Brightness-Invariant Tracking Estimation in Tagged MRI
This work addresses a specific challenge in medical imaging for researchers and clinicians, offering an incremental improvement over existing Fourier and optical flow methods by combining denoising diffusion models and physics-informed neural networks.
The paper tackled the problem of tracking tissue motion in tagged MRI, where brightness changes over time cause errors in existing methods, and introduced the BRITE technique that disentangles anatomy from tag patterns to estimate motion, achieving more accurate motion and strain estimates compared to state-of-the-art methods while being resistant to tag fading.
Magnetic resonance (MR) tagging is an imaging technique for noninvasively tracking tissue motion in vivo by creating a visible pattern of magnetization saturation (tags) that deforms with the tissue. Due to longitudinal relaxation and progression to steady-state, the tags and tissue brightnesses change over time, which makes tracking with optical flow methods error-prone. Although Fourier methods can alleviate these problems, they are also sensitive to brightness changes as well as spectral spreading due to motion. To address these problems, we introduce the brightness-invariant tracking estimation (BRITE) technique for tagged MRI. BRITE disentangles the anatomy from the tag pattern in the observed tagged image sequence and simultaneously estimates the Lagrangian motion. The inherent ill-posedness of this problem is addressed by leveraging the expressive power of denoising diffusion probabilistic models to represent the probabilistic distribution of the underlying anatomy and the flexibility of physics-informed neural networks to estimate biologically-plausible motion. A set of tagged MR images of a gel phantom was acquired with various tag periods and imaging flip angles to demonstrate the impact of brightness variations and to validate our method. The results show that BRITE achieves more accurate motion and strain estimates as compared to other state of the art methods, while also being resistant to tag fading.