The technique chart is an invaluable resource for a radiographer. Its purpose is to provide a consistent method of choosing the proper exposure factors to create a diagnostic radiograph. On the basis of the thickness of tissue and anatomic area of the body, the radiographer can consult the technique chart for a predetermined machine setting. Without this resource, one would have to calculate a new technique each time a radiograph is taken or use a questionable technique performed previously. A technique chart prevents the need for second radiographs due to inappropriate exposure factors.
Technique chart formulation
There are several methods are used to formulate a technique chart; they vary slightly, but all are effective. The two widely used types of technique charts are Variable kVp technique chart and Fixed kVp technique chart. In some literatures High kVp technique chart, which is a type of technique chart, Anatomically Programed Radiography (APR), and Automatic Exposure Control (AEC) are wrongly listed as types of technique charts.
To create a workable technique chart, a series of trial exposures must be made using phantoms and data gathered from actual exposures performed for diagnostic purposes (not for technique chart development). For this project, however, you will use information gathered from your procedures textbook, your personal technique notebook, APR of the x-ray machine you are preparing the technique chart, and technical factor readout from exams set with AEC to compile a technique chart.
The type of technique chart you will prepare a for one x-ray machines at your current clinical site will be fixed (high) kVp. Fixed kVp technique chart uses a fixed optimum kVp and mAs that varies with thickness. It requires higher kVp to minimize patient dose. Fixed kVp technique produce long scale contrast and precise part measurement is not required.
Proper exposure of a patient to x-radiation is necessary to produce a diagnostic radiograph. The factors that influence and determine the quantity and quality of x-radiation to which the patient is exposed are called exposure factors. Kilovolt peak, Milliampere, Exposure time, Milliampere seconds, Distance, Voltage ripple, and Filtration, are some of the factors that control radiographic image quality.
All of these factors, except those fixed by the design of the x-ray imaging system, are under the control of the radiologic technologist. Specially kilovolt peak (kVp), current (mA), exposure time (s), and source-to-image receptor distance (SID) are identified as prime exposure factors.