Temporal Multivariate Pattern Analysis (tMVPA): a single trial approach exploring the temporal dynamics of the BOLD signal

fMRI provides spatial resolution that is unmatched by non-invasive neuroimaging techniques. Its temporal dynamics however are typically neglected due to the sluggishness of the hemodynamic signal. We present temporal multivariate pattern analysis (tMVPA), a method for investigating the temporal evolution of neural representations in fMRI data, computed on single-trial BOLD time-courses, leveraging both spatial and temporal components of the fMRI signal. We implemented an expanding sliding window approach that allows identifying the time-window of an effect. We demonstrate that tMVPA can successfully detect condition-specific multivariate modulations over time, in the absence of mean BOLD amplitude differences. Using Monte-Carlo simulations and synthetic data, we quantified family-wise error rate (FWER) and statistical power. Both at the group and single-subject levels, FWER was either at or significantly below 5%. We reached the desired power with 18 subjects and 12 trials for the group level, and with 14 trials in the single-subject scenario. We compare the tMVPA statistical evaluation to that of a linear support vector machine (SVM). SVM outperformed tMVPA with large N and trial numbers. Conversely, tMVPA, leveraging on single trials analyses, outperformed SVM in low N and trials and in a single-subject scenario. Recent evidence suggesting that the BOLD signal carries finer-grained temporal information than previously thought, advocates the need for analytical tools, such as tMVPA, tailored to investigate BOLD temporal dynamics. The comparable performance between tMVPA and SVM, a powerful and reliable tool for fMRI, supports the validity of our technique

A Combined, Fine-Tune B0 Shimming and RF Receive Array using Transmission Line Resonators for Functional Imaging of the Human Temporal Lobe at 7 Tesla

University of Minnesota M.S. thesis. August 2020. Major: Biomedical Engineering. Advisor: Gregory Metzger. 1 computer file (PDF); 62 pages.Functional MRI has become a one of the most powerful tools for non-invasive investigation of brain function. Increases in the magnetic field strength of these systems have yielded improvements in SNR that enable the investigation of fine-scale neural systems. However, with this increase in field strength comes an increase in artifacts arising from magnetic field homogeneity. Specifically, artifacts which occur near air-tissue boundaries (e.g., ear canals and frontal sinuses) become dramatically worse with higher field strengths, limiting the ability to derive useful information from brain areas adjacent to these regions. In recent years, a number of attempts have been made to develop technology which can help mitigate the artifacts arising in these areas. Such approaches make use of either fully external shim arrays, or shimming circuity integrated within standard array technology. Here, the use of transmission line resonators (TLRs) is proposed for use as a combined receive-only/B0 shimming element for imaging and local shimming of the ventral temporal lobe. Simulations were conducted and initial evaluations showed both good bench and in-scanner performance of prototypes. Further design refinements led to the development of an array structure and proposed shimming routine. The resulting TLR coil array structure was integrated into a larger 32 channel RF head array, and associated hardware for selectively driving the shim elements was built. Preliminary results demonstrated strong convergence with simulated shim performance, suggesting the viability of this array design and for the use of TLRs in this application

Theoretical study of a membrane reactor for the water gas shift reaction under nonisothermal conditions

A simulation of a membrane reactor for the water gas shift reaction is carried out by means of a 1D pseudo-homogeneous nonisothermal mathematical model. The composite membrane consists of a dense layer of Pd (selective to H2) supported over a porous ceramic layer. The effect of temperature, overall heat-transfer coefficient, and mode of operation on the membrane reactor performance and stability are analyzed, and the results obtained are compared with those corresponding to a reactor with no hydrogen permeation. © 2009 American Institute of Chemical Engineers.Fil: Adrover, María Esperanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Lopez, Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Borio, Daniel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Pedernera, Marisa Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentin