1. Part No...., Module No....Lesson No
Module title
Chapter 3 DIAGNOSTIC RADIOLOGY Image quality Dr M A Oghabian Medical Physics Group, Tehran University of Medical Sciences
IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

2. Part No...., Module No....Lesson No
Module title
Aim:
To become familiar with the factors that determine the image clarity and the way the image quality can be improved
IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

3. Part No...., Module No....Lesson No
Module title
Contents
Image contrast
Blur or lack of sharpness
Distortion and Artifacts
Image noise
Explanation or/and additional information
Instructions for the lecturer/trainer
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

4. خصوصيات تصوير در راديولژي
Part No...., Module No....Lesson No
Module title
خصوصيات تصوير در راديولژي
1- دانسيته تصوير غيرخطي است. اما اين يك عدم مزيت نيست.
2- تصویرداراي زمينه (Background) تشكيل شده از هر دو دانسيته و noise مي باشد.
-3داراي عدم وضوح(Unsharpness) بدليل focal spot size و Screen مي باشد.
-4داراي تغييرات فوتوني و نوري عمدتاً Random بنام noise مي باشد.
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

5. Factors affecting image quality
Part No...., Module No....Lesson No
Module title
Factors affecting image quality
Blurring or
Unsharpness
Contrast
Image quality
Distortion
& artifact
Noise
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

6. Part No...., Module No....Lesson No
Module title
Topic 1 : Image contrast
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

7. Part No...., Module No....Lesson No
Module title
Image contrast
Difference in optical density between adjacent points on an image represents contrast
Contrast depends on:
 Density (air, bone)
 Thickness (micro calcifications)
 Atomic number
 kVp
 Film, intensifying screen, contrast agents
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

8. Part No...., Module No....Lesson No
Module title
Receptor contrast
The film as receptor has a major role to play in altering the image contrast
There are high contrast and high sensitivity films
The characteristic curve of the film describes the intrinsic properties of the receptor
(base + fog, sensitivity, mean gradient, maximum optical density)
N.B.: Film processing strongly has a pronounced effect on fog and contrast
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

9. Part No...., Module No....Lesson No
Module title
Video monitor
The video monitor is commonly used in fluoroscopy and digital imaging
The display on the monitor adds flexibility in the choice of image contrast
The dynamic range of the monitor is limited (limitation in displaying wide range of exposures)
Increased flexibility in displaying image contrast is achieved by adjustment of the window level or gray levels of a digital image
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

10. Topic 2 : Blur or lack of sharpness
Part No...., Module No....Lesson No
Module title
Topic 2 : Blur or lack of sharpness
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

11. Blur or lack of sharpness
Part No...., Module No....Lesson No
Module title
Blur or lack of sharpness
The boundaries of an organ or lesion may be very sharp but the image shows a lack of sharpness
Different factors may be responsible for such a degree of “fuzziness” or blurring
The radiologist viewing the image might express an opinion that the image lacks “detail”
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

12. Factors affecting image sharpness
Part No...., Module No....Lesson No
Module title
Factors affecting image sharpness
Geometric
Unsharpness
Subject
Unsharpness
Image
Unsharpness
Motion
Unsharpness
Receptor
Unsharpness
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

13. Part No...., Module No....Lesson No
Module title
Geometric blur
If the focal spot is effectively small, the blur is minimized because of minimal geometric unsharpness
As the focal spot increases, the blur in the image increases
Large focal spot
Small focal spot
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

14. Geometric Unsharpness
Part No...., Module No....Lesson No
Module title
Geometric Unsharpness
-مـحـوي مـربوط به اندازه نقطه كانوني با كاهش فـاصـله شئ تـا فـيـلـم يـا افـزايـش فـاصـلـة مـنـبـع تـشــعـشـع تــا شئ، كــاهــش مــي يــابـد.
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

15. Lack of sharpness in the subject
Part No...., Module No....Lesson No
Module title
Lack of sharpness in the subject
Not all structures in the body have well-defined boundaries (superimposition essentially present in most situations)
The organs do not have square or rectangular boundaries
The amount of required details in the object, is an essential requirement of any imaging system
The absence of sharpness, in the subject/object is reflected in the image
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

16. ِAbsorption unsharpness
Part No...., Module No....Lesson No
Module title
ِAbsorption unsharpness
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

