Data processing

Methodological differences between centres A and B were identified for the framing of dynamic PET data and data reconstruction (Table ​(Table1).1). Therefore, the PET data were processed in two different ways according to the individual approach established in centre A and centre B. For centre A, the dynamic data set was framed into time intervals of 6 × 10 s, 4 × 30 s, 1 × 2 min, 3 × 5 min and 2 × 10 min and the data were reconstructed by filtered back projection (FBP) using a 5-mm Hann filter. For centre B, the framing was 5 × 1 min, 5 × 3 min and 4 × 5 min followed by iterative reconstruction (ITR) (ordered-subset expectation maximization, 6 iterations, 16 subsets). ¹⁸F-FET uptake in the tissue was expressed as standardized uptake value (SUV) by dividing the radioactivity (kBq/ml) in the tissue by the radioactivity injected per gram of body weight. An example of a brain tumour for the time interval from 20 to 40 min after injection for the different data processing in centres A and B is shown in Fig. ​Fig.1.1. Corresponding evaluation of a Jaszczak phantom with the two methods is shown in Fig. ​Fig.22.

Comparison of methodology centre A and centre B

Glioblastoma in the right parietal lobe. Contrast-enhanced T1-weighted MRI (a) shows a ring-enhancing lesion. FET PET image based on the method of centre A (b) shows lower noise but the image based on the method of centre B (c) shows a sharper demarcation of the metabolically active tumour parts

Jasczack phantom (a) with tubes of different size filled with radioactivity and reconstructed according to the procedure in centre A (b, blue profile line) and centre B (c, red profile line). The method of centre A shows about 20% lower maximum values in the tubes with a diameter of 9.3 mm which is mainly due to reconstruction by filtered back projection in centre A instead of iterative reconstruction (centre B)