We have all been amazed, when we were younger, at how light from a torch or lamp could illuminate our fingers and make them glow red. Little did we know that we were at the foundations of new cutting-edge medical technology. We had independently discovered the phenomenon that light, especially red light and near-IR light can pass straight through human tissue.
Does this mean that by simply shining red light we can see through and image the body? Well, a red laser pointer, which will produce a single focused beam of light, can go straight through your hand, and be visible on the other end – but due to the scattering of light by layered human tissue, instead of seeing a straight beam on the other end we would merely see a faint red glow. Oh well. A generic red glow doesn’t show much at all, so I guess the answer is no, shining red lights is of no medical use. Wishful thinking. Unless there was something that….
It’s true that when red light scatters, due to layers of human tissue, it’s not very useful at all. The question is, therefore, is it possible for light which is scattered by human tissue to be ‘un-scattered’ somehow to make the phenomenon of our tissue being translucent medically useful. It turns out that light can be descattered using a technique called holography. To understand holography, we have to understand the basics of holograms. Hmm – sounds futuristic?
HOW DOES A HOLOGRAM WORK?
A hologram is a type of image that captures all of the light and all of the photons hitting it from every angle at the same time. We’re familiar with them as shiny logos on the backs of credit cards, passports and even money.
To form a hologram of an image, a laser beam is used due to light from a laser being ‘coherent’, essentially meaning it produces a ‘straighter’ beam than a torch.
- The laser is reflected through a half-mirror, a special mirror which reflects half of the light (at 90°) and lets half of the light pass through. THIS MEANS THE SINGLE LASER BEAM SPLITS INTO TWO. Both light waves are travelling identically initially
- When the waves recombine on the photographic film, the object beam (bottom) will have travelled via a different path due to the rays reflecting of the object (stethoscope)
- Therefore, recombining the beams shows how the light rays of the object beam have changed compared to the unaffected reference beam of laser light. This information is burned onto photographic film by the laser. Hence, whichever direction you look at the hologram, it is as if you are looking at the object in real life.
If a hologram gives us information about the angle of every photon hitting an object, new ground-breaking research shows that we can use that hologram to re-angle light that has been scattered back to its original position so that scattered light once again emerges as straight laser beam. To make this easier to understand, consider an analogy of marbles falling in a straight line into a box and then bouncing off wooden pegs randomly, where the marbles represent photons. Gravity is pulling the marbles down so they eventually exit the box.
- Recording a hologram at the bottom inside a screen, we can record the position of each marble in the maze at one point in time.
- We can then bring in the marbles from below, getting the hologram to direct it at the same angle so they come back in a straight line
But instead of a few marbles being descattered by a hologram, its trillions of photons. Now we’ve got the principles out of the way – the application of holography enabling descattering (HED) is extremely exciting. You may be thinking that one of the major obstacles to HED red light imaging is that bone will block any light that passes through tissue so that it cannot be detected – but amazingly bone shares the same translucent properties as tissue, meaning red light holography works straight through the body and deep into tissue, while not causing tumours unlike X-Ray and Gamma Ray Radiation.
This cutting-edge discovery was demonstrated to the public for the first time ever two months ago, where laser light was shined through a human skull and descattered using holography, producing a single focused laser on the other end of the skull. By shining red/ near IR lasers through the body, a focus of 7 microns is achievable: the diameter of the smallest neuron in the human brain. In comparison, an MRI scanner which costs millions to produce and run has a focus of 1mm, 140x less than the newly developed HED. The descattering technology can be implemented into display computer chips the size of a fingernail, resulting in lower cost, far higher resolution and smaller medical imaging. Integrating HED descattering technology in computer display chips means that light can be descattered and interpreted electronically in 1 millionth of a second. This is ground-breaking:
Combining directional and focused sonic pings with red light allows us to map up the brain, neuron, by neuron with the extremely high-resolution focus of HED red light imaging, through computer chips which can be placed on our skull.
While flesh scatters IR/red light, blood absorbs it, meaning that by passing light through our bodies, we can instantly detect blood in places where it should or shouldn’t be. Combine this with knowing that every tumour bigger than 1mm3 contains five times the amount of blood than normal means that a red laser can enable early cancer detection.
There is no way to know whether a patient’s stroke has been caused by either an arterial clog or a rupture without rushing them to an MRI machine within an hour, and not being able to administer the specific medicine for the specific stroke can easily result in death. HED red light imaging that is integrated in small computer chips can allow every ambulance to quickly determine the blood flow in a patient, and rapidly improve chances of recovery.
Given that 2/3 of the world lacks access to basic medical imaging, and that non-renewable helium which is essential for Magnetic Resonance Imaging to operate is rapidly running out, this new, simple imaging could soon replace the MRI.
Photo Credits due to: Zak Shah, https://www.videvo.net/stock-video-footage/holographic/