Noise Transfer Analysis of Base Material Decomposition Methods

摘要

A generalized method to evaluate the noise transfer properties of the base material decomposition has been developed. We apply the method to a typical dual-energy CT scan with energy weightings and doses of a 80kV / 140kV scan. For sets {P_1, P_2} of dual-energy projections with P_i = 10~(-4.5)... 1, both the water and bone decomposition and the Compton and Photo Effect decomposition are analyzed. As a figure of merit we determine the noise amplification factors A_1, A_2. They are given by the ratio of the relative noise of the dual-energy projections B_1, B_2 to the relative noise of the combined projection data P. The B_1, B_2 and their variance are simulated by numerical inversion and integration. For the water and bone decomposition an average noise amplification of 3 to 5 is shown. For small contributions of one base material, the noise amplification becomes critically large. In this case the water and bone base material decomposition seems not to be usable for quantitative CT. The Compton and Photo effect decomposition are shown to be more robust in this respect. Physically, both coefficients can only reach zero simultaneously. The Compton coefficient has significantly better noise characteristics than the Photo Effect coefficient. For a partial region of the P_1, P_2 plane it shows better noise performance than the combined raw data P.