Certain surgical procedures can now be carried by inserting tiny surgical instruments through small cuts in the human body. Known as “minimal access surgery”, a surgeon carries out the procedure by watching a monitor showing images taken by a fibre-optic camera inserted into the body. The technique would, however, benefit from improved imaging methods. Although magnetic resonance imaging (MRI) can provide good images of tissue below the surface of the body, the scanning equipment is usually far too big to be used in an operating theatre.

The new device made by Dickinson and Kitney takes images using ultrasound. It contains 64 crystal piezoelectric transducers that are made to generate pulses of sound waves, which reflect off the tissue under investigation. This pulse is then received by the transducers working in “reverse”, which convert the mechanical vibrations into an electrical signal. A detailed 3D image of the structure producing the echo can be built up by measuring the time taken for the pulse to return, together with the position of the transducer.

Dickinson and Kitney were able to make their tiny probe thanks to an improved fabrication method. They started by assembling all the necessary components on a flat flexible substrate — a 0.019-mm thick polyimide sheet with a 3-4 micron copper layer, etched using photolithography techniques. Next, they bonded a 2.4-mm squared rectangle of metallized piezo-electric transducer, 0.05-mm thick, to the substrate. They then diced the transducer using a carefully controlled diamond saw to create 64 elements, each 0.8-mm long, 0.03-mm wide and 0.05-mm thick. Finally, they rolled the substrate into a cylinder (figures 1 and 2).

The scans provided by the new probe will provide information on the extent to which diseased arteries are thickened and blocked (figure 3). The team also plans to investigate other applications such as keyhole surgery of shoulder and knee joints.