Measurements of capillary x-ray optics with potential for use in mammographic imaging.

Capillary optic arrays are bundles of hollow glass capillaries which guide x rays in a manner similar to the way fiber optics guide light. Focused postpatient capillary optic arrays have the potential to significantly improve both contrast and resolution of mammographic images compared to conventional antiscatter grids. Contrast can be improved by the nearly total scatter rejection of the optic. Effective resolution can be improved by geometric magnification without increased focal spot blurring. The best results were found for borosilicate glasses, with transmissions in excess of 60% for 22-cm-long fibers. To evaluate the scatter rejection properties, the transmission of off-axis radiation was measured. Transmission drops to < 1% at an angular displacement of 2.7 mrad. Transmission of a bulk capillary array dropped to near zero if the source was at an angle of 2.5 mrad. This implies excellent scatter rejection capabilities. To evaluate whether unchanneled photons might still reach the detector, absorption measurements were also performed on fibers and arrays. Absorption was found to be adequate for scatter rejection. All of the data agreed well with numerical simulations. Performance calculations for two potential optics geometries gave promising results.