Can "time of flight" reconstruction algorithms be used to reduce administered dose or acquisition time in F-18 positron emission tomography? A phantom study

2000 Objectives To determine whether a "time of flight" (TOF) reconstruction algorithm leads to qualitative changes in image appearance or quantitative differences in calculated SUV uptake values as compared to a conventional reconstruction algorithm in a phantom model across a range of acquisition times. Methods In two experiments, a NEMA phantom containing six spheres ranging from 37mm to 10mm was filled with a target background ratio of 4.8: 1 and 10:1 respectively. The phantom was imaged in a single three minute list mode acquisition with the data retrospectively divided into two minute, 1.5 minute, one minute and 30 second subsets. Each set of acquisition data was reconstructed with TOF and non TOF algorithms. For each sphere, a qualitative assessment of lesion visibility was made along with measurements of SUV max and SUV mean. Results With the target to background ratio of 10:1, the spheres were all visible on all reconstructions except for the 10mm sphere on the 30 second non TOF acquisition. However on the 4:1 target to background ratio there were significant qualitative and quantitative differences between the TOF and non TOF acquisitions. On the non TOF acquisition, the 10mm sphere could no longer be visualised on acquisitions of 1.5 minutes or less, whereas on the TOF acquisitions, the 10mm sphere was visible on all but the 30 second acquisition. For all of the experiments, the measured SUV mean and SUV max values were consistently lower in the smaller spheres, and this effect was more pronounced on the non TOF acquisition. Conclusions The TOF reconstruction algorithm improves the visualisation of small lesions at lower target to background levels. This effect becomes significant at lower acquisition times. This implies that the use of TOF reconstruction algorithms may allow preserved lesion visualisation with lower administered doses or shorter scan times