Fig. 3

Graphs reported to centers of the involved scanners as example of the differences between the scanner vendors. Linear fit of measured and reference activity data according to A _m,0 = α _cal + β _cal · A _r. Top row: scanner number 5 (vendor A; α _cal = 13 kBq and β _cal = 0.947), bottom row: scanner number 15 (vendor B; α _cal = 5.5 kBq and β _cal = 0.901). Note that the graphs on the right side (3a and d) are the same as the corresponding ones on the left side (3a and c), apart from the scales of the axes. Furthermore, the larger offset α _cal of scanner 5 compared to that of scanner 15 can be foreseen from the larger background signal, shown in a and c, respectively