C-Arm Image Intensifiers

Question 1

What is image intensification?

Answer 1

A method of intensifying or amplifying the very dim image formed on a fluorescent screen during fluoroscopy.

Question 2

What is Automatic Brightness Control (ABC)?

Answer 2

• ensures image brightness is constant
• compensates for differences in tissue thickness and attenuation
• monitors the signal from the TV camera
• ↓brightness = ABC automatically adjusts kV & mA to achieve predefined image brightness

Question 3

What are different ABC modes?

Answer 3

Standard – increases kV and mA together
Contrast – keeps kV low, increases mA
Low dose – keeps mA low, increases kV

Question 4

What factors should be considered when selecting a mobile image intensifier (II)?

Answer 4

• Type of procedures to be undertaken
• Size, weight and manoeuvrability of each component
• Size of II
• Image quality, dose levels and dose saving features
• Ease of data entry, image manipulation and storage
• System security

Question 5

What design features should a mobile II have?

Answer 5

• C-arm, allowing angulation in more than one plane.
• Isocentric (all beams have a common focus point)
• Light and compact as possible for easy steering and positioning.
• Twin monitors.
  
  • • Flat screen monitors are compact, and tend to produce better images with varying external light sources in theatre.
• Compact image intensifier
• Small tube head with stationary anode tube
• Flat panel detector may be used instead of an II

Question 6

What are the advantages of a flat panel detector?

Answer 6

• High resolution in a mobile C-arm
• Large Field Of View is unaffected by geometrical distortions and supports wide range of applications
• Flat detector is not affected by magnetic distortions.

Question 7

What affects the intensifier input rate?

Answer 7

• Increased to reduce noise
• Increased for magnified views
• Increased as intensifier ages
• Usually in a range from 0.2µGy/s to 1µGy/s

Question 8

What are the different methods/strategies for radiation protection in theatre?

Answer 8

• Pulsed exposure can dramatically reduce overall exposure.
• Pulse duration and rate will affect visualisation of image as well as dose.
• Pregnancy status of patient and staff.
• Fluoroscopy time to be controlled.
• Collimation.
• Watch the surgeon – Use fluoroscopy only when needed.
• Final frame hold
• Increase SID
• Minimise patient to intensifier distance

Question 9

What controls should a C-arm have?

Answer 9

• Types of locks and movements.
• Controls on main panel
• Fluoroscopy and radiography exposure controls;
• Collimation;
• Image orientation;
• Pulse or non-pulsed exposure – pulse duration and rate;
• Monitor brightness and contrast.