Measurement of resolution and recovery in recent generation positron tomographs

In positron tomographic images, the ability to differentiate closely lying structures, the spillover of activity from a region into adjacent regions and the reduction in apparent isotope concentration in small structures are all dependent on spatial resolution. Resolution in the reconstructed image is affected by (i) detector size, (ii) the spatial sampling used (e.g. stationary, wobble), (iii) the amount of smoothing in the reconstruction process (or subsequent to reconstruction) and (iv) the image pixel size. Under ideal conditions, modern commercial tomographs can produce a reconstructed spatial resolution of 5 mm or less. However, this is rarely realizable in a clinical study due to the inadequacy of counting statistics and the amplification of statistical noise. In practice, a smoother filter has to be used. This paper presents a summary of practical measurements of spatial resolution, and the related count recovery, performed on recent generation positron tomographs. It is intended to contribute to the definition of methods of measuring these parameters which is part of an on going concerted action in positron tomography supported by the European Commission.