Rad Technique 1

Technique

systematic procedure to produce a high-quality radiograph.

Technique includes being able to…

pick out the right factors to make an x-ray beam that’ll adequately penetrate the body part and provide the appropriate level of blackening (density) and subject contrast on the image

Exposure Factors governing density…

• Kilovoltage (kV)

• Milliampereseconds (mAs)

• Distance

Kilovoltage (kV) 

• force that accelerates the electrons from cathode to anode

• energy or quality of the x-ray beam is determined by the kV selected 

X-rays travel through matter in a…

wave-like fashion aka Wavelength

Wavelength

the distance from one crest of the wave to the crest of the next wave 

An increase in kV will produce…

x-rays photons of shorter wavelength and high energy levels

Penetrometer

As kV increases, so will its ……… ability

penetration ability

As kV increases, so will its penetration ability, which increases amount of…

radiation reaching the image receptor, producing more density on the image

kV DOES NOT produce…

…more x-ray photons! It is the increase in energy that allows more x-rays to penetrate the body part, producing increased blackening (density) of the image

Fifteen Percent Rule

Increase in kV by 15% will result in doubling the amount of overall blackening or density on the image.

Decrease in kV by 15% will reduce the overall density of the image by one half

15% rule is a nonlinear and nonproportional relationship

It serves the technologist as a practical tool when changes in kV are necessary in order to control the amount of exposure to the image

Caution must be used when using kV to decrease density bc…

significant reduction in kV may result in x-ray energy inadequate to penetrate the body part of interest

Penetration of the Part means…

x-ray photons have sufficient energy to pass through the part and emerge as remnant radiation

Below 60 kV may not be adequate for part penetration…

fine markings in skeletal tissue would not be visible and hairline fractures would be missed

kV is NOT the primary choice for…

controlling density on the image

kV selected based on average body part thickness…

• Chest 110 kV

• Abdomen 70 kV

• Upper extremity 60 kV

•kV is a factor in the production of…

scatter radiation

As x-ray photons strike the body part, especially with higher kV’s…

the x-ray photons undergo a change in direction.

X-ray photon travel in a direction different from its original “straight-line” path 

Scatter radiation exits the body traveling in…

many directions with different energy levels

Scatter radiation is a danger…

to the patient and the technologist

Scatter radiation is…

detriment to image quality

Higher kV means increased…

scatter radiation, fog (unwanted density) on image

Lower kV means not enough…

penetration and most of the radiation is absorbed by the patient

Milliamperes (mA)

controls the current flow to the cathode filament at the time of exposure

thermionic emission

As mA is increased, filament temperature rises increasing the number of electrons released

An increase in mA will increase the number of…

x-ray photons in the primary beam (quantity)

A doubling of mA will double…

radiographic density

The relationship of mA selected and overall image density is proportional

If the mA is doubled from 200 to 400, the amount of density is also doubled

A minimal change in mA of …. is needed to visually see a change in density

30-35%

mA has […] […] to the penetrating ability of the x-ray photons, therefore…

no relation, does not affect scatter radiation

An increase in mA will […] the amount of…

increase, exposure absorbed by the patient

Time (S)

factor that controls the length of the exposure

Milliamperes and time are combined and recognized as a single quantitative factor…

(mAs) milliampereseconds

An increase in mAs, increases the…

number of photons exposing the image receptor

kV and mAs Relationship

A decrease in kV by 15% may be compensated for doubling the mAs; or an increase in kV by 15% may be compensated for by decreasing the mAs by half

indicates that blackening (density) of the image will remain constant as long as the total energy (total mAs) exposing the image receptor is constant

reciprocity law

Time, like mA, has […] on the…

no effect, penetrating ability of the x-ray photons

Short exposure times are necessary to prevent…

patient motion during exposure, which is detrimental to image quality