Sylvie Doré

Experimental determination of CT point spread function anisotropy and shift-variance

The authors propose an experimental method to quantitatively assess the shift-variance and anisotropy of commercial CT scanners. A custom phantom consisting of 89 wires arranged in concentric circles was built for this purpose. A separable Gaussian model, expressed in a polar coordinate system, is proposed along with the corresponding estimation method. The estimated model parameters provide the quantitative information sought. The authors conclude that the scanner presents a rotating blur, i.e., that the PSF is independent of angular position when expressed in a polar coordinate system, and that the PSF shape broadens more quickly in the tangential direction than along the radial axis. Both of these observations agree with theoretical studies.

Experimental correlation-based identification of X-ray CT point spread function. Part 1: Method and experimental results.

Knowledge of the point spread function (PSF) of an imaging system is important when studying the characteristics of the blur present in the images. Published experimental PSF identification techniques adapt classical one-dimensional linear system identification strategies using impulse, step function or periodic input signals. This study proposes and successfully applies a correlation method based on the Wiener-Hopf equation to identify the PSF of a CT scanner. The input consists of a series of pseudorandomly located holes. Results are found to be statistically equivalent to those obtained with the impulse method at a 90% two-sided confidence interval. Like the impulse method, it readily yields two-dimensional estimate, but the larger input circumvents the major objection to the use of a wire input. Furthermore, it is relatively immune to output noise, offering an advantage over edge methods. This resistance to noise may prove helpful for nuclear medicine imaging techniques, for which the signal-to-noise ratio is much lower than that X-ray for CT.

Experimental determination of CT point spread function

An approach is presented to the experimental identification of the noise power spectrum (NPS) of a computed tomography (CT) scanner, using a method based on the Weiner-Hopf equation. Simulations show that the identification process is very robust in the presence of noise but quite sensitive to subpixel misregistration. This situation can be easily corrected if the relative shift between input and output images can be quantified.<<ETX>>

Gesture as an important factor in 3D kinematic assessment of the knee

Contradictions exist between studies of the 3D kinematics of the knee. We hypothesize that they are in part due to differences in the gesture performed by the subjects during kinematic assessment. The purpose of this study is to evaluate the impact of gesture variations on knee kinematics. Seventeen healthy male subjects performed 20-s series of knee-bends in a knee-bend standardizing structure. All series differed regarding either foot rotation, knee excursion, or hip rotation. 3D knee kinematics were recorded using optical position sensors mounted on a skin-motion-reducing harness. Kinematic comparisons were made between a gesture of reference (the standard gesture) and every other gesture. Analyses were performed on average differences. Differences of up to 15° of tibial rotation were found for gestures involving different foot rotation. Gestures involving different knee excursion brought on differences of more than 4° of tibial rotation while hip rotation induced more than 5° of tibial rotation. It is hereby demonstrated that gesture differences can have a dramatic impact on measured knee kinematics. Hence gesture performance needs to be carefully monitored during 3D kinematic assessment of the weight-bearing human knee.

Experimental correlation-based identification of X-ray CT point spread function. Part 2 : simulation and design of input signal

The preferred signals for non-parametric correlation-based point spread function identification are white noise or pseudo-random binary sequences (PRBSs). Given the difficulty of building a phantom based on either of these signals, a new input is devised that corresponds to pseudo-randomly located holes. The positions of the holes correspond to zeros in a 2-D PRBS. To optimise the design of the phantom and to ensure proper imaging procedure, a number of simulations are conducted. The effects of the following parameters on identification quality are investigated: the size of the holes and their minimum separation, the period of the PRBS, input-output translational and rotational mis-registration, pixel size and the presence of cupping. The factors affecting identification quality the most are rotational alignment, hole size and separation, as well as sequence length. During simulations, a point spread function offering characteristics similar to the Philips Tomoscan CX is identified. Optimal results are obtained when the signal consists of 0·6 mm holes, separated by 0·9 mm, whose position is based on a 32×32 PRBS generated with a ten-stage shift-register. When adequate rotational alignment is provided, it is shown that the pseudo-randomly located holes signal is a good substitute for a purely white signal when identifying the PSF of a CT scanner.

