Gonzalo Muyo's research while affiliated with University of Glasgow and other places

Publications (39)

Article
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We demonstrate a multimode detection system in a scanning laser ophthalmoscope (SLO) that enables simultaneous operation in confocal, indirect, and direct modes to permit an agile trade between image contrast and optical sensitivity across the retinal field of view to optimize the overall imaging performance, enabling increased contrast in very wid...
Chapter
Hybrid optical–digital imaging involves a combination of optical coding during image formation and digital decoding and image reconstruction. This process offers enhanced functionality beyond what is possible using conventional purely optical imaging, for example, in the fields of miniaturization, cost reduction, extended depth of field and three-d...
Conference Paper
Full-text available
While the performance of optical imaging systems is fundamentally limited by diffraction, the design and manufacture of practical systems is intricately associated with the control of optical aberrations. The fundamental Shannon limit for the number of resolvable pixels by an optical aperture is generally therefore not achieved due to the presence...
Article
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Optical coherence tomography (OCT) and reflectance imaging are used in clinical practice to measure the thickness and transverse dimensions of retinal features. The recent trend towards increasing the field of view (FOV) of these devices has led to an increasing significance of the optical aberrations of both the human eye and the device. We report...
Article
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Previous reports have demonstrated that it is possible to emulate the imaging function of a single conventional lens with an N×N array of identical lenslets to provide an N-fold reduction in imaging-system track length. This approach limits the application to low-resolution imaging. We highlight how using an array of dissimilar lenslets, with an ar...
Article
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PurposeTo determine whether there are differences in retinal vascular oxygen saturation measurements, estimated using a hyperspectral fundus camera, between normal eyes and treated eyes of subjects with asymmetrical primary open-angle glaucoma (POAG).MethodsA noninvasive hyperspectral fundus camera was used to acquire spectral images of the retina...
Conference Paper
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Synergistic combination of innovative optical design with computational image recovery promises high performance imaging from cheaper, lighter and more compact optics. We describe practical multi-aperture, multi-scale and hybrid-imaging systems.
Article
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A Monte Carlo simulation of light propagation through the retina has been developed to understand the path-length distributions within the retinal vessel. For full-field illumination, the path-length distribution within the vessel comprises directly backscattered light and light that has passed once or twice through the vessel. The origins of these...
Conference Paper
Multi-aperture imaging brings super-resolution as an additional tool for computational imaging. Optical design and simulation results for a 3x3-multi-aperture system and experimental results using a 5x5-multi-camera device are reported.
Patent
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PSF coding has become well known in recent years. Although it enables significant increases in the depth of field, defocus introduces artifacts in images that are a major detraction from the final image quality. A method is described that enables the deduction or defocus and consequently the removal of these artifacts. The principle of the disclose...
Article
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Multichanneled imaging systems rely on nonredundant images recorded by an array of low-resolution imagers to enable construction of a high-resolution image. We show how the varying degree of redundancy associated with imaging throughout the imaged volume effects image quality. Using ray-traced image simulations and a metric used as a proxy for huma...
Article
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We report the design of binary-amplitude masks that in conjunction with digital restoration enable mitigation of optical aberrations. Essentially, the design process aims to maintain high modulation-transfer functions by reducing destructive interference of optical-transfer-function phasors. Two optimization techniques are described: so-called cont...
Article
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We report the design of binary-amplitude masks that in conjunction with digital restoration enable mitigation of optical aberrations. Essentially, the design process aims to reduce destructive interferences in the optical transfer function.
Article
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To assess the accuracy of human blood oximetry measurements in a model eye with a hyperspectral fundus camera. Seven human whole blood samples (two arterial, five venous) were obtained, the oxygen saturations measured with a CO oximeter, and the samples inserted into quartz tubes with internal diameters of 100 and 150 μm. The tubes (n = 20; ten 100...
Article
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The work described here involved the use of a modified fundus camera to obtain sequential hyperspectral images of the retina in 14 normal volunteers and in 1 illustrative patient with a retinal vascular occlusion. The paper describes analysis techniques, which allow oximetry within retinal vessels; these results are presented as retinal oximetry ma...
Article
Purpose To develop an instrument and techniques for useful absolute and relative clinical oximetry of the retina.Methods A novel snapshot multispectral imaging system has been optimised for retinal oximetry. Eight monochromatic images of the retina are recorded with a field of view of 24 degrees. Algorithms calculate the absorption of light at each...
Article
The use of hybrid optical-digital techniques facilitates improved optimisation of imaging systems. It involves the combined use of optical coding of an image using pupil-plane phase-modulation of the transmitted wavefront and postdetection digital decoding. Previous research in hybrid imaging tends to emphasize constancy of the modulation transfer...
