C.J. Hall

Imaging lung aeration and lung liquid clearance at birth

Aeration of the lung and the transition to air‐breathing at birth is fundamental to mammalian life and initiates major changes in cardiopulmonary physiology. However, the dynamics of this process and the factors involved are largely unknown, because it has not been possible to observe or measure lung aeration on a breath‐by‐breath basis. We have used the high contrast and spatial resolution of phase contrast X‐ray imaging to study lung aeration at birth in spontaneously breathing neonatal rabbits. As the liquid‐filled fetal lungs provide little absorption or phase contrast, they are not visible and only become visible as they aerate, allowing a detailed examination of this process. Pups were imaged live from birth to determine the timing and spatial pattern of lung aeration, and relative levels of lung aeration were measured from the images using a power spectral analysis. We report the first detailed observations and measurements of lung aeration, demonstrating its dependence on inspiratory activity and body position; dependent regions aerated at much slower rates. The air/liquid interface moved toward the distal airways only during inspiration, with little proximal movement during expiration, indicating that trans‐pulmonary pressures play an important role in airway liquid clearance at birth. Using these imaging techniques, the dynamics of lung aeration and the critical role it plays in regulating the physiological changes at birth can be fully explored.—Hooper S. B., Kitchen, M. J., Wallace, M. J., Yagi, N., Uesugi, K., Morgan M. J., Hall, C., Siu, K. K. W., Williams, I. M., Siew, M., Irvine, S. C., Pavlov, K., Lewis R. A. Imaging lung aeration and lung liquid clearance at birth. FASEB J. 21, 3329–3337 (2007)

Dynamic imaging of the lungs using x-ray phase contrast

High quality real-time imaging of lungs in vivo presents considerable challenges. We demonstrate here that phase contrast x-ray imaging is capable of dynamically imaging the lungs. It retains many of the advantages of simple x-ray imaging, whilst also being able to map weakly absorbing soft tissues based on refractive index differences. Preliminary results reported herein show that this novel imaging technique can identify and locate airway liquid and allows lung aeration in newborn rabbit pups to be dynamically visualized.

Simultaneous time resolved SAXS and WAXS experiments using synchrotron radiation

Abstract Instrumentation has been developed which offers the possibility of performing simultaneous time resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) experiments in the range from approximately 0.007–0.21 A −1 and 0.31–4.2 A −1 . A synchrotron SAXS beamline is therefore equipped with two gas filled proportional detectors. The ultimate system time resolution will be of the order of 1 μs. Successful test experiments have been performed on block copolymer samples and polyethylene.

MINERAL PRECIPITATION AND DISSOLUTION IN AQUEOUS SOLUTION: IN-SITU MICROSCOPIC OBSERVATIONS ON BARITE (001) WITH ATOMIC FORCE MICROSCOPY

Abstract Crystal growth and dissolution mechanisms on the barite (001) surface have been observed in-situ in aqueous solution as a function of the saturation state at molecular scales using Atomic Force Microscopy (AFM). On freshly cleaved barite (001) surfaces, cleavage steps with a step height of 7 A occur, representing the height of a unit cell in the c direction. Growth and dissolution occurs via the advance and retreat of steps with a step height of half a unit cell (3.5 A). In supersaturated BaSO4 solution, monolayer step growth increases linearly with the BaSO4 concentration. Step velocities of one BaSO4 half-unit cell layer are faster in [100] relative to [−100], whereas in the underlying BaSO4 half-unit cell layer, step velocities are faster in [−100] than in [100]. A 21 screw axis parallel to [001] causes the directional growth in opposite directions in different half-unit cell layers. At low to moderate supersaturations, up to about 80 μM BaSO4, spiral growth is the dominant growth mechanism, whereas at higher BaSO4 concentrations, surface nucleation dominates the growth process. In the presence of a crystal growth inhibitor (NTMP, nitrilotri(methylenephosphonic) acid), the nucleation rate as well as step growth is retarded depending on the inhibitor concentration. The morphology of monolayer step edges becomes irregularly curved and jagged, thus suggesting that NTMP molecules attach preferentially to step edges. In pure water, shallow etch pits form with a morphology defined by monolayer steps parallel to [010] and [110]. All etch pits within one BaSO4 layer point in the same direction, whereas etch pits in the underlying BaSO4 layer point in the opposite direction, as a result of the 21 screw axis. Chelating agents, such as EDTA, ethylenediaminetetraacetic acid, dissolve barite effectively by the formation of Ba-EDTA surface complexes and their desorption resulting in an increased etch pit formation rate. Different types of etch pits could be distinguished: (i) shallow etch pits are defined by steps parallel to [010] and [110], (ii) whereas deep etch pits are defined by steps parallel to [100] and [010]. Step velocities of retreating monolayer steps parallel to [110] retreat faster than steps parallel to [010] resulting in an elongated etch pit morphology. With increasing EDTA concentration from 0.1 mM to 100 mM, the velocity of steps parallel to [110] is reduced by one order of magnitude. Etch pit morphology as well as monolayer step kinetics suggest that EDTA molecules attach to the barite (001) surface and detach a BaEDTA2− complex preferentially from steps parallel to [110].

