The control console allows the technologist to set technical factors like mAs and kVp and make exposures. It contains meters to measure kVp, mA, and exposure time. The console has several circuits including high voltage, filament, and primary circuits. Automatic exposure control uses an ion chamber or photodiode to automatically terminate the exposure when the proper optical density is reached on the image receptor. High voltage generation converts line voltage to kilovolts needed for x-ray production using transformers and rectifiers.

1. The X-ray Imaging
System
Week 4-5

2. Bucky slot cover
 During fluoroscopy the Bucky tray is
moved to the end of the table
 This leaves an opening in the side of the
table about 5cm
 Approximately at what level is the bucky?

3. Bucky slot cover
• The opening should
automatically be
covered with at least
0.25 mm Pb equiv..

4. Fluoroscopy

5. 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.

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

7. Operating Console
Controls:
 Line Compensation, kVp, mA and time
 Quantity = # of x-rays
 Milliroentges (mR) or (mR/mAs)
 Quality = the pentrability
 Kilovolts peak (kVp)

8. Operating Console has
meters to measure
 kVp, mA, & exposure time
 Modern units only display mAs
 Units with ACE’s will have a separate
meter for mAs

9. Control Panel

10. AEC
 Automatic Exposure Control
 Uses an ionization chamber
 Technologist sets kVp, mA, back-up
time & sensors
 Exposure terminates the IR has proper
OD
 Patient positioning must be absolutely
accurate

11. AEC
Sensors

12. APR
 Anatomically Programmed Radiography
(Ch 15)
 Radiologic Technologist selects on the
console a picture or a written
description of the anatomic part to be
imaged and the patient body habitus
 A computer selects the appropriate
kVp and mAs.

13. APR
 The whole process uses an AEC
 Precise patient positioning over the
phototiming sensor is critical

14. APR

15. X-RAY CIRCUITY
Contributions by Mosby, Thompson Publisher, Carlton, Bushberg, and the WWW.

16. 3 Divisions of Circuit Board
• PRIMARY
(CONTROL PANEL)
yellow
• SECONDARY
(HIGH VOLTAGE)
blue
• FILAMENT
(LOW CURRENT)
purple

19. Functional Position
Control Console Transformers Tube

20. Line Compensation
 Most imaging systems are designed to operate
on 220 V. (some 110 V or 440 V)
 However power from the wall is not always
accurate continuously

21. Line Compensation
 Wired to the autotransformer is the line
compensator
 Designed to maintain the accurate
voltage required for consistent production
of high-quality images
 Today’s line compensators are automatic
and are not displayed on the control panel

22. Line Compensator

23. Autotransformer
 The power for the x-ray imaging system
is delivered first to the autotransformer
 The autotransformer works on the
principle of electromagnetic induction
 It has one winding and one core
 There are a number of connections along
its length

24. Autotransformer
• A’s = primary
connections &
power into the
transformer
• Other connections
allow for variations
of voltages

25. Autotransformer
 Is designed to step up voltage to about
twice the input voltage value
 The increase in voltage is directly related
to the number of turns

26. kVp selection

27. X-ray tube current or
Filament circuit
 A separate circuit crossing from cathode
to anode
 Measured in milliampers (mA)
 What determines how many x-rays are
created?

28. X-ray tube current or
Filament circuit
 # of e- is determined by the temperature
of the filament. The hotter the filament
the more e-
 Are their any limiting factors to thermionic
emission?

30. mA selection

31. Filaments
Operate at currents of 3 to 6 amperes (A)

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

33. Exposure Timers
 The timer circuit is separate from the other
main circuits of the imaging system
 It is a mechanical or electronic device
whose action is to “make” and “break” the
high voltage across the x-ray tube
 This is done on the primary side of the high
voltage transformer.

34. mAs Timers
 Monitors the product of mA and exposure
time
 Terminates the exposure when the
desired mAs value is reached
 Located on the secondary side of the
high-voltage transformer since actual
tube current must be monitored

35. mAs Timers
 Designed to proved the highest mA for
the shortest exposure
 Modern X-ray machines have falling-load
generator
 Automatically adjusts to the highest mA at
the shortest exposure time possible

36. AEC Control
 AEC measure the quantity of radiation
reaching the IR
 Automatically terminates when the IR has
received enough radiation for desired OD
 Two types are common

37. Flat, parallel plate
ionization chamber
 Located between the patient and the IR
 Made radiolucent
 Ionization w/in the chamber creates a
charge; calibrated to produce a given OD
on the IR

38. Photomultiplier (Photodiode)
detector assembly
 Located behind the IR
 Contains a fluorescent screen and a
photomultiplier
 The photomultiplier detects the light from
the fluorescent screen until the desired
OD on the IR is reached terminating the
exposure

40. AEC’s
 Upon instillation must be calibrated by
the service engineer
 Technologists selects the desired OD
which then sets the mA & kVp

41. AEC’s
 A back up timer usually automatically set
to prevent over exposure if the AEC fails
 Should be set to 1.5 times the expected
exposure time Why?
 When the ionization chamber or
photodiode reaches the preset level, a
signal is returned to the operating
console to terminate the exposure

42. High-Voltage Generator
 Responsible for increasing the output
voltage from the autotransformer to the
kVp necessary for x-ray production
 3 parts: High-voltage transformer (step-
up), filament transformer (step-down) and
rectifiers

43. High voltage transformer
 Or step up transformer
 Connected to the Major and Minor kVp
selector
 Increases the volts from the
autotransformer to kilovolts

44. Step Up Transformer

45. Voltage Rectification
 Converts AC to DC current
 During the negative cycle current can
only flow from anode to cathode
 E- must travel cathode to anode – DC
current keeps e- traveling in the correct
direction, cathode to anode
 Attracted to the positive anode

46. Voltage Rectification

47. X-Ray Tube Circuit

48. Filament transformer
 Or step down
transformer
 Reduces the
current to the
filament

49. 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

51. How does this effect technique
selection?

52. Questions on imaging systems?