A better target-to-background activity ratio using a large-sized colloid compared to a nano-sized colloid for scintigraphy of the peripheral bone marrow. A study in mice and humans.

Small-sized radiocolloids with a diameter less than 100 nm (nanocolloids), reduce the confounding liver and spleen uptake compared to large-sized colloids at bone marrow scintigraphy. Consequently, nanocolloids are today generally used for this purpose. Such colloids, though, seem to produce considerable background activity, especially from the large vessels and the urinary tract. This has been studied in mice and humans using a nanocolloid and a large-sized colloid, both composed of human albumin. In mice, the findings confirm a lower relative and absolute uptake of the nanocolloid in the liver and spleen compared to the large-sized colloid, whereas the bone marrow activity relative to the activity of kidneys, heart, lungs, intestines and peripheral blood is higher for the large-sized colloid than for the nanocolloid. The latter was confirmed in humans who were examined by single photon emission computed tomography corrected for attenuation and scattering of photons. It is concluded that a large-sized colloid should be used for spot examination of a specific marrow region outside the liver and spleen, while a nanocolloid must be used when examining structures close to the liver and spleen as well as for depiction of the entire bone marrow.