A ground truth for volumetric MRI cardiac tracking using the XCAT phantom

Introduction: A real-time cardiac MRI tracking technique based on template matching has been developed centred on the findings of a cardiac target localisation in real-time MRI investigations [1]. Real-time volumetric tracking of cardiac structures that undergo respiratory and cardiac motion with MRI is required if the novel method of treating atrial fibrillation with radiosurgery is to be realised. MR imaging currently lacks the required spatial and temporal resolution to provide a ground truth for comparison with the real-time cardiac MRI tracking technique.
Aim: Utilisation of the XCAT digital phantom software [2] to provide a ground truth for cardiac motion to provide verification of the accuracy of the template matching real-time cardiac tracking technique.
Method: The XCAT digital phantom software allows respiratory and cardiac motion to be simulated, in addition to user defined voxel values for cardiac structures. The left atrium is isolated through thresholding and the volumetric centroid is tracked over a period of multiple respiratory and cardiac cycles. The left atrium 3D centroid position from the XCAT phantom and template matching software are compared. XCAT phantom simulations with varying cardiac and respiratory motion traces are utilised to test the robustness of the real-time cardiac tracking MRI template matching approach.
Results: Sub-voxel accuracy has been demonstrated in phantoms with small cardiac LR respiratory motion and single voxel accuracy has been demonstrated in phantoms with larger cardiac LR respiratory motion. The presence of a ground truth has allowed optimisation of the template matching approach with dynamic search and absolute motion functions.
Conclusion: The XCAT digital phantom software has provided verification and identified areas of improvement with the real-time cardiac tracking MRI template matching method.