Standard Artifact Research Articles

Seeing Is Believing: Photon Counting Computed Tomography Clearly Images Directional Deep Brain Stimulation Lead Segments and Markers After Implantation

Background and ObjectivesDirectional deep brain stimulation (DBS) electrodes are increasingly used, but conventional computed tomography (CT) is unable to directly image segmented contacts owing to physics-based resolution constraints. Postoperative electrode segment orientation assessment is necessary because of the possibility of significant deviation during or immediately after insertion. Photon-counting detector (PCD) CT is a relatively novel technology that enables high resolution imaging while addressing several limitations intrinsic to CT. We show how PCD CT can enable clear in vivo imaging of DBS electrodes, including segmented contacts and markers for all major lead manufacturers. Materials and MethodsWe describe postoperative imaging and reconstruction protocols we have developed to enable optimal lead visualization. PCD CT images were obtained of directional leads from the three major manufacturers and fused with preoperative 3T magnetic resonance imaging (MRI). Radiation dosimetry also was evaluated and compared with conventional imaging controls. Orientation estimates from directly imaged leads were compared with validated software-based reconstructions (derived from standard CT imaging artifact analysis) to quantify congruence in alignment and directional orientation. ResultsHigh-fidelity images were obtained for 15 patients, clearly indicating the segmented contacts and directional markers both on CT alone and when fused to MRI. Our routine imaging protocol is described. Ionizing radiation doses were significantly lower than with conventional CT. For most leads, the directly imaged lead orientations and depths corresponded closely to those predicted by CT artifact-based reconstructions. However, unlike direct imaging, the software reconstructions were susceptible to 180° error in orientation assessment. ConclusionsHigh-resolution photon-counting CT can very clearly image segmented DBS electrode contacts and directional markers and unambiguously determine lead orientation, with lower radiation than in conventional imaging. This obviates the need for further imaging and may facilitate anatomically tailored directional programming.

Broadly applicable methods for the detection of artefacts in electroencephalography acquired simultaneously with hemodynamic recordings

Electroencephalography (EEG) data, acquired simultaneously with magnetic resonance imaging (MRI), must be corrected for artefacts related to MR gradient switches (GS) and the cardioballistic (CB) effect. Canonical approaches require additional signal acquisition for artefact detection (e.g., MR volume onsets, ECG), without which the EEG data would be rendered uncleanable from these artefacts.•We present two broadly applicable methods for artefact detection based on peak detection combined with temporal constraints with respect to periodicity directly from the EEG data itself; no additional signals are required.We validated the performance of our methods versus the two canonical approaches for detection of GS/CB artefact, respectively, on 26 healthy human EEG-functional MRI resting-state datasets. Utilising various performance metrics, we found our methods to perform as well as – and sometimes better than - the canonical standard approaches. With as little as one EEG channel recording, our methods can be applied to detect GS/CB artefacts in EEG data acquired simultaneously with MRI in the absence of MR volume onsets and/or an ECG recording. The detected artefact onsets can then be fed into the standard artefact correction software.

THE SECONDARY PHONEME FROM THE PERSPECTIVE OF KAMAL BISHR AN APPLIED STUDY IN THE IRAQI VERNACULAR

Secondary phoneme: It is the term that was approved by a number of researchers for the concept of stress.. they called it a (secondary phoneme) according to a concept that preceded it and they called it: (phoneme). from which the word is composed in any language in the world, so the letter - for example - is a phonetic unit with significance, which contributes with other phonemic units in building the word, and revolves around each phoneme, a possible package of articulatory colors, which has no effect on the meaning, called (phones)... In terms of the functional importance with which the (phoneme) was distinguished; We found another importance in (emphasis), which means in the term: an intentional increase in the amount of utterance that diverts the meaning from its destination. In order to prove and confirm it, or turn it around and deny it, this addition - which may come, excuse me, at no cost, is important. Because it often carries a new connotation that was not present in the original phoneme.. In this study, we found that the (colloquial) devoid of the syntactic industry is suitable in terms of application in the phonetic study; Because it leads to accurate results that cannot be obtained in the standard sentence, and Kamal Bishr took advantage of the Egyptian spoken in his applications and examples in his book (Science of Phonetics) without indicating the reason that prompted him to do so, so we expanded on the statement of what he concluded, with applications reproduced from our linguistic reality. The Iraqi, full of spontaneity, the results of (spontaneity) - as we can see - are more accurate than the results of the decoration and care that surrounded it (the standard artifact)

