Chaiya Luengviriya

Combined prospective and retrospective motion correction to relax navigator requirements

Prospective motion correction can prevent motion artifacts in magnetic resonance imaging of the brain. However, for high‐resolution imaging, the technique relies on precise tracking of head motion. This precision is often limited by tracking noise, which leads to residual errors in the prospectively‐corrected k‐space data and artifacts in the image. This work shows that it is possible to estimate these tracking errors, and hence the true k‐space sample locations, by applying a two‐sided filter to the tracking data after imaging. A conjugate gradient reconstruction is compared to gridding as a means of using this information to retrospectively correct for the effects of the residual errors. Magn Reson Med, 2011.

Correction of B 0-induced geometric distortion variations in prospective motion correction for 7T MRI.

ObjectiveProspective motion correction can effectively fix the imaging volume of interest. For large motion, this can lead to relative motion of coil sensitivities, distortions associated with imaging gradients and B0 field variations. This work accounts for the B0 field change due to subject movement, and proposes a method for correcting tissue magnetic susceptibility-related distortion in prospective motion correction.Materials and methodsThe B0 field shifts at the different head orientations were characterized. A volunteer performed large motion with prospective motion correction enabled. The acquired data were divided into multiple groups according to the object positions. The correction of B0-related distortion was applied to each group of data individually via augmented sensitivity encoding with additionally integrated gradient nonlinearity correction.ResultsThe relative motion of the gradients, B0 field and coil sensitivities in prospective motion correction results in residual spatial distortion, blurring, and coil artifacts. These errors can be mitigated by the proposed method. Moreover, iterative conjugate gradient optimization with regularization provided superior results with smaller RMSE in comparison to standard conjugate gradient.ConclusionThe combined correction of B0-related distortion and gradient nonlinearity leads to a reduction of residual motion artifacts in prospective motion correction data.

Correction of gradient nonlinearity artifacts in prospective motion correction for 7T MRI.

To demonstrate the effect of gradient nonlinearity and develop a method for correction of gradient nonlinearity artifacts in prospective motion correction (Mo‐Co).

Robustness of free and pinned spiral waves against breakup by electrical forcing in excitable chemical media

We present an investigation on the breakup of free and pinned spiral waves under an applied electrical current in the Belousov-Zhabotinsky reaction. Spiral fronts propagating towards the negative electrode are decelerated. A breakup of the spiral waves occurs when some segments of the fronts are stopped by a sufficiently strong electrical current. In the absence of obstacles (i.e., free spiral waves), the critical value of the electrical current for the wave breakup increases with the excitability of the medium. For spiral waves pinned to circular obstacles, the critical electrical current increases with the obstacle diameter. Analysis of spiral dynamics shows that the enhancement of the robustness against the breakup of both free and pinned spiral waves is originated by the increment of wave speed when either the excitability is strengthened or the obstacle size is enlarged. The experimental findings are reproduced by numerical simulations using the Oregonator model. In addition, the simulations reveal that the robustness against the forced breakup increases with the activator level in both cases of free and pinned spiral waves.

Laser scattering measurement for laser removal of graffiti

In this contribution, a technical development of the laser scattering measurement for laser removal of graffiti is reported. This study concentrates on the removal of graffiti from metal surfaces. Four colored graffiti paints were applied to stainless steel samples. Cleaning efficiency was evaluated by the laser scattering system. In this study, an angular laser removal of graffiti was attempted to examine the removal process under practical conditions. A Q-switched Nd:YAG laser operating at 1.06 microns with the repetition rate of 1 Hz was used to remove graffiti from stainless steel samples. The laser fluence was investigated from 0.1 J/cm2 to 7 J/cm2. The laser parameters to achieve the removal effectiveness were determined by using the laser scattering system. This study strongly leads to further development of the potential online surface inspection for the removal of graffiti.

