Latent Diffusion Model With Estimation Posterior Sampling: A Unified Framework for General Medical Image Restoration

Clinical imaging protocols designed to accelerate acquisition or reduce radiation dose often lead to degraded image quality, compromising diagnostic confidence. The heterogeneity in degradation types and severities across imaging modalities further challenges the development of generalized restoration solutions. In this work, we introduce a unified framework that formulates medical image restoration as posterior sampling from self-supervised Latent Diffusion Models (LDMs), pretrained on multi-modal high-quality images. At the core of our method is an Estimation Posterior Sampling (EPS) strategy, which enhances both data fidelity and anatomical detail retention. EPS incorporates two key components: (i) estimated diffusion initialization to constrain sampling within the measurement-consistent solution space, and (ii) gradient-balanced optimization to adaptively trade off denoising strength and detail preservation throughout the diffusion trajectory. Unlike traditional task-specific models, our approach enables Plug-and-Play (PnP) deployment, supporting diverse degradations without retraining. Extensive experiments conducted on deterministic degradations (e.g., under-sampled MRI, sparse-view CT) and blind degradations (e.g., low-dose PET) across multiple degradation levels demonstrate superior quantitative and qualitative performance compared to both supervised baselines and state-of-the-art posterior sampling methods. Notably, our method achieves PSNR improvements of up to +2.9 dB (MRI), +1.1 dB (CT), and +0.9 dB (PET) in PnP mode. These results highlight the robustness and broad applicability of our framework for clinical deployment.