Measurement of additively manufactured freeform artefacts: The influence of surface texture on measurements carried out with optical techniques

Quality control of additively manufactured parts is a crucial topic, since it includes the measurement of freeform geometries, i.e. lattice structures, and parts characterized by surface topographies several times more rough than conventional machining. Freeform surfaces and their related measurands can be effectively assessed via areal optical scanning techniques and X-ray-based systems, while it is still of great interest to evaluate the effect of the surface quality on their measuring performance.In this work, an experimental investigation about the influence of a typical additive manufacturing surface texture on optical measurements was conducted. As test object, the geometry of a standard freeform artefact developed by the NPL Institute was considered and it was realized by using a Material Extrusion Additive Manufacturing (MEX) technology and micro-milling. By comparing results coming from the two realized artefacts, it was possible to evaluate the influence of the AM surface texture on the conducted measurements.

Evaluation of the Effects of Differences in Metal Artifact Type and Location on Image Quality in Computed Tomography Scans.

Artifacts in computed tomography scans distort anatomical information and prevent an accurate diagnosis. Therefore, this study aims to determine the most effective method for reducing metal-induced artifacts by evaluating the effects of the metal artifact type and location, and the tube voltage on the image quality. Fe and Cu wires were inserted into a Virtual Water™ phantom at 6.5 and 11 cm distances from the center point (DPs). The contrast-to-noise ratios (CNRs) and signal-to-noise ratios (SNRs) were calculated to compare the images. The results reveal higher CNRs and SNRs when using standard and Smart metal artifact reduction (Smart MAR) algorithms for Cu and Fe insertions, respectively. The standard algorithm leads to a higher CNR and SNR for Fe and Cu at DPs of 6.5 and 11 cm, respectively. The Smart MAR algorithm provides effective outcomes at voltages of 100 and 120 kVp for wires located at 11 and 6.5 cm DP, respectively. The most effective imaging conditions for MAR is generated by the Smart MAR algorithm with a tube voltage for 100 kVp for Fe located at a DP of 11 cm. MAR can be improved by setting suitable tube voltage conditions according to the type and location of inserted metal.

Metrology Benchmarking of 3D Scanning Sensors Using a Ceramic GD&T-Based Artefact.

The use of non-contact scanning equipment in metrology and in dimensional and geometric inspection applications is increasing due to its ease of use, the speed and density of scans, and the current costs. In fact, these technologies are becoming increasingly dominant in the industrial environment, thus moving from reverse engineering applications to metrological applications. However, this planned transfer requires actions to ensure the achievable accuracy by providing traceability of measurements. In the present study, a comparison between the devices is carried out and a specific standard artefact is designed, equipped with multiple ceramic optically friendly entities, and allowing a wide variety of geometric dimensioning and tolerancing (GD&T). Four different 3D scanning sensors are used in the experimentation. Three of them are based on laser triangulation, and the fourth is a structured blue light sensor (fringe pattern projection). The standard artefact is calibrated with a high accuracy, using a coordinate measuring machine (CMM) and probing sensors. With this CMM, reference values of multiple predefined GD&T are obtained. The evaluation methodology maximises the accuracy of each device in measuring the dimensions of the artefact due to the good dimensional (milling and turning), surface (control of machining variables), and the dimensional and spatial distribution characteristics. The procedure also includes the same treatment of the captured point clouds (trimming, filtering, and best-fit algorithm, etc.) in each of the four 3D scanning sensors considered. From this process, very reliable measurements of the maximum achievable accuracy of each device (deviations from the CMM measurements) are finally obtained, and a multi-characteristic comparison between the four sensors is performed, also with high reliability.

