Week 11 - Equipment Design Flashcards
What do the designs of radiologic equipment all technologists to do?
- Optimize the quality of the image
- Reduce radiation exposure to patients
Who are protected when radiographic equipment is used safely?
Patients and all personnel
What are the two required features for every diagnostic imaging system?
- protective tube housing
- correctly functioning control panel
What other components of diagnostic systems have been designed to reduce patient dose?
Radiographic exam tables and other devices
What material is required of tube housing?
Needs to be lead lined
What does a lead-line tube housing protect patients and personnel from?
Off focus or leakage radiation
How do lead lined tube housing reduce off-focus and leakage radiation?
Restrict the emission of x-rays to the area of the primary beam
What are the leakage requirements for tube housing?
It needs to be constructed so that any leakage measured 1 m from the x-ray source does not exceed 0.88 mGy/hr
Where does a control panel/console need to be located?
Behind a suitable protective barrier
What are the features of the suitable protective barrier?
Has a radiation-absorbent window that permits observation of the patient during a procedure
What features are required of a control panel?
Must indicate the conditions of exposure and provide a positive indication when the tube is energized
How are exposure conditions represented on a console?
Through visible mA and kVp readouts
What happens on the console when the exposure begins?
A tone is emitted and then stops when it terminates
What does the audible sound indicate?
That the x-ray tube is energized and ionizing radiation is being emitted
What is the main feature of a radiographic examination table?
It needs to be strong enough to support patient whose weight is in excess of 400 lbs
What feature do exam table usually have?
A floating tabletop that makes it easier to maneuver a patient
What needs to remain uniform on an exam table?
Thickness
What is an important function of the material of a exam table?
Needs to be radiolucent so that it only absorbs a minimum amount of radiation
What material are exam tables usually made of?
Carbon fiber
What are two additional features of an exam table?
Have a grid and slot cover
What does the SID indicator provide?
A way to measure the distance from the anode focal spot is maintained
What are used to measure SID?
Lasers or tape measures
At what range are distance and centering indicator accurate?
Within 2% and 1% of the SID, respectively
What is a standard rule for the primary beam?
That it should be not larger than the size of the IR being used
What is light-localizing variable-aperture rectangular collimator used for?
Its used to adjust the size of the x-ray beam automatically or manually
What is the predominant x-ray beam limitation device?
Collimator
What is the purpose of a collimator?
To reduce scatter radiation
How are light-localizing variable-aperture rectangular collimators constructed?
With 2 sets of lead shutters, a light source and a mirror
What do the 1st shutter placed close to the window do?
Reduce off-focus radiation
What are the minimum skin sparing distance for fixed machines?
15 cm
What is the minimum skin sparing distance for mobile machines?
30 cm
What is luminance?
Brightness of the light source
What are the benefits of restricting x-ray field size to only include area of interest?
- Significant reduction in patient dose, because less scatter is produced
- Improves overall quality of the image
What is positive beam limitation?
When the beam of light is automatically adjusted to the size of the IR being used
What must the radiographer ensure when PBL is in use?
That the collimation is accurate and adjusted to the size of the part and no bigger than the IR
What are radiographic cones?
Circular metal tubes that attach to the x-ray tube housing and limit the beam to a predetermined size and shape
What are the two types of cones?
Flared metal tubes and straight cylinders
What types of cones are used in dental radiography?
Beam-defining cones
What is another type of beam limiting device?
Aperture diaphragm
What is an aperture diaphragm?
A flat piece of lead with a hole in it of a designated size and shape
Where is an aperture diaphragm placed?
Directly below the window of the x-ray tube to confine the primary beam to the given size of the hole
What do sizes of aperture diaphragms relate to?
Each size IR and SID
What is the purpose of beam filtration?
To remove low energy photons
How does beam filtration effect patient dose?
It lowers patient dose, by hardening the beam and making it more penetrating
How is the energy of the beam affected by filtration?
