Radiography

Radiography is an X-ray-based technique. Initial film-based radiography used layered film cassettes to detect X-rays attenuated by absorption and scattering effects on the target tissue, depending on the tissue’s density, thickness, and composition. The film cassettes contain a screen consisting of a fluorescent coating, which emits light as X-rays pass through the tissue and interact with it. These rays then expose areas on the photographic layer of the cassette, which is developed by automated chemical photograph processing techniques. Thus radiography is a 2-D imaging technique. The development of computed radiography, and a phosphor-coated imaging plate (Moore, 1980), eliminated the use of films and allowed the production of digital radiographs. Once X-rays are captured on the plate it is then “read” using a helium- neon laser which emits lights. Emitted light is captured by a photomultiplier tube and a digital image is produced (Fig. 5.1). The main advantage of computed radiography over the initial film-based system is that the receptor may be erased and used repeatedly. Current radiographic imaging systems are purely digital, i.e., no cassette or plate is required. The X-rays are detected electronically and an image is produced by direct read-out detectors, making the technique faster and less costly. To produce live images fluoroscopy may also be employed, wherein X-rays are continuously detected by a fluorescing screen, which amplifies the signal and produces an image on a monitor (Korner et al., 2007).

Images produced through radiography are black, white, and gray with everything appearing black where little of the X-ray beam is attenuated. Thus dense tissues, such as bone, appear white on the final image. With such high contrast, the availability of radiography, its cheap running costs, the speed at which a scan may be made, and the relatively simple equipment used, it remains a popular technique for examining bone damage and defects (Geusens et al., 2014). For the analysis of biomaterials and biomineralization, it is possible radiography may serve as an initial screening test for radio-dense areas but may be better coupled to more sensitive techniques, such as X-ray computed tomography (Wojtowicz et al., 2010; Seto et al., 2012). Furthermore, as an X-ray-based technique the ionizing radiation poses a health risk to patients and as such the X-ray beam and duration of test must be tightly controlled (Einstein et al., 2016).

 
Source
< Prev   CONTENTS   Source   Next >