Brief Answer: CT scans is the gold standard for assessing patients with proximal ureter and pelvic-calyceal system distention. Detailed Answer: Hello, Thank you for using HCM. It is important to find the cause of the proximal ureter and pelvic-calyceal system distention. It usually happens due to stones and other causes of obstruction from outside the ureters. Ultrasound is a sensitive and practical exam and it should be always the initial test for patients with suspected kidney stones, but sometimes it is not successful enough in discovering small ureteral or juxtavesical (in the place where the ureters open in bladder) stones and other causes of obstruction. CT scan is recommended in such a case. CT scan is the gold standard for assessing patients with kidneys pain or suspected urinary tract stones. It is a near-perfect test with exemplary sensitivity, specificity, and accuracy. It can detect whether there is an intra or extra urinary obstruction, therefore deciding for the best way of treatment (only some fluid intake, lithotripsy based on ultrasound shock wave or open surgery). The amount of radiation that the patient receives during a CT scan performance is low when compared to the benefits, even though, it should be avoided in recurrent stone former s, because the diagnosis is yet done. Abdominal ultrasound and kidney, ureter, bladder x-ray (KUB), can be used for follow up. Hope this is helpful. Let me know if you need more clarifications. Otherwise please close and rate the answer. Kind Regards, Dr. Juarda