Hello!! I am a Biomedical Engineer working on medical imaging.
Currently, I have two lines of research: optimization of super-resolution ultrasound imaging and liver magnetic resonance spectroscopy.
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Woking at: Universidad de Santiago de Chile (USACH)
News
Just got excelent news today: I have an academic position as assistent profesor (YEAHHH!!) starting on august 2nd, 2022 :)
Today I presented my work at the iHealth symposium (27-07-22). It was a very interesting symposium that showed the importance of IA in health. Click HERE to see on twitter.
Abstract accepted for IUS 2022 (Venice, October 10-13)
Presenting my work at ISMRM 2022: A clustering method to classify stages of NALFD based on the metabolites results obtained in two mouse models with MRS (London, May 2022)
Just received an e-mail that my paper "Characterization of direct localization algorithms for ultrasound super-resolution imaging in a multi-bubble environment: A numerical and experimental study" has been accepted for publication in IEEE Access (April 27, 2022)
My preferred papers
My preferred papers
ABSTRACT
Localization plays a significant role in the production of ultrasound localization microscopy images. For instance, detecting more microbubbles reduces the time of acquisition, while localizing them more accurately improves the resolution of the images. Previous approaches to compare the multiple localization algorithms rely on numerical simulation of a single steady microbubble, with or without modeling its nonlinear response. In real-life situations, vessels have a nonconstant velocity profile, which creates relative movement, producing dynamically overlapped microbubbles even at low concentrations. These complexities deteriorate the behavior of the localization algorithms. To incorporate these effects on the characterization of the localization methods, we designed a virtual medium containing four microtubes of different inner diameters, where single-pixel microbubbles were allowed to flow within each microtube with a parabolic velocity profile. A finite difference method was used to simulate the propagation of ultrasound waves to obtain B-mode images that fed four direct microbubbles localization algorithms (i.e., weighted centroid, 2D-spline interpolation, parabolic fitting, and onset detection). The performance of these methods was quantified using the number of microbubbles detected, the microbubbles distribution, the full width at half maximum, the maximum velocity, and the computational time as metrics. Our simulation results suggest that 2D-spline and paraboloid fitting were the best methods, detecting 100% of the microbubbles with an error in their distribution of 249 and 244 microbubbles, respectively. Both methods with a computational time cost of 18% and 7% lower than weighted centroid, respectively. We also present an experimental comparison of these localization methods, finding results similar to the numerical ones.
Xavier, A., Alarcón, H., & Espíndola, D. (2022). Characterization of Direct Localization Algorithms for Ultrasound Super-Resolution Imaging in a Multibubble Environment: A Numerical and Experimental Study. IEEE Access, 10, 49991-49999.
Xavier, A., Zacconi, F., Santana-Romo, F., Eykyn, T. R., Lavin, B., Phinikaridou, A., ... & Andia, M. E. (2021). Assessment of hepatic fatty acids during non-alcoholic steatohepatitis progression using magnetic resonance spectroscopy. Annals of Hepatology, 25, 100358.
ABSTRACT
Non-alcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver abnormalities including steatosis, steatohepatitis, fibrosis, and cirrhosis. Liver biopsy remains the gold standard method to determine the disease stage in NAFLD but is an invasive and risky procedure. Studies have previously reported that changes in intrahepatic fatty acids (FA) composition are related to the progression of NAFLD, mainly in its early stages. The aim of this study was to characterize the liver FA composition in mice fed a Choline-deficient L-amino-defined (CDAA) diet at different stages of NAFLD using magnetic resonance spectroscopy (MRS). We used in-vivo MRS to perform a longitudinal characterization of hepatic FA changes in NAFLD mice for 10 weeks. We validated our findings with ex-vivo MRS, gas chromatography-mass spectrometry and histology. In-vivo and ex-vivo results showed that livers from CDAA-fed mice exhibit a significant increase in liver FA content as well as a change in FA composition compared with control mice. After 4 weeks of CDAA diet, a decrease in polyunsaturated and an increase in monounsaturated FA were observed. These changes were associated with the appearance of early stages of steatohepatitis, confirmed by histology (NAFLD Activity Score (NAS) = 4.5). After 10 weeks of CDAA-diet, the liver FA composition remained stable while the NAS increased further to 6 showing a combination of early and late stages of steatohepatitis. Our results suggest that monitoring lipid composition in addition to total water/fat with MRS may yield additional insights that can be translated for non-invasive stratification of high-risk NAFLD patients.
ABSTRACT
Single‐voxel ¹H MRS in body applications often suffers from respiratory and other motion induced phase and frequency shifts, which lead to incoherent averaging and hence to suboptimal results. Here we show the application of metabolite cycling (MC) for liver STEAM‐localized ¹H MRS on a 7 T parallel transmit system, using eight transmit‐receive fractionated dipole antennas with 16 additional, integrated receive loops. MC‐STEAM measurements were made in six healthy, lean subjects and compared with STEAM measurements using VAPOR water suppression. Measurements were performed during free breathing and during synchronized breathing, for which the subjects did breathe in between the MRS acquisitions. Both intra‐session repeatability and inter‐session reproducibility of liver lipid quantification with MC‐STEAM and VAPOR‐STEAM were determined. The preserved water signal in MC‐STEAM allowed for robust phase and frequency correction of individual acquisitions before averaging, which resulted in in vivo liver spectra that were of equal quality when measurements were made with free breathing or synchronized breathing. Intra‐session repeatability and inter‐session reproducibility of liver lipid quantification were better for MC‐STEAM than for VAPOR‐STEAM. This may also be explained by the more robust phase and frequency correction of the individual MC‐STEAM acquisitions as compared with the VAPOR‐STEAM acquisitions, for which the low‐signal‐to‐noise ratio lipid signals had to be used for the corrections. Non‐water‐suppressed MC‐STEAM on a 7 T system with parallel transmit is a promising approach for ¹H MRS applications in the body that are affected by motion, such as in the liver, and yields better repeatability and reproducibility compared with water‐suppressed measurements.
Xavier, A., Arteaga de Castro, C., Andia, M. E., Luijten, P. R., Klomp, D. W., Fillmer, A., & Prompers, J. J. (2020). Metabolite cycled liver 1H MRS on a 7 T parallel transmit system. NMR in Biomedicine, 33(8), e4343.
Xavier, A. et al.(2019). Intrahepatic fatty acids composition as a biomarker of NAFLD progression from steatosis to NASH by using 1 H-MRS. RSC advances, 9(72), 42132-42139.
ABSTRACT
Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world and it is becoming one of the most frequent cause of liver transplantation. Unfortunately, the only available method that can reliably determine the stage of this disease is liver biopsy, however, it is invasive and risky for patients.
The purpose of this study is to investigate changes in the intracellular composition of the liver fatty acids during the progression of the NAFLD in a mouse model fed with Western diet, with the aim of identify non-invasive biomarkers of NAFLD progression based in 1H-MRS.
Our results showed that the intracellular liver fatty acid composition changes as NAFLD progresses from simple steatosis to steatohepatitis (NASH). Using principal component analysis with a clustering method, it was possible to identify the three most relevant clinical groups: normal, steatosis and NASH by using 1H-MRS. These results showed a good agreement with the results obtained by GC-MS and histology.
Our results suggest that it would be possible to detect the progression of simple steatosis to NASH using 1H-MRS, that has the potential to be used routinely in clinical application for screening high-risk patients.
You can contact me: aline.xavier@usach.cl
You can contact me: aline.xavier@usach.cl
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