Vaso-occlusion coil and method

A flexible, preferably coiled wire for use in small-vessel vaso-occlusion. The wire has a stretched, linear condition in which it can be advanced through a catheter lumen to a selected vessel, and a relaxed, convoluted condition produced by a combination of a helical winding of the wire, and irregularities of the helical winding. When the wire is released from a catheter into a vessel, it assumes a randomly coiled, substantially space-filling mass which is lodged at the site of release. In a preferred embodiment, the helical winding in the wire's relaxed condition has about the same diameter as that of the vessel, and the wire, in its stretched condition, has a length of about 15-20 times the vessel diameter.

FIELD OF THE INVENTION 
The present invention relates to vaso-occlusion devices and methods, and in 
particular to coiled wires designed for delivery through a catheter at an 
occlusion site. 
References 
Ethanasoulis, C. A., New Eng J Med (1980), 302:(20)(21). 
Berenstein, A., et al, Radiology (1979), B2:631. 
Battista, O. A., et al, J. Appl. Polyser Sci (1967), 11:481. 
Hilal, S. K., et al, J. Neurosurg (1975), 43:255. 
Kaufman, S. L., et al, Investigative Radiology (1978), vol. 1, no. 3, pp. 
200-204. 
Kumar, A. J., et al, J Neuroradiology (1982), 3:163-168. 
Latchow, R. E., et al, Radiology (1979), 131:669. 
Reuter, S. R., et al, AJR (1975), 125:119-126. 
Roberson, G. H., et al, AJR (1979), 133:657. 
Wallace, S., et al, Cancer (1979), 43:322-328. 
BACKGROUND OF THE INVENTION 
Endovascular therapy has been used in treating a variety of conditions, 
such as in controlling internal bleeding, occluding blood supply to 
tumors, and relieving vessel-wall pressure in a region of a vessel 
aneurism (Athanosoulis, Wallace, Reuter). 
The embolic agent may be an injectable fluid, such as a microfibrillar 
collagen (Battista, Kaufman, Kumar), Gelfoam (Berenstein, Roberson) 
silastic beads (Hilal), and polyvinyl alcohol foam (Latchaw). Co-owned 
U.S. patent application Ser. No. 823,635 describes a cross-linked 
vaso-occlusive agent whose persistence at a vaso-occlusive site can be 
extended up to several months, depending on the degree of cross-linking. 
These fluid agents can be injected into a selected vessel site through a 
catheter, and there gel into a solid, space-filling mass at the injection 
site. Typically such fluid agents provide good short-term vaso-occlusion, 
but are ultimately resorbed in the process of vessel recanalization. 
Polymer resins, such as cyanoacrylate resins, have also been employed as an 
injectable vaso-occlusive material. Like injectable gel materials, the 
resins are typically mixed with a radiocontrast material in order to be 
seen fluoroscopically. A risk with this material is inadvertent embolism 
in normal vasculature due to the inability to control the destination of 
pre-gelled resins. The material is also difficult or impossible to 
retrieve, once placed. 
Two types of mechanical vaso-occlusion devices are known. The first is a 
balloon which can be carried to the vessel site at the end of a catheter, 
and there inflated with a suitable fluid, typically a polymerizable resin, 
and released from the end of the catheter. The balloon device has the 
advantage that it effectively fills the cross section of the occluded 
vessel. A vascular balloon is difficult or impossible to retrieve after 
the resin in the balloon sets up, and the balloon cannot be visualized 
unless it is filled with a contrast material. Also the balloon can rupture 
during filling, or release prematurely during filling, leaking monomer 
resin into the vasculature. 
