1. Brightness Control Systems

2. X-Ray Generators X-ray generators
X-ray generators used for static radiography
are also used for fluoroscopy
X-ray generators
Static Radiography
Operator’s console has a control that will engage or activate the fluoroscopic system and bypass the static radiography system
Fluoroscopy

3. Brightness Control Systems
Wide variety of systems with different names are used to automatically maintain satisfactory fluoroscopic image density and contrast
Automatic Brightness Control (ABC)
Automatic Density Control (ADC)
Automatic Brightness Stabilization (ABS)
All terms relate to and accomplish the same result:
Maintain brightness of viewable image
Automatically adjust exposure factors as necessary according to subject density and contrast

4. Or monitors light intensity of output screen
ABC Systems Monitor
Monitor electrical (electron) current flow between cathode and anode of image intensification tube
cathode
Image Intensification Tube
anode
Or monitors light intensity of output screen
Output Screen

5. ABC Systems Monitor
In all systems, the “primary x-ray beam” intensity is increased or decreased when the intensified light output varies from established brightness levels
Established Levels
Current
Intensity

6. Regulation of Primary Beam
Regulation of primary beam is accomplished by varying:
kVp mA
Pulse time
Most ABC’s will use a combination of these methods in a manner similar to stepped variable kVp systems:
kVp is gradually increased to the maximum acceptable contrast level
Then mA is doubled while kVp is stepped down to the lowest acceptable contrast level
This process constantly repeated over and over

7. Response Time Lung Field
Most ABC’s have a relatively slow response time
(noticeable during routine fluoro)
This is realized as a lag in the image brightness adjustment when rapid changes in tissue density are present
Lung Field
Example: Fluoro from lung field to abdomen

8. Automatic Gain Control (AGC)
AGC is part of the video camera control system
AGC will respond very quickly to change image brightness and density
Does NOT change x-ray exposure factors!

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What’s Next?
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Presented by
Based on:
Principles of Radiographic Imaging, 4th Ed.
By: R. Carlton & A. Adler
Radiologic Science for Technologists, 8th Ed.
By: S. Bushong
Syllabus on Fluoroscopy Radiation Protection, 6th Rev.
By: Radiologic Health Branch – Certification Unit