Evaluation of image quality and dose in renal colic: comparison of different spiral-CT protocols

The aim of this study was to test different technical spiral-CT parameters to obtain optimal image quality with reduced X-ray dose. Images were acquir ed with a spiral-CT system Philips Tomoscan AVE1, using 250 mA, 120 kV, and 1-s rotational time. Three protocols were tested: protocol A with 5-mm thi ckness, pitch 1.6, slice reconstruction every 2.5 mm; protocol B with 3-mm thickness, pitch 1.6, slice reconstruction every 1.5 mm: and protocol C wit h 3-mm thickness, pitch 2, slice reconstruction every 1.5 mm. Two phantoms were employed to evaluate the image quality. Axial images were acquired, th en sagittal and coronal images were reconstructed. Finally, the absorbed X- ray dose for each protocol was measured. Regarding image quality, 5-mm-thic k images (protocol A) showed greater spatial resolution and lower noise com pared with 3-mm-thick images (protocols B and C) on the axial plane; 3-mm r econstructed sagittal and coronal images (protocols B and C) showed an impr oved image quality compared with 5-mm reformatted images (protocol A). Conc erning X-ray dose, the mean dose was: protocol A 19.6 +/- 0.8 mGy; protocol B 14.4 +/- 0.6 mGy; protocol C 12.5 +/- 1.0 mGy. Our study supports the us e of thin slices (3 mm) combined with pitch of 1.6 or 2 in renal colic for X-ray dose reduction to the patient and good image quality.