A second type of mechanical vaso-occlusive device is a wire coil which can 
be introduced through a catheter in a stretched linear form, and which 
assumes a helical wire shape when released into a vessel. In 
vaso-occlusion coils used heretofore, the wire itself is a relatively 
stiff, shape-retaining stainless steel coil. The wire is shaped to have 
1-2 helical windings dimensioned to engage the walls of the vessel. The 
wire is also coated with filaments, such as dacron or cotton fibers, which 
provide a substrate for clot formation in the interior region of the 
vessel, while the coil itself serves to anchor the device on the vessel 
wall at the site of release. This type of coil is also known as a 
Gianturco coil (Cook Corp, Bloomington, Ill.). The coil is relatively 
permanent, can be imaged radiographically, can be located at a 
well-defined vessel site, and has the possibility at least of being 
retrieved. A limitation of fibercoated coils is that recanalization of the 
vessel can occur, presumably by resorption of the clot by endothelial 
cells. Further, the fiber-coated coils are difficult to introduce into 
vessel sites which require tortuous path access and/or involve vessel size 
less than about 1-3 mm. This is because a fiber-coated coil is generally 
too stiff and has too high a frictional coefficient to be readily advanced 
through a small-diameter catheter, especially in a region of catheter 
bends. 
SUMMARY OF THE INVENTION 
It is therefore a general object of the present invention to provide a 
vaso-occlusion wire which has the advantages of existing vaso-occlusion 
coil wire devices, but overcomes the above-mentioned limitations of such 
devices. 
It is a more specific object of the invention to provide such a wire 
capable of forming a convoluted, substantially space-filling mass when 
introduced into a vessel. 
It is another specific object of the invention to provide such a wire which 
can be easily advanced through a flexible, small-diameter catheter. 
It is still another object of the invention to provide a vaso-occlusive 
coil which can be retrieved from a vessel site by a catheter wire tool. 
Providing a catheter system and method of vaso-occlusion is still another 
object of the invention. 
The present invention includes a flexible, vaso-occlusive wire designed for 
occluding a vessel having a selected crosssectional area, when the wire is 
released into the vessel from a small-diameter catheter. The wire is 
characterized by: 
(a) a relaxed condition in which the wire assumes a folded, convoluted 
conformation which is adapted to form a substantially space-filling mass 
when the wire is released into the vessel, 
(b) a stretched condition in which the wire has a linear configuration in 
which the wire can be pushed through the catheter, and 
(c) a memory which returns the wire from its stretched to its relaxed 
condition, as the wire is released from the catheter into the vessel, thus 
forming a space-filling, vaso-occlusive mass which is lodged in the vessel 
at the site of release. 
In a preferred embodiment, the relaxed conformation of the wire is produced 
by a combination of a helical winding in the wire which has a winding 
diameter substantially that of the vessel to be occluded, and 
irregularities in helical winding which cause the wire to adopt a 
substantially random folding pattern when released from a catheter into 
such a vessel. The irregularities in the helical conformation may be 
produced by bends in the windings and/or variations in the coil wrapping 
which predispose the wire to bend in certain directions. 
Also in a preferred embodiment, the wire in its stretched condition is a 
coiled wire formed by helical wrappings of a metal thread, preferably 
platinum, tungsten, or gold thread. The diameter of coiled wire is 
preferably between about 10-30 mils. The length of the coiled wire is at 
least about 15-20 times the diameter of the vessel to be occluded. 
In another embodiment, the winding which characterizes relaxed conformation 
has a spiral shape dimensioned to fill the cross section of the vessel to 
be occluded. 
The wire may be coated or filled with a water-soluble material which acts 
to hold the wire in its linear condition until the material is contacted 
with aqueous medium, either in the delivery catheter or at the vessel 
site. Alternatively, the wire may be coated or filled with a drug-release 
material designed to provide slow release of a drug from the wire at the 
vessel site. 
Also forming a part of the invention is a catheter system for use in 
occluding a vessel having a selected cross-sectional area. The system 
includes a vaso-occlusion wire of the type described above, and a 
small-diameter catheter which is designed for delivering the coil to a 
selected site in a small vessel, e.g., 0.5 to 6 mm diameter vessel. The 
catheter is preferably designed for accessing a vessel site along a 
tortuous vessel path. Also included in the system is a pusher for 
advancing the occlusion wire through the catheter. The pusher has a 
relatively stiff proximal segment which extends over most of the pusher 
length, and a relatively flexible distal portion formed of an extruded 
polymer, preferably a fluorocarbon polymer. 
