The initial examination is a plain film of the abdomen to evaluate for the presence or absence of visible stones. This also excludes gross bowel obstruction or other processes that may masquerade as "flank pain". The next examination should be a CT of the abdomen & pelvis without oral or IV contrast i.e. "stone hunt" protocol. Some clinicians prefer an IVP instead of CT. The IVP provides detail evaluation of the ureters. The CT provides better visualization of the kidneys. If the patient is allergic to IV contrast, a good alternative is renal ultrasound. This is particularly sensitive to the presence of hydronephrosis, but will not visualize the ureters beyond the UPJ unless they are grossly dilated. Renal ultrasound is also a less expensive and less risky alternative than CT or IVP. CT with IV contrast is reserved for subsequent evaluation of renal mass or other incompletely defined abnormalities seen on the non-contrasted CT exam.