The effective energy of the beam is increased
What are the 3 types of filtration?
- inherent
- added
- total filtration
How do beam filters work?
They absorb the low energy photons and permit high energy photons to pass through
What is the minimum total filtration required when more than 70 kVp is used?
2.5 mm Al equivalent
What is the minimum total filtration required when 50-70 kVp is used?
1.5 mm Al equivalent
What is the minimum total filtration required when less than 50 kVp is used?
0.5 Al equivalent
How is filtration most widely expressed?
In aluminum or its equivalent
What is the required Al eq for inherent filtration?
0.5 mm Al eq - glass and oil
1.0 mm Al eq - collimator mirrors
What is the required Al eq for added filtration?
1.0 Al (thin sheets of aluminum
What is the Al equivalent for total filtration?
2.5 Al eq
What is the minimum Al eq filtration for mobile diagnostic and fluoroscopic equipment?
2.5 mm Al eq
What is half value layer?
The thickness of a designated absorbed required to decrease the intensity of the primary beam by 50% of its initial value
Why must the HVL be measured?
To verify that the x-ray beam is adequately filtered
Who should obtain the HVL measurement?
A radiologic physicist
When should a radiologic physicist obtain the HVL?
At least once a year, after an x-ray tube is replaced or when the housing or collimator have been repaired
How is HVL expressed?
In millimeters of aluminum
What does HVL measure specifically?
Beam quality or effective energy of the x-ray beam
What are compensating filters made up of?
Aluminum, lead acrylic or other suitable material
What are compensating filters used for?
To accomplish dose reduction and uniform imaging of body parts that vary considerably in thickness/tissue composition
How do compensating filters work?
They partially attenuate x-rays directed towards the thinner areas and allow more x-rays to strike the thicker areas
What are the two types of compensating filters?
- wedge filter
- trough, or bilateral wedge filter
What are the two required radiation exposure characteristics?
- Exposure reproducibility
- Exposure linearity
What does exposure reproducibility provide?
Consistency in output radiation intensity for identical generator settings between individuals
What variance is accepted for exposure reproducibility?
A variance of 5% or less
How can reproducibility be verified?
By using the same technical exposure factors to make a series of repeated exposures and then observing with a calibrated ion chamber and seeing how the intensity varies
What does exposure linearity provide?
Consistency in output radiation intensity at selected kVp settings when generator settings are changed from on Mas and time combination to another
What is linearity?
The ratio of the differences in mSv/mAs or mR/mAs between two successive generator stations to the sum of these mSv/mAs or mR/mAs values
What does the linearity ratio need to be?
Less that 0.1
What is the variation percent when settings are changed from one mA to a neighboring mA station?
10%
What is AEC?
An x-ray terminating device that ends the radiation when a predetermined amount of radiation is received by an arrangement of sensors
What does AEC produce?
An acceptable image while limiting radiation exposure to a patient
What is a safety feature that is part of AEC?
A backup timer
What is phototiming?
Old terminology referring to photomultiplier tubes
What do today’s AEC systems utilize?
Ionization chambers
What is a radiographic grid?
A device made of parallel radiopaque strips alternately separated with low-attenuation strips of aluminum, plastic or wood
Where is a radiographic grid placed?
Between the patient and the IR
What do radiographic grids do?
Remove scattered x-ray photons that emerge from the patient before it can reach the IR and decrease image quality
What impact do radiographic grids have on image quality?
They increase radiographic contrast and visibility of detail
What size parts require the use of radiographic grids?
Parts that are 10 cm or more
What is grid ratio?
Refers to the height of the lead strips divided by the distance between each strip
What is the minimum SSD that should be used for mobile units?
Minimum SSD is at least 30 cm (12 inches)
What is the distance generally used for mobile radiography?
100 cm (40 inches) or 120 cm (48 inches)
What effect does SSD have on patient entrance exposure?