17. Lack of sharpness due to motion (1)
Part No...., Module No....Lesson No
Module title
Lack of sharpness due to motion (1)
Common and understandable blur in medical imaging
Patient movement :
uncooperative child
organ contraction or relaxation
heart beating, breathing etc.
Voluntary motion can be controlled by keeping examination time short and asking the patient to remain still during the examination
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

18. Lack of sharpness due to motion (2)
Part No...., Module No....Lesson No
Module title
Lack of sharpness due to motion (2)
Shorter exposure times are achieved by the use of fast intensifying screens
N.B.: Faster screens result in loss of details (receptor sharpness)
Further, the use of shorter exposure time has to be compensated with increased mA to achieve a good image
This often implies use of large focal spot (geometric sharpness)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

19. Part No...., Module No....Lesson No
Module title
Movement Unsharpness
-مـحـوي مــربـوط بــه حـركــت بـيـمـار بــا كــاهــش زمــان تــصـويـربـرداري و يـا استـفـاده از آشـكـارسازهـاي سـريــع مـثل Cine- Fluorography مــي تـوانـد مـحــدود شـود
-از مـحـوي حـركـتـي جهت مـحـوكـردن بـخشهـايي از عـمـق بـافـت در تـومـوگــرافــي اسـتــفــاده مــيشـود
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

20. Lack of receptor sharpness
Part No...., Module No....Lesson No
Module title
Lack of receptor sharpness
The intensifying screen in radiography has a crystal size which is larger than that of the emulsion on the film
An image obtained without the screen will be sharper than that obtained with the screen, but will require much more dose
The thickness of the screen further results in degradation of sharpness
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

21. Part No...., Module No....Lesson No
Module title
Total Unsharpness
2/1 (Ua2 + Us2 + Um 2 + Ug 2 ) = Ut
در تــصــويـــربــرداري از اجســام بـــزرگ فـــقــط لبة ( edge) شئ تحت تأثير مــحــوي قـــابـــل تـشـخيـص نمی شود.
در تـــصـــويـــربـرداري از اجسـام كــوچـك
(مــثـل مـــيـكـروكـلسيـفـيـكـيـشن و عروق كوچك - سنگ كوچك)، توزيع نور حاصل از محوي باعث از بين رفتن خصوصيات شكل شئ مي شود وً شدت و كنتراست تصوير نيزكاهش مي يابد.
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

22. Topic 3 : Distortion and artifacts
Part No...., Module No....Lesson No
Module title
Topic 3 : Distortion and artifacts
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

23. Distortion and artifacts
Part No...., Module No....Lesson No
Module title
Distortion and artifacts
Unequal magnification of various anatomical structures
Inability to give an accurate impression of the real size, shape and relative positions
Grid artifact (grid visualized on the film)
Light spot simulating micro-calcifications (dust on the screen)
Bad film screen contact, bad patient positioning
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

24. Part No...., Module No....Lesson No
Module title
Magnification
از آنجائـيكه تـابش واگرا (Divergent) است، بـزرگـنمائـي تـصوير نـسبـت بـه شيئ ايـجـاد مـي شـود.
جهت كاهش اثر بزرگنمائـي، فاصله شيء تا فيلم را كم كرده و لذا در مواردي مثل عكسبرداري از سينه، فاصله تيوب تا فيلم زياد مي شود.
همچنين طريقه قرارگرفتن بيمار (بطورAP يا PA)
بزرگنمائـي در بعضي مواقع مثل ماكروراديوگرافي تعمدا ايجاد مي شود.
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

25. Part No...., Module No....Lesson No
Module title
Distortion
تغيير شكل ( Distortion) اجزا ناشي از زاويه متفاوت تابش و بـزرگــنمائـي حاصل مي شود.
جهت كاهش اثر تغيير شكل، فاصله شيء تا فيلم را كم كرده و بافت مورد تصويربرداري تا حد ممكن در مركز ميدان قرار داده مي شود.
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

26. Part No...., Module No....Lesson No
Module title
Artifacts
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

27. Part No...., Module No....Lesson No
Module title
Topic 4 : Image noise
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

28. Part No...., Module No....Lesson No
Module title
Image noise
Information that is not useful is noise
The snowing in a TV image, the speckles in an ultrasound image are examples of noise
Noise interferes with visualization of image features useful for diagnosis
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

29. Part No...., Module No....Lesson No
Module title
Main Sources of Noise
Radiation noise (eg; heel effect) (1
2 - Random or Stochastic noise:
جذب Random فوتونهاي x در صفحات تشديد كننده (Quantum noise).
Photon Statistical Noise by low photon flux)
(e.g; Screen or Coarse Grain Noise)
جذب Random فوتونهاي نوري توسط ذرات نقره در امولسيون فيلم
Receptor or Fine Grain Noise
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

