RT Journal Article SR Electronic T1 99mTc-Labeled Superparamagnetic Iron Oxide Nanoparticles for Multimodality SPECT/MRI of Sentinel Lymph Nodes JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 459 OP 463 DO 10.2967/jnumed.111.092437 VO 53 IS 3 A1 Renata Madru A1 Pontus Kjellman A1 Fredrik Olsson A1 Karin Wingårdh A1 Christian Ingvar A1 Freddy Ståhlberg A1 Johan Olsrud A1 Jimmy Lätt A1 Sarah Fredriksson A1 Linda Knutsson A1 Sven-Erik Strand YR 2012 UL http://jnm.snmjournals.org/content/53/3/459.abstract AB The purpose of this study was to develop multimodality SPECT/MRI contrast agents for sentinel lymph node (SLN) mapping in vivo. Methods: Nanoparticles with a solid iron oxide core and a polyethylene glycol coating were labeled with 99mTc. The labeling efficiency was determined with instant thin-layer chromatography and magnetic separation. The stability of the radiolabeled superparamagnetic iron oxide nanoparticles (SPIONs) was verified in both sterile water and human serum at room temperature 6 and 24 h after labeling. Five Wistar rats were injected subcutaneously in the right hind paw with 99mTc-SPIONs (25–50 MBq, ∼0.2 mg of Fe) and sacrificed 4 h after injection. Two animals were imaged with SPECT/MRI. All 5 rats were dissected; the lymph nodes, liver, kidneys, spleen, and hind paw containing the injection site were removed and weighed; and activity in the samples was measured. The microdistribution within the lymph nodes was studied with digital autoradiography. Results: The efficiency of labeling of the SPIONs was 99% 6 h after labeling in both water and human serum. The labeling yield was 98% in water and 97% in human serum 24 h after labeling. The SLN could be identified in vivo with SPECT/MRI. The accumulation of 99mTc-SPIONs (as the percentage injected dose/g [%ID/g]) in the SLN was 100 %ID/g, whereas in the liver and spleen it was less than 2 %ID/g. Digital autoradiography images revealed a nonhomogeneous distribution of 99mTc-SPIONs within the lymph nodes; nanoparticles were found in the cortical, subcapsular, and medullary sinuses. Conclusion: This study revealed the feasibility of labeling SPIONs with 99mTc. The accumulation of 99mTc-SPIONs in lymph nodes after subcutaneous injection in animals, verified by SPECT/MRI, is encouraging for applications in breast cancer and malignant melanoma.