In vivo imaging of A431/CCK2R tumours and probe kinetics of QE and bivQ. (a) The probes QE and bivQ clearly depict A431/CCK2R but not A431/WT subcutaneous xenografts in vivo. (b) Tumours could be detected up to 72 h after probe injection. (c) Semiquantitative fluorescence signal intensities from 0 to 8 h p.i. for QE, bivQ and DY-754 in A431/CCK2R tumours, A431/WT tumours and normal tissue. Means and standard deviations of n = 5 animals. All images were obtained with a NIRF small-animal scanner (excitation 615 to 665 nm, emission >750 nm), thresholded for their fluorescence intensity (blue, lowest FI; red, highest FI) and overlaid with their respective white light image. Plus sign, A431/CCK2R tumour; minus sign, A431/WT tumour.