Shortened Acquisition Protocols for the Quantitative Assessment of the 2-Tissue-Compartment Model Using Dynamic PET/CT ¹⁸F-FDG Studies

Abstract

18 F-FDG kinetics are quantified by a 2-tissue-compartment model. The routine use of dynamic PET is limited because of this modality's 1-h acquisition time. We evaluated shortened acquisition protocols up to 0-30 min regarding the accuracy for data analysis with the 2-tissue-compartment model. Methods: Full dynamic series for 0-60 min were analyzed using a 2-tissue-compartment model. The time-activity curves and the resulting parameters for the model were stored in a database. Shortened acquisition data were generated from the database using the following time intervals: 0-10, 0-16, 0-20, 0-25, and 0-30 min. Furthermore, the impact of adding a 60-min uptake value to the dynamic series was evaluated. The datasets were analyzed using dedicated software to predict the results of the full dynamic series. The software is based on a modified support vector machines (SVM) algorithm and predicts the compartment parameters of the full dynamic series. Results: The SVM-based software provides user-independent results and was accurate at predicting the compartment parameters of the full dynamic series. If a squared correlation coefficient of 0.8 (corresponding to 80% explained variance of the data) was used as a limit, a shortened acquisition of 0-16 min was accurate at predicting the 60-min 2-tissue-compartment parameters. If a limit of 0.9 (90% explained variance) was used, a dynamic series of at least 0-20 min together with the 60-min uptake values is required. Conclusion: Shortened acquisition protocols can be used to predict the parameters of the 2-tissue-compartment model. Either a dynamic PET series of 0-16 min or a combination of a dynamic PET/CT series of 0-20 min and a 60-min uptake value is accurate for analysis with a 2-tissue-compartment model. Thest andard radiopharmaceutical for PET examinations in oncologic patients is 18 F-FDG, a marker of tumor viability, which has been used with PET for many years now (1). The basic quantitative assessment of the tracer uptake is usually calculated using standardized uptake values (SUVs)-a method introduced by our group more than 19 y ago as a ratio of the local tracer concentration with the injected dose and body volume (2). SUV is a distribution value, which is equal to 1 for a homogeneous distribution of the tracer and exceeds 1 if retention occurs in the tissue. The SUV or, alternatively, the maximum SUV in a volume of interest (VOI) has been used in many publications and was found to be useful as an additional parameter for tumor diagnosis and assessment of therapeutic effects. However, the SUV reflects the global uptake of a tracer and is dependent not only on the specific retention of 18 F-FDG but also on the fractional blood volume and other parameters (3). More detailed information can be obtained by compartment modeling. Vriens et al. reviewed the methodologic aspects of tracer quantification in oncologic patients (4). The authors concluded that the SUV is helpful despite these limitations. Pharmacokinetic quantification is mainly confined to application in a re...

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