Conditional Recurrent Flow: Conditional Generation of Longitudinal Samples with Applications to Neuroimaging
This work addresses the challenge of generating progressive longitudinal data for neuroimaging studies, which is incremental as it adapts existing generative models to handle sequential data with smooth transitions.
The paper tackles the problem of generating realistic longitudinal data for neuroimaging studies with small sample sizes by proposing a conditional generative model that incorporates recurrent subnetwork and context gating to ensure smooth transitions in sequences. The results on an Alzheimer's disease dataset capture disease-specific group differences with generated samples consistent with existing literature, demonstrating potential applicability to other diseases.
Generative models using neural network have opened a door to large-scale studies for various application domains, especially for studies that suffer from lack of real samples to obtain statistically robust inference. Typically, these generative models would train on existing data to learn the underlying distribution of the measurements (e.g., images) in latent spaces conditioned on covariates (e.g., image labels), and generate independent samples that are identically distributed in the latent space. Such models may work for cross-sectional studies, however, they are not suitable to generate data for longitudinal studies that focus on "progressive" behavior in a sequence of data. In practice, this is a quite common case in various neuroimaging studies whose goal is to characterize a trajectory of pathologies of a specific disease even from early stages. This may be too ambitious especially when the sample size is small (e.g., up to a few hundreds). Motivated from the setup above, we seek to develop a conditional generative model for longitudinal data generation by designing an invertable neural network. Inspired by recurrent nature of longitudinal data, we propose a novel neural network that incorporates recurrent subnetwork and context gating to include smooth transition in a sequence of generated data. Our model is validated on a video sequence dataset and a longitudinal AD dataset with various experimental settings for qualitative and quantitative evaluations of the generated samples. The results with the AD dataset captures AD specific group differences with sufficiently generated longitudinal samples that are consistent with existing literature, which implies a great potential to be applicable to other disease studies.