Detectability of Brain Metastases by Using Frequency-Selective Nonlinear Blending in Contrast-Enhanced Computed Tomography

Interindividual Comparison of Frequency-Selective Nonlinear Blending to Conventional CT for Detection of Focal Liver Lesions Using MRI as the Reference Standard

Background: Diagnosing liver lesions is challenging. CT is used for primary diagnosis; however, its contrast resolution is limited. Investigating methods for better detection of liver lesions is important. Objective: To evaluate the effect of frequency-selective nonlinear blending (NLB) on the detectability of liver lesions on CT. Methods: Retrospective search yielded 109 patients with malignant and benign liver lesions (n = 356; 191 principally diagnosed, 165 incidental findings) underwent contrast-enhanced CT (CECT) in portal venous phase and liver MRI between January 2012 and December 2017. Nonlinear blending (NLB) was applied to CECTs, and three readers rated image quality (5-point Likert scale) in blinded, independent, and randomized fashion. Focal lesions (n = 356) were evaluated for lesion identification and categorization to assess sensitivity. For 191 lesions (primary diagnosis) two readers evaluated CECT and NLB CT to compare size and subjective measurement accuracy. A fourth reader conducted ROI measurements for calculation of contrast-to-noise ratio (CNR), and a fifth reader reviewed MRI as standard of reference. Statistics included interobserver agreement, quantitative comparisons of CNR, lesion size, and subjective image analyses of image quality and sensitivity of detecting liver lesions. Results: Three readers rated image quality of NLB CT higher than for CECT (NLB CT, 4 [10% and 90% percentile: 4, 5]; CECT, 2 [1, 3]; p < .001). CECT showed good interreader agreement (interclass coefficient [ICC], 0.81 [95% CI, 0.76¬-0.85]); NLB CT also (ICC, 0.75 [95% CI, 0.69-0.79]). Mean CNR of liver lesions was increased using NLB (CECT, 4.18 [range, 1.67-9.06]; NLB CT, 12.49 [range, 6.18-23.39]; p < .001). Bland-Altman analysis of lesion size showed reduced underestimation from 2.5 mm (SD, 9.2 [95% CI, 1.2-3.9]) in CECT to 0.1 mm (SD, 3.9 [95% CI, -0.68 to 0.46) for NLB CT (concordance correlation coefficient, 0.99). Sensitivity for detecting liver lesions was increased to 86% for NLB CT (CECT, 76%). Conclusion: Frequency-selective NLB of CECT allows increased image quality and CNR, more precise size measurement, and higher sensitivity for detecting liver lesions. Clinical Impact: NLB CT improves liver lesion detection and increases the accuracy of lesion size measurement, which is important when considering local ablation or liver transplant.