Biomedical subjects

Andrea Bassi

Publications and source records attributed to Andrea Bassi.

11 recordsLinked to original sources

PubMed2005

Spontaneous sleep modulates the firing pattern of parkinsonian subthalamic nucleus.

In Parkinson's disease, the subthalamic nucleus (STN) is a common target for functional neurosurgery. Recent investigations have suggested that physiological non-motor stimuli may dramatically alter STN firing properties. By maintaining long-lasting micro-recordings of STN single units in Parkinson's disease (PD) patients, here we show that the neurons that are responsive to passive movements are also strongly modulated by altered vigilance state (awake vs. sleep). In addition, sleep was characterized by a distinctive irregular train-like firing pattern. These findings suggest that the reduction of the somato-sensory input modifies rigidity and, hence, STN discharge mode. Further, it is suggested that specific STN electrophysiological features are potential targets for future therapeutic interventions.

Action Potentials↗

PubMed2005

Dynamic time-resolved diffuse spectroscopy based on supercontinuum light pulses.

We present a detailed characterization of a system for fast time-resolved spectroscopy of turbid media based on supercontinuum generation in a photonic crystal fiber. The light source provides subpicosecond pulses in the 550-1000-nm spectral range, at 85 MHz, at an average power of up to 50 mW. Wavelength-resolved detection is accomplished by means of a spectrometer coupled to a 16-channel, multianode photomultiplier tube, giving a resolution of 4.5-35 nm/channel, depending on the grating. Time-dispersion curves are acquired with time-correlated single-photon counting, and absorption and reduced scattering coefficients are determined by fitting the data to the diffusion equation. We characterized the system by measuring the time-resolved diffuse reflectance of epoxy phantoms and by assessing the performance in terms of accuracy, linearity, noise sensitivity, stability, and reproducibility. The results were similar to those from previous systems, whereas the full-spectrum (610-810 nm) acquisition time was as short as 1 s owing to the parallel acquisition. We also present the first in vivo real-time dynamic spectral measurements showing tissue oxygenation changes in the arm of a human subject.

Algorithms↗

PubMed2005

Prognostic implications of right-sided insular damage, cardiac autonomic derangement, and arrhythmias after acute ischemic stroke.

BACKGROUND AND PURPOSE: Acute stroke is associated with impairment of cardiac autonomic balance and increased incidence of arrhythmias. These abnormalities appear more relevant in the case of involvement of the right insula in the infarct area. The aim of this study was to assess the impact of right-sided insular damage, cardiac autonomic derangement, and arrhythmias on clinical outcome after acute ischemic stroke. METHODS: Holter monitoring for 24 hours was performed in 208 consecutive patients with first-ever acute ischemic stroke. Time- and frequency-domain measures of heart rate variability and arrhythmias were considered in all cases. All patients were followed for a 12-month period after the initial event. RESULTS: During the 12-month follow-up period, 48 patients died (1-year probability of death, 0.23; 95% CI, 0.17 to 0.30). Multivariate analysis demonstrated that age (hazard ratio [HR], 1.06; 95% CI, 1.01 to 1.10; P=0.0087), stroke severity on admission (HR, 1.25; 95% CI, 1.13 to 1.39; P=0.0001), presence of right-sided insular damage (HR, 2.01; 95% CI, 1.13 to 1.39; P=0.0187), as well as lower values of the SD of all normal-to-normal RR intervals (HR, 3.32; 95% CI, 1.67 to 6.24; P=0.002), and presence of nonsustained ventricular tachycardia during Holter monitoring (HR, 2.99; 95% CI, 1.58 to 5.67; P=0.0007) were independent predictors of 1-year mortality. CONCLUSIONS: The integration of traditional risk stratifiers with autonomic and arrhythmic markers, and the careful search for right-sided insular involvement, may represent an effective approach for identification of stroke patients at risk for early mortality.

Aged↗

PubMed2005

Performance assessment of photon migration instruments: the MEDPHOT protocol.

We propose a comprehensive protocol for the performance assessment of photon migration instruments. The protocol has been developed within the European Thematic Network MEDPHOT (optical methods for medical diagnosis and monitoring of diseases) and is based on five criteria: accuracy, linearity, noise, stability, and reproducibility. This protocol was applied to a total of 8 instruments with a set of 32 phantoms, covering a wide range of optical properties.

