Fluoroscopically-visible flexible graft structures

A fluoroscopically-visible graft structure is provided. The graft structure may be formed from a tubular metal wire mesh coated with an elastomeric material. The graft structure is flexible and distensible like natural body organ tubing and is suitable for repairing or replacing body organ tubing such as vascular tubing (e.g., arteries and veins). A radiopaque filler compound may be provided throughout a substantial portion of the graft structure or throughout the entire graft structure, so that a physician can determine the size and location of the graft structure during implantation of the graft structure in the body of a patient. The radiopacity of the graft structure also allows the physician to monitor status of the graft structure after installation. The radiopacity of the graft structure is preferably sufficient to allow the graft structure to be clearly viewable on a fluoroscope, but is not so great that the radiopacity of the graft obscures radiopaque dyes introduced into the patient and passed through the graft.

BACKGROUND OF THE INVENTION 
This invention relates to graft structures and particularly to 
fluoroscopically-visible flexible graft structures. 
A patient's weakened or diseased body organ tubing can be replaced, 
repaired, or supplemented using artificial graft structures. For example, 
an aneurysm may be repaired by lining the patient's artery with an 
artificial graft structure to help contain the patient's blood within the 
weakened portion of the artery. Other procedures involve bypassing a 
section of diseased or blocked body organ tubing with artificial graft 
tubing. 
Some artificial graft structures are flexible and distensible like natural 
body organ tubing. Such flexible graft structures may be formed from 
elastic polymer tubing or from a tube frame of a first highly elastic 
material (such as nitinol) covered with a second highly elastic material 
(such as silicone rubber). Flexible graft structures are a good 
replacement for a patient's natural body organ tubing. In addition, 
flexible graft structures are suitable for intraluminal installation, 
which is a relatively non-invasive technique by which grafts are 
introduced into the patient's body through the patient's existing body 
organ tubing. Such intraluminal installation techniques may be used, for 
example, to deliver and install grafts through a patient's vascular system 
as an alternative to open heart surgery. If desired, flexible graft 
structures can be made porous and may be provided with various coatings to 
improve bio-utility. 
However, flexible graft structures are not inherently visible under 
fluoroscopic illumination. As a result, it may be difficult for a 
physician to view a flexible graft structure during an intraluminal 
insertion procedure or to determine the status of the graft structure 
during follow-up monitoring. 
It is therefore an object of the present invention to provide 
fluoroscopically-visible flexible graft structures that allow the 
physician to view the graft structure during intraluminal installation and 
that allow the physician to monitor the status of the installed flexible 
graft structure during follow-up procedures. 
SUMMARY OF THE INVENTION 
These and other objects of the invention are accomplished in accordance 
with the principles of the present invention by providing a 
fluoroscopically-visible flexible graft structure. The graft structure may 
be used to replace, repair, or supplement a diseased or damaged portion of 
the patient's vascular system or other body organ tubing. The graft 
structure is preferably flexible and distensible like natural body organ 
tubing and may be provided with bio-compatible coatings or be made porous 
to enhance bio-compatibility. 
In a preferred embodiment, the flexible graft structure is made from an 
elastic tubular wire mesh coated with an elastic polymer such as silicone. 
A radiopaque substance such as a radiopaque filler compound containing 
barium, bismuth, or tungsten is added to the elastic polymer to make the 
flexible graft structure radiopaque. The graft structure is preferably 
radiopaque enough to be clearly visible on a fluoroscope when inside the 
patient's body, but is not so radiopaque as to obscure standard radiopaque 
dyes when they pass through the graft structure. The radiopaque filler 
compound is preferably distributed fairly uniformly throughout a 
substantial portion (e.g. greater than about 50%) of the elastic material 
or throughout the entire elastic material, so that the size and shape of 
the graft structure may be viewed fluoroscopically during installation of 
the graft structure into the body of the patient. 
