Absolute Thickness Research Articles

Effects of adding salmeterol/fluticasone propionate to tiotropium on airway dimensions in patients with chronic obstructive pulmonary disease

Although salmeterol/fluticasone propionate combination (SFC) therapy has been widely used for the treatment of COPD, the relationship between airway dimensions and improvement in pulmonary function remains unknown. The aim of this study was to compare the effects of SFC in combination with tiotropium (Tio) and Tio alone, on airway dimensions and pulmonary function in COPD patients. Thirty COPD patients were randomized to receive inhaled Tio (18 µg once daily) or inhaled SFC (50/250 µg twice daily) plus Tio for 12 weeks. Spirometry and CT were performed, and the St. George's Respiratory Questionnaire (SGRQ) was completed, before and after the trial. Airway dimensions were assessed by a validated CT technique, and airway wall area (WA) corrected for body surface area (BSA), percentage wall area (WA%), absolute wall thickness T/√BSA, and luminal area Ai/BSA at the right apical segmental bronchus, were measured. Treatment with SFC plus Tio significantly decreased WA/BSA (P < 0.05), WA% (P < 0.01) and T/√BSA (P < 0.01), and increased Ai/BSA (P < 0.01), whereas treatment with Tio alone had no effect. The changes in WA/BSA and Ai/BSA were significantly correlated with increases in FEV1 (r = 0.48, P < 0.05, and r = 0.36, P < 0.05, respectively). There were significant improvements in SGRQ scores after treatment with SFC plus Tio. Airway wall thickening and airway narrowing decreased after treatment with SFC plus Tio, and the changes in airway dimensions were proportional to the improvements in FEV1 . These results suggest that SFC plus Tio is more effective than Tio alone in the management of COPD patients.

Calcium supplementation does not rescue the programmed adult bone deficits associated with perinatal growth restriction

Low birth weight and poor childhood growth program a variety of adult diseases including bone disorders such as osteoporosis. We have previously reported that offspring born small, as a result of uteroplacental insufficiency, have shorter femurs, lower bone mineral content and a bone strength deficit as adults. The aim of this study was to determine the effects of calcium supplementation from adolescence on growth restricted male and female offspring which have a programmed bone deficit. Bilateral uterine vessel ligation (Restricted) or sham surgery (Control) was performed on gestational day 18 in WKY rats to induce uteroplacental insufficiency and growth restriction. At 2 months pups were allocated to one of four diet groups: diet 1—constant normal calcium diet, diet 2—variable normal calcium diet, diet 3—constant high calcium diet, diet 4—variable high calcium diet. Diet groups 1 and 3 were fed their respective diets constantly for the duration of the study. In groups 2 and 4, rats were fed one diet for 5 days, followed by a switch to a low calcium diet for the next 5 days. At 6 months Dual Energy Xray Absorptiometry (DXA) and Peripheral Quantitative Computed Tomography (pQCT) were performed on the right femur. Bone turnover markers were measured at 4 months. Male and female Restricted offspring were born 14% lighter compared to Controls ( p < 0.05). At 6 months both male and female Restricted offspring remained smaller and had shorter femurs compared to Controls ( p < 0.05). Restricted males and females had reduced trabecular and cortical content compared to Controls, regardless of diet ( p < 0.05). Trabecular bone density was lower in Restricted females only ( p < 0.05). A constant high calcium diet increased cortical BMD in Restricted male and both female groups ( p < 0.05). Measures of bone geometry indicated that Restricted offspring have narrower bones with preservation of absolute cortical thickness ( p < 0.05). Importantly, the stress strain index of bone bending strength was lower in male and female Restricted offspring, regardless of diet by up to 9.0% and 7.8%, respectively. DXA results were similar to pQCT results. Being born small, due to uteroplacental insufficiency, programs reduced adult femur length, dimensions and stress strain index. Supplementation with a high calcium diet from adolescence can increase adult cortical bone density in low birth weight males and females, and normal weight females. This increase in bone density was not sufficient to rescue the bone dimension and strength deficits which were programmed in utero, suggesting that the early life environment is critical for bone programming.

