Interequipment Variability Research Articles

Standardization procedure to provide a unified multi-method elemental compositional dataset, application to ferruginous colouring matters from Namibia

Curation of archaeological materials often leads to carrying out multi-analytical methodologies that combine non-invasive and invasive elemental analyses. Such materials are often analysed with different techniques. It results in the production of complementary but apparently non-compatible compositional datasets that cannot be easily compared. In the present paper, we propose to compare results acquired on geological ferruginous colouring matters from Namibia with analytical techniques (X-Ray Fluorescence spectrometry (XRF), Proton-Induced-X-ray Emission spectrometry (PIXE), Inductively Coupled Plasma coupled to Optical Emission spectrometry (ICP-OES) and Inductively Coupled Plasma coupled to Mass Spectrometry (ICP-MS)). We aim to provide a unified elemental dataset about these ferruginous colouring matters, usually referred to as “ochre” in archaeology. Analysed geological samples come from three distinct tectonostratigraphic zones of Namibia surveyed in the frame of rock art research. When compared directly, three of the four datasets obtained from these measurements appear as non-compatible because of the inter-equipment variability. However, through a simple standardization procedure, we demonstrate that it is possible to unify these datasets. This procedure minimizes the inter-equipment variability, making the inter-zones of provenance predominant and allowing distinctions of the samples according to their sole origin. Beyond shedding new light on the possibility to compare different elemental analytical techniques, this procedure paves the way for complementary multimodal studies of ferruginous colouring matters.

P045] Neonatal brain: Contrast to noise ratio (CNR) optimization of T1-weighted (T1W) and T2-weighted (T2W) sequences at multiple 1.5T MRI systems, utilizing a neonatal brain tissue mimicking phantom

Purpose To optimize clinical T1w and T2w sequences at multiple 1.5T MRI systems of different vendors, using an in house developed phantom simulating neonatal brain relaxometric characteristics. Materials Methods A neonatal brain phantom, fabricated from paramagnetically doped agarose gel solutions, underwent quantitative MR relaxometry utilizing an Inversion Recovery Spin Echo (IRTSE) method to estimate T1 relaxation times and a Car-Purcell-Meiboom-Gill (CPMG) method to estimate T2 relaxation times at multiple 1.5T MRI systems. Multi-TI turbo spin-echo and multi-TE spin-echo sequences were utilized for direct T1 and T2 relaxation time measurements. Results Signal data S(TR, TE) were reproduced mathematically according to the standard SE signal acquisition equation: S(TR, TE) = PD*(1-exp(-TR/T1)*(exp(-TE/T2). Consequently, TR and TE values at which the maximum CNR between neonatal gray and white matter was recorded were used for the final optimization of T1w and T2w clinical sequences respectively. Based on the above values, TR and TE parameters were modified resulting in an optimized T1wSE sequence TR/TE = 1200 ms/10 ms and an optimized T2wTSE sequence TR/TE = 9500 ms/280 ms as estimated on a clinical MAGNETOM Sonata 1.5T system. Clinical MRI inter-equipment variability for T1 and T2 measurements remained TR and TE parameter variation in optimized T1w and T2w sequences remained less than 7% amongst the selected MRI systems included in this study. Conclusions CNR optimization of T1w and T2w sequences for neonatal brain imaging at multiple 1.5T clinical MRI systems was accomplished with the aid of an in house developed tissue-mimicking phantom.

Comparison and Correction of the Light Sensor Output from 48 Wearable Light Exposure Devices by Using a Side-by-Side Field Calibration Method

ABSTRACTMeasurement of personal light exposures and activity has gained popularity in studies of the circadian rhythm and its effects on human health. Calibration of a batch of measuring devices may be needed, especially before initiating interventional studies, but manufactory calibration of devices before every initiated study is costly for the researcher and therefore often left out. Still, knowledge of inter-equipment variability is essential and seldom provided by the manufactory. The aim of the present study was to develop and test a method for field calibration of Actiwatch Spectrum devices. We tested 48 Actiwatch devices side by side under various light sources and present the red, green, blue, and white light response variability among the Actiwatches. The influence of different spatial and spectral light environments on the white light response when compared with the output from a calibrated photometer is discussed. In agreement with previous studies by Price and others [2012] and Figueiro and others [2013], we confirm the devices’ white light responses to be highly dependent on both the spatial and the spectral composition of the light. The white light response represents photopic illuminance only to a minor degree and light source-specific calibration may therefore be needed in some cases. Moreover, light responses were found to vary between devices by up to 60%. Implications are that the results of light effects on health issues in studies using Actiwatches are blurred by the equipment variability. To compensate for inter-equipment variability we stress the need for a field calibration procedure. When light exposure devices of lower grade quality are used in spectrally and spatially changing light environments, daylight from a diffused overcast sky is suggested to be used for side-by-side calibration of Actiwatches and similar personal light exposure devices. We suggest that the calibration methods presented can be used for calibration of other practical field devices, with respect to the various sensors already on the market and devices that will be introduced in the future.

