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Magnetic Resonance Imaging

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Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is an imaging technique used in medical physics that produces two- and three-dimensional images of the interior of the human body. MRI is based on the nuclear magnetic resonance (NMR) effect, which explains the interaction between an external magnetic field and the nuclei of certain atoms, mainly hydrogen. Similar to electrons and current loops, these nuclei have their own tiny magnetic fields. Tissues in the human body respond to an external magnetic field in a certain way, and this response can be used to probe the human body.

Magnetic resonance imaging An MRI machine StudySmarterAn MRI machine, Wikimedia Commons

How does magnetic resonance imaging work?

NMR has been used to produce highly-detailed images in MRI for over twenty years. MRI is used to gather medically useful information about the human body. This information includes the condition of tissues, organ functioning, the presence of tumours, infections, and the shape of bone structures, such as vertebral disks and knee-joint surfaces.

The name MRI is used instead of NMR because the word “nuclear” can lead people to think that MRI techniques include nuclear radiation, which they don’t.

The process of producing an MRI scan

The main part of an MRI machine is a superconductive magnet that produces a magnetic field. This magnetic field has a relatively large intensity and interacts with the nuclei of particular atoms (mainly hydrogen).

Since about two-thirds of the atoms in a human body are hydrogen atoms, their nuclei experience a torque that aligns them and creates new energy levels. The atoms’ alignment with the magnetic field and the direction of the torque they experience depends on their spin. This is similar to the north and south poles of a superconductive magnet. Usually, the hydrogen atoms in the human body are randomly spread, but the magnetic field created by the MRI machine causes the hydrogen atoms to align either in the direction of north or south.

The magnetic field is turned on and off in a series of quick pulses by passing electricity through the coils. This is also the reason for the noise in an MRI machine. In these series of quick pulses, the hydrogen atoms in the body align in one direction and then quickly go back to their normal state. The scanners in the machine detect these changes (the patient can’t!) and produce an MRI image for the radiologist.

Because hard bones contain few hydrogen atoms, they do not produce a strong MRI signal. As a result, they appear black on the final image. The machine’s settings and the quantity of fat and water present in each tissue affect the colour. Spinal fluid, blood, and soft tissues range from black to white in the final image.

Magnetic resonance imaging An MRI technologist at work StudySmarterAn MRI technologist conducts an MRI scan of a patient’s brain, Flickr

Functional magnetic resonance imaging: different MRI types

There are five types of MRI used in today’s medical physics. These include functional MRI (fMRI), magnetic resonance venography (MRV), cardiac MRI, breast scans, and magnetic resonance angiography (MRA).

  • Functional MRI (fMRI) is a specific MRI technique where the patient is asked to perform particular movements so that medical professionals can map the functional areas of the human brain before surgery.
  • Magnetic resonance venography (MRV) is a particular MRI technique that uses magnetic resonance to create a precise image of the veins.
  • Cardiac MRI is the technique that uses MRI to image the heart.
  • Breast scans are another technique that uses MRI to create precise images of human breasts to look for abnormalities.
  • Magnetic resonance angiography (MRA) is an MRI technique that also uses intravenous (IV) contrast dye to examine blood vessels and assess blood flow.

The advantages and disadvantages of magnetic resonance imaging

Although MRI procedures have many advantages, there are also disadvantages to using MRI techniques. Let’s look at these in more detail.

Advantages

  • MRI scans can create images of any part of the human body and in any imaging direction.
  • MRI scans can provide better quality images of soft tissues than CT scans. MRI images can also differentiate better between fat, water, muscle, and other tissues.
  • MRI scans don’t include nuclear radiation.
  • MRI scans can create more precise and helpful images of blood vessels compared to other imaging techniques.

Disadvantages

  • MRI scans happen in a loud and closed space, which is not ideal for people with claustrophobia.
  • The time it takes to complete an MRI scan is longer than CT scans.
  • The magnetic field can affect metal devices or structures implanted within the body.

