Biology subjects

Möller, H. E.

Publications and source records attributed to Möller, H. E..

4 recordsLinked to original sources

bioRxiv2022

High-Resolution Magnetization-Transfer Imaging of Post-Mortem Marmoset Brain: Comparisons with Relaxometry and Histology

Cell membranes and macromolecules or paramagnetic compounds interact with water proton spins, which modulates magnetic resonance imaging (MRI) contrast providing information on tissue composition. For a further investigation, quantitative magnetization transfer (qMT) parameters (at 3T), including the ratio of the macromolecular and water proton pools, [F], and the exchange-rate constant as well as the (observed) longitudinal and the effective transverse relaxation rates (at 3T and 7T), [Formula] and [Formula] respectively, were measured at high spatial resolution (200 m) in a slice of fixed marmoset brain and compared to histology results obtained with Gallyas myelin stain and Perls iron stain. [Formula] and [Formula] were linearly correlated with the iron content for the entire slice, whereas distinct differences were obtained between gray and white matter for correlations of relaxometry and qMT parameters with myelin content. The combined results suggest that the macromolecular pool interacting with water consists of myelin and (less efficient) non-myelin contributions. Despite strong correlation of [F] and [Formula] none of these parameters was uniquely specific to myelination. Due to additional sensitivity to iron stores, [Formula] and [Formula] were more sensitive for depicting microstructural differences between cortical layers than [F]. HighlightsO_LIMRI (200m) is correlated with myelin and iron histology in fixed marmoset brain. C_LIO_LIDetailed z-spectra are employed for precise magnetization-transfer (MT) measurements. C_LIO_LILongitudinal and effective transverse relaxation rates depend linearly on tissue iron. C_LIO_LILongitudinal relaxation and MT are not uniquely specific to myelin. C_LIO_LIMyelin and non-myelin macromolecules impact water relaxation and MT contrast. C_LI

neuroscience↗

bioRxiv2022

Multi-Echo Investigations of Positive and Negative CBF and Concomitant BOLD Changes

Unlike the positive blood oxygenation level-dependent (BOLD) response (PBR), commonly taken as an indication of an activated brain region, the physiological origin of negative BOLD signal changes (i.e. a negative BOLD response, NBR), also referred to as deactivation is still being debated. In this work, an attempt was made to gain a better understanding of the underlying mechanism by obtaining a comprehensive measure of the contributing cerebral blood flow (CBF) and its relationship to the NBR in the human visual cortex, in comparison to a simultaneously induced PBR in surrounding visual regions. To overcome the low signal-to-noise ratio (SNR) of CBF measurements, a newly developed multi-echo version of a center-out echo planar-imaging (EPI) readout was employed with pseudo-continuous arterial spin labeling (pCASL). It achieved very short echo and inter-echo times and facilitated a simultaneous detection of functional CBF and BOLD changes at 3 T with improved sensitivity. Evaluations of the absolute and relative changes of CBF and the effective transverse relaxation rate, [Formula], the coupling ratios, and their dependence on CBF at rest, CBFrest, indicated differences between activated and deactivated regions. Analysis of the shape of the respective functional responses also revealed faster negative responses with more pronounced post-stimulus transients. Resulting differences in the flow-metabolism coupling ratios were further examined for potential distinctions in the underlying neuronal contributions. HighlightsO_LIIntroduction of multi-echo center-out EPI for investigating concomitant CBF and BOLD changes in regions of positive (PBR) and negative BOLD response (NBR). C_LIO_LI{Delta}CBF timecourses closely follow those of [Formula] with negative signals exhibiting faster responses and more pronounced post-stimulus transients. C_LIO_LIDecreases in CBF appear to warrant a larger change in NBR than CBF increases in PBR regions. C_LIO_LIConsideration of baseline CBF values is important in comparisons of relative coupling ratios ({delta}sBOLD/{delta}cbf) between brain regions. C_LIO_LIDiscussion of potential excitatory and inhibitory neuronal feed forward control of CBF and CMRO2 in PBR and NBR. C_LI

neuroscience↗

bioRxiv2022

Improving fMRI in Parkinson's Disease by Accounting for Brain Region-Specific Activity Patterns

In functional magnetic imaging (fMRI) in Parkinsons disease (PD), a paradigm consisting of blocks of finger tapping and rest along with a corresponding general linear model (GLM) is often used to assess motor activity. However, this method has three limitations: (i) Due to the strong magnetic field and the confined environment of the cylindrical bore, it is troublesome to accurately monitor motor output and, therefore, variability in the performed movement is typically ignored. (ii) Given the loss of dopaminergic neurons and ongoing compensatory brain mechanisms, motor control is abnormal in PD. Therefore, modeling of patients tapping with a constant amplitude (using a boxcar function) and the expected Parkinsonian motor output are prone to mismatch. (iii) The motor loop involves structures with distinct hemodynamic responses, for which only one type of modeling (e.g., modeling the whole block of finger tapping) may not suffice to capture these structures temporal activation. The first two limitations call for considering results from online recordings of the real motor output that may lead to significant sensitivity improvements. This was shown in previous work using a non-magnetic glove to capture details of the patients finger movements in a so-called kinematic approach. For the third limitation, modeling motion initiation instead of the whole tapping block has been suggested to account for different temporal activation signatures of the motor loops structures. In the present study we propose improvements to the GLM as a tool to study motor disorders. For this, we test the robustness of the kinematic approach in an expanded cohort (n=31), apply more conservative statistics than in previous work, and evaluate the benefits of an event-related model function. Our findings suggest that the integration of the kinematic approach offers a general improvement in detecting activations in subcortical structures, such as the basal ganglia. Additionally, modeling motion initiation using an event-related design yielded superior performance in capturing medication-related effects in the putamen. Our results may guide adaptations in analysis strategies for functional motor studies related to PD and also in more general applications.

neuroscience↗

bioRxiv2020

Increased Sensitivity and Signal-to-Noise Ratio in Diffusion-Weighted MRI using Multi-Echo Acquisitions

Post-mortem diffusion MRI (dMRI) enables acquisitions of structural imaging data with otherwise unreachable resolutions - at the expense of longer scanning times. These data are typically acquired using highly segmented image acquisition strategies, thereby resulting in an incomplete signal decay before the MRI encoding continues. Especially in dMRI, with low signal intensities and lengthy contrast encoding, such temporal inefficiency translates into reduced image quality and longer scanning times. This study introduces Multi Echo (ME) acquisitions to dMRI on a human MRI system - a time-efficient approach, which increases SNR (Signal-to-Noise Ratio) and reduces noise bias for dMRI images. The benefit of the introduced ME dMRI method was validated using numerical Monte Carlo simulations and showcased on a post-mortem brain of a wild chimpanzee. The proposed Maximum Likelihood Estimation echo combination results in an optimal SNR without detectable signal bias. The combined strategy comes at a small price in scanning time (here 30% additional) and leads to a substantial SNR increase (here up to 1.9x which is equivalent to 3.6 averages) and a general reduction of the noise bias.

neuroscience↗