The system may further include a retrieving wire effective to penetrate the 
space-filling mass of vaso-occlusion wire in the vessel. The retrieving 
wire preferably adopts a preformed corkscrew shape as it is released from 
the catheter, for engaging the convoluted windings of the vaso-occlusion 
wire. 
In another aspect, the invention includes a method employing the above 
system for producing vaso-occlusion at a small-vessel site. The method may 
be used to achieve permanent vaso-occlusion in a small vessel, 
vaso-occlusion with depot drug release from the vessel site, and/or 
vaso-occlusion with a temporary backfill of a fluid material, such as 
collagen or a drug or contrast-containing material. In the latter method, 
the vessel region immediately upstream of the vaso-occlusion wire is 
filled with the fluid through the catheter after wire placement. The 
method may further include a procedure for retrieving the wire from the 
vessel. 
These and other objects and features of the invention will become more 
fully apparent when the following detailed description of the invention is 
read in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a catheter system 10 composed of a small-diameter catheter 12, 
a vaso-occlusion wire 14 constructed according to the invention, and a 
wire pusher 16 for advancing wire 14 through the catheter. The 
construction and characteristics of wire 14, and alternative-embodiment 
vaso-occlusive wires, are detailed in Section A. Section B describes the 
catheter system, including pusher 16 and a retrieving wire used for 
removing the wire from a vessel. The operation of the system for use in 
placing the wire at a selected site in a vessel is given in Section C. 
A. Vaso-Occlusion Wire 
The steps in the construction of vaso-occlusion wire 14 are illustrated in 
FIGS. 2A-2C. The wire itself is formed by wrappings or windings of a fine 
wire thread 18, preferably 0.002 mils to 0.006 mils platinum, tungsten, or 
gold thread which is available, for example, from California Fine Wire 
Company (Grover City, Calif.). The windings are preferably made by 
wrapping the thread on a spinning mandrel, according to known 
coil-manufacturing methods. The wire advance on the mandrel is adjusted to 
produce a single-layer coil with a minimum helical pitch, i.e., in which 
the windings are close packed. Typically, the mandrel has a diameter of 
between about 5-25 mils (1/1000 inch), yielding a coil wire whose outer 
diameter is between about 10-30 mils. The soft, flexible coil produced on 
the mandrel is cut to desired lengths after removal from the mandrel. For 
wires intended for use in vessels with diameters of about 2 mm and 
smaller, the wire has a preferred length of about 3-6 cm. For vessels in 
the 2-6 mm size range, wire lengths of between about 5-10 cm are 
preferred. 
The coiled wire is wound on a larger-diameter mandrel to form a helical 
winding 20 whose helix diameter, indicated at 22, is approximately that of 
the vessel for which the coil is intended. The helical axis is indicated 
at 23. Thus, for a wire designed for vaso-occlusion of a vessel of about 
2-6 mm, the diameter of the helical winding formed is preferably 2-6 mm, 
respectively. It is noted, however, that a wire winding of about 2 mm 
diameter is also suitable for the smallest vessels which can be occluded 
by the present invention, in the range of about 0.5 to 2 mm. It can be 
appreciated from the above-mentioned wire lengths and winding diameters, 
that the wires typically will contain 4-8 helical windings, as illustrated 
in FIG. 2B. 
The wire is further preformed to contain irregularities in the helical 
winding, such that the wire adopts a folded, convoluted conformation in a 
relaxed condition, as illustrated in FIG. 2C. As seen, the irregularities 
in this embodiment are such as to offset the helical axis (indicated by 
arrows in the figure) of each winding by 20-40 degrees. The irregularities 
are preferably made by deforming, as by twisting, the wire in the region 
of desired bends with the wire on the helical winding mandrel. The wire is 
treated by heating at about 800.degree. F. for 24 hours for memory 
retention after it is shaped. 
