you have taken your first dental image on your patient. the contrast is high and you are looking for periodontal disease. you are using a dc machine and you have control of your settings. you have a 60- to 70-kv range and a 6- to 8-ma range. you had the kv set at 60, the ma set at 7, and the impulses set at 6/100. while leaving all other settings the same, which setting would you adjust to create better contrast for detecting periodontal disease?