Benchmarking↗

PubMed2004

Time-resolved spectrophotometer for turbid media based on supercontinuum generation in a photonic crystal fiber.

We describe an instrument for the time-resolved spectroscopy of turbid media that is based on supercontinuum generation in a photonic crystal fiber. The light injected into the sample consists of subpicosecond pulses that cover 550-1000 nm at 85 MHz at an average power of as much as 40 mW. A spectrometer coupled to a multianode photomultiplier tube is used to detect the light simultaneously in 16 wavelength channels, with a resolution of 5-20 nm/channel, depending on the grating. Time-correlated single-photon counting is used to produce time-dispersion curves, which one fits to the diffusion equation to determine absorption and reduced scattering coefficients. We tested the instrument by measuring the time-resolved diffuse reflectance of epoxy phantoms and by performing in vivo measurements on volunteers. The results were similar to those obtained with previous discrete wavelength systems, whereas the full spectrum (610-810 nm) acquisition time was as short as 1 s owing to the parallel acquisition.

Abdomen↗

PubMed2004

Phantom validation and in vivo application of an inversion procedure for retrieving the optical properties of diffusive layered media from time-resolved reflectance measurements.

An experimental validation of an inversion procedure for retrieving the optical properties of layered media from multidistance time-resolved reflectance measurements is presented. The results cover a wide range of optical properties, showing excellent effectiveness and reliability of the procedure in reconstructing the optical properties of a two-layered medium. The optical properties of the first layer and the absorption of the second layer could be retrieved with excellent precision, whereas the reduced scattering coefficient of the second layer was reconstructed with a large error. The first layer thickness could be retrieved with an error less than 50%. An example of retrieval of the optical properties of muscle from in vivo measurements during an arterial occlusion is shown.

Algorithms↗

PubMed2004

Cardiac autonomic derangement and arrhythmias in right-sided stroke with insular involvement.

BACKGROUND AND PURPOSE: The insula of the right cerebral hemisphere may have a major role in cardiac autonomic control. This study was aimed at assessing the effects of acute right insular ischemic damage on heart rate variability (HRV) and arrhythmias. METHODS: Holter monitoring for 24 hours was performed in 103 consecutive patients with first-ever acute ischemic stroke. Time and frequency domain measures of HRV and arrhythmias were considered in all cases. RESULTS: Forty-nine patients (47.5%) had a right-sided infarction, whereas 54 (52.5%) had a left-sided infarction. Insular involvement was present in 33 patients with right-sided stroke (67.3%) and in 36 patients with left-sided stroke (66.6%). When compared with all other stroke patients, subjects with right-sided insular damage showed significantly lower values of the standard deviation of all normal-to-normal (SDNN) R wave to R wave (RR) intervals and of the root mean square of differences (rMSSD) of adjacent normal-to-normal RR intervals, and higher low-frequency/high-frequency ratio values (P<0.05). Right insular stroke was also associated with more complex arrhythmias than any other localization (P<0.05). Moreover, in the whole population of stroke patients, lower values of SDNN were associated with the presence of more frequent and complex arrhythmias. CONCLUSIONS: These findings further support the notion that the right insula is implicated in the autonomic control of cardiac activity and that acute right insular damage may lead to a derangement of cardiac function with potential prognostic implications.

Aged↗

PubMed2004

Stimulation of the subthalamic nucleus compared with the globus pallidus internus in patients with Parkinson disease.

