MRI in mice that received either no cell transplant or magnetically labeled Sca1⁺ bone marrow cells at day 5 of tumor growth and were imaged 7 days later to investigate detection of labeled cells by several MRI techniques. (A) Mouse with 12-day tumor and no cell transplant on 2D spin echo and gradient echo (GE) images. (B) Mouse with 12-day tumor and 7 days from labeled cell transplant on spin echo, GE, and fast GE images. Hypointense areas in the tumor were detectable with all sequences in the labeled mouse. The fast gradient echo had the greatest sensitivity to iron and the least anatomic definition.