Accuracy Of Thickness Measurements Research Articles

Corneal thickness mapping by 3D swept‐source anterior segment optical coherence tomography

To assess accuracy and repeatability of central corneal thickness (CCT) measurements obtained by swept-source anterior segment optical coherence tomography (AS-OCT), spectral-domain retinal OCT with corneal module and ultrasound pachymetry (USP), and to assess repeatability of pachymetric mapping with AS-OCT. 50 healthy volunteers were recruited. A single, experienced operator analysed the right eye of each participant twice in the same session with AS-OCT ('corneal map' routine), retinal OCT and USP. CCT measurements were compared using repeated-measures analysis of variance, Bonferroni test, Pearson correlation and Bland-Altman plots. Repeatability of thickness maps and CCT measurements were assessed using Alpha of Cronbach, intraclass correlation coefficient (ICC) and coefficient of repeatability. Mean CCT±SD was 540±28.9 μm for AS-OCT, 544±29.5 μm for retinal OCT and 549.3±31.7 μm for USP; the differences were statistically significant (p<0.01). CCT measurements obtained with the three instruments were highly correlated: r was 0.965 for AS-OCT/USP, 0.962 for retinal OCT/USP and 0.984 for AS-OCT/retinal OCT comparison. The repeatability of CCT measurements was higher for AS-OCT than for the other devices (p<0.001). Repeatability of pachymetric maps was excellent (ICC=0.999). Pachymetric maps by swept-source AS-OCT showed excellent repeatability. CCT measurements obtained by AS-OCT, USP and retinal OCT were highly correlated although not identical.

Comparison of Cortical Bone Measurements Between pQCT and HR-pQCT

The primary purpose of this study was to determine the accuracy of tibial cortical thickness measurements derived from peripheral quantitative computed tomography (pQCT) with analysis based on the circular ring model, using high-resolution peripheral quantitative computed tomography (HR-pQCT) (isotopic voxel size of 82μm) as a gold standard. The secondary objective was to evaluate whether the accuracy of the pQCT-based estimates of cortical thickness (CTh), cortical area (CoA), cortical density (CDen), and total area (TotA) improve with alterations of voxel size from the standard 0.5–0.2mm. Fifteen dry tibia specimens were immersed in saline in a sealed cylinder and scanned 22.5mm from the distal tibia plateau using pQCT and HR-pQCT. pQCT yielded higher values for CTh and CDen and lower values for CoA. The differences between imaging techniques increased as the average CTh increased. No systematic bias was observed for CDen, CoA, and TotA. Similar differences were found between pQCT with voxel size 0.2mm and HR-pQCT. Significant correlations were observed for CTh (R=0.97, p≤0.0001), CDen (R=0.99, p≤0.0001), CoA (R=0.98, p≤0.0001), and TotA (R=1.0, p≤0.0001) when pQCT- and HR-pQCT-derived values were compared irrespective of which voxel size was used. Measurement variability between the imaging techniques was evident. Future studies aimed at examining cortical structure with pQCT should note that there are differences between the 2 techniques.

Accuracy of bone surface size and cortical layer thickness measurements using cone beam computerized tomography

The purpose of this study was to determine the accuracy of Cone Beam Computerized Tomography (CBCT) reconstructions in displaying bone surface size and cortical layer thickness. Two fresh frozen cadaver heads were scanned using a CBCT (i-CAT(™) 3D Imaging System; Imaging Sciences International Inc.). The mandibles were sectioned and digitalized for histological evaluation. Dimensions as measured on these sections were compared with CBCT measurements of the same region with the use of 3D image-based planning software (Procera System NobelGuide(™); Nobel Biocare). To allow optimal comparison between histological and CBCT sections, reference markers were placed into the mandibles. The Student t-test was utilized to analyze the data. Differences with P-values <0.05 were considered significant. The total height and width of the mandibular body, as measured on CBCT views, were larger compared with the histological values with a maximum difference of 0.33 mm (SD ± 0.34). Cortical thickness measurements were significantly thicker on CBCT sections (P < 0.006) with absolute differences ranging up to ±0.63 mm (SD ±0.28) and relative differences ranging up to 82.6%. CBCT images (i-CAT 3D Imaging System), viewed on the planning software Procera System NobelGuide, tend to overestimate the anatomical truth in assessing both bone height and width; especially cortical thicknesses are depicted thicker than in reality. When using CBCT images for presurgical assessment, one should be aware of this phenomenon of exaggeration of dimensions.

