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Dual Energy

Dual Energy. Introduction. Reduce false alarms from EDS using dual energy techniques Use density and (effective) atomic number to identify harmful objects Limitations include : approximation error, boundary constraints, image artifacts, x-ray spectral drift. Overview of dual-energy.

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Dual Energy

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  1. Dual Energy

  2. Introduction • Reduce false alarms from EDS using dual energy techniques • Use density and (effective) atomic number to identify harmful objects • Limitations include : approximation error, boundary constraints, image artifacts, x-ray spectral drift

  3. Overview of dual-energy • μ(x, y, z, E) = ac(x, y, z)fKN(E) + ap(x, y, z)fp(E) Compton scatter photoelectric effect • fP(E) = E^-3 and fKN(E) is the Klein-Nishina cross section • 2 logarithmic projects are then found, pL, pH • Atomic number is then calculated

  4. 14,400 (AC, AP) calibration points generated (PL , PH) calculated for each (AC, AP) Newton – Raphson for CDM method was used Solved 8,997 linear equations for AM for 16 polynomial coefficients calibration points reduced by 8,997 by setting max bound CDM (Constrained Decomposition Method) Goal: decompose the dual energy projection PL and PH into AC (Compton projection) and AP (photoelectronic projection) Problem: find (AC, AP) = arg min (PL (AC, AP) - PL)^2 + (PH (AC, AP) - PH)^2 s.t. AC >= 0, AP >= 0 CDM vs. indirect polynomial approximation Method (AM) Approach Results: Error percentage was calculated for both methods CDM error is due to numerical error AM error is due to the approximation error Conclusion: AM should not be used for dual energy CT due to the big dynamic range of photoelectronic coefficients

  5. CDM vs. Truncation Method for handling the Boundary Conditions (TM) random (AC, AP) pairs were generated (PL , PH) calculated for each (AC, AP) Approach: Results: Number of error cases : TM – 6,355 cases, CDM – 3,119 cases Scatter Correction Results: TM used 2D Newton –Raphson iterative method to solve for (AC, AP) 100,000 truncation cases were identified noise modeled by Poisson process was added

  6. Destreaking

  7. Spectral Correction

  8. DISCUSSION • Constrained decomposition algorithm • Spectral correction algorithm • Adaptive scatter collection algorithm • Limitations: • Conversion gain factor and charge collection efficiency different for high and low energy x-ray data • - correction operations include offset, air and monitor correction • -noise in the photoelectric image compensated by destreaking algorithm and adaptive filters • Dual energy CT scanner used in this paper passes the TSA explosive detection certification test

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