Nuestros investigadores

María Asunción Fernández Seara

Clínica Universidad de Navarra. Clínica Universidad de Navarra
Ingeniería Biomédica
Escuela de Ingenieros (TECNUN). Universidad de Navarra
Líneas de investigación
Desarrollo de nuevas técnicas de imagen utilizando la resonancia magnética y su traslación a la aplicación clínica, Imagen funcional, imagen de perfusión, imagen estructural, Analisis de imagen médica, Aplicación de técnicas de neuroimagen en enfermedades neurodegenerativas (Parkinson, Alzheimer)
Índice H
24, (WoS, 21/07/2017)

Publicaciones científicas más recientes (desde 2010)

Autores: Garcia-Fernandez, N; Slon, M. F.; et al.
ISSN 1053-1807  2017 
Purpose To investigate whether arterial spin labeling (ASL) MRI could detect renal hemodynamic impairment in diabetes mellitus (DM) along different stages of chronic kidney disease (CKD). Materials and Methods Three Tesla (3T) ASL-MRI was performed to evaluate renal blood flow (RBF) in 91 subjects (46 healthy volunteers and 45 type 2 diabetic patients). Patients were classified according to their estimated glomerular filtration rate (eGFR) as group I (eGFR > 60 mL/min/1.73 m2), group II (60 >= eGFR > 30 mL/min/1.73¿m2), or group III (eGFR<= 30 mL/min/1.73 m2), to determine differences depending on renal function. Studies were performed at 3T using a 12-channel flexible body array combined with the spine array coil as receiver. Results A 28% reduction in cortical RBF was seen in diabetics in comparison with healthy controls (185.79 [54.60] versus 258.83 [37.96] mL/min/100 g, P< 3 × 10-6). Differences were also seen between controls and diabetic patients despite normal eGFR and absence of overt albuminuria (RBF [mL/min/100 g]: controls=258.83 [37.96], group I=208.89 [58.83], P = 0.0018; eGFR [mL/min/1.73 m2]: controls = 95.50 [12.60], group I = 82.00 [20.76], P > 0.05; albumin-creatinine ratio [mg/g]: controls = 3.50 [4.45], group I = 17.50 [21.20], P > 0.05). A marked decrease in RBF was noted a long with progression of diabetic nephropathy (DN) through the five stages of CKD (Chi2 = 43.58; P = 1.85 × 10-9). Strong correlation (r = 0.62; P = 4 × 10-10) was obtained between RBF
Autores: Vidorreta, M.; Wang, Z.; Chang, Y.L.V. ; et al.
Revista: PLOS ONE
ISSN 1932-6203  Vol. 12  Nº 8  2017  págs. e0183762
Arterial Spin Labeled (ASL) perfusion MRI enables non-invasive, quantitative measurements of tissue perfusion, and has a broad range of applications including brain functional imaging. However, ASL suffers from low signal-to-noise ratio (SNR), limiting image resolution. Acquisitions using 3D readouts are optimal for background-suppression of static signals, but can be SAR intensive and typically suffer from through-plane blurring. In this study, we investigated the use of accelerated 3D readouts to obtain whole-brain, high-SNR ASL perfusion maps and reduce SAR deposition. Parallel imaging was implemented along the partition-encoding direction in a pseudo-continuous ASL sequence with background-suppression and 3D RARE Stack-Of-Spirals readout, and its performance was evaluated in three small cohorts. First, both non-accelerated and two-fold accelerated single-shot versions of the sequence were evaluated in healthy volunteers during a motor-photic task, and the performance was compared in terms of temporal SNR, GM-WM contrast, and statistical significance of the detected activation. Secondly, single-shot 1D-accelerated imaging was compared to a two-shot accelerated version to assess benefits of SNR and spatial resolution for applications in which temporal resolution is not paramount. Third, the efficacy of this approach in clinical populations was assessed by applying the single-shot 1D-accelerated version to a larger cohort of elderly volunteers. Accelerated data demonstrated the ability to detect functional activation at the subject level, including cerebellar activity, without loss in the perfusion signal temporal stability and the statistical power of the activations. The use of acceleration also resulted in increased GM-WM contrast, likely due to reduced through-plane partial volume effects, that were further attenuated with the use of two-shot readouts. In a clinical cohort, image quality remained excellent, and expected effects of age and sex on cerebral blood flow could be detected. The sequence is freely available upon request for academic use and could benefit a broad range of cognitive and clinical neuroscience research.
