Salvatore Andrea Sciuto

Comparative evaluation of ultrasound scanner accuracy in distance measurement

The aim of the present study is to develop and compare two different automatic methods for accuracy evaluation in ultrasound phantom measurements on B-mode images: both of them give as a result the relative error e between measured distances, performed by 14 brand new ultrasound medical scanners, and nominal distances, among nylon wires embedded in a reference test object. The first method is based on a least squares estimation, while the second one applies the mean value of the same distance evaluated at different locations in ultrasound image (same distance method). Results for both of them are proposed and explained.

Linear Model and Algorithm to Automatically Estimate the Pressure Limit of Pressure Controlled Ventilation for Delivering a Target Tidal Volume

Objective. To theoretically assess the viability of an automatic procedure to support the anesthesiologist in properly setting mechanical ventilators when the operating conditions are switched from volume controlled to pressure controlled ventilation whilst maintaining the preset tidal volume. The procedure is based on a simple linear model of the ventilator breathing system with constant parameters and utilizes the signals gathered by the ventilator without the need to add further equipment. After a short period of stable volume controlled ventilation with the desired tidal volume, the herewith described algorithm allows the calculation of the value of pressure limit to set in pressure controlled mode which assures the previously settled tidal volume with the same breathing frequency and inspiratory-expiratory time ratio. Methods. The algorithm allows the online identification of the four parameters necessary for the mathematical model that are obtained by means of a direct comparison between the pressure, flow and volume waveforms generated by the model and the analog signals provided by the ventilator. The theoretical approach was validated by two different ventilators, various settings, two breathing circuits, endotracheal tubes of various sizes and two mechanical simulators of the respiratory system operating in various conditions. Results. Errors usually less than 5% (p < 0.05) on the target tidal volume were obtained for various settings typically used for adult ventilation in less than 10 s. The theoretical approach shows its limitations (errors of 10± 5%, p < 0.05) at high breathing frequencies (30–40 bpm) and low tidal volumes (200–300 ml). Conclusions. The proposed theoretical approach shows the viability, for adult settings, of one of the simplest mathematical model for mechanical ventilation in order to quickly and safely switch from volume controlled to pressure controlled ventilation. The algorithm could easily be in perspective implemented in the software of the ventilator providing the anesthesiologist with an indication on the value of pressure limit to set in order to safely switch ventilation mode.

A novel approach to a phantom based method for maximum depth of penetration measurement in diagnostic ultrasound: a preliminary study

In the present work a new approach for maximum depth of ultrasound signal visualization has been proposed by means of a tissue mimicking phantoms: the novel method is based on a threshold on the tangent applied to the mean depth profile that is drawn by averaging adjacent columns in the diagnostic image. It has been implemented and preliminary tested on three different diagnostic systems equipped with linear array probes under similar settings: results have been compared with the mean judgment of 5 observer and with output from another method, based on a threshold of the mean depth profile above the noise level, as suggested in literature. Even though a not negligible difference among some results is observed, due likely to the high electronic noise level displayed in the ultrasound image, the tangent method seems to agree with observer judgment and be more sensitive to echo signal than the other one, even at higher noise levels. Nevertheless other test are going to be performed in the next future for a more detailed characterization of the method.

Design and development of a rheometer for biological fluids of limited availability

From studies on the dynamic characterization of human bones, it is noticed that reference data on the viscous behavior of the bone marrow are quite poor. Dependently from marrow limited availability and its opacity, we have not been able to retrieve a tool of appropriate characteristics able to measure bone marrow viscosity. Therefore, principal techniques for the viscosity measurement have been preliminarily examined, and a device suitable for viscosity measurements of biological fluids has been realized. In particular, a rotational rheometer has been developed: it is a coaxial cylinders system, where the fluid flows dragged by the inner cylinder. The device is an absolute rheometer, that is, particularly useful as nowadays it is not known the classification of the bone as far as it concerns its viscous behavior. In this work a preliminary evaluation of the metrological characteristics of the measurement system has been carried out and its main metrological performances have been evaluated.