The radiopacity of the flexible graft structure allows the physician to 
monitor the status of the flexible graft structure during follow-up 
procedures. Characteristics of the flexible graft structure that may be 
monitored include the compliance of the graft, the anastomosis of the 
graft to the patient's body organ tubing, and the presence or absence of 
conditions such as holes, kink failures, bursts, aneurysm, etc. 
Further features of the invention, its nature and various advantages will 
be more apparent from the accompanying drawings and the following detailed 
description of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An illustrative flexible graft structure 10 in accordance with the present 
invention is shown in FIG. 1. Graft structure 10 may be formed from any 
suitable elastic tubing structure such as a polymer tube, but is 
preferably formed from a highly elastic tubular frame 12 with an 
integrally-formed highly elastic fluid-retaining coating 14. In the 
illustrative example of FIG. 1, graft structure 10 is connected to a 
patient's body organ tubing 16 with connectors 18. Connectors 18 may be 
formed from sutures, crimp or clamp connectors, connectors with barbs or 
hooks, or any other suitable connector structures. Connector structures 
for attaching graft structure 10 to body organ tubing 16 are described in 
Goldsteen et al. U.S. patent application Ser. No. 08/745,618, filed Nov. 
7, 1996, which is hereby incorporated by reference herein in its entirety. 
Graft structure 10 is extremely elastic, flexible, pliable, and resilient. 
For example, it can be stretched to a small fraction of its original 
diameter, after which it returns by itself to its original size and shape 
without damage or permanent deformation of any kind. Graft structure 10 is 
also preferably distensible, so that it may pulsate very much like natural 
circulatory system tubing in response to pressure waves in the blood flow. 
Graft structure 10 may also be modular in construction, may accept natural 
body organ tubing concentrically inside itself, may support development of 
an endothelial layer, and may be compatible with magnetic resonance 
imaging (MRI) procedures. 
The preferred materials for forming frame 12 of graft structure 10 are 
metals, although polymeric materials may also be used. The presently most 
preferred material is a braid of nitinol wire. Coating 14 is preferably an 
elastic bio-compatible material such as silicone, which fills the 
apertures formed by the wires in frame 12. Other materials that may be 
used for coating 14 include polymeric materials such as stretchable 
urethane, stretchable polytetrafluoroethylene (PTFE), natural rubber, and 
the like. 
If desired, coating 14 can be formed with microscopic pores to help improve 
bio-compatibility. A preferred method of providing a desired porosity is 
to make coating 14 from an elastic material that is mixed with particles 
of a material that can be removed (e.g., by vaporization) after coating 14 
has been applied to frame 12. When the particles are removed, voids are 
left in coating 14 that give it porosity. Whether porous or not, coating 
14 is preferably capable of retaining fluids. Graft structure 10 is 
therefore suitable for confining blood within a weakened artery and 
relieving pressure from the weakened artery wall. 
If desired, graft structure 10 may be provided with additional coatings 
such as medicated coatings, hydrophilic coatings, smoothing coatings, 
collagen coatings, human cell seeding coatings, etc., as described in the 
above-mentioned Goldsteen et al. U.S. patent application. The porosity of 
coating 14 may help graft structure 10 to retain these coatings. 
The highly elastic nature of frame 12 and coating 14 make it possible to 
axially stretch and thereby radially compress graft structure 10 prior to 
installation in the body organ tubing of the patient. Graft structure 10 
may therefore be deployed through tubes (e.g., arteries) of smaller 
diameter in the patient's body after which graft structure 10 
automatically returns to nearly its full nominal diameter. Intraluminal 
installation procedures for flexible artificial graft structures are 
described in the above-mentioned Goldsteen et al. U.S. patent application. 
Using such intraluminal installation procedures, graft structure 10 may be 
used to replace, repair, or supplement the patient's body organ tubing. In 
the example of FIG. 1, graft structure 10 has been used to replace a 
length of natural body organ tubing. In FIG. 2, graft structure 10 has 
been used to line an existing artery 20 to support weakened artery wall 
portion 22. Although intraluminal installation is a preferred technique 
for implanting graft structure 10 in the patient's body, alternative 
installation techniques such as conventional surgery may also be used if 
desired. 
