Cross-modal conditional latent diffusion model for brain MRI to ultrasound image translation

Objective. Intraoperative brain ultrasound (US) provides real-time information on lesions and tissues, making it crucial for brain tumor resection. However, due to limitations such as imaging angles and operator techniques, US data is limited in size and difficult to annotate, hindering advancements in intelligent image processing. In contrast, magnetic resonance imaging (MRI) data is more abundant and easier to annotate. If MRI data and models can be effectively transferred to the US domain, generating high-quality US data would greatly enhance US image processing and improve intraoperative US readability.Approach. We propose a cross-modal conditional latent diffusion model (CCLD) for brain MRI-to-US image translation. We employ a noise mask restoration strategy to pretrain an efficient encoder-decoder, enhancing feature extraction, compression, and reconstruction capabilities while reducing computational costs. Furthermore, CCLD integrates the frequency-decomposed feature optimization module and the adaptive multi-frequency feature fusion module to effectively leverage MRI structural information and US texture characteristics, ensuring structural accuracy while enhancing texture details in the synthetic US (sUS) images.Main results. Compared with state-of-the-art methods, our approach achieves superior performance on the ReMIND dataset, obtaining the best learned perceptual image patch similarity score of 19.1%, mean absolute error of 4.21%, as well as the highest peak signal-to-noise ratio of 25.36 dB and structural similarity index of 86.91%.Significance. Experimental results demonstrate that CCLD effectively improves the quality and realism of sUS images, offering a new research direction for the generation of high-quality US datasets and the enhancement of US image readability.