Magnetic resonance imaging device

Abstract

The invention relates to a magnetic resonance imaging device, comprising: at least one magnetic shielding element (7); an electric component (8); and a coil arrangement (2) comprising at least two coil rings (3, 4), wherein the at least two coil rings (3, 4) are arranged offset in the longitudinal direction of a patient accommodation portion (5), and the coil arrangement (2) is designed to form a magnetic field in an inner volume (6) partially surrounded by the coil rings (3, 4) and at least partially including the patient accommodation portion (5), wherein the shielding element (7) and the electric component (8) are arranged centrally between the coil rings (3, 4) in the longitudinal direction outside the inner volume (6), wherein the shielding element (7) shields the electric component (8) from the magnetic field outside the inner volume (6).

Description

Technical Field

[0001] The present invention relates to a magnetic resonance imaging device comprising at least one magnetic shielding element, at least one electrical component, and a coil arrangement, wherein the coil arrangement comprises at least two coil rings, wherein the two coil rings are arranged offset in the longitudinal direction of a patient accommodating portion, and the coil arrangement is designed to form a magnetic field in an interior volume partially enclosed by the coil rings and at least partially including the patient accommodating portion. Background Art

[0002] Magnetic resonance imaging, by its very nature, relies on the generation of a strong magnetic field in the area of ​​the patient accommodating portion of the MRI device. These strong magnetic fields, in addition to the patient accommodating portion or the patient located therein, also affect other components of the imaging device and / or equipment located in the surrounding area of ​​the imaging device. This is because, in addition to the magnetic field within the patient accommodating portion, the coil arrangement also generates stray fields outside the patient accommodating portion or outside the interior volume encompassing the patient accommodating portion. In particular, it may be necessary for the circuitry of the MRI device to be fully or at least partially shielded from the magnetic field generated by the coil arrangement in order to ensure proper operation of the circuitry. For example, it is known to locate the entire MRI device in a shielded space, with electrical components that cannot operate in stray fields located outside of this space and connected to the imaging device.

[0003] However, it may also be necessary to shield electrical components integrated into the magnetic resonance imaging device when their placement outside the shielded space is not feasible or desirable. For the shielding elements used herein, it is desirable to influence the imaging performed by the imaging device as little as possible. Summary of the Invention

[0004] The present invention is therefore based on the object of specifying a magnetic resonance imaging apparatus having a shielding element, which achieves improved magnetic shielding.

[0005] To achieve this object, according to the invention, in a magnetic resonance imaging device of the type mentioned at the outset, a shielding element and the electrical component are arranged centrally between the coil rings in the longitudinal direction outside the interior volume, wherein the shielding element shields the electrical component from a magnetic field outside the interior volume.

[0006] A coil arrangement comprising at least two coil loops is used to generate a magnetic field that is homogeneous, at least in sections, within an image recording area of ​​a patient receiving area, also referred to as the "field of view," in order to enable magnetic resonance imaging there. The coil loops, arranged offset in the longitudinal direction, correspond at least substantially to a Helmholtz coil in terms of their operating principle, which enables a locally homogeneous magnetic field to be generated within the region of an interior volume at least partially enclosed by the coil loops. This occurs by constructively superimposing the magnetic fields generated by the two coil loops in the region of the central axis of the interior volume enclosed by the coil loops. To this end, current can flow through each coil loop in the same direction.

[0007] In the area outside the inner volume and centrally between the coil rings, the magnetic fields of the two coil rings, however, add up destructively (destructively), resulting in a lower overall magnetic field strength at this location. The arrangement of the shielding element and the electrical components to be shielded in this area according to the invention results in an improved shielding effect by the shielding element, thereby providing better protection for the electrical components shielded by the shielding element.

[0008] The shielding element advantageously creates a localized shield that shields only the at least one electrical component to be shielded. The shielding element can thus be designed to be on the same scale as the electrical component or components to be shielded. In particular, the shielding element extends only over a short portion of the path between the coil rings in the longitudinal direction. The shielding element can also be short in the radial direction. In particular, it is possible to ensure that the shielding element is exposed only to stray fields, i.e., small gradients of the magnetic field of the coil arrangement outside the interior volume.

