Elimination Of Artefact Research Articles

Theoretical advantages of a triaxial optically pumped magnetometer magnetoencephalography system

The optically pumped magnetometer (OPM) is a viable means to detect magnetic fields generated by human brain activity. Compared to conventional detectors (superconducting quantum interference devices) OPMs are small, lightweight, flexible, and operate without cryogenics. This has led to a step change in instrumentation for magnetoencephalography (MEG), enabling a “wearable” scanner platform, adaptable to fit any head size, able to acquire data whilst subjects move, and offering improved data quality. Although many studies have shown the efficacy of ‘OPM-MEG’, one relatively untapped advantage relates to improved array design. Specifically, OPMs enable the simultaneous measurement of magnetic field components along multiple axes (distinct from a single radial orientation, as used in most conventional MEG systems). This enables characterisation of the magnetic field vector at all sensors, affording extra information which has the potential to improve source reconstruction. Here, we conduct a theoretical analysis of the critical parameters that should be optimised for effective source reconstruction. We show that these parameters can be optimised by judicious array design incorporating triaxial MEG measurements. Using simulations, we demonstrate how a triaxial array offers a dramatic improvement on our ability to differentiate real brain activity from sources of magnetic interference (external to the brain). Further, a triaxial system is shown to offer a marked improvement in the elimination of artefact caused by head movement. Theoretical results are supplemented by an experimental recording demonstrating improved interference reduction. These findings offer new insights into how future OPM-MEG arrays can be designed with improved performance.

Benchmarking of three-dimensional multicomponent lattice Boltzmann equation.

We present a challenging validation of phase field multicomponent lattice Boltzmann equation (MCLBE) simulation against the Re=0 Stokes flow regime Taylor-Einstein theory of dilute suspension viscosity. By applying a number of recent advances in the understanding and the elimination of the interfacial microcurrent artefact, extending to a three-dimensional class of stability-enhancing multiple relaxation time collision models (which require no explicit collision matrix, note) and developing new interfacial interpolation schemes, we are able to obtain data that show that MCLBE may be applied in new flow regimes. Our data represent one of the most stringent tests yet attempted on LBE-one which received wisdom would preclude on grounds of overwhelming artefact flow.

Characterization and correction of cupping effect artefacts in cone beam CT

The purpose of this study was to demonstrate and correct the cupping effect artefact that occurs owing to the presence of beam hardening and scatter radiation during image acquisition in cone beam CT (CBCT). A uniform aluminium cylinder (6061) was used to demonstrate the cupping effect artefact on the Planmeca Promax 3D CBCT unit (Planmeca OY, Helsinki, Finland). The cupping effect was studied using a line profile plot of the grey level values using ImageJ software (National Institutes of Health, Bethesda, MD). A hardware-based correction method using copper pre-filtration was used to address this artefact caused by beam hardening and a software-based subtraction algorithm was used to address scatter contamination. The hardware-based correction used to address the effects of beam hardening suppressed the cupping effect artefact but did not eliminate it. The software-based correction used to address the effects of scatter resulted in elimination of the cupping effect artefact. Compensating for the presence of beam hardening and scatter radiation improves grey level uniformity in CBCT.

Apneic oxygenation for elimination of respiratory motion artefact in an intubated patient undergoing helical chest computed tomography angiography.

Respiratory motion artifact in intubated and mechanically ventilated patients often reduces the quality of helical computed tomography pulmonary angiography (CTPA). Apneic oxygenation is a well established intra-operative technique that allows adequate oxygenation for short periods (up to 10 min) in sedated and paralyzed patients. We describe the use of the apneic oxygenation for elimination of respiratory motion artefact in an intubated patient undergoing CTPA.

Elimination of line dimming artefact in liquid crystal display monitors

A new technology for improved dynamic performance of liquid crystal monitors is presented. The limitation and additional artefact of conventional overdrive are addressed and new requirements are expressed. The proposed overdrive improves line dimming effectively without any additional artefacts.

