Equipment Operation and Quality Assurance Flashcards
What makes up the cathode?
Filament
Filament wires
Focusing cup
What is the filament made of?
Thoriated tungsten
What charge is the focusing cup?
Negative
How do electrons flow in the tube?
Negative to positive (cathode to anode)
The size of the focal spot directed toward the IR is ________ (smaller/larger) than the size of the focal spot measured on the surface of the anode
Smaller
Benefits of line focus principle
Longer tube life
Greater spatial resolution
The smaller the anode angle, the _______ the spatial resolution
Greater
The smaller the anode angle, the ________ the heel effect
Greater
What is the anode made of?
Tungsten with rhenium
What is the neck and base of the anode made of?
Molybdenum or graphite
What makes up the induction motor?
Stator and rotor
The stators are comprised of:
Paired sets of electromagnets
X-rays are produced isotropically, which means:
They are produced with equal intensity in all directions
Leakage radiation should not exceed:
1 mGy/hr at 1 meter
Flow of x-rays from tube to bucky
Tube
Patient
Table
Grid
AEC
IR
Bucky
Benefits of AEC
Images taken on a mixed population will fall within an acceptable range
Less repeats due to over or under exposure
Cons of AEC
Improper positioning
Purpose of the back-up timer in AEC
Provides a level of radiation protection fo the patient
What is MRT (minimum response time)?
The time it takes for a system to respond and send the signal to terminate the exposure
Ohm’s Law
V=IR
How to convert milliseconds to seconds
Divide by 1000
How to determine total resistance in series circuit:
R1+R2+R3+R4
How to determine total resistance in parallel circuit?
1/(1/R1)+(1/R2)+(1/R3)
What is the shortcut to determine total resistance in a parallel circuit?
Total resistance must always be less than the least resistor and will be appox. 1/2 of it
Which side of the circuit is the AC supply located?
Primary side
What supplies the x-ray unti with 220 volts?
AC supply
What type of current is the electrical energy supplied to the x-ray unit?
AC
What is the principle function of the transformer?
Covert incoming low voltage into high voltage necessary to produce x-rays
How efficient are transformers?
95%
What regulates voltage within the x-ray circuit?
Transformers
Transformers operate on the principle of electromagnetic induction and require ____________ current to operate
Alternating
What is electromagnetic induction?
Creating an electromotive force (voltage) within a conductor material that cuts across magnetic lines of force
What are the two types of induction?
Self induction
Mutual induction
What factors determine the strength of the EMF induced within the conductor material?
Speed
Strength
Angle
Number of turns
As speed increases, a _______ EMF is produced
Greater
As the magnetic field increases, a __________ EMF is produced
Greater
As the angle between the conductor and the direction of the magnetic field _________ (approches 90 degrees), a greater EMF is produced
Increases
As the number of turns ___________, a greater EMF is produced
Increases
That magnitude of a voltage change in a transformer is dependent on:
The turns ratio
What is the turns ratio?
Secondary turns:primary turns
What is the source for kVp?
Autotransformer
Which circuit is the autotransformer located in?
Primary
What is the purpose of the autotransformer?
Determine the amount of line voltage that will be sent to the step-up transformer
The autotransformer operates on the principle of:
Self-induction (one wire)
What separates the x-ray circuit into primary and secondary voltage sections?
Step-up transformer
Step-up transformer operates on the principle of:
Mutual induction (two wires)
Which part of the circuit is the filament transformer located in?
Low voltage
Formula for power
P=IV
Which part of the circuit is the exposure time located in?
Low voltage circuit
What is the purpose of the exposure timer?
Controls the duration of the exposure
What is the most accurate type of exposure timer?
Electronic - accurate up to 1 millisecond
What type of exposure timer establishes the highest, safest mA at the shortest exposure time?
mAs timer
What type of exposure timer utilizes an ionization chamber placed between the patient and the IR?
AEC
What is a rheostat and where is it located?
Variable resistor within the filament circuit
What is the function of a capacitor?
Momentarily stores electrical charge
What type of wave is unrectified? (AC or DC)
AC
What is the function of rectifiers?
Convert AC to DC
How are x-rays converted to visible light in an image intensifier?
X-rays - Light - Electrons - Light - Monitor
What is the function of the input phosphor in an image intensifier?
Coverts x-ray photons into light photons
What is the input phosphor made of in an image intensifier?
Cesium iodide
What is the purpose of the photo cathode in an image intensifier?
Converts light photons from input phosphor into free elctrons
What are the components of the image intensifier?
Input phosphor
Photo cathode
Electrostatic focusing lens
Anode
Output phosphor
What is the purpose of the electrostatic lenses of the image intensifier?
Focuses path of electrons from the photocathode to the surface of the output phosphor screen
Where are the electrostatic lenses of the image intensifier located?
Along the full length of the image intensifier tube
What is the purpose of the output phosphor in the image intensifier?
Converts electrons into light photons
What is the output phosphor in the image intensifier made of?
Zinc cadmium sulfide
What type of array is used in flat panel detectors for fluoroscopy?
Solid state detection
How are x-rays converted to light in indirect solid state systems?
X-rays are converted into light and then into electronic signal
What are the advantages of a flat panel detector?
Better stability
Lower patient dose
Wider dynamic range
What is the equation for brightness gain?
