in this description the expression “ approximately ” or “ generally ” is intended to mean at or near but not always exactly such that an exact dimension or location is not considered critical in those contexts where those expressions appear . in this description focus will be directed to a guide catheter for angioplasty , with bifurcation stenting , at a renal artery junction with an aorta . this renal artery bifurcation focus , however , is intended to be one of illustration and example and is not intended as a limitation . the subject invention is appropriate and advantageous for most human vascular system bifurcation locations and junctions where a guide catheter finds application . turning initially now to fig1 and 2 there is shown a front 10 and back 12 view of a human figure with outline views of generalized and basic components of a circulatory system with front and back views of a heart 14 , an ascending aorta 16 connected to a left ventricle of the heart , an aorta arch 18 and a descending abdominal aorta 20 with renal branch arteries 22 and 24 extending to left and right kidneys 26 and 28 respectively . as indicated above , the human body has a number of arteries stemming from the aorta but for purposes of this description only the renal arteries going to a patient &# 39 ; s kidneys are depicted as being representative . in addition to lateral left and right renal arteries extending from a patient &# 39 ; s aorta to a patient &# 39 ; s kidneys fig1 and 2 generally depict left and right carotid arteries 30 and 32 as well as left and right femoral arteries 34 and 36 which bifurcate to superficial femoral and profunda arteries which are illustrative of arteries in a human vascular system . finally , the figures depict left 38 and right 40 brachial arteries in the figure &# 39 ; s arms . a conventional percutaneous entry site for angioplasty , with stenting , is in a patient &# 39 ; s common femoral artery at approximately location 42 shown in fig1 or in a brachial arm artery at approximately site 44 also depicted in fig1 . although a renal artery branch is specifically illustrated in the drawings the subject guide catheter with a distal marker balloon segment or balloon segments in addition to use in stenting renal arteries has particular application in other regions of a human circulatory system such as for example stenting an osteal or very proximal stenosis region in a left main coronary artery , a right coronary artery , arteries originating from the aortic arch , iliac arteries at a bifurcation of the abdominal aorta and superficial femoral arteries at a bifurcation of the common femoral arteries . referring now to fig3 an aorta 20 is shown in broken away section at a junction location 46 with a renal artery 24 , as an example of one specific application of the subject guide and marker catheter . a guide wire 48 is shown extending through the aorta 20 and a plaque stenosis 50 . a wire mesh stent 52 surrounds a cylindrical high pressure stent balloon 54 . high pressure as used in this disclosure means approximately nine to eighteen atmospheres of pressure . the stent lattice , scaffolding 52 and high pressure stent expansion balloon 54 extends through a guide catheter 56 . the stent balloon is generally cylindrical and , is carried along the guide wire 48 to be operably directed by a physician toward the plaque stenotic segment 50 to be treated . the guide catheter 56 is fitted at a distal end with an arcuate , low pressure , marker balloon segment ( s ) 58 . this marker balloon segment ( s ) 58 is connected to an inflation tube that extends within the guide catheter 56 to a surgeon &# 39 ; s access station . the marker balloon segment ( s ) 58 can be operably connected to a syringe containing radiopaque marker fluid for injection into the marker balloon segment ( s ) 58 with a relatively low operating pressure . as used in this description the term low operating pressure means one or two atmospheres of pressure which is low relative to the stent balloon pressure of nine to eighteen atmospheres or more . in fig4 a a wire mesh stent 52 and interior , high pressure , expansion balloon 54 are shown advanced along the guide wire 48 and through the guide catheter 56 to a posture of partial insertion into a lesion zone of a plaque stenosis at a bifurcation junction of the renal artery 24 with the aorta 20 . fig4 b is an exploded bubble view of this initial insertion of the balloon stent 52 . in this view , an arcuate marker balloon segment 58 is at least partially inflated with a low pressure radiopaque marker fluid at the distal end of the guide catheter 56 . this inflation is performed as the guide catheter nears the renal artery bifurcation junction with the aorta 20 . fig5 a shows a guide catheter 56 and low pressure marker balloon 58 injected with radiopaque media and positioned adjacent an aorta renal artery bifurcation with a balloon stent 52 extended into a patient stenosis 50 at the bifurcation junction . bubble expansion image fig5 b illustrates a low pressure marker balloon segment 58 