A Continuously-Resolved 3D Organisation of the Rat Stomach

The anatomy of the stomach informs about the specific inter-regional functions of the digestive process. Eight whole stomachs from Sprague-Dawley rats were stained with phosphotungstic acid (PTA) and imaged using a SkyScan 1172 $\mu$ CT scanner. Following segmentation of the mucosal-submucosal and muscle-serosal layers, thickness, fractional anisotropy, and muscle fibre orientation were calculated and reconstructed over three-dimensional anatomies. In the mucosal-submucosal layers, thickness increased from the forestomach through the glandular corpus to the antrum, with characteristic transitions at both sphincters and into the duodenum. In the muscle-serosal layers, thickness was greatest at the lower oesophageal sphincter and consistently greater along the lesser curvature than the greater curvature. Smooth muscles exhibited a bimodal orientation distribution, with circumferential fibres more prominent in the corpus and antrum and longitudinal fibres more prominent in the forestomach. Fractional anisotropy further reflected regional functional differentiation, with denser fibre convergence and lower directional coherence near the lower oesophageal junction. The findings revealed continuous structural transitions between gastric regions, regional gradients in fibre density and organisation, and provide an anatomical basis for the motility of the rat stomach during digestion.