A novel method for geometric quality assurance of rock joint replicas in direct shear testing-Part 1:Derivation of quality assurance parameters and geometric reproducibility

Since each rock joint is unique by nature,the utilization of replicas in direct shear testing is required to carry out experimental parameter studies.However,information about the ability of the replicas to simulate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.With the aim to facilitate generation of high-quality direct shear test data from replicas,a novel component in the testing procedure is introduced by presenting two parameters for geometric quality assurance.The parameters are derived from surface comparisons of three-dimensional(3D)scanning data of the rock joint and its replicas.The first parameter,smf,captures morphological deviations between the replica and the rock joint surfaces.smf is derived as the standard deviation of the deviations between the coordinate points of the replica and the rock joint.Four sources of errors introduced in the replica manufacturing process employed in this study could be identified.These errors could be minimized,yielding replicas with smf
0.06 mm.The second parameter is a vector,VHp100,which describes deviations with respect to the shear direction.It is the projection of the 100 mm long normal vector of the best-fit plane of the replica joint surface to the corresponding plane of the rock joint.

VHp100

was found to be less than or equal to 0.36 mm in this study.Application of these two geometric quality assurance parameters demonstrates that it is possible to manufacture replicas with high geometric similarity to the rock joint.In a subsequent paper(part 2),smf and VHp100 are incorporated in a novel quality assurance method,in which the parameters shall be evaluated prior to direct shear testing.Replicas having parameter values below established thresholds shall have a known and narrow dispersion and imitate the shear mechanical behavior of the rock joint.

Reproducibility of Test-Retest Cortical Evoked Responses in Patients with Focal Epilepsy

This exploratory study examined the short-term reliability of cortical auditory evoked responses recorded from patients undergoing whole-head scalp elec-troencephalography (EEG) monitoring to assess their candidacy for surgical treatment of intractable focal seizures. Participants were 26 patients with either left-sided (N = 13) or right-sided focal epilepsy admitted to the hospital for continuous scalp EEG monitoring for possible epilepsy surgery planning. Cortical auditory evoked responses were recorded over multiple days from scalp EEG electrodes using tones presented binaurally in a passive oddball paradigm. Test-retest intervals were 1 - 6 days (mean 2 days). Test-retest reproducibility of the auditory N1 response was assessed by paired t-test (latency) and cross-correlation analysis (amplitude and latency). Within-patient comparisons of test-retest auditory N1 peak latencies revealed no significant differences. The cross-correlation coefficient indicated high test-retest reproducibility of the N1 waveform (rcc = 0.88). Seizure lateralization was not associated with asymmetries in N1 latencies or amplitudes. An N1 amplitude asymmetry (right > left) in patients with focal seizures originating from the left hemisphere was initially observed, but disappeared when patients with prior resections were excluded, suggesting that reduced left hemisphere tissue volume may account for the smaller N1 amplitudes. Test-retest reliability of cortical auditory evoked responses was unexpectedly high in patients with focal epilepsy regardless of seizure lateralization or localization. These findings challenge the view that neural responses are intrinsically unstable (unreliable) in patients with seizures.

Computational Reproducibility Within Prognostics and Health Management

Scientific research frequently involves the use of computational tools and methods.Providing thorough documentation,open-source code,and data–the creation of reproducible computational research(RCR)–helps others understand a researcher’s work.In this study,we investigate the state of reproducible computational research,broadly,and from within the field of prognostics and health management(PHM).In a text mining survey of more than 300 articles,we show that fewer than 1%of PHM researchers make their code and data available to others.To promote the RCR further,our work also highlights several personal benefits for those engaged in the practice.Finally,we introduce an open-source software tool,called PyPHM,to assist PHM researchers in accessing and preprocessing common industrial datasets.

