THE XRAY MACHINE DEPARTMENT OF ORAL MEDICINE RADIOLOGY

THE X-RAY MACHINE DEPARTMENT OF ORAL MEDICINE & RADIOLOGY Dentistry Explorer

LEARNING OBJECTIVES • AT THE END OF THIS CLASS YOU WILL BE ABLE TO – Identify Parts Of An X-ray Machine – Know In Detail About The X-ray Tube – Understand The Concept Of Production Of X-rays From The Machine – Understand the Concept of Line Focus Principle Dentistry Explorer

THE DENTAL X-RAY MACHINE CAN BE DIVIDED INTO 3 STUDY AREAS 1. THE COMPONENT PARTS 2. THE X-RAY TUBE 3. THE X-RAY GENERATING APPARATUS Dentistry Explorer

THE COMPONENT PARTS THE CONTROL PANEL THE EXTENSION ARM THE TUBE HEAD Dentistry Explorer

THE CONTROL PANEL The control panel of the dental x-ray machine contains : On- off switch and an indicator light An exposure button and indicator light Control devices (time, kilovoltage and Miliamperage selectors) The control panel is plugged in to the electrical outlet Dentistry Explorer

THE EXTENSION ARM The extension arm suspends the x-ray tube head and houses the electrical wires that extended from the control panel to the tube head Allows for the movement and positioning Dentistry Explorer

THE TUBE HEAD Tube head is a tightly sealed, heavy metal housing that contains the x-ray tubes The components include 1. METAL HOUSING - surrounds the x-ray tube and transformers and is filled with oil; it protects the x-ray tubes and grounds the high voltage components Dentistry Explorer

2. INSULATING OIL – prevents overheating by absorbing the heat created by the production of x-rays 3. TUBEHEAD SEAL – the aluminium or leaded glass covering of the tube head Ø Permits the x-rays from the tube head Ø It also seals oil in the tube head Ø Acts as a filter to the x-ray beam Dentistry Explorer

4. TRANSFORMER – or a device that alters the voltage of incoming electricity. 5. ALUMINUM DISCS – sheets of 0. 5 -2 mm thick aluminum placed of the x-ray beam; they filter out the nonpenetrating, longer wavelength x-rays. 6. LEAD COLLIMATORS – or a lead plate with a central hole that metal housing where the x-ray exits : it restricts the size of the x-ray beam. Dentistry Explorer

TYPES OF COLLIMATORS Round Collimator Rectangular Collimator Cylindrical Collimator Dentistry Explorer

7. POSITION INDICATING DEVICE (PID) Open ended, lead –lined cylinder that extend from the opening of the metal housing of the tube head ; it aims and shapes the x-ray beam Dentistry Explorer

THE X-RAY TUBE The x-ray tube is a glass vacuum tube from which all the air has been removed The x-ray tube used in dentistry measures approximately several inches long by 1 inch in diameter. The components of x-ray tube include - A leaded glass housing - A negative cathode - A positive anode Dentistry Explorer

LEADED – GLASS HOUSING The leaded glass housing is a leaded glass vacuum tube that prevents x-ray from escaping in all directions. One central area of the leaded – glass tube has a “WINDOW” that permits the x-ray beam to exit the tube and directs the x-ray beam toward the aluminum disk, lead collimator and PID. Dentistry Explorer

CATHODE - A NEGATIVE ELECTRODE THE cathode of the two principal parts: 1) The filament – Tungsten 2) The focusing cup – Molybdenum THE FILAMENT – TUNGSTEN is the source of electrons within the x-ray tube, is a coil of tungsten wire about 0. 2 cm in diameter and 1 cm or less in length. THE FOCUSING CUP – MOLYBDENUM The filament is located in a focusing cup, a negatively charged concave reflector cup of molybdenum which focuses the electrons into a narrow beam and directs the beam across the tube toward the tungsten target of the anode. Dentistry Explorer

