Energy-Harvesting Coil for Circularly Polarized Fields in Magnetic Resonance Imaging

Stealth RF energy harvesting in MRI using selective shielding

“…This ensures that even with worst-case orientation, at least one linear B 1 polarization is fully captured. 9 With optimal orientation (shield plane normal to z), the quadrature pair captures the circularly polarized field fully. Its efficiency thus varies between 0.5 and 1.0 rather than between 0 and 0.5 for a single coil.…”

“…10 However, tapping into the excitation RF field, also referred to as B 1 , alters that field and thus its effect on spin dynamics. 7,9,10 B 1 perturbations near a harvester alter flip angles, causing artefacts in resulting images. Beyond artefacts, change in B 1 also alters local RF power deposition in the tissue (SAR), which is, again, a safety concern.…”

“…As an alternative, it has been suggested to harvest energy from the powerful radiofrequency (RF) pulses involved in MRI in the first place. [7][8][9][10] Equally wireless, this completely parasitic approach avoids the need for additional power transmission and the hardware involved. It has been reported to harvest average power in the order of 100 mW from standard medical imaging sequences, using receiver form factors of just a few centimeters.…”

“…It has been reported to harvest average power in the order of 100 mW from standard medical imaging sequences, using receiver form factors of just a few centimeters 10 . However, tapping into the excitation RF field, also referred to as $$$ {\mathrm{B}}_1 $$$, alters that field and thus its effect on spin dynamics 7,9,10 . $$$ {\mathrm{B}}_1 $$$ perturbations near a harvester alter flip angles, causing artefacts in resulting images.…”

“…As an alternative, it has been suggested to harvest energy from the powerful radiofrequency (RF) pulses involved in MRI in the first place 7–10 . Equally wireless, this completely parasitic approach avoids the need for additional power transmission and the hardware involved.…”