Chapter 11 Flashcards by Rachel Brenner

Measures must be taken to ensure that radiographic equipment operates safely to protect:

Patients
All personnel

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Every diagnostic imaging system must have a:

Protective tube housing
Correctly functioning control panel

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What type of tube housing is required to protect the patient

Lead-lined metal

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Lead-lined metal housing protects the patient and personnel from what type of radiation

Off-focus or leakage

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What is off-focus radiation

Radiation that is not useful - outside of the primary beam

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What is the maximum leakage radiation allowed at 1m from the x-ray source

1 mGy/hr (100 mR/hr)

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Where is the control panel located?

Behind a suitable protective barrier that has a radiation-absorbent window

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Control panel must indicate the conditions of exposure and provide a ______ indication when the x-ray tube is energized

Positive

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Control panel must have visible ___ and ___ digital readouts

mA and kVp

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Radiographic examination table is frequently made of _______________ material

Carbon fiber

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How is SID measured

From anode focal spot to the IR

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SID distance and centering indicators must be accurate to within ___% and ___% of the SID, respectively

2% distance
1% centering

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How is the x-ray beam limited to the size of the IR

Light-localizing variable-aperture rectangular collimator

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Types of x-ray beam limitation devices

Light-localizing variable-aperture rectangular collimator

Aperture diaphragms

Cones

Cylinders

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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

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Simplest of all beam limitation devices

Aperture diaphragms

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What x-ray beam limitation device is used most in dental radiography

Cones

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What types of cones are used for limitation devices

Flared metal tubes and straight cylinders

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Purpose of filtration

Removes low-energy photons (long wavelength or “soft” xrays) by absorbing them

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Minimum total filtration required for radiographic units operating above 70 kVp

2.5mm Al eq

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Types of filtration used for mammographic equipment

Molybdenum and rhodium

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The thickness of a designated absorber required to decrease the intensity of the primary beam by 50% of its initial value

Half-value layer

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Who measures the half-value layer to verify the x-ray beam is adequately filtered

Radiologic physicist

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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

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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

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