The application of fluid dynamic gauging in characterising cake deposition during the cross-flow microfiltration of a yeast suspension

Abstract Fluid dynamic gauging (FDG) has been used to study cake fouling during cross-flow microfiltration of inactive Saccharomyces cerevisiae yeast suspensions through a 5 μm nominal pore size mixed cellulose ester membrane. Cake thickness was measured in situ and in real-time during fouling, for which an initial growth rate of ca. 0.81 μm s −1 was observed at TMP = 35 mbar and Re duct = 1000. The thickness increased asymptotically to a terminal value of 130 μm, limited by the FDG process. Although it influences the evolution of the cake thickness, FDG can nevertheless be used to perform strength tests on preformed cakes, by imposing controlled shear stresses to the surface and measuring the thickness following deformation. Cake deformation via incremental increases in shear stress demonstrated that the cake's resilience to tangential fluid shear was inversely proportional to its thickness. It was found that preformed cakes over 250 μm thick were deformed by shear stresses −2 , indicating very loose cohesion between cells on the cake's surface. The range and accuracy of thickness measurements is subject to the strength of fouling layers and the operating conditions of the apparatus. Measures to enhance the technique's efficacy have been identified and are currently underway.

Application of Fiber Optical Sensor in Thickness Measurement of Mechanical Seal

Due to film thickness is one of important parameters which has great influence on the performance of mechanical seal, the accuracy of thickness measurement is significant on mechanical seal condition monitoring and performance study. Some limitations were faced when common sensors were used under water of seal face. As new type sensor, FOS has many advantages such as smaller diameter, higher sensitivity, better anti-jamming ability, larger applicable scope than common sensors. In this paper, an enclosed and rotatable calibration test-bed was designed to imitate seal structure by which the feasibility and specifications of FOS application to measuring the seal film thickness had been discussed

Study of ultrasonic signal processing in thickness measurement for non-smooth surface sheet metal

The corrosion pits, rust, slag and dust of metal surface can cause a sharp bottom echo noise signal, and affect the accuracy of the thickness measurement values. This paper designed a set of ultrasonic reflection signal acquisition and processing circuit and wavelet packet analysis and reconstruction software, which can suppress noise and improve signal to noise ratio. Experiments show that the signal processing circuit and the wavelet packet technologies in non-smooth surface metal plate ultrasonic thickness measurement is effective and useful, which can obtain a more pure reflection of the ultrasonic bottom signal, thereby enhance the accuracy of thickness measurement.

Multi-focus image fusion for enhancing fiber microscopic images

Accurate measurement and identification of fibers using magnified digital images relies mainly on the quality of the fiber image. At a given power of magnification, a light microscope has a limited depth of field that may not cover the entire depth space of a fiber sample on the slide and thus disallows all fibers in the image from being well focused, regardless of focus positions. This paper introduces an image-fusion technique to solve mal-focused fibers in a microscopic image to ensure optimal image quality for fiber measurements. This new technique utilizes multiple images of the same view taken at consecutive depths, calculates a focus measure of every pixel in each image, and constructs a matrix to register the image layer that has the maximum focus measure for every pixel. The matrix can be further modified and then used as a map to reconstruct a new image that contains only the best-focused pixels out of the captured images. The fused image combines selected features of multi-focus images so that unfocused fibers can be realistically amended and blurring fiber edges can be sharpened. Compared to the data measured from a single-focus image, the data taken from the fused image can greatly improve the accuracy of fiber thickness measurements.

