Image Analysis Radiographic Contrast 1.3 Flashcards
Visibility of detail factor that describes the difference between adjacent densities on an image
contrast
What must be present on an image for anatomic structures to be visualized?
entity it must exhibit contrasting shades of black, white, and gray compared to the structures that surround it
Define short scale contrast
images the display just a few gray shades and appear mostly black and white
define long scale contrast
images that display many shades of gray and few blacks and whites
Contrast caused by the anatomic density, atomic number, and thickness differences of the patients body parts, and how differently each tissue composition will absorb x-ray photons
subject contrast
what the kVp factor determines
the energy of x-ray photons produced and the differential absorption that occurs in the patinets tissues as the x-ray pass thru the patients body
what is the penetrating power of the beam?
kVp
What type of images does using high kVp produce?
low contrast images
Using high kVp causes more what?
scatter
How does an image appear when using high kVp?
long-scale contrast (few blacks and whites and many grays)
What type of image does low kVp produce?
high contrast images–produces low energy photons that are easily absorbed
What images will exhibit when using low kVp
short scale contrast (mostly black and white with few grays)
How images will appear when using low KVP?
appear mostly black and white
What must be evaluated to obtain desired level of contrast and gray scale
each patients body part being imaged and select the appropriate kVp for that specific patient
Define optimum kVp
the kVp that will provide adequate part penetration and sufficient image contrast
what to do to the technique when you need higher contrast and will have to alter the technical factors always from optimum kVp
decrease original kVp by 15%, and increase mAs by 100% alter factors away from optimum kVp
What to do the technique when you need lower contrast and must deviate from optimum kVp?
increase original kVp used by 15%, decrease mAs by 50%
what is the general rule with adjusting the contrast with kVp?
you should stay relatively close to optimum kVp level for the specific structure being imaged to maintain sufficient penetration
how scatter radiation affects radiographic contrast
scatter radiation decreases contrast by putting a blanket of density (fog) over the image
what happens to the radiographic contrast as the amount of scatter increases
the greater the decrease in contrast and decrease in visibility
how to control the amount of scatter reaching the IR and improve contrast
by reducing the amount of tissue irradiated, collimate, decreasing the field size, and using a grid
what higher grid ratios does to an image
the greater the scatter cleanup and the higher the radiographic contrast
how to improve the visibility of recorded detail on an area of interest that will have an increased thickness
place a large, flat contact shield or straight edge of a lead apron along appropriate border
define artifact
any undesirable structure or substance recorded on an image
Groups that artifacts can be categorized into
- anatomic structure that obscure area of interest or have no purpose for being there and can be removed from an image
- externally removable objects (possessions)
- internal objects (prostheses or monitoring lines)
- appearances that result from improper equipment use (grid cutoff)
define anatomic artifact
any anatomic structure that is within the image that could have been removed
best way to avoid anatomic artifacts
explaining to the patient the importance of remaining in that position; visually check
define external artifacts
artifacts found outside the patients body
what are some common external artifacts
earrings, rings, necklaces, bra hooks, dental structures, hair pins, monitoring lines, gown snaps
define internal artifacts
artifacts found within the patient
examples of internal artifacts
prosthesis and pacemaker and port a caths
define grid alignment artifacts
grid lines that result from the use of stationary grids and the improper use of all grid type
when do grid lines occur and what do they look like
because the lead strips absorb primary radiation and are visible as small white lines on an image
what are the causes of grid lines
1.Parallel grid was tilted or CR was angled toward the lead strips, image will demonstrate grid lines on the side toward which the CR is angled
2. if parallel or focused grid was off focus (taken at an SID outside focusing range) image will demonstrate grid lines on the entire image
3. if focused grid was tilted or CR was angled entire image will demonstrate grid lines
4/ if focused grid was upside down, image demonstrates grid lines on both sides
5. if focused grid was off centered (CR not centered on the center of grid) image demonstrated grid lines on entire image
what are film handling and processing artifacts
improper film handling and processing can cause artifacts such as film creases, static, fog, stains, scratches, and hesitation marks
when must an image be repeated in regards to artifacts
if an artifact can be eliminated obscures any portion of area of interest the image needs to be repeated
when does it not need to be repeated in regard to artifacts
if the artifact is located outside the area of interest the image does not need to be repeated
define what an optimal image is
when an image meets all necessary requirements and does not need to be repeated
factors to consider when deciding if an image is acceptable or not
- your facilities standards
- age and condition of patient
- conditions under which the patient was imaged
- whether obvious pathology is evident
- whether the indications for the exam were met
who decides if an image is acceptable
each facility has its own standards that will determine whether an image should be repeated, has to be acceptable in the yes of the radiologist and the technologist to a point
why would less than optimal images be accepted
because repeating the image may be impossible, as in a surgery cases or in other cases where patient cannot cooperate
what must you do when a less than optimal image is accepted
record on requisition or in the computer any information about the patients condition or situation that resulted in the acceptance of that image