One of the concerns of the physician during installation of structures such 
as graft structure 10 is whether the graft has been placed properly in the 
body. Proper graft placement is of particular concern during intraluminal 
installation, because the physician cannot view the graft site directly. 
Another concern of the physician is providing adequate follow-up 
monitoring of the implanted graft. Assessing proper graft placement and 
monitoring the status of the graft after implantation is difficult with 
flexible grafts, because the polymer coating and wire mesh frames of such 
grafts typically do not image well using fluoroscopic imaging devices. 
In accordance with the present invention, graft structure 10 is radiopaque, 
so that graft structure 10 may be viewed during intraluminal installation 
procedures and during follow-up monitoring. As shown in FIG. 3, graft 10 
may be viewed using a radiation source 26 and a radiation imaging device 
28. Radiation source 26 is preferably an x-ray source and radiation 
imaging device 28 is preferably a fluoroscope for imaging graft 10 in real 
time. 
Graft structure 10 is preferably made radiopaque by providing a radiopaque 
substance such as radiopaque filler 24 in coating 14. Filler 24 is 
preferably provided fairly uniformly throughout a substantial portion 
(e.g., greater than about 50%) of coating 14 or throughout substantially 
the entire coating 14 so that a physician viewing graft structure 10 with 
a fluoroscope can readily ascertain the size and position of graft 
structure 10. The large discrete particles of filler 24 shown in FIG. 3 
are for illustrative purposes only. Filler 24 is preferably a radiopaque 
compound containing fairly fine particles of barium, bismuth, tungsten, 
etc. The concentration of radiopaque filler to be used for a given 
radiopaque graft depends on the size of graft structure 10 and the 
radiopacity of the filler. A suitable filler concentration may be in the 
range of approximately 10-20 per cent. Graft structure 10 is preferably 
radiopaque enough to allow graft structure 10 to be fluoroscopically 
viewed, but is preferably not so radiopaque that graft structure 10 
obscures the viewing of commonly-used radiopaque dyes. 
As shown in FIG. 3, incident radiation 30 from radiation source 26 passes 
through the patient's body 31 and body organ tubing 32, graft structure 
10, and dye 34. The intensity of transmitted radiation 36 is greatest 
where neither graft structure 10 nor radiopaque dye 34 are present. Graft 
structure 10 reduces the intensity of transmitted radiation 36 
sufficiently where graft structure 10 is present that graft structure 10 
may be clearly viewed using radiation imaging device 28. Because graft 
structure 10 is fluoroscopically viewable, the physician can view the 
position of graft structure 10 during graft installation. In addition, 
during follow-up monitoring of an installed graft, the physician can 
assess the compliance (distensibility) of graft 10 by observing the 
behavior of graft 10 (e.g., as blood pulses through graft 10). Compliance 
monitoring over a period of days or weeks may allow the physician to asses 
whether there is ingrowth of natural tissue into the graft, because such 
tissue ingrowth typically reduces compliance. The physician can also 
assess the anastomosis of graft structures 10 to body organ tubing 16 and 
can detect the presence of holes, kink failures, bursts, etc. The 
physician can view the position of graft structure 10 during graft 
installation and can visually monitor graft structure 10 during follow-up 
monitoring without introducing a radiopaque dye into the patient. 
Sometimes the physician may desire to introduce radiopaque dye into the 
patient's body organ tubing. For example, the physician may want to 
ascertain whether blood is flowing properly through the patient's vascular 
system in the vicinity of a vascular surgery site. The use of radiopaque 
dyes to visualize the patient's vascular system is well known and many 
physicians rely upon this technique, particularly during surgery and 
during the first 48 hours after surgery, before the patient has been 
discharged from the hospital. 
