Scatter-free breast imaging using a monochromator coupled to a pixellated spectroscopic detector

Abstract

This project uses the combination of a spectroscopic detector and a monochromator to produce scatter free images for use in mammography. Reducing scatter is vital in mammography, where typical structures have either low contrast or small dimensions. The typical method to reduce scatter is the anti-scatter grid, which has the drawback of absorbing a fraction of the primary beam as well as scattered radiation. An increase in the dose is then required in order to compensate. Compton-scattered X-rays have lower energy than the primary beam. When using a monochromatic beam and a spectroscopic detector the scattered beam will appear at lower energies than the primary beam in the detected spectrum. Therefore if the spectrum of the detected X-rays is available, the scattered component can be windowed out of the spectrum, essentially producing a scatter free image. The monochromator used in this study is made from a Highly Orientated Pyrolytic Graphite (HOPG) crystal with a mosaic spread of 0.4°±0.1°. The detector is a pixellated spectroscopic detector that is made from a 2 cm x 2 cm x 0.1 cm CdTe crystal with a pixel pitch of 250 µm and an energy resolution of 0.8 keV at 59.5 keV. This work presents the characterisation of the monochromator and initial imaging data. The work shows a contrast increase of 20% with the removal of the low energy Compton scattered X-rays.

Scatter free imaging for the improvement of breast cancer detection in mammography

“…Note that the IQF in the next section is independent of N 0 and therefore this value was not calculated in this study. For the study in Green et al (2015) an N 0 value of 20 000 was chosen…”

“…The calculations of the IQF are explained in previous work (Green et al 2015). Table 1 lists the calculated optimum energies for a range of thicknesses and this was used for all the imaging in this study.…”

“…In order to increase the intensity of the monochromatic beam a higher Note. The values were calculated for both the nylon and wax details of the low contrast test object and averaged to find these optimum energy values (Green et al 2015).…”

“…A tube voltage of 60 kVp was chosen in order to provide a sufficient beam intensity for imaging. The images were then formed using the methods described in previous work (Green et al 2015). Images were formed using both the full energy spectrum and the energy spectrum windowed around the monochromatic peak, figure 5.…”