照射野影像对比度低、图像质量差使常规照射野验证易产生误差。

The contrast and quality of portal image is so low that it is difficult to avoid errors in routine verification.

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血管影像的特点是受噪声影响、血管形态模糊、背景噪声和目标混杂，以及目标与背景对比度低，这些都给分割任务带来困难。

Vascular tree angiograms suffer from noise and they are fuzzy, low-contrast with the vessel disturbed by background. Thus, segmentation is a difficult task.

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血管影像的特点是受噪声影响、血管形态模糊、背景噪声和目标混杂，以及目标与背景对比度低，这些都给分割任务带来困难。

Vascular tree angiograms suffer from noise and they are fuzzy, low-contrast with the vessel disturbed by background. Thus, segmentation is a difficult task.

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