A COIL ASSEMBLY FOR MR IMAGING APPLICATIONS

Abstract

A coil assembly for MR imaging applications comprises—an electrically conducting RF transmitter coil arrangement (2) for generating an excitation field at an MR operating frequency, the transmitter coil arrangement forming a tubular structure disposed around an imaging volume (4) and having a longitudinal axis (A); —an external RF shield (6) surrounding the transmitter coil arrangement; —at least one electrically conducting RF receiver coil (8; 8a, 8b) disposed within the imaging volume for receiving MR signal from a subject or object disposed therein, the receiver coil being electrically connected, at a connection point (10; 10a, 10b) thereof, to a respective RF receive line (12; 12a, 12b) connectable to a receiver device (14) located outside of the external RF shield. In order to improve the performance of the coil assembly, the respective RF receive line of each receiver coil is oriented substantially perpendicular to the longitudinal axis (A) in a receiver-proximal segment (16; 16a, 16b) between the connection point (10; 10a, 10b) and a neighboring face portion (18; 18a, 18b) of the external RF shield through which the receive line (12; 12a, 12b) is conducted.

Claims

1. A coil assembly for MR (magnetic resonance) imaging applications, comprising an electrically conducting RF (radio frequency) transmitter coil arrangement for generating an excitation field at an MR operating frequency, the transmitter coil arrangement forming a tubular structure disposed around an imaging volume and having a longitudinal axis; an external RF shield surrounding the transmitter coil arrangement; at least one electrically conducting RF receiver coil disposed within the imaging volume for receiving MR signal from a subject or object disposed therein, the receiver coil being electrically connected, at a connection point, to a RF receive line which is connectable to a receiver device located outside of the external RF shield; wherein the RF receive line of said receiver coil is oriented substantially perpendicular to the longitudinal axis in a receiver-proximal segment between (i) the connection point and (ii) a neighboring face portion of the external RF shield through which the receive line is conducted.

2. The coil assembly according to claim 1, further comprising a support structure made of a non-conducting material and arranged within the external RF shield, to which support structure the transmitter coil arrangement is rigidly connected and to which each receiver coil is rigidly connectable.

3. The coil assembly according to claim 1, wherein the tubular structure is substantially cylindrical.

4. The coil assembly according to claim 1, wherein the transmitter coil arrangement is of birdcage or TEM resonator type.

5. The coil assembly according to claim 1, wherein the transmitter coil arrangement is an array of loops, dipoles, strip lines or TEM lines.

6. The coil assembly according to one of claim 1, wherein the transmitter coil arrangement is provided with at least one RF transmitter line traversing the RF shield at a transmitter passage region to reach an RF transmitter supply device located outside of the external RF shield, at least one of said RF transmitter lines being oriented substantially perpendicular to the longitudinal axis in a region proximal to said transmitter passage region.

7. The coil assembly according to claim 1, further comprising at least one magnetic field probe rigidly connected to the transmitter coil arrangement.

8. The coil assembly according to claim 7, wherein the magnetic field probe is electrically connected, at a connection point, to a respective RF probe line leading to a probe receiver device located outside of the external RF shield, the respective RF probe line of each magnetic field probe being oriented substantially perpendicular to the longitudinal axis in a field probe-proximal segment between the connection point and a neighboring face portion of the external RF shield.

9. The coil assembly according to claim 1, wherein the ground of the receiver device and/or the ground of the transmitter device and/or the ground of the probe receiver device are each connected to the RF shield by a respective connection, each of which is a DC galvanic connection or an AC connection.

10. The coil assembly according to claim 1, wherein the external RF shield is a capacitively slotted shield.

11. The coil assembly according to claim 1, comprising a free line of sight for optical stimulation in a region between the RF receiver arrangement and the RF shield.

