A bstractIncorporation of a resolution model during statistical image reconstruction often produces images of improved resolution and signal-to-noise ratio (SNR). A novel and practical methodology to rapidly and accurately determine the overall emission and detection blurring component of the system matrix using a printed point source array within a custom-made Perspex phantom is presented. The array was scanned at different positions and orientations within the field of view (FOV) to examine the feasibility of extrapolating the measured point source blurring to other locations in the FOV and the robustness of measurements from a single point source array scan. We measured the spatially-variant image based blurring on two PET/CT scanners, the B-Hi-Rez and the TruePoint TrueV. These measured spatiallyvariant kernels and the spatially-invariant kernel at the FOV centre were then incorporated within an ordinary Poisson ordered subsets expectation maximization (OP-OSEM) algorithm and compared to resolution modelling. Comparisons were based on a point source array, the NEMA IEC image quality phantom, the Cologne resolution phantom and 2 clinical studies (carbon-11 labelled anti-sense oligonucleotide [ 11 C]-ASO and fluorine-18 labelled fluoro-L-thymidine [ 18 F]-FLT). Robust and accurate measurements of spatially-variant image blurring were successfully obtained from a single scan. Spatially-variant resolution modelling resulted in notable resolution improvements away from the centre of the FOV. Comparison between spatiallyvariant image-space methods and the projection-space approach (the first such report, using a range of studies for two distinct PET/CT systems) demonstrated very similar performance with our image-based implementation producing slightly better contrast recovery (CR) for the same level of image roughness (IR). These results demonstrate that image-based resolution modelling within reconstruction is a valid alternative to projection based modelling, and that, when using the proposed practical methodology, the necessary resolution measurements can be obtained from a single scan. This approach avoids the relatively time-consuming and involved procedures previously proposed in the literature.

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Positron emission tomography (PET) is a highly quantitative imaging modality that can probe a number of functional and biological processes, depending on the radiolabelled tracer used. Static imaging, followed by analysis using semi-quantitative indices, such as the standardised uptake value, is used in the majority of clinical assessments in which PET has a role. However, considerably more information can be extracted from dynamic image acquisition protocols, followed by application of appropriate image reconstruction and tracer kinetic modelling techniques, but the latter approaches have mainly been restricted to drug development and clinical research applications due to their complexity in terms of both protocol design and parameter estimation methodology. To make dynamic imaging more feasible and valuable in routine clinical imaging, novel research outcomes are needed. Research areas include noninvasive input function extraction, protocol design for wholebody imaging application, and kinetic parameter estimation methods using spatiotemporal (4D) image reconstruction algorithms. Furthermore, with the advent of sequential and simultaneous PET/magnetic resonance (MR) data acquisition, strategies for obtaining synergistic benefits in kinetic modelling are emerging and potentially enhancing the role and clinical importance of PET/MR imaging. In this article, we review and discuss various advances in kinetic modelling both from a protocol design and a methodological development perspective. Moreover, we discuss future trends and potential outcomes, which could facilitate more routine use of tracer kinetic modelling techniques in clinical practice.