How many days before ct scan (for head-routine and sinuses ) shall a person not to smoke cigarette & weed inorder not to be founded & interfere result?

Don't understand ?: there is no way that a CT scan can determine whether someone had cigarettes or weed prior to the testing, unless the smell is on your clothes/hair/breath and the technician tells on you, or you smoke it inside the machine. They can often tell if you are a smoker because of the acute and chronic changes in your tissues (not always though). It doesnt interfere with the results