12. An arrangement for carrying out MR imaging or spectroscopy of a subject or object, the arrangement comprising: an MR apparatus operatively connected to a coil assembly according to claim 1, the MR apparatus comprising: a) magnetic field generator adapted to generate a main magnetic field (B.sub.0) along a field direction within the imaging volume of the coil assembly; b) magnetic field encoder adapted to encode magnetic fields superimposed to the main magnetic field; c) RF transmitter connected to the assembly's RF transmitter coil arrangement to generate said excitation field at said MR operating frequency; d) driver adapted to operate the magnetic field encoder and RF transmitter to generate superimposed time dependent encoding fields and radiofrequency fields according to an MR sequence for forming images or spectra; and e) acquisition means comprising a receiver device located outside of the assembly's external RF shield, the receiver device being connected to at least one RF receive line for acquiring MR signal; the longitudinal axis being substantially parallel to the main magnetic field.

13. The arrangement according to claim 12, wherein the receiver device is attached to the external RF shield on the outside thereof.

14. The arrangement according to claim 13, comprising at least one balun or RF trap in the: (i) RF receive line, (ii) RF transmitter line, (iii) RF probe line or combinations of two or three of (i), (ii) and (iii).

15. The arrangement according to claim 14, wherein the balun or the receiver device is electrically connected via a DC (direct current) or AC (alternating current) connection to the RF shield at least at one point.

16. An arrangement for carrying out MR imaging or spectroscopy of a subject or object, the arrangement comprising: the coil assembly of claim 1, and a MR apparatus operatively connected to the coil assembly, the MR apparatus comprising: a) magnetic field generator adapted to generate a main magnetic field (B.sub.0) along a field direction within the imaging volume of the coil assembly; b) magnetic field encoder adapted to encode magnetic fields superimposed to the main magnetic field; c) RF transmitter connected to the assembly's RF transmitter coil arrangement to generate said excitation field at said MR operating frequency; d) driver adapted to operate the magnetic field encoder and RF transmitter to generate superimposed time dependent encoding fields and radiofrequency fields according to an MR sequence for forming images or spectra; and e) acquisition means comprising a receiver device located outside of the assembly's external RF shield, the receiver device being connected to at least one RF receive line for acquiring MR signal; the longitudinal axis being substantially parallel to the main magnetic field.

17. The coil assembly according to claim 1, wherein the tubular structure is cylindrical.

18. The coil assembly according to claim 2, wherein the transmitter coil arrangement is provided with at least one RF transmitter line traversing the RF shield at a transmitter passage region to reach an RF transmitter supply device located outside of the external RF shield, at least one of said RF transmitter lines being oriented substantially perpendicular to the longitudinal axis in a region proximal to said transmitter passage region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The above mentioned and other features and objects of this invention and the manner of achieving them will become more apparent and this invention itself will be better understood by reference to the following description of embodiments of this invention taken in conjunction with the accompanying drawings, wherein are shown:

[0068] FIG. 1 an arrangement for carrying out MR imaging of a subject or object according to prior art, as a schematic vertical section;

[0069] FIG. 2 an arrangement for carrying out MR imaging of a subject or object according to the present invention, as a schematic vertical section;

[0070] FIG. 3 a coil assembly according to the present invention, as a schematic perspective representation partially cut away;

[0071] FIG. 4 a coil assembly according to the present invention, as a cross-sectional axial view, and

[0072] FIG. 5 the coil assembly of FIG. 4, as a schematical perspective view.

DETAILED DESCRIPTION OF THE INVENTION

[0073] In general, the same reference signs will be used for functionally identical or similar features in the various drawings and will thus not be described multiple times unless necessary for understanding the invention.

[0074] An arrangement for carrying out MR imaging of a subject or object S generally comprises an MR apparatus operatively connected to a coil assembly. Such an arrangement according to prior art is partially shown in FIG. 1. The coil assembly comprises an electrically conducting RF transmitter coil arrangement 2 for generating an excitation field at an MR operating frequency. The transmitter coil arrangement forms a tubular structure disposed around an imaging volume 4 and having a longitudinal axis A. An external RF shield 6, which in the example shown is also substantially tubular, surrounds the transmitter coil arrangement. The coil assembly further comprises an electrically conducting RF receiver coil 8 disposed within the imaging volume for receiving MR signal from the subject or object S disposed therein. The receiver coil 8 has a connection point 10 at which it is electrically connected to a respective RF receive line 12 connectable to a receiver device 14 located outside of the external RF shield 6.

