M Part I Flashcards
Three Principles of X-ray Imaging System
- X-ray Tube
- Operating Console
- High Voltage Generator
It is attached to an overhead
Movable assembly
Location: examination room
Radiographic X-ray Tube
Localized under examination table
Fluoroscopic X-ray Tube
It must be transparent to x-rays as much as possible
Examination Table
Composition of examination table
Strong and absorbs a little bit of radiation
Carbon fiber
Fluoroscopic table degree of tilt
[..] to the foot side
[..] to the head side
90 degrees
30 degrees
It is housed in an equipment cabinet positioned against the wall
It is always close to the x-ray tube
High voltage generator
Material familiar to the radiographic table
Used to control the X-ray tube current and voltage applied to x-ray tube
Provides control of line compensation
KVp, mA, exposure time
Operating Console
Number of x-ray
Intensity of the x-ray beams
Units: mR/mAs
Radiation quantity
Penetrability of the x-ray beam
Expressed in kilovolt peak (kvp)
Radiation quality
Inside operating console
Measures the voltage provided to the x-ray imaging system
Ph - 120 V
US - 110 V
Line Compensator
Consists of only one winding of wire
Autotransformer
[function, location] Autotransformer
Supplies the precise voltage circuit controls the kVp
Inside operating console
Autotransformer require [..] to approximately increase twice the input voltage value
Step up voltage
It conducts the input power to the autotransformer
Primary connection
State the AUTOTRANSFORMER LAW/ formula
It states that the voltage receive & provide by the transformer is directly proportional to the no of turns
Vs/Vp = Ns/Np
Adjustment of Kilovoltage Peak (kVp) [adjustment controls]
represent two separate series of connections on the autotransformer.
Major and minor kVp
It determines the quality of the x-ray beam
-kVp
[part, location] It reads voltage (not kVp)
-kVp meter
-location: output terminals of the autotransformer
It allows the voltage to be monitored before an exposure
Prereading kVp Meter
It is measured in milliamperes (mA)
X-ray tube current
It determines the number of electrons emitted by the filament
Filament Temperature
It controls the filament temperature
It is measured in amperes (A)
Filament Current
Filament Current [Range]
3-6 A
It controls x-ray tube current
Filament Circuit
Explain SPACE CHARGE EFFECT
A phenomenon of the space charge that makes it difficult for subsequent electrons to be emitted by the filament because of electrostatic repulsion
Electron cloud near the filament
Space Charge
The release of electrons from a heated filament
Thermionic Emission
It is used to reduce the voltage to a value that corresponds to the selected milliampere
Precision Resistor
Design in which exposure factors are adjusted automatically to the highest mA at the shortest exposure time allowed by the high-voltage generator
Exposure behind at maximum mA and it drops as the anode heats
Falling Load Generator
Result of falling load generator
Minimum exposure time
The product of X-ray tube current (mA) and exposure time (s)
A measure of electrostatic charge
-mAs
It monitors the X-ray tube current
-mA Meter
[location, rationale] mA Meter
It is connected at the center of the secondary winding of the high voltage step up transformer
rationale: ensures electrical safety
Filament Transformer [full name]
Filament Heating Isolation Step-down Transformer
Received the voltage from the mA selector switch
Provides the current to heat the filament
Filament Transformer
Filament transformer step down the voltage to approximately [..]
12 V
Primary Windings
[material]
Current: [..]
Voltage: [..]
Thin copper
0.5-1 A
150 V
Secondary Windings
[material]
Current: [..]
Voltage: [..]
Thick
5-8 A
12 V
It terminates an exposure after a prescribed time (6s)
Guard Timer
It consists of an electronic device
-make and breaks the high voltage across the x-ray tube
-always done on the primary side
Time Circuit
Time circuit [rationale]
Lower voltage
Four types of Timing Circuits
- Synchronous Timer
- Electronic Timer
- MAs Timer
- Automatic Exposure Control
A precision device assigned to friends a shaft at precisely 60 revolution per second
Synchronous Timer
Disadv of synchronous timer
It cannot be used for serial exposures
Most sophisticated, most complicated and most accurate (as small as 1 ms)
Electronic Timer
[adv] Electronic Timer
Allows a wide range of time intervals to be selected
Used for rapid serial exposures
Most exposure timers are [..] and are controlled by a [..]
