In patients with acute renal colic the region of the VUJ must be scrutinised for reflective stones. While this stone is fairly large and thus easily appreciated on B-mode imaging, for small stones the use of color Doppler and search for twinkling can enhance sensitivity. Waiting for color jets to appear in the bladder can also be used as an indirect way of confirming obstruction but in some patients no jets will appear even during prolonged observation regardless of the presence/absence of ureteric obstruction.