Magnetic Resonance Imaging - Key takeaways

  • Magnetic resonance imaging (MRI) is an imaging technique that produces two- and three-dimensional images of the interior of the human body.
  • MRI is based on the nuclear magnetic resonance (NMR) effect, which explains the interaction between an external magnetic field and the nuclei of certain atoms.
  • The main part of an MRI machine is a superconductive magnet that produces a magnetic field.
  • The magnetic field is turned on and off in a series of quick pulses by passing electricity through coils. The hydrogen atoms in the body align in one direction and then quickly go back to their normal state. The scanners in the machine can detect these changes to produce an image.
  • Because hard bones contain few hydrogen atoms, they do not produce a strong MRI signal. As a result, they appear black on the final image. MRI scans produce a range of colours between black and white depending on the tissue’s hydrogen atoms.
  • MRI provides better quality images of soft tissues and can create more precise and helpful images of blood vessels.
  • Some disadvantages of using MRI include the time it takes to produce a scan and their effect on metal devices in the human body.

Frequently Asked Questions about Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) works via a superconductive magnet that produces a magnetic field. This magnetic field has a relatively large intensity and interacts with the nuclei of particular atoms (mainly hydrogen). The magnetic field is turned on and off in a series of quick pulses by passing electricity through the coils. In these series of quick pulses, the hydrogen atoms in the body align in one direction and then quickly go back to their normal state. The scanners in the machine detect these changes and produce an MRI image for the radiologist. 

Magnetic resonance imaging (MRI) is an imaging technique used in medical physics that produces two- and three-dimensional images of the interior of the human body by creating a magnetic field. 

Magnetic resonance imaging (MRI) is used to create images of the inside of the human body. It gathers a lot of useful information about organ function, tumours, infections, conditions of tissue, etc.

A magnetic resonance scanner uses strong magnetic fields that affect hydrogen atoms in the human body, causing them to align in certain directions. The scanners pick up signals from the nuclei of the hydrogen atoms to form an image.

An MRI scan is used to gather medically useful information about the human body. This information includes the condition of tissues, organ functioning, the presence of tumours, infections, and the shape of bone structures, such as vertebral disks and knee-joint surfaces.

Final Magnetic Resonance Imaging Quiz

Question

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

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Answer

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

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Question

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

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Answer

MRI scans can scan bones better than CT scans.

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Question

Why do certain parts of the image created by MRI appear black?


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Answer

The scanner picks up signals from the nuclei of the hydrogen atoms. When there are fewer hydrogen atoms contained in certain structures, they don’t provide a strong signal.

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Question

Why do certain parts of the image created by MRI appear white?


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Answer

Because those certain areas contain a lot of hydrogen atoms.

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Question

Which of the following statements is false?


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Answer

The magnetic field always stays at a high level during an MRI scan.

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Question

Which MRI technique is used to create a precise image of the veins?


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Answer

Magnetic resonance venography (MRV).

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Question

Which MRI technique allows neurosurgeons to map the functional areas of the human brain?


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Answer

Functional MRI (fMRI).

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Question

Which MRI technique is used to create an image of the heart?


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Answer

Cardiac MRI.

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Which MRI technique is used to create an image of the breasts?


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Answer

 Breast scans.

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Question

Can MRI scans be used to create images of any part of the human body?


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Answer

Yes, MRI scans are used to create images of any part of the human body.

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Question

Does MRI include nuclear radiation?


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Answer

No, MRI doesn’t use nuclear radiation.

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Question

In which colours do the MRI results appear?


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Answer

MRI results appear in black and white.

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Question

Which effect is MRI based upon?


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Answer

Nuclear magnetic resonance (NMR).

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Question

Can MRI scans produce two- and three-dimensional images?


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Answer

Yes, MRI scans produce two- and three-dimensional images.

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Question

Do MRI scans include the hazards that come along with X-ray imaging?


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Answer

No, MRI doesn’t use nuclear radiation. 

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