Valentina Hartwig

Is the genotoxic effect of magnetic resonance negligible? Low persistence of micronucleus frequency in lymphocytes of individuals after cardiac scan.

Magnetic resonance imaging is a diagnostic technique widely used in medicine and showing a growing impact in cardiology. Biological effects associated to magnetic resonance electromagnetic fields have received far little attention, but it cannot be ruled out that these fields can alter DNA structure. The present study aimed at to identify possible DNA damage induced by magnetic resonance scan in humans. Lymphocyte cultures from healthy subjects had been exposed into magnetic resonance device for different times and under different variable magnetic exposure in order to build dose-effect curves, using micronuclei induction as biological marker. Replicate cultures were also left for 24h at room temperature before stimulation, to verify possible damage recovery. Furthermore, micronuclei induction and recovery up to 120h have been also evaluated in circulating lymphocytes of individuals after cardiac scan. A dose-dependent increase of micronuclei frequency was observed in vitro. However after 24h, the frequency returns to control value when the exposure is within diagnostic dosage. After in vivo scan, a significant increase in micronuclei is found till 24h, after the frequencies slowly return to control value.

Sensing Glove for Brain Studies: Design and Assessment of Its Compatibility for fMRI With a Robust Test

In this paper, we describe a biomimetic-fabric-based sensing glove that can be used to monitor hand posture and gesture. Our device is made of a distributed sensor network of piezoresistive conductive elastomers integrated into an elastic fabric. This solution does not affect natural movement and hand gestures, and can be worn for a long time with no discomfort. The glove could be fruitfully employed in behavioral and functional studies with functional MRI (fMRI) during specific tactile or motor tasks. To assess MR compatibility of the system, a statistical test on phantoms is introduced. This test can also be used for testing the compatibility of mechatronic devices designed to produce different stimuli inside the MR environment. We propose a statistical test to evaluate changes in SNR and time-domain standard deviations between image sequences acquired under different experimental conditions. fMRI experiments on subjects wearing the glove are reported. The reproducibility of fMRI results obtained with and without the glove was estimated. A good similarity between the activated regions was found in the two conditions.

Active mechatronic interface for haptic perception studies with functional magnetic resonance imaging: compatibility and design criteria

Functional brain exploration methodologies such as functional magnetic resonance imaging (fMRI) are critical tools to study perceptual and cognitive processes. In order to develop complex and well-controlled fMRI paradigms, researchers are interested in using active interfaces with electrically powered actuators and sensors. Due to the particularity of the MR environment, safety and compatibility criteria have to be strictly followed to avoid risks to the subject under test, the operators or the environment, as well as to prevent artifacts in the images. This paper describes the design of an fMRI compatible mechatronic interface based on MR compatibility tests of materials and actuators. In particular, a statistical test is introduced to evaluate the presence of artifacts in the image sequences that could negatively affect the fMRI studies. The device with two degrees of freedom, allowing one translation with position-feedback along a horizontal axis and one rotation about a vertical axis linked to the translation, was realized to investigate the brain mechanisms of dynamic tactile perception tasks. It can be used to move and orient various objects below the finger for controlled tactile stimulation. The MR compatibility of the complete interface is shown using the statistical test as well as a functional study with a human subject

B 1 + /actual flip angle and reception sensitivity mapping methods: simulation and comparison

Knowledge of the spatial distribution of transmission field B(1)(+) and reception sensitivity maps is important in high-field (≥3 T) human magnetic resonance (MR) imaging for several reasons: these include post-acquisition correction of intensity inhomogeneities, which may affect the quality of images; modeling and design of radiofrequency (RF) coils and pulses; validating theoretical models for electromagnetic field calculations; testing the compatibility with MR environment of biomedical implants. Moreover, inhomogeneities in the RF field are an essential source of error for quantitative MR spectroscopy. Recent studies have also shown that B(1)(+) and reception sensitivity maps can be used for direct calculation of tissue electrical parameters and for estimating the local specific absorption rate (SAR) in vivo. Several B(1)(+) mapping techniques have been introduced in the past few years based on actual flip angle (FA) mapping, but, to date, none has emerged as a standard. For reception sensitivity calculation, the signal intensity equation can be used where the nominal FA distribution must be replaced with the actual FA distribution calculated by one of the B(1)(+) mapping techniques. This study introduces a quantitative comparison between two known methods for B(1)(+)/actual FA and reception sensitivity mapping: the double-angle method (DAM) and the fitting (FIT) method. Experimental data obtained using DAM and FIT methods are also compared with numerical simulation results.

Study for a portable IR sensor to detect the blood temperature during coronary bypass implantation

The objective of this research was to investigate the possibility of using an infrared prototype device for the detection of the blood temperature during a surgical operation for coronary bypass implantation. The correlation between the fluid temperature time behavior and the fluid flow rate was demonstrated. Each blood vessel acts like a thermal wave emitter, so the amount of heat is proportional to the blood flow detected by the IR sensor. The idea was to design a low cost portable device with the advantage that it can be placed near the region of interest. We chose a pyroelectric sensor for its high-quality cost ratio. Because this kind of sensor detects only a variable infrared source, we used an electromechanical chopper for modulating the radiation. It consists of an electronic shutter whose opening speed is controlled by an astable multivibrator. The output signal was analyzed using a dedicated electronic circuit including a bandpass filter and an amplifier; then an acquisition board was employed f...

