Endoscopy is a non-ionising imaging technique used in medical physics to examine the interior of the human body. The difference between other imaging techniques and endoscopy is that endoscopy uses a device called an endoscope, which is inserted directly into the human body. This classifies it as an invasive medical procedure, unlike other imaging techniques based on radiation or sound.
Explore our app and discover over 50 million learning materials for free.
Lerne mit deinen Freunden und bleibe auf dem richtigen Kurs mit deinen persönlichen Lernstatistiken
Jetzt kostenlos anmeldenNie wieder prokastinieren mit unseren Lernerinnerungen.
Jetzt kostenlos anmeldenEndoscopy is a non-ionising imaging technique used in medical physics to examine the interior of the human body. The difference between other imaging techniques and endoscopy is that endoscopy uses a device called an endoscope, which is inserted directly into the human body. This classifies it as an invasive medical procedure, unlike other imaging techniques based on radiation or sound.
Fibre optics is used in endoscopy. Optical fibres are flexible and transparent fibres with a diameter just a little bigger than a human hair. They are primarily used for transmitting light.
In fibre optics, a core is usually surrounded by a transparent cladding material with a lower index of refraction. The way light is transmitted in fibre optics, which allows doctors to use endoscopes to see the body’s interior, depends on the total internal reflection principle.
Total internal reflection is the optical event in which light waves reach the boundary between two media. The light is not refracted to the opposite medium but is completely reflected back to the initial medium instead. This phenomenon occurs when the opposite medium has a higher refractive index than the initial medium.
Refractive index (n) is the number that shows how fast light can travel through the medium. The refractive index and the speed of light in the medium are inversely proportional.
We can calculate the refractive index of a medium with this equation:
\[n = \frac{c}{v}\]
Here, c is the speed of light in a vacuum (3.00 ⋅ 108m/s), and v is the phase velocity of light in the medium.
For this phenomenon to occur, the angle of incidence at the boundary between two mediums must be greater than the critical angle. Let’s say that a light beam travels from a medium that has a refractive index of n1 to a second medium with a refractive index of n2, and n2 ≤ n1. We can then find the critical angle (θc) with this equation:
\[\theta_c = \arcsin \Big(\frac{n_2}{n_1} \Big)\]
If the angle of incidence (θ1) is lower than the critical angle, then the wave will refract to the opposite medium with an angle of θ2 (yellow arrows in the illustration below). We can now find the relation between these angles with this equation:
\[n_1 \cdot \sin \theta_1 = n_2 \sin \theta_2\]
If the angle of incidence (θ1) is equal to the critical angle (θc), then the wave will continue on its way in alignment with the boundary (purple arrows in the illustration).
If the angle of incidence is greater than the critical angle, total internal reflection occurs, and the wave will reflect back to the initial medium with the same angle it had initially (red arrows in the illustration).
When using endoscopes with fibre optics, a light source in the tip of the endoscope illuminates the passageways. The light is reflected from the passageways back into this tip. Light is guided by a step-index structure inside the optical fibre that induces total internal reflection and directs coupled light from one end to the other without loss. For this to happen, the refractive index of the fibre core material (n1) must be greater than that of the fibre cladding material (n2).
Light with an incidence angle greater than the maximum acceptance angle θa will be partially refracted outside of the fibre. Light with an incidence angle less than the maximum acceptance angle θa will be partially refracted inside the fibre. After several encounters with the fibre core-cladding interface, the residual partly reflected light is finally lost.
The requirement for 100% internal reflection at the core-cladding contact determines the maximum acceptance angle θa. To determine the acceptance angle θa, remember that to find the critical angle θc, we use the equation:
\[\sin(\theta_c) = \frac{n_2}{n_1}\]
Thus, assuming the fibre is in the air with a refractive index of 1, the following equation helps us find the acceptance angle θa. Note that θc' = 90° - θc.
\[\sin (\theta_a) = \frac{n_1}{1} \cdot \sin(\theta'_c)\]
Another important characteristic of fibre optics in an endoscope is that light will enter and exit the optical fibre with the same angle with regard to the fibre’s central axis. This means that in the illustration above, θa = θa'. This important characteristic is valid for a curved fibre as well.
In conclusion, the light wave, which reflects from the passageways of the human body and enters the optical fibres in the endoscope, travels through the optical fibres with total internal reflection. As a result, the light exits the optical fibres in the same way it entered them (with the same angle). The image is then transferred for a viewer to examine.
Endoscopy is currently used in a variety of applications in medical physics. While endoscopy is mainly used in surgeries to allow surgeons to visualise the interior of the human body while operating, other uses include looking into the passageways of the human body to determine any abnormalities. Here are some other uses of endoscopy:
Fibre optics is used in endoscopy, and it is primarily used for transmitting light. In fibre optics, a core is usually surrounded by a transparent cladding material with a lower index of refraction. The way light is transmitted in fibre optics, which allows doctors to use endoscopes to see the body’s interior, depends on the total internal reflection principle.
Fibre optic endoscopy is an imaging technique that uses fibre optic endoscopes in order to look into the passageways of the human body.
One disadvantage of endoscopy is that it is an invasive procedure unlike other imaging techniques based on radiation or sound.
The core with the refractive index of n1 in the optical fibres in an endoscope is surrounded by a cladding material with a refraction index of n2. Which of the following describes the relation between n1 and n2?
n2 ≤ n1
If the angle of incidence is greater than the critical angle, then total internal reflection will occur and the wave will reflect back to the initial medium at which angle?
The same angle at which it came to the boundary.
What is the relation between the angle at which light enters the optical fibre and the angle at which it exits the optical fibre?
They are the same angle with respect to the fibre’s central axis.
Which of the following is not one of the uses of fibre optic endoscopy?
Creating an image of the human brain.
In fibre optics in endoscopes, if a light wave with an incidence angle greater than the maximum acceptance angle θa enters the optical fibres, what happens to this light wave?
It will be partially refracted inside the fibre, and this partly reflected light will be lost after several encounters.
Which optical principle does the fibre optic endoscopy depend on?
The total internal reflection principle.
Already have an account? Log in
Open in AppThe first learning app that truly has everything you need to ace your exams in one place
Sign up to highlight and take notes. It’s 100% free.
Save explanations to your personalised space and access them anytime, anywhere!
Sign up with Email Sign up with AppleBy signing up, you agree to the Terms and Conditions and the Privacy Policy of StudySmarter.
Already have an account? Log in
Already have an account? Log in
The first learning app that truly has everything you need to ace your exams in one place
Already have an account? Log in