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Introduction: We evaluated feasibility of submillisievert computed tomography (CT) examinations reconstructed with iterative reconstruction (IR) techniques in patients with urolithiasis.
Materials & Methods: 26 patients (mean age-38 yrs) with diagnosed urolithiasis, treated and on follow up underwent submillisievert dose unenhanced scan on 64 MDCT (Discovery CT750 HDCT, GE Healthcare) and 128 MDCT (Somatom Definition Flash, Siemens Health care). The scan protocol included 80 kV, auto mA 75-150 or Ref mA - 80, slice thickness 5mm for < 200 lbs and 100 kV, auto mA 75-150 or Ref mA - 80, slice thickness 5mm for > 200 lbs. Images were reconstructed using filtered back projection (FBP) and IR [ASIR(GE) 60% & 80% and IRIS (Siemens)]. All images were reviewed for image quality (scale 1-5), noise (scale 1-3), number and size of calculi and reader confidence on PACS work station. Comparison was made with the prior low dose FBP baseline CT scan.
Results: All 34 stones mean size (6.4mm, range 4-15 mm) was confidently diagnosed by two readers, yielding 100% sensitivity and accuracy. In 8 patients, stones had passed/resolved after treatment. In giving a differential diagnosis IR images were rated better than FBP (2.8 vs 1.7). The mean CTDI, DLP and mSv for submillisievert protocol was 1.2, 65.3 and 0.86 in comparison to 10.6, 363.4, and 5.4 for our baseline low dose exam with 82-88% dose reduction (p-0.0013).
Conclusions: Submillisievert unenhanced CT is a clinically feasible for diagnosis of urolithiasis with 82-88% dose reduction compared with standard non-contrast CT.