X-Ray System PDF

The X-ray System RAD 231 Module 1 X-ray Room Main Components Locations The x-ray tube is in the room, the console X-ray tube, operating console (control is behind...

The X-ray System RAD 231 Module 1 X-ray Room Main Components Locations The x-ray tube is in the room, the console X-ray tube, operating console (control is behind a protective barrier, and the panel), high-voltage generator. generator is near the tube. Operating Console Console Circuits allows the technologist to in the console are low voltage control tube current and to reduce the risk of shock voltage Quantity Quality X-ray intensity (mAs) X-ray penetrability (kVp) Operating Console Voltage provided by the Most x-ray systems are Electric companies are not electric company could vary designed to operate on 220 capable of providing 220 V by as V power accurately and continuously much as 5% Operating Console o A variation in supply voltage results in a large variation in the x-ray beam. o Line compensator: measures the voltage provided to the x-ray imaging system and adjusts that voltage to exactly 220 V. o Older units required technologists to adjust the supply voltage while observing a line voltage meter. Newer x-ray systems have automatic line compensation. Autotransformer o The power supplied to the x-ray system is delivered to the autotransformer first. o The voltage supplied from the autotransformer to the high-voltage transformer can be adjusted and controlled. o It is much safer and easier to control a low voltage and then increase to the kilovolt level. Adjustment of Kilovolt Peak The primary voltage to the The low voltage from the autotransformer is 220 V so the autotransformer becomes the output of the autotransformer is input to the high-voltage step-up usually controllable from 100 to transformer that increases the 400 V. voltage to the chosen kilovolt peak Control of Milliamperage mA Filament Temperature a coil of wire similar to the number of electrons tube current is measured in that in a toaster or emitted is determined by milliamperes lightbulb. Approximately the temperature of the 2 mm in diameter and 1 filament or 2 cm long Control of Milliamperage filament temperature is As current increases, the controlled by the filament filament becomes hotter, and current, which is measured in more electrons are released amperes (A). Thermionic emission: release of electrons from a heated Filaments normally operate at filament currents of 3 to 6 A Control of Milliamperage X-ray tube current is Connections on the controlled through a dedicated autotransformer provide circuit called the filament voltage for the filament circuit circuit Control of Milliamperage o The filament transformer is a step-down transformer. o The voltage supplied to the filament is lower than the voltage supplied to the filament transformer. o Current is increased across the filament transformer because current and voltage are inversely proportional.  Exposure Timers The number of x-rays that reach the image receptor is directly related to the x- ray tube current and the length of time that the x-ray tube is energized. mAs: milliamperage x seconds 400 mA x 100 ms 400 x 0.1 s = 40 mAs Exposure Timers o The technologist initiates the exposure by pressing the exposure switch. o The x-ray system ends the exposure when it reaches the selected time. o Backup timer: terminates exposure at a set time, usually 5 or 6 seconds, regardless of the mAs set. Synchronous Timers minimum exposure time possible is 1/60 second (17 ms) timing intervals increase by multiples thereof (1/30, 1/20, etc.) cannot be used for serial exposures because they must be reset after each exposure Electronic Timers The most sophisticated, Consist of complex Are accurate to complicated, and circuitry and allow a intervals as small as 1 accurate of the exposure wide range of time ms and can be used for timers intervals to be selected rapid serial exposures Milliampere-second Timers Monitors the product of mA and exposure time and Designed to provide the terminates exposure when highest safe tube current the desired mAs value is for the shortest exposure attained The mAs timer must monitor the actual tube current so it is located on the secondary side of the high-voltage transformer AEC Automatic exposure control: measures the quantity of radiation that reaches the image receptor and automatically terminates the exposure when it has received the required radiation intensity AEC uses a backup timer to terminate the exposure should it continue past the necessary mAs High-voltage Generator Responsible for increasing Some heat is generated in The oil is used primarily for the output voltage from the the high-voltage section electrical insulation autotransformer and it is conducted to oil High-voltage Generator High-Voltage Filament Rectifiers Transformer Transformer High-voltage Transformer o Is a step-up transformer. o Voltage is increased to kV. o Amperage is decreased to mA. Voltage Rectification The current from a wall The current changes outlet is 60-Hz AC direction 120 times each second An x-ray tube How do we fix this? requires DC Voltage Rectification Rectifier Rectification electronic device that allows the process of converting AC current to flow in only one to DC direction Voltage Rectification X-rays are produced by the acceleration of electrons from the cathode to the anode They cannot be produced by electrons flowing in the reverse direction