Catheter which is visible under MRI

In accordance with the present invention there is provided a catheter which is visible during magnetic resonance imaging of body tissue. The catheter includes a body having a proximal end, a distal end and at least one lumen extending therethrough. The body is formed from a solid material. The solid material is made from plastic and enough paramagnetic substance to render at least a predetermined portion of the catheter visible during magnetic resonance imaging of body tissue.

FIELD OF THE INVENTION 
The present invention relates to a catheters which are visible under 
magnetic resonance imaging (MRI) and under X-ray. The present invention 
has further relation to such catheters which are made from a tube-like 
body extruded from a plastic material and having a proximal end, a distal 
end and at least one lumen extending therethrough. The present invention 
has even further relation to such catheter that are used in medicine for 
diagnostic and interventional purposes. 
BACKGROUND OF THE INVENTION 
Catheters are widely used in a number of medical procedures such as 
percutaneous coronary angioplasty. With certain applications it is 
standard practice to make the position of the catheter inside the body of 
the patient visible by means of X-ray imaging. Often the tip of guiding 
catheters and diagnostic catheters are made from or are coated with 
radiopaque materials and become clearly visible on an X-ray screen. 
Examples of such catheters are given in commonly assigned U.S. Pat. Nos. 
5,171,232 issued to Castillo et al. on Dec. 15, 1992 and 5,045,072 issued 
to Castillo et al. on Sep. 3, 1991, both of which are hereby incorporated 
herein by reference. 
However, other medical applications, such as neurology, use procedures 
which are performed under MRI instead of X-ray. For these applications it 
is desirable to make catheters visible when employing MRI techniques. An 
example of such a catheter is shown in U.S. Pat. No. 5,154,179 issued to 
Ratner on Oct. 13, 1992, which is hereby incorporated herein by reference. 
That patent discloses a catheter wherein ferromagnetic particles have been 
incorporated in the material of the body of the catheter. These particles 
disturb the magnetic field in the MRI device and result in a deviation in 
the picture which is formed, thus indicating the position of the catheter. 
However, the ferromagnetic material often causes a severe distortion of 
the image. The Ratner reference also discloses the use of a liquid 
paramagnetic material which is injected into a lumen of the catheter to 
make it visible under MRI. While the image is clearer, many paramagnetic 
materials are harmful to humans. The use of a liquid paramagnetic material 
runs the risk that some of it may leak into the patient. Furthermore, the 
diameter of the catheter must be relatively large to accommodate the limen 
for the liquid paramagnetic material. This is undesirable, especially for 
neurological applications. There has, therefore, been a desire to have a 
catheter which is visible under MRI, has a less distorted picture than 
that given by using ferromagnetic materials, and which is not harmful to 
the patient. 
SUMMARY OF THE INVENTION 
In accordance with the present invention there is provided a catheter which 
is visible during magnetic resonance imaging of body tissue. The catheter 
includes a body having a proximal end, a distal end and at least one lumen 
extending therethrough. The body has a circumference and a longitudinal 
axis running between the proximal and distal ends. The body is formed from 
one or more plastics and enough paramagnetic substance to render at least 
a predetermined portion of the catheter visible during magnetic resonance 
imaging of body tissue.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings in detail wherein like numerals indicate the same 
element throughout the views there is shown in FIG. 24 a catheter 1 in 
accordance with the present invention. Catheter 1 includes a body 2 having 
a proximal end 3 and a hub 7 attached thereto. The body further includes a 
distal end 4 and at least one lumen 5 (shown in FIG. 1) extending along 
the longitudinal axis 6 of the catheter 1. As seen from FIGS. 1 and 2, 
body 2 is made from a paramagnetic compound 10. As used throughout this 
specification a paramagnetic compound is a solid material comprising a 
plastic, such as polyurethane, nylon, Teflon or polyethylene, and a 
paramagnetic substance. The use of a paramagnetic substance gives a clear 
picture of the catheter under an MRI, but not so distorted, as with 
ferromagnetic materials. This feature makes the catheter particularly 
suitable for medical applications done under MRI. The catheters of the 
present invention are preferably made by extrusion processes which are 
well known to those of ordinary skill in the art. 
Suitable paramagnetic substances include transition metals such as copper, 
manganese, chromium, nickel and especially gadolinium and dysprosium 
because of their high susceptibilities. Also mixtures, alloys and salts of 
these materials have suitable properties for application according to the 
invention. The quantity of paramagnetic substance is to be used in the 
plastic material, such as by way of a filler incorporated into the 
plastic, depends in particular on the properties of the MRI device used 
for the detection of the catheter. Also the properties of the paramagnetic 
substance to be used are decisive. With weak paramagnetic substances one 
will use a stronger concentration of this material than with strong 
paramagnetic substances. In practice the concentration may vary for 
instance from 0.001% in the case of strong paramagnetic substances such as 
dysprosium oxide (DyO.sub.3) to 60% in the case of a weak paramagnetic 
substance such as for instance titanium dioxide. These percentages are 
percentages by weight. 
FIGS. 3 and 4 show an alternative embodiment of the catheter of the present 
invention wherein the body of the catheter is made up of two concentric 
layers 31 and 32. The inner layer 31 comprises a paramagnetic compound, 
whereas the outer layer 32 is free of paramagnetic substance and 
preferably comprises plastic. Consequently there is no direct contact 
between body tissue and the inner layer 31 of paramagnetic compound. This 
is often preferred because many paramagnetic substances are harmful to the 
human body. 
