A method for determining the modulation transfer function from thick microwire profiles measured with x-ray microcomputed tomography
A method for determining the modulation transfer function from thick microwire profiles measured with x-ray microcomputed tomography
复制标题
一种根据 X 射线微计算机断层扫描测量的粗微丝轮廓确定调制传递函数的方法
DOI：
10.1118/1.4729711
复制
发表时间：
2012
期刊：
影响因子：
3.8
通讯作者：
N.Moriyama
中科院分区：
文献类型：
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作者：
Y.Nakaya;Y.Kawata;N.Niki;K.Umetani;H.Ohmatsu;N.Moriyama
目的本研究描述了一种依赖于模型的方法来确定调制传递函数（MTF）在横向平面，获得了微计算机断层扫描（micro-CT）系统从粗线体模而不是细线体模的轮廓，该研究评估了所提出的方法在确定micro-CT系统的MTF的可行性。从通过扫描细线体模获得的点扩散函数变换。由于金属丝不是点源，原始MTF会针对金属丝体模的有限尺寸进行校正;直径过大的金属丝会导致MTF值不准确。因此，我们解决了MTF的确定从厚线体模的轮廓通过MTF建模的基础上，对称的Lévy函数，广义高斯和洛伦兹函数。然后，我们将该方法应用于由临床CT系统测量的金属丝体模（直径为1 mm、2 mm和3 mm）的轮廓，以评估粗金属丝体模的适用直径范围。在临床CT中使用了两种类型的重建内核（标准和锐化）。使用同步辐射微CT（SRμCT）系统测量的微丝体模（直径为10和30μm）评价了该方法的性能，其中Shepp-Logan滤波器和Ramachandran-Lakshminarayanan滤波器用作重建核。以0.1mm和3μm细线体模获得的MTF分别作为临床CT和SRμCT的金标准MTF。用MTF的10%值的均方根误差（RMSE）和相对误差（RE）来衡量该方法测定的MTF与金标准之间的差异。ResultsThe mean RMSE为两种类型的重建核的三线体模（直径为1，2，3 mm）分别为0.0085，0.012，和0.021，分别。对于两种类型的重建内核，1 mm、2 mm和3 mm钢丝体模的平均RE值相同，分别为2.0%、3.5%和3.5%。从粗线幻影确定的MTF揭示了两个内核的空间分辨率。直径为10 μ m和30μm的两种重建核的平均RMSE分别为0.0045和0.0035。10和30μm直径的两个线材模型的平均RE分别为4.0%和3.1%，对于两种类型的重建kernel.ConclusionsExperimental数据本文提出的支持基于对称Lévy函数的模型依赖方法的有效性。我们的结论是，该方法是一种有用的方法，用于测量x/y扫描平面（横向方向）的micro-CT系统的空间分辨率，用粗线体模代替细线体模。
PurposeThis study describes a model‐dependent method to determine the modulation transfer function (MTF) in the transversal plane, obtained by a microcomputed tomography (micro‐CT) system from profiles of a thick wire phantom instead of a thin wire phantom, and the study evaluates the feasibility of the proposed method in the MTF determination of micro‐CT systems.MethodsThe MTF is generally calculated as the absolute value of the normalized Fourier transform from the point spread function obtained by scanning a thin wire phantom. Since the wire is not a point source, the raw MTF is corrected for the finite size of the wire phantom; a wire with too large a diameter introduces inaccuracies in the MTF values. Therefore, we solved the MTF determination from profiles of a thick wire phantom via MTF modeling on the basis of the symmetric Lévy function that generalizes Gaussian and Lorentzian functions. We then applied the method to profiles of wire phantoms (1 mm, 2 mm, and 3 mm in diameter) measured by a clinical CT system to evaluate the applicable diameter range of the thick wire phantom. Two types of reconstruction kernels (standard and sharp) were used in the clinical CT. The performance of the method was evaluated using microwire phantoms (10 and 30μm in diameter) measured by a synchrotron radiation micro‐CT (SRμCT) system, in which the Shepp–Logan filter and Ramachandran–Lakshminarayanan filter were used as the reconstruction kernel. The MTFs obtained using thin wire phantoms of 0.1 mm and 3μm in diameter were regarded as the gold standard MTFs for the clinical CT and SRμCT, respectively. The root‐mean‐square error (RMSE) and relative error (RE) of the 10% value of the MTF were used to measure the difference between the MTF determined by the method and the gold standard.ResultsThe mean RMSEs for two types of reconstruction kernels of three wire phantoms (1, 2, and 3 mm in diameter) were 0.0085, 0.012, and 0.021, respectively. The mean REs for the 1‐, 2‐, and 3‐mm wire phantoms gave the same values of 2.0%, 3.5%, and 3.5%, respectively, for two types of reconstruction kernel. The MTFs determined from thick wire phantoms reveal the spatial resolution for the two kernels. The mean RMSEs for two types of reconstruction kernels of the microwire phantoms of 10 and 30μm in diameter were 0.0045 and 0.0035, respectively. The mean REs of the two wire phantoms of 10 and 30μm diameter had 4.0% and 3.1%, respectively, for two types of reconstruction kernel.ConclusionsExperimental data presented in this paper support the effectiveness of the model‐dependent method based on the symmetric Lévy function. We conclude that the method is a useful approach for measuring the spatial resolution in the x/y‐scan plane (transversal orientation) of micro‐CT systems by substituting a thick wire phantom for a thin wire phantom.