Ivan Amat-Roldan

Altered small-world topology of structural brain networks in infants with intrauterine growth restriction and its association with later neurodevelopmental outcome.

Intrauterine growth restriction (IUGR) due to placental insufficiency affects 5-10% of all pregnancies and it is associated with a wide range of short- and long-term neurodevelopmental disorders. Prediction of neurodevelopmental outcomes in IUGR is among the clinical challenges of modern fetal medicine and pediatrics. In recent years several studies have used magnetic resonance imaging (MRI) to demonstrate differences in brain structure in IUGR subjects, but the ability to use MRI for individual predictive purposes in IUGR is limited. Recent research suggests that MRI in vivo access to brain connectivity might have the potential to help understanding cognitive and neurodevelopment processes. Specifically, MRI based connectomics is an emerging approach to extract information from MRI data that exhaustively maps inter-regional connectivity within the brain to build a graph model of its neural circuitry known as brain network. In the present study we used diffusion MRI based connectomics to obtain structural brain networks of a prospective cohort of one year old infants (32 controls and 24 IUGR) and analyze the existence of quantifiable brain reorganization of white matter circuitry in IUGR group by means of global and regional graph theory features of brain networks. Based on global and regional analyses of the brain network topology we demonstrated brain reorganization in IUGR infants at one year of age. Specifically, IUGR infants presented decreased global and local weighted efficiency, and a pattern of altered regional graph theory features. By means of binomial logistic regression, we also demonstrated that connectivity measures were associated with abnormal performance in later neurodevelopmental outcome as measured by Bayley Scale for Infant and Toddler Development, Third edition (BSID-III) at two years of age. These findings show the potential of diffusion MRI based connectomics and graph theory based network characteristics for estimating differences in the architecture of neural circuitry and developing imaging biomarkers of poor neurodevelopment outcome in infants with prenatal diseases.

In vivo, pixel-resolution mapping of thick filaments' orientation in nonfibrilar muscle using polarization-sensitive second harmonic generation microscopy

The polarization dependence of second harmonic generation (SHG) microscopy is used to uncover structural information in different muscle cells in a living Caenorhabditis elegans (C. elegans) nematode. This is done by using a generalized biophysical model in which element ratios for the associated second-order nonlinear tensor and angular orientations for thick filaments are retrieved using a pixel-by-pixel fitting algorithm. As a result, multiple arbitrary orientations of thick filaments, at the pixel-resolution level, are revealed in the same image. The validity of our method is first corroborated in well-organized thick filaments such as the nonfibrilar body wall muscles. Next, a region of the nonstriated muscular cells of the pharynx is analyzed by showing different regions with homogenous orientations of thick filament as well as their radial distribution. As a result, different sets of the nonstriated muscle cell groups in the pharynx of this nematode were exposed. This methodology is presented as a filtering mechanism to uncover biological information unreachable by common intensity SHG microscopy. Finally, a method to experimentally retrieve the distribution of the effective orientation of active SHG molecules is proposed and tested.

Ultrashort pulse characterisation with SHG collinear-FROG

We outline criteria for fast and accurate acquisition of collinear FROG (CFROG) trace and how it can be transformed into the more traditional noncollinear FROG trace. The CFROG has an intrinsically simple geometry that provides greater versatility as well as the ability for built-in delay calibration and enhanced error-checking. The procedure, based on data processing, allows conventional SHG-FROG retrieval algorithms to be used. This technique is tested numerically and experimentally giving excellent results. This work represents an attractive alternative to the traditional, more complex non-collinear FROG technique while, at the same time, extending its use to experiments where collinear geometry is imposed.

Technical aspects of fetal endoscopic tracheal occlusion for congenital diaphragmatic hernia

In isolated congenital diaphragmatic hernia, prenatal prediction is made based on measurements of lung size and the presence of liver herniation into the thorax. A subset of fetuses likely to die in the postnatal period is eligible for fetal intervention that can promote lung growth. Rather than anatomical repair, this is now attempted by temporary fetal endoscopic tracheal occlusion (FETO). Herein we describe purpose-designed instruments that were developed thanks to a grant from the European Commission. The feasibility and safety of FETO have now been demonstrated in several active fetal surgery programs. The most frequent complication of the procedure is preterm premature rupture of the membranes, which is probably iatrogenic in nature. It does have an impact on gestational age at delivery and complicates balloon removal. FETO is associated with an apparent increase in survival compared with same severity controls, although this needs to be evaluated in a formal trial. The time has come to do so.