Accurate nanoparticle size determination using electrical mobility measurements in the step and scan modes

A critical and extensive comparison was made between differential mobility analysis (DMA) measurements of the mean diameter of monodisperse gold nanoparticles (AuNPs), based on step-voltage mode and the more commonly used scan-voltage mode (commercially known as scanning mobility particle sizer, SMPS). Under specific conditions including a long scan time, the difference between mean diameters measured by the two modes of operation was less than the expanded combined uncertainty (95% confidence interval) for the step-voltage mode. In addition, a comparison was made between two different calibration methods for DMA: the use of a certified nanoparticle size standard (artifact) versus a direct measurement of the sheath flow rate. Important variables and limitations for accurate measurements by the scan-voltage method were identified and evaluated. The mean size shifts to smaller electrical mobility diameters as the scan time is reduced and the scan mode is unable to measure sufficient points across the peak of very narrow size distributions, leading to systematic errors. The use of a calibration particle corrects for the flow and DMA column geometric effects and was found to minimize the effect of a reduced scan time. A methodology is presented for the use of these AuNPs and other monodisperse calibration particles for accurately calibrating SMPS instruments for the measurement of the electrical mobility diameter distribution.Copyright © 2022 American Association for Aerosol Research

Unified Retrospective EEG Motion Educated Artefact Suppression for EEG-fMRI to Suppress Magnetic Field Gradient Artefacts During Motion.

The data quality of simultaneously acquired electroencephalography and functional magnetic resonance imaging (EEG-fMRI) can be strongly affected by motion. Recent work has shown that the quality of fMRI data can be improved by using a Moiré-Phase-Tracker (MPT)-camera system for prospective motion correction. The use of the head position acquired by the MPT-camera-system has also been shown to correct motion-induced voltages, ballistocardiogram (BCG) and gradient artefact residuals separately. In this work we show the concept of an integrated framework based on the general linear model to provide a unified motion informed model of in-MRI artefacts. This model (retrospective EEG motion educated gradient artefact suppression, REEG-MEGAS) is capable of correcting voltage-induced, BCG and gradient artefact residuals of EEG data acquired simultaneously with prospective motion corrected fMRI. In our results, we have verified that applying REEG-MEGAS correction to EEG data acquired during subject motion improves the data quality in terms of motion induced voltages and also GA residuals in comparison to standard Artefact Averaging Subtraction and Retrospective EEG Motion Artefact Suppression. Besides that, we provide preliminary evidence that although adding more regressors to a model may slightly affect the power of physiological signals such as the alpha-rhythm, its application may increase the overall quality of a dataset, particularly when strongly affected by motion. This was verified by analysing the EEG traces, power spectra density and the topographic distribution from two healthy subjects. We also have verified that the correction by REEG-MEGAS improves higher frequency artefact correction by decreasing the power of Gradient Artefact harmonics. Our method showed promising results for decreasing the power of artefacts for frequencies up to 250Hz. Additionally, REEG-MEGAS is a hybrid framework that can be implemented for real time prospective motion correction of EEG and fMRI data. Among other EEG-fMRI applications, the approach described here may benefit applications such as EEG-fMRI neurofeedback and brain computer interface, which strongly rely on the prospective acquisition and application of motion artefact removal.

