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Simulating effects of brain atrophy in longitudinal PET imaging with an anthropomorphic brain phantom
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Diagnostic Radiology. Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI). Umeå University, Faculty of Social Sciences, Centre for Demographic and Ageing Research (CEDAR). (Umeå Center for Functional Brain Imaging)ORCID iD: 0000-0001-6169-5836
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics. Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI).ORCID iD: 0000-0002-3731-3612
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Diagnostic Radiology. Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI).ORCID iD: 000-0001-5227-8117
Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI). Umeå University, Faculty of Social Sciences, Centre for Demographic and Ageing Research (CEDAR). Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital, Hvidovre, Denmark.ORCID iD: 0000-0002-4458-6475
2017 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 13, 5213-5227 p.Article in journal (Refereed) Published
Abstract [en]

In longitudinal positron emission tomography (PET), the presence of volumetric changes over time can lead to an overestimation or underestimation of the true changes in the quantified PET signal due to the partial volume effect (PVE) introduced by the limited spatial resolution of existing PET cameras and reconstruction algorithms. Here, a 3D-printed anthropomorphic brain phantom with attachable striata in three sizes was designed to enable controlled volumetric changes. Using a method to eliminate the non-radioactive plastic wall, and manipulating BP levels by adding different number of events from list-mode acquisitions, we investigated the artificial volume dependence of BP due to PVE, and potential bias arising from varying BP. Comparing multiple reconstruction algorithms we found that a high-resolution ordered- subsets maximization algorithm with spatially variant point-spread function resolution modeling provided the most accurate data. For striatum, the BP changed by 0.08% for every 1% volume change, but for smaller volumes such as the posterior caudate the artificial change in BP was as high as 0.7% per 1% volume change. A simple gross correction for striatal volume is unsatisfactory, as the amplitude of the PVE on the BP differs depending on where in the striatum the change occurred. Therefore, to correctly interpret age-related longitudinal changes in the BP, we must account for volumetric changes also within a structure, rather than across the whole volume. The present 3D-printing technology, combined with the wall removal method, can be implemented to gain knowledge about the predictable bias introduced by the PVE differences in uptake regions of varying shape.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2017. Vol. 62, no 13, 5213-5227 p.
Keyword [en]
longitudinal, PET, partial volume effect, brain phantom, dopamine
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
radiofysik
Identifiers
URN: urn:nbn:se:umu:diva-136030DOI: 10.1088/1361-6560/aa6e1bISI: 000402879700001PubMedID: 28561014OAI: oai:DiVA.org:umu-136030DiVA: diva2:1108839
Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2017-09-06Bibliographically approved
In thesis
1. Aerobic fitness and healthy brain aging: cognition, brain structure, and dopamine
Open this publication in new window or tab >>Aerobic fitness and healthy brain aging: cognition, brain structure, and dopamine
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Aerobisk träning och hjärnans hälsosamma åldrande : kognition, hjärnstruktur och dopamin
Abstract [en]

Background: Performing aerobic exercise and maintaining high levels of aerobic fitness may have positive effects on both brain structure and function in older adults. Despite decades of research however, there is still a rather poor understanding of the neurocognitive mechanisms explaining the positive effects of aerobic exercise on cognition. Changes in prefrontal gray matter as well as dopaminergic neurotransmission in striatum are both candidate neurocognitive mechanisms. The main aims of this thesis are: 1. To investigate the effects of aerobic exercise and fitness on cognition and magnetic resonance imaging (MRI) derived gray matter volumes using data from a 6 month physical exercise intervention in older adults (Study I). 2. To simulate the effect of atrophy in longitudinal positron emission tomography (PET) which could pose a challenge to interpreting changes in longitudinal PET imaging (Study II). 3. To study the influence of aerobic exercise and fitness on the dopamine D2-receptor (D2R) system in striatum using [11C]raclopride PET as a potential mechanism for improved cognition (Study III).

Results: In Study I, aerobic exercise was found to improve cognitive performance in a broad, rather than domain-specific sense. Moreover, aerobic fitness was related to prefrontal cortical thickness, and improved aerobic fitness over 6 months was related to increased hippocampal volume. In Study II, we identified areas in the striatum vulnerable to the effect of shrinkage, which should be considered in longitudinal PET imaging. Finally, in Study III, the effect of being aerobically fit, and improving fitness levels was found to impact dopaminergic neurotransmission in the striatum, which in turn mediated fitness-induced improvements in working memory updating performance.

Conclusion: The findings in this thesis provide novel evidence regarding the neurocognitive mechanisms of aerobic exercise-induced improvements in cognition, and impacts the interpretation of longitudinal PET imaging. Performing aerobic exercise and staying aerobically fit at an older age have positive effects on cognition and brain systems important for memory and cognition. Specifically, fitness-induced changes to the dopaminergic system stands out as one novel neurocognitive mechanism explaining the positive effects of aerobic fitness on working-memory performance in healthy older adults.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2017. 81 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1908
Keyword
Aerobic exercise, VO2, working memory, executive function, freesurfer, striatum, dopamine, D2-receptors, [11C]raclopride
National Category
Neurosciences Sport and Fitness Sciences
Identifiers
urn:nbn:se:umu:diva-139056 (URN)978-91-7601-753-1 (ISBN)
Public defence
2017-09-29, Sal 933, Building 3B, Norrland University Hospital, Umeå, 09:35 (English)
Opponent
Supervisors
Available from: 2017-09-08 Created: 2017-09-06 Last updated: 2017-09-26Bibliographically approved

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Jonasson, LarsAxelsson, JanRiklund, KatrineBoraxbekk, Carl-Johan
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