referring now to the drawings , a ptca catheter 10 , in accordance with a preferred embodiment of the present invention , is described in detail . the catheter 10 , as best shown in fig1 and 3 , includes an elongate , flexible tubular sheath 12 , formed from a single extruded length of a suitable , biocompatible polymer . the interior of the sheath 12 contains first and second longitudinally - extending partitions , 14 and 16 , respectively . the first partition 14 is substantially diametric , dividing the interior of the sheath approximately in half . the second partition 16 extends from the first partition 14 to the interior wall of the sheath and is located so as to divide its half of the interior of the sheath 12 into two longitudinal sections of unequal cross - sectional areas . thus , the two partitions 14 and 16 divide the interior of the sheath 12 into three longitudinal sections , each of which may be of a different cross - sectional area . these sections define three longitudinal lumens : a large lumen 18 , an intermediate - sized lumen 20 and a small lumen 22 . attached to the distal end of the sheath 12 , so as to surround its exterior surface coaxially , is an angioplasty balloon 24 . the balloon 24 is made of a polymeric material ( e . g ., polyvinylchloride or polyethylene ) that provides high strength , relatively low elasticity and relatively high rigidity upon inflation . such angioplasty balloons are well - known in the art and need not be described in further detail herein . each of the three lumens mentioned above serves a different function . the large lumen 18 serves principally as a passage for the infusion of optically - transparent liquids to flush blood away from the field of view of the imaging optics of the catheter , as will be described below . another important function of this large lumen 18 is to provide a passage for a guidewire 26 that is employed to guide the catheter 12 to the desired location within a blood vessel . the guidewire 26 , which is shown in fig1 and 3 , does not need to be withdrawn from the lumen 18 after the catheter is in place . the large lumen 18 is large enough to provide a passage for infusion of radiopaque contrast fluids , thrombolytic drugs , etc . and , when the guidewire is removed , for introduction of various instruments , such as mechanical cutters , laser angioplasty fibers and blood pressure transducers . for the purpose described above , the large lumen 18 has a distal opening 28 through which the fluids and / or the guidewire 26 , or the instruments referred to above , emerge . the proximal end of the large lumen is connected , via a strain relief connection 30 , to a first inlet tube 32 , as shown in fig1 . the proximal end of the first inlet tube , in turn , is attachable to a y - shaped inlet fitting 34 , having a first branch 36 that serves as a liquid infusion port and a second branch 38 that serves as an entrance for the guidewire 26 , or the other instruments , mentioned above , that can be passed through the large lumen 18 . the small lumen 22 serves as an inflation passage for the balloon 24 . for this purpose , the small lumen has a peripheral orifice 40 passing through the wall of the sheath 12 and into the interior of the balloon 24 . that part of the small lumen 22 between the orifice 40 and the distal end of the catheter is closed by a plug 42 or equivalent sealing means . the proximal end of the small lumen 22 is connected , via the strain relief connection 30 , to a second inlet tube , or inflation tube 44 . the proximal end of the inflation tube 44 , in turn , is connected to an inflation port fitting 46 , as shown in fig1 . the intermediate - sized lumen 20 contains a plurality of illuminating optical fibers 48 and at least one imaging optical fiber bundle 50 with an imaging lens 52 at its distal end . these optical components will be described in detail below . the intermediate - sized lumen 20 runs the entire length of the sheath 12 , the distal end of this lumen having an opening 54 at the distal end of the catheter ( fig3 ) and the proximal end terminating at the strain relief connection 30 ( fig1 ). the optical fibers 48 and 50 are carried from the strain relief connection 30 to an eyepiece 56 by means of a flexible , opaque conduit ( tube 58 ). in some applications , the eyepiece can be replaced by an adaptor for coupling to a video camera ( not shown ). the eyepiece 56 also includes means ( not shown ) for transmitting light from a source ( not shown ) to the proximal ends of the illumination fibers 48 . in some applications , tube 58 may consist of two separate conduits , one carrying the optical fibers 48 and the other carrying the optical fibers 50 . as mentioned above , the intermediate - sized lumen 20 contains the illuminating optical fibers 48 and the imaging optical fiber bundle 50 . the illuminating optical fibers 48 are formed of an optical - quality transparent plastic , preferably polymethylmethacrylate or a suitable polymeric equivalent . made of such a material , the illuminating fibers 48 offer several advantages over the glass fibers used in prior art angioscopes : ( 1 ) more efficient light - gathering characteristics ; ( 2 ) greater flexibility ; ( 3 ) ease of manufacture ; and ( 4 ) lower cost . the imaging optical bundle 50 , shown most clearly in fig6 and 8 , comprises a very large number of very small individual image fibers or pixels 60 , only some of which are shown ( not to scale ) in the drawings . in a preferred embodiment of the invention , there are about 2000 to 3000 pixels , made of fused silica glass doped with germanium dioxide to increase the index of refraction . the pixels 60 are preferably about three to four microns in diameter and are bound together by a cladding 62 ( fig8 ), made of a glass doped with fluorine to lower its index of refraction , so that the cladding 62 has a much lower index of refraction than the pixels 60 . the relationship between the indices of refraction of the pixels 60 and the surrounding cladding 62 provides an increased numerical aperture for the imaging fiber bundle , the significance of which will be discussed below . the bundle of pixels 60 is coated with an opaque plastic coating 64 , preferably an ultraviolet - cured acrylate epoxy , for structural strength and flexibility and for shielding the pixels 60 from ambient light . as mentioned above , the relationship of the pixel index of refraction to the cladding index of refraction yields a high &# 34 ; numerical aperture &# 34 ; ( n . a .). the numerical aperture can be defined by the following equation : where n p is the pixel index of refraction , and n c is the cladding index of refraction . it can be seen that if the pixel index of refraction is much greater than the cladding index of refraction , the numerical aperture will be large . the larger the numerical index , the more light that can be accepted by the imaging fiber bundle , and , therefore , the brighter the image . this is particularly important for intracardiovascular imaging , where it is desirable to minimize the amount of light necessary to illuminate the target and transmit the image . since the imaging fiber bundle of the present invention can gather more light per unit area than the imaging fiber optics in prior art angioscopes , fewer illumination fibers ( of the type described above ) are needed . moreover , &# 34 ; cross - talk &# 34 ; or the transmission of light from one pixel to another , is reduced , resulting in increased contrast as compared to prior art imaging optics . still another advantage that obtains from the high light - gathering abilities of the above - described fiber bundle is that smaller pixels can be used . as mentioned above , pixels in the present invention can be from three to four microns in diameter , as compared to eight to ten microns in prior art devices . with smaller pixels , resolution is enhanced . in the preferred embodiment of the invention , the pixel material is optimized for chromatic transmission , by techniques well - known in the art , to minimize color distortion . the imaging fiber bundle , constructed in the manner described above , thus features improved optical characteristics , at lower cost , than prior art imaging fiber optics . moreover , the resulting fiber bundle is highly flexible , having a bending radius as small as 30 mm on a sustained basis . this means that the bundle can be wrapped around a 30 mm mandrel with a weight suspended by the bundle , and the bundle does not fail or become damaged . in operation , the bundle can be satisfactorily bent through smaller radii . in addition , the improved optical characteristics of the fiber bundle allow its overall diameter to be substantially reduced , and because fewer imaging fibers are needed , the diameter of the entire catheter can be decreased , as compared to prior art fiberscopes . the imaging lens 52 , shown most clearly in fig4 and 6 , is attached to the distal end of the imaging fiber bundle 50 by an optically transparent , biocompatible epoxy adhesive . a suitable epoxy adhesive is the one sold under the trademark epo - tex 301 - 2 by epoxy technology , inc . of billerica , mass . this epoxy has an optical transmission of 98 - 99 % from 0 . 31 to 2 . 5 microns , which includes the entire visible spectrum . it can be cured in 11 / 2 hours at 80 ° c ., and , when cured , has a shore d hardness of 82 , allowing it to be effectively polished . the lens 52 itself is a gradient index objective lens , comprising a cylinder of optical quality glass having a refractive index that decreases , gradually and continuously , in the radially outward direction . thus , referring to fig5 which shows the end face of the lens 52 , the highest index of refraction n 3 is at the center of the lens , with refractive indices n 2 , n 1 and n 0 indicating progressively lower refractive indices at selected points along a radius 66 of the lens 52 . as shown in fig4 the gradients index lens 52 , is optically coupled to the image fiber bundle 50 so as to focus an inverted image 68 of an object 70 onto the distal end of the image fiber bundle 50 , in a manner essentially equivalent to a conventional geometric lens . the inverted image 68 is then transmitted to the proximal end of the imaging fiber bundle , and from there to an optical receiver such as the eyepiece 56 , where it is magnified and returned to its original orientation by suitable lenses ( not shown ). in a preferred embodiment of the invention , the lens 52 has a diameter of about 0 . 