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 Solutionsm, Forchheim, Germany). The PS3 processes 35 slices per second (512² pixels, 512 views per half rotation, two forward pro- jections, decomposition, filtering, one backprojection); a typical volume of thousand slices is processed in half a minute.