U.S. patent application number 12/764044 was filed with the patent office on 2011-01-20 for cryogenically cooled superconductor rf head coil array and head-only magnetic resonance imaging (mri) system using same.
Invention is credited to Erzhen Gao, Qiyuan Ma.
Application Number | 20110011102 12/764044 |
Document ID | / |
Family ID | 42225243 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110011102 |
Kind Code |
A1 |
Gao; Erzhen ; et
al. |
January 20, 2011 |
CRYOGENICALLY COOLED SUPERCONDUCTOR RF HEAD COIL ARRAY AND
HEAD-ONLY MAGNETIC RESONANCE IMAGING (MRI) SYSTEM USING SAME
Abstract
A cryogenically-cooled superconducting RF head-coil array which
may be used in whole-body MRI scanners and/or in dedicated,
head-only MRI systems. An RF head-coil array module may comprise a
vacuum thermal isolation housing comprising a double wall
hermetically sealed jacket that (i) encloses a hermetically sealed
interior space under a vacuum condition, and (ii) substantially
encloses an interior chamber region that is separate from the
hermetically sealed interior space and is configured to be
evacuated to a vacuum condition. A plurality of superconductor
radiofrequency coils are disposed in the interior chamber region,
and each radiofrequency coil is configured for at least one of
generating and receiving a radiofrequency signal for at least one
of magnetic resonance imaging and magnetic resonance spectroscopy.
At least one thermal sink member may be disposed in the interior
chamber region and in thermal contact with the superconductor
radiofrequency coils. A port is configured for cryogenically
cooling the thermal sink members.
Inventors: |
Gao; Erzhen; (Milburn,
NJ) ; Ma; Qiyuan; (Milburn, NJ) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG
745 FIFTH AVENUE- 10TH FL.
NEW YORK
NY
10151
US
|
Family ID: |
42225243 |
Appl. No.: |
12/764044 |
Filed: |
April 20, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61171074 |
Apr 20, 2009 |
|
|
|
Current U.S.
Class: |
62/51.1 ;
62/259.2 |
Current CPC
Class: |
G01R 33/3403 20130101;
G01R 33/3415 20130101; G01R 33/3815 20130101; G01R 33/34023
20130101; G01R 33/3635 20130101; G01R 33/3806 20130101; G01R
33/3804 20130101 |
Class at
Publication: |
62/51.1 ;
62/259.2 |
International
Class: |
F25B 19/00 20060101
F25B019/00; F25D 31/00 20060101 F25D031/00 |
Claims
1. A superconducting radiofrequency coil array module configured
for cryogenic cooling, comprising: a vacuum thermal isolation
housing comprising a double wall hermetically sealed jacket that
(i) encloses a hermetically sealed interior space under a vacuum
condition, and (ii) substantially encloses an interior chamber
region that is separate from the hermetically sealed interior space
and is configured to be evacuated to a vacuum condition; a
plurality of superconductor radiofrequency coils disposed in said
interior chamber region, each radiofrequency coil configured for at
least one of generating and receiving a radiofrequency signal for
at least one of magnetic resonance imaging and magnetic resonance
spectroscopy; at least one thermal sink member disposed in said
interior chamber region and in thermal contact with the
superconductor radiofrequency coils; and a port configured for
cryogenically cooling at least the thermal sink member.
2. The module according to claim 1, wherein the port is coupled to
a cryocooler that is thermally coupled to the at least one thermal
sink member.
3. The module according to claim 2, wherein the coupling of the
cryocooler to the port provides for sealing said interior chamber
region such that the interior chamber region is under a vacuum
condition.
4. The module according to claim 1, wherein said hermetically
sealed jacket is sealedly joined to a chamber having an interior
space that is coextensive with and is configured to be evacuated to
substantially the same vacuum condition as said interior chamber
region, wherein said port is provided in said chamber.
5. The module according to claim 4, wherein said chamber is
configured as a double walled chamber that encloses a hermetically
sealed intra-wall cavity that is under vacuum.
6. The module according to claim 4, wherein the port is coupled to
a cryocooler that is thermally coupled to the at least one the
thermal sink member.
7. The module according to claim 6, wherein the coupling of the
cryocooler to the port provides for sealing said interior chamber
region such that the interior chamber region is under a vacuum
condition.
8. The module according to claim 4, wherein the chamber is a double
walled stainless steel chamber.
9. The module according to claim 4, wherein the hermetically sealed
interior space is under a vacuum condition having a vacuum pressure
in the range of about 10-6 to about 10-12 Torr, and the interior
chamber region is under a vacuum condition having a vacuum pressure
in the a range of about 10-2 to about 10-6 Torr.
10. The module according to claim 9, wherein said chamber is
configured as a double walled chamber that encloses a hermetically
sealed intra-wall cavity that is under vacuum condition having a
vacuum pressure in the range of about 10-6 to about 10-12 Torr.
11. The module according to claim 1, wherein the hermetically
sealed interior space is under a vacuum condition having a vacuum
pressure in the range of about 10-6 to about 10-12 Torr, and the
interior chamber region is under a vacuum condition having a vacuum
pressure in the a range of about 10-2 to about 10-6 Torr.
12. The module according to claim 1, wherein each radiofrequency
coil is in direct thermal contact with a respective one of said
thermal sink members that are each in direct thermal contact with
another of said thermal sink members that is in thermal contact
with said cryocooler.
13. The module according to claim 1, wherein said radiofrequency
coils comprise at least eight radiofrequency coils that are
azimuthally displaced about a common longitudinal axis at a
substantially common displacement along said longitudinal axis, and
are configured for imaging a region surrounded by the
radiofrequency coils.
14. The module according to claim 1, wherein each of the
radiofrequency coils is configured to receive and not transmit
radiofrequency signals.
15. The module according to claim 1, wherein the superconductor
material comprises an HTS material.
16. The module according to claim 1, wherein the vacuum thermal
isolation housing and radiofrequency coils are dimensioned and
configured for head imaging and not whole body imaging.
17. The module according to claim 16, wherein said radiofrequency
coils comprise at least eight radiofrequency coils that are
azimuthally displaced about a common longitudinal axis at a
substantially common displacement along said longitudinal axis, and
are configured for imaging a region surrounded by the
radiofrequency coils.
