Image formation & rad quality

Copyright © 2017, Elsevier Inc. All Rights Reserved.
Chapter 3 ~Fauber
Image Formation and Radiographic Quality

Objectives – Image Formation
2
1. Describe the process of radiographic image formation.
2. Explain the process of beam attenuation.
3. Identify the factors that affect beam attenuation.
4. Describe the x-ray interactions termed photoelectric
effect and Compton effect.
5. State the composition of exit radiation.
6. Explain the process of creating the various shades of
image brightness.

Objectives ~ Radiographic Quality
3
7. Describe the necessary components of radiographic
quality.
8. Explain the importance of brightness and contrast to
image quality.
9. Differentiate between high-contrast and low-contrast
images.
10. Explain the importance of spatial resolution - both size
& shape distortion in image quality.
11. State the effects of quantum noise, scatter, and image
artifacts on image quality.
12. Recognize the advantages of digital imaging and
limitations of screen film imaging.

Key Terms
• absorption
• artifact
• attenuation
• brightness
• contrast resolution
• density
• differential absorption
• distortion
• dynamic range
• elongation
4
• foreshortening
• gray scale
• high contrast
• latent image
• low contrast
• magnification
• manifest image
• quantum noise
• scattering
IS A RESULT OF TO FEW PHOTONS IN THE IR

The Human Body as an Attenuator
Composition of human body determines its radiographic
appearance

Image Formation
6
• Differential absorption
• Anatomic tissues absorb and transmit x-rays differently
based on their composition (atomic number and tissue
density).
• Bone absorbs more x-rays than muscle.
• Attenuation: the primary x-ray beam loses some of its
energy (number of photons) as it interacts with anatomic
tissue.
• Absorption
• Scattering = Attenuation

Copyright © 2017, Elsevier Inc. All Rights
Reserved.
7
only 5 % exit body to IR
she said smth 20 % ____ shushka

Differential Absorption
8
• As the primary x-ray beam interacts with an anatomic
part, photons are absorbed, scattered, and transmitted.
• The differences in the absorption characteristics of the
anatomic part create an image that structurally represents
the part.

X-ray Beam Absorption
10
• During absorption, the energy of the primary beam is
deposited within the atoms comprising the tissue.
• Photoelectric effect: complete absorption of the incoming
photon
• X-ray ionizes atom.
• Low-energy secondary x-ray photon created.
• Probability of photoelectric effect dependent on the energy of the
incoming x-ray photon and tissue atomic number.

• Incident photon ejects a K- or L-shell
electron
• Termed a photoelectron
• Photon totally absorbed by the electron
• Vacancy filled with an outer shell electron
• Characteristic photon produced
(secondary radiation)
Photoelectric Effect

Reserved.
12

Scattering
13
• The Compton effect occurs when an
incoming photon loses some but not all of
its energy, then changes its direction.
• It can occur within all diagnostic x-ray
energies and is dependent only on the
energy of the incoming photon, not the
atomic number of the tissue.
• Higher kVp reduces the number of
interactions overall, but the number of
Compton interactions increases in
comparison to the number of
photoelectric interactions.

Compton Interaction
• Incident photon ejects an outer shell electron
• Recoil or Compton electron
• Photon partially absorbed by the electron
• Scatter photon emitted equal to the residual energy
couse fog in the image; different from photoelectric interaction

Absorption Versus Scattering
15

Copyright © 2017, Elsevier Inc. All Rights Reserved.16
pay attention to this
high kvp increase the compton and less photoelectric happen
when increasing kvp less interaction with matter occures because photons get transimited, thus
less photoelectric and scatter. Nevertheless, of those interaction that accures, most are compton
then photoelectric interactions

Photoelectric Effect & Compton Scattering
how to avoid compton: collimation and grid;

Reserved.
18
Notice many shades of gray
in the image receptor bar.

19
Is attenuation the same as
absorption?NO!
ATTENUATION = SCATTER AND ABSORPTION

Factors Affecting Beam Attenuation
20
• Tissue thickness
• X-rays are attenuated exponentially and generally reduced by ~
50% for each 4 to 5 cm (1.6 to 2 in) of tissue thickness.
• Type of tissue
• Tissues composed of a higher atomic number will increase beam
attenuation.
• Tissue density
• Increasing the compactness of the atomic particles will increase
beam attenuation.
• X-ray beam quality
• Higher kVp increases the energy of the x-ray beam and will
decrease beam attenuation.
2 PROCESSES ACCURES WITH BEAM ATTENUATION:
ABSORBTION AND SCATERING= Question
what comes out?
when you take
PA is better because less x rays will interact anteriory with breast or gonadal tissues
ESE = enter skin exposure
because x rays will be transmited through body and go to image receptor therefore will not
be attenuated, absorbed in the tissue

Tissue Thickness
AEC help out
when you take your exposure take a look at mAs that come out; pay attention; AEC
chooose mas for you but still you see what mAs is used in the exposure you took.

