Khin Wee Lai

Synthesis and Characterization of Silver Nanoparticles and Silver Inks: Review on the Past and Recent Technology Roadmaps

AbstractThe synthesis of silver nanoparticles for silver ink formation has attracted broad interest in the electronic part printing and semiconductor chip industry due to the extraordinary electrical and mechanical properties of these materials. The preparation of silver nanoparticles through a physical or chemical reduction process is the most common methodology applied to obtain nanoparticles with the required size, shape and surface morphology. The chemical solution or solvent carrier applied for silver ink formulation must be applied simultaneously with the direct writing technique to produce the desired adherence, viscosity, and reliable performance. This review paper discusses the details concerning the past and recent advancement of the synthesis and characterization of silver nanoparticles and silver ink formation. A review on the advantages of various sintering techniques, which aim to achieve the electrical and mechanical properties of the required printed structure, is also included. A brief summary concerning the recent challenges and improvement approaches is presented at the end of this review.

Thermal distribution analysis of three-dimensional tumor-embedded breast models with different breast density compositions

Breast cancer is the most common cancer among women globally, and the number of young women diagnosed with this disease is gradually increasing over the years. Mammography is the current gold-standard technique although it is known to be less sensitive in detecting tumors in woman with dense breast tissue. Detecting an early-stage tumor in young women is very crucial for better survival chance and treatment. The thermography technique has the capability to provide an additional functional information on physiological changes to mammography by describing thermal and vascular properties of the tissues. Studies on breast thermography have been carried out to improve the accuracy level of the thermography technique in various perspectives. However, the limitation of gathering women affected by cancer in different age groups had necessitated this comprehensive study which is aimed to investigate the effect of different density levels on the surface temperature distribution profile of the breast models. These models, namely extremely dense (ED), heterogeneously dense (HD), scattered fibroglandular (SF), and predominantly fatty (PF), with embedded tumors were developed using the finite element method. A conventional Pennes’ bioheat model was used to perform the numerical simulation on different case studies, and the results obtained were then compared using a hypothesis statistical analysis method to the reference breast model developed previously. The results obtained show that ED, SF, and PF breast models had significant mean differences in surface temperature profile with a p value <0.025, while HD breast model data pair agreed with the null hypothesis formulated due to the comparable tissue composition percentage to the reference model. The findings suggested that various breast density levels should be considered as a contributing factor to the surface thermal distribution profile alteration in both breast cancer detection and analysis when using the thermography technique.

Motion corrected LV quantification based on 3D modelling for improved functional assessment in cardiac MRI.

Cine MRI is a clinical reference standard for the quantitative assessment of cardiac function, but reproducibility is confounded by motion artefacts. We explore the feasibility of a motion corrected 3D left ventricle (LV) quantification method, incorporating multislice image registration into the 3D model reconstruction, to improve reproducibility of 3D LV functional quantification. Multi-breath-hold short-axis and radial long-axis images were acquired from 10 patients and 10 healthy subjects. The proposed framework reduced misalignment between slices to subpixel accuracy (2.88 to 1.21 mm), and improved interstudy reproducibility for 5 important clinical functional measures, i.e. end-diastolic volume, end-systolic volume, ejection fraction, myocardial mass and 3D-sphericity index, as reflected in a reduction in the sample size required to detect statistically significant cardiac changes: a reduction of 21-66%. Our investigation on the optimum registration parameters, including both cardiac time frames and number of long-axis (LA) slices, suggested that a single time frame is adequate for motion correction whereas integrating more LA slices can improve registration and model reconstruction accuracy for improved functional quantification especially on datasets with severe motion artefacts.

Multiple LREK Active Contours for Knee Meniscus Ultrasound Image Segmentation

Quantification of knee meniscus degeneration and displacement in an ultrasound image requires simultaneous segmentation of femoral condyle, meniscus, and tibial plateau in order to determine the area and the position of the meniscus. In this paper, we present an active contour for image segmentation that uses scalable local regional information on expandable kernel (LREK). It includes using a strategy to adapt the size of a local window in order to avoid being confined locally in a homogeneous region during the segmentation process. We also provide a multiple active contours framework called multiple LREK (MLREK) to deal with multiple object segmentation without merging and overlapping between the neighboring contours in the shared boundaries of separate regions. We compare its performance to other existing active contour models and show an improvement offered by our model. We then investigate the choice of various parameters in the proposed framework in response to the segmentation outcome. Dice coefficient and Hausdorff distance measures over a set of real knee meniscus ultrasound images indicate a potential application of MLREK for assessment of knee meniscus degeneration and displacement.