With increased SSD there is a more uniform distribution of exposure throughout the patient
When are mobile units used?
For patients who can’t be transported to a fixed unit
What are the 5 digital processed radiography imaging modes?
- Computed tomography (CT)
- Computed radiography (CR)
- Digital Radiography (DR)
- Digital Fluoroscopy (DF)
- Digital Mammography (DM)
What are negative features of conventional radiography: analog images?
- Latent image creation and latent imaging processing
- Time consuming processing time
- Images often lost
What is a positive feature of conventional radiography: analog images?
Produced optimal-quality images
What has conventional radiography: analog images been replaced by?
Digital imaging
What is digital imaging?
Process of producing an electronic image
What are some limitations of digital imaging?
Inherent limitations with respect to spatial and contrast resolution due to dimensions of pixels
What is digital imaging subject to?
Artifacts because digital imaging are produced collectively by a matrix of elements and are subject to noise
How are images formed in digital imaging?
Latent image is formed by x-ray photons on a radiation detector
What is brightness in digital imaging?
The amount of luminance (light emission) on a display monitor
What are digital images composed of?
Numerical data that is stored in rows and columns called the image matrix
How does digital radiography work?
Image receptors convert energy into electric signals
What is a scintillator?
Converts x-ray energy into visible light and is made of amorphous silicone
What is visible light transformed into in digital radiography?
Transformed into electrical signals by charge-coupled devices (CCDs)
What is a photoconductor?
Converts x-ray energy directly into electrical signals which are then read by transistors.
What are photoconductors made of?
Amorphous selenium
Where can digital images be accessed?
At multiple workstations
What are the two types of conversion in digital imaging?
Indirect and direct conversion
What are the two types of indirect conversion?
Scintillator > Photodiode > Thin-film transistor array > Electrical signals
Scintillator > Charge-coupled device array > Electrical Signals
What is the process of direct conversion?
Photoconductor > Thin-film transistor array > Electrical signals
How are images generated in computed radiography?
Using photostimulable luminescence (PSL)
How is CR different than DR?
CR uses conventional radiographic equipment, traditional positioning and standard technical exposure factors
What doe CR cassettes contain?
Photostimulable phosphors
How are images read in CR?
A read unit scans the photostimulable phosphor plate with a laser beam and then displays it on a monitor
Which type of radiography has a greater KV flexibility?
CR
What type of radiography requires a more frequent use of grids?
CR since the imaging patients are more sensitive to scatter
What are the advantages of DR?
- lower doses
- greater ease of use and faster patient throughput
- immediate imaging results
- additional image manipulation
- less overall maintenance
What are the disadvantages of DR?
- more costly
- not cross compatible
- single detector size
- PSP imaging plates are subject to mechanical damage and chemical oxidation
- high replacement costs
What are the 3 types of artifacts DR are subject to?
Image aliasing, Moire patterns and contouring defects
How does DR eliminate the need for retakes?
Improper technical selections that produce contrast or brightness issues can be manipulated after image acquisition
Why is there an increased repeat rate in DR?
Because of the ease of repeating images
How are mispositioning repeats monitored?
An independent quality control technologist at a separate monitor
Where does the body area need to be positioned on a CR IR?
In or near the center of the IR
What are fluoroscopic procedures used for?
To capture dynamic or active motion images of selected anatomic structures
Which type of radiography produces the greatest patient radiation exposure rate?
Fluoroscopic radiography
How are fluoroscopic procedures performed?
With a fluoroscopic tube inside the xray table facing up toward the surface of the table
How does an image intensifier fluoroscopic unit work?
It converts the pattern of x-rays transmitted through the patient into a corresponding and amplified visible light patternW
What are the benefits of image intensification fluoroscopy?
- increased image brightness
- saving of time for the radiologist
- patient dose reduction
How is an image intensifier used?