In vivo characterisation of bioresorbable vascular scaffold strut interfaces using optical coherence tomography with Gaussian line spread function analysis

Optical coherence tomography (OCT) of a bioresorbable vascular scaffold (BVS) produces a highly reflective signal outlining struts. This signal interferes with the measurement of strut thickness, as the boundaries cannot be accurately identified, and with the assessment of coverage, because the neointimal backscattering convolutes that of the polymer, frequently making them indistinguishable from one another. We hypothesise that Gaussian line spread functions (LSFs) can facilitate identification of strut boundaries, improving the accuracy of strut thickness measurements and coverage assessment. Forty-eight randomly selected BVS struts from 12 patients in the ABSORB Cohort B clinical study and four Yucatan minipigs were analysed at baseline and follow-up (six months in humans, 28 days in pigs). Signal intensities from the raw OCT backscattering were fit to Gaussian LSFs for each interface, from which peak intensity and full-width-at-half-maximum (FWHM) were calculated. Neointimal coverage resulted in significantly different LSFs and higher FWHM values relative to uncovered struts at baseline (p<0.0001). Abluminal polymer-tissue interfaces were also significantly different between baseline and follow-up (p=0.0004 in humans, p<0.0001 in pigs). Using the location of the half-max of the LSF as the polymer-tissue boundary, the average strut thickness was 158±11 µm at baseline and 152±20 µm at six months (p=0.886), not significantly different from nominal strut thickness. Fitting the raw OCT backscattering signal to a Gaussian LSF facilitates identification of the interfaces between BVS polymer and lumen or tissue. Such analysis enables more precise measurement of the strut thickness and an objective assessment of coverage.

Evaluation of the Accuracy of Articular Cartilage Thickness Measurement by B-Mode Ultrasonography with Conventional Imaging and Real-Time Spatial Compound Ultrasonography Imaging

The present study aimed to quantify the thickness of articular cartilage (Tc) in vitro using both conventional and real-time spatial compound B-mode ultrasonography (US) with a clinically used transducer and to evaluate the accuracy of measurement by comparing the results with values obtained microscopically. Femoral condyle samples were obtained from a 6-month-old pig and a 3-year-old pig. B-mode US images with conventional imaging and real-time spatial compound imaging (RTSCI) of osteochondral blocks were acquired. Tc determined using US (Tc-US) was measured from line data parallel to US beam direction acquired from B-mode images with an objective method for determining cartilage surface and bone-cartilage interfaces at the peak brightness values. Tc was also determined under microscopy (Tc-optical) using the corresponding points from US measurement. Tc-US was compared with Tc-optical to assess accuracy. Tc-US correlated significantly with Tc in both conventional imaging and RTSCI (r = 0.961, 0.976, respectively). Bland-Altman plots showed mean differences between Tc-optical and Tc-US were −0.0073 mm and 0.0139 mm with standard deviations of 0.171 mm and 0.131 mm for conventional imaging and RTSCI, respectively. Our results show that Tc-US measurement using B-mode US allows accurate measurement of Tc. Considering correlation coefficients between Tc-US and Tc-optical, RTSCI US may offer higher accuracy for measuring Tc than conventional methods when an objective tissue border determination algorithm is used, even though both showed good accuracy in our study.

J042033 音響共鳴現象を利用した塗膜厚さ測定のための超音波探触子の選定について

Thicknesses of both side coatings on a steel plate are measured by means of acoustic resonant spectroscopy. Focused and non-focused ultrasonic transducers are employed in this study, and effect of acoustic focusing on the accuracy of thickness measurements is investigated. Focused ultrasonic transducer is useful for measuring the thickness of coating at the local area. On the other hand, non-focused ultrasonic transducer enables us to realize the simultaneous measurement of coating thickness at both sides.

