#129 Risks of CT and MRI (English)

Risks of CT and MRI

CT Scanner

 A computerized tomography (CT) scan combines a series of X-ray images taken from various angles and uses computer processing to create cross-sectional images of the bones, blood vessels and soft tissues inside the body. Thus, CT scan provides more precise image than plain X-rays do. In the CT scanner, the X-ray tube rotates around the patient. The X-ray detector on the opposite side receives the beam that penetrates it through the patient. The signal received by each and 764 channels is digitized to a 16bit value and sent to the reconstruction processor. Measurements are processed about 1000 times per second. Based on the calibration scan data of air, water and polyethene, previously acquired in the exact same relative location, scan data from each channel is compared. The comparisons lead to materializing the image pixels to have a known value for particular substance in the body regardless of differences in patient size and exposure factors.





MRI Scanner

 Magnetic resonance imaging (MRI) is a type of scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body. Using a very strong magnet and pulsing radio waves, the detection coils in the MRI scanner read the energy produced by water molecules as they realign themselves after each RF alignment pulse. The collected data is reconstituted into 2D image through any axis of the body. Bones are essentially void of water and accordingly, do not generate any image data. Consequently, bones are not indicated on the images.

 

 There are many risks appertained to CT and MRI. For instance, the amount of radiation released by a CT scan is about one in three hundred chance of a CT scan spurring a cancer, and this may be fatal for young and pregnant women. Although MRI scanners do not emit radiation, it builds up a very powerful magnetic field to stimulate the atoms in the patient’s body. The excited atoms release a type of energy, and it is detected by the scanner. Not only does this magnetic field instigate the atoms but also heats up the metal that may be present inside patient’s body. Furthermore, the use of contrast agents, dyes that highlight the blood vessels, in CT like iodine can be lethal for patients will iodine allergy. Also, the contrast agents of MRI scanners, highlight lesions that cause a breakdown in the blood-brain barrier, like gadolinium could case nephrogenic systemic fibrosis for people with kidney disease.

MRI Image of the Brain
Before and After Injections of Gadolinium

 Blood-brain barrier is a highly selective permeability barrier that separates the circulating blood from the bran extracellular fluid in the central nervous system.

[Reference]

http://www.mayoclinic.org/tests-procedures/ct-scan/basics/definition/prc-20014610
http://www.nhs.uk/conditions/MRI-scan/Pages/Introduction.aspx
http://www.diffen.com/difference/CT_Scan_vs_MRI
http://neurology.about.com/od/Radiology/a/MRI-vs-CT.htm
https://en.wikipedia.org/wiki/Blood%E2%80%93brain_barrier

KSJ