Diagnostic Performance in Low- and High-Contrast Tasks of an Image-Based Denoising Algorithm Applied to Radiation Dose-Reduced Multiphase Abdominal CT Examinations.

Background: Anatomic redundancy between phases can be used to achieve denoising of multiphase CT examinations. A limitation of iterative reconstruction (IR) techniques is that they generally require use of CT projection data. A frequency-split multiband-filtration algorithm applies denoising to the multiphase CT images themselves. This method does not require knowledge of acquisition process or integration into the scanner's reconstruction system and can be implemented as a supplement to commercially available IR algorithms. Objective: To compare radiologists' performance for low-contrast and high-contrast diagnostic tasks evaluated on multiphase abdominal CT between routine-dose images and radiation dose-reduced images processed by a frequency-split multiband-filtration denoising algorithm. Methods: This retrospective single-center study included 47 patients who underwent multiphase contrast-enhanced CT for known or suspected liver metastases (low-contrast task) and 45 patients who underwent multiphase contrast-enhanced CT for pancreatic cancer staging (high-contrast task). Radiation dose-reduced images corresponding to ≥50% dose reduction were created using a validated noise insertion technique and then underwent denoising using the frequency-split multiband-filtration algorithm. Images were independently evaluated in multiple sessions by different groups of abdominal radiologists for each task (low-contrast arm: 3 readers; high-contrast arm: 4 readers). Noninferiority of denoised dose-reduced images to routine-dose images was assessed using the jackknife alternative free-response ROC (JAFROC) figure-of-merit (FOM; limit of noninferiority: -0.10) for liver metastases detection, and using Cohen's kappa statistic and reader confidence scores (100-point scale) for pancreatic cancer vascular invasion. Results: JAFROC FOM for denoised dose-reduced images for liver metastases detection was 0.644 (95% CI: 0.510- 0.778) and for routine-dose images was 0.668 (95% CI: 0.543-0.792; estimated difference, -0.024 [95%CI: 0.084- 0.037]). Intra-observer agreement for pancreatic cancer vascular invasion was substantial to near-perfect when comparing the two image sets (ĸ=0.53-1.00); 95% CI's of all differences in confidence scores between image sets contained zero. Conclusions: Multiphase contrast-enhanced abdominal CT images with ≥50% radiation dose reduction that undergo denoising by a frequency-split multiband-filtration algorithm yield similar performance to routine-dose images for liver metastases detection and pancreatic cancer vascular staging. Clinical Impact: The image-based denoising algorithm facilitates radiation dose reduction of multiphase examinations for both low- and high-contrast diagnostic tasks without requiring manufacturer-specific hardware or software.