Biomedical subjects

Nicola J Ferrier

Publications and source records attributed to Nicola J Ferrier.

6 recordsLinked to original sources

PubMed2006

Comparison of retinal vessel measurements in digital vs film images.

PURPOSE: To compare central retinal artery equivalents (CRAE) and central retinal vein equivalents (CRVE) from vessels measured from images captured with a digital camera and digitized images taken with a film camera. DESIGN: Comparison of techniques. METHODS SETTING: Clinic. PATIENTS: A total of 75 eyes of 48 adults. OBSERVATION PROCEDURES: Gradings of retinal vessel diameters from images produced by using two photographic techniques: directly from a 45 degrees digital camera and digitized by scanning from a 30 degrees film-based camera. MAIN OUTCOME MEASURE: Differences in CRAE and CRVE from two types of images. RESULTS: CRAE and CRVE were highly comparable between the two techniques with correlation coefficients of 0.88 and 0.87, respectively. CONCLUSION: Estimates of CRAE and CRVE from measurements taken from digitally captured and digitized film-based images were highly comparable. It is likely that inferences about factors associated with retinal vessel diameters will be unbiased by the method of imaging.

Adult↗

PubMed2005

Detecting progression of nuclear sclerosis by using human grading versus semiautomated computer grading.

PURPOSE: To assess indices of nuclear sclerosis derived from digitized images made from color (slide) photographs. METHODS: Film-based slit lamp images taken at baseline and at 5- and 10-year follow-up examinations of the Beaver Dam Eye Study cohort were digitized, and optical traces were taken along an axis through the center of the cornea and lens. Four indices of the severity of sclerosis were calculated based on the optical densities. The associations of the original Beaver Dam grades and these indices to age, vision, and change in severity of sclerosis over two subsequent visits were compared. RESULTS: At baseline photographs, the Spearman correlation between age and severity was 0.65 for the original film-based grading (n = 4518 right eyes) and varied between 0.46 and 0.71 for the measures from digitized images. Correlations of the indices to visual acuity were 0.38 for the film-based grading and ranged from 0.32 to 0.38 for the other indices. The authors assume that nuclear sclerosis does not regress and the percentage of regression is a reflection of error in grading. The percentage of regression and progression of sclerosis over 5- and 10-year intervals was determined for each index. After 5 years, 48.2% progressed and 4.9% regressed, using the Beaver Dam grades; progression occurred in 4.9% to 9.9%, and regression occurred in 4.5% to 7.0% for the other indices. After 10 years, 61.9% progressed and 3.2% regressed using the Beaver Dam grades; progression occurred in 8.0% to 19.7%, and regression occurred in 2.6% to 9.7% for the other indices. CONCLUSIONS: Semiautomated grading of the digitized images can be used to process thousands of images with little oversight by a trained grader. Indices of sclerosis that closely parallel human grading in their relationships to age and visual acuity can be easily computed. However, the indices appear to identify significantly less progression of nuclear sclerosis than does human grading. Further development to define a useful metric for identifying severity and progression of nuclear sclerosis is needed.

Adult↗

PubMed2004

A digital video system for the automated measurement of repetitive joint motion.

Automated measurement and analysis of human motion during performance of workplace tasks are desirable for ergonomic studies. While numerous technologies exist for accurate measurement of biomechanical data, their use is often not feasible in the workplace environment. We present a digital-video based system suitable for measuring human motion of repetitive workplace tasks. Due to practical considerations, a single-camera solution is exploited by adding some control over the environment. We present an analysis of experiments demonstrating the accuracy of our system.

Algorithms↗

PubMed2004

Repetitive motion analysis: segmentation and event classification.

Acquisition, analysis, and classification of repetitive human motion for the assessment of postural stress is of central importance to ergonomics practitioners. We present a two-threshold, multidimensional segmentation algorithm to automatically decompose a complex motion into a sequence of simple linear dynamic models. No a priori assumptions were made about the number of models that comprise the full motion or about the duration of the task cycle. A compact motion representation is obtained for each segment using parameters of a damped harmonic dynamic model. Event classification was performed using cluster analysis with the model parameters as input. Experiments demonstrate the technique on complex motion.

Algorithms↗

PubMed2003

Epitaxial self-assembly of block copolymers on lithographically defined nanopatterned substrates.

Parallel processes for patterning densely packed nanometre-scale structures are critical for many diverse areas of nanotechnology. Thin films of diblock copolymers can self-assemble into ordered periodic structures at the molecular scale (approximately 5 to 50 nm), and have been used as templates to fabricate quantum dots, nanowires, magnetic storage media, nanopores and silicon capacitors. Unfortunately, perfect periodic domain ordering can only be achieved over micrometre-scale areas at best and defects exist at the edges of grain boundaries. These limitations preclude the use of block-copolymer lithography for many advanced applications. Graphoepitaxy, in-plane electric fields, temperature gradients, and directional solidification have also been demonstrated to induce orientation or long-range order with varying degrees of success. Here we demonstrate the integration of thin films of block copolymer with advanced lithographic techniques to induce epitaxial self-assembly of domains. The resulting patterns are defect-free, are oriented and registered with the underlying substrate and can be created over arbitrarily large areas. These structures are determined by the size and quality of the lithographically defined surface pattern rather than by the inherent limitations of the self-assembly process. Our results illustrate how hybrid strategies to nanofabrication allow for molecular level control in existing manufacturing processes.

Journal Article↗

PubMed2003

Automated analysis of repetitive joint motion.

Automated measurement, analysis, and comparison of human motion during performance of workplace tasks or exercise therapy are core competencies required to realize many telemedicine applications. Ergonomic studies and telemonitoring of patients performing rehabilitation exercises are examples of applications that would benefit from a representation of complex human motion in a form amenable to comparison. We present a representation of joint motion suitable for the analysis of multidimensional angular joint motion time series data. Complex motion is reduced to a concatenation motion segments, where simple dynamic models approximate the observed motion on each segment. This compact representation still enables measurement of statistics familiar to ergonomics practitioners such as cycle length and task duration. An algorithm to obtain this representation from observed motion data (time series) is given. We introduce a metric, based on a kinetic energy-like measure, to compare motions. Experiments are presented to demonstrate the representation, its relationship to previous measures and the applicability of the kinetic energy metric for motion comparison.

Algorithms↗