Autores: García de Eulate, María Reyes; Goñi, I.; Galiano, A.; et al.
ISSN 1387-2877  Vol. 58  Nº 2  2017  págs. 585 - 595
There is increasing evidence of a vascular contribution to Alzheimer's disease (AD). In some cases, prior work suggests that chronic brain hypoperfusion could play a prime pathogenic role contributing to the accumulation of amyloid-ß,while other studies favor the hypothesis that vascular dysfunction and amyloid pathology are independent, although synergistic, mechanisms contributing to cognitive impairment. Vascular dysfunction can be evaluated by assessing cerebral blood flow impairment. Phase contrast velocity mapping by MRI offers a non-invasive means of quantifying the total inflow of blood to the brain. This quantitative parameter could be a sensitive indicator of vascular disease at early stages of AD. In this work, phase contrast MRI was used to evaluate cerebral hemodynamics in patients with subjective memory complaints, amnestic mild cognitive impairment, and mild to moderate AD, and compare them with control subjects. Results showed that blood flow and velocity were decreased in the patients with cognitive dysfunction and the decrease correlated with the degree of cognitive impairment as assessed by means of neuropsychological tests. Total cerebral blood flow measurements were clearly reduced in AD patients, but more importantly appeared to be sensitive enough to distinguish between healthy subjects and those with mild cognitive impairment. A quantitative measurement of total brain blood flow could potentially predict vascular dysfunction and compromised brain perfu
Autores: Song, H. ; Ruan, D. ; Liu, W.; et al.
ISSN 0094-2405  Vol. 44  Nº 3  2017  págs. 962 - 973
PURPOSE: Respiratory motion prediction using an artificial neural network (ANN) was integrated with pseudocontinuous arterial spin labeling (pCASL) MRI to allow free-breathing perfusion measurements in the kidney. In this study, we evaluated the performance of the ANN to accurately predict the location of the kidneys during image acquisition. METHODS: A pencil-beam navigator was integrated with a pCASL sequence to measure lung/diaphragm motion during ANN training and the pCASL transit delay. The ANN algorithm ran concurrently in the background to predict organ location during the 0.7 s 15-slice acquisition based on the navigator data. The predictions were supplied to the pulse sequence to prospectively adjust the axial slice acquisition to match the predicted organ location. Additional navigators were acquired immediately after the multislice acquisition to assess the performance and accuracy of the ANN. The technique was tested in 8 healthy volunteers. RESULTS: The root mean square error (RMSE) and mean absolute error (MAE) for the 8 volunteers were 1.91 ± 0.17 mm and 1.43 ± 0.17 mm, respectively, for the ANN. The RMSE increased with transit delay. The MAE typically increased from the first to last prediction in the image acquisition. The overshoot was 23.58% ± 3.05% using the target prediction accuracy of ± 1 mm. CONCLUSION: Respiratory motion prediction with prospective motion correction was successfully demonstrated for free-breathing perfusion MRI of the kidney. The method serves as an alternative to multiple breathholds and requires minimal effort on the part of the patient. This article is protected by copyright. All rights reserved.
Autores: Aznárez-Sanado, Maite; Luis, Elkin ; et al.
ISSN 1931-7557  Vol. 11  Nº 4  2017  págs. 986 - 997
Previous research on motor sequence learning (MSL) in the elderly has focused mainly on unilateral tasks, even though bilateral coordination might be impaired in this age group. In this fMRI study, 28 right-handed elderly subjects were recruited. The paradigm consisted of a Novel and a simple Control sequence executed with the right (R), left (L) and both hands (B). Behavioral performance (Accuracy[AC], Inter-tap Interval[ITI]) and associated brain activity were assessed during early learning. Behavioral performance in the Novel task was similar between unilateral conditions whereas in the bimanual condition more errors and slower motor execution were observed. Brain activity increases during learning showed differences between Conditions: R showed increased activity in pre-SMA, basal ganglia and left hippocampus while B showed activity increments mainly in posterior parietal cortex and cerebellum. L did not show any activity modulation during learning. Performance correlates for AC (related to spatial success) and ITI (related to accurate timing) shared a cortico-basal-cerebellar network. However, it was found that the ITI regressor presented additional significant correlations with activity in SMA and basal ganglia in R. The AC regressor showed additional significant correlations with activity in more extended thalamic and cerebellar areas in B. The present findings suggest that, behaviorally, the spatial and temporal components of MSL are impaired in elderly subjects when using both hands. Additionally, differential brain activity patterns were found across hand modalities. The results obtained reveal the existence of a highly specialized network in the dominant hand and identify areas specifically involved in bimanual coordination.