Minificiation gain x flux gain
Bright light vision uses which type of cells (cone or rod)?
Cone cells
Low/night vision uses which type of cells (cone or rod)?
Rod cells
Fluoroscopic mA is directly related to the ___________ of the image
Brightness
What is the relationship between the input phosphor and magnificiation?
As the input phosphor size decreases, magnification increases
How does the electron focal point move in mag mode?
Closer to the input phosphor
What happens to patient dose when the distance from the II to the fixed source of radiaiton decreases?
Patient dose decreases
How does mag mode affect patient dose, spatial resolution, and contrast?
Increased patient dose
Increased spat. res.
Increases contrast
What is the single greatest source of acute radiation exposure to the patient in the diagnostic radiology environment?
Fluoroscopy
What is a bit?
A single unit of data
1 byte = __ bits
8 bits
Formula for bit depth
2^bit depth
Number of bit values
2 (0 or 1)
What are the layers of the cassette used for CR?
Protective layer
Phosphor layer
Light reflective layer
Conductive layer
Support layer
Light shielding layer
Backing layer
What is the function of the phosphor layer in a PSP imaging cassette?
Traps electrons
What is the phosphor layer made of in a PSP imaging cassette?
Europium-activated barium fluorohalide
What is a latent image in CR?
Electronic image of valence electrons stored in high-energy traps
What is the manifest image in CR?
Visible image made by exposure to the latent image with a high energy laser
What is the function of the laser in CR?
Causes the stored electrons to return to their valence bands with the emission of violet light
How does an imaging plate reader work in CR?
Employs the laser that reads the energy stored in the conductive layer, causing light to be emitted
What are the two types of scans in an imaging plate reader?
Fast scan - raster pattern movement of the laser across the PSP plate
Slow scan - mechanical movement of the PSP plate into the CR reader
How are CR plates erased?
Bright light
Exposure terms used by manufactures that indiciate amount are:
S, EI, lgM
What type of relationship do S numbers have with the amount of exposure?
Indirect
What type of relationship do EI numbers have with the amount of exposure?
Direct
What type of relationship do lgM numbers have with the amount of exposure?
Direct
If the deviation index is +3.0 or greater, what is exposure deviation? Patient exposure? Recommended action?
100% too hgih
Excessive patient exposure
No repeat, unless burnout occurs
If the deviation index is -3.0 or less what is exposure deviation? Patient exposure? Recommended action?
<50% low
Excessive under-exposure
Repeat
What is the process in indirect DR to convert x-rays into a digital image?
- Scintillator converts x-ray photons to light photons
- Light from the scintillator strikes the CCD and is converted to electric signal
- TFT amplifies signal
- The signal is sent to an ADC where is becomes a data set to form the digital images
What is the scintillator material in indirect DR?
Amorphous silicon
What is the process in direct DR to convert x-rays into a digital image?
- Uses amorphous selenium to convert x-rays to electrons
- TFT collects electrons and amplifies signal. Sends to ADC
- Converts electric signal to digital signal
What is a histogram?
Graphical representation of optimal densities during an exposure
What are values of interest?
Digital data set of information that is arranged into a histogram distribution
What is gray scale?
The number of shades of gray in an image
A reference to evaluate the raw information and to correct the luminance values
LUT
Results when the signal average inludes fewer pixels in the neighborhood. Used when fine details in an image are shown with some blur
Edge enhancement
How do high pass and low pass filters work in edge enhancement processing?
High pass filers increase contrast by amplifying areas of interest
Low pass filters causes a smoothing effect by averaging pixel values
What is the image processing technique that provides contrast enhancement or grayscale enhancement?
Equaliziation
Describes the contribution of all system components towards total resolution.
Modulation Transfer Function
What is the MTF value with the best resolution
1
What is the intensity of light that represents each pixel on the monitor?
Brightness
What is the differences in brightness?
Contrast
What is the boundaries of an object on an image?
Region of interest
What is accomplished by suppressing frequencies of lesser importance?
Cropping/masking
What is shuttering and when is it used?
Removes or replaces the background
Used when distracting light surrounds an image
Ability to alter the receptor exposure and contrast of a digital image
Windowing
As the number of pixels in the image matrix increases; spatial resolution:
Increases
Each pixel is given a numeric value known as:
CT number or Hounsfield unit
Diameter of the image reconstruction is called:
Field of view
When the FOV is increased for a fixed matrix size, the size of each pixel is:
Increased
Volume of tissue imaged is given a value called:
Value element or voxel
Window level determines: (brightness or contrast?)
Brightness
Window width determines: (brightness or contrast?)
Contrast
Which information system contrains full patient information?
Hopsital information system
Which information system contains radiology specific imformation?
Radiology information system
What is the difference between WAN and LAN?
WAN - spans great distances such as cities or states
LAN - small in size, computers are connected with wireless access points, much faster than WAN
Accepted standard for networked medical devices to exchange images and information
DICOM
Laser image receptor digitizers use a ________ type of laser beam for conversion of analog images into digital images
Helium-neon
Beam restricition must be within plus or minus __% of the source to image distance
2%
Linearity variation cannot exceed plus or minus __%
10%
Reproducibility must be within + or - ___%
5%
How often should lead aprons and gloves be tested?
Annually
Aprons and gloves should be tested under fluoro. What color will a crack show up?
White
