Raquel Valdés Cristerna - Academia.edu (original) (raw)

Papers by Raquel Valdés Cristerna

Ciencia - Academia Mexicana de Ciencias, 2002

Frontiers in Neurology

COVID-19 may increase the risk of acute ischemic stroke that can cause a loss of upper limb funct... more COVID-19 may increase the risk of acute ischemic stroke that can cause a loss of upper limb function, even in patients with low risk factors. However, only individual cases have been reported assessing different degrees of hospitalization outcomes. Therefore, outpatient recovery profiles during rehabilitation interventions are needed to better understand neuroplasticity mechanisms required for upper limb motor recovery. Here, we report the progression of physiological and clinical outcomes during upper limb rehabilitation of a 41-year-old patient, without any stroke risk factors, which presented a stroke on the same day as being diagnosed with COVID-19. The patient, who presented hemiparesis with incomplete motor recovery after conventional treatment, participated in a clinical trial consisting of an experimental brain-computer interface (BCI) therapy focused on upper limb rehabilitation during the chronic stage of stroke. Clinical and physiological features were measured throughout...

2022 Global Medical Engineering Physics Exchanges/ Pan American Health Care Exchanges (GMEPE/PAHCE)

The aim of this project is to develop a computerized system, called VentriQuant, for the quantita... more The aim of this project is to develop a computerized system, called VentriQuant, for the quantitative assessment of cardiac dyssynchrony (CDS). Impaired CDS is one of the main clinical indicators of the evolution of heart failure (HF) syndrome, considered the leading cause of death worldwide. The VentriQuant system incorporates quantification methods that have already been validated and used in the clinic, but also aims to incorporate new algorithms and indices in order to expand its use and evaluate its clinical utility. The VentriQuant system is expected to provide support by expanding access to cardiovascular imaging specialists to new tools and methods of analysis, and to generate the possibility of remote diagnosis and increased reproducibility in quantitative and objective assessment, with a direct impact on better diagnosis and follow-up of HF patients. The VentriQuant system is easy to use, its operation is simple and intuitive, and it displays important information for the evaluation of the contraction synchrony of both ventricles.

Journal of Neural Engineering, 2021

Objective.This study assesses upper limb recovery prognosis after stroke with solely physiologica... more Objective.This study assesses upper limb recovery prognosis after stroke with solely physiological information, which can provide an objective estimation of recovery.Approach.Clinical recovery was forecasted using EEG-derived Event-Related Desynchronization/Synchronization and coherence, in addition to Transcranial Magnetic Stimulation elicited motor-evoked potentials and upper limb grip and pinch strength. A Regression Tree Ensemble predicted clinical recovery of a stroke database (n= 10) measured after a two-month intervention with the Fugl-Meyer Assessment for the Upper Extremity (FMA-UE) and the Action Research Arm Test (ARAT).Main results.There were no significant differences between predicted and actual outcomes with FMA-UE (p= 0.29) and ARAT (p= 0.5). Median prediction error for FMA-UE and ARAT were of 0.3 (IQR = 6.2) and 3.4 (IQR = 9.4) points, respectively. Predictions with the most pronounced errors were due to an underestimation of high upper limb recovery. The best featu...

2017 IEEE International Conference on Systems, Man, and Cybernetics (SMC), 2017

Electroencephalography (EEG) is the most frequently used technique to monitor functional activity... more Electroencephalography (EEG) is the most frequently used technique to monitor functional activity of the brain. It has been widely employed in brain-computer interfaces based on the detection of P300 potentials. However, the P300 waves often contain physiological and non-physiological artifacts such as steady state visually evoked potential, power line or environment noise. The aim of this work is to eliminate undesirable periodic independent components from EEG, in order to enhance the P300 wave. The proposed method combines independent component analysis with a suitable selection of the most representative P300 components according to power features estimated from time measures using Parseval's theorem. The results show statistical differences (p<0.001) between the power spectral densities of raw and restored EEG, after Parseval-based component elimination. Additionally, the comparison of P300 latencies between raw and filtered EEG, showed statistical differences (p<0.001). Our findings suggest that this method can be helpful to eliminate undesirable components with significant narrow-band power, in order to preserve information required to enhance the P300 potential.

17th International Symposium on Medical Information Processing and Analysis, 2021

Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No.03CH37439)

The most frequently used imaging procedure for the diagnosis of diverse neurological illnesses is... more The most frequently used imaging procedure for the diagnosis of diverse neurological illnesses is magnetic resonance. Improved benefits have been obtained from multi-spectral information under this imaging modality. Both supervised and unsupervised segmentation procedures have been reported for this kind of images, many of which require a preprocessing stage for contrast adjustment within the intensity space. This paper presents a

Journal of Electronic Imaging, 2003

... artifacts. For the case of active surface modeling, the reference segmentation method used wa... more ... artifacts. For the case of active surface modeling, the reference segmentation method used was the one proposed by Cohen and Cohen, which was applied to both CATstacks. Table summarizes the corresponding error measures. ...

