the local coil device comprising: a local coil including at least one local coil element and a receiver for the head of the patient in which the head is receivable in a desired pose.

17. A method for compensating basic field inhomogeneities in a region of interest of the prefrontal cortex of a patient in a magnetic resonance device, the method comprising: supplying at least one shim coil element of a shim coil arrangement with current for homogenization of a basic field in the region of interest, wherein the at least one shim coil element is arranged anterior to the head of the patient.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 shows a schematic diagram relating to a first embodiment of a local coil device;

[0034] FIG. 2 shows a schematic diagram relating to a second embodiment of a local coil device;

[0035] FIG. 3 shows a first embodiment of a usable shim coil element;

[0036] FIG. 4 shows a second embodiment of a usable shim coil element;

[0037] FIG. 5 shows a view relating to a position of a shim coil elements relative to the head of a patient;

[0038] FIG. 6 shows a diagram to illustrate the generation of a compensating shim field;

[0039] FIG. 7 shows one embodiment of an arrangement of shim coil elements in an array;

[0040] FIG. 8 shows a first possibility for controlling shim coil elements;

[0041] FIG. 9 shows a second possibility for controlling shim coil elements; and

[0042] FIG. 10 shows one embodiment of an arrangement of the local coil device in a magnetic resonance device.

DETAILED DESCRIPTION

[0043] FIG. 1 shows a first exemplary embodiment of a local coil device 1. The local coil device 1 includes a local coil 2 (e.g., a head coil) that has a receiver 3 for a head 4 of a patient to be examined, indicated in FIG. 1 in a desired pose. In the present case, the local coil 2 has a lower housing part 5 and an upper housing part 6 in which local coil elements 7 that are each only indicated in FIG. 1 are arranged. The local coil elements 7 may be operated as receiver coils and/or transmitter coils in order to be able to record high-quality images having, for example, a lower signal-to-noise ratio, of a head 4 received in the receiver 3 with a magnetic resonance device (not shown). A holding mechanism 9, which may also be used as a guide device 8, is provided on the housing part 6 and forms a receiver 10 for a shim coil device 11. The shim coil device 11 may be removably inserted in the receiver 10. The shim coil device 11 includes a support 12, in which at least one shim coil element 13 is cast. The support 12 may be moved in the guide device 8 in the cranial-caudal direction 14 of the head 4 in the desired pose that is perpendicular to the drawing plane according to FIG. 1, which may also correspond to the z direction of the magnetic resonance device in which the local coil device 1 is to be inserted, and therefore, the direction of the basic field of the magnetic resonance device. The at least one shim coil element 13 may therefore be moved to different positions in the cranial-caudal direction 14.

[0044] The at least one shim coil element 13 is used for generating a shim field to compensate field inhomogeneities of the basic field that result due to the anatomy of the head 4 (e.g., the air in the frontal sinuses and paranasal sinuses), which may reduce the image quality, for example, in the case of recordings of the prefrontal cortex. To achieve this, the shim coil element 13 is arranged anterior to the head 4 having a rostral direction 15 that is likewise shown in FIG. 1 for orientation. The at least one shim coil element 13 is metallically isolated from the local coil elements 7 and has at least one radio frequency choke 16 to achieve radio frequency decoupling from the local coil elements 7. The radio frequency choke 16 has a high blocking resistance in a region around the Larmor frequency of the magnetic resonance device.

[0045] Before possible embodiments and effects of the at least one shim coil element 13 are to be discussed in more detail, FIG. 2 shows an alternative embodiment of a local coil device 17. Same components are provided with same reference numerals for the sake of simplicity.

[0046] In contrast to the embodiment in FIG. 1, the shim coil device 11 is integrated in the local coil 2, for which purpose the upper housing part 6 is enlarged in order to be able to receive the support 12 having the at least one shim coil element. However, the support 12 is also moveably mounted in the cranial-caudal direction 14 in order to be able to carry out adjustments to the specific position and anatomy of a head 4 for current recording. As shown, the shim coil element 13 is located anterior to the head 4 in this way as well.

[0047] FIG. 3 shows a first possible embodiment of the at least one shim coil element 13, as may be used in the local coil devices 1, 17. As shown, the shim coil element 13 is configured as a connected butterfly coil 18 that, therefore, as is basically known, has two current loops 19 that are electrically connected in such a way that a shim current I.sub.1 conducted through the butterfly coil 18 flows in opposite directions in each of the two current loops 19. As the alternative embodiment in FIG. 4 shows, the individual current loops 19 may also be implemented as separate coil sections 20, through which different currents I.sub.1, I.sub.2 that are always oriented in opposing directions, may then also flow.

