Artifacts & Radiation Safety

sihirlifil's version from 2017-09-03 01:46


Question Answer
Definition of artifactUnwanted optical density in an image that does not properly show the area of interest being examined
Causes of artifact during exposureUnder/overexposed
Grid cutoff
Coarse grid lines
Excessive scatter
Movement blur
Objects (collars, dirt, wet coat...)
Double exposure
Quantum mottle
Causes of artifact during processingOver/underdeveloped
Poor washing
Chemical staining
Air bubbles
Causes of artifact from handlingLight fogging
Finger prints
Dirty hangers
Causes of artifact from storageLight fogging
Wrong safe light
Old film
What is grid cutoff?Improper alignment of x-ray tube to grid (tube should be centered to grid)
How does a kink look on a radiograph?Hyperdense crescent mark
How does light fogging happen?White light leak, e.g. darkroom too bright, poorly closed cassette...
How does static happen? What does it look like?Can happen if you pull a film from a box when there are a bunch next too each other. Looks like hyperdense lightning
What is quantum mottle?Underexposure of an area (poor positioning). Looks grainy
How do you avoid movement artifact?Sedate, GA (hip, contrast studies, etc)
Use short exposure times (lowest possible mA for enough film blackening)
End-insp/exp exposures for thorax & abdomen
Use fast screens
Causes of geometric unsharpnessIncreased focal spot size --> penumbra
Increased object film distance
Object not perpendicular to x-ray beam (depends on anatomy, can't flatten everything)
X-ray not centered over area of interest
FFD too short
When does magnification occur?Increasing the distance between object and film / cassette (OFD)
Advantages of magnificationImproves resolution of small ojects
Enlarged images are easier to interpret
Air gap eliminates some scatter
Disadvantages of magnificationPenumbra increases
Needs more output
Exacerbates motion blur
How do you minimize OFD?Place area of interest of the patient as close to the film as possible
Distortion =Unequal magnification of various parts of the patient due to differences in distance to the source
Why will there always be some distortion?Patients are 3-D. Different parts are at different distances to the x-ray source
Solution for distortion?Consistent radiographic positioning
Causes of distortionIncreased patient to film distance
Object not perpendicular to the beam
X-ray beam not centered over area of interest
How does foreshortening happen?Tilting/lifting object so it's not parallel to the cassette
Summary of good radiographic technique (9)Use exposure chart
Measure patient/object thickness
Area of interest parallel to film
Area of interest under center of x-ray beam
Use short OFD
Take 2 orthogonal views
Use constant FFD
Use a grid if thickness >10cm
Use rare earth intensifying screens

Radiation Safety & Protection

Question Answer
All ionizing radiation is potentially harmful, depends on what?Type of radiation & dose
Which types of ionizing radiation are used in vet med?X-rays (radiography, CT, fluoroscopy)
Gamma rays (scintigraphy)
Naturally occurring radiation sourcesCosmic (high energy particulate radiation that interacts with the earth's atmosphere)
Terrestrial (Primordial radionuclides have been present on earth since its formation, decay to stable end-products)
Artificial sources of radiationMedical dx & therapy
Fallout from nuclear weapon testing
Nuclear energy production
Depleted uranium in army explosives
The most radiosensitive tissues are? (General)The most rapidly dividing cells
Specific tissues that are most radiosensitive (8)Hemopoietic cells / hemolymphatics
GI tract
Types of adverse effects of radiationDeterministic (increases severity with dose, certain threshold for effects)
Stochastic (random effects, no dose threshold e.g. cancer)
Exposure is quantified byAmount of electrical charge produced by the radiation flux resulting from ionization of air
Unit for radiation exposureCoulombs per kg of air (C/kg)
Radiation absorption is...Tissue dependent
SI unit for absorbed doseGray (Gy)
Amount of radiation leading to the absorption of 1 joule/kg of tissue
T/F The same absorbed dose from different types of ionizing radiation has the same biological effectFalse
The higher the ionization density, the ___ the biological damageGreater
What is a weighting factor?Assigned to different types of radiation to calculate the dose equivalent, since different types of ionizing radiation have different ionization densities (e.g. higher in alpha-particles)
Dose equivalent =Absorbed dose (in Gy) x weighting factor
Unit is Sievert (Sv)
___ sets whole-body limits for radiation exposureInternational Committee for Radiation Protection (ICRP)
The limit for radiation exposure is set in order to avoidStochastic effects
The whole-body limit is20mSv averaged over 5 years with no single annual dose exceeding 50mSv
Possible effects of radiation exposureCell death (degenerative changes in exposed tissue)
Cataracts, erythema, fibrosis, hematopoietic damage (deterministic)
Damage to repro organs (temporary sterility)
Acute radiation syndrome (nausea, anorexia, v+/d+)
Lethal dose5Gy/5 hours (0.13C/kg)
Basic principle of radiation protection?ALARA (as low as reasonably achievable)
How does shielding occur?Thick walls with lead, x-ray machine housing provides
Exposure depends onDistance & time
Sources of exposurePrimary radiation (x-ray beam)
Scatter (1% at 1m distance from patient)
Leakage (escapes x-ray tube housing)
T/F Lead protects from all kinds of radiationFalse, only scatter
Lead protection equipment (4)Apron, goggles, gloves, thyroid shield
What is dosimetry?Monitoring method. Small sealed film worn underneath the lead apron that darkens when x-rays hit the emulsion, changed every month
Types of dosimetry (3)TLD (thermoluminescence dosimetry) - beta, gamma, x-ray. Absorbs energy, re-released when stimulated by light or heat
OSL (optically stimulated luminance) - beta, gamma, x-ray
Pocket dosimeter - gamma & x-ray (can read exposure instantaneously)
3 basics of radiation safety =Time, distance, shielding!
Basic safety rules for Dx radiology (11)Only necessary personnel in room
<18y.o. & pregnant women not allowed in room
Rotate personnel used for holding patients
Sandbags, sponges, ties, chemical restraint
No part of human in primary beam
Protective aprons when holding animal
Gloves if hands *near* primary beam
Thyroid shield, goggles
Collimate primary beam to cassette
Wear radiation monitoring system
Careful planning & positioning, reduce need for 2nd exposures
Special consideration for horizontal beam?Need additional shielding
Large animal radiography: special radiation safety thing?Cassette holders. Usually use horizontal beam
Lead equivalent =Thickness of lead that affords the same protection as 10cm thick concrete barrier
10cm concrete = 1mmPbEq
(Gloves = PbEq 0.5mm; aprons = PbEq 0.35mm)

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