Poster - Thur Eve - 75: Towards MR only simulation: MR based digitally reconstructed radiograph of head and neck.
PURPOSE
To develop a practical method to obtain bony structures from Magnetic Resonance (MR) images and to create MR- based digitally reconstructed radiographs (DRR) for MR only simulation.


METHODS AND MATERIALS
Using T1-weighted MR images, air regions including the sinuses and the airway in the head and neck were manually contoured. The bone and soft tissue masks were automatically generated based on the statistical data calculated from the air contour and MR intensities. "CT like" MR images were generated by mapping the MR intensities of the voxels within these masks into the CT number ranges of these tissues. The MR-based DRRs created from "CT like" MR images were quantitatively evaluated using the co-registered MR and CT images of 10 stereotactic radiosurgery CNS patients. Ten anatomical control points, set on the contours of the skull segmented using a threshold of 300 HU were used to determine the differences in distance between MR-based DRRs and CT-based DRRs, and to evaluate the geometrical accuracy of MR-based DRRs.


RESULTS
The bony structures were visible in the MR-based DRRs. The mean geometric difference and standard deviation between the ten anatomical control points on MR- based and CT-based DRRs were -0.03±1.11 mm (including uncertainty of image fusion). The maximum distance difference was 1.67mm.


CONCLUSIONS
The study provides a practical method to generate MR- based DRRs from MR-only simulations of the head and neck regions. The image quality and anatomical accuracy of MR-based DRRs is comparable to that of CT-based DRRs.