Francis Lilley

Fast and robust three-dimensional best path phase unwrapping algorithm

What we believe to be a novel three-dimensional (3D) phase unwrapping algorithm is proposed to unwrap 3D wrapped-phase volumes. It depends on a quality map to unwrap the most reliable voxels first and the least reliable voxels last. The technique follows a discrete unwrapping path to perform the unwrapping process. The performance of this technique was tested on both simulated and real wrapped-phase maps. And it is found to be robust and fast compared with other 3D phase unwrapping algorithms.

Robust fringe analysis system for human body shape measurement

This paper describes the development and practical application of a fringe analysis system for the high-speed measurement of human body shape and position. The application for this system is in the measurement of patient surface location and shape during the delivery of radiotherapy treatment for cancer. The system uses a twin-fiber interferometer as the basis for fringe production. The fringes are then projected onto the surface to be measured and captured by a CCD camera before being analyzed using Fourier-transform fringe analysis by a computer system. The novel features of this work are in the way in which the system has been realized, with maximum robustness and speed as primary goals. This has led to the development of a number of new techniques in data preprocessing, use of the algorithm itself, and calibration. Particular features include the larger than customary field of view, the use of noncollimated fringes, toleration of the damaging radiation environment, robustness to the variable color, texture, and profile of the surface, and the ability to operate at high speed with a conventional PC platform. The system is capable of measuring in excess of 32,000 surface points per second. Further developments of the system are also described, which are intended to extend its capabilities further.

Spatial fringe pattern analysis using the two-dimensional continuous wavelet transform employing a cost function

We present a novel ridge extraction algorithm for use with the two-dimensional continuous wavelet transform to extract the phase information from a fringe pattern. A cost function is employed for the detection of the ridge. The results of the proposed algorithm on simulated and real fringe patterns are illustrated. Moreover, the proposed algorithm outperforms the maximum ridge extraction algorithm and it is found to be robust and reliable.

Opto-electronic sensing of body surface topology changes during radiotherapy for rectal cancer☆

PURPOSE The CT body surface underpins millimeter scale dose computation in radical radiotherapy. A lack of technology has prevented measurement of surface topology changes during irradiation. Consequently, body changes are incorporated into plans statistically. We describe the technology for dynamic measurement of continuous surface topology at submillimeter resolution and suggest appropriately modified planning. MATERIALS AND METHODS An interferometer casts cosinusoidal fringes across the surface of a patient on a treatment couch. Motion-induced changes to the spatial phase of the fringes are used to generate dynamic sequences of body height maps. Volume-conserving CT warping, guided by height change, is used to illustrate potential planning perturbations. RESULTS We present the results for a prone patient with rectal carcinoma. At most of the simultaneously measured 440 x 440 points in each of the 898 body height maps in a dynamic sequence, the standard deviations were <1-2 mm, with occasional points of 6 mm. Surface motion predominantly occurred along the small of the back. This motion was periodic and could take the spine and bladder across the 95% isodose contour. CONCLUSIONS Surface changes are most likely to be within 3 mm during irradiation, despite the effects of breathing and the discomfort of lying prone. The dosimetric effects are acceptable.

Quantization error of CCD cameras and their influence on phase calculation in fringe pattern analysis

We present an investigation into the phase errors that occur in fringe pattern analysis that are caused by quantization effects. When acquisition devices with a limited value of camera bit depth are used, there are a limited number of quantization levels available to record the signal. This may adversely affect the recorded signal and adds a potential source of instrumental error to the measurement system. Quantization effects also determine the accuracy that may be achieved by acquisition devices in a measurement system. We used the Fourier fringe analysis measurement technique. However, the principles can be applied equally well for other phase measuring techniques to yield a phase error distribution that is caused by the camera bit depth.

Actin bundling and polymerisation properties of eukaryotic elongation factor 1 alpha (eEF1A), histone H2A-H2B and lysozyme in vitro.

