‫بسم هللا الرحمن الرحيم‬
Dr. Mustafa Zuhair Mahmoud
Mr.Ali B Alhailiy
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Influences on Image Quality
5. Image Noise:
• Every radiologic image contains information that is not
useful for diagnosis and characterization of the patient’s
condition.
• This information not only is of little interest to the
observer, but often also interferes with visualization of
image features crucial to the diagnosis.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5. Image Noise:
• Irrelevant information in the image is defined as image
noise.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5. Image Noise:
• Image noise has four components:
1.
2.
3.
4.
Structure noise.
Radiation noise.
Receptor noise.
Quantum mottle.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5. Image Noise:
• Image noise has four components:
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.1 Structure Noise:
• Information about the structure of the patient that is
unimportant to diagnosis and characterization of the
patient’s condition is known as structure noise.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.1 Structure Noise:
• For example, shadows of the ribs not only are irrelevant
in chest radiographs taken to examine the lung
parenchyma, but also can hide small lesions in the
parenchyma that could be important to characterization of
the patient’s condition.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.1 Structure Noise:
• In radiography, patients frequently are positioned for
examination so that structure noise is reduced in the
region of interest in the image.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.1 Structure Noise:
• The most obvious methods of reducing structure noise
are:
1. Computed tomography (CT).
2. Magnetic resonance imaging (MRI).
(Because they blur structures above and below
the plane of interest within the patient).
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.2 Radiation Noise:
• Radiation noise is information present in a radiation beam
that does not contribute to the usefulness of the image.
• For example, many x-ray beams exhibit a nonuniform
intensity from one side to the other.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.2 Radiation Noise:
• This nonuniformity, termed the heel
effect, is a result of the production and
filtration of the beam in the anode of the
x-ray tube.
• the x-ray intensity greater at the cathode
end of the x-ray field and lower at the
anode end because of absorption in the
target material
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.2 Radiation Noise:
• Similarly, the radiation beam exiting from the patient
contains considerable scattered radiation.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.2 Radiation Noise:
• Scattered radiation interferes with the visualization of
patient anatomy. Hence, scattered radiation is radiation
noise.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.3 Receptor Noise:
• In radiography, intensifying screens and film are fairly
uniform in their sensitivity to radiation, and their
contribution to image noise is usually undetectable.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.3 Receptor Noise:
• However, contamination on a screen can add substantial
noise to the image known as receptor noise.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.4 Quantum Motel:
• Quantum motel is defined as mottle caused by the number
of photons absorbed by the intensifying screens to form
the light image on the film.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.4 Quantum Motel:
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
5.4 Quantum Motel:
• Quantum mottle can be reduced only by using more
information carriers to form the image (slow intensifying
screens).
• Technical error due to inefficient exposure factors that
can be corrected by adjusting mAs or kVp.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
6. Image Distortion and Artifacts:
• Any opacity on the radiograph that does not correspond to
an actual anatomic structure
• • Any misrepresentation of an actual anatomic structure
• • Anything decreasing radiographic quality
• Image distortion is caused by unequal magnification of
various structure in the image.
• Distortion and artifacts are present to some degree in
every diagnostic image.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
6. Image Distortion and Artifacts:
• For example in radiography, structures
near the intensifying screens are
magnified less than those farther away.
• it can be concluded that finer
resolution radiographs can be obtained
with a smaller focal spot, a large
source-to-image distance (SID) and a
minimal distance between the body
part and the image receptor.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Influences on Image Quality
6. Image Distortion and Artifacts:
• Magnification M in an image is the ratio of image to
object size.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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Image Distortion
Influences on Image Quality
7. Summary
• Image noise is influenced by four factors:
1.
2.
3.
4.
Structure noise.
Radiation noise.
Receptor noise.
Quantum mottle.
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
Influences on Image Quality
7. Summary
• Image distortion is caused by unequal magnification
of structure in the object.
• Image artifacts can arise from a multitude of
conditions. (to be discussed later).
Assistant Prof. Dr. Mustafa Zuhair Mahmoud
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