LIMITED DATA RECONSTRUCTIONS FOR ION MICROTOMOGRAPHY (IMT)

Ion microtomography (IMT) is based on measuring the residual energy of ions as they pass through the sample. However, for some samples, the maximum range of the ions can prevent acquiring a complete projection data set for the density reconstruction, i.e., only a limited set of a ngles will allow the beam to penetrate the sample. Limited angle data sets from flat planar objects are a commonly occurring class for limit ed data reconstructions in IMT. Such a target can pose an additional p roblem in that the ion beam may not ''see'' its edges - the target is not finite in extent to the beam. Two reconstruction methods are exami ned to treat limited data for IMT. The first uses mathematical models of the sample to produce simulated ray-sums that are incorporated into the reconstruction of experimentally measured data. The second method produces a partial reconstruction of the region of interest. A techni que is also devised, using a marker, for determining the projected cen ter of rotation - a necessary parameter for the reconstruction algorit hms - which cannot be determined from the limited data by usual method s. Examples are presented for two specific planar samples: one made of an artificial heart valve material and the other a metal matrix compo site.