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30/6/2014 SHEET # 3 AsmaSaleem

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What dose the tube current contrast your image ?what happen if I increase my meli-amperage( mA) ? what happen to the current of the beam ??

>> For the image it will be darker .

>> For beam itself it will increase the number of photon , energy doesn’t change just the num .

More number of photon are getting in >> so more number are getting out -- image darker

And the same thing happen if I increase the time ( thenum of photon will increase and the image will be darker ) .

The factors controlling x-ray beam :

1- Kilo-voltage ( kVp) - Its affected the 1- energy of the beam.- 2- contrast of the image .- The higher ( kVp) I go, the higher energy i get ( avg energy and max energy )

What is the energy of Bremsstrahlung to produce beam ? Its not single , it’s a major spectrum .

Description of spectrum include where its start , end , and peak .- When I increase (kVp) -- the end and peak will increase . - When I change the filtration - the start of the spectrum will change . -

2 - meli-amperage( mA) :- It is the current .- Affect the number of photons.- The more ( mA ) the image is darker. - The less ( mA ) the image is lighter.


* what is the other thing that I can change to have the same effects as amperage ?

the time

3- Filtration : What does filtration change in the beam ?1- Removal of low energy photons .2- Mean energy of whole beam increase , why?Because we remove the low energy photons then calculate mean of the rest of photons that have a relatively high energy , so the mean will increase .3- Maximum energy doesn’t change .4- Its change the start and the beak of the spectrum but dosent affect the

max energy . This filtration done by adding a thin small aluminum foil which would be

enough to stop low energy photons . Why we need to eliminate low energy photons ?Because without filtration ;• The dose will increase without increasing diagnostic quality • The low energy photons are very weak to penetrate patient’s tissue to the other side to get a receptor and make an image , so these photons will be absorbed by patient’s tissue which increase the harm effect of radiograph on the patients .

What is the scatter radiation ?

ليضرب , " ومستمر ماشي وبضل طريقه بغير ما فوتون بيدخل الزمان قديم في مكان يا كانفيه مر الدي الجسم معلومات معه حامال . بالفلم

How ever light is much muchcomplicated ..


When the light inter it will repulsion and change its energy state ( change the speed and direction ) ." منه اجوا الي المكان عن سليمة تشريحية معلومات يحملوا بطلوا

الشمال : , العين جنب الفلم على وضربوا اتجاههم غيروا بس اليمين العين من دخلوا بكونو متالوبنسميها, لالستخدام منيحة مش الفوتونات وهاي ( scatter radiation )

Scatter radiation :

Its one of the most important factor that cause noise to the image quality .andtheres a lot of ways to decrease noise ………

4- collimation :an other factor affecting central beam and image quality .

means , shaping of beam to coincide with region of interest that I want to photo .

• an example to understand what collimation means :

if I want to take a photo to lumber part of spinal cord , it does not make sense to take a photo for the whole abdomen because doing so will not give me a diagnostic information , will increase patient exposure to extra radiation .

• I need to focus on the lumber spine by shaping the radiation using collimation .

Notes :

-The photons are not smart creature ( they are electromagnetic waves ) , and waves interact with matter .

- A few number of photons that enter the body and walk in a straight way to hit the target .

- Most of photons do scatter ; which mean that the photons change their direction. foreg. , photon (x) enters from right side of abdomen but exist more closer to midline ( this deviation in the direction called scatter ) .


- scatter radiation : 1- doesn’t include good diagnostic information .

2- doesn’t contribute to the image .

• Good diagnostic information comes from photons that enter and exit from the same level of entry to hold the right location information .

-when I direct the radiation to large area , I increase the likelihood of scatter , but when I focus the radiation to small area then the scatter is less.

- when scatter decrease; the image contrast will increase ; because scatter kills contrast , and decrease the harmful effects to patients .

Collimator : instead of using wide beam , we use smaller size ( rectangular collimator , which we don’t have in our clinic ).

Rectangular collimator : rectangular in shape , and has an area equal to the area of size(2) film , so its size equal to the size of the teeth that I want to image so the scatter is so minimal , which will decrease the dose and improve quality of radiographs . ( rectangular collimator gives an optimal beam )

• Some collimator fixed on the machine and some on receptor holders ( we will talk about it later ).

Why collimation doesn’t use frequently in dentistry ?

Collimation take more time and it need more knowledge about the anatomy and geometry .

Why collimation doesn’t everybody do it ?

Because it’s not easy for technician.


There’s two image taken by the same cavity , mA , time , all thing the same , the only differences is the size of the cone .

Pic on the left : less contrast

Pic on the right : better contrast , able to distinguish between enamel and dentine and able to see better details in periodontal space ( dentine , root surface , periodontal ligament and lamina durra ) .

*** the contrast here occur due to collimation without changing kVp or developing time or other variable .

5-Distance :

- Important in image quality and more imp. For patient protection from radiation ( the spread of electromagnetic waves and scatter radiation ) .


if you are next to the source of radiation then you will get more photon per area as compared when you stand more distance away .

This is applied by a law called ; inverse square low .

Inverse square law : Intensity of an x-ray beam is inversely proportional to the square of the distance between the source and point of measure .