Type of Tissue
22
• Bone absorbs more radiation than fat and air.
• Air transmits more radiation than fat and bone.
Z# 13.6 Z# 6.3
calcium = 20
what is absorbtion happen what interaction happen
here? photoelectric interaction
13.8 7.6
7.4
Muscle
this is because air is less dense than fat and bone, this doesnt have to do anything with atomic number
so, just ignore the number in the boxes, use them for page 23 better

Type of Tissue & Tissue
Density
23
Material Atomic Number
Air 7.6
Lung 7.4
Fat 6.3
Muscle 7.4
Bone 13.8
Iodine ___
Barium ___
Lead 82
Reference: Bushong 11edition – Ch 9, pg 152
Materials in
Human Body
Atomic Number
Hydrogen
Carbon
Nitrogen
Oxygen
1
6
7
8
53
56
barium high atomic number that is why they use high kVp in fluoroscopy
less mass

Reserved.
24

Reserved.
Differential Absorption & Attenuation depends
on the following factors…
25
• Atomic number (Z#) of atoms in the tissues
• The mass density of the atoms in the tissues
(compactness)
• The X-ray energy
• Thickness of atomic part
1
2
3
4

X-ray Beam Quality
27
1. The energy of the x-ray beam affects its interaction
2. Lower kVp results in more absorption in the tissue;
3. Higher kVp results in more transmission through
the tissue.

Exit Radiation
• Exit radiation (aka
___________) composed of
transmitted and scattered
radiation.
• The varying amounts of
transmitted and absorbed
radiation create an image that
structurally represents the
anatomic area of interest.
• Scatter radiation reaching the image
receptor creates unwanted
exposure called _ _ _.
28
ESE = enter skin exposure
FOG
REMNANT

Reserved.
Brightness vs. density
29
FILM SCREEN - DO NOT LOOK AT THIS
each picel display an amount of gray; if picxel is dark is = decreased brightness, without
brightness we can not see the image;

Radiographic Image
• Absorbed radiation creates increased brightness or white on the
displayed image.
• Transmitted radiation creates decreased brightness or black on the
displayed image.
• The various shades of gray recorded in the image make anatomic
tissue visible.
30
calcaneous bone is shown up
bright; no differentiation betwene
muscle and fat; msot brightly
bright and gray- few shades of
gray; we need certain shades of
gray in order to see smth in the
image

Radiographic Quality (Cont.)
31
we look at brightness- its light emission from the monitor; brighteness is a function of the
monitor too; playing in iphone; brighter or grayer - but here are two separate things; brightes
and contrast
distrotion is a good thing; sometimes we use it for purpose = ex. elongation of the scaphoid
bones

Radiographic Quality
32
• A quality radiographic image accurately represents
the anatomic area of interest, and its information is
well visualized for diagnosis.
• Visibility of anatomic structures
• Brightness
• Contrast
• Accuracy of structural lines (sharpness)
• Spatial Resolution
• Distortion
radiographs has to show distortion of the patient;

Image Brightness
• A digital image is evaluated by the amount of brightness
or luminance (light emission) of the display monitor.
A radiographic image must have
sufficient brightness to visualize the
anatomic structures of interest.
33
bit deep = how many shades of gray you have;
how many shades of gray for our human eye ? = 32
shades
brioghtnes has to do with light emission in the monitor
never chanmge the broghtness; just see AEC; so
PACK can make changes
43..2.1.0

Image Brightness (Cont.)
34
exposure indicator = ask at clinical for this
dicreased brightness increased brigtness

Image Contrast
35
• The radiograph must exhibit differences in the
brightness levels or densities (image contrast) in order
to differentiate among the anatomic tissues.
• The range of brightness levels is a result of the tissues'
differential absorption of the x-ray photons.
slitly
changes in
the level of
brightness
in order to
see contrast;
image
contast, we
need an
amount of
brigtness
and contrast
bladder ,
conrast
media; gas is
in the
rectum not
in the
bladdrer
contreast in the kidney; low contrast; maybe some compton scater in it a little off center; we
should use grid; for larger pretioon squiss them down lay on the belly for this if you can