According to an important feature of the invention, the combination of the 
helical winding and the irregularities in the winding cause the wire to 
form a randomly shaped, substantially space-filling mass when released 
into a vessel, as will be illustrated below. In particular, the memory in 
the wire is effective to return the wire from a stretched, linear 
condition in which it is advanced through a catheter to a randomly 
oriented, space-filling relaxed condition as the wire is released from the 
catheter. The high memory in the wire is achieved, in part, by the overall 
length of the thread used in forming the wire, i.e., the high ratio of 
thread length:change in wire shape. 
The wire just described may be thought of as having a primary structure 
formed by the coil wrapping making up the wire, a secondary structure 
formed by the helical winding, and a tertiary structure formed by the 
irregularities in the winding. It will be appreciated that the random 
shape of the wire in its relaxed condition can be achieved by other, 
related secondary structures in the wire, such as a series of arcs which 
are interrupted at intervals by bends which orient the arcs in different 
directions. 
FIGS. 3A and 3B illustrate a vaso-occlusion wire 30 which is formed as 
described above, but where the irregularities in the helical winding are 
produced by flattening the wire coil in different directions. This is 
done, for example, by squeezing the coil wire at several regions along the 
winding, such as region 32, each at different angles with respect to the 
wire axis. The wire so formed will have the general appearance shown in 
FIG. 3A when stretched to its linear condition, and the appearance shown 
in FIG. 3B in its relaxed condition. The flattened regions of the coil 
must, of course, be less than the inner diameter of the catheter used in 
delivering the wire in its stretched condition. The flattened coil 
embodiment just described has the advantage that the flattened regions 
enhance the wire memory, i.e., predispose the wire toward its preformed, 
relaxed condition when it is released into a vessel. 
FIG. 4A shows a vaso-occlusion wire 34 formed according to another 
embodiment of the invention. The wire differs from wire 14 in that its 
inner wall region is coated with a rigid, water-soluble material 36, as 
seen in the cross sectional view in FIG. 4B. This material may be any 
biocompatible crystalline, non-crystalline, or a water-soluble material, 
such as agarose, collagen, a sugar, or the like, which can be applied to 
the interior wire region and dehydrated, as by reduced pressure, to form a 
rigid shell within the wire coil. It will be recognized that the 
rigidfying material may alternatively coat the outer wall or encapsulate 
the wire coil. 
A vaso-occlusion wire 38 formed according to another embodiment of the 
invention is shown in FIG. 5. The wire has a coiled primary structure, 
formed as above, and a helical winding 40 having at least about 1 helical 
turn whose diameter, indicated at 42, is approximately that of the vessel 
to be occluded. In this embodiment, the irregularities in the helical 
winding take the form of continuous change in helical diameter, forming 
spirals which are dimensioned to span the cross-sectional area of a 
vessel. 
FIG. 6 shows a vaso-occlusion wire 46 formed from a flexible, preshaped 
polymer tube 48. That is, the wire does not have a primary structure (wire 
coil) but has a secondary and tertiary structure formed by a combination 
of a helical winding and irregularities in the winding. The wire can be 
formed from a straight section of rod or tube, where the helical winding 
and winding irregularities are imparted during heat treatment, or by 
shaping the wire as it is extruded, before cooling, or by injection 
molding. Suitable polymers for use in preparing this type of wire include 
any biocompatible, polymer such as polyethylene, polyurethane, 
polypropylene, and the like, which is capable (by its inherent memory) of 
substantially reversible shape-retention between stretched and preformed, 
relaxed conditions. 
After wire formation, the interior of the tube may be filled with a drug 
material, such as a sterile drug concentrate, and its ends partially 
sealed for slow drug release from the tube, in an aqueous environment. The 
ends of the tube can be sealed by a water-soluble plug for storage. 