A novel tool for the removal of muscle artefacts from EEG: Improving data quality in the gamma frequency range

BackgroundThe past two decades have seen a particular focus towards high-frequency neural activity in the gamma band (>30 Hz). However, gamma band activity shares frequency range with unwanted artefacts from muscular activity. New MethodWe developed a novel approach to remove muscle artefacts from neurophysiological data. We re-analysed existing EEG data that were decomposed by a blind source separation method (independent component analysis, ICA), which helped to better spatially and temporally separate single muscle spikes. We then applied an adapting algorithm that detects these singled-out muscle spikes. ResultsWe obtained data almost free from muscle artefacts; we needed to remove significantly fewer artefact components from the ICA and we included more trials for the statistical analysis compared to standard ICA artefact removal. All pain-related cortical effects in the gamma band have been preserved, which underlines the high efficacy and precision of this algorithm. ConclusionsOur results show a significant improvement of data quality by preserving task-relevant gamma oscillations of presumed cortical origin. We were able to precisely detect, gauge, and carve out single muscle spikes from the time course of neurophysiological measures without perturbing cortical gamma.We advocate the application of the tool for studies investigating gamma activity that contain a rather low number of trials, as well as for data that are highly contaminated with muscle artefacts. This validation of our tool allows for the application on event-free continuous EEG, for which the artefact removal is more challenging.

Multi-sensor registration method based on a composite standard artefact

Registration is a critical and essential procedure in any multi-sensor dimensional measuring systems. Most of the traditional registration methods are achieved by measuring a common standard by multiple sensors; however, it is difficult to ensure that heterogeneous sensors measure the same feature points. In this study, a new multi-sensor registration method based on a composite standard artefact is proposed. The base of the standard artefact is equipped with a standard sphere and a standard chrome-circle for registering the visual sensor (VS) and the tactile probe sensor (TPS) on a multi-sensor dimensional measuring machine. The VS and TPS measure the standard chrome-circle and the standard sphere, respectively. The coordinate system conversion parameters between the two sensors were solved based on the constant distance between the standard chrome-circle centre and the standard sphere centre. Both the simulations and experiments demonstrate higher precision and stability of the proposed method for the registration of multiple heterogeneous sensors in high-precision dimensional measurement systems. The root mean square errors of the registration experiments in X and Y -directions are 6μm and 4μm, respectively. The combined standard uncertainties are uc(tx)=1.6μm and uc(ty)=1.2μm.

Event Related Potentials (ERPs) and other EEG Based Methods for Extracting Biomarkers of Brain Dysfunction: Examples from Pediatric Attention Deficit/Hyperactivity Disorder (ADHD).

Neuropsychiatric diagnoses like ADHD are based on subjective methods like interviews, rating scales and observations. There is a need for more brain-based supplements. Stimulant medication is the most common treatment for ADHD. Clinically useful predictors of response have so far not been reported. The aim of this paper is to describe the EEG based methods we apply to extract potential biomarkers for brain dysfunction. Examples relate to biomarkers for pediatric ADHD, and prediction of medication response. The main emphasis is on Event Related Potentials (ERPs). A nineteen channel EEG is recorded during a 3 min eyes-opened task, a 3 min eyes-closed task, and a 20 min cued visual GO/NOGO task (VCPT). ERPs are recorded during this task. The goal of the ERP protocol is to extract biomarkers of assumed brain dysfunctions that significantly differentiate between a patient group and healthy controls. The protocol includes recording during standard conditions and artifact correction. ERP waves can be used or transformed into latent components. The components of the patient group are compared with controls, empathizing components that, when compared, show relatively high effect sizes. Sub-groups of the patients are selected on the basis of the cluster analysis in the space of the components. Treatment procedure (such as medication, tDCS or neurofeedback protocol) can be applied and the changes in components related to treatment in the subgroups are observed, forming the basis for clinical recommendations. The methods described were applied in a study of 87 pediatric ADHD patients. The index of medication response discriminated significantly between responders and non-responders with a large, and clinically meaningful effect size (d = 1.84). In an ongoing study comparing ADHD children with matched controls, several variables discriminate significantly between patients and controls. The global index will exceed d = .8. The EEG based methods described here could be clinically meaningful.

