Measurement of Carotid Plaque Volume by 3-Dimensional Ultrasound

Background and Purpose-Measurement of carotid plaque volume and its progression are important tools for research and patient management. In this study, we investigate the observer variability in the measurement of plaque volume as determined by 3-dimensional (3D) ultrasound (US). We also investigate the effect of interslice distances (ISD) and repeated 3D US scans on measurement variability. Materials and Methods-Forty 3D US patient images of plaques (range, 37.43 to 604.1 mm3) were measured by manual planimetry. We applied ANOVA to determine plaque volume measurement variability and reliability. Plaque volumes were measured with 9 ISDs to determine the effect of ISD on measurement variability. Additional plaque volumes were also measured from multiple 3D US scans to investigate repeated scan acquisition variability. Results-Intraobserver and interobserver measurement reliabilities were 94% and 93.2%, respectively. Plaque volume measurement variability decreased with increasing plaque volume (range, 27.1% to 2.2%). Measurement precision was constant for ISDs between 1.0 and 3.0 mm, whereas plaque volume measurement variability increased with ISD. Repeated 3D US scan measurements were not different from single-scan measurements (P=0.867). Conclusions-The coefficient of variation in the measurement of plaque volume decreased with plaque size. The volumetric change that must be observed to establish with 95% confidence that a plaque has undergone change is ≈20% to 35% for plaques \u3c100 mm3 and ≈10% to 20% for plaques \u3e100 mm3. Measurement precision was unchanged for ISDs \u3e3.0 mm, whereas measurement variability increased with ISD. Repeated 3D US scans did not affect plaque volume measurement variability

Measurement variability following MRI system upgrade

Major hardware/software changes to MRI platforms, either planned or unplanned, will almost invariably occur in longitudinal studies. Our objective was to assess the resulting variability on relevant imaging measurements in such context, specifically for three Siemens Healthcare Magnetom Trio upgrades to the Prismafit platform. We report data acquired on three healthy volunteers scanned before and after three different platform upgrades. We assessed differences in image signal (contrast-to-noise ratio (CNR)) on T1-weighted images (T1w) and fluid-attenuated inversion recovery images (FLAIR); brain morphometry on T1w image; and small vessel disease (white matter hyperintensities; WMH) on FLAIR image. Prismafit upgrade resulted in higher (30%) and more variable neocortical CNR and higher brain volume and thickness mainly in frontal areas. A significant relationship was observed between neocortical CNR and cortical volume. For FLAIR images, no significant CNR difference was observed, but WMH volumes were significantly smaller (-68%) after Prismafit upgrade, when compared to results on the Magnetom Trio. Together, these results indicate that Prismafit upgrade significantly influenced image signal, brain morphometry measures and small vessel diseases measures and that these effects need to be taken into account when analyzing results from any longitudinal study undergoing similar changes

Krill biomass estimation : sampling and measurement variability

FB is funded by an EPSRC studentship (grant code: EP/R513337/1).Krill are the subject of growing commercial fisheries and therefore fisheries management is necessary to ensure long-term sustainability. Krill catch limits, set by Commission for the Conservation of Antarctic Marine Living Resources, are based on absolute krill biomass, estimated from acoustic-trawl surveys. In this work, we develop a method for determining an error budget for acoustic-trawl surveys of krill which includes sampling and measurement variability. We use our error budget method to examine the sensitivity of biomass estimates to parameters in acoustic target strength (TS) models, length frequency distribution and length to wetmass relationships derived from net data. We determined that the average coefficient of variation (CV) of estimated biomass was 17.7% and the average CV due from scaling acoustic observations to biomass density was 5.3%. We found that a large proportion of the variability of biomass estimates is due to the krill orientation distribution, a parameter in the TS model. Orientation distributions with narrow standard deviations were found to emphasise the results of nulls in the TS to length relationship, which has to potential to lead to biologically implausible results.Publisher PDFPeer reviewe

The prediction of measurement variability in an automotive application by the use of a coherence formulation

Variability between nominally identical vehicles is an ever present problem in automotive vehicle design. In this paper it is shown that it is possible to quantify and, therefore, separate the measurement variability arising from a number of tests on an individual vehicle from the vehicle to vehicle variability arising from the manufacturing process from a series of controlled experiments. In this paper the coherence data is used to identify the measurement variability and, thus, to separate these two variability sources. In order to illustrate the methodology a range of nominally identical automotive vehicles have been tested for NVH (noise, vibration and harshness) variability by exciting the engine mount with an impact hammer and measuring the excitation force and corresponding velocity responses at different points on the vehicle. Normalised standard deviations were calculated for the transfer mobility data, giving variability values of 25.3 %, 33.5 % and 37.3 % for the responses taken at the suspension Strut, Upper A Pillar and B Pillar respectively. The measurement variability was determined by taking repeat measurements on a single vehicle, and was found to be 2.9 %. The measurement variability predicted by the coherence data on the multi-vehicle tests was compared with the directly taken repeat measurements taken on a single vehicle and was shown to agree well with one another over the frequency range of interest

