Cishen Zhang

Constrained Least Squares Filtering Algorithm for Ultrasound Image Deconvolution

A new medical ultrasound tissue model is considered in this paper, which incorporates random fluctuations of the tissue response and provides more realistic interpretation of the received pulse-echo ultrasound signal. Using this new model, we propose an algorithm for restoration of the degraded ultrasound image. The proposed deconvolution is a modification of the classical regularization technique which combines Wiener filter and the constrained least squares (LS) algorithm for restoration of the ultrasound image. The performance of the algorithm is evaluated based on both the simulated phantom images and real ultrasound radio frequency (RF) data. The results show that the algorithm can provide improved ultrasound imaging performance in terms of the resolution gain. The deconvolved images visually show better resolved tissue structures and reduce speckle, which are confirmed by a medical expert

Data correction for gantry-tilted local CT.

The gantry-tilted helical cone-beam computed tomography (CT) has an inherent problem that the relative shift of the region of interest (ROI) blurs the reconstructed image. This problem becomes more serious in the gantry-tilted local CT imaging due to the nature of local scanning. This paper proposes a new method to improve the gantry-tilted local imaging by correcting the local scanning data. Computer simulations show that the proposed method can enhance the local imaging performance to a certain extent in terms of the image sharpening and artifacts reduction.

Ultrasound image deconvolution in symmetrical mirror wavelet bases

Observed medical ultrasound images are degraded representations of true tissue images. The degradation is a combination of blurring due to the finite resolution of the imaging system and the observation noise. This paper presents a new wavelet based deconvolution method for medical ultrasound imaging. We design a new orthogonal wavelet basis known as the symmetrical mirror wavelet basis that can provide more desirable frequency resolution. Our proposed ultrasound image restoration with wavelets consists of an inversion of the observed ultrasound image using the estimated two-dimensional (2-D) point spread function (PSF) followed by denoising in the designed wavelet basis. The tissue image restoration is then accomplished by modelling the tissue structures with the generalized Gaussian density (GGD) function using the Bayesian estimation. Both subjective and objective measures show that the deconvolved images are more appealing in the visualization and resolution gain.

A Feldkamp-type approximate algorithm for helical multislice CT using extended scanning helix

In this paper, a Feldkamp-type approximate algorithm is proposed for helical multislice Computed Tomography (CT) image reconstruction. For reconstruction of practically required planar transversal image slices, the algorithm proposes a new short scan helical trajectory which satisfies Tuys exact reconstruction condition. A planar slice reconstructed using this new trajectory has potential to be exactly reconstructed. This method improves the approximate helical reconstruction in terms of artifacts reduction and efficiency enhancement.

Modeling and Identification of practical ultrasound transducers in ultrasound imaging systems

This paper provides linear analysis for a practical ultrasound imaging system with single-element transducers. A proper eighth-order linear ARMA model with inputs and outputs of voltage traces is given to present the transfer characteristics of such a practical system, so that echo signals containing tissue information can be collected and analyzed more properly

A new scheme and reconstruction algorithm for dual source circular CT

Circular cone beam scanning has been a most popular scheme for computed tomography (CT) imaging, which is simple and can achieve symmetric projection data of the interested object. Many algorithms have been developed for circular cone beam CT. Many of these are FDK type algorithms, which can achieve good reconstruction quality when cone angle is small but may cause image deformation and density reduction at off plane when the cone angle is large. With the recently introduced dual source circular cone beam CT, we can deal with this problem under a new dual source geometry. In this paper, we propose a novel reconstruction scheme dual source circular cone beam CT by placing X-ray sources on two circular planes perpendicular to the rotating axis. We propose a reconstruction algorithm for this scanning scheme and evaluate the scanning scheme and the reconstruction algorithm with a 3D Shepp Logan phantom and a disk phantom. Simulation results show that the proposed method can provide improved reconstruction image quality for both in plane and off plane of the object

An Approximate Cone Beam Reconstruction Algorithm for Gantry-Tilted CT Using Tangential Filtering.

FDK algorithm is a well-known 3D (three-dimensional) approximate algorithm for CT (computed tomography) image reconstruction and is also known to suffer from considerable artifacts when the scanning cone angle is large. Recently, it has been improved by performing the ramp filtering along the tangential direction of the X-ray source helix for dealing with the large cone angle problem. In this paper, we present an FDK-type approximate reconstruction algorithm for gantry-tilted CT imaging. The proposed method improves the image reconstruction by filtering the projection data along a proper direction which is determined by CT parameters and gantry-tilted angle. As a result, the proposed algorithm for gantry-tilted CT reconstruction can provide more scanning flexibilities in clinical CT scanning and is efficient in computation. The performance of the proposed algorithm is evaluated with turbell clock phantom and thorax phantom and compared with FDK algorithm and a popular 2D (two-dimensional) approximate algorithm. The results show that the proposed algorithm can achieve better image quality for gantry-tilted CT image reconstruction.

Data Correction for Gantry-tilted Local CT

Gantry-tilted helical multi-slice computed tomography (CT) refers to the helical scanning CT system equipped with multi-row detector operating at some gantry tilting angle. Its purpose is to avoid the area which is vulnerable to the X-ray radiation. The local tomography is to reduce the total radiation dose by only scanning the region of interest for image reconstruction. In this paper we consider the scanning scheme, and incorporate the local tomography technique with the gantry-tilted helical multi-slice CT. The image degradation problem caused by gantry tilting is studied, and a new error correction method is proposed to deal with this problem in the local CT. Computer simulation shows that the proposed method can enhance the local imaging performance in terms of image sharpness and artifacts reduction

An iterative constrained least squares filter for ultrasound image deconvolution.

This paper describes how the recently developed constrained least squares (CLS) filtering algorithm can be made iterative to improve the resolution gain (RG) of medical ultrasound images. We propose the use of the iterative CLS (ICLS) filter, by incorporating the recently proposed ultrasound tissue model, to account for the random fluctuations of the tissue signal within the received ultrasound radio frequency (RF) echo signal. The resulting improvement in RG is demonstrated by eight different abdomen ultrasound images where progressive improvements in both the axial and lateral directions can be observed

A Reconstruction Algorithm for Helical CT Imaging on PI-planes

In this paper, a Feldkamp type approximate reconstruction algorithm is presented for helical cone-beam Computed Tomography. To effectively suppress artifacts due to large cone angle scanning, it is proposed to reconstruct the object pointwisely on unique customized tilted PI-planes which are close to the data collecting helices of the corresponding points. Such a reconstruction scheme can considerably suppress the artifacts in the cone-angle scanning. Computer simulations show that the proposed algorithm can provide improved imaging performance compared with the existing approximate cone-beam reconstruction algorithms