Bland-Altman Coefficient Of Repeatability Research Articles

Test-retest repeatability in macular retinal oximetry

ABSTRACT Clinical relevance Evaluation of retinal macular oxygen saturation in healthy controls can aid in understanding the pathological changes seen in similar locations of those with vascular diseases like diabetes. Background The aim of this study was to determine the test-retest repeatability of localised retinal oximetry measurements in the macula on the Zilia Oximeter within healthy subjects of different races, 18–40 years old. Oxygen saturation was measured between three time points within the same locations of the right eye. Methods Twenty seven subjects were included (aged 26.3 ± 3.6 years). All were confirmed to have healthy retinas and at least 6/9 vision. Oximetry measurements were taken using the Zilia to acquire local oxygen saturation measurements (300 µm diameter) at four points 3.1 degrees from the fovea in the superior/temporal, superior/nasal, inferior/temporal, and inferior/nasal locations. Oximetry measurements were taken twice on the same day 20 minutes apart and then again 1–2 weeks later. Oximetry data was analysed with intraclass correlation between visits. To assess intrasubject repeatability, the Bland-Altman repeatability coefficient and coefficient of variation were calculated. Results Average Intraclass correlation for the three acquisition times of the right eye was 0.78. The averaged intrasubject repeatability coefficient for the three acquisition times was 8.4. The averaged coefficient of variation was 5.4%. Conclusion The Zilia oximeter has good macular test-retest repeatability; however, multiple measurements may be needed to ensure accuracy.

Test-retest Reliability of the qReading Method in Normally Sighted Young Adults.

We recently developed a novel Bayesian adaptive method, qReading, to measure reading function. The qReading method has both the efficiency and excellent test-retest reliability in normally sighted young adults to make it an excellent candidate for future studies of its value in diagnosis and longitudinal evaluation of treatment and/or rehabilitation outcomes. A novel Bayesian adaptive method, qReading, was recently developed to measure reading function. Here we performed a systematic assessment of the test-retest reliability of the qReading method. The variability of five repeated measurements of the reading curve was examined in two settings: within session and between sessions. For the within-session design, we considered two subpopulations: naive observers and experienced observers. All observers were normally sighted young adults. For each set of data, in addition to examining the intrinsic precision of the qReading method (the half width of the credible interval of the posterior distribution of the estimated performance), we computed four metrics to assess repeatability: standard deviation, Bland-Altman coefficient of repeatability, correlation coefficient, and Fractional Rank Precision. Extrinsic factors such as observer, time interval between repeated measures, and observer experience all contribute to the variation across measurements. Nevertheless, the four metrics consistently show that the variability across five repeated measurements is small for each set of data. This is true even without taking learning effects into account (standard deviations, ≤0.092 log10 units; Bland-Altman coefficient of repeatability, ≤0.15 (log10)2 units; correlation coefficient, ≥0.91; and Fractional Rank Precision, ≥0.81). The qReading method has excellent test-retest reliability in normally sighted young adults.

Reliable quantification of myocardial sympathetic innervation and regional denervation using [11C]meta-hydroxyephedrine PET.

Cardiac sympathetic nervous system (SNS) dysfunction is associated with poor prognosis in chronic heart failure patients. This study characterized the reproducibility and repeatability of [11C]meta-hydroxyephedrine (HED) positron emission tomography (PET) quantification of cardiac SNS innervation, regional denervation, and myocardial blood flow (MBF). Dynamic HED PET-CT scans were performed 47 ± 22days apart in 20 patients with stable heart failure and reduced ejection fraction. Three observers, blinded to clinical data, used FlowQuant® to evaluate the test-retest repeatability and inter- and intra-observer reproducibility of HED tracer uptake and clearance rates to measure global (LV-mean) retention index (RI), volume of distribution (VT), and MBF. Values were also compared with and without regional partial-volume correction. Regional denervation was quantified as %LV defect size of values < 75% of the LV-maximum. Test-retest repeatability and observer reproducibility were evaluated using intra-class-correlation (ICC) and Bland-Altman coefficient of repeatability (NPC). Intra- and inter-observer correlations of both VT and RI were excellent (ICC = 0.93-0.99). Observer reproducibility (NPC = 3-13%) was lower than test-retest repeatability (NPC = 12-61%). Both regional (%LV defect size) and global (LV-mean) measures of sympathetic innervation were more repeatable using the simple RI model compared to VT (NPC = 12% vs. 19% and 30% vs. 54%). Using either model, quantification of regional denervation (defect size) was consistently more reliable than the global LV-mean values of RI or VT. Regional partial-volume correction degraded repeatability of both the global and regional VT measures by 2-12%. Test-retest repeatability of MBF estimation was relatively poor (NPC = 30-61%) compared with the RI. Quantitative measures of global and regional SNS innervation were most repeatable using the simple RI method of analysis compared with the more complex VT. Observer variability was significantly lower than the test-retest repeatability using a highly automated analysis program. These results support the use of the simple RI method for reliable analysis of HED PET images in clinical research studies for future evaluation of new therapies and for risk stratification in patients with heart failure.

