Dual energy contrast-enhanced spectral mammography (CESM) technique has been introduced to overcome the standard mammography's performance on dense breasts. To enhance the visualization of the tumour, iodine contrast is used followed by an acquisition of images at low and high energies, which are then combined into a single image for additional information. This study used a model of a compressed breast made from clear resin with holes on the top. The holes were filled with iodine-based contrast and images with six different energies (50 kVp, 70 kVp, 80 kVp, 90 kVp, 100 kVp, 120 kVp) were obtained at a general purpose x-ray unit. Then, 15 subtraction images were calculated by performing a pixel by pixel subtraction of each possible image pair and the contrast was evaluated. The results indicated that the best contrast rates are achieved on 50 kVp and 70 kVp as low energy and 100 kVp and 120 kVp as high energy. The best contrast was evaluated for the pair 70-120 kVp.