A conformable phased-array ultrasound patch for bladder volume monitoring

Ultrasound can be used to image soft tissues in vivo for the early diagnosis and monitoring of disease progression. However, conventional ultrasound probes are rigid, have a narrow field of view and are operator dependent. Conformable transducers have been proposed, but they lack efficient element localization and effective spatial resolution during mechanical deformations. Here we report a conformable ultrasound bladder patch that is based on multiple phased arrays embedded in a stretchable substrate and can provide mechanically robust, conformable and in vivo volumetric organ monitoring. The phased arrays use Sm/La-doped Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ ceramics as the piezoelectric material, which offers superior properties (d ₃₃ = 1,000 pC N⁻¹, ε _r = 7,500 and k ₃₃ = 0.77) than conventional piezoelectric ceramics. We use the conformable ultrasound patch in a pilot clinical study of bladder monitoring. Bladder volume estimation with the patch is comparable (relative errors of 3.2 ± 6.4% and 10.8 ± 8.2% with and without ultrasound gel, respectively) to that obtained using standard clinical ultrasound equipment, and not requiring manual translation or rotation by an operator.