X-ray technicians must understand the electrical components of the machine to properly administer radiation.
Electronics education is very important for the radiologic technologist (X-ray tech or radiographer). By understanding how X-rays are generated and controlled, the radiographer can safely and accurately set technical factors (voltage and amperage) to create diagnostic radiographs and prevent overexposure to the patient. The X-ray generating system has three major components, the operating console, the X-ray tube (where X-rays are produced), and the generator (where electricity is transformed and rectified). Thorough knowledge of the generator will help the radiographer make and apply appropriate decisions regarding technical factors.
Volts and Amps: Two Terms the Radiographer Uses Every Day
Voltage is defined as electrical pressure that forces an electrical current through a conductor. When the radiographer sets the voltage (kVp) on the console, this determines the penetrating power of the X-ray beam. Different size patients and body parts require different voltage settings. 1 ampere (amp) is equal to 1 coulomb flowing through a conductor each second. A coulomb is a specific quantity (63,000,000,000,000,000,000 electrons). By setting the amperage (mA) on the console, the radiographer controls the quantity of radiation per second used for the exam.
Timing Circuitry
Modern X-ray equipment uses electronic timing devices to set exposure times. Technologists need to be able to calculate milliamp-seconds to control the total amount of radiation they are using to perform an X-ray examination. Modern timers express exposure times in milliseconds. Older timers express exposure durations in decimals or fractions of a second.
Rectification
The radiographer must understand how the generator's rectification effects the output of radiation to be able to use different X-ray machines. Rectification essentially changes alternating current (supplied by the power company) to direct current (usable by the X-ray tube). Typical X-ray units have single-phase half-wave rectification; single-phase full-wave rectification; three-phase, 12-pulse rectification; or high-frequency rectification. The different generators vary in X-ray production efficiency. Understanding the differences in efficiency of the rectifiers is essential to setting accurate technical factors (kVp and mAs) on the console.
Transformers
The function of the transformers in an X-ray generating system is to increase or decrease the voltage of the supplied electricity. X-ray production requires very high voltage (up to 150,000 for some examanations). If the X-ray unit is supplied with 440 volt electricity, the incoming voltage has to be "stepped-up" hundreds of times by the transformer to produce X-rays. When the radiographer sets the kVp on the console, the autotransformer (variable transformer) changes the voltage supplied to the X-ray tube and the penetrating power of the beam.
Image Evaluation and the X-ray Generating system
Insufficient image quality must be corrected before the films are submitted for reading by the radiologist (doctor who specializes in radiology). The radiographer must evaluate the image quality for accurate density (darkness), contrast, and clarity. These are largely controlled by setting technical factors. By thoroughly understanding the components of the X-ray generating system, the radiographer is able to make necessary corrections.
Tags: technical factors, generating system, X-ray generating, X-ray generating system, X-ray tube, exposure times, express exposure