Medical & Biological Engineering & Computing, 2021

Transcranial magnetic stimulation (TMS) allows the assessment of stroke patients' cortical ex... more Transcranial magnetic stimulation (TMS) allows the assessment of stroke patients' cortical excitability and corticospinal tract integrity, which provide information regarding motor function recovery. However, the extraction of features from motor-evoked potentials (MEP) elicited by TMS, such as amplitude and latency, is performed manually, increasing variability due to observer-dependent subjectivity. Therefore, an automatic methodology could improve MEP analysis, especially in stroke, which increases the difficulty of manual MEP measurements due to brain lesions. A methodology based on time-frequency features of stroke patients' MEPs that allows to automatically select and extract MEP amplitude and latency is proposed. The method was validated using manual measurements, performed by three experts, computed from patients' affected and unaffected hemispheres. Results showed a coincidence of 58.3 to 80% between automatic and manual MEP selection. There were no significant differences between the amplitudes and latencies computed by two of the experts with those obtained with the automatic method, for most comparisons. The median relative error of amplitudes and latencies computed by the automatic method was 5% and 23%, respectively. Therefore, the proposed method has the potential to reduce processing time and improve the computation of MEP features, by eliminating observer-dependent variability due to the subjectivity of manual measurements.

STEAM-H: Science, Technology, Engineering, Agriculture, Mathematics & Health, 2020

Heart failure is defined as a syndrome characterized by a remodeling in the cardiac muscle struct... more Heart failure is defined as a syndrome characterized by a remodeling in the cardiac muscle structure that diminishes the strength and synchrony of contractions, leading the subject to a functional capacity deterioration that progressively triggers fatal clinical outcomes. There are specific pharmacological therapies to reduce failure progression. However, once the symptoms have developed, it is necessary to combine different treatments to alleviate them and to improve the quality of life. The most advanced therapies in recent years utilize implantable electronic devices known as cardiac resynchronizers. Cardiac resynchronization therapy has proven to be highly beneficial to patients with severe heart failure, because it reduces the number of hospitalizations, increases exercise resistance, and improves left ventricle systolic function and patient’s survival. Nonetheless, 20–30% of patients do not respond to this therapy, thus requiring reliable techniques to predict the probability of a successful outcome in a case-by-case basis. This chapter analyzes several methods that have been proposed to achieve this goal.

Transcranial magnetic stimulation can be used as a tool for assessment of corticospinal tract int... more Transcranial magnetic stimulation can be used as a tool for assessment of corticospinal tract integrity by extracting features from elicited motor evoked potentials (MEPs). However, the selection of MEPs from recordings that present them, and the computation of amplitude and latency are usually performed manually. A methodology based on computing summed power calculated by means of the Discrete Fourier Transform in 10-ms windows was used for automatization of this process and compared to manual measurements. Results showed that MEP selection coincided in 69% of cases, and amplitude and latency had average differences of 7% between methods. Therefore, automatization of MEP computations is feasible using frequency-based features.

Diverse neuro-psychological tasks have been designed for expressing intention mostly in the form ... more Diverse neuro-psychological tasks have been designed for expressing intention mostly in the form of evoked potentials uncovered by time-coherent averaging, spectral analysis, or other digital signal processing techniques. Among others, the elicitation of the so-called P300 event-related potential has been found reproducible, reliable and suitable for environment control and communication applications that are not time-critical. The nature, elicitation and exploitation of the P300 potential for BCI is the subject of this chapter, organized in three sections: P300 event-related potential, P300 for spelling task and P300 for non-spelling tasks.

Computational and Mathematical Methods in Medicine, 2018

P300 spellers have been widely modified to implement nonspelling tasks. In this work, we propose ... more P300 spellers have been widely modified to implement nonspelling tasks. In this work, we propose a “scenario” stimulation screen that is a P300 speller variation to command a wheelchair. Our approach utilized a stimulation screen with an image background (scenario snapshot for a wheelchair) and stimulation markers arranged asymmetrically over relevant landmarks, such as suitable paths, doors, windows, and wall signs. Other scenario stimulation screen features were green/blue stimulation marker color scheme, variable Interstimulus Interval, single marker stimulus mode, and optimized stimulus sequence generator. Eighteen able-bodied subjects participated in the experiment; 78% had no experience in BCI usage. A waveform feature analysis and a Mann–WhitneyUtest performed over the pairs of target and nontarget coherent averages confirmed that 94% of the subjects elicit P300 (p<.005) on this modified stimulator. Least Absolute Shrinkage and Selection Operator optimization and Linear Di...