30. Part No...., Module No....Lesson No
Module title
Main Sources of Noise
2- Structured or nonstochastic:
- اختلاف در ضخامت مواد لايه تشديد كننده Screen باعث دانسيته غيريكنواخت فيلم میشود
Receptor noise, Non-uniformed film, screen defects,…
 4- Electronic noise :
زماني كه تقويت شديد سيگنال انجام مي شود باعث تقويت Random noise هم مي شود
5- Random neural Process :
در چشم در زمان ديدن تصوير همچنين ايجاد نويز مي شود.
6) Scattered Radiation in Both Subject and Imaging Receptors
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

31. Part No...., Module No....Lesson No
Module title
Photon Statistical Noise (Quantum Mottle):
x-ray photons have a statistical character in nature
(the counts per unit time follows Gaussian distribution):
1- One x-ray exposure is not identical to a second x-ray exposure
2- The number of photons incident on different areas of the patient is not identical for a single exposure.
3- Flow of x-ray energy is non-uniform
4- There is a random variation in the number of photons striking each small area of the image receptor (Screen).
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

32. Part No...., Module No....Lesson No
Module title
3. The Gaussian or Normal Distribution
The Gaussian distribution is a probability distribution of a
continuous random variable.
If independent trails are
conducted with an outcome having an arithmetic mean m
and a standard deviation s, then
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

33. Part No...., Module No....Lesson No
Module title
s=0.2
s=0.5
FWHM
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

34. Part No...., Module No....Lesson No
Module title
Gaussian Distribution as a limiting case of the
Poisson Distribution
As n becomes large (eg; x-ray photon production)
Poisson distribution becomes a Gaussian distribution.
Since s 2 = m,
This distribution has the properties of a Gaussian distribution:
68.3% of the events fall in the range of
95.5%
99.7%
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

35. Noise and Detective Quantum Efficiency
Part No...., Module No....Lesson No
Module title
Noise and Detective Quantum Efficiency
Noise is defined as the uncertainty in a signal due to
random fluctuations in that signal. s 2s
Density
Measurement
Noise=s DD
SNR = DD/ s
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

36. Part No...., Module No....Lesson No
Module title s s
Noise is more prominent for low subject-contrast object
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

37. Signal-to -noise Ratio:
Part No...., Module No....Lesson No
Module title
Signal-to -noise Ratio:
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

38. Part No...., Module No....Lesson No
Module title
Signal to Noise Ratio
Standard Deviation of a poisson distribution is:
Where N represents the average number of photons striking a unit area. Most areas (68%) will then be struck by a number of photons in the range N- s to N+s.
SNR ratio is the real measure of noise level.
Quantum Noise
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

39. Noise Power Spectrum of film-screen system
Part No...., Module No....Lesson No
Module title
Noise Power Spectrum of film-screen system
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

40. Part No...., Module No....Lesson No
Add module code number and lesson title 40
Module title
ناحيه A در اثر تغييرات ساختاري (structure)در سيستم تصويربرداري(مثل ضخامت screen و غير يكنواختي صفحه تشديد كننده يا غير يكنواختي تشعشع مي باشد.
ناحيه B جايي كه نويز تقريباً ثابت است white noise ناميده مي شود و بدليل تغييرات اتفاقي مربوط به x-ray quantum يا نويز مدار الكتروني صورت مي پذيرد
ناحيه C كه كاهش شديد نويز را نشان مي دهد بدليل خصوصيات transfer function است كه فركانس هاي در اين حد را با gain پايينتري انتقال مي دهد.
Khjkhk
ناحيه D (white noise), است مربوط به ذرات فركانس بالاي فيلم و اسكرين (grains) مي باشد.
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

41. Where to Get More Information
Part No...., Module No....Lesson No
Module title
Where to Get More Information
Hendee WR, Riternour ER, eds. Medical Imaging physics, 3rd ed. St. Louis: Mosby Year Book, 1992
Sprawls Perry Jr. Ed. Pysical principles of medical imaging. Maddison: Medical Physics Publishing, 1993
Moores BM, Wall BF, Eriskat H and Schibilla H, eds. Optimization of image quality and patient exposures in diagnostic radiology. London: British Institute of Radiology 1989.
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources