1. A method for imaging a patient's unprepared colon for colorectal polyp screening, comprising: prescribing the administration of a stool marker protocol enabling marked stool to be discriminated from polyps having a diameter of at least 1 cm when imaged, wherein the protocol includes administering at least about 10 grams of stool marker in at least six doses to the patient over at least a 48 hour administration period; and with the patient free from colon preparation, including from the administration of laxatives or cathartics for at least 24 hours, imaging the patient's colon after the administration period to generate image data representative of a sequence of image slices along a length of the colon, the imaging being performed by an imaging modality capable of generating image slice data with slice thicknesses no greater than 5 mm and reconstruction intervals no greater than 3 mm enabling the discrimination of polyps having a diameter of at least 1 cm from marked stool in the image slices.