Segmentation-based MR attenuation correction including bones also affects quantitation in brain studies: an initial result of 18F-FP-CIT PET/MR for patients with parkinsonism.

Attenuation correction (AC) with an ultrashort echo time (UTE) sequence has recently been used in combination with segmentation for cortical bone identification for brain PET/MR studies. The purpose of this study was to evaluate the quantification of (18)F-fluoropropyl-carbomethoxyiodophenylnortropane ((18)F-FP-CIT) binding in brain PET/MR, particularly focusing on effects of UTE-based AC including bone segmentation. Sixteen patients with initially suspected parkinsonism were prospectively enrolled. An emission scan was acquired 110 min after (18)F-FP-CIT injection on a dedicated PET/MR scanner, immediately followed by another emission scan using a PET/CT scanner 120 min after the injection. A UTE-based attenuation map was used to classify the voxels into 3 tissues: bone, soft tissue, and air. All PET images were spatially normalized, and a specific-to-nonspecific dopamine transporter (DAT) binding ratio (BR) was calculated using statistical probabilistic anatomic mapping. The level of agreement was assessed with intraclass correlation coefficients (ICCs). Voxelwise comparison between PET images acquired from PET/MR and PET/CT was performed. We compared non-attenuation-corrected images to analyze UTE-based AC effects on DAT quantification. BR in the putamen obtained from PET/MR and PET/CT showed low interequipment variability, whereas BR in the caudate nucleus showed significant variability (ICC = 0.967 and 0.682 for putamen and caudate nucleus, respectively). BR in the caudate nucleus was significantly underestimated by PET/MR, compared with PET/CT (mean difference of BR = 0.66, P < 0.0001). Voxelwise analysis revealed that PET/MR showed significantly low BR in the periventricular regions, which was caused by a misclassification of the ventricle as air on the attenuation map. We also compared non-AC images, revealing low interequipment variability even in the caudate nucleus (ICC = 0.937 and 0.832 for putamen and caudate nucleus, respectively). Our data demonstrate spatial bias of the DAT BR on (18)F-FP-CIT PET/MR. Voxelwise analysis and comparison to non-AC images identified the misclassification of ventricle as air to be the cause of bias. To obtain reliable quantification for brain PET/MR studies including (18)F-FP-CIT PET, alternative and more reliable segmentation strategies are required.

Hepatic Arterial Doppler Sonography in Patients with Cirrhosis and Controls: Observer and Equipment Variability with use of the Ultrasonic Contrast Agent SHU 508A

The aims of this study on hepatic arterial Doppler sonography were to ascertain interobserver and interequipment variability, to investigate any potential artificial influence of the ultrasonic contrast agent on the Doppler measurements and to compare the results in healthy and cirrhotic subjects. Doppler sonography of the left hepatic artery was performed in nine healthy and nine cirrhotic subjects by three independent observers using three different devices. Continuous infusion of the ultrasonic contrast agent SHU 508A and placebo were administered in a double blind fashion. Systolic, mean and end diastolic peak velocities as well as resistive and pulsatility indices were measured. Equipment associated variances (5.8 - 12.7 %) of the five Doppler parameters were greater than interobserver variances (0.3 - 3.6 %). No significant differences were observed between the velocities using ultrasonic contrast agent and placebo. Systolic (65.9 +/- 3.6 vs. 47.7 +/- 4.2 cm/s mean +/- SE, p = 0.02) and mean peak velocity (35.4 +/- 1.6 vs. 24.5 +/- 1.8 cm/s, p = 0.007) were significantly higher in cirrhotic than in healthy subjects whereas the resistive and pulsatility indices were not different. Doppler sonography of the left hepatic artery performed by various observers is reproducible as long as the same device is used. Under clinical conditions, velocities are correctly measured with the use of ultrasonic contrast agent and are elevated in patients with cirrhosis.