Subject Contrast
36
Result of the absorption characteristics of
the anatomic tissue radiographed
The quality of the x-ray beam.
The ability to distinguish among types of
tissues is determined by the differences in
brightness levels in the image, or contrast.
Text

Subject Contrast
37
Higher contrast resulting from great differences in radiation absorption between tissues
that vary greatly in composition.
Lower contrast resulting from fewer differences in the radiation absorption for tissues that
are more similarly composed.
ex. chest x ray has higher Text

High Subject Contrast38
• High Subject Contrast
• Tissue attenuate x-ray
differently
Example: CHEST
• Bony thorax
• Lungs
• Heart
• Example: wrist
Subject Contrast
bukkle fracture
children epiphysial plate
children calciu, is lower

Low Subject Contrast
39
• Low subject contrast
• Tissues attenuate beam
similarly
• Brightness levels of organs
are similar
Subject Contrast

40
• Tissue thickness
• Density of tissue/structure
• Effective atomic number
• Can affect subject contrast
Subject Contrast
vary shades of grays = contrast

Spatial Resolution
41
⬤ Anatomic details must be
accurately recorded and with
the greatest amount of
sharpness.
➢ Spatial resolution refers to the
smallest object that can be detected
in a digital image.
➢ All radiographic images have some
degree of unsharpness. TRUE - true false question

42 Copyright © 2017, Elsevier Inc. All Rights Reserved.
⬤ Anatomic details must be
accurately recorded and with
the greatest amount of
sharpness.
➢ Spatial resolution refers to
the smallest object that can
be detected in a digital
image.
➢ All radiographic images have
some degree of
unsharpness.
image contrast is the variation of brightness,
image receptors has ability to distingush among these
small focal spot

bony trabeculae very well seen

44 Copyright © 2017, Elsevier Inc. All Rights Reserved.
⬤ Radiographic misrepresentation of either
the size or shape of the anatomic part
➢ Size distortion or magnification is an
increase in the object's image size
compared to its true or actual size.
• SID and OID affect magnification.
➢ Shape distortion is a
misrepresentation of an object's image
shape.
• Elongation and foreshortening.
• Central ray (CR) alignment of the x-
ray tube, part, and image receptor
affect distortion.

Factors Affecting Size Distortion
⬤ Radiographic distances
➢ Controlled by SID and OID
➢ Magnification only
decrease SID b=vs Increased SID

Factors Affecting Shape Distortion
⬤ Alignment
➢ Central ray
➢ Anatomical part
➢ Image receptor
⬤ Angulation
➢ Degree
➢ Direction

47
⬤ Unwanted exposure to the image receptor resulting in fog
➢ A result of Compton interactions
➢ Provides no useful information.
➢ Scatter decreases image contrast.
➢ Digital image receptors can detect lower levels
of radiation intensity and therefore are more
sensitive to scatter.
less gray because of grid used
brighter less gray; still, i have to increase technique, mAS

Image Artifacts
49
⬤ Any unwanted information on an
image
⬤ Impedes anatomy, pathology,
patient ID information
⬤ Decreases the overall quality of an
image
⬤ Patient-related
⬤ Imaging Equipment
diagnoses efficasy

50
not scater - is noise
there is not enough
info, photons mAs, we
might have enough
kVp but not mAs

Digital vs Film-Screen Imaging
51
• Range of exposure intensities an image receptor can
accurately detect.
• Digital imaging has higher dynamic range than film-screen
• Digital imaging has improved contrast resolution

Comprehension Check
54
1. What is the term that describes the reduction in the
intensity of the primary beam?
2. Describe differential absorption
3. Are absorption and attenuation the same thing?
4. What is the relationship between brightness and
exposure?
5. What is subject contrast?
6. What is difference between latent, manifest, visible,
invisible image?
7. If the energy of the x-ray beam is 120, what
happens to Photoelectric effect?
8. Can quantum noise be an artifact?
1. attenuation
3. no! Attenuatiuon = absorbtion + scatering
2. different absorbtion of the x
ray due to to the different
anatomic number of bones,
tissues, air, muscle, fat
7. Decreases because photons energy is high and photons can be trasmited, and do
not get absorb from the tissue
yes
4. Digital IRs separate acquisition from processing and image display; their response to changes in
radiation exposure does not affect the amount of brightness displayed on the image. The level of
brightness and contrast can be altered during computer processing and image display.

An image having sufficient
brightness but no differences
An image with varying levels
of brightness

Image formation & rad quality

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