X-ray Image Formation And Contrast

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The five radiographic image quality characteristics.  Contrast sensitivity is a major characteristic that determines what tissues and body structures are visible in a radiograph.

 

 

 

 

 

 

 

 

 

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The many factors that have an effect on radiographic contrast sensitivity.

 

 

 

 

 

 

 

 

 

 

 

 

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The total attenuation by soft tissue is determined by both photoelectric and Compton interactions.  Attenuation generally decreases with increased photon energy because of the energy dependence of the photoelectric effect.

 

 

 

 

 

 

 

 

 

 

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The photon energy spectrum of an x-ray beam determines its quality.

 

 

 

 

 

 

 

 

 

 

 

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An x-ray image is formed by the different attenuations of the x-ray beam within a patient's body.  Objects with increased attenuation produce shadows.

 

 

 

 

 

 

 

 

 

 

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The image contrast produced by an object depends on its attenuation of the x-ray beam.

 

 

 

 

 

 

 

 

 

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Generally increased penetration through an object decreases contrast.  In creased penetration through the total body generally decreases the radiation dose to the patient.

 

 

 

 

 

 

 

 

 

 

 

 

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Penetration through the body is generally increased by increasing the KV.

 

 

 

 

 

 

 

 

 

 

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Calculation of the amount of contrast coming from a patient's body and also recorded on film.

 

 

 

 

 

 

 

 

 

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Changing KV is the principle control of contrast in radiography.

 

 

 

 

 

 

 

 

 

 

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The x-ray image of an object in a patient's body is in the form of a shadow.

 

 

 

 

 

 

 

 

 

 

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Object penetration and contrast can be changed by changing KV.

 

 

 

 

 

 

 

 

 

 

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The x-ray attenuation and total body penetration changes with photon energy.

 

 

 

 

 

 

 

 

 

 

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An object must have some form of physical contrast in order to be visible in an x-ray image.

 

 

 

 

 

 

 

 

 

 

 

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The forms of physical contrast that contribute to contrast in x-ray imaging.

 

 

 

 

 

 

 

 

 

 

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The penetration through soft tissue can be changed by changing the KV which changes the spectrum.

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X-ray spectra produced by different KV values.

 

 

 

 

 

 

 

 

 

 

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The spectrum of an x-ray beam is determined by: the anode material, the KV value, and the filtration.

 

 

 

 

 

 

 

 

 

 

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The chest has high physical contrast primarily because of the air within the lungs.

 

 

 

 

 

 

 

 

 

 

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Good chest radiographs are produced by using a high KV value and a heavily filtered beam with a spectrum that gives good penetration.

 

 

 

 

 

 

 

 

 

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An image showing good penetration through the bones.

 

 

 

 

 

 

 

 

 

 

 

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An image with high area contrast is not desirable.

 

 

 

 

 

 

 

 

 

 

 

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Generally, relatively low contrast between large areas within the body produce better local object contrast and visibility.

 

 

 

 

 

 

 

 

 

 

 

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Bone image.

 

 

 

 

 

 

 

 

 

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Good contrast of iodine requires a spectrum with a significant amount of radiation above the K-edge energy of iodine.  This is usually produced with KV values in the range of 65-75.

 

 

 

 

 

 

 

 

 

 

 

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KV values for the different radiographic procedures.

 

 

 

 

 

 

 

 

 

 

 

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The breast generally has low physical contrast.  It is in the form of relatively small differences in density among the soft tissues and the low contrast of small calcifications.

 

 

 

 

 

 

 

 

 

 

 

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The x-ray spectrum used for mammography is determined by the anode material, selected KV value, and type of filter.

 

 

 

 

 

 

 

 

 

 

 

 

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The spectrum and the resulting breast penetration can be changed by alternating between different filter materials.

 

 

 

 

 

 

 

 

 

 

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