Multiobjectives bihistogram equalization for image contrast enhancement

The global histogram equalization HE has been the most frequently adopted image contrast enhancement technique. A brightness and detail-preserving HE method with good contrast enhancement effect has been a goal of much recent research in HE. Nevertheless, producing a well-balanced HE is deemed to be a daunting task. In this article, we propose a novel framework of HE with the aim of taking three desirable properties into account: brightness preservation, detail preservation, and contrast enhancement. We termed the proposed method as multipurpose beta optimized bi-HE MBOBHE. MBOBHE consists of performing the histogram optimization separately in both subhistograms after the segmentation of histogram using an optimized separating point based on the three performance criteria using a weighted-sum aggregated objective function AOF. Both quantitative and qualitative results indicate that MBOBHE outperforms other existing bi-HE methods, in terms of comprehensive performance of HE that is capable of providing a holistic view.

Regional assessment of LV wall in infarcted heart using tagged MRI and cardiac modelling

A segmental two-parameter empirical deformable model is proposed for evaluating regional motion abnormality of the left ventricle. Short-axis tagged MRI scans were acquired from 10 healthy subjects and 10 postinfarct patients. Two motion parameters, contraction and rotation, were quantified for each cardiac segment by fitting the proposed model using a non-rigid registration algorithm. The accuracy in motion estimation was compared to a global model approach. Motion parameters extracted from patients were correlated to infarct transmurality assessed with delayed-contrast-enhanced MRI. The proposed segmental model allows markedly improved accuracy in regional motion analysis as compared to the global model for both subject groups (1.22-1.40 mm versus 2.31-2.55 mm error). By end-systole, all healthy segments experienced radial displacement by ~25-35% of the epicardial radius, whereas the 3 short-axis planes rotated differently (basal: 3.3°; mid:  -1° and apical:  -4.6°) to create a twisting motion. While systolic contraction showed clear correspondence to infarct transmurality, rotation was nonspecific to either infarct location or transmurality but could indicate the presence of functional abnormality. Regional contraction and rotation derived using this model could potentially aid in the assessment of severity of regional dysfunction of infarcted myocardium.

Position Tracking Systems for Ultrasound Imaging: A Survey

With the rapid advancement of position tracking devices, the application of such system in medical imaging is increasing correspondingly. The uses of position tracking systems in ultrasound imaging have been established for more than a decade. Its implementation ranges from two-dimensional (2D) to three-dimensional (3D) ultrasound reconstruction, image registration for multimodality imaging, to image-guided navigation. This progression has brought the ultrasound imaging system become more accurate, interactive, multidimensional, and ubiquitous with other systems. This chapter provides an appraisal of various position tracking systems for ultrasound biomedical imaging applications. We highlight our study on the position tracking devices, methods overview, and position tracking implementation in ultrasound imaging systems and applications.

Advances in Medical Diagnostic Technology

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Review on Image Guided Lung Biopsy

Lung biopsy is an established field. Throughout years physician and scientist have been exploring the field, from technical and clinical point of view. Mainly there are three types of lung biopsy, open, bronchoscopic, and fine needle aspiration biopsy. Open biopsy is essentially a surgery, thus not really dependent on image guiding system. On the other hand, bronchoscopic and fine needle aspiration biopsy relay heavily in image guiding system. Curiously, it is rare to find both biopsy types talked side by side. In this paper, both biopsy types explored and compared from technical and clinical point of view. Technical wise, bronchoscopic biopsy trend is toward path finding algorithm, while fine needle aspiration biopsy trend is toward breathing compensation algorithm and automatization. Clinical wise, there is no evidence that one type hold better diagnostic value than the other.

Bulk substrate porosity verification by applying Monte Carlo modeling and Castaing’s formula using energy-dispersive x-rays

Abstract. The leadframe fabrication process normally involves additional thin-metal layer plating on the bulk copper substrate surface for wire bonding purposes. Silver, tin, and copper flakes are commonly adopted as plating materials. It is critical to assess the density of the plated metal layer, and in particular to look for porosity or voids underneath the layer, which may reduce the reliability during high-temperature stress. A fast, reliable inspection technique is needed to assess the porosity or void weakness. To this end, the characteristics of x-rays generated from bulk samples were examined using an energy-dispersive x-ray (EDX) detector to examine the porosity percentage. Monte Carlo modeling was integrated with Castaing’s formula to verify the integrity of the experimental data. Samples with different porosity percentages were considered to test the correlation between the intensity of the collected x-ray signal and the material density. To further verify the integrity of the model, conventional cross-sectional samples were also taken to observe the porosity percentage using Image J software measurement. A breakthrough in bulk substrate assessment was achieved by applying EDX for the first time to nonelemental analysis. The experimental data showed that the EDX features were not only useful for elemental analysis, but also applicable to thin-film metal layer thickness measurement and bulk material density determination. A detailed experiment was conducted using EDX to assess the plating metal layer and bulk material porosity.