The calculation of the Reproducibility Error in the technological system with the clamp on the gas power

The paper deduced a calculation formula by the classic control theory on the Reproducibility Error of parts processing in the technology system,the flexible clamp system, with the clamping device on the gas power,and analyzed its influencing factor with examples,the Reproducibility Error law:\ The larger the diameter of the cylinder,the smaller the error; the slower the tool speed,(k values smaller),the smaller the error.

Quantitative diffusion-weighted magnetic resonance enterography in ileal Crohn’s disease: A systematic analysis of intra and interobserver reproducibility

BACKGROUND Magnetic resonance enterography(MRE) is increasingly attractive as a noninvasive and radiation-free tool for assessing Crohn’s disease(CD). Diffusionweighted imaging(DWI) is recommended as an optional MRE sequence for CD by the European Society of Gastrointestinal and Abdominal Radiology, and has shown a superb potential as a quantitative modality for bowel inflammation evaluation. However, the measurement reproducibility of quantitative DWI analysis in MRE has not been ascertained so far. To facilitate the application of quantitative diffusion-weighted MRE in the clinical routine, systematic investigations of the intra and interobserver reproducibility of DWI quantitative parameters should be performed.AIM To evaluate the intra and interobserver reproducibility of quantitative analysis for diffusion-weighted MRE(DW-MRE) in ileal CD.METHODS Forty-four subjects(21 with CD and 23 control subjects) who underwent ileocolonoscopy and DW-MRE(b = 800 s/mm2) within one week were included.Two radiologists independently measured apparent diffusion coefficients(ADC)of the terminal ileum and signal intensity ratio(SR) of the terminal ileum to ipsilateral psoas muscle on DWI images(b = 800 s/mm2). Between-and withinreader agreements were assessed using intraclass correlation coefficients(ICC),coefficients of variation(CoV), and 95% limits of agreement of Bland-Altman plots(BA-LA LoA). Diagnostic performances of ADC and SR for identifying inflamed terminal ileum from the normal were evaluated by receiver operating characteristic(ROC) curve analysis.RESULTS There were no significant differences in ADC or SR values between the two sessions or between the two radiologists either in the CD or control group(paired t-test, P > 0.05). The intra and interobserver reproducibility of ADC(ICC: 0.952-0.984;CoV: 3.73-6.28%;BA-LA LoA: ±11.27% to ±15.88%) and SR(ICC: 0.969-0.989;CoV: 3.51%-4.64%;BA-LA LoA: ±10.62% to ±15.45%) was excellent for CD.Agreement of ADC measurements was slightly less in control subjects(ICC:0.641-0.736;CoV: 10.47%-11.43%;BA-LA LoA: ± 26.59% to ± 30.83%). SR of normal terminal ileum demonstrated high intra and interobserver reproducibility(ICC: 0.944-0.974;CoV: 3.73%-6.28%;BA-LA LoA: ± 18.58% to ± 24.43%). ADC and SR of two readers had outstanding diagnostic efficiencies(area under the ROC curve: 0.923-0.988).CONCLUSION Quantitative parameters derived from DW-MRE have good to excellent intra and interobserver agreements with high diagnostic accuracy, and can serve as robust and efficient quantitative biomarkers for CD evaluation.

Reproducibility of optical quality parameters measured at objective and subjective best focuses in a doublepass system

