RADI 299 Review: Operation and Quality Assurance

A set of 200 flashcards based on lecture notes covering x-ray equipment operation, circuits, tubes, AEC, beam restriction, generators, digital radiography, and quality assurance.

What side of the x-ray circuit is the operating console located on?

The primary (low voltage) side

List three technical factors typically selected at the operating console.

kV, mA, and time (mAs)

Identify three components located on the secondary (high voltage) side of the x-ray circuit.

The x-ray tube, the rectifier, and the mA meter

True or False: The operator console is supplied with high voltage.

False (It is on the low voltage side)

Which component of the anode assembly is located outside the vacuum tube?

The stator (electromagnets)

What is the typical rotation speed for a standard rotating anode?

$3,200$ to $3,600\,rpm$

What is the rotation speed for a high-speed rotating anode?

$$10,000\,rpm$$

The rotor of an induction motor consists of what materials?

A copper core surrounded by iron bars

How much of a total electron's kinetic energy is converted to x-rays at the anode target?

Less than $1\%$

Approximately what percentage of energy is given off as heat during x-ray production?

$$99\%$$

What is the atomic number (Z#) of Tungsten?

$$74$$

What is the melting point of Tungsten?

Approximately $3,410^{\circ}\text{Celsius}$

Why is Rhenium added to the Tungsten in an anode alloy?

It provides greater elasticity for expansion

What material can be used as a backing for the anode to double heat-loading capabilities?

Graphite

What is the purpose of the vacuum within the glass envelope?

To preserve the tube vacuum for efficient electron travel

Define the 'space charge effect'.

The collection of electrons around the filament that limits further thermionic emission

What is the primary cause of x-ray tube failure?

Vaporized Tungsten

How does vaporized tungsten affect tube output?

It acts as additional filtration and decreases tube output

A 'gassy tube' is a result of what process?

Tungsten vaporization

What is the life expectancy of a standard x-ray tube in terms of exposures?

$10,000$ to $20,000$ exposures

Holding down the rotor switch for too long can shorten tube life by what percentage?

$$50\text{-}60\%$$

What effect does excessive heat to a cold anode have?

Cracking of the anode

What is the cause of anode pitting?

Excessive heat to the target

What is the result of excessive heat to the rotor bearings?

Increase in friction, loss of anode rotation, or rotor wobble

To prolong tube life, what combination of kV and mA is recommended?

High-kV and low mA settings

What three factors determine the total number of x-rays produced at the anode target?

1. Tube Current (mA), 2. Target material (atomic number), 3. Square of the kV

How does a higher atomic number target material affect x-ray production?

The atoms are more dense, providing more electrons for interaction and high-energy x-ray efficiency

What is the function of the molybdenum or nickel focusing cup?

It narrows and focuses the beam of electrons toward the anode

At what speed do electrons travel across the 2-inch gap between cathode and anode?

Approximately $\frac{1}{2}$ the speed of light

At what temperature does thermionic emission typically occur?

Not below $2,200^{\circ}\text{C}$

What is the aluminum equivalent inherent filtration of the glass envelope and dielectric oil?

$0.5$ to $1.0\,mm\,Al\,eq$

Define leakage radiation.

X-rays that escape the tube housing from anywhere except the port window

What is the federal limit for leakage radiation?

$100\,mR/hr$ at $1\,meter$ (or $1\,mGy/hr$ at $1\,meter$)

What is the purpose of the oil coolant surrounding the x-ray tube?

To insulate the tube and absorb heat from the structures

What is a grid-controlled x-ray tube?

A tube that can be turned on and off rapidly using the molybdenum focusing cup as a switch

Where are grid-controlled tubes commonly used?

In fluoroscopy and capacitor-discharge mobile units

What is the recharge time for a battery-powered mobile unit?

$$12\,hours$$

What is the essential function of Automatic Exposure Control (AEC)?

To terminate the x-ray exposure once the IR has been correctly exposed

Which exposure factor is eliminated when using AEC?

Exposure time

What are the two modern types of AEC sensors?

1. Ionization chamber, 2. Phototimer (photomultiplier)

Where is the ionization chamber located?

Just beneath the tabletop, above the cassette (between the patient and IR)

Where was the older phototimer fluorescent screen positioned?

Beneath the cassette

A backup timer for AEC should be set to what percentage of the anticipated manual time?

$$150\%$$

U.S. public law requires AEC generators to terminate at what mAs level?

$600\,mAs$ (above $50\,kVp$)

What is the minimum response time for modern AEC systems?

Approximately $0.001\,second$ ($1\,ms$)

Three basic types of beam-restricting devices include:

Aperture diaphragms, cones/cylinders, and collimators

What is the simplest type of beam-restricting device?

