Patent Publication Number: US-2023142561-A1

Title: System and Method for Determination of Connected Neurostimulation Leads

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of U.S. patent application Ser. No. 16/128,283, filed Sep. 11, 2018, which is a non-provisional of U.S. Provisional Patent Application Ser. No. 62/557,640, filed Sep. 12, 2017. These applications are incorporated herein by reference, and priority is claimed to them. 
    
    
     FIELD OF THE TECHNOLOGY 
     The present disclosure relates to the identification of the types of leads that are connected to an implantable medical device (IMD) based on different physical electrode arrangements of the different types of leads. 
     INTRODUCTION 
     Neurostimulation devices are devices that generate and deliver electrical stimuli to nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows focuses on a Deep Brain Stimulation (DBS) system, such as is disclosed in U.S. Patent Application Publication No. 2013/0184794, but the disclosed techniques are applicable to other neurostimulation devices as well. 
     As shown in  FIG.  1   , a DBS system typically includes an implantable pulse generator (IPG)  10  (more generally an implantable medical device), which includes a biocompatible device case  12  that is formed from a metallic material such as titanium. The case  12  typically comprises two components that are welded together, and it holds the circuitry and battery  14  ( FIG.  2   ) necessary for the IPG  10  to function. The battery  14  may be either rechargeable or primary (non-rechargeable) in nature. The IPG  10  is coupled to electrodes  16  via one or more electrode leads  18  (four of which are shown). The proximal ends of the leads  18  include lead connectors  20  that are coupled to the IPG  10  at connector blocks  22  fixed in a header  24 , which can comprise an epoxy for example. The lead connectors  20  are inserted into the connector blocks  22  through ports  8  in the header  24 . Together, a port  8  and its associated connector block  22  form a device connector with which a lead connector  20  is associated. Contacts in the connector blocks  22  make electrical contact with corresponding contacts on the lead connectors  20 , and communicate with the circuitry inside the case  12  via feedthrough pins  26  passing through a hermetic feedthrough  28  to allow such circuitry to provide stimulation to or monitor the various electrodes  16 . The feedthrough assembly  28 , which is typically a glass, ceramic, or metallic material, is affixed to the case  12  at its edges to form a hermetic seal. In the illustrated system, each connector block  22  includes eight contacts and thus supports eight electrodes  16 . Therefore, two four-electrode leads  18  include a single lead connector  20  that is inserted into a single connector block  22 , one eight-electrode lead  18  includes a single lead connector  20  that is inserted into a single connector block  22 , and one 16-electrode lead  18  includes two lead connectors  20  that are inserted into two connector blocks  22 . Also shown in  FIG.  1    is a lead adapter  19 , which includes a female adapter connector  21  that is configured to receive a lead connector  20 ′ that is not compatible with the IPG  10 &#39;s connector block  22  and wire the lead  18 &#39;s contacts to the compliant adapter connector  20 . This can be useful, for example, for utilizing legacy leads  18  with a newer IPG  10  or for using a different manufacturer&#39;s leads  18  (e.g., previously-implanted leads  18  provided by a different manufacturer than the manufacturer of the IPG  10 ) with the IPG  10 . While the illustrated system supports 32 electrodes  16  (i.e., eight electrodes for each of its four ports  8 ), the configuration of the connector blocks  22  and the number of supported electrodes  16  are application specific and can vary. 
     As shown in  FIG.  2   , IPG  10  contains a charging coil  30  for wireless charging of the IPG&#39;s battery  14  using an external charging device  50 , assuming that battery  14  is a rechargeable battery. If IPG  10  has a primary battery  14 , charging coil  30  in the IPG  10  and external charger  50  can be eliminated. IPG  10  also contains a telemetry coil antenna  32  for wirelessly communicating data with an external controller device  40 , which is explained further below. In other examples, antenna  32  can comprise a short-range RF antenna such as a slot, patch, or wire antenna. IPG  10  also contains control circuitry such as a microcontroller  34 , and one or more Application Specific Integrated Circuit (ASICs)  36 , which can be as described for example in U.S. Pat. No. 8,768,453. ASIC(s)  36  can include current generation circuitry for providing stimulation pulses at one or more of the electrodes  16  and may also include telemetry modulation and demodulation circuitry for enabling bidirectional wireless communications at antenna  32 , battery charging and protection circuitry coupleable to charging coil  30 , DC-blocking capacitors in each of the current paths proceeding to the electrodes  16 , etc. Components within the case  12  are integrated via a printed circuit board (PCB)  38 . 
       FIG.  2    further shows the external components referenced above, which may be used to communicate with the IPG  10 , in plan and cross section views. External controller  40  may be used to control and monitor the IPG  10  via a bidirectional wireless communication link  42  passing through a patient&#39;s tissue  5 . For example, the external controller  40  may be used to provide or adjust a stimulation program for the IPG  10  to execute that provides stimulation to the patient. The stimulation program may specify a number of stimulation parameters, such as which electrodes are selected for stimulation; whether such active electrodes are to act as anodes or cathodes; and the amplitude (e.g., current), frequency, and duration of stimulation at the active electrodes, assuming such stimulation comprises stimulation pulses as is typical. 
     Communication on link  42  can occur via magnetic inductive coupling between a coil antenna  44  in the external controller  40  and the IPG  10 &#39;s telemetry coil  32  as is well known. Typically, the magnetic field comprising link  42  is modulated via Frequency Shift Keying (FSK) or the like, to encode transmitted data. For example, data telemetry via FSK can occur around a center frequency of fc=125 kHz, with a 129 kHz signal representing transmission of a logic ‘1’ bit and 121 kHz representing a logic ‘0’ bit. However, transcutaneous communications on link  42  need not be by magnetic induction, and may comprise short-range RF telemetry (e.g., Bluetooth, WiFi, Zigbee, MICS, etc.) if antennas  44  and  32  and their associated communication circuitry are so configured. The external controller  40  is generally similar to a cell phone and includes a hand-held, portable housing. 
     External charger  50  provides power to recharge the IPG  10 &#39;s battery  14  should that battery be rechargeable. Such power transfer occurs by energizing a charging coil  54  in the external charger  50 , which produces a magnetic field comprising transcutaneous link  52 , which may occur with a different frequency (f2=80 kHz) than data communications on link  42 . This magnetic field  52  energizes the charging coil  30  in the IPG  10 , which is rectified, filtered, and used to recharge the battery  14 . Link  52 , like link  42 , can be bidirectional to allow the IPG  10  to report status information back to the external charger  50 , such as by using Load Shift Keying as is well-known. For example, once circuitry in the IPG  10  detects that the battery  14  is fully charged, it can cause charging coil  30  to signal that fact back to the external charger  50  so that charging can cease. Like the external controller  40 , external charger  50  generally comprises a hand-holdable and portable housing. 
     In a DBS application, as is useful in the treatment of neurological disorders such as Parkinson&#39;s disease, the IPG  10  is typically implanted under the patient&#39;s clavicle (collarbone), and the leads  18  are tunneled through the neck and between the skull and the scalp where the electrodes  16  are implanted through holes drilled in the skull in the left and right sides of the patient&#39;s brain, as shown in  FIG.  3   . Specifically, the electrodes  16  may be implanted in the subthalamic nucleus (STN), the pedunculopontine nucleus (PPN), or the globus pallidus internus (GPi). Stimulation therapy provided by the IPG  10  has shown promise in reducing the symptoms of neurological disorders, including rigidity, bradykinesia, tremor, gait and turning impairment, postural instability, freezing, arm swing, balance impairment, and dystonia. 
