Lujie Chen

Bio: Lujie Chen is an academic researcher from Singapore University of Technology and Design. The author has contributed to research in topics: Phase (waves) & Structured-light 3D scanner. The author has an hindex of 15, co-authored 38 publications receiving 663 citations. Previous affiliations of Lujie Chen include National University of Singapore & University of Cambridge.

Real-time quasi-static ultrasound elastography.

Abstract: Ultrasound elastography is a technique used for clinical imaging of tissue stiffness with a conventional ultrasound machine. It was first proposed two decades ago, but active research continues in this area to the present day. Numerous clinical applications have been investigated, mostly related to cancer imaging, and though these have yet to prove conclusive, the technique has seen increasing commercial and clinical interest. This paper presents a review of the most widely adopted, non-quantitative, techniques focusing on technical innovations rather than clinical applications. The review is not intended to be exhaustive, concentrating instead on placing the various techniques in context according to the authors' perspective of the field.

Fringe projection profilometry with nonparallel illumination: a least-squares approach.

Abstract: Under a nonparallel illumination condition, fringe patterns projected on an object have unequal fringe spacing that would introduce a nonlinear carrier phase component. This Letter describes a nonlinear carrier removal technique based on a least-squares approach. In contrast with conventional methods, the proposed algorithm would not magnify phase measurement uncertainty, nor does it require direct estimation of system geometrical parameters. The theoretical expression of the carrier phase function on the reference is derived and expanded in a power series. The unknown coefficients in the series are determined by a least-squares method. By subtracting the calculated carrier phase function from the unwrapped phase map, the phase distribution of the object profile is obtained.

Temporal wavelet analysis for deformation and velocity measurement in speckle interferometry

Abstract: When a continuously deforming object is measured by electronic speckle pattern interferometry (ESPI), the speckle pattern recorded on a camera sensor changes constantly. These time-dependent speckle patterns would provide the deformation history of the object. Various objects are applied with both linearly and nonlinearly varying loads and speckle patterns are captured using a high-speed CCD camera. The temporal intensity variation of each pixel on the recorded images is analyzed by a robust mathematical tool—Morlet wavelet transform instead of conventional Fourier transform. The transient velocity and displacement of each point can be retrieved without the necessity of the temporal or spatial phase unwrapping process. The displacements obtained are compared with those from a temporal Fourier transform, and the results show that the wavelet transform minimizes the influence of noise and provides better results for a linearly varying load. System error in the wavelet analysis for nonlinear load is also discussed.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

EFSUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography. Part 1: Basic Principles and Technology

Abstract: The technical part of these Guidelines and Recommendations, produced under the auspices of EFSUMB, provides an introduction to the physical principles and technology on which all forms of current commercially available ultrasound elastography are based. A difference in shear modulus is the common underlying physical mechanism that provides tissue contrast in all elastograms. The relationship between the alternative technologies is considered in terms of the method used to take advantage of this. The practical advantages and disadvantages associated with each of the techniques are described, and guidance is provided on optimisation of scanning technique, image display, image interpretation and some of the known image artefacts.

A fast normalized cross-correlation calculation method for motion estimation

Abstract: High-precision motion estimation has become essential in ultrasound-based techniques such as time-domain Doppler and elastography. Normalized cross-correlation (NCC) has been shown as one of the best motion estimators. However, a significant drawback is its associated computational cost, especially when RF signals are used. In this paper, a method based on sum tables developed elsewhere is adapted for fast NCC calculation in ultrasound-based motion estimation, and is tested with respect to the speed enhancement of the specific application of ultrasound-based motion estimation. Both the numerator and denominator in the NCC definition are obtained through pre-calculated sum tables to eliminate redundancy of repeated NCC calculations. Unlike a previously reported method, a search region following the principle of motion estimation is applied in the construction of sum tables. Because an exhaustive search and high window overlap are typically used for highest quality imaging, the computational cost of the proposed method is significantly lower than that of the direct method using the NCC definition, without increasing bias and variance characteristics of the motion estimation or sacrificing the spatial resolution. Therefore, high quality, high spatial resolution, and high calculation speed can be all simultaneously obtained using the proposed methodology. The high efficiency of this method was verified using RF signals from a human abdominal aorta in vivo. For the parameters typically used, a real-time, very high frame rate of 310 frames/s was achieved for the motion estimation. The proposed method was also extended to 2-D NCC motion estimation and motion estimation with other algorithms. The technique could thus prove very useful and flexible for real-time motion estimation as well as in other fields such as optical flow and image registration.