A hybrid transducer to evaluate stomach emptying by ultrasound and susceptometric measurements: an in vivo feasibility study

Gastric emptying reflects a diversity of important physiological functions. Alternating current biosusceptometry (ACB) is an inexpensive, radiation-free, and minimally invasive method to evaluate gastric emptying, but its response depends on the spatial distribution of the magnetized material and does not provide precise anatomical information. The hybrid transducer, which combines ACB and an ultrasound probe, is an alternative to improve susceptometry measurements, namely the spatial localization of the magnetized source. In this study, initial stomach emptying, in rats, was monitored with the aid of the hybrid transducer. Yogurt mixed with ferrite particles was injected into the rat´s stomach. The hybrid transducer was placed on the rat´s abdomen during experiments, and the susceptometry signal and magnetomotive ultrasound (MMUS) images were saved and postprocessed. MMUS highlighted the movement of magnetic particles due to magnetic force from ACB excitation coils, and showed the rat´s stomach location. In this feasibility study, we monitored the stomach emptying of 4 rats for 20 min. The mean relative ACB signal decayed by 4.6 ± 0.1%, and the mean relative area of MMUS images decreased by 4.5 ± 0.2%, after 20 min postingestion of the magnetic meal due to stomach emptying. In a second experiment, 3-D MMUS images from axial sequences were obtained by spatially translating the hybrid transducer, providing details of the stomach wall, which may enable minimally invasive detection of abnormalities. In conclusion, the MMUS image increased ACB spatial resolution and furnished additional anatomical information.