Radiographic Technique and Image Acquisition Overview

Kilovolt Peak (kVp)

Controls x-ray quality and beam penetrability.

Milliamperes (mA)

Determines x-ray quantity and patient radiation dose.

Exposure Time (s)

Duration of x-ray exposure to minimize motion blur.

Source-to-Image Distance (SID)

Affects image receptor exposure via inverse square law.

Optical Density (OD)

Measure of film blackening due to x-ray exposure.

mAs

Product of mA and exposure time controlling intensity.

Direct Square Law

Calculates mAs change with SID adjustments.

Focal-Spot Size

Influences x-ray production capacity and detail.

Filtration

Reduces patient dose and improves beam quality.

Inherent Filtration

Filtration from tube envelope and collimator.

Added Filtration

Additional filters to enhance beam quality.

Compensating Filtration

Balances beam intensity using shaped filters.

High-Voltage Generator

Supplies power for x-ray production.

Half Wave Rectification

x-rays are produced and emitted only half the time. results in the same radiation quality as is produced by full wave rectification, but the radiation quantity is halfed (100 % ripple)

Full Wave Rectification

Continuous x-ray emission with no dead time, xrays are being emitted continuously as pulses

Three Phase Generator

Higher efficiency with constant radiation output, results in higher xray quantity and quality

High Frequency Generator

Produces stable voltage with minimal ripple (1%)

Compton Interactions

Increased with higher kVp, causing scatter radiation.

Spatial Resolution

Ability to distinguish small details in images.

Magnification Radiography

Used for detailed imaging of small structures.

Examples of added filtration

collimator

Examples of inherent filtration

envelope of tube, oil surrounding housing and mirror in the collimator.

What is the primary purpose of filtration

reduce patient dose

Most common filtration material

Aluminum

Filtration does what to the quantity of x-rays

decreases

Filtration does what to the quality of the x-rays?

increases

Density Maintenance

if you increase distance, you have to increase mAs

direct relationship

mAs reciprocity

Any combination of mA and time that equals a particular mAs value will produce the same density (and exposure).

100 mA @ 0.1 sec. = 10 mAs

500 mA @ 0.02 sec. = 10 mAs

1000 mA @ 0.01 sec. = 10 mAs

15 % rule

Changing the kVp by 15% has the same effect as doubling the mAs or reducing the mAs by 50%

What does a long SID result in

less mag, less focal spot blur, improved spatial resolution

Which factor would the radiographer choose to maximize recorded detail in the image?

Small focal spot

Large focal spot

can withstand heat produced by large exposures

Has a shorter exposure time, minimizes motion blur

Large Focal spot

AEC

uses ionization chambers to measure the radiation passing to the receptor and shuts down the exposure when the appropriate receptor exposure is achieved

Automatically adjusts exposure time

AEC

What do the ionization chambers do?

measure the exposure to the receptor

What does AEC do in regard to patient dose

reduces patient dose

Destructive pathologies

causes tissues to become more radiolucent, requires a decrease in technique to avoid over penetration

Constructive pathologies

increases the mass density of tissues, requires increased technique to penetrate the denser tissue

What technique is used for soft tissue

low kvp and high mAs

What technique is used for extremities

low kvp is used because the body part is thin

What technique is used for CXR

high kvp and low mAs

Pneumothorax, active tb, emphysema, atrophy, bowel obstruction, cancer, degenerative arthritis, osteoporosis

destructive pathologies (decrease technique)

atelectasis, cirrhosis, metastases, aortic aneurysm, ascites, hypertrophy, pleural effusion, pneumonia, sclerosis

constructive pathologies (increase technique)

Elongation

poor alignment of the IR and x-ray tube

Foreshortening

poor alignment of the anatomical part

What happens to x-ray energies with a change in mA

they remain fixed

4 prime exposure factors

kvp, ma, time and sid