Observer Variability in CT Perfusion Parameters in Primary and Metastatic Tumors in the Lung

PURPOSE: Evaluate observer variability in computed tomography perfusion measurements in lung tumors and assess the relative contributions of individual factors to overall variability. MATERIALS AND METHODS: Four observers independently delineated tumor and defined arterial input function region of interests (tumor region of interest and arterial input function region of interest) on each of 4 contiguous slice levels of computed tomography perfusion images (arterial input function level), in 12 computed tomography perfusion data sets containing lung tumors (>2.5 cm size), on 2 separate occasions. Computed tomography perfusion parameters (blood flow, blood volume, mean transit time, and permeability surface area product) for tumor volumes of interest were computed for all combinations of these factors, totaling up to 1024 combinations per patient. Overall, inter- and intraobserver variability were assessed by within-patient coefficient of variation, variance components analyses, and intraclass correlation. RESULTS: Overall observer within-patient coefficient of variations for tumor blood flow, blood volume, mean transit time, and permeability surface area product were 20.3%, 11.9%, 6.3%, and 31.7%, and intraclass correlations were 0.94, 0.91, 0.82, and 0.72, respectively. Interobserver tumor volume of interest and arterial input function level were the highest contributors to overall variance for blood flow, blood volume, and mean transit time. Overall intraobserver wCVs for blood flow, blood volume, mean transit time, and permeability surface area product (4.3%, 2.4%, 0.9%, and 3.1%) were smaller than interobserver within-patient coefficient of variations (9.5%, 5.6%, 1.6%, and 7.0%), respectively. CONCLUSION: The largest contributors to observer variability were interobserver tumor volume of interest and arterial input function level. Overall variability in computed tomography perfusion studies can potentially be minimized by using a single observer and a consistent level for arterial input function, which would be important considerations in longitudinal and multicenter studies. Methods to reliably define arterial input function and delineate tumor volumes would help to reduce variability in estimations of computed tomography perfusion parameter values.