Assessment of the benefits and drawbacks of high resolution PET for the imaging of cancer in the head

UoM administered thesis: Phd

  • Authors:
  • Jose Anton-Rodriguez

Abstract

Introduction: In Positron Emission Tomography (PET), the use of resolution modelling (RM) in iterative image reconstruction enables the modelling of aspects of detection which result in mispositioning of measured data and the subsequent blurring of reconstructed images. RM reconstruction can result in significant improvements in spatial resolution, voxel variance and count rate bias and could be a software alternative to detection hardware that is able to achieve higher resolution. Such hardware typically consists of small scintillation crystals, small bore diameters and depth of interaction discrimination, such as for the High Resolution Research Tomograph (HRRT, Siemens), which used a double crystal layer phoswich detector system. However, RM implementation comes with penalties such as slower rates of convergence, potentially higher region of interest variance and Gibbs artefacts. Methods: Assessment of the benefits and drawbacks of RM was done in the first part of this thesis together with the measurement and modelling of spatially varying resolution kernels for different scanner configurations and PET isotopes for the HRRT. It is also unclear as to whether high resolution scanning offers significant advantages over clinical PET-CT scanners for applications in the head. Through direct comparison to our HRRT, we explore whether there are significant advantages of high resolution scanning for an application in the head over clinical PET-CT. For this comparison our Biograph TruePoint TrueV (Siemens) optimised for whole body imaging was used and a novel clinical study using both scanners was set where we scanned Neurofibromatosis 2 (NF2) patients with vestibular schwannomas (VS) using [18F]fluorodeoxyglucose (FDG) and [18F]fluorothymidine (FLT). The clinical objective was to assess if uptake within VS of FLT and FDG could be measured and whether this uptake was predictive of tumour growth. Finally an assessment of the feasibility and impact of reducing the original injected activities in our clinical study was performed using bootstrapping resampling. Conclusions: RM provides greater but additive improvements in image resolution compared to DOI on the HRRT. Isotope specific image based RM could be estimated from published positron range distributions and measurements using fluorine-18. With the clinical project, uptake of FDG and FLT within the VS lesions was observed, these uptake values were correlated to each other, and high uptake was predictive of tumour growth with little differences in predictive power between FLT and FDG. Although there were benefits of the HRRT for imaging small lesions, in our clinical application there was little difference between the two scanners to discriminate lesion growth. Using the PET-CT scanner data and knowledge of lesion location, doses could be reduced to 5-10% without any significant loss of ability to discriminate lesion growth.

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Original languageEnglish
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Award date1 Aug 2018