The present invention relates to an apparatus for the mounting of
at least one open flat coil on a cilindrical support structure.
For instance such open flat coils are used in apparatusses for the
examination of bodies by means of nuclear magnetic resonance. Generally in such
apparatusses for examination a static magnetic main field generated by a magnet
is used, in which magnetic main field a set of so called gradient coils is located.
This set of gradient coils is often mounted on a cilindrical support structure.
Within the cilindrical support structure a third set of coils, the so called RF
coils are mounted on another support structure and during the examination the body
to be examined is located within said support structure.
The present invention relates in particular to the mounting of the
gradient coils. Generally the gradient coils are supplied with rapidly switched
DC-currents. The gradient coils, through which a current flows are subjected to
major rapidly varying forces caused by the magnetic main field. This implies that
these coils will be subjected to an oscillating movement, causing a disturbing
The aim of the present invention is to provide a mounting apparatus
in which the coils are mounted on the cilindrical support structure wherein the
coils are subjected to such a limited movement that the volume of sound thus generated
is reduced considerably.
Another aim is to provide such an apparatus, which can withstand
major forces acting on the coils.
A further aim of the present invention is to provide such an apparatus
which is relatively simple, which has only a limited extension in the radial direction,
and wherein the coils are mounted upon the support structure in a relatively simple
These aims are reached by a pair of clamping plates located within
each coil, in which each clamping plate is connected with a pulling element, and
wherein adjacent pulling elements are connected through a tensioning element.
This mounting apparatus applies a tensioning force to the coils,
causing the coils to be clamped stiffly on the support structure, so that the coils
can only be subjected to a movement with a very limited amplitude. The volume of
sound generated is thus limited considerably.
Subsequently the present invention will be elucidated with the help
of embodiments depicted in the accompanying drawings showing:
- Figure 1: a schematic perspective view of an apparatus for the examination
of a body by means of nuclear magnetic resonance;
- Figure 2: a schematic perspective view of a support structure, onto which gradient
coils are mounted;
- Figure 3: a cross-sectional view of the location of gradient coils on the cilindrical
- Figure 4: a perspective view of a part of the support structure with a set
of gradient coils mounted thereon; and
- Figure 5: a detailed perspective view, partially broken away, of the mounting
apparatus according to the present invention.
In figure 1 an apparatus for examination by means of nuclear magnetic
resonance is schematically shown, in which apparatus the magnetic main field is
generated by a super conducting magnet. This apparatus 1 comprises a cryostat
2, wherein super conducting coils, not depicted in the drawings are located. The
cryostat 2 is supported by a supporting plate 3. Within the cryostat 2 a cilindrical
support structure 4 is mounted.
A set of saddle shaped X-coils 5 is mounted on the support structure
4, which coils are located to generate a magnetic field during excitation of which
the axis is vertical. Shifted over an angle of 90° relative to the X-coils 5 a
set of Y-coils 6 is mounted . These Y-coils 6 generate during excitation a magnetic
field, the axis thereof extending horizontally. Finally a set of Z-coils, not
depicted in figure 1, is mounted on the support structure 4, which coils during
excitation generate a magnetic field with an axis parallel to the axis of the cilinder.
Within the cilindrical support structure 4 a second cilindrical support
structure 7 is provided, whereon the so called RF coils (not depicted) are mounted.
Finally a table 8, onto which the body 9 to be examined can be located is provided
within the support structure 7 for the RF-coils.
Figure 2 shows schematically the location of the X-coils 5 and the
Y-coils 6 on the cilindrical support structure 4. The cilindrical support structure
4 is manufactured from a non-magnetic material, like epoxy resin reinforced with
The saddle shaped coils 5 are mounted adjacent to the surface of
the cilinder. The Y-coils 6 are mounted on the layer formed by the X-coils and
wherein the Y-coils are supported by separate support structures in the locations,
wherein the Y-coils are not supported by the X-coils.
Subsequently the mounting of the coils on the support structure 4
will be described with the help of figures 3 and 4. Each of the X-coils 5 has a
longitudinal annular shape and comprises two coil sides 13 and two coil heads
12 together surrounding a coil aperture. In the aperture of each coil adjacent
to the coil head 12 large clamping plates 14 are located. To each of the clamping
plates 14 two pulling strips 15 are attached.
If only the X-coils whould have to be mounted the ends of the pulling
strips 15 concerned could have been connected through tensioning elements 16. By
tensioning the tensioning elements 16 the X-coils 5 would be mounted securely
on the support structure 4. To fixate the location of the coils one of each pair
of clamping plates 14 could have been connected to the support structure 4 by means
of a bolt 17.