Autores: Fernández-Seara, M. A.; Rodgers, Z. B. ; Englund, E. K. ; et al.
ISSN 1053-8119  Vol. 142  2016  págs. 474 - 482
Calibrated fMRI techniques estimate task-induced changes in the cerebral metabolic rate of oxygen (CMRO2) based on simultaneous measurements of cerebral blood flow (CBF) and blood-oxygen-level-dependent (BOLD) signal changes evoked by stimulation. To determine the calibration factor M (corresponding to the maximum possible BOLD signal increase), BOLD signal and CBF are measured in response to a gas breathing challenge (usually CO2 or O2). Here we describe an ASL dual-acquisition sequence that combines a background-suppressed 3D-GRASE readout with 2D multi-slice EPI. The concatenation of these two imaging sequences allowed separate optimization of the acquisition for CBF and BOLD data. The dual-acquisition sequence was validated by comparison to an ASL sequence with a dual-echo EPI readout, using a visual fMRI paradigm. Results showed a 3-fold increase in temporal signal-to-noise ratio (tSNR) of the ASL time-series data while BOLD tSNR was similar to that obtained with the dual-echo sequence. The longer TR of the proposed dual-acquisition sequence, however, resulted in slightly lower T-scores (by 30%) in the BOLD activation maps. Further, the potential of the dual-acquisition sequence for M-mapping on the basis of a hypercapnia gas breathing challenge and for quantification of CMRO2 changes in response to a motor activation task was assessed. In five subjects, an average gray matter M-value of 8.71±1.03 and fractional changes of CMRO2 of 12.5±5% were found. The new sequence remedies the deficiencies of prior combined BOLD-ASL acquisition strategies by substantially enhancing perfusion tSNR, which is essential for accurate BOLD calibration.
Autores: Martínez, Martín; Valencia, Miguel; Vidorreta, Marta; et al.
ISSN 1065-9471  Vol. 37  Nº 5  2016  págs. 1722 - 1737
The central nervous system has the ability to adapt our locomotor pattern to produce a wide range of gait modalities and velocities. In reacting to external pacing stimuli, deviations from an individual preferred cadence provoke a concurrent decrease in accuracy that suggests the existence of a trade-off between frequency and precision; a compromise that could result from the specialization within the control centers of locomotion to ensure a stable transition and optimal adaptation to changing environment. Here, we explore the neural correlates of such adaptive mechanisms by visually guiding a group of healthy subjects to follow three comfortable stepping frequencies while simultaneously recording their BOLD responses and lower limb kinematics with the use of a custom-built treadmill device. In following the visual stimuli, subjects adopt a common pattern of symmetric and anti-phase movements across pace conditions. However, when increasing the stimulus frequency, an improvement in motor performance (precision and stability) was found, which suggests a change in the control mode from reactive to predictive schemes. Brain activity patterns showed similar BOLD responses across pace conditions though significant differences were observed in parietal and cerebellar regions. Neural correlates of stepping precision were found in the insula, cerebellum, dorsolateral pons and inferior olivary nucleus, whereas neural correlates of stepping stability were found in a distributed network, suggesting a transition in the control strategy across the stimulated range of frequencies: from unstable/reactive at lower paces (i.e., stepping stability managed by subcortical regions) to stable/predictive at higher paces (i.e., stability managed by cortical regions).
Autores: Pan, X.; Qian, T. ; Fernández-Seara, M. A.; et al.
