Exam 2 Flashcards
as the Bucky factor increases, the rad technique & pt dose ________ proportionately
increases
what is the formula for calculating contrast improvement factor?
k = rad contrast w grid/rad contrast w/o grid
high ratio grid has _______ contrast improvement factor
higher
How do you calculate Bucky Factor?
B = Incident remnant XRs/Transmitted Img-forming XRs = pt dose w grid/pt dose w/o grid
what does contrast improvement factor measure?
improvement in img quality when grids are used
what does Bucky factor measure?
how much of an increase in technique will be required compared w non grid exposure; or how large an + in pt dose will accompany the use of particular grid
the higher the grid ratio, the ______ the Bucky factor
higher
Bucky factor increases with _______ kVp
increasing
purpose of moving grid?
to get rid of grid lines
what are the different types of grid motions used?
reciprocating (back & forth) and oscillating (circular)
how will the img appear if the grid is off-level?
overall - in density
how will the img appear if the grid is off-center?
overall - in density
how will the img appear if the grid is off-focus?
loss of density along the edges
how will the img appear if the grid is upside-down?
loss of density along the edges
List the layers of radiographic film
- supercoat
- emulsion
- adhesive layer
- film base
What is the thickness of the film base
150-300 µm
Film base is made of what material?
polyester (plastic)
The emulsion is made of what materials?
Ag Halide Crystals (w 90-99% of Ag bromide + 1-10% Ag iodide) suspended in gelatin
Which film gives better detail? Why? A) Single emulsion film B) Double emulsion film
Single Emulsion Film; less loss of transmitted light, so better detail
Which film is faster? Why? A) Single emulsion film B) Double emulsion film
Double Emulsion Film; More SHC —> more speed
Which film causes more radiation dose to patients? Why? A) Single emulsion film B) Double emulsion film
Single Emulsion; less speed, more exposure T required
What is a sensitivity center or sensitivity speck?
physical imperfections in the crystal lattice of the emulsion layers from the manufacturing process; serves as an e- trap from the bromide —> they are neg. charged
What is spectral matching?
matching the spectral sensitivity of the film w the spectral emission of the IS to increase speed of IR
What filter is best for blue sensitive film?
amber color filter - transmits wavelengths longer than 550 nanometer (red also suitable)
What filter is best for green sensitive film?
red color filter - transmits wavelengths longer than 600 nm
What is the ideal temperature and humidity to store film?
68 F & 40-60% humidity
What will be the effect of storing a film at high temperature?
causes fog
What will be the effect of storing a film at low humidity?
causes static artifact (tree, crown, smudge) - (static artifact also caused by friction)
What is the name of the image after exposure and before processing?
latent image (after exposure AND processing - manifest image)
List the layers of the intensifying screen
- protective layer
- phosphor layer
- reflecting layer (+ speed, - detail) OR absorbing layer (- speed, + detail)
- base
What are the phosphors used to manufacture intensifying screen?
calcium tungstate, zinc sulfide, barium lead sulfate, oxysulfide of rare earth elements, lanthanum oxybromide, yttrium/gadolinium/lanthanum oxysulfide
Learn the spectral emission of various type of phosphors
zinc sulfide - ultraviolet; calcium tungstate, lanthanum oxybromide, yttrium oxysulfide - blue; gadolinium/lanthanum oxysulfide - green**; Barium fluorochloride/strontium/sulfate - ultraviolet
Explain fluorescence
ability of phosphors to emit visible light only while exposed to XRs
explain phosphorescence
when phosphors continue to emit light after XR exposure stopped; aka “screen lag/afterglow”; causes fog
Name the phosphors used in rare earth screens
Gadolinium (green), lanthanum (green), and yttrium (blue)
What is screen lag and how does it affect the image?
the phosphorescence in an IS; caused by aged/defective IS’s; causes fog
How do you check for screen film contact?
wire mesh test - areas of poor contact will appear darker b/c will be overexposed; should be performed every 6-12 months; (poor screen-film contact —> poor detail)
What happens during developing?
(acidic) latent image —> visible image (principle component of developer - hydroquinon; responsible for black shades of gray, acts slowly); chem responsible called “reducing agent”
What happens during fixing?
