Fig. 1.

A simple cylindrical detector inside the digestive tract can sensitively detect and simultaneously amplify MR signals emitted from deep-lying tissues. As shown in the picture (left) and the schematic diagram (right), the WAND has four diodes (BAS3005A, Infineon) equally distributed on its two end rings. It has a longitudinal resonance mode to receive pumping signal and a homogeneous transverse resonance mode to receive weak MR signals. The pumping loop (red) provides magnetic energy into the WAND through wireless coupling. Aided by multi-stage signal mixing, this pumping energy is converted to amplified MR signals that are re-emitted by the WAND for signal reception in the external coil (cyan). For better operation stability, the WAND has an additional ring placed in its cylindrical center to neutralize accumulated charge across end-ring diodes.