     After the leads  18  and IPG  10  are implanted, the IPG  10  is configured. The configuration process is typically performed using a clinician&#39;s programmer system (CP System)  200  such as that illustrated in  FIG.  4   . CP system  200  can comprise a computing device  202 , such as a desktop, laptop, or notebook computer, a tablet, a mobile smart phone, a Personal Data Assistant (PDA)-type mobile computing device, etc. (hereinafter “CP computer”). In  FIG.  4   , CP computer  202  is shown as a laptop computer that includes typical computer user interface means such as a screen  204 , a mouse, a keyboard, speakers, a stylus, a printer, etc., not all of which are shown for convenience. CP computer  202  executes CP software  96 , which software may be stored in the CP computer  202 &#39;s non-volatile memory  220 . One skilled in the art will recognize that execution of the CP software  96  in the CP computer  202  can be facilitated by control circuitry  222  such as a microprocessor, microcomputer, an FPGA, other digital logic structures, etc., which is capable of executing programs in a computing device. Execution of the CP software  96  causes the control circuitry  222  or other dedicated graphical processing circuitry to render a graphical user interface (GUI)  94 . 
     Also shown in  FIG.  4    is an accessory communication head  210  that is coupleable to a port of the CP computer  202 , such as a USB port  206 , to enable the CP computer  202  to communicate with the IPG  10  via a communication link  92  (e.g., to cause the IPG  10  to execute stimulation routines with different parameters in order to evaluate their effectiveness). Communication between the CP system  200  and the IPG  10  may comprise magnetic inductive or short-range RF telemetry schemes (as described above with respect to communications between the IPG  10  and the programmer  40 ), and in this regard the IPG  10  and the CP computer  202  and/or the communication head  210  (which can be placed proximate to the IPG  10 ) may include antennas compliant with the telemetry means chosen. For example, the communication head  210  can include a coil antenna  212   a , a short-range RF antenna  212   b , or both. The CP computer  202  may also communicate directly with the IPG  10 , for example using an integral short-range RF antenna  212   b , without the use of the communication head  210 . 
     If the CP system  200  includes a short-range RF antenna (either in CP computer  202  or communication head  210 ), such antenna can also be used to establish communication between the CP system  200  and other devices, and ultimately to larger communication networks such as the Internet. The CP system  200  can typically also communicate with such other networks via a wired link provided at an Ethernet or network port  208  on the CP computer  202 , or with other devices or networks using other wired connections (e.g., at USB ports  206 ). 
     An initial step in the IPG configuration process involves the specification of the type of electrode leads  18  that have been implanted (e.g., from a list of leads that are configured in the software  96 ) and the port  8  in which each lead connector  20  is positioned. While  FIG.  1    generically illustrates electrodes  16  as aligned linearly along leads  18 , such leads  18  commonly include different electrode arrangements. A particular IPG  10  may be compatible with a number of different types of leads  18 , which can include, perhaps, leads  18  produced by a different manufacturer than the manufacturer of the IPG  10  through the use of adapters. 
       FIGS.  5 A- 5 D  illustrate examples of electrode leads  18  with different physical electrode arrangements. Lead  18 A&#39;s eight electrodes  16  are all circumferential electrodes that are arranged linearly along the lead  18 A. Lead  18 B&#39;s eight electrodes  16  include circumferential electrodes at the proximal and distal ends (electrodes E 1  and E 8 ) of the electrode array and six segmented electrodes (electrodes E 2 -E 7 ) between the circumferential electrodes. As used herein, segmented electrodes (or split-ring electrodes) are electrodes that extend around a portion of a lead  18 B. Often multiple segmented electrodes are positioned at the same axial position along a lead  18 . Lead  18 B&#39;s segmented electrodes (electrodes E 2 -E 7 ) are arranged with three electrodes at each of two axial positions, each segmented electrode spanning an approximately 110 degree arc around the lead  18 B with approximately 10 degree spaces between neighboring segmented electrodes. Lead  18 C&#39;s eight electrodes include three circumferential electrodes at its distal end (E 1 -E 3 ), two circumferential electrodes at its proximal end (E 7  and E 8 ), and three segmented electrodes (E 4 -E 6 ) between the two groups of circumferential electrodes. The space between the segmented electrodes E 4 -E 6  and the circumferential electrode E 7  is larger than the spacing between other adjacent electrode axial positions. Lead  18 D is a paddle lead that includes eight surface electrodes that are arranged in a two-by-four array. 
     Although particular example leads  18  are illustrated in  FIGS.  5 A- 5 D , the type and placement of electrodes  16  along a lead is application-specific and therefore can vary. For example, a lead may include more or fewer segmented electrodes at a given axial position and more or fewer circumferential electrodes in addition to the segmented electrodes. As will be understood, because the segmented electrodes are separated by a non-conductive break, electrical stimulation that is directed to a segmented electrode propagates outward in the direction of the electrode rather than uniformly about the lead  18  as with circumferential electrodes. While the electrode leads  18  illustrated in  FIGS.  5 A- 5 D  are referenced below to illustrate different patterns in the measurements acquired from their electrodes based on their different physical electrode arrangements, it will be understood that these examples are merely illustrative and that the techniques described below can be utilized to identify leads having different physical electrode arrangements from those depicted in  FIGS.  5 A- 5 D . Moreover, the example data sets below are ordered according to electrode number. For example, the first data point corresponds to electrode E 1 , the second data point corresponds to electrode E 2 , and so on. 
     In order to associate the implanted electrodes  16  with the current generation circuitry to which the electrodes  16  are connected, the CP GUI  94  may present a depiction such as that shown in  FIG.  6   , which shows the header  24  of the implanted IPG  10  with the ports  8  labeled as they are labeled on the actual IPG  10 . Through the CP GUI  94 , a user may then select the implanted leads  18  from a list of leads  18  that are configured in the CP software  96  and associate the lead connectors  20  with the port  8  in which they are positioned. In the illustrated example, the user has indicated that two leads  18 A were implanted with their lead connectors  20 A connected to ports “A” and “B” and that two leads  18 B were implanted with their lead connectors  20 B connected to ports “C” and “D”. Given the known connection between the electrode nodes in the current generation circuitry (i.e., the node to which current designated for a particular contact in a particular connector block  22  is provided) and the contacts in the connector blocks  22  and the known connection between the contacts in the lead connectors  20  and electrodes  16  for the selected electrode leads  18 , this designation establishes the connection between each electrode  16  and its corresponding electrode node in the current generation circuitry. With this association established, the connectivity between the current generation circuitry and the electrodes  16  is abstracted from the user and the stimulation therapy can be customized (e.g., via the CP software  96 ) by specifying the parameters of stimulation for the various electrodes  16  on the selected electrode leads  18 . Such parameters can include pulse width, stimulation amplitude, frequency, and the electrode(s)  16  that serve as anodes and cathodes, for example. The IPG configuration process typically involves testing different stimulation parameters in order to identify the parameters that provide the most beneficial therapy for the patient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows an implantable pulse generator (IPG) with different electrode leads in accordance with the prior art. 
         FIG.  2    shows a cross section of the IPG of  FIG.  1    as implanted in a patient, as well as external devices that support the IPG, including an external charger and external controller in accordance with the prior art. 
         FIG.  3    shows implantation of the IPG in a patient in a Deep Brain Stimulation (DBS) application in accordance with the prior art. 