ISSN 1053-1807  Vol. 43  Nº 5  2016  págs. 1046 - 1054
PURPOSE: To develop a free-breathing multidelay pseudocontinuous arterial spin labeling (pCASL) technique for quantitative measurement of liver perfusion of the hepatic artery and portal vein, respectively. MATERIALS AND METHODS: A navigator-gated pCASL sequence with balanced steady-state free precession (bSSFP) readout was developed and applied on five healthy young volunteers at 3T. Two labeling schemes were performed with the labeling plane applied on the descending aorta above the liver, and perpendicular to the portal vein before its entry to liver to label the hepatic artery and portal vein, respectively. For each labeling scheme, pCASL scans were performed at five or six postlabeling delays between 200 and 2000 msec or 2500 msec with an interval of 400 or 500 msec. Multidelay pCASL images were processed offline with nonrigid motion correction, outlier removal, and fitted for estimation of liver perfusion and transit time. RESULTS: Estimated liver perfusion of the hepatic artery and hepatic portal vein were 21.8¿±¿1.9 and 95.1¿±¿8.9¿mL/100g/min, with the corresponding transit time of 1227.3¿±¿355.5 and 667.2¿±¿85.0 msec, respectively. The estimated liver perfusion and transit time without motion correction were less reliable with greater residual variance compared to those processed with motion correction (P < 0.05). CONCLUSION: The liver perfusion measurement using multidelay pCASL showed good correspondence with values noted in the literature. The capability to noninvasively and selectively label the hepatic artery and portal vein is a unique strength of pCASL as compared to other liver perfusion imaging techniques, such as computed tomography perfusion and dynamic contrast-enhanced MRI.
Autores: Castellanos, G.; Fernández-Seara, M. A.; Lorenzo-Betancor, O.; et al.
ISSN 0885-3185  Vol. 30  Nº 7  2015  págs. 945-952
BACKGROUND: We aimed to analyze the diagnostic accuracy of an automated segmentation and quantification method of the SNc and locus coeruleus (LC) volumes based on neuromelanin (NM)-sensitive MRI (NM-MRI) in patients with idiopathic (iPD) and monogenic (iPD) Parkinson's disease (PD). METHODS: Thirty-six patients (23 idiopathic and 13 monogenic PARKIN or LRRK2 mutations) and 37 age-matched healthy controls underwent 3T-NM-MRI. SNc and LC volumetry were performed using fully automated multi-image atlas segmentation. The diagnostic performance to differentiate PD from controls was measured using the area under the curve (AUC) and likelihood ratios based on receiver operating characteristic (ROC) analyses. RESULTS: We found a significant reduction of SNc and LC volumes in patients, when compared to controls. ROC analysis showed better diagnostic accuracy when using SNc volume than LC volume. Significant differences between ipsilateral and contralateral SNc volumes, in relation to the more clinically affected side, were found in patients with iPD (P¿=¿0.007). Contralateral atrophy in the SNc showed the highest power to discriminate PD subjects from controls (AUC, 0.93-0.94; sensitivity, 91%-92%; specificity, 89%; positive likelihood ratio: 8.4-8.5; negative likelihood ratio: 0.09-0.1 at a single cut-off point). Interval likelihood ratios for contralateral SNc volume improved the diagnostic accuracy of volumetric measurements. CONCLUSION: SNc and LC volumetry based on NM-MRI resulting from the automated segmentation and quantification technique can yield high diagnostic accuracy for differentiating PD from health and might be an unbiased disease biomarker. © 2015 International Parkinson and Movement Disorder Society.
Autores: Fernández-Seara, M. A.; Mengual, Elisa; Vidorreta, Marta; et al.
ISSN 1065-9471  Vol. 36  Nº 5  2015  págs. 1937 - 1950
Neurophysiological changes within the cortico-basal ganglia-thalamocortical circuits appear to be a characteristic of Parkinson's disease (PD) pathophysiology. The subthalamic nucleus (STN) is one of the basal ganglia components showing pathological neural activity patterns in PD. In this study, perfusion imaging data, acquired noninvasively using arterial spin-labeled (ASL) perfusion MRI, were used to assess the resting state functional connectivity (FC) of the STN in 24 early-to-moderate PD patients and 34 age-matched healthy controls, to determine whether altered FC in the very low frequency range of the perfusion time signal occurs as a result of the disease. Our results showed that the healthy STN was functionally connected with other nuclei of the basal ganglia and the thalamus, as well as with discrete cortical areas including the insular cortex and the hippocampus. In PD patients, connectivity of the STN was increased with two cortical areas involved in motor and cognitive processes. These findings suggest that hyperconnectivity of the STN could underlie some of the motor and cognitive deficits often present even at early stages of the disease. The FC measures provided good discrimination between controls and patients, suggesting that ASL-derived FC metrics could be a putative PD biomarker.
Autores: Mutsaerts, H. J. ; Van Osch, M. J. ; Zelaya, F. O. ; et al.
