Radt Exam 4 Notes

Sources of ionizing radiation

Terrestrial, cosmic, internal, and man-made sources

Radiation Syndromes

specific symptom patterns that occur after whole-body exposure to high radiation doses

Coulombs per kilogram

Measure of radiation exposure in air

Gray

Measure of energy absorbed in any medium

Sievert

Unit of dose equivalence

Becquerel

Unit of radioactivity

X-ray tube design

Diode tube, glass envelope maintains vacuum, produces heterogeneous x-ray beam

X-ray beam energy unit

Kiloelectron volts (keV)

Classic coherent scattering

Interaction where x-ray photon changes direction without losing energy

Photoelectric effect

X-ray photon is completely absorbed, causing ejection of inner-shell electron

Compton scattering

Partial absorption of x-ray photon, outer-shell electron ejected, scattered photon continues

Dose-response relationship

Risk vs benefit: benefits of imaging must outweigh radiation risks

Radiation exposure guidelines

No dose considered totally permissible; all doses should be kept as low as possible

Radiation effects on cells

Can cause damage; most cells can recover

Dosimeter placement

At collar level, outside lead apron; second device for pregnant workers at waist under apron

Luxel OSL dosimeter

Optically Stimulated Luminescence device used to monitor exposure

Cardinal rules of protection

Time, distance, shielding

Purpose of personnel monitoring

Estimate occupational radiation exposure and maintain dose records

When monitoring is required

When worker may receive more than 1/10 of recommended dose-equivalent limit

When were x-rays discovered?

1895

What is required to produce x-ray beam energy?

High-voltage electricity

What are the classes of diagnostic radiographic imaging?

Film-screen radiography, fluoroscopic imaging, digital or computerized imaging

What are the requirements for x-ray production?

X-ray tube with a vacuum, source of electrons, cathode filament, voltage for acceleration, and a target to stop electrons

What is primary radiation?

X-ray beam after it leaves the x-ray tube and before it reaches the object

What is scatter radiation?

Radiation from x-ray interactions with matter that travels in different directions

What is absorbed radiation?

Radiation that remains in the patient

What is remnant radiation?

Radiation that exits the object and strikes the image receptor

What is attenuation in radiography?

Loss of radiation energy as it passes through absorbing material

What causes high attenuation and how does it appear on a radiograph?

Radiopaque matter; appears white

What causes low attenuation and how does it appear on a radiograph?

Radiolucent matter; appears dark

What is the imaging chain in radiography?

Radiation travels through matter and is detected by an image receptor, creating a latent image

What is a latent image?

An invisible image created after exposure but before processing

What are the prime technical exposure factors?

Milliamperage (mA), time (s), kilovoltage peak (kVp), and source-to-image distance (SID)

How is mAs calculated?

mA × time

What does mAs control?

The amount of radiation produced

What does kVp control?

The beam's penetrability (quality) and affects both quality and quantity

What does SID affect?

Intensity of the x-ray beam at the receptor

Common SID presets?

40", 48", 72"

Types of image receptors?

Film-screen, photostimulable phosphor (CR), digital detector systems (indirect/direct)

What does digital radiography eliminate?

The need for an x-ray film darkroom

In computed radiography, what stores the exposure?

Barium fluorohalide crystals

Ideal kVp range for computed radiography?

45 to 120 kVp

How does a CR reader work?

Laser scans IP, releases trapped energy, converts to a manifest image

Digital cassetteless system capture methods?

Indirect and direct

What technology do both direct and indirect DR systems use?

Thin-film transistor (TFT)

What is exposure latitude?

Range of exposures that can produce a quality image

What is system speed?

Sensitivity level of a digital detector

What is exposure index (EI)?

Numeric representation of total x-ray exposure to the receptor

Does EI indicate patient dose?

No

What is automatic rescaling?

Software adjusts image brightness/contrast based on receptor exposure

What is window level (WL)?