Synchrotron infrared spectroscopic ellipsometry for characterization of biofunctional surfaces

AbstractThe structural and thickness homogeneity of different biofunctional surfaces after coating an Au substrate was studied by infrared spectroscopic ellipsometry (IRSE). Monolayer coverage was achieved by washing the samples in aqueous solution. A selected cysteine‐modified CHL peptide and an anti‐glutathione S‐transfer (GST) antibody produced a characteristic change in the IR ellipsometric spectra after peptide and antibody adsorption, confirming the biosensing ability of this technique. IR ellipsometric mapping at the synchrotron storage ring BESSY II in Berlin allowed laterally resolved characterization of the protein films. The IR ellipsometric tanΨ and Δ maps revealed that the protein films are inhomogeneous in structure and thickness after adsorption of the peptide and antibody. The absolute thickness of the protein films varied considerably by up to 3 to 7 nm. We also studied cytosine films with different thicknesses (d = 58 nm and 125 nm) and a guanine film (d = 84 nm). For the two cytosine films the synchrotron spectra revealed that the thicker film in particular was rather homogeneous in thickness but inhomogeneous in structure. For the guanine film the shape of vibrational bands in the ellipsometric spectra correlated with anisotropic molecular orientations.

Ligamentum Flavum Thickness in Normal and Stenotic Lumbar Spines

A descriptive computed tomography (CT) study of the ligamentum flavum (LF) thickness in individuals with normal and stenotic lumbar spines. To establish standards for normal and pathologic range of LF thickness and its asymmetry as indicated in CT images and to examine its association with vertebral body size, age, and gender. LF lines a considerable part of the posterior and lateral walls of the spinal canal and is a major role contributor to spinal canal stenosis. Due to methodologic deficiencies (e.g., small sample size, lack of control for vertebral body size, gender, and age), the normal range of LF thickness is still controversial. Furthermore, data on important aspect of LF thickness such as left-right differences are missing. Two groups of individuals were studied. The first group included 65 individuals with lumbar spinal stenosis (LSS) (mean age: 66 +/- 9.7 years) and the second, 150 individuals (mean age: 52 +/- 19 years) without LSS-related symptoms. LF thickness was measured on CT images (Philips Brilliance 64), obtained from axial plane scan at the intervertebral disc level. Measurements were performed at the levels of L3-L4, L4-L5, and L5-S1. Analysis of variance and t test were carried out to evaluate the association between LF thickness and demographic factors. Absolute and relative LF thickness were significantly greater in the LSS group at the levels of L3-L4 and L4-L5 on both sides, compared to control group (P < 0.05). LF thickness was independent of gender (absolute and relative thickness). Even though LF thickness at all levels significantly increases with age, significant changes after the age of 60 occurred only at L3-L4. Significant asymmetry in LF thickness was found at L3-L4 (2.9 +/- 0.90 mm on the right vs. 2.76 +/- 0.90 mm on the left) and L5-S1 (3.42 +/- 1.1 mm on the right vs. 3.22 +/- 1.22 mm on the left) (P < 0.05). LF thickness is an age-dependent and gender-independent phenomenon. LF is significantly thicker on the right side. The borderline between normal and pathologic LF thickness should not be set at 4 mm.

Disparity Between Unusual Left Ventricular Morphology and Clinical Presentation and Course in Hypertrophic Cardiomyopathy

Phenotypic expression of hypertrophic cardiomyopathy (HC) is particularly heterogenous, with a wide spectrum of patterns of left ventricular (LV) hypertrophy reported.1 Although absolute maximal LV wall thickness is predictive of outcome,2 it is unresolved whether there is a relation between the precise distribution of LV wall thickening and clinical course.

Multifrequency continuous wave terahertz spectroscopy for absolute thickness determination

We present a tunable multifrequency continuous wave terahertz spectrometer based on two laser diodes, photoconductive antennas, and a coherent detection scheme. The system is employed to determine the absolute thickness of samples utilizing a proposed synthetic difference frequency method to circumvent the 2π uncertainty known from conventional photomixing systems while preserving a high spatial resolution.

