Resting-State Functional Magnetic Resonance Imaging of the Human Brainstem and Cervical Spinal Cord
Resting-state functional magnetic resonance imaging (rs-fMRI) has been used to map extensive networks within the cortex, but its use to study resting-state connectivity in the brainstem (BS) and spinal cord (SC) has been limited. This is because of the challenge associated with using fMRI in this region. One reason for this is the small cross sectional area of the SC. The proximity of the BS and SC to the heart and lungs increases the amount of noise arising from physiological sources. The noise has a larger effect on the MR data acquired from the BS and SC than the cortex. Therefore, having a larger source of noise makes it harder to identify the source and separate from the data. The studies presented in this thesis try to tackle this problem. Data for both studies in chapters two and three, were obtained from 16 healthy participants. The study in chapter two used axially acquired images at the level of the periaqueductal gray, the rostral ventro-medial medulla and the sixth cervical SC segment. The study presented in chapter three used sagittal slice images from the thalamus to the T1/T2 vertebral disk spanning 9 sagittal slices centered on the SC. The results of the study in chapter two identify specific sources of noise and quantify their contribution to the overall signal variance. The largest contributor to the signal variance was bulk motion (19%). Cardiac-related motion accounted for 14% of the signal variance followed by non-specific signal variations detected in white matter (10%), respiratory-related motion (2.6%), and end-tidal CO2 variations (0.7%). Significant left-right connectivity was detected in the dorsal horns and ventral horns of the SC after the noise was removed from the data. The study presented in the chapter three saw extensive connectivity within and across the BS and SC. Resting-state networks were observed between the BS and SC which involved primarily dorsal or ventral SC regions, and included specific anatomical regions within the BS as well. These results demonstrate the presence of resting-state connectivity within the BS and SC and are an important step towards developing rs-fMRI in this region.
URI for this recordhttp://hdl.handle.net/1974/15902
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