[Noise Nonuniformity Dependency on Exposure Settings in Computed Tomography].

Nihon Hoshasen Gijutsu Gakkai zasshi Pub Date : 2024-05-20 Epub Date: 2024-03-15 DOI:10.6009/jjrt.2024-1417

Mitsuo Narita, Masayuki Nishiki

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Abstract

Purpose: In X-ray computed tomography (CT), noise distribution within images is nonuniform and thought to vary with imaging conditions. This study aimed to evaluate noise nonuniformity by altering specific imaging conditions, such as tube voltage, bow-tie filter (BTF), and phantom size.

Methods: Using four tube voltages (80, 100, 120, and 135 kV), two BTF types (L and M), and circular water phantoms with diameters of 240, 320, and 400 mm, we employed filtered back projection (FBP) for reconstruction. Noise nonuniformity was assessed by defining six regions of interest (ROI) from the image center to the periphery, and the noise nonuniformity index (NNI) was calculated based on the standard deviation (SD) values within these ROIs.

Results: Results showed consistently larger noise SD values in the central region compared to the peripheral region under all imaging conditions, with the maximum NNI reaching 32.1%. Variations in NNI were observed, reaching up to 5.5 points for tube voltage, 7.8 points for BTF, and 8.2 points for phantom size.

Conclusion: In conclusion, our quantitative assessment revealed moderate dependence of noise nonuniformity on imaging conditions in CT images.

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[计算机断层扫描中噪声不均匀性与曝光设置的关系]。

目的：在 X 射线计算机断层扫描（CT）中，图像内的噪声分布是不均匀的，而且被认为会随着成像条件的变化而变化。本研究旨在通过改变特定的成像条件，如管电压、弓形滤波器（BTF）和模型尺寸，来评估噪声的不均匀性：我们使用四种管电压（80、100、120 和 135 kV）、两种 BTF 类型（L 和 M）以及直径分别为 240、320 和 400 mm 的圆形水模型，采用滤波背投影（FBP）进行重建。通过定义从图像中心到外围的六个感兴趣区（ROI）来评估噪声不均匀性，并根据这些感兴趣区内的标准偏差（SD）值计算噪声不均匀性指数（NNI）：结果显示，在所有成像条件下，中心区域的噪声标准偏差值始终大于外围区域，最大 NNI 达到 32.1%。我们还观察到 NNI 的变化，管电压的变化达到 5.5 点，BTF 的变化达到 7.8 点，模型尺寸的变化达到 8.2 点：总之，我们的定量评估显示 CT 图像的噪声不均匀性与成像条件有一定的关系。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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Nihon Hoshasen Gijutsu Gakkai zasshi

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