Uranium pinhole collimators for I-131SPECT imaging

Pinhole apertures made of depleted uranium were evaluated for high-resoluti on SPE:CT brain tumor imaging of therapeutic doses (30-100 mCi) of intratum orally administered I-131 radiolabeled monoclonal antibodies. High resoluti on is required for imaging residual tumor tissue, although for therapeutic doses, high collimator sensitivity is less important. Resolution of uranium and tungsten pinhole apertures was compared in planar and SPECT images of I-131 sources. Planar sensitivity was studied on- and off-axis. On-axis pla nar resolution for uranium pinholes is higher than that of tungsten pinhole s for all cases examined; full-width-half-max (FWHM) is narrower for a 3 mm uranium pinhole than for a I mm tungsten pinhole, indicating significantly lower penetration at pinhole edges for uranium than for tungsten. Collimat or sensitivity is higher for tungsten than for uranium, which also indicate s higher edge penetration for tungsten. On-axis SPECT(14.4 cm radius) scans also show better resolution for a 2 mm uranium pinhole (7.8 mm FWHM) than for a 2 mm tungsten pinhole (9.5 mm FWHM). Background radiation from a uran ium collimator (102 cts/sec) is acceptably low compared to expected clinica l count rates.