Concurrent validity and reliability of a low-cost gait analysis system for assessment of spatiotemporal gait parameters.

To determine the concurrent validity and reliability of a low-cost spatiotemporal gait analysis system for clinical use in rehabilitation medicine. Cross-sectional study. Thirty-three healthy adults. The spatiotemporal gait analysis system consists of a video camera placed perpendicular to a 10-m walkway and calibrated for spatial reference. The conditions evaluated in this study were: barefoot walking at comfortable and slow speed, toe and shod walking using a stationary camera setup and barefoot walking at comfortable speed using a moving camera setup. The GAITRite® was used as reference. High intraclass correlation coefficients (ICC≥ 0.97; 95% lower limit confidence intervals (95% CIs) ≥ 0.77) were found between systems for step and stride length, and step, stance and stride time, across setups and conditions. Standard error of measurement and Bland-Altman repeatability coefficients were ≤ 2.4% and ≤ 6.3%, respectively. A minimum of 4 footsteps was required to obtain ICC >0.90 and coefficient of variation < 10%. For double support and swing time, ICCs were generally low (ICC≥ 0.21). Inter-rater reliability was excellent for step length, step and stance time (ICC≥ 0.94; lower limit 95% CIs ≥ 0.86). The spatiotemporal gait analysis system is valid and reliable for assessing spatiotemporal parameters in different walking conditions. However, the validity of double support and swing time could not be confirmed.

Blood volume measurement using cardiovascular magnetic resonance and ferumoxytol: preclinical validation

BackgroundThe hallmark of heart failure is increased blood volume. Quantitative blood volume measures are not conveniently available and are not tested in heart failure management. We assess ferumoxytol, a marketed parenteral iron supplement having a long intravascular half-life, to measure the blood volume with cardiovascular magnetic resonance (CMR).MethodsSwine were administered 0.7 mg/kg ferumoxytol and blood pool T1 was measured repeatedly for an hour to characterize contrast agent extraction and subsequent effect on Vblood estimates. We compared CMR blood volume with a standard carbon monoxide rebreathing method. We then evaluated three abbreviated acquisition protocols for bias and precision.ResultsMean plasma volume estimated by ferumoxytol was 61.9 ± 4.3 ml/kg. After adjustment for hematocrit the resultant mean blood volume was 88.1 ± 9.4 ml/kg, which agreed with carbon monoxide measures (91.1 ± 18.9 ml/kg). Repeated measurements yielded a coefficient of variation of 6.9%, and Bland-Altman repeatability coefficient of 14%. The blood volume estimates with abbreviated protocols yielded small biases (mean differences between 0.01–0.06 L) and strong correlations (r2 between 0.97–0.99) to the reference values indicating clinical feasibility.ConclusionsIn this swine model, ferumoxytol CMR accurately measures plasma volume, and with correction for hematocrit, blood volume. Abbreviated protocols can be added to diagnostic CMR examination for heart failure within 8 min.

New Precision Metrics for Contrast Sensitivity Testing.

