Guiding surgical needles

Doctors frequently use thin, hollow needles to apply anesthetic to individual nerves, to extract samples of amniotic fluid, and to perform other minimally invasive procedures. Knowing the precise needle-tip location is crucially important—and challenging. Ultrasound can help, but with the two-dimensional scans that are typically used, it can be unclear what part of the needle is in view, and the tip is often out of sight. And if the needle’s angle of insertion is steep, it will not be seen with ultrasound imaging. To address those limitations, Wenfeng Xia of University College London and his colleagues have installed a tiny fiber-optic ultrasound sensor with a Fabry–Pérot cavity into a surgical needle. The reflectance of the cavity is altered by impinging ultrasound waves, and it is measured continuously by a wavelength-tunable laser via the optical fiber in the needle’s cannula. During an ultrasound-guided procedure, transducer elements in the ultrasound probe...