Rad T 290 Generators

Generator Components control console  kVp adjust  mA adjust  time adjust transformer  high voltage (step up)  filament »low voltage (step down) electronics cabinet  support circuitry or mAs adjust

Incoming Power Line affects generator performance –diameter of wire –length or wire –other devices sharing branch circuit Resistance of power line wires can reduce generator voltage during exposure affecting  power available to x-ray tube  calibration

Line Voltage Compensation Incoming voltage can vary during day Generators need to correct for changes in line voltage  power line fluctuations affect calibration Incoming Power Line Generator Circuit Breaker

Line Line Voltage Compensation Compensation may be  Automatic »Almost everything today  Manual »user must make adjustment Line Compensation

Line Auto- trans- former High Voltage Transformer Rectifier Circuit Timer Circuit + High voltage Transformer has fixed ratio Autotransformer has variable ratio Autotransformer needed to provide variable kilovoltage to tube Autotransformer Filament Transformer mA regulator

Autotransformer Line Compensation Timer Circuit to high voltage transformer primary to filament transformer primary mA regulator major kV selector minor kV selector Autotransformer does line compensation & kVp selection

Generator Voltages Input line voltage  single or three phase  Volts AC Autotransformer  provides variable voltage to primary of high voltage transformer 11  Power Line Auto Transformer High Voltage Transformer Timer Circuit

High Voltage Circuit Supplies high voltage for x-ray tube Step-up transformer  primary from autotransformer  secondary to rectifier circuit  mA monitored at center grounded point of secondary Auto- transformer Rectifier Circuit mA High Voltage Transformer

Grounded metal box filled with oil  electrical insulator Function  increases or decreases alternating voltage Also contains rectifier circuit  changes alternating current into direct current

Fullwave Rectifier Four diodes 120 pulses/second exposure times half of halfwave circuit Secondary of High Voltage Transformer Voltage applied to tube (also mA waveform)

Fullwave Rectifier + - X X First Half CycleSecond Half Cycle Voltage applied to tube (also mA waveform) X X + -

Full-Wave Rectification Rectifiers  Four diode “bridge” configuration used with single phase both + & - half cycle of high tension transformer used  efficient  circuit reverses negative half cycle & applies to x-ray tube Applied to X-ray Tube Output of High Tension Transformer Tube

Pulsed Radiation single phase input power results in pulsed radiation Disadvantages  intensity only significant when voltage is near peak  low voltage heats target and produces low-energy photons »absorbed in tube, filter, or patient can contribute to dose Applied to X-ray Tube Radiation Waveform

Three-Phase Generators Commercial power generally delivered as 3 phase phases 120 o apart Single Phase PowerThree Phase Power

Three-Phase Generators Rectifier circuit  Inverts negative voltage  sends highest of 3 phases to x-ray tube To X-Ray TubeInput 3 Phase Voltage Rectified

Three-Phase Generators much higher tube ratings than single phase more efficient than single phase  shorter exposures  lower exposure Three Phase OutputSingle Phase Power

3  Generator Circuits pulses  number of peaks per 1/60 second (16.6 msec) power line cycle windings  3 primary coils (one for each phase)  3 or 6 secondary »with 6 secondaries, 2 secondary coils induced per primary Three Phase Output

Three Phase Transforming 3 coils can be hooked up in 2 ways Delta Wye

3-phase generator Primary windings  generally delta Secondary windings  may be delta or wye Primary Secondary

3 Phase Generator 6-Pulse Twelve Rectifier  1 delta primary  2 wye secondaries »6 secondary windings two diodes per winding  13.5% ripple Three Phase Output Ripple Primary Secondary

3 Phase Generator 12-Pulse Twelve Rectifier  1 delta primary  2 secondaries, 1 wye, 1 secondary »30 o phase difference between secondaries »6 secondary windings 2 diodes per winding  3.5% ripple Three Phase Output Ripple Primary Secondary

Line Auto- trans- former High Voltage Transformer Rectifier Circuit Timer Circuit + Circuitry for mA selection Adjusts mA on the fly during exposure. mA regulator Filament Transformer mA regulator

Line Auto- trans- former High Voltage Transformer Rectifier Circuit Timer Circuit + Steps down AC voltage from Autotransformer & mA selector to smaller AC voltage required by filament (8-12 volts typical) Filament Transformer mA selector

mA selection Line Compensation to filament transformer primary mA stabilizer Allows selection from available discrete mA stations. Applies correct voltage to primary of filament transformer. 10 mA 25 mA 50 mA 100 mA 200 mA 300 mA 400 mA

mA Stabilization During Exposure On first trigger  mA regulator supplies anticipated voltage to filament transformer primary mA monitored during exposure Corrections made to filament voltage during exposure as necessary  if mA low, filament voltage boosted  if mA high, filament voltage lowered

1  vs. 3  Generators Typical home & small business power inexpensive transformer windings  1 primary coil  1 secondary coil u Industrial power u expensive u transformer windings 3 primary coils one for each phase 6 secondary coils »2 secondary coils induced per primary) 11 33

1  vs. 3  Generators 100% ripple 8 ms minimum exp. Time  1/120th second lower output intensity puts less heat in tube for same technique u 4-13% ripple higher average kVp slightly less patient exposure u <=1 ms minimum exp. time u higher output intensity u puts more heat in tube 11 33

Exposure Time Control electronic, measuring »time (crystal) »power line pulses phototimingautomatic (phototiming)  terminates exposure based on radiation received by receptor

Phototiming Geometry entrance type  detector in front of film  detector must be essentially invisible exit type  detector behind film  obsolete except for mammography »detector visible because of high contrast image Exit type Sensor Grid Film Entrance type Sensor

Phototiming Radiation Detectors ionization chambers solid-state detectors

Ionization Chambers Almost always entrance type Notes  thin parallel aluminum plates are electrodes »voltage applied between plates »collect ions produced by radiation in air between electrodes  collected ions produce electric current Photon -

Solid State Detectors PN semiconductor junction generates current when struck by radiation small fast response little beam attenuation Photon Electric Current

Phototiming Fields 1, 2, or 3 fields may be selected individually or in combination proper positioning critical

Phototiming Notes must be calibrated for particular film-screen system some generators allow selection from several preset film/screen combinations

Phototiming Notes phototimer must correct for  rate response  kVp response of » film/screen system »phototiming sensor  Higher kVp beam more penetrating »Less attenuated by phototimer detector safety  exposure limited to 600 mAs if phototimer does not terminate exposure (2000 mAs for < 50 kV)