http://hdl.handle.net/10379/716 Sun, 29 Oct 2017 23:53:48 GMT 2017-10-29T23:53:48Z http://hdl.handle.net/10379/6314 Understanding the changes of cone reflectance in adaptive optics flood illumination retinal images over three years Mariotti, Letizia; Devaney, Nicholas; Lombardo, Giuseppe; Lombardo, Marco Although there is increasing interest in the investigation of cone reflectance variability, little is understood about its characteristics over long time scales. Cone detection and its automation is now becoming a fundamental step in the assessment and monitoring of the health of the retina and in the understanding of the photoreceptor physiology. In this work we provide an insight into the cone reflectance variability over time scales ranging from minutes to three years on the same eye, and for large areas of the retina (>= 2.0 x 2.0 degrees) at two different retinal eccentricities using a commercial adaptive optics (AO) flood illumination retinal camera. We observed that the difference in reflectance observed in the cones increases with the time separation between the data acquisitions and this may have a negative impact on algorithms attempting to track cones over time. In addition, we determined that displacements of the light source within 0.35 mm of the pupil center, which is the farthest location from the pupil center used by operators of the AO camera to acquire high-quality images of the cone mosaic in clinical studies, does not significantly affect the cone detection and density estimation. (C) 2016 Optical Society of America Fri, 01 Jan 2016 00:00:00 GMT http://hdl.handle.net/10379/6314 2016-01-01T00:00:00Z http://hdl.handle.net/10379/6116 Performance analysis of cone detection algorithms Mariotti, Letizia; Devaney, Nicholas Many algorithms have been proposed to help clinicians evaluate cone density and spacing, as these may be related to the onset of retinal diseases. However, there has been no rigorous comparison of the performance of these algorithms. In addition, the performance of such algorithms is typically determined by comparison with human observers. Here we propose a technique to simulate realistic images of the cone mosaic. We use the simulated images to test the performance of two popular cone detection algorithms and we introduce an algorithm which is used by astronomers to detect stars in astronomical images. We use Free Response Operating Characteristic (FROC) curves to evaluate and compare the performance of the three algorithms. This allows us to optimize the performance of each algorithm. We observe that performance is signicantly enhanced by up-sampling the images. We investigate the eect of noise and image quality on cone mosaic parameters estimated using the dierent algorithms, nding that the estimated regularity is the most sensitive parameter. Wed, 01 Apr 2015 00:00:00 GMT http://hdl.handle.net/10379/6116 2015-04-01T00:00:00Z http://hdl.handle.net/10379/5835 In vivo correlation mapping microscopy McGrath, James; Alexandrov, Sergey; Owens, Peter; Subhash, Hrebesh; Leahy, Martin To facilitate regular assessment of the microcirculation in vivo, noninvasive imaging techniques such as nailfold capillaroscopy are required in clinics. Recently, a correlation mapping technique has been applied to optical coherence tomography (OCT), which extends the capabilities of OCT to microcirculation morphology imaging. This technique, known as correlation mapping optical coherence tomography, has been shown to extract parameters, such as capillary density and vessel diameter, and key clinical markers associated with early changes in microvascular diseases. However, OCT has limited spatial resolution in both the transverse and depth directions. Here, we extend this correlation mapping technique to other microscopy modalities, including confocal microscopy, and take advantage of the higher spatial resolution offered by these modalities. The technique is achieved as a processing step on microscopy images and does not require any modification to the microscope hardware. Results are presented which show that this correlation mapping microscopy technique can extend the capabilities of conventional microscopy to enable mapping of vascular networks in vivo with high spatial resolution in both the transverse and depth directions. Tue, 01 Mar 2016 00:00:00 GMT http://hdl.handle.net/10379/5835 2016-03-01T00:00:00Z http://hdl.handle.net/10379/5785 A recent change in the optical and gamma ray polarization of the Crab nebula and pulsar Moran, Paul; Kyne, Gillian; Redfern, R. M.; Shearer, Andrew We report on observations of the polarization of optical and γ-ray photons from the Crab nebula and pulsar system using the Galway Astronomical Stokes Polarimeter (GASP), the Hubble Space Telescope, Advanced Camera for Surveys and the International Gamma-Ray Astrophysics Laboratory satellite (INTEGRAL). These, when combined with other optical polarization observations, suggest that the polarized optical emission and γ-ray polarization changes in a similar manner. A change in the optical polarization angle has been observed by this work, from 109.5 ± 0 ∘ . .∘ 7 in 2005 to 85.3 ± 1 ∘ . .∘ 4 in 2012. On the other hand, the γ-ray polarization angle changed from 115 ± 11° in 2003–2007 to 80 ± 12° in 2012–2014. Strong flaring activities have been detected in the Crab nebula over the past few years by the high-energy γ-ray missions Agile and Fermi, and magnetic reconnection processes have been suggested to explain these observations. The change in the polarized optical and γ-ray emission of the Crab nebula/pulsar as observed, for the first time, by GASP and INTEGRAL may indicate that reconnection is possibly at work in the Crab nebula. We also report, for the first time, a non-zero measure of the optical circular polarization from the Crab pulsar+knot system. Journal article Thu, 31 Dec 2015 00:00:00 GMT http://hdl.handle.net/10379/5785 2015-12-31T00:00:00Z