18. The module according to claim 1, wherein the radiofrequency
coil array module is dimensioned and configured for use in a
head-only magnetic resonance imaging system that comprises a main
electromagnet system comprising: a first and second set of high
temperature superconductor coils which are configured to be coaxial
relative to a common longitudinal axis; wherein the first coil set
includes at least two coils having an inner radius and disposed in
a first region of a length along the common axis to cover a head
and neck of a human body, and the second coil set includes at least
one coil having an inner radius and disposed in a second region of
a length along the common axis to cover a portion of a human torso,
wherein the inner radius of the second coil set is greater than the
inner radius of the first coil set; and wherein the first and
second coils are configured to provide a uniform magnetic field in
the first region to provide for imaging a region of interest of the
individual's head when positioned within the first region.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/171,074, filed Apr. 20, 2009, which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates generally to magnetic
resonance imaging and spectroscopy, and, more particularly, to
magnetic resonance imaging and spectroscopy apparatus employing
superconductor components, and to methods for manufacturing such
apparatus.
BACKGROUND
[0003] Magnetic Resonance Imaging (MRI) technology is commonly used
today in larger medical institutions worldwide, and has led to
significant and unique benefits in the practice of medicine. While
MRI has been developed as a well-established diagnostic tool for
imaging structure and anatomy, it has also been developed for
imaging functional activities and other biophysical and biochemical
characteristics or processes (e.g., blood flow,
metabolites/metabolism, diffusion), some of these magnetic
resonance (MR) imaging techniques being known as functional MRI,
spectroscopic MRI or Magnetic Resonance Spectroscopic Imaging
(MRSI), diffusion weighted imaging (DWI), and diffusion tensor
imaging (DTI). These magnetic resonance imaging techniques have
broad clinical and research applications in addition to their
medical diagnostic value for identifying and assessing pathology
and determining the state of health of the tissue examined.
[0004] During a typical MRI examination, a patient's body (or a
sample object) is placed within the examination region and is
supported by a patient support in an MRI scanner where a
substantially constant and uniform primary (main) magnetic field is
provided by a primary (main) magnet. The magnetic field aligns the
nuclear magnetization of precessing atoms such as hydrogen
(protons) in the body. A gradient coil assembly within the magnet
creates a small variation of the magnetic field in a given
location, thus providing resonance frequency encoding in the
imaging region. A radio frequency (RF) coil is selectively driven
under computer control according to a pulse sequence to generate in
the patient a temporary oscillating transverse magnetization signal
that is detected by the RF coil and that, by computer processing,
may be mapped to spatially localized regions of the patient, thus
providing an image of the region-of-interest under examination.
[0005] In a common MRI configuration, the static main magnetic
field is typically produced by a solenoid magnet apparatus, and a
patient platform is disposed in the cylindrical space bounded by
the solenoid windings (i.e. the main magnet bore). The windings of
the main field are typically implemented as a low temperature
superconductor (LTS) material, and are super-cooled with liquid
helium in order to reduce resistance, and, therefore, to minimize
the amount of heat generated and the amount of power necessary to
create and maintain the main field. The majority of existing LTS
superconducting MRI magnets are made of a niobium-titanium (NbTi)
and/or Nb.sub.3Sn material which is cooled with a cryostat to a
temperature of 4.2 K.
[0006] As is known to those skilled in the art, the magnetic field
gradient coils generally are configured to selectively provide
linear magnetic field gradients along each of three principal
Cartesian axes in space (one of these axes being the direction of
the main magnetic field), so that the magnitude of the magnetic
field varies with location inside the examination region, and
characteristics of the magnetic resonance signals from different
locations within the region of interest, such as the frequency and
phase of the signals, are encoded according to position within the
region (thus providing for spatial localization). Typically, the
gradient fields are created by current passing through coiled
saddle or solenoid windings, which are affixed to cylinders
concentric with and fitted within a larger cylinder containing the
windings of the main magnetic field. Unlike the main magnetic
field, the coils used to create the gradient fields typically are
common room temperature copper windings. The gradient strength and
field linearity are of fundamental importance both to the accuracy
of the details of the image produced and to the information on
tissue chemistry (e.g., in MRSI).
[0007] Since MRI's inception, there has been a relentless pursuit
for improving MRI quality and capabilities, such as by providing
higher spatial resolution, higher spectral resolution (e.g., for
MRSI), higher contrast, and faster acquisition speed. For example,
increased imaging (acquisition) speed is desired to minimize
imaging blurring caused by temporal variations in the imaged region
during image acquisition, such as variations due to patient
movement, natural anatomical and/or functional movements (e.g.,
heart beat, respiration, blood flow), and/or natural biochemical
variations (e.g., caused by metabolism during MRSI). Similarly, for
example, because in spectroscopic MRI the pulse sequence for
acquiring data encodes spectral information in addition to spatial
information, minimizing the time required for acquiring sufficient
spectral and spatial information to provide desired spectral
resolution and spatial localization is particularly important for
improving the clinical practicality and utility of spectroscopic
MRI.
[0008] Several factors contribute to better MRI image quality in
terms of high contrast, resolution, and acquisition speed. An
important parameter impacting image quality and acquisition speed
is the signal-to-noise ratio (SNR). Increasing SNR by increasing
the signal before the preamplifier of the MRI system is important
in terms of increasing the quality of the image. One way to improve
SNR is to increase the magnetic field strength of the magnet as the
SNR is proportional to the magnitude of the magnetic field. In
clinical applications, however, MRI has a ceiling on the field
strength of the magnet (the US FDA's current ceiling is 3 T
(Tesla)). Other ways of improving the SNR involve, where possible,
reducing sample noise by reducing the field-of-view (where
possible), decreasing the distance between the sample and the RF
coils, and/or reducing RF coil noise.
[0009] Despite the relentless efforts and many advancements for
improving MRI, there is nevertheless a continuing need for yet
further improvements in MRI, such as for providing greater
contrast, improved SNR, higher acquisition speeds, higher spatial
and temporal resolution, and/or higher spectral resolution.
[0010] Additionally, a significant factor affecting further use of
MRI technology is the high cost associated with high magnetic field
systems, both for purchase and maintenance. Thus, it would be
advantageous to provide a high quality MRI imaging system that is
capable of being manufactured and/or maintained at reasonable cost,
permitting MRI technology to be more widely used.