Visual sensitivity is comprehensively described by the contrast sensitivity function (CSF), but current routine clinical care does not include its assessment because of the time-consuming need to estimate thresholds for a large number of spatial frequencies. The quick CSF method, however, dramatically reduces testing times by using a Bayesian information maximization rule. We evaluate the test-retest variability of a tablet-based quick CSF implementation in a study with 100 subjects who repeatedly assessed their vision with and without optical correction. We first discuss two commonly used measures of repeatability, intraclass correlation and the Bland-Altman Coefficient of Repeatability, and show that they are vulnerable to artifacts. Instead, we propose to formulate precision as an information retrieval task: from all repeat test scores, can we retrieve a certain individual based on their first test score? We then use rank-based analyses such as mean average precision as a better measure to compare different test metrics, and show that the highest test-retest precision is achieved using a summary statistic, the area under the log CSF (AULCSF). This demonstrates the benefit of assessment of the whole CSF compared to sensitivity at individual spatial frequencies only. AULCSF also yields best discrimination performance (99.2%) between measurements that were taken with and without glasses, respectively, even better than CSF Acuity. The tablet-based quick CSF thus enables the rapid and reliable home monitoring of visual function, which has the potential to improve early diagnosis and treatment of ophthalmic pathologies such as diabetic retinopathy or age-related macular degeneration.

MR Enterography Assessment of Bowel Inflammation Severity in Crohn Disease Using the MR Index of Activity Score: Modifying Roles of DWI and Effects of Contrast Phases.

The purpose of this article is to appraise the use of the MR index of activity (MaRIA) score in evaluating Crohn disease (CD) on present-day MR enterography images, with an emphasis on determining the modifying roles of DWI and the effects of different contrast enhancement phases. Fifty patients prospectively underwent MR enterography, including DWI and enteric and portal phase scans, and ileocolonoscopy with segmental CD endoscopic index of severity (CDEIS) scoring within a week. Thirty-nine terminal ilea and 40 right-sided colons (mean [± SD] segmental CDEIS score, 14.3 ± 12.1) from 42 patients with CD (mean age, 27 ± 6.2 years) were finally analyzed by three independent readers. Original and modified (ulcer replaced with DWI grade) MaRIA scores were compared regarding their correlation with segmental CDEIS score, accuracy in diagnosing active (segmental CDEIS score ≥ 3) and severe (segmental CDEIS score ≥ 12) inflammation, and interobserver reproducibility. The primary analysis used portal phase data, and the agreement between portal and enteric phase scores was analyzed. MaRIA and modified MaRIA scores correlated similarly with CDEIS scores (r = 0.737 and 0.742; p = 0.387) and did not significantly differ in terms of AUC values for the diagnosis of active (0.909 and 0.903; p = 0.571) or severe (0.907 and 0.892; p = 0.443) inflammation. The intraclass correlation coefficient was significantly higher for modified MaRIA than for MaRIA (0.845 and 0.701; p < 0.001). The mean difference between portal and enteric phase scores (i.e., portal minus enteric) was 0.33-0.36 score points for individual readers, and the Bland-Altman repeatability coefficient was 0.9-1.42 score points. Interobserver reproducibility in evaluating the severity of bowel inflammation in CD using the MaRIA score can be improved by modification with DWI. MaRIA scoring provides steady results across enteric and portal phases.

Preliminary validation of the Rating of Outcome Scale and equivalence of ultra-brief measures of well-being.

Three brief psychotherapy outcome measures were assessed for equivalence. The Rating of Outcome Scale (ROS), a 3-item patient-reported outcome measure, was evaluated for interitem consistency, test-retest reliability, discriminant validity, repeatability, sensitivity to change, and agreement with the Outcome Rating Scale (ORS) and Outcome Questionnaire (OQ) in 1 clinical sample and 3 community samples. Clinical cutoffs, reliable change indices, and Bland-Altman repeatability coefficients were calculated. Week-to-week change on each instrument was compared via repeated-measures-corrected effect size. Community-normed T scores and Bland-Altman plots were generated to aid comparisons between instruments. The ROS showed good psychometric properties, sensitivity to change in treatment, and discrimination between outpatients and nonpatients. Agreement between the ROS and ORS was good, but neither the agreement between these nor that between ultrabrief instruments and the OQ were as good as correlations might suggest. The ROS showed incremental advantages over the ORS: improvements in concordance with the OQ, better absolute reliability, and less oversensitivity to change. The ROS had high patient acceptance and usability, and scores showed good reliability, cross-instrument validity, and responsiveness to change for the routine monitoring of clinical outcomes. (PsycINFO Database Record

Plain film measurement error in acute displaced midshaft clavicle fractures.

