Physics, Techniques and ProceduresGadolinium filter
a filter for filtration of the
X-ray beam. The filters commonly used in radiography are made of aluminium or sometimes copper. For certain applications it can be favourable to use filters whith higher atomic number, thereby using their K edges in their absorption curve in order to produce more narrow
X-ray spectra (see
K edge). Examples of such elements are gadolinium, holmium and erbium with K edges at 50, 56 and 58 keV, respectively. When in use, they will filter out low energy photons - which contribute to patient dose only - just as well as an aluminium filter would have done. They will, however, also effectively reduce the number of photons in the
X-ray spectra from their K edge and up to 2030 keV above it. This can result in better image contrast but will require increased tube loading.
When imaging with iodine contrast agents, X-ray spectra filtered with elements such as gadolinium will have their maximum number of photons in the energy interval where iodine has its maximal absorption (Fig.1). This will amplify the contrast effect given by iodine.
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Already registered? Enter your e-mail in the window below.Re-registerFig.1
X-ray attenuation curves of iodine (K edge 33 keV) and gadolinium (K edge 50 keV).
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Gadolinium filter, Fig.1 | |