Rawdata-Based Dual Energy CT (DECT) from inconsistent scans

Dual energy CT (DECT) acquires an object at two different detected spectra w₁(E) and w₂(E). Rawdata-based techniques can be applied whenever the integration lines (rays) of both spectra are identical. Then, the rawdata q₁ and q₂ undergo a decomposition process of type p = p(q₁, q₂). For spiral cone-beam dual source CT (DSCT) and for micro-DSCT the integration lines are disjunct and therefore inconsistent. Hence, one typically uses image-based subtraction techniques that are inferior to the rawdata-based methods. Our technique provides consistent rawdata in two steps. Starting from standard reconstructions of both scans, polychromatic forward projections of the volumes 1 and 2 yield the desired consistent rawdata q₁ and q₂. The second step computes the decomposition p(q₁, q₂) and reconstructs these sinograms using filtered backprojection. All computations are done in parallel beam geometry. To avoid loosing spatial resolution the linear terms of p are handled in image domain. Only the higher order terms undergo the two-step process. The algorithm was run on a Cell Broadband Engine (CBE) at 3.2 GHz in a Playstation 3 (PS3) computer (Sony Computer Entertainment, Japan). To evaluate our approach we decompose patient rawdata acquired with a SOMATOM Definition clinical DSCT scanner (Siemens Medical Solutions, Forchheim, Germany). The PS3 processes 35 slices per second (512² pixels, 512 views per half rotation, two forward projections, decomposition, filtering, one backprojection); a typical volume of thousand slices is processed in half a minute.