3D shape sensing of an epidural needle based on simultaneous spatial multiplexing of optical backscattering reflectometry

Here a novel paradigm of fiber optics 3D shape sensing is presented. Fiber optics technology offers a great potential for minimal invasive medical applications. The approach is supported by two basic cornerstones: the first is the Optical Backscattering Reflectometry (OBR), which gives the possibility of distributed strain sensing along the length of fiber sensor installed on the needle; the second is the principle of simultaneous scattering-level multiplexing (SLMux), which permits to interrogate a parallel of optical sensor in the same OBR scan. SLMux, which overtakes the OBR limitation to the interrogation of a single optical sensor, is possible by using a custommade MgO nanoparticles doped fiber (NPDF), which presents a core doped with a randomly distributed pattern of particles. NP-fiber shows a backscattering power of more than 40 dB higher than a standard single-mode fibers (SMF). By splicing NP-fiber cuts with different SMF pigtail it is possible to achieve a parallel where the higher NP-fiber backscattering can be effectively discriminated. With this approach it is possible to pack several sensors along the needle length to detect all the strain components. Experimentally, a parallel of four sensors has been fixed along the length of an epidural needle at 90 degrees from each other. 3D shape sensing is achieved by strain measurement from each fibers and distributed strain sensing along the needle. As a result of strain elaboration, shape deformation and bending of the needle during its insertion into a custom-made phantom, which mimics human spine anatomy, have been obtained.