Article
Full-text available
We demonstrate an experimental method to obtain a continuously variable hybrid imaging system that uses two generalized cubic phase masks, to enable real-time optimization of the trade between extended depth-of-field and noise gain. We obtain point-spread functions as a function of the rotation angle and show an example of optimization based on rec...
Conference Paper
A snapshot multi-spectral imaging technique is described which employs cascaded birefringent interferometers to simultaneously project multiple spectral images onto a single detector array. Example images are also shown.
Conference Paper
Previous research in hybrid imaging tends to have emphasized constancy of the modulation transfer function and ignored the significant variations in the phase-transfer function.
Article
Full-text available
A wavefront-coded imaging system employing a spatial light modulator (SLM) for the agile implementation of phase masks is presented. The SLM is a liquid crystal display that can be modulated to implement cubic phase masks of variable coding strength. These phase masks produce broad point spread functions insensitive to defocus aberration and are us...
Article
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We describe the use of wavefront coding for the mitigation of optical aberrations in a thermal imaging system. Diffraction-limited imaging is demonstrated with a simple singlet which enables an approximate halving in length and mass of the optical system compared to an equivalent two-element lens.
Conference Paper
Whereas previous reported wavefront coding research has emphasised constancy of the PSF, we show that optimal image quality normally occurs for systems in which the PSF varies significantly; placing increased demands on image restoration algorithms.
Article
Purpose Use of sequential, and 'snapshot' hyperspectral imagers to measure oxygen saturation in retinal vessels in normals, and examples of eye disease, eg glaucoma, and retinovascular diseases. Validation of estimated oximetry values using a model eye.Methods A sequential hyperspectral imager was constructed using a fundus camera with built-in liq...
Article
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We present a comprehensive study of the effect of detector sampling on wavefront-coded systems. Two important results are obtained: the spurious response ratios are reduced in wavefront-coded systems with a cubic phase mask and detector sampling does not compromise the restoration of wavefront-coded images with extended depth of field. Rigorous com...
Article
Full-text available
The design of modern imaging systems is intricately concerned with the control of optical aberrations. Traditionally this involves a multi-parameter optimisation of the lens optics to achieve acceptable image quality at the detector. There is increasing interest in a more generalised approach whereby digital image processing is incorporated into th...
Article
Full-text available
We present the results of the utilization of a Spatial Light Modulator Liquid Crystal Display for the implementation of wavefront codification procedures in an imaging system. The light modulator works in transmission mode at the pupil of the instrument. The main disadvantage is that the procedure implies a calibration of the device as well as an i...
Article
Full-text available
The design of modern imaging systems is intricately concerned with the control of optical aberrations in systems that can be manufactured at acceptable cost and with acceptable manufacturing tolerances. Traditionally this involves a multi-parameter optimisation of the lens optics to achieve acceptable image quality at the detector. There is increas...
Article
Full-text available
Hyperspectral imaging of the retina presents a unique opportunity for direct and quantitative mapping of retinal biochemistry — particularly of the vasculature where blood oximetry is enabled by the strong variation of absorption spectra with oxygenation. This is particularly pertinent both to research and to clinical investigation and diagnosis of...
Article
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Purpose There is increasing interest in the application of spectral imaging for biochemical functional mapping of the retina. The solution to recording the required three-dimensional data cube using a two-dimensional detector array is normally to record images in time sequence in a way that scans one of the cube dimensions; typically either a seque...
Article
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Pupil plane encoding has shown to be a useful technique to extend the depth of field of optical systems. Recently, further studies have demonstrated its potential in reducing the impact of other common focus-related aberrations (such as thermally induced defocus, field curvature, etc) which enables to employ simple and low-cost optical systems whil...
Article
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A quartic phase retardation function is described that reduces the variation of the intensity of the focal point of incoherent imaging systems suffering from primary third-order aberrations limited to coma and astigmatism. Corresponding modulation transfer functions are shown to remain practically invariant for moderate amounts of coma and astigmat...
Article
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We describe the mapping of the optical transfer function (OTF) of an incoherent imaging system into a geometrical representation. We show that for defocused traditional and wavefront-coded systems the OTF can be represented as a generalized Cornu spiral. This representation provides a physical insight into the way in which wavefront coding can incr...
Article
Pupil plane encoding enables extended depth of field and greatly reduced sensitivity to aberrations in an imaging system (field curvature, thermally induced defocus, astigmatism, etc.). The application of pupil plane encoding has potential in thermal imaging where it can enable the use of simple, low-cost, light-weight lens systems. We present nume...
Article
A recent paper by Sherif et al. (S.S. Sherif, E.R. Dowski, W.T. Cathey, J. Mod. Opt. 51 1191 (2004).) reported the derivation of an aspherical phase plate, which when placed at the exit pupil of a conventional imaging system and combined with digital processing of the recorded images, increases the depth of field by an order of magnitude. An error...
