The best investigation to detect renal stone is-

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.