IAEA International Atomic Energy Agency General Radiography Radiation Sources in medicine diagnostic Radiology Day 7 – Lecture 1(1)

IAEA 2 Objective To become familiar with the technology used in general radiographic x-ray systems; To know the specific radiation risk linked with these devices.

IAEA 3 Contents Description of a general radiographic x-ray system; Influence of exposure parameters on patient dose and image quality; Equipment malfunction affecting radiation protection.

IAEA 4 provides static (radiographic) images using either x-ray film and intensifying screens or digital image receptors; may be used to examine most parts of the body such as the chest, abdomen, pelvis, head, spine, extremities etc.; However, the available power of the x-ray equipment may be a limiting factor in determining the range of examinations that can be best performed while ensuring optimal image quality; Conventional systems for general purposes General purpose radiography equipment:

IAEA 5 is also used for contrast examinations where contrast media such as barium sulphate or iodine based compounds are ingested by, or injected into, the patient. (For chest x-ray examinations, air is the contrast medium and an important reason the examination is taken on full inspiration); In addition to fixed installations, mobile equipment for general radiography are also commonly used. However, those with lower tube currents, longer exposure times and larger focal spots (i.e. low powered x-ray equipment) may not be suitable for some thick body sections, e.g. the abdomen, spine, etc. Conventional systems for general purposes General purpose radiography equipment:

IAEA 6 Basic system for general x-ray examinations Conventional systems for general purposes

IAEA 7 Example of a mobile system for general radiographic purposes Conventional systems for general purposes (cont)

IAEA 8 For general radiography, the generator and x-ray tube should operate in an energy range from kV peak to kV peak. X-ray tube currents from 50 to 1000 mA or more are not uncommon. An adjustable (rectangular) light beam collimator must be fitted to the x-ray tube assembly so that the operator can restrict the size and shape of the x-ray beam to the area of clinical interest. Proper collimation is perhaps the most important means of minimizing patient (and operator) radiation dose and in improving image quality. Specific Equipment Requirements

IAEA 9 Additional and variable filtration (added filtration) should be available to the operator to reduce low energy radiation which does not reach the image receptor and which unnecessarily increases patient dose. Specific Equipment Requirements (cont) The light and x-ray beams of the light beam collimator must be congruent (within a specified error) and indicate the extent of the radiation field. However, the operator must not be able to remove any permanent filtration required to meet the minimum filtration specifications.

IAEA 10 An anti-scatter-grid is essential for the examination of most thick body parts. It is a (preferably removable) device positioned after the patient, (but before and close to the image receptor) to reduce the level of scattered radiation reaching the receptor. Specific Equipment Requirements (cont) Fundamentals of Radiography. Kodak

IAEA 11 However, a grid necessarily increases the exposure required (and therefore patient dose) by factors ranging from 2 to 5 times. Grids should only be used when essential to image quality. Specific Equipment Requirements (cont) The use of an automatic exposure control device (AEC) is recommended. With such devices, the exposure time is terminated when a pre-set radiation dose to the image receptor is reached. However, correct beam centring and collimation are required for reliable results i.e. users must be properly trained.

IAEA 12 The x-ray tube voltage (kV peak), tube current (mA), and exposure time (or mAs) are the minimum parameters to be displayed at the control panel prior to the radiographic exposure (the mAs also should be displayed after an exposure with an AEC). Information about radiation field size, focus to image receptor distance, the selection and position of the AEC detector also should be available. If practicable, a device informing the operator of the quantity of radiation delivered to the patient should be integrated with the equipment (e.g. a Dose-Area Product meter). Specific Equipment Requirements (cont)

IAEA 13 Dose-area product meter DAP readout Specific Equipment Requirements (cont)

IAEA 14 Filtration inappropriate to the imaging task. Equipment malfunctions affecting radiation protection Lack of congruency between the x-ray and light beams. Misalignment between the x-ray beam and image receptor. Inappropriate use of an anti-scatter grid (e.g. unnecessary use, incorrect ratio, alignment errors, etc.) leading to unnecessarily increased patient doses and poor image quality. AEC malfunction or poor calibration.