An investigation of factors affecting detector and geometric correction in normalisation of 3D PET data

Normalisation in 3D PET comprises two aspects: correction for differential detector response and correction for geometric effects. Comparison of rotating rod source and uniform cylinder data suggest that the position of the source used to correct for sensitivity should be similar to that of the emission data. A plane source method has been devised which uses a moving line source that traverses the transaxial field-of-view, emulating a plane source, but without the problems associated with using a conventional plane source in 3D (uniformity, scatter, cost, etc.). This device has been used to record high count density acquisitions for normalisation of emission data, and also to define geometric effects with increasing azimuthal (φ) and polar (θ) angles in the 3D data set. The data have revealed two distinct geometric patterns: an overall transaxial sensitivity profile that decreases towards the centre of the projection (due to the increasing collinearity of the cuts between detectors in the crystal block and the lines-of-response), and a crystal interference profile which changes with position in each block. Correction for the first geometric component removes a low-sensitivity `hole´ in 3D PET reconstructions, and correction for the second component removes ´ring´ artefacts. The moving line source provides high quality data and may be the ideal normalisation device for 3D PET