In recent years, statistical studies highlighted an increasing incidence of cardiovascular diseases (CVD) which reflected on additional costs on the healthcare systems worldwide. Pulse wave velocity (PWV) measurement is commonly considered a CVD predictor factor as well as a marker of Arterial Stiffness (AS), since it is closely related to the mechanical characteristics of the arterial wall. An increase in PWV is due to a more rigid arterial system. Because of the prevalence of the elastic component, in young people the PWV is lower than in the elderly. Nowadays, invasive and non-invasive methods for PWV assessment are employed: there is an increasing attention in the development of non-invasive devices which mostly perform a regional PWV measurement (over a long arterial portion) rather than local (over a short arterial portion). The accepted gold-standard for non-invasive AS measurement is the carotid-femoral PWV used to evaluate the arterial damage, the corresponding cardiovascular risk and to adapt the proper therapy. This review article considers the main commercially available devices underlining their operating principles in terms of sensors, execution mode, pulse waveform acquired, site of measurement, distance and time estimation methods, as well as their main limitations in clinical practice.

Arterial simulators are a useful tool to simulate the cardiovascular system in many different fields of application and to carry out in vitro tests that would constitute a danger when performed in in vivo conditions. In the literature, a thriving series of in vitro experimental set-up examples can be found. Nevertheless, in the current scientific panorama on this topic, it seems that organic research from a metrological and functional perspective is still lacking. In this regard, the present review study aims to make a contribution by analyzing and classifying the main concerns for the cardiovascular simulators proposed in the literature from a metrological and functional point of view, according to their field of application, as well as for the transducers in the arterial experimental set-ups, measuring the main hemodynamic quantities in order to study their trends in specific testing conditions and to estimate some parameters or indicators of interest for the scientific community.

Maximum depth of penetration (DOP) is among the most relevant parameters in quality assurance programs for Ultrasound (US) scanners. Nowadays, a generally-accepted protocol for DOP estimation is still awaited and, in common practice, DOP is visually assessed despite the low accuracy. To overcome the eye-based assessment subjectivity, automatic image analysis methods have been proposed in literature. The present work focuses on a novel automatic method, namely the adaptive Signal to Noise Ratio (SNR) threshold method (AdSTM), developed in the MATLAB environment, by comparing it with an existing automatic approach, namely the tangent threshold method (TTM), and the mean judgment of eight observers (naked eye method). The three investigated methods were applied on data acquired from four US scanners for general purpose imaging, equipped with linear, convex, and vector array probes. Tests were carried out in two different configuration settings (raw scanner and default preset working conditions). AdSTM outcomes were tested by means of Monte Carlo Simulations. Most of measurement results were compatible despite the fact that the AdSTM seemed to be more sensitive and faster than the TTM. The results analysis confirms the higher dispersion of the naked eye method in DOP assessment with respect to the proposed automatic methods.

Young Modulus estimation in arteries is a relevant issue, since such parameter is characteristic of their mechanical and structural properties. It is well-known that human arteries undergo modifications due to physiological aging and/or cardiovascular pathologies resulting in Young Modulus variations through time. In literature, the validation of specific techniques for in vivo monitoring of arterial stiffness is carried out through vessel phantoms that reproduce the pressure waves propagation for different stiffness conditions. A physical model widely used in the current state of the art is based on the well-known Moens-Korteweg equation which correlates the Young Modulus to the Pulse Wave Velocity (PWV). In the present work a novel experimental set-up has been designed and tested to simulate Young Modulus variation of a natural rubber (NR) tube through the application of different tensioning states. Such variation has been estimated by transit time measurements on the pressure waves acquired through Linear Variable Differential Transformer (LVDT) sensors. The relevance of the present study lies in the possibility to simulate human vessel stiffness increase and to provide a testing device for the validation of in vivo techniques able to assess arterial stiffness.

Depth of penetration (DOP) has been investigated in the scientific literature as an informative parameter able to monitor over time both the sensitivity and the general performance of ultrasound (US) diagnostic systems. In common practice, this parameter may suffer from operator-related errors due to its visual assessment. Different image analysis algorithms have been proposed in the literature to address this issue. In this regard, this work evaluates the adaptive SNR threshold method (AdSTM) on six US diagnostic systems equipped with three US probe models, operating at four frequencies. Data were collected from a US phantom with two distinct zones with different attenuation coefficients. The AdSTM results were compared to the outcomes provided by the naked eye method (NEM), which was performed by five non-medical observers. Despite the small population sample of observers, the obtained results were generally consistent across methods, and suggest the implementation of a calibration procedure for AdSTM, and more extensive testing.

Nowadays, Doppler system performance evaluation is a widespread issue because a shared worldwide standard is still awaited. Among the recommended Doppler test parameters, the lowest detectable signal could be considered mandatory in Quality Control (QC) protocols for Pulsed Wave (PW) Doppler. Such parameter is defined as the minimum signal level that can be clearly distinguished from noise and therefore, it is considered as related to PW Doppler sensitivity. The present study focuses on proposing and validating a novel image analysis based method for the estimation of the Lowest Detectable Signal in the spectrogram image (LDSIMG), namely Automatic Doppler Sensitivity Measurement Method (ADSMM), as well as to compare its results with the outcomes retrieved from the Naked Eye Doppler Sensitivity Method (NEDSM), based on the mean judgment of three independent observers. Data have been collected from a Doppler flow phantom, through three ultrasound systems for general purpose imaging, equipped with two linear array probes each and with two configuration settings. Results are globally compatible among the proposed methods, US systems and settings. Further studies could be carried out on a higher number of US diagnostic systems, Doppler frequencies and observers, as well as with different probe and phantom models.