WO2007048032A1

WO2007048032A1 - Conforming multichannel shoulder coil

Info

Publication number: WO2007048032A1
Application number: PCT/US2006/041231
Authority: WO
Inventors: Brian Sean Brown; Yoshinori Hamamura; Kyle Marcus Johnson; Jeff Manley Hathaway
Original assignee: Invivo Corporation
Priority date: 2005-10-20
Filing date: 2006-10-20
Publication date: 2007-04-26

Abstract

A local coil for MRI imaging of the shoulder employs a cup-like shell having rigid elements that embrace the shoulder by curving about the shoulder along two axes. The rigid elements may be hinged with respect to one another to assist in positioning the shell about the shoulder and to accommodate different sized patients.

Description

CONFORMING MULTICHANNEL SHOULDER COIL

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U. S. Provisional Application 60/728,637 hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The field of the invention is magnetic resonance imaging (MRI) and in particular local coils for use in receiving MRI signals for the region of the shoulder. [0003] In MRI, a uniform magnetic field is applied to an imaged object to align the object's nuclear spins along an axis. In response to a radio frequency (RF) excitation signal of the proper frequency, the nuclear spins are excited into precession at their Larmor frequencies. [0004] In a slice select imaging sequence, the RF excitation signal is applied to the imaged object at the same time as a magnetic field gradient. The gradient field causes only the nuclei in a slice through the object to have the necessary resonant frequency to be excited into resonance. [0005] After the excitation of the nuclei in this slice, magnetic field gradients are applied along perpendicular axes to cause the nuclei to precess at different frequencies depending on their position along these axes. The gradients spatially encodes the precessing nuclei by frequency and phase so that the nuclear spins may be mapped to an image.

[0006] A weak nuclear magnetic resonance generated by the precessing nuclei is normally sensed by a whole body coil forming part of the MRI machine. The quality of the image produced by MRI techniques is dependent, in part, on the strength of the NMR signal received from the precessing nuclei. For this reason, it is known to use an independent RF receiving coil placed in close proximity to the region of interest of the image object to improve the strength of this received signal. Such coils are termed "local coils" or "surface coils" and are used in lieu of the whole body coil. The smaller area of the local coil permits it to accurately focus on NMR signal from the region of interest. Further, such local coils may be of higher quality factor or "Q" than the RF transmitting coil increasing the selectivity of the local coil and the relative strength of the acquired NMR signal.

[0007] Local coils may be particularly useful for imaging the soft tissue of the shoulder. As a general matter, supporting the coils structure in the area of the shoulder can be difficult because of the complex surface presented by this region of the body. One solution, presented by U. S. Patent 5,136,244 assigned to the same assignee as the present application and hereby incorporated by reference provides a shoulder local coil using opposed "paddles" each holding a coil that can be fit to the front and back of a patient's shoulder through a mechanically adjustable joint. The rigid construction ensures minimal movement of this coil during the imaging process. [0008] In an alternative approach, a local coils for the shoulder may be constructed using flexible, fabric-like, materials that may be wrapped around the shoulder to fit a variety of individuals. While such coils in theory, can provide close positioning of the coil conductors to the patient, in practice, it can be difficult to correctly position the coils and to get the material of the coils properly pulled against the patient without billowing out from the patient under the natural stiffness of the flexible materials. The use of straps and tie-downs to counter this effect, can make installation of the coil time consuming and cumbersome.

SUMMARY OF THE INVENTION

[0009] The present invention provides a local shoulder coil that employs a semi-rigid cup-like shell that embraces the shoulder by curving about the shoulder along two axes. As a result, the contained coil elements may be held in close conformance to the tissue of the shoulder using a structure that minimizes motion artifacts and is simple and intuitive to position on the patient. [0010] Specifically, the present invention provides a local coil having at least two shells curving about two substantially perpendicular axes and joined by at least one hinge axis to close together defining a volume, open at one end along each axis to admit a portion of a body. Coils supported by the two shells follow the curvature of the shells to be held against a portion of the body. [0011] Thus it is a feature of at least one embodiment of the invention to provide a coil support for a local coil that conforms closely to the shoulder tissue yet is easy to position and provides a solid support for the coil elements

[0012] The two shells may be hinged about a third shell, each shell attached to the third shell by independent hinges.