The radiopacity of graft structure 10 is sufficiently low that graft 
structure 10 does not obscure standard radiopaque dyes when such dyes flow 
through graft structure 10. As schematically illustrated in FIG. 3, the 
intensity of transmitted radiation 36 through the portion of graft 
structure 10 that contains radiopaque dye 34 is substantially less than 
the intensity of transmitted radiation 36 through the portion of graft 
structure 10 that does not contain radiopaque dye 34. This allows 
physicians to use standard radiopaque dye diagnostic procedures to detect, 
e.g., the formation of blood clots in and around graft structure 10. The 
ability to view the flow of dye 34 through graft structure 10 is therefore 
an important attribute of graft structure 10 that may be used during 
follow-up monitoring of the patient. 
The transmission of radiation through various structures is shown in FIG. 4 
(in arbitrary units). Area I shows a level of radiation transmission 
(i.e., 5 a.u.) for a typical patient's body (including body organ tubing). 
Area II shows how transmission is reduced (i.e., to 4 a.u.) in those 
regions of the patient in which incident radiation passes through both the 
body and a region (i.e., body organ tubing of average size) containing dye 
34 (FIG. 3). This allows the physician to view the flow of radiopaque dye 
through the patient's body. Area III shows that the level of radiation 
transmission is reduced further (i.e., to 2.5 a.u.) when incident 
radiation passes through graft structure 10 in addition to the body and 
radiopaque dye regions of area II. In area IV, transmission is greater 
than in area III, because incident radiation only passes through the 
patient's body and graft structure 10. 
If the total level of transmitted radiation in any region falls below a 
given detection threshold (e.g., below 0.5 a.u. in the example of FIG. 4), 
then radiation imaging device 28 will not be able to discriminate pattern 
or structure within that region. The ability to view the flow of 
radiopaque dye through graft structure 10 therefore depends upon the 
transmitted radiation level of area IV being above this threshold level. 
With the arrangement shown in FIG. 4, the level of radiation transmission 
through body and graft regions (area IV) is significantly greater than the 
level of transmission through body, graft, and dye regions (area III) and 
the radiation transmission level in body and graft regions (area IV) is 
well above the detection threshold limit. Dye 34 passing through graft 
structure 10 is therefore not obscured (i.e., lowered below the detection 
threshold) by the radiopacity of graft structure 10. 
Steps involved in using graft structures 10 are shown in FIG. 5. At step 
38, the physician installs graft structure 10 into the patient's body. 
Graft installation may be surgical or may involve intraluminal delivery 
(e.g., delivery through the patient's vascular system). During step 38, 
the physician may view graft structure 10 with a radiation imaging device 
such as a fluoroscope. Viewing graft structure 10 in real time during 
installation of graft structure 10 aids proper placement of graft 
structure 10 by the physician. 
At step 40, the physician may introduce a standard radiopaque dye into the 
patient's body organ tubing (e.g., by injecting the dye into the patient's 
vascular system). The radiopaque dye may be fluoroscopically viewed at 
step 42. The flow of radiopaque dye may be viewed inside graft structure 
10 without obscuring the dye with graft structure 10. In vascular 
applications, this allows the physician to observe whether blood clots 
have formed in graft structure 10. 
Regardless of whether radiopaque dye has been introduced into the patient, 
the physician can fluoroscopically monitor the status of the installed 
graft structure 10 during a follow-up procedure at step 44. Fluoroscopic 
follow-up monitoring is possible due to the radiopacity of graft structure 
10. Follow-up monitoring may involve fluoroscopically observing the 
distensibility of graft structure 10 and fluoroscopically monitoring graft 
structure 10 for leaks, kink failures, bursts, aneurysms, etc. Follow-up 
monitoring may also involve fluoroscopically assessing the anastomosis of 
graft structure 10 to the patient's body organ tubing. 
It will be understood that the foregoing is only illustrative of the 
principles of the invention, and that various modifications can be made by 
those skilled in the art without departing from the scope and spirit of 
the invention.