Local geometric error corrections for a metrological scanning probe microscope

A local geometric error correction method is developed for a metrological scanning probe microscope. The method corrects geometric errors in stage displacements using the interferometric measurements of angular position and known geometric offsets. Local and global error correction methods are considered and general scaling dependences on the number of measured steps or points are derived and compared. For the local method, the total uncertainty scales the same or decreases with a sufficient number of measurement steps compared with the global method. Implementation of the local geometric error correction method is demonstrated on measurements of a three-dimensional height standard artefact. The applied error correction method reduces the contribution of geometric errors to the uncertainty budget by two orders of magnitude. The presented approach can be extended to any scanning technique where a measurement translation mechanism can be identified and accurately quantified by relating the measured values with a measurand.

Characterization and Correction of the Geometric Errors in Using Confocal Microscope for Extended Topography Measurement. Part I: Models, Algorithms Development and Validation

This work presents a method for characterizing and correcting the geometric errors of the movement of the lateral stage of Imaging Confocal Microscope (CM) in extended topography measurement. For an extended topography measurement, a defined number of 2D images are taken and stitched by correlation methods. Inaccuracies due to linear displacement, vertical and horizontal straightness errors, angular errors, and squareness errors based on the assumption of the rigid body kinematics are described. A mathematical model for the scale calibration of the X- and Y- coordinates is derived according to the system kinematics, the axis chain vector of CM, and the geometric error functions and their approximations by Legendre polynomials. The correction coefficients of the kinematic modelling are determined by the measured and certified data of a dot grid target standard artefact. To process the measurement data, algorithms for data partitions, fittings of cylinder centers, and determinations of coefficients are developed and validated. During which methods such as form removal, K-means clustering, linear and non-linear Least Squares are implemented. Results of the correction coefficients are presented in Part II based on the experimental studies. The mean residual reduces 29.6% after the correction of the lateral stage errors.

Measurement and analysis of the radial motion error of aerostatic ultra-precision spindle

The measurement of the rotation error of an aerostatic ultra-precision spindle is critically important to evaluate and hence ensure the precision of machine tools. The Donaldson reversal method, which was taken as the efficient method for error separation theoretically, has been widely used to separate shape errors of standard artifact. However, the accuracy analysis of the Donaldson reversal method has not been fully studied and understood. In this study, a nanometer system for measuring the radial rotation error of aerostatic ultra-precision spindle was constructed based on the Donaldson reversal method. The comparative experiments were carried out to investigate the effects of the motor drive, and an angle correction algorithm was proposed to alleviate the effect of angle deviation. The method of harmonic analysis was applied to investigate the effect of artifact eccentricity, and the relationship between the axial motion and measuring error was also studied. The measuring accuracy can be improved by reducing the cogging torque of motor, the angle deviation, artifact eccentricity and spindle axial motion. Experimental results showed that the measurement uncertainty of both the spindle rotation error and artifact form error can be controlled in nanometer level. Besides, the separated value of the artifact form error was very close to the nominal roundness, which verifies the accuracy of the measurement system and the validity of the error separation method.

Protocol for Rapid, Accurate, Electrophysiologic, Auditory Assessment of Infants and Toddlers