A design of experiments for statistically predicting risk of adverse health effects on drivers exposed to vertical vibrations.

An injury risk factor (IRF), which indicates the risk of adverse health effect to lumbar rachis arising from mechanical vibrations, is developed. Experiments have been conducted that consider acceleration levels at the seat of drivers, posture, morphology, density, damping rate and body mass as independent variables. A parametric finite-element model of the lumbar rachis has been generated. It is shown that the IRF increases with ageing and an IRF of 30% is proposed as a threshold for fatigue purposes. This level is reached if a peak acceleration level greater than 3 m/s2 is applied to a light (55 kg) and an old driver with a low bone density and a damping rate of 20%. This vibration threshold must be reduced to 2.7 m/s2 if the driver’s weight increases to 75 kg and to 2 m/s2 if the driver is heavy (98 kg).

Design and fabrication of intake manifold for formula SAE (Society of Automotive Engineers) race car

Every year, a group of students from Ecole de technologie superieure (ETS) in Montreal design and build a formula-type race car and compete in the Formula SAE competition. In this paper, we examine the design and fabrication of the ir intake system, A number of constraints challenge the designers. For example, to ensure the security of amateur drivers, motors are restrained to 600 cc and a circular restriction of 20 mm in diameter is placed at the entry of the system. Under these conditions, it is important to optimize the quality of the air/fuel mixture which depends mostly on the air intake system. A theoretical analysis reduced the field of possible runner length. However, the influence of runner configuration, plenum shape and size can only be determined experimentally. Polyacrylic functional prototypes were produced and tested on a dynamometric bench. A stereolithography model representing the inner passageways of the optimal intake manifold was built and used as a positive for a polyurethane mold. A composite lamination process was used to laminate the pre-production prototype over a molded wax plug. The major advantage of this approach over craftsmanship or even machining is the time saved to make the mold and the unlimited complexity of the shape permitted by the rapid prototyping systems.

A comparison of strategies to encourage regular study and foster deep learning

One of the challenges facing engineers is efficiently using a growing number of sophisticated tools and methods. This requires not only procedural knowledge on how to use them, but conditional knowledge, which determines under which conditions a given tool or method should be used (when, by whom, where, etc.) as well as conceptual knowledge which is necessary for efficient learning and use of tools and methods as well as for knowledge transfer. This paper presents a learning activity devised to improve deep learning of conceptual knowledge. It was implemented in a second year undergraduate compulsory course in mechanical engineering using three different strategies. Students were: 1. asked to draw a map of the course material that was to be covered in the coming week; 2. asked to produce an individual map of the material covered the previous week; 3. given the choice between drawing a map, writing a summary or attending a 10 minute quiz given at the beginning of the lecture, all on the material covered the previous week. The third strategy proved the most effective. To explain this result, it is hypothesized that motivation played an important role. When students have a better sense of control over their learning – for example, by having a choice of learning strategies and selecting the one which corresponds most to their learning style – their motivation increases. Furthermore, sense of competence was increased for the students who handed in maps or summaries by performing well in the quizzes. These conditions foster a deep approach to learning.

Experimental evaluation of computerised tomography point spread function variability within the field of view: Parametric models

The objective of the paper was to validate non-linear parametric models of computerised tomography point spread function (PSF), to investigate the role of model parameters and to verify the effect of different imaging conditions on estimated parameters. These models were then to be used experimentally to estimate the variation of PSF shape within the field of view of a scanner. Two parametric models of the PSF are presented. The Gaussian model is appropriate when PSF values are positive, and the damped cosine model can account for negative values. These models are non-linear and fully two-dimensional and do not assume radial symmetry. The models were fitted to images of a point source. The models accounted for over 99% of the variance in the PSF signal. Errors in modulation transfer function were limited to 5% when the appropriate model was selected. The difference in the blurring characteristics of three image reconstruction filters was well quantified by shape parameters, and position parameters located the PSF with subpixel accuracy. With a point source located 50 mm directly above the centre of the field of view, the PSF was found to be anisotropic.