[0013] Thus it is a feature of at least one embodiment of the invention to provide a coil that can be opened for easy installation, removal and cleaning and to accommodate different sizes of patients. [0014] The coil may be further supported by the third shell. [0015] Thus, it is a feature of at least one embodiment of the invention to provided a local coil that provides reception coil elements that better surround the shoulder tissue.

[0016] The independent hinges may have non-parallel axes.

[0017] Thus, it is a feature of at least one embodiment of the invention to provide a hinged structure that in the hinging action preserves a desired conformance to the shape of shoulders of different sizes so that the hinging may be used to accommodate different patients.

[0018] At least one of the first, second and third shells is supported by a base fitting against a patient supporting table.

[0019] Thus, it is a feature of at least one embodiment of the invention to provide improved stability for the supported coils and to assist in positioning of the coil.

[0020] The base may include a portion that fits beneath a patient lying on the patient supporting table when the local coil is on the patient.

[0021] Thus, it is a feature of at least one embodiment of the invention to provide a simple means of holding the local coils against the support of the table.

[0022] The two shells may each include a removable fastener element for alternately attaching one shell to the base.

[0023] Thus, it is a feature of at least one embodiment of the invention to allow the orientation of the local coil to be altered for use on a left or right patient shoulder. [0024] The shells may be attached to the base by means of an attachment element allowing superior/inferior sliding adjustment of the at least one of the first, second, and third shells with respect to the base.

[0025] Thus, it is a feature of at least one embodiment of the invention to allow the local coil to be adjusted after the patient is positioned on the table on top of the base. [0026] The third shell is lateral to the shoulder when the coil is positioned on the shoulder. [0027] Thus, it is a feature of at least one embodiment of the invention to allow the hinges to be positioned to provide improved orientation between the first and second shells for different openings of the hinges.

[0028] The coils may be multiple phased array coil loops.

[0029] Thus, it is a feature of at least one embodiment of the invention to provide a multichannel local coil for the shoulder. [0030] These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Fig. 1 is a perspective view of the local coil of the present invention showing distal- proximal curvature of the coils supports;

[0032] Fig. 2 is a side elevational view of the local coil of claim 1 showing the superior-inferior curvature of the coil supports; and

[0033] Fig. 3 is a phantom view of the coils supports showing the incorporation of multiple phased array loops in opposition about the shoulder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0034] Referring now to Fig. 1, the present invention provides local coil 8 suitable for use in imaging the shoulder. In a preferred embodiment, the local coil 8 may include a base 10 that may fit against an upper surface of a patient support table 11 on an MRI device (not shown) to be supported under a patient lying on the patient support table 11. The base 10 may have a lower surface 12 conforming generally to the upper surface of the patient support table 11 and an upper planar surface 14 against which the patient presses.

[0035] A keyway 16 may be attached to the upper planar surface 14 of the base 10 near a distal edge of the base 10 providing a slot extending generally along a superior/inferior axis 42. The keyway 16 may receive one of a downward extending and upward extending boss 20 and 22 to support a coil form 24 of the present invention against the base 10 to resist angulation with respect to the base 10 but to allow sliding adjustment along the superior/inferior axis 13. [0036] The coil form 24 generally includes an upper and lower shell 28 and 26, each hingedly attached to an intervening third shell 30 by means of hinges 32 and 34. [0037] Referring both to Fig. 1 and Fig. 2, the axes 35 of hinging of the hinges 32 and 34 generally converge toward a superior end 40 of the coil fomi 24. The shells 26 and 28 curve, both along an superior/inferior axis 42 shown in Fig. 2 and a proximal/distal axis 44 shown in Fig. 1 , and provide therefore, a cup-shaped enclosure that may conform to a shoulder of a patient and which is open at the proximal end of the proximal/distal axis 44 and the inferior end of the superior/inferior axis 42 to admit the patient's shoulder therein. Generally the shells 26 and 28 diverge from one another as one moves from the superior end of the superior/inferior axis 42 and as one moves from the proximal end of the proximal/distal axis 44.

