Properties of the xray Beam

Question 1

Photon Energy and penetration

Answer 1

At the atomic level, matter is mostly full of empty space, so high energy photons can pass straight through.

But the EM fields of low energy photons are more likely to interact with the electrical fields produced by the atoms with matter

Question 2

Photon Energy and penetration

Answer 2

The impression that you have is that everything is solid in matter but at atomic level is not
-Space is mostly empty
For this reason an energy bean can pass through matter
The more energy it has the less likely is to interact with matter and most likely to pass through
Particles have EM fields that interact with EM wave . Higher the Energy less they interact.
Asteroidswith a 1 km (0.62 mi) diameter strikeEarthevery 500,000 years on average. Large collisions – with 5 km (3 mi) objects – happen approximately once every twenty million years. ( Earth Diameter 12,742km)

Good thing X Rays Sometimes they interact sometimes they do not.
X-rays interact the most with dense Matter . What is dense Matter? Air? ( NO) Metal ?( yes e.g. Lead) Bones( Yes)_
Air Formula : Nitrogen (N2), Oxygen (O2), Carbon Dioxide (CO2), Water (H2O)
Lead Formula : Lead,82Pb

IS or A Therapy System Out of X ray is based on penetration and absorption.

Question 3

Photon Energy and penetration

Answer 3

So higher energy photons are more penetrative than low energy photons.

Similarly, high frequency photons with short wavelengths are more penetrative

Question 4

Beam Penetration: Example

Answer 4

Chest in general with High KV technique
High Kv and Low KV

Too High KV = over penetration dark image
Modulation of mas and Kv
Understand penetration is Very difficult and is often confused with over exposure. High Kv techniques
Big patient
Lateral for neck injuries
More mas , more scattering

Question 5

The Diverging Beam: Magnification

Answer 5

Source Image Distance (SID)
Object Image Distance (OID)
Source Object Distance (SOD)
Mag= SID/(SID-OID)
Mag= SID/(SOD)

Mag = 1 if BC is in contact with DE
Or the magnification is 1 if the object is in contact with the detector

Question 6

The Diverging Beam: Magnification

Answer 6

The position of the object is very important for both the magnification effect but also for the modulation of the mas (as the intensity varies)

What is A in the tube? ( the anode/ the focus)
What is BC object? (Human Being)
DE ? (Detector)

EXAMPLE patient not in contact with the detector affects a lot the way radiographers work
Do you understand magnification? it is a consequence of the shape of the beam. (cone, diverging..) If there was a parallel source of radiation there would be no magnification

Question 7

Magnification Calculation

Answer 7

SID = 100 cm
OID = 50 cm
Object is 10 cm
Image = Object X Magnification

M = SID/(SID-OID)
M = 100 /(100-50)
M = 2
Image = 10 X 2
Image = 20 cm

Question 8

Magnification Calculation for you

Answer 8

SID = 50, 100, 150, 180 cm
OID = 15 cm
Object is 15 cm
Image = Object X Magnification

M = SID/(SID-OID)
M = 50 /(50-15)
M = 1.4
Image = 15 X 1.4
Image = 21 cm

Question 9

The Divergent Beam: Intensity

Answer 9

Due to the inverse square law the intensity of the beam decreases exponentially away from the point source

Question 10

Inverse Square Law: Calculations

Answer 10

ix = 10 e-hx

i1/i2 = d22/d12

Question 11

The Divergent Beam: Penumbra

Answer 11

For imaging, radiation should come from an infinitely small point source.

In reality, the focus of the beam always has some size. This creates unharness in the image due to the penumbra effect.

This is why you should use a fine focus filament for detailed images.

If there the source is infinitive small , there is no penumbra.
For therapy penumbra may mean irradiating larger area.

Question 12

The Divergent Beam: Penumbra

Answer 12

For imaging, Patient should be close to the image receptor.

In reality, the closeness of the patient is fixed due to the equipment structure. This creates unsharpness in the image due to the penumbra effect.

Think ED trollies, Bucky trays etc

Question 13

Distortion

Answer 13

Shape distortion is the misrepresentation of the shape (length or width) of an object

Last effect is Geometric distortion. Is not less important and can lead to misdiagnosis.
It depends from the position and orientation of the object (patient ) in relation to the detector plane.
If they are not parallel Geometric distortion will occur.