chapter 15 image acquisition

Combination of settings on the x-ray control panel to produce a high quality image

image acquisition

factors that affect image acquisition

position of tube

patient

IR

factors that influence and determine the intensity and energy of x-radiation to the patient

exposure factors

radiation intensity

radiation quantity (mGy)

beam energy and penetrability

radiation quality (HVL)

4 prime exposure factors

kvp

mA (tube current)

sec (exposure time)

SID

secondary exposure factors

focal spot size

filtration

primary controller of xray beam energy and penetrability

kVp

as kVp increases __

higher energy and greater penetrability

as kVp increases, what happens to contrast?

decreases bc of increased compton scatter

what is the main contrast enhancement factor in digital imaging?

post processing

kVp is also main

patient radiation dose factor

Number of electrons that boil off the filament by thermionic emission, which determines the number of projectile electrons

mA

mA is controlling factor of

x-ray intensity

increasing mA also increases what proportionally?

patient dose

changing mA changes the number of

electrons going from cathode to anode

exposure time is (long/short) to minimize motion blur

short

exposure time works with what to achieve required radiation exposure

mA

mAs determines

number of xrays in the primary beam (not energy)

Measure of tube current, which is number of electrons flowing through the tube for an exposure

mAs

different combinations of mA and time produce the same mAs

mAs reciprocity

only mAs can be selected, so it automatically selected the highest mA at the shortest exposure

falling load generator

mAs and intensity are

directly proportional

t/f distance effects energy

false

distance affects intensity based on

inverse square law

the relationship between mAs and distance can be shown by

direct square law (mas₁/mas₂) = (d₁)²/(d₂)²

many tubes have two focal spot sizes aka

dual focus tubes

what kind of procedures use small focal spot sizes?

IR

mammography

general imaging with higher mA

large focal spot

fine detail radiography, low quantity

small focal spot

glass or metal envelope for general purpose tube (0.5 mm Al)

usually the lowest about allowable (tube must have total 2.5 mm Al eq. of inherent plus added)

create more uniform exposure, shapes like wedge, trough

compensating

as added filtration increases, beam energy increases which

increases scatter

reduces image contrast

both have 100% ripple, so energy is the same

half wave and full wave

why is intensity of a full wave generation doubled?

entire wave is being used

more efficient than single phase, produces more x-rays with a higher energy

three phase

voltage ripple for 3 phase 6 pulse

14%

voltage ripple for 3 phase 12 pulse

4%

voltage ripple for high frequency, more intensity and greater energy

less than 1%

radiation intensity is measured with a

solid state detector or ionization chamber

when is the exposure terminated in AEC

when proper radiation exposure reaches IR

how many sensors used on AEC

2 or 3

mAs backup time on mAs

600

increase or decrease exposure to IR by 25-50%

exposure compensation dial or button

uses microprocessor and graphics to guide technologist

anatomically programmed radiography

technologist selects part and body habitus ___ selects kVp and mAs

microprocessor

__ is essential to APR

precise patient positioning relative to sensors

magnification radiography is used mainly in

mammography and interventional

magnification radiography works by

increasing OID but leaving SID the same

__ is used to reduce loss of spatial resolution

small focal spot

why are grids usually not required for magnification radiography?

air gap technique

disadvantage to magnification radiography

increased patient dose