Electronic
Microprocessor
[function] mAs timer
- Monitors the product of mA and exposure time
- Terminates exposure when desired mAs value is attained
- Provides the highest safe tube current for the shortest exposure for any mAs selected
[location] mAs timer
Secondary side of the high-voltage transformer
[applications] mAs timer
Falling-load
Capacitor discharge imaging system
A device that measures the quantity of radiation that reaches the image receptor
It automatically terminates the exposure when the image receptor has received the required radiation intensity
Automatic Exposure Control (AEC)
It is used to check timer accurately (as short as 1 ms)
Solid-State Detectors
It increases the output voltage from the autotransformer to the kVp necessary for x-ray production
High Voltage Generator
Three Primary Parts of a High Voltage Generator
- High Voltage Transformer
- Filament
- Rectifiers
Explain relationship of primary and secondary: voltage, current, windings [high voltage transformer - step-up transformer]
Secondary Voltage (kVp) > primary Voltage (V)
Secondary Current (mA) < primary Current (A)
Secondary Windings > primary Windings
Voltage waveform: [..]
Sinusoidal
[..] only difference in the primary and secondary waveform
Amplitude
The ratio of the no of secondary windings to the no of primary windings
Turns Ratio
Turns Ratio relationship with voltage and current
Directly proportional to the voltage
Inversely proportional to the current
It ensures that electrons flow from cathode to anode only
Voltage Rectifiation
The process of converting alternating current flow in only one direction
Rectification
An electronic device that contains two electrodes
Diode
A vacuum tube (original rectifiers)
Replaced by solid-state rectifier
Valve tube
Composition of valve tube
Silicon
Lies between insulators and conductors
Semiconductor
Two types of semiconductor
P-type and n-type
Have loosely bound electrons (free to move)
P-type Semiconductor
[p-type] Spaces with no electrons
As mobile as electrons
Holes
N-type material placed in contact with p-type crystal
It conducts electricity in only one direction
Solid-State p-n junction
Rectifier of solid-state p-n junction
Solid-state diode
[..] used when medical imaging systems are described
Electron Flow
The voltage is not allowed to swing negatively during the negative half of its cycle
Half-wave Rectification
Half-Wave Rectifification [Diodes, Pulses]
0, 1 or 2
60 pulses/second
Half-Wave Rectification [disadv]
It wastes half of the supply of power
It requires twice the exposure time
The negative half-cycle corresponding to the inverse voltage is reverse
Full-wave Rectification
Full-wave rectification [diodes, pulses]
4
120 pulses/sec
Full-wave rectification [adv]
Exposure time reduced
It results in a pulsating x-ray beam
Single-phase power
Single-Phase Power [disadv]
X-ray produced has a value near zero
The voltage impressed across the X-ray tube is nearly constant
Three-Phase Power
Three-Phase Power [pulses]
6 pulses/ 1 /60 sec
Three-Phase Power [adv, disadv]
Adv. voltage never drops to zero during exposure
Disadv. It’s size and cost
Starting an exposure time
Initiation Time
Ending an exposure
Extinction Time
It produces a nearly constant potential voltage waveform
It uses inverter circuits
High Frequency Generator
High Frequency Generator [adv]
- Much smaller & less costly & more efficient
- Improves image quality at lower patient radiation dose
A high speed switchers or choppers that convert DC into a series of square pulses
Inverter Circuit
T/F FULL-WAVE RECTIFICATION OR HIGH FREQUENCY VOLTAGE GENERATOR IS USED IN ALMOST ALL STATIONARY X-RAY
TRUE
Tube voltage falls during exposure
Approx. 1 kV/mAs
Capacitor Discharge Voltage
An automatic lead beam stopper
It stops continuous x-ray emission of capacitor bank
It is designed to be turned on and off very rapidly
Grid-Controlled X-ray Tube
Grid-Controlled X-ray Tube [applications]
Portable capacitor discharge imaging systems
Digital subtraction angiography
Digital radiography
Cineradiography
Refers to an element in the tube that acts as a switch
Grid
Less voltage ripple means
- Greater radiation quantity
- High efficiency f x-ray production
- Greater radiation quality because of fewer electrons that pass from cathode to anode
Characteristics of High Frequency
Frequency range : <1 kHz
[inverter features]
Thyristors
Characteristics of High Frequency
Frequency range : 1-10 kHz
[inverter features]
Large silicon-controlled rectifier
Characteristics of High Frequency
Frequency range : 10-100 kHz
[inverter features]
Power field effect transistors
Means of characterizing voltage waveforms
Voltage Ripple
Waveform
Single Phase
Half-Wave [ripple, voltage]
Full-Wave [ripple, voltage]
Ripple: 100%
Voltage: Varies from zero to maximum
Waveform
Three Phase
6-pulse [ripple, voltage]
12-pulse [ripple, voltage]
Ripple: 14%
4%
Voltage: never falls below 86% max value
Never falls below 96% max value
Waveform
High frequency
[ripple, voltage]
<1%
Never falls below 99% of max value
Incentivizes the transformers and high-voltage generators
Power Rating (kW)
Power Rating
Three-phase & high frequency [formula]
(MA x kVp)/1000
Power Rating
For single-phase [formula]
(O.7)(mA x kVp/1000)