<prompt> The best investigation to detect renal stone is-X- rayCTMRIUS  <response>: Ans. is b i.e., CT Non - contrast spiral CT has now become the investigation of choice to diagnose renal and ureteric stones.Urinary stones radiography1 Plane abdominal X-ray KUB or kidney - ureter - Bladder X-ray: - The first radiological test that is performed is the plain abdominal X-ray. Because majority of stones 90 are radiopaque, these can be easily identified on X-ray :-a Radiolucent stones Uric acid stone, Orotic acid stones, Xanthine, Triamterens, Dihydroxyadenine.b Radiopaque stonesCystine, Struvite, calcium oxolate, calcium phosphate.2 Intravenous pyelogram IVP:- IVP can demonstrate urinary obstruction from renal stone and can demonstrate the position of non - opaque radiolucent stones.3 CT scan:- Non - contrast helical CT is 95 to 100 sensitive and specific for detection of renal calculi and, therefore, is the imagining modality of choice for urinary stones.4 USG:- USG provide excellent assessments of kidney and bladder but inferior to IVP and CT scan in evaluation of the ureters. 