ISSN 1053-8119  Vol. 113  2015  págs. 143 - 152
INTRODUCTION: A main obstacle that impedes standardized clinical and research applications of arterial spin labeling (ASL), is the substantial differences between the commercial implementations of ASL from major MRI vendors. In this study, we compare a single identical 2D gradient-echo EPI pseudo-continuous ASL (PCASL) sequence implemented on 3T scanners from three vendors (General Electric Healthcare, Philips Healthcare and Siemens Healthcare) within the same center and with the same subjects. MATERIAL AND METHODS: Fourteen healthy volunteers (50% male, age 26.4±4.7years) were scanned twice on each scanner in an interleaved manner within 3h. Because of differences in gradient and coil specifications, two separate studies were performed with slightly different sequence parameters, with one scanner used across both studies for comparison. Reproducibility was evaluated by means of quantitative cerebral blood flow (CBF) agreement and inter-session variation, both on a region-of-interest (ROI) and voxel level. In addition, a qualitative similarity comparison of the CBF maps was performed by three experienced neuro-radiologists. RESULTS: There were no CBF differences between vendors in study 1 (p>0.1), but there were CBF differences of 2-19% between vendors in study 2 (p<0.001 in most gray matter ROIs) and 10-22% difference in CBF values obtained with the same vendor between studies (p<0.001 in most gray matter ROIs). The inter-vendor inter-session variation was not significantly larger than the intra-vendor variation in all (p>0.1) but one of the ROIs (p<0.001). CONCLUSION: This study demonstrates the possibility to acquire comparable cerebral CBF maps on scanners of different vendors. Small differences in sequence parameters can have a larger effect on the reproducibility of ASL than hardware or software differences between vendors. These results suggest that researchers should strive to employ identical labeling and readout strategies in multi-center ASL studies.
Autores: Arrondo, Gonzalo; Aznárez-Sanado, Maite; Fernández-Seara, M. A.; et al.
ISSN 0924-977X  Vol. 25  Nº 6  2015  págs. 817 - 827
Studies on animals and humans have demonstrated the importance of dopamine in modulating decision-making processes. In this work, we have tested dopaminergic modulation of economic decision-making and its neural correlates by administering either placebo or metoclopramide, a dopamine D2-receptor antagonist, to healthy subjects, during a functional MRI study. The decision-making task combined probability and time delay with a fixed monetary reward. For individual behavioral characterization, we used the Probability Time Trade-off (PTT) economic model, which integrates the traditional trade-offs of reward magnitude-time and reward magnitude-probability into a single measurement, thereby quantifying the subjective value of a delayed and probabilistic outcome. A regression analysis between BOLD signal and the PTT model index permitted to identify the neural substrate encoding the subjective reward-value. Behaviorally, medication reduced the rate of temporal discounting over probability, reflected in medicated subjects being more prone to postpone the reward in order to increase the outcome probability. In addition, medicated subjects showed less activity during the task in the postcentral gyrus as well as frontomedian areas, whereas there were no differences in the ventromedial orbitofrontal cortex (VMOFC) between groups when coding the subjective value. The present study demonstrates by means of behavior and imaging that dopamine modulation alters the probability-time trade-off in human economic decision-making.
Autores: Luis, Elkin ; Arrondo, Gonzalo; Vidorreta, Marta; et al.
Revista: PLOS ONE
ISSN 1932-6203  Vol. 10  Nº 7  2015  págs. e0131536
BACKGROUND: Imaging studies help to understand the evolution of key cognitive processes related to aging, such as working memory (WM). This study aimed to test three hypotheses in older adults. First, that the brain activation pattern associated to WM processes in elderly during successful low load tasks is located in posterior sensory and associative areas; second, that the prefrontal and parietal cortex and basal ganglia should be more active during high-demand tasks; third, that cerebellar activations are related to high-demand cognitive tasks and have a specific lateralization depending on the condition. METHODS: We used a neuropsychological assessment with functional magnetic resonance imaging and a core N-back paradigm design that was maintained across the combination of four conditions of stimuli and two memory loads in a sample of twenty elderly subjects. RESULTS: During low-loads, activations were located in the visual ventral network. In high loads, there was an involvement of the basal ganglia and cerebellum in addition to the frontal and parietal cortices. Moreover, we detected an executive control role of the cerebellum in a relatively symmetric fronto-parietal network. Nevertheless, this network showed a predominantly left lateralization in parietal regions associated presumably with an overuse of verbal storage strategies. The differential activations between conditions were stimuli-dependent and were located in sensory areas. CONCLUSION: Successful WM processes in the elderly population are accompanied by an activation pattern that involves cerebellar regions working together with a fronto-parietal network.
