M Part I Flashcards by Queenie Francisco

Three Principles of X-ray Imaging System

X-ray Tube
Operating Console
High Voltage Generator

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It is attached to an overhead
Movable assembly
Location: examination room

Radiographic X-ray Tube

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Localized under examination table

Fluoroscopic X-ray Tube

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It must be transparent to x-rays as much as possible

Examination Table

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Composition of examination table
Strong and absorbs a little bit of radiation

Carbon fiber

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Fluoroscopic table degree of tilt
[..] to the foot side
[..] to the head side

90 degrees
30 degrees

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It is housed in an equipment cabinet positioned against the wall
It is always close to the x-ray tube

High voltage generator

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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

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Number of x-ray
Intensity of the x-ray beams
Units: mR/mAs

Radiation quantity

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Penetrability of the x-ray beam
Expressed in kilovolt peak (kvp)

Radiation quality

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Inside operating console
Measures the voltage provided to the x-ray imaging system
Ph - 120 V
US - 110 V

Line Compensator

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Consists of only one winding of wire

Autotransformer

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[function, location] Autotransformer

Supplies the precise voltage circuit controls the kVp
Inside operating console

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Autotransformer require [..] to approximately increase twice the input voltage value

Step up voltage

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It conducts the input power to the autotransformer

Primary connection

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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

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Adjustment of Kilovoltage Peak (kVp) [adjustment controls]
represent two separate series of connections on the autotransformer.

Major and minor kVp

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It determines the quality of the x-ray beam

-kVp

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[part, location] It reads voltage (not kVp)

-kVp meter
-location: output terminals of the autotransformer

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It allows the voltage to be monitored before an exposure

Prereading kVp Meter

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It is measured in milliamperes (mA)

X-ray tube current

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It determines the number of electrons emitted by the filament

Filament Temperature

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It controls the filament temperature
It is measured in amperes (A)

Filament Current

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Filament Current [Range]

3-6 A

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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

1. Synchronous Timer 2. Electronic Timer 3. MAs Timer 4. 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

1. Monitors the product of mA and exposure time 2. Terminates exposure when desired mAs value is attained 3. 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

1. High Voltage Transformer 2. Filament 3. 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]

1. Much smaller & less costly & more efficient 2. 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

1. Greater radiation quantity 2. High efficiency f x-ray production 3. 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)