This paper presents the challenge report for the 2021 Kidney and Kidney Tumor
Segmentation Challenge (KiTS21) held in conjunction with the 2021 international
conference on Medical Image Computing and Computer Assisted Interventions
(MICCAI). KiTS21 is a sequel to its first edition in 2019, and it features a
variety of innovations in how the challenge was designed, in addition to a
larger dataset. A novel annotation method was used to collect three separate
annotations for each region of interest, and these annotations were performed
in a fully transparent setting using a web-based annotation tool. Further, the
KiTS21 test set was collected from an outside institution, challenging
participants to develop methods that generalize well to new populations.
Nonetheless, the top-performing teams achieved a significant improvement over
the state of the art set in 2019, and this performance is shown to inch ever
closer to human-level performance. An in-depth meta-analysis is presented
describing which methods were used and how they faired on the leaderboard, as
well as the characteristics of which cases generally saw good performance, and
which did not. Overall KiTS21 facilitated a significant advancement in the
state of the art in kidney tumor segmentation, and provides useful insights
that are applicable to the field of semantic segmentation as a whole.

本文介绍 2021 年肾脏和肾脏肿瘤分割挑战 (KiTS21) 的挑战报告，该挑战目的是针对医学图像计算和计算机辅助干预领域的肾肿瘤分割进行不断改进和提高，以提供有用的见解。