In the application of the present invention in an apparatus for nuclear
magnetic resonance a pair of Y-coils 6, shifted over an angle of 90° relative to
the X-coils 5 is necessary apart from the pair of X-coils 5. These Y-coils 6 are
just as well mounted on the cilindrical support structure in the same way. The
pulling strips 15 for the X-coil are for the time being not connected to eachother
and initially the Y-coils 6 are applied such that the pulling strips extend over
the coil heads 18 of the X-coils 6. Small clamping plates 20 for the Y-coils 6
are located adjacent to the coil heads 18 of the Y-coils 6. Pulling strips 21 for
the Y-coils are attached to said small clamping plates 20. Hereafter both the
pulling strips 15 for the X-coils and the pulling strips 21 for the Y-coils can
be connected by means of tensioning elements 16 and tensioning elements 22, respectively.
As the clamping plates 14, 20 are locked up by the pulling strips
15 and 21 the danger is avoided that the clamping plates 14, 20 will deflect outwardly
as a cause of the pulling force exerted by the tensioning elements 16, 22. Thus
the pulling strips 15 lock up the clamping plates 20 and the pulling strips 21
lock up the clamping plates 14.
Both the X-coils 5 as well as the Y-coils 6 are mounted onto the
surface of the cilindrical support structure 4 by both tensioning elements, such
that, when this support structure is applied in an apparatus for examination by
means of nuclear magnetic resonance, during excitation the coils will generate
a sound volume, which is reduced considerably.
In the embodiment described above the subject is the mounting of
a pair of coils. It will be obvious that the apparatus according to the present
invention is also fit for the mounting of a single coil, and that it is also fit
for the mounting of a multilayer coil. It is noted that the apparatus is not limited
to a rectangular coil but is also suitable for the mounting of e.g. a round or
an oval shaped coil.
Figure 4 shows a perspective view of a support structure, whereon
X- and Y-coils are mounted with an apparatus according to the present invention.
The X-coil 5 is mounted on the support structure 4, and in the coil aperture of
the X-coil 5 a pair of large clamping plates 14 is located. One of each clamping
plates 14 is provided with holes, through which a bolt 17 is inserted. Two pulling
strips 15 are attached to each of the clamping plates 14, which pulling strips
are attached to pulling strips 15, not depicted, and which belong to a coil 5,
not depicted, and located unto the back side of the support structure 4. The pulling
strips 15 are all guided over the coil heads 18 of the X-coil 6. Y-coils 6 are
mounted in a position over the X-coils 5, and shifted over a angle of 90° relative
to the position of the X-coils 5. Small clamping plates 20 are located in the
coil apertures of these Y-coils adjacent to the coil heads. To each of said clamping
plates 20 two pulling strips 21 are attached, of which the relevant are connected
to eachother through a tensioning element 22.
In the embodiment shown each of the tensioning elements 16 comprises
two bars 23, over each of which a free end of the relevant pulling strip 15, 21
respectively is folded. After folding the free ends are attached to the strip
itself, so that a loop 25 is developed, through which the relevant bar 23 extends.
Between one of the bars 23 of each tensioning element and the relevant pulling
strip an isolating sleeve is provided. This isolating sleeve avoids that the field
generated by the coils generates currents in the pulling strip. Both bars 23 are
connected to eachother by means of two studs 26, which extend through apertures
provided in the bars 23. Nuts 27 are screwed upon the ends of the studs 26. By
tightening these nuts the pulling strips can be tensioned.
The mounting apparatus according to the present invention provides
a good fixation of the coils on the support structure but it is also important
that the branches of the coils, like the branch 28 is pushed firmly against the
support structure. For that purpose extra pulling strips 29 are provided for every
set of coils, pushing the branches 28 of the coils against the support structure.
Both ends of each pulling strip 29 are connected again through tensioning elements.
In figure 5 the fixation of a large clamping plate 14 and a small
clamping plate 20 located therein is showed in more detail. The small clamping
plate 20 extends at least partially over a part of the clamping plate 14, so that
both clamping plates at the same time can be connected to the support structure
4 by a connection, comprising a bolt 17 and a sleeve 31 screwed into the support
The clamping plates 14, 20 located on the other side of the support
structure 4 are fixed in the same way, while the other clamping plates 14, 20 are
not connected directly to the support structure. Thus only one coil head of each
coil 5, 6 is fixed, while the other coil head is free, so that its location can
be determined by the tensioning element. This provides both a good fixation of
locations and a good mounting of the coils.
As the mounting apparatus according to the present invention has
only a limited extension in the radial direction a compact set of gradient coils
is provided, of which the diameter exceeds the outer diameter of the outer layer
of coils by a limited extent only.