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IMAGE NOISELecture No.5

Dr. Mustafa Zuhair Mahmoud

Mr.Ali B Alhailiy

الرحيم الرحمن الله بسم

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 2

Influences on Image Quality

5. Image Noise:

• Irrelevant information in the image is defined as image noise.

Assistant Prof. Dr. Mustafa Zuhair Mahmoud 3

Influences on Image Quality

5. Image Noise:

• Image noise has four components:

1. Structure noise.

2. Radiation noise.

3. Receptor noise.

4. Quantum mottle.

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Influences on Image Quality

5. Image Noise:

• Image noise has four components:

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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.

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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.

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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.

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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).

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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.

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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

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Influences on Image Quality

5.2 Radiation Noise:

• Similarly, the radiation beam exiting from the patient contains considerable scattered radiation.

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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.

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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.

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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.

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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.

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Influences on Image Quality

5.4 Quantum Motel:

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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.

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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.

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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.

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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.

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Image Distortion

Influences on Image Quality

7. Summary

• Image noise is influenced by four factors:1. Structure noise.

2. Radiation noise.

3. Receptor noise.

4. 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).

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