Balloon dilatation catheter with varying radiopacity

A balloon dilatation catheter, usable in percutaneous transluminal angioplasty, is formed so that portions of the catheter both distally and proximally of the balloon have varyinq degrees of radiopacity. A portion of the catheter distally of the balloon presents a dark image under fluoroscopy while a portion located proximally of the balloon displays a moderately radiopaque image under fluoroscopy. The portion of the catheter in the region of the balloon may have a moderate, light or no radiopaque means.

FIELD OF THE INVENTION 
This invention relates to improvements in catheters for performing balloon 
angioplasty procedures in stenosed blood vessels. 
BACKGROUND OF THE INVENTION 
Balloon angioplasty procedures have been used in recent years with 
increasing success in the treatment of obstructed arteries, such as the 
coronary arteries. The procedure involves advancing a catheter having a 
special balloon at its distal end to the location of the stenosis. The 
balloon portion of the catheter is placed, in its deflated condition, in 
the stenosis and then is inflated under high pressure to compress radially 
and outwardly the biological material such as plaque which forms the 
stenosis. Balloon dilatation systems of this type are illustrated in U.S. 
Pat. Nos. 4,195,637 and 4,323,071. In those situations in which balloon 
angioplasty can be used, its successful use avoids the greater risk of 
complex and expensive bypass surgery. 
Not all arterial stenoses are treatable by balloon angioplasty. Among the 
types of vascular obstructions which have not been treatable with the 
angioplasty technology are those in which the passage through the stenosis 
is so narrow that the balloon angioplasty catheter cannot be inserted into 
the stenosis, even when the balloon is in its collapsed, deflated 
condition. Thus, where the opening in a stenosis was only enough to permit 
passage of a guide wire, but not enough to permit passage of a deflated 
angioplasty balloon, the procedure could not be performed. In order to 
enable balloon angioplasty to be performed in such narrowly stenosed 
arteries, low profile dilatation catheters have been developed. The low 
profile dilatation catheters typically are capable of assuming relatively 
low cross sectional dimensions, particularly in the region of the balloon, 
so that when the balloon is deflated, it may be inserted, in that 
configuration, into a tight stenosis. Typically, such low profile 
dilatation catheters incorporate a fixed guidewire as an integral part of 
the catheter. The guidewire forms part of or extends through the catheter 
and facilitates manipulation of the catheter so that it can be steered 
through branches in the patient's vasculature. Among the significant 
advances in such low profile catheters is that disclosed in U.S. patent 
application Ser. No. 303,908 filed Jan. 30, 1989. The probe-like catheter 
described in application Ser. No. 303,908 is very small in diameter and 
has a small diameter thin walled balloon at its distal portion. The 
catheter is constructed and arranged to be advanceable through the 
patient's vascular system and can be controlled and manipulated from its 
proximal end so that it can be steered selectively at forks in the 
vascular system. The main body of the catheter includes a flexible 
elongate hollow main shaft adapted to transmit torque from a proximal to 
the distal end of the catheter. The smaller diameter balloon support wire 
is attached to and extends from the distal end of the flexible hollow 
shaft. A helical spring is mounted to the distal portion of the support 
wire. The dilatation balloon is attached at its proximal end to the distal 
portion of the main shaft and the distal end of the balloon is attached to 
the proximal end of the helical spring. An inflation/deflation port is 
formed in the hollow main shaft distally of the proximal balloon 
connection to communicate with the interior of the balloon for inflating 
and deflating the balloon. A distal segment of the catheter which projects 
beyond the balloon includes the helical spring and a portion of the 
support wire. The support wire is tapered within the helical spring to 
provide progressively increasing flexibility in a distal direction. The 
distal end of the distal segment is adapted to be bent to a curve and 
enables the catheter to be selectively directed and steered by rotating 
the catheter from its proximal end. The balloon is very thin. The diameter 
of the collapsed folded balloon portion of the catheter is very small and 
defines a very small profile. 
In order to enable steering of the catheter, a distal portion of the 
catheter is formed from a highly radiopaque material so that it is readily 
observable under X-ray fluoroscopy. Typically, such catheters have 
included radiopaque elements in the distal segment of the catheter, 
distally beyond the balloon. Additionally, small radiopaque markers may be 
disposed at other locations along the catheter to enable fluoroscopic 
determination of the location of other portions of the catheter, such as 
the proximal end of the balloon. In the catheter described in 
aforementioned application Ser. No. 303,908, the helical spring in the 
distal segment of the catheter is formed from a highly radiopaque alloy so 
that it appears quite dark on the fluoroscopic screen. Although providing 
a highly radiopaque portion of the catheter distally of the balloon is 
important in positioning the catheter, it is relatively short and provides 
relatively little indication of the shape and configuration of the artery 
or arteries in which the catheter is disposed. The configuration of the 
patient's coronary anatomy is important to the physician. Typically, 
during an angioplasty procedure, the physician will cause a radiographic 
contrast liquid to be emitted into the arteries being treated that so for 
a brief interval, the contour and anatomy of the arteries may be observed. 
Often the physician also activates a camera to make a permanent, 
replayable recording of the coronary anatomy. The injection of radiopaque 
contrast liquid also enables the physician to examine and determine the 
location and nature of the stenosis or stenoses to be treated. Although it 
would be desirable for the physician to have a continuous fluoroscopic 
indication of the coronary anatomy, that cannot be done because it would 
require continuous infusion of radiopaque contrast liquid. The amount of 
radiopaque contrast liquid that can be infused into a patient is limited. 
Therefore, it is believed that there is a need for a means by which the 
coronary anatomy may be observed continuously but without requiring 
continuous use of radiopaque contrast liquid. It is among the objects of 
the invention to provide a balloon dilatation catheter which facilitates 
fluoroscopic observation of the coronary anatomy through which a 
substantial portion of the catheter is disposed. 
SUMMARY OF THE INVENTION 
In accordance with the invention, the catheter, proximally of the highly 
radiopaque distal segment, is modified to include a moderately radiopaque 
material extending along a substantial portion of the distal length of the 
catheter at and proximally of the balloon. The moderately radiopaque 
portion which trails the highly radiopaque portion thus is observable as a 
light but discernible shade of grey and enables the physician to observe 
the contours and paths of the coronary anatomy through which the balloon 
has been placed. Additionally, by providing only a moderate radiopacity, 
the physician also may infuse radiopaque contrast liquid to observe 
further details of the coronary anatomy. By providing only a moderately 
radiopaque segment, there is no interference with the physician's 
observation of such details. 
More particularly, in the present invention, the balloon support wire is 
coated with a thin film of radiopaque material, such as gold, to a degree 
sufficient to form a light grey, but discernible image on the fluoroscope. 
In a modification of the invention, the portion of the balloon support 
wire that extends through the balloon is not rendered radiopaque so that 
when the physician infuses radiopaque liquid into the region of the 
stenosis, where the balloon is located, no radiopacity will be caused by 
the balloon support wire. In that configuration, all of the radiopacity 
will be the result of the radiopaque contrast liquid, thus providing the 
physician with the most detailed, unobstructed picture possible. 
Thus, it is among the general objects of the invention to provide a balloon 
dilatation catheter that is adapted to provide a radiopaque image, in 
varyinq shades of intensity, of a substantial portion of the arterial 
anatomy both proximally of and distally of the dilatation balloon. 
A further object of the invention is to provide a catheter of the type 
described in which different portions of the catheter display different 
intensities of radiopacity under fluoroscopic observation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates a low profile balloon dilatation catheter adapted for 
use in the coronary arteries. The dilatation catheter 12 is of very 
slender construction having a cross-section approximately equal to that of 
a small diameter guide wire. The dilatation catheter 12 has a balloon 26 
which, when collapsed, defines a small cross-sectional configuration so 
that it can pass through tight stenoses. In its collapsed configuration 
the balloon 26 as well as the remaining portions of the catheter 12 define 
an outer diameter corresponding to that of a small diameter guide wire. It 
should be understood, however, that the invention may be incorporated in 
catheters of other sizes as well. 
The catheter 12, illustrated in FIG. 1, is of the order of about 150 
centimeters when used in coronary arteries with a percutaneous femoral 
artery approach. 
