# Multi-spatial-attention U-Net: a novel framework for automated gallbladder segmentation on CT images

## TL;DR

A new U-Net model with a Multi-Spatial Attention block improves gallbladder segmentation accuracy in CT images, showing strong potential for clinical use.

## Contribution

The novel Multi-Spatial Attention U-Net (MSAU-Net) with two versions (V1 and V2) is introduced for gallbladder segmentation on CT images.

## Key findings

- MSAU-Net V1 and V2 outperformed other models in segmentation accuracy and boundary delineation.
- V2 showed better generalization in external validation.
- The optimal number of MSA blocks was three for V1 and two for V2.

## Abstract

This study aimed to construct a novel model, Multi-Spatial Attention U-Net (MSAU-Net) by incorporating our proposed Multi-Spatial Attention (MSA) block into the U-Net for the automated segmentation of the gallbladder on CT images.

The gallbladder dataset consists of CT images of retrospectively-collected 152 liver cancer patients and corresponding ground truth delineated by experienced physicians. Our proposed MSAU-Net model was transformed into two versions V1(with one Multi-Scale Feature Extraction and Fusion (MSFEF) module in each MSA block) and V2 (with two parallel MSEFE modules in each MSA blcok). The performances of V1 and V2 were evaluated and compared with four other derivatives of U-Net or state-of-the-art models quantitatively using seven commonly-used metrics, and qualitatively by comparison against experienced physicians’ assessment.

MSAU-Net V1 and V2 models both outperformed the comparative models across most quantitative metrics with better segmentation accuracy and boundary delineation. The optimal number of MSA was three for V1 and two for V2. Qualitative evaluations confirmed that they produced results closer to physicians’ annotations. External validation revealed that MSAU-Net V2 exhibited better generalization capability.

The MSAU-Net V1 and V2 both exhibited outstanding performance in gallbladder segmentation, demonstrating strong potential for clinical application. The MSA block enhances spatial information capture, improving the model’s ability to segment small and complex structures with greater precision. These advantages position the MSAU-Net V1 and V2 as valuable tools for broader clinical adoption.

The online version contains supplementary material available at 10.1186/s12880-025-01737-7.