Methods of imaging a portion of a body of a patient are provided. In the methods, a contrast agent including an iso-osmotic contrast agent is administered to the patient. In a preferred embodiment, the iso-osmotic contrast agent comprises polyethylene glycol (PEG) and electrolytes, which make the PEG iso-osmotic. In a preferred embodiment, a positive contrast agent, such as an iodine-based contrast agent, is added to the PEG. The iso-osmotic contrast agent can be administered in volumes that are lower than previous contrast agents. The iso-osmotic contrast agent can be administered in combination with a positive intravenous contrast agent. At least one image of the portion of the patient's body is obtained, such as by computed tomography, after the contrast agent is administered. The methods can be used to image a pelvis, GI tract, and/or appendix of the patient. Iso-osmotic contrast agents are also provided.