Latent-k-space of refinement diffusion model for accelerated MRI reconstruction

<i>-</i>Recent advances have applied diffusion model (DM) to magnetic resonance imaging (MRI) reconstruction, demonstrating impressive performance. However, current DM-based MRI reconstruction methods suffer from two critical limitations. First, they model image features at the pixel-level and require numerous iterations for the final image reconstruction, leading to high computational costs. Second, most of these methods operate in the image domain, which cannot avoid the introduction of secondary artifacts. To address these challenges, we propose a novel latent-k-space refinement diffusion model (LRDM) for MRI reconstruction. Specifically, we encode the original k-space data into a highly compact latent space to capture the primary features for accelerated acquisition and apply DM in the low-dimensional latent-k-space to generate prior knowledge. The compact latent space allows the DM to require only 4 iterations to generate accurate priors. To compensate for the inevitable loss of detail during latent-k-space diffusion, we incorporate an additional diffusion model focused exclusively on refining high-frequency structures and features. The results from both models are then decoded and combined to obtain the final reconstructed image. Experimental results demonstrate that the proposed method significantly reduces reconstruction time while delivering comparable image reconstruction quality to conventional DM-based approaches.