35 mm ( slightly smaller than the inner diameter of the coating 64 of the imaging fiber bundle 50 as seen in fig7 ). there is also a thin silica jacket 61 encasing the pixels 60 . the lens 52 has a working distance , or focal length ( in air ), of approximately 5 mm , as indicated by the arrow 72 in fig4 . the &# 34 ; depth of field ,&# 34 ; however , is greater , ranging from about 2 to 10 mm . the gradient index lens 52 offers optical qualities and performance similar to the conventional geometric lenses of prior art fiberscopes , but at considerably lower cost , especially in the very small sizes , the use of which is made possible by the present invention . a ptca catheter constructed in accordance with the present invention is inserted into a blood vessel ( such as a coronary artery ) by means of the guidewire 26 . as the distal end approaches the suspected site of a stenosis , a transparent flushing liquid is passed through the large lumen 18 from the infusion port 36 , emerging from the distal orifice 28 to clear blood away from the optical path of the illuminating and imaging optics . visualization of the stenosis site is achieved by transmitting light through the illumination fibers 48 , and then transmitting the illuminated image back to the eyepiece 56 by means of the lens 52 and the imaging fiber bundle 50 . when the balloon 24 is properly located with respect to the stenosis , it is inflated to relieve the stenosis by means of a suitable inflation fluid injected through the small lumen 22 and into the balloon 24 through the lumen orifice 40 . alternatively , the balloon 24 can be inflated for the purpose of facilitating visualization , in the manner described above in connection with the description of u . s . pat . no . 4 , 576 , 145 to tsuno , et al . it is important to note that in small vessels , it generally will not be necessary to inflate the balloon for the purpose of occluding blood flow to facilitate visualization . when the balloon is employed for this purpose , it may be advantageous to inflate it only partially , since the purpose is only to reduce the blood flow through the vessel and not to exert pressure against its walls . when the catheter is used in this manner , the large lumen may be used for the passage of a variety of mechanical instruments to the desired location in the blood vessel , the guidewire 26 having been withdrawn . as previously mentioned , these instruments may include a laser for laser angioplasty , a micro - cutter , etc . thus , the present invention offers the physician the option of performing accurate angioscopy , along with a variety of other procedures . of considerable importance is that both visualization ( angioscopy ) and treatment ( angioplasty ), can be performed with the same catheter . thus , there is no need to insert and remove two different catheters , as was the common practiced with the prior art devices , as previously described . using the construction described above , the cost of the catheter can be minimized . this cost reduction is achieved mostly with the novel optical components of the present invention , which also achieves superior optical performance as compared to the prior art . as a result , the cost of the catheter is reduced sufficiently to allow the entire unit to be disposable , thereby eliminating the cleaning and resterilization required for the prior art angioscopy devices . because the device is designed to be disposable , the illuminating fiber 48 and the imaging fiber bundle 50 are permanently fixed in the lumen 20 by a suitable biocompatible adhesive , such as an epoxy or polyurethane . this further reduces costs and increases structural strength , as compared to prior art devices , in which the optical components are removable from the sheath to facilitate cleaning . furthermore , as previously mentioned , the improved optical components in the present invention allow the overall diameter to be significantly reduced . for example , the outside diameter may be as small as 1 . 5 mm and , in a prototype , is about 1 . 45 mm . such small sizes allow the present invention to be used in blood vessels that are significantly smaller than those that have been accessible with prior art devices . all of the above - described advantages provide a ptca catheter , in accordance with the present invention , that offers improved performance , greater versatility , increased cost - effectiveness , and improved convenience and ease of use , as compared to prior art devices of this general nature . it will be appreciated that , while a preferred embodiment of the invention has been described herein , various modifications will suggest themselves to those skilled in the pertinent arts . for example , variations in the configuration of the invention may be devised to adapt the present invention for use in bodily passages or cavities other than blood vessels . the specific configuration of the lumens and their relative sizes may be modified to accommodate optical components of different sizes . these and other modifications that may suggest themselves to those skilled in the pertinent arts are considered to be within the spirit and scope of the present invention , as defined in the claims which follow .
a balloon - type catheter is provided with an integral optical system utilizing illuminating fibers made of optical grade plastic , and an imaging bundle of many very small , flexible , fused glass fibers of pixels doped to increase the index of refraction and cladded together by doped glass with a much lower index of refraction than the pixels . a gradient index objective lens in the form of a cylinder of optical quality glass is attached to the distal end of the imaging fiber bundle . an inflation lumen is provided in the catheter for inflating the balloon , and a separate lumen conducts optically - transparent liquids to flush the field of view . the resulting catheter can be very small in diameter , is very flexible and is sufficiently inexpensive to be practically disposable .