Be-Shan Chiang

Exact image reconstruction for a circle and line trajectory with a gantry tilt

We investigate image reconstruction with a circle and line trajectory with a tilted gantry. We derive new equations for reconstruction from the line data, such as equations of filtering lines, range of filtering lines and range of the line scan. We analyze the detector requirements and show that the line scan does not impose extra requirements on the cylindrical detector size with our algorithm, that is, the axial truncation of the filtering lines does not occur. We discuss full-scan and short-scan versions of the algorithm. Evaluation of our algorithm uses simulated and real 256-slice data.

Implementation of the circle-and-line algorithm for 256-detector row CT

In this work we apply the circle-and-line acquisition for the 256-detector row medical CT scanner. Reconstruction is based on the exact algorithm of the FBP type suggested recently by one of the co-authors. We derived equations for the cylindrical detector, common for medical CT scanners. To minimize hardware development efforts we use ramp-based reconstruction of the circle data. The line data provides an additional term that corrects the cone beam artifacts that are caused by the incompleteness of the circular trajectory. We illustrate feasibility of our approach using simulated data and real scanned data of the anthropomorphic phantom and evaluate stability of reconstruction to motion and misalignments during the scan. The additional patient dose from the line scan is relatively low compared to the circle scan. The proposed algorithm allows cone beam artifact-free reconstruction with large cone angle.

Cone beam artifact reduction in circular computed tomography

Cone beam artifact is a well known problem in circular computed tomography. The artifact can be removed by applying exact reconstruction, for example with circle and line trajectory. However, an additional scan often is not available for reconstruction, nor it is practical to collect. Then, methods that can accurately reconstruct image volume from circular data only are of particular interest. In this work we propose a new approach that combines elements of exact reconstruction and iterative reconstruction (SART). We apply iterative procedure to estimate missing line data; at each iteration line data becomes more accurate and cone beam artifacts are further reduced. Evaluation with numerical disc phantom and clinical head data shows effectiveness of the proposed approach in cone beam artifact reduction.

Reduction of the streak artifacts in circular cone beam CT using scanograms

We propose a method to estimate line data from scanogram in a CT scan. Combining the circle data with the estimated line data, we can reconstruct the volumetric images by use of an exact filtered backprojection or backprojection filtration algorithm for circle-line trajectories. The results show that the streak artifacts are reduced significantly compared to that of circle-only reconstruction.

A combined local and global motion estimation and compensation method for cardiac CT

A new motion estimation and compensation method for cardiac computed tomography (CT) was developed. By combining two motion estimation (ME) approaches the proposed method estimates the local and global cardiac motion and then preforms motion compensated reconstruction. The combined motion estimation method has two parts: one is the local motion estimation, which estimates the coronary artery motion by using coronary artery tree tracking and registration; the other one is the global motion estimation, which estimates the entire cardiac motion estimation by image registration. The final cardiac motion is the linear combination of the coronary artery motion and entire cardiac motion the. We use the backproject-then-warp method proposed by Pack et al. to perform motion compensation reconstruction (MCR). The proposed method was evaluated with 5 patient data and improvements in sharpness of both coronary arteries and heart chamber boundaries were obtained.

Motion weighting in helical computed tomography with wide cone angle

We describe an approach to improve image quality and temporal resolution in helical CT scans with large cone angle, when patient motion is present, such as cardiac or lung. We present evaluation results with numerical data and real scanner data.

Image registration for motion estimation in cardiac CT

Motion estimation is a very important method for improving image quality by compensating the cardiac motion at the best phase reconstructed. We tackle the cardiac motion estimation problem using an image registration approach. We compare the performance of three gradient-based registration methods on clinical data. In addition to simple gradient descent, we test the Nesterov accelerated descent and conjugate gradient algorithms. The results show that accelerated gradient methods provide significant speedup over conventional gradient descent with no loss of image quality.

A physics-based fast approach to scatter correction for large cone angle computed tomographic systems

An efficient scatter correction model is developed for large cone angle CT systems. The scatter intensities are expressed as a 2D convolution of forward functions with two Gaussian kernels. The kernels are derived from the differential cross sections of the Rayleigh (coherent) and Compton (incoherent) scattering. The results of water phantoms show good CT number uniformity and accuracy. The clinical images demonstrate a significant improvement on image quality.