10. LO3_The Operating Console and X-ray Generator.pptx

6. The Operating Console and X-ray Generator HMI 2002 (202110) The Radiographic Unit The x-ray imaging system basic component: 1. X-ray tube 2. Operating console 3. X-ray generator 4. Ancillary parts 2 of 24 2- Operating Conso...

6. The Operating Console and X-ray Generator HMI 2002 (202110) The Radiographic Unit The x-ray imaging system basic component: 1. X-ray tube 2. Operating console 3. X-ray generator 4. Ancillary parts 2 of 24 2- Operating Console The console is the part of the machine that the operator controls the operation of the x-ray machine. All machine console are a little different but there are always similarities. The console will have controls for: - mA and time or mAs - kVp - Make an exposure (switch) - Focal Spot - Automatic Exposure Control (AEC) (discussed later) - Anatomically Programmed Radiography (APR) (discussed later) 3 of 24 3- The X-ray Generator Circuit diagram of the x-ray imaging system 4 of 24 Functions 1. Provides the operator control of the radiographic techniques. 2. Modify incoming voltage and current in order to provide the x-ray tube with the power to provide an x-ray beam. 5 of 24 Transformers A transformer is a passive electrical device that transfers electrical energy from one circuit to another through the process of electromagnetic induction. It is most commonly used to increase (‘step up’) or decrease (‘step down’) voltage levels between circuits. It consists of two 2 coils (windings) and a core. An alternating current (AC) in the first coil will create a flux (magnetic field). If a second coil brought close enough, the flux will induce an AC in it. 6 of 24 Transformers The voltage in the second coil (VS) depends on its number of windings (NS) in relation to the number of windings in the first coil (NP). VP: primary voltage NS > NP  VS increases (step up) NS < NP  VS decreases (step down) NS = NP  VS doesn’t change 7 of 24 Types of Transformers 1. Step up transformer: - NS > NP  VS > VP - Used in the x-ray tube high-voltage circuit. 2. Step down transformer - NS < NP  VS < VP - Used in the filament low-voltage circuit. 3. Autotransformer - Has a single winding. - Supply a precise VP to the x-ray tube and filament circuits. 8 of 24 High Voltage Section It consists of three primary sections: 1. Filament Transformer (step-down) 2. High voltage transformer (step up) 3. Rectifiers (Diodes) All components immersed in oil for electrical insulation. 9 of 24 1. X-ray Tube Current or Filament Circuit The tube current is the # of electrons crossing from the cathode to anode per second (mA). The # of electrons is determined by the temperature of the filament (thermionic emission). The tube current is controlled through a separate circuit called the filament circuit. The filament normally operates at currents between 3 and 6 A. Voltage is provided by the autotransformer. This voltage is reduced (stepped down). 10 of 24 2. High Voltage Step Up Transformer 220 v 1000s v Supplies the x-ray tube with high voltage (kilovolts!). Voltage induced in the secondary winding of a high-voltage step-up transformer is alternating like the primary voltage but has a higher value. NS > NP  VS increases (step up) Transformer is responsible for stepping up the voltage, to the high voltage needed to accelerate electrons across the X-ray tube. It supplies the high voltage to the anode, creating the potential difference required for X-ray production. 11 of 24 Voltage Rectification The current from a common wall plug is 60 Hz (AC) in USA and 50 Hz in the middle east. The current changes direction 100-120 times each second. However, an x-ray tube requires a direct current (DC), that is, electron flow in only one direction. Therefore, some means must be provided for converting AC to DC. - This means is known as rectification. - AC (Alternating current): occurs when the electric current periodically inverts its direction 12 of 24 - DC (Direct current): occurs when the current flows in one constant Voltage Rectification Rectification is the process of converting AC to DC. A diode (rectifier) an electrical device that allows current to move through it in one direction. Voltage rectification is required to ensure that electrons flow from x-ray tube cathode to anode only. 13 of 24 Half-wave Rectification Requires only one diode. Disadvantages: - It wastes half the supply of power. - It requires twice the exposure time. 14 of 24 Full-Wave Rectification Uses a circuit with 4 diodes that rectifies the entire AC waveform. 15 of 24 Types of X-ray Generators 1. Single phase 2. Three phase 3. High frequency The generator types affects the quality and quantity of photons produced per unit of time. 16 of 24 Single-phase Generator Uses a single-phase input line voltage source (e.g., 220 V at 50 A), and produces either a single-pulse or a two-pulse DC waveform, depending on the high- voltage rectifier circuits. Voltage swings from zero to maximum potential 100-120 times each second under full-wave rectification. The x-rays produced when the single-phase voltage waveform has a value near zero are of little diagnostic value because of their low energy (i.e., low penetrability). 17 of 24 Three-phase Generator Three voltage waveforms are superimposed on one another, resulting in a waveform that maintains a nearly constant high voltage. There are 6 or 12 pulses per cycle (1/50 s) compared with the 2 pulses characteristic of single-phase power. The voltage applied across the x-ray tube is nearly constant, never dropping to zero during exposure. 18 of 24 Cont’d 19 of 24 Cont’d Three-phase radiographic equipment is manufactured with tube currents as high as 1200 mA; therefore, exceedingly short, high- intensity exposures are possible. - Particularly helpful in interventional radiology procedures. Advantages: Deliver a more constant voltage and can produce very short exposure times. Disadvantages: More expensive, bulky, and occupy significant floor space. 20 of 24 High-frequency Generator The most advanced generator. Full-wave–rectified power at 50-60 Hz is converted to a higher frequency, from 500 to 40,000 Hz, and then is transferred to high voltage. Produces a nearly constant potential voltage waveform, improving image quality at lower patient radiation dose. Inverter circuits are high-speed switches, or choppers, that convert DC into a series of square AC pulses. 21 of 24 Cont’d Advantages: 1. Single-phase or three-phase input voltage can be used. 2. More efficient. 3. More compact. 4. Less costly. 5. Equipment siting and repairs are relatively easy. 22 of 24 Voltage Ripple The most efficient method of x-ray production involves the waveform with the lowest voltage ripple. An x-ray tube voltage with less ripple offers many advantages: 1. Greater radiation quantity: The efficiency of x-ray production is higher when x-ray tube voltage is high. 2. Greater radiation quality: Fewer low-energy projectile electrons pass from cathode to anode to produce low-energy x-rays. 23 of 24 What Have we Learned? The functions of the operating console and the x-ray generator. The components of the x-ray generator and their functions. Transformers and the x-ray tube and filament circuits. What rectification is, why is it important, and its types. Types of x-ray generators and their pros and cons. What voltage ripple is and how it is calculated. 24 of 24 800 MyHCT (800 69428) [email protected] www.hct.ac.ae Happiness Center PO Box 25026 Abu Dhabi, UAE HCT_UAE hctuae