AIMTo evaluate intra-session repeatability and reproducibility of optical quality parameters measured at objective and subjective best focuses in a double-pass system.METHODSThirty Chinese healthy adults (19 to 40 years old) meeting our inclusion criterion were enrolled in the study. After a basic eye examination, two methods of optical quality measurement, based on subjective and objective best focuses were performed using the Optical Quality Analysis System (OQAS) with an artificial pupil diameter of 4.0 mm.RESULTSWith each method, three consecutive measurements of the following parameters: the modulation transfer function cutoff frequency (MTFcutoff), the Strehl2D ratio, the OQAS values (OVs) at contrasts of 100%, 20%, 9% and the objective scatter index (OSI) were performed by an experienced examiner. The repeatability of each method was evaluated by the repeatability limit (RL) and the coefficient of repeatability (COR). Reproducibility of the two methods was evaluated by intra-class correlation coefficient (ICC) and the 95% limits of agreement (Bland and Altman analysis). Thirty subjects, seven females and twenty three males, of whom 15 right eyes and 15 left eyes were selected randomly for recruitment in the study. The RLs (percentage) for the six parameters measured at objective focus and subjective focus ranged from 8.44% to 15.13% and 10.85% to 16.26%, respectively. The CORs for the two measurement methods ranged from 8.27% to 14.83% and 10.63% to 15.93%, respectively. With regard to reproducibility, the ICCs for the six parameters of OQAS ranged from 0.024 to 0.276. The 95% limits of agreement obtained for the six parameters (in comparison of the two methods) ranged from -0.57 to 42.18 (MTFcutoff), -0.01 to 0.23 (Strehl2D ratio), -0.02 to 1.40 (OV100%), -0.10 to 1.75 (OV20%), -0.14 to 1.80 (OV9%) and -1.46 to 0.18 (OSI).CONCLUSIONMeasurements provided by OQAS with either method showed a good repeatability. However, the results obtained from the two different measurement methods showed a poor reproducibility. These findings suggest that it might be best to evaluate patients' optical quality by OQAS using the best focus as chosen automatically by the instrument.

Evaluation of Glycosaminoglycan in the Lumbar Disc Using Chemical Exchange Saturation Transfer MR at 3.0 Tesla:Reproducibility and Correlation with Disc Degeneration

Objective This study aims to explore the clinical applicability and relevance of giycosaminoglycan Chemical Exchange Saturation Transfer （gagCEST） for intervertebral disc. Methods 25 subjects ranging in age from 24 yrs to 74 yrs were enrolled, gagCEST was acquired using a single-slice TSE sequence on a 3T. Saturation used a continuous rectangular RF pulse with B1=0.8 I^T and a fixed duration time =1100 ms. Sagittal image was obtained firstly without saturation pulse, and then saturated images were acquired at 52 offsets ranging from ＋0.i25 to ＋_7 parts per million （ppm）. MR T2 relaxivity map was acquired at the identical location. Six subjects were scanned twice to assess scan-rescan reproducibility. Results GagCEST intraclass correlation coefficient （ICC） of six subjects was 0.759 for nucleus pulposus （NP） and 0.508 for annulus fibrosus （AF）. Bland-Altman plots showed NP had a mean difference of 0.10% （95% limits of agreement： -3.02% to 3.22%）; while that of AF was 0.34% （95% limits of agreement： -2.28% to 2.95%）. For the 25 subjects, gag CEST in NP decreased as disc degeneration increased, with a similar trend to T2 relaxivity. Gag CEST of AF showed a better correlation with disc degeneration than T2 relaxivity. Conclusion GagCEST in NP and AF decreased as disc degeneration increased, while gagCEST in AF showed a better correlation than T2 relaxivity.

Repeatability and Reproducibility of Quantitative Assessment of the Retinal Microvasculature Using Optical Coherence Tomography Angiography Based on Optical Microangiography

Objective The aim of this study was to determine the repeatability and reproducibility of optical coherence tomography angiography（OCTA） based on optical microangiography（OMAG） measurements of macular vessels in normal eyes. Methods In this prospective cohort study, 40 eyes of 40 healthy volunteers underwent repeated OCTA（Cirrus HD-OCT 5000 angiography system, Carl Zeiss Meditec, Inc.） scans on two separate visit days. On each visit day, the eyes were scanned three times. The following parameters were used to quantitatively describe the OCTA images of the superficial vascular network： vessel area density（VAD）, vessel skeleton density（VSD）, vessel diameter index（VDI）, vessel perimeter index（VPI）, vessel complexity index（VCI）, flux, and foveal avascular zone（FAZ）. Coefficient of variation（CV） and intraclass correlation coefficient（ICC） were calculated for evaluating intravisit and intervisit repeatability, as well as interobserver reproducibility. Results The measurements showed high repeatability [CVs ≤ 4.2%（intravisit） and ≤ 4.6%（intervisit）] and interobserver reproducibility（ICCs ≥ 0.923） for all parameters. Conclusion This study demonstrated good repeatability and reproducibility of OCTA based on OMAG for the measurement of superficial vessel parameters in normal eyes.

