Multivariate analysis and digital twin modelling: Alternative approaches to evaluate molecular relaxation in photoacoustic spectroscopy

A comparative analysis of two different approaches developed to deal with molecular relaxation in photoacoustic spectroscopy is here reported. The first method employs a statistical analysis based on partial least squares regression, while the second method relies on the development of a digital twin of the photoacoustic sensor based on the theoretical modelling of the occurring relaxations. Methane detection within a gas matrix of synthetic air with variable humidity level is selected as case study. An interband cascade laser emitting at 3.345 µm is used to target methane absorption features. Two methane concentration ranges are explored targeting different absorptions, one in the order of part-per-million and one in the order of percent, while water vapor absolute concentration was varied from 0.3 % up to 2 %. The results achieved employing the detection techniques demonstrated the possibility to efficiently retrieve the target gas concentrations with accuracy > 95 % even in the case of strong influence of relaxation effects.

Widely-tunable mid-infrared fiber-coupled quartz-enhanced photoacoustic sensor for environmental monitoring

A compact widely-tunable fiber-coupled sensor for trace gas detection of hydrogen sulfide (H₂S) in the mid infrared is reported. The sensor is based on an external-cavity quantum cascade laser (EC-QCL) tunable between 7.6 and 8.3 μm wavelengths coupled into a single-mode hollow-core waveguide. Quartz-enhanced photoacoustic spectroscopy has been selected as detecting technique. The fiber coupling system converts the astigmatic beam exiting the laser into a TEM(00) mode. During a full laser scan, we observed no misalignment between the optical beam and the tuning fork, thus making our system applicable for multi-gas or broad absorber detections. The sensor has been tested on N₂:H₂S gas mixtures. The minimum detectable H₂S concentration is 450 ppb in ~3 s integration time, which is the best value till now reported in literature for H₂S optical sensors.

Computer analysis of ultrasonic plaque echolucency in identifying high risk carotid bifurcation lesions

OBJECTIVES

to confirm that plaque echogenicity evaluated by computer analysis, as suggested by preliminary studies, can identify plaques associated with a high incidence of strokes.

MATERIALS AND METHODS

a series of 96 patients with carotid stenosis in the range of 50-99% were studied retrospectively (41 with TIAs and 55 asymptomatic). Carotid plaque echogenicity was evaluated using a computerised measurement of the median grey scale value (GSM). All patients had a CT brain scan to determine the presence of infarction in the carotid territory.

RESULTS

the incidence of ipsilateral brain CT infarctions was 16% in the asymptomatic and 32% in the symptomatic plaques (p =0.076). It was 20% for <70% stenosis and 25% for >70% stenosis (p =0.52). It was 9% for plaques which had a GSM >50 and 40% in those with GSM <50 (p <0.001) with a relative risk of 4.6 (95% CI 1.8 to 11.6).

CONCLUSIONS

the results confirm that computer analysis of plaque echogenicity is better than the degree of stenosis in identifying plaques associated with an increased incidence of CT brain-scan infarction and consequently useful for identifying individuals at high risk of stroke. What is required is a form of image standardisation in order to apply this method to natural history studies with stroke as the endpoint.

Processed bovine pericardium as patch angioplasty for carotid endarterectomy: a preliminary report

Although the routine use of a patch for closure of the arteriotomy after carotid endarterectomy is still debated, patch angioplasty is frequently used to avoid residual stenosis and to lower the incidence of later restenosis. Several materials are widely used for carotid patching, notably, autologous vein, Dacron and polytetrafluorethylene (PTFE). During recent years a heterologous stabilized graft made from bovine pericardium has been introduced. This paper reports the authors' experience of 52 carotid endarterectomies in which a patch of bovine pericardium was used to close the arteriotomy. The patients were followed with colour-duplex scanning over 12-30 months. This biograft did not require preclotting and proved to be easy to suture. Follow-up did not uncover any complications related to graft use. Although this is a preliminary report, it is concluded that bovine pericardium is a promising material for carotid patch angioplasty.

Processed bovine pericardium as patch angioplasty for carotid endarterectomy: a preliminary report

Although the routine use of a patch for closure of the arteriotomy after carotid endarterectomy is still debated, patch angioplasty is frequently used to avoid residual stenosis and to lower the incidence of later restenosis. Several materials are widely used for carotid patching, notably, autologous vein, Dacron and polytetrafluorethylene (PTFE). During recent years a heterologous stabilized graft made from bovine pericardium has been introduced. This paper reports the authors' experience of 52 carotid endarterectomies in which a patch of bovine pericardium was used to close the arteriotomy. The patients were followed with colour-duplex scanning over 12-30 months. This biograft did not require preclotting and proved to be easy to suture. Follow-up did not uncover any complications related to graft use. Although this is a preliminary report, it is concluded that bovine pericardium is a promising material for carotid patch angioplasty.

Improvement of a practical method for priority selection and risk assessment among existing chemicals

In a previous paper (A. Sampaolo and R. Binetti (1986). Regul. Toxicol. Pharmacol. 6, 129-154) an original pragmatic approach for priority setting and risk assessment among existing chemicals was presented. The experience subsequently acquired in the use of the method suggested some improvements, relevant for an easier application. The priority coefficient R has been redefined so that now it can range between zero (all data available) and 1 (no data available). In order to make the final figures more comparable with each other, the indexes are now expressed as percentage with reference to the maximum score obtainable if all parameters of the equation used had reached the maximum score. New general priority index and general risk index formulas, both for personal direct and environmental exposure, are also defined. Another modification concerns the application of the method to specific aspects, such as irreversible effects, immediate and delayed toxic effects, and so on. The method has then been validated on 80 known substances obtaining the respective ranking according to the specific kind of risk.

Elaboration of a practical method for priority selections and risk assessment among existing chemicals

An original pragmatic approach is presented for priority setting among existing chemicals, as a result of a study requested by the European Community Commission. On the basis of a set of physicochemical, toxicological, and ecotoxicological properties considered as fundamental for a first evaluation of the substance, the proposed system develops a score for each property in both the presence and absence of the datum. The properties in this first set are considered additive. Other information on the substance (quantity on the market, plurality of possible exposures, bioconcentration, environmental diffusion, persistence and size of risk population) is included in a second set of multiplier parameters. Through this simple and self-improving system it is possible to work out, using different final formulas, different lists for different needs. Using 30 well-known substances as examples with which to check the system, it is possible to see how these substances distribute themselves as to priority for environmental or for direct personal exposure.