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Method for Reducing the Energy Dependence of the Resolution of Focused Collimators

Western Regional Hospital Board, Glasgow, Scotland

Correspondence: For reprints contact: D. J. Wyper, Dept. of Clinical Physics and Bioengineering, Western Regional Hospital Board, 11 W. Graham St., Glasgow, Scotland.

ABSTRACT

It is shown that the addition of mid-penumbral shielding at the inlet and outlet faces of a focused collimator considerably reduces the deterioration in resolution with increasing incident photon energy. In particular, it is shown that the comparative optimum response wavelength of a collimator incorporating mid-penumbral shielding increases from 2.3 cm for 27-keV photons, to 2.9 cm for 48-keV photons, and to 3.1 cm for 660-keV photons, whereas for an equivalent collimator of current conventional design, the corresponding comparative optimum response wavelengths are 2.6 cm, 3.7 cm, and 5.4 cm. The improvements in resolution characteristics are not achieved at the expense of overall performance, as defined using the figure of merit. In fact, in the case considered overall performance is improved.