Reproducibility and Validity of a Chinese Food Frequency Questionnaire

Objectives This study was design to develop a semi-quantitative Chinese Food Frequency Questionnaire （FFQ） and to conduct a validation study for the questionnaire. Methods Based on the survey experience in recent years, a new Chinese food frequency questionnaire （FFQ） with 149 items in 17 food categories was developed. A validation study on this new FFQ was conducted in Jiangsu and Beijing of China between 1999 and 2001. The period of study covered 1 year and the FFQ was validated by comparing with data obtained by a six repeated 24-hour recalls for 3 consecutive days, or a totally 18-day 24- hour recall throughout the year. A total of 271 healthy adult subjects were enrolled in the study. Food and nutrient intakes measured by the 18-day dietary recalls and food frequency questionnaires （FFQs） were computed in the National Institute for Nutrition and Food Safety, China CDC using the existing nutrition database. The average daily intake of foods and nutrients over the 18-day recall was used to compare with FFQ1 and FFQ2, which was conducted at the beginning and the end of the year, respectively. All statistical analyses were carried out using SAS software version 6.12.

Short- and medium-term reproducibility of gastric emptying of a solid meal determined by a low dose of ^(13)C-octanoic acid and nondispersive isotope-selective infrared spectrometry

AIM： To evaluate the reproducibility of a modified 13^C breath test-based measurement of solid phase gastric emptying （GE） within the frames of a simple-repeated measure study protocol. METHODS： Twelve healthy subjects （6 females and 6 males, mean age 24.9＋0.7 years） were recruited to undergo three identical GE examinations. In six subjects the first two examinations were performed 2 d apart, and the third session was carried out at a median interval of 19.5 d （range 18 - 20 d） from the second one. In another six subjects the first two measurements were taken 20 d apart （median, range： 17-23 d）, whereas the third session took place 2 d after the second one. Probes of expiratory air collected before and during six hours after intake of a solid meal （378 kcal） labelled with 75 μL （68 mg） 13^C-octanoic acid, were measured for 13^CO2 enrichment with the nondispersive isotopeselective infrared spectrometry NDIRS apparatus. RESULTS： Taking coefficients of variation for paired examinations into account, the short-term reproducibility of the GE measurement was slightly but not significantly better than the medium-term one： 7.7% and 11.2% for the lag phase （T-Lag）, 7.3% and 10.9% for the gastric half emptying time （T1/2）. The least differences in GE parameters detectable at P= 0.05 level in the 12 paired examinations were 9.6 and 15.6 min for T-Lag, 11.6 and 19.7 min for T1/2 by a two-day or two to three-week time gap, respectively CONCLUSION： The low-cost modification of the breath test involving a lower dose of 13^C-octanoic acid and NDIRS, renders good short- and medium-term reproducibility, as well as sensitivity of the measurement of gastric emptying of solids.

Diffusion-weighted magnetic resonance imaging in cancer: Reported apparent diffusion coefficients,in-vitro and invivo reproducibility

