Retrospective Distortion Correction Using the ADNI Phantom to Salvage Unusable Exams

Bogdan Dzyubak¹, Jeffrey L. Gunter¹, Edward Brian Welch², Ron J. Killiany³, Clifford R. Jack¹, Matt A. Bernstein¹

During the Alzheimers Disease Neuroimaging Initiative (ADNI) multicenter study, a laser alignment light was mis-calibrated on one scanner, leading to a displacement error in the isocenter location used during image reconstruction. Consequently, the standard gradient distortion correction was inaccurate and the resulting data were unusable for longitudinally tracking brain changes. Off-line processing was used to remove the aberrant distortion correction from ADNI phantom data, then those images were shifted by a variable displacement, and finally the images were re-corrected for gradient distortion. The actual displacement error was determined by this method and the subject data could be re-corrected and salvaged.