SUMMARY OF INVENTION
[0011] Various embodiments of the present invention provide a
cryogenically cooled superconducting RF head-coil array which may
be used in whole-body MRI scanners and/or in dedicated, head-only
MRI systems (also referred to herein as "head-dedicated MRI
systems," "head-only MRI systems," or the like). Some embodiments
of the invention provide a head-dedicated MRI system and, more
particularly, various embodiments provide a superconducting main
magnet for a head-dedicated MRI system which, in some embodiments,
further comprises a cryogenically-cooled superconducting RF
head-coil array according to embodiments of the present
invention.
[0012] In accordance with some embodiments, a superconducting
radiofrequency coil array module configured for cryogenic cooling
comprises: a vacuum thermal isolation housing comprising a double
wall hermetically sealed jacket that (i) encloses a hermetically
sealed interior space under a vacuum condition, and (ii)
substantially encloses an interior chamber region that is separate
from the hermetically sealed interior space and is configured to be
evacuated to a vacuum condition; a plurality of superconductor
radiofrequency coils disposed in said interior chamber region and
configured, each radiofrequency coil configured for at least one of
generating and receiving a radiofrequency signal for at least one
of magnetic resonance imaging and magnetic resonance spectroscopy;
at least one thermal sink member disposed in said interior chamber
region and in thermal contact with the superconductor
radiofrequency coils; and a port configured for cryogenically
cooling at least the thermal sink member. The port may be coupled
to a cryocooler that is thermally coupled to the at least one
thermal sink member.
[0013] In some embodiments, each radiofrequency coil is in direct
thermal contact with a respective one of the thermal sink members
that are each in direct thermal contact with another of the thermal
sink members that is in thermal contact with the cryocooler.
[0014] The radiofrequency coils may comprise at least eight
radiofrequency coils that are azimuthally displaced about a common
longitudinal axis at a substantially common displacement along the
longitudinal axis, and are configured for imaging a region
surrounded by the radiofrequency coils. Each of the radiofrequency
coils may be configured to receive and not transmit radiofrequency
signals.
[0015] The vacuum thermal isolation housing and radiofrequency
coils may be dimensioned and configured for head imaging and not
whole body imaging. In some embodiments, the radiofrequency coil
array module is dimensioned and configured for use in a head-only
magnetic resonance imaging system that comprises a main
electromagnet system comprising: a first and second set of high
temperature superconductor coils which are configured to be coaxial
relative to a common longitudinal axis; wherein the first coil set
includes at least two coils having an inner radius and disposed in
a first region of a length along the common axis to cover a head
and neck of a human body, and the second coil set includes at least
one coil having an inner radius and disposed in a second region of
a length along the common axis to cover a portion of a human torso;
and wherein the first and second coils are configured to provide a
uniform magnetic field in the first region to provide for imaging a
region of interest of the individual's head when positioned within
the first region.
[0016] It will be appreciated by those skilled in the art that the
foregoing brief description and the following detailed description
are exemplary and explanatory of the present invention, but are not
intended to be restrictive thereof or limiting of the advantages
which can be achieved by this invention. Additionally, it is
understood that the foregoing summary of the invention is
representative of some embodiments of the invention, and is neither
representative nor inclusive of all subject matter and embodiments
within the scope of the present invention. Thus, the accompanying
drawings, referred to herein and constituting a part hereof,
illustrate embodiments of this invention, and, together with the
detailed description, serve to explain principles of embodiments of
the invention. Aspects, features, and advantages of embodiments of
the invention, both as to structure and operation, will be
understood and will become more readily apparent when the invention
is considered in the light of the following description made in
conjunction with the accompanying drawings, in which like reference
numerals designate the same or similar parts throughout the various
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Aspects, features, and advantages of embodiments of the
invention, both as to structure and operation, will be understood
and will become more readily apparent when the invention is
considered in the light of the following description made in
conjunction with the accompanying drawings, in which like reference
numerals designate the same or similar parts throughout the various
figures, and wherein:
[0018] FIGS. 1A and 1B schematically depict orthogonal views of an
illustrative cryogenically cooled superconducting RF head coil
array, in accordance with some embodiments of the present
invention;
[0019] FIG. 2 schematically illustrates wall(s) of the vacuum
chamber depicted in FIG. 1A being implemented as a double-walled
glass Dewar, in accordance with some embodiments of the present
invention;
[0020] FIG. 3 schematically depicts an illustrative cross-sectional
view along the longitudinal axis of a superconductor RF head coil
array corresponding to embodiments depicted in FIGS. 1A and 1B with
the vacuum chamber comprising a Dewar 1 according to various
embodiments represented by FIG. 2, in accordance with some
embodiments of the present invention;
[0021] FIGS. 4A and 4B, depict an illustrative alternative
implementation of a superconductor RF head coil array (module), in
accordance with some embodiments of the present invention;
[0022] FIG. 5 schematically depicts a cross section of an
illustrative MRI system, in accordance with some embodiments of the
present invention;
[0023] FIG. 6 schematically depicts an illustrative RF head coil
array that includes thermal radiation screening, in accordance with
some embodiments of the present invention;
[0024] FIG. 7 schematically depicts a cross-sectional view of a
superconducting main magnet of a head-only MRI system, in
accordance with some embodiments of the present invention;
[0025] FIG. 8 depicts with reference to the z-r plane a coil
configuration of a superconducting main magnet system, in
accordance with some embodiments of the present invention;
[0026] FIG. 9 depicts a normalized current distribution for the
main magnet coil arrangement corresponding to the illustrative
embodiment of FIGS. 7 and 8, in accordance with some embodiments of
the present invention;
[0027] FIG. 10 is an illustrative coil pattern (depicted in the z-r
plane, with units normalized to meters) of a 3 T head magnetic
resonance imaging scanner, in accordance with various embodiments
of the present invention;
[0028] FIG. 11 is a plot showing the magnetic field distribution
for the illustrative embodiment depicted in FIG. 10, in accordance
with some embodiments of the present invention; and
[0029] FIG. 12 shows the fringe fields of one Gauss (1 G), three
Gauss (3 G) and five Gauss (5 G) lines for the field distribution
of FIG. 11, in accordance with an illustrative embodiment of the
present invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0030] The ensuing description discloses (i) various embodiments of
a cryogenically cooled superconducting RF head-coil array which may
be used in whole-body MRI scanners and/or in dedicated, head-only
MRI systems (also referred to herein as "head-dedicated MRI
systems," "head-only MRI systems," or the like) and (ii) various
embodiments of a head-dedicated MRI system and, more particularly,
various embodiments of a superconducting main magnet for a
head-dedicated MRI system which, in some embodiments, further
comprises a cryogenically-cooled superconducting RF head-coil array
according to embodiments of the present invention.
