Acquisition of linograms in SPET: implementation and benefits

Compared with other tomographic modalities, single-photon emission tomography (SPET), the most widely used tomographic modality in nuclear medicine, suffers from poor quality image since the collimator stops 99.99% of the emitted gamma rays reaching the detector. This paper describes a new SPET acquisition modality using a very short focal length (12.5 cm) fan-beam collimator and a very short transverse field of view detector (25 cm). The detector moves along at least two linear orthogonal orbits in such a way that the focal line travels through the source target. This linear orbit acquisition (LOrA) generates linograms forming a complete set of tomographic data, i.e. sufficient to exactly reconstruct the activity map using a modified filtered back-projection algorithm. In contrast to the classical fan-beam tomography, truncation is not a problem, even when the source transverse size is much larger than the detector transverse size. When the collimator hole length/diameter ratio is adapted to obtain a spatial resolution similar to that of classical SPET, LOrA SPET offers an improvement in sensitivity by a factor of about 2.5 for a 20-cm source size. This improvement is achieved with a detector that is half as large, and thus half as expensive. As with classical fan-beam SPET, the sensitivity increases further if the target size decreases. When fitting the collimator to obtain a similar sensitivity to that of classical SPET, a significant improvement in spatial resolution is obtained.