Magnetic Resonance Imaging scan

CONTENT

Introduction………………………………………………………………………………………. 2

Magnet…………………………………………………………………………………………… 3

Gradient coils…………………………………………………………………………………….. 4

Shim coils…………………………………………………………………………………………5

Radio frequency coils……………………………………………………………………………. 6

Antenna/computer…………………………………………………………………………………7

Conclusion…………………………………………………………………………………………8

References………………………………………………………………………………………… 8

 

INTRODUCTION

A magnetic resonance imaging scan, commonly known by its initials MRI is a medical device used for the purpose of creating images of the human. This is possible through the use of very strong magnets that create he magnetic field and forces protons in the body to align with it (NIBIB, n.d.). Magnetic resonance is the absorption of electromagnetic radiation by electrons or atomic nuclei in response to the implementation of certain magnetic fields. Long before MRI scanners came to be what they are today, magnetic resonance state was called nuclear magnetic resonance also known by its initials NMR and it was used mostly to analyze the structure of chemical substances and was developed by a physics professor, Isidor Rabi, in Columbia University in 1937. However, in the 1960’s Raymond Damadian, a doctor, had the idea that maybe magnetic resonance could also be used in living organisms (Department of Radiology University of Washington, n.d.). He believed that cancerous cells could be distinguished from non-cancerous cells by using magnetic resonance (GE Healthcare, 2019). In 1971, he came to the conclusion that because cancerous tissues contained more water than healthy tissues, the scanners could detect that part of the human body in radio waves and measured the emissions from the local hydrogen atoms (Department of Radiology University of Washington, n.d). This led to the building of magnetic resonance scanners that would be big enough for a human body and what we know today as magnetic resonance imaging scanners, MRI scanners. MRIs are tube-like structures called the bore that hold many different components which are: magnets, gradient coils, shim coils, radio frequency coils, and a computer.

MAGNET

Figure 1. Lopez, M. (2015). MRI magnet. Retrieved from https://www.anl.gov/article/used-mri-magnets-get-a-second-chance-at-life-in-highenergy-physics-experiments

Figure 2. Unknown. MRI magnet. Retrieved from http://mriquestions.com/active-shielded-gradients.html

The magnets are one of the most important parts of an MRI scanner because the magnets are what allows the system to create the detailed images. This magnet is a particular one. It can produce a large,stable magnetic field. The most commonly used for these scanners are superconducting scanners because they are more capable of producing much stronger and stable magnetic fields than other magnets (Sprawls, 2000). The magnets used for imaging produce a magnetic field that runsthrough the bore (tube structure) of themagnet and parallel to the major patient axis (Components and Functions, n.d.). As the magnetic field leaves the bore, it spreads out and encircles the magnet, creating an external fringe field. The external field can be a source of interference with other devices and is usually contained by some form of shielding (Components and Functions, n.d.). The strength of these magnetic fields is measured in tesla or gauss where 1 tesla= 10000 gauss and usually the magnetic fields can range from 0.5 to 2.0 tesla; earth’s magnetic field is only 0.5 gauss (Components and Functions, n.d.). The magnetic field createdby the magnets is produced by passing through three different that are inside the magnet; gradient coils, shim coils and radio frequency coils.

GRADIENT COILS

Figure 3. Unknown. Gradient coils. Retrieved from https://snc2dmri.weebly.com/components–functions.html    

Figure 4. Unknown. Gradient coils. Retrieved from https://radiologykey.com/secondary-magnetic-resonance-imaging-magnets/

Gradient coils distort the magnetic field in gradients during the process of imaging. A gradient is just the change in the magnetic field strength. The strength of each field distorted by the coils is weaker than the original magnetic field. Each field distorted by the coils can increase or decrease depending on the specific and different part of the body being scanned by adjusting the main magnetic field (Components and Functions, n.d.). The gradients are the ones responsible for creating the different spatial characteristics.

SHIM COILS

Figure 5. Unknown. Magnetic resonance imaging hardware. Retrieved from https://radiologykey.com/magnetic-resonance-imaging-hardware/

Figure 6.  Unknown. MRI shimming. Retrieved from https://www.youtube.com/watch?v=__dp4d4UT9Q

In order to obtain good imaging from the scan the magnetic field must be uniform. Shimming is the process that adjusts the magnetic field in order to make it more uniform. This process involves many times placing steel bars in the magnet at precise positions in trays located along the inside of the magnet bore (Sprawls, 2000).

RADIO FREQUENCY COILS

Figure 7. Unknown. Radio frequency coils. Retrieved from https://onlinelibrary.wiley.com/doi/pdf/10.1002/jmri.26187

Figure 8. Unknown. Radio frequency coils. Retrieved from https://services.gehealthcare.com/gehcstorefront/p/2208999-19

Radio frequency coils are the coils closest to the patient compared to the other coils. They are within the magnet. Their function is to transmit frequency waves into the patient’s body with the purpose of producing an image (Components and Functions, n.d.). There are different coil designs for different regions of the body. It uses a form of non-ionizing radiation as energy which is a series of energy waves composed of oscillating electric andmagnetic fields traveling at the speed of light (Sprawls,2000). The radio frequency coils signals provide data from which the image is reconstructed by the computer.

ANTENNA/COMPUTER

Figure 9. Unknown. MRI computer system. Retrieved from https://snc2dmri.weebly.com/components–functions.html

The antenna/computer system detects the radio frequency signals sent by the patient’s body while being scanned by the MRI. The information retrieved by the Radio frequency coils is sent to the computer system. The computer receives it, records it, and analyzes it to then help create a clear and accurate image of the body part being scanned (Components and Functions, n.d.).

CONCLUSION

A magnetic resonance imaging scan (MRI) is a medical device used with the purpose of creating images of the human body and its physiological processes. An MRI is composed by a giant magnet which is composed of different coils; gradient, shim and radio frequency coils. The magnetic field created by the magnet is produced by passing through these multiple coils to lastly send the data to the computer system of the MRI creating a clear image of the specific part of the patient’s body.

REFERENCES

Components & Functions. (n.d.). Retrieved October 23, 2020, from https://snc2dmri.weebly.com/components–functions.html

Featured History: Magnetic resonance imaging. (2016, July 21). Retrieved October 23, 2020, from https://rad.washington.edu/blog/featured-history-magnetic-resonance-imaging/

Magnetic Resonance Imaging (MRI). (n.d.). Retrieved October 23, 2020, from https://www.nibib.nih.gov/science-education/science-topics/magnetic-resonance-imaging-mri

Sprawls, P. (2000). Magnetic resonance imaging: Principles, methods, and techniques.

Madison, Wis: Medical Physics.

Themes, U. (2016, January 10). Secondary Magnetic Resonance Imaging Magnets. Retrieved October 23, 2020, from https://radiologykey.com/secondary-magnetic-resonance-imaging-magnets/