A method for calibrating three-dimensional positron emission tomography without scatter correction

Calibration for three-dimensional positron emission tomography (3D PET) using a uniform cylinder and cross-calibration with aliquots requires correction for scatter and attenuation. Thus the accuracy of the calibration is dependent on the scatter correction method, and on the applicability of the scatter correction for different regions of the body. A method has been developed which provides a calibration which does not require correction for scatter or attenuation, making it generally applicable and independent of the scatter correction. The method has been previously described for measurement of the absolute sensitivity of tomographic devices. This approach has been extended to give a calibration of the PET camera "in air" in units of kBq/pixel. The reconstructed images are multiplied by this factor to give accurate activity concentrations, after attenuation and scatter correction. The method has been used with a fully 3D filtered backprojection (reprojection) algorithm and iterative convolution-subtraction scatter correction on data from an ECAT 953B. Using this method 3D PET images have been calibrated to within +/-5% accuracy, but this is highly dependent on the accuracy of the scatter correction. The method described here is practical and provides a means of calibrating a 3D PET system without the need for correction for scatter or attenuation of the calibration data.