The X-ray Imaging The X-ray Imaging SystemSystem

Week 4-5 Week 4-5

Bucky slot coverBucky slot cover

During fluoroscopy the Bucky tray is During fluoroscopy the Bucky tray is moved to the end of the tablemoved to the end of the table

This leaves an opening in the side of the This leaves an opening in the side of the table about 5cm table about 5cm

Approximately at what level is the bucky?Approximately at what level is the bucky?

Bucky slot cover

• The opening should

automatically be

covered with at least

0.25 mm Pb equiv..

Fluoroscopy

The Control Console

• The control console is device that allows the technologist to set technical factors (mAs & kVp) and to make an exposure.

• Only a legally licensed individual is authorized to energize the console.

Control Panel

• All the electric circuits connecting the meters and controls are at low voltage to minimize the possibility of shock.

Operating Console Operating Console Controls:Controls:

Line Compensation, kVp, mA and timeLine Compensation, kVp, mA and time

Quantity = # of x-raysQuantity = # of x-rays Milliroentges (mR) or (mR/mAs)Milliroentges (mR) or (mR/mAs)

Quality = the pentrabilityQuality = the pentrability Kilovolts peak (kVp) Kilovolts peak (kVp)

Operating Console has Operating Console has meters to measuremeters to measure

kVp, mA, & exposure timekVp, mA, & exposure time

Modern units only display mAsModern units only display mAs

Units with ACE’s will have a separate Units with ACE’s will have a separate meter for mAsmeter for mAs

Control Panel

AEC AEC

Automatic Exposure Control Automatic Exposure Control Uses an ionization chamberUses an ionization chamber Technologist sets kVp, mA, back-up Technologist sets kVp, mA, back-up

time & sensorstime & sensors Exposure terminates the IR has proper Exposure terminates the IR has proper

ODOD Patient positioning must be Patient positioning must be absolutely absolutely

accurateaccurate

AEC Sensors

APRAPR

Anatomically Programmed Radiography Anatomically Programmed Radiography (Ch 15)(Ch 15) Radiologic Technologist selects on the Radiologic Technologist selects on the

console a picture or a written console a picture or a written description of the anatomic part to be description of the anatomic part to be imaged and the patient body habitusimaged and the patient body habitus

A computer selects the appropriate A computer selects the appropriate kVp and mAs. kVp and mAs.

APRAPR

The whole process uses an AECThe whole process uses an AEC Precise patient positioning over the Precise patient positioning over the

phototiming sensor is critical phototiming sensor is critical

APRAPR

X-RAY CIRCUITYX-RAY CIRCUITY

Contributions by Mosby, Thompson Publisher, Carlton, Bushberg, and the WWW.

3 Divisions of Circuit Board

• PRIMARY (CONTROL PANEL) yellow

• SECONDARY

(HIGH VOLTAGE) blue

• FILAMENT

(LOW CURRENT) purple

Functional Position

Control Console Transformers Tube

Line CompensationLine Compensation

Most imaging systems are designed to operate Most imaging systems are designed to operate on 220 V. (some 110 V or 440 V)on 220 V. (some 110 V or 440 V)

However power from the wall is not always However power from the wall is not always accurate continuously accurate continuously

Line CompensationLine Compensation

Wired to the autotransformer is the line Wired to the autotransformer is the line compensator compensator

Designed to maintain the accurate Designed to maintain the accurate voltage required for consistent production voltage required for consistent production of high-quality imagesof high-quality images

Today’s line compensators are automatic Today’s line compensators are automatic and are not displayed on the control paneland are not displayed on the control panel

Line Compensator

AutotransformerAutotransformer

The power for the x-ray imaging system The power for the x-ray imaging system is delivered first to the autotransformeris delivered first to the autotransformer

The autotransformer works on the The autotransformer works on the principle of electromagnetic inductionprinciple of electromagnetic induction

It has one winding and one coreIt has one winding and one core There are a number of connections along There are a number of connections along

its lengthits length

Autotransformer

• A’s = primary connections & power into the transformer

• Other connections allow for variations of voltages

AutotransformerAutotransformer

Is designed to step up voltage to about Is designed to step up voltage to about twice the input voltage valuetwice the input voltage value

The increase in voltage is directly related The increase in voltage is directly related to the number of turns to the number of turns

kVp selection

X-ray tube current or X-ray tube current or Filament circuitFilament circuit

A separate circuit crossing from cathode A separate circuit crossing from cathode to anodeto anode

Measured in milliampers (mA)Measured in milliampers (mA)

What determines how many x-rays are What determines how many x-rays are created?created?