Near infrared image processing to quantitate and visualize oxygen saturation during vascular occlusion

The assessment of microcirculation spatial heterogeneity on the hand skin is the main objective of this work. Near-infrared spectroscopy based 2D imaging is a non-invasive technique for the assessment of tissue oxygenation. The haemoglobin oxygen saturation images were acquired by a dedicated camera (Kent Imaging) during baseline, ischaemia (brachial artery cuff occlusion) and reperfusion. Acquired images underwent a preliminary restoration process aimed at removing degradations occurring during signal capturing. Then, wavelet transform based multiscale analysis was applied to identify edges by detecting local maxima and minima across successive scales. Segmentation of test areas during different conditions was obtained by thresholding-based region growing approach. The method identifies the differences in microcirculatory control of blood flow in different regions of the hand skin. The obtained results demonstrate the potential use of NIRS images for the clinical evaluation of skin disease and microcirculatory dysfunction.

Correlational analysis of electroencephalographic and end-tidal carbon dioxide signals during breath-hold exercise.

The central mechanism of breathing control is not totally understood. Several studies evaluated the correlation between electroencephalographic (EEG) power spectra and respiratory signals by performing resting state tasks or adopting hypercapnic/hypoxic stimuli. The observation of brain activity during voluntary breath hold tasks, might be an useful approach to highlight the areas involved in mechanism of breath regulation. Nevertheless, studies of brain activity with EEG could present some limitations due to presence of severe artifacts. When artifact rejection methods, as independent component analysis, cannot reliably clean EEG data, it is necessary to exclude noisy segments. In this study, global field power in the delta band and end-tidal CO2 were derived from EEG and CO2 signals respectively in 4 healthy subjects during a breath-hold task. The cross correlation function between the two signals was estimated taking into account the presence of missing samples. The statistical significance of the correlation coefficients at different time lags was assessed using surrogate data. Some simulations are introduced to evaluate the effect of missing data on the correlational analysis and their results are discussed. Results obtained on subjects show a significant correlation between changes in EEG power in the delta band and end-tidal CO2. Moreover, the changes in end-tidal CO2 were found to precede those of global field power. These results might help to better understand the cortical mechanisms involved in the control of breathing.

Two-dimensional near infrared spectroscopic imaging of the hand to assess microvascular abnormalities in systemic sclerosis: a pilot study

Patients affected by systemic sclerosis (SSc) develop functional and structural microvascular alterations and progressive fibrosis of the skin and internal organs. Evaluation of skin microcirculation is an important clinical step in the workup of SSc patients. Near infrared (NIR) spectroscopy is a well-established non-invasive technique to assess haemoglobin oxygen saturation (StO2) in the illuminated tissue. The recent development of NIR spectroscopic two-dimensional (2D) imaging offers the possibility of visualising StO2 distribution in large tissue areas. This is particularly important in SSc characterised by a very heterogeneous spatial distribution of the microvascular abnormalities. In addition, the short acquisition time of NIR spectroscopic images allows microvascular “dynamic” conditions, such as the vascular response to physical or pharmacological stimuli, to be evaluated. The present study reports the results of the test application of NIR spectroscopic 2D imaging of the palmar whole-hand surface for the evaluation of peripheral microcirculatory dysfunction in one patient with SSc, as compared with a healthy control, both in “static” (resting) and in “dynamic” (ischaemia-reperfusion) conditions. Spatial heterogeneity of microvascular alterations associated with temporal heterogeneity in vascular reactivity to ischaemic challenge make 2D NIR spectroscopic imaging a promising tool in the assessment of SSc, as compared with the current available techniques. A NIR spectroscopic camera by Kent Imaging Inc, Calgary, Canada was used.

Neural correlates of human-robot handshaking

Handshaking represents a complex motor and cognitive task that poses several challenges from both engineering and neuroscientific viewpoints. In particular, it is an intriguing application which can be profitably studied in the field of Human Robot Interaction (HRI). In this work an experimental paradigm is proposed to investigate the neural correlates of handshaking between humans and between humans and robots using functional Magnetic Resonance Imaging. More specifically the role of visual and haptic components during handshaking interaction will be studied. A wearable sensing glove will be used to monitor hand finger position and movement. Preliminary results will be reported and discussed.

First prototype of a near infrared tomograph for mapping the myocardial oxygenation in small animal isolated hearts

Over the past decade near infrared spectroscopy (NIRS) and imaging are rapidly evolving for a large number of new clinical applications. These techniques, based upon near-infrared light transmission through biological tissues, aim to monitor the hemoglobin and myoglobin concentration changes due to particular physiological state. Clinical applications regard, for instance, the monitoring of muscles and cerebral oxygenation, functional brain activation studies and heart perfusion research. Recently, some works presented tissue oxygenation studies in beating or arrested isolated small animal hearts. Lately, diffuse optical tomography (DOT) has been developed: it employs tissue arrays of infrared sources and detectors to obtain maps of optical properties of illuminated tissues. In this paper we present the design and realization of a first prototype of a near infrared tomograph for the myocardial perfusion analysis of isolated small animal hearts. Preliminary tests have been performed using some phantoms with different NIR absorption coefficients and an isolated rat heart. The device is able to distinguish objects with different absorption coefficients in the imaging area and to provide 2D map of small animals heart IR light absorption.