5 & 6 X-Ray Contrast, Radiation Dose, & Image Artifacts

x rays

In ________, contrast represents the difference in attenuation properties (μ) of materials along a path.

Exposure

________ is measured in roentgen (R) and coulomb /kg.

photons

As ________ interact with matter, they are absorbed, scattered, or transmitted.

Effective energy

________ is the weighted average of the spectrum energies (needed because x- rays are polychromatic)

Risk

________ to different tissue is dependant on tissue type and the type of radiation.

Exposure

The amount if radiation in air measured by radiation monitors

Absorbed dose

The dose of radiation (energy) you are delivering to the tissue, measured by the energy absorbed

Dose equivalent

A measure of the biological damage to living tissue as a result of the absorbed dose; the biological dose that delivers the same degree of risk to a tissue regardless of the radiation type

Effective dose

An estimate ofo the stochastic effect that a non-uniform radiation dose has on the whole body; weighted sum of dose equivalent by all organs

Sum of each organ

weighting factor times (absorbed dose of the organ times f)

Contrast

The difference between foreground and background on an image

Beam intensity

The rate of change of the number of photons per unit area, represented by I

Filters

Something used to reshape the radiation spectrum to eliminate energies that dont contribute to the image, but do deliver dose

R

Units for exposure

Gy

Units for absorbed dose

Sv

Units for dose equivalent

Sv

Units for effective dose

J, Kg

The absorbed dose is the amount of energy per mass of tissue, measured in Gy or (BLANK) per (BLANK)

Absorbed dose times quality factor

Dose equivalent is equal to Sv, calculated as…

Heart (tissue more readily affected by radiation)

Which will have a higher effective dose, the heart or the hand? Why?

Fan

_____ beam geometry has a more compact, practical design, and is more consistent with physics

Parallel

The ideal beam geometry, stating that all the beams from an x-ray move parallel to one another

True

T or F: No magnification effect from a parallel beam

Magnification

Fan beam geometry requires the __________ factor to be taken into account, as well as depth dependent magnification (objects must be the same distance from tube)

tube-side collimator

To reduce the radiation sent to parts of the body that we don’t want to image, we use a __________, which focuses beam on the center of the object, making the beams closer to parallel

\

radiographic grid

To reduce non-parallel beams and scattered photons, we use a detector-side collimator, or more commonly a _________, to absorb any scattered photons that are trying to reach the detector that would otherwise create noise

radiographic grid

An object added to the detector that eliminates perpendicular rays to improve image quality, but may reduce the number of usable photons

Septa

The thin, usually lead strips that make up a radiographic grid are called…