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.
Nonenhanced abdominal computed tomography (CT) is considered the reference standard imaging technique in patients with suspected or known urinary stone disease . This is due to the superiority of nonenhanced abdominal CT compared to abdominal plain film radiography in regard to the sensitivity and specificity for the diagnosis of urinary stones . The downside of abdominal CT compared to plain film radiography, however, is the higher radiation dose of the technique. This has triggered various strategies for radiation dose reduction, such as noise reduction filters or low tube current scanning .
By doing so, some studies could demonstrate that nonenhanced low radiation dose abdominal CT may be an appropriate imaging tool for the diagnosis of urinary stone disease . However, other studies reported limited diagnostic capabilities of low-radiation-dose abdominal CT, mainly due to increased noise leading to reduced confidence . It is likely that these concerns have precluded the wide application of low-radiation-dose abdominal CT protocols as the standard initial imaging test in patients with urinary stone disease .
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Materials and methods
Patient Population
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CT Protocol
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CT Data Reconstruction
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CT Data Analysis
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Quantitative analysis
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Image noise
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Image quality
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Urinary stone disease
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Statistical Analysis
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Results
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Table 1
Patient Demographics
Total No. of patients 50 Female 12 Age (years) 50.3 ± 17.4 (18–88) Height (m) 1.7 ± 0.1 (1.55–1.87) Weight (kg) 80.4 ± 13.6 (48–98) Body mass index (kg/m 2 ) 26.8 ± 4.8 (18.8–34.7)
Values are mean ± standard deviation with range in parentheses.
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Quantitative Assessment
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![Figure 2, Comparison of computed tomography attenuation values (in Hounsfield units [HU]) in datasets reconstructed with filtered back-projection (FBP) and iterative reconstruction (IR) at strength levels from 1 to 5 showing similar values in the urinary bladder (a) ( P = .208, reader 1; P = .123, reader 2) and subcutaneous fat (b) ( P = .568, reader 1; P = .834, reader 2). (c) Noise was significantly reduced with IR ( P < .001). In FBP images, noise was lower in patients with a body mass index (BMI) <30 kg/m 2 compared to patients with a BMI ≥30 kg/m 2 ( P < .001), while there was no such difference in patients with IR ( P = .806).](https://storage.googleapis.com/dl.dentistrykey.com/clinical/IterativeReconstructionsversusFilteredBackProjectionforUrinaryStoneDetectioninLowDoseCT/1_1s20S1076633213003899.jpg)
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Image Noise
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Image Quality
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Table 2
Image Quality and Image Quality–Reducing Factors Among Datasets Reconstructed with Filtered Back-Projection (FBP) and Iterative Reconstruction (IR)
FBP IR_P_ -Value Image quality Kidney Median (range) 3 (2–4) 3 (2–4) .001 Mean 3.24 2.96 Ureter Median (range) 3 (3–5) 3 (2–5) .001 Mean 3.40 3.18 Urinary bladder Median (range) 3 (3–5) 3 (3–4) .763 Mean 3.40 3.38 Image quality–reducing factors Obesity Median (range) 3 (2–4) 3 (2–4) <.05 Mean 2.94 2.76
Image quality: score 1, excellent; score 2, above average; score 3, acceptable; score 4, substandard; score 5, not acceptable. Image quality-reducing factors: Score 1, no artifacts; score 2, minor artifacts not affecting the visualization of any structure; score 3, major artifacts affecting the visualization of any structure; score 4, affecting diagnostic information.
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Urinary Stone Disease
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Discussion
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