Accuracy and reliability of buccal bone height and thickness measurements from cone-beam computed tomography imaging

Cone-beam computed tomography (CBCT) imaging has broadened opportunities for examining morphologic aspects of the craniofacial complex, including alveolar bone, but limitations of the technology have yet to be defined. Through the use of comparisons with direct measurements, the purpose of this study was to investigate the accuracy and reliability of buccal alveolar bone height and thickness measurements derived from CBCT images. Twelve embalmed cadaver heads (5 female, 7 male; mean age: 77 years) were scanned with an i-CAT 17-19 unit (Imaging Sciences International, Hatfield, Pa) at 0.3 mm voxel size. Buccal alveolar bone height and thickness measurements of 65 teeth were made in standardized radiographic slices and compared with direct measurements made by dissection. All measurements were repeated 3 times by 2 independent raters and examined for intrarater and interrater reliability. Measurement means were compared with 2-tailed t tests. Agreement between direct and CBCT measurements was assessed by concordance correlation coefficients, Pearson correlation coefficients, and Bland-Altman plots. Intrarater reliability was high as were interrater correlations for all measurements (≥0.97) except CBCT buccal bone thickness (0.90). CBCT measurements did not differ significantly from direct measurements, and there was no pattern of underestimation or overestimation. The mean absolute differences were 0.30 mm in buccal bone height and 0.13 mm in buccal bone thickness with 95% limits of agreement of -0.77 to 0.81 mm, and -0.32 to 0.38 mm, respectively. Agreement between the 2 methods was higher for the measurements of buccal bone height than buccal bone thickness, as demonstrated by concordance correlation coefficients of 0.98 and 0.86, respectively. For the protocol used in this study, CBCT can be used to quantitatively assess buccal bone height and buccal bone thickness with high precision and accuracy. Comparing the 2 sets of CBCT measurements, buccal bone height had greater reliability and agreement with direct measurements than did the buccal bone thickness measurements.

Computerized nuchal translucency three dimensional reconstruction, visualization and measurement for trisomy 21 prenatal early assessment

Conventionally, measurement of ultrasonic marker, nuchal translucency or NT is accomplished by manual assessment in two dimensional ultrasound images for trisomy 21 early detection. Nonetheless, the efficiency of 2D measurement depends heavily on the image position and any deviation will prompt inaccurate measurement. Therefore, in this paper we proposed the reconstruction, visualization and measurement of nuchal translucency using three dimensional approaches for real time computation. Open-source visualization toolkit VTK was implemented for 3D interactive graphics supports. The methodology entails the virtual slider cutting plane to explicit the internal structure of ultrasound marker. It is concluded in our findings that 3D measurements of nuchal translucency provide higher accuracy and consistency of thickness measurement.

Using optical coherence tomography for the longitudinal non‐invasive evaluation of epidermal thickness in a murine model of chronic skin inflammation

Non-invasive methods are desirable for longitudinal studies examining drug efficacy and disease resolution defined as decreases in epidermal thickness in mouse models of psoriasiform skin disease. This would eliminate the need for either sacrificing animals or collecting serial skin biopsies to evaluate changes in disease progression during an individual study. The quantitation of epidermal thickness using optical coherence tomography (OCT) provides an alternative to traditional histology techniques. Using the KC-Tie2 doxycycline-repressible psoriasiform skin disease mouse model, OCT imaging was completed on diseased back skin of adult KC-Tie2 (n = 3-4) and control (n = 3-4) mice, followed immediately by the surgical excision of the same region for histologic analyses. Animals were then treated with doxycycline to suppress transgene expression and to reverse the skin disease and additional OCT images and tissues were collected 2 and 4 weeks following. Epidermal thickness was measured using OCT and histology. Optical coherence tomography and histology both demonstrated that KC-Tie2 mice had significantly thicker epidermis (~4-fold; P < 0.0001) than control animals. By 2 weeks following gene repression, decreases in epidermal thickness were observed using both OCT and histology, and were sustained through 4 weeks. Correlation analyses between histology and OCT values at all time points and in all animals revealed high significance (R(2) = 0.78); with correlation being highest in KC-Tie2 mice (R(2) = 0.92) compared to control animals (R(2) = 0.16). Non-invasive OCT imaging provided similar values as those collected using standard histologic measures in thick skin of KC-Tie2 mice but became less reliable in thinner control mouse skin, possibly reflecting limitations in resolution of OCT. Future advances in resolution of OCT may improve and allow greater accuracy of epidermal thickness measurements.