Aperture diaphragm

Define 'penumbra'.

Geometric unsharpness around the periphery of an image

Which beam restrictor is most efficient and permits an infinite number of field sizes?

The collimator

What is another name for off-focus radiation?

Extra-focal or stem radiation

How much of the total primary beam can be comprised of off-focus radiation?

$$25\text{-}30\%$$

What component in the collimator assembly reduces off-focus radiation?

The upper (top) shutters

What component in the collimator assembly reduces penumbra along the periphery?

The bottom shutters

In a collimator, why must the focal spot and light bulb be the same distance from the mirror?

To ensure the projected light beam is the same size as the x-ray beam

What does PBL stand for?

Positive Beam Limitation (automatic collimation)

Between what years was PBL mandatory on fixed radiographic machines in the U.S.?

$1974$ to $1993$

What is the purpose of a lead blocker?

To absorb scatter produced in soft tissue (e.g., patient's back during lateral lumbar x-ray)

State Ohm's Law formula.

$$V = IR$$

What is the relationship between mAs, mA, and time?

$$mAs = mA \times \text{time (seconds)}$$

What device converts mechanical energy to electrical energy?

A generator (dynamo)

What law does a generator operate under?

Faraday's Law

What is the standard frequency of alternating current in the United States?

$60\,Hz$ (cycles per second)

How many times does the energy on a sine wave drop to zero in a single cycle in the U.S.?

Twice ($120\,times$ per second)

What principle do transformers operate on?

Mutual induction

Write the Transformer Law for voltage.

$$\frac{V_s}{V_p} = \frac{N_s}{N_p}$$

A step-up transformer has a secondary voltage that is _______ than the primary voltage.

Higher

What principle does an autotransformer operate on?

Self-induction

Where is the autotransformer located in the x-ray circuit?

Between the AC source and the primary side of the high-voltage transformer

What device is used to select the mA station in the filament circuit?

Rheostat (potentiometer or variable resistor)

A rectifier converts _______ to _______.

AC (Alternating Current) to DC (Direct Current)

An inverter converts _______ to _______.

DC (Direct Current) to AC (Alternating Current)

In what type of generator are inverters found?

High-frequency generators

What is the function of the capacitor in an x-ray circuit?

To temporarily store electric charge and smooth the voltage waveform

What is the role of the filament circuit?

To supply power to the filament for thermionic emission (step-down transformer)

The voltage in the filament circuit is typically decreased to what range?

$5\text{-}15$ volts

What is another name for the x-ray tube circuit?

Main circuit

The kVp meter is located on which side of the circuit?

The primary (low voltage) side

Identify the rectification system's location in the circuit.

The secondary (high voltage) side

The mA meter is located on which side of the circuit?

The secondary (high voltage) side

Increasing kVp has what effect on wavelength?

It decreases wavelength

Increasing kVp has what effect on exposure rate?

It increases exposure rate

A full-wave rectified single-phase generator produces how many pulses per second?

$$120\,pulses$$

What is the voltage ripple for a single-phase generator?

$$100\%$$

How many dots would be seen on a manual spinning top test for a single-phase generator at $0.10\,seconds$?

$$12\,dots$$

What is the voltage ripple for a three-phase, six-pulse generator?

Approximately $13\text{-}25\%$ (Bushong states $14\%$)

What is the voltage ripple for a three-phase, twelve-pulse generator?

Approximately $4\text{-}10\%$

High-frequency generators have a voltage ripple of less than:

$$1\%$$

What is the rectification constant for a single-phase unit?

$$1.0$$

What is the rectification constant for a three-phase, twelve-pulse unit?

$1.4$ (Note: some use $1.35$)

How do you calculate Heat Units (HU) for a three-phase unit?

$$HU = kVp \times mA \times \text{time} \times 1.4$$

Which chart determines if a single exposure combination is safe for the tube?

Radiographic tube rating chart

What does an anode cooling chart determine?

The time necessary for the tube to cool before additional exposures

When moving from 3-phase, 12-pulse to single-phase, how must mAs be adjusted?

Double the mAs

The basic sequence for a high-frequency generator circuit is:

Rectifier, Capacitor, Inverter, Transformer, Rectifier, Capacitor (RCITRC)

What is the function of the input phosphor in an Image Intensifier (II)?

To convert x-rays to fluorescent light

What is the input phosphor made of in modern Image Intensifiers?

Cesium Iodide (CsI)

The photocathode converts _______ to _______.

Light photons to electrons

What are the 'electrostatic focusing lenses' used for in the II?

To accelerate and focus electrons toward the output phosphor

The output phosphor converts _______ back to _______.

Electrons back to light

Define 'Minification Gain'.

The increase in brightness caused by the compression of electrons from a large input area to a small output area