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Time-of-Flight (TOF) PET data determines the attenuation map up to a constant. MLAA (Maximum Likelihood Activity and Attenuation Estimation) was proposed for this purpose. However, in real systems the estimated attenuation map usually results in bias and artifacts, due to various factors such as non-uniform timing resolution, detector timing drift, and biased scatter estimation. Moreover, MLAA has...
The goal of this study is to develop and evaluate two 4D statistical iterative image reconstruction (SIIR) methods with respiratory motion (RM) and cardiac motion (CM) compensation for improving the detection of motion defects in 4D gated cardiac PET. The first 4D SIIR method, motion correction after reconstruction (MCAR) was developed previously, where the dual RM&CM compensation was achieved...
Respiratory motion is one image degradation factor that affects the resolution and may cause artifacts in PET imaging. Respiratory gating technique is able to reduce the blurring effects but results in higher noise level. Conventional motion correction methods that model motion effects during or after image reconstruction not only increases reconstruction time, but also requires a gated or blurred...
The calculation formulas of hydraulic impedance of turbine are derived under tow turbine operation modes: one is constant guide vane opening and constant speed, the other is constant output and constant speed. The differences of hydraulic impedance between the tow operation modes are studied, and the effects on the hydraulic vibration characteristics of pressurized conveyance system in hydropower...
Calculation formula of hydraulic impedance of surge tank is derived in this paper, which is suitable to both simple tank and throttled tank. And the effects of surge tank on the hydraulic vibration of pressurized conveyance system of hydropower are studied. The investigation shows that the attenuation factors of system decrease if the hydraulic resistance coefficient of surge tank increases. The hydraulic...
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