There is considerable disparity in the published apparent diffusion coefficient(ADC) values across different anatomies. Institutions are increasingly assessing repeatability and reproducibility of the derived ADC to determine its variation,which could potentially be used as an indicator in determining tumour aggressiveness or assessing tumour response. In this manuscript,a review of selected articles published to date in healthy extracranial body diffusion-weighted magnetic resonance imaging is presented,detailing reported ADC values and discussing their variation across different studies. In total 115 studies were selected including 28 for liver parenchyma,15 for kidney(renal parenchyma),14 for spleen,13 for pancreatic body,6 for gallbladder,13 for prostate,13 for uterus(endometrium,myometrium,cervix) and 13 for fibroglandular breast tissue. Median ADC values in selected studies were found to be 1.28 × 10-3 mm2/s in liver,1.94 × 10-3 mm2/s in kidney,1.60 × 10-3 mm2/s in pancreatic body,0.85 × 10-3 mm2/s in spleen,2.73 × 10-3 mm2/s in gallbladder,1.64 × 10-3 mm2/s and 1.31 × 10-3 mm2/s in prostate peripheral zone and central gland respectively(combined median value of 1.54×10-3 mm2/s),1.44 × 10-3 mm2/s in endometrium,1.53 × 10-3 mm2/s in myometrium,1.71 × 10-3 mm2/s in cervix and 1.92 × 10-3 mm2/s in breast. In addition,six phantom studies and thirteen in vivo studies were summarized to compare repeatability and reproducibility of the measured ADC. All selected phantom studies demonstrated lower intra-scanner and inter-scanner variation compared to in vivo studies. Based on the findings of this manuscript,it is recommended that protocols need to be optimised for the body part studied and that system-induced variability must be established using a standardized phantom in any clinical study. Reproducibility of the measured ADC must also be assessed in a volunteer population,as variations are far more significant in vivo compared with phantom studies.

Reproducibility of peripapillary retinal nerve fiber layer thickness measurements with Cirrus HD-OCT in glaucomatous eyes

AIM: To assess the reproducibility of Cirrus high-definition optical coherence tomography(HD-OCT; Carl Zeiss Meditec, Dublin, CA, USA) for analysis of peripapillary retinal nerve fiber layer(RNFL) thickness in glaucomatous eyesMETHODS: Forty-five eyes(one eye from each glaucomatous patient) were imaged with Cirrus HD-OCT.Each eye was imaged three times by two separate operators. Intraclass correlation coefficient(ICC),coefficient of variation(CV), and test-retest variability were evaluated for both intraobserver and interobsever measurementsRESULTS: In intraobserver measurements, the average RNFL thickness ICC was 0.983. CV and test-retest variability were 2.3% and 4.4 μm respectively. In quadrants ICC ranged from 0.886 to 0.956, the lowest associated with nasal quadrant and CV ranged from 3.6%to 7.7%. In interobsever measurements, the average RNFL thickness ICC was 0.979. CV and test-retest variability were 2.4% and 4.5 μm respectively. In quadrants ICC ranged from 0.886 to 0.957, the lowest associated with nasal quadrant and CV ranged from 3.8%to 8.6%.CONCLUSION: The reproducibility of Cirrus OCT for RNFL thickness is sufficiently good to be useful clinically as a measure of glaucoma progression.

Reproducibility of macular perfusion parameters in non-proliferative diabetic retinopathy patients by two different OCTA sweep modes

·AIM:To assess the reproducibility of macular perfusion parameters in non-proliferative diabetic retinopathy(NPDR)patients measured by different examiners and two different sweep modes of optical coherence tomography angiography(OCTA).·METHODS:Ninety-eight(98 eyes)patients with NPDR were included in this study.All participates were performed three times using Cirrus OCTA with Angiography 3×3 mm^(2)and 6×6 mm^(2)sweep mode by two examiners.The macular foveal avascular zone(FAZ)and vessel density(VD)in the superficial retinal layer(SRL)were measured.The reproducibility of the measurements was evaluated with intraclass correlation coefficients(ICC)and coefficient of variation(CoV).·RESULTS:The intra-mode ICCs of Angiography 3×3 mm^(2)and 6×6 mm^(2)sweep mode were 0.957 to 0.959 and 0.964 to 0.977,respectively;and the inter-mode ICCs were 0.962 to 0.970.The intra-examiner ICCs of macular perfusion parameters were>0.950;and the inter-examiner ICCs were0.928 to 0.969.All CoVs were<1.0%.·CONCLUSION:Cirrus OCTA can measure macular perfusion parameters in NPDR patients with excellent reproducibility.The measurements of FAZ and VD in the SRL determined by Angiography 3×3 mm^(2)and 6×6 mm^(2)sweep mode are highly consistent and both sweep modes are suitable for macular perfusion parameters measurement.