FIGS. 5 and 6 illustrate an embodiment wherein the catheter has three 
layers 51, 52 and 53. The intermediate layer 52 comprises paramagnetic 
compound, whereas the inner layer 51 and outer layer 53 are free of 
paramagnetic substance and preferably comprise plastic. Because the inner 
and outer layers are both free of paramagnetic substance, contact of 
paramagnetic substances with the body is reduced on both the outside and 
on the inside of the catheter. The lumen of the catheter often conveys 
fluids which ultimately end up inside the body of the patient. This 
embodiment reduces the likelihood that such fluids will carry paramagnetic 
substance from the lumen into the body. 
FIGS. 7, 8 and 9 illustrate an embodiment where only a predetermined length 
of the catheter body is comprised of a paramagnetic compound. That is the 
paramagnetic substance does not extend over the entire length of the 
catheter body. The left-hand section 71 is free of paramagnetic substance 
and preferably is made from plastic. The fight-hand section 72 is made 
from a paramagnetic compound. The two sections 71 and 72 may have been 
manufactured separately and bonded together by glueing or the like. This 
embodiment, where the paramagnetic compound does not extend over the 
entire length of the catheter, is useful for some medical applications. 
Sometimes it is only necessary to render part of the catheter, usually the 
distal end, visible on the MRI screen. 
The embodiment shown in FIGS. 10, 11 and 12 show a catheter with three 
layers 101, 102 and 103, similar to the catheter shown in FIGS. 5 and 6. 
As with the catheter shown in FIG. 7, the intermediate layer 102 is a 
paramagnetic compound, but it extends only over part of the length of the 
catheter. FIG. 11 shows a cross section of that part of the catheter which 
comprises three layers, whereas FIG. 12 shows a cross-section along line 
XII--XII where the catheter only has the two layers 101 and 103 made from 
plastic. The layers may have been formed simultaneously by co-extrusion or 
any other type of extrusion. This embodiment can be manufactured by 
cutting off the supply of the paramagnetic compound, during the extrusion 
process. This embodiment is preferred in that the paramagnetic compound 
cannot come into contact with the surrounding tissue. 
The embodiments shown in FIGS. 13 and 14, show a catheter wherein the 
paramagnetic compound is disposed within the catheter as three strips 131, 
132 and 133. Preferably, the strips are completely surrounded by plastic, 
so that the compound 10 has no contact with the surrounding tissue. 
FIGS. 15 and 16 illustrate an embodiment of a catheter in accordance with 
the present invention wherein the body is made from two strips 151 and 152 
of different materials. Strip 151 is made from paramagnetic compound. 
Strip 152 is made from a compound of plastic and a radiopaque substance 
such as bismuth salts or the like. This embodiment is, therefore, clearly 
visible both on an MRI screen and on an X-ray screen. The paramagnetic 
compound and the radiopaque substance could be mixed together and disposed 
on one strip the strip could rotate axially to obtain better mechanical 
features. 
FIGS. 17, 18 and 19 show an embodiment similar to that shown in FIG. 13, 
wherein the strips 171, 172 and 173 of paramagnetic compound are reduced 
from the proximal end of the catheter towards the distal end of the 
catheter and eventually tapering off completely. 
FIGS. 20 and 21 show an embodiment of a catheter similar to that shown in 
FIG. 17. However, instead of tapering the paramagnetic substance down from 
the proximal to distal ends, the distal tip 210 is made completely from a 
non-paramagnetic substance which is connected to the catheter. Preferably 
distal tip 210 is made of a softer plastic material than the plastic used 
proximal thereto so it is as less traumatic as possible. 
A similar solution is obviously possible with a catheter of the embodiment 
as shown in FIG. 5. In FIG. 22 the distal tip 220 is made completely from 
a non-paramagnetic substance which is connected to the catheter. 
Often catheters of the type described herein are made from plastic and have 
at least one reinforcing layer comprising braided wires. Catheters of this 
type are described in U.S. Pat. Nos. 3,485,234 issued to Stevens on Dec. 
23, 1969 and 3,585,707 issued to Stevens on Jun. 22, 1971, both of which 
are hereby incorporated herein by reference. The embodiment of the 
catheter of the present invention disclosed in FIG. 25, shows a catheter 
251 having a tube-like body 252 with a lumen 253. Body 252 comprises a 
plastic having a reinforcing layer 254 comprising a braided of metal wire. 
Layer 254 comprises two different types of metal wire. Wires 256 are made 
from a paramagnetic substance, wherein wires 255 have been made of a 
non-magnetic material. Wires 255 remain invisible under MRI conditions, 
whereas wires 256 cause just enough disturbance of the uniformity of the 
magnetic field, to render the catheter visible on the screen. Wires 256 
are preferably made from an alloy of non-magnetic material and a strong 
paramagnetic substance, such as an alloy of titanium and copper or nickel. 
Another embodiment of the present invention is disclosed in FIG. 26 where 
there is shown catheter 261. Catheter 261 has a helically wound wire 263 
embedded in the plastic material of the body 262. Wire 263 is screened off 
by plastic material which the body 262 has been made, so that there is not 
objection to choose paramagnetic substances for the wire 263, material 
which has optimal properties where image formation under MRI conditions is 
concerned but which as such may be harmful to humans. By winding the wire 
in a helical fashion, it does not effect the flexibility of the distal end 
of the catheter 261. 
While particular embodiments of the present invention have been illustrated 
and described herein, various modifications will be apparent to those 
skilled in the art without departing from the spirit and scope of the 
present invention. Accordingly, the scope of the present invention should 
be considered in terms of the following claims and is understood not to be 
limited to the details described and shown in the specification and 
drawings.