[0009] The shielding element's extension along the circumference of the coil ring is essentially unlimited, since the region with low field strength extends annularly between the coil rings for symmetry reasons. However, the shielding element preferably extends only over a portion of the circumference in the circumferential direction to achieve a compact design of the shielding element. Using the shielding element advantageously eliminates the need for a large-area shield.

[0010] The shielding element advantageously enables an electrical component including at least one magnetizable element to be positioned near the coil arrangement of an MRI device without causing undesirable effects caused by stray magnetic fields from the coil ring during operation of the electrical component, such as complete magnetization of the magnetizable element of the electrical component. Advantageously, the forces acting on the electrical component due to the magnetic field of the MRI device can be minimized. Furthermore, the shielding element can advantageously reduce the effect of the magnetic field in the MRI device, thereby also reducing the effect on imaging, as will be explained in more detail below.

[0011] The positioning of the shielding element relates to the arrangement of the coil rings of the coil arrangement for generating the magnetic field and can also be used when there are more than two coil rings, for example, when they are arranged symmetrically about a center point, a center axis, or a center plane. The coil rings can, for example, each be arranged around a support ring, also known as a buttress ring, wherein the coil rings are formed, for example, by an electrical conductor, in particular a superconductor, wound around the support ring. It is possible for the coil arrangement to include further coils, for example, to improve the homogeneity of the magnetic field generated by the coil arrangement in the area of ​​the patient accommodating portion. The coil rings are arranged offset in a longitudinal direction, which corresponds to the longitudinal direction of the patient accommodating portion and is also known as the z-direction.

[0012] According to the present invention, it can be provided that a shielding element at least partially encloses a shielding volume, which is shielded by the shielding element, wherein the electrical components are arranged in the shielding volume. This allows, for example, the electrical components, which are part of a circuit arrangement comprising multiple components, to be magnetically shielded in the shielding volume. The shielding element is shaped so that it magnetically shields the electrical components in the shielding volume from stray fields of the coil arrangement, i.e., the magnetic field generated by the coil arrangement outside the inner volume.

[0013] According to the present invention, it can be provided that the shielding element has a U-shaped cross-section, wherein the shielding element surrounds the shielding volume on at least three sides. Advantageously, the arrangement of the shielding element relative to the coil ring of the coil arrangement makes it possible to dispense with the complete encapsulation of the shielding volume by the shielding element. This reduces the amount of material required to form the shielding element, which has a particularly beneficial effect on the homogeneity of the magnetic field generated by the coil arrangement. Thus, shielding of the shielding volume can be achieved advantageously with a minimal amount of material or minimal mass of the shielding element.

[0014] Due to the U-shaped cross-section of the shielding element, the shielding element is enclosed on at least three sides, namely by the closed side of the U-shaped cross-section opposite the open side and by the two side edges of the U-shaped cross-section. In particular, the shielding element can be arranged such that the side edges of the U-shaped cross-section are spaced apart from one another in the longitudinal direction and extend in the radial direction of the coil ring.

[0015] According to the present invention, it can be provided that the shielding element alternatively has a pot-shaped, box-shaped, or trough-shaped configuration, wherein the shielding element completely encloses the shielding volume except for the open side of the shielding element. The pot-shaped, box-shaped, or trough-shaped shielding element can have a base section, from which one or more wall sections extend according to the cross-sectional geometry, wherein the shielding volume is enclosed or bounded by the base section and the one or more wall sections. In addition to rectangular cross-sectional shapes with four wall sections, oval or circular shapes with only one wall section are also conceivable. The shielding element has an open side relative to the base section. This open side allows, for example, electrical components secured to a planar support element to be arranged in the shielding volume of the shielding element pushed onto it, so that the electrical components are completely enclosed by the shielding element except for the open side. The base section can be straight or curved, wherein in the case of a curved section, the wall sections extend from the concave side of the base section, or the interior volume enclosed by the shielding element is adjacent to the concave side of the base section.

