http://hdl.handle.net/10379/715 Sun, 29 Oct 2017 23:53:01 GMT 2017-10-29T23:53:01Z http://aran.library.nuigalway.ie/:80/bitstream/id/2095/ http://hdl.handle.net/10379/715 http://hdl.handle.net/10379/6943 Experimental and numerical assessment of MRI-induced temperature change and SAR distributions in phantoms Colgan, Niall; Van der Putten, Wil; Tuohy, Brendan Eskola, H., Väisänen, O., Viik, J., Hyttinen, J. During an MR procedure, most of the transmitted RF power is transformed into heat within the patient’s tissue and implants as a result of resistive losses which is referred to as the specific energy absorption rate (SAR) (1). The European committee for electrotechnical standardisation (CENELEC) has mandated that all scanners must measure the specific absorption rate of radiofrequency in patients and develop system safeguards to ensure that the limits set out IEC 60602-3-33 are not exceeded. Accurate estimation of SAR is critical to safeguard in unconscious/sedated patients, patients with compromised thermoregulation, implant patients, pregnant patients and neonates who require an MRI procedure. The increased static field strength and RF duty cycle capabilities in modern MRI scanners means that systems can easily exceed safe SAR levels for patients (2). Advisory protocols routine used to establish QA protocols do not have advise on the testing of SAR levels in MRI and this is not routinely measured in annual medical physics QA. There is increasing need to verify the manufacturers SAR estimations. Thu, 01 Jun 2017 00:00:00 GMT http://hdl.handle.net/10379/6943 2017-06-01T00:00:00Z 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/10379/6136 Irish Machine Vision and Image Processing Conference Proceedings 2016 Devaney, Nicholas Nicholas Devaney [No abstract available] Fri, 01 Jan 2016 00:00:00 GMT http://hdl.handle.net/10379/6136 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