Chapter 11 Flashcards
Measures must be taken to ensure that radiographic equipment operates safely to protect:
Patients
All personnel
Every diagnostic imaging system must have a:
Protective tube housing
Correctly functioning control panel
What type of tube housing is required to protect the patient
Lead-lined metal
Lead-lined metal housing protects the patient and personnel from what type of radiation
Off-focus or leakage
What is off-focus radiation
Radiation that is not useful - outside of the primary beam
What is the maximum leakage radiation allowed at 1m from the x-ray source
1 mGy/hr (100 mR/hr)
Where is the control panel located?
Behind a suitable protective barrier that has a radiation-absorbent window
Control panel must indicate the conditions of exposure and provide a ______ indication when the x-ray tube is energized
Positive
Control panel must have visible ___ and ___ digital readouts
mA and kVp
Radiographic examination table is frequently made of _______________ material
Carbon fiber
How is SID measured
From anode focal spot to the IR
SID distance and centering indicators must be accurate to within ___% and ___% of the SID, respectively
2% distance
1% centering
How is the x-ray beam limited to the size of the IR
Light-localizing variable-aperture rectangular collimator
Types of x-ray beam limitation devices
Light-localizing variable-aperture rectangular collimator
Aperture diaphragms
Cones
Cylinders
Benefit of restricting x-ray field size to include only the anatomic structures of clinical interest
Significant reduction in patient dose because less scatter radiation is produced
Improves the overall quality of the image
Simplest of all beam limitation devices
Aperture diaphragms
What x-ray beam limitation device is used most in dental radiography
Cones
What types of cones are used for limitation devices
Flared metal tubes and straight cylinders
Purpose of filtration
Removes low-energy photons (long wavelength or “soft” xrays) by absorbing them
Minimum total filtration required for radiographic units operating above 70 kVp
2.5mm Al eq
Types of filtration used for mammographic equipment
Molybdenum and rhodium
The thickness of a designated absorber required to decrease the intensity of the primary beam by 50% of its initial value
Half-value layer
Who measures the half-value layer to verify the x-ray beam is adequately filtered
Radiologic physicist
How often must the HVL be measured
Annually and after an x-ray tube is replaced or repairs have been made on the housing or collimation system
HVL is expressed in:
mm of Al
HVL is a measure of beam:
Quality
Compensating filters are made of
Aluminium
Lead-acrylic
Types of compensating filters
Wedge
Trough
Consistency in output in radiation for identical generator settings from one indvidual exposure to subsequent exposures
Exposure reproducibility
What is the variance percentage for exposure reproducibility
5% or less
How is reproducibility verified
Using the same technical factors for repeated exposures and then observing with a calibrated ion chamber how intensity varies
Consistency in output radiation intensity at selected kVp settings when generator settings are changed from one mA and time combination to another
Exposure linearity
Ratio of the different in mR/mAs values between two successive generator settings to the sum of those mR/mAs values
Linearity
What must the value be of linearity
Less than .1
When settings are changed from one mA to a neighboring mA station, the most that linearity can vary is:
10%
Intensifying screens convert xray energy into ______ to produce radiographic density on the film
Visible light
Appox ___% of the radiographic density of the recorded image results from the visible light photons that are emitted from the intensifying screens
95%
A single x-ray photon can produce how many light photons with an intensifying screen
80 to 95
Intensifying screens enhances the film exposure process and __________ exposure time
Reduces
Rare-earth screen phosphors
Gadolinium
Lanthanum
Yttrium
What are the speeds for rare-earth screens and matching film combinations
200-1200
What screen-film speeds are currently standard for general radiography
400 speed
When the speed of the screen-film system doubles, radiation exposure is reduced by
50%
As kV increases, effective screen speed __________ for rare-earth screens, which _________ patient dose
Increases
Reduces
What is used as a front material in screen-film
Carbon
Carbon fiber absorbs approximately ____ as much radiation as previously used materials
Half
What is the result of using asymmetric film emulsion and intensifying screen combinations
Image with greater uniformity and a decrease in patient dose
A device made of parallel radiopaque strips alternately separated with low-attenuation material
Grid
What are the strips made of in a grid
Aluminum, plastic or wood
Minimum skin-to-source distance for mobile radiography
30cm (12 inches)
Distance generally used for mobile radiography is
100cm - 120cm (40-48 inches)
With _________ SSD there is a more uniform distribution of exposure throughout the patient
Increased
CR produces what type of image
Analog
DR produces what type of image
Digital
How are x-rays turned into electrical signals in indirect conversions using thin-film transistor arrays
Scintillator
Photodiode
TFT array
Electrical signals
How are x-rays turned into electrical signals in indirect conversions using CCD
Scintillator
CCD
Electrical signal
How are x-rays turned into electrical signals in direct converions
Photoconductor
TFT array
Electrical signal
How are repeat rates in DR effected
Eliminates the need for retakes due to improper technical selection
Does not effect reports for positoning
CR contains what type of phosphor
Photostimulable
What type of laser beam is used to read the PSP plate
Helium-neon laser
Sensitivity of the phosphor used in CR is approximately equal to a ______ - speed screen-film combination
200
CR has a ______ kV flexibility than does conventional screen-film radiography
Greater
CR is _________ sensitive to scatter so a grid should be used more frequently
More
What type of imaging has the greatest patient radiation exposure rate in diagnostic radiology
Fluoroscopy
Benefits of image intensification in Fluoroscopy
Increased image brightness
Saving of time for the radiologist
Patient dose reduction
What is the kVp range for fluoroscopic procedures on adults
75-110
What is the SSD for stationary fluoroscopes
Not less than 38cm (15 inches)
In fluoroscopic procedures, how is kVp changes for children
Decrease by as much as 25%
How to minimize exposure to children
Decrease technical factors
Maintain SSD
Minimize the height of the image intensifier entrance surface above the patient
What is the HVL for fluoroscopy units when the kVp is between 80-100
3-4.5mm aluminum
What is the maxium exposure rate limitation for general purpose fluorscopy
100 mGy per minute (10 R/min)
What is the maximum exposure rate for high-level control fluorscopic units
200 mGy per minute (20 R/min)
What is the primary protective barrier required for a fluoroscopic unit
2-mm lead
Fluoroscopic exposure control switch must be what type
Dead-man
For C-arms, source-to-end of collimator assembly distance is required to a minimum of
30cm (12 inches)
For C-arms, patient-image intensifier distance should be as ______ as possible to reduce entrance does
Short
Dose reduction methods when using fluoro
Pulsed imaging
Last-image-hold
FDA has recommended that a notation be placed in the patient’s record if a skin dose is in the rank of:
1 to 2 Gy
Procedures involving extended fluoroscopic time
Percutaneous transluminal angioplasty
Radiofrequency cardiac catheter ablation
Vascular embolization
Stent and filter placement
Thrombolytic and fibrinolytic procedures
Percutaneous thanshepatic cholangiopancreatography
Transjugular intrahepatic portosystemic shunt
Percutaneous nephrostomy
Biliary drainage
Urinary or biliary stone removal