Toward a consensus on reference values for thyroid volume in iodine-replete schoolchildren: results of a workshop on inter-observer and inter-equipment variation in sonographic measurement of thyroid volume.

Interpretation of thyroid ultrasonography for assessing goiter prevalence requires valid reference criteria from iodine-sufficient populations. Reports have suggested the current reference criteria for thyroid volume (T(vol)) of WHO/ICCIDD (International Council for the Control of Iodine Deficiency Disorders) may be too high. Our objective was to determine if inter-observer and/or inter-equipment variability contributes to the disagreement in sonographic T(vol) in children reported from iodine-sufficient areas. A 2-day workshop in which four experienced ultrasound examiners from around Europe measured T(vol) in 45 6--12-year-old Swiss schoolchildren using four different portable ultrasound machines. One of the participating examiners (observer A) had generated the T(vol) data in European children that are the basis for the WHO/ICCIDD reference criteria. Sonographic T(vol) was measured in each child by all four examiners on all four machines. Six hundred and eighty-four examinations were completed, with examiners having no knowledge of one another's results. Inter-observer and inter-equipment variation was calculated. Mean inter-equipment variation in T(vol) was 15.2% (95% CI: 14.1, 16.3%). There were no significant differences in T(vol) between equipment (P=0.51). For all observers, the mean inter-observer variation in T(vol) was 25.6% (95% CI: 23.9, 27.2%). At all ages and all body surface areas, there was a large systematic measurement bias (+30% volume) between the mean T(vol) of observer A and the mean Tvol of observers B, C and D. Reanalysis using data from observers B, C and D reduced the mean inter-observer variation in T(vol) to 13.3% (95% CI: 11.9, 14.7%). A correction factor for the systematic difference of operator A for the P50 and P97 of T(vol) was estimated using analysis of covariance. When applied to the WHO/ICCIDD reference data, it sharply reduced the discrepancy between the WHO/ICCIDD criteria and those from other iodine-sufficient children around the world. Inter-equipment error contributes minimally to reported differences in sonographic T(vol). Even among experienced examiners, inter-observer variation in sonographic T(vol) in children can be high, and probably contributes to the current disagreement on normative values in iodine-sufficient children. A systematic bias at least partially explains why the WHO/ICCIDD reference data differ from those reported from other iodine-sufficient children around the world. The findings argue strongly for the standardization of methods used for sonographic measurement of T(vol) in children.

Standardization of Carotid Ultrasound: A Hemodynamic Method to Normalize for Interindividual and Interequipment Variability

Standardization of Carotid Ultrasound: A Hemodynamic Method to Normalize for Interindividual and Interequipment Variability

Interobserver, interequipment and intersubject variability of echo-Doppler examination of the common carotid and vertebral arteries

Objective: We evaluated interobserver and interequipment variability in common carotid and vertebral flow measurements, using seven female members of nursing staff as subjects, four different ultrasound machines and three different radiologists as operators. Methods: The flow of the common carotid and vertebral arteries in each subject was examined at 0, 10, 20 and 30 min after lying down in a supine position. Peak velocity, end-diastolic velocity, mean velocity, systolic acceleration, cross-sectional area of the vessel, flow volume/min, resistance index and Doppler angle were measured. Results: A large proportion of the variance of peak velocity, cross-sectional area of the vessel and flow volume was patient-related. Significantly different values of end-diastolic velocity, mean velocity, resistance index, Doppler angle and systolic acceleration were obtained with different equipment. Significantly different values of systolic acceleration, vertebral peak velocity, common carotid artery flow and Doppler angle were obtained by different operators. However, part of the variability may be physiological due to the study protocol. Conclusion: The use of the same operator and equipment is recommended in follow-up examinations.

