Absolute Temperature Mapping Using Chiral Terbium Parashift Complexes for MRI Thermometry

A noninvasive imaging approach for absolute temperature mapping has been demonstrated using Parashift molecular imaging probes for MRI. Temperature readout is achieved by exploiting the chemical shift difference between the CH₂ SAP and CH₃ TSAP resonances of two nonexchanging (SAP and TSAP) isomers of a single chiral lanthanide complex, without the need for external calibration. Variable-temperature NMR analyses of [LnL]^- complexesderived from S-tetraethyl cyclenidentified the CH₂ SAP and CH₃ TSAP resonances as optimal reporters for Parashift spectral imaging, owing to their large hyperfine shifts and narrow spectral line widths. Temperature coefficients as high as 0.46 ppm K^-1 were observed for individual resonances of the square antiprismatic (SAP) isomer of [DyL]^-, while normalized coefficients (temperature shift per unit line width) reached 1.7 K^-1 for [TmL]^-. Among the complexes studied, [TbL]^- emerged as the most suitable for temperature imaging, considering the overall temperature sensitivity of the chemical shift difference. In phantom imaging experiments at 9.4 T (preclinical field) temperature variations across phantom tubes were successfully mapped with a resolution of 0.1 K.