[0048] The illustrated shim coil elements 13 extend in a plane parallel to a frontal plane of the head 4, therefore a horizontal plane, which is spanned by the cranial-caudal direction 14 or z direction and a horizontal direction (x direction of the magnetic resonance device) perpendicular thereto. The current loops 19 are arranged in the z direction so as to follow each other. FIG. 5 shows this arrangement relative to the head 4 again with respect to the butterfly coil 18 in a coronal view.

[0049] The schematic sagittal view in FIG. 6 outlines the mode of operation of the shim coil element 13 configured as a butterfly coil 18 in FIG. 3 or FIG. 4 again in more detail. The head 4 is shown inside the local coil 2, anterior to which the shim coil device 11 having the shim coil element 13 is arranged. Overlaying of the fields of the current loops 19 with different orientations produces a shim field course 21 that has a highly localized component, oriented in the z direction and symbolized by the arrow 22, which merge fairly quickly again into components in the y direction or to the anterior-posterior direction 23 with respect to the desired position of the head 4, and therefore do not affect imaging, or at least not in a relevant way. With the shim coil element 13, the localized, strong inhomogeneities in the basic field caused by the anatomy of the head 4 may therefore be compensated. Different positions of the inhomogeneities in the z direction due to the movement of the shim coil element 13 indicated by the double arrow 36 may be taken into account.

[0050] With a change in the ratio of I.sub.1 and I.sub.2 in the case of the separated butterfly coil 18 in FIG. 4, the field form may also be adjusted to the individual anatomy of a head 4 for current recording.

[0051] The current loops 19 (and therefore also the entire butterfly coil 18) may have a plurality of windings with which, for example, radio frequency chokes 16 may in each case be associated.

[0052] A plurality of shim coil elements 13 may also be arranged in a shim coil device 11 to optionally be able to achieve, in addition to a movement, an adjustment to the anatomy and position of the head 4 for current recording by choosing the shim coil elements 13 to be supplied with current and/or determining suitable shim currents for the shim coil elements 13 to be supplied with overcurrent. For this, it may, for example, be provided that a plurality of shim coil elements 13 arranged congruently one above the other in the y direction is used as a stack; as is shown in FIG. 7, arrays 24 of shim coil elements 13 (e.g., butterfly coils 18) may be arranged in other directions in the z-x plane, in the x direction in FIG. 7. To switch shim currents to a plurality of shim coil elements 13 (e.g., if a small number of shim channels/current sources exist as shim coil elements 13), a switching device may be used, with exemplary embodiments being shown in FIGS. 8 and 9. FIG. 8 shows a configuration of the switching device 25 as a switching matrix 26 that may selectively connect a number of current sources 27 to a number of shim coil elements 13. Operation of the switching device 25 is controlled by a controller 28 that may use, for example, an item of patient information describing the anatomy and pose (e.g., position and orientation) of the head for current examination in order to determine shim coil elements to be supplied with current 13 and shim currents such that optimum compensation of basic field distortions caused by the anatomy is achieved. Such an item of patient information may includes, for example, a B0 field map (basic field map) from which, by the known shim field generating properties of the shim coil elements 13, corresponding compensation configurations and control signals derived therefrom, (e.g., also at the current sources 27) may be generated.

[0053] FIG. 9 shows a variant that may optionally also be used in addition to the embodiment according to FIG. 8, in which a current divider 30 having an adjustable resistor 29 is used as switching device 25 in order to divide a basic current into two different shim currents for different shim coil elements 13. This process is also controlled by the controller 28.

[0054] The controller 28 does not have to be part of the shim coil device 11 or the local coil device 1, 17 but may also be provided externally, for example, as part of the magnetic resonance device, so the control signals may then be routed via appropriate control lines to the switching devices 25.

[0055] FIG. 10 shows the arrangement of one embodiment of a local coil device 1, 17 inside a magnetic resonance device 31 that is shown schematically in cross-section. The magnetic resonance device 31 includes a main magnet unit 32 in which a patient receiver 33 is formed. The main magnet unit 32 contains the superconducting main magnet generating the basic field, with a gradient coil arrangement and a radio frequency coil arrangement (e.g., body coil) often also being provided so as to surround the patient receiver 33. A patient 34, whose head is to be recorded, may be moved by an examination table 35 into the patient receiver 33. The head 4 and the local coil device 1, 17 surrounding the head 4 are positioned in the homogeneity volume of the magnetic resonance device 31 to perform the scans. Shimming of inhomogeneities in the basic field, induced by the anatomy, occurs in the prefrontal cortex region by the shim coil device 11 during recording of the magnetic resonance data.

[0056] Although the invention has been illustrated and described in detail by the exemplary embodiments, the invention is not limited by the disclosed examples, and a person skilled in the art may derive other variations herefrom without departing from the scope of the invention.

[0057] The elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent. Such new combinations are to be understood as forming a part of the present specification.

[0058] While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.