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