Iterative reconstructions versus filtered back-projection for urinary stone detection in low-dose CT

Abstract

RATIONALE AND OBJECTIVES: To evaluate prospectively, in patients with suspected or known urinary stone disease, the image quality and diagnostic confidence of nonenhanced abdominal low-dose computed tomography (CT) with iterative reconstruction (IR) compared to filtered back-projection (FBP). MATERIALS AND METHODS: Fifty consecutive patients with suspected (n = 33) or known (n = 17) urinary stone disease underwent nonenhanced abdominal low-dose CT (120 kVp, 30 effective mAs, 1.6 ± 0.5 mSv). Reconstructions were performed with sinogram-affirmed IR and with FBP. Attenuation (in Hounsfield units) was measured in subcutaneous fat and urinary bladder; image noise was determined. Two readers assessed image quality, number and location of urinary calculi were recorded, and diagnostic confidence was assessed. Statistical analyses included Mann-Whitney, Friedman's two-way, Wilcoxon signed rank, Pearson's, and Spearman's rank order correction tests. RESULTS: Attenuation of urinary bladder (P = .208, reader 1; P = .123, reader 2) and fat (P = .568, reader 1; P = .834, reader 2) was similar among FBP and IR datasets. Image noise was reduced in IR datasets by 40.1% (P < .001). IR improved image quality (P < .01), and obesity as factor impairing image quality was noted in FBP but not in IR images (P < .05). There was no significant difference in number of calculi in datasets reconstructed with IR and FBP (P = .102, reader 1; P = .059, reader 2). Diagnostic confidence regarding identification of urinary calculi improved with IR (P < .05, reader 1; P < .01, reader 2). CONCLUSION: IR improves image quality and confidence for diagnosing urinary stone disease in abdominal low-dose CT