基于透射测量X射线谱的重建方法

X-Ray Spectral Reconstruction Methods Based on Transmission Measurements

对透射测量X射线谱两种重建方法进行评估。医用直线加速器产生的最大能量为10MeV X射线谱，用蒙特卡罗方法（Montecarlo，MC）模拟得到的值作为基准X射线谱，代入矩阵系统AF=T得到的穿透系数T，由穿透系数T分别应用谱向量代数法（Spectra vectorial algebra，SVA）与双共轭梯度法（Biconjugate gradients，BiCG）来解矩阵系统AF=T，得到重建后的该X射线谱-↑F0与基准X射线谱F相比较，BiCG法比SVA法重建后的X射线谱声更加接近F，且T引入白高斯噪声项，以模拟穿透系数的测量误差，这一结果依然成立。当信噪比SNR高于90dB时，BiCG法比SVA法重建的X射线谱结果更理想。

The two X-ray spectral reconstruction methods based on transmission measurements are evaluated. The X-ray spectrum of 10 MeV of maximum energy generated by the medical linear accelerator is simulated as theoretical X-ray spectrum by the Monte Carlo （MC） method. The X-ray spectrum is used as the benchmark spectrum. The transmission coefficient T is calculated by the matrix system AF=T. In reverse, the reconstruction spectrum -↑F is determined by solving the matrix system AF=T with the spectra vectorial algebra （SVA） and the biconjugate gradient （BiCG） methods. The reconstruction results show that the BiCG method provides more accurate results than the SVA method compared with the benchmark spectrum. Even the white Gaussian noise is induced into T to simulate measurement errors of the transmission coefficient, the result still exists. The BiCG method provides better results than the SVA method when signal noise ratio （SNR） is higher than 90 dB.