We present a new dequantization technique for discrete cosine transform (DCT) based encoding. For the lack of better dequantization methods, the currently existing image compression standards states simply to multiply the received quantized DCT coefficients by the quantization matrix. Therefore, for each DCT coefficient, the quantization noise as large as half quantizer step size may be introduced (in the DCT domain). Our proposed technique, through regularization, dequantizes the quantized DCT coefficients so that the resulting decoded image will be visually more pleasing. Through simulation studies, we show improvements in the visual characteristics and also in terms of the peak-signal-to-noise-ratio (PSNR).

A visual rhythm is a special 2D image reduced from a 3D video data in a way that the pixels along a vertical line of the visual rhythm are the pixels uniformly sampled along the diagonal line of a video frame. Using the distinct visual patterns to appear on the visual rhythm, we propose a video segmentation method to effectively detect both abrupt and gradual shot transitions. Specifically, the algorithms to detect cut, wipe and dissolve transitions are outlined. It is noted that the proposed method operates on a small fraction of the original video data, and thus offers remarkable computational savings.

The authors have developed a technique based on a solution of the Poisson equation to unwrap the phase in magnetic resonance (MR) phase images. The method is based on the assumption that the magnitude of the inter-pixel phase change is less than pi per pixel. Therefore, the authors obtain an estimate of the phase gradient by "wrapping" the gradient of the original phase image. The problem is then to obtain the absolute phase given the estimate of the phase gradient. The least-squares (LS) solution to this problem is shown to be a solution of the Poisson equation allowing the use of fast Poisson solvers. The absolute phase is then obtained by mapping the LS phase to the nearest multiple of 2 K from the measured phase. The proposed technique is evaluated using MR phase images and is proven to be robust in the presence of noise. An application of the proposed method to the 3-point Dixon technique for water and fat separation is demonstrated.

A method of computing the velocity field and pressure distribution from a sequence of ultrafast CT (UFCT) cardiac images is demonstrated. UFCT multi-slice cine imaging gives a series of tomographic slices covering the volume of the heart at a rate of 17 frames per second. The complete volume data set can be modeled using equations of continuum theory and through regularization, velocity vectors of both blood and tissue can be determined at each voxel in the volume. The authors present a technique to determine the pressure distribution throughout the volume of the left ventricle using the computed velocity field. A numerical algorithm is developed by discretizing the pressure Poisson equation (PPE), which Is based on the Navier-Stokes equation. The algorithm is evaluated using a mathematical phantom of known velocity and pressure-Couette flow. It is shown that the algorithm based on the PPE can reconstruct the pressure distribution using only the velocity data. Furthermore, the PPE is shown to be robust in the presence of noise. The velocity field and pressure distribution derived from a UFCT study of a patient are also presented.