Abstract
Purpose:There is always a parameter in compressive sensing based iterative reconstruction (IR) methods low dose cone‐beam CT (CBCT), which controls the weight of regularization relative to data fidelity. A clear understanding of the relationship between image quality and parameter values is important. The purpose of this study is to investigate this subject based on experimental data and a representative advanced IR algorithm using Tight‐frame (TF) regularization.Methods:Three data sets of a Catphan phantom acquired at low, regular and high dose levels are used. For each tests, 90 projections covering a 200‐degree scan range are used for reconstruction. Three different regions‐of‐interest (ROIs) of different contrasts are used to calculate contrast‐to‐noise ratios (CNR) for contrast evaluation. A single point structure is used to measure modulation transfer function (MTF) for spatial‐resolution evaluation. Finally, we analyze CNRs and MTFs to study the relationship between image quality and parameter selections.Results:It was found that: 1) there is no universal optimal parameter. The optimal parameter value depends on specific task and dose level. 2) There is a clear trade‐off between CNR and resolution. The parameter for the best CNR is always smaller than that for the best resolution. 3) Optimal parameters are also dose‐specific. Data acquired under a high dose protocol require less regularization, yielding smaller optimal parameter values. 4) Comparing with conventional FDK images, TF‐based CBCT images are better under a certain optimally selected parameters. The advantages are more obvious for low dose data.Conclusion:We have investigated the relationship between image quality and parameter values in the TF‐based IR algorithm. Preliminary results indicate optimal parameters are specific to both the task types and dose levels, providing guidance for selecting parameters in advanced IR algorithms.This work is supported in part by NIH (1R01CA154747‐01)
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