Emergency unenhanced multi-slice computed tomography in suspected urinary calculi—with dose reduction method (care dose 4D)

Abstract

Objectives: To assess urinary calculi and the secondary signs of obstruction, in patients referred from the accident and emergency department, by unenhanced computed tomography examination and to review the radiation dose the patients received with the use of automatic dose modulation technique, care dose 4D. Material and methods: Medical records of unenhanced multi-slice computed tomography (MSCT) examinations for 114 patients referred to the emergency department for analysis of suspected urinary calculi were reviewed retrospectively. Their treatment involved automatic tube current modulation, a dose reduction method (care dose 4D), in Hamad General Hospital. The cases were analyzed for the presence of stones, size, site, density and the secondary signs of obstruction, namely hydronephrosis, hydroureter, perinephric fat stranding, peri-ureteric fat stranding and renal enlargement. A search for alternate diagnosis was made if no stone was found. The final diagnosis was noted from the discharge summary in medical records. The radiation dose, Computed Tomographic Dose Index volume (CTDI) and Dose Length Product (DLP) in each patient was recorded from patient protocol. Results: Of 114 patients referred to CT scan for suspected urinary calculi, between March and June 2008, urinary calculi were noted in 75.4 %. An alternate diagnosis was offered to 5.3 % and a diagnosis of normal was given to 19.3 %. The size of stones detected varied from 2mm-35mm. Density of stones varied from 110-1250 hounsfield units (HU). Solitary stones were seen in 54.4 % of cases observed and multiple stones in 22 %. Renal stones were observed in 6.1 % of cases, urteric stones in 26.3%, vesico-uretric junction stones in 18.4%, multiple sites in 23.7%. Hydronephrosis was seen in 68% of cases, hydroureter in 63%, perinephric fat stranding in 51%, periureteral fat stranding in 34%, ureteric rim sign in 28% and renomegaly in 24%. Time interval between onset of symptoms to imaging varied from 4 to 12 hours. The radiation dose, CTDI, ranged from 6.5-15.8 mGy and DLP from 257 to 918 mGy/cm with the use of automatic tube current modulation, care dose 4D. Final diagnosis and MSCT diagnosis were in concordance in 86 (75% of) patients of renal calculi and alternate diagnosis in 6 (5.3%) of patients and normal in rest of the patients. Conclusion: In clinically-suspected urinary calculi, unenhanced MSCT of abdomen with the use of care dose 4D, an automatic tube current modulation technique, is a fast and reliable investigation in an emergency setting to detect stones and secondary signs of obstruction. It offers alternate diagnosis with substantial reduction in radiation dose—both the computed tomography dose index (CTDI) and dose length product (DLP).