[0016] Compared to shielding elements with a U-shaped cross section, pot-shaped, box-shaped or trough-shaped shielding elements further enclose the inner volume, so that better shielding can be achieved depending on the field course of the stray field to be shielded.

[0017] According to the present invention, the open side of the U-shaped cross section or the open side of the shielding element can face the interior volume. Correspondingly, the closed side of the U-shaped cross section or the base section of the U-shaped shielding element, or the base section of the pot-shaped, box-shaped, or trough-shaped shielding element, that is opposite the open side, is directed away from the interior volume and, therefore, further away from the patient accommodation area or the image recording area in the patient accommodation area. This further reduces the shielding element's influence on the magnetic field generated by the coil arrangement.

[0018] In a preferred embodiment of the present invention, an air gap is formed between the electrical component and the shielding element and / or a non-magnetic spacer element is provided. The air gap and / or the non-magnetic spacer element prevents the magnetic flux guided through the shielding element from entering the electrical component. Thus, by forming an air gap between the shielding element and the electrical component or providing a non-magnetic spacer element, the contact magnetic resistance between the shield and the electrical component is increased, thereby improving the shielding effect of the shielding element.

[0019] According to the present invention, it can be proposed that the shielding element is longer along the circumferential direction of the coil ring or tangential to the circumferential direction of the coil ring than along the longitudinal direction of the coil ring and / or along the radial direction of the coil ring. That is, preferably, the shielding element extends along the circumferential direction of the coil ring or tangential to the circumferential direction of the coil ring with its longest extension. In particular, it is possible to achieve that the shielding element extends only in an area with a small gradient of the stray field by virtue of the narrow configuration of the shielding element with respect to the longitudinal direction. It is feasible that the shielding element extends around the entire circumference of the internal volume so that the shielding element has an annular shape. However, it is also feasible that the shielding element extends only over a section of the circumference, wherein the shielding element is straight along the circumferential direction or is bent in particular corresponding to the radius of the circumference.

[0020] Shielding elements with a U-shaped cross section are preferably arranged such that the sides of the U-shaped segments are spaced apart in the longitudinal direction and extend in the radial direction of the coil ring. The open side of the U-shaped cross section extends in the longitudinal direction and in the circumferential direction and preferably faces the interior volume. Pot-shaped, box-shaped, or trough-shaped shielding elements are also preferably arranged such that the open side of the shielding element faces the interior volume.

[0021] In this case, the shielding element can have a length in the radial direction, for example, between 5 cm and 25 cm, in particular 10 cm. In the longitudinal direction, the shielding element can also have a length between 5 cm and 25 cm, in particular 10 cm. In the circumferential direction of the coil ring or tangentially to the circumferential direction of the coil ring, the shielding element can have a length between 15 cm and 50 cm, in particular 25 cm.

[0022] According to the present invention, it can be provided that the shielding element is at least partially composed of iron. For example, the shielding element can be composed of structural steel and have a material thickness or wall thickness of between 5 mm and 15 mm, in particular 10 mm. Using a shielding element composed at least partially of iron has the advantage that iron has a higher saturation magnetization than other materials used for magnetic shielding. This prevents saturation of the magnetization of the shielding element when it is positioned between the coil rings. A high saturation magnetization of the shielding element is particularly desirable because magnetic flux densities in the range of 50 mT to 500 mT can exist in this region, even in air.

[0023] In a preferred embodiment of the present invention, the magnetic resonance imaging device includes an inner cover that surrounds the coil arrangement, wherein the shielding element is arranged on the inner cover. The inner cover can, for example, have at least substantially the shape of a cylindrical housing. The inner cover can, for example, surround the cooling medium required for generating superconductivity in the coil arrangement. The cover of the shielding element can be arranged or fixed on the outside, that is, on the side of the inner cover opposite the inner volume. The fixing can be performed directly or indirectly via at least one supporting element.

[0024] The shielding element and at least one electrical component shielded by the shielding element can be arranged in the interior of the magnetic resonance imaging device in the manner described. The inner cover surrounding the coil arrangement can, for its part, be covered by an external device cover of the magnetic resonance imaging device, which, when the shielding element is arranged on the inner cover, also encloses the shielding element and the electrical components and / or circuit arrangements including the electrical components arranged therein. In the case of an at least substantially cylindrical, shell-like design of the inner cover, the longest extension of the shielding element can, in particular, extend along the circumferential direction of the inner cover or tangentially thereto, wherein the shielding element can, in particular, be arranged at any position on or around the inner cover.