on a distal end of the guide catheter 56 at the renal bifurcation junction and a separate radiopaque band 60 ( note fig9 a and 9b ), or a separate low pressure stent marker balloon segment at a proximal end of the high pressure stent balloon 54 . when the two radiopaque markers 58 and 60 abut into a single radiopaque image the physician is visually alerted to a correct position of a proximal end of the stent at the aorta - renal artery bifurcation location and thus the stent 52 is in an accurate junction location for high pressure expansion of the stent balloon 54 to open the metal stent scaffolding and push the aorta — renal artery junction stenosis 50 outwardly . viewed in the direction of arrow “ a ” in fig5 b , fig6 depicts one preferred embodiment of a single low pressure , arcuate , marker balloon 64 that preferably extends approximately three hundred and forty degrees around a distal end of guide catheter 56 . the low pressure , marker balloon segment 64 has a small , low pressure line 66 that extends along or within the guide catheter 56 and is used to inflate the marker balloon segment 64 . at a location exterior to a patient &# 39 ; s vascular system a physician is able to inject low pressure ( one or two atmospheres ) radiopaque media into marker balloon 64 by injection from a hand syringe ( not shown ). the marker balloon segment 64 preferably occupies an arcuate expanse of approximately three hundred and forty degrees so that there is a minimal gap of at least approximately twenty degrees past the marker balloon for passage of blood through the renal artery during a stenting procedure . although three hundred and forty degrees is preferred for the arcuate extent of the marker balloon segment 64 a degree of operative advantage can be realized by the subject invention where the arcuate extent of the single marker balloon segment 64 shown in fig6 is as little as forty five degrees . fig7 is a view similar to fig6 but discloses an alternate preferred embodiment of the invention disclosing a low pressure marker balloon system including placement of two arcuate low pressure marker balloon segments 68 and 70 positioned in an opposing posture at a distal end of the guide catheter 56 . this balanced arrangement of arcuate marker balloon segments , which can be independently inflated with marker fluid , enhances an ability to establish approximately coaxial placement of the opening of a guide catheter with a branch artery . in this embodiment each of the two balloon segments subtends an angle of at least one hundred degrees but less than one hundred and forty degrees and preferably one hundred and twenty degrees . the substantial open region , of approximately eighty to one hundred and sixty degrees , provides relatively unobstructed blood flow during a stenting procedure . each of the marker balloon arcuate segments is fitted with an independent thin tube 72 and 74 extending through the guide catheter for use in separately filling the low pressure marker balloons 68 and 70 respectively with a radiopaque fluid by using a syringe . the capacity to separately inflate each marker balloon enables a physician to selectively orient the end of the guide catheter 56 with respect to a branch artery as necessary or desirable to facilitate a normal or near normal positioning of the end of a guide catheter 56 with respect to placement at a desired branch artery . fig8 discloses yet another preferred embodiment of the invention including three approximately uniform arcuate marker balloons composed of low pressure balloon segments 76 , 78 and 80 and independent fill lines 82 , 84 and 86 . this enables transmission of a low pressure radiopaque marker media via a syringe to the marker balloon segments at the distal end of the guide catheter 56 . the marker balloon segments each extend peripherally around a distal end of the guide catheter at least approximately twenty degrees but less than one hundred degrees and preferably sixty degrees in arcuate extent around a distal end of the guide catheter 56 . in this embodiment it is preferred that there is symmetric positioning of the marker balloon segments . this preferred marker balloon spacing concomitantly provides at least approximately sixty degrees of open space for blood flow during a stenting procedure and with three independent pressure zone capacity there is enhanced positioning capability of a distal end of a guide catheter 56 with respect to a branch artery by appropriate selection of pressure within each marker balloon segment . fig9 a - 9c disclose a stenting procedure sequence in accordance with a preferred embodiment of the invention . in this , fig9 a depicts a guide wire 48 inserted through a stenosis 50 at a problem bifurcation junction of a renal artery 22 or 24 ( note again fig1 and 2 ) with an aorta sidewall 20 . in fig9 a the guide catheter 56 is shown advanced along the guide wire 48 until a low pressure , marker balloon 58 at a distal end of the guide catheter 56 abuts the aorta side wall 20 at the renal artery branch 22 . a syringe is used to