B. Vaso-occlusion Catheter System 
With reference again to FIG. 1, catheter 12 used in delivering the 
vaso-occlusion wire is a flexible, small-diameter catheter designed for 
use with a guidewire (not shown) for accessing small-vessel sites within a 
body. The vessel to be accessed has a diameter typically between about 
0.5-6 mm, and may include any arterial or venous vessel, or an organ duct, 
such as a bile duct, which can be accessed by a small-diameter catheter. 
In particular, the site to be accessed may be along a soft-tissue, 
tortuous-path vessel, such as a deep-brain site. One preferred catheter 
construction is described in co-owned U.S. Pat. No. 4,739,768 for 
"Catheter and Tissue-Accessing Method". Briefly, this catheter has a 
relatively stiff proximal section 12a suitable for advancing the catheter 
tube along a guide wire from an access site to the tissue of interest, and 
a relatively flexible proximal section 12b about 10-50 cm in length, 
designed to track the guide wire along a tortuous path in the tissue. 
FIG. 7 shows an enlarged fragmentary portion of the catheter system, 
including pusher 16 and vaso-occlusion wire 14. The inner diameter of the 
catheter is typically about 40-80% larger than the diameter of the wire, 
e.g., between about 14-18 mils for a 10-mil diameter wire, and between 
about 42-54 mils for a 30 mil diameter wire. 
Pusher 16 has a novel construction which is specially designed for 
advancing wire 14 through the catheter positioned along a tortuous path. 
The problem faced in advancing the stretched wire through a catheter is 
that considerable axial force must be applied to the wire, to overcome the 
frictional force produced by the preformed wire against the sides of the 
catheter. The limitation of using a guide wire for this purpose is that 
when the catheter is positioned in a tortuous vessel path, a guide wire 
flexible enough in its distal section to follow along this path may not 
provide the column strength necessary to advance the wire axially. For 
example, the distal end of the guidewire may be a tapered wire covered by 
a soft flexible coil tip, and this structure can readily buckle as it is 
forced against the wire where sharp bends in the catheter are encountered. 
Reducing the guidewire flexibility increases the probability that the that 
the wire will either be too difficult to advance through the catheter, or 
that the catheter will be repositioned as the guide wire is advanced. 
Also, a guide wire may have a tapered distal portion which can overlap the 
coil wire inside the catheter. Ideally then, the pusher should be 
fabricated from a material that has high column strength, good 
flexibility, and a low frictional coefficient. 
Pusher 16 which achieves these goals is formed of a relatively stiff 
proximal portion 54 preferably fabricated from a constant-diameter portion 
of a stainless steel wire 56 or the like, and a distal portion 58 composed 
of low-friction polymer tubing 60, preferably a fluorocarbon polymer 
(Teflon.TM.) tubing, formed by known extrusion methods and an inner 
tapered portion of the wire. The proximal portion provides high column 
strength and torqueability in a more proximal region of the catheter where 
flexibility can be sacrificed. The distal region provides relatively high 
column strength, good flexibility, and low frictional coefficient. 
The outer diameter of the polymer tube is preferably about 75% of the 
catheter inner diameter, to prevent the pusher from overlapping the wire 
inside the catheter. The length of the tubing in the pusher is typically 
between about 25-50 cm. The distal end of the tubing is filled with a 
radio-opaque plug 62 formed of gold, platinum, or tungsten, or is provided 
with a radio-opaque band. 
