Physics of radiography

Chapter 7 Physics of radiography





KEY POINTS














SI BASE UNITS RELEVANT TO RADIOGRAPHIC PRACTICE






DERIVED SI UNITS RELEVANT TO RADIOGRAPHIC PRACTICE


Derived SI units result from a combination of the base units and some of them are used frequently in radiography. Practitioners are required to name them and define their values (Table 7.1). Some of these derived SI units are outlined below.


Table 7.1 Common SI units used in radiographic practice











































Term and SI unit Definition Application to radiography
Energy (joule; J) The ability to do work Production of X-rays
Mass (kilogram; kg) A measure of the number of atoms and molecules in a body Important when determining the radiation dose to a patient
Gray (joules per kilogram; Gy) The energy imparted to a body by ionising radiation Unit of absorbed radiation dose measurement
Sievert (joules per kilogram, Sv) The energy imparted to a body by ionising radiation multiplied by the quality factor Unit of radiation dose equivalent, which takes biological factors into account
Power (joules per second) The rate of doing work Output of X-ray generator
Electric current (ampere; A) The movement of electrons flowing per unit time Quantity of electrons flowing per unit time
Electric charge (coulomb; C) 1 ampere flowing per second Quantity of electrons flowing per second
Electrical potential (volt; V) The force which moves electrons within a conductive material Potential difference across an X-ray tube, acceleration of electrons and quality of X-ray beam
Frequency (hertz; Hz) The number of cycles per second Electromagnetic radiation



Feb 20, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Physics of radiography
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