Energy spectra of scattered x-rays around a CT scanner
I have carried out some research into the energy spectra and transmission characteristics of scattered x-rays from medical computed tomography (CT) scanners. This has been published in the June 2014 edition of the Journal of Radiological Protection (JRP). The paper can be found on the JRP website here. A local electronic copy of the accepted manuscript can be downloaded here. This is an author-created, un-copyedited version of an article accepted for publication in JRP. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.
Figure 1 below shows similar colour maps to those shown in the paper's figure 3. Moving the mouse pointer over the colour map will display the corresponding scatter energy spectrum at that location in figure 2. Note that the surface area represented by each colour patch varies across the map: patches at the equator have the largest area (the horizontal band across the centre of the map); patches at the poles have the smallest area (horizontal bands at the top and bottom of the map). The area under the spectra (the number of scattered photons) varies with position over the map. The variation in the number of scattered photons across the surface is partly due to the change in surface area represented by the colour patches: the patches will a smaller surface area will have a lower number of scattered photons. However, some of the variation is due to the angular variation in Compton scattering. Arthur Compton's original 1923 paper is available here.
Figure 1.Colour map of the mean energy of scattered photons leaving the spherical simulation geometry. The colour scale is in keV. The x-axis represents longitude from 180° west to 180° east. The y-axis represents latidude from 90° north to 90° south. Note that the surface area represented by each colour patch varies across the map: patches at the equator have the largest area (the horizontal band across the centre of the map); patches at the poles have the smallest area (horizontal bands at the top and bottom of the map). The mean energy, latitude and longitude at the current mouse pointer position are shown in the top-left hand corner of the map.
Figure 2. Energy spectrum of scattered photons leaving the pixel at the current mouse pointer location. The x-axis shows photon energy (keV). The y-axis shows counts per 2 keV energy bin if "absolute" is selected, or values normalised to the maximum number of counts in the currently displayed spectrum if "normalised" is selected. When the "normalised" option is selected an additional green-coloured spectrum is displayed: this is the energy spectrum calculated from all scattered photons at all primary beam angles, as see in figure 2b in the JRP paper.