Wire 56, whose constant-diameter region forms the proximal portion of the 
pusher, is preferably a straightened stainless steel wire having an outer 
diameter of between about 8-25 mils, and preferably slightly less than 
that of the associated extruded tubing, but in any case, within about 30% 
of the tubing diameter. The wire is joined to the tubing by forming a 
tapered distal end region 64 in the wire, for example, by grinding. The 
length of the tapered region is typically between about 25-50 cm. In the 
usual case, the inner diameter of the tube is less than that of the 
untapered portion of the wire so that when the tube is placed on the wire 
initially, it covers only a portion of the tapered region of the wire. The 
tube can be forced over the remaining tapered wire region by heating the 
proximal tube region, e.g., the proximal 10-25 cm, to a temperature of 
between about 400.degree.-600.degree. F. and forcing the heated tube over 
the wire until the tube's proximal end is approximately flush with the 
wire's taper boundary. The heated tube is now pulled distally, stretching 
and "thinning" the tube in its heated region, with the heated, thinned 
portions of the tube adhering to the proximal portion of the tapered wire 
region. As seen from FIG. 7, the stretching operation produces a smooth 
tapered interface where the tube is joined to the wire typically covering 
about 10-25. According to an important feature of the invention, the 
proximal-to-distal taper in the wire, and the distal-to-proximal taper in 
the tubing act to produce a substantially smooth, i.e., monotonic 
transition in pusher flexibility in progressing from the more rigid wire 
to the more flexible tubing. One preferred pusher, for use with a 21 mil 
inner diameter inner diameter catheter, is formed by joining a 40 cm 
Teflon.TM. tube, 14-17 mils outer diameter, 4-5 mils inner diameter to a 
100-200 cm stainless steel wire, 14-18 mils diameter and having a 40 cm 
taper down to a final diameter of about 2-4 mils. 
The vaso-occlusion system of the invention may also include a retrieving 
wire 66 shown in FIGS. 9A-9C. This wire has the same general dimensions as 
the guidewire used for catheter placement, but differs from a standard 
guidewire in that the distal end is preformed to adopt a corkscrew-like 
looped end 68 after it is advanced beyond the end of the catheter. The 
operation of the system, including that of the retrieving wire will now be 
described. 
C. Vaso-occlusion Method 
The method of occluding a selected site in a vessel is illustrated in FIGS. 
8A-8D. The figures show a portion of a vessel 70 which is to be occluded 
at a selected site 72, and the distal end region of catheter system used 
in practicing the method. As indicated above, the vessel may be located 
along a tortuous vessel path characterized by relatively small vessels, 
e.g., less than 2-4 mm in diameter, and sharp vessel bends, within a soft 
tissue, such as a deep brain vessel site. 
Initially, catheter 12 in the system is guided to the selected site by 
standard guidewire/catheter procedures in which a guidewire with a bent 
end tip is guided by torquing along the selected vessel path, either by 
moving the guidewire and catheter as a unit, or by alternately advancing 
the guidewire, then the catheter. After reaching the selected vessel site, 
the guidewire is removed. 
The vaso-occlusion wire is preferably supplied in prepackaged form in a 
sterile canula (not shown) which is adapted to engage the proximal end of 
the catheter. With the catheter placed at the desired vessel site, the 
canula is attached to the catheter and the wire is transferred into the 
catheter by a short guidewire. The canula is then removed and the pusher 
is used to advance the wire through the catheter. Alternatively, the wire 
may be supplied in a straight rigidified form, such as described for wire 
34 above. In this form, the wire can be easily threaded into a catheter, 
where contact with fluid in the catheter dissolves the material which is 
maintaining the coil in a linear conformation. 
As seen in FIG. 8B, the wire initially contacts the vessel wall as it is 
pushed out of the catheter, with continued wire advance forcing the wire 
to engage the vessel along a section of the helical winding and/or against 
the opposite side wall of the vessel. At this stage, the wire is anchored 
in the vessel by the arcuate contact between the wire and vessel wall, as 
can be appreciated from FIG. 8B. With continued release of the wire from 
the catheter, the irregularities in the wire winding cause wire folding 
toward a space-filling, ball-like mass, as indicated in FIG. 8C. The 
vaso-occlusion mass formed after complete release of the wire is shown at 
76 in FIG. 8D. The catheter is then be withdrawn to complete the 
vaso-occlusion method. 
