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# Non Ionising Imaging

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Non-ionizing imaging is an area of medical physics that includes ultrasound, magnetic resonance imaging, also known as MRI, and optical imaging. These methods are preferred in medical areas because they are less harmful than imaging using ionization. To understand the concept of non-ionizing imaging better, we need to explore non-ionizing radiation.

Ionization is the process of giving an electron enough energy to break away from an atom. Non-ionizing radiation does not have sufficient energy to cause ionization. It is found in the long-wavelength end of the spectrum and has the potential to excite molecules and atoms, thus causing them to vibrate faster. Here are some examples of non-ionizing radiation:

• Infrared radiation as used in heat lamps.
• Ultraviolet (UV) radiation from the sun and used in tanning beds.

Take a look at the diagram below. Wavelengths shorter than 125 nm are considered to be ionizing radiation.

Electromagnetic Spectrum. Flickr

Now that you have learned about non-ionizing radiation, you can understand better which methods in the medical world include non-ionizing imaging and why they are used.

## What does non-ionizing imaging include?

Non-ionizing imaging is used in many different areas of medical physics for a variety of reasons. These areas include ultrasound imaging, magnetic resonance scanning, and fiber optics and endoscopy.

### Ultrasound imaging

Ultrasound imaging (sonography) is a technique for seeing the interior of the body using high-frequency sound waves. Because ultrasound pictures are taken in real time, they can reveal internal organ movement as well as blood moving via blood vessels. When sound waves are transmitted into the body and then reflected back to a scanner, pictures are generated. Ultrasound imaging, unlike X-ray imaging, does not expose people to ionizing radiation.

A 2D fetal ultrasound. flickr.com

In medical physics, ultrasound imaging can be used to identify the reasons for pain, swelling, and infection in the body's internal organs, as well as to inspect a baby in pregnant women or the brain and hips in infants. Abdominal scans often use a 7MHz frequency (f). On top of this, if you consider the fact that the speed of sound in tissue (vw) is approximately 1540m/s, then the wavelength (λ) of ultrasound would be:

$\lambda =\frac{{v}_{w}}{f}=\frac{1540m/s}{7*{10}^{6}Hz}=0.22\left[mm\right]$

The general consensus is that you can successfully scan tissue to a depth of around 500λ. For 7MHz, that is 500 * 0.22mm = 0.11m.

There are no echoes when sound waves flow smoothly through uniform material. As a result, the ultrasound image on the screen is black, with no echoes. A wave is reflected back to the probe when sound waves strike tissue that absorbs or transmits the sound.

Depending on the strength of the reflection, the ultrasound picture is white or gray. Ultrasound, unlike x-rays or CAT scans, cannot identify tissue density. Instead, it looks for sonotransmission (the passage or reflection of sound).

On an ultrasound, very thick tissues, such as bone or kidney stones, rapidly reflect echoes and appear bright white. Echoes are also easily reflected in air, such as in the intestine. As a result, the bowel's border also looks white on an ultrasound. Therefore, things with vastly different densities (such as air and bone) may show on ultrasound as bright white.

### Magnetic resonance scanning

Magnetic resonance imaging (MRI) is a radiological imaging method that creates images of the body's anatomy and physiological processes without using X-rays or ionizing radiation.

Strong magnetic fields, magnetic field gradients, and radio waves are used in MRI scanners to create pictures of the body's organs. The MRI equipment transmits magnetic and radio frequency waves into the patient's body to obtain a picture.

The atoms in the magnetic field produce energy that transmits a signal to a computer. The computer then converts the signal into an image using mathematical algorithms.

Example of an MRI result. flickr.com

An MRI device picks up signals from the nuclei (centers) of hydrogen atoms in your body using a strong magnetic field and a burst of radio frequency waves. Because they contain few hydrogen atoms, air and hard bone do not produce an MRI signal. As a result, these regions appear in black.

The quantity of fat and water present in each tissue, as well as the machine settings utilized for the scan, affect the intensity of bone marrow, spinal fluid, blood, and soft tissues, which range from black to white.