Autores: Vidorreta, Marta; Balteau, E.; Wang, Z.; et al.
ISSN 0952-3480  Vol. 27  Nº 11  2014  págs. 1387 - 1396
Recent technical developments have significantly increased the signal-to-noise ratio (SNR) of arterial spin labeled (ASL) perfusion MRI. Despite this, typical ASL acquisitions still employ large voxel sizes. The purpose of this work was to implement and evaluate two ASL sequences optimized for whole-brain high-resolution perfusion imaging, combining pseudo-continuous ASL (pCASL), background suppression (BS) and 3D segmented readouts, with different in-plane k-space trajectories. Identical labeling and BS pulses were implemented for both sequences. Two segmented 3D readout schemes with different in-plane trajectories were compared: Cartesian (3D GRASE) and spiral (3D RARE Stack-Of-Spirals). High-resolution perfusion images (2¿×¿2¿×¿4¿mm(3) ) were acquired in 15 young healthy volunteers with the two ASL sequences at 3¿T. The quality of the perfusion maps was evaluated in terms of SNR and gray-to-white matter contrast. Point-spread-function simulations were carried out to assess the impact of readout differences on the effective resolution. The combination of pCASL, in-plane segmented 3D readouts and BS provided high-SNR high-resolution ASL perfusion images of the whole brain. Although both sequences produced excellent image quality, the 3D RARE Stack-Of-Spirals readout yielded higher temporal and spatial SNR than 3D GRASE (spatial SNR¿=¿8.5¿±¿2.8 and 3.7¿±¿1.4; temporal SNR¿=¿27.4¿±¿12.5 and 15.6¿±¿7.6, respectively) and decreased through-plane blurring due to its inherent oversampling of the central k-space region, its reduced effective TE and shorter total readout time, at the expense of a slight increase in the effective in-plane voxel size.
Autores: Martínez, Martín; et al.
ISSN 0278-0062  Vol. 33  Nº 5  2014  págs. 1044 - 1053
Repetitive and alternating lower limb movements are a specific component of human gait. Due to technical challenges, the neural mechanisms underlying such movements have not been previously studied with functional magnetic resonance imaging. In this study, we present a novel treadmill device employed to investigate the kinematics and the brain activation patterns involved in alternating and repetitive movements of the lower limbs. Once inside the scanner, 19 healthy subjects were guided by two visual cues and instructed to perform a motor task which involved repetitive and alternating movements of both lower limbs while selecting their individual comfortable amplitude on the treadmill. The device facilitated the performance of coordinated stepping while registering the concurrent lower-limb displacements, which allowed us to quantify some movement primary kinematic features such as amplitude and frequency. During stepping, significant blood oxygen level dependent signal increases were observed bilaterally in primary and secondary sensorimotor cortex, the supplementary motor area, premotor cortex, prefrontal cortex, superior and inferior parietal lobules, putamen and cerebellum, regions that are known to be involved in lower limb motor control. Brain activations related to individual adjustments during motor performance were identified in a right lateralized network including striatal, extrastriatal, and fronto-parietal areas.
Autores: Fernández-Seara, M. A.; et al.
ISSN 0028-3878  Vol. 80  Nº 21  2013  págs. E224 - E227
Autores: Aznárez-Sanado, Maite; Fernández-Seara, M. A.; et al.
ISSN 1053-1807  Vol. 37  Nº 3  2013  págs. 619-631
Purpose: To elucidate differences in activity and connectivity during early learning due to the performing hand. Materials and Methods: Twenty right-handed subjects were recruited. The neural correlates of explicit visuospatial learning executed with the right, the left hand, and bimanually were investigated using functional magnetic resonance imaging. Connectivity analyses were carried out using the psychophysiological interactions model, considering right and left anterior putamen as index regions. Results: A common neural network was found for the three tasks during learning. Main activity increases were located in posterior cingulate cortex, supplementary motor area, parietal cortex, anterior putamen, and cerebellum (IVV), whereas activity decrements were observed in prefrontal regions. However, the left hand task showed a greater recruitment of left hippocampal areas when compared with the other tasks. In addition, enhanced connectivity between the right anterior putamen and motor cortical and cerebellar regions was found for the left hand when compared with the right hand task. Conclusion: An additional recruitment of brain regions and increased striato-cortical and striato-cerebellar functional connections is needed when early learning is performed with the nondominant hand. In addition, access to brain resources during learning may be directed by the dominant hand in the bimanual task. J. Magn. Reson. Imaging 2013;37:619631. (c) 2012 Wiley Periodicals, Inc.
