Design and performance of a single photon transmission measurement for the ECAT ART

We have implemented dual multi-slit collimator singles transmission sources on the ECAT ART comprising two sets of 12 slits having an axial pitch of twice the axial crystal ring pitch. The slits illuminating opposing detector banks are interleaved, achieving full coverage of all crystal rings as two Cs-137 point sources are simultaneously rastered axially behind the collimators. Transmission data are normalized to a slab phantom scan and corrected for scatter and cross section variation using a log-linear transformation of the attenuation factors. The value of the linear attenuation coefficient in water phantoms has been measured as 0.0946 +/- 0.0044 cm(-l) for 2 min scans employing two 6 mCi sources. A quasi-simultaneous mock scan capability permits direct acquisition and subtraction of the emission background in post-injection transmission acquisitions.