The catheter 12 has a relatively long proximal segment 28 which is formed 
from narrow, solid wall tubing, such as hypodermic tubing. In the 
illustrative embodiment, the proximal segment 28 may be of the order of 
120 centimeters long. The proximal segment 28 is rigid torsionally so that 
it can transmit substantially fully to its distal end rotational motion 
imparted to the proximal end. As will be described, the distal tip of the 
catheter can be bent to a preset curve. Rotation applied to the catheter 
can be controlled to selectively direct and steer the curved distal end of 
the catheter as it is advanced. The proximal segment 28 also is flexible 
and can bend longitudinally to follow the curvature of the patient's 
arterial system. The proximal segment 28 of the catheter 12 may be 
sufficiently flexible that it can bend to follow the curve of a patient's 
aortic arch which has a radius of the order of between 2.5 to 3.5 inches 
in an adult. Alternately, it may be preferred to select a length for the 
proximal segment 28 so that it need not pass through the aortic arch. 
As shown more clearly in enlarged FIG. 2, in the preferred embodiment of 
the invention the hollow tubular segment 28 has an outer diameter of 0.022 
inches, a wall thickness of about 0.003 inches and an internal diameter 
passage 30 of 0.016 inches. A conventional fitting 32 is secured to the 
proximal end of segment 28 to facilitate connection with an 
inflation/deflation device, such as a syringe (not shown). 
The catheter 12 includes a distal segment 34 which extends from the distal 
end of the proximal segment 28 to the distal end of the catheter 12. The 
distal segment 34 includes a narrow diameter elongate support wire 44 
which is connected to and extends distally of the proximal segment 28. The 
support wire 44 is connected to the proximal tubing 28 by a short 
transition tube 36. The transition tube 36 is about three inches long and 
also is formed from slender, flexible hypodermic tubing with a smaller 
diameter than the proximal tube 28. In the illustrative embodiment, the 
transition tube 36 is formed from hypodermic tubing having an outer 
diameter of 0.015 inches, a wall thickness of 0.0035 inches and an inner 
diameter of 0.008 inches. The proximal end of the tubing 36 is received 
within the distal end of the internal passage 30 of the proximal segment 
28 and is secured thereto as by soldering or brazing. The solid support 
wire 44 is attached to the distal end of the transition tube 36. The 
support wire 44, which in the illustrative embodiment is very slender, 
preferably 0.008 inches diameter, is received in the distal end of the 
passage 38 of the tubing 36 and is secured by soldering or brazing. The 
support wire 44 plugs the distal end of the tubing 36. In order to permit 
the balloon 26 to be inflated and deflated, the transition tube 36 is 
provided with apertures 46 on opposite sides of the tube wall to provide 
communication with the internal passages 38, 30 of the catheter. The 
apertures 46 may be defined by forming a pair of oval ports about 
0.005.times.0.020 inches in the wall of the tubing 36. The support wire 44 
provides support for the balloon 26 and also extends distally beyond the 
balloon 26, to form the core of a leader segment 48. The leader segment 
includes a helically wound radiopaque coil spring 50 which is attached to 
the distal end of the core wire 44 in a manner described below. The coil 
50 may be formed from a platinum alloy, having a high percentage of 
platinum. 
The balloon 26 is formed by molding high strength polymeric material in a 
manner which provides a thin balloon wall not greater than about 0.001 
inches thickness and, preferably, having a thickness of the order of 
0.0005 inches. The balloon may be manufactured as described in U.S. Pat. 
No. 4,490,421 issued Dec. 25, 1984 and reference is made thereto for 
further details concerning the manufacture of the balloon. 
As shown in enlarged detail in FIG. 3, the balloon includes a main 
cylindrical portion 52. In the illustrative embodiment, the balloon 26 
preferably has an outer diameter of 2.0 to 4.0 millimeters. As mentioned 
above, the balloon is formed from a high strength material which will not 
tend to stretch when inflated. The length of the balloon 26 may be of the 
order of 15 millimeters. The balloon is formed to include tapering 
portions 54, 56 at the proximal and distal ends respectively. The distal 
tapering portion 56 merges into a narrowed neck 58 which fits snugly about 
and against the proximal end of the coil spring 50. The distal neck 58 of 
the balloon 26 is adhesively attached to the coil spring 50. As will be 
described in further detail, the proximal end of the coil spring is 
soldered securely to the core wire at the region where the distal neck 58 
of the balloon 26 is joined. The proximal tapering portion 54 merges into 
a narrowed proximal neck 60. 