Computational Intelligence and Neuroscience, 2018

Most EEG phase synchrony measures are of bivariate nature. Those that are multivariate focus on p... more Most EEG phase synchrony measures are of bivariate nature. Those that are multivariate focus on producing global indices of the synchronization state of the system. Thus, better descriptions of spatial and temporal local interactions are still in demand. A framework for characterization of phase synchrony relationships between multivariate neural time series is presented, applied either in a single epoch or over an intertrial assessment, relying on a proposed clustering algorithm, termed Multivariate Time Series Clustering by Phase Synchrony, which generates fuzzy clusters for each multivalued time sample and thereupon obtains hard clusters according to a circular variance threshold; such cluster modes are then depicted in Time-Frequency-Topography representations of synchrony state beyond mere global indices. EEG signals from P300 Speller sessions of four subjects were analyzed, obtaining useful insights of synchrony patterns related to the ERP and even revealing steady-state artif...

Neural Plasticity, 2019

Stroke is a leading cause of motor disability worldwide. Upper limb rehabilitation is particularl... more Stroke is a leading cause of motor disability worldwide. Upper limb rehabilitation is particularly challenging since approximately 35% of patients recover significant hand function after 6 months of the stroke’s onset. Therefore, new therapies, especially those based on brain-computer interfaces (BCI) and robotic assistive devices, are currently under research. Electroencephalography (EEG) acquired brain rhythms in alpha and beta bands, during motor tasks, such as motor imagery/intention (MI), could provide insight of motor-related neural plasticity occurring during a BCI intervention. Hence, a longitudinal analysis of subacute stroke patients’ brain rhythms during a BCI coupled to robotic device intervention was performed in this study. Data of 9 stroke patients were acquired across 12 sessions of the BCI intervention. Alpha and beta event-related desynchronization/synchronization (ERD/ERS) trends across sessions and their association with time since stroke onset and clinical upper...

14th International Symposium on Medical Information Processing and Analysis, 2018

Ultrasound (US) images are necessary in obstetrics because they provide the most important clinic... more Ultrasound (US) images are necessary in obstetrics because they provide the most important clinical parameters for fetal health assessment during the second and third trimesters: head circumference, biparietal diameter, abdominal circumference and femur length. These fetometric indices are helpful for gestational age and fetal weight estimation; they are also helpful for obstetricians to diagnose fetal development abnormalities. However, these indices are obtained manually, which provokes high intra and interobserver variability and lack of repeatability. A fully automatic method to segment and measure femur’s length is presented in this paper. The proposed methodology incorporates texture information and introduces a novel curvature analysis to adequately detect the femur. It consists on pre–processing US images with an anisotropic diffusion filter, followed by morphological operations and thresholding to isolate femur–candidate regions. A normalized metric composed of intensity, length, centroid position and entropy is assigned to each region in order to select the most probable candidate to be femur. This selected region is afterwards thinned to a one–pixel line, whose curvature is analyzed with an angle threshold criterion to accurately locate femur’s extrema. The method was tested on 64 US images (20 taken on the second and 44 on the third trimester of pregnancy); a correlation coefficient of 0.984 and an error of 1.016±2.764 mm were achieved between expert–obtained manual measures and automatically calculated indices. Results are consistent, outperform those reported previously by other authors and show a high correlation with measures obtained by experts; therefore, the developed method is suitable to be adapted for clinical use.

Computational and Mathematical Methods in Medicine, 2017

Cardiac resynchronization therapy (CRT) improves functional classification among patients with le... more Cardiac resynchronization therapy (CRT) improves functional classification among patients with left ventricle malfunction and ventricular electric conduction disorders. However, a high percentage of subjects under CRT (20%–30%) do not show any improvement. Nonetheless the presence of mechanical contraction dyssynchrony in ventricles has been proposed as an indicator of CRT response. This work proposes an automated classification model of severity in ventricular contraction dyssynchrony. The model includes clinical data such as left ventricular ejection fraction (LVEF), QRS and P-R intervals, and the 3 most significant factors extracted from the factor analysis of dynamic structures applied to a set of equilibrium radionuclide angiography images representing the mechanical behavior of cardiac contraction. A control group of 33 normal volunteers (28±5years, LVEF of59.7%±5.8%) and a HF group of 42 subjects (53.12±15.05years, LVEF < 35%) were studied. The proposed classifiers had hit...

12th International Symposium on Medical Information Processing and Analysis, 2017

A previously introduced variation of a conventional P300 speller, consisting on a modifiable imag... more A previously introduced variation of a conventional P300 speller, consisting on a modifiable image background and asymmetrically arranged stimulation markers for controlling wheelchair navigation, was used in this study. Five commonly used classifiers for solving P300 speller-like tasks, namely, Linear-SVM, RBF-SVM, LASSO-LDA, Shrinkage-LDA and SWLDA, were designed and trained and their performances contrasted, seeking the classifier with highest performance on our proposed screen. 19 able-bodied subjects participated in this study. The highest median sensitivity and specificity were respectively 1.00 (IQR = 0.61-1.00) and 1.00 (IQR = 0.96-1.00), which were obtained with the LASSO approach. These performances are suitable for the planned application and they are comparable with the conventional P300 speller performances reported, despite of our speller variation. Friedman tests showed that there are no statistical differences on the sensitivity and specificity performances among the five classifiers evaluated. However, the customized selection of the classifier approach improves the sensitivity by 66.7% in some cases.