X-ray tube current or X-ray tube current or Filament circuitFilament circuit

# of e- is determined by the temperature # of e- is determined by the temperature of the filament. The hotter the filament of the filament. The hotter the filament the more e-the more e-

Are their any limiting factors to thermionic Are their any limiting factors to thermionic emission?emission?

mA selection

FilamentsFilaments Operate at currents of 3 to 6 amperes (A)Operate at currents of 3 to 6 amperes (A)

Question?Question?

What is directly proportional to What is directly proportional to the number of x-rays reaching the number of x-rays reaching the IR?the IR?

Exposure TimersExposure Timers

The timer circuit is separate from the other The timer circuit is separate from the other main circuits of the imaging systemmain circuits of the imaging system

It is a mechanical or electronic device It is a mechanical or electronic device whose action is to “make” and “break” the whose action is to “make” and “break” the high voltage across the x-ray tubehigh voltage across the x-ray tube

This is done on the This is done on the primary sideprimary side of the high of the high voltage transformer. voltage transformer.

mAs TimersmAs Timers

Monitors the product of mA and exposure Monitors the product of mA and exposure timetime

Terminates the exposure when the Terminates the exposure when the desired mAs value is reacheddesired mAs value is reached

Located on the Located on the secondary sidesecondary side of the of the high-voltage transformer since actual high-voltage transformer since actual tube current must be monitored tube current must be monitored

mAs TimersmAs Timers

Designed to proved the highest mA for Designed to proved the highest mA for the shortest exposurethe shortest exposure

Modern X-ray machines have falling-load Modern X-ray machines have falling-load generatorgenerator Automatically adjusts to the highest mA at Automatically adjusts to the highest mA at

the shortest exposure time possiblethe shortest exposure time possible

AEC ControlAEC Control

AEC measure the quantity of radiation AEC measure the quantity of radiation reaching the IRreaching the IR

Automatically terminates when the IR has Automatically terminates when the IR has received enough radiation for desired ODreceived enough radiation for desired OD

Two types are commonTwo types are common

Flat, parallel plate Flat, parallel plate ionization chamberionization chamber

Located between the patient and the IRLocated between the patient and the IR

Made radiolucent Made radiolucent

Ionization w/in the chamber creates a Ionization w/in the chamber creates a charge; calibrated to produce a given OD charge; calibrated to produce a given OD on the IRon the IR

Photomultiplier Photomultiplier (Photodiode)(Photodiode) detector detector assemblyassembly

Located behind the IRLocated behind the IR Contains a fluorescent screen and a Contains a fluorescent screen and a

photomultiplierphotomultiplier The photomultiplier detects the light from The photomultiplier detects the light from

the fluorescent screen until the desired the fluorescent screen until the desired OD on the IR is reached terminating the OD on the IR is reached terminating the exposureexposure

AEC’sAEC’s

Upon instillation must be calibrated by Upon instillation must be calibrated by the service engineer the service engineer

Technologists selects the desired OD Technologists selects the desired OD which then sets the mA & kVpwhich then sets the mA & kVp

AEC’sAEC’s

A back up timer usually automatically set A back up timer usually automatically set to prevent over exposure if the AEC failsto prevent over exposure if the AEC fails Should be set to 1.5 times the expected Should be set to 1.5 times the expected

exposure time Why?exposure time Why?

When the ionization chamber or When the ionization chamber or photodiode reaches the preset level, a photodiode reaches the preset level, a signal is returned to the operating signal is returned to the operating console to terminate the exposureconsole to terminate the exposure

High-Voltage GeneratorHigh-Voltage Generator

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

3 parts: High-voltage transformer (step-3 parts: High-voltage transformer (step-up), filament transformer (step-down) and up), filament transformer (step-down) and rectifiersrectifiers

High voltage transformerHigh voltage transformer

Or step up transformer Or step up transformer

Connected to the Major and Minor kVp Connected to the Major and Minor kVp selectorselector

Increases the volts from the Increases the volts from the autotransformer to kilovolts autotransformer to kilovolts

Step Up Transformer

Voltage RectificationVoltage Rectification

Converts AC to DC currentConverts AC to DC current During the negative cycle current can During the negative cycle current can

only flow from anode to cathodeonly flow from anode to cathode

E- must travel cathode to anode – DC E- must travel cathode to anode – DC current keeps e- traveling in the correct current keeps e- traveling in the correct direction, cathode to anodedirection, cathode to anode

Attracted to the positive anodeAttracted to the positive anode

Voltage Rectification

X-Ray Tube Circuit

Filament transformerFilament transformer

Or step down Or step down transformertransformer

Reduces the Reduces the current to the current to the filamentfilament

High-Voltage Generation – converts 220 volts of AC to kilovolts of DC

The generator is a FIXED component of the imaging system, not under the control of the technologist

Three basic types: single phase, three phase, and high frequency

The generator affects the quality and quantity of photons produced

How does this effect technique selection?

Questions on imaging systems?