A chest, abdominal, or pelvic MRI can be used to help diagnose or monitor therapy for a number of diseases.

### Fiber optics and endoscopy

Endoscopy is a procedure that enables doctors to look into the body's pathways. The use of an endoscope to examine and check the interior of body organs, joints, or cavities is known as endoscopy.

An endoscope is a device that provides lighting and visibility into the interior of a joint using fiber optics and lens systems. Depending on the medical procedure, the part of the endoscope introduced into the body may be stiff or flexible. In endoscopy, the total internal reflection principle of optics is used. This is a phenomenon that happens at the border between two mediums, in which all light is reflected back into the first medium if the incidence angle in the first medium is larger than the critical angle.

This is how the principle works in endoscopy step by step:

1. One of the two main endoscope cables carries the light from a bright lamp into the body.
2. The light that reflects off of the internal body parts travels back through a separate fiber-optic cable, bouncing off the glass walls as it travels back.
3. The total internal reflection principle in this process works like this: due to the thinness of the fibers, light entering a fiber is more likely to contact the inner surface at an angle larger than the critical angle. It will, therefore, be completely reflected, making it all the way to the end of the endoscope where the operator is looking.

Endoscope. flickr.com

An endoscopy may be used to obtain tissue samples (biopsy) to screen for illnesses and disorders, including anemia, bleeding, inflammation, diarrhea, or cancers of the digestive system.

## Non-ionizing imaging - key takeaways

• Non-ionizing imaging is used in medical physics to see the interior of the body, such as internal organs and joints.
• Non-ionizing imaging includes ultrasound imaging, magnetic resonance imaging, and endoscopy. These methods are used in important areas of medical physics.
• Ultrasound imaging can reveal internal organ movement as well as blood moving via blood vessels because ultrasound pictures are taken in real time.
• Endoscopy is a procedure in which an instrument is introduced into the body to give a view of its internal parts.
• Magnetic resonance imaging (MRI) is a type of radiological imaging that produces images of the body's anatomy and physiological processes using strong magnetic fields, magnetic field gradients, and radio waves.

The three types of non-ionizing imaging used in medical physics are ultrasound imaging, magnetic resonance scanning (MRI), and endoscopy.

Non-ionizing imaging is preferred in medical physics because non-ionizing radiation is much less harmful to the human body than ionizing radiation

Non-ionizing imaging is used to look into the interior of the body and help diagnose or monitor therapy for a number of diseases.

The radiation used in the MRI procedure is non-ionising radiation and the X-rays are not involved either. Instead, Strong magnetic fields, magnetic field gradients, and radio waves are used in MRI scanners to create pictures of the body's organs.

Ultrasound imaging, unlike X-ray imaging, does not expose people to ionizing radiation. It is a technique for seeing the interior of the body using high-frequency sound waves.

Non-ionizing imaging is an area of medical physics that includes ultrasound, magnetic resonance imaging, also known as MRI, and optical imaging. These methods are preferred in medical areas because they are less harmful than imaging using ionization.

## Final Non Ionising Imaging Quiz

Question

Does non-ionizing radiation conserve enough energy to cause an electron to break away from the atom?

No, it doesn't.

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Question

Non-ionizing radiation waves have a long wavelength. True or false?

True.

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Question

What is another name for ultrasound imaging?

Sonography.

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Question

Which one of the techniques in non-ionizing imaging does not capture the interior of the human body in real time?

Magnetic resonance imaging (MRI).

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Question

An endoscope is a device that provides lighting and visibility into the interior of a joint. True or false?

True.

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Question

λ <125nm.

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Question

Which non-ionizing imaging technique can be used to see internal organ movement?

Ultrasound imaging.

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Question

Do non-ionizing radiation waves have the potential to excite molecules and atoms, thus causing them to vibrate faster?

Yes, they do.

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Question

Which non-ionizing imaging technique is used to diagnose digestive system illnesses?