It’s placed over the patient on this table during the examination and is used in conjunction with the tube
How much is the brightness of the fluoroscopic image increased compared to non-image intensified fluoroscopy?
10,000 times
How much mA is reduced when fluoroscopic vs intensified fluoroscopic?
Reduced from 3-5 mA to 1-1.5 mA
What does an image intensifier tube produce?
A magnified image
What are the benefits of pulsed and interrupted fluoroscopy?
- Significantly decreases patient dose
- Extends tube life
- Has a last-image hold feature
What is the standard kVp range for adult patients using non-digital fluoroscopic imaging systems?
75-100 kVp
What is the SSD for stationary fluoroscopes?
No less that 38 cm
What is the SSD for mobile fluoroscope?
No less than 30 cm
How should kVp be adjusted for children in non-digital fluoroscopic imaging systems?
KVp should be decreased as much as 25%
In what ways are exposures limited for children using fluoroscoping imaging systems?
- Decreasing technical factors, maintaining SSD and minimizing height of image intensifier entrance surface above patient
What is the HVL for non-digital fluoroscopic image systems?
HVL of 3-4.5 mm Al acceptable when kVp ranges from 80-100
Who sets up current standard limits for entrance skin exposure rates?
Federal government
What is the maximum entrance skin exposure rate for non-digital fluoroscopic imaging systems?
Maximum of 88 mGya/min (10R/min)
What is the maximum entrance skin exposure for fluoroscopic units equipped with high level control?
Maximum of 176 mGya/min (20 R/min)
What is the primary protective barrier of non-digital fluoroscopic imaging systems?
2mm lead equivalent
What type of exposure control switch does fluoroscopic machine need to have?
A dead man type
What is the shape of a portable fluoroscopic unit?
C shaped with c-ray tube attached at one end and an image intensifier at the other
What are portable fluoroscopic units used for?
In the operating room for orthopedic procedures, cardiac imaging and interventional procedures
What risk do patients and personnel have with mobile fluoroscopic units?
Risk of large radiation doses from scatter
What must C-arm equipment operate have?
Appropriate education and training to ensure they follow safety guidelines and meet safety protocols
What is the source to end collimator distance required for mobile fluoroscopic units?
30 cm
What should the distance be for image-intensifiers in mobile fluoroscopy units?
As short as possible to reduce entrance dose
How should the C arm be positioned to reduce patient dose?
Under the patient since it limits scatter
What happens when the C arm is positive over the patient?
Scatter becomes more intense and exposure increases correspondingly
What system do digital fluoroscopy systems use for dose reduction?
Pulse progressive systems
What is last image hold?
The last image formed remains on the monitor so that no further radiation exposure is needed to regenerate it
What are interventional procedures?
Locate high contrast using small objects such as catheters, stems or electrical leads
What is digital subtraction angiography?
Visualization of blood vessels
What is roadmapping?
A static image of the vasculature may be obtained through subtraction, pre and post contrast injection
Where is a catheter inserted?
Into vessels or tissues
What is the purpose of a catheter?
- Drainage
- Biopsy
- Alteration of vascular occlusions or malformation
What is High-level-control fluoroscopy?
An operating mode for state of the art fluoroscopic equipment in which exposure rates are substantially higher than those normally allowed in routine procedures
What has the FDA recommended for procedures involving fluoroscopic radiology?
That a notation be placed in their record if skin dose is in the range of 1-2 Gy received
What are the procedures that involve extended fluoroscopic time?
- percutaneous transluminal angioplasty
- radio frequency cardiac catheter ablation
- vascular embolozation
- stent and filter placement
- thrombocytes and fibrinolytic procedures
- Percutaneous trashepatic cholangiograpy
- Endoscopic retrograde cholangiopancreatography
- transjugular intrahepatic portosystemic shunt
- percuraneous neprostomy
- biliary drainage
- urinary or biliary stone removal
What do non-radiologist physicians need when using fluoroscopic equipment?
Ongoing education and training