In order to communicate the interior of the balloon 26 with the 
inflation/deflation passages 30, 38 of the tubing, an extension sleeve 62 
is adhesively attached to the proximal neck 60. The extension sleeve 62 
extends proximally over the support wire 44. The proximal end of the 
extension sleeve 62 preferably is formed from the same material as the 
balloon 26 and is securely and adhesively attached to the outer surface of 
the transition tube 36, where it joins the main tube 28. The extension 
sleeve 62 defines an annular passage 64 about the support wire 44. The 
annular passage 64 provides communication between the apertures 46 and the 
interior of the balloon 26 for inflation and deflation of the balloon. 
As shown in FIG. 3 the leader segment 48 which extends distally of the 
balloon 26 is of increasing flexibility in a distal direction to provide a 
relatively soft, flexible leading tip which reduces the chance of trauma 
or injury to the blood vessel. In the illustrative embodiment the leader 
segment is about 3 centimeters long. The coil spring 50 is soldered, at 
its proximal end to the support wire 44, as indicated at 66. The distal 
end of the support wire 44 also is soldered to the coil spring 50 as 
indicated at 68. Soldered joint 68 and the distal tip 69 of the support 
wire 44 terminate short of the distal tip of the coil spring 50. The 
distal tip 70 of the coil spring 50 may extend about five millimeters 
beyond the soldered joint 68 and defines a highly flexible bumper tip. A 
rounded weld bead 67 is formed at the distal tip of the spring 50. The 
leader segment 48 is of increasing flexibility in a distal direction. The 
support wire 44 is taper ground and, for example, may be ground smoothly 
to a 0.002 inch diameter at its distal tip 69. 
The distal tip 70 of the coil spring 50 includes a flexible and bendable 
stainless steel shaping ribbon 71 which is secured to the distal tip 69 of 
the support wire at one end, and to the distal weld bead 67 at its other 
end. The shaping ribbon is of slender, rectangular cross section, of the 
order of 0.001 inches by 0.002 inches. The shaping ribbon is adapted to be 
bent to a desired curve and to retain that curve when relaxed. The preset 
curve enables the catheter 12 to be steered by rotation of the catheter 
from its proximal end. The catheter can be rotated to direct the prebent 
distal tip 70 in selective directions as desired within the patient's 
blood vessels. 
The catheter also is provided with a radiopaque marker band 72 which 
preferably is formed from platinum. The marker band 72 is located 
proximally of the main portion of the balloon 26. In the illustrative 
embodiment it is securely attached to the support wire 44. The marker band 
72 provides a means by which the physician can verify, fluoroscopically, 
the position of the balloon 26. 
In order that the catheter may be passed through the lumen of a catheter 
which may guide the balloon catheter to the coronary arteries, the balloon 
26 also must be collapsible to a shape and size which can be passed 
through the lumen of that guiding catheter. The invention accomplishes 
these objectives by using the slender, small diameter support wire 44 
extending through the balloon and by using a balloon with a very thin but 
high strength wall. When the catheter 12 is to be inserted through the 
guiding catheter, the balloon 26 first is collapsed by applying suction, 
such as by a syringe, to the fitting 32. The balloon 26 and the extension 
sleeve 62 collapse, tending to form radially projecting wings as 
illustrated in FIGS. 3A-1 and 3B 1, respectively. The wings 62W and 26W 
wrap about the support wire 44 when the catheter is advanced through the 
main lumen of the guiding catheter. The wings 26W may wrap about the core 
wire 44 either in an S shaped configuration suggested in FIG. 3A-2 or in a 
C-shaped configuration shown in FIG. 3A-3. In either configuration the 
overall diameter through the collapsed and folded balloon portion of the 
catheter 12 includes six layers of the balloon material in addition to the 
diameter of the support wire 44. The balloon is formed from a high 
strength thin material having a wall thickness preferably not more than 
about 0.001". Thus, the aggregate diameter of six balloon layers plus the 
support wire is about 0.014 inches. The balloon thus is collapsible to a 
diameter which is about one fourth of its inflated diameter and which can 
pass easily through the main lumen of the guiding catheter. 
