Exam 1 Flashcards
ability to img small objects that have high subject contrast
spatial resolution
the random fluctuation in the OD of the img
noise
2 other terms for spatial resolution
detail, recorded detail
what factors affect the visibility of detail
img contrast and OD
what is quantum mottle? how does it appear on the img?
the random nature by which XRs interacts w/ IR. If produced w fewer XRs, quantum mottle increases; causes grainy appearance
how do you minimize quantum mottle?
high mAs, low kVp, slow IR
what’s contrast resolution?
ability to img 2 separate objects and visually distinguish btw the 2
how does speed affect detail?
fast IRs = high noise, low spatial/contrast resolution slow IRs = low noise, high spatial/contrast resolution
what is sensitometry?
study of relationship btw intensity of exposure and blackness (density) on img
what is on the x and y axis on a sensitometric curve?
X-axis: LRE, y-axis: OD
3 parts of a characteristic curve?
- toe, 2. straight-line portion, 3. shoulder
what part of characteristic curve represents optimum contrast?
straight-line portion
what part of characteristic curve represents over exposure?
shoulder
what part of characteristic curve represents under exposure
toe
density can be measured using a
densitometer
formula for calculating OD?
OD=log(Lo/Lt); Lo - original light, Lt - light transmitted
what is the diagnostically useful density range for an XR?
0.25 - 2.5
what is the range for base plus fog density?
approx 0.1 - 0.3
radiographic contrast is the product of ______ and ______
IR contrast & subject contrast
film contrast is related to the ______ of the _______ part of the characteristic curve
slope & straight-line
how do you calculate the slope of a characteristic curve
calculate the avg gradient
what is the formula for calculating avg gradient?
avg gradient = (OD2 - OD1)/(LRE2 - LRE1); OD2 - OD of 2.0 + base and fog densities (LRE2 assoc w OD2); OD1 - OD of 0.25 + base and fog densities (LRE1 assoc w OD1)
how do you ID the faster characteristic curve?
faster films located to the L of slower films (on x-axis) (curve closest to y-axis)
how do you ID the characteristic curve that has more contrast?
steeper slope –> higher contrast
how do you ID the characteristic curve that has narrow latitude?
steeper slope –> less/narrow latitude
how do you ID the characteristic curve w short scale contrast?
steeper slope (narrow latitude = short scale contrast)
how do you ID the characteristic curve w long scale contrast?
(wider slope) wide latitude = long-scale contrast
how do you ID characteristic curve w less latitude?
narrow latitude = less latitude = steeper slope
latitude and contrast are ________ proportional
inversely
3 principal geometric factors that affect XR quality?
sharpness, recorded detail, distortion
2 formulas that can be used to calculate the magnification factor?
MF = Img Size/Object Size MF = SID/SOD
factors that affect magnification?
size, shape, SID & OID
how can you minimize magnification?
increase SID, decrease OID
what is shape distortion?
unequal magnification of different portions of the same object
what factors affect distortion?
object thickness, object position, object shape, SID/OID
will thicker/thinner object be most distorted?
thicker
will object in path of CR or away from CR be distorted the most?
away from CR
if img of an object is smaller than the object, the img is _________
foreshortened
if img of object is longer than the object, it is said to be _________
elongated
what is spatial distortion?
misrepresentation in the img of the actual spatial relationships among objects
focal spot blur is ______ on the anode side and ______ on the cathode side of the img
small (anode); large (cathode)
6 factors that affect subject contrast?
pt thickness, tissue mass density, effective atomic #, object shape, kVp, subject contrast
what is the most important influence on subject contrast?
kVp
low kVp produces ________ contrast
high subject/short scale contrast
high kVp produces __________ contrast
low subject/long scale contrast
motion blur will be more visible when using _________ SID
short
motion blur will be more visible when using _______ OID
long
3 factors that control the amount of scatter produced?
kVp, field size, pt thickness
increasing kVp will produce _______ scatter
more
increasing collimation will produce ______ scatter
less
increasing the field size will produce ________ scatter
more
thicker pt will produce _____ scatter
more
using compression during a KUB will produce ______ scatter
less
will a KUB have more contrast if pt in supine or prone pos?
prone
will a cone or cylinder collimation device produce an XR w better contrast?
cone
f(x) of the 1st stage entrance shutter?
to prevent off-focus rad
f(x) of PBL?
to limit the field size to the IR size
what does PBL stand for?
positive beam limiting device
what devices can be used to minimize the amount of rad reaching the IR?
Grid and beam restrictors (*variable aperture collimator, cones, cylinders, aperture diaphragm)
what is the grid ratio?
ratio of the height of pb strips to the D btw them
how do you calculate grid ratio?
Grid Ratio = H/D
what is grid frequency?
the # of pb strips per unit length (in/cm)
principal f(x) of rad grid?
absorb scatter rad
interspacing materials used in rad grids?
Al & plastic fiber
types of grids used in rad
linear and crossed
most common type of grid used
linear
which grid type produces more contrast?
crossed
which grid type has more pos latitude?
linear
does a high or low ratio grid have more pos latitude?
low ratio grid
main disadvantages of a parallel grid?
less contrast, removes less scatter
main disadvantages of crossed grids?
less pos latitude, absorbs more primary beam (may need to increase mAs to replace beam, which is more pt dose)
factors that control/affect detail?
screen blur, geometric blur, and motion blur
as the speed of the IR increases, rad noise ______ and spatial res is _______
increases (rad noise); decreased (spatial res)
what is the avg grid frequency used in rad depts?