[0031] More specifically, as will be further understood by those
skilled in the art in view of the ensuing description, a
cryogenically-cooled superconducting RF head-coil array coil
according to various embodiments of the present invention may be
implemented in myriad magnetic resonance imaging and spectroscopy
systems, such as systems employing conventional copper gradient
coils, systems employing superconducting gradient coils (e.g., such
as disclosed in U.S. patent application Ser. No. 12/416,606, filed
April 1, 2009, and in Provisional Application No. 61/170,135, filed
Apr. 17, 2009, each of which is hereby incorporated by reference in
its entirety), whole body systems, dedicated head-only systems,
systems with a vertically or horizontally oriented main magnetic
field, open or closed systems, etc. Similarly, as will be further
understood by those skilled in the art in view of the ensuing
description, a head-dedicated MRI system employing a
superconducting main magnet according to various embodiments of the
present invention may be implemented in myriad magnetic resonance
imaging and spectroscopy systems, such as systems employing
conventional copper gradient coils, systems employing
superconducting gradient coils (e.g., such as disclosed in U.S.
patent application Ser. No. 12/416,606, filed Apr. 1, 2009, and in
Provisional Application No. 61/170,135, filed Apr. 17, 2009, each
of which is hereby incorporated by reference in its entirety),
systems employing conventional (e.g., copper) head coils or coil
arrays, and/or systems employing a superconducting RF head coil
array (e.g., according to superconducting RF head-coil embodiments
described herein), etc. Similarly, it will also be understood by
those skilled in the art that while various portions of the ensuing
description may be set forth in the context of an MRI system that
may be used for structural examination of a patient, various
embodiments of the present invention may be employed in connection
with magnetic resonance (MR) systems operated and/or configured for
other modalities, such as functional MRI, diffusion weighted and/or
diffusion tensor MRI, MR spectroscopy and/or spectroscopic imaging,
etc. Additionally, as used herein, MRI includes and embraces
magnetic resonance spectroscopic imaging, diffusion tensor imaging
(DTI), as well as any other imaging modality based on nuclear
magnetic resonance.
[0032] FIGS. 1A and 1B schematically depict orthogonal views of an
illustrative cryogenically cooled superconducting RF head coil
array 10, in accordance with some embodiments of the present
invention. (For convenience and ease of reference and additional
clarity of exposition, orthogonal x, y, z coordinates are depicted
as a reference frame.) More specifically, FIG. 1A is a
cross-sectional view in the x-y plane indicated by reference IA-IA'
in FIG. 1B, and illustrates a configuration of eight
superconducting RF coils 3a-3h (also referred to herein
collectively as superconductor RF coils 3 or RF coil array 3) each
disposed in thermal contact with a respective one of eight thermal
conductors 5a-5h (e.g., non-metallic high thermal conductivity
materials, such as high thermal conductivity ceramic, such as
sapphire or alumina), with the RF coils 3a-3h and thermal
conductors 5a-5h being disposed within a sealed vacuum chamber
having vacuum chamber wall(s) 2.
[0033] FIG. 1B is a side view along the longitudinal axis (i.e., z
axis) viewed from the direction indicated by reference IB in FIG.
1A, and illustrates components comprising the cooling system of
superconducting RF head coil array 10, the cooling system including
thermal conductor 15 (e.g., non-metallic high thermal conductivity
materials, such as high thermal conductivity ceramic, such as
sapphire or alumina) in thermal contact with each of thermal
conductors 5a-5h, cold head 9 in thermal contact with thermal
conductor (sink) 15, and cryocooler 7 configured for maintaining
the cold head 9 at a desired cryogenic temperature. For clarity of
exposition, however, FIG. 1B does not show (i) the vacuum chamber
comprising vacuum chamber wall(s) 2, (ii) coils 3b and 3d, and
(iii) thermal conductors 5b and 5d (as will be further understood
from the ensuing description (e.g., in connection with FIG. 3),
FIG. 1B also does not show a vacuum chamber portion into which
cryocooler 7 is mounted).
[0034] Accordingly, in the configuration of the superconducting RF
head coil array 10 depicted in FIGS. 1A and 1B, coils 3a-3h are in
vacuum and cooled by the thermal conductors 5a-5b, which conduct
heat away from the coils to the thermal conductor/sink 15, which is
thermally coupled with a cryogenic cooler 7. As will be understood
by those skilled in the art, in some embodiments (e.g., low main
magnetic field implementations, such as less than 3 T, or less than
1.5 T, etc.) small amounts of metal, such as copper, may be used
for thermal conductor/sink 15 and/or possibly thermal conductors
5a-5h. In some embodiments, thermal conductors 5a-5h may be
integrally formed with thermal conductor/sink 15, whereas in some
embodiments, one or more of thermal conductors 5a-5h are distinct
members that are mechanically joined (e.g., using epoxy, etc.) to
thermal conductor/sink 15 to provide a good thermal conduction
therebetween. In various embodiments, the coils 3a-3h may be cooled
to a temperature in the range of about 4K to 100K, and more
particularly, to a temperature below the critical temperature of
the superconducting material (e.g., in some embodiments, below the
critical temperature of a high temperature superconductor (HTS)
material used for the RF coils 3a-3h).
[0035] More particularly, in accordance with various embodiments of
the present invention, each of RF coil elements 3a-3h is
implemented as a high temperature superconductor (HTS), such as
YBCO and/or BSCCO, etc. (e.g., using an HTS thin film or HTS tape),
though a low temperature superconductor (LTS) may be used in
various embodiments. For example, in some embodiments, each of RF
coil elements 3a-3h is an HTS thin film spiral coil and/or an HTS
thin film spiral-interdigitated coil on a substrate such as
sapphire or lanthanum aluminate. The design and fabrication of such
coils is further described in and/or may be further understood in
view of, for example, Ma et al., "Superconducting RF Coils for
Clinical MR Imaging at Low Field," Academic Radiology, vol. 10, no.
