In vivo xenograft imaging of mice using a nano-single-photon emission computed tomography/X-ray computed tomography (nano-SPECT-CT) scanner. Scans were performed at 3, 10, 17, and 24 days after intravenous injection of human sodium iodine symporter (hNIS)-labeled mesenchymal stem cells (MSCs) and human induced pluripotent stem cells (hiPSCs). An intravenous dose of 18.5 MBq of 99mTc was administered before the acquisitions. The same animals are represented over the entire period. hNIS expression is indicated by red crosses in transverse sections. Scans were performed after intravenous injection of hNIS-labeled MSCs or hiPSCs. (A) Images at days 3, 10, 17 and 24; (B) images at day 3; (C): 99mTc tumor/muscle uptake ratio by hNIS-labeled MSCs or hiPSCs from days 3 to 24.