(alkaline) removes remaining SHC from emulsion and hardens gelatin; “archival quality” refers to permanence
Why fixing is important?
makes img permanent
Why washing is important?
removes excess chem’s
What material is used as fixing agent?
ammonium thiosulfate aka “hypo”
What are the prime exposure factors?
kVp mA and exposure time (∆Density) Distance (+ Distance, - Density —> magnification)
What factor control radiographic contrast?
kVp (primary control of beam qual, controls penetration, affects quantity); + kVp, -’s differential absorption (how beam absorbs/penetrates body) and -’s img contrast
What factor control radiographic density?
mA (controls quant.; w k exposureT, mA controls XR quant and pt dose; does NOT ∆ the KE/speed of e-’s OR + penetration; XR QUAL remains fixed w ∆mA) exposure T (short to - motion blur); **mAs controls OD, 2x’s mAs —> 2x’s density
Does kVp influence radiographic density?
yes, + kVp will + it’s pos. attraction e-’s and + e-’s will come and thus affect quat.)
Does mAs Influence radiographic contrast?
Img quality —> YES it does influence. (BEAM qual —> no)
What will be the effect of using kVp to manipulate the density?
affects contrast (low kVp = high/short-scale contrast [+ differential absorption], high kVp = low/long-scale contrast [- differential absorption])
What is the definition of optical density?
degree of blackening on XR
What is the definition of contrast?
degree of diff btw light & dark areas of XR
What factor controls the radiation penetrability?
kVp
What factor controls the energy of the x-ray beam?
kVp
What factor controls the number of x-ray photons produced?
mA
What change in quality occurs when changing the mA?
quality remains fixed w ∆mA
How can you reduce motion blur?
use short exposure T
How does distance affect radiographic quality?
yes; - SID —> overexposed; + SID —> underexposed; NO AFFECT ON BEAM QUAL
What is the effect of changing the focal spot size for a given kVp/mAs setting?
small focal spot - better detail (more exposure T needed); large focal spot - less detail (less exposure T needed) NO AFFECT ON QUANT
What is the purpose of filtration?
to increase XR beam quality and penetrability
What is inherent filtration?
0.5 mm Al equivalent; glass/metal envelope of tube
What is total filtration?
2.5 mm of Al equivalent
What is the function of a compensating filter?
provide uniform density for non-uniform objects on XR
A compensating filter is also known as?
wedge filter (T-spine), trough filter (Chest)
What change will occur in radiation quantity when changing from a half wave rectification to a full wave rectification?
quant 2x’s
Radiographic technique charts are based on what type of patients?
sthenic
Name the 4 types of body habitus
hypersthenic 5%; asthenic 10%; hyposthenic 35%; sthenic 50%
What change will occur in radiation quality when changing from a half wave rectification to a full wave rectification?
no ∆
Identify radiolucent pathologies
destructive path (- kVp) - osteoporosis, pneumothorax
Identify radiopaque pathologies
constructive/additive path (+ kVp) - osteopetrosis, pleural effusion, hemothorax
What technique change is required for radiopaque pathologies?
increase
The mAs value must be changed ____% to produce a perceptible change in OD.
30
The kVp must be changed ____% to produce a perceptible change in OD.
4
What will the effect on density be if you increase the kVp by 15%?
2x density
What will be the effect if you decrease the kVp by 15%?
1/2 density
Properly exposed Rib radiograph demonstrate_______(long scale or short scale)
short scale
Properly exposed chest x-ray demonstrate_______(long scale or short scale)
long scale
High contrast is also known as _______ (long scale or short scale)
short scale
Low contrast is also known as _______(long scale or short scale)
long scale
Explain anatomically programmed radiography. (APR)
microprocessor determines kVp and mAs based on settings of anatomic part and body habitus, while using AEC
Explain the construction of a grid.
contain thin pb strips w precise height/thickness/space btw them; radioluscent interspace material separates strips (aluminum or plastic fiber), both covered by aluminum front/back panel
What is grid ratio?
ratio of height of pb strips and D btw them
Learn to calculate grid ratio.
grid ratio = H/D (height strips, D btw them)
What is Bucky factor?
measures how much of an increase in technique will be required compared w non grid exposure; or how large an + in pt dose will accompany the use of particular grid
Change in Exposure btw Grid w Diff Grid Ratio formula?
mAs1/mAs2 = GCF1/GCF2
inverse square law?
I1/I2 = D2^2/D1^2
direct square formula?
mAs1/mAs2 = D1^2/D2^2
Bucky factor for non grid?
1
Bucky factor for 5:1?
2
Bucky factor for 6:1?
3
Bucky factor for 8:1?
4
Bucky factor for 12:1
5
Bucky factor for 16:1?
6
What is grid frequency?
No. of lines per unit length (25-45 lines/cm, 60-110 lines/in)