Article
Full-text available
Wavefront coding involves the insertion of an asymmetric refractive mask close to the pupil plane of an imaging system so as to encode the image with a specific point spread function that, when combined with decoding of the recorded image, can enable greatly reduced sensitivity to imaging aberrations. The application of wavefront coding has potenti...
Article
Full-text available
This paper gives a review on the design and use of both amplitude filters and phase filters to achieve a large focal depth in incoherent imaging systems. Traditional optical system design enhances the resolution of incoherent imaging systems by optical-only manipulations or some type of post-processing of an image that has been already recorded. A...

Citations

... The summation of the detector pixels can be configured to implement various modalities of SLO. Confocal detection is simulated using a small pinhole, bucket (that is, non-confocal) detection is simulated by summing a larger disc of pixels and hybrid schemes involving arbitrary compound pinholes 32,[34][35][36] can also be easily and accurately modelled. While a large bucket detector yields the highest signal at the detector, reduction of the detector (pinhole) diameter towards confocality provides a useful increase in vascular contrast 37 , which is also particularly beneficial for vascular oximetry 32 , but with a reduced signal power. ...
... For example, Delori (1988) used three narrowly separated wavelengths and obtained improved results by compensating for the wavelength-independent scattering. Later on, more wavelengths were employed in retinal oximetry by other groups (Vucea et al., 2011) until hyperspectral oximetry was reported (Desjardins et al., 2016;Mordant et al., 2009), where over 50 optical wavelengths can be employed. ...
... Traditionally used models such as Navarro's schematic eye have inspired the creation of 3Dprinted models for research and training. Model eyes have been printed to assess the fundus viewing range of various lenses as well as the quality of wide-angle imaging and OCT instruments [38,39]. Model eyes have also been printed for retinal laser training [40]. ...
... Many researchers have considered methods of calculating three-dimensional bodies, convex bodies. In these works, mathematical formulas and various research methods are given in detail [5][6][7][8][9][10][11][12][13][14][15]. ...
... Due to the central role of oxygen in multiple physiological and pathophysiological processes, oxygen supply to and oxygen regulation in the retina have been found to be important factors in ocular diseases. In fact, an increasing number of studies show that oxygen dysregulation is associated with several ocular pathologies such as glaucoma [1][2][3][4][5][6], diabetic retinopathy (DR) [1,2,[7][8][9][10], retinal vessel occlusions [1,2,11,12], retinitis pigmentosa [13,14], and age-related macular degeneration (AMD) [15]. Retinal oximetry has also shown the potential for non-invasively monitoring some neurodegenerative diseases [16]. ...
... An alternative snapshot multispectral imaging system which has found significant use for oximetry is the Image Replicating Imaging Spectrometer (IRIS). [14,48] This optically efficient device enables video-rate imaging at eight distinct wavebands, chosen for multispectral retinal oximetry. The high temporal resolution and 8 wavebands afforded by IRIS has enabled several new oximetry applications, including direct observation of oxygen release by red blood cells, [49] and the observation of rapid oxygen diffusion in the bulbar conjunctival microvasculature. ...
... We have previously reported the possibility of using wavefront coding to enable elimination of the Petzval field-flattening element from a two-element infrared lens to yield a singlet with software image recovery for correction of aberrations [15,16]. Without wavefront coding, the performance of the optimised singlet lens was limited by high levels of off-axis aberrations. ...
... The uncertainty in oximetry due to noise-induced uncertainty in measured vascular contrast is lowest when the vascular contrast is close to 46% (corresponding to an optical density of log 10 (1/e)) and improves with increasing signal-to-noise ratio. Inference of oxygen saturation requires however knowledge of optical path lengths through the blood, an understanding of the effects of scatter and how they interact with the imaging system 38,39 . Typically a simplified model is employed: light detected using confocal imaging is considered to have been transmitted twice through a blood vessel (the dominant reflection is normally considered to be scattering by the choroid or the sclera), whereas for imaging using a large-area detector, light is considered to be transmitted only once through a vessel. ...
... Y(x , y) = YD (x 2 +y 2 )+ YS (x 2 +y 2 ) 2 (4) Here, YD and YS are the out of focusing effect and the Control parameters in the main spherical aberration respectively [17,18]. Now, the distribution of image intensity formed by the apodized visual system can obtain by the "square parameter" of expression [1]. ...
... 14 The PSF of the cubic-phase WFC has direction dependence, and the modulation transfer function (MTF) along the diagonal direction tends to be null within the spatial-frequency pass band, which degrades the contrast of the restored image in the diagonal direction pattern. 15 Therefore, various patterns of axially symmetric modulated WFC have been proposed, including a logarithmic function, 16 a quartic function, 17,18 and an annular phase mask. 19 In this report, we present three key contributions: (a) a compound eye optical system can be applied to an image scanner product that requires compactness and high image quality, shown by specific design examples and the evaluation results of prototypes. ...