Scalable Diffusion Transformer for Conditional 4D fMRI Synthesis

Jungwoo Seo, David Keetae Park, Shinjae Yoo, Jiook Cha

Keywords: scalable diffusion modeling, conditional fMRI synthesis, 4D spatiotemporal modeling

TL;DR: We introduce first scalable diffusion transformer for conditional 4D fMRI synthesis, faithfully modeling task-specific brain dynamics.

Abstract: Generating whole-brain 4D fMRI sequences conditioned on cognitive tasks remains challenging due to the high-dimensional, heterogeneous BOLD dynamics across subjects/acquisitions and the lack of neuroscience-grounded validation. We introduce the first diffusion transformer for voxelwise 4D fMRI conditional generation, combining 3D VQ-GAN latent compression with a CNN–Transformer backbone and strong task conditioning via AdaLN-Zero and cross-attention. On HCP task fMRI, our model reproduces task-evoked activation maps, preserves the inter-task representational structure observed in real data (RSA), achieves perfect condition specificity, and aligns ROI time-courses with canonical hemodynamic responses. Performance improves predictably with scale, reaching task-evoked map correlation of 0.83 and RSA of 0.98, consistently surpassing a U-Net baseline on all metrics. By coupling latent diffusion with a scalable backbone and strong conditioning, this work establishes a practical path to conditional 4D fMRI synthesis, paving the way for future applications such as virtual experiments, cross-site harmonization, and principled augmentation for downstream neuroimaging models.

Submission Number: 64