Assessment of Tumour Growth in Murine Cancer Models with Three-Dimensional High-Frequency Ultrasound

Preclinical cancer research could benefit from quantitative, non-invasive measurements of tumour growth provided by three-dimensional high-frequency ultrasound imaging. High-frequency ultrasound has been shown to be appropriate for tracking experimental liver metastases from a variety of cell fines without exogenous contrast agents. Tumour growth over time can be monitored on an individual tumour basis, allowing a growth curve to be constructed and the tumour to act as its own control in a treatment study. In order to quantify tumour volume and growth, the measurement variability must be known. Inter- and intra-observer variability was determined for tumours in four size ranges with average volume from 0.43 mm3 to 60.42 mm3. Intrarobserver variability was as low as 4% for mid-sized tumours averaging 2.39 mm3, while the inter-observer variability for the smallest and largest tumours measured had the highest variability at 25% and 15%, respectively. Breathing motion did not significantly effect the volume measurements, however, having the region of interest beyond the geometric focus resulted in significantly different measured volumes. Measurement variability is one factor that influences how well growth data can be characterized mathematically through curve fitting. Simulations of tumour growth were performed to relate experimental imaging parameters, such as intervals between acquiring images, minimum and maximum volume recorded and length of time over which data is acquired, to the quality of curve fitting results. Simulations show that improving the ability of the ultrasound system to image small (\u3c1 mm diameter) tumours would improve the ability to draw conclusions from growth parameters. The spatially variant point-spread function influences lesion-size measurement variability and consequently growth curve fitting. The transducer employed is tightly focused, so spatial image resolution is high at the focus but rapidly degrades away from the focus. Synthetic aperture focusing was employed with a variety of weighting techniques to retrospectively focus the images through a range of depths. The iii improvement in focusing was measured using point-like targets and the effect on measurement variability was evaluated using lesion phantom images. Synthetic aperture focusing did not produce a significant reduction in lesion-size measurement variability but did diminish the sensitivity of the measured size to lesion depth

Impact of analyzing fewer image frames per segment during offline volumetric radiofrequency-based intravascular ultrasound measurements of target lesions prior to percutaneous coronary interventions

In the present study, we evaluated the impact of a 50% reduction in number of image frames (every second frame) on the analysis time and variability of offline volumetric radiofrequency-based intravascular ultrasound (RF-IVUS) measurements in target lesions prior to percutaneous coronary interventions (PCI). Volumetric RF-IVUS data of vessel geometry and plaque composition are generally obtained by a semi-automated analysis process that includes time-consuming manual contour editing. A reduction in the number of frames used for volumetric analysis may speed up the analysis, but could increase measurement variability. We repeatedly performed offline volumetric analyses in RF-IVUS image sets of 20 mm-long coronary segments that contained 30 de novo lesions prior to PCI. A 50% reduction in frames decreased the analysis time significantly (from 57.5 ± 7.3 to 35.7 ± 3.7 min; P < 0.0001) while geometric and compositional RF-IVUS measurements did not differ significantly from measurements obtained from all frames. The variability between measurements on the reduced number of frames versus all frames was comparable to the intra-observer measurement variability. In target lesions prior to PCI, offline volumetric RF-IVUS analyses can be performed using a reduced number of image frames (every second frame). This reduces the time of analysis without substantially increasing measurement variability

Quantitative Assessment of Blood Pressure Measurement Accuracy and Variability from Visual Auscultation Method by Observers without Receiving Medical Training

This study aimed to quantify blood pressure (BP) measurement accuracy and variability with determinations from visualizing Korotkoff sound waveform. Thirty video clips of BP recordings from the educational training database of the British Hypertension Society were converted to Korotkoff sound waveforms. Ten observers without receiving medical training were asked to determine systolic and diastolic BPs (SBP and DBP) from the randomly arranged video clips and Korotkoff sound waveforms using two measurement methods: a) traditional manual auscultatory method of listening for Korotkoff sounds; and b) visual auscultation method by visualising the Korotkoff sound waveform, which was repeated three times on different days, making a total of 6 BP measurements from each observer on each BP recording. The measurement variability was calculated from the standard deviation of the three repeats, and the measurement error was calculated against the reference answers. Statistical analysis showed that, in comparison with the traditional manual auscultatory method, visual auscultation method significantly reduced overall measurement variability from 2.2 to 1.1 mmHg for SBP and from 1.9 to 0.9 mmHg for DBP (both p<0.001). It also showed that BP measurement errors were significant for both techniques (all p<0.01, except DBP from the traditional method). Although significant, the overall mean measurement errors were small, which were -1.5 and -1.2 mmHg for SBP, and -0.7 and 2.6 mmHg for DBP, respectively from the traditional manual auscultatory and visual auscultation methods. In conclusion, the visual auscultation method had the ability to achieve an acceptable degree of BP measurement accuracy, with smaller measurement variability in comparison with the traditional manual auscultatory method

