Projection In Frequency Domain Research Articles

Frequency domain despeckling technique for medical ultrasound images

Abstract This work proposes a novel frequency domain despeckling technique pertaining to the enhancement of the quality of medical ultrasound images. The results of the proposed method have been validated in comparison to both the time-domain and the frequency-domain projections of the schur decomposition as well as with several other benchmark schemes such as frost, lee, probabilistic non-local means (PNLM) and total variation filtering (TVF). The proposed algorithm has shown significant improvements in edge detection and signal to noise ratio (SNR) levels when compared with the performance of the other techniques. Both real and simulated medical ultrasound images have been used to evaluate the numerical and visual effects of each algorithm used in this work.

The entropy weighted non-uniform scanning algorithm for diffraction tomography

This paper studies diffraction tomography based on Fourier diffraction projection theorem. By the observation of frequency domain projecting image, one can find that projection in frequency domain is not uniformly distributed when the spatial domain scanning angle is equispaced. This results in loss of information. We analyze the conditions under which the information lost most. Then, we define the information entropy of each scanning and propose a non-uniform scanning algorithm to maximize the amount of information under conditions of a fixed number of sampling points and scanning angles. The algorithm has five different kinds of the weighting vectors based on different weighting programs. The simulation result supports our hypotheses and indicates that the algorithm proposed in this paper can obviously improve the reconstruction quality.

Rotation and Translation Invariant Feature Extraction Using Angular Projection in Frequency Domain

Rotation and Translation Invariant Feature Extraction Using Angular Projection in Frequency Domain

Fast multidimensional NMR: radial sampling of evolution space

Multidimensional NMR spectroscopy can be speeded up by limited radial sampling of the time-domain evolution data. The resulting frequency-domain projections are used to reconstruct the full NMR spectrum. New algorithms are proposed to suppress back-projection artifacts while retaining optimum sensitivity. The method is illustrated by experiments on the 900 MHz HNCO spectrum of a protein, HasA.

Poor man's TBR: a simple model reduction scheme

This work presents a model reduction algorithm motivated by a connection between frequency-domain projection methods and approximation of truncated balanced realizations. The method is computationally simple to implement, has near-optimal error properties, and possesses simple error estimation and order-control procedures. Usage of the method also enables straightforward exploitation of information about the particular application and setting, as well as circuit functional information, such as frequency weighting information and correlations between network port waveforms. When such specific information is available, standard truncated balanced realization algorithms generate models far from optimal according to statistical decision criteria. Examples are shown to demonstrate that the method can outperform the standard order reduction techniques by providing similar accuracy with lower order models or superior accuracy for the same size model.

Poor man's TBR: a simple model reduction scheme

This work presents a model reduction algorithm motivated by a connection between frequency-domain projection methods and approximation of truncated balanced realizations. The method is computationally simple to implement, has near-optimal error properties, and possesses simple error estimation and order-control procedures. Usage of the method also enables straightforward exploitation of information about the particular application and setting, as well as circuit functional information, such as frequency weighting information and correlations between network port waveforms. When such specific information is available, standard truncated balanced realization algorithms generate models far from optimal according to statistical decision criteria. Examples are shown to demonstrate that the method can outperform the standard order reduction techniques by providing similar accuracy with lower order models or superior accuracy for the same size model.

Projection-reconstruction technique for speeding up multidimensional NMR spectroscopy.

The acquisition of multidimensional NMR spectra can be speeded up by a large factor by a projection-reconstruction method related to a technique used in X-ray scanners. The information from a small number of plane projections is used to recreate the full multidimensional spectrum in the familiar format. Projections at any desired angle of incidence are obtained by Fourier transformation of time-domain signals acquired when two or more evolution intervals are incremented simultaneously at different rates. The new technique relies on an established Fourier transform theorem that relates time-domain sections to frequency-domain projections. Recent developments in NMR instrumentation, such as increased resolution and sensitivity, make fast methods for data gathering much more practical for protein and RNA research. Hypercomplex Fourier transformation generates projections in symmetrically related pairs that provide two independent "views" of the spectrum. A new reconstruction algorithm is proposed, based on the inverse Radon transform. Examples are presented of three- and four-dimensional NMR spectra of nuclease A inhibitor reconstructed by this technique with significant savings in measurement time.

Field characterization of therapeutic ultrasound phased arrays through forward and backward planar projection

Spatial planar projection techniques propagate field measurements from a single plane in front of a transmitter to arbitrary new planes closer to or further away from the source. A linear wave vector frequency-domain projection algorithm is applied to the acoustic fields measured from several focused transducer arrays designed for ultrasound therapy. A polyvinylidene difluoride hydrophone is first scanned in a water tank over a plane using a three-dimensional positioning system to measure the complex pressure field as a function of position. The field is then projected to a series of new planes using the algorithm. Results of the projected fields are compared with direct measurements taken at corresponding distances. Excellent correlation is found between the projected and measured data. The method is shown to be accurate for use with phase-controlled field patterns, providing a rapid and accurate method for obtaining field information over a large spatial volume. This method can significantly simplify the characterization procedure required for phased-array application used for therapy. Most significantly, the wavefront propagated back to a phased array can be used to predict the field produced by different phase and amplitude settings of the array elements. A field back-projected to the source could be used as an improved source function in acoustic modeling.