Optimized 0.35T Cine MRI with Implicit Neural Representation Reconstruction for Improved Real-Time Motion Monitoring In MR-Guided Radiotherapy
Abstract
Purpose
While MR-guided radiotherapy enables real-time, soft-tissue–based motion management, clinical 2D cine MRI often sacrifices spatial resolution to maintain frame rate, which can contrast oncological contrast. This study aims to optimize a 2D cine MRI protocol on a 0.35T MR-guided radiotherapy system and evaluate an AI-based method for improving cine image quality and spatial resolution.
Methods
Cine sequence optimization was first evaluated using a CIRS Triple Modality 3D Abdominal Phantom and subsequently validated in a liver cancer patient under an IRB-approved protocol. Key parameters (flip angle, bandwidth, average number, and matrix size) were systematically adjusted to improve soft-tissue visualization while maintaining ~4 frames per second imaging rate. Contrast-to-noise ratio (CNR) between the liver and surrounding tissue was quantified to objectively assess contrast improvements. For AI-based image enhancement, an implicit neural representation(NeRP) framework with prior embedding was developed. The high-resolution 3D setup scan was encoded into a coordinate-based multilayer perceptron as an anatomical prior, and cine images were reconstructed by constraining the network using acquired cine k-space data. NeRP-based reconstruction was compared against image-domain interpolation and k-space zero-padding.
Results
The optimized cine MRI protocol substantially improved tissue visualization in both phantom and patient. CNR increased from 13.6 to 34.1 in the phantom and from 48.5 to 69.0 in the patient, indicating markedly improved tissue contrast for motion monitoring. NeRP-based reconstruction further enhanced cine image quality beyond standard post-processing, producing sharper anatomical boundaries, improved soft-tissue definition, and more coherent structural detail compared with interpolation or k-space zero-padding.
Conclusion
Systematic optimization of a 2D cine MRI protocol on a 0.35T MR-guided radiotherapy system significantly improved soft-tissue contrast and visualization for real-time imaging. In addition, NeRP-based reconstruction enhanced cine sharpness and effective spatial resolution, thus showing promise for improved target and organ visualization for motion monitoring and adaptive MR-guided radiotherapy.