Potential of polycapillary optics for hard x-ray medical imaging applications

Polycapillary optics are shaped arrays of tiny hollow tubes through which x rays are guided by total external reflection at grazing incidence. In previous work,(1.2) it has been demonstrated that a small prototype optic can provide nearly total scatter rejection at mammographic energies with simultaneous resolution enhancement due to geometrical-blur-free magnification. Recent measurements on straight capillaries and lenses show that capillary optics could possibly be applied to higher energy imaging applications, such as angiography and chest radiography. Transmission efficiency for straight bundles was measured to be fairly flat out to 60 keV and in excess of 30% at 80 keV. Extensive simulations and measurements have been performed for prototype capillary optics at photon energies from 20 to 100 keV. Transmission of the central part (0.5 mm diameter) of a 166 mm long prototype tapered lens was as high as 60% near 30 keV and in excess of 40% up to 70 keV. The reduction of transmission at high energies was found to be caused by optic profile defects: surface waviness and centerline bending. Absorption and scatter rejection measurements indicate that almost total scatter rejection is achievable at high energies. Scatter transmission of the tapered borosilicate glass lens is around 5% at 60 keV. Even better scatter rejection could be achieved by using lead glass capillaries. By estimating the contrast improvement factor and Signal to Noise Ratio (SNR) with the scaled up lenses, this paper demonstrates the potential for polycapillary optics in various medical x-ray imaging applications.