Data preprocessing is an important step in a deep learning pipeline. Within the context of computed tomography image segmentation, preprocessing includes a Hounsfield unit (HU) windowing step. HU windowing ensures that the contrast of the region of interest is maximized to highlight the important features for the given task. HU windowing is defined by the window level and width. There are general guidelines for optimal window level and width for a given tissue, however, there’s a certain degree of subjectivity involved within the setting. Moreover, the CT imaging protocol and the type of scan (contrast-enhanced vs. none) has an impact on the HU window. In this paper, we evaluate the impact of varying the HU window level and window width at both training and test time to assess whether liver lesion segmentation models can generalize to different contrasts in input data, as well as a method for estimating uncertainty within the task. The experiments show that HU windowing can have a significant impact on model performance at train and test times. Moreover, we show that HU variation at test time is a computationally cheap alternative to test-time augmentation through spatial transformation for estimating uncertainty.
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