Researchers at Royal Philips (Eindhoven, Netherlands) and the Erasmus Medical Center (Rotterdam, Netherlands) have built a prototype of an all-optically powered catheter intended for intracardiac echocardiography (ICE). In such a procedure, the catheter, which contains an ultrasound transducer at its end, is threaded through a leg or arm artery or vein all the way to the heart to image the features of the inner heart. Powering the ICE catheter optically rather than electrically will allow the device to be used safely while the patient is in a magnetic resonance imaging (MRI) machine. In addition, an optically powered catheter could be a model for other instrument-holding catheters used for minimally invasive diagnostic and therapeutic procedures.
The catheter contains three segments: an interrogator console, the catheter shaft, and the catheter tip. The catheter shaft contains three optical fibers (which will ultimately be reduced in number to only one fiber). For power, light from two gallium nitride (GaN)-based, 405-nm-emitting lasers is sent down two of the fibers and received by GaN-type LEDs in the tip operated in photovoltaic mode. Using GaN rather than silicon as photovoltaic devices results in a higher delivered voltage because of the high GaN bandgap of 2.8 eV-in addition, the GaN receiver can handle up to 1 W/mm2 power density. A third fiber carries the ultrasound signal, converted to an optical signal by an 850 nm vertical-cavity surface-emitting laser (VCSEL). The catheter prototype also contains a few signal-sending wires, but these will be replaced by all-optical data transmission in a future version. Signal transfer of synthetic-aperture ultrasound images at a frequency of 12 MHz was demonstrated. The benchtop prototype can be scaled down to catheter dimensions, say the researchers. Reference: M. Pekar et al., Opt. Express (2017); https://doi.org/10.1364/OE.25.008534.