Your chances of being split open sternum to sphincter for a medical procedure are quickly declining (whew) thanks to the advent of endoscopic surgery and robotic surgical platforms like the Da Vinci, though even these revolutionary procedures have their limitations. But thanks to a team of Stanford researchers, size is no longer one of them.
Endoscopes are medical devices used in the process of Endoscopy, you know, looking inside body cavities and organs for medical reasons. They operate by shining a bright light source into one end of the scope, which travels the length of the device and shines on the interior of the body. Some of this light will reflect back up the endoscope and can be observed by the physician. The very first endoscope was developed at the turn of the 19th century by Austrian physician, Philipp Bozzini. In the 1950s, renowned British physicist Harold Hopkins revolutionised the device’s design by devising a “fibroscope” consisting of of numerous flexible glass fibres bundled together to transmit light and images. Combined with a powerful light source, the fibroscope and its immediate successors — such as the first fibre optic endoscope created by Fernando Alves Martins in 1963 — were capable of transmitting detailed, full-spectrum colour images, giving doctors an unprecedented look inside a living person and ushering in the era of “keyhole” surgery.
The problem with these endoscopes is that their resolution is physically limited by the number of fibres in the bundle. A 50,000-strand bundle delivers 50,000 pixels, no more. And as the bundles age, fibres will break, reducing the resolution until the entire thing has to be replaced. And doctors can’t just go jamming 300,000 fibres into you to improve the resolution either — everything from the scope itself to surgical tools have to fit through body-size-limited incisions. Plus, it’s not like you’d want a six-figure bundle of glass tubes being shoved up your pee hole during your next ureteroscopy anyway — it’s uncomfortable.
But that’s what makes this new micro-endoscope from a Stanford research team so awesome — it uses a single fibre to deliver the same resolution as four standard strands. The human eye can see items as small as about 125 microns across whereas standard fibre optic scopes can resolve down to about 10. The Stanford prototype: 2.5 microns. The team, led by Joseph Kahn, professor of electrical engineering at the Stanford School of Engineering, recently published the results of their endoscopic study in the journal Optics Express:
In our method, a sequence of random field patterns is input to the fibre, generating a sequence of random intensity patterns at the output, which are used to sample an object. Reflected power values are returned through the fibre and linear optimization is used to reconstruct an image. The factor-of-four resolution enhancement is due to mixing of modes by the squaring inherent in field-to-intensity conversion. The incoherent point-spread function (PSF) at the centre of the fibre output plane is an Airy disk equivalent to the coherent PSF of a conventional diffraction-limited imaging system having a numerical aperture twice that of the fibre. All previous methods for imaging through MMF can only resolve a number of features equal to the number of modes. Most of these methods use localised intensity patterns for sampling the object and use local image reconstruction.
In English, Kahn and his team developed a multimode fibre — one in which light can travel through many different paths or “modes.” Such fibres can carry a large amount of information — either digital or images — but have a tendency to scramble that information since the light that carries it is moving over a bunch of different routes to reach the end of the scope. Kahn, with the help of graduate students, developed a miniature LED display, known as a spatial light modulator (SLM), to project light through the endoscope. The light returning from the SLM is then fed through a computer running a custom algorithm that reconstructs the image based on the strength of the reflected light and displays the image on a monitor.
While this isn’t the first single-strand endoscope ever invented, its four-fold resolution over similar systems could lead to the most minimally invasive surgery this side of a Tricorder. Kahn’s team anticipates the day when a micro-endoscope two-tenths of a millimetre in diameter will resolve 80,000 pixels-worth of your insides — everything from watching your neurons fire to detecting cancer in its earliest stages.