Chang-Beom Ahn

Fast terahertz reflection tomography using block-based compressed sensing

In this paper, a new fast terahertz reflection tomography is proposed using block-based compressed sensing. Since measuring the time-domain signal on two-dimensional grid requires excessive time, reducing measurement time is highly demanding in terahertz tomography. The proposed technique directly reduces the number of sampling points in the spatial domain without modulation or transformation of the signal. Compressed sensing in spatial domain suggests a block-based reconstruction, which substantially reduces computational time without degrading the image quality. An overlap-average method is proposed to remove the block artifact in the block-based compressed sensing. Fast terahertz reflection tomography using the block-based compressed sensing is demonstrated with an integrated circuit and parched anchovy as examples.

Efficient video coding algorithm using multi-dimensional transform

This paper proposes a new video coding algorithm using the multi-dimensional transform. The multi-dimensional transform achieves both the accuracy of temporal prediction as well as effective use of spatial redundancy. Moreover, two additional methods for multi-dimensional transform are proposed, which are cube forming and modified transform coefficient thresholding. These combined schemes lead to a bitrate saving on FRExt profile, compared to an H.264/AVC standard codec, which reach up to 2.88%.

EEG and artifact classification using a neural network

A multilayer perceptron based classifier is proposed for automatic EEG and artifact classification. Conventionally this task has been carried out by a human expert spending a lot of examination time. For efficient network learning, a preprocessor is designed by which expert knowledge is more effectively utilized. A neural network operating characteristic (NOC) with correct and false classification probabilities is introduced for objective performance evaluation, by which an optimal neural network is constructed. From experiments, the neural-network based classifier performs as well as human experts.

Field inhomogeneity correction using partial differential phases in magnetic resonance imaging

Correction of an inhomogeneous magnetic field is proposed using partial differential phases in magnetic resonance imaging. Estimation of the inhomogeneous magnetic field from a measured phase is not an easy task due to phase wrapping and chemical-dependent phase shifts. Using the proposed partial differential phase technique, such problems are resolved. The proposed technique uses most of the 3D pixel data regardless of chemical compounds for the estimation of the inhomogeneous magnetic field. A large number of partial difference data compared to the number of expansion terms for the model of inhomogeneous magnetic field provides a very stable estimation, robust to noise. The technique is applicable to in vivo shimming, water-fat imaging, eddy current compensation, and most phase-related measurements and imaging. The efficacy of the proposed technique is demonstrated with in vivo water-fat imaging.

Multi-biological Signal-based Smart Trigger System for Cardiac MRI

In cardiac magnetic resonance imaging (CMRI), heart and respiratory motions are one of main obstacles in obtaining diagnostic quality of images. To synchronize CMRI to the physiological motions, ECG and respiratory gatings are commonly used. In this paper multi-biological signal (ECG, respiratory, and SPO2) based smart trigger system is proposed. By using multi-biological signal, the proposed system is robust to the induced noise such as eddy current when gradient pulsing is continuously applied during the examination. Digital conversion of the multi-biological signal makes the system flexible in implementing smart and intelligent algorithm to detect cardiac and respiratory motion and to reject arrhythmia of the heart. The digital data is used for real-time trigger, as well as signal display, and data storage which may be used for retrospective signal processing.

Vote Decision-based Deinterlacing Scheme For Directional Error Correction

This paper presents a vote decision-based deinterlacing scheme for false directional error correction(VDD) to convert interlaced signal into non-interlaced signal using only one fields. The VDD using the vote decision goes through four steps process. The first step extracts regions having doubt of false edge using MM-ELA method. In these regions, the edge direction is decided by the majority vote using upper adjacent pixels`s information through the second step. But, we still have undecided directions, which will be decided by the majority vote and the directional average decision at the third step. This step preserves the edge directions and minimizes visual degradation. Finally, the last step interpolates undecided pixels using DOI method which can consider the fine edge direction. Although the VDD with hierarchical structure has a high complexity, it can extract delicate edge compared to other pixel-by-pixel or window-by-window deinterlacing algorithms. Simulation results show that it has significantly improved both the subjective and objective qualities of the reconstructed images.

Enhancement of terahertz reflection tomographic imaging by interference cancellation between layers

This paper proposes a method to enhance terahertz reflection tomographic imaging by interference cancellation between layers. When the gap between layers is small, the signal reflected on the upper layer interferes with that on the lower layer, which degrades the quality of the reconstructed tomographic image in the lower layer. The proposed method estimates the upper-layer reflection signal by system modeling, which is then eliminated from the acquired signal. In this way, it can provide the correct lower-layer reflection signal, thereby improving the quality of the lower-layer tomographic image. The performance of the proposed method was confirmed using computer simulation data and real terahertz reflection data.

Pre- and post-processing for tomographic reconstruction of terahertz time-domain spectroscopy

Reflection-type terahertz tomography is obtained using time-domain spectroscopy. Due to different velocities of the terahertz ray in free space and inside a sample, the tomographic transverse plane is not obtained by a simple reconstruction using time index. A pre-processing method is proposed to compensate for the different velocities of the terahertz ray for tomographic reconstruction. Maximum intensity projection, averaging, and short-time Fourier transform are proposed as post-processing methods along the depth direction for the terahertz tomography. Log-scale display is also suggested for a better visualization. Some experimental results with the pre- and post-processing are demonstrated.

Principles of Tomography Imaging: From X-ray CT, MRI to THz Tomography

A digital image is a digital representation of a 2D (dimensional) image which is expressed mathematically by a 2D matrix of pixel (picture element) values where each element position corresponds to the pixel location in 2D space. To specify a digital image, some parameters related to the image format need to be defined. The image width, w, and the image height, h, in the number of pixels are necessary. Then, the image consists of w × h pixels and is called a w × h pixel image, and the dimension of corresponding matrix is also w × h. In a digital image, the pixel values are expressed in a bit format. Hence, the number of bits assigned to each pixel value needs to be defined. If the value is represented with b bits, each value is an integer between 0 and 2 b − 1, and can represent 2 b different colors. In this way, the overall number of bits required to represent the given digital image becomes b × (w × h).

The Efficient Coding Tools based 3-Dimensional Transform in H.264/AVC

In this paper, we propose 3DTE(3-Dimensional Transform Environment) that is based on 3DT(Dimensional Transform) that performs 2-dimensional integer DCT(Discrete Cosine Transform) based on 4x4 block and 1-dimensional integer DCT based on 4x1 block after collecting same frequency coefficients in neighboring 4x4 block and supports its additional coding tools for high performance. The transform of 3DT can keep prediction error by using 4x4 block and reduce spatial redundancy additionally. The proposed 3DTE can provide coding tools to improve the coding efficiency with using 3DT. The performance of 3DTE compared to JM11.0 is average 3.58% and 5.40% bit savings for all test sequences and HD sequences, respectively, with keeping subjective video quality in High profile.