@article {Tanguay1940, author = {Jesse Tanguay and Hillgan Ma and Xinchi Hou and Francois Benard and Anna Celler}, title = {An experimental framework for task-based assessment of spatial resolution in quantitative PET/CT}, volume = {57}, number = {supplement 2}, pages = {1940--1940}, year = {2016}, publisher = {Society of Nuclear Medicine}, abstract = {1940Objectives The spatial resolution of a PET/CT image is determined by the scanner configuration and reconstruction algorithm used to produce the image. Spatial resolution impacts: 1) the ability of a physician to detect a lesion, and; 2) the quantitative accuracy of PET/CT-derived metrics of tumor burden. Assessment of spatial resolution is an important criteria when choosing a reconstruction algorithm and evaluating system performance, but is non-trivial due to the non-linear nature of modern iterative reconstruction algorithms. Our objective is to develop a framework to compare the spatial resolution of different reconstruction algorithms for imaging conditions used in PET/CT imaging.Methods We implemented a method for quantifying PET/CT spatial resolution in terms of the task-based modulation transfer function (MTF). Our approach extracts the trans-axial MTF from PET/CT images of a NEMA IEC phantom containing F-18-filled spheres in a hot background. We used this method to study the effects of resolution recovery (RR) and time-of-flight (TOF) reconstruction on spatial resolution. A NEMA IEC phantom (sphere concentration = 24 kBq/mL, SBR=7) was imaged 10 times (GE Discovery 690) and reconstructed using four ordered subsets expectation maximization (OSEM) reconstructions (clinical protocol = 32 subsets and 2 iterations, with and w/o post-reconstruction filtering): 1) standard OSEM; 2) OSEM with TOF; 3) OSEM with RR, and; 4) OSEM with TOF and RR. For each image, the edge of the largest sphere (diameter = 3.7 cm, 6 cm from the center of phantom) was analyzed to obtain the edge-spread function (ESF), from which MTF was calculated. For each reconstruction algorithm, MTF was calculated as the average of the 10 data sets. We also calculated the quantitative accuracy of each reconstruction algorithm by calculating the activity concentration within spherical ROIs (1 cm in diameter) located at the centers of the three largest spheres (2.2 - 3.7 cm in diameter). For each reconstruction algorithm, concentrations were calculated for each image and averaged over the 10 data sets. Measured concentrations were compared with known concentrations and reported as recovery coefficients (RCs).Results As expected, the MTFs of images that were filtered post-reconstruction were lower at high frequencies relative to those that were not filtered. Investigation of the ESFs showed that RR resulted in {\textquotedblleft}over-shoot{\textquotedblright} at the edges of the spheres, which is common for reconstruction algorithms that implement RR. Relative to standard OSEM, OSEM+RR resulted in a modest increase in MTF across all spatial frequencies; exploiting TOF information resulted in additional (modest) improvements. However, all differences in the MTFs for reconstructions with and without RR and TOF remained within experimental uncertainty. This was also true for the RC values and is likely because only 2 iterations of the OSEM algorithm were used; using more iterations is expected to improve spatial resolution and quantitation accuracy but may come at the cost of increased image noise.Conclusions This framework enables quantitative and comprehensive assessment of PET/CT spatial resolution across different reconstruction algorithms and imaging tasks, and can be implemented using standard image quality phantoms. Investigation of penalized reconstruction algorithms and the relationships between spatial resolution, image contrast, and image noise is ongoing. Since spatial resolution affects quantitative accuracy, this approach provides a segmentation-independent method for identifying algorithms that will produce the highest accuracy. Additionally, when combined with image-noise metrics, this approach could be used to standardize PET/CT image quality in multi-center clinical trials.}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/57/supplement_2/1940}, eprint = {https://jnm.snmjournals.org/content}, journal = {Journal of Nuclear Medicine} }