Spatial resolution of drug crystallisation in the skin by X-ray micro-computed tomography

Drug crystallisation in the skin is recognised as a significant problem in topical and transdermal drug delivery. Our recent investigations provided new evidence of drug crystallisation in the skin, however, confirming the precise location of crystals remains challenging. Of note, most approaches used have required disruption of the membrane by tape stripping, with crystal detection limited to the superficial skin layers. Hence, a non-destructive method for complete spatial resolution of crystallised drug in skin is still lacking. In this communication, we report the application of X-ray micro-computed tomography (microCT) to examine drug crystallisation in mammalian skin ex vivo. Permeation studies of a saturated solution of diclofenac sodium were conducted in porcine skin; subsequently, tissue samples were scanned using microCT to generate 2D and 3D maps. A layer of drug crystals was observed on the skin surface; microCT maps also confirmed the distribution of drug crystals up to a skin depth of 0.2 – 0.3 mm. MicroCT also allowed the identification of drug crystallisation as a distinct and confirmed event in the skin and as an extension from drug crystals formed on the skin. These preliminary results confirm the potential of microCT to study this important phenomenon in topical and transdermal drug delivery

Imaging Cerenkov emission as a quality assurance tool in electron radiotherapy

A new potential quality assurance (QA) method is explored (including assessment of depth dose, dose linearity, dose rate linearity and beam profile) for clinical electron beams based on imaging Cerenkov light. The potential of using a standard commercial camera to image Cerenkov light generated from electrons in water for fast QA measurement of a clinical electron beam was explored and compared to ionization chamber measurements. The new method was found to be linear with dose and independent of dose rate (to within 3%). The uncorrected practical range measured in Cerenkov images was found to overestimate the actual value by 3 mm in the worst case. The field size measurements underestimated the dose at the edges by 5% without applying any correction factor. Still, the measured field size could be used to monitor relative changes in the beam profile. Finally, the beam-direction profile measurements were independent of the field size within 2%. A simulation was also performed of the deposited energy and of Cerenkov production in water using GEANT4. Monte Carlo simulation was used to predict the measured light distribution around the water phantom, to reproduce Cerenkov images and to find the relation between deposited energy and Cerenkov production. The camera was modelled as a pinhole camera in GEANT4, to attempt to reproduce Cerenkov images. Simulations of the deposited energy and the Cerenkov light production agreed with each other for a pencil beam of electrons, while for a realistic field size, Cerenkov production in the build-up region overestimated the dose by +8%

Strain in epitaxial MnSi films on Si(111) in the thick film limit studied by polarization-dependent extended x-ray absorption fine structure

We report a study of the strain state of epitaxial MnSi films on Si(111) substrates in the thick film limit (100-500~\AA) as a function of film thickness using polarization-dependent extended x-ray absorption fine structure (EXAFS). All films investigated are phase-pure and of high quality with a sharp interface between MnSi and Si. The investigated MnSi films are in a thickness regime where the magnetic transition temperature $T_\mathrm{c}$ assumes a thickness-independent enhanced value of $\geq$43~K as compared with that of bulk MnSi, where $T_\mathrm{c} \approx 29~{\rm K}$. A detailed refinement of the EXAFS data reveals that the Mn positions are unchanged, whereas the Si positions vary along the out-of-plane [111]-direction, alternating in orientation from unit cell to unit cell. Thus, for thick MnSi films, the unit cell volume is essentially that of bulk MnSi --- except in the vicinity of the interface with the Si substrate (thin film limit). In view of the enhanced magnetic transition temperature we conclude that the mere presence of the interface, and its specific characteristics, strongly affects the magnetic properties of the entire MnSi film, even far from the interface. Our analysis provides invaluable information about the local strain at the MnSi/Si(111) interface. The presented methodology of polarization dependent EXAFS can also be employed to investigate the local structure of other interesting interfaces.Comment: 11 pages, 10 figure

Performance of a novel wafer scale CMOS active pixel sensor for bio-medical imaging

