8 research outputs found
Advanced Statistical Modeling for Model-Based Iterative Reconstruction for Single-Energy and Dual-Energy X-Ray CT
Model-based iterative reconstruction (MBIR) has been increasingly broadly applied as an improvement over traditional, analytical image reconstruction methods in X-ray CT, primarily due to its significant advantage in drastic dose reduction without diagnostic loss. Early success of the method in conventional CT has encouraged the extension to a wide range of applications that includes more advanced imaging modalities, such as dual-energy X-ray CT, and more challenging imaging conditions, such as low-dose and sparse-sampling scans, each requiring refined statistical models including the data model and the prior model. In this dissertation, we developed an MBIR algorithm for dual-energy CT that included a joint data-likelihood model to account for correlated data noise. Moreover, we developed a Gaussian-Mixture Markov random filed (GM-MRF) image model that can be used as a very expressive prior model in MBIR for X-ray CT reconstruction. The GM-MRF model is formed by merging individual patch-based Gaussian-mixture models and therefore leads to an expressive MRF model with easily estimated parameters. Experimental results with phantom and clinical datasets have demonstrated the improvement in image quality due to the advanced statistical modeling
Comprehensive evaluations of a prototype full field-of-view photon counting CT system through phantom studies
Photon counting CT (PCCT) has been a research focus in the last two decades.
Recent studies and advancements have demonstrated that systems using
semiconductor-based photon counting detectors (PCDs) have the potential to
provide better contrast, noise and spatial resolution performance compared to
conventional scintillator-based systems. With multi-energy threshold detection,
PCD can simultaneously provide the photon energy measurement and enable
material decomposition for spectral imaging. In this work, we report a
performance evaluation of our first CdZnTe-based prototype full-size photon
counting CT system through various phantom imaging studies. This prototype
system supports a 500 mm scan field-of-view (FOV) and 10 mm cone coverage at
isocenter. Phantom scans were acquired using 120 kVp from 50 to 400 mAs to
assess the imaging performance on: CT number accuracy, uniformity, noise,
spatial resolution, material differentiation and quantification. Both
qualitative and quantitative evaluations show that PCCT has superior image
quality with lower noise and improved spatial resolution compared to
conventional energy integrating detector (EID)-CT. Using projection domain
material decomposition approach with multiple energy bin measurements, PCCT
virtual monoenergetic images (VMIs) have lower noise, and superior performance
in quantifying iodine and calcium concentrations. These improvements lead to
increased contrast-to-noise ratio (CNR) for both high and low contrast study
objects and can significantly reduce the iodine contrast agent to achieve the
same CNR as EID-CT. PCCT can also generate super-high resolution (SHR) images
using much smaller detector pixel size than EID-CT and dramatically push the
spatial resolution limit. These initial results demonstrate that PCCT based on
CdZnTe detectors has huge potential in clinical settings
X-Band Active Phased Array Antenna Using Dual-Port Waveguide for High-Power Microwave Applications
An X-band active phased array horn antenna with high power capacity and high peak power is proposed in this paper. At the horn aperture, the baffles are loaded to suppress higher-order modes and eliminate blind spots during beam scanning. Straight walls are added to improve impedance matching. Considering that the peak power that T/R modules can provide is very limited, the proposal of a dual-port waveguide breaks through the bottleneck of the power capacity of a single-port input for the first time. The proposed curved dual-port waveguide is used to connect the horn antenna and the T/R module, which is verified to improve the power capacity of the overall internal structure. Simulated and measured results show that VSWR ≤ 2 in the frequency range of 7.5–8.5 GHz. There is no grating lobe in the ±10° scanning range and the maximum gain drop does not exceed 0.4 dB. The power capacity of the proposed HPM array is 56.34 MW. The phased array antenna has the characteristics of flexible scanning, small size, and high gain, and can be applied in high-power microwave systems