         FIG.  4    shows components of a clinician&#39;s programmer system, including components for communicating with a neurostimulator in accordance with the prior art. 
         FIGS.  5 A- 5 D  show electrode leads with different physical electrode arrangements in accordance with an aspect of this disclosure. 
         FIG.  6    shows an example graphical user interface that allows a user to assign lead connectors to the ports of the IPG in which they are inserted in accordance with an aspect of the disclosure. 
         FIG.  7    shows an example of an incorrect assignment of lead connectors to IPG ports in accordance with an aspect of the disclosure. 
         FIGS.  8 A- 8 C  show the configuration of an IPG&#39;s current generation circuitry in order to collect monopolar impedance data, bipolar impedance data, and induced field potential data to be used in determining which lead connectors are inserted into different ports of an IPG in accordance with an aspect of this disclosure. 
         FIG.  9    shows an example distribution of monopolar impedance data for different types of electrodes in accordance with an aspect of this disclosure. 
         FIG.  10    shows an example distribution of monopolar impedance data for the circumferential and segmented electrodes for the electrode leads shown in  FIGS.  5 A- 5 C , in accordance with an aspect of this disclosure. 
         FIGS.  11 A and  11 B  show example monopolar impedance data sets for the electrode leads shown in  FIGS.  5 A and  5 B , respectively, in accordance with an aspect of this disclosure. 
         FIG.  12    shows example normalized monopolar impedance data for the data sets shown in  FIG.  11 B  in accordance with an aspect of this disclosure. 
         FIG.  13    shows an example bipolar impedance data set for the lead shown in  FIG.  5 B  in accordance with an aspect of this disclosure. 
         FIG.  14    shows partial idealized bipolar impedance data sets for various ones of the leads shown in  FIGS.  5 A- 5 D  to illustrate differences in the bipolar impedance data in accordance with an aspect of this disclosure. 
         FIG.  15    shows idealized induced field potential data for the lead shown in  FIG.  5 B  in accordance with an aspect of this disclosure. 
         FIG.  16    shows partial idealized induced field potential data sets for various ones of the leads shown in  FIGS.  5 A- 5 D  to illustrate differences in the induced field potential data in accordance with an aspect of this disclosure. 
         FIG.  17    shows idealized induced field potential data sets for electrodes on different example leads in accordance with an aspect of this disclosure. 
         FIG.  18    shows a flowchart indicating the steps in a process to determine the types of lead connectors that are connected to the different ports of an IPG in accordance with an aspect of this disclosure. 
         FIG.  19    shows different types of operations that can be performed on data measured from the electrodes connected to an IPG&#39;s ports in order to determine the types of leads (and their associated lead connectors) that are connected to the different ports in accordance with an aspect of this disclosure. 
         FIG.  20    shows an example graphical user interface that displays the determined types of leads (and their associated lead connectors) that are connected to an IPG&#39;s ports in conjunction with a user&#39;s assignment of types of leads (and their associated lead connectors) to the ports in accordance with an aspect of this disclosure. 
         FIG.  21    illustrates a representative computing environment on which software that provides a process for determining the types of leads (and their associated lead connectors) that are connected to an IPG&#39;s ports may be executed in accordance with an aspect of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The inventors have observed that the user association of lead connectors  20  with corresponding ports  8  of the implanted IPG  10  is subject to user error. For example, as illustrated in  FIG.  7   , the user&#39;s association established in the CP software  96  may not match the actual connections. In the example in  FIG.  7   , in the software configuration, the user has flipped the assignment of one of the leads  18 A with one of the leads  18 B. That is, one of the leads  18 B is actually connected to port “B” of the IPG  10  and one of the leads  18 A is actually connected to port “C” of the IPG  10 . This type of error can have significant consequences. First, incorrect assignment in the CP software  96  can make it very difficult to configure the stimulation therapy. This is because stimulation that is being specified for a particular electrode is actually being delivered to a different electrode, and, therefore, a different anatomical location than what is intended. In addition, the software  96  relies upon the user assignments to configure other parameters in the IPG  10 . For example, a segmented electrode may have a lower safe current limit than a circumferential electrode and therefore an incorrect assignment could enable a segmented electrode that is understood to be a circumferential electrode based on the incorrect assignment to be stimulated at a current that is higher than the specified safe current limit. Furthermore, the IPG  10  may be configured with various parameters that specify operation in a magnetic resonance imaging (MRI) environment. These MRI parameters often rely on the electrode type and can therefore be inaccurate based on an incorrect assignment. 
     The present disclosure describes a system and technique to identify the types of leads  18  (or groups of electrodes) that are connected to an IPG  10 &#39;s ports  8  to either verify a user&#39;s software port assignment or to eliminate the need for such user software assignments altogether. The disclosed system and technique rely upon the measurement and evaluation of impedance and induced field potential data from the connected electrodes.  FIGS.  8 A- 8 C  show how the different impedance and induced field potential measurements used in the evaluation are collected. 
     The IPG  10 &#39;s current generation circuitry includes one or more Digital-to-Analog Converters (DACs)  72  for receiving stimulation parameters and for forming the prescribed pulses at the selected electrodes.  FIG.  8 A  shows a simple example of DAC circuitry  72  as used to provide a current pulse between selected electrode E 1  and the IPG  10 &#39;s case  12  (EC), which can be configured to act as an electrode, through a patient&#39;s tissue, R. DAC circuitry  72  as shown comprises two portions, denoted as PDAC  72   p  and NDAC  72   n . These portions of DAC circuitry  72  are so named due to the polarity of the transistors used to build them and the polarity of the current they provide. Thus, PDAC  72   p  is formed from P-channel transistors and is used to source a current +I to the patient&#39;s tissue R via a selected electrode E 1  operating as an anode. NDAC  72   n  is formed of N-channel transistors and is used to sink current −I from the patient&#39;s tissue via a selected electrode EC (i.e., the IPG  10 &#39;s case  12 ) operating as a cathode. It is important that current sourced to the tissue at any given time equal that sunk from the tissue to prevent charge from building in the tissue, although more than one anode electrode and more than one cathode electrode may be operable at a given time. 
     PDAC  72   p  and NDAC  72   n  receive digital control signals, denoted &lt;Pstim&gt; and &lt;Nstim&gt; respectively, to generate the prescribed pulses with the prescribed timing. In the example shown, PDAC  72   p  and NDAC  72   n  comprise current sources, and in particular include current-mirrored transistors for mirroring (amplifying) a reference current Iref to produce pulses with an amplitude (A). PDAC  72   p  and NDAC  72   n  could however also comprise constant voltage sources. Control signals &lt;Pstim&gt; and &lt;Nstim&gt; also prescribe the timing of the pulses, including their duration (D) and frequency (f). The PDAC  72   p  and NDAC  72   n  along with the intervening tissue R complete a circuit between a power supply +V and ground. The compliance voltage +V is adjustable to an optimal level to ensure that current pulses of a prescribed amplitude can be produced without unnecessarily wasting IPG power. 
     The DAC circuitry  72  (PDAC  72   p  and NDAC  72   n ) may be dedicated at each of the electrodes, and thus may be activated only when its associated electrode is to be selected as an anode or cathode. See, e.g., U.S. Pat. No. 6,181,969. Alternatively, one or more DACs (or one or more current sources within a DAC) may be distributed to a selected electrode by a switch matrix (not shown), in which case optional control signals &lt;Psel&gt; and &lt;Nsel&gt; would be used to control the switch matrix and establish the connection between the selected electrode and the PDAC  72   p  or NDAC  72   n . See, e.g., U.S. Pat. No. 8,606,362. DAC circuitry  72  may also use a combination of these dedicated and distributed approaches. See, e.g., U.S. Pat. No. 8,620,436. 
