Search PubMed⌕ Search

Biomedical subjects

K A Nugent

Publications and source records attributed to K A Nugent.

5 recordsLinked to original sources
PubMed2001

Phase retrieval from images in the presence of first-order vortices.

We discuss retrieval of the phase of quantum-mechanical and classical wave fields in the presence of first-order vortices. A practical method of phase retrieval is demonstrated which is robust in the presence of noise. Conditions for the uniqueness of the retrieved phase are discussed and we show that determination of the phase in a given plane requires a series of at least three two-dimensional intensity images at different propagation distances. The method is applicable to a wide range of scenarios such as the imaging of imperfect crystals, quantitative determination of the strength of vortex filaments in high-temperature superconductors, and x-ray and electron holography.

Journal Article↗
PubMed2000

Confocal laser scanning ophthalmoscope and spherical harmonics used as a possible aid to detect glaucoma.

We present a procedure whereby the confocal laser scanning ophthalmoscope can be used to extract information about the three-dimensional structure of the central excavated area or the cup of the optic nerve head of the eye. The data are analyzed in terms of spherical harmonics. It is hypothesized that the shape of the cup of the optic nerve head for a normal eye can be parameterized by a specific set of spherical harmonic coefficients and is different from the set of coefficients describing a glaucomatous eye. The sets of coefficients are analyzed by using multivariate statistics and can in turn be used to classify new observations. Preliminary results indicate that there are significant differences in the coefficients and that the procedure might have potential as a diagnostic aid for the detection or the screening of glaucoma.

Glaucoma↗
PubMed2000

Noninterferometric quantitative phase imaging with soft x rays.

We demonstrate quantitative noninterferometric x-ray phase-amplitude measurement. We present results from two experimental geometries. The first geometry uses x rays diverging from a point source to produce high-resolution holograms of submicrometer-sized objects. The measured phase of the projected image agrees with the geometrically determined phase to within +/-7%. The second geometry uses a direct imaging microscope setup that allows the formation of a magnified image with a zone-plate lens. Here a direct measure of the object phase is made and agrees with that of the magnified object to better than +/-10%. In both cases the accuracy of the phase is limited by the pixel resolution.

Journal Article↗
PubMed1997

Use of a confocal laser scanning ophthalmoscope to detect glaucomatous cupping of the optic disc.

PURPOSE: The aim of the present study was to test the hypothesis that the three-dimensional (3-D) topography of the optic disc contains sufficient information to diagnose glaucoma with a high degree of reliability. METHODS: The Zeiss 'Confocal Laser Scanning Ophthalmoscope' (CLSO) was used to obtain digitized samples of 3-D images of optic nerve heads from the following three groups of patients: (i) 40 normals with normal optic discs, normal Humphrey 24-2 full threshold visual fields and an intraocular pressure (IOP) < or = 21 mmHg, (ii) 20 established glaucoma patients with cupping, glaucomatous field loss and an IOP > 21 mmHg; and (iii) 20 early glaucoma patients with early cupping, field loss with a mean defect less than -10 dB and IOP > 21 mmHg. The cupping in these patients was paramaterized by spherical harmonics and was classified by multivariate statistical analysis. RESULTS: Of 40 glaucoma patients, 39 were correctly classified. Of 40 normal patients one was classified as glaucoma. CONCLUSIONS: This study demonstrates that the CLSO, with the use of spherical harmonics, can differentiate glaucomatous from normal optic discs in this selected group of patients without the need for a skilled observer. This constitutes a promising technique to be tested on a large, unselected body of patients as a screening tool.

Adult↗