Background: Audiologists often lack confidence in results produced by current protocols for diagnosticelectrophysiologic testing of infants. This leads to repeat testing appointments and slow protocols whichextend the time needed to complete the testing and consequently delay fitting of amplification. A recentpublication (Sininger et al, 2018) has shown how new technologies can be applied to electrophysiologictesting systems to improve confidence in results and allow faster test protocols. Average test times forcomplete audiogram predictions when using new technologies and protocols were found to be just over32 minutes using auditory brainstem response (ABR) and just under 20 minutes using auditory steadystateresponse (ASSR) technology.<br />Purpose: The purpose of this manuscript is to provide details of expedited test protocols for infant andtoddler diagnostic electrophysiologic testing.<br />Summary: Several new technologies and their role in test speed and confidence are described includingCE-Chirp stimuli, automated detection of ABRs using a technique called FMP, Bayesian weighting which isan alternative to standard artifact rejection and Next-Generation ASSR with improved response detectionand chirp stimuli. The test protocol has the following features: (1) preliminary testing includes impedancemeasures and otoacoustic emissions, (2) starting test levels are based on Broad-Band CE-Chirp thresholdsin each ear, (3) ABRs or ASSRs are considered present based on automated detection rather thanon replication of responses, (4) number of test levels is minimized, (5) ASSR generally evaluates fourfrequencies in each ear simultaneously with flexibility to change all test levels independently.<br />Conclusions: Combining new technologies with common-sense strategies has been shown to substantiallyreduce test times for predicting audiometric thresholds in infants and toddlers (Sininger et al, 2018).Details and rationales for changing test strategies and protocols are given and case examples are used toillustrate.

Evaluation of the dental spectral cone beam CT for metal artefact reduction.

Metal artefacts are highly common in dental CT images because of the high X-ray attenuation of metallic dental fillings and implants. This study presents an evaluation of the virtual monochromatic imaging for metal artefact reduction by a recently introduced dental spectral cone beam CT, which is the first commercial dental spectral CBCT with flat-panel detector. We carried out phantom experiments and clinical trials in this study. In the phantom study, the head phantom with metallic dental fillings and implants of various materials was scanned. Moreover, standard deviation, metal artefact index, and contrast-to-noise ratio were analyzed for fixed region of interest. Patient study included 23 patients with metallic fillings and metal implants. Traditional CT images and virtual monochromatic images were produced in a single scan, ensuring that the comparison can be made within the same patient and same location. Standard deviation and metal artefact index were analyzed for fixed region of interest. The phantom study and patient study showed that the metal artefacts caused by metallic dental fillings are well-suppressed by the virtual monochromatic imaging. Moreover, the improvements in virtual monochromatic imaging in terms of image quality are more pronounced for small dental fillings.. The noise increase in image slices without metallic objects is a side-effect of the virtual monochromatic images. Virtual monochromatic imaging by spectral cone beam CT reduces the metal artefact and improves the image contrast-to-noise ratio around dental metallic fillings. This kind of imaging would be recommended for patients with dental metallic fillings.

Two methods for reducing moving metal artifacts in cone-beam CT.

In image-guided radiation therapy, fiducial markers or clips are often used to determine the position of the tumor. These markers lead to streak artifacts in cone-beam CT (CBCT) scans. Standard inpainting-based metal artifact reduction (MAR) methods fail to remove these artifacts in cases of large motion. We propose two methods to effectively reduce artifacts caused by moving metal inserts. The first method (MMAR) utilizes a coarse metal segmentation in the image domain and a refined segmentation in the rawdata domain. After an initial reconstruction, metal is segmented and forward projected giving a coarse metal mask in the rawdata domain. Inside the coarse mask, metal is segmented by utilizing a 2D Sobel filter. Metal is removed by linear interpolation in the refined metal mask. The second method (MoCoMAR) utilizes a motion compensation (MoCo) algorithm [Med Phys. 2013;40:101913] that provides us with a motion-free volume (3D) or with a time series of motion-free volumes (4D). We then apply the normalized metal artifact reduction (NMAR) [Med Phys. 2010;37:5482-5493] to these MoCo volumes. Both methods were applied to three CBCT data sets of patients with metal inserts in the thorax or abdomen region and a 4D thorax simulation. The results were compared to volumes corrected by a standard MAR1 [Radiology. 1987;164:576-577]. MMAR and MoCoMAR were able to remove all artifacts caused by moving metal inserts for the patients and the simulation. Both new methods outperformed the standard MAR1, which was only able to remove artifacts caused by metal inserts with little or no motion. In this work, two new methods to remove artifacts caused by moving metal inserts are introduced. Both methods showed good results for a simulation and three patients. While the first method (MMAR) works without any prior knowledge, the second method (MoCoMAR) requires a respiratory signal for the MoCo step and is computationally more demanding and gives no benefit over MMAR, unless MoCo images are desired.