25-45 lines/cm or 60-110 lines/in
which grid ratio has more pos latitude?
low ratio grid
what are the most important characteristics of img qual? (4)
spatial res., contrast res., noise & artifacts
primary control of rad contrast?
kVp
primary control of OD?
mAs
film factors? (3)
characteristic curve, OD, film processing
Geometric factors? 3(4)
magnification, distortion, focal spot blur, (heel effect)
detail is controlled by what? influenced by?
focal spot size; SID/OID and motion
factors that control/affect detail?
screen blur, geometric blur, & motion blur
if the speed of the IR is doubled, what will you do to maintain the density?
reduce mAs by 1/2 new IR speed/old IR speed = old mAs/new mAs
MATH: If 3600 light beams strike an XR and 36 light beams pass through it, what’s the OD?
3
in a particular grid the length of the pb strips are 12 mm and are positioned 1 mm apart. what is the grid ratio?
12:1
grids are required when?
anatomical part 10 cm or greater or more than 60 kVp needed
which grid ratio will have better contrast?
high grid ratio (absorbs more scatter)
a grid is made w pb strips that are 16 mm long and separated by an interspacing material of 2 mm wide. what is the grid ratio?
8:1
how do you calculate D to grid cutoff?
D to cutoff = SID/grid ratio
what happens to img contrast when grids are used?
img contrast approximately doubles
Reverse:
noise
the random fluctuation in the OD of the img
Reverse:
spatial resolution
ability to img small objects that have high subject contrast
Reverse:
detail, recorded detail
2 other terms for spatial resolution
Reverse:
img contrast and OD
what factors affect the visibility of detail
Reverse:
the random nature by which XRs interacts w/ IR. If produced w fewer XRs, quantum mottle increases; causes grainy appearance
what is quantum mottle? how does it appear on the img?
Reverse:
high mAs, low kVp, slow IR
how do you minimize quantum mottle?
Reverse:
ability to img 2 separate objects and visually distinguish btw the 2
what’s contrast resolution?
Reverse:
study of relationship btw intensity of exposure and blackness (density) on img
what is sensitometry?
Reverse:
densitometer
density can be measured using a
Reverse:
IR contrast & subject contrast
radiographic contrast is the product of ______ and ______
Reverse:
calculate the avg gradient
how do you calculate the slope of a characteristic curve
Reverse:
sharpness, recorded detail, distortion
3 principal geometric factors that affect XR quality?
Reverse:
size, shape, SID & OID
factors that affect magnification?
Reverse:
increase SID, decrease OID
how can you minimize magnification?
Reverse:
unequal magnification of different portions of the same object
what is shape distortion?
Reverse:
object thickness, object position, object shape, SID/OID
what factors affect distortion?
Reverse:
foreshortened
if img of an object is smaller than the object, the img is _________
Reverse:
elongated
if img of object is longer than the object, it is said to be _________
Reverse:
misrepresentation in the img of the actual spatial relationships among objects
what is spatial distortion?
Reverse:
pt thickness, tissue mass density, effective atomic #, object shape, kVp, subject contrast
6 factors that affect subject contrast?
Reverse:
kVp, field size, pt thickness
3 factors that control the amount of scatter produced?
Reverse:
to prevent off-focus rad
f(x) of the 1st stage entrance shutter?
Reverse:
to limit the field size to the IR size
f(x) of PBL?
Reverse:
Grid and beam restrictors (*variable aperture collimator, cones, cylinders, aperture diaphragm)
what devices can be used to minimize the amount of rad reaching the IR?
Reverse:
ratio of the height of pb strips to the D btw them
what is the grid ratio?
Reverse:
the # of pb strips per unit length (in/cm)
what is grid frequency?
Reverse:
less contrast, removes less scatter
main disadvantages of a parallel grid?
Reverse:
less pos latitude, absorbs more primary beam (may need to increase mAs to replace beam, which is more pt dose)
main disadvantages of crossed grids?
Reverse:
screen blur, geometric blur, and motion blur
factors that control/affect detail?
Reverse:
25-45 lines/cm or 60-110 lines/in
what is the avg grid frequency used in rad depts?
Reverse:
spatial res., contrast res., noise & artifacts
what are the most important characteristics of img qual? (4)
Reverse:
kVp
primary control of rad contrast?
Reverse:
mAs
primary control of OD?
Reverse:
characteristic curve, OD, film processing
film factors? (3)
Reverse:
magnification, distortion, focal spot blur, (heel effect)
Geometric factors? 3(4)
Reverse:
focal spot size; SID/OID and motion
detail is controlled by what? influenced by?
Reverse:
screen blur, geometric blur, & motion blur
factors that control/affect detail?
Reverse:
reduce mAs by 1/2 new IR speed/old IR speed = old mAs/new mAs
if the speed of the IR is doubled, what will you do to maintain the density?
Reverse:
img contrast approximately doubles
what happens to img contrast when grids are used?
What is IR contrast?
inherent in screen-film and is somewhat influenced by film processing
What is subject contrast?
determined by size, shape, and XR attenuating char.’s of anatomy and the energy (kVp) of XR
