CHAPTER 6: THE X-RAY IMAGING SYSTEM

Which combination represents the three principal parts of an x-ray imaging system?

X-ray tube, operating console, high-voltage generator

Where is the radiographic x-ray tube commonly attached?

To an overhead movable crane assembly

Where is the fluoroscopic x-ray tube located?

Under the examination table

What material is commonly used for a fluoroscopic examination table because it is strong and absorbs little radiation?

Carbon fiber

What is the tilt range of the fluoroscopic table according to the summary?

90° foot / 30° head

What is the primary function of the operating console?

Control x-ray tube current and voltage

Which factors can be controlled at the operating console?

kVp, mA, and exposure time

The number or intensity of x-rays in the beam is referred to as:

Radiation quantity

Radiation quality primarily refers to the:

Penetrability of the x-ray beam

Radiation quantity is commonly expressed in:

mR or mR/mAs

Radiation quality is expressed in kVp or, more precisely, in:

HVL

Which transformer consists of only one winding and one core?

Autotransformer

What is the primary function of the autotransformer?

Supply precise voltage to the filament and high-voltage circuits

Which control is primarily determined by the autotransformer?

kVp

Where is the autotransformer located?

Operating console

An autotransformer has 100 primary turns and 500 secondary turns. If the primary voltage is 120 V, what is the secondary voltage?

600 V

According to the transformer law, voltage is directly proportional to the:

Number of turns

What does the kVp meter actually read?

Voltage

Where is the kVp meter located?

At the output terminals of the autotransformer

What determines the number of electrons emitted by the filament?

Filament temperature

What controls filament temperature?

Filament current

What is the approximate filament current range given in the summary?

3–6 A

What is the primary function of the filament circuit?

Control x-ray tube current

What is thermionic emission?

Release of electrons from a heated filament

The cloud of electrons surrounding the filament is called the:

Space charge

Why can the space charge effect limit additional electron emission?

Electrons are repelled electrostatically

A radiographic exposure uses 400 mA for 0.05 seconds. What is the mAs?

20 mAs

What does mAs represent?

Product of mA and exposure time

A falling-load generator automatically adjusts exposure factors to use:

Highest mA and shortest allowable exposure time

In a falling-load generator, what happens to mA as the anode heats?

It decreases

The filament heating transformer is a:

Step-down transformer

The filament transformer steps voltage down to approximately:

12 V

What is the primary purpose of the filament transformer?

Provide current to heat the filament

Which correctly describes the secondary side of the filament transformer?

Thick wire, high current, low voltage

Which timer terminates an exposure after a prescribed time of approximately 6 seconds?

Guard timer

Why is the timer circuit located on the primary side of the high-voltage transformer?

To reduce voltage and improve safety

Which timer is designed around a shaft rotating precisely 60 revolutions per second?

Synchronous timer

Which timer cannot be used for serial exposures?

Synchronous timer

Which exposure timer is the most sophisticated and can measure exposure times as short as 1 ms?

Electronic timer

Which timer monitors the product of mA and exposure time?

mAs timer

The mAs timer is particularly useful in which systems?

Falling-load and capacitor-discharge systems

What does an automatic exposure control (AEC) measure?

Radiation reaching the image receptor

What is the function of an AEC?

Automatically terminate exposure when the required radiation reaches the receptor

What is the primary function of the high-voltage generator?

Increase voltage to the kVp required for x-ray production

Which three components are the primary parts of the high-voltage generator?

High-voltage transformer, filament transformer, rectifiers

The high-voltage transformer is classified as a:

Step-up transformer

In a high-voltage transformer, the secondary voltage is ______ the primary voltage.

Greater than

In the high-voltage transformer, the secondary current is ______ the primary current.

Less than

The secondary winding of a step-up transformer has:

More turns than the primary

Turns ratio is defined as the ratio of:

Secondary windings to primary windings

What is rectification?

