Measurement Of Lateral Dimensions Research Articles

Features of choroidal naevi on swept source optical coherence tomography angiography and structural reverse flow optical coherence tomography

The purpose of our study was to describe features of choroidal naevi as seen on swept source optical coherence tomography angiography (OCTA) and also on en face images derived from structural data from OCTA. A prospective observational cohort study was carried out. Patients attending a specialised choroidal naevomelanocytic with known naevi were imaged with swept source OCTA. Seventy-one eyes of 70 patients were imaged. Forty-three patients and 44 eyes were included. Mean age was 57.7years (SD 14.9), range 29-81years. Male to female ratio was 20:23. On OCTA after manual segmentation, naevi could be seen in 47.6% of cases, whereas in the en face images, naevi could be clearly visualised in 79.5% of cases. In OCTA, the superficial and deep capillary plexuses appeared undisturbed as did the outer retinal layer appeared in all cases of flat naevi. In choroidal naevi with mild elevation, the outer retinal layer appeared more susceptible to projection artefacts from overlying retinal vasculature. The choriocapillaris layer showed a fading of the normal homogenous vascular mosaic corresponding to the area of the naevus. In the en face images, even the faintest and thinnest naevi could be visualised in striking detail, and naevi greater than 120μm thickness appeared darker (p = 0.0034). OCTA presents characteristic changes in the choriocapillaris layers in cases of choroidal naevi. The association of naevus substance appearing darker with increasing thickness may offer a novel prognostic clue. En face structural OCT may allow accurate, detailed measurement of lateral dimensions which could be of value in the monitoring of suspicious naevi.

Use of Airborne and Terrestrial Lidar to Detect Ground Displacement Hazards to Water Systems

We investigate the use of multiepoch airborne and terrestrial lidar to detect and measure ground displacements of sufficient magnitude to damage buried pipelines and other water system facilities that might result, for example, from earthquake or rainfall-induced landslides. Lidar scans are performed at three sites with coincident measurements by total station surveying. Relative horizontal accuracy is evaluated by measurements of lateral dimensions of well defined objects such as buildings and tanks; we find misfits ranging from approximately 5 to 12 cm , which is consistent with previous work. The bias and dispersion of lidar elevation measurements, relative to total station surveying, is assessed at two sites: (1) a power plant site (PP2) with vegetated steeply sloping terrain; and (2) a relatively flat and unvegetated site before and after trenching operations were performed. At PP2, airborne lidar showed minimal elevation bias and a standard deviation of approximately 70 cm , whereas terrestrial lida...

Metrology study of high precision mm parts made by the deep x-ray lithography (LIGA) technique

Microcomponents are increasingly applied in industrial products, e.g. smallest gears, springs or the watch industry. Apart from their small dimensions, such components are characterized by a high contour accuracy. Industry requires the tolerances to be in the µm range. Measurement of lateral dimensions in the mm range with submicrometer accuracy and precision, however, results in high requirements on measurement technology. The relevance of this problem is illustrated by the fact that the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) has launched the Collaborative Research Center 1159 on ‘New Strategies of Measurement and Inspection for the Production of Microsystems and Nanostructures’. The Institut für Mikrostrukturtechnik, Karlsruhe (Institute of Microstructure Technology, Karlsruhe), produces microstructures by means of the LIG(A) technique (German acronym for lithography, electrodeposition, molding). Presently, a coordinate measurement machine equipped with an optical fiber probe to measure these microstructures is being tested. This paper will particularly focus on the precision and accuracy of the machine. The rules of measurement system analysis will be applied for this purpose. Following the elimination of the systematic error, reproducibility of deep-etch x-ray lithography will be highlighted using the LIGA production of gold gears as an example.

Accuracy, repeatability, and reproducibility of Artemis very high-frequency digital ultrasound arc-scan lateral dimension measurements

To determine the accuracy, repeatability, and reproducibility of measurement of lateral dimensions using the Artemis (Ultralink LLC) very high-frequency (VHF) digital ultrasound (US) arc scanner. London Vision Clinic, London, United Kingdom. A test object was measured first with a micrometer and then with the Artemis arc scanner. Five sets of 10 consecutive B-scans of the test object were performed with the scanner. The test object was removed from the system between each scan set. One expert observer and one newly trained observer separately measured the lateral dimension of the test object. Two-factor analysis of variance was performed. The accuracy was calculated as the average bias of the scan set averages. The repeatability and reproducibility coefficients were calculated. The coefficient of variation (CV) was calculated for repeatability and reproducibility. The test object was measured to be 10.80 mm wide. The mean lateral dimension bias was 0.00 mm. The repeatability coefficient was 0.114 mm. The reproducibility coefficient was 0.026 mm. The repeatability CV was 0.38%, and the reproducibility CV was 0.09%. There was no statistically significant variation between observers (P = .0965). There was a statistically significant variation between scan sets (P = .0036) attributed to minor vertical changes in the alignment of the test object between consecutive scan sets. The Artemis VHF digital US arc scanner obtained accurate, repeatable, and reproducible measurements of lateral dimensions of the size commonly found in the anterior segment.

Spectroscopic anisotropy micro-ellipsometry for determination of lateral dimensions of form birefringent structures

Spectroscopic anisotropy micro-ellipsometry (SAME) is employed for a rapid and precise measurement of lateral dimensions of periodic structures showing form birefringence. For this, the ellipsometric parameters Δ and Ψ were measured as a function of the Euler angle α which describes sample rotation about the surface normal. Analysis of the resulting Δ(α) and Ψ(α)-curves, the so-called SAME curves, allows determination of the components of the permittivity tensor of the form birefringent pattern in the UV–VIS range. From this, the volume fractions of the pattern constituents can be deduced. Once the volume fractions are known the critical dimensions (CD) can be calculated using the pitch of the periodic structures as an additional input. As an example, results for determination of CD of sub-micron lithographic patterns used in dynamic random access memory fabrication are given. The lateral pattern dimensions averaged over the ellipsometer spot size of approximately 120 μm could be determined with an accuracy in the nm range either for lines and spaces—by quantitative simulation of the SAME curve or for more complex pattern, e.g. deep trench patterns, by applying empirical calibration curves of Δ(α) or λ max(Ψ).