Epithelial, Stromal, and Total Corneal Thickness in Keratoconus: Three-dimensional Display With Artemis Very-high Frequency Digital Ultrasound

To characterize the epithelial, stromal, and total corneal thickness profile in a population of eyes with keratoconus. Epithelial, stromal, and total corneal thickness profiles were measured in vivo by Artemis very high-frequency (VHF) digital ultrasound scanning (ArcScan) across the central 6- to 10-mm diameter of the cornea on 54 keratoconic eyes. Maps of the average, standard deviation, minimum, maximum, and range of epithelial, stromal, and total corneal thickness were plotted. The average location of the thinnest epithelium, stroma, and total cornea were found. The cross-sectional semi-meridional stromal and total corneal thickness profiles were calculated using annular averaging. The absolute stromal and total corneal thickness progressions relative to the thinnest point were calculated using annular averaging as well as for 8 semi-meridians individually. The mean corneal vertex epithelial, stromal, and total corneal thicknesses were 45.7+/-5.9 microm, 426.4+/-38.5 microm, and 472.2+/-41.4 microm, respectively. The average epithelial thickness profile showed an epithelial doughnut pattern characterized by localized central thinning surrounded by an annulus of thick epithelium. The thinnest epithelium, stroma, and total cornea were displaced on average by 0.48+/-0.66 mm temporally and 0.32+/-0.67 mm inferiorly, 0.31+/-0.45 mm temporally and 0.54+/-0.37 mm inferiorly, and 0.31+/-0.43 mm temporally and 0.50+/-0.35 mm inferiorly, respectively, with reference to the corneal vertex. The increase in semi-meridional absolute stromal and total corneal thickness progressions was greatest inferiorly and lowest temporally. Three-dimensional thickness mapping of the epithelial, stromal, and total corneal thickness profiles characterized thickness changes associated with keratoconus and may help in early diagnosis of keratoconus.

Measurement of Skull Bone Thickness for Bone-Anchored Hearing Aids

A-mode ultrasound scanning with coded signals allows bone thickness measurements at the site of bone-anchored hearing aid surgery as compared to computed tomographic scanning and mechanical measurements. Adequate bone thickness is a prerequisite for successful, long-lasting osseointegration of titanium fixtures for bone-anchored hearing aids. Computed tomography can be used to measure bone thickness but has several drawbacks. Bone thickness was measured at the site of bone-anchored hearing aids surgery in 28 formaldehyde-preserved human cadaver temporoparietal bones. Four blinded investigators used a hand-held, A-mode ultrasound system with direct coupling at 2.25 MHz transducer using coded signals (SonoPointer) and repeated the measurements twice. Comparisons were made with high-resolution computed tomographic scanning and mechanical micrometer caliper measurements. There was significant anatomical variation in the temporoparietal bones. Computed tomography was in good agreement with the mechanical reference. All specimens could be measured by the SonoPointer. The mean difference between the mechanical control and ultrasound scanning averaged for all measurements by all investigators was 0.3 mm (standard deviation, 1.2 mm). Trained ultrasound experts yielded better results (mean difference, 0.3 mm; standard deviation, 1.0 mm). Agreement was best for bone thickness up to 5 mm. Outliers occurred in bones thicker than 7.5 mm. The SonoPointer is a promising, noninvasive, hand-held tool for real-time measurement of bone thickness in bone-anchored hearing aid surgery, especially for children. Even disregarding the absolute thickness reading, the SonoPointer could be used to search intraoperatively for a local maximum of bone thickness.

