MRI Thermometry Based on PARACEST Agents

A novel magnetic resonance imaging (MRI) thermometry technique is demonstrated in vitro based upon the use of a PARACEST (PARAmagnetic Chemical Exchange Saturation Transfer) agent. This new method takes advantage of the high concentration of bulk water (the readout signal for imaging) and the hyperfine frequency shift properties of PARACEST agents. For two prototypes, Dy(1)3+ and Eu(2)-, the chemical shifts (δ, in ppm) of the Ln3+-bound water molecules are linearly dependent on temperature (T, in °C) over the range of 20−50 °C (δ = 6.9 × T − 944.7 and δ = −0.4 × T + 64.6, respectively). This offers the exciting possibility of improving the temperature dependencies ∼690- and ∼40-fold over the most widely used water PRF thermometry (Proton Resonance Frequency: −0.01 ppm/°C).