Quality and Reproducibility of Retinal Thickness Measurements in Two Spectral-Domain Optical Coherence Tomography Machines

To evaluate the accuracy and reproducibility of retinal thickness measurements in exudative age-related macular degeneration (AMD) by the Spectralis (Heidelberg Engineering, Heidelberg, Germany) and the Cirrus (Carl Zeiss Meditec, Dublin, CA) optical coherence tomography (OCT) systems. Eyes with exudative age-related macular degeneration were randomly assigned to one of eight groups, each different in the sequence of examiner and OCT system. The 512 × 128 cube program of the Cirrus and the 30° × 25° volume scan containing 32 lines of the Spectralis were performed twice. The correlation between the examinations was expressed by the interclass correlation coefficient (ICC). Enrolled in the study were 112 patients and 112 eyes (mean age, 76.5 ± 7.9 years; range 51-89), with 14 patients in each group. The mean error scores per line were 0.53 and 0.52 in the Cirrus, significantly (P < 0.001) lower than in the Spectralis (0.83 and 0.98). For automatic central retinal thickness (CRT), the ICC for Cirrus (all examinations calculated) was 0.61 for groups 1 to 4 (the same examiner) and 0.65 for groups 5 to 8 (two different examiners); for Spectralis (13.4% not calculated) the ICC was 0.93 for groups 1 to 4 and 0.86 for groups 5 to 8. After error correction, the Cirrus ICC improved to 1.0 and 0.99 and the Spectralis ICC to 1.0 in both groups. Considerable differences were found between the two systems, both of which incorporate the spectral-domain technology. Different positioning of segmentation lines, control of localization, density of included scan lines, and number of available maps explain the differences in segmentation quality and reproducibility. Manual correction of segmentation and centralization improves the reproducibility.

Research on Intelligentized Recognition Technology for Double Wavelength Laser Measurement of Thin Film Thickness

Interference image processing is the key technology of optical interference measurement. This paper introduced the problems on automatic interference fringe processing in absolutely measurement based on laser interference, digital image processing technology. The image acquisition of the SiO2 film and the pre-processing of interferogram was performed.Decimal part of the interference fringes is obtained. Using high-resolution image acquisition system and computer reads and processes the interference image, replaces the traditional work of skilled workers of high intensity for a long time and improves the film thickness measurement accuracy.

Accuracy of Oral Mucosal Thickness Measurements Using Spiral Computed Tomography

Assessment of oral mucosal thickness is important in implant surgery; however, examining the soft tissue three dimensionally is difficult. A reamer method is invasive, and a non-invasive ultrasonic method produces only low-resolution images depending on anatomic variations. The emerging technology of spiral computed tomography (CT) is an alternative to the conventional methods. Spiral CT has been a useful diagnostic tool in implant surgery. Although it delivers high radiation doses, spiral CT provides three-dimensional imaging of low-contrast structures. The purpose of the present study is to assess the accuracy of oral mucosal measurements using spiral CT. Thickness of maxillary oral mucosa was measured in five cadavers. The measurement sites were set up in buccal, palatal, and middle of the crest in the missing tooth area in the incisor, canine, premolar, and molar regions. Each cadaver was exposed to spiral CT after installing the measurement guide. After that, each site was physically measured by reamer. Linear regression and correlation analysis were performed to describe the association between radiographic and physical measurements. A total of 114 measurements were performed with statistical analyses. Mean values and standard deviations of physical and radiographic measurements were 3.12 ± 1.43 and 2.83 ± 1.70 mm, respectively. The radiographic and physical measurements demonstrate strong correlation (r = 0.90; P <0.01). Measurement error was 0.52 ± 0.36 mm. According to the regions, the measurements in buccal, palatal, and missing tooth region depicted a significant correlation (r = 0.92, r = 0.85, and r = 0.91, respectively). The boundary of the bone and mucosa was indistinguishable at 23 buccal sites. Twenty-three measurements that could not be distinguished with CT had a mean of 0.69 and standard deviation ± 0.13 mm. The correlation between spiral CT and physical measurement was high except in sites of very thin mucosa. Spiral CT can be considered an alternative method for the measurement of oral mucosal thickness. Because of the higher radiation exposure, caution should be exercised and radiation dosage versus clinical benefit assessment is required.