9, September 2003, pp. 978-987; Gao et al., "Simulation of the
Sensitivity of HTS Coil and Coil Array for Head Imaging,"
ISMRM-2003, no. 1412; Fang et al., "Design of Superconducting MRI
Surface Coil by Using Method of Moment," IEEE Trans. on Applied
Superconductivity, vol. 12, no. 2, pp. 1823-1827 (2002); and Miller
et al., "Performance of a High Temperature Superconducting Probe
for In Vivo Microscopy at 2.0 T," Magnetic Resonance in Medicine,
41:72-79 (1999), each of which is incorporated by reference herein
in its entirety. Accordingly, in some embodiments, superconducting
RF head coil array 10 is implemented as an HTS thin film RF head
coil array.
[0036] As depicted in FIG. 2, in accordance with some embodiments
of the present invention, vacuum chamber comprising wall(s) 2 may
comprise a double-walled Dewar 1 made of glass and/or other
non-conductive, mechanically strong material(s), such as G10, RF4,
plastic, and/or ceramic. More specifically, FIG. 2 schematically
illustrates wall(s) 2 of the vacuum chamber depicted in FIG. 1A
being implemented as a double-walled glass Dewar 1, in accordance
with some embodiments of the present invention. It will be
understood that the dimensions and shape of a cryogenically cooled
superconducting RF head-coil array module may be modified according
to various implementations of the present invention. In accordance
with some implementations, FIG. 2 schematically illustrates a glass
dewar portion 1 of a cryogenically cooled superconducting RF
head-coil array module that may be used, for example, in a magnetic
resonance imaging system dedicated to head imaging, wherein the
glass dewar components may have the following approximate
dimensions, provided merely by way of example and for additional
clarity of exposition: cylinder 60 has an inner diameter, outer
diameter, and axial length of 230 mm, 236 mm, and 254 mm,
respectively; cylinder 62 has an inner diameter, outer diameter,
and axial length of 246 mm, 252 mm, and 254 mm, respectively;
cylinder 64 has an inner diameter, outer diameter, and axial length
of 280 mm, 286 mm, and 312 mm, respectively; cylinder 66 has an
inner diameter, outer diameter, and axial length of 296 mm, 302 mm,
and 330 mm, respectively; inner bottom plate (circular/cylindrical)
74 has a diameter of 236 mm and a thickness of 12.7 mm; outer
bottom plate (circular/cylindrical) 76 has a diameter of 252 mm and
a thickness of 12.7 mm; ring (annular) 66 has an inner diameter,
outer diameter, and thickness (axial) of 246 mm, 286 mm, and 12.7
mm, respectively; ring (annular) 68 has an inner diameter, outer
diameter, and thickness (axial) of 230 mm, 302 mm, and 12.7 mm,
respectively; and ring (annular) 72 has an inner diameter, outer
diameter, and thickness (axial) of 280 mm, 302 mm, and 12.7 mm,
respectively. Also shown are two of eight small spacer disks 78,
having an approximate diameter of 5 mm as well as a height that
provides for a gap of about 5 mm between the inner bottom plate 74
and outer bottom plate 76. In this illustrative embodiment, a plug
70 seals off a standard vacuum port in ring 68 through which the
intra-dewar cavity is evacuated.
[0037] It will be understood that double-walled Dewar 1 may be
constructed, in a variety of ways, as a continuous, hermetically
sealed glass housing enclosing an interior chamber (or cavity) 4 in
which at least a low vacuum condition and, in accordance with some
embodiments, preferably at least a high vacuum condition (e.g.,
about 10.sup.-6 Torr or lower pressure) is maintained. For example,
in accordance with some embodiments, double-walled Dewar 1 may be
manufactured as follows: (i) forming two generally cylindrical
(e.g., but hexagonal in cross-section transverse to the
longitudinal/cylindrical access) double-walled structures each
having a generally U-shaped wall cross-section, the first
corresponding to continuous glass wall portion 1a (comprising
cylinders 60 and 66, ring 68 and plate 74) and the second
corresponding to continuous wall portion 1b (comprising cylinders
62 and 64, ring 66, and plate 76), (ii) fitting the generally
cylindrical continuous glass wall portion 1b into the annular space
of generally cylindrical continuous glass wall portion 1a, possibly
using glass spacers therebetween (e.g., identified in FIG. 2 as
disks 78), and (iii) glass-bonding, fusing, or otherwise sealing
the open end between 1a and 1b (i.e., the end that is later
sealably mounted to stainless steel chamber 8, further described
below in connection with FIG. 3), (e.g., by bonding, fusing, or
otherwise sealing ring 72 to the open end) to hermetically seal
cavity 4 under high vacuum, and (iv) pumping the cavity 4 to a high
vacuum through the depicted standard vacuum port, which is
hermetically sealed (e.g., using cap 70) after pumping to the
desired vacuum pressure. It may be appreciated that the vacuum
sealing step may be performed in myriad ways. For example, portions
1a and 1b may be joined and sealed to each other within a vacuum
chamber, or, as described, the ends of 1a and 1b may be fused to
each other except for a small region that is used as a vacuum
pumping port and that is sealed after pumping the cavity to high
vacuum therethrough. In various embodiments, double-walled Dewar 1
may be implemented in accordance with, or similar to, the
hermetically sealed double-walled structures (and vacuum thermal
isolation housing) described in U.S. application Ser. No.
12/212,122, filed Sep. 17, 2008, and in U.S. application Ser. No.
12/212,147, filed Sep. 17, 2008, each of which is herein
incorporated by reference in its entirety.
[0038] FIG. 3 schematically depicts an illustrative cross-sectional
view along the longitudinal axis of a superconductor (e.g., HTS) RF
head coil array corresponding to embodiments depicted in FIGS. 1A
and 1B with the vacuum chamber comprising a Dewar 1 according to
various embodiments represented by FIG. 2. As shown, Dewar 1 is
sealably joined to a double-walled stainless steel chamber 8 that
includes a flange to which cryocooler 7 is sealably mounted. In
various embodiments, double-walled stainless steel chamber 8 is
hermetically sealed, enclosing an interior chamber (or cavity) 12
in which at least a low vacuum condition and, in accordance with
some embodiments, preferably at least a high vacuum condition
(e.g., about 10.sup.-6 Torr or lower pressure) is maintained. By
way of example, the joint between the hermetically sealed
double-walled Dewar 1 (e.g., glass) and the stainless steel chamber
may be formed by epoxy bonding, welding, or other hermetically
sealed flange connection, providing a sufficient seal to maintain
at least a low vacuum condition (e.g., about 10.sup.-2 to about
10.sup.-5 Torr) in the interior chamber portion 6 that houses the
superconducting RF coils 3 and thermal conductors 5 (i.e., 5a-5h)
and 15. Also by way of example, the vacuum seal between cryocooler
7 and the flange of stainless steel chamber 8 may be provided by an
O-ring or other sealing mechanism (e.g., metal gasket/knife-edge
connection) to, similarly, maintain the at least low vacuum
condition in the interior chamber portion 6 that houses the RF
coils 3 and thermal conductors 5 and 15. Those skilled in the art
understand, however, that chamber 8 may be made of materials other
than stainless steel, e.g., aluminum or other metallic or other
non-metallic material, such as glass, ceramic, plastics, or
combination of these materials, and such other materials may be
appropriately joined to Dewar 1 and cryocooler 7.
