Figures & data
Notes: (A) Exchangeable protons are saturated with a radiofrequency pulse. (B) Saturated protons are exchanged between the CEST agents and the bulk water. (C) The bulk water loses part of its net MR signal due to the exchange of saturated protons. (D) Water signals are collected with a range of radiofrequencies. Direct saturation of bulk water is set as the reference (0 ppm). (E) Connecting the signals of bulk water generates a Z-spectrum.
Abbreviation: MR, magnetic resonance.
Abbreviation: MR, magnetic resonance.
Notes: Agents have been designed that detect (A) caspase-3, (B) urokinase plasminogen activator, (C) cathepsin D, (D) transglutaminase, (E) β-galactosidase, and (F) esterase.
Abbreviation: ParaCEST, paramagnetic chemical exchange saturation transfer.
Abbreviation: ParaCEST, paramagnetic chemical exchange saturation transfer.
Notes: (A) Deamination of cytosine by deaminase enzyme. Other agents can detect (B and C) DNA, (D) glucose, (E) lactate, (F) methyl phosphate, and (G) nitric oxide.
Abbreviation: CEST, chemical exchange saturation transfer.
Abbreviation: CEST, chemical exchange saturation transfer.
Notes: Agents have been designed that detect (A) Zn2+, (B) Ca2+, and (C–E) redox conditions. (F–H) Other agents can measure temperature.
Abbreviation: ParaCEST, paramagnetic chemical exchange saturation transfer.
Abbreviation: ParaCEST, paramagnetic chemical exchange saturation transfer.
Notes: (A) T2 is measured by rotating the net magnetization into the transverse plane by an excitation pulse, then components of the net magnetization evolve to defocus, and then a 180° pulse causes these components to refocus. (B) The chemical exchange of protons with different phases causes cancelation of net magnetization, creating a shorter T2 relaxation time constant for the bulk water due to T2ex.
Abbreviation: T2ex, T2 exchange.
Abbreviation: T2ex, T2 exchange.
Notes: (A) An increase in temperature increases relaxivities on the rising side of Swift–Connick plot (shown by the white arrow), while an increase in temperature decreases relaxivities on the falling side of the Swift–Connick plot (shown by the gray arrow). (B) Triangles show relaxivities due to exchange of a proton with the same chemical shift and chemical exchange rate in three different magnetic fields. The chemical structures of (C) Dy-DOTAM-(Gly)x complexes, (D) Eu(III) complexes, and (E) Tm-DO3A-oAA show similar features that lead to T2ex relaxation.
Abbreviation: T2ex, T2 exchange.
Abbreviation: T2ex, T2 exchange.