In vivo measurement of central corneal thickness in normal chicks (Gallus gallus domesticus) with the optical low-coherence reflectometer

To determine the practicability and accuracy of central corneal thickness (CCT) measurements in living chicks utilizing a noncontact, high-speed optical low-coherence reflectometer (OLCR) mounted on a slit lamp. Twelve male chicks (Gallus gallus domesticus). Procedures Measurements of CCT were obtained in triplicate in 24 eyes of twelve 1-day-old anaesthetized chicks using OLCR. Every single measurement taken by OLCR consisted of the average result of 20 scans obtained within seconds. Additionally, corneal thickness was determined histologically after immersion fixation in Karnovsky's solution alone (20 eyes) or with a previous injection of the fixative into the anterior chamber before enucleation (4 eyes). Central corneal thickness measurements using OLCR in 1-day-old living chicks provide a rapid and feasible examination technique. Mean CCT measured with OLCR (189.7 ± 3.34 μm) was significantly lower than histological measurements (242.1 ± 47.27 μm) in eyes with fixation in Karnovsky's solution (P = 0.0005). In eyes with additional injection of Karnovsky's fixative into the anterior chamber, mean histologically determined CCT was 195.2 ± 8.25 μm vs. 191.9 ± 8.90 μm with OLCR. A trend for a lower variance was found compared to the eyes that had only been immersion fixed. Optical low-coherence reflectometry is an accurate examination technique to measure in vivo CCT in the eye of newborn chicks. The knowledge of the thickness of the chick cornea and the ability to obtain noninvasive, noncontact measurements of CCT in the living animal may be of interest for research and development of eye diseases in chick models.

Reproducibility of segmentation error correction in age-related macular degeneration: Stratus versus Cirrus OCT

IntroductionThe accuracy of retinal thickness measurement in age-related macular degeneration by optical coherence tomography (OCT) is affected by threshold algorithm line errors. The reproducibility of error correction in Stratus and...

Non-destructive thickness characterization of Si based heterostructure by X-ray diffraction and reflectivity

High-resolution X-ray diffraction rocking curve (RC) and X-ray reflectivity (XRR) were used to characterize the Si based heterostructures grown by reduced pressure chemical vapour deposition. The investigation focused on the reliability and accuracy of thickness measurement by the different techniques. For smooth Si epilayers grown on a thin (20 nm) strained Si 0.9Ge 0.1 buffer, it is found that both XRR and RC produce reliable values that agree well with transmission electron microscope (TEM) results over a wide range. The best-fit thickness from both XRR and RC is within ±5% of the TEM measurement, with XRR producing more accurate values than RC. However, the agreement is not good for Si epilayer grown on a thick (2 μm) relaxed Si 07Ge 0.3 virtual substrate due to the presence of rough surface.

Accuracy of thickness measurement for Ge epilayers grown on SiGe/Ge/Si(100) heterostructure by x-ray diffraction and reflectivity

High-resolution x-ray diffraction rocking curve (RC), x-ray reflectivity (XRR), and transmission electron microscopy (TEM) were used to characterize strained Ge epilayers grown on relaxed SiGe/Ge/Si(100) virtual substrates by reduced pressure chemical vapor deposition. The investigation focused on the reliability and accuracy of thickness measurement by these different techniques. The authors found that both XRR and RC could give reliable values that agree well with TEM results over a wide range of Ge epilayer thicknesses. The best-fit thickness from both XRR and RC is within ±5% of the TEM measurement for a thickness in the range of 10–120 nm, with XRR producing more accurate values than RC. However, neither RC nor XRR could give reliable results for very thin Ge epilayers ( 122 nm) due to surface roughening caused by strain relaxation.