[0039] In various embodiments, cryocooler 7 may be implemented as
any of various single stage or multi-stage cryocoolers, such as,
for example, a Gifford McMahon (GM) cryocooler, a pulse tube (PT)
cooler, a Joule-Thomson (JT) cooler, a Stirling cooler, or other
cryocooler. In various alternative embodiments, the superconductor
RF head coil array 10 may be configured for cooling such that coils
3 are cooled by a cryogen, such as liquid helium and liquid
nitrogen.
[0040] It is understood that while not shown in the drawings, a
cryogenically cooled superconductor RF coil array (e.g., array 10)
in accordance with various embodiments of the present invention
includes at least one electrical feedthrough (e.g., through chamber
8) to provide for coupling electrical signals into and/or out of
the array (e.g., for the RF coils, for controlling and/or
monitoring any sensors (e.g., pressure and/or temperature, etc.)
that may be provided in the module). Additionally, it will be
understood that at least a portion of receiver and/or, if
applicable, transmitter circuitry (e.g., amplifiers and/or filters
and/or appropriate matching and/or decoupling circuitry) for each
of the RF coils may be provided within the vacuum chamber; for
example, it may be disposed on and in thermal contact with thermal
conductors 5a-5h, wherein such cooling may provide for improving
noise properties and/or for using superconducting components for at
least a portion of such circuitry.
[0041] As understood in view of the foregoing description, in
accordance with various embodiments of the present invention,
superconducting RF head coil array 10 is implemented as a
receive-only array, with an RF transmitter being implemented as a
separate RF coil (not shown), which in various embodiments may be a
conventional (e.g., non-superconducting, such as a conventional
copper RF coil) RF transmitter coil or a superconducting RF
transmitting coil. Such a separate transmitter coil may be
configured external to the vacuum chamber comprising wall(s) 2
(e.g., external to Dewar 1) or, in some embodiments, within the
vacuum chamber comprising wall(s) 2 (e.g., within Dewar 1). For
instance, in the case that an RF transmission coil is implemented
as one or more superconducting RF transmission coils (e.g., a high
temperature superconductor (HTS) RF transmitter) that are separate
from the RF receiver coils, then, in some embodiments, such one or
more superconducting RF transmission coils may be disposed in
thermal contact with one or more of thermal conductors 5a-5h.
[0042] In some embodiments, superconducting RF head coil array 10
may be implemented as a transmit and receive coil array (a
transceiver array), with each of one or more of the superconducting
RF coils 3a-3h being used for both transmission and reception of RF
signals.
[0043] In accordance with various embodiments of the present
invention, one or more of the superconducting RF coil elements
3a-3h may be implemented as a multiple resonance RF coil element
(e.g., comprising two or more receiving coils having different
resonant frequencies, such as for detecting sodium and hydrogen
resonances at a given magnetic field (e.g., at 3 Tesla (T)). In
some embodiments, two or more different ones of superconducting RF
coil elements 3a-3h may be designed to have different resonant
frequencies; for example, RF coil elements 3a, 3c, 3e, and 3g may
be tuned to a first resonant frequency (e.g., that of hydrogen
nuclei at 3 T) and RF coil elements 3b, 3d, 3f, and 3h may be tuned
to a second resonant frequency (e.g., that of sodium nuclei at 3
T). As such, a superconducting RF head coil array in accordance
with various embodiments of the present invention may be used for
acquiring magnetic resonance signals from different types of nuclei
in a simultaneous or time-multiplexed manner.
[0044] It is further understood that while the hereinabove
described figures depict an illustrative embodiment of a
superconducting RF head coil array having eight RF receiving
channels (e.g., eight receiver coils), alternative embodiments of
the present invention may comprise superconducting RF head coil
arrays having less or more than eight superconducting RF receiving
channels (e.g., less or more than eight RF receiver.
[0045] Additionally, as indicated above, it is understood that
according to some embodiments of the present invention, a
cryogenically-cooled superconducting RF head-coil array coil
according to various embodiments of the present invention may be
implemented in a magnetic resonance imaging system that employs
superconducting gradient coils such as those disclosed in U.S.
patent application Ser. No. 12/416,606, filed Apr. 1, 2009, and in
Provisional Application No. 61/170,135, filed Apr. 17, 2009, each
of which is hereby incorporated by reference in its entirety. In
some embodiments, one or more of the superconducting gradient coils
may be disposed within the same vacuum chamber as the
superconducting RF coils (e.g., the gradient coils may be in
thermal contact with the surfaces of thermal conductors 5a-5h that
are opposite the surfaces in contact with coils 3a-3h).
[0046] Referring now to FIGS. 4A and 4B, there is shown an
illustrative alternative implementation of a superconductor RF head
coil array (module), in accordance with some embodiments of the
present invention. More specifically, FIG. 4A schematically depicts
a cross-sectional view in a plane containing the longitudinal axis,
similar to the cross-sectional view depicted with respect to the
embodiment of FIG. 3 (e.g., viewing an x-z plane cross-section,
using a coordinate system oriented similarly to that for the
embodiment of FIGS. 1A, 1B, 2 and 3), while FIG. 4B generally
depicts a plan or end-on view, viewed from the left-hand side of
FIG. 4A, but showing a cut-away or cross-section of stainless steel
chamber 8 to reveal the portion of cryocooler 7 within the chamber
8. As may be appreciated, because the embodiment depicted in FIGS.
4A and 4B is similar to that of FIGS. 1A, 1B, 2 and 3, for
convenience and ease of reference, identical reference numerals
have been used to identify corresponding or similar elements. As
may also be understood, a difference between the embodiment
depicted in FIGS. 1B, 2 and 3 and the embodiment depicted in FIG.
