MRI Scanning Techniques

By Nieve Powell, 9G

1. When and how was this technology invented and by whom?

Magnetic Resonance Imaging (MRI) technology has been developed and adjusted by many scientists, however according to Barbara Moe, some very influential players in its creation were Dr Raymond Damadian along with his co-workers and colleagues at the Downstate Medical Centre in Brooklyn, New York. They worked on and improved the first MRI machine between 1970 and 1977.


As to how MRI machines were first invented, they are actually the result of a huge amount of independent research and discovery leading up to the design and creation of the machine itself. In order to create the first MRI technology, Dr Damadian had to have a knowledge of magnets, atoms, radio frequency, imaging techniques, computers and the behaviour of hydrogen ions. Although the vision of MRI technology was first brought to fruition in 1977, many years of scientific discovery had gone on before that in order to make it possible.

2. How does it work?

Magnetic Resonance Machines work by manipulating the nuclei of hydrogen atoms within the body in order to view the placement of water (water formed from hydrogen and oxygen atoms) throughout the body. Because the body is predominantly made out of water, this imaging technique allows one to view almost any type of tissue within the body.


MRI machines image protons, meaning the ions of hydrogen atoms (not the primary subatomic particles). One large, primary magnetic field generated by the machine aligns the axis and the nuclei of the hydrogen ions. A second magnetic field is generated and creates pulses of a different magnetic field multiple times per second. This process adjusts the orbits of the protons. When the orbits swing back to the primary magnetic field, they release small pulses of energy in radio frequency pulses. These pulses are converted into digital data and then transmitted to an external computer which converts them into an image. In short, the pulses of energy given off by the protons allow the radio frequency coil or coils within the MRI machine to detect them and convert this data into an image. Generally the image or graphic is generated outside the MRI machine by a computer with specially designed software.

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In this diagram, one can see that the simplified process of an MRI scan; including the creation of a magnetic field to align the protons, as shown in point one. One can also see the omission of radio waves by the hydrogen ions are then picked up by a radio frequency coil, shown points three and four. The final step in this process (point four) is the generation of the image by a specially programmed computer, exterior to the MRI machine.

3. How has this technology benefitted people or society?

MRI machines are an incredible development in body imaging technologies and have many benefits over other types of scans. Older imaging techniques such as ultra sounds or x-rays have their downfalls, but MRI scans have many benefits which make them safer or more effective that these older techniques. One of these benefits is the fact that the magnets used in MRI do not have any (known) negative impacts upon the body. Unlike x-rays which use ionizing radiation to scan the body, the MRI uses radio waves which do not emit radiation. This means that where x-rays could potentially cause cancer (from prolonged or repeated exposure), MRI scans have no negative effects on the cells and tissues of the body. This makes them safe for young children and people who need repeated scans.


Another benefit of MRI is that they create clear images with good definition. MRI scans are much more detailed and highly defined than other more traditional scan types such as x-rays or ultrasounds. Magnetic Resonance Imaging records voxels which are effectively imaginary three-dimensional cubes. Voxels can be a small as one millimetre in diameter. If the scan is to create a two dimensional image then each voxel in the area scanned will be measured for its water content (hydrogen ions are found inside water molecules) and then an image will be created from that data, effectively representing a squashed one millimetre thick slice of the body. This image can have very high definition due to the fact that the voxels of data recordings can be very tiny. Another benefit which follows from this is that the body can be viewed on any plane. The magnets inside the machine can be set at different angles and so the 'slice' of the body viewed can be on any plane, unlike x-rays and other scanning machines.


Because MRI machines view the placement of water throughout the body (not density), it's easy to see the definition between tissues and bones or distinct tissues. X-rays, for example, will show a kind of 'fuzziness' around the edges of bones and between fats and muscles. MRI scans can show things such as blood vessels, nerves and perforations in the bone surface very distinctly. As we can see, the development of MRI scans has helped to advance medical research and procedures due to its use as a safe and more informative alternative to other, older imaging techniques.

4. What some limitations of this technology?

MRI machines do also have few disadvantages- among them the danger of extremely strong magnets. MRI machines are built in specially designed rooms with few metal objects and carefully designed equipment. The magnets in the machine are strong enough to even pull metal objects as small as paperclips and as large as oxygen tanks towards and into the machine; plus there can be detrimental effects if there is metal inside the patient. For this reason, it is highly unadvisable for people with metal clips and brackets inside their bodies to have an MRI scan, as well as people with pacemakers or people who have had a high exposure to small fragments of metal such as welders. In this case, scanning patients using an MRI machine can be dangerous and even fatal as the metals inside the body may move and cause their own very serious issues.

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In this image, you can see that there are specially designed tools and lights in the room because the surgery takes place right next to the MRI machine- making everything used in surgery very susceptible to the magnetic field generated.


A second limitation of an MRI scan is that the patient must stay absolutely still. This is not as big of an issue in some other types of scans such as CT scans. Due to the very sensitive nature of the MRI scan, it is very important that the patient stays absolutely still, and to this end, small children must sometimes be sedated in order to get a clear scan.

5. Find one article from the last 12 months related to your topic. Summarise the key points of this article and include it in your bibliography. It should be from a reliable source.

I found an article on an online Magnetic Resonance Imaging journal, which investigated the blood flow to the brain in people affected by Alzheimer's disease. The study involved using a type of MRI scan to image the blood flow to the brain and decide whether lack of blood flow could be one of the causes or stimulants of Alzheimer's Disease. The study was conducted by comparing scans done on 19 control subjects and 16 Alzheimer's patients, using a correlation analysis between Cerebral blood flow (CBF) and cognition, focussing specifically on the posterior cingulate region of the brain. The result of the study was that it was discovered that Alzheimer's patients generally had less blood flow to the temporal lobes, precuneus, and several other areas of the brain than the control subjects. This was also observed in patients with a slower Post label delay, although the article did not suggest a reason as to why this was the case.

Bibliography:

Book:


  • Moe, B 2003, The Revolution in Medical Imaging, The Rosen Publishing Group, New York.


Websites

  • Eden, Guinevere. "Magnetic resonance imaging (MRI)." World Book Student. World Book, 2015. Web. 30 Oct. 2015.

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