Clavicle fractures are common and optimal treatment remains controversial. Recent literature suggests operative fixation of acute displaced mid-shaft clavicle fractures (DMCFs) shortened more than 2 cm improves outcomes. We aimed to identify correlation between plain film and computed tomography (CT) measurement of displacement and the inter- and intraobserver reliability of repeated radiographic measurements. We obtained radiographs and CT scans of patients with acute DMCFs. Three orthopedic staff and 3 residents measured radiographic displacement at time zero and 2 weeks later. The CT measurements identified absolute shortening in 3 dimensions (by subtracting the length of the fractured from the intact clavicle). We then compared shortening measured on radiographs and shortening measured in 3 dimensions on CT. Interobserver and intraobserver reliability were calculated. We reviewed the fractures of 22 patients. Bland-Altman repeatability coefficient calculations indicated that radiograph and CT measurements of shortening could not be correlated owing to an unacceptable amount of measurement error (6 cm). Interobserver reliability for plain radiograph measurements was excellent (Cronbach α = 0.90). Likewise, intraobserver reliabilities for plain radiograph measurements as calculated with paired t tests indicated excellent correlation (p > 0.05 in all but 1 observer [p = 0.04]). To establish shortening as an indication for DMCF fixation, reliable measurement tools are required. The low correlation between plain film and CT measurements we observed suggests further research is necessary to establish what imaging modality reliably predicts shortening. Our results indicate weak correlation between radiograph and CT measurement of acute DMCF shortening.

Repeatability of Foveal Measurements Using Spectralis Optical Coherence Tomography Segmentation Software.

PurposeTo investigate repeatability and reproducibility of thickness of eight individual retinal layers at axial and lateral foveal locations, as well as foveal width, measured from Spectralis spectral domain optical coherence tomography (SD-OCT) scans using newly available retinal layer segmentation software.MethodsHigh-resolution SD-OCT scans were acquired for 40 eyes of 40 young healthy volunteers. Two scans were obtained in a single visit for each participant. Using new Spectralis segmentation software, two investigators independently obtained thickness of each of eight individual retinal layers at 0°, 2° and 5° eccentricities nasal and temporal to foveal centre, as well as foveal width measurements. Bland-Altman Coefficient of Repeatability (CoR) was calculated for inter-investigator and inter-scan agreement of all retinal measurements. Spearman's ρ indicated correlation of manually located central retinal thickness (RT0) with automated minimum foveal thickness (MFT) measurements. In addition, we investigated nasal-temporal symmetry of individual retinal layer thickness within the foveal pit.ResultsInter-scan CoR values ranged from 3.1μm for axial retinal nerve fibre layer thickness to 15.0μm for the ganglion cell layer at 5° eccentricity. Mean foveal width was 2550μm ± 322μm with a CoR of 13μm for inter-investigator and 40μm for inter-scan agreement. Correlation of RT0 and MFT was very good (ρ = 0.97, P < 0.0005). There were no significant differences in thickness of any individual retinal layers at 2° nasal compared to temporal to fovea (P > 0.05); however this symmetry could not be found at 5° eccentricity.ConclusionsWe demonstrate excellent repeatability and reproducibility of each of eight individual retinal layer thickness measurements within the fovea as well as foveal width using Spectralis SD-OCT segmentation software in a young, healthy cohort. Thickness of all individual retinal layers were symmetrical at 2°, but not at 5° eccentricity away from the fovea.

Hepatic arterial spin labelling MRI: an initial evaluation in mice.

