Reducing the radiation dose for low-dose CT of the paranasal sinuses using iterative reconstruction: feasibility and image quality.

Purpose: To evaluate image quality of dose-reduced CT of the paranasal-sinus using an iterative reconstruction technique.
Methods: In this study 80 patients (mean age: 46.9±18 years) underwent CT of the paranasalsinus (Siemens Definition, Forchheim, Germany), with either standard settings (A: 120 kV, 60 mAs) reconstructed with conventional filtered back projection (FBP) or with tube current-time product lowering of 20%, 40% and 60% (B: 48 mAs, C: 36 mAs and D: 24 mAs) using iterative reconstruction (n=20 each). Subjective image quality was independently assessed by four blinded observers using a semiquantitative five-point grading scale (1=poor, 5=excellent). Effective dose was calculated from the dose-length product. Mann-Whitney-U-test was used for statistical analysis.
Results: Mean effective dose was 0.28±0.03 mSv(A), 0.23±0.02 mSv(B), 0.17±0.02 mSv(C) and 0.11±0.01 mSv(D) resulting in a maximum dose reduction of 60% with iterative reconstruction technique as compared to the standard low-dose CT. Best image quality was observed at 48 mAs (mean 4.8; p<0.05), whereas standard low-dose CT (A) and maximum dose reduced scans (D) showed no significant difference in subjective image quality (mean 4.37 (A) and 4.31 (B); p=0.72). Interobserver agreement was excellent (κ values 0.79-0.93).
Conclusion: As compared to filtered back projection, the iterative reconstruction technique allows for significant dose reduction of up to 60% for paranasal-sinus CT without impairing the diagnostic image quality.
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