[0025] According to the present invention, it can be provided that the electrical component is a coil including a magnetizable core and / or a transformer including a magnetizable core. For example, other electrical components that, together with at least one electrical component disposed within the shielding element, form a circuit arrangement can be disposed adjacent to the shielding element on any side if magnetic shielding is not required. In this manner, only components that also require magnetic shielding can be shielded by the shielding element. This advantageously reduces the volume or mass of the shielding element, thereby reducing the amount of material required to construct the shielding element. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Further advantages and details of the invention are apparent from the exemplary embodiments described below and with reference to the accompanying drawings. These drawings show:

[0027] Figure 1 An embodiment of a magnetic resonance imaging apparatus according to the present invention is shown.

[0028] Figure 2 A schematic diagram illustrating the arrangement of the shielding element is shown, and

[0029] Figure 3 a cross section showing one embodiment of a shielding element of said embodiment of a magnetic resonance imaging apparatus according to the invention, and

[0030] Figure 4A perspective view showing another embodiment of a shielding element according to the embodiment of the magnetic resonance imaging apparatus of the present invention. DETAILED DESCRIPTION

[0031] exist Figure 1 An embodiment of a magnetic resonance imaging device 1 is shown in FIG. The magnetic resonance imaging device 1 comprises a coil arrangement 2, which comprises at least two coil rings 3, 4. The coil rings 3, 4 can be arranged, for example, along a support ring, also referred to as a buttress ring, of the magnetic resonance imaging device 1. The coil rings 3, 4 are arranged offset in the longitudinal direction of the patient receiving portion 5 of the magnetic resonance imaging device 1. The longitudinal direction corresponds to the longitudinal direction of the patient receiving portion 5 of the magnetic resonance imaging device 1. Figure 1 The coil arrangement 2 is designed to generate a homogeneous magnetic field in an interior volume 6 at least partially surrounding the patient receiving area 5 , at least partially in the image acquisition region.

[0032] The magnetic resonance imaging device 1 also includes a magnetic shielding element 7 that shields at least one electrical component 8 of a circuit arrangement 9 of the magnetic resonance imaging device 1. The shielding element 7 and the electrical component 8 are arranged outside the interior volume 6 and centrally between the coil rings 3 and 4 in the longitudinal direction. This allows for advantageous magnetic shielding of the at least one electrical component 8. The electrical component 8 can be, for example, a coil having a magnetizable core and / or a transformer including a magnetizable core. The electrical component 8 is an integral part of the circuit arrangement 9, with other components of the circuit arrangement 9 that do not require shielding being arranged adjacent to the shielding element, and the shielding element 7 shielding only the at least one electrical component 8. The central placement of the shielding element 7 between the coil rings 3 and 4 advantageously allows the shielding element 7 to be arranged in an area with relatively low magnetic field strength.

[0033] As in Figure 2 As schematically shown in FIG, coil rings 3, 4 serve to generate a homogeneous magnetic field in the area of ​​patient accommodation 5. Coil rings 3, 4 here at least essentially form Helmholtz coils, so that a magnetic field that is as homogeneous as possible can be generated in the imaging area in the patient accommodation and between coil rings 3, 4.

[0034] To illustrate the magnetic field generation by the coil rings 3 and 4, Figure 2 shows the field lines of magnetic flux density B1 of first coil ring 3 and the field lines of magnetic flux density B2 of second coil ring 4. It can be seen that the field lines also run in the same direction in the longitudinal direction within interior volume 6 and, in particular, within patient accommodation 5. This results in the field lines running in different directions in the area centrally located between coil rings 3, 4 and outside interior volume 6, i.e., in the area where shielding element 7 is provided. As a result, magnetic flux density B1 of first coil ring 3 and magnetic flux density B2 of second coil ring 4 are destructively superimposed, resulting in no or at least only a low magnetic flux density overall.