     The current I is routed from the PDAC ‘ 72   p  to electrode node E 1 ’ (a node in the IPG  10 &#39;s current generation circuitry that is coupled to electrode E 1  and is differentiated from electrode E 1  by the prime designator). From electrode node E 1 ′, the current I flows through a blocking capacitor C 1  to the electrode E 1  and through the patient&#39;s tissue R to the IPG  10 &#39;s case  12  (EC). The NDAC  72   n  pulls the current I from the case EC through the blocking capacitor CC and to the electrode node EC′. Measurement circuitry in the IPG  10  is configured to measure the voltage between selected nodes. In  FIG.  8 A , the measurement circuitry is configured such that the voltage V 1 ′ between electrode nodes E 1 ′ and EC is measured. U.S. Pat. No. 9,061,140, which is incorporated herein by reference in its entirety, describes measurement circuitry and a corresponding measurement technique that can be utilized to remove the voltage across the blocking capacitors (C 1  and CC) from the V 1 ′ measurement, thus providing the voltage V 1  between electrodes E 1  and EC. Using the measured voltage V 1  and the known current I, the impedance R 1  between electrodes E 1  and EC can be calculated as R 1 =V 1 /I. 
     This initial type of monopolar impedance data (i.e., impedance between an electrode and the IPG  10 &#39;s case  12 ) can be collected for each of the connected electrodes (using a common current amplitude for each), and it provides information about the types of electrodes that are connected to a particular port  8 , and thus the type of lead(s) or portion thereof connected to the port  8 . 
       FIG.  9    illustrates example distributions of monopolar impedance measurements for example electrodes of different types (A, B, and C). The different types of electrodes can include circumferential electrodes of different dimensions, segmented electrodes of different dimensions, and/or paddle electrodes of different dimensions. The purpose of  FIG.  9    is to illustrate that electrodes of different types have different monopolar impedance signatures that enable the different types of electrodes to be distinguished from each other. 
       FIG.  10    offers a more concrete example of this using actual data for the circumferential and segmented electrodes for the leads shown in  FIGS.  5 A- 5 C . As illustrated, the circumferential electrodes generally display lower monopolar impedances than the segmented electrodes. This is due to the fact that circumferential electrodes result in the flow of current through a larger volume of tissue than segmented electrodes. While there is some variance in the data that results in an overlap in measured impedances between the different electrode types, the electrodes arranged on a single lead  18  (and thus positioned in the same tissue) often exhibit a pattern as a result of the distinction in monopolar impedances of circumferential and segmented electrodes. Accordingly, this feature (i.e., the physical arrangement of circumferential and segmented electrodes) results in a pattern in the monopolar impedance data that enables different lead types to be distinguished from one another. 
       FIGS.  11 A and  11 B  illustrate three sample sets of measured monopolar impedance data along with an “ideal” data set for leads  18 A and  18 B, respectively. The different electrodes are plotted along the horizontal axis and their corresponding measured monopolar impedances are plotted along the vertical axis. As illustrated in  FIG.  11 A , because lead  18 A includes eight circumferential electrodes, the measured impedance for each of the electrodes is approximately constant. While there is variation between the different data sets (e.g., data sets A and C exhibit higher impedances than data set B), the impedance measurements within any particular data set are relatively constant (i.e., they do not include a particular measurement that is substantially higher than other measurements as would be indicative of a segmented electrode). In  FIG.  11 B , on the other hand, in each of the data sets, the impedance measurements for electrodes E 2 -E 7  are substantially higher (e.g., on the order of two times higher) than the impedance measurements for electrodes E 1  and E 8 . This pattern corresponds to lead  18 B&#39;s physical electrode arrangement (i.e., electrodes E 1  and E 8  are circumferential electrodes and electrodes E 2 -E 7  are segmented electrodes).  FIG.  12    shows the data sets in  FIG.  11 B  (corresponding to lead  18 B) as normalized. The normalized data sets are very well-aligned with the “ideal” data set. As can be seen from the example data sets in  FIGS.  11 A,  11 B and  12   , measured monopolar impedance values can be utilized to distinguish between different types of leads that are connected to an IPG. 
       FIG.  8 B  shows DAC circuitry  72  as configured to provide a current pulse between selected electrodes E 1  and E 2 , through the patient&#39;s tissue, R. This arrangement is substantially similar to the arrangement shown in  FIG.  8 A  except a lead-based electrode is selected to operate as the cathode rather than the IPG  10 &#39;s case  12 . The impedance measurement can be obtained in the same manner as described above by selecting the active anode and cathode electrode nodes in the measurement circuitry. In the specific example illustrated in  FIG.  8 B , the impedance R 1 , 2  is measured between electrodes E 1  and E 2 . Such bipolar impedance measurements can be collected for each pair of electrodes (using a common current amplitude for each). In one embodiment, the impedance between a pair of electrodes can be assumed to be equal regardless of the polarity of the electrodes (i.e., regardless of which electrode acts as the cathode and which acts as the anode), thus reducing the number of impedance measurements by one-half. Alternatively, the bipolar impedance measurements can be collected for both polarity arrangements for each electrode pair. 
       FIG.  13    illustrates a full set of bipolar impedance measurements for lead  18 B. In the graph in  FIG.  13   , each group of data points connected by a dashed line represents the impedance measurements collected in conjunction with a particular electrode. For example, the group of data points connected by the dashed line labeled E 1  represents impedance measurements between electrode E 1  and each of the other electrodes E 2 -E 7 . Each group includes seven data points that are representative of the impedance between the electrode associated with the data group and the other seven electrodes. In the data set shown, impedance measurements between a pair of electrodes are assumed to be equal regardless of electrode polarity. In order to better illustrate the relationships between the data points in each group, the groups have been separated vertically and therefore the vertical axis does not represent absolute impedance (only relative impedance within each particular group). The vertical lines separate electrodes at different axial positions along the lead  18 B. 
     In general, the measured impedance in each of the groups is lower at electrodes E 1  and E 8 . Just as with the monopolar impedance measurements described above, this provides an indication that electrodes E 1  and E 8  are circumferential electrodes while electrodes E 2 -E 7  are segmented electrodes. In addition, the bipolar impedance data provides information about the location and grouping of electrodes. For example, in each of the groups, the electrode E 2 -E 4  measurements are substantially similar and the electrode E 5 -E 7  measurements are substantially similar, but the electrode E 2 -E 4  measurements differ from the electrode E 5 -E 7  measurements. This is due to the fact that the E 2 -E 4  electrodes are identical segmented electrodes located at a first axial position on lead  18 B and the E 5 -E 7  electrodes are identical segmented electrodes located at a second axial position on the lead  18 B. Notice also that the relationship between the electrode E 2 -E 4  measurements and the electrode E 5 -E 7  measurements changes based on the data group. In the electrode E 1 -E 4  data groups, the electrode E 2 -E 4  measurements are generally lower than the electrode E 5 -E 7  measurements, but, in the electrode E 5 -E 8  groups, the electrode E 2 -E 4  measurements are generally higher than the electrode E 5 -E 7  measurements. This relationship is due to the positioning of the electrodes along the lead  18 B. The shorter distance through resistive tissue between any of electrodes E 1 -E 4  and the segmented electrodes E 2 -E 4  as compared to the distance between any of electrodes E 1 -E 4  and the segmented electrodes E 5 -E 7  results in lower impedance measurements. Similarly, the shorter distance through resistive tissue between any of electrodes E 5 -E 8  and the segmented electrodes E 5 -E 7  as compared to the distance between any of electrodes E 5 -E 8  and the segmented electrodes E 2 -E 4  results in lower impedance measurements. Thus, the bipolar impedance measurements provide additional information regarding the type of connected lead. 