A fast recursive-least-squares adaptive notch filter and its applications to biomedical signals.

A fast recursive-least-squares (FRLS) adaptive notch filter (ANF) for cancellation of sinusoidal interference from recorded biomedical signals is investigated. The FRLS ANF is derived by making an approximation to the conventional recursive-least-squares (RLS) ANF for computation economy. It outperforms the commonly adopted least-mean-squares (LMS) ANF, demonstrating a rapid and bandwidth-insensitive initial convergence. A novel application of the FRLS ANF is for the elimination of the tonal artefact in distortion product otoacoustic emission (DPOAE) signals.

Non-invasive electrogastrography. Part 2. Human electrogastrogram.

The electrical activity of human stomach muscle wall-electrogastrogram (EGG), was led off by surface (cutaneous) electrodes placed on the abdominal wall and recorded on an electrogastrograph. A method for complete elimination of the cardiac artefact was elaborated and successfully implemented. It consists of a preliminary elimination of the QRS complex, based on its higher amplitude and slope. The eliminated intervals were replaced by linear segments. A subsequent low-pass filtering allowed to obtain a high quality EGG signal. The electrical activity of the stomach of healthy volunteers was characterized by waves with a frequency of 3.35 +/- 0.09 cpm during the quiescent periods and 2.99 +/- 0.14 cpm during the activity periods of the migrating myoelectrical complex (MMC). Bearing in mind the correlation between the bursts of spike potentials with the slow waves in the dog EGMG and the high-amplitude waves, characterizing the periods of activity in the dog EGG, we can better differentiate the periods of quiescence and activity by the amplitude of the waves. The wave amplitude during periods of quiescence was 81.13 +/- 20.61 microV, significantly different from the wave amplitude during periods of activity being 164.74 +/- 43.34 microV (n = 7). Thus with this method in visual inspection it is possible to identify MMC of the human stomach by the changes in the amplitude of the waves in the EGG.

Digital subtraction of eye movement artefact from pattern ERG recordings

The electroretinal response to phase-alternating spatial patterns, the pattern electroretinogram (PERG). appears to originate in and reflect function of the ganglion cell layer of the retina. Consequently, PERG recording may have utility for the evaluation of central disorders of vision in Neuro-Ophthalmology. Many neurological patients have uncontrollable eye movements in the form of nystagmus, which is often enhanced by viewing the phase-alternating stimulus used to elicit the PERG, thereby producing gross eye movement and electrode movement artefacts. A technique is described for the elimination of electrode movement artefact and for the digital subtraction of averaged eye movement artefact from the contaminated PERG recordings, thereby deriving a purer PERG tracing.

Description of a coverslip holder for, and observations on, the critical point drying of cell cultures.

The elimination of artefact during the preparation of cell cultures for scanning electron microscopy is difficult. Collapse of cellular projections, cytoplasmic cracks, perforations and fracturing of cell-cell processes and cell-substrate attachments occur during fixation, dehydration and critical point drying. Coating and storage may cause further artefact. A specimen holder which serves to minimize turbulence in the critical point dryer and which allows for the simultaneous processing of up to five coverslips, as well as a reproducible technique for the preparation of cell cultures are described.

Staining of vascular elastic fibres in mummified and dried human tissues.

IT has been clearly established in mummified and other dried human material that the connective tissues are frequently well preserved while the epithelia are less-often recognizable1,2. This is probably a reflexion of relative susceptibility to any autolysis which may precede effective desiccation. Neurovascular bundles are readily recognized in some Egyptian mummies and in dried bodies from other ancient cultures; for this reason direct study of vascular disease in antiquity is possible1,3,4. Nevertheless, desiccation produces considerable distortion of blood vessels, and interpretation of changes and elimination of artefact is greatly aided by delineation of elastic fibres, which are valuable landmarks in vessel structure.