Determining cement composition by Fourier transform infrared spectroscopy

Abstract A diffuse reflectance mid-infrared Fourier transform spectroscopy (DRIFTS) method is described for obtaining high quality Fourier transform infrared (FTIR) spectra of cements. DRIFT spectra of synthetic C3S, C2S, C3A, and C4AF and of pure gypsum, bassanite, anhydrite, syngenite, and calcite are shown. Typical spectra of American Petroleum Institute class G and class A cements display characteristic features which can be related qualitatively to variations in the constituent minerals. For quantitative analysis, the FTIR spectra of 156 cements of varied origin and known elemental composition have been used to construct multivariate calibration models. These relate the spectrum to composition (expressed in terms of nine mineral components and five minor oxides) and allow the composition of unknown cements to be determined rapidly from the FTIR spectrum alone. Error estimates are given.

The “RAPID” high rate large area X-ray detector system

The multiwire proportional counter (MWPC) is a well-established device for capturing X-ray images from synchrotron sources and is particularly well suited to dynamic experiments. Its advantages include, almost zero noise, high dynamic range limited only by the electronic memory depth, large area and time resolutions of microseconds. It does however have some limitations, notably in global and local count rate performance. The RAPID two-dimensional detector system delivers a more than twentyfold increase in throughput over present systems. It comprises a “wire MicroGap” detector, which has much higher count rate performance than coventional MWPCs and a sophisticated multi-channel data acquisition system. The system has a global count rate capability of greater than 2 × 107 photons s−1 with a maximum local count rate of ∼106 photons mm−2s−1. A spatial resolution of ∼200 μm, over an active area of 12.8 × 12.8 cm, has been achieved which compares well with exiting read-out systems. Each electrode of the detector is instrumented with a preamplifier and ADC and the position of the event is determined independently in X and Y by centroiding the induced charge distribution. The X and Y coordinates are correlated using a unique time stamp. This paper described the design and performance of the detector and read-out system and presents some recent beamline results.

Wavelet-based feature extraction applied to small-angle x-ray scattering patterns from breast tissue: a tool for differentiating between tissue types

This paper reports on the application of wavelet decomposition to small-angle x-ray scattering (SAXS) patterns from human breast tissue produced by a synchrotron source. The pixel intensities of SAXS patterns of normal, benign and malignant tissue types were transformed into wavelet coefficients. Statistical analysis found significant differences between the wavelet coefficients describing the patterns produced by different tissue types. These differences were then correlated with position in the image and have been linked to the supra-molecular structural changes that occur in breast tissue in the presence of disease. Specifically, results indicate that there are significant differences between healthy and diseased tissues in the wavelet coefficients that describe the peaks produced by the axial d-spacing of collagen. These differences suggest that a useful classification tool could be based upon the spectral information within the axial peaks.

Oilwell cement clinkers x-ray microanalysis and phase composition

X-ray microanalysis have been made on a suite of nine oilwell cement clinkers. Elemental data were obtained on alite, belite, and ferrite phases and, for two clinkers only, also on aluminate. The alite and belite compositions are broadly similar to those previously reported for other portland cements. Guest ion concentrations suggest that several charge-balancing substitutions occur. bulk MgO and SO3 levels determine the Mg and S contents of both phases, but for Fe and Al the substitution levels are not strongly correlated with bulk composition. For ferrites the data are generally consistent with the results of Bergstrom et al. (Adv Cem Res 1992, 4, 141-147): the Mg content varies widely, is controlled by the bulk MgO, and is coupled with Si in a charge-balancing substitution for Fe. Estimates of the total phase assembly using the directly determined mineral compositions are compared with the predictions of a modified Bogue calculation (similar to that of Taylor, Adv Cem Res, 1989, 2, 73-77). The agreement is variable and some refinements to the method of calculation are indicated.

In-situ hydration studies using multi-angle energy-dispersive diffraction.

A new diffractometer has been built with which energy-dispersive diffraction patterns can be collected simultaneously at different angles. The first use of this system for dynamic (time-resolved) studies--the hydration of cements under various conditions--is reported. It is found that the optimization available with a three-element detector system enables collection of high-quality patterns over a much wider and more effective range of reciprocal space, and this yields improved and new information on the hydration processes.

High counting rate gaseous x‐ray detectors for synchrotron radiation applications (invited)

Multiwire gas proportional detectors have been used for many years on synchrotron radiation experiments and offer unrivaled dynamic range and detection efficiency but have been somewhat limited in count rate performance. We report here recent test results from two new rapid data acquisition systems developed at Daresbury and in addition the results of comparative tests on a new design of gas detector, the Microgap, and a gas Microstrip detector. Both designs appear capable of high rate ≳100 kHz/mm2 operation and combined with the new acquisition systems should begin to alleviate the count rate problems for some types of experiment.