Multimodal applications of functional near-infrared spectroscopy

Tiina Näsi

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    With the population of the world getting older, the number of patients suffering from brain disorders is increasing. To tackle this challenge, safe, affordable, and easy-to-use methods for screening, diagnosing, and treating these disorders are needed. Functional near-infrared spectroscopy (fNIRS), an optical method for monitoring blood circulatory changes related to brain activity, fulfills these requirements. However, it is still not in wide clinical use­—partly because the measured physiological phenomena are complex and therefore sometimes difficult to interpret. This Thesis demonstrates that fNIRS can be combined with other modalities to investigate phenomena that cannot be studied with separate recordings. Such multimodal measurements aid in characterizing and understanding physiological artifacts in fNIRS signals, and they can be used in various clinical applications. This Thesis focuses on the applications of monitoring sleep and characterizing effects of transcranial magnetic stimulation (TMS), a technique for diagnosing and treating various neurological and psychiatric disorders. The results in sleep monitoring show that circulatory changes recorded with fNIRS complement previous knowledge of the electrophysiological characteristics of sleep. Furthermore, some observations may be related to harmful effects of sleep disorders on the vasculature. In awake subjects, the developed multimodal method can serve in investigating neurovascular coupling. Altogether, the work contributes to methodology and analysis techniques for monitoring circulation during sleep and establishes a solid base for applying them in clinical settings. The results in recording effects of TMS suggest that TMS-evoked fNIRS responses should be interpreted with caution; fNIRS signals contain physiological artifacts during TMS. Furthermore, fNIRS signals are affected by changes in scalp circulation during mental and physical stress, but this problem can be alleviated by separating the changes in scalp and brain circulation with diffuse optical tomography. The reported observations increase the understanding about the origin of fNIRS signals, contribute to techniques for removing artifacts, and thus advance the usability of fNIRS in monitoring effects of TMS or sleep.
    Translated title of the contributionToiminnallinen lähi-infrapunaspektroskopia monimenetelmäsovelluksissa
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Ilmoniemi, Risto, Supervising Professor
    • Ilmoniemi, Risto, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-5069-0
    Electronic ISBNs978-952-60-5070-6
    Publication statusPublished - 2013
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • near-infrared spectroscopy
    • diffuse optical tomography
    • transcranial magnetic stimulation
    • sleep
    • hemodynamic monitoring
    • physiological artifact

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