Capture of manufacturing uncertainty in turbine blades through probabilistic techniques

Efficient designing of the turbine blades is critical to the performance of an aircraft engine. An area of significant research interest is the capture of manufacturing uncertainty in the shapes of these turbine blades. The available data used for estimation of this manufacturing uncertainty inevitably contains the effects of measurement error/noise. In the present work, we propose the application of Principal Component Analysis (PCA) for de-noising the measurement data and quantifying the underlying manufacturing uncertainty. Once the PCA is performed, a method for dimensionality reduction has been proposed which utilizes prior information available on the variance of measurement error for different measurement types. Numerical studies indicate that approximately 82% of the variation in the measurements from their design values is accounted for by the manufacturing uncertainty, while the remaining 18% variation is filtered out as measurement error

Does eye examination order for standard automated perimetry matter?

PURPOSE: In spite of faster examination procedures, visual field (VF) results are potentially influenced by fatigue. We use large-scale VF data collected from clinics to test the hypothesis that perimetric fatigue effects are greater in the eye examined second. METHODS: Series of six Humphrey Swedish Interactive Testing Algorithm (SITA) VFs from 6901 patients were retrospectively extracted from a VF database from four different glaucoma clinics. Mean deviation (MD) was compared between first and second tested eyes. A surrogate measure of longitudinal MD variability over time was estimated from errors using linear regression of MD against time then compared between first and second tested eye. RESULTS: Right eye VF was tested consistently first throughout in 6320 (91.6%) patients. Median (interquartile range; IQR) MD in the first tested (right) eye and second tested (left) eye was -2.57 (-6.15, -0.58) dB and -2.70 (-6.34, -0.80) dB respectively (median reduction VF sensitivity of 0.13 dB; p < 0.001). Median (IQR) increase in our surrogate measure of longitudinal MD variability in the second eye tested was 3% (-43%, 50%); this effect was not associated with patient age or rest time between examinations. CONCLUSION: Statistically significant perimetric fatigue effects manifest on average in the second eye tested in routine clinics using Humphrey Field Analyzer SITA examinations. However, the average effects were very small and there was enormous variation among patients. We recommend starting with a right eye examination so that any perimetric fatigue effects, if they exist in an individual, will be as constant as possible from visit to visit

Impact of analyzing less image frames per segment for radiofrequency-based volumetric intravascular ultrasound measurements in mild-to-moderate coronary atherosclerosis

Volumetric radiofrequency-based intravascular ultrasound (RF–IVUS) data of coronary segments are increasingly used as endpoints in serial trials of novel anti-atherosclerotic therapies. In a relatively time-consuming process, vessel and lumen contours are defined; these contours are first automatically detected, then visually checked, and finally (in most cases) manually edited to generate reliable volumetric data of vessel geometry and plaque composition. Reduction in number of cross-sectional images for volumetric analysis could save analysis time but may also increase measurement variability of volumetric data. To assess whether a 50% reduction in number of frames per segment (every second frame) alters the reproducibility of volumetric measurements, we performed repeated RF–IVUS analyses of 15 coronary segments with mild-to-moderate atherosclerosis (20.2 ± 0.2 mm-long segments with 46 ± 13% plaque burden). Volumes were calculated based on a total of 731 image frames. Reducing the number of cross-sectional image frames for volumetric measurements saved analysis time (38 ± 9 vs. 68 ± 17 min/segment; P < 0.0001) and resulted for only a few parameters in (borderline) significant but mild differences versus measurements based on all frames (fibrous volume, P < 0.05; necrotic-core volume, P = 0.07). Compared to the intra-observer variability, there was a mild increase in measurement variability for most geometrical and compositional volumetric RF–IVUS parameters. In RF–IVUS studies of mild-to-moderate coronary disease, analyzing less image frames saved analysis time, left most volumetric parameters greatly unaffected, and resulted in a no more than mild increase in measurement variability of volumetric data