Peter Wells

Section Modulus Is the Optimum Geometric Predictor for Stress Fractures and Medial Tibial Stress Syndrome in Both Male and Female Athletes

Background Various tibial dimensions and geometric parameters have been linked to stress fractures in athletes and military recruits, but many mechanical parameters have still not been investigated. Hypotheses Sedentary people, athletes with medial tibial stress syndrome, and athletes with stress fractures have smaller tibial geometric dimensions and parameters than do uninjured athletes. Study Design Cohort study; Level of evidence, 3. Methods Using a total of 88 subjects, male and female patients with either a tibial stress fracture or medial tibial stress syndrome were compared with both uninjured aerobically active controls and uninjured sedentary controls. Tibial scout radiographs and cross-sectional computed tomography images of all subjects were scanned at the junction of the midthird and distal third of the tibia. Tibial dimensions were measured directly from the films; other parameters were calculated numerically. Results Uninjured exercising men have a greater tibial cortical cross-sectional area than do their sedentary and injured counterparts, resulting in a greater value of some other cross-sectional geometric parameters, particularly the section modulus. However, for women, the cross-sectional areas are either not different or only marginally different, and there are few tibial dimensions or geometric parameters that distinguish the uninjured exercisers from the sedentary and injured subjects. In women, the main difference between the groups was the distribution of cortical bone about the centroid as a result of the different values of section modulus. Last, medial tibial stress syndrome subjects had smaller tibial cross-sectional dimensions than did their uninjured exercising counterparts, suggesting that medial tibial stress syndrome is not just a soft-tissue injury but also a bony injury. Conclusion The results show that in men, the cross-sectional area and the section modulus are the key parameters in the tibia to distinguish exercise and injury status, whereas for women, it is the section modulus only.

X-RAY DIFFRACTION MICROTOMOGRAPHY

A table-top system has been developed for tomographic imaging of the internal structure of objects of low mass density at sub-millimetre resolution. Images are based on the X-ray diffraction properties of constituent materials, and are reconstructed from tomographic data using summation-filtered back-projection. Typical images are presented, the apparatus used for data acquisition is described, and the application of summation-filtered back-projection is discussed.

X-ray diffraction tomography at the Australian National Beamline Facility

Preliminary x-ray diffraction tomographic experiments utilizing synchrotron radiation have been performed at the Australian National Beamline Facility (BL20B) of the Photon Factory, National Laboratory for High Energy Physics in Japan. The tomographic instrument arrangement consisted of a double silicon crystal monochromator, motor-driven beam-defining collimation slits, and microcomputer-controlled specimen movement stages and was designed to simultaneously record tomographic data from multiple transmission and scatter radiation detectors. Image plates were used to record the scattering properties of specimen constituents, which facilitated registration of the scatter detectors. The design of the instrument is described and some preliminary results are presented.

A simple transmission X-ray microtomography instrument

Abstract The construction and performance of a simple (translate-rotate) transmission X-ray microtomography instrument is discussed. The system is configured around a conventional X-ray powder diffractometer and utilises 8.028 and 17.445 keV K α X-rays. A microcomputer controls the specimen motion and data acquisition. Images are reconstructed using centroid correction and filtered backprojection summation. With a modest arrangement of collimators, the instrument is capable of producing images with a spatial resolution of 10 μm and a contrast (density) resolution of better than 5%. It is well suited for the examination of the microstructural features of low mass density materials, such as wood and polymers.

X-ray and gamma-ray computed tomography for industrial nondestructive testing and evaluation

This paper presents an overview of two recently constructed computed tomography (CT) scanners that have been designed to provide structural information for industrially relevant materials and components. CT enables cross-sectional slices of an object to be nondestructively imaged and represented as a map of linear attenuation coefficient. As linear attenuation is the product of mass attenuation and density, this usually enables a straightforward interpretation of the image in terms of density. The two instruments are a transportable scanner using a 160 kV(peak) powered x-ray tube for the inspection of wooden power poles up to 450 mm in diameter, and an industrial scanning system designed around an Ir-192 gamma-ray source for materials characterization and the testing and evaluation of castings, ceramics, and composites. The images presented in this paper have generally been reconstructed using the summation convolution back-projection (SCBP) method, and this technique is outlined. Direct Fourier reconstruction is also used and compared with the SCBP method. A brief discussion is offered on incorporating edge detection methods into the image reconstruction process for the improved identification of defects such as cracks and voids.

SOLAR: student oriented learning about radiography

The success or otherwise of a radiographic examination is like other health-related interventions, crucially dependent upon the knowledge base of the radiographer and the quality of his/her clinical acumen. Traditional curricular approaches are limited in their ability to assist students to make vital connections between science and clinical decision making. This paper describes a computer-based case-oriented program called SOLAR (student oriented learning about radiography) that has been designed to achieve the necessary level of integration. The key feature of SOLAR is the requirement for students to construct a clinical action plan in response to a scenario provided. Upon submitting this plan, the student can then compare his/her plan to that prepared by an expert. The browsing configuration of SOLAR makes it highly attractive for other health professions as well. Student feedback indicates a high degree of approval for this approach.

Unambiguous x-ray phase retrieval from Fraunhofer diffraction data

An unambiguous inverse solution from Fraunhofer diffraction data has been achieved for an amorphous sample of low-molecular weight. The complex scattering amplitude has been reconstructed with submicron spatial resolution using the phase retrieval x-ray diffractometry technique. The technique relies on a logarithmic dispersion relation to determine the x-ray wave phase from the scattered intensity profile. Successful experimental localization of the zeros of the complex scattering amplitude was achieved by utilizing two data sets taken at different incident x-ray energies, permitting a unique solution.