^(13)C-methacetin breath test reproducibility study reveals persistent CYP1A2 stimulation on repeat examinations

AIM: To find the most reproducible quantitative parameter of a standard 13C-methacetin breath test (13C-MBT). METHODS: Twenty healthy volunteers (10 female, 10 male) underwent the 13C-MBT after intake of 75 mg 13C-methacetin p.o. on three occasions. Short-and medium-term reproducibility was assessed with paired examinations taken at an interval of 2 and 18 d (medians), respectively. RESULTS: The reproducibility of the 1-h cumulative 13C recovery (AUC0-60), characterized by a coefficient of variation of 10%, appeared to be considerably better than the reproducibility of the maximum momentary 13C recovery or the time of reaching it. Remarkably, as opposed to the short gap between consecutive examinations, the capacity of the liver to handle 13C-methacetin increased slightly but statistically significantly when a repeat dose was administered after two to three weeks.Regarding the AUC0-60, the magnitude of this fixed bias amounted to 7.5%. Neither the time gap between the repeat examinations nor the gender of the subjects affected the 13C-MBT reproducibility. CONCLUSION: 13C-MBT is most reproducibly quantified by the cumulative 13C recovery, but the exactitude thereof may be modestly affected by persistent stimulation of CYP1A2 on repeat examinations.

The role of the gut microbiota on animal model reproducibility

The gut microbiota is composed of approximately 10^(10)-10^(14) cells, including fungi,bacteria, archaea, protozoa, viruses, and bacteriophages; their genes and their various metabolites were found throughout the gastrointestinal tract. It has co-evolved with each species to assist with day to day bodily functions, such as digestion,metabolism of xenobiotics, development of mucosal immunity and immunomodulation, and protection against invading pathogens. Because of the significant beneficial impact that gut microbiota may have, there is interest in learning more about it and translating these findings into clinical therapies. Results from recent studies characterizing the gut microbiota of various species have demonstrated the range of influences that may affect gut microbiota diversity, including animal strain, obesity, types of enrichment used, bedding and housing methods, treatment with antimicrobials,vendor source, specific animal housing, diet, and intercurrent disease. Relatively little is known about the functional consequences of alterations of the gut microbiota and exactly how changes in richness and diversity of the microbiota translate into changes in health and susceptibility to disease. Furthermore, questions have been raised as to whether germ-free or even ultraclean, barrier-raised mice are relevant models of human disease, given their significantly reduced gut microbiota diversity and complexity compared with conventionally housed mice. In addition, evidence suggests that the specific anatomical location selected for assessing the gut microbiota has a highly significant effect on study outcomes, in that bacterial phyla change significantly along the gastrointestinal tract. This paper will explore animal model reproducibility in light of this information about the gut microbiota.

Monitoring recovery by physical therapists using the FIM scale during rehabilitation programs: An inter-rater and intra-rater reproducibility study

Our aim was to evaluate the reproducibility of the Functional Independence Measure (FIM) scale when assessed by physical therapists in the routine setting of a Rehabilitation Hospital. We included a consecutive series of patients with spinal cord or cerebral lesions. Each of the 50 selected patients was evaluated by two of the 5 experienced physical therapists participating in the study. The degree of inter-rater and intrarater agreement was measured by a weighted k statistic, k for perfect agreement, and k for the agreement with tolerance. The weighted k index for inter-rater agreement on the FIM score was in the almost perfect range (k 0.87;95% CI = 0.79 - 0.95), but a 20-point tolerance was necessary to reach a k value of 0.81 (95% CI = 0.66 - 0.95). Agreement was substantial or almost perfect for most subscales, but the k index with 1-point tolerance reached the almost perfect rating for comprehension only. For intra-rater agreement, weighted k index was in the almost perfect range for the FIM score and for all subscales;kappa index reached the almost perfect range with a 4-point tolerance for FIM score and with 1-point of tolerance for all subscales except interpersonal relations. FIM is useful to monitor patient improvement during rehabilitation treatment, mostly when assessed by the same physical therapist.

