CD34 and injury: Zhu et al. (2006) injected autologous NPCs labeled with SPIOs into patients with traumatic brain injury, and migration of the cells toward the lesion was visible, even with a 3.0T system. In a study of the spine transplanted CD34+ cells labeled with large particles were visible with a 1.0T magnet (Callera and de Melo, 2007). High-field human MRI systems (7.0T) are becoming more common but still present technical challenges related to coil design and energy deposition; however, their use might increase the feasibility and significance of NPC tracking in humans (van der Kolk et al., 2013).