The sequence of events shown in FIG. 8A-8D illustrate two features of the 
wire folding events which take place in the vessel. First, the wire will 
engage and become anchored to the sides of the vessel wall at the site of 
wire release, regardless of the initial disposition between the wire and 
vessel wall. This is because the helical winding in the wire will 
initially contact a side wall of the vessel, then be forced into contact 
against an opposite wall portion of the vessel. Secondly, as has been 
confirmed by many in vivo vaso-occlusion studies conducted in support of 
the present invention, the wire in all cases adopts a randomly coiled, 
space-filling conformation when released into the vessel. This is due to 
the fact that (a) the wire region being released is constrained axially 
between the catheter end and the adjacent site of wire anchorage, and (b) 
the axial constraint is accommodated by irregularities in the helical 
winding which bias the wire in seemingly random directions as it is 
released from the catheter. Note that the random, space-filling 
conformation within a vessel does not necessarily correspond to the 
initial preformed relaxed condition of the wire, nor is it necessarily the 
condition which would be adopted if the same wire were released into the 
vessel a second time. 
In another embodiment of the method, illustrated in FIG. 10, pusher 16 is 
withdrawn from the catheter, and a vaso-occlusive fluid material, such as 
a collagen bolus 74, is injected as backfill against the wire mass. The 
space-filling vaso-occlusion wire here provides a substrate or matrix 
against which the injected fluid material can be trapped. The injected 
fluid material may contain entrapped drug or hormone compounds, for depot 
release from the bolus site as the trapped fluid material is slowly 
replaced in the vessel. Thus for example, in tumor treatment, the 
vaso-occlusion coil can reduce blood supply to the tumor, and/or be used 
to potentiate hyperthermic treatment. At the same time, an injected bolus 
material can provide slow, target-directed drug release into the tumor. 
In still another embodiment of the method, drug release from a selected 
vascular site is achieved by inserting a vaso-occlusion wire, such as wire 
46, designed for depot drug release from the wire in situ. 
In another aspect, the method of the invention allows for retrieval of the 
vaso-occlusion wire from a vessel site, e.g., following tumor therapy. 
This is done with use of the retrieval wire described above, and as 
illustrated in FIGS. 9A-9C. With reference to these figures, a catheter 12 
is positioned immediately adjacent the vaso-occlusion site, and the guide 
wire is replaced with retrieval wire 66. As seen in FIGS. 9A and 9B, as 
the wire end is advanced into the random vaso-occlusion mass, its 
relaxed-condition corkscrew shape becomes entwined in the random 
vaso-occlusion winding. Withdrawing the catheter and retrieving wire from 
the site then acts to knot the two coiled wires together, allowing the 
vaso-occlusion wire to be withdrawn. 
From the foregoing, it can be appreciated how various objects and features 
of the invention are met. The vaso-occlusion wire of the invention, both 
because of its relatively smooth surface and its flexible construction, 
can be advanced through sharp bends in a small-diameter catheter, allowing 
wire placement in small vessels positioned in a tortuous vessel path. The 
irregular winding conformation of the wire insures the formation of a 
randomly coiled space-filling mass in the vessel, when the wire is 
released from the catheter. The wire can be designed for depot delivery of 
drugs, e.g., to combine vaso-occlusion and drug therapy at a tumor region. 
The vaso-occlusion system of the invention allows for placement of a 
permanent, space-filling vaso-occlusion mass in small-diameter, 
difficult-to-reach vessels. The method of the invention also provides for 
backfilling with a drug-containing bolus, to achieve temporary drug 
release from the site, combined with permanent vaso-occlusion. Finally, 
the method can be practiced to retrieve a vaso-occlusion wire from a 
vessel, once the purpose of the occlusion has been served. 
Although the invention has been described with respect to specific 
embodiments and uses, it will be appreciated that various modifications in 
construction and use can be made without departing from the invention. For 
example, it is contemplated that the vaso-occlusion wire can be used for 
contraceptive purposes as an intrauterine device (IUD), by wire placement 
within the Fallopian tube of a woman.