[0035] As schematically shown in the diagram, the entire magnetic flux density B of the coil arrangement 2 occurs outside the inner volume 6. g , the magnetic flux density changes along the longitudinal direction. It can be seen that the shielding element 7 arranged centrally between the coil rings 3 and 4 is arranged at a magnetic flux density B that is as small as possible. g The shielding element 7 is furthermore advantageously shaped such that its extension in the longitudinal direction of the coil rings 3 , 4 and its extension in the radial direction of the coil rings are each smaller than its extension in the circumferential direction of the coil rings 3 , 4 .

[0036] It is possible that the shielding element 7 extends around the entire circumference of the inner volume 6, so that the shielding element has an annular shape. However, it is also possible that the shielding element 7, as shown, extends only over a section of the circumference, wherein the shielding element 7 is straight in the circumferential direction or, in particular, is curved corresponding to the radius of the circumference. The shielding element is shorter in the longitudinal direction of the coil rings 3, 4 and in the radial direction of the coil rings than in the circumferential direction. This makes it possible to achieve that the shielding element 7 is only in the longitudinal direction and in the radial direction with the entire magnetic flux density B of the coil rings 3, 4. g The region of the small gradient extends.

[0037] exist Figure 3 shows a cross-section of an embodiment of a shielding element 7. The shielding element 7 at least partially encloses a shielding volume 11, in which the electrical component 8 is disposed. An air gap 12 is formed between the electrical component 8 and the interior of the shielding element 7. The air gap 12 prevents the magnetic flux guided through the shielding element from passing into the electrical component 8, as schematically illustrated by the field line segments of the magnetic fluxes B1 and B2. In addition to or as an alternative to the air gap 35, a non-magnetic spacer element can be disposed between the shielding element 7 and the electrical component 8. The air gap or spacer element can have a thickness of between 0.5 cm and 1.5 cm, in particular 1 cm.

[0038] The shielding element 7 comprises a U-shaped cross section 13. The open side 14 of the U-shaped cross section 13 is arranged facing the interior volume 6, i.e., the patient receiving area 5. This has the advantage that the closed side 15 of the U-shaped cross section 13, which is opposite the open side 14, is arranged further away from the image recording area in the interior volume 6 or the patient receiving area 5. This reduces the influence of the shielding element 7 on the magnetic field that is formed, particularly in the image recording area.

[0039] The sides 16 of the U-shaped cross section 13 can each have a length of between 5 cm and 25 cm, in particular 10 cm, in the radial direction r of the coil rings 3, 4. The open side 14 and the closed side 15 opposite the open side can each have an extension of between 5 cm and 25 cm, in particular 10 cm, in the longitudinal direction. The shielding element 7 can extend in the circumferential direction or tangentially to the circumferential direction, i.e. perpendicularly to the circumferential direction. Figure 3 The length of the drawing plane in FIG is longer than the side 16 and longer than the open side 14 and the closed side 15. The length of the shielding element along the circumferential direction or tangentially thereto can be between 5 cm and 50 cm, in particular 25 cm. The shielding element 7 can be made at least partially of iron, in particular structural steel. The material thickness of the shielding element 7 can be between 5 mm and 38 mm, in particular 10 mm.

[0040] exist Figure 4 shows a perspective view of another embodiment of a shielding element 7. The shielding element 7 comprises a base section 17 and four wall sections 18 and 19, which form the trough shape of the shielding element. The base section 17 is curved along the circumferential direction U, with the wall sections 18 and 19 adjoining the concave sides of the base section 17. The base section 17 and the wall sections 18 enclose the shielding volume 11 of the shielding element 7, except for the open side 14 of the shielding element 7 opposite the base section 17.

[0041] The length of the wall segments 18, 19 in the radial direction r and in the longitudinal direction z can be between 5 cm and 25 cm, in particular 10 cm. The length of the wall segment 19 and the base segment 17 in the longitudinal direction z can also be between 5 cm and 25 cm, in particular 10 cm. The base segment 17 and the wall segment 18 can have an extension in the circumferential direction U of between 5 cm and 50 cm, in particular 25 cm, wherein the shielding element is longer in the circumferential direction U than in the radial direction r and in the longitudinal direction z.

