Trishna PokhrelToday in this article we will discuss about the differnt parts of dental X-ray machine. The dental X-ray is made up of three components. i.e. Control panel, extension arm and tube head. We will discuss each of these in details:
Control Panel:
- It consists of switches, lights, control devices to regulate the x-ray beam.
- Tube current: Step-down transformer provides a low voltage current to heat x-ray tube filament.
- Tube Voltage: Auto transfer converts the primary voltage into secondary voltage and control voltage between anode and cathode.
Extension Arm:
- This connects control panel to tube head.
- It hold the X-ray tube head and houses electric wires.
- It allow movement and positioning of X-ray tube head.
Tube Head :
- It is highly seal with the heavy metal housing.
- It consists of following parts:
- X-ray tube
- Metal housing
- Insulating oil
- Tube head seal
- Aluminium disk (Altration)
- Lead collimator
- Position indicating device (PID)
a) Metal Housing:
- This is the external body of tube head made up of metal, which is tightly sealed and contains oil.
- It consists of x-ray tube, transformer, filter etc.
b) Position Indicating device (PID):
- It is connected to tube head.
- Also called as cone.
- It is made up of lead, plastic.
- Length of PID: Short - 8 inches; Long - 16 inches.
- Types: Conical, rectangular, round
- Function: It shapes the X-ray beam and prevent overdivergence of beam.
- Advantage of long cone: It causes lesser divergence of beam compared to short cone.
c) Insulating Oil:
- It surrounds X-ray tube and transformes.
- Function:
- Act as insulator.
- Prevent overheating of X-ray machine by absorbing heat created by production of X-ray.
d) Tube head seal:
- It is aluminum or loaded glass.
- It seals oil in tube head.
- Also filters X-ray beam.
e) Collimator :
- It is a lead plate with central hole.
- It is used to restrict the size and shape of X-ray beam, reduce exposure to patient.
- It consists of 2 Types:
a) Fixed : Round, Rectangle
b) Adjustable: Slit
- Advantages:
a) Improve Image quality.
b) Reduces exposure area
f) Filtration (Aluminium Disks) :
- It is that component of X-ray machine, which re-moces low-energy X-rays.
- Low-energy X-rays can penetrate only through superficial tissue and have no use in making image.
- Low-energy X-rays also causes unwanted absorption of rays in patients.
- So, filter is used to remove these low energy X-rays, decreasing pt. exposure with no loss of radiographic information.
Types of Filtration:
1) Inherent Filtration:
- It takes place when 1o beam passes through the glass window of X-ray tube, insulating oil and tube head seal.
- It is equivalent to 0.5 - 1 mm aluminium.
2) Added Filtration:
- Placement of aluminium disks between the collimator and tube head seal.
- It is added in 0.5 mm increment.
- It is equivalent to 1-1.5 mm aluminium.
3) Total Filtration:
- Inherent + Added filtration
- When at or below 70 kvp => 1.5 mm aluminium
Above 70 kvp => 2.5 mm aluminium
g) X-ray Tube:
- It is most important component of X-ray machine.
- It is a heart of X-ray generating system.
- It consists of glass envelope (Lead flass housing), Cathode and anode.
Leaded glass housing:
- It is made up of borosilicate glass along with the lead.
- It acts as a envelope.
- It is completely evacuated inside to prevent ionization of air inside the tube, which can decrease the speed of electron and their efficiency.
- It is Unleaded at the central area.
- Function: Prevent radiation leakage, i.e X-rays from escaping in all direction.
Cathode:
- It is negatively charged.
- It composed of 2 parts: Focusing cup and filament.
- The main function of cathode is to generate electron (by filament) and focus it to anode (by focusing cup).
Filament:
- Made of Tungsten,
- Atomic Number : 74
- Diameter : 1-2 mm wide
- Melting point: 3380oC
- Function: Emission of electron by thermionic emission.
Focusing Cup:
- Made of - Molybdenium, Nickel
- Atomic number : 42
- Melting Point : 2620oC
- Function: It focuses the electron towards the anode by electostaic forces.
Anode:
- It is positively charged.
- Compossed of tungsten target embedded in the copper stem.
- Main function is to generate X-ray (by target) and dissipation of heat (by copper stem)
- Types - anode can be stationary or rotatory.
Tungsten target:
- Made of Tungsten.
- Atomic number - 74
- Melting point - 3380oC
- Thermal conductivity: High
- Function: The purpose of tungsten target is to convert kinetic energy of electron into X-ray photons.
Copper stem:
- Tungsten is embedded into copper block.
- Thermal Conductivity: High so that it dissipates the heat.
- Function: Dissipation of heat by conduct.