The hot filaments emits electrons that are separated from the outer orbit of the tungsten atoms at a rate proportional to its temperature by a process called THERMIONIC EMISSION. These electrons are directed at a small rectangular area on the anode called as FOCAL SPOT. The x-ray tube is evacuated as completely as possible to preclude collision of the moving electrons with gas molecules, which would significantly reduce their speed. It also prevents oxidation and ‘burnout’ of the filament. Dentistry Explorer

ANODE - A POSITIVE ELECTRODE Consists of a tungsten target embedded in a solid copper rod. TUNGSTEN TARGET – (Plate of tungsten of size) The purpose of the target is to convert the kinetic energy of the electrons generated from the filament into the x-ray photons. COPPER STEM – The function is to dissipate the heat away from the tungsten target. Dentistry Explorer

X-RAY TUBE WITH MAJOR COMPONENTS Dentistry Explorer

WHY TUNGSTEN IS USED ? Because it represents an effective compromise between the features of the ideal target material. 1) HIGH ATOMIC NUMBER -- 74 2) MELTING POINT -- 3370 o 3) LOW VAPOUR PRESSURE of tungsten at high temperatures also precludes compromising the vaccum in the tube at operating conditions. Dentistry Explorer

The thermal conductivity of tungsten is relatively low, the tungsten target (usually a button of metal) is frequently backed by a large block of copper (as it is a good thermal conductor and dissipates heat from the tungsten and copper anode). A cooling electrically insulating oil may circulate between the envelope and the protective tube housing. This type of anode is called as STATIONARY ANODE. Dentistry Explorer

• Radiographic image quality is dependant in part on the geometry of the target. • The sharpness of the image increases as the size of the radiation source, the focal spot (area on target where electrons strike), decreases. However the heat generated per unit area increases Dentistry Explorer

Therefore to take the advantage of smaller focal spot, the target is placed at an angle of 20 w. r. t. electron beam. The projection of the focal spot perpendicular to the electron beam called as EFFECTIVE FOCAL SPOT will be smaller than the actual size of the focal spot that is projected from the target (ACTUAL FOCAL SPOT). Dentistry Explorer

This provides the geometry to cause the effective focal spot to be almost 1 x 1 mm in contrast to the actual focal spot which is 1 x 3 mm. This is called as LINE FOCUS PRINCIPLE. The effective focal spot size may be decreased, & the sharpness of the image increased, by continuing reducing the angle of the anode. However, this is limited by HEEL EFFECT. Dentistry Explorer

LINE FOCUS PRINCIPLE Dentistry Explorer

Another method of dissipating heat the heat from a small focal spot is to use ROTATING ANODE, in this the tungsten target is beveled disk that rotates (about 3000 rpm) when tube is in operation. Such rotating anodes are not used in conventional dental xray machines but may be used in cephalometric units or in medical x-ray machines. Dentistry Explorer

ROTATORY ANODE (long life as rotating) Dentistry Explorer

THE X-RAY GENERATING APPARATUS ELECTRICITY AND ELECTRIC CURRENTS CIRCUITS TRANSFORMERS STEP-DOWN TRANSFORMER STEP-UP TRANSFORMER AUTO TRANSFORMER Dentistry Explorer

TUBE HEAD (Including the recessed x-ray tube), Components of power supply, and the oil that conducts heat away from the x-ray tube Dentistry Explorer

ELECTRICITY AND ELECTRIC CURRENTS ELECTRICITY – is the energy that is used to make x-rays. ELECTRIC CURRENT – is the flow of electrons through a conductor DIRECT CURRENT (DC) - is the flow of electrons in one direction. ALTERNATING CURRENT (AC) - is the flow of electrons in two opposite directions. Dentistry Explorer

RECTIFICATION – is the conversion of AC to DC. The dental x-ray tube acts a self rectifier in that it changes AC into DC while producing x-ray. This ensures that the current flows in same direction. AMPERAGE – is the measurement of number of electrons through the conductor. Current is measured in amperes or milliamperes (m. A) VOLTAGE – is the measurement of the electric force that causes electrons to move from a negative pole to a positive pole. Voltage is measured in volts or kilovolts (k. V). Dentistry Explorer

