in the following description , numerous specific details are set forth in order to provide a thorough understanding of the various principles of the present invention . it will be apparent to one skilled in the art , however , that not all these details are necessarily always needed for practicing the present invention . in this instance , well - known circuits , control logic , and the details of computer program instructions for conventional algorithms and processes have not been shown in detail in order not to obscure the general concepts unnecessarily . turning now to the drawings , reference is initially made to fig1 , which is a schematic , pictorial illustration of a vascular catheterization system 10 in accordance with an embodiment of the present invention . use of the system 10 involves inserting a catheter 12 into the body of a subject 14 at an insertion point 30 , for example a femoral artery or vein ; thence into an internal body cavity , such as a heart chamber . typically , the catheter 12 is used for diagnostic or therapeutic treatment performed by a medical practitioner 16 , such as mapping electrical potentials in the heart or performing ablation of heart tissue . the catheter 12 may alternatively be used for other purposes , by itself or in conjunction with other treatment devices . supporting elements related to the medical procedure are found in a control unit 26 , which contains processors for data reported by signals from sensors in the catheter 12 , e . g ., via a cable 32 . the control unit 26 may include an ablator power generator , irrigation pump and electrocardiographic circuitry . events and data reported to the control unit 26 may be displayed on a monitor 34 . however , as explained below , the control unit 26 need not include position - locating circuitry to track the location and orientation of the catheter 12 in the heart and elsewhere in the body of the subject 14 . the catheter 12 typically contains hydraulic lines to transfer fluid from the irrigation pump via the catheter &# 39 ; s handle to the distal portion of the catheter 12 as explained below . the hydraulic connection to the pump is not shown in fig1 in order to preserve clarity of illustration . reference is now made to fig2 , which is a longitudinal schematic view of the distal portion of a catheter 36 , which is useful for mapping regions in and around the heart and for tissue ablation in accordance with an embodiment of the invention . the catheter 36 comprises an elongated tubular shaft 38 . an inflatable balloon assembly 40 is provided at the distal end of the catheter body . the inflatable balloon assembly 40 comprises a containment chamber , which is internally partitioned into sectors 42 , 44 , 46 , 48 by a plurality of septa . the septa extend to an outer surface 50 from an axial core 52 and are oriented longitudinally about the axial core 52 . the sectors 42 , 44 , 46 , 48 are externally delimited by respective bounding portions of the outer surface 50 . although four sectors are shown in fig2 , the inflatable balloon assembly 40 may comprise any number of sectors greater than four . surface features and functionality of the inflatable balloon assembly 40 are described below . the sectors 42 , 44 , 46 , 48 of the inflatable balloon assembly 40 must be flexible enough to maintain mechanical contact between the outer surface 50 and the wall of the heart chamber so that when inflated , they stably press the outer surface of the pairs of the inflated sectors against the wall of the heart chamber , but are not so rigid as to interfere with the movements of heart wall . the inflation pressure may be determined empirically by the operator , or may be determined using the teachings of u . s . patent application ser . no . 13 / 343 , 024 , entitled “ contact assessment based on phase measurement ”, govari et al ., now published as u . s . patent publication no . 2013 / 0172875 , which is herein incorporated by reference . the deflated sectors occupy little space and blood readily flows around them through the heart chamber , and thus blood flow through the heart is not substantially obstructed . a tip electrode 54 can optionally be used for local measurements and ablation when the inflatable balloon assembly 40 is deflated . reference is now made to fig3 , which is a schematic cross - sectional view of the catheter 36 through line 3 - 3 of fig2 , in accordance with an embodiment of the invention . on this view , it can be appreciated that the inflatable balloon assembly 40 comprises a tubular structure comprising a pre - formed generally circular main region generally transverse and distal to the catheter body and having a circumferential outer surface 50 . septa 56 , 58 , 60 , 62 extending radially from the core 52 to the outer surface 50 and define the sectors 42 , 44 , 46 , 48 . each of the sectors 42 , 44 , 46 , 48 is independently connected to a fluid source 64 , and is selectively inflatable using control valves 66 , which deliver an irrigation fluid , typically saline , to the sectors 42 , 44 , 46 , 48 via respective fluid lines 68 . for example , sectors 44 , 48 , which oppose one another diametrically , are inflated concurrently , while the other sectors 42 , 46 remain deflated . fluid may be supplied to the sectors 44 , 48 by simultaneously opening their respective control valves 66 . in any case , both of the sectors 44 , 48 become inflated in an operating position for taking measurements . the control unit 26 ( fig1 ) may comprise a processor to regulate the control valves 66 . alternatively , the control valves 66 may be controlled manually by the practitioner 16 or an assistant . the portion of the outer surface 50 overlying respective sectors 42 , 44 , 46 , 48 has a flexible array of electrodes 70 mounted thereon , which can be used for mapping and ablation . the electrodes 70 and associated connectors are required to deform as the sectors 42 , 44 , 46 , 48 expand and contract . construction of flexible , stretchable electronic elements is known , for example from the documents controlled buckling of semiconductor nanoribbons for stretchable electronics , yugang sun et al ., nature nanotechnology 1 , 201 - 207 ( 2006 ) and u . s . patent application publication no . 2011 / 0254171 . devices constructed in such manner are capable of conforming to curved surfaces and withstanding mechanical deformations . optionally , perforations 72 may be formed through the outer surface 50 near the electrodes 70 . in such case , the fluid selectively delivered to the sectors 42 , 44 , 46 , 48 from the fluid source 64 egresses the inflatable balloon assembly 40 via the perforations 72 and cools the electrodes 70 and the ablation site during ablation . reference is now made to fig4 , which is a flow chart of a method of cardiac catheterization using a segmented balloon catheter , in accordance with an embodiment of the invention . not all illustrated process steps may be required to implement the process . at initial step 74 the catheter 36 ( fig2 ) is inserted into the heart in a known manner , and positioned within a chamber of interest . at this point the sectors 42 , 44 , 46 , 48 are all deflated . next , at step 76 , a diametrically opposing pair of sectors is selected , for example the sectors 44 , 48 ( fig3 ). next , at step 78 , the pair of sectors selected in step 76 are inflated . all non - selected sectors remain deflated . next , at step 80 , electrical contact between the wall of the cardiac chamber and those electrodes 70 that are mounted on the selected sectors is verified . next , at step 82 a measurement or procedure is performed using the electrodes 70 of the two opposing inflated sectors , for example bipolar measurements of electrical potentials during the cardiac cycle . next , at decision step 84 , it is determined if more pairs of sectors of the inflatable balloon assembly 40 remain to be processed . if the determination at decision step 84 is affirmative , then control proceeds to step 86 . the current pair of inflated sectors is deflated . control returns to step 76 to iterate the procedure with another pair of sectors . if the determination at decision step 84 is negative then at step 88 the current pair of inflated sectors is deflated . this could occur if all pairs have been inflated , or if it was decided to evaluate the signals obtained from fewer than all pairs of sectors . indeed , it may be appropriate to evaluate the signals obtained from one pair of sectors before inflating the next pair . at step 90 , signals thus far collected from the endocardial surfaces via the electrodes of the pairs of inflated sectors are evaluated , either by the physician or automatically . after evaluating the ecg signals , as indicated by a broken line , selected pairs of sectors may optionally be reflated , and control would then return to step 76 . alternatively , the physician typically makes a decision regarding ablation at final step 92 . it will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove . rather , the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove , as well as variations and modifications thereof that are not in the prior art , which would occur to persons skilled in the art upon reading the foregoing description .
a catheter has an inflatable assembly at its distal portion , including a containment chamber , an axial core and a plurality of longitudinally oriented partitions extending from the axial core to the wall of the chamber to divide the containment chamber into at least four inflatable sectors . hydraulic valves are connected to respective sectors to enable selective inflation of the sectors by a fluid when the valves are connected to a source of the fluid , and at least one surface electrode is mounted on each of the sectors . when introduced into a heart chamber and diametrically opposed sectors are inflated the assembly is stably fixed against the walls of the heart chamber and readings can be obtained from the surface electrodes of the inflated sectors .