DESIGNING A LOW ANGLE X-RAY SCATTERING (LAXS) SYSTEM AND ITS USE IN CHARACTERISATION OF SOME BIOMEDICAL MATERIALS
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Date
2004-05
Authors
HUSSEIN, NAGI ABDALLAH
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Abstract
Scattering of X-rays photons from low Z materials at diagnostic energies «140 keV)
and low scattering angles «12°) is mainly coherent in nature. This coherence property
will lead to interference effects between these scattered photons resulting in diffraction
patterns, which are related to the interatomic and intermolecular structure of the
scattering medium.
These diffraction patterns are unique signatures 9f the interacted materials and therefore
can be used to characterise them. Diffraction patterns in this work are produced by the
energy dispersive method where polyenergetic photons from an X-ray tube impinge on
a target at a fixed low angles and hence the names Low Angle X-ray Scattering
(LAXS). This method is also referred to as the Energy Dispersive X-Ray Diffraction
(EDXRD) method.
A LAXS system that complies with the above principles has been constructed at the
Biophysics Laboratory, School of Physics, USM. The system comprises an X-ray tube,
collimators and target assembly, shielding, detection and data ,acquisition equipments.
The performance of each individual component in the setup has been tested separately
and its characteristics are recorded for optimal use. The LAXS system was then
examined as an integrated assembly. Alignment of the incident and scattered photons
through the manufactured lead collimators and into the LEGe detector was the most
challenging aspect of the experimental work.
The results of geometrical optimisation of the LAXS system to decide on the best
performance parameters can be summarised as follows: the X-ray tube should be
working at an applied voltage of 50 kV and current of 25 mA for collection period of
300 seconds using 2 mm slit collimators and at scattering angles of 8°, 9°or 10° for
certain employed distances. The criteria taken for this selection are to obtain highly
intense diffraction pattern with well-resolved peaks and contain as much as possible
peak details in the shortest time possible.
The LAXS system has been utilised in studying fabricated bone phantoms, which mimic
the changes of bone density during osteoporosis. Phantoms were fabricated to simulate
trabecular bone loss and cortical bone loss. The LAXS system was found capable to
disHnguish between the various mixture concentrations of theses phantoms by
comparing their EDXRD patterns. Several quantitative parameters that relate to the
composition of the phantoms with good linear behaviour have been established.
Reduction in dose received by the target for future in vivo measurements was
accomplished by the reduction in collection time without the loss of linearity or
sensitivity. Examples of some biomedical su()stitute materials and biomaterials such as water,
PMMA, LLDPE, rubber, dried bone, fresh bone, tissue and others have been examined
in the LAXS setup and their diffraction patterns analysed. The diffraction patterns
reflected the structure and composition of the materials so that they can be used as
signature patterns for future database identification procedures. Fabricated bone
phantom materials gave diffraction patterns which closely resemble real bone patterns.
The linear differential scattering coefficient of these biomedical substitute materials
have been measured. Compounds, mixtures, metals, solutions, liquids, powders and solids produced signature diffraction patterns that reflect their structural order being amorphous, semi amorphous
or crystalline. This also serves to show the versatility of the LAXS system.
The LAXS system has been used to identify materials by evaluating their interatomic
spacings and comparing them with PDF files with the advantage of fast collection time
over resolution. The effect of thickness on the diffraction patterns were investigated to
determine the optimal thickness of the scattering material, Aluminium and copper were
used for this purpose. In addition the effect of concentration and density of solutions
samples were investigated with density appearing to be more sensitive.
Description
Keywords
ANGLE X-RAY , BIOMEDICAL