TH-A-BRF-07: Retrospective Reconstruction of 3D Radial MRI Data to Evaluate the Effect of Abdominal Compression On 4D Abdominal Organ Motion

PURPOSE: To assess the immobilization effect of an abdominal corset on the spatial and temporal motion characteristics of the pancreas and kidneys using a novel 4D-MRI method.

METHODS: Four healthy subjects were scanned with and without a fiberglass corset on a 1.5T clinical MRI. For each subject the best fitting corset was chosen from a range of available corsets. For one subject a custom-fit corset was used. The free-breathing 4D-MRI scan consisted of a balanced-TFE sequence with radial in-plane sampling (TE/TR=1.45ms/3.0ms, FA=30°, FOV=350×350×96mm(3) , voxelsize=2.0×2.0×4.0mm(3) , 30 dynamics, Tacq=10m17s). Turbo direction was along kz acquiring all kz lines within a single TFE shot (shot duration 93ms). A respiratory diaphragm navigator was interleaved with the TFE shots to acquire the breathing signal, which was used to retrospectively assign each k-space segment to one of the ten respiratory phases. A 3D optical flow algorithm was used to estimate the non-rigid displacement between the respiratory phases. The respiration frequency changes were assessed by means of power spectrum analysis (PSA) of the navigator signal.

RESULTS: Image quality was adequate for delineation and registration. Cranio-caudal motion calculated by the 3D optical flow algorithm correlated with the navigator signal, but inter-organ motion amplitude variation was observed between all organs. Motion reduction induced by the corset was primarily observed in the CC-direction, but varied substantially across the subjects. Our method additionally showed that the antero-posterior motion was slightly increased for both kidneys in all subjects (left: 1.2mm, right: 0.8mm). Visual inspection of PSA showed no trend in breathing frequency changes.

CONCLUSION: We have demonstrated a novel, navigator based, freebreathing 4D-MRI technique to assess the immobilization effect of abdominal compression in four healthy subjects. This technique can be clinically used to assess the effect of a custom-fit corset on the motion of both tumor motion and surrounding organs at risk.