Endosonographic radial tumor thickness after neoadjuvant chemoradiation therapy to predict response and survival in patients with locally advanced esophageal cancer: a prospective multicenter phase ll study by the Swiss Group for Clinical Cancer Research (SAKK 75/02)

EUS response assessment in patients with locally advanced esophageal cancer undergoing neoadjuvant chemoradiation therapy (CRT) is limited by disintegration of the involved anatomic structures. Predictive and prognostic values of a prospectively defined maximum tumor thickness (MTT). Prospective open-label phase ll study (SAKK 75/02). Multicenter, nationwide. Of 66 patients with primary CRT, 56 underwent en bloc esophagectomy. EUS-measured MTT before and 2-5 weeks after CRT (yMTT). Cutoffs: (1) absolute thickness (yMTT) after CRT < or = 6 mm; (2) relative reduction compared with baseline (ratio yMTT/MTT) < or = 50%. Correlation between EUS measurements and histopathologic tumor regression grade (TRG) and overall survival (OS). Sixteen of 56 patients were not included for EUS evaluation (10 severe stenosis, 5 MTT not measured, 1 intolerance to second EUS). Characteristics (n = 40) were as follow: median age, 60 years; squamous cell carcinoma, 42%; and adenocarcinoma (AC), 58%. Initial stage was: 10 T2N1, 3 T3N0, 26 T3N1, 1 T3Nx; 14 of 23 AC Siewert type 1. Wilcoxon rank sum test showed significant correlation of TRG1 with yMTT < or = 6 mm (P = .008) and yMTT/MTT < or = 50% (P = .003). The effect of yMTT on TRG1 was significant (P = .0193; odds ratio, 0.687 [95% CI, 0.502-0.941]). The predefined cutoff of < or = 6 mm for yMTT was predictive for TRG1 (P = .0037; Fisher exact test). After a median follow-up of 28.6 months, there was a clear trend for benefit in OS with yMTT < or = 6 mm and yMTT/MTT < or = 50%. Small sample size. In a multicenter setting, MTT measured by EUS after CRT was highly predictive for response and showed a clear trend for predicting survival.

Stabilization of a very high- k crystalline ZrO 2 phase by post deposition annealing of atomic layer deposited ZrO 2/La 2O 3 dielectrics on germanium

The impact of the ZrO 2/La 2O 3 film thickness ratio and the post deposition annealing in the temperature range between 400 °C and 600 °C on the electrical properties of ultrathin ZrO 2/La 2O 3 high- k dielectrics grown by atomic layer deposition on (1 0 0) germanium is investigated. As-deposited stacks have a relative dielectric constant of 24 which is increased to a value of 35 after annealing at 500 °C due to the stabilization of tetragonal/cubic ZrO 2 phases. This effect depends on the absolute thickness of ZrO 2 within the dielectric stack and is limited due to possible interfacial reactions at the oxide/Ge interface. We show that adequate processing leads to very high- k dielectrics with EOT values below 1 nm, leakage current densities in the range of 0.01 A/cm 2, and interface trap densities in the range of 2–5 × 10 12 eV −1 cm −2.

Measurement of the Absolute Optical Thickness Distribution of a Mask-blank Glass by a Phase-shifting, Wavelength Tuning Interferometry

The uniformity of the surface flatness, optical thickness distribution, and refractive index have been requested in semi-conductor industry. The absolute optical thickness of a mask-blank glass of seven-inch square and 3.1 mm thickness was measured by three-surface interferometry in a wavelength tuning Fizeau interferometer. Wavelength-tuning interferometry can separate three interference signals of the front surface shape, the rear surface shape and the optical thickness in frequency space. The wavelength of a tunable laser diode source was scanned linearly from 632 nm to 642 nm and a CCD detector recorded two thousand interference images. The number of phase variation of the interference fringes during the wavelength scanning was counted by a temporal discrete Fourier transformation. The initial and final phases of the interferograms before and after the scanning were measured by a phase shifting technique with fine tunings of the wavelengths at 632nm and 642 nm. The optical thickness defined by the group refractive index at the central wavelength of 637 nm can be measured by this technique. Experimental results show that the cross talk in multiple-surface interferometry caused a systematic error of 0.6 microns in the measured optical thickness.

