OPTIMIZATION OF BEAM PARAMETERS FOR DUAL-ENERGY DIGITAL SUBTRACTION ANGIOGRAPHY

Dual-energy digital subtraction angiography (DSA) is immune to the misregistration artifacts which plague conventional temporal subtraction DSA. However, since the signal-to-noise ratio (SNR) of dual-energy DSA is lower than temporal subtraction it is important to optimize the dual-energy technique with respect to the SNR. This study-investigates the optimization of x-ray exposure parameters for the low- and high-energy x-ray beams, drawing upon our experience with dual-energy DSA studies in 20 cardiac patients. It is shown that tide SNR is optimized, with respect to patient exposure, when the image intensifier (II) exposure for the high-energy beam is approximately 5 times higher than the low-energy beam. The unequal distribution of exposure between the low- and high-energy beams is achieved by selecting different video apertures for the two beams, and is therefore referred teas the ''dual-aperture'' technique. The dual-aperture technique achieves the same SNR as the single-aperture technique (which uses equal II exposures for the two beams) with 45% less patient exposure. In addition, the dual-aperture technique enhances the ability to maintain an optimum low-energy kVp, which increases the dual-energy signal amplitude. The optimum high-beam filter thickness for use with the dual-aperture approach is determined. The optimum filter thickness, which is dependent upon the:desired tube loading, is found to range from 1.3 to 2.0 mm Cu for tube loads ranging from 188 to 688 J/beam pair.