42 Part I Chapter 2 The activity to be administered to children should be a fraction of the adult activity calculated from body weight according to the factors given by the EANM/ SNMMI Paediatric Dosage Harmonization Working Group [9, 48]. In children, the recommendations of the EANM suggest a baseline activity of 35 MBq for 99mTcbisphosphonates (with aminimumof activity 40MBq) that should be adjusted based on the class of the radiopharmaceutical (class B) and the weight of child (table 1). Table 1. Summary of the applicable dose reference levels for bone scintigraphy. Children Adults Weight (kg) 3.5kg 10kg 20kg 30kg 40kg 50kg Activity (MBq) 40 95 170 240 310 375 300-740 Effective dose (mSv) 2.0 2.4 2.5 2.6 2.7 2.8 2.9 – 4.0 Protocol/image acquisition 1. Instrumentation Single or double head gamma-camera equipped with a low-energy, high-resolution parallel-hole collimator. A low energy general purpose collimator may alternatively be used for early dynamic and blood pool images. The energy window is centered on the photon energy peak of 99mTc (140 keV) and the window width is generally set at 15 or 20%. An asymmetric windowmay be used to improve resolution (e.g. 20% with 3% offset) but its use must be supported by a physicist and an appropriately tailored QA programme [49, 50]. 2. Planar and whole-body acquisitions For the vascular phase of the examination, the camera is positioned centered on the area of interest. The dynamic acquisition of 30 to 60 images with a duration of one to two seconds each and with a matrix of 64x64 or 128x128 pixels, is started simultaneously with the intravenous tracer injection. The early and late planar images are focused on one or more region(s). The early images are acquired between one and ten minutes after intravenous injection of 99mTc-labeled bisphosphonate, with an acquisition time of three to five minutes and a matrix size of 128x128 or 256x256. Delayed images are usually acquired two to five hours after injection of the radiolabeled bisphosphonate using a predefined duration (four to ten minutes) or number of counts, with a matrix size of 128x128 or 256x256. When using a predefined number of counts, at least 700,000 to 1,000,000 counts are required for scanning the thoraco-abdominal region, 250,000 to 400,000 counts for the large joints and skull, and 150,000 to 250,000 for the distal joints, depending on