Neonatal Neurobehavior and Diffusion MRI Changes in Brain Reorganization Due to Intrauterine Growth Restriction in a Rabbit Model

Background Intrauterine growth restriction (IUGR) affects 5–10% of all newborns and is associated with a high risk of abnormal neurodevelopment. The timing and patterns of brain reorganization underlying IUGR are poorly documented. We developed a rabbit model of IUGR allowing neonatal neurobehavioral assessment and high resolution brain diffusion magnetic resonance imaging (MRI). The aim of the study was to describe the pattern and functional correlates of fetal brain reorganization induced by IUGR. Methodology/Principal Findings IUGR was induced in 10 New Zealand fetal rabbits by ligation of 40–50% of uteroplacental vessels in one horn at 25 days of gestation. Ten contralateral horn fetuses were used as controls. Cesarean section was performed at 30 days (term 31 days). At postnatal day +1, neonates were assessed by validated neurobehavioral tests including evaluation of tone, spontaneous locomotion, reflex motor activity, motor responses to olfactory stimuli, and coordination of suck and swallow. Subsequently, brains were collected and fixed and MRI was performed using a high resolution acquisition scheme. Global and regional (manual delineation and voxel based analysis) diffusion tensor imaging parameters were analyzed. IUGR was associated with significantly poorer neurobehavioral performance in most domains. Voxel based analysis revealed fractional anisotropy (FA) differences in multiple brain regions of gray and white matter, including frontal, insular, occipital and temporal cortex, hippocampus, putamen, thalamus, claustrum, medial septal nucleus, anterior commissure, internal capsule, fimbria of hippocampus, medial lemniscus and olfactory tract. Regional FA changes were correlated with poorer outcome in neurobehavioral tests. Conclusions IUGR is associated with a complex pattern of brain reorganization already at birth, which may open opportunities for early intervention. Diffusion MRI can offer suitable imaging biomarkers to characterize and monitor brain reorganization due to fetal diseases.

Measurement of electric field by interferometric spectral trace observation.

We present a new methodology that obtains, in an analytical way, the complex electric field of ultrashort pulses. This methodology is based only on Fourier analysis of the frequency components of spectrally resolved interferometric collinear autocorrelations. We present an experimental demonstration of this technique and the results are compared with the conventional second-harmonic generation frequency-resolved optical gating technique.

Quantitative discrimination between endogenous SHG sources in mammalian tissue, based on their polarization response

In this study, the second harmonic generation (SHG) response to polarization and subsequent data analysis is used to discriminate, in the same image, different SHG source architectures with pixel resolution. This is demonstrated in a mammalian tissue containing both skeletal muscle and fibrilar collagen. The SHG intensity variation with the input polarization (PSHG) is fitted pixel by pixel in the image using an algorithm based on a generalized biophysical model. The analysis provides the effective orientation, theta(e), of the different SHG active structures (harmonophores) at every pixel. This results in a new image in which collagen and muscle are clearly differentiated. In order to quantify the SHG response, the distribution of theta(e) for every harmonophore is obtained. We found that for collagen, the distribution was centered at theta(e) = 42.7 degrees with a full width at half maximum of theta = 5.9 degrees while for muscle theta(e) = 65.3 degrees , with theta = 7.7 degrees . By comparing these distributions, a quantitative measurement of the discrimination procedure is provided.

Estimation of the effective orientation of the SHG source in primary cortical neurons

In this paper we provide, for the first time to our knowledge, the effective orientation of the SHG source in cultured cortical neuronal processes in vitro. This is done by the use of the polarization sensitive second harmonic generation (PSHG) imaging microscopy technique. By performing a pixel-level resolution analysis we found that the SHG dipole source has a distribution of angles centered at thetae =33.96 degrees , with a bandwidth of Deltathetae = 12.85 degrees . This orientation can be related with the molecular geometry of the tubulin heterodimmer contained in microtubules.

Fast image analysis in polarization SHG microscopy.

Pixel resolution polarization-sensitive second harmonic generation (PSHG) imaging has been recently shown as a promising imaging modality, by largely enhancing the capabilities of conventional intensity-based SHG microscopy. PSHG is able to obtain structural information from the elementary SHG active structures, which play an important role in many biological processes. Although the technique is of major interest, acquiring such information requires long offline processing, even with current computers. In this paper, we present an approach based on Fourier analysis of the anisotropy signature that allows processing the PSHG images in less than a second in standard single core computers. This represents a temporal improvement of several orders of magnitude compared to conventional fitting algorithms. This opens up the possibility for fast PSHG information with the subsequent benefit of potential use in medical applications.

Starch-based second-harmonic-generated collinear frequency-resolved optical gating pulse characterization at the focal plane of a high-numerical-aperture lens

We report the use of starch as an ideal nonlinear medium with which to perform collinear frequency-resolved optical gating measurements of ultrashort pulses at the focal plane of a high-numerical-aperture (NA) lens. We achieved these measurements by simply sandwiching starch granules (suspended in water) between two coverslips and placing them within the focal plane of a high-NA lens. The natural nonlinear characteristics of starch allow the correct phase matching of pulses at the focal plane of a high-NA lens at different wavelengths. This elegant arrangement overcomes all the complexity and problems that were previously associated with pulse characterization within a multiphoton microscope.