Instrumentation Chapter 1-5

Name FIVE major components of an X-ray machine and state the function of each

X-ray Tube

Table

Tube Column/Tube Support

Generator

Control Panel

-X-ray Tube - Produces X-ray photons by converting electrical energy into X-rays

- Table - Supports and positions the patient for radiographic examination

- Tube Column/Tube Support - Allows movement and positioning of the X-ray tube for different projections

- Generator - Supplies high-voltage electrical power to the X-ray tube

- Control Panel - Allows the radiographer to control exposure factors such as kVp, mA, and time

Define biological hazards

Biological hazards are biological substances that are a threat to the health of living organisms through contact with infectious patients, body secretions, or contaminated surfaces and equipment

Explain the prevention of biological hazards

- Use of chemical disinfectants to decontaminate surfaces and infectious materials;

- Use of personal protective equipment such as gloves, masks, and eye protection

- Wearing masks to protect the mucous membranes of the nose and mouth

Define chemical hazards

Chemical hazards are chemical substances or mixtures that can pose a risk to the health of living organisms or the environment

Explain the types of chemical hazards in radiography

-Exposure to radioactive materials in Nuclear Medicine

- Exposure to film processing chemicals

-Exposure to glutaraldehyde or other cold steriiants

-Exposure to lead from shielding materials

Define physical hazards

Physical hazards are environmental factors or agents that can cause harm or injury through physical contact or exposure

Explain the types of physical hazards

- Ergonomic hazards from patient handling; Ergonomic hazards from computer use or poor workstation design

- Hazards from lifting, carrying, pushing, or pulling equipment

- Slips, trips, and falls

- Electrical hazards from cords and electrical equipment

Compare ionizing and non-ionizing radiation

- Non-ionizing radiation is low energy and cannot remove electrons from atoms and is generally less harmful;

- Ionizing radiation is high energy, can remove electrons from atoms, deposit energy in tissues, damage DNA, and may cause cancer

State the function of the main breaker in the X-ray circuit

Supplies alternating current from the power source to the X-ray circuit and provides electrical protection

State the function of the exposure switch

Closes the circuit and initiates the X-ray exposure when pressed

State the function of the autotransformer

Adjusts the kVp by varying the voltage supplied to the primary side of the step-up transformer

State the function of the timer circuit

Controls the duration of the exposure and terminates the exposure at the selected time

State the function of the high-voltage step-up transformer

Increases the voltage to provide high voltage to the X-ray tube

State the function of the four-diode rectification circuit

Allows current to flow in one direction only by converting AC to DC

State the function of the filament circuit variable resistance

Adjusts the current flowing to the filament and controls filament heating

State the function of the filament step-down transformer

Reduces the voltage and increases the current supplied to the filament

State the function of the X-ray tube

Responsible for the production of X-rays

State the function of the rotor-stator assembly

Causes rotation of the anode in a rotating anode X-ray tube

Different types of generator: Single phase full-wave (1Φ 2P)

Symbol: 1Φ 2P

Usable pulses per cycle: 2

Pulses per Hz: 2

Pulses per second: 120

Voltage ripple: 100% where tube voltage drops to zero twice per cycle

Different types of generator: Three phase 6 pulse (3Φ 6P)

Symbol: 3Φ 6P

Usable pulses per cycle: 6

Pulses per Hz: 6

Pulses per second: 360

Voltage ripple: 13-25% where tube voltage never falls below 75-87% of peak kVp

Different types of generator: Three phase 12 pulse (3Φ 12P)

Symbol: 3Φ 12P

Usable pulses per cycle: 12

Pulses per Hz: 12

Pulses per second: 720

Voltage ripple: 4-10% where tube voltage never falls below 90-96% of peak kVp

State three differences between high frequency and three phase six pulse generators

- High frequency generators convert incoming AC to high frequency DC around 6000 Hz whereas three phase six pulse uses 60 Hz

- High frequency reaches peak kVp faster

- Voltage ripple is 3-4% for high frequency compared to 13-25% for three phase six pulse

State two limitations of capacitor discharge generators

- Capacitor continues to discharge after usable exposure causing wavetail cutoff;

- Residual kV causes radiation leakage due to slow discharge

State solutions for limitations of capacitor discharge generators

- Grid-biased X-ray tube to cut photon transmission

- Capacitors supplied by batteries charged from line current

- Tube collimator with lead shutters to stop radiation leakage

State the function of the cathode assembly

- Produces thermionic electron cloud

- Conducts high voltage across cathode-anode gap

- Focuses electrons onto the anode

State the function of the filament

Provides resistance so heat is produced causing thermionic emission of electrons

State the function of the focusing cup

Focuses the electron stream onto the anode target in the required shape and size

State the function of the anode assembly

- Acts as target for high-speed electrons to produce X-rays

- Conducts high voltage back to generator circuit

Serves as primary thermal conductor

Explain two factors affecting effective focal spot size

- Anode angle: larger angle increases effective focal spot size while smaller angle decreases it;

- Actual focal spot size: larger actual focal spot produces larger effective focal spot

Define thermionic emission

Emission of electrons due to heating of the filament resulting in formation of an electron cloud around the filament

Compare stationary and rotating anode

Stationary anode: low power operation, static target area, limited heat loading

Rotating anode: high rate of X-ray production, rotating target, larger target area, greater heat loading capacity

Describe the line focus principle

Used to reduce effective focal spot size

Decreasing anode angle decreases effective focal spot size while actual focal spot remains larger

Describe the anode heel effect

Occurs due to angled anode target; X-ray intensity is greater on cathode side than anode side

Cathode side should face thicker body parts

Describe the principle operation of an X-ray tube

Filament heating causes thermionic emission

Electron cloud forms at cathode

High voltage accelerates electrons to anode

Electron bombardment produces X-rays at anode target

Describe the heat dissipation process in an X-ray tube

Most electron energy is converted to heat

Tube components are designed to remove heat to extend tube life and maintain output

List components that help in heat dissipation

Oil surrounding the X-ray tube

Tungsten target

Rotating anode

List methods to conserve X-ray tube life

Minimize filament boost preparation time

Use lower tube current

Follow tube rating charts and anode heating and cooling curves

Avoid high mA exposures on a cold anode

Explain the effect of the anode heel effect on the X-ray beam

X-ray intensity decreases toward the anode side due to absorption in the angled target.

The effect is reduced with a longer source-to-image distance.

The cathode side should be positioned over thicker anatomy