Endoscopy.

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Question

Which optic principle is used by endoscopy?

The total internal reflection principle.

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Question

The general consensus is that you can successfully scan tissue to a depth of around which number?

500 times the wavelength of the wave.

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Question

Which non-ionizing imaging technique uses fiber optics and advanced lens systems?

Endoscopy.

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Question

Are X-rays non-ionizing or ionizing?

Ionizing.

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Question

Which non-ionizing imaging technique is used to see a baby inside the womb?

Ultrasound imaging.

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Question

Is infrared radiation non-ionizing or ionizing?

Non-ionizing.

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Question

When a radiation wave's wavelength increases, does its energy increase or decrease?

It decreases.

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Which non-ionizing imaging technique uses strong magnetic fields and radio waves?

Magnetic resonance scanning (MRI).

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Are gamma rays non-ionizing or ionizing?

Ionizing.

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Which non-ionizing imaging technique is used to get a better image of the human brain?

Magnetic resonance imaging (MRI).

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What distinguishes non-ionizing waves from ionizing waves?

Having enough energy to cause ionization.

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Question

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

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Question

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.

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Question

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.

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Question

Which of the following is not one of the uses of fibre optic endoscopy?

Creating an image of the human brain.

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Question

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.

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Question

Which optical principle does the fibre optic endoscopy depend on?

The total internal reflection principle.

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Question

The angle of incidence with the boundary between two mediums has to be greater than which angle in order for total internal reflection to occur?

The angle of incidence has to be greater than the critical angle for total internal reflection to occur.

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Question

What is the name of the number that tells how fast light can travel through the medium?

The refractive index.

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What is the relation between the refractive index and how fast can light travel through a medium?

The refractive index and how fast can light travel through a medium are inversely proportional.

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Question

When the optical fibres are curved in an endoscope during an examination, can the total internal reflection of light still be present?

Yes.

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Question

What is the name of the phenomenon that occurs when a light beam reaches the boundary between two mediums and completely reflects back to the initial medium?

Total internal reflection is the name of the phenomenon that occurs when a light beam reaches the boundary between two mediums and completely reflects back to the initial medium.

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Question

What is the symbol for the refractive index?

n

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Question

Can endoscopy be used in surgeries to view the interior of the human body in real-time?

Yes, endoscopy can be used in surgeries to view the interior of the human body in real-time.

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Question

Is endoscopy an ionising imaging technique?

No.

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Question

At which range of frequencies are sound waves accepted as ultrasound?

f > 20kHz

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Question

Which of the following is true?

You can’t observe details that are smaller than the wavelength of your probe.

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Question

Which of the following is not one of the applications of ultrasound imaging?

Whole-body imager.

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Question

When the ultrasound doesn’t come up against a medium with a different acoustic impedance, what colour will appear on the screen?

Black.

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Question

Which of the following does ultrasound imaging identify?

Sonotransmission.

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Question

What is the name of sound waves with a frequency of 20Hz or less?

Infrasound.

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Question

Which range of sound wave frequencies can a human hear?

Between 20Hz to 20kHz.

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Is ultrasound imaging captured in real-time?

Yes, ultrasound imaging is captured in real-time.

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Question

Which formula is used to find the acoustic impedance of a medium?

Z = · v

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Question

What is the name of sound waves with a frequency of 20kHz or more?

Ultrasound.

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Question

Can ultrasound imaging reveal both internal organ movement and blood flow through blood vessels?

Yes, ultrasound imaging can reveal both internal organ movement and blood flow through blood vessels.

Show question

Question

What is the symbol used to describe frequency?

f

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Question

What is the symbol used to describe acoustic impedance?

Z

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Question

Does ultrasound imaging identify tissue density?

No, ultrasound imaging can’t identify tissue density.

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Question

What is the medical name for ultrasound imaging?

Sonography.

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Question

Which of the following is not one of the disadvantages of MRI?

MRI scans can’t scan any part of the body.

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