[0038] The third shell 30, when the local coil 8 is positioned on the shoulder, is against a distal surface of the shoulder.

[0039] The bi-directional curvature of the shells 26 and 28, together with the hinging action, allows coils supported by the shells 26, 30 and 28 to closely conform to the shoulder while allowing the shells to adjust to meet the size differences between different patients,

[0040] Referring now to Fig. 3 each of the shells 26, 28 and 30 may support loops 50 providing a phased array coils structure, each phased array coil providing an electrically independent signal largely isolated from the signals of the other loops 50. In the preferred embodiment, three loops

50 may be placed in opposition in each of the shells 26 and 28 with the loops arrayed substantially vertically. A seventh loop 50 follows the third shell 30 to provide an additional channel. Alternatively, the seventh loop 50 may be a so called "butterfly" loop to provide a quadrature sensitivity of a type known in the art. Each of the loops may be provided with decoupling and isolation circuitry of a type known in the art and a preamplifier to provide a separate channel of NMR data.

[0041] It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.

Claims

CLAIMS What we claim is:

1. A local coil comprising: at least two shells curving about two substantially perpendicular axes and joined by at least one hinge axis to close together defining a volume, open at one end along each axis to admit a portion of a body; and coils supported by the two shells following a curvature of the shells to be held against a portion of the body.

2. The local coil of claim 1 wherein the two shells are hinged about a third shell, each shell attached to the third shell by independent hinges.

3. The local coil of claim 2 wherein the coil is further supported by the third shell.

4. The local coil of claim 2 wherein the independent hinges have non-parallel axes.

5. The local coil of claim 2 wherein at least one of a first, second and third shells is supported by a base fitting against a patient supporting table.

6. The local coil of claim 5 wherein the base includes a portion that fits beneath a patient lying on the patient supporting table when the local coil is on the patient.

7. The local coil of claim 5 wherein two shells each include a removable fastener element for alternately attaching one shell to the base so that an orientation of the local coil with respect to the base may be altered for use on a left or right patient shoulder.

8. The local coil of claim 5 wherein the at least one of the first, second and third shells is supported by a base fitting against a patient supporting table by means of an attachment element allowing superior/inferior sliding adjustment of the at least one of the first, second, and third shells with respect to the base.

9. The local coil of claim 1 wherein the shells are sized to receive a human shoulder.

10. The local coil of claim 9 wherein the two shells are hinged about a third shell, each shell attached to the third shell by independent hinges and wherein the third shell is lateral to the shoulder when the coil is positioned on the shoulder.

11. The local coil of claim 1 wherein the coils comprise multiple phased array coil loops.

12. The local coil of claim 11 wherein multiple different coil loops are positioned in opposition in each of the shells.

13. The local coil of claim 1 wherein each shell holds three coil loops.

14. A local coil comprising: a flexing support postionable about a patient's shoulder to provide two opposing coils support surfaces curving away from each other along a sup erior-to -inferior axis and along a distal-to-proximal axis when the flexing support is so positioned; and at least two coils supported one by each of the two opposing coils support surfaces following the curvature of the coil support surfaces to be held against the shoulder.

15. The local coil of claim 14 wherein the flexing support is attached to a base fitting against a patient supporting table.

16. The local coil of claim 15 wherein the base includes a portion that fits beneath a patient lying on the patient supporting table when the local coil is on the patient.

17. The local coil of claim 15 wherein the flexing support include at least two removable fastener element for alternately attaching one side of the flexing support to the base so that an orientation of the local coil with respect to the base may be altered for use on a left or right patient shoulder.

18. The local coil of claim 15 wherein the flexing support is attached to the base by means of an attachment element allowing superior/inferior sliding adjustment of the flexing support with respect to the base.

19. The local coil of claim 14 wherein the coils comprise multiple phased array coil loops.

20. The local coil of claim 19 wherein multiple different coil loops are positioned in opposition in each of the shells.