OBJECT: The authors compared the effects of deep brain stimulation (DBS) in the globus pallidus internus (GPi) with those in the subthalamic nucleus (STN) in patients with Parkinson disease (PD) in whom electrodes had been bilaterally implanted in both targets. METHODS: Eight of 14 patients with advanced PD in whom electrodes had been implanted bilaterally in both the GPi and STN for DBS were selected on the basis of optimal DBS effects and were studied 2 months postsurgery in off- and on-stimulus conditions and after at least 1 month of pharmacological withdrawal. Subcutaneous administration of an apomorphine test dose (0.04 mg/kg) was also performed in both conditions. Compared with the off status, the results showed less reduction in the Unified PD Rating Scale Section III scores during DBS in the GPi (43.1%) than during DBS of the STN (54.5%) or DBS of both the STN and GPi (57.1%). The difference between the effects of DBS in the GPi compared with that in the STN or simultaneous DBS was statistically significant (p < 0.01). In contrast, no statistical difference was found between DBS in the STN and simultaneous DBS in the STN and GPi (p < 0.9). The improvement induced by adding apomorphine administration to DBS was similar in all three stimulus modalities. The abnormal involuntary movements (AIMs) induced by apomorphine were almost abolished by DBS of the GPi, but were not affected by stimulation of the STN. The simultaneous stimulation of STN and GPi produced both antiparkinsonian and anti-AIM effects. CONCLUSIONS: The improvement of parkinsonian symptoms during stimulation of the GPi, STN, and both nuclei simultaneously may indicate a similar DBS mechanism for both nuclei in inducing antiparkinsonian effects, although STN is more effective. The antidyskinetic effects produced only by DBS of the GPi, with or without STN, may indicate different mechanisms for the antidyskinetic and antiparkinsonian activity related to DBS of the GPi or an additional mechanism in the GPi. These findings indicate that implantation of double electrodes for DBS should not be proposed as a routine procedure, but could be considered as a possible subsequent choice if electrode implantation for DBS of the STN does not control AIMs.

Adult↗

PubMedDate not supplied

Optical biopsy of bone tissue: a step toward the diagnosis of bone pathologies.

In vivo absorption and reduced scattering spectra of the human calcaneous from 650 to 1000 nm were assessed using a laboratory system for time-resolved transmittance spectroscopy. Measurements were performed on the calcaneous of seven female volunteers ranging from 26 to 82 years of age. The analysis of the absorption spectra, using a linear combination of the key tissue absorbers (bone mineral, water, lipids, oxy- and deoxyhemoglobin), revealed a general decrease in bone mineral content and an increase in lipids with age, which is in agreement with the aging transformations that occur in bone tissues. The scattering spectra were less effective in detecting such changes in older subjects, showing only a minor decrease in the coefficient for these subjects. The capability to noninvasively quantify bone tissue composition suggests a possible use of optical biopsy for the diagnosis of bone pathologies such as osteoporosis, which are characterized by a progressive reduction and transformation of the mineral in the bone matrix.

Adult↗

PubMedDate not supplied

Spectroscopic time-resolved diffuse reflectance and transmittance measurements of the female breast at different interfiber distances.

The first, to our knowledge, in-vivo broadband spectroscopic characterization of breast tissue using different interfiber distances as well as transmittance measurements is presented. Absorption and scattering properties are measured on six healthy subjects, using time-resolved diffuse spectroscopy and an inverse model based on the diffusion equation. Wavelength-tunable picosecond-pulse lasers and time-correlated single-photon counting detection are employed, enabling fully spectroscopic measurements in the range 610 to 1040 nm. Characterization of the absorption and reduced scattering coefficients of breast tissue is made with the aim of investigating individual variations, as well as variations due to different measurement geometries. Diffuse reflectance measurements at different interfiber distances (2, 3, and 4 cm) are performed, as well as measurements in transmittance mode, meaning that different sampling volumes are involved. The results show a large variation in the absorption and scattering properties depending on the subject, correlating mainly with the water versus lipid content of the breast. Intrasubject variations, due to different interfiber distances or transmittance modes, correlate with the known structures of the breast, but these variations are small compared to the subject-to-subject variation. The intrasubject variations are larger for the scattering data than the absorption data; this is consistent with different spatial localization of the measurements of these parameters, which is explained by the photon migration theory.

Adult↗

PubMedDate not supplied

Feasibility of white-light time-resolved optical mammography.

We demonstrate the feasibility of white-light time-resolved optical mammography. The instrumentation is based on supercontinuum light generated in photonic crystal fiber and 32-channel parallel time-correlated single-photon-counting detection. Total measurement time is of the order of 10 min for typical clinical applications. Preliminary measurements performed on volunteers show the ability of the system to determine tissue constituent concentrations and structure over the entire breast area. Furthermore, measurements on a tissue-like sample demonstrate detection and characterization of inclusions.

Adult↗