Introducing NV-Reason-CT Open 3D CT VLM for Radiologist Chain-of-Thought Reasoning | NVIDIA Technical Blog

Introduces NV-Reason-CT, a vision language model purpose-built for 3D CT analysis. It extends chain-of-thought reasoning to volumetric imaging by combining a full 3D vision transformer encoder with a Qwen3.5-4B language model. The model achieves state-of-the-art results on the CT-RATE benchmark and has been validated by radiologists for clinical plausibility. The post details the architectural choices for volumetric reasoning, including the use of 3D MRoPE for spatial relationships, and the two-stage training methodology involving supervised fine-tuning on radiologist reasoning data and reinforcement learning for reasoning quality.