Imaging Equipment and Maintenance

Electrostatics

Study of stationary electric charges

Electrons and protons

What are the smallest units of electric charge?

electrified

An object is said to be _____ if it h as to o few or too many electrons.

By contact, friction, or induction

How can electrification be created?

1. Unlike charges attract; like charges repel.

2. Electric charge of a conductor is concentrated a long the sharpest curvature of its surface.

3. Electric charge distribution is uniform throughout or on the surface of a conductor.

4. The electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance between them.

What are the 4 general laws of electrostatics?

electric field

Associated with each electric charge is an _____ _____

outward = positive

inward = negative

The electric field points _____ from a positive charge and

_____ to a negative charge

Electrostatic force

The force of attraction between unlike charges or repulsion between like charges, and is attributable to the electric field.

potential

stored

work

A system that possesses _____ energy is a system with _____ energy. Such system has the ability to do ____.

volt (V)

The unit of electric potential is the ____.

Voltage

Electric potential is sometimes called _____.

The volt is potential energy/unit charge, or joule/coulomb (1 V = 1 J/C).

What is the volt?

⬆

⬆ voltage = __ potential to do work

electricity

The electrodynamic phenomena is recognized as _____.

electric current, or electricity

If an electric potential is applied to objects su ch as copper wire, then electrons move along the wire. This is called an _____ _____ or _____.

Electrodynamics

The study of electric charges in motion

opposite

The direction of electric current is always _____ of that of the electron flow.

Electric circuit

When resistance is controlled and the conductor is made into a closed path, the result is an _____ _____.

Amperes (A)

Electric current is measured in _____.

number of electrons

1 C

second

The ampere is proportional to the _____ of _____ flowing in the electric circuit.

One ampere is equal to an electric charge of ___ flowing through a conductor each _____.

volts (V)

ohms (Ω)

Electric potential is measured in _____ and electric resistance is measured in _____.

Ohm’s Law

V=IR

where V is the electric potential in volts, I is the electric current in amperes, and R is the electric resistance in ohms.

The manner in which the electric currents behave in an electric circuit is described by a relationship known as ____ ____, which is _____.

Series circuit

A circuit where all the elements are connected in a line along the same conductor.

Parallel circuit

A circuit where the elements are connected at their ends rather than lying in a line along the conductor.

direct current

When the electrons are made to flow to one direction along the conductor, the electric current is called _____ _____.

Alternating current

Current in which the electrons oscillate back and forth is called _____ _____.

watts (W)

Electric power is measured in ______.

One watt is equal to 1 A of current owing through an electric potential o f 1 V. Power (W) = voltage (V) × current (A ).

What is the formula for power?

magnetic field

Any charged particle in motion creates a _____ _____.

perpendicular

imaginary lines

The magnetic field of a charged particle is _____ to the motion of that particle. The intensity of the magnetic field is represented by _____ _____.

1. Naturally occurring magnets

2. Artificially induced permanent magnets

3. Electromagnets

Three principal types of magnets

Nonmagnetic

Magnetic state where the material is unaffected by a magnetic field

Diamagnetic

The magnetic state where the material is weakly repelled from both poles of a magnetic field

Paramagnetic

The magnetic state where the material is weakly attracted to both piles of a magnetic field

Ferromagnetic

The magnetic state where the material can be strongly magnetized

induction

Ferromagnetic objects can be made into magnets by _____.

Luigi Galvani

Italian anatomist who discovered that the dissected frog leg twitched when touched by two different metals, just as if it had been touched by an electrostatic force.

Voltaic pile, copper-zinc plates stacked to form a battery

What did Allessandro Volta create?

source

Any device that converts some form of energy into electric energy is said to be a _____ of electric potential.

Any charge in motion produces a magnetic field

What did Hans Oersted discover in 1820?

Solenoid

A coil of wire

⬆

Stacking more loops of wire on top of each other __ the intensity of the magnetic field running through the center of the stack of loops.

Electromagnet

A current-carrying coil of wire wrapped around an iron core

Michael Faraday

Who discovered that when the mag eat is moved, the coiled wire does have a current, indicated in the ammeter.

constant

changing

To induce a current with the use of a magnetic field, the magnetic field cannot be. _____ but must be _____.

1. The strength of the magnetic field

2. The velocity of the magnetic field as it moves past the conductor

3. The angle of the conductor to the magnetic field

4. The number of turns in the conductor

Faraday’s Law

The magnitude of the induced current depends on four factors

transformer

The _____ does not convert one form of energy to another but rather transforms electric potential and current into higher or lower intensity

Changes the intensity of alternating voltage and current

What does a transformer do?

alternating current

The transformer is used to change the magnitude of voltage and current in an _____ _____ circuit.

directly

number of turns

The change in voltage is _____ proportional to the ratio of the _____ of _____ (windings) of the secondary coil (Ns) to the number of turns in the primary coil (Np).

turns ratio

The voltage across the transformer is proportional to the _____ _____.

step-up transformer

step-down transformer

A transformer with a turns ratio greater than 1 is a _____ because the voltage is increased or stepped up from the primary side to the secondary side.

When the turns ratio is less than 1, the transformer is a _____.

