U1 P3

techinical factors that govern radiation exposure

milliampere (mA), exposure time, mAs (product of mA and exposure time), kVp, SID, filtration

5 factors affecting radiation exposure

mA, time, kilovoltage, distance, thickness and condition of anatomic part

Radiographic variables & affect on x-ray emission casue what changes?

quantitative (mAs) & qaulitative (kVp)

quantitative change

mAs (mA & time), kv, distance, filtration

qaulitative change

kv & filtration; refers to photon energy, & penetrability

quality measured in

HVL (half value life)

xray beam quantity

amount of xray photons; refers to output, intensity, exposure rate

Quantity measured in

Couloumb/kilogram (C/kG) or Air kerma (Gy)

quality or quantity of image represents information that is well visualized for diagnosis?

quality

visibility of the anatomic structures is accomplished by balancing

brightness, contrast, exposure indicator #

A _________ radiographic image accurately represents [records] the anatomic area of interest with high sharpness.

quality

quality criteria for image evaluation

exposure index, brightness, contrast/grayscale, SNR, spatial resolution, artifacts, distortion

expusure index

used to determine incident exposure to the image receptor (S/EI#)

brightness

amount o luminance/light emission of the display monitor

contrast/grayscale

difference in areas of brightness on the display monitor; result of differential absorption of x-ray photons within body tissues

SNR

signal to noise ratio

spatial resolution

sharpness of anatomic details or structural anatomy

quantum noise

described as brightness or density fluctuations (grainy appearance)

quantum noise is caused by?

photon deficiency: too few xray photons reaching IR, decreasing detail visibility

What can be seen on digital images that are underexposed?

quantum noise

scatter radiation (a form of noise)

a type of secondary radiation produced when the useful x-ray beam intercepts any object, causing some x-rays to scatter (change direction)

most significant source of scatter radiation on patients?

x-ray exposure or fluoroscopic exam

Scatter degrades what?

image quality decreasing visibility of anatomic details

increase/decrease?
⬆/⬇ scatter production = ⬆/⬇ receptor exposure

increase; increase

subject contrast is produced by

differential absorption

How do x-ray photons interact with the digital receptor?

They pass through anatomic tissues to interact with the IR.

beam attenuation

reduction in number/intensity of x-ray photons as the beam passes through matter

beam attenuation proccesses include:

absorption and scattering

transmission

xray photons pass through matter without interaction with tissue atoms

Receptor Exposure (RE) is dependent upon?

the amount of exposure

S#

- inverse relationship
- Fuji and Konica
- S# of 200 = 1mR exposure to the IR

An increase in the S# from 200 to 400 indicates a decrease in RE Solution: to lower S# by one half, do what?

double mAs

EI#

- direct relationship
- Carestream and Kodak

An increase in the E# by 300 indicates a doubling of the RE Solution: to lower EI# by 300 points, do what?

1/2 mAs

LgM#

- direct relationship
- Agfa

What is the primary controller of receptor exposure?

mAs

underexposed or overexposed

underexposed appear whiter; overexposed appear darker

mA: directly proportional to? inversely related to?

direct: radiation quantity
inverse: exposure time to maintain exposure to IR

exposure time: directly proportional to? inversely related to?

direct: radiation quantity
inverse: mA to maintain exposure to IR

exposure time equation

mA × time (seconds) = mAs

kVp: directly related to? inversely related to?

direct: radiation quality & quantity
inverse: radiographic contrast

Milliampere (mA)

measure of the quantity of electrons or electrical current flowing per second

Doubling mA = 2x what 3 things?

#electrons produced, # of x-rays produced, receptor exposure

Changing the mA station on control panel changes what?

amount of electrical current delivered to filament wire (cathode)

Inverse Square Law

the intensity of radiation at given distance is inversely related to square of distance between object & source

inverse square law formula

I₁(D₁)² = I₂(D₂)²

inverse square law:
↓SID = ?
↑SID = ?

- more radiation exposure/intensity to IR
- less radiation exposure/intensity to IR

to maintain xray intensityt (quantity) use?

direct square law
mAs-distance compensation

direct square law:
↓SID = ?
↑SID = ?

- decrease mAs/mA
- increase mAs/mA

2x SID gives you?
1/2 SID gives you?

1/4 intensity ∴ use 4x mAs
4x intensity ∴ use 1/4 mAs

Reciprocity Law

exposure on x-ray should remain unchanged as long as intensity & duration of x-ray exposure remains unchanged

Reciprocity Law fails for?

extremely short exposures

15% rule of kVp

⬆kVp 15% = RE doubles (100% or 2)
⬇kVp 15% = RE halves (50%)
(kVp & RE have direct but not proportional relationship)

Maintenance of Receptor Exposure using 15% Rule:

⬆kVp 15% (1.15) & ⬇mAs by 1/2
⬇kVp 15% (0.85) & ⬆mAs by 2x

How will changing kVp affect beam quality and quantity?

⬆kVp: ⬆beam penetrability & quantity
⬇kVp: ⬇beam penetrability & quantity