       FIG.  14    shows an example of the usefulness of bipolar impedance data in differentiating between different types of leads  18 . In particular,  FIG.  14    illustrates idealized bipolar impedance measurements for common electrode groups for the other leads illustrated in  FIGS.  5 A- 5 D . Each of the electrode groups (i.e., the groups of data points connected by a dashed line) include bipolar impedance measurements between the electrode associated with the group and the other seven electrodes connected to the same lead connector. For each of the different leads, corresponding electrode groups for electrodes E 1  and E 5  are shown. 
     As illustrated, the bipolar impedance measurements for lead  18 A increase linearly at each electrode away from the electrode associated with the group. For example, the impedance measurements for the electrode E 1  group increase linearly from electrodes E 2 -E 8 . Similarly, the impedance measurements for the electrode E 5  group increase linearly from electrodes E 4 -E 1  and from electrodes E 6 -E 8 . This linear increase corresponds to the equal spacing of the circumferential electrodes along the lead  18 A. The lead  18 C, having different electrode spacing, exhibits different bipolar impedance data. The impedance measurements for the electrode E 1  group increase at electrodes E 2  and E 3 , which are circumferential electrodes at increasing distance from electrode E 1 , increase further and remain constant across electrodes E 4 -E 6 , which are segmented electrodes at a common axial location, and slightly decrease at electrode E 7  before again increasing at electrode E 8 , which electrodes E 7  and E 8  are circumferential electrodes at increasing distance from electrode E 1 . The electrode E 5  group exhibits the same impedance pattern related to electrode positioning. Note that in the E 5  group, the impedance measured at electrodes E 7  and E 8  are higher than the impedance measured at electrodes E 2  and E 3  due to the increased spacing between electrode E 5  and electrodes E 7  and E 8  as compared to the distance between electrode E 5  and electrodes E 2  and E 3 . 
     The bipolar impedance data for lead  18 D displays a unique pattern as a result of its arrangement of leads in a two-by-four array. The bipolar impedance between any pair of electrodes positioned on the paddle lead  18 F is a function of the distance between the electrodes. Because the electrodes are equally-spaced in rows of four with electrodes E 1  through E 4  in a first row and electrodes E 5  through E 8  in a second row, the bipolar impedance measurements are approximately linear across the electrodes in a particular row. 
     While the data depicted in  FIG.  14    is idealized and is only shown for two of the eight electrodes associated with each lead, the full set of bipolar impedance data for a set of eight electrodes includes clearly identifiable trends that enable the differentiation of different types of leads. This bipolar impedance data can enable differentiations between electrode leads that are difficult or impossible using monopolar impedance data alone. 
       FIG.  8 C  shows DAC circuitry  72  as configured to provide a current pulse between electrode E 1  and the IPG  10 &#39;s case  12  (EC) in the same manner as described above with respect to  FIG.  8 A . However, in  FIG.  8 C , the measurement circuitry is configured to measure the voltage at an electrode (electrode E 4  in the configuration illustrated in  FIG.  8 C ) other than those that are used for stimulation. During a stimulation pulse (between E 1  and EC in the configuration illustrated in  FIG.  8 C ), an electric field  150  is generated in the patient&#39;s tissue, R. The field  150  is strongest nearest to the stimulating electrode, and its strength decreases with increasing distance from the stimulating electrode. As a result, the measurement of a voltage between a non-stimulating electrode (e.g., E 4 ) and a reference voltage (e.g., a ground reference) provides an indication of the distance between the stimulating electrode and the electrode at which the measurement was taken. In  FIG.  8 C , the voltage at electrode E 4  couples through the capacitor C 4 , and the induced voltage measurement V 1 , 4  in d is measured between the electrode node E 4 ′ and a ground reference node. Induced voltage measurements can be obtained for each different pair of electrodes (i.e., between electrode E 1  and each of the other electrodes when stimulation is between electrode E 1  and the case  12 , between electrode E 2  and each of the other electrodes when stimulation is between electrode E 2  and the case  12 , and so on). While it is not strictly necessary, in a preferred embodiment, the IPG  10 &#39;s case  12  is selected as one of the stimulating electrodes and the selected amplitude of stimulation is held constant for the collection of all of the induced field potential measurements. Selection of the case  12  as one of the stimulating electrodes provides a cleaner induced field potential data set as its distance from the leads  18  avoids any interference that may otherwise be present were two lead-based electrodes used as stimulating electrodes. The induced field potential measurements can be obtained at any point during the stimulation pulse. 
     In one embodiment, the induced voltage measurements can be assumed to be the same for a pair of electrodes regardless of which electrode was used as the stimulating electrode and which was used as the measuring electrode. For example, the voltage induced at electrode E 2  when electrode E 1  operates as the stimulating electrode can be assumed to be the same as the voltage induced at electrode E 1  when electrode E 2  operates as the stimulating electrode. Alternatively, two separate measurements can be taken for each pair of electrodes with each electrode in the pair operating as the stimulating electrode in one measurement and the measuring electrode in the other measurement. 
       FIG.  15    illustrates a full set of idealized induced field potential measurements for lead  18 B. In the graph in  FIG.  15   , each group of data points connected by a dashed line represents the field potentials induced by stimulation of a single electrode. For example, the group of data points connected by the dashed line labeled E 1  represents the field potential that is induced at each of the other electrodes E 2 -E 7  when electrode E 1  operates as the stimulating electrode. Each group includes seven data points that are representative of the field potential that is induced at the other seven electrodes. In the data set shown, induced field potential is assumed to be equal regardless of which electrode is the stimulating electrode (e.g., the induced potential at electrode E 2  as a result of stimulation using electrode E 1  is assumed to be equal to the induced potential at electrode E 1  as a result of stimulation using electrode E 2 ), but, again, this is not strictly necessary. In order to better illustrate the relationships between the data points in each group, the groups have been separated vertically and therefore the vertical axis does not represent absolute potential (only relative potential within each particular group). 
     The induced field potential data is similar to the bipolar impedance data in that it provides information regarding the relative positioning of electrodes along the lead. It differs from bipolar impedance data, however, in that it is not affected by electrode type (e.g., circumferential or segmented). Thus, the induced field potential data provides a purer indication of relative electrode positioning. This is indicated in the data set that is plotted in  FIG.  15   . As illustrated in  FIG.  5 B , electrodes E 1  and E 8  are circumferential electrodes that are separated by two groups of segmented electrodes (E 2 -E 4  and E 5 -E 7 ) at different axial locations. The vertical lines in  FIG.  15    separate electrodes that are positioned at different axial locations along the lead  18 B. The induced field potential data provide clear indications about the grouping of electrodes on the lead  18 B as well as the electrodes&#39; position. As illustrated, within each data group, the induced field potential is similar for segmented electrodes at a common axial position but different from the induced field potential for segmented electrodes at a different axial position. Moreover, the magnitude of the induced field potential for the segmented electrodes at a common axial position differs as a function of the distance between the stimulating and measuring electrodes. For example, the induced field potential at electrodes E 2 -E 4  is higher than the induced field potential at electrodes E 5 -E 7  for data groups E 1 -E 4 , but the opposite is true for data groups E 5 -E 8 . This illustrates that, as would be expected, the induced field potential is greater when the measuring electrode is closer to the stimulating electrode. The induced field potential at each of the circumferential electrodes E 1  and E 8  is a function of the electrode&#39;s distance from the stimulating electrode. 