I1 = intensity at point 1

I 2 = intensity at point 2

D 2 = distance at point 2

D 1 = distance at point 1

• The relation : is inverse to the square of distance .

• As you go further from the source as the intensity decrease

• When the distance is doubled the intensity of x-ray decrease 4 times.

• This mathematic law applied when the question said that you have (x) amount of radiation at 1 m distance , calculate the amount of radiation at 2 m from the source .

- In some cases , dentist need to be very close to the source of radiation during taking radiograph to patients ;

- For patient : radiation exposure once in time to treat her\ his case.


- For dentist : you takes radiographs all day long .

- For endodontist : they take 4-5 radiographs per patient during day .

• These cases are not advisable and against the guideline;You need to respect the distance from the radiation source .

If you 1.2 m away from the primary beam then you are safe .

X-ray produced by two ways : Bremsstrahlung and characteristic , its happen at the anode inside x- ray tube , these interaction that happen inside the patient have two things :

1- Create the image 2- Harmful effect for the patient

X-ray interaction is similar in mechanism to the x-ray production , but it occurs at different places so we called the steps in x-ray interaction in different names .

We have 3 types of x-ray interaction :1- Photoelectric absorption 2- Coherent scattering 3- Compton scattering These interactions happen in the head of patient ( tissue of recipient ).Related to the figure :


1- No interaction between the beam and tissue ( enter and exit as it is ), very small fraction ( about 9% ).2- Coherent scatter ( enter the tissue without exit )3- Photoelectric absorption (enter the tissue without exit )4- Compton scatter : small amount of beam fluctuated.

1- Coherent scattering :

Low energy photon hit atoms , atoms have kinetic energy (osculated)

The incidence photon enter , and the atom change the direction of the photon , but there’s no energy exchange , because of that its called scattering .

Its majorly seen in low energy photon , but in dentistry applications most of the photons are high energy photon ( photoelectric interaction ) so there is no coherent scattering in diagnostic radiology .

2- Photoelectric absorption :

- Photon has a huge energy , hit the atom and enter the inner orbital to knocked the inner orbital electrons out then cascading occur .

- X-ray interact with the atom to cause these changes :

1- Energy of photon decrease a little bit

2- Some of this energy is given to the knocked electron


3- This knocked electron may hit the neighboring atom which may cause photoelectric absorption or Compton scatter .

Notes :• Photoelectric interaction is responsible for the bad effect of radiology on patient’s tissues ; because the tissue takes energy , the atom destroys and the electrons go out that atom .• Anybody exposed to x-ray beam with a lot of frequency is able to absorb these electrons and have photoelectric absorption ( not only the patients but also the doctors ) .• Electron that knocked out has energy higher than the photon , because the photon gives high amount of energy to knocked inner shell electrons .

3-Compton scattering

By No interaction, Coherent scatter ,Photoelectric absorption , Compton scatter the image produced . If all photon enter and completely exit , - then the image will be completely black .

** Attenuation :

- Every tissue type , tissue thickness , and shape of tissue have different profile in having HOW much percentage of photoelectric or


Compton or coherent scattering in it and how much photon will enter and exit without affecting this tissue . the collective effect of beam on tissue called attenuation .• Enamel appears very white in pre-apical radiograph ; why ? because enamel is a hard tissue and has a high density , so photoelectric is more , absorption of photon is more and little amount of photon pass to the other side . so enamel appear white in color .• Less dense tissue ( as in dentine ) , there is no enough absorption of photon , so this photon either scatter or pass through the whole way which will give us shade more gray or black in color .• So these shades come from attenuation characteristic of that tissue which has specific shape and thickness.

*** so attenuation : is the quality of the interaction between incidence photon ( x- ray beam ) and the physical body to creat an image .

• The dr shows us a photo to a skull having a reconstruction titanium bar to rebound the mandible .• each piece of anatomy interact with incident beam in different way which will give different color .-Color of titanium differ than the color of bone - Color of bone differ than the color of soft tissue - Color of soft tissue differ than the color of air in sphenoid sinuses .• So when the beam enter it has been handling differently by different type of tissues .• So the diagnosis of certain anatomy based on the idea of attenuation ..


** Factor affecting attenuation ( absorption of beam depend on ):1- Thickness and density of the tissues .2- Energy of beam .

Because of that we say when I chang the voltage , the contrast will change , because I change the attenuation profile of certin tissue .

If I increase the energy of the beam , the absorbtionincrase or decrease ???It will decrease ..( , مدفع بدفشها الي الكبيرة الكرة فكرة نفس

يكون الزم بوقفها الي االشي ؟؟ يوقفها بيقدر اشي & dense فيthick )

• (step wedge) : its metal aluminum piece has a ladder shape and has degradation.• we took the energy on different kVp :kVp=100 then 70 then 40 .1- 100 kvp : more gradation in colors , more option in color ( pale gray , gray , dark gray )2- 40 kvp : high contrast because of accentuated differences ( the cuts between the colors are very clear and there is no degradation in the shades )

• Subject contrast :This depend on the patient’s physical characteristic ;1- Bone density : is the bone healthy , more dense or less dense .2- Soft tissue .3- Size of patient ( thickness of tissue ) .

GOOD LUCK

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