[0042] Alternatively, it is possible to also design the base section 17 to be straight, so that it extends tangentially to the circumferential direction U and creates a box shape for the shielding element 30. Additionally or alternatively, the expansion of the shielding element 7 in the circumferential direction or tangentially to the circumferential direction can at least substantially correspond to the expansion of the shielding element in the longitudinal direction, so that a pot shape for the shielding element is created.

[0043] As in Figure 1As shown in FIG, the shielding element 7 is arranged on the inner cover surrounding the coil arrangement 2 and is fixed there directly or indirectly via at least one supporting element. The circuit arrangement 9 or the supporting element holding the circuit arrangement 9 can be fixed on the inner cover 10. The inner cover 10 can, for example, surround a volume through which a coolant flows in order to produce superconductivity in the coil rings 3, 4 and / or in other components of the coil arrangement 2. Alternatively, other arrangements and / or fixations of the electrical components 8 and / or the shielding element 7 in the magnetic resonance imaging device 1 are also possible. In this case, any type of supporting structure that holds the electrical components 8 and / or the shielding element 7 in a fixed position in the magnetic resonance imaging device 1 can be used.

[0044] Although the present application is described in detail with reference to preferred embodiments, the present invention is not limited to the disclosed examples, and those skilled in the art can derive other variations therefrom without departing from the scope of protection of the present invention.

Claims

1. A magnetic resonance imaging apparatus, comprising: At least one magnetic shielding element (7); at least one electrical component (8); and a coil arrangement (2), the coil arrangement (2) comprising at least two coil rings (3, 4), wherein the at least two coil rings (3, 4) are arranged offset in the longitudinal direction of a patient accommodating portion (5), and the coil arrangement (2) is designed to form a magnetic field in an inner volume (6) partially enclosed by the coil rings (3, 4) and at least partially including the patient accommodating portion (5), It is characterized in that The shielding element (7) and the electrical component (8) are arranged centrally between the coil rings (3, 4) in the longitudinal direction outside the inner volume (6), wherein the shielding element (7) shields the electrical component (8) from a magnetic field outside the inner volume (6). The shielding element (7) at least partially surrounds a shielding volume (11), the shielding volume (11) being shielded by the shielding element (7), wherein the electrical component (8) is arranged in the shielding volume (11), The shielding element (7) has a U-shaped cross section (13), wherein the shielding element (7) surrounds the shielding volume (11) on three sides.

2. The magnetic resonance imaging apparatus according to claim 1, It is characterized in that The shielding element is pot-shaped, box-shaped or trough-shaped, wherein the shielding element completely surrounds the shielding volume (11) except for the open side of the shielding element (7).

3. The magnetic resonance imaging apparatus according to claim 1 or 2, It is characterized in that The open side (14) of the U-shaped cross section (13) or the open side of the shielding element (7) faces the inner volume (6).

4. The magnetic resonance imaging apparatus according to claim 1 or 2, It is characterized in that An air gap (12) is formed between the electrical component (8) and the shielding element (7) and / or a non-magnetic spacer element is provided.

5. The magnetic resonance imaging apparatus according to claim 1 or 2, It is characterized in that The shielding element (7) is longer in the circumferential direction of the coil ring (3, 4) or tangential to the circumferential direction of the coil ring (3, 4) than in the longitudinal direction of the coil ring (3, 4) and / or in the radial direction of the coil ring (3, 4).

6. The magnetic resonance imaging apparatus according to claim 1 or 2, It is characterized in that The shielding element (7) is at least partially composed of iron.

7. The magnetic resonance imaging apparatus according to claim 1 or 2, It is characterized in that The magnetic resonance imaging device (1) has an inner cover (10) which surrounds the coil arrangement (2), wherein the shielding element (7) is arranged on the inner cover (10).

8. The magnetic resonance imaging apparatus according to claim 1 or 2, It is characterized in that The electrical component (8) is a coil comprising a magnetizable core and / or a transformer comprising a magnetizable core.

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