Controls brightness

What is window width (WW)?

Controls contrast

What material is used in direct detector tech?

Amorphous selenium

What converts light to electrons in indirect detection?

Amorphous silicon

What are some key features of digital radiography?

No cassettes, image in seconds, uses TFT, direct or indirect detectors

What are photographic qualities in radiographic quality?

Receptor exposure and contrast

What are geometric qualities in radiographic quality?

Spatial resolution and distortion

What mainly affects image receptor exposure?

mAs

What primarily controls contrast?

kVp

What is spatial resolution?

Sharpness of an object's structural edges

What factors affect recorded detail?

Motion, object unsharpness, focal spot size, SID, OID

What is distortion?

Misrepresentation of anatomy's true size or shape

Types of distortion?

Size and shape distortion

What causes shape distortion?

Misalignment of central ray, anatomy, or image receptor

What is deliberate distortion?

Angling/rotating anatomy to avoid superimposition

What is fluoroscopy?

Real-time x-ray imaging of anatomy and function

What does fluoroscopy require?

Radiographic/fluoroscopic (R/F) system with image intensification

What is the conclusion of radiographic imaging?

Digital technology improves exposure latitude and lowers dose, technologist must optimize quality with lowest exposure

What is diagnostic yield?

The amount of clinically useful information on a diagnostic image

Which modalities provide different diagnostic information?

Radiography, Sonography, CT scanning, MRI, Nuclear medicine

What does sonography show?

Differentiation between cystic vs. solid structures

What does CT scanning offer?

Many views from various projections, low-contrast resolution, tissue differentiation

What does MRI scanning provide?

Excellent for inflammatory processes, distinguishes between subtle tissue differences

What must diagnostic yield outweigh?

The input factors of the procedure

What is diagnostic efficacy?

The accuracy of diagnostic information on a medical image

What detracts from diagnostic efficacy?

Extraneous information that doesn't reflect true patient condition

What must be optimized in diagnostic imaging?

Diagnostic yield and diagnostic efficacy

Key components of x-ray machine design?

X-ray tube, tube support, collimator, table, generator/control, upright image receptor

What is the x-ray tube made of?

Pyrex glass with a high vacuum

Main components of the x-ray tube?

Anode (+) and Cathode (-) - it's a diode

How is x-radiation produced?

By high-energy electricity passing through the tube

What is the purpose of the collimator assembly?

Controls the size/shape of the x-ray field; projects a light field for alignment

What types of collimators exist?

Manual and automatic (PBL)

What is special about radiographic tables?

May be fixed or variable height, with four-way "floating" tops, radiolucent

What do tilting tables allow?

Horizontal to vertical tilting and Trendelenburg position

What is a Bucky assembly?

A receptor tray and oscillating grid to reduce visible grid lines

How is DR different from cassette systems?

Replaces cassette tray and moving grid with stationary grid

What is the control console?

Interface for the radiographer and x-ray system electronics

What can you do from the control console?

Select mA, kVp, exposure time, activate exposure, monitor displays

Three key factors in exposure technique?

mA, time, and kVp

What does mA × time equal?

mAs

What is AEC?

Automatic Exposure Control - optional feature for exposure

What is APR?

Anatomically Programmed Radiography - presets techniques for body parts

Two types of x-ray tube support designs?

Floor-mounted and ceiling-suspended tubecrane

Movements of an overhead tubecrane (OTC)?

Vertical, longitudinal, transverse, rotation, tube angulation

What makes modern OTC systems user-friendly?

Flat-panel screen at tubehead, exposure review, ergonomic design

What does an upright Bucky assembly include?

Upright receptor, lateral support arm, AEC detector chambers

What does image receptor technology do?

Captures remnant radiation and converts it for display/processing

Types of image receptors?

Cassette-based (film-screen, CR) and cassetteless (DR/flat panel)

What technology do DR systems use?

Thin-film transistors (TFTs)