Coronal slice microSPECT/CT [(a) and (b)] or microPET/CT images [(c) and (d)]. Athymic mice with s.c. MDA-MB-361 tumor xenografts (solid arrows) with intermediate HER2 density (5.1 × 105 receptors/cell) at 24 h p.i. of 70 MBq (10 μg) of 111In-DOTA-trastuzumab Fab or 22 MBq (10 μg) of 64Cu-DOTA-trastuzumab Fab, respectively. (a) and (c) Mouse with 5 to 10 mm diameter tumor. (b) and (d) Mouse with 10 to 15 mm diameter tumor. Image acquisition time was 85 to 120 min for microSPECT and 20 min for microPET. Anaesthesia was induced and maintained by inhalation of 2% isoflurane in oxygen. Images were adjusted to approximately equal intensity within each modality.