Figure 3. ¹⁸F-NaF signal detection depends on the sensitivity of the detection modality.

(a,b) If the carotid is sectioned first and incubated in ¹⁸F-NaF second, binding occurs to all macro- (closed arrowheads) and microcalcification (open arrowheads) surfaces. (c,d) However, if the carotid is incubated in ¹⁸F-NaF first and then sectioned, ¹⁸F-NaF is able to bind only to the surface level of macrocalcifications (closed arrowheads), while binding occurs to all microcalcifications (open arrowheads). (e,f) ¹⁸F-NaF binding solely to the surface level of macrocalcifications can also be observed in a μPET/μCT scan, if the macrocalcification size is larger than μPET resolution. (g,i) Microcalcifications that are detected with Alizarin Red histology cannot be seen in a μCT scan, due to insufficient sensitivity. (h,j) Yet, ¹⁸F-NaF μPET scan closely matches autoradiography signal and can detect microcalcifications. (k,l) μPET/μCT signal quantification by measuring the intensity of the ¹⁸F-NaF μPET signal and the μCT density measure along the same transects. (m) ¹⁸F-NaF binding can be observed throughout the three macrocalcification peaks due to macrocalcification size being smaller than μPET resolution (PET+/CT+, blue arrowheads); (n) Microcalcifications detected with ¹⁸F-NaF μPET and autoradiography (see h) as well as Alizarin Red histology (see g) but not μCT (PET+/CT−, magenta arrowheads); (o) If macrocalcifications are larger than μPET resolution, ¹⁸F-NaF binding solely around the surface level of macrocalcifications can be observed, similarly as in autoradiography (center green arrowhead PET−/CT+, blue arrowheads PET+/CT+). Scale bar, 1 mm.