4A and 4B is that the former embodiment is configured such that the
end disposed near the cryocooler is closed, whereas the dewar 1 and
chamber 8 (sealably connected via, e.g., epoxy bond/sealing 16) of
the latter embodiment are configured to provide for the end
disposed near the cryocooler being open. Similarly, in connection
with the open-ended design of FIGS. 4A and 4B, a thermal conductive
ring 25 (cylindrical ring) is thermally coupled to each thermal
conductor 5a-h (5a and 5e shown in FIG. 4A) and to cryocooler 7,
which is sealably mounted (e.g., via an O-ring sealed flange 19) to
chamber 8.
[0047] As will be understood by those skilled in the art, a
generally cylindrically shaped RF head coil array module such as
depicted in the foregoing described embodiments may be well suited
for use, for example, in an MRI system that employs a cylindrical,
solenoid main magnet structure that generates a substantially
uniform, horizontal magnetic field. For example, such an MRI system
is schematically depicted in FIG. 5 in longitudinal cross section,
and includes cylindrical main magnet 17 having a bore in which a
superconductor RF head coil array (module) 10 corresponding to that
of FIGS. 4A and 4B is disposed, and which also includes gradient
coil(s) 13. It will be understood, however, that cryogenically
cooled superconducting RF head coil array 10 may be implemented
with main magnet configurations other than a cylindrical, solenoid
magnet that provides horizontal fields and/or, for example, may be
implemented with open magnet configurations, such as vertical
magnet or a double-donut magnet. It is also understood that,
according to various embodiments, main magnet 17 may be the main
magnet of a whole-body scanner or may be the main magnet of a
dedicated (e.g., head-only) system (e.g., such as the main magnet
described hereinbelow in connection with FIGS. 7-12).
[0048] FIG. 6 schematically depicts an illustrative RF head coil
array that includes thermal radiation screening, in accordance with
some embodiments of the present invention. More specifically, FIG.
6 depicts the upper half of the coil depicted in FIG. 4A, further
showing thermal radiation screens 17 that are used as an option to
further protect the low temperature of the RF coil 3a and the
non-metallic thermal conductor 5a from heating by the radiation
from the outer wall of the double-walled glass dewar and the
environment outside the dewar. Thermal radiation screen 17 may be
made from one or more materials, such as foam, fabricate, cotton,
or other non-metallic, good thermal insulation materials or
combinations thereof.
[0049] As indicated above, while a superconductor RF head coil
array in accordance with the hereinabove embodiments may be
implemented in connection with a whole-body MRI scanner, such RF
head coil arrays may alternatively be used in dedicated, head-only
MRI scanners. In accordance with some embodiments of the present
invention, a dedicated head-only scanner may implement a
superconductor main magnet in accordance with embodiments
represented by, and described in connection with, the following
drawings. It will be understood, however, that MRI scanners
employing a superconductor main magnet according to the ensuing
embodiments may employ various RF coil configurations (e.g., array,
non-array type, superconducting, non-superconducting, etc.), though
some embodiments may employ superconducting RF head coil arrays
implemented in accordance with embodiments described
hereinabove.
[0050] FIG. 7 schematically depicts a cross-sectional view of a
superconducting main magnet of a head-only MRI system, the
superconducting main magnet comprising double-walled housing 41 and
solenoid/helical coils 42, with a subject illustrated disposed
therein with the subject's head arranged within the
diameter-sensitive volume 43 of the main magnet. As shown,
double-walled housing 41 encloses a hermetically sealed region 47
that is under at least a low vacuum condition, but preferably is
under high vacuum (e.g., 10.sup.-6 to 10.sup.-12 Torr), and also
encloses an interior chamber region 45 in which superconducting
coils 42 are disposed and which is under at least a low vacuum
condition (e.g., 10.sup.-3 to 10.sup.-6 Torr).
[0051] More specifically, in accordance with some embodiments, the
superconducting main magnet is an electromagnet system comprising a
vacuum thermal isolation housing 41 (e.g., a dewar) that is
integrated with a cryogenic system (not shown) to provide for
cooling superconducting coils 42 via a heat pipe (not shown) and a
heat sink assembly (not shown) in thermal contact with the
superconducting coils. Superconducting coils may be implemented as
high temperature superconductor (HTS) coils and, in some
embodiments, may comprise at least one of the following
superconductor materials: YBaCuO, BiSrCaCuO, TIBiCaCuO, and
MgB.sub.2. By way of example, the temperature in the interior
chamber region in which the coils are disposed may be in the range
of about 77K-80K.
[0052] In accordance with some embodiments, as shown, the coils are
configured as (i) a first coil set that is disposed in a first
region to cover or surround or otherwise be disposed adjacent to an
individual's head, and (ii) a second coil set that is coaxial with
the first coil set and is disposed in a second region to cover or
surround or otherwise be disposed adjacent to the individuals
shoulders or upper torso, wherein the inner radius of the first set
of coils is less than the inner radius of the second set of coils,
and the coils are configured to provide a uniform magnetic field in
the region of the individual's head. As will be understood by those
skilled in the art in view of the herein disclosure, various
embodiments may vary the number of coils per set, the coil radii,
number of turns, longitudinal position and length, and electric
current magnitude and direction in each coil to provide a desired
magnetic field distribution. In accordance with some embodiments of
the present invention, the longitudinal position and extension, the
number of turns, and electric current direction of each coil are
designed to provide 1-10 ppm uniform magnetic field within the
first region for head imaging.
[0053] By way of example, the first set of coils may include at
least two coils having an inner radius in a range of about 25-35 cm
and disposed in a first region of a length along the common axis in
a range of 40-60 cm to cover a head and neck of a human body, and
the second set of coils may include at least one coil having an
inner radius in a range of about 30-40 cm and disposed in a second
region of a length along the common axis in a range of 15-25 cm to
cover a portion of a human torso. In various alternative
embodiments, the length of the first and second regions may, for
example, range from about 20-70 cm and 10-40 cm, respectively, and
the inner radii of the first and second set of coils may range from
about 10-40 com and 20-50 cm, respectively. Some embodiments, may
employ a length of the first and second regions in a range from
about 10-20 cm and 20-30 cm respectively. Additionally, some
embodiments may employ an inner radius of the first and second
coils of about 10-20 cm and 20-30 cm, respectively.
