How Does Optical Coherence Tomography Work to Image Different Tissue Layers?

[DariusP]

Anyone familiar with how this device works?

I'm having trouble understanding how different layers of tissue can be imaged using interference.

I am sort of familiar with michaelson interferometer and what is low coherence light if that helps.

 

[sophiecentaur]

Do you have any useful links about this? It would save us all reinventing the wheel, independently.

 

[DariusP]

Do you have any useful links about this? It would save us all reinventing the wheel, independently.

Well if you don't know it's okay, I was just hoping maybe there are someone in this forum who's very familiar with this imaging technique and could explain it to me how he understands it.

 

[LURCH]

Can you tell us where you first heard of it? If everyone started from the same source, the conversation will be much more beneficial. Personally, I’m not familiar with the term, but I would like to have a look at what you’ve seen so far; it sounds pretty interesting (I have a lot of my own ideas about ways to use interferometry, and sometimes wonder if anyone is putting some of these notions to practical use).

 

[DariusP]

Can you tell us where you first heard of it? If everyone started from the same source, the conversation will be much more beneficial. Personally, I’m not familiar with the term, but I would like to have a look at what you’ve seen so far; it sounds pretty interesting (I have a lot of my own ideas about ways to use interferometry, and sometimes wonder if anyone is putting some of these notions to practical use).

I'm reading optical diagnostics book. OCT is mainly used for transparent tissue (like retina scanning) because it can't penetrate very deep into a scattering matterial. Ultrasound can penetrate deeper. However, OCT is much better than ultrasound in terms of contrast of the image.

Hmm, I don't know what else I can add. I really want to learn the working principle. Even the basic idea of how an image (matrix of many dots) is formed with the help of interference. Maybe your IQ is higher (lol) and can quickly pick up this schematic? Explain it to me, if so.

 

[anorlunda]

I'm reading optical diagnostics book.

Here on PF, we should always give links to our sources. Frequently, people misread their source and post questions based on those misunderstandings. Other PF members like to read the actual source to put the question in context.

 

[LURCH]

Oh my goodness, that is extremely clever! From the schematic it appears that the device works a lot like LIGO, or a long baseline interferometer telescope. A single beam of light travels to a beam splitter, then proceeds along two separate paths. One path leads to the target of the scan ( the tissue to be scanned), and the other leads to an adjustable mirror, set to the same depth as that target. The light that is sent to the mirror bounces back and goes into the photo receptor. Of The light that goes into the target tissue, some returns. Some of that return signal is light that was reflected off the target, but a lot of it is light that was reflected off the surface (the skin of the patient), and some of it was refracted multiple times, and returned as backscatter. These latter two signals are “noise”, which would normally clutter up the picture and make it hard to see.

However, the light that reflects off of the skin travels a shortened distance, and arrives too soon, while the backscatter noise has traveled a longer distance, and arrives too late. Light that reflects off of the intended target travels exactly the same distance as light returning from the carefully placed mirror, and so it arrives at exactly the same time. This light gets amplified by positive interference, and the image processor can probably filter out much of the remaining noise, just by ignoring any signal that doesn’t arrive at the same time as the reference signal (from the mirror).

This is absolutely brilliant! Thank you for introducing me to it.

 

[DariusP]

Oh my goodness, that is extremely clever! From the schematic it appears that the device works a lot like LIGO, or a long baseline interferometer telescope. A single beam of light travels to a beam splitter, then proceeds along two separate paths. One path leads to the target of the scan ( the tissue to be scanned), and the other leads to an adjustable mirror, set to the same depth as that target. The light that is sent to the mirror bounces back and goes into the photo receptor. Of The light that goes into the target tissue, some returns. Some of that return signal is light that was reflected off the target, but a lot of it is light that was reflected off the surface (the skin of the patient), and some of it was refracted multiple times, and returned as backscatter. These latter two signals are “noise”, which would normally clutter up the picture and make it hard to see.

However, the light that reflects off of the skin travels a shortened distance, and arrives too soon, while the backscatter noise has traveled a longer distance, and arrives too late. Light that reflects off of the intended target travels exactly the same distance as light returning from the carefully placed mirror, and so it arrives at exactly the same time. This light gets amplified by positive interference, and the image processor can probably filter out much of the remaining noise, just by ignoring any signal that doesn’t arrive at the same time as the reference signal (from the mirror).

This is absolutely brilliant! Thank you for introducing me to it.

Thank you for your awesome reply. I think I understand it well now.

P.S. Deeper layers can be obtained by moving the mirror back? What about the lens? As I understand it doesn't need to move and we only move the reference mirror?