Andrea Bandera

Non-invasive in vivo infrared laser spectroscopy to analyse endogenous oxy-haemoglobin, deoxy-haemoglobin, and blood volume in the rat CNS.

Oxy-haemoglobin (HbO2) and deoxy-haemoglobin (Hb) are chromophores present in biological tissues. Near infrared spectroscopy (NIRS) is a non-invasive methodology based on the low extinction coefficient of tissue in the near infrared region. NIRS can be used to measure changes in the concentration of these chromophores, i.e., haemoglobin, in muscular tissue. In the present work, NIRS has been used for the non-invasive monitoring of HbO2, Hb, and blood volume (V: representing total haemoglobin, i.e., HbO2+Hb) in vivo in the whole rat brain. This has been performed by means of prototype instrumentation based on optic fibre probes placed in contact with the head of anaesthetised rats held in a stereotaxic frame. A preliminary test of the instrument has been performed on human muscle, i.e., lateral gastrocnemius, in order to evaluate the ability of the instrument to detect oxygenation changes. Afterwards, the effects of pharmacological treatments, such as systemic amphetamine and nicotine treatments on the CNS have been detected.

Design and performance of a wide-bandwidth and sensitive instrument for near-infrared spectroscopic measurements on human tissue

The article describes an instrument designed to perform in vivo near-infrared spectroscopic measurements on human tissues. The system integrates five continuous-wave laser diode sources emitting in the near-infrared spectral region and a low-noise detection system based on an avalanche photodiode. The optical probe is based on a compact, reliable, and low-cost fiber based system with four quantitative measuring points. The excellent sensitivity of the instrument allows one to perform quantitative assessments of the hemoglobin concentration exploiting precise absorption measurements close to the absorption peak of the water: 975 nm. Moreover, a good signal to noise ratio is obtained also at a high acquisition rate, allowing us to follow rapid changes in oxidative metabolism. The system bandwidth is selectable within the range 2.3–27 Hz, i.e., 20 channels (five chromatic and four spatial channels) can be acquired 27 times for each measuring second, whereas the system amplification can be set to measure opti...

A novel tissue oxymeter combining the multidistance approach with an accurate spectral analysis

In this paper a novel optical tissue oxymeter that integrates the multidistance approach and the evaluation of the differential pathlength exploiting the absorption features of water is presented. This system takes advantage from the peculiarities of these techniques to extract the scattering and the absorption coefficient reducing errors introduced by the heterogeneous structure of the tissue and improving the signal-to-noise ratio. I. INTRODUCTION Continuous-Wave Near-InfraRed Spectroscopy (CW- NIRS) was first introduced more than twenty years ago as a tool for in-vivo monitoring of the tissue oxygenation (1). This technique is based on the low extinction coefficient of tissue in the near infrared region combined with the fact that tissue contains chromophores, principally water, lipids, melanin, deoxyhaemoglobin, oxyhaemoglobin, and cytochrome oxidase. In the spectral range 700-1000nm, light can interrogate the whole brain or muscle allows assessing changes in concentration of these chromophores. One of the major limitations of the CW-NIRS systems is the coupling between the scattering and the absorption coefficient causing the lack of quantitative assessment. Two possible ways to uncouple absorption from scattering have so far been proposed: (i) the multidistance approach, i.e. the analysis of the spatial decay of re-emitted light (2, 3) and (ii) the evaluation of the differential pathlength of photons utilizing the absorption features of water (4). Both these techniques suffer by errors introduced by the heterogeneous structure of the tissue. In this article, we present a novel optical tissue oxymeter that integrates these two techniques to achieve more quantitative data and to improve the quality of the signal. Particularly, we describe the system configuration, the system performance and the theory of operation. Moreover, the calibration procedure and a preliminary in-vivo test are discussed.

Near-infrared oxymeter prototype for noninvasive analysis of rat brain oxygenation

The feasibility of non-invasive analysis of brain activities was studied in the attempt to overcome the major limitation of actual in vivo methodologies i.e. invasiveness. Optic fibre probes were used as optical head of a novel, highly sensitive near infrared continuous wave spectroscopy (CW-NIR) instrument. This prototype was designed for non-invasive analysis of the two main forms of haemoglobin: oxy-haemoglobin (HbO2) and deoxy-haemoglobin (Hb), chromophores present in biological tissues. It was tested in peripheral tissue (human gastrocnemius muscle) and then reset to perform measurement on rat brain. In animal studies, the optical head was firmly placed using stereotaxic apparatus upon the sagittal line of anaesthetised adult rats head, without any surgery. Then pharmacological treatments with saline (300μl s.c.) amphetamine (2mg/kg) or nicotine (0.4mg/kg) were performed. Within 10-20 min amphetamine substantially increased HbO2 and reduced Hb control levels. Nicotine produced a rapid initial increase followed by a decrease of HbO2. In contrast to amphetamine, nicotine treatment also reduced Hb and blood volume. These results support the capacity of our CW-NIR prototype to measure non-invasively HbO2 and Hb levels in the rat brain, markers of the degree of tissue oxygenation, index of blood level then of the state of brain metabolism.

Functional cerebral activation detected by an integrated system combining CW-NIR spectroscopy and EEG

The aim of this study is to explore the possibility of correlating hemodynamic changes and neural activities in the brain by using an integrated system combining Near Infrared Spectroscopy (NIRS) and electroencephalographic activity (EEG). We present brain hemodynamic changes and EEG recordings obtained from four volunteers during the performance of two different sequential thumb-finger opposition tasks, with and without a related mental activity. The optical and electrical signals were recorded simultaneously on the subject forehead. The coupling of the two systems could be useful to demonstrate correlation between cognitive paradigms and hemodynamic signals.

Combined bio-engineering and neurophysiological in vivo technologies allow studying rat brain metabolism and neuronal activities in vivo in real time

Franz Joebsis first used near infrared spectroscopy (NIRS) as a tool for the in vivo monitoring of tissue oxygenation. Today, NIRS instruments are more and more used in clinical environments since these systems are now easy to use, sensitive, robust, give rapid analysis and have multiple measuring points. In the present work, optic fibre probes were used as optical head of a CW-NIR instrument adapted for in vivo NIRS measurements in the brain of rodents. This prototype was designed for non-invasive analysis of the two main forms of haemoglobin: oxy-haemoglobin (HbO2) and deoxy-haemoglobin (Hb), chromophores present in biological tissues. In the present experiments it was applied to measure non- invasively HbO2 and Hb levels in the rat brain; that are markers of the degree of tissue oxygenation, thus providing an index of blood levels and therefore of brain metabolism. In addition, the same animals set for central NIRS studies, were also surgically prepared for electrophysiological monitoring of cell firing in discrete brain areas. These are raphe dorsalis nucleus, locus coeruleus, ventral tegmental area that are defined as main serotoninergic, noradrenergic and dopaminergic cell containing regions of the CNS and therefore involved in the major cerebral syndromes. Then, following a control recording period, exogenous oxygen (O2, 0.1bar, 2min) or carbon dioxide (CO2 0.1bar, 20min) was inflated orally. The data gathered indicate an original relationship between NIRS analysis of brain metabolism and electrical changes in three major nuclei of CNS involved in neurophysiologic and pathologic activities.