The development of strategies to combat hepatic disease and augment tissue regeneration has created a need for methods to assess regional liver function. Liver perfusion imaging has the potential to fulfil this need, across a range of hepatic diseases, alongside the assessment of therapeutic response. In this study, the feasibility of hepatic arterial spin labelling (HASL) was assessed for the first time in mice at 9.4 T, its variability and repeatability were evaluated, and it was applied to a model of colorectal liver metastasis. Data were acquired using flow-sensitive alternating inversion recovery-arterial spin labelling (FAIR-ASL) with a Look–Locker readout, and analysed using retrospective respiratory gating and a T1-based quantification. This study shows that preclinical HASL is feasible and exhibits good repeatability and reproducibility. Mean estimated liver perfusion was 2.2 ± 0.8 mL/g/min (mean ± standard error, n = 10), which agrees well with previous measurements using invasive approaches. Estimates of the variation gave a within-session coefficient of variation (CVWS) of 7%, a between-session coefficient of variation (CVBS) of 9% and a between-animal coefficient of variation (CVA) of 15%. The within-session Bland–Altman repeatability coefficient (RCWS) was 18% and the between-session repeatability coefficient (RCBS) was 29%. Finally, the HASL method was applied to a mouse model of liver metastasis, in which significantly lower mean perfusion (1.1 ± 0.5 mL/g/min, n = 6) was measured within the tumours, as seen by fluorescence histology. These data indicate that precise and accurate liver perfusion estimates can be achieved using ASL techniques, and provide a platform for future studies investigating hepatic perfusion in mouse models of disease. Copyright © 2014 John Wiley & Sons, Ltd.

Refractive index measurement of the mouse crystalline lens using optical coherence tomography

In recent years, there has been a growing interest for using mouse models in refractive development and myopia research. The crystalline lens is a critical optical component of the mouse eye that occupies greater than 50% of the ocular space, and significant increases in thickness with age. However, changes in refractive index of the mouse crystalline lens are less known. In this study, we examined the changes in thickness and refractive index of the mouse crystalline lens for two different strains, wild-type (WT) and a nyx mutant (nob) over the course of normal visual development or after form deprivation. Refractive index and lens thickness measurements were made on ex vivo lenses using spectral domain optical coherence tomography (SD-OCT). Comparison of refractive index measurements on 5 standard ball lenses using the SD-OCT and their known refractive indices (manufacturer provided) indicated good precision (intra-class correlation coefficient, 0.998 and Bland-Altman coefficient of repeatability, 0.116) of the SD-OCT to calculate mouse lens refractive index ex vivo. During normal visual development, lens thickness increased significantly with age for three different cohorts of mice, aged 4 (average thickness from both eyes; WT: 1.78 ± 0.03, nob: 1.79 ± 0.08 mm), 10 (WT: 2.02 ± 0.05, nob: 2.01 ± 0.04 mm) and 16 weeks (WT: 2.12 ± 0.06, nob: 2.09 ± 0.06 mm, p < 0.001). Lens thickness was not significantly different between the two strains at any age (p = 0.557). For mice with normal vision, refractive index for isolated crystalline lenses in nob mice was significantly greater than WT mice (mean for all ages; WT: 1.42 ± 0.01, nob: 1.44 ± 0.001, p < 0.001). After 4 weeks of form deprivation to the right eye using a skull-mounted goggling apparatus, a thinning of the crystalline lens was observed in both right and left eyes of goggled animals compared to their naïve controls (average from both the right and the left eye) for both strains (p = 0.052). In form deprived mice, lens refractive index was significantly different between the goggled animals and non-goggled naïve controls in nob mice, but not in WT mice (p = 0.009). Both eyes of goggled nob mice had significantly greater lens refractive index (goggled, 1.49 ± 0.01; opposite, 1.47 ± 0.03) compared to their naïve controls (1.45 ± 0.02, p < 0.05). The results presented here suggest that there are genetic differences in the crystalline lens refractive index of the mouse eye, and that the lens refractive index in mice significantly increase with form deprivation. Research applications requiring precise optical measurements of the mouse eye should take these lens refractive indices into account when interpreting SD-OCT data.

