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首页> 外文期刊>Journal of applied clinical medical physics / >A pitfall of using the circular‐edge technique with image averaging for spatial resolution measurement in iteratively reconstructed CT images
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A pitfall of using the circular‐edge technique with image averaging for spatial resolution measurement in iteratively reconstructed CT images

机译：使用圆形边缘技术的缺陷与图像平均用于空间分辨率测量在迭代重建CT图像中

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The circular‐edge technique using a low‐contrast cylindrical object is commonly used to measure the modulation transfer functions (MTFs) in computed tomography (CT) images reconstructed with iterative reconstruction (IR) algorithms. This method generally entails averaging multiple images of the cylinder to reduce the image noise. We suspected that the cylinder edge shape depicted in the IR images might exhibit slight deformation with respect to the true shape because of the intrinsic nonlinearity of IR algorithms. Image averaging can reduce the image noise, but does not effectively improve the deformation of the edge shape; thereby causing errors in the MTF measurements. We address this issue and propose a method to correct the MTF. We scanned a phantom including cylindrical objects with a CT scanner (Ingenuity Elite, Philips Healthcare). We obtained cylinder images with iterative model reconstruction (IMR) algorithms. The images suggested that the depicted edge shape deforms and fluctuates depending on slice positions. Because of this deformation, image averaging can potentially cause additional blurring. We define the deformation function D that describes the additional blurring, and obtain D by analyzing multiple images. The MTF measured by the circular‐edge method (referred to as MTF') can be thought of as the multiplication of the true MTF by the Fourier transformation (FT) of D . We thus obtain the corrected MTF (MTF subcorrected/sub ) by dividing MTF' by the FT of D . We validate our correction method by comparing the calculated images based on the convolution theorem using MTF' and MTF subcorrected/sub with the actual images obtained with the scanner. The calculated image using MTF subcorrected/sub is more similar to the actual image compared with the image calculated using MTF', particularly in edge regions. We describe a pitfall in MTF measurement using the circular‐edge technique with image averaging, and suggest a method to correct it.
机译：使用低对比度圆柱对象的循环技术通常用于测量与迭代重建（IR）算法重建的计算机断层扫描（CT）图像中的调制传递函数（MTF）。该方法通常需要平均汽缸的多个图像以降低图像噪声。我们怀疑IR图像中描绘的气缸边缘形状可能表现出相对于真实形状的轻微变形，因为IR算法的内在非线性。图像平均可以降低图像噪声，但没有有效地改善边缘形状的变形;从而导致MTF测量中的错误。我们解决了这个问题并提出了一种纠正MTF的方法。我们扫描了一个幻影，包括带有CT扫描仪（聪明精英，飞利浦医疗保健）的圆柱形物体。我们利用迭代模型重建（IMR）算法获得了气缸映像。图像表明描绘边缘形状根据切片位置而变形并波动。由于这种变形，图像平均可能导致额外的模糊。我们通过分析多个图像来定义描述附加模糊的变形函数D，并获得D。通过圆形边缘方法（称为MTF'）测量的MTF可以被认为是通过D的傅里叶变换（FT）作为真实MTF的乘法。因此，我们通过将MTF'划分为d的ft来获得校正的MTF（MTF 校正）。通过使用MTF'和MTF 校正与扫描仪获得的实际图像进行比较，通过将计算的图像与卷积定理进行比较来验证我们的校正方法。与使用MTF'计算的图像相比，使用MTF 校正的计算图像与实际图像更类似于实际图像，特别是在边缘区域中。我们使用具有图像平均的圆形边缘技术来描述MTF测量中的缺陷，并建议校正它的方法。

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