[0054] By way of illustrative example, FIG. 8 depicts with
reference to the z-r plane, with dimensions in meters (m), the
longitudinal extent L2 of a first set of coils (e.g., corresponding
to the four leftmost coil sets depicted in FIG. 7) having an inner
radius of 0.28 meters, the longitudinal extent L1 of a second coil
set (e.g., corresponding to the rightmost coil set in FIG. 7)
having an inner radius of 0.38 meters, and DSV 43 having a radius
that is about 0.1 meters and offset by about 0.05 meters from the
transition from the first to second set of coils (from L2 to L1)
along the z-axis, in accordance with an illustrative example
according to some embodiments of the present invention.
[0055] FIG. 9 depicts a normalized current distribution for the
main magnet coil arrangement corresponding to the illustrative
embodiment of FIGS. 7 and 8. As shown, in accordance with some
embodiments, at least one coil is wound to carry current in the
reverse direction relative to other coils.
[0056] FIG. 10 is an illustrative coil pattern (depicted in the z-r
plane, with units normalized to meters) of a 3 T head magnetic
resonance imaging scanner, in accordance with various embodiments
of the present invention. More specifically, active shield coil 51
is disposed at the outer side, main magnet coils 52 comprise eight
coil sets, and a diameter-sensitive volume (DSV) 53 of homogeneous
fields is about 200 mm in diameter (i.e., a radius of about 0.1
meter). The shield coil 51 may have a radius, for example, in the
range of about 60-70 cm, though other radii are possible depending
on the particular implementation. By way of illustrative,
non-limiting example, the following table provides dimensions and
current direction for coils arranged according to the embodiment of
FIG. 10, wherein the first set of coils comprise coil numbers 1
through 6, the second set of coils comprise coil numbers 7 and 8,
the shielding coil is identified as coil 9, R1 is the inner radius,
R2 is the outer radius, Z1 is the first longitudinal position, Z2
is the second longitudinal position, and the current direction J is
identified as positive (+) or negative (-):
TABLE-US-00001 Coil no. R.sub.1 (m) R.sub.2(m) Z.sub.1(m)
Z.sub.2(m) J 1 0.2501 0.3028 -0.4132 -0.2897 + 2 0.2702 0.2916
-0.2519 -0.2325 + 3 0.2592 0.3033 -0.1873 -0.1327 + 4 0.2569 0.3032
-0.0765 -0.0349 + 5 0.2573 0.3027 0.0213 0.0606 + 6 0.2669 0.3012
0.1157 0.1680 + 7 0.3561 0.3821 0.1822 0.1980 - 8 0.3329 0.3929
0.2610 0.4433 + 9 0.6608 0.6615 -0.450 0.450 +
[0057] FIG. 11 is a plot showing the magnetic field distribution
for the illustrative embodiment depicted in FIG. 10, with
illustrative dimensions and current directions as per the foregoing
table. As shown, a 3 T homogeneous field provides a 200 mm DSV.
[0058] FIG. 12 shows the fringe fields of one Gauss, three Gauss
and five Gauss lines for the field distribution of FIG. 11, in
accordance with an illustrative embodiment of the present
invention.
[0059] Accordingly, as may be appreciated, FIG. 10 illustrates a
non-limiting example of an embodiment according to the present
invention. In this example, as described, the outer layer is an
active shield coil 51, and the depicted inner layer comprises main
magnet coils 52 having eight coil sets providing an asymmetric
structure, with the coils on the right hand side (towards
increasing z) having a bigger diameter for accommodating a
patient's shoulders. In this illustrative and non-limiting
embodiment, total length of the magnet is 0.86 m, the peak magnetic
field is 5.04 Tesla at a current density J=1.2.times.10.sup.8
A/m.sup.2, and the DSV 53 is 200 mm in diameter. According to these
parameters, FIG. 11 plots the field distribution in cylinder of
z=-0.10.quadrature.+-0.1 m, r=0.2 m. In cylinder of
z=-0.10.quadrature.+-0.1 m, r=0.1 m, the fringe fields of one
Gauss, three Gauss and five Gauss lines is drawn in FIG. 12, and
the 200 mm DSV is inside one Gauss line as expected and
desired.
[0060] Accordingly, it may also be understood in view of the
foregoing that for a head-only magnetic resonance imaging scanner
according to embodiments of the present invention, the bore
surrounding a DSV 43 of homogeneous fields is preferably not much
larger in diameter than what is necessary to fit a patient's head,
while the main magnet bore also includes a portion designed with a
diameter having an appropriate size to accommodate the shoulder as
shown in FIG. 7. By contrast with a whole-body MRI, a head-only
main magnet in accordance with some embodiments of the present
invention has a smaller DSV, so the size of superconducting magnet
can be reduced, and a smaller Dewar and magnet system can be
achieved, and the costs can be thus also be reduced.
[0061] The present invention has been illustrated and described
with respect to specific embodiments thereof, which embodiments are
merely illustrative of the principles of the invention and are not
intended to be exclusive or otherwise limiting embodiments.
Accordingly, although the above description of illustrative
embodiments of the present invention, as well as various
illustrative modifications and features thereof, provides many
specificities, these enabling details should not be construed as
limiting the scope of the invention, and it will be readily
understood by those persons skilled in the art that the present
invention is susceptible to many modifications, adaptations,
variations, omissions, additions, and equivalent implementations
without departing from this scope and without diminishing its
attendant advantages. For instance, except to the extent necessary
or inherent in the processes themselves, no particular order to
steps or stages of methods or processes described in this
disclosure, including the figures, is implied. In many cases the
order of process steps may be varied, and various illustrative
steps may be combined, altered, or omitted, without changing the
purpose, effect or import of the methods described. It is further
noted that the terms and expressions have been used as terms of
description and not terms of limitation. There is no intention to
use the terms or expressions to exclude any equivalents of features
shown and described or portions thereof. Additionally, the present
invention may be practiced without necessarily providing one or
more of the advantages described herein or otherwise understood in
view of the disclosure and/or that may be realized in some
embodiments thereof. It is therefore intended that the present
invention is not limited to the disclosed embodiments but should be
defined in accordance with the claims that follow.
* * * * *