back (Japanese ver.)

Schedule

Speaker

Fiber-specific white matter alterations in early-stage Parkinson’s disease: a fixel-based analysis

Tremor dominant (TD) and postural instability and gait disorder (PIGD) are two main motor subtypes of Parkinson’s disease (PD), where TD-PD is known to have a slower disease progression. Although PD has generally been associated with reduced fractional anisotropy (FA), a recent study reported higher FA in the white matter in early-stage TD-PD patients compared to controls and PIGD-PD patients. However, the tensor model cannot resolve multiple fiber orientations in a voxel, potentially leading to unreliable interpretation of the tensor-wise measures. For instance, increased FA might reflect increased white matter integrity or a selective loss of specific fiber directions in crossing fiber regions. Fixel-based analysis (FBA) is a framework that facilitates the measurement of specific fiber-bundle populations within a voxel or so-called “fixel”. In brief, FBA utilizes the fiber orientation distributions estimated using constrained spherical deconvolution techniques, which enables the measurement of microstructural fiber density (FD), macrostructural fiber bundle cross-section (FC), and a combination of FD and FC (FDC). In the present study, we implemented FBA in early-stage (Hoehn and Yahr scale 1 or 2) nonmedicated TD-PD patients. As results, we observed white matter neural compensation mechanisms within the bilateral corticospinal tracts as indicated by increased FC and FDC.

Depth dependence of high-frequency stimulus-driven BOLD oscillations in the human primary somatosensory and motor cortex

Functional magnetic resonance imaging is a prevalent neuroscientific tool that leverages hemodynamic signal changes to make inferences about neuronal activation. However, viewed through the lens of hemodynamics, such inferences are blurred in time and space. The sluggish hemodynamic response suppresses high frequency blood oxygenation dependent signal (BOLD) changes and the drainage of deoxygenated blood complicates precise localization. Here we investigated high frequency stimulus driven BOLD oscillations as a function of cortical depth. Stimuli up to 0.50 Hz were used to evoke activation in the somatosensory- (S1) and primary motor-cortex (M1), known for their cyto- and angio-architectural differences. Our results reveal reduced BOLD responses near the pail surface at high frequencies, which could be related to the elastic properties of large draining veins or mixing of out of phase signal contributions. In addition, we observed evidence of destructive interference of BOLD response from different level of cortical depth, especially in M1, which may hint at angio-architectural differences between S1 and M1.  

Transmembrane water transport MRI: from technical development to brain applications

The transport of water molecules across membranes is an important physiological process in the brain and plays essential roles in tissue and cell balancing, metabolism, and functions. Abnormal transmembrane water transport has also observed in stroke, Alzheimer's disease, glioma and many other brain diseases. In the past 5 years, Dr. Bai’s lab at Zhejiang University has conducted in-depth research on developing quantitative MRI methods of the key transmembrane water transport processes in the brain and the related clinical/application transfer. In this talk, Dr. Bai will share their most recent results, which include: 1) The development of MRI technology for quantitative imaging of Aquaporin 4 (AQP4) in glioma and the clinical value of AQP4 imaging in predicting the treatment responses of radio/chemical therapy in glioma; 2) The development of contrast-agent-fee MRI method for blood-brain barrier (BBB) assessment and its clinical value in detecting the BBB impairment in Alzheimer's disease; 3)The discovery of the transmembrane water transport as a promising fMRI biomarker to detect neuronal activity specifically.