Microwave-Pumped Electric-Dipole Resonance Absorption for Noninvasive Functional Imaging

Traditional microwave-induced thermoacoustic imaging is regarded as a structural imaging method that can recover the water content of biological tissues. Here, an alternative noninvasive functional imaging system based on microwave-pumped electric-dipole resonance absorption is reported. On the basis of the resonance principle, microwave radiation of a specific frequency can be used to selectively excite the polar molecules of interest. The microwave energy deposited creates an ultrasound disturbance through thermoelastic expansion. By detection of the ultrasound field, in vivo imaging of the target polar molecules with ultrasound resolution at the submillimeter level is realized. We show the thermoacoustic signal intensity of biological polar molecules with different electric dipole moments. We perform large-field-of-view thermoacoustic imaging of arterial and venous blood vessels in vivo, and find the thermoacoustic signal intensity increases synchronously on injection of exogenous polar molecules into the venous blood vessels of a rabbit ear. We also demonstrate the functional imaging capability of the thermoacoustic system in a study of the sensitivity of microwave absorption to changes in the concentration of polar molecules in the blood vessels of a rabbit ear. This imaging technique may find application in the detection of abnormal concentrations of biological polar molecules with large electric-dipole moments.