A novel approach for determining the trajectory and speed of a supersonic object

An experimental set-up is presented for tracking the trajectory of a supersonic object using minimal resources. The proposed set-up, based on the use of low-cost pressure transducers, a general-purpose conditioning system and off-the-shelf instrumentation, is capable of determining the bullet trajectory, speed and hit point in open air use. The methodology is based on the post-processing of shock wave information gathered by means of three spaced sensor clusters, each one comprising three pressure transducers. The pressure sensors are used to detect the times of arrival of the shock wave generated by the bullet; on the basis of geometrical considerations, from the six time delays measured by means of the nine pressure sensors, the bullet direction and its speed are calculated. The novel contribution of the methodology described here, with respect to similar methods described in the literature, is the post-processing method used. The metrological performance of the realized experimental set-up was calculated by means of a priori analysis to theoretically determine the uncertainty maps as a function of bullet direction, after the geometry of the clusters, their relative positions and the time resolution were chosen. The theoretical analysis was then verified with field tests in a marksmanship training range with series of straight shots hitting the target plane from different positions at a distance of about 100 m, with both perpendicular and inclined shots. The results obtained with the shots perpendicular to target plate are: the error in hit points is always less than 65 mm while the error associated in angle values lies in the range from −0.017 to 0.010 rad (from −1.0° to 0.6°). The worst results obtained with inclined shots, i.e. those not perpendicular to the target plane, are: hit point error always less than 196 mm and range of variation of error angle of −0.017 and 0.038 rad (−1.0° and 6.8°). Overall examination of the theoretical and experimental results indicates the critical strengths of the method, namely accounting for environmental parameter fluctuations and accuracy in the evaluation of relative positions among the clusters.

A preliminary study on a method for objective uniformity assessment in diagnostic ultrasound imaging

Ultrasound image uniformity is a parameter often used in medical ultrasound system testing, as an object can be displayed in different shapes and textures within the field of view, depending on instrumentation performances. Therefore Ultrasound Image Uniformity evaluation can be used for failures detection as well for quality assurance. In this paper a novel method is developed to measure B-mode image uniformity over the whole field of view or its part (Region Of Interest): it is based on the image gray level histogram weighted by a sigmoid function to detect non uniformities. Preliminary results are explained and discussed.

A novel fiber-optic measurement system for the evaluation of performances of neonatal pulmonary ventilators

Published standards for the performance evaluation of pulmonary ventilators are mainly directed to manufacturers rather than to end-users and often considered inadequate or not comprehensive. In order to contribute to overcome the problems above, a novel measurement system was proposed and tested with waveforms of mechanical ventilation by means of experimental trials carried out with infant ventilators typically used in neonatal intensive care units: the main quantities of mechanical ventilation in newborns are monitored, i.e. air flow rate, differential pressure and volume from infant ventilator are measured by means of two novel fiber-optic sensors (OFSs) developed and characterized by the authors, while temperature and relative humidity of air mass are obtained by two commercial transducers. The proposed fiber-optic sensors (flow sensor Q-OFS, pressure sensor P-OFS) showed measurement ranges of air flow and pressure typically encountered in neonatal mechanical ventilation, i.e. the air flow rate Q ranged from 3 l min−1 to 18 l min−1 (inspiratory) and from −3 l min−1 to −18 l min−1 (expiratory), the differential pressure ΔP ranged from −15 cmH2O to 15 cmH2O. In each experimental trial carried out with different settings of the ventilator, outputs of the OFSs are compared with data from two reference sensors (reference flow sensor RF, reference pressure sensor RP) and results are found consistent: flow rate Q showed a maximum error between Q-OFS and RF up to 13 percent, with an output ratio Q RF/Q OFS of not more than 1.06 ± 0.09 (least square estimation, 95 percent confidence level, R 2 between 0.9822 and 0.9931). On the other hand the maximum error between P-OFS and RP on differential pressure ΔP was lower than 10 percent, with an output ratio ΔP RP/ΔP OFS between 0.977 ± 0.022 and 1.0 ± 0.8 (least square estimation, 95 percent confidence level, R 2 between 0.9864 and 0.9876). Despite the possible improvements, results were encouraging and suggested the proposed measurement system can be considered suitable for performances evaluation of neonatal ventilators and useful for both end-users and manufacturers.

