Recovery of the human striatal signal in a slice oriented positron emission tomograph

The human striatum is small enough for partial volume effects to be important when imaged in positron tomographs with slice widths 10 mm or greater. The combination of interslice distance and slice width in such tomographs results in an axial undersampling of the striatal activity which introduces the additional problem of variation of axial recovery as a function of position of the striatum along the tomograph axis. Using striatal phantoms, we have developed a method that corrects the recovered striatal signal to a maximum value equivalent to that measured when the object is centered with respect to a slice. This makes the recovery independent of the axial position of the striatum. The method also provides an estimate of the total striatal activity by integrating the axial image intensity distribution along the tomograph axis. The method is able to detect and correct for relative axial tilt of the left and right striatum. We applied it to 26 human [18F]-6-L-fluorodopa scans and obtained an average uptake rate constant k value of 0.25 +/- 0.05 ml/min/striatum and a left to right k value percentage asymmetry of 0.1% +/- 6.3%.