Wednesday, June 6, 2018

Radiology series #1 X-rays 1.0


Hello awesomites!

Today I am starting a new series of posts on radiology. Here I will be mostly dealing with the theory and technical part of radiology which as an undergraduate student we rarely read. Starting off with x-rays in this post and CT, USG, MRI to follow in the consecutive ones!


X-rays


A little bit of history,
X-rays were discovered by W. C. Roentgen in Germany on 8th nov 1895 and for which he received a Nobel Prize in 1901.
First let us know a few technical terms, collectively known as the ‘exposure factors: 

     1) kVP: kilovolt peak
     It determines the penetration of the x-ray beam through the body. High kVP implies more penetration of the body tissues

     2) mAS: milliampere second
     It determines the amount of blackening of the film. A high mAS will cause more blackening of the film for the same amount of x-rays hitting it.

      3) Contrast: It is the contrast shadow that is produced on the film i.e. white for bone and black for soft tissues. It is influenced mainly by the penetration of the x-rays i.e. the kVP and partly by mAS.

A low kVP (low penetration) means high contrast.

Contrast is proportional to 1/kVP

But,

A low mAS (less blackening) means low contrast.

Contrast is directly proportional to mAS


Let us take up an example,

In obese and heavily built patients, more penetrance is needed so we need to increase the kVP but if we do so by increasing the kVP we are reducing the contrast which is not good.
So to achieve both high contrast and good penetrance, kVP is increased as well as mAS is increased.Increased kVP will take care of the required penetrance while high mAS will ensure good contrast.
The general protocol to increase the contrast is first by reducing the kVP and then if necessary increasing the mAS to desired levels.


That’s all for now, more about the actual working of the x-ray machine and different settings in the next post. Hope you liked it !

Until then,
Keep calm and keep studying
Stay awesome!
-          Ashish G. Gokhale

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