In use a larger diameter guiding catheter through which the dilatation 
catheter 12 can be passed is inserted initially in the patient's arterial 
system, usually through the femoral artery, and is advanced through the 
aortic arch to locate the distal tip of the guiding catheter at the 
coronary ostium leading to the coronary artery or into the coronary artery 
to be treated. After the larger guiding catheter has been positioned the 
catheter 12 is advanced through the larger catheter with its balloon 26 in 
a collapsed configuration. The diameter of the catheter 12, in the 
illustrative embodiment, is about the same as a conventional guide wire. 
The dilatation catheter 12 thus can be advanced out of the distal opening 
of the guiding catheter with the balloon 26, in its collapsed 
configuration, and by advancing and rotationally manipulating the catheter 
through the patient's artery, can be inserted into and through the 
stenosis. The dilatation balloon 26 then may be inflated under pressure to 
expand forcefully the balloon 26 to its maximum diameter thereby enlarging 
the passageway through the stenosis. 
When the balloon 26 has been inflated to enlarge the opening through the 
stenosis the balloon 26 is collapsed by aspirating the balloon. The 
catheter then may be withdrawn from the patient. 
As described above, the catheter 12 is very flexible through its distal 
segment 34. The proximal segment 28 may be sufficiently flexible so that 
it can bend relatively easily through the aortic arch. It may be 
preferred, however, to dimension the catheter so that the juncture of the 
proximal segment 28 and distal segment 34 will be disposed proximally of 
the aortic arch. The bend from the aorta, into the coronary ostium and 
thereafter through the coronary arteries are sharper and shorter radiused. 
The length of the more flexible distal segment 34 is sufficient so that 
the balloon can reach deeply into the coronary arterial tree without 
requiring the stiffer proximal tubing 28 to pass through relatively sharp 
bends, such as the bend from a guide catheter to the coronary ostium. The 
distal segment 34, which consists substantially of the thin, flexible 
support wire 44 is able to make the relatively sharp bends with ease. 
Thus, the only portion of the catheter 12 which actually enters the 
coronary artery is that which includes the slender support wire 44. This 
support wire is very flexible and is more easily bent to be able to 
negotiate shorter radius bends encountered in the coronary arterial tree. 
The catheter is highly steerable due in large measure to the solid wall of 
the tubing in the elongate proximal segment 28. The tubing is 
substantially torsionally rigid and tends to transmit substantially all of 
its rotation applied at the proximal end to the distal end. Although the 
intermediate segment of the catheter, which includes the slender 0.008 
inch diameter wire is too small a diameter to effectively transmit torque 
over relatively long distances, the distal segment 34 is relatively short, 
preferably about 25 cm to 32 cm and, therefore, does not have too great of 
an adverse effect on the torque transmission from the proximal end of the 
catheter to the distal end. The distal segment preferably is no longer 
than about 25 cm to 32 cm, as compared to the solid wall tubular proximal 
segment which is approximately 143 cm to 150 cm long. Thus, by forming a 
bend in the distal tip 70 of the leading segment, the direction of the 
catheter 12 can be controlled by rotating the catheter from the proximal 
end. 
The helical coil 50 and the marker band 72 are formed from highly 
radiopaque material, such as platinum or an alloy containing a high 
percentage of platinum. The coil 50 and marker band 72 thus are useful to 
indicate the location of the leader segment 48 and the proximal end of the 
balloon under fluoroscopy. It is important when performing an angioplasty 
that the physician be aware of the configuration and shape of the 
patient's coronary arteries. Typically, that is achieved by infusing 
radiopaque contrast liquid into the patient's artery and observing the 
patient's arteries under fluoroscopy for the brief interval that the 
radiopaque contrast liquid is in the artery, usually a few seconds. The 
physician thus is not provided with continuous information as to the 
configuration of the artery through which the catheter is passed. It would 
be desirable for the physician to have such information. Thus, in order to 
provide a means by which the physician may continually observe the 
orientation of the catheter and the configuration of the coronary artery 
through which the catheter is passed, the present invention provides an 
elongate radiopaque element extending along most or all of the distal 
segment 34 of the catheter. In the illustrative embodiment, the means for 
rendering the distal segment 34 radiopaque under fluoroscopy preferably is 
achieved by plating the support wire 44 with a radiopaque material, such 
as gold indicated schematically at 45 in FIG. 5. The support wire 44 may 
be coated fully along its length, from its junction with the tubing 36 
distally through the balloon. Alternately, the region of the support wire 
44 that extends through the balloon 26 may remain unplated so as not to be 
observable under fluoroscopy. Thus, when the catheter is disposed in the 
patient's arteries, a substantial length of the catheter, proximally of 
the balloon will be fluoroscopically observable, thus providing the 
physician with an indication of the contour and path of the coronary 
artery without requiring the infusion of radiopaque contrast liquid. 