A traceable calibration method for spectroscopic ellipsometry

A method for calibrating the spectroscopic ellipsometry by X-ray reflectivity is presented. As an indirect method，spectroscopic ellipsometry does not have the traceability because the measured film thickness is dependent on its optical constant. In contrast，at the grazing angle，the X-ray reflectivity can be used to measure the absolute thickness of thin film with sub-nanometer precision，and is independent of the optical constant. Five SiO2 films were deposited on the substrate of single crystal silicon with the thickness of 2 nm，18 nm，34 nm，61 nm，and 170 nm，respectively. The results of spectroscopic ellipsometry and X-ray reflectivity were well fitted by a liner equation with slope of 1013±0013 and its intercept was set to zero，which means this calibration method is valid for spectroscopic ellipsometry in the determination of the thickness of thin films.

Maksymilian Rose, neurolog, psychiatra i wybitny znawca cytoarchitektoniki kory mózgu

<dm:abstracts xmlns:dm="http://www.elsevier.com/xml/dm/dtd"><ce:abstract xmlns:ce="http://www.elsevier.com/xml/common/dtd" view="all" class="author" id="aep-abstract-id1"><ce:section-title>Publisher Summary</ce:section-title><ce:abstract-sec view="all" id="aep-abstract-sec-id1"><ce:simple-para id="SP0005" view="all">This chapter discusses the principles of classical architectonic mapping in the context of recent imaging techniques. It presents an observer-independent approach for a quantitative analysis of cortical areas and their borders, which is based on a multivariate statistical analysis of the cytoarchitecture and illustrates the application of this approach for the cytoarchitectonic mapping of the human visual cortex. Important criteria for cytoarchitectonic mapping are the absolute thickness of cortical layers, the proportionate thickness of a layer relative to the other cortical layers and to the total cortical depth, the presence of clearly recognizable laminar borders and vertical columns, the packing density and size of neuronal cell bodies, the homogeneous or clustered distribution of cell bodies throughout the layers, and the presence of special cell types such as Betz cells. Understanding the regional distributions of neurotransmitter receptors is likely to provide a crucial intermediary level of description between function and structure, since different cytoarchitectonic and functional areas have different mean receptor densities as well as distinct laminar distribution patterns. Another way for a better understanding of brain function and the underlying anatomy is to compare architectonic maps obtained in postmortem brains with activation maps obtained in functional imaging studies in a common spatial reference system. Since these two kinds of maps stem from different subsets of brains, such a comparison must be performed on a probabilistic basis.</ce:simple-para></ce:abstract-sec></ce:abstract></dm:abstracts>

New Modeling of Reflection Interference Contrast Microscopy Including Polarization and Numerical Aperture Effects: Application to Nanometric Distance Measurements and Object Profile Reconstruction

We have developed a new and improved optical model of reflection interference contrast microscopy (RICM) to determine with a precision of a few nanometers the absolute thickness h of thin films on a flat surface in immersed conditions. The model takes into account multiple reflections between a planar surface and a multistratified object, finite aperture illumination (INA), and, for the first time, the polarization of light. RICM intensity I is typically oscillating with h. We introduce a new normalization procedure that uses the intensity extrema of the same oscillation order for both experimental and theoretical intensity values and permits us to avoid significant error in the absolute height determination, especially at high INA. We also show how the problem of solution degeneracy can be solved by taking pictures at two different INA values. The model is applied to filled polystyrene beads and giant unilamellar vesicles of radius 10-40 microm sitting on a glass substrate. The RICM profiles I(h) can be fitted for up to two to three oscillation orders, and extrema positions are correct for up to five to seven oscillation orders. The precision of the absolute distance and of the shape of objects near a substrate is about 5 nm in a range from 0 to 500 nm, even under large numerical aperture conditions. The method is especially valuable for dynamic RICM experiments and with living cells where large illumination apertures are required.

