FlowSeed: Continuous-Time Contrast-Enhanced CT Synthesis via Organ-Aware Gaussian-Weighted Residual Splatting

Multiphase contrast-enhanced computed tomography (CECT) sparsely samples a continuous, organ-dependent enhancement process. However, existing synthesis methods treat arterial, venous, and delayed scans as discrete targets and reconstruct anatomy already available in non-contrast CT (NCCT). We introduce FlowSeed, a continuous-time residual contrast-rendering framework that retains NCCT as the anatomical base and renders only its time-dependent enhancement. FlowSeed uses soft organ maps to route time-conditioned affine modulation at each voxel. A slice-aware Gaussian residual decoder then predicts intensity, opacity, axis-aligned scale, and center offset to render enhancement onto queried axial slices. Physiology-inspired ordinal constraints regularize liver and aortic enhancement, while a conditional PatchGAN provides adversarial supervision for local appearance fidelity. On held-out MCT-LTDiag studies, FlowSeed reduces mean absolute error by 6.7–18.8% relative to the strongest comparator across three anatomical groups. On external WAW-TACE data, it achieves the lowest mean absolute error and highest SSIM in all groups. Ablations support the contributions of organ-aware temporal routing and Gaussian-weighted residual decoding. Dense-query visualizations further show that FlowSeed can synthesize continuous enhancement sequences with distinct organ-dependent responses across time.