Autores: Fernández-Seara, M. A.; Mengual, Elisa; Vidorreta, Marta; et al.
ISSN 1053-8119  Vol. 59  Nº 3  2012  págs. 2743-2750
Alterations in cerebral perfusion and metabolism in Parkinson's disease have been assessed in several studies, using nuclear imaging techniques and more recently magnetic resonance imaging. However, to date there is no consensus in the literature regarding the extent and the magnitude of these alterations. In this work, arterial spin labeled perfusion MRI was employed to quantify absolute cerebral blood flow in a group of early-to-moderate Parkinson's disease patients and age-matched healthy controls. Perfusion comparisons between the two groups showed that Parkinson's disease is characterized by wide-spread cortical hypoperfusion. Subcortically, hypoperfusion was also found in the caudate nucleus. This pattern of hypoperfusion could be related to cognitive dysfunctions that have been previously observed even at the disease early stages. The present results were obtained by means of whole brain voxel-wise comparisons of absolute perfusion values, using statistical parametric mapping, thus avoiding the potentially biased global mean normalization procedure. In addition, this work demonstrates that between-group comparison of relative perfusion values after global mean normalization, introduced artifactual relative perfusion increases, where absolute perfusion was in fact preserved. This has implications for perfusion studies of other brain disorders. (C) 2011 Elsevier Inc. All rights reserved.
Autores: Vidorreta, Marta; Wang, Z.; Rodriguez, I.; et al.
ISSN 1053-8119  Vol. 66  2012  págs. 662 - 671
Arterial spin labeling (ASL) can be implemented by combining different labeling schemes and readout sequences. In this study, the performance of 2D and 3D single-shot pulsed-continuous ASL (pCASL) sequences was assessed in a group of young healthy volunteers undergoing a baseline perfusion and a functional study with a sensory-motor activation paradigm. The evaluated sequences were 2D echo-planar imaging (2D EPI), 3D single-shot fast spin-echo with in-plane spiral readout (3D FSE spiral), and 3D single-shot gradientand-spin-echo (3D GRASE). The 3D sequences were implemented with and without the addition of an optimized background suppression (BS) scheme. Labeling efficiency, signal-to-noise ratio (SNR), and gray matter (GM) to white matter (WM) contrast ratio were assessed in baseline perfusion measurements. 3D acquisitions without BS yielded 2-fold increments in spatial SNR, but no change in temporal SNR. The addition of BS to the 3D sequences yielded a 3-fold temporal SNR increase compared to the unsuppressed sequences. 2D EPI provided better GM-to-WM contrast ratio than the 3D sequences. The analysis of functional data at the subject level showed a 3-fold increase in statistical power for the BS 3D sequences, although the improvement was attenuated at the group level. 3D without BS did not increase the maximum t-values, however, it yielded larger activation clusters than 2D. These results demonstrate that BS 3D single-shot imaging sequences improve the performance of pCASL in baseline and activation studies, particularly for individual subject analyses where the improvement in temporal SNR translates into markedly enhanced power for task activation detection.
Autores: Aznárez-Sanado, Maite; Arrondo, Gonzalo; et al.
Revista: PLOS ONE
ISSN 1932-6203  Vol. 6   Nº 3  2011  págs. e17408
Decision making can be regarded as the outcome of cognitive processes leading to the selection of a course of action among several alternatives. Borrowing a central measurement from information theory, Shannon entropy, we quantified the uncertainties produced by decisions of participants within an economic decision task under different configurations of reward probability and time. These descriptors were used to obtain blood oxygen level-dependent (BOLD) signal correlates of uncertainty and two clusters codifying the Shannon entropy of task configurations were identified: a large cluster including parts of the right middle cingulate cortex (MCC) and left and right pre-supplementary motor areas (pre-SMA) and a small cluster at the left anterior thalamus. Subsequent functional connectivity analyses using the psycho-physiological interactions model identified areas involved in the functional integration of uncertainty. Results indicate that clusters mostly located at frontal and temporal cortices experienced an increased connectivity with the right MCC and left and right pre-SMA as the uncertainty was higher. Furthermore, pre-SMA was also functionally connected to a rich set of areas, most of them associative areas located at occipital and parietal lobes. This study provides a map of the human brain segregation and integration (i.e., neural substrate and functional connectivity respectively) of the uncertainty associated to an economic decision making paradigm.