[0075] The MR apparatus, which is not shown in detail, comprises: magnet means for generating a main magnetic field B.sub.0 along a field direction within the imaging volume 4; encoding means for generating encoding magnetic fields superimposed to the main magnetic field; RF transmitter means 15 connected to the assembly's RF transmitter coil arrangement 2 to generate said excitation field at said MR operating frequency; driver means for operating the encoding means and RF transmitter means to generate superimposed time dependent encoding fields and radiofrequency fields according to an MR sequence for forming images or spectra; and acquisition means comprising said receiver device 14 located outside of the assembly's external RF shield 6. Under operating conditions, the receiver device 14 is connected to at least one RF receive line 12 for acquiring MR signal. As shown in FIG. 1, the longitudinal axis A of the coil assembly is substantially parallel to the main magnetic field B.sub.0. Moreover, the RF receive line 12 is oriented substantially along the longitudinal axis A of the tubular transmitter coil arrangement and, correspondingly, substantially along the main magnetic field B.sub.0.

[0076] An arrangement configured according to the present invention is shown in FIGS. 2 and 3. In contrast to the arrangement of FIG. 1, the respective RF receive line 12 of the receiver coil 8 is oriented substantially perpendicular to the longitudinal axis in a receiver-proximal segment 16 between the connection point 10 and a neighboring face portion 18 of the external RF shield 6 through which the receive line 12 is conducted. As particularly seen from FIG. 2, the transmitter coil arrangement 2 is configured as a substantially cylindrical cage of a type widely used in MRI. The external RF shield 6 surrounding the transmitter coil arrangement is also substantially cylindrical and is arranged substantially co-axially to the transmitter coil. A RF receive line 12 connected to a receiver coil 8 at a connection point 10 thereof has a receiver-proximal segment 16 directed in a substantially radial direction, i.e. substantially perpendicular to the longitudinal axis A and transverses the RF shield 6 at a face portion 18 thereof through a small opening 20. Analogously, the transmitter coil arrangement 2 is provided with at least one RF transmitter line 13 traversing the RF shield at a transmitter passage region 19 to reach an RF transmitter supply device 15 located outside of the external RF shield, the RF transmitter line being oriented substantially perpendicular to the longitudinal axis (A) in a region proximal to the transmitter passage region 19.

[0077] Moreover, the ground of the receiver device 14 and/or the ground of the transmitter device 15 and/or the ground of the probe receiver device 30 are each connected to the RF shield 6 by a respective connection line 17, each of which can be a simple DC galvanic connection or an appropriate AC connection comprising, for example, a single capacitor or an RC element. For simplicity of drawing, the ground of each device is shown as a dot located at the periphery/housing of the respective device.

[0078] In order to be mechanically stable, a support structure 22 made of a non-conducting material is arranged within the external RF shield 6. The transmitter coil arrangement and the receiver coil 10 are rigidly connected to the support structure 22.

[0079] A coil assembly of a further arrangement according to the present invention is shown in FIGS. 4 and 5. In contrast to the embodiment of FIGS. 2 and 3, the coil assembly comprises two receive coils 8a and 8b, which in the example shown are disposed in a mutually overlapping manner.

[0080] As schematically shown in FIG. 4, the coil assembly according to an advantageous embodiment further comprises at least one magnetic field probe 24 rigidly connected thereto. The magnetic field probe is electrically connected, at a connection point 26 thereof, to a respective RF probe line 28 leading to a probe receiver device 30 located outside of the external RF shield. The respective RF probe line of each magnetic field probe is oriented substantially perpendicular to the longitudinal axis (A) in a field probe-proximal segment 32 between the connection point 26 and a neighboring face portion 34 of the external RF shield. In the example of FIG. 5 the receiver device 14 is mechanically attached to the external RF shield 6 by a mechanical anchoring element 36.

REFERENCES

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