Functional Activities Detected in the Olfactory Bulb and Associated Olfactory Regions in the Human Brain Using T2-Prepared BOLD Functional MRI at 7T

Abstract

Olfaction is a fundamental sense that plays a vital role in daily life in humans, and can be altered in neuropsychiatric and neurodegenerative diseases. Blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) using conventional echo-planar-imaging (EPI) based sequences can be challenging in brain regions important for olfactory processing, such as the olfactory bulb (OB) and orbitofrontal cortex, mainly due to the signal dropout and distortion artifacts caused by large susceptibility effects from the sinonasal cavity and temporal bone. To date, few studies have demonstrated successful fMRI in the OB in humans. T2-prepared (T2prep) BOLD fMRI is an alternative approach developed especially for performing fMRI in regions affected by large susceptibility artifacts. The purpose of this technical study is to evaluate T2prep BOLD fMRI for olfactory functional experiments in humans. Olfactory fMRI scans were performed on 7T in 14 healthy participants. T2prep BOLD showed greater sensitivity than GRE EPI BOLD in the OB, orbitofrontal cortex and the temporal pole. Functional activation was detected using T2prep BOLD in the OB and associated olfactory regions. Habituation effects and a bi-phasic pattern of fMRI signal changes during olfactory stimulation were observed in all regions. Both positively and negatively activated regions were observed during olfactory stimulation. These signal characteristics are generally consistent with literature and showed a good intra-subject reproducibility comparable to previous human BOLD fMRI studies. In conclusion, the methodology demonstrated in this study holds promise for future olfactory fMRI studies in the OB and other brain regions that suffer from large susceptibility artifacts.

Evaluation of T2-prepared blood oxygenation level dependent functional magnetic resonance imaging with an event-related task: Hemodynamic response function and reproducibility

“…The spatial locations of activated clusters in the visual cortex showed a good reproducibility with Dice coefficients ranging from 0.76 to 0.80. The fitted HRF parameters showed comparable reproducibility (ICC) to BOLD fMRI measures reported in our previous 3T (Landman et al, 2011) and 7T studies (Miao et al, 2021). No significant difference was found in the reproducibility measures among the three fMRI methods.…”

“…The definition of ICC in a textbook (Rosner, 2011) was adopted: σ A 2 /(σ A 2 + σ 2 ), where σ A 2 and σ 2 are the between-subject and within-subject variance, respectively. The procedure described in the paragraph is identical to that in our previous reproducibility studies (Landman et al, 2011;Miao et al, 2021).…”

“…SE EPI has been the regular pulse sequence adopted for SE-based fMRI. More recently, a whole-brain T2prepared (T2prep) BOLD fMRI approach (Hua et al, 2014(Hua et al, , 2017Miao et al, 2020Miao et al, , 2021 was proposed, in which a double refocusing T2 preparation module was applied for generating the T2-weighted SE BOLD contrast, followed by a single-shot 3D fast GRE (also known as turbo field echo or TFE) readout. The T2prep BOLD fMRI approach was originally developed on 7T (Hua et al, 2014) in order to mitigate susceptibility artifacts in brain regions near air-filled cavities typically observed in EPI based fMRI images especially on 7T.…”

Olfactory system measurements in COVID-19: a systematic review and meta-analysis

“…After the exclusion of two studies for which full-text manuscripts were not available, 41 possibly relevant articles were further evaluated thoroughly based upon full-text manuscripts leading to the exclusion of 31 other studies for the following reasons: irrelevant to the subject ( n = 4), non-original studies ( n = 8), case reports ( n = 5), not reporting the desired variables ( n = 6), and lack of a control group ( n = 8). Discrepancies occurred during the study selection process for six studies [ 27 – 32 ]. After discussing with a third reviewer, one of these studies was included [ 31 ], and the rest were excluded.…”

Brain Activation During Processing of Depression Emotion in College Students With Premenstrual Syndrome in China: Preliminary Findings

“…Although PMS pathogenesis remains unclear, the application of brain imaging technology has facilitated its intrinsic neural mechanism of neuropsychiatric disorders ( 12 ). Among them, blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) has had a tremendous influence on human neuroscience over the last two decades ( 13 ). Qing Liu demonstrated decreased connectivity in the middle frontal gyrus (MFG) and parahippocampal gyrus (PHG) in PMS patients, as well as increased connectivity in the left medial/superior temporal gyri (MTG/STG) and precentral gyrus within the default mode network (DMN) using fMRI ( 14 ).…”