Image-derived input function for assessment of 18F-FDG uptake by the inflamed lung.

UNLABELLED: Pulmonary uptake of (18)F-FDG assessed with PET has been used to quantify the metabolic activity of inflammatory cells in the lung. This assessment involves modeling of tracer kinetics and knowledge of a time-activity curve in pulmonary artery plasma as an input function, usually acquired by manual blood sampling. This paper presents and validates a method to accurately derive an input function from a blood-pool region of interest (ROI) defined in dynamic PET images. METHODS: The method is based on a 2-parameter model describing the activity of blood and that from spillover into the time-activity curve for the ROI. The model parameters are determined using an iterative algorithm, with 2 blood samples used to calibrate the raw PET-derived activity data. We validated both the 2-parameter model and the method to derive a quantitative input function from ROIs defined for the cavities of the right and left heart and for the descending aorta by comparing them against the time-activity curve obtained by manual blood sampling from the pulmonary artery in lungs with acute inflammation. RESULTS: The model accurately described the time-activity curve from sampled blood. The 2-sample calibration method provided an efficient algorithm to derive input functions that were virtually identical to those sampled manually, including the fast kinetics of the early phase. The (18)F-FDG uptake rates in acutely injured lungs obtained using this method correlated well with those obtained exclusively using manual blood sampling (R(2) > 0.993). Within some bounds, the model was found quite insensitive to the timing of calibration blood samples or the exact definition of the blood-pool ROIs. CONCLUSION: Using 2 mixed venous blood samples, the method accurately assesses the entire time course of the pulmonary (18)F-FDG input function and does not require the precise geometry of a specific blood-pool ROI or a population-based input function. This method may substantially facilitate studies involving modeling of pulmonary (18)F-FDG in patients with viral or bacterial infections, pulmonary fibrosis, and chronic obstructive pulmonary disease.

Improved assessment of functional resectability in repeated hepatectomy by computer-assisted operation planning.

Assessment of the post-resectional functioning liver parenchyma is one of the most important issues in operation planning of liver resections. However, preoperative assessment of the future liver remnant's vascularization is in particular difficult in repeated hepatectomy because of the often altered intrahepatic vascular system after prior vascular dissection. Therefore, in these resections preoperative calculation of the remaining liver parenchyma with unimpaired vascular function is uncertain and imprecise. Based on the case of a 62-year-old woman with a recurrent colorectal liver metastasis in segments VII and VIII after prior left-lateral liver resection (segments II/III) we describe the potential use of computer-assisted operation planning for assessment of functional resectability in repeated hepatectomy.