Interobserver and interequipment variability of hepatic, splenic, and renal arterial Doppler resistance indices in normal subjects and patients with cirrhosis

Background/Aims: Doppler arterial resistance indices are used to evaluate alterations in arterial hemodynamics in the liver, spleen, and kidney. The purpose of this study was to determine the interobserver and interequipment variability of hepatic, splenic, and renal arterial Doppler resistance indices, and the influence of a cooperative training program of the operators on the reproducibility of the results. Methods: In the first part of the study, hepatic (PI-L, RI-L), splenic (PI-S, RI-S), and renal (PI-K, RI-K) pulsatility and resistive indices were measured by echo-color-Doppler in eight control subjects and ten patients with cirrhosis by three operators using three different machines. In the second part of the study, measurements were taken by the three operators in nine controls and nine patients with cirrhosis, after cooperative training, with a single machine. Results: Significant interobserver variability was present for all parameters except RI-L. Significant inter-equipment variability was present for all parameters except PI-S and RI-S. Only 0–3% of variance was equipment- or operator-related, while 58–72% was patient-related. Hepatic and renal coefficients of variation were similar in patients with cirrhosis and controls, while splenic coefficients of variation were higher in patients with cirrhosis than in controls. After training, differences among operators disappeared for all variables except RI-K, and the operator-related component of variance nearly disappeared for all parameters. Conclusions: Hepatic, splenic, and renal arterial resistance indices show small but significant interobserver and interequipment variability. Interobserver variability can be decreased to non-significant levels by a common training program. Thus, these indices can be widely applied to the study of arterial circulation in these organs.

Interobserver and Interequipment Variability of Echo-Doppler Sonographic Evaluation of the Superior Mesenteric Artery

Interobserver and Interequipment Variability of Echo-Doppler Sonographic Evaluation of the Superior Mesenteric Artery

Interobserver and inter-equipment variability of echo-Doppler sonographic evaluation of the superior mesenteric artery.

The aim of this study was to assess the interobserver and inter-equipment variabilities of echo-Doppler sonographic measurement of superior mesenteric artery flow parameters. In the first part of the study the echo-Doppler sonographic parameters (maximum systolic velocity, minimum diastolic velocity, mean velocity, restrictive index, and pulsatility index) were measured independently in nine patients by four skilled operators using four different equipment models. In the second part of the study measurements were taken by the four operators in seven different patients, after one day of cooperative training; the purpose of this part was to define a strict and uniform protocol of Doppler sonographic examination. Significantly different values of maximum systolic velocity, minimum diastolic velocity, mean velocity, and pulsatility index were obtained by the different operators, whereas the inter-equipment variability was significant only for maximum systolic velocity, mean velocity, and pulsatility index. The analysis of the components of variance showed that a large part of this variance was nonsystematic. After training and definition of the protocol no significant differences were found among the operators for any of the parameters, and the 95% confidence limits and coefficients of variation showed a decrease as for maximum systolic velocity, mean velocity, and pulsatility index. This study demonstrates that a significant systematic variability exists among mesenteric Doppler measurements obtained by different operators using different commercially available equipment. Cooperative training can reduce the interobserver variability significantly and bring to an acceptable level the reproducibility of Doppler measurements of superior mesenteric artery flow parameters.

Interobserver and interequipment variability of echo-doppler examination of the portal vein: Effect of a cooperative training program

The aim of this study was to assess the interobserver, interequipment, and time-dependent variabilities of echo-Doppler measurements of portal blood flow velocity (PBV), portal vein diameters (PVDs) and their derived parameters, portal blood flow (PBF), and congestion index (CI) in cirrhotic patients. The influence of a cooperative training program of the operators on the reproducibility of the results was also investigated. The echo-Doppler parameters were independently measured in 15 patients by four skilled operators, using four echo-Doppler machines (Acuson, ATL, Hitachi-Esaote, Toshiba. Eight of the 15 patients were restudied after 15 days by the same operators using only one machine. Significantly different values of PBV, PBF, and CI were obtained. PBV variance was equipment-related (32%) and operator-related in a smaller portion (5%). No systematic effect related to the time of investigation was found. After training to define a precise protocol, new measurements were performed by four operators on 8 different patients. No significant differences were found among the operators for any of the parameters and the 95% confidence limits (CL) and coefficients of variation (CV) of PBV showed a marked decrease (CL from ±26.4% to ±15.6%). These results indicate that (1) a significant systematic variability exists between Doppler measurements with different equipment; (2) there is no significant time-dependent systematic variability of Doppler measurements; and (3) a cooperative training program reduces the interobserver variability for direct measurements, such as PBV.