OBJECTIVES: We report validation of OsiriXV R -an image processing freeware-to measure multi-slice computed tomography-derived annulus diameters for preprocedural transcatheter aortic valve implantation planning. METHODS: A total of 137 patients (82 ± 6.5 years, 42.3% male, logistic EuroSCORE 24.1 ± 14.2%) with severe aortic stenosis at high surgical risk underwent transcatheter aortic valve implantation assessment: transoesophageal echocardiography, angiography and multi-slice computed

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... hy. Retrospectively, 3D multi-slice computed tomography reconstructions were generated using OsiriX and the reliability evaluated regarding inter-and intraobserver variability, intermodality correlation and estimation of the clinical impact on transcatheter aortic valve implantation sizing. RESULTS: Reliability of the novel OsiriX software was high with an interobserver mean difference of 0.6 ± 1.4 mm and intraclass correlation of absolute agreement of 0.84 (95% confidence interval 0.74-0.90). The intermodality accuracy between OsiriX measurements and conventional 2D computed tomography reconstructions, transoesophageal echocardiography and angiography revealed significantly larger sizing with OsiriX, with a mean difference to 2D computed tomography of 0.4 ± 2.2 mm, which would have changed valve sizing in 38% of patients. In 28%, a larger size would have been chosen, and this correlated highly with the occurrence of postoperative severe aortic regurgitation (P < 0.001). CONCLUSIONS: While OsiriX measurements are an accurate and reproducible assessment of the aortic annulus, there are distinct and clinically relevant differences in aortic annulus dimensions between OsiriX measurements and previously standard imaging modalities. Sizing with OsiriX resulted in a larger perimeter compared with conventional 2D imaging. Careful assessment of valve size will take into account multiple imaging modalities.