Andre Souza

Model-based super-resolution for MRI

Conventional 1.5T magnetic resonance imaging (MRI) systems suffer from poor out-of-plane resolution (slice dimension), usually with in-plane resolution being several times higher than the former. Post-acquisition, super-resolution (SR) filtering is a viable alternative and a less expensive, off-line image processing approach that is employed to improve tissue resolution and contrast on acquired three-dimensional (3D) MR images. We introduce an SR framework that models a true acquired volume information by taking into account slice thickness and spacing between slices. Previous SR schemes have not considered this type of acquisition information or they have required specialized MR acquisition techniques. Evaluations based on synthetic data and clinical knee MRI data show superior performance of this method over an existing averaging method.

Optoelectronic specifications of emerging coherent optical solutions for data center interconnect

Emerging short-reach data center interconnect is a scenario wherein the capacity has to be maximized over point- to-point optical links without intermediate optical amplification. Most of the transceiver solutions are based on 100G modules with direct detection modulation. Although these legacy solutions are cost-efficient in a short- term, they are not scalable in a long-term, when the capacity x distance product will become more and more stringent. This paper addresses coherent optical solutions for emerging data center interconnect, with optical transmission reach being limited to around unrepeated 100 km. The main advantage of coherent solutions, when compared to legacy direct detection technologies, is the inherently improved spectral efficiency (e.g. 400 Gb/s channels in a 50 GHz grid) and receiver sensitivity provided with high baudrate (>40 GBd) transceiver modules. In this paper, two technological options for single-carrier optical 400 Gb/s modules are exploited for high capacity links over short reach scenarios: 43 GBd polarization-division-multiplexed (PDM)-64QAM, suitable for a 50-GHz grid; and 64 GBd PDM-16QAM, suitable for a 75-GHz grid. These two solutions are compared in terms of capacity allocated in C band (∼4 THz bandwidth), when considering 50 GHz (80 channels at 400G, 32 Tb/s) and 75 GHz (53 channels with 21.2 Tb/s) grids and back-to-back requirements in terms of optoelectronics (digital-to-analog and analog-to-digital converters, modulators, receivers etc.).

Digital Nonlinear Compensation for Spectrally Sliced Optical Receivers With MIMO Reconstruction

We experimentally investigate, in a 20×56-GBd 400 G WDM transmission system, different approaches for nonlinear compensation in spectrally sliced optical receivers with MIMO-based signal reconstruction. Slice-by-slice nonlinear compensation shows comparable performance to inter-slice nonlinear compensation in a WDM system. In addition, an eight-stages compensation yields a 0.4-dB Q2 gain equivalent to 250-km distance increase, resulting in 2000-km transparent reach.

3-D examination of dental fractures with minimum user intervention

We developed a novel, powerful segmentation algorithm and an intuitive 3-D visualization tool for the examination of root fractures with minimum user intervention. The application computes and displays a suitable oblique orientation on a selected tooth by placing at least two splines (inside and outside of the tooth) in just one slice of the volume. Next, it allows the user to scroll through the volume, slice-by-slice in parallel to the plane, or to examine the tooth by changing the orientation of a 3-D object plane (called a virtual bitewing), which is placed, at the same time, in a volume rendition. Both the root canal and the root fracture are highlighted during the examination phase. Doctors (end users) are in control to quickly and confidently examine root fractures in 3-D, for any given oblique orientation, without worrying about missing a selected tooth. We have designed and implemented these algorithms using the image foresting transform (IFT) technique for interactive tooth segmentation and used a multi-scale parameter search for automatic oblique orientation estimation.

