A. Evangelisti

Texture Classification of Retinal Layers in Optical Coherence Tomography

This work investigates the ability of texture analysis to yield discrimination of retinal tissue layers in the images provided by Optical Coherence Tomography (OCT). In fact, this relatively new imaging technology allows noninvasive visualization of retinal layers. Their segmentation is a prerequisite for any computer method that aims to objectively extract valuable information, regarding the condition and the progression of disease and therapy. Since the regularities of biological tissue can be captured by texture analysis in a straightforward way, a computer approach is proposed based on co-occurence matrices and artificial neural networks (ANN) for the classification and analysis of single retinal layers. A subset of ten normal eyes has been used for the training phase, and another subset of ten normal eyes has been used for testing the system performance. For inner retinal layers, accuracy was 79%, specificity about 71% and sensibility was 87%. Slightly lower values were obtained for outer retinal layers. These preliminary results suggest that this approach may be useful as a prototype system for a quantitative characterization of retinal tissue.

Recovery of 0.1 Hz microvascular skin blood flow in dysautonomic diabetic (type 2) neuropathy by using Frequency Rhythmic Electrical Modulation System (FREMS)

Synchronized oscillation of smooth muscle cells tension in arterioles is the main control system of microvascular skin blood flow. An important autogenic vasomotion activity is recognized in 0.1Hz oscillations through power spectrum analysis of laser Doppler flowmetry. Severe dysautonomia in diabetic neuropathy is correlated with loss of 0.1Hz vasomotor activity, hence with impaired blood microcirculation. FREMS is a novel transcutaneous electrotherapy characterized by sequences of electrical stimuli of high voltage and low pulse duration which vary both in frequency and duration. We have evaluated the changes in laser Doppler flow in the volar part of the forearm before, during and after FREMS. Normal controls (n=10, 6 females, age range 21-39 years) demonstrated significant 0.1Hz vasomotion power spectra at baseline conditions associated with large oscillations of adrenergic cutaneous sweat activity sampled from the hand; people with diabetes type 2 and severe dysautonomia (n=10, 5 females, age range 63-75 years) displayed a significant decrease of 0.1Hz vasomotion power spectra. During FREMS application we observed an increase (p<0.05) of 0.1Hz vasomotion power spectra only in the diabetic group, despite persistence of adrenergic cutaneous sweat activity suppression in this group. However, after the application of the stimuli, the relative energy values around the 0.1Hz peak remained significantly higher than preapplication values in the diabetic group (p<0.05). From these findings, we suggest that FREMS is able to synchronize smooth cell activity, inducing and increasing 0.1Hz vasomotion, independently from the autonomic nervous system.

Effect of local blood flow in thermal regulation in diabetic patient

The presence of dysautonomia in diabetic neuropathy is correlated with impairment of vasomotor activity that drives blood microcirculation. Microcirculation, in turn, plays an important role in thermoregulation. In this work, we investigate the changes between two different physiological conditions of diabetic patients, induced by FREMS application, in the control of skin temperature, using a minimally invasive experiment. Skin is warmed up to a fixed temperature (44 °C) for a few minutes, then the heat source is turned off, letting the skin recover its physiological temperature. Both temperature and local blood flow, the latter measured with laser Doppler, are monitored during the experiment. A simple model of the cooling phase is used to evaluate the time constants involved in the process. Results indicate that significant differences exist in the model parameters between the two conditions.

Modelling of Thermal Hyperemia in the Skin of Type 2 Diabetic Patients

The microcirculatory response to thermal stimulation involves both an axon reflex and NO-mediated activation. The analysis of the microcirculatory flow following thermal stimulation may therefore enhance the detection of any impairment of the small unmyelinated fibres that are involved in the axon reflex. The aim of this work is to establish a method of non-invasive measurement of small fibre impairment. The microcirculatory flow in response to local heating is measured by using a laser Doppler instrument, and mathematically modelled to extract a set of quantitative parameters. The results confirm that there is a significant difference in the parameters modelling the axon reflex between diabetic and control subjects, while no significant difference is found in the parameters modelling the NO-mediated activation.

A Theoretical Study of Arterial Disease by Transfer Function Analysis

A general method is proposed for a theoretical evaluation of the hemodynamic effects of stenosis on the arterial subsystem affected by it. In particular, it is applied to a lower limb stenosis, so as to compare the results of the theoretical analysis to those that other authors have obtained experimentally by processing Doppler ultrasound blood flow velocity measurements proximal and distal to a stenosis in the superficial femoral artery (SFA).

Shape analysis of the microcirculatory flow wave.

The cardiovascular system and its alterations are a crucial aspect of physiology and medicine. Non-invasive assessment of the functional properties of circulation is of considerable interest to clinicians and physiologists. In this work we investigate the possibility of detecting alterations of the flow waveform in microcirculation, using non-invasive measurements based on a laser Doppler flowmeter. As a test case, we focus on the effect of ageing. Skin is warmed up to a fixed temperature (44 °C) during measurement, to increase blood flow. The shape of the perfusion waveform during each heart beat after the flow was stabilized was used to estimate dynamic parameters of the microcirculatory system. Both the wave rise time, defined as the delay between the diastolic minimum and the following systolic maximum, and the oscillation fraction, defined as the normalized difference between the maximum and minimum flow, present significant variation with age.

Analysis of the microcirculatory pulse wave: age-related alterations

Morphological analysis of the pulse wave of central blood pressure signal is commonly used for the study of cardiac and vascular properties, but very few attempts were performed for analyzing the peripheral pulse wave of blood flow. In this work, we analyzed this waveform using classical methods, based on the application of FFT, followed by principal components analysis, for assessing the properties of the blood flow. As a sample problem, we evaluated the capability of the proposed method of assessing the alterations correlated with the aging of the vascular system. Results show a good discrimination between the different age groups, confirming the validity of the approach.

Effect of Frequency Rhythmic Electrical Modulation System (FREMS) on 0.1 Hz microvascular skin blood flow in dysautonomic diabetic (type 2) neuropathy

Synchronized oscillation of smooth muscle cells tension in arterioles is the main control system of microcirculation. An important autogenic vasomotion activity is recognized in the 0.1 Hz oscillations observed by means of power spectrum analysis of laser doppler flowmetry. Severe dysautonomia in diabetic neuropathy is correlated with the loss of 0.1 Hz vasomotion activity. FREMS is a novel transcutaneous electrotherapy characterized by sequences of high voltage and short width electrical pulses which vary both in frequency and width, but not in voltage. We have evaluated the changes in laser doppler flow in the volar part of the forearm before, during and after FREMS. During FREMS application we observed an increase (p < 0.05) of 0.1 Hz power spectra, despite the suppression of adrenergic cutaneous sweat activity. From these findings, we suggest that FREMS is able to synchronize the smooth cells activity, inducing and increasing 0.1 Hz vasomotion activity, independently from the adrenergic influence.

Symbolic Indexing of Cardiological Sequences Through Dynamic Curve Representations

Digital image analysis supports diagnostic activities by highlighting geometric and temporal features of physiological phenomena that are not perceivable to the human observation. These features can be exploited to build up symbolic representations of visual data in medical reports and to index them within large databases. The comparison of such representations against descriptive queries capturing the properties of significant physiological phenomena supports new diagnostic approaches through the systematic analysis of database reports. A prototype system is presented which supports the construction of symbolic representations and their comparison against descriptive queries capturing geometric and temporal properties of time-varying 2D shapes deriving from dynamic cardiac analyses. The system is embedded within a visual shell allowing physicians to compose content-oriented queries through iconic interaction.