Photoreceptor outer segment layer thickness measured manually on images from spectral domain optical coherence tomography in healthy volunteers

To investigate photoreceptor outer segment layer thickness measured with a manual technique on images from spectral domain optical coherence tomography (OCT) in healthy volunteers. In 60 eyes of 30 healthy volunteers, a spectral domain OCT device (Spectralis, Heidelberg Engineering) was used to obtain cross-sectional images of the retina. For each volunteer, two images of each eye were obtained in one sitting. Images were digitally enlarged and the manual calipers feature of the device's software was used to measure, at the lowest point in the fovea, the thickness of the photoreceptor outer segment layer. All measurements were performed by the same investigator. Repeatability was evaluated with the Bland-Altman repeatability coefficient, and intersubject variability with Pearson's coefficient of variation. The mean values of measurements across all the volunteers were as follows: right eye first image 38.1 micrometers, right eye second image 37.9 micrometers, left eye first image 37.9 micrometers, left eye second image 37.9 micrometers. The repeatability coefficient, i.e. the difference between repeated measurements which would be exceeded in only 5% of cases, was 1.6 micrometers. Coefficients of variation for the right eye were 3.4% for the first images and 3.4% for the second images, and for the left eye they were 3.2 and 4.0% respectively. With a manual method based on spectral domain OCT, the thickness of the photoreceptor outer segment layer at the central fovea can be measured within a useful range of repeatability and appears to be relatively constant across healthy volunteers.

Intra- and inter-observer reliability of ten major histological scoring systems used for the evaluation of in vivo cartilage repair

In the last two decades, many surgical techniques have been described for articular cartilage repair. Reliable histological scoring systems are fundamental tools to evaluate new procedures. Several histological scoring systems have been described, and these can be divided in elementary and comprehensive scores, according to the number of sub-items. The aim of this study was to test the inter- and intra-observer reliability of ten main scores used for the histological evaluation of in vivo cartilage repair. The authors tested the starting hypothesis that elementary scores would show superior intra- and inter-observer reliability compared with comprehensive scores. Fifty histological sections obtained from the trochlea of New Zealand Rabbit and stained with Safranin-O fast green were used. The histological sections were analysed by 4 observers: 2 experienced in cartilage histology and 2 inexperienced. Histological evaluations were performed at time 1 and time 2, separated by a 30-day interval. The following scores were used: Mankin, O'Driscoll, Pineda, Wakitani, Fortier, Selleres, ICRS, ICRSII, Oswestry (OsScore) and modified O'Driscoll. Intra- and inter-observer reliability were evaluated for each score. In addition, the pavement-ceiling effect and the Bland-Altman Coefficient of Repeatability were then evaluated for each sub-item of every score. Intra-observer reliability was high for all observers in every score, even though the reliability was significantly lower for non-expert observers compared with expert counterparts. In terms of Coefficient of Repeatability, some scores performed better (O'Driscoll, Modified O'Driscoll and ICRSII) than others (Fortier, Seller). Inter-observer reliability was high for all observers in every score, but significantly lower for non-expert compared with expert observers. In expert hands, all the scores showed high intra- and inter-observer reliability, independently of the complexity. Although every score has advantages and disadvantages, ICRSII, O'Driscoll and Modified O'Driscoll scores should be preferred for the evaluation of in vivo cartilage repair in animal models.

Quantitative Fundus Autofluorescence in Mice: Correlation With HPLC Quantitation of RPE Lipofuscin and Measurement of Retina Outer Nuclear Layer Thickness

Our study was conducted to establish procedures and protocols for quantitative autofluorescence (qAF) measurements in mice, and to report changes in qAF, A2E bisretinoid concentration, and outer nuclear layer (ONL) thickness in mice of different genotypes and age. Fundus autofluorescence (AF) images (55° lens, 488 nm excitation) were acquired in albino Abca4(-/-), Abca4(+/-), and Abca4(+/+) mice (ages 2-12 months) with a confocal scanning laser ophthalmoscope (cSLO). Gray levels (GLs) in each image were calibrated to an internal fluorescence reference. The bisretinoid A2E was measured by quantitative high performance liquid chromatography (HPLC). Histometric analysis of ONL thicknesses was performed. The Bland-Altman coefficient of repeatability (95% confidence interval) was ±18% for between-session qAF measurements. Mean qAF values increased with age (2-12 months) in all groups of mice. qAF was approximately 2-fold higher in Abca4(-/-) mice than in Abca4(+/+) mice and approximately 20% higher in heterozygous mice. HPLC measurements of the lipofuscin fluorophore A2E also revealed age-associated increases, and the fold difference between Abca4(-/-) and wild-type mice was more pronounced (approximately 3-4-fold) than measurable by qAF. Moreover, A2E levels declined after 8 months of age, a change not observed with qAF. The decline in A2E levels in the Abca4(-/-) mice corresponded to reduced photoreceptor cell viability as reflected in ONL thinning beginning at 8 months of age. The qAF method enables measurement of in vivo lipofuscin and the detection of genotype and age-associated differences. The use of this approach has the potential to aid in understanding retinal disease processes and will facilitate preclinical studies.