Recently CMOS Active Pixels Sensors (APSs) have become a valuable alternative to amorphous Silicon and Selenium Flat Panel Imagers (FPIs) in bio-medical imaging applications. CMOS APSs can now be scaled up to the standard 20 cm diameter wafer size by means of a reticle stitching block process. However despite wafer scale CMOS APS being monolithic, sources of non-uniformity of response and regional variations can persist representing a significant challenge for wafer scale sensor response. Non-uniformity of stitched sensors can arise from a number of factors related to the manufacturing process, including variation of amplification, variation between readout components, wafer defects and process variations across the wafer due to manufacturing processes. This paper reports on an investigation into the spatial non-uniformity and regional variations of a wafer scale stitched CMOS APS. For the first time a per-pixel analysis of the electro-optical performance of a wafer CMOS APS is presented, to address inhomogeneity issues arising from the stitching techniques used to manufacture wafer scale sensors. A complete model of the signal generation in the pixel array has been provided and proved capable of accounting for noise and gain variations across the pixel array. This novel analysis leads to readout noise and conversion gain being evaluated at pixel level, stitching block level and in regions of interest, resulting in a coefficient of variation ≤ 1.9%. The uniformity of the image quality performance has been further investigated in a typical X-ray application, i.e. mammography, showing a uniformity in terms of CNR among the highest when compared with mammography detectors commonly used in clinical practise. Finally, in order to compare the detection capability of this novel APS with the currently used technology (i.e. FPIs), theoretical evaluation of the Detection Quantum Efficiency (DQE) at zero-frequency has been performed, resulting in a higher DQE for this detector compared to FPIs. Optical characterization, X-ray contrast measurements and theoretical DQE evaluation suggest that a trade off can be found between the need of a large imaging area and the requirement of a uniform imaging performance, making the DynAMITe large area CMOS APS suitable for a range of bio-medical applications

Linhas gráficas de publicações diárias em Portugal: Estudo comparativo de publicações diárias nos anos 1985, 1995 e 2005

Com esta investigação pretendi analisar o design gráfico ao nível do projecto (linha) gráfico em quatro publicações portuguesas, jornais diários (Diário, Diário de Notícias, Correio da Manhã e Jornal de Notícias e, posteriormente, substituído o Diário, que encerrou, pelo Público). A análise incidirá em três momentos distintos (1985, 1995 e 2005) separados por intervalos de uma década. Através do estudo comparativo do design gráfico de informação destas publicações, procurarei identificar e avaliar as diferenças de alteração gráfica, afirmando ou infirmando que estas foram motivadas pela mudança e introdução de novas tecnologias como pelas grandes alterações económicas e sociais em Portugal

Characterization of breast tissue using energy-dispersive X-ray diffraction computed tomography

Abstract A method for sample characterization using energy-dispersive X-ray diffraction computed tomography (EDXRDCT) is presented. The procedures for extracting diffraction patterns from the data and the corrections applied are discussed. The procedures were applied to the characterization of breast tissue samples, 6 mm in diameter. Comparison with histological sections of the samples confirmed the possibility of grouping the patterns into five families, corresponding to adipose tissue, fibrosis, poorly differentiated cancer, well differentiated cancer, and benign tumour

Energy-windowed, pixellated X-ray diffraction using the Pixirad CdTe detector

X-ray diffraction (XRD) is a powerful tool for material identification. In order to interpret XRD data, knowledge is required of the scattering angles and energies of X-rays which interact with the sample. By using a pixellated, energy-resolving detector, this knowledge can be gained when using a spectrum of unfiltered X-rays, and without the need to collimate the scattered radiation. Here we present results of XRD measurements taken with the Pixirad detector and a laboratory-based X-ray source. The cadmium telluride sensor allows energy windows to be selected, and the 62 μm pixel pitch enables accurate spatial information to be preserved for XRD measurements, in addition to the ability to take high resolution radiographic images. Diffraction data are presented for a variety of samples to demonstrate the capability of the technique for materials discrimination in laboratory, security and pharmaceutical environments. Distinct diffraction patterns were obtained, from which details on the molecular structures of the items under study were determined

Conformity of spin fluctuations in alkali-metal iron selenide superconductors inferred from the observation of a magnetic resonant mode in K(x)Fe(2-y)Se(2)

Spin excitations stemming from the metallic phase of the ferrochalcogenide superconductor K(0.77)Fe(1.85)Se(2) (T_c=32 K) were mapped out in the ab plane by means of the time-of-flight neutron spectroscopy. We observed a magnetic resonant mode at Q_res=(1/2 1/4), whose energy and in-plane shape are almost identical to those in the related compound Rb(0.8)Fe(1.6)Se(2). This lets us infer that there is a unique underlying electronic structure of the bulk superconducting phase K(x)Fe(2)Se(2), which is universal for all alkali-metal iron selenide superconductors and stands in contrast to the doping-tunable phase diagrams of the related iron pnictides. Furthermore, the spectral weight of the resonance on the absolute scale, normalized to the volume fraction of the superconducting phase, is several times larger than in optimally doped BaFe(2-x)Co(x)As(2). We also found no evidence for any additional low-energy branches of spin excitations away from Q_res. Our results provide new input for theoretical models of the spin dynamics in iron based superconductors