Antonio Napolitano

Test-retest reliability of graph metrics of resting state MRI functional brain networks: A review.

The employment of graph theory to analyze spontaneous fluctuations in resting state BOLD fMRI data has become a dominant theme in brain imaging studies and neuroscience. Analysis of resting state functional brain networks based on graph theory has proven to be a powerful tool to quantitatively characterize functional architecture of the brain and it has provided a new platform to explore the overall structure of local and global functional connectivity in the brain. Due to its increased use and possible expansion to clinical use, it is essential that the reliability of such a technique is very strongly assessed. In this review, we explore the outcome of recent studies in network reliability which apply graph theory to analyze connectome resting state networks. Therefore, we investigate which preprocessing steps may affect reproducibility the most. In order to investigate network reliability, we compared the test-retest (TRT) reliability of functional data of published neuroimaging studies with different preprocessing steps. In particular we tested influence of global signal regression, correlation metric choice, binary versus weighted link definition, frequency band selection and length of time-series. Statistical analysis shows that only frequency band selection and length of time-series seem to affect TRT reliability. Our results highlight the importance of the choice of the preprocessing steps to achieve more reproducible measurements.

Conventional magnetic resonance imaging and diffusion tensor imaging studies in children with novel GPR56 mutations: further delineation of a cobblestone-like phenotype

GPR56-related bilateral frontoparietal polymicrogyria (BFPP) is a rare recessively inherited disorder of neuronal migration caused by mutations of GPR56. To better delineate the clinical, molecular, and neuroradiological phenotypes associated with BFPP, we performed conventional magnetic resonance imaging and diffusion tensor imaging studies in a series of prospectively enrolled patients carrying novel GPR56 mutations. All subjects with GPR56-related BFPP showed a characteristic morphological pattern, including abnormalities of the cerebellar cortex with cerebellar cysts located at the periphery, a mildly thick corpus callosum, and a flat pons. Significant alterations of myelination and white matter tract abnormalities were documented. The present study confirms the phenotypic overlap between GPR56-related brain dysgenesis and other cobblestone-like syndromes and illustrates the contribution of 3D neuroimaging in the characterization of malformations of cortical development.

Accidental Exposure to UV Radiation Produced by Germicidal Lamp: Case Report and Risk Assessment

Ultraviolet radiation is known to cause both benefits and harmful effects on humans. The adverse effects mainly involve two target organs, skin and eye, and can be further divided into short‐ and long‐term effects. The present case report describes an accidental exposure of two health‐care workers to ultraviolet radiation produced by a germicidal lamp in a hospital pharmacy. The germicidal lamp presented a spectrum with an intense UV‐C component as well as a modest UV‐B contribution. Overexposure to UV‐C radiation was over 100 times as large as the ICNIRP exposure limits. A few hours after the exposure, the two subjects reported symptoms of acute UV injury and both of them continued having significant clinical signs for over 2 years. In this study, we describe acute and potentially irreversible effects caused by high UV exposure. In addition, we present the results of risk assessment by occupational exposure to germicidal lamps.

Fractal Dimension Estimation Methods for Biomedical Images

The use of medical images has its main aim in the detection of potential abnormalities. This goal is accurately achieved with the synergy between the ability in recognizing unique image patterns and finding the relationship between them and possible diagnoses. One of the methods used to aid this process is the extrapolation of important features from the images called texture; texture is an important source of visual information and is a key component in image analysis.

White matter disruption is associated with persistent seizures in tuberous sclerosis complex

BACKGROUND AND AIMS White matter is diffusely altered in tuberous sclerosis complex (TSC), and these alterations appear to be more evident in subjects with a more severe neurologic phenotype. However, little is known on the correlation between white matter alterations and epilepsy in TSC. The aims of this study were to evaluate the effects of early onset and refractory seizures on white matter by using diffusion tensor imaging (DTI). METHODS We enrolled 20 children with TSC and epilepsy onset in the first 3years of life and grouped them according to seizure persistence or freedom. All patients underwent brain MRI with DTI. Specific ROIs have were placed to generate tracks to calculate fractional anisotropy (FA) and apparent diffusion coefficient (ADC). Statistical analysis was performed by ANOVA. RESULTS Children with persistent seizures presented an overall reduced FA, with statistically significant differences on the cingulum (right p=0.003, left p=0.016), the left cerebral peduncle (p=0.020), the superior cerebellar peduncles (right p=0.008, left p=0.002), the posterior limbs of internal capsule (right p=0.037, left p=0.015), the external capsule (right p=0.018, left p=0.031), the inferior frontooccipital fasciculus (right p=0.010, left p=0.026), and the temporal trunk (right p=0.017, left p=0.001). CONCLUSIONS Our study demonstrated that children with persistent seizures present more significant alterations of brain connectivity in areas crucial for global cognitive maturation, executive functions, and verbal abilities, implying a higher risk of cognitive impairment, attention-deficit hyperactivity disorder, and autism.

Gadolinium-Based Contrast Agent-Related Toxicities

In recent years, gadolinium-based contrast agents have been associated with different types of toxicity. In particular, nephrogenic systemic fibrosis, a progressive sclerotic-myxedematous systemic disease of unknown etiology, is related to gadolinium-based contrast agent administration in patients with kidney dysfunction. More recently, evidence of magnetic resonance signal intensity changes on pre-contrast T1-weighted images after multiple gadolinium-based contrast agent administrations resulted in the hypothesis of gadolinium brain accumulation in patients with normal renal function, subsequently confirmed in pathological samples. However, there is limited current data and further investigations are necessary before drawing definite conclusions on the clinical consequences of gadolinium-based contrast agent accumulation in human tissues and particularly in the brain. Gadolinium-based contrast agent-related toxicity appears connected to molecular stability, which varies together with the pharmacokinetic properties of the compound and depends on the individual characteristics of the subject. During a lifetime, the physiological changes occurring in the human body may influence its interaction with gadolinium-based contrast agents: the integrity and developmental stage of the organs has an effect on the dynamics of gadolinium-based contrast agent distribution and excretion, thus leading to different possible mechanisms of deposition and toxicity. Therefore, the aim of this work is to discuss the pharmacokinetics and pharmacodynamics of gadolinium-based contrast agents, with a special focus on the brain, and to explore potential predominant gadolinium-based contrast agent-related toxicity in two cornerstone periods of the human life cycle: fetal/neonatal and adulthood/aged.

Multiparametric evaluation of low grade gliomas at follow-up: comparison between diffusion and perfusion MR with 18F-FDOPA PET

OBJECTIVE To compare MRI using perfusion and diffusion techniques with 6-[(18)F]-fluoro-L-3,4-dihydroxyphenylalanine ((18)F-FDOPA) positron emission tomography (PET) in the follow-up of low-grade gliomas (LGGs) and to identify the best imaging parameter to differentiate patients with different prognosis. METHODS Between 2010 and 2015, 12 patients with a pathology-proven diagnosis of LGG and MR (with perfusion and diffusion sequences) and a PET study during their follow-up were retrospectively included in our study. Cerebral blood volume (CBV) and apparent diffusion coefficient (ADC) maps on MR studies and PET images were evaluated using a region of interest-based method. All patients were categorized as stable or as having progressive disease at 1-year follow-up. Statistical analysis was performed using Pearsons correlation test and multivariate analysis of variance (p < 0.05). RESULTS No significant correlations were found between PET parameters [maximum tumour-to-controlateral normal brain ratio (T/Nmax) and tumour-to-striatum ratio] and ADC or relative CBV values measured in both PET hotspot regions and areas of maximum signal alterations. T/Nmax demonstrated a good sensitivity (83%) and specificity (100%) for differentiating two subgroups of patients with different outcomes at 1-year-follow-up (p < 0.05). CONCLUSION Perfusion and diffusion MR images provide different information compared with (18)F-FDOPA PET in LGGs during follow-up and therefore, they should be considered as complementary tools in the evaluation of these tumours. (18)F-FDOPA PET showed a significant prognostic role in the follow-up of LGGs and appeared to be a better tool than MR advanced techniques for outcome prediction. These results need to be confirmed with longitudinal studies on a larger population. ADVANCES IN KNOWLEDGE This is the first study that compared (18)F-FDOPA PET with perfusion and diffusion MR in LGGs during follow-up. These preliminary results highlight the importance of a multimodality approach in this field and evidence a potential role for (18)F-FDOPA PET to predict patients at risk for tumour progression.