Short-term repeatability of resting myocardial blood flow measurements using rubidium-82 PET imaging

BackgroundRubidium-82 (82Rb) PET imaging has been proposed for routine myocardial blood flow (MBF) quantification. However, few studies have investigated the test-retest repeatability of this method. The aim of this study was to optimize same-day repeatability of rest MBF imaging with a highly automated analysis program (FlowQuant) using image-derived input functions and dual spillover corrections (SOC). MethodsTest-retest repeatability of resting left-ventricle (LV) MBF was measured in patients (n = 27) with suspected coronary artery disease (CAD) and healthy volunteers (n = 9). The effects of scan-time, reconstruction, and quantification methods were assessed with correlation and Bland-Altman repeatability coefficients. ResultsFactors affecting rest MBF included gender, suspected CAD, and SOC (P < .001). Significant test-retest correlations were found using all analysis methods tested (r > 0.79). The best repeatability coefficient for same-day MBF was 0.20 mL/minute/g using a 6-minute scan-time, iterative reconstruction, SOC, resting rate-pressure-product (RPP) adjustment, and left atrium input function. This protocol was significantly less variable than standard protocols using filtered back-projection reconstruction, longer scan-time, no SOC, or LV input function. ConclusionAbsolute MBF can be measured with good repeatability using FlowQuant analysis of 82Rb PET scans with a 6-minute scan time, iterative reconstruction, dual SOC, RPP-adjustment, and an image-derived input function in the left atrium cavity.

Assessment of Axial Length Measurements in Mouse Eyes

To compare measurements of murine ocular axial lengths (ALs) made with 780 nm partial coherence interferometry (PCI) and 1310 nm spectral domain-optical coherence tomography (SD-OCT). AL was measured at postnatal day (P) 58 in C57BL/6J mice. Repeated AL measurements were taken using a custom-made 780 nm PCI and a commercial 1310 nm SD-OCT. Intra- and interuser variability was assessed along the central optical axis and 2-degree off-axes angles with the SD-OCT. Data were collected and analyzed using Cronbach alpha (α), Bland-Altman coefficient of repeatability, agreement plots, and intraclass correlation coefficients (ICC). AL measurements agreed well between the two instruments (3.262 ± 0.042 mm for PCI; 3.264 ± 0.047 mm for SD-OCT; n = 20 eyes). The ICC for PCI compared with SD-OCT was 0.92, confirming high agreement between the two instruments. Intrauser ICC for the PCI and SD-OCT were 0.814 and 0.995, respectively. Similarly, interuser ICC for PCI and SD-OCT were 0.970 and 0.943, respectively. Using SD-OCT, a 2-degree misalignment of the eye along the horizontal meridian produced mean differences in AL of -0.002 ± 0.017 mm relative to the centrally aligned images, whereas similar misalignment along the vertical meridian created 0.005 ± 0.018 mm differences in AL measurements. AL measurements from the 780 nm PCI and 1310 nm SD-OCT correlate well. Multiple statistical indices indicate that both instruments have good precision and agreement for measuring murine ocular AL in vivo. Although the vertical meridian had the greater variability in AL in the small mouse eye; 2-degree off-axes differences were within the SD of centrally aligned AL.

