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A Variable Angle Slant-Hole Collimator

Massachusetts General Hospital, Boston, Massachusetts

Correspondence: For reprints contact: H. William Strauss, MD, Nucl. Med. Div., Massachusetts General Hospital, Boston, MA 02114.

ABSTRACT

A variable-angle slant-hole (VASH) collimator was constructed to show the feasibility of using multiple sliding plates to achieve a range of collimator channel inclinations. One hundred and sixty tungsten plates, 0.125 mm thick and 14 cm square, were photoetched to produce 3025 1.5-mm² holes in each plate, separated by 0.8-mm septa. Along with the collimator holes, registration holes and positioning grooves were also etched. The plates were placed in a holder and stacked to form a collimator 2.0 cm high. The holder permitted the plates to be "sheared" to achieve viewing angles from 0 to 40° from the vertical. Resolution and sensitivity were determined both across and along the shear directions. Resolution of a thin Tc-99m source, 1.24 mm diam and 7 cm long, located 5 cm from the collimator face in air, was 1.1 cm FWHM at 0° shear and remained unchanged with increasing slant. The resolution was similar both across and along the shear plane. Sensitivity was determined with a point source placed 7 cm from the collimator face. At 0° slant the sensitivity was 169 cps/MBq (6.24 cps/µCi). A general all purpose (GAP) collimator had a FWHM of 1 cm for the line source in air at 5 cm, and a sensitivity of 205 cps/MBq (7.58 cps/µCi) for the point source at 7 cm. The data suggest that a variable-angle slant-hole collimator can be constructed of laminated plates.