Richard Jones

Time-domain whole-field fluorescence lifetime imaging with optical sectioning

A whole‐field time‐domain fluorescence lifetime imaging (FLIM) microscope with the capability to perform optical sectioning is described. The excitation source is a mode‐locked Ti:Sapphire laser that is regeneratively amplified and frequency doubled to 415 nm. Time‐gated fluorescence intensity images at increasing delays after excitation are acquired using a gated microchannel plate image intensifier combined with an intensified CCD camera. By fitting a single or multiple exponential decay to each pixel in the field of view of the time‐gated images, 2‐D FLIM maps are obtained for each component of the fluorescence lifetime. This FLIM instrument was demonstrated to exhibit a temporal discrimination of better than 10 ps. It has been applied to chemically specific imaging, quantitative imaging of concentration ratios of mixed fluorophores and quantitative imaging of perturbations to fluorophore environment. Initially, standard fluorescent dyes were studied and then this FLIM microscope was applied to the imaging of biological tissue, successfully contrasting different tissues and different states of tissue using autofluorescence. To demonstrate the potential for real‐world applications, the FLIM microscope has been configured using potentially compact, portable and low cost all‐solid‐state diode‐pumped laser technology. Whole‐field FLIM with optical sectioning (3D FLIM) has been realized using a structured illumination technique.

A wide-field time-domain fluorescence lifetime imaging microscope with optical sectioning

This article describes a wide-field time-domain fluorescence lifetime imaging (FLIM) microscope with optical sectioning. The FLIM system utilizes a wide-field time-gated optical image intensifier, with a minimum gate width of 85 ps, to achieve high temporal resolution of fluorescence decays induced by ultrashort laser pulses. Different configurations, using excitation pulses of picojoule energy at 80 MHz repetition rate and of nanojoule energy at 10 kHz, are compared. The instrument has a temporal dynamic range spanning from 100 ps to tens of μs and is shown to have a temporal discrimination better than 10 ps. When applied to laser dye samples, it has produced FLIM maps demonstrating sensitivity to variations in both chemical species and local environment, e.g., viscosity. Wide-field optical sectioning is achieved using the technique of structured illumination, which is applied to remove out-of-focus light that can result in lifetime artifacts. The sectioning strength, which may be adjusted by choosing an appropriate spatial modulation frequency, is characterized and shown to be comparable to that of a confocal microscope. Practical considerations concerned with improving the quality of sectioned fluorescence lifetime maps, including using a large bit depth camera, are discussed.

Whole-field optically sectioned fluorescence lifetime imaging

We describe a novel three-dimensional fluorescence lifetime imaging microscope that exploits structured illumination to achieve whole-field sectioned fluorescence lifetime images with a spatial resolution of a few micrometers.

Holographic storage and high background imaging using photorefractive multiple quantum wells

We report holographic, real time, depth‐resolved image acquisition, storage, and reconstruction in photorefractive GaAs/AlGaAs multiple quantum wells under high background radiation conditions. Reconstructed images of 50 μm transverse and depth resolution have been achieved using this device as a coherence gate to image through 9 mean free paths of turbid scattering medial

High resolution depth resolved imaging through scattering media using time resolved holography

Abstract We report on time-gated holographic imaging at 450 nm using photorefractive media to achieve high depth and transverse resolution through a turbid medium. Using 70 fs pulses from a frequency-doubled mode-locked Ti: sapphire, we have demonstrated that both depth and transverse spatial resolution of 50 μm are achievable through a depth of 10 scattering mean free paths. Whole-field depth-resolved 2-D image planes were acquired in a single integration of a few seconds.

Viewpoint: Giving birth to next generation repositories

At a time when the ground work for Institutional Repositories has been done, and the focus in the field has shifted to higher things, we consider potentially the most significant of issues. Interoperability is a word that means many things, depending on who you ask, and most definitions are far from definitive. This article shows why Interoperability, in its many forms, is important, how it characterises the coming generation of repositories, in what ways it might be used, and even a little on how it is done. It also dares to speculate briefly on the future, and the incredible things we might achieve by working together. But it also reminds us that we do these things to improve the visibility and dissemination of scholarly work, and that this should always guide us.

Harmonising Research Reporting in the UK – Experiences and Outputs from UKRISS☆

Abstract The Jisc-funded UK Research Information Shared Service (UKRISS) project investigated the reporting of research information across the UK HE sector and assessed the feasibility of a national infrastructure based on CERIF with the objective of increasing the efficiency, productivity and reporting quality across the sector. A core reporting profile was developed that would enable harmonised reporting on RCUK-funded research, taking into account the HE-BCI survey as well as REF reporting elements. In this paper we describe the UKRISS modelling approach and provide some insight into the UKRISS reporting objects to support understanding of their formal CERIF representations, i.e. the selection of underlying CERIF entities; the challenges with managing objects and aggregations in CERIF. Example data extracts demonstrate the work.

Feasibility Study Into the Reporting of Research Information at a National Level Within the UK Higher Education Sector

This article presents the key findings of feasibility and scoping study into the reporting of research information at a national level within the United Kingdom, based on Common European Research Information Format (CERIF). The study was carried out by the Jisc-funded UK Research Information Shared Service (UKRISS) project. The reporting of research information to funders and statutory bodies is a major burden on researchers and institutions. The landscape for research reporting in the UK Higher Education sector is complex and fragmented. There is limited harmonization in reporting requests made on institutions and researchers, resulting in duplication of effort and limiting the potential for reuse of the information. The paper describes the current landscape for research reporting in the United Kingdom. The methodology and findings from a study involving interviews with a cross-section of major stakeholders is described. Recommendations for further work in the area are proposed.

Application of the stretched exponential function to fluorescence lifetime imaging of biological tissue

The fluorescence decay in fluorescence lifetime imaging (FLIM) is typically fitted to a multi-exponential model with discrete lifetimes. The interaction between fluorophores in heterogeneous samples (e.g. biological tissue) can, however, produce complex decay characteristics that do not correspond to such models. Although they appear to provide a better fit to fluorescence decay data than the assumption of a mono-exponential decay, the assumption of multiple discrete components is essentially arbitrary and often erroneous. The stretched exponential function (StrEF) describes fluorescence decay profiles using a continuous lifetime distribution as has been reported for tryptophan, being one of the main fluorophores in tissue. We have demonstrated that this model represents our time-domain FLIM data better than multi-exponential discrete decay components, yielding excellent contrast in tissue discrimination without compromising the goodness of fit, and it significantly decreases the required processing time. In addition, the stretched exponential decay model can provide a direct measure of the sample heterogeneity and the resulting heterogeneity map can reveal subtle tissue differences that other models fail to show.

High-speed 3D imaging using photorefractive holography with novel low-coherence interferometers

We report high speed (~ 470 frames/s) 3-D imaging using photorefractive holography with sources of diverse temporal and spatial coherence and discuss design considerations for real-world high bit-rate imaging systems. We also propose a new real-time optical sectioning technique based on structured illumination with photorefractive holography to detect fluorescence.