. Author manuscript; available in PMC: 2014 Jan 9.

Published in final edited form as: Nat Rev Immunol. 2013 Sep 10;13(10):10.1038/nri3531. doi: 10.1038/nri3531

Table 2.

Overview of available in vivo MRI-based cell tracking techniques

Probe	MRI technique	Type of contrast	Minimum number of detectable cells	Quantification of cell number?	Clinical trial approval?
Gd³⁺ or Mn²⁺ labelling	T1-weighted ¹H MRI^*	Positive	~10³	No	No
SPIO labelling	T2-weighted ¹H MRI^‡	Negative	1	No	Yes (in the Netherlands, China, Switzerland, Czech Republic, Israel, Poland and United Kingdom)
PFC labelling	¹⁹F MRI	Hot spot (also known as tracer)	10³–10⁵	Yes	Yes (in USA)
Metal-binding reporter genes	T2-weighted ¹H MRI^‡	Negative	10⁴	No	No
CEST agents and reporter genes	¹H CEST MRI	Differential (can be colour encoded)	10⁴	No	No

CEST, chemical exchange saturation transfer; MRI, magnetic resonance imaging; PFC, perfluorocarbon; SPIO, superparamagnetic iron oxide.

T1 is the nuclear spin–lattice relaxation time.

^‡

T2 is the spin–spin relaxation time.