Elongation factor 1 alpha (eEF1A) is a positively charged protein which has been shown to interact with the actin cytoskeleton. However, to date, a specific actin binding site within the eEF1A sequence has not been identified and the mechanism by which eEF1A interacts with actin remains unresolved. Many protein-protein interactions occur as a consequence of their physicochemical properties and actin bundle formation has been shown to result from non-specific electrostatic interaction with basic proteins. This study investigated interactions between actin, eEF1A and two other positively charged proteins which are not regarded as classic actin binding proteins (namely lysozyme and H2A-H2B) in order to compare their actin organising effects in vitro. For the first time using atomic force microscopy (AFM) we have been able to image the interaction of eEF1A with actin and the subsequent bundling of actin in vitro. Interestingly, we found that eEF1A dramatically increases the rate of polymerisation (45-fold above control levels). We also show for the first time that H2A-H2B has remarkably similar effects upon actin bundling (relative bundle size/number) and polymerisation (35-fold increase above control levels) as eEF1a. The presence of lysozyme resulted in bundles which were distinct from those formed due to eEF1A and H2A-H2B. Lysozyme also increased the rate of actin polymerisation above the control level (by 10-fold). Given the striking similarities between the actin bundling and polymerisation properties of eEF1A and H2A-H2B, our results hint that dimerisation and electrostatic binding may provide clues to the mechanism through which eEF1A-actin bundling occurs.

Robust three-dimensional best-path phase-unwrapping algorithm that avoids singularity loops

In this paper we propose a novel hybrid three-dimensional phase-unwrapping algorithm, which we refer to here as the three-dimensional best-path avoiding singularity loops (3DBPASL) algorithm. This algorithm combines the advantages and avoids the drawbacks of two well-known 3D phase-unwrapping algorithms, namely, the 3D phase-unwrapping noise-immune technique and the 3D phase-unwrapping best-path technique. The hybrid technique presented here is more robust than its predecessors since it not only follows a discrete unwrapping path depending on a 3D quality map, but it also avoids any singularity loops that may occur in the unwrapping path. Simulation and experimental results have shown that the proposed algorithm outperforms its parent techniques in terms of reliability and robustness.

The application of digital filtering to phase recovery when surface contouring using fringe projection techniques

Abstract If structured light consisting of parallel stripes, or fringes, is projected onto a surface, then the surface acts as a phase modulator, with the amount of modulation at any point depending upon the height of the surface at that point. In recent years considerable effort has been devoted to the problem of fringe demodulation, with prominence given to techniques using fringe-phase stepping and Fourier analysis. It has long been known that phase demodulation is possible using a system of filters, and the technique has been widely used in the related area of frequency demodulation in radio. In this paper the development of phase demodulation using a system of digital filters is considered. For the accurate recovery of image phase it is necessary for the filters to introduce zero phase shift, or to have a phase shift proportional to frequency. The design of the digital filters is considered and their performance is assessed using the signal from a real modulated fringe pattern and a simulated signal. It is shown that the demodulation technique works well, even with a poor signal-to-noise ratio.

Three-dimensional phase unwrapping using the Hungarian algorithm

We propose a three-dimensional phase unwrapping technique that uses the Hungarian algorithm to join together all the partial residual loops that may occur in a wrapped phase volume. Experimental results have shown that the proposed algorithm is more robust and reliable than other well-known three-dimensional phase unwrapping algorithms. Additionally, the proposed algorithm is fast in terms of computational complexity, which makes it suitable for practical applications.

Absolute distance measurement with micrometer accuracy using a Michelson interferometer and the iterative synthetic wavelength principle.

We present a novel system that can measure absolute distances of up to 300 mm with an uncertainty of the order of one micrometer, within a timeframe of 40 seconds. The proposed system uses a Michelson interferometer, a tunable laser, a wavelength meter and a computer for analysis. The principle of synthetic wave creation is used in a novel way in that the system employs an initial low precision estimate of the distance, obtained using a triangulation, or time-of-flight, laser system, or similar, and then iterates through a sequence of progressively smaller synthetic wavelengths until it reaches micrometer uncertainties in the determination of the distance. A further novel feature of the system is its use of Fourier transform phase analysis techniques to achieve sub-wavelength accuracy. This method has the major advantages of being relatively simple to realize, offering demonstrated high relative precisions better than 5 × 10(-5). Finally, the fact that this device does not require a continuous line-of-sight to the target as is the case with other configurations offers significant advantages.