fig1 shows a balloon catheter that can be used to illustrate the features of the invention . the catheter 10 of the invention generally comprises an elongated catheter shaft 11 having a proximal section 12 , a distal section 13 , an inflatable balloon 14 on the distal section 13 of the catheter shaft 11 , and an adapter 17 mounted on the proximal section 12 of shaft 11 . in fig1 , the catheter 10 is illustrated within a greatly enlarged view of a patient &# 39 ; s body lumen 18 , prior to expansion of the balloon 14 , adjacent the tissue to be injected with therapeutic agents . in the embodiment illustrated in fig1 , the catheter shaft 11 has an outer tubular member 19 and an inner tubular member 20 disposed within the outer tubular member and defining , with the outer tubular member , inflation lumen 21 . inflation lumen 21 is in fluid communication with the interior chamber 15 of the inflatable balloon 14 . the inner tubular member 20 has an inner lumen 22 extending therein which is configured to slidably receive a guidewire 23 suitable for advancement through a patient &# 39 ; s coronary arteries . the distal extremity of the inflatable balloon 14 is sealingly secured to the distal extremity of the inner tubular member 20 and the proximal extremity of the balloon is sealingly secured to the distal extremity of the outer tubular member 19 . fig2 and 3 show transverse cross sections of the catheter shaft 11 and balloon 14 , respectively , illustrating the guidewire receiving lumen 22 of the guidewire &# 39 ; s inner tubular member 20 and inflation lumen 21 leading to the balloon interior 15 . the balloon 14 can be inflated by a fluid such as air , saline , or other fluid that is introduced at the port in the side arm 24 into inflation lumen 21 contained in the catheter shaft 11 , or by other means , such as from a passageway formed between the outside of the catheter shaft 11 and the member forming the balloon 14 , depending on the particular design of the catheter . the details and mechanics of the mode of inflating the balloon vary according to the specific design of the catheter , and are omitted from the present discussion . fig1 and 4 illustrate an embodiment of the catheter of fig1 with a vascular stent 16 mounted thereon . the stent 16 can be made in many ways . one method of making the stent is to cut a thin - walled tubular member , such as stainless steel tubing to remove portions of the tubing in the desired pattern for the stent , leaving relatively untouched the portions of the metallic tubing which are to form the stent . the stent also can be made from other metal alloys such as tantalum , nickel - titanium , cobalt - chromium , titanium , shape memory and superelastic alloys , and the nobel metals such as gold or platinum . it is preferred to cut the tubing in the desired pattern by means of a machine - controlled laser as is well known in the art . stents function to hold open a segment of a blood vessel or other body lumen such as a renal or coronary artery . at present , there are numerous commercial stents being marketed throughout the world . while some of these stents are flexible and have the appropriate radial rigidity needed to hold open a vessel or artery , there typically is a tradeoff between flexibility and radial strength and the ability to tightly compress or crimp the stent onto a catheter so that it does not move relative to the catheter or dislodge prematurely prior to controlled implantation in a vessel . currently , to secure a stent 16 on a balloon 14 , after the stent is crimped onto the deflated balloon such that the balloon partially protrudes through the stent struts . during this process , the balloon and stent are placed in a heated mold and pressurized . the balloon protrusions then acts as holds to secure the stent in place . in a typical procedure to implant stent 16 , the guide wire 23 is advanced through the patient &# 39 ; s vascular system by well known methods so that the distal end of the guide wire is advanced past the location for the placement of the stent in the body lumen 18 . prior to implanting the stent 16 , the cardiologist may wish to perform an angioplasty procedure or other procedure ( i . e ., atherectomy ) in order to open the vessel and remodel the diseased area . thereafter , the stent delivery catheter assembly 10 is advanced over the guide wire 23 so that the stent 16 is positioned in the target area . the balloon 14 is inflated so that it expands radially outwardly and in turn expands the stent 16 radially outwardly until the stent 16 bears against the vessel wall of the body lumen 18 . the balloon 14 is then deflated and the catheter withdrawn from the patient &# 39 ; s vascular system , leaving the stent 16 in place to dilate the body lumen . the guide wire 23 typically is left in the lumen for post - dilatation procedures , if any , and subsequently is withdrawn from the patient &# 39 ; s vascular system . as depicted in fig4 , the balloon 14 is fully inflated with the stent 16 expanded and pressed against the vessel wall , and thereafter the implanted stent 16 remains in the vessel after the balloon has been deflated and the catheter assembly and guide wire have been withdrawn from the patient . fig4 further illustrates a close up section of the balloon 14 showing the inner member 20 extending through the balloon &# 39 ; s working portion 63 to the shoulder 50 , taper portion 52 , and out the balloon &# 39 ; s distal end 54 . the soft tip 56 is located to the distal end of the inner member 20 . as can be seen , a support sleeve 58 is placed over the inner member 20 beginning at the axial location of the shoulder 50 and extending to the end of the taper portion of the balloon . the support sleeve 58 is preferably bonded to the inner member 20 and provides added stiffness to the balloon 14 through the taper portion 52 . the support sleeve 58 can extend into the working portion 63 of the balloon 14 and beyond the taper portion in the distal direction . however , an advantage of the support sleeve 58 terminating at the shoulder 50 of the balloon 14 is that a radio opaque marker band 60 can be located in abutment with the support sleeve 58 and the marker band 60 will have a distal end 62 that coincides with the precise location of the shoulder 50 . this allows the marker band 60 to indicate to a physician the precise location of the balloon &# 39 ; s taper portion 52 and promote more accurate placement of the balloon &# 39 ; s stent 16 . a similar support sleeve 59 can be applied to the proximal taper portion to locate a second opaque marker band 61 such that the two markers define the working portion 63 of the balloon . in another embodiment , the marker band 60 can be placed over the support sleeve 58 in the taper portion 52 of the balloon 14 to identify the taper portion 52 . a physician can then ensure that the stent is proximal to the radio opaque marker band 60 that lies in the taper section of the balloon . the support sleeve can be made of one or more materials so as to establish either a constant or an increasing force / stiffness profile as the transition between the soft tip 56 and the stent / working body portion 63 of the balloon 14 . for example , multiple rings 65 a , 65 b of materials increasing in stiffness can be joined together to create a multiphase transition across the sleeve 58 . alternatively , a support 59 made of a single material of varying thickness can be used to create a desired force profile . that is , the sleeve can be made thinner at the distal portion adjacent the soft tip to provide a more flexible area , while increasing in thickness in the proximal direction to ramp up to the more stiff stent / working portion 63 portion of the balloon 14 . various materials can be used to form the support sleeve , such as materials used to make the marker band ( tungsten , platinum / iridium ) and one or more polymers ( pebax , nylon , etc .). the marker band 60 and support sleeve 58 can be laser bonded to each other and to the inner member 20 , or heat bonding , swaging , adhesive , or other bonding methods can be used . while particular forms of the invention have been illustrated and described , it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention . accordingly , it is not intended that the invention be limited except by the appended claims .
a catheter balloon having improved steerability is disclosed having a transition between a soft distal tip and a relatively stiffer working portion of a balloon carrying a stent , in the form of a support sleeve on the inner member . the support sleeve provides stiffness to the taper portion of the balloon and also allows precise location of a radio opaque marker . the support sleeve can have a varying thickness or be made of a combination of materials to yield an increasing or decreasing stiffness along the support sleeve to provide an even smoother transition along the balloon &# 39 ; s length .