Appropriate Time Interval to Repeat Ambulatory Blood Pressure Monitoring in Patients With White-Coat Resistant Hypertension

Resistant hypertension is defined as uncontrolled office blood pressure, despite the use of ≥3 antihypertensive drugs. Ambulatory blood pressure monitoring (ABPM) is mandatory to diagnose 2 different groups, those with true and white-coat resistant hypertension. Patients are found to change categories between controlled/uncontrolled ambulatory pressures without changing their office blood pressures. In this way, ABPM should be periodically repeated. The aim of this study was to evaluate the most appropriate time interval to repeat ABPM to assure sustained blood pressure control in patients with white-coat resistant hypertension. This prospective study enrolled 198 patients (69% women; mean age: 68.9±9.9 years) diagnosed as white-coat resistant hypertension on ABPM. Patients were submitted to a second confirmatory examination 3 months later and repeated twice at 6-month intervals. Statistical analyses included Bland-Altman repeatability coefficients and multivariate logistic regression. Mean office blood pressure was 163±20/84±17 mm Hg, and mean 24-hour blood pressure was 118±8/66±7 mm Hg. White-coat resistant hypertension diagnosis presented a moderate reproducibility and was confirmed in 144 patients after 3 months. In the third and fourth ABPMs, 74% and 79% of patients sustained the diagnosis. In multivariate regression, a daytime systolic blood pressure ≤115 mm Hg in the confirmatory ABPM triplicated the chance of white-coat resistant hypertension status persistence after 1 year. In conclusion, a confirmatory ABPM is necessary after 3 months of the first white-coat-resistant hypertension diagnosis, and the procedure should be repeated at 6-month intervals, except in patients with daytime systolic blood pressure ≤115 mm Hg, in whom it may be repeated annually.

A change in the apparent diffusion coefficient after treatment with bevacizumab is associated with decreased survival in patients with recurrent glioblastoma multiforme.

The aim of this study was to determine the prognostic significance of changes in parameters derived from diffusion tensor imaging (DTI) that occur in response to treatment with bevacizumab and irinotecan in patients with recurrent glioblastoma multiforme. 15 patients with recurrent glioblastoma multiforme underwent serial 1.5 T MRI. Axial single-shot echo planar DTI was obtained on scans performed 3 days and 1 day prior to and 6 weeks after initiation of therapy with bevacizumab and irinotecan. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps were registered to whole brain contrast-enhanced three-dimensional (3D) spoiled gradient recalled and 3D fluid attenuation inversion recovery (FLAIR) image volumes. Anatomic image volumes were segmented to isolate regions of interest defined by tumour-related enhancement (TRE) and FLAIR signal abnormality (FSA). Mean ADC and mean FA were calculated for each region. A Bland-Altman repeatability coefficient was also calculated for each parameter based on the two pre-treatment studies. A patient was considered to have a change in FA or ADC after therapy if the difference between the pre- and post-treatment values was greater than the repeatability coefficient for that parameter. Survival was compared using a Cox proportional hazard model. DTI detected a change in ADC within FSA after therapy in nine patients (five in whom ADC was increased; four in whom it was decreased). Patients with a change in ADC within FSA had significantly shorter overall survival (p=0.032) and progression free survival (p=0.046) than those with no change. In patients with recurrent glioblastoma multiforme treated with bevacizumab and irinotecan, a change in ADC after therapy in FSA is associated with decreased survival.

Intrasession repeatability of optical coherence tomography measures in active neovascular age-related macular degeneration

To determine the repeatability of Stratus optical coherence tomography fast macular thickness map analysis in patients with active neovascular age-related macular degeneration (nAMD). Consecutive pairs of scans from 112 eyes of 112 consecutive patients with active nAMD were analyzed. The Bland-Altman coefficient of repeatability (CR) was calculated for each retinal thickness or volume measure. The CR for the central 1 mm macular subfield was 59 μm (18% of retinal thickness) and did not exceed 69 μm in any subfield. There was much poorer repeatability for the center-point thickness (CPT) measure (CR of 78 μm; 24%). However, in the subgroup of 38 patients with no Stratus software low analysis confidence message on either analysis map, the revised CR (42 μm) for the CPT measure and the A1 subfield (40 μm) were similar. Optical coherence tomography-derived retinal thickness measurements are subject to measurement variability in patients with active nAMD. The results suggest a change criterion of more than 59 μm in central 1 mm (A1) subfield macular thickness is necessary to distinguish true clinical change from measurement variability in these patients.