Electric Field Effects in Chemical Patterns

Excitation waves are a prototype of self-organized dynamic patterns in non-equilibrium systems. They develop their own intrinsic dynamics resulting in traveling waves of various forms and shapes. Prominent examples are rotating spirals and scroll waves. Their behavior can be controlled by applying external electrical signals, upon which these propagating waves react. We apply such electric fields to the excitable Belousov-Zhabotinsky (BZ) reaction. Remarkable effects include the change of wave speed, reversal of propagation direction, annihilation of counter-rotating spiral waves and reorientation of scroll wave filaments. Recently, we have investigated electric field effects in the BZ reaction dissolved in a sodium-bis (2-ethylhexyl) sulfosuccinate (AOT) water-in-oil microemulsion. A drift of complex patterns following nonlinear rules can be observed. We discuss the assumption that this system can act as a model for long range communication between neurons.

Unpinning of Spiral Waves

Spiral waves are propagating self-organized structures commonly found in excitable media. Spiral waves of electrical excitation in cardiac systems connect to some arrhythmias, such as tachycardia and fibrillations, potentially leading to sudden cardiac death so that they should be eliminated. Such waves may drift and eventually annihilate at the boundary. However, they can be stabilized, when they are pinned to obstacles, that are weakly excitable or unexcitable regions in the medium. Recently, we used the Belousov-Zhabotinsky solutions, the well-known excitable chemical systems, to study the propagation of spiral waves pinned to obstacles and applied electrical forcing to unpin them in different situations of obstacle size and excitability. We employed simulations with the Oregonator model, a realistic scheme for the Belousov-Zhabotinsky reaction, to confirm the experimental findings as well as to reveal the detailed motions of the spiral waves under some specific conditions that are difficult to be realized in the experiments.

Improvement of electrocardiogram by empirical wavelet transform

Electrocardiogram (ECG) is a crucial tool in the detection of cardiac arrhythmia. It is also often used in a routine physical exam, especially, for elderly people. This graphical representation of electrical activity of heart is obtained by a measurement of voltage at the skin; therefore, the signal is always contaminated by noise from various sources. For a proper interpretation, the quality of the ECG should be improved by a noise reduction. In this article, we present a study of a noise filtration in the ECG by using an empirical wavelet transform (EWT). Unlike the traditional wavelet method, EWT is adaptive since the frequency spectrum of the ECG is taken into account in the construction of the wavelet basis. We show that the signal-to-noise ratio increases after the noise filtration for different noise artefacts.

A simplified nitrogen laser setup operated at atmospheric pressure

A transversely excited atmospheric pressure nitrogen laser (TEA N2 Laser) is a molecular pulse gas laser, operated at atmospheric pressure, which generates an electromagnetic wave in ultraviolet wavelength of 337.1 nm. It can operate without an optical resonator. We present a TEA N2 laser setup excited by an electronic discharge circuit known as the Blumlein circuit. Our setup is composed of simple components commonly found in everyday life. The setup can be utilized in classroom to demonstrate the dependence of the laser intensity on the flow rate of nitrogen gas.

Influence of Acidity on Spiral Waves in a Bubble-Free Belousov-Zhabotinsky Reaction with Pyrogallol

Spiral waves are ubiquitously observed in a variety of physical and biological systems, including superconductors, superfluids, CO-oxidation on platinum surfaces, cell aggregation of slime mold and arrhythmia in cardiac tissues. Such spiral waves are uniquely explained by a reaction-diffusion mechanism. Due to easy preparation and convenient detection, the excitable chemical Belousov-Zhabotinsky (BZ) reaction is employed to study spiral waves in experiments. We studied the influence of initial concentration of H 2 SO 4 ((H 2 SO 4 )) on the dynamics of spiral waves in a thin layer of the BZ reaction with pyrogallol. This reaction has an advantage over the classical BZ reaction with malonic acid, as it is bubble-free. We found that the spiral tip, i.e., the organizing center, moved along so-called meandering trajectories with three or four outward petals. In addition, the area occupied by the spiral tip decreased when (H 2 SO 4 ) was increased. We further investigated the dynamics far from the organizing center by measuring properties of propagating fronts. An increase of (H 2 SO 4 ) resulted in a simultaneous decrease of the wavelength and wave period. In contrast, the wave speed grew with (H 2 SO 4 ). Since disturbances by the byproduct CO 2 bubbles are avoided and the wave velocity is sufficiently low, the results present a suitable guideline for further investigations on propagating excitation waves in two- and three-dimensional excitable media, especially observations of wave instabilities in three-dimensional systems using optical tomography.