     In addition to providing information regarding the grouping of segmented electrodes, the induced field potential data also illustrates an azimuthal linking between segmented electrodes at a same azimuthal position about the lead  18 B. For example, in the electrode E 2  group, the induced field is higher at electrode ES than at electrodes E 6  and E 7 , which are positioned at the same axial location as electrode ES. The higher field that is induced is a result of the common azimuthal position of electrodes E 2  and ES and the corresponding reduced distance between those electrodes. This same relationship can be seen in each of the data groups between pairs of azimuthally aligned electrodes E 2  and ES, E 3  and E 6 , and E 4  and E 7 . As can be seen from  FIG.  15   , induced field potential data provides further information that can be used to differentiate between different types of leads  18 . 
       FIG.  16    illustrates idealized induced field potential measurements for common electrode groups for the other leads illustrated in  FIGS.  5 A- 5 D . Each of the electrode groups (i.e., the groups of data points connected by a dashed line) include induced field potential measurements between the electrode associated with the group and the other seven electrodes connected to the same lead. Moreover, for each of the different leads, corresponding electrode groups for electrodes E 1  and E 5  are shown. 
     As illustrated, the induced field potential data for lead  18 A decreases linearly with increasing distance from the stimulating electrode. This is again related to the even spacing between the circumferential electrodes along lead  18 A. The induced field potential data for lead  18 C shows the positioning of electrodes E 1 , E 2 , E 3 , E 4 -E 6 , E 7 , and E 8  at different axial locations along the lead  18 C. In addition, the induced field potential data for lead  18 C illustrates the large spacing between electrodes E 4 -E 6  and electrode E 7  as a larger difference in induced potential between the electrodes at these positions than between other adjacent axial positions. The induced field potential data for lead  18 D shows a linear decrease with increasing distance from the stimulating electrode. While the data depicted in  FIG.  16    is idealized and is only shown for two of the eight electrodes associated with each lead  18 , the full set of induced field potential data for a set of eight electrodes includes clearly identifiable trends based on different physical electrode arrangements that enable the differentiation of different types of leads. 
       FIG.  17    illustrates the use of induced field potential data to distinguish between electrodes that are associated with different leads. This can be particularly useful, for example, for identifying the type of electrode leads when there is not a  1 : 1  correspondence between a lead  18  and a lead connector  20  (e.g., two four-electrode leads sharing a single lead connector, one 16-electrode lead having two separate lead connectors, etc.).  FIG.  17    illustrates idealized induced field potential data for the two four-electrode leads shown at the top of the figure. As can be seen in the data, the groups of electrodes on the different leads are clearly distinguishable. When any electrode on a lead is stimulated, the induced field potential is much higher at the other electrodes that are positioned on the same lead as the stimulating electrode and much lower at each of the electrodes on the other lead. 
     As the above example monopolar impedance, bipolar impedance, and induced field potential data indicates, different groups of electrodes can be distinguished from each other based on data that is indicative of their different physical electrode arrangements. Such different physical electrode arrangements may include different types of electrodes (e.g., segmented and circumferential electrodes of different dimensions), different axial positions and groupings of electrodes, different azimuthal alignment of electrodes on a lead, and different electrode spacings along a lead. 
       FIG.  18    illustrates a process  300  that utilizes properties in a data set that are indicative of a physical arrangement of electrodes in a known electrode group to associate a group of electrodes that is connected to an IPG  10  with the known electrode group. The term electrode group is used here to describe electrodes that are associated with each other such as being connected to a common lead connector  20 , positioned on a common lead  18 , etc. While process  300  could be performed at any time, it is typically executed after implantation of an IPG  10  and as part of the above-described IPG configuration process. In a preferred embodiment, process  300  is executed on an external device such as CP computer  202  and is therefore incorporated into CP software  96 . In another embodiment, process  300  may be executed on a different external device such as controller  40 . For purposes of this description, process  300  is described in terms of its execution on CP computer  202 . 
     Process  300  begins with the optional receipt of user port assignments (step  302 ). Such port assignments can be received in the manner described above through user selection of the leads  18  (or lead connectors  20 ) that are inserted in each port  8  of the IPG  10  via the software  96 , for example. After receiving the user port assignments, or, alternatively, if no user port assignments are received, connected electrode data is requested from the IPG  10  (step  304 ). The connected electrode data can include all or a subset of the monopolar impedance, bipolar impedance, and induced field potential data described above. In one embodiment, a first subset of the data may be initially requested and additional data may be subsequently requested if needed. For example, the initial data request may include a request for monopolar impedance data and intra-port bipolar impedance and induced field potential data (i.e., bipolar impedance and induced field potential data between electrodes connected to the same port  8  but not across different ports  8 ). Similarly, the initial data request may include a request for monopolar impedance data only. In one embodiment, the amount and type of data requested may be based upon the user port assignment. For example, if the user port assignment specifies leads  18  that can likely be verified with a subset of data, only the required subset of data may be requested. Likewise, if the user port assignment specifies leads  18  that will necessarily require a larger set of data for verification, the larger set of data may be requested. In any event, the data request is communicated to the IPG  10 , such as via the communication link  92 . 
     In response to the data request, the requested data is received (step  306 ). The requested data may comprise data that is routinely collected by the IPG  10  and may therefore be readily available. Alternatively, all or some portion of the data may be collected by the IPG  10  only upon request, in which case the process  300  may wait while the data is collected by the IPG  10 . Once received, the connected electrode data is processed (step  308 ) to associate connected electrode groups with known electrode groups. More specifically, the connected electrode data is evaluated using a classifier to associate connected groups of electrodes with one of the known electrode groups (i.e., the lead groups that are programmed into the software) based on properties in the data that are indicative of different physical arrangements of electrodes in known electrode groups. 
     In one embodiment, the connected electrode data is initially evaluated on a port-by-port basis, so the classifier is configured to discriminate between different groups of electrodes connected to different lead connectors  20  (and thus different ports  8 ) as opposed to the electrodes on a full lead (e.g., a 16-electrode lead). In one embodiment, a classifier is manually configured to identify patterns or characteristics in the connected electrode data that are indicative of different known electrode groups. 
       FIG.  19    illustrates several examples of the operations that might be performed to identify patterns in the data that are associated with different physical arrangements of electrodes for the different known electrode groups (e.g., the group of electrodes on a single lead  18  or the group of electrodes connected to a single lead connector  20 ). The operations may be performed on the raw data from the IPG  10 , or the data may be pre-processed to normalize the data, remove anomalies, etc. In one embodiment, such anomalies may be indicative of improper connection of a lead connector  20  with a device port  8 . For example, the impedance data may be very high for one of the terminal contacts associated with a port  8  but normal for the other contacts. Such a situation is indicative of a failure to fully seat the lead connector  20  in the connector block  22 , which results in the incorrect alignment of contacts in the lead connector  20  and connector block  22  (i.e., contact  2  in the lead connector block is coupled to contact  1  in the lead connector  20 , and so on). This type of situation may therefore be presented to the user as a warning of the incorrect insertion. In one embodiment, the user may be prompted to correct the issue before attempting to initiate the process  300  again. In an alternative embodiment, the process  300  may shift the data to accommodate the incorrect insertion (i.e., shift the contact  2  data to contact  1 , etc.) in order to attempt to identify or verify the type of known electrode group that is improperly connected. After manipulation of the data to account for any anomalies, etc. the various operations illustrated in  FIG.  19   , as well as other related operations, may be performed. 