inflate the low pressure marker balloon segment or segments 58 with a radiopaque marker media and the guide catheter 56 is positioned against the side wall of the aorta 20 at the renal artery bifurcation site . a balloon stent is slid over the guide wire 48 generally coaxially within the interior of the guide catheter 56 until a radiopaque stent marker 60 is positioned into the region of a bifurcation stenosis 50 as illustrated in fig9 a . in fig9 b a physician is operably drawing the balloon stent 52 back along the guide wire 48 until a stent proximal marker 60 , or low pressure balloon arcuate segment or segments , such as depicted in fig6 - 8 , comes into register with a distal end of the guide catheter and the low pressure marker balloon segment or segments 58 at the distal end of the guide catheter 56 . in this , the radiopaque image will become essentially one as the proximal end of the stent marker 60 slides into registry with the inflated marker balloon region 58 at a distal end of the guide catheter . when the radiopaque marker 60 or low pressure marker balloon segment or segments at a proximal end of the balloon stent overlaps with the cover of the guide catheter marker balloon segment or segments 58 a physician accurately knows that a proximal end of the stent 52 is in a proper posture at a bifurcation location of , for example , the aorta — renal artery junction . at this point the interior stent balloon 54 is inflated with approximately nine to eighteen atmospheres of pressure to expand the wire stent scaffolding 52 as shown in fig9 c . once expanded the plaque stenosis 50 is pushed outwardly allowing the damaged site to be enlarged internally to restore a flow of blood through the stenotic site . the arcuate marker balloon segment gap ( s ) around the distal end of the guide catheter 56 enables blood perfusion to the diseased branch during accurate positioning of the stent at a bifurcation which may take minutes . the marker balloon segment gap ( s ) will also allow continuous measuring of blood pressure in the aorta by the guide catheter , when the marker balloon segment or segments are inflated . when injecting radiopaque media through the guide catheter 56 radiopaque contrast media passes between the marker balloon segment ( s ) and into the side branch lumen thus providing a view of the downstream side vessel geometry and confirming a desired position of the marker balloon and stent relative to the main vessel and the side branch lumen . in general the low pressure marker balloon ( s ) will cover varying degrees of the blood vessel opening , and the degree of coverage and marker balloon pressure may vary to allow matching the branching angle , such as when positioning the stent at a bifurcation that is less than 90 degrees . this might occur at the bifurcation of the abdominal aorta into the iliac arteries and the bifurcation of the common femoral arteries . in these instances the interventional physician , may prefer a marker balloon extending less than one hundred and eight degrees , in a way that the marker balloon will fall on the shoulder of the bifurcation , rather in the lumen of the branching vessel . the low pressure marker balloon segment or segments outer cross sectional diameter is smaller the diameter of the main artery , to allow proper inflation , however , the cross sectional diameter is larger than a diameter of the side branch , in a way that prevents a prolapse into the side branch . in this connection , and as an example , the outside diameter of the marker balloon segment or segments should be between four and ten millimeters to butt against a junction location of an artery with the aorta side wall . the longitudinal extent of the catheter marker balloon segment or segments , when inflated , should reach but not unduly impinge upon the expanded stent . the advantages provided by a low pressure marker balloon segment or segments mounted on a distal end of a guide catheter facilitates , for example , accurate positioning of a stent downstream of the aorta side wall and into a patient &# 39 ; s branch vascular system . in this context the low pressure balloon market segment or segments permits both a flow of blood during a downstream stenting procedure and also a flow of radiopaque marker media to facilitate accurate placement of a stent at a downstream stenosis site . although the structure of a low pressure marker balloon segment ( or segments ) are depicted , for example , in fig6 - 8 , it will be appreciated by those skilled in the art that the physical size of the arcuate marker balloon segment , and arcuate marker balloon segments , in certain instances , may be selected to suit the anatomy of a patient of interest . in describing the invention , reference has been made to preferred embodiments . those skilled in the art however , and familiar with the disclosure of the subject invention , may recognize additions , deletions , substitutions , modifications and / or other changes which will fall within the scope of the invention as defined in the following claims .