An experimental method for calibration of the plasmon mean free path

Transmission electron microscopy specimens in the form of elongated, conical needles were made using a dual-beam focused ion beam system, allowing the specimen thickness to be geometrically determined for a range of thickness values. From the same samples electron energy loss maps were acquired and the plasmon mean free path (lambda) for inelastic scattering was determined experimentally from the measured values of specimen thickness. To test the method lambda was determined for Ni (174 +/- 17 nm), alpha-Al(2)O(3) (143 +/- 14 nm), Si (199 +/- 20 nm) and amorphous SiO(2) (238 +/- 12 nm), and compared both to experimental values of lambda taken from the literature and to calculated values. The calculated values of lambda significantly underestimate the true sample thickness for high accelerating voltages (300 kV) and large collection angles. A linear dependence of lambda on thickness was confirmed for t/lambda < 0.5-0.6, but this method also provides an approach for calibrating lambda at sample thicknesses for which multiple scattering occurs, thus expanding the thickness range over which electron energy loss spectroscopy can be used to determine the absolute sample thickness (t/lambda > 0.6). The experimental method proposed in this contribution offers a means to calibrate lambda for any type of material or phase that can be milled using a focused ion beam system.

Left atrial wall thickness in paroxysmal atrial fibrillation by multislice-CT is initial marker of structural remodeling and predictor of transition from paroxysmal to chronic form

Purpose We used ECG-gated MSCT to evaluate alterations in the LA wall in patients with paroxysmal atrial fibrillation (AF) (PAF) and compared with chronic AF (CAF) and normal sinus rhythm (NSR). Materials and methods We enrolled 3 groups, each consisting of 62 patients with either recurrent PAF (48 males, 65 ± 11 years), CAF (43 males, 69 ± 9 years), or NSR without any history of AF (40 males, 64 ± 11 years) for a total of 186 study patients. In CT, the absolute LA wall thickness (LAT) and LA volumes were calculated. Results In CT, patients with PAF had significantly thicker LAT than those with either CAF or NSR (2.4 ± 0.2 mm in PAF > 2.1 ± 0.2 mm in CAF or 1.9 ± 0.2 mm in NSR, p < 0.01). Patients with CAF had significantly larger LA volume than those with either PAF or NSR ( p < 0.01). Subsequently, 9 of the 62 patients with PAF developed CAF over a mean follow-up period of 19 ± 22 months. The mean LAT was significantly thinner in patients who had transitioned from PAF to CAF than in those who had not (2.2 ± 0.2 mm and 2.4 ± 0.2 mm, respectively) ( p < 0.01). Receiver operating characteristic analysis demonstrated that the area under the curve for LAT was greater than that for LA volume in CT and LAD in transthoracic echocardiogram. In the Kaplan–Meier analysis, the transition from PAF to CAF was observed more frequently in patients with LAT < 2.4 mm than LAT ≥ 2.4 mm ( p = 0.018). Conclusions Alteration of the LA wall may suggest a part of structural remodeling in AF before the occurrence of LA dilatation. LAT in CT seems to be a useful predictor of the transition from PAF to CAF in patients with PAF.

Retinal Nerve Fiber Layer Thickness Measurement Comparability between Time Domain Optical Coherence Tomography (OCT) and Spectral Domain OCT

Time domain optical coherence tomography (TD-OCT) has been used commonly in clinical practice, producing a large inventory of circular scan data for retinal nerve fiber layer (RNFL) assessment. Spectral domain (SD)-OCT produces three-dimensional (3-D) data volumes. The purpose of this study was to create a robust technique that makes TD-OCT circular scan RNFL thickness measurements comparable with those from 3-D SD-OCT volumes. Eleven eyes of 11 healthy subjects and 7 eyes of 7 subjects with glaucoma were enrolled. Each eye was scanned with one centered and eight displaced TD-OCT scanning circles. One 3-D SD-OCT cube scan was obtained at the same visit. The matching location of the TD-OCT scanning circle was automatically detected within the corresponding 3-D SD-OCT scan. Algorithm performance was assessed by estimating the difference between the detected scanning circle location on 3-D SD-OCT volume and the TD-OCT circle location. Global and sectoral RNFL thickness measurement errors between the two devices were also compared. The difference (95% confidence interval) in scanning circle center locations between TD- and SD-OCT was 2.3 (1.5-3.2) pixels (69.0 [45.0-96.0] microm on the retina) for healthy eyes and 3.1 (2.0-4.1) pixels (93.0 [60.0-123.0] microm on the retina) for glaucomatous eyes. The absolute RNFL thickness measurement difference was significantly smaller with the matched scanning circle. Scan location matching may bridge the gap in RNFL thickness measurements between TD-OCT circular scan data and 3-D SD-OCT scan data, providing follow-up comparability across the two generations of OCTs.

