This work reports the measured dependence of the DSA image's iodine contrast on kVp, patient thickness, X-ray scatter, and DSA system's veiling glare. It also reports the measured patient skin dose at a constant X-ray image intensifier (XRII) entrance dose for the various kVp and the patient thickness settings. It is found that, for any given patient skin dose, the DSA image quality is most optimal in the 80 - 100 kVp range. However, the DSA image quality is markedly reduced by increasing patient thickness and by the combined effect of X-ray scatter and the DSA system's veiling glare. Clinical examples indeed show that 80 - 100 kVp operation yields very satisfactory images for all range of patient thickness and for both intravenous and intra-arterial DSA examinations.