Dr. Mustafa Zuhair Mahmoud Mr.Ali B Alhailiy بسم الله الرحمن الرحيم 1

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

5. Image Noise: Irrelevant information in the image is defined as image noise. Assistant Prof. Dr. Mustafa Zuhair Mahmoud 3

5. Image Noise: Image noise has four components: 1.Structure noise. 2.Radiation noise. 3.Receptor noise. 4.Quantum mottle. Assistant Prof. Dr. Mustafa Zuhair Mahmoud 4

5. Image Noise: Image noise has four components: Assistant Prof. Dr. Mustafa Zuhair Mahmoud 5

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 6

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 7

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 10

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 11

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 12

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 13

5.2 Radiation Noise: Similarly, the radiation beam exiting from the patient contains considerable scattered radiation. Assistant Prof. Dr. Mustafa Zuhair Mahmoud 14

5.2 Radiation Noise: Scattered radiation interferes with the visualization of patient anatomy. Hence, scattered radiation is radiation noise. 15 Assistant Prof. Dr. Mustafa Zuhair Mahmoud

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 16

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 17

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 18

5.4 Quantum Motel: Assistant Prof. Dr. Mustafa Zuhair Mahmoud 19

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 20

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 21

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 22

6. Image Distortion and Artifacts: Magnification M in an image is the ratio of image to object size. Assistant Prof. Dr. Mustafa Zuhair Mahmoud 23

Image Distortion

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

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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