On the uncertainty of surface determination in x-ray computed tomography for dimensional metrology

With x-ray computed tomography (CT) it is possible to evaluate the dimensions of an object’s internal and external features non-destructively. Dimensional measurements evaluated via x-ray CT require the object’s surfaces first be estimated; this work is concerned with evaluating the uncertainty of this surface estimate and how it impacts the uncertainty of fitted geometric features. The measurement uncertainty due to surface determination is evaluated through the use of a discrete ramp edge model and a Monte Carlo simulation. Based on the results of the Monte Carlo simulation the uncertainty structure of a coordinate set is estimated, allowing individual coordinate uncertainties to be propagated through the geometry fit to the final measurement result. The developed methodology enables the uncertainty due to surface determination to be evaluated for a given measurement task; the method is demonstrated for both measured and simulated data