Comparison of methods for outlier identification in surface characterization

Raw data provided by measurement instruments like confocal microscopy often contains non-measured points and outliers. Ten statistical methods for outlier identification which can be implemented in the area of surface metrology are analysed and compared. These methods for outlier identification are introduced and their corresponding algorithms for data pre-processing before surface characterization are developed. Twenty-four Mat files were created based on two standard data sets provided by the National Institute of Standards and Technology. These files were assigned by four factors with two to three levels to represent all possible surface types. Based on processing the same series of contaminated data sets, the number of missed outliers, the difference of the height parameters, and the elapsed time by each method are compared. Algorithm efficiency, robustness, breakdown point, limitations, advantages, etc. are compared and analysed. Two of those ten methods were combined to know their potential. A type C1 spacing standard artefact was measured by 3D image confocal microscopy, and the data was processed by those algorithms. The difference of Sa and that of elapsed time are compared.

Microdebris Analysis from the Early Bronze Age Levels at Tell eṣ-Ṣâfi/Gath

Microdebris are the tiny remnants of activities that are not cleaned up after an activity is completed (fig. 1). Such activities are often archaeologically invisible with standard macrolevel artifact collection and analysis techniques. If microdebris are systematically and spatially collected across surfaces and different depositional contexts, their analysis can help guide excavation strategies (identification where such debris is located, which deposits are worth floating), identify activity areas, pest distributions, when, and which, rooms were used or abandoned, missing food sources that cannot be recovered through hand collections (plants, fish, and smaller remains), and so on (Rainville 2012; Steadman 1996; Rosen 1989; Weiner 2010). The utility of this approach is demonstrated with data from the Early Bronze Age excavations in Area E at Tell eṣ-Ṣâfi/Gath.

Effect of Stimulus Polarity on Physiological Spread of Excitation in Cochlear Implants.

Contemporary cochlear implants (CIs) use cathodic-leading, symmetrical, biphasic current pulses, despite a growing body of evidence that suggests anodic-leading pulses may be more effective at stimulating the auditory system. However, since much of this research on humans has used pseudomonophasic pulses or biphasic pulses with unusually long interphase gaps, the effects of stimulus polarity are unclear for clinically relevant (i.e., symmetric biphasic) stimuli. The purpose of this study was to examine the effects of stimulus polarity on basic characteristics of physiological spread-of-excitation (SOE) measures obtained with the electrically evoked compound action potential (ECAP) in CI recipients using clinically relevant stimuli. Using a within-subjects (repeated measures) design, we examined the differences in mean amplitude, peak electrode location, area under the curve, and spatial separation between SOE curves obtained with anodic- and cathodic-leading symmetrical, biphasic pulses. Fifteen CI recipients (ages 13-77) participated in this study. All were users of Cochlear Ltd. devices. SOE functions were obtained using the standard forward-masking artifact reduction method. Probe electrodes were 5-18, and they were stimulated at an 8 (of 10) loudness rating ("loud"). Outcome measures (mean amplitude, peak electrode location, curve area, and spatial separation) for each polarity were compared within subjects. Anodic-leading current pulses produced ECAPs with larger average amplitudes, greater curve area, and less spatial separation between SOE patterns compared with that for cathodic-leading pulses. There was no effect of polarity on peak electrode location. These results indicate that for equal current levels, the anodic-leading polarity produces broader excitation patterns compared with cathodic-leading pulses, which reduces the spatial separation between functions. This result is likely due to preferential stimulation of the central axon. Further research is needed to determine whether SOE patterns obtained with anodic-leading pulses better predict pitch discrimination.