Improved distinct bone segmentation in upper-body CT through multi-resolution networks

TL;DR

This paper introduces a multi-resolution 3D U-Net architecture that enhances distinct bone segmentation in upper-body CT scans by capturing larger spatial context without excessive computational costs, outperforming previous methods.

Contribution

The authors propose a novel multi-resolution 3D U-Net approach that generalizes HookNet and MRN, improving bone segmentation accuracy and efficiency in large field-of-view upper-body CT scans.

Findings

Achieved median DSC of 0.86 across 125 bone classes.

Reduced confusion among similar-looking bones.

Outperformed previous 3D U-Net baseline results.

Abstract

Purpose: Automated distinct bone segmentation from CT scans is widely used in planning and navigation workflows. U-Net variants are known to provide excellent results in supervised semantic segmentation. However, in distinct bone segmentation from upper body CTs a large field of view and a computationally taxing 3D architecture are required. This leads to low-resolution results lacking detail or localisation errors due to missing spatial context when using high-resolution inputs. Methods: We propose to solve this problem by using end-to-end trainable segmentation networks that combine several 3D U-Nets working at different resolutions. Our approach, which extends and generalizes HookNet and MRN, captures spatial information at a lower resolution and skips the encoded information to the target network, which operates on smaller high-resolution inputs. We evaluated our proposed architecture against single resolution networks and performed an ablation study on information concatenation and the number of context networks. Results: Our proposed best network achieves a median DSC of 0.86 taken over all 125 segmented bone classes and reduces the confusion among similar-looking bones in different locations. These results outperform our previously published 3D U-Net baseline results on the task and distinct-bone segmentation results reported by other groups. Conclusion: The presented multi-resolution 3D U-Nets address current shortcomings in bone segmentation from upper-body CT scans by allowing for capturing a larger field of view while avoiding the cubic growth of the input pixels and intermediate computations that quickly outgrow the computational capacities in 3D. The approach thus improves the accuracy and efficiency of distinct bone segmentation from upper-body CT.