Browsing by Author "Milovic, Carlos"

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    Quantitative Susceptibility Mapping MRI in Deep-Brain Nuclei in First-Episode Psychosis
    (2023) García Saborit, Marisleydis; Jara Vallejos, Alejandro Antonio; Muñoz Camelo, Néstor Andrés; Milovic, Carlos; Tepper, Angeles; Alliende Correa, Luz María; Mena, Carlos; Iruretagoyena Bruce, Bárbara Arantzazu; Ramírez Mahaluf, Juan Pablo; Diaz, Camila; Nachar, Rubén; Castaneda, Carmen Paz; Gonzalez, Alfonso; Undurraga, Juan; Crossley, Nicolás; Tejos Núñez, Cristián Andrés
    Background Psychosis is related to neurochemical changes in deep-brain nuclei, particularly suggesting dopamine dysfunctions. We used an magnetic resonance imaging-based technique called quantitative susceptibility mapping (QSM) to study these regions in psychosis. QSM quantifies magnetic susceptibility in the brain, which is associated with iron concentrations. Since iron is a cofactor in dopamine pathways and co-localizes with inhibitory neurons, differences in QSM could reflect changes in these processes. Methods We scanned 83 patients with first-episode psychosis and 64 healthy subjects. We reassessed 22 patients and 21 control subjects after 3 months. Mean susceptibility was measured in 6 deep-brain nuclei. Using linear mixed models, we analyzed the effect of case-control differences, region, age, gender, volume, framewise displacement (FD), treatment duration, dose, laterality, session, and psychotic symptoms on QSM. Results Patients showed a significant susceptibility reduction in the putamen and globus pallidus externa (GPe). Patients also showed a significant R2* reduction in GPe. Age, gender, FD, session, group, and region are significant predictor variables for QSM. Dose, treatment duration, and volume were not predictor variables of QSM. Conclusions Reduction in QSM and R2* suggests a decreased iron concentration in the GPe of patients. Susceptibility reduction in putamen cannot be associated with iron changes. Since changes observed in putamen and GPe were not associated with symptoms, dose, and treatment duration, we hypothesize that susceptibility may be a trait marker rather than a state marker, but this must be verified with long-term studies.
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    Toward a realistic in silico abdominal phantom for QSM
    (2023) Silva, Javier; Milovic, Carlos; Lambert Villanueva, Mathias Gabriel; Montalba Zalaquett, Cristián Andrés; Arrieta Pellegrin, Cristóbal Ignacio; Irarrázaval Mena Pablo; Uribe Arancibia, Sergio Andres; Tejos Nuñez, Cristián Andrés
    Purpose: QSM outside the brain has recently gained interest, particularly in the abdominal region. However, the absence of reliable ground truths makes difficult to assess reconstruction algorithms, whose quality is already compromised by additional signal contributions from fat, gases, and different kinds of motion. This work presents a realistic in silico phantom for the development, evaluation and comparison of abdominal QSM reconstruction algorithms. Methods: Synthetic susceptibility and R∗2𝑅2* maps were generated by segmenting and postprocessing the abdominal 3T MRI data from a healthy volunteer. Susceptibility and R∗2𝑅2* values in different tissues/organs were assigned according to literature and experimental values and were also provided with realistic textures. The signal was simulated using as input the synthetic QSM and R∗2𝑅2* maps and fat contributions. Three susceptibility scenarios and two acquisition protocols were simulated to compare different reconstruction algorithms. Results: QSM reconstructions show that the phantom allows to identify the main strengths and limitations of the acquisition approaches and reconstruction algorithms, such as in-phase acquisitions, water-fat separation methods, and QSM dipole inversion algorithms. Conclusion: The phantom showed its potential as a ground truth to evaluate and compare reconstruction pipelines and algorithms. The publicly available source code, designed in a modular framework, allows users to easily modify the susceptibility, R∗2𝑅2* and TEs, and thus creates different abdominal scenarios.