     The global operations do not rely upon the known properties of the different types of leads  18 . That is, the global operations are applied to the data associated with a group of electrodes as a whole and not to subsets of such data based on different electrode arrangements of the known electrode groups. The coefficient of variation of monopolar impedance  402  represents the variance in the monopolar impedance data set, which variance is higher for electrode groups that include different electrode types (i.e., both circumferential and segmented). By way of example, for the monopolar impedance data illustrated in  FIGS.  11 A and  11 B , the coefficient of variation for electrode groups associated with a single electrode type (i.e., lead  18 A) is generally less than 15% whereas the coefficient of variation for electrode groups associated with different electrode types (i.e., lead  18 B) is generally greater than 20%. Similarly, the normalized range of monopolar impedance data  404  (i.e., the ratio of the range of the data to the mean), like operation  402 , provides an indication of variability in the monopolar impedance data set, which is much higher for electrode groups having different types of electrodes. For the monopolar impedance data illustrated in  FIGS.  11 A and  11 B , the normalized range for electrode groups associated with a single electrode type is generally less than about 50% whereas the normalized range for leads associated with different electrode types is generally greater than about 80%. Thus, the operations  402  and  404  can provide a beneficial first indication of the type of electrode groups that are connected to an IMD. 
     The max increase between any pair of consecutive data points in an ordered set of monopolar impedance data  406  associated with a particular electrode group, like the variance metrics described above, provides an indication about whether the electrode group includes connections to electrodes of different types. A higher max increase indicates a higher likelihood that the electrode group includes connections to electrodes of different types. The location of the max increase  408  (i.e., the position in the data set at which the max increase occurs such as between the second and third data points in the ordered set) indicates the number of circumferential electrodes and the number of segmented electrodes in the electrode group. The specific data points  410  that are on each side of the max increase  408  provide an indication of the electrode numbers of the segmented electrodes and the circumferential electrodes in the electrode group. The table below shows the monopolar impedance data for lead  18 B that is identified as data set “A” in  FIG.  11 B . 
                                        Data Point                                                     1   2   3   4   5   6   7   8                                                             Impedance   1137   2124   2259   2246   2299   2263   2385   1206       (ohms)                    
The ordered data set is shown in the table below along with the point-to-point increases between consecutive data points.
 
                                        Data Point                                                     1   8   2   4   3   6   5   7                                                             Impedance   1137   1206   2124   2246   2259   2263   2299   2385       (ohms)                                             Point-to-point   69   918   122   13   4   36   86       Increase                    
As indicated in the ordered data set, the largest point-to-point increase occurs between the second and third points in the ordered set, and data points one and eight (which correspond to electrodes E 1  and E 8 ) are below the max increase. This correctly indicates that electrodes E 1  and E 8  are circumferential electrodes and electrodes E 2 -E 7  are segmented electrodes.
 
     The coefficient of determination (i.e., R 2 ) of the linear regression of bipolar impedance data  412  and induced field potential data  414  provide an indication of the linearity of the increase/decrease of the impedance and field potential with increasing/decreasing electrode number. A linear regression may be performed, for example, on the bipolar impedance and/or induced field potential data for a terminal electrode data group (i.e., the first or eighth electrode data group) for the lead connector being evaluated, and the coefficient of determination may be calculated to determine how well the linear regression fits the data. Because the bipolar impedance and induced field potential data for segmented electrodes at a common axial position are substantially equal, the data is less linear than corresponding data for circumferential electrodes. Thus, a higher coefficient of determination of a linear regression of either bipolar impedance or induced field potential data is generally indicative of the presence of a larger number of circumferential electrodes as opposed to segmented electrodes. 
     Unlike the global operations, the lead-specific operations take advantage of the known properties of the known electrode groups to manipulate the connected electrode data in different ways. The ratio of segmented-to-circumferential monopolar impedance  420 , for example, may be calculated for a given monopolar impedance data set using the known electrode arrangements associated with the different lead connectors. For example, the ratio  420  may be calculated using the average monopolar impedance at data points two through seven (corresponding to segmented electrodes E 2 -E 7 ) and the average monopolar impedance at data points one and eight (corresponding to circumferential electrodes E 1  and E 8 ) to determine if the monopolar impedance data set matches lead  18 B. When the correct electrode grouping is utilized, the ratio  420  typically approaches a value of 2:1. 
     The coefficient of variation in bipolar impedance  422  and induced field potential  424  data can be evaluated across different electrode subgroupings within a group of electrodes to identify groups of segmented electrodes that are located at a common axial position. The coefficient of variation is relatively small in both the bipolar impedance and induced field potential data sets for segmented electrodes that are positioned at the same axial location, and the values can therefore help distinguish between different electrode groups. For example, the coefficient of variation across data points two through four and data points five through seven would typically be lower for lead  18 B than for lead  18 C, because the data points are associated with axially-grouped segmented electrodes in the former but span across different axial groups in the latter. Conversely, the coefficient of variation across data points four through six would typically be lower for lead  18 C than lead  18 B for the same reason. 
     The ratio of the induced field potential at azimuthally-linked electrodes to other segmented electrodes positioned at the same axial position  426  also provides an indication of segmented electrode grouping, and, thus, the type of electrode group. The ratio  426  can be computed for different electrode arrangements of known electrode groups, and the ratio is typically higher when the correct arrangement is used. By way of example, for lead  18 B, the following pairs of electrodes are azimuthally linked: E 2  and E 5 , E 3  and E 6 , and E 4  and E 7 . In the induced field potential data group for any one of these electrodes, its pair electrode will typically have a higher induced field potential than the other segmented electrodes at the same axial position. For example, as indicated in  FIG.  15   , in the electrode E 2  group, electrode E 5  has a higher induced field potential than electrodes E 6  and E 7 , in the electrode E 3  group, electrode E 6  has a higher induced field potential than electrodes E 5  and E 7 , and so on. As a result, the ratio of the induced field potential of azimuthally-linked segmented electrodes to other segmented electrodes at the same axial position is higher when the correct grouping is identified. 
     The slope and coefficient of determination of a linear regression of bipolar impedance data  428  and induced field potential data  430  across a series of data points can provide an indication about whether the data points correspond to a sequence of evenly-spaced circumferential electrodes at different axial positions (as opposed to segmented electrodes at the same axial position). These values can therefore be calculated for data points corresponding to known sequences of circumferential electrodes such as data points one through eight of lead  18 A. When the slope and coefficient of determination, which can be calculated for different electrode groups, indicate a linear relationship across the selected data points, there is a higher likelihood that the electrodes corresponding to those data points are circumferential electrodes. Therefore, the values  428  and  430  can be used to distinguish between different leads  18 . 
     The ratio of average bipolar impedance data  432  and induced field potential data  434  across different sets of data points, and the point at which the ratio flips, provides an indication of segmented electrode grouping. For example, as illustrated in  FIG.  15   , the ratio of the average induced field potential for data points two through four (corresponding to electrodes E 2 -E 4 ) to the average induced field potential for data points five through seven (corresponding to electrodes E 5 -E 7 ) in the electrode E 1 -E 4  data groups is greater than unity. However, the same ratio for the electrode E 5 -E 8  data groups is less than unity. The ratio flips starting at the fifth data group because the fifth data group corresponds to an electrode (E 5 ) at a new axial position. These ratios therefore provide an additional indicator of segmented electrode grouping. 
     It will be understood that the listed operations are merely illustrative and not exhaustive. Based on the disclosed relationships, one of ordinary skill in the art will be capable of identifying further operations for classifying connected electrode data for electrode groups having different electrode arrangements. Moreover, it will be understood that the operations may be arranged in a manner that efficiently arrives at a determination of a known electrode group such as a decision tree. While the operations have been described in terms of their performance on data sets corresponding to a single lead  18  or lead connector  20 , the classifier may include operations that are performed across data sets for different lead connectors  20  (e.g., bipolar impedance and/or induced field potential measurements between electrodes associated with different lead connectors  20 ). In one embodiment, intra-connector data may be evaluated initially and inter-connector measurements may be subsequently evaluated to confirm and/or further classify connected leads. 
     In addition to the described data classification operations, the classifier may also be programmed with various logical rules. For example, the classifier may be programmed such that both lead connectors of a multi-connector lead must be identified together (i.e., there can&#39;t be one connector of a multi-connector lead without the other connector). 
     While different manual classification operations have been described, classification may also be performed using a classifier that is trained using machine learning techniques. In this context, machine learning involves supplying a program a (preferably large) number of connected electrode data sets and their associated known electrode group (i.e., the known lead connector  20  or lead  18  that is associated with the data set). The program recognizes patterns in the data in the supplied data sets and, based on the patterns, generates a model that can be used to identify the electrode group that results in a future set. The data sets that are provided to the machine learning program may include the user port assignments, which may be considered by the program. 
     Regardless of the configuration of the classifier, its output is the determined known group of electrodes that is associated with each of the IMD  10 &#39;s ports  8 , which is presented to the user ( 310 ). The classifier may additionally be configured to determine and present one or more confidence measures. A first confidence measure may be described as a match confidence measure. A match confidence measure may represent the level of agreement between the data associated with a connected group of electrodes and the corresponding data for its determined known electrode group. Such a match confidence measure may be calculated using known statistical techniques for the comparison of the degree of similarity between two sets of data. A second confidence measure may be described as an evaluation confidence measure. The evaluation confidence measure may represent the degree of confidence in the determination of the matching known electrode group. The evaluation confidence measure may differ from the match confidence measure, for example, when a determination of a known electrode group is made on the basis of a more limited amount of data. For example, the limited amount of data may agree strongly with corresponding data for the determined known electrode group thus resulting in a high match confidence, but, because the amount of data is limited, the evaluation confidence may still be lower. The use of limited data may occur, for example, when statistical anomalies that are believed to be associated with open or short circuits are removed from a sample data set or when the analysis is performed on a more limited set of data (e.g., based on monopolar impedance alone, based on intra-port bipolar and/or induced field potential data, etc.). The evaluation confidence measure may be determined based on the amount of data that is utilized in associating the connected electrode group with a known electrode group as compared to the total amount of data that could be utilized. In making this determination, the different types of data may be weighted differently based on their usefulness in distinguishing between different groups of electrodes. 
       FIG.  20    shows an example improved GUI  94 ′ that may be used to present the determined electrode groups that are associated with each port of the IPG  10 . As indicated in the GUI  94 ′, when the port assignment matches that supplied by the user, a verification  502  of the user&#39;s assignment (e.g., a check mark or some other symbol of verification) is presented via the GUI  94 ′. When the port assignment disagrees with that supplied by the user, a mismatch indicator  504  (e.g., an “X” or some other symbol of the mismatch) is presented to the user via the GUI  94 ′. Regardless of whether the determined port assignment matches the user assignment or whether the user even made an assignment, the user may be presented with an interface  506  to confirm and accept the determined port assignments via the GUI  94 ′. As can be seen, the process  300  provides a mechanism for associating a group of electrodes that are connected to an IPG  10  with a known electrode group (e.g., a group of electrodes connected to a particular lead connector  20 ) based on properties in data from the connected group of electrodes that is indicative of a physical electrode arrangement in the associated known electrode group. 
       FIG.  21    illustrates the various components of an example CP computer  202  that may be configured to execute CP software  96  that incorporates the process  300 . The CP computer  202  can include the processor  222 , memory  224 , storage  220 , graphics hardware  226 , communication interface  230 , user interface adapter  232  and display adapter  234 —all of which may be coupled via system bus or backplane  236 . Memory  224  may include one or more different types of media (typically solid-state) used by the processor  222  and graphics hardware  228 . For example, memory  224  may include memory cache, read-only memory (ROM), and/or random access memory (RAM). Storage  220  may store media, computer program instructions or software (e.g., CP software  96 ), preference information, device profile information, and any other suitable data. Storage  220  may include one or more non-transitory computer-readable storage mediums including, for example, magnetic disks (fixed, floppy, and removable) and tape, optical media such as CD-ROMs and digital video disks (DVDs), and semiconductor memory devices such as Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), and USB or thumb drive. Memory  224  and storage  220  may be used to tangibly retain computer program instructions or code organized into one or more modules and written in any desired computer programming language. Communication interface  230  (which may comprise, for example, the ports  206  or  208 ) may be used to connect the CP computer  202  to a network. Communications directed to the CP computer  202  may be passed through a protective firewall  238 . Such communications may be interpreted via web interface  240  or voice communications interface  242 . Illustrative networks include, but are not limited to: a local network such as a USB network; a business&#39; local area network; or a wide area network such as the Internet. User interface adapter  232  may be used to connect a keyboard  244 , microphone  246 , pointer device  248 , speaker  250  and other user interface devices such as a touch-pad and/or a touch screen (not shown). Display adapter  234  may be used to connect display  204  and printer  252 . 
     Processor  222  may include any programmable control device. Processor  222  may also be implemented as a custom designed circuit that may be embodied in hardware devices such as application specific integrated circuits (ASICs) and field programmable gate arrays (FPGAs). The CP computer  202  may have resident thereon any desired operating system. 
     While the CP system  200  has been described and illustrated as communicating directly with the IPG  10 , the CP system  200  may additionally or alternatively be configured to communicate with different types of neurostimulators. For example, the CP system  200  may interface with an external trial stimulator that mimics the operation of the IPG  10  but that is positioned outside of the body to evaluate therapies during a trial phase. As will be understood, the CP software  96  may be stored on a medium such as a CD or a USB drive, pre-loaded on a computing device such as the CP computer  202 , or made available for download from a program repository via a network connection. Moreover, while process  300  has been described as being performed on an external device, certain portions of the process  300  may instead be performed by the IPG  10  itself. For example, the IPG may measure the connected electrode data and the IPG&#39;s control circuitry may be configured to process such connected electrode data itself to associate connected groups of electrodes with known electrode groups. In such an embodiment, the IPG  10  may be configured to transmit its results to an external device so that the determined known electrode groups might be displayed to a user. 
     Although particular embodiments have been shown and described, it should be understood that the above discussion is not intended to limit the present disclosure to these embodiments. It will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the claims.