X-ray diffraction tomography: Application to imaging heterogeneous systems

Publisher Summary This chapter describes a relatively new tomographic technique, where the imaging process is based upon the measurement of diffracted x-radiation, rather than the attenuation of an x-ray beam. By recording the angular distribution of scattered photons as an object is scanned with a pencil beam of radiation, tomographic data sets are produced that contain information about the scattering properties of the materials within the object. The tomographic data sets are then processed to produce images, which map the spatial distribution of these scattering properties throughout the interior of the object. The reconstructed scattering information at a given spatial coordinate may then be used as a means for the characterisation or identification of the material at that site. The use of scattered radiation as a basis for tomographic imaging is particularly effective when the constituents within the object preferentially scatter into different, well-defined angular ranges. This may occur when the radiation is diffracted by materials having an ordered arrangement of scattering sites. Even when the arrangement of scattering sites is of a statistical nature, as in liquids and amorphous materials, the height and angular position of the associated diffuse x-ray diffraction peaks, may be used as a basis for materials discrimination.Fixed-energy x-ray transmission computed tomography produces images with a single value at each spatial image coordinate, or pixel, and this value represents the x-ray linear attenuation coefficient, μ. The angular variation in the radiation scattered from a material may also be used as a basis for materials discrimination.Publisher Summary This chapter describes a relatively new tomographic technique, where the imaging process is based upon the measurement of diffracted x-radiation, rather than the attenuation of an x-ray beam. By recording the angular distribution of scattered photons as an object is scanned with a pencil beam of radiation, tomographic data sets are produced that contain information about the scattering properties of the materials within the object. The tomographic data sets are then processed to produce images, which map the spatial distribution of these scattering properties throughout the interior of the object. The reconstructed scattering information at a given spatial coordinate may then be used as a means for the characterisation or identification of the material at that site. The use of scattered radiation as a basis for tomographic imaging is particularly effective when the constituents within the object preferentially scatter into different, well-defined angular ranges. This may occur when the radiation is diffracted by materials having an ordered arrangement of scattering sites. Even when the arrangement of scattering sites is of a statistical nature, as in liquids and amorphous materials, the height and angular position of the associated diffuse x-ray diffraction peaks, may be used as a basis for materials discrimination.Fixed-energy x-ray transmission computed tomography produces images with a single value at each spatial image coordinate, or pixel, and this value represents the x-ray linear attenuation coefficient, μ. The angular variation in the radiation scattered from a material may also be used as a basis for materials discrimination.

X-ray diffraction tomography: laboratory and synchrotron instruments

X-ray diffraction tomographic imaging has been performed with laboratory and synchrotron- based instruments. Both instruments consist of beam-defining collimation slits, microcomputer-controlled specimen positioning stages, and multiple x-ray detectors that measure scattered and transmitted intensities as the specimen is moved through the primary pencil beam of radiation. This report describes the design of the instruments, and presents some preliminary results obtained with radiation of approximately 17 keV.

Chapter 7 – X-ray diffraction tomography: Application to imaging heterogeneous systems

Publisher Summary This chapter describes a relatively new tomographic technique, where the imaging process is based upon the measurement of diffracted x-radiation, rather than the attenuation of an x-ray beam. By recording the angular distribution of scattered photons as an object is scanned with a pencil beam of radiation, tomographic data sets are produced that contain information about the scattering properties of the materials within the object. The tomographic data sets are then processed to produce images, which map the spatial distribution of these scattering properties throughout the interior of the object. The reconstructed scattering information at a given spatial coordinate may then be used as a means for the characterisation or identification of the material at that site. The use of scattered radiation as a basis for tomographic imaging is particularly effective when the constituents within the object preferentially scatter into different, well-defined angular ranges. This may occur when the radiation is diffracted by materials having an ordered arrangement of scattering sites. Even when the arrangement of scattering sites is of a statistical nature, as in liquids and amorphous materials, the height and angular position of the associated diffuse x-ray diffraction peaks, may be used as a basis for materials discrimination.Fixed-energy x-ray transmission computed tomography produces images with a single value at each spatial image coordinate, or pixel, and this value represents the x-ray linear attenuation coefficient, μ. The angular variation in the radiation scattered from a material may also be used as a basis for materials discrimination.Publisher Summary This chapter describes a relatively new tomographic technique, where the imaging process is based upon the measurement of diffracted x-radiation, rather than the attenuation of an x-ray beam. By recording the angular distribution of scattered photons as an object is scanned with a pencil beam of radiation, tomographic data sets are produced that contain information about the scattering properties of the materials within the object. The tomographic data sets are then processed to produce images, which map the spatial distribution of these scattering properties throughout the interior of the object. The reconstructed scattering information at a given spatial coordinate may then be used as a means for the characterisation or identification of the material at that site. The use of scattered radiation as a basis for tomographic imaging is particularly effective when the constituents within the object preferentially scatter into different, well-defined angular ranges. This may occur when the radiation is diffracted by materials having an ordered arrangement of scattering sites. Even when the arrangement of scattering sites is of a statistical nature, as in liquids and amorphous materials, the height and angular position of the associated diffuse x-ray diffraction peaks, may be used as a basis for materials discrimination.Fixed-energy x-ray transmission computed tomography produces images with a single value at each spatial image coordinate, or pixel, and this value represents the x-ray linear attenuation coefficient, μ. The angular variation in the radiation scattered from a material may also be used as a basis for materials discrimination.