Autores: Fernández-Seara, M. A.; Aznárez-Sanado, Maite; Mengual, Elisa; et al.
Revista: British Journal of Pharmacology
ISSN 0007-1188  Vol. 163   Nº 8  2011  págs. 1639 - 1652
Autores: Fernández-Seara, M. A.; Aznárez-Sanado, Maite; et al.
ISSN 1053-8119  Vol. 55  Nº 2  2011  págs. 635 - 643
Egocentric tactile perception is crucial for skilled hand motor control. In order to better understand the brain functional underpinnings related to this basic sensorial perception, we performed a tactile perception functional magnetic resonance imaging (fMRI) experiment with two aims. The first aim consisted of characterizing the neural substrate of two types of egocentric tactile discrimination: the spatial localization (SLD) and simultaneity succession discrimination (SSD) in both hands to define hemispheric dominance for these tasks. The second goal consisted of characterizing the brain activation related to the spatial attentional load, the functional changes and their connectivity patterns induced by the psychometric performance (PP) during SLD. We used fMRI in 25 right-handed volunteers, applying pairs of sinusoidal vibratory stimuli on eight different positions in the palmar surface of both hands. Subjects were required either to identify the stimulus location with respect to an imaginary midline (SLD), to discriminate the simultaneity or succession of a stimuli pair (SSD) or to simply respond to stimulus detection. We found a fronto-parietal network for SLD and frontal network for SSD. During SLD we identified right hemispheric dominance with increased BOLD activation and functional interaction of the right supramarginal gyrus with contralateral intra-parietal sulcus for right and left hand independently. Brain activity correlated to spatial attentional load was found in bilateral structures of intra-parietal sulcus, precuneus extended to superior parietal lobule, pre-supplementary motor area, frontal eye fields and anterior insulae for both hands. We suggest that the right supramarginal gyrus and its interaction with intra-parietal lobule may play a pivotal role in the phenomenon of tactile neglect in right fronto-parietal lesions.
Autores: Wang, D. J. ; Cheng, Y. ; Fernández-Seara, M. A.; et al.
ISSN 0022-3565  Vol. 337  Nº 2  2011  págs. 359 - 366
Pharmacological magnetic resonance imaging (phMRI) is increasingly being used in drug discovery and development to speed the translation from the laboratory to the clinic. The two primary methods in phMRI include blood-oxygen-level-dependent (BOLD) contrast and arterial spin-labeled (ASL) perfusion MRI. BOLD contrast has been widely applied in existing phMRI studies. However, because of the lack of absolute quantification and poor reproducibility over time scales longer than hours or across scanning sessions, BOLD fMRI may not be suitable to track oral and other long-term drug effects on baseline brain function. As an alternative method, ASL provides noninvasive, absolute quantification of cerebral blood flow both at rest and during task activation. ASL perfusion measurements have been shown to be highly reproducible over minutes and hours to days and weeks. These two characteristics make ASL an ideal tool for phMRI for studying both intravenous and oral drug action as well as understanding drug effects on baseline brain function and brain activation to cognitive or sensory processing. When ASL is combined with BOLD fMRI, drug-induced changes in cerebral metabolic rate of oxygen may also be inferred. Representative phMRI studies using ASL perfusion MRI on caffeine, remifentanil, and metoclopramide (dopamine antagonist) are reviewed here, with an emphasis on the methodologies used to control for potentially confounding vascular and systemic effects. Both the potentials and limitations of using ASL as an imaging marker of drug action are discussed.
Autores: Fernández-Seara, M. A.;
Libro:  MR and CT Perfusion and Pharmacokinetic Imaging: Clinical Applications and Theory
2016  págs. 200 - 220
Autores: Fernández-Seara, M. A.;
Libro:  MR and CT Perfusion and Pharmacokinetic Imaging: Clinical Applications and Theory
2016  págs. 1-10