IA Ch. 12 Workbook

Alll interactions _____ the x-ray beam to one degree or another

attenuate

Differentail absorption is controlled by the overall ______ of attenuation, as opposed to unhindered penetration, of x-rays passing through adjacent tissues

percentage

To measure the contrast between two tissues, mathematically, it is best to use a ____, dividing the percentage of attenuation for one tissue into the other, rather than subtracting the difference

ratio

What are the three essential aspects of tissues which determine their attenuation properties and the resulting subject contrast

Thickness of each tissue area, physical density of tissue, average atomic number of each tissue

Changes in the body part thickness may cause the subject contrast to either _____ or ______, depending on which part has changed

decrease, increase

In the patient, the physical density may be considered as the _____ of atoms or molecules within a tissue

concentration

The occurance of all interactions is ______ proportional to the physical density of the tissue through which the x-rays pass

directly

Fairly _____ differences in physical density between tisues are necessary to result in high subject contrast

extreme

List the three types of body tissues that may be distinguished from each other in a radiographic image primarily on the basis of their differences in physical density

Soft tissue( glondular organs, muscles, & connective tissue), Gases (air in the lungs), Fat

Bones, contrast agents and metals appear in a radiographic image primarily because of their high ____ _____

atomic numbers

The concentration of electrons within the orbitals is osmetimes referred to as the atom’s electron ______

density

Contrast agents are usually based on the ____ and atom (Z#=53) or the ____ atom (Z#56)

iodine, barium

The molecular atomic number or averaged Z# of soft tissue is about _____

7.4

X-ray attenuation is proportional to the ____ of the tissues atomic number

cube

Cubing the atomic numbers for bone and soft tissue, then making a ratio of these numbers, we find that bone is approximately ____ times more effective in attenuating x-rays than is soft tissue on account of threir atomic numbers only

20

Bone is also twice as effective at absorbing x-rays than soft tissue on account of its physcial _____

denstiy

Because fo its random nature, scatter radiation lays down a “blanket” of exposure _______ distributed across an area of the imaging plate, adding roughly the same amount of exposure throughout that area

evenly

This random distribution of scatter radiation constitues image noise, and reduces ______ contrast in the remnant beam reaching the image detectors

subject

At high kVp levels, increased penetration of the beam results in a beneficial _______ of grayscale, such that more different types of tissues are demonstrated

lengthened

Occurrence of the phototelectric effect is inversely proportional to the _____ of the kVp

cube

On the other hand, occurrence of the Compton interaction is decreased only very ______ by a similar increase in kVp

slightly

Since photoelectric interactions plummet much more quickly in number than Compton interactions, the _____ becomes the more prevalent of the two ineractions at hight kVp’s

compton

Therefore, even though there is less scatter radiation generated, that scatter reaching the image receptor makes a larger _____ contribution to the final image

percentage

Inversely, by lowering the kVp, the occurrence of photoelectric interactions increases by a _____ relationship, quickly increasing subject contrast

The proper amount of subject contrast is never the maximum nor the minimum achievable, but rather an _______ level that presents the greatest amount of diagnostic information

Bone tissue, iodine and barium all produce many more _____ interaction sthan soft tissue does

photoelectric

The greatest number of photoelectric interactions is achieved when the kVp is _____ adn the tissue atomic number is _______

low, high

However, this high number of photoelectric interactions must be balanced agaisnt the necessity for adequate _______ so that sufficient gray scale is also produced in teh image

penetration

Contrast agents effectively increae the _________ energies within the tissue until theya re just under the average energies of the x-ray beam

The likelihood of a compton scatter interaction occuring is essentially _____ for all types of tissues

same

This is because electrons in the outer shells, where compton occurs, are not affected much by the atomic number because of their distance from the ________ of the atom

At higher kVp levels, the more forward direction of scatter is offset by the fact that less scatter radiation is produced in the first place, such taht the image recepter recieves only ______ more scatter radiation

slightly

Therefore, high kVp is relatively _____- factor in the produciton of scatter radiation when compared with the collimated field size and the thickness of the patient

minor

__________ changes in kVp are requred to substantially affect the amount of scatter radiation reaching the image detectors