It is preferred that the radiopaque image provided along the length of the 
distal segment of the catheter is sufficiently dark so that it is 
observable under fluoroscopy but not so dark that it might interfere with 
the physician's more detailed observation of specific portions of the 
coronary anatomy by infusing radiopaque contrast liquid. Therefore, it is 
preferred that the means by which the distal segment 34 is rendered 
radiopaque is configured so that the fluoroscopic image that it creates is 
lighter than the darkest image achievable. Preferably, the degree of 
radiopacity is such as to present a "gray" image, as compared with the 
very dark image provided by the radiopaque coil 50 in the leader segment 
and the marker band 72. By providing a "gray" image, the physician is able 
to observe the path and orientation of the distal segment of the catheter 
34 but without adversely obstructing the fluoroscopic image presented when 
radiopaque contrast liquid is infused into the artery. By way of example, 
the support wire 44 may be in the form of an inner core 44A plated with a 
layer 45 of gold of the order of 0.0002" to 0.0007" thick. The helical 
coil 50 is wound from a platinum alloy wire of the order of 0.003" in 
diameter. The marker band 72 may be formed from a platinum alloy ring. 
Thus, in the illustrative embodiment, the catheter would provide a 
fluoroscopic image in which the relatively short leader segment 48 and 
marker band 72 at the proximal end of the balloon 26 appear quite dark 
while the support wire 44 would appear as a lighter, gray image. It may be 
desirable to avoid any radiopaque means along the length of the balloon 
itself so that the region of the artery in which the balloon is located, 
namely, the critical region of the stenosis, can be observed completely 
and only with radiopaque contrast liquid without even minor fluoroscopic 
obstruction. That may be achieved simply by omitting the gold plating from 
that portion of the support wire 44 that extends through the balloon. 
As an alternative to plating the support wire 44 with a highly radiopaque 
material such as gold, the moderately radiopaque, "gray" distal segment 34 
may be achieved by forming the wire 44 itself from a moderately radiopaque 
alloy. For example, alloys of platinum, gold and ruthenium may be 
employed, selected as to maintain adequate torsional riqidity for the 
distal segment 34 of the catheter. 
Yet another alternative for providing the moderately radiopaque segment is 
to make a support wire 44 from clad wire, as illustrated in enlarged and 
exaggerated cross sectional detail in FIG. 6. As shown in FIG. 6 a clad 
support wire 44 includes an inner core 44B about which is mechanically 
constricted a tubular cladding or jacket 74 of radiopaque material. The 
clad wire arrangement is preferable where it is desired to provide a 
thicker layer of radiopaque material about the inner core 44B. In 
contrast, conventional electroplating is a relatively time consuming 
procedure and the approximate maximum thickness to which gold plating may 
be made is of the order of 0.0005 inches. Considerably thicker layers may 
be achieved when using the clad wire. The clad wire is made by providing a 
core wire 44B and a thin wall tube of the metal from which the jacket 74 
is to be made. By way of example, in order to make a support wire 0.008 
inches in diameter the core wire 44B may be formed from stainless steel 
0.003 inches in diameter. A length of gold hypodermic tubing, having a 
wall thickness in the order of 0.003 inches and an internal diameter just 
slightly greater than that of the inner core 44B, such as 0.0035 inches, 
is provided. The gold hypodermic tubing is slipped over the inner core 44B 
and together, they are drawn through a die having an outer diameter of 
0.008 inches. The die constricts and draws the gold hypodermic tubing to a 
smaller diameter, tightly about the core wire 44B to secure them together 
mechanically into the composite wire. Similarly clad wire is available 
commercially from a number of commercial sources, such as the Sigmund Cohn 
Company in Mt. Vernon, N.Y. Of course, other materials and dimensions for 
the inner core 44B and jacket 74 may be selected, depending on the desired 
characteristics of the wire. By way of further example, the core wire 44B 
could be 0.006 inches in diameter with the cladding 74 having a final 
thickness in the order of 0.001 inches. 