Noise-resistant adaptive scale using stabilized diffusion

Semi-locally adaptive models have appeared in medical imaging literature in the past years. In particular, generalized scale models (or g-scale for short) have been introduced to effectively overcome the shape, size, or anisotropic constraints imposed by previous local morphometric scale models. The g-scale models have shown interesting theoretical properties and an ability to drive improved image processing as shown in previous works. In this paper, we present a noise-resistant variant for g-scale set formation, which we refer to as stabilized scale (s-scale) because of its stabilized diffusive properties. This is a modified diffusion process wherein a well-conditioned and stable behavior in the vicinity of boundaries is defined. Yet, s-scale includes an intensity-merging dynamics behavior in the same manner as that found in the switching control of a nonlinear system. Basically we introduce, in the evolution of the diffusive model, a behavior state to drive neighboring voxel intensities to larger and larger iso-intensity regions. In other words, we drive our diffusion process to a coarser and coarser piecewise-constant approximation of the original scene. This strategy reveals a well-known behavior in control theory, called sliding modes. Evaluations on a mathematical phantom, the Brainweb, MR and CT data sets were conducted. The s-scale has shown better performance than the original g-scale under moderate to high noise levels.

High-Capacity Unrepeatered Optical Transmission

In the global telecommunications scenario, a great deal of interest has recently been devoted to taking the internet to country remote communities that are densely populated but in which the challenges imposed by climatic and environmental limitations are not straightforward to overcome. This chapter focuses on high-capacity unrepeatered optical transmission systems to enable high-speed connectivity in hard-to-reach areas. An optimization method for the unrepeatered optical system design is provided and detailed, followed by laboratory demonstrations showing the potential of repeaterless transmission in WDM systems with 400 Gb/s per carrier over distances greater than 400 km.

Soft-Decision Forward Error Correction in Optical Communications

In order to effectively design good error-correcting codes for a given application, it is important to know how they work, how to assess the reliability of a given implementation and to be aware of the available codes and its features. In this chapter, a background about error correction is given so the reader can grasp the ideas behind error-correcting codes. Derivations about the confidence of error rate estimates are presented. These derivations turn out to be useful in the assessment of a system reliability when it is not possible to simulate enough codewords to observe a considerable number of errors. Finally, a brief historical review is presented and the authors present their view about promising codes for optical communications.

Multilevel Pulse Amplitude Modulation Transmissions for Data Center Applications

Four-level pulse amplitude modulation (PAM4) is appearing as an important option for many applications that require optical communications at high data rate for short distances and/or with low complexity, such as Data Center interconnects. In this sense, this chapter aims to evaluate key features requirements for PAM4 transmissions focusing on short-reach DC applications. Therefore, we present a software to emulate PAM4 transmission at a high baud rate (56 GBd) in order to evaluate different configurations and impairments that could affect data transmission in the C-band, namely the digital signal processing (DSP) complexity, bandwidth limitation, chromatic dispersion tolerance, differential group delay (DGD) tolerance, and analog-to-digital converter (ADC) sampling requirements.

Detection of tooth fractures in CBCT images using attention index estimation

The attention index (𝜑) is a number from zero to one that indicates a possible fracture is detected inside a selected tooth. The higher the 𝜑 number, the greater the likelihood for needed attention in the visual examination. The method developed for the 𝜑 estimation extracts a connected component with image properties that are similar to those of a typical tooth fracture. That is, in cone-beam computed tomography (CBCT) images, a fracture appears as a dark canyon inside the tooth. In order to start the visual examination process, the method provides a plane across the geometric center of the suspicious fracture component, which maximizes the number of pixels from that component inside the plane. During visual examination, the user (doctor) can change plane orientations and locations, by manipulating the mouse toward different graphical elements that represent the plane on a 3-D rendition of the tooth, while the corresponding image of the plane is shown at its side. The visual examination aims at confirming or disproving the fracture-detection event. We have designed and implemented these algorithms using the image-foresting transform methodology.

Fast-forward projection approach for 3D iterative metal artifact suppression

Despite the advance in iterative reconstruction methods for reducing metal artifacts, Feldkamp (FDK) based algorithms continue to be the most widely used CT reconstruction in medicine. While computationally efficient, FDK performs poorly in the presence of metallic objects. Projection-completion algorithms have been used to suppress metallic artifacts and, hence, improve image quality in FDK reconstruction. Here, we present a threedimensional adaptive filtering method that performs projection completion. It takes into account the metal content fraction in the voxel and applies a correction in the projections. This algorithm uses a fast, simple, forward-projection method to obtain accurate metal probability regions in the projection space. We compare our results with those obtained using projection completion by linear interpolation on a dental cone-beam CT.