Pablo Vanegas

Hepatic Steatosis detection using the co-occurrence matrix in tomography and ultrasound images

Hepatic Steatosis (HS) or Fatty Liver is a disease due to fat accumulation within hepatocytes. This disease requires treatment to avoid clinical complications such as hepatic inflammation, fibrosis and finally chronic hepatic damage and hepatic carcinoma. An algorithm for performing the manual segmentation was used. A polygon is traced for representing the region of interest in tomography (CT) images as well as in Ultrasound (US) images. These regions are then subdivided in a set of windows of size 4×4. For each of the windows the co-occurrence matrix is estimated as well as several descriptive statistical parameters. From these matrices, 9 descriptive statistical parameters were estimated. A Binary Logistic Regression (BLR) model was fitted considering as dependent variable the presence or absence of the disease and the descriptive statistical parameters as predictor variables. The model attains classification results of HS with a sensibility of 95.45% in US images and 93.75% in CT images in the venous phase.

A Novel Approach for Facile Synthesis of Biocompatible PVA-Coated PLA Nanofibers as Composite Membrane Scaffolds for Enhanced Osteoblast Proliferation

This chapter discusses a novel approach for facile synthesis of biocompatible poly(vinyl alcohol) PVA-coated polylactide (PLA) as composite membrane scaffolds for enhanced osteoblast proliferation. The composite scaffolds combined from PLA nanofiber-based materials coated with PVA thin layer were fabricated using hydrothermal treatment. The effects of deposition of the hydrophilic PVA on the MC3T3-E1 osteoblast cell attachment and proliferation were investigated by in vitro cell compatibility tests. The morphology, structure, chemical interfacial bonding, and thermal and mechanical properties of the scaffolds were studied. Results showed that PVA thin layer was successfully deposited onto the electrospun PLA fiber surfaces during hydrothermal treatment. The hydrothermal process induced crystalline conformation due to enhanced chain mobility of PLA. The mechanical tests showed that PLA could be turned from rigid to ductile with enhanced tensile strength, due to maximizing the hydrogen bond interaction during the heat treatment and the presence of PVA. The adhesion and proliferation properties of MC3T3-E1 cells on composite scaffolds were significantly higher than on the pristine fibers. The treatment process on PLA and producing composite samples from substrates could contribute to decelerating the rapid acidic phase release from the PLA molecules in the surrounding physiological environment. Based on the experimental results, PVA-coated PLA mats could be of particular interest in bone tissue engineering for tissue regeneration.

Peak control current in boundary conduction mode and discontinuous conduction mode for inverter with flyback topology

This paper proposes a hybrid control scheme peak current, applied to a single-phase micro inverter with flyback topology coupled to a LC filter, the proposed scheme allows the inverter to operate by boundary conduction mode when the output current exceeds a predetermined value. Otherwise, it operates in the discontinuous conduction mode, limiting the switching frequency. To set the control system in both modes of operation, the inverter is identified by averaging the model state and small signal, the control scheme used, presents a classic PI control and is tuned by pole placement. The proposed control scheme is verified through computer simulation.

Optical Flow as a Tool for Cardiac Motion Estimation

A sparse based algorithm for optical flow estimation is presented and compared with several classical optical flow estimation algorithms. The comparison is performed using several video sequences available from the Middlebury benchmark where the ground truth optical flow is known. The sparse algorithm attains competitive results with average angular errors as low as 2.09° and average magnitude errors as low as 0.100. The algorithms are also tested using a 4-D cardiac Magnetic Resonance Image (MRI) sequence. The sparse algorithm estimates an optical flow field that represents the motion of contraction during the systole interval.

Level set algorithms comparison for multi-slice CT left ventricle segmentation

The comparison of several Level Set algorithms is performed with respect to 2D left ventricle segmentation in Multi-Slice CT images. Five algorithms are compared by calculating the Dice coefficient between the resulting segmentation contour and a reference contour traced by a cardiologist. The algorithms are also tested on images contaminated with Gaussian noise for several values of PSNR. Additionally an algorithm for providing the initialization shape is proposed. This algorithm is based on a combination of mathematical morphology tools with watershed and region growing algorithms. Results on the set of test images are promising and suggest the extension to 3{D MSCT database segmentation.

Left ventricle myocardium segmentation in multi-slice computerized tomography

This paper briefly describes a left ventricle myocardium segmentation method in multi-slice computerized tomography images. The segmentation technique is based on level-sets deformable contours. The proposed method has two stages: in the first stage the left ventricle internal wall or endocardium is segmented. In the second stage the external wall is segmented starting with an initialization based on the endocardial segmented shape. This algorithm is intended for incorporation within a software platform for visualization and processing of cardiac images. This platform would help the diagnosis of the left ventricle hypertrophy (LVH).

Cardiac Motion Estimation in Magnetic Resonance Images Using Optical Flow

This paper reports an optical based method for quantification of cardiac motion in MRI images. The cardiac motion is quantified in a Short-Axis (SAX) slice located at the mid-cavity of the left ventricle. In this slice, the left ventricle wall is segmented for extracting the endocardium, the epicardium and the mid-wall. The velocity field for these contours is available after performing the optical flow estimation for the given slice. Post-processing of this motion field enables estimation of the radial displacement. The core of this cardiac motion quantification method is a sparse based algorithm for optical flow estimation. This algorithm is presented and compared with several classical optical flow estimation algorithms. The comparison is performed using several video sequences available from the Middlebury benchmark where the ground truth optical flow is known. The algorithms with better performance are also tested using a 4- D cardiac Magnetic Resonance Image (MRI) sequence. Results show that the sparse algorithm estimates an optical flow field that represents the motion of contraction during the systole interval. Moreover, results about radial displacement estimation on real MRI sequences for a normal subject and a patient with hypertrophy show that the proposed quantification method could be useful for quantification of left ventricle motion.