CH 17 PATIENT AS BEAM EMITTER EXAM 3 physics

Attenuation is

Is the reduction in the total number of x-ray full times remaining in the beam after passing through a thickness material it is a result of x-rays interacting with matter and being absorbed or scattered,

_________ provides radiologically significant  information whereas r_________contributes no useful information.

PHOTOELECTRIC absorption, Compton scatter

Attenuation is also affected by the thickness of the patient. The thicker, the body part being radiographed the greater———— will be

Attenuation will be

Attenuation is also affected by the type of absober? For example high atomic #

HIGHER-atomic number materials (lead and barium) attenuate a greater percentage of the beam than LOW-atomic number materials (hydrogen, carbon, and oxygen)

•This is due to the presence of a greater number of electrons with which photons may interact

•The presence of calcium in bone, results in more attenuation than soft tissue

Density  of the absorbing material also affects attenuation. Density is defined as?

Density is the quantity of matter per unit of volume measured in kilograms per cubic meter

The Human Body is an AttenuatoR ;Four major substances account for variable attenuation:

–Air

–Fat

–Muscle

–Bone

Air has atomic number of ?

Air has an atomic number of 7.78 which is greater than fat or muscle

-It has significantly lower tissue density as a result. Air will absorb photons as they pass through it..Results in increased area of exposure on image receptor

Fat as an absorber

A soft tissue structure, the Effective atomic number of FAT and tissue density is similar to water

•Effective atomic number slightly less than muscle

•Tissue density less than muscle (muscle cells are more closely packed)

Muscle as an absorber

• Soft tissue

•Slightly higher atomic number and tissue density than fat

•Muscle is a greater attenuator of the beam

Bone as an absorber

Calcium among highest atomic number of elements found in body

•Greatest tissue density of four basic substances

•Absorbs a lot of photons

–Decreased area of exposure on image receptor

The relationship between the subjects (patients) and these factors are termed _____

subject density, subject contrast, subject detail, and subject distortion

Subject:

–Density

–Contrast

–Detail

–Distortion

Subject density refers to

Refers to the impact the patient has on final radiographic density.

-image receptor exposure will be altered by changes in amount or type of tissue being irradiated, Thicker and denser body parts absorb MORE radiation, and produce LESS image receptor exposure.

Subject contrast refers to

Subject contrast is the difference in addition exposure level levels on a recorded images

Degree of differential absorption resulting from differing absorption characteristics of tissues in body

Subject detail refers to

Subject detail is dependent on their position with the body, and also the bodies place placement in relationship to the IR, overall size affects subject detail

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The larger the patient, the greater the distance between the anatomical structures and the IR and results in Less sharpness

Subject DistortioN refers to

distortion is a misrepresentation of the size or shape of the structure of interest because of the way in which certain structures lie in the body.