Conversion of AC to DC

What is the purpose of voltage rectification in an x-ray imaging system?

Ensure electrons flow from cathode to anode only

An electronic device that allows current to flow in only one direction is a:

Diode

A diode contains how many electrodes?

Two

What replaced the original valve-tube rectifier?

Solid-state rectifier

What material is used in solid-state rectifiers according to the summary?

Silicon

A semiconductor behaves between which two types of materials?

Insulators and conductors

What are the two types of semiconductor materials?

P-type and N-type

Which characteristic describes a P-type semiconductor in the summary?

It has loosely bound electrons and holes

A hole in a semiconductor represents:

A space where an electron is absent

When N-type material is placed in contact with P-type material, the resulting structure is called a:

Solid-state p-n junction

What is the important characteristic of a solid-state p-n junction?

It conducts electricity in only one direction

How many pulses per second are produced by half-wave rectification?

60

What is a major disadvantage of half-wave rectification?

It wastes half the power supply

How many diodes are used in full-wave rectification according to the summary?

4

Full-wave rectification produces approximately:

120 pulses/second

Compared with half-wave rectification, full-wave rectification allows exposure time to be:

Reduced by half

What type of x-ray beam is produced by single-phase power?

Pulsating x-ray beam

What is a disadvantage of single-phase power?

X-ray production has a value near zero during part of the cycle

In three-phase power, the voltage impressed across the x-ray tube is:

Nearly constant

What is a major advantage of three-phase power?

Voltage never drops to zero during exposure

What are disadvantages of three-phase generators?

Large size and cost

What is initiation time?

Time required to start an exposure

What is extinction time?

Time required to end an exposure

A high-frequency generator produces a:

Nearly constant potential voltage waveform

Which is an advantage of a high-frequency generator?

Smaller, less costly, and more efficient

High-frequency generators can improve image quality while:

Decreasing patient radiation dose

What circuit converts DC into a series of square pulses in a high-frequency generator?

Inverter circuit

An inverter circuit consists of high-speed switches or choppers that convert:

DC into a series of square pulses

In a capacitor-discharge generator, tube voltage:

Falls during exposure

Approximately how much does tube voltage fall per mAs in a capacitor-discharge generator according to the summary?

1 kV/mAs

A grid-controlled x-ray tube functions primarily as a rapid:

Lead beam stopper/switch

The grid-controlled x-ray tube is designed to:

Turn x-ray emission on and off rapidly

Which is NOT listed as an application of a grid-controlled x-ray tube?

MRI

Voltage ripple is used to characterize:

Voltage waveforms

What is the voltage ripple for single-phase half-wave and full-wave generators?

100%

A three-phase 6-pulse generator has approximately what voltage ripple?

14%

A three-phase 12-pulse generator has approximately what voltage ripple?

4%.

Which generator has the lowest voltage ripple?

High-frequency

The voltage ripple of a high-frequency generator is approximately:

Less than 1%.

Which generator's voltage never falls below approximately 99% of its maximum value?

High-frequency.

Which waveform never falls below approximately 96% of maximum?

Three-phase 12-pulse.

Which waveform never falls below approximately 86% of maximum?

Three-phase 6-pulse.

Which inverter component is associated with frequencies below 1 kHz?

Thyristors.

Which component is associated with a frequency range of 1–10 kHz?

Large silicon-controlled rectifier.

Which component is associated with a frequency range of 10–100 kHz?

Power field-effect transistors.

A three-phase x-ray generator operates at 500 mA and 100 kVp. What is its power rating?

50 kW.

A single-phase generator operates at 500 mA and 100 kVp. What is its approximate power rating?

35 kW.

Which combination correctly matches the component with its function?

Filament transformer — heats filament.

A technologist wants to obtain a shorter exposure time while maintaining the selected mAs. Which device is specifically designed to provide the highest safe tube current for the shortest exposure time?

mAs timer.