Among the advantages of using clad wire for the support wire 44 is that by 
grinding away segments of the radiopaque cladding, as desired, the 
radiopacity along the length of the support wire 44 may be varied as 
desired. For example, if it is desired to make a catheter in which the 
portion of the distal segment proximally of the balloon has a moderate 
"gray" radiopacity while the portion under the balloon has no radiopacity, 
of the cladding 74 can be ground away in the region of the support wire 
that will be disposed of within the balloon. In such an embodiment, it 
also may be desirable to provide a highly radiopaque marker band on the 
support wire 44 or in the region of the proximal and distal end of the 
balloon so as to highlight the ends of the balloon fluoroscopically. 
FIG. 7 illustrates a further embodiment having a support wire with a step 
tapered configuration at its distal region as well as a clad configuration 
for the support wire. As shown in FIG. 7, the support wire 44 has a 
proximal portion 45 that is of a continuous diameter such as 0.008 inches 
for most of its length. The distal, approximately 8.5 centimeters of the 
support wire may be progressively tapered in a step tapered arrangement to 
provide for increasing flexibility in a distal direction. For example, the 
0.008 inch diameter cylindrical support wire may include a tapering, 
conical segment 76, about 3 centimeters in length and tapering down to 
about 0.006 inches. The segment 76 then merges into a cylindrical barrel 
segment 78 of constant diameter (0.006 inches). The barrel segment 78 may 
be of the order of 2.5 centimeters in length. The distal most segment 80 
may form a second conically tapered portion, tapering down to a distal tip 
approximately 0.002 inches in diameter. In this embodiment the proximal 
end of the coil spring may be attached to the segment 80 so that the 
proximal edge of the spring is approximately 1.8 centimeters from the 
distal tip of the segment 80. The balloon, which may be of the order of 
2.5 centimeters long is attached adhesively at its distal end to the 
proximal end of the spring. The proximal end of the balloon is attached to 
the extension 60 in the region of the barrel segment 78. Such a core wire 
may be formed from nonradiopaque wire or from wire plated with a 
radiopaque metal or made from clad wire. In the plated configuration, the 
wire may be made with plated and unplated segments using conventional 
selected plating techniques relating to those in the plating art. Should 
it be preferred to use clad wire, a length of such clad wire may be 
provided and then its distal end may be centerless ground to provide the 
desired tapered configuration for the catheter. Depending on the final 
dimension, some or all of the cladding may be ground away at the distal 
region of the wire. For example, in the embodiment illustrated in FIG. 7, 
if the cladding were approximately 0.001 inches thick, the barrel segments 
78, 80 would be free of cladding, the cladding having been ground away 
during the centerless grinding operation. The moderately radiopaque 
segment may have a proximal extremity about 35 cm from the distal tip of 
the wire 44, as suggested in phantom at 82 in FIG. 7. The support wire 44 
is shown in exaggerated diameter, out of scale, for purpose of 
illustration. 
From the foregoing, it will be appreciated that the invention provides 
improvements to balloon dilatation catheters, particularly those used in 
coronary angioplasty, by providing a means by which the physician may be 
provided with a continuous fluoroscopic indication of the configuration of 
the coronary artery through which the catheter passes along a substantial 
distance along a proximal segment of the catheter. Moreover, that object 
is achieved without unduly obstructing the fluoroscopic image of the 
coronary anatomy when it is desired to infuse radiopaque contrast liquid. 
It should be understood, however, that the foregoing description of the 
invention is intended merely to be illustrative thereof and that other 
modifications, embodiments and equivalents of the invention will be 
apparent to those skilled in the art without departing from its spirit.