lecture 6 part 1

Overview of the X-Ray Circuit

• The X-ray circuit comprises three main components:

  • Console

  • Voltage Transformer

  • X-ray Tube

• Distinction made between the X-ray tube (part of X-ray imaging system) and the X-ray imaging system itself.

X-Ray Imaging System Components

• Key components include:

  • Operating Console: Where technical factors are adjusted, usually digital and touchscreen.

  • Auto Transformer: Contains one winding; crucial for voltage regulation.

  • High-Voltage Generator: Often housed in a cabinet; contains various electrical components.

  • Exposure Timers: Control timing related to exposure.

• Understanding the layout of the X-ray room and components is essential for learning.

Tube and Image Receptor Placement

• Routine X-ray Room:

  • X-ray tube is mounted above the table; image receptor may be in or below the table.

• Fluoroscopy Room:

  • X-ray tube is below the table; uses an image intensifier above the table for live video.

• C-Arm Configuration: Similar to fluoroscopy, with the tube below and the image intensifier above.

Formation of X-Rays

• Created when high-speed electrons collide with a metal target (anode).

• Kinetic energy of electrons is transformed into electromagnetic energy (X-rays).

Control Panel Functions

• Key settings include:

  • kVp (Kilovoltage Peak): Controls the quality/energy/penetrability of the X-ray beam.

  • mA (Milliamperage): Controls the quantity or intensity of the X-ray, related to the current.

  • Time: Duration of exposure.

• A line compensator ensures precise voltage entering the system, typically from a wall outlet.

• Standard input voltage expected is 120 or 220 volts, with tolerable variations of up to 5%.

Auto Transformer Details

• The auto transformer has one winding, serving multiple functions:

  • Supplies voltage to both the high-voltage circuit and filament circuit.

• Different voltages available based on the number of turns on the transformer.

• Primary connections bring in voltage, while secondary connections distribute the modified voltage.

kVp and Exposure Settings

• Major and Minor kVp Adjustments:

  • Major settings lead to larger adjustments; minor settings for precise control.

• Important to understand the relationship between kVp, mA, and exposure times for various body parts.

Thermionic Emission & Space Charge Effect

• Thermionic emission refers to the boiling off of electrons from a heated filament.

• Space Charge Effect: Excess electrons repel each other due to similar charges, affecting their movement towards the anode.

• Understanding interplay between kVp and electron attraction to the anode essential for X-ray production.

Efficiency of the X-ray Tube

• Efficiency of X-ray production is not affected by tube current (mA).

• 99% of energy produced through the X-ray tube is converted to heat.

Miscellaneous Points

• The step-down transformer increases current while decreasing voltage for the filament.

• Falling Load Generator: Operates initially at maximum mA which decreases during exposure, minimizing patient dose.

• Reminder that mass is understood as a product of mA and exposure time, impacting the overall charge in an electrostatic sense.