M. Calzolai

A real-time two-dimensional pulsed-wave Doppler system

An experimental system was developed to acquire and visualise in real-time two-dimensional (2-D) velocity maps. Data acquisition is performed by using a modified commercial echograph based on a 5-MHz, 128-element linear-array transducer with electronic focussing and beam steering. Additional electronics were integrated into the echograph to implement a 2-D Doppler system capable of measuring the velocity component on the scanning plane. Suitable axial and lateral scanning methods were studied to obtain Doppler measurements over a scanning area. A colour image of the estimated velocity field is presented in real time on a personal computer using different visualisation techniques. The system performance was tested experimentally both in vitro and in vivo on a human carotid artery.

A 3-D PW ultrasonic Doppler flowmeter: theory and experimental characterization

A complete 3-D ultrasonic pulsed Doppler system has been developed to measure quantitatively the velocity vector field of a fluid flow independently of the probe position. The probe consists of four 2.5 MHz piezocomposite ultrasonic transducers (one central transmitter and three receivers separated by 120/spl deg/) to measure the velocity projections along three different directions. The Doppler shift of the three channels is calculated by analog phase and quadrature demodulation, then digitally processed to extract the mean velocity from the complex spectrum. The accuracy of the 3-D Doppler technique has been tested on a moving string phantom providing an error of about 4% for both amplitude and direction with an acquisition window of 100 ms.

Respiratory rate assessments using a dual-accelerometer device.

Monitoring of respiration-related thoracic movements may be useful to assess respiratory rate (RR) objectively. RR was measured during spontaneous breathing, voluntarily modified breathing, and exercise hyperpnoea in normal subjects via visual inspection, spirometry and a pair of accelerometers positioned on the torso. Spirometric and accelerometric values of RR recorded during relaxed breathing were (mean±SD) 21.44±1.41bpm and 21.06±2.17bpm; during voluntarily augmented breathing, these values rose to 29.44±4.61bpm and 29.23±5.33bpm, respectively; spirometric and accelerometric RR values did not differ in any of the cases. RR assessment was unaffected by recumbence. During handgrip, spirometric (16.43±3.10bpm) and accelerometeric (16.22±2.76bpm) control RR values did not differ and increased to comparable levels (24.22±7.30 and 24.82±5.45bpm, respectively) by the end of exercise. At rest, visual (18.94±3.45bpm) and accelerometric (19.27±3.83bpm) RR values were compliant in normal subjects as well as in scoliotic and obese patients. Accelerometers are a reliable tool for monitoring RR, during both eupnoea and stressed breathing.

FEMMINA: a fast echographic multiparametric multi-imaging novel apparatus

The aim of the work is to present a novel apparatus for experimental activity in research of new methods for studying material and biological tissue with ultrasound. FEMMINA (Fast Echographic Multiparametric Multi Imaging Novel Apparatus) is a hardware and software platform dedicated to ultrasonic signal and image processing. It uses the radiofrequency signal for multiparametric calculation and presentation with a multiprocessing digital architecture. The architecture is designed to be modular, expandable and aimed at embracing different ultrasonic investigation techniques. It provides a multianalysis and interactive image system not only for clinical usage but also for all applications where a high image rate production is required. In order to obtain an efficient interactive system, it was also necessary to realize a fast signal processing, as well as to implement a fast visualization tool for managing multiple images. The platform is completely programmable, and for a specific application it can be on-line reconfigured in dependence of the parameters that, from time to time, must be evaluated. Spectral images of biological in-vitro and in-vivo tissue, obtained through the Discrete Wavelet Transform (DWT) by using new processing algorithms are presented as preliminary applications of the platform, as well as vector images for blood flow 2-D Doppler investigation. Innovative blood images, obtained without using the Doppler effect, and novel vector distribution images for blood velocity are reported.

RADIOFREQUENCY REAL TIME PROCESSING: ULTRASONIC SPECTRAL IMAGES AND VECTOR DOPPLER INVESTIGATION

Novel radio frequency processing techniques for biological tissue characterization with ultrasound are presented in order to improve the diagnostic power of ultrasonic echographic systems. Spectral images of biological “in-vitro” and “in-vivo” tissue, obtained through the Discrete Wavelet Packet Transform (DWPT) are presented, as well as velocity vector maps of blood flow obtained with 2-D Doppler investigation. The implementation of the Discrete Wavelet Packet Transform through a digital filter produces, for each acquired frame, real time spectral maps, in different frequency bands. Multi-parametric images are composed by merging these maps using a dedicated “balance image fusion” algorithm. New blood images, obtained without using the Doppler effect, for “in-vivo” and “in-vitro” experiments are presented based on the exploitation of non-linear ultrasound-medium interaction effects [1,2,3,4]. The proposed spectral processing procedure seems to be suitable to perform tissue characterization. Pathological portions inside tissue could be detected thanks to their different echo frequency content which in turns is determined by linear and non-linear ultrasonicmedium interaction. The target of future clinical applications is to investigate the potential of the procedure as a “virtual biopsy”. Vector Doppler multi parametric images are obtained with compound measurements of Doppler shifts along different directions, and superimposing the resulting 2-D velocity vector maps to the conventional morphological B-mode representation [5,6,7] The results, here presented, were produced by employing a hardware and software platform dedicated to ultrasonic signal and image processing [8,9,10]. The radiofrequency signal for multi parametric calculation and presentation with a multiprocessing digital architecture was used. This platform provides a multi analysis and

Ultrasonic Images of Tissue Local Power Spectrum by Means of Wavelet Packets for Prostate Cancer Detection

The aim of this work is to present a novel apparatus for experimental activity in research where a high frequency signal must be acquired and processed in real-time, and represented through a multi-image visualization tool. The proposed apparatus is a hardware and software platform dedicated to signal and/or image processing and fast data visualization. Currently the system is employed for studying new algorithms for biological tissue ultrasound investigation 1,2. Real-time operation mode designates clinical environment as its elective application because fast data processing is a necessary prerequisite in order to evaluate the on-line diagnostic performance of different investigation methods. Furthermore, for research purposes, the possibility to have simultaneous views of different ultrasonic parameters is essential for an efficient analysis, verification and modelling of the specific ultrasound-media interaction phenomenon .

Real Time Processing of the Radiofrequency Echo Signal for On-Line Spectral Maps

In this work we presented a hardware-software platform, which was designed to be expandable, modular, and adaptable to any other system which needs to produce significant and easily readable real time images. Such platform, being completely programmable, can also be reconfigured in dependence of the object being investigated.

An Integrated Acousto/Ultrasonic Structural Health Monitoring System for Composite Pressure Vessels

This paper describes the implementation of a structural health monitoring