TractOracle: towards an anatomically-informed reward function for RL-based tractography
This work addresses the issue of false positives in brain white matter tractography for medical imaging applications, representing an incremental improvement by integrating anatomical knowledge into the reward function.
The paper tackles the problem of spurious false positives in reinforcement learning-based tractography by introducing TractOracle, a system that uses a reward network trained for streamline classification to improve anatomical accuracy. The result is an almost 20% increase in true positive ratios and a 3x reduction in false positive ratios on one dataset, with a 2x to 7x increase in true positive streamlines on another.
Reinforcement learning (RL)-based tractography is a competitive alternative to machine learning and classical tractography algorithms due to its high anatomical accuracy obtained without the need for any annotated data. However, the reward functions so far used to train RL agents do not encapsulate anatomical knowledge which causes agents to generate spurious false positives tracts. In this paper, we propose a new RL tractography system, TractOracle, which relies on a reward network trained for streamline classification. This network is used both as a reward function during training as well as a mean for stopping the tracking process early and thus reduce the number of false positive streamlines. This makes our system a unique method that evaluates and reconstructs WM streamlines at the same time. We report an improvement of true positive ratios by almost 20\% and a reduction of 3x of false positive ratios on one dataset and an increase between 2x and 7x in the number true positive streamlines on another dataset.