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Olfactory fMRI: Implications of Stimulation Length and Repetition Time
Linköping University, Department of Medical and Health Sciences, Division of Radiological Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
Linköping University, Center for Medical Image Science and Visualization (CMIV).
Affidea CDRC Ctr Diagnost Radiol Carouge SA, Switzerland; Uppsala Univ, Sweden.
Linköping University, Department of Clinical and Experimental Medicine, Division of Neuro and Inflammation Science. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Local Health Care Services in Central Östergötland, Department of Neurology.
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2018 (English)In: Chemical Senses, ISSN 0379-864X, E-ISSN 1464-3553, Vol. 43, no 6, p. 389-398Article in journal (Refereed) Published
Abstract [en]

Studying olfaction with functional magnetic resonance imaging (fMRI) poses various methodological challenges. This study aimed to investigate the effects of stimulation length and repetition time (TR) on the activation pattern of 4 olfactory brain regions: the anterior and the posterior piriform cortex, the orbitofrontal cortex, and the insula. Twenty-two healthy participants with normal olfaction were examined with fMRI, with 2 stimulation lengths (6 s and 15 s) and 2 TRs (0.901 s and 1.34 s). Data were analyzed using General Linear Model (GLM), Tensorial Independent Component Analysis (TICA), and by plotting the event-related time course of brain activation in the 4 olfactory regions of interest. The statistical analysis of the time courses revealed that short TR was associated with more pronounced signal increase and short stimulation was associated with shorter time to peak signal. Additionally, both long stimulation and short TR were associated with oscillatory time courses, whereas both short stimulation and short TR resulted in more typical time courses. GLM analysis showed that the combination of short stimulation and short TR could result in visually larger activation within these olfactory areas. TICA validated that the tested paradigm was spatially and temporally associated with a functionally connected network that included all 4 olfactory regions. In conclusion, the combination of short stimulation and short TR is associated with higher signal increase and shorter time to peak, making it more amenable to standard GLM-type analyses than long stimulation and long TR, and it should, thus, be preferable for olfactory fMRI.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS , 2018. Vol. 43, no 6, p. 389-398
Keywords [en]
fMRI; olfaction; smell; repetition time
National Category
Neurosciences
Identifiers
URN: urn:nbn:se:liu:diva-149862DOI: 10.1093/chemse/bjy025ISI: 000438293600001PubMedID: 29726890OAI: oai:DiVA.org:liu-149862DiVA, id: diva2:1236436
Note

Funding Agencies|Swedish Parkinson Foundation, Linkoping University Hospital Research Fund; ALF Grants from Region Ostergotland

Available from: 2018-08-02 Created: 2018-08-02 Last updated: 2019-04-17
In thesis
1. Imaging Studies of Olfaction in Health and Parkinsonism
Open this publication in new window or tab >>Imaging Studies of Olfaction in Health and Parkinsonism
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Olfactory loss is a common non-motor symptom of Parkinson’s disease (PD), often preceding the cardinal motor symptoms of the disease. The aim of this thesis was to: (a) evaluate whether olfactory examination can increase diagnostic accuracy, and (b) study the structural and functional neural basis of olfactory dysfunction in PD with different applications of Magnetic Resonance Imaging (MRI).

Paper I was a comparison of the diagnostic accuracy between a simple smell identification test and DaTSCAN Single Photon Emission Computerized Tomography (SPECT), a nuclear medicine tomographic imaging technique that is commonly used in patients with suspected parkinsonism. The results indicate that smell test is inferior to DaTSCAN SPECT, but the combination of these two methods can lead to improved diagnostic accuracy.

Paper II showed that diffusion MRI could detect discrete microstructural changes in the white matter of brain areas that participate in higher order olfactory neurotransmission, whereas MRI with Magnetization Transfer contrast could not.

Paper III was a methodological study on how two different acquisition parameters can affect the activation pattern of olfactory brain areas, as observed with functional MRI (fMRI). The results indicate that brief olfactory stimulation and fast sampling rate should be preferred on olfactory fMRI studies.

Paper IV used olfactory fMRI and resting-state fMRI in order to elucidate potentially altered activation patterns and functional connectivity within olfactory brain areas, between PD patients and healthy controls. Olfactory fMRI showed that olfactory impairment in PD is associated with significantly lower recruitment of the olfactory network. Resting-state fMRI did not detect any significant changes in the functional connectivity within the olfactory network of PD patients.

In conclusion, the included studies provide evidence of: (a) disease-related structural and functional changes in olfactory brain areas, and (b) beneficial addition of olfactory tests in the clinical work-up of patients with parkinsonism.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. p. 72
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1661
National Category
Radiology, Nuclear Medicine and Medical Imaging Neurology Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:liu:diva-154919 (URN)10.3384/diss.diva-154919 (DOI)9789176851357 (ISBN)
Public defence
2019-04-05, Granitsalen, Campus US, Linköping, 09:00 (Swedish)
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Available from: 2019-03-05 Created: 2019-03-05 Last updated: 2019-03-05Bibliographically approved

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Division of Radiological SciencesFaculty of Medicine and Health SciencesDepartment of Radiology in LinköpingCenter for Medical Image Science and Visualization (CMIV)Division of Neuro and Inflammation ScienceDepartment of NeurologyDivision of Cardiovascular MedicineDepartment of Clinical Physiology in Linköping
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