Unenhanced helical CT using increased pitch for suspected renal colic: An effective technique for radiation dose reduction?

Purpose: To determine the accuracy and utility of unenhanced helical CT for suspected renal colic, using a pitch of either 2.5 or 3.0, Methods: 59 consecutive patients underwent unenhanced helical CT. 5 mm cont iguous images were obtained at a kVP of 120 and an mA of 260. Thirty-four p atients were imaged at a pitch of 2.5, and 25 patients were imaged at a pit ch of 3.0. Two radiologists, an attending treader 1), and a second-year res ident treader 2), independently and retrospectively reviewed the CT images, blinded to the clinical outcome. The presence or absence of a ureteral sto ne was recorded and image quality was graded. A third radiologist determine d accuracy for each reader. Average entrance exposure was estimated using a CT phantom at a variety of pitches. Results: Overall sensitivity, specificity: and accuracy for reader 1 were 9 1, 96, and 93%. For reader 2, they were 86, 93, and 90%. There was no signi ficant difference in accuracy using a pitch of 3.0 compared with 2.5 for ei ther reader. Readers 1 and 2 rated image quality at 2.5 pitch as excellent for 88 and 76% of scans, respectively; at 3.0 pitch the scans were rated by both readers as excellent for 40% and acceptable for 60%. Average entrance exposures were estimated at 461, 553, and 913 mR at pitches of 3.0, 2.5, a nd 1.5, Conclusion: Increasing the pitch on unenhanced helical CT for suspected ren al colic to 2.5 or 3.0 appears to be an effective method of reducing radiat ion dose. Although accuracy of the technique did not significantly change u sing a pitch of 3.0 in one group of patients, compared with a pitch of 2.5 in another group of patients, image quality did decrease.