CIRCUITS A circuit is a path of electric current Two electrical circuits are used in the production of x-rays A LOW-VOLTAGE FILAMENT CIRCUIT A HIGH-VOLTAGE CIRCUIT A LOW-VOLTAGE FILAMENT CIRCUIT: uses 3 to 5 volts, regulates the flow of electrical current to the filament of the x-ray tube, and is controlled by the milliampere settings. A HIGH-VOLTAGE CIRCUIT: uses 65, 000 to 100, 000 volts, provides the high voltage required to accelerate electrons and to generate xrays in the x-ray tube and is controlled by the kilovoltage settings Dentistry Explorer

TRANSFORMERS A TRANSFORMER is a device that is used to either increase or decrease the voltage in an electrical circuit. Transformers alters the voltage of the incoming electric current and then route the electrical energy to the x-ray tube. Three types of transformers are used to adjust electrical circuits. These transformers and x-ray tube are contained within an electrically grounded metal housing called as the tube head and are surrounded by an electrically insulating oil. Dentistry Explorer

STEP DOWN TRANSFORMER: • The filament circuit uses 3 to 5 volts. A Step Down Transformer is used to decrease the voltage from incoming 110 or 220 line voltage to the 3 to 5 volts required • The Step Down Transformer has more wire coils in the primary coil (input coil) than in the secondary coil (output coil) Dentistry Explorer

STEP UP TRANSFORMER : • The high voltage circuit requires 65, 000 to 100, 000 volts and uses a step up transformer and an automatic transformer. • A step up transformer is used to increase the voltage from the incoming 110 to 220 line voltage to the 65, 000 to 100, 000 volts required. • The Step Up Transformer has more wire coils in the secondary coil than in the primary coil. Dentistry Explorer

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AUTO TRANSFORMER Serves as a voltage compensator that corrects for minor fluctuation in the current. The output of auto transformer is regulated by k. Vp selector dial Dentistry Explorer

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THE INSIDE STORY OF THE X-RAY TUBE Dentistry Explorer

X-RAY TUBE HEAD Dentistry Explorer

ALUMINUM ADDED FILTRATION Dentistry Explorer

ANODE END OF X-RAY TUBE Dentistry Explorer

ANODE END OF X-RAY TUBE Dentistry Explorer

TUBE HEAD FILLED WITH OIL Dentistry Explorer

THIN YELLOWISH OIL IN THE TUBE Dentistry Explorer

Insulating paper Thermal cut out High tension wire Red & white Low tension wire Yellow STEP UP TRANSFORMER Dentistry Explorer

GLASS TUBE CONTAINING CATHODE & ANODE Dentistry Explorer

BROKEN GLASS ENVELOPE Dentistry Explorer

LOW & HIGH TENSION CIRCUIT Dentistry Explorer

Opening to allow electrons from cathode Window ANODE MADE OF COPPER STEM & TUNGSTEN FOCAL SPOT Dentistry Explorer

CATHODE & ANODE Dentistry Explorer

CATHODE & ANODE Dentistry Explorer

Tungsten filament 2 mm X 5 mm CATHODE- the negative end of the tube Dentistry Explorer

Window ANODE- the positive end of the tube Dentistry Explorer

TUBE END OF COLLIMATOR Dentistry Explorer

RECENT ADVANCES IN THE X-RAY TUBE 1. METAL CERAMIC X-RAY TUBE - Higher beam stability - More robust design - Eliminate the need of oil or resin insulation - Heat conductivity is more 2. Graphite backed anode 3. Metal center section X-ray tube 4. Double filament X-ray tubes Dentistry Explorer

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Photon of maximum energy Dentistry Explorer

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CHACTERISTIC RADIATION Dentistry Explorer

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THANK YOU Dentistry Explorer