Exhibit Hall | Forum 9
Purpose: Cardiac radioablation (CR) is a novel treatment approach for ventricular tachycardia (VT). Toxicity is a major concern and could be proactively minimized via online MRI-guidance on an MR-linac. Most VT patients carry an implantable cardioverter defibrillator (ICD), which visually compromises MR images. Robust MR-linac sequences are required for planning and active motion mitigation in presence of an ICD. We evaluate the quality of available imaging sequences on a 1.5 T MR-linac in-vivo in the presence of an ICD.
Methods: We scanned 3 healthy volunteers (wrapped ICD placed on chest) and 1 VT patient (with ICD, scanned on a 1.5 T MR-sim system), while complying with ICD safety guidelines for MRI. For planning, a free-breathing T₂-weighted 3D-TSE and respiratory motion-mitigated multi-slice T₂-weighted TSE-PROPELLER sequences were used. For motion estimation, real-time single-slice 2D bSSFP (8.8 Hz) and T₁-GRE (6.7 Hz) cine images were acquired with and without ICD. Cardiorespiratory motion was locally estimated with rigid registration using the cine images. For the patient data, the acquired planning MRI images were visually compared with the corresponding CT and CBCT and spatial distortions were estimated using a B₀-map.
Results: The TSE-PROPELLER sequence shows potential in visualising the myocardium and cardiac substructures with reduced ICD-induced artefacts (maximum 42 mm from ICD) compared to the 3D-TSE (maximum 62 mm from ICD). Severe off-resonance artefacts were observed in the bSSFP cine images and hampers automatic motion estimation in a large part of the heart, while the T₁-GRE cine has a minimal number of artefacts within the heart. However, the SNR and CNR decreased considerably when using the T₁-GRE sequence with respect to the bSSFP sequence. Spatial distortions with a maximum of 0.90 mm were estimated in the patient cine dataset.
Conclusion: First exploratory steps show that ICD-induced artefacts can be drastically reduced by proper sequence selection.
MRI, Image-guided Therapy, Distortion
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined- IGRT and tracking