Recently, circle representation has been introduced for medical imaging, designed specifically to enhance the detection of instance objects that are spherically shaped (e.g., cells, glomeruli, and nuclei). Given its outstanding effectiveness in instance detection, it is compelling to consider the application of circle representation for segmenting instance medical objects. In this study, we introduce CircleSnake, a simple end-to-end segmentation approach that utilizes circle contour deformation for segmenting ball-shaped medical objects at the instance level. The innovation of CircleSnake lies in these three areas: (1) It substitutes the complex bounding box-to-octagon contour transformation with a more consistent and rotation-invariant bounding circle-to-circle contour adaptation. This adaptation specifically targets ball-shaped medical objects. (2) The circle representation employed in CircleSnake significantly reduces the degrees of freedom to two, compared to eight in the octagon representation. This reduction enhances both the robustness of the segmentation performance and the rotational consistency of the method. (3) CircleSnake is the first end-to-end deep instance segmentation pipeline to incorporate circle representation, encompassing consistent circle detection, circle contour proposal, and circular convolution in a unified framework. This integration is achieved through the novel application of circular graph convolution within the context of circle detection and instance segmentation. In practical applications, such as the detection of glomeruli, nuclei, and eosinophils in pathological images, CircleSnake has demonstrated superior performance and greater rotation invariance when compared to benchmarks. The code has been made publicly available: https://github.com/hrlblab/CircleSnake.

翻译：近年来，圆形表示被引入医学影像领域，旨在提升球形实例目标（如细胞、肾小球和细胞核）的检测效果。鉴于其在实例检测中的卓越有效性，探索将圆形表示应用于医学实例目标分割具有重要价值。本研究提出CircleSnake——一种基于圆形轮廓变形的简单端到端分割方法，用于实现球形医学目标的实例级分割。CircleSnake的创新体现在三个方面：（1）将复杂的边界框到八边形轮廓变换替换为更一致且旋转不变的边界圆到圆形轮廓适配，该适配专为球形医学目标设计。（2）相比八边形表示，CircleSnake采用的圆形表示将自由度从八维降至二维，既提升了分割性能的鲁棒性，又增强了方法的旋转一致性。（3）CircleSnake是首个将圆形表示纳入端到端深度实例分割管道的框架，其统一集成了圆形检测、圆形轮廓提议和圆形卷积三大模块，通过将圆形图卷积创新性地应用于圆形检测与实例分割场景实现该集成。在病理图像中肾小球、细胞核和嗜酸性粒细胞检测等实际应用中，CircleSnake相比基准方法展现出更优性能与更强的旋转不变性。代码已开源：https://github.com/hrlblab/CircleSnake