Three�beam K�edge imaging of iodine using differences between fluoroscopic video images: Theoretical considerations

Our lab has previously generated selective iodine images with an image intensifier fluoroscopic system using a threeâ€Â�beam Kâ€Â�edge approach. Logarithmically amplified video images L_i were linearly combined to yield the final image k₁L₁+k₂L₂+k₃L₃. This paper discusses refinements of the Kâ€Â�edge technique. A study is made of the manner in which contrastâ€Â�reducing effects such as xâ€Â�ray scatter and image intensifier veiling glare enter into the final image. If such biases can be approximated as multiplicative and independent of the xâ€Â�ray spectrum, and if the sum of the k_i is zero, then the biases are canceled. Experimental data is presented which demonstrates that the inaccuracy due to such biases can be reduced by a factor as large as 10. The theorem that k₁+k₂+k₃≊0 is proven rigorously and discussed. Because the k_i add to zero, the final image can be expressed as a linear combination of two of the differences between the L_i. A differenceâ€Â�based algorithm which reduces biases and make allowance for nonlinearities such as beam hardening is proposed and discussed.