Glossary

Electron backscatter - A method to investigate crystallographic properties of a sample in an SEM by placing a stationary beam on the sample and record the patterns of backscattered electrons emitted from that area. The recording is done by making the electron pattern visible on a fluorescent screen and record the image with a TV camera.

Neutron Backscatter – A method used for oil exploration by logging the relative hydrogen bulk density of the material down a drilled well. The technique works by ejecting high energy neutrons from the source to react with the immediate surrounding. The moderated neutrons (called slow neutrons or thermal neutrons) are scattered back towards the detector and counted. Materials rich in hydrogen produce high count rates while materials with little hydrogen concentration give low count rates. The results are typically plotted versus distance.

X-ray backscatter – A method used for discrimination of organic or "low Z" (i.e., low atomic number) materials such as explosives, drugs, cigarettes, and people, especially when hidden within a complex environment.

A 2D imaging device made up of rows and columns of pixels. Charge is generated within the active area of each pixel when light is incident. Every pixel’s charge is then transferred through to an output node to be converted to a voltage, buffered and sent off chip as an analogue signal. Further electronic circuits are then needed to process this signal so that the image can be read by a computer.

Caesium Iodide doped with Thallium is a high efficiency x-ray scintillator favoured for its columnar growth structure when deposited by evaporation. The columnar structure reduces scatter from exiting photons by light guiding within the columns.

A mathematical function that expresses the ability of an optical or electronic device to transfer signals as a function of the spatial or temporal frequency of the signal. The CTF is the ratio of percentage Contrast of a square wave signal leaving to that entering the object over the range of frequencies of interest. The CTF is usually presented as a graph of Contrast versus frequency (line pairs per mm – lp/mm).

The resolution measurement system at AST uses a square wave ‘Line pair’ lead phantom as the basis of square wave input signal, and measures the peak contrast in the resulting x-ray image. This measurement is performed from 2 lp/mm to 10 lp/mm and the peak contrast value is averaged over many images.

This is a matrix of optical fibres bonded together to form a coherent fiber optic plate that precisely transmits an image from its input surface to its output surface.

This is the capture and storage of Gel analysis data. Electrophoresis is an extremely common technique in molecular biology, used routinely to analyse DNA preparations in order to check quantity, size, structure and constitution of prepared samples. After separation on a gel (usually agarose), DNA is normally visualised under UV light after treatment with a fluorescent stain. Whatever the sample or method of visualisation, it is often required to keep a record of the analysis for future reference and analysis. This can be achieved with instant photography to produce a “hard copy” print of the illuminated gel and its visible bands.

Image quality is made up of many perceived factors such as contrast, resolution, mottle, noise etc. As a result there is no simple absolute measure of Image quality, but rather a user/application specific judgement.

Imaging from within the mouth. A compact digital imaging device held within the mouth enables dentists to look at specific areas whilst minimising dose to the patient.

A line-pair is 1 cycle of an attenuating mark followed by a non-attenuating mark with equal spacing which produces a square wave. 1 lp/mm would then be a 500 micron attenuation followed by a 500 micron transmission.