Super-resolution T2-weighted 4D MRI for image guided radiotherapy

Publication date: Available online 2 June 2018
Source:Radiotherapy and Oncology
Author(s): Joshua N. Freedman, David J. Collins, Oliver J. Gurney-Champion, Jamie R. McClelland, Simeon Nill, Uwe Oelfke, Martin O. Leach, Andreas Wetscherek
Background and purposeThe superior soft-tissue contrast of 4D-T2w MRI motivates its use for delineation in radiotherapy treatment planning. We address current limitations of slice-selective implementations, including thick slices and artefacts originating from data incompleteness and variable breathing.Materials and methodsA method was developed to calculate midposition and 4D-T2w images of the whole thorax from continuously acquired axial and sagittal 2D-T2w MRI (1.5 × 1.5 × 5.0 mm³). The method employed image-derived respiratory surrogates, deformable image registration and super-resolution reconstruction. Volunteer imaging and a respiratory motion phantom were used for validation. The minimum number of dynamic acquisitions needed to calculate a representative midposition image was investigated by retrospectively subsampling the data (10–30 dynamic acquisitions).ResultsSuper-resolution 4D-T2w MRI (1.0 × 1.0 × 1.0 mm³, 8 respiratory phases) did not suffer from data incompleteness and exhibited reduced stitching artefacts compared to sorted multi-slice MRI. Experiments using a respiratory motion phantom and colour-intensity projection images demonstrated a minor underestimation of the motion range. Midposition diaphragm differences in retrospectively subsampled acquisitions were <1.1 mm compared to the full dataset. 10 dynamic acquisitions were found sufficient to generate midposition MRI.ConclusionsA motion-modelling and super-resolution method was developed to calculate high quality 4D/midposition T2w MRI from orthogonal 2D-T2w MRI.



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