A texture analysis approach for objective uniformity evaluation in diagnostic ultrasound imaging: A preliminary study.

Ultrasound image uniformity is an important parameter for quality assurance in diagnostic ultrasounds, but it is usually assessed by a qualitative judgement of technicians so its estimation is rough and subjective. In this work a novel method is developed to give an objective measurement of the Bmode image uniformity over the whole field of view or some of its part: the Texture Distribution Analysis Method (TDAM) is based on a segmentation of the Region of Interest, depending on some texture features calculated from co-occurrence matrices. Results on a set of 10 test images with different non-uniformities (Uniformity Image Test Set or UITS) show a good sensitivity and agreement of TDAM with the mean judgment by 5 human observers (TUV): TDAM and TUV uniformity values are coherent for the whole UITS, nevertheless a high uncertainty in uniformity values has been observed (up to 28 percent). Preliminary results look encouraging and more efforts are worth to refine the method.

A Comparative Study on the Influence of Probe Placement on Quality Assurance Measurements in B-mode Ultrasound by Means of Ultrasound Phantoms

To check or to prevent failures in ultrasound medical systems, some tests should be scheduled for both clinical suitability and technical functionality evaluation: among them, image quality assurance tests performed by technicians through ultrasound phantoms are widespread today and their results depend on issues related to scanner settings as well as phantom features and operator experience. In the present study variations on some features of the B-mode image were measured when the ultrasound probe is handled by the technician in a routine image quality test: ultrasound phantom images from two array transducers are processed to evaluate measurement dispersion in distance accuracy, high contrast spatial resolution and penetration depth when probe is handled by the operator. All measurements are done by means of an in-house image analysis software that minimizes errors due to operator’s visual acuity and subjective judgment while influences of ultrasound transducer position on quality assurance test results are estimated as expanded uncertainties on parameters above (measurement reproducibility at 95 percent confidence level): depending on the probe model, they ranged from ±0.1 to ±1.9 mm in high contrast spatial resolution, from ±0.1 to ±5.5 percent in distance measurements error and from ±1 to ±10 mm in maximum depth of signal visualization. Although numerical results are limited to the two examined probes, they confirm some predictions based on general working principles of diagnostic ultrasound systems: (a) measurements strongly depend on settings as well on phantoms features, probes and parameters investigated; (b) relative uncertainty due to probe manipulation on spatial resolution can be very high, i.e. from 10 to more than 30 percent; (c) Field of View settings must be taken into account for measurement reproducibility as well as Dynamic Range compression and phantom attenuation.

The “Strain-Gauge Thermocouple”: A novel device for simultaneous strain and temperature measurement

A novel methodology for simultaneous strain and temperature measurements by means of an ac powered electrical resistance strain gauge connected to a strain conditioner using thermocouple wires is proposed and validated. To this aim a specific device has been designed and implemented; the characteristics of the electronic circuit for signal conditioning have then been tested in order to determine the overall performances in temperature and strain measurements. The field verification of the method is conducted by imposing strain fields in the range from 0 to about 700 μm/m and temperature variations in the range from −10 to 100 °C. The difference between the strain measured by the proposed device and the one evaluated by a conventional digital strain meter was always less than 4 μm/m while the mean temperature discrepancy was 0.5 °C with respect to the reference temperature measured with a K-type thermocouple. Finally, compensation of temperature effects on the actual strain value has been performed while t...