Discussion on Repeatability and Reproducibility of Measuring Method in ISO 5725

This paper discusses the repeatability and reproducibility of the international standard of ISO 5725：1994 Accuracy （trueness and precision） of Measurement Methods and Results, two concepts of ＂inter-laboratory variance＂ and ＂reproducible variance＂ in the standard are questioned, the corresponding improvement idea is introduced, which aims to make this standard more rigorous, scientific and logical.

A Sputtering Deposition of Al Enhances the Output Reproducibility in a Conducting Rubber Force Sensor

Compressive force sensors or pressure sensors are indispensable to tactile sensors in humanoid robots. It is investigated that low-cost electro-conducting rubber sheets are applied to the force sensor, of which the biggest problem is its poor reproducibility. It was found that the aluminum deposition by a vacuum evaporation method shows excellent characteristics but suffers deterioration by a radiation heating effect. The aluminum electrode was deposited by a sputtering method, known to have an advantage of a low-temperature method, and the reproducibility of the output was improved.

Reproducibility of deposition and industrial applications of stable superhard nanocomposites

After a brief introduction regarding the different approaches to superhard coatings we shall concentrate on the problem of the reproducibility of the deposition of superhard and thermally very stable nanocomposites according to the design principle published by Veprek and Reiprich in 1995. It will be shown that either the choice of inappropriate deposition conditions, in contradiction to our design principle, or impurities in the coatings are the reason for the lack of reproducibility of our earlier results by many other workers. We shall also briefly summarize the recent industrial applications.

Helvacioglu reproducibility index: a new algorithm to evaluate the effects of misalignments on the measurements of retinal nerve fiber layer by spectraldomain OCT

AIMTo evaluate the effect of misalignment on the measurements of retinal nerve fiber layer (RNFL) by spectral-domain optical coherence tomography (OCT).METHODSA total of 42 eyes from 21 healthy young subjects underwent RNFL measurements with RTVue spectral-domain OCT (Optovue Inc., Fremont, California, USA). Two baseline measurements with perfectly aligned central circle to the borders of the optic nerve and four misaligned measurements which were misaligned towards to four quadrants were taken. The differences in RNFL between the baseline and misaligned measurements were analyzed with a new algorithm called Helvacioglu reproducibility index (HRI) which is designed to measure the reproducibility of the scans by evaluating the RNFL changes in the four main quadrants.RESULTSThe average RNFL scores of the first two baseline measurements have good correlation (c=0.930) and good reproducibility scores (0.15&#x000b1;0.07). Superior misaligned measurements had significantly lower superior quadrant score and higher inferior quadrant score, similar nasal and little higher temporal scores (P1, P2&#x0003c;0.001, P3=0.553, P4=0.001). Inferior misaligned measurements had significantly higher superior quadrant score and lower inferior quadrant score with similar temporal and little lower nasal scores (P1, P2&#x0003c;0.001, P3=0.315, P4=0.016). Nasal misaligned measurements had significantly higher temporal quadrant score and lower nasal quadrant score with little lower superior and inferior scores (P1, P2, P4&#x0003c;0.001, P3=0.005). Temporal misaligned measurements had significantly higher nasal quadrant score and lower temporal quadrant score with similar superior and little higher inferior scores (P1, P2&#x0003c;0.001, P3=0.943, P4=0.001).CONCLUSIONGood alignment of the central circle to the borders of optic nerve is crucial to have correct and repeatable RNFL measurements. Misalignment to a quadrant resulted in falsely low readings at that quadrant and falsely high readings at the opposite quadrant.