Stromal Thickness in the Normal Cornea: Three-dimensional Display With Artemis Very High-Frequency Digital Ultrasound

To characterize the stromal thickness profile in a population of normal eyes. Stromal thickness profile was measured in vivo by Artemis very high-frequency digital ultrasound scanning (ArcScan, Morrison, Colo) across the central 10-mm corneal diameter on 110 normal eyes. Maps of the average, standard deviation, minimum, maximum, and range of stromal thickness were plotted. The average location of the thinnest stroma was found. The cross-sectional hemi-meridional stromal thickness profile was calculated using annular averaging. The absolute stromal thickness progression relative to the thinnest point was calculated using annular averaging as well as for 8 hemi-meridians individually. The mean stromal thickness at the corneal vertex and at the thinnest point were 465.4+/-36.9 mum and 461.8+/-37.3 mum, respectively. The thinnest stroma was displaced on average 0.17+/-0.31 mm inferiorly and 0.33+/-0.40 mm temporally from the corneal vertex. The average absolute stromal thickness progression from the thinnest point could be described by the quadratic equation: stromal thickness = 6.411 x radius(2) + 2.444 x radius (R(2) = 0.999). Absolute stromal thickness progression was independent of stromal thickness at the thinnest point. The increase in hemi-meridional absolute stromal thickness progression was greatest superiorly and lowest temporally. Three-dimensional thickness mapping of the corneal stroma and stromal thickness progression in a population of normal eyes represent a normative data set, which may help in early diagnosis of corneal abnormalities such as keratoconus and pellucid marginal degeneration. Absolute stromal thickness progression was found to be independent of stromal thickness.

White-light scanning interferometer for absolute nano-scale gap thickness measurement

A special configuration of white-light scanning interferometer is described for measuring the absolute air gap thickness between two planar plates brought into close proximity. The measured gap is not located in any interference arm of the interferometer, but acts as an amplitude-and-phase modulator of the light source. Compared with the common white-light interferometer our approach avoids the influence of the chromatic dispersion of the planar plates on the gap thickness quantification. It covers a large measurement range of from approximate contact to tens of microns with a high resolution of 0.1 nm. Detailed analytical models are presented and signal-processing algorithms based on convolution and correlation techniques are developed. Practical measurements are carried out and the experimental results match well with the analysis and simulation. Short-time and long-time repeatabilities are both tested to prove the high performance of our method.

Automatic Segmentation and Quantitative Analysis of the Articular Cartilages From Magnetic Resonance Images of the Knee

In this paper, we present a segmentation scheme that automatically and accurately segments all the cartilages from magnetic resonance (MR) images of nonpathological knees. Our scheme involves the automatic segmentation of the bones using a three-dimensional active shape model, the extraction of the expected bone-cartilage interface (BCI), and cartilage segmentation from the BCI using a deformable model that utilizes localization, patient specific tissue estimation and a model of the thickness variation. The accuracy of this scheme was experimentally validated using leave one out experiments on a database of fat suppressed spoiled gradient recall MR images. The scheme was compared to three state of the art approaches, tissue classification, a modified semi-automatic watershed algorithm and nonrigid registration (B-spline based free form deformation). Our scheme obtained an average Dice similarity coefficient (DSC) of (0.83, 0.83, 0.85) for the (patellar, tibial, femoral) cartilages, while (0.82, 0.81, 0.86) was obtained with a tissue classifier and (0.73, 0.79, 0.76) was obtained with nonrigid registration. The average DSC obtained for all the cartilages using a semi-automatic watershed algorithm (0.90) was slightly higher than our approach (0.89), however unlike this approach we segment each cartilage as a separate object. The effectiveness of our approach for quantitative analysis was evaluated using volume and thickness measures with a median volume difference error of (5.92, 4.65, 5.69) and absolute Laplacian thickness difference of (0.13, 0.24, 0.12) mm.