I1/I2 = Np/Ns

Transformer law

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

Three principle parts of the x-ray imaging system

Operating console

The part of the x-ray imaging system most familiar to radiologic technologists

Radiation quantity, expressed in milligram (mGya) or milligram/ampere-second (mGya/mAs)

What refers to the number of x-rays in an x-ray beam, and how is it usually expressed?

Radiation quality, expressed in kilovoltage peak (kVp), or half-value layer (HVL)

What refers to the energy of the x-ray beam and how is it expressed?

Operating console

Provides control for line compensation, kVp, mA, and exposure time

line compensator

In the operating console, the ____ ______ measures the voltage provided to the x-ray imaging system and adjusts that voltage to precisely 220 V.

autotransformer

The power supplied to the x-ray imaging system is first delivered to the _____

variable but controlled

The voltage supplied from the autotransformer to the high-voltage transformer is _____ but _____.

filament circuit

high-voltage circuit

The autotransformer has a single winding and is designed to supply a precise voltage to the _____ _____ and to the _____ _____ of the x-ray imaging system.

kVp

What determines the quality of the x-ray beam?

Registers the kVp ugh no exposure dis being made and the circuit has no current, allowing the voltage to be monitored before an exposure

What does the pre-reading kVp meter do?

milliamperage (mA)

The x-ray tube current, crossing from cathode to anode, is measured in _____

temperature of the filament

The number of electrons emitted from the filament is determined by the _____ of the _____.

filament current

Amperes (A)

The filament temperature is controlled by the _____ _____, which is measured in _____.

⬆ filament current = ⬆ filament heat = ⬆ electrons released in thermionic emission

⬆filament current = ⬜ filament heat = ⬜ electrons released in thermionic emission

Thermionic emission

Release of electrons from a heated filament

3-6 A

Filaments normally operate at currents of ___ A.

filament circuit

The x-ray tube current is controlled through a separate circuit called the _____ _____.

Precision resistors

falling load generator

X-ray tube current normally is not continuously variable.

_____ _____ result in fixed stations that provide x-ray tube currents of 100, 200, or 300 mA, and higher, except in the _____ ____ generator.

The exposure begins at maximum mA, and the mA drops as the anode heats, resulting in minimum exposure time

How does the falling load generator operate?

x-ray tube current

exposure time

electrostatic charge

The product of ____ _____ (mA) and _____ ____ (s) is mAs, which is also _____ _____ (C).

filament transformer

The voltage from the mA selector switch is then delivered to the _____ _____.

step-down

What kind of transformer is the filament transformer?

filament

filament transformer

turns ratio

The filament transformer is a step-down transformer; therefore, the voltage supplied to the _____ is lower (by a factor equal to the turns ratio) than the voltage supplied to the _____ _____.

Similarly, the current is increased across the filament transformer in proportion to the _____ _____.

Filament heating isolation step-down transformer

What is the full title for the filament transformer?

thin copper

0.5 to 1 A

150 V

thick

12 V

5-8 A

In the filament transformer the primary windings are of ____ _____ and carry a current of ___ A and approximately ___ V.

The secondary windings are _____ and at approximately __ V electric potential, and carry a current of __ A (not mA!).

1. Synchronous timer

2. Electronic time

3. mAs timer

4. AEC

Four types of timing circuits

1/60 s (17 ms)

What is the minimum exposure time possible for synchronous timers?

Because they must be reset after each exposure

Why can’t synchronous timers be used for serial exposures?

Most sophisticated, most complicated, and most accurate of the x-ray exposure timers

Describe electronic timers

1 ms

Timer that allows a wide range of time intervals to be selected and are accurate to intervals as small as __.

Suitable for interventional radiology procedures because they can be used for rapid serial exposures

Where are electronic timers particularly suitable for, and why?

microprocessor

Most exposure timers are electronic and are controlled by a _____.

mAs timer

A special kind of electronic timer that monitors the product of mA and exposure time and terminates exposure when the desired mAs value is attained.

Provide the highest safe tube current for the shortest exposure for any mAs selected.

What is the mAs timer designed to do?

It is located on the secondary side of the high-voltage transformer because it must monitor the actual tube current

Where is the mAs timer located and why?

Automatic Exposure Control (AEC)

A device that measures the quantity of radiation that reaches the image receptor

When the IR has received the required radiation intensity

When does AEC automatically terminate the exposure?

between

The type of AEC used by most manufacturers incorporates a flat, parallel plate ionization chamber positioned _____ the patient and the image receptor.

High voltage generator

Responsible for increasing the output voltage from the autotransformer to the kVp necessary for x-ray production

1. High-voltage transformer

2. Filament transformer

3. Rectifiers

Three primary parts of the high voltage generator

step-up

The high voltage transformer is a _____ transformer

500:1 and 1000:1

alternating

sinusoidal

The turns ratio of a high-voltage transformer is usually between _____ and _____. Because transformers operate only on _____ current, the voltage waveform on both sides of a high-voltage transformer is _____

Direct current

What kind of current does the x-ray tube require?

Rectification

What is the process of converting AC to DC?

Rectifier

The electronic device that allows current to flow in only one direction

Voltage rectification

_____ _____ is required to ensure the electrons flow from the x-ray tube cathode to anode only