Magnetic resonance imaging patterns of treatment-related toxicity in the pediatric brain: an update and review of the literature

Treatment-related neurotoxicity is a potentially life-threatening clinical condition that can represent a diagnostic challenge. Differentiating diagnoses between therapy-associated brain injury and recurrent disease can be difficult, and the immediate recognition of neurotoxicity is crucial to providing correct therapeutic management, ensuring damage reversibility. For these purposes, the knowledge of clinical timing and specific treatment protocols is extremely important for interpreting MRI patterns. Neuroradiologic findings are heterogeneous and sometimes overlapping, representing the compounding effect of the different treatments. Moreover, MRI patterns can be acute, subacute or delayed and involve different brain regions, depending on (1) the mechanism of action of the specific medication and (2) which brain regions are selectively vulnerable to specific toxic effects. This review illustrates the most common radiologic appearance of radiotherapy, chemotherapy and medication-associated brain injury in children, with special focus on the application of advanced MRI techniques (diffusion, perfusion and proton spectroscopy) in the diagnosis of the underlying processes leading to brain toxicity.

The impact of vision on the dynamic characteristics of the gait: strategies in children with blindness

Visually impaired persons present an atypical gait pattern characterized by slower walking speed, shorter stride length and longer time of stance. Three explanatory hypotheses have been advanced in the literature: balance deficit, lack of an anticipatory mechanisms and foot probing the ground. In the present study, we compared the three hypotheses by applying their predictions to gait analysis and posturography of blind children without neurological impairment and compared their performance with that of an age-matched control group. The gait analysis results documented that blind children presented reduced walking velocity and step length, increased step width and external rotation of the foot progression angle, reduced ground reaction force and ankle maximum angle, moment and power in late stance, increased head flexion, decreased thorax flexion and pelvis anteversion, compared with the control group. The posturographic analysis showed equal skill level between blind children and normally sighted children when they close their eyes. The results are consistent with only one of the three hypotheses: namely, they prove that blind children’s gait is influenced only by the absence of visually driven anticipatory control mechanisms. Finally, rehabilitative recommendations for children with blindness are advanced in discussion.

Currents induced by fast movements inside the MRI room may cause inhibition in an implanted pacemaker

The static magnetic field generated by MRI systems is highly non-homogenous and rapidly decreases when moving away from the bore of the scanner. Consequently, the movement around the MRI scanner is equivalent to an exposure to a time-varying magnetic field at very low frequency (few Hz). If people with an implanted pacemaker (PM) enter the MRI room, fast movements may thus induce voltages on the loop formed by the PM lead, with the potential to modify the correct behavior of the stimulator. In this study, we performed in-vitro measurements on a human-shaped phantom, equipped with an implantable PM and with a current sensor, able to monitor the activity of the PM while moving the phantom in the MRI room. Fast rotational movements in close proximity of the bore of the scanner caused the inappropriate inhibition of the PM, programmed in VVI modality, maximum sensitivity, unipolar sensing and pacing. The inhibition occurred for a variation of the magnetic field of about 3 T/s. These findings demonstrate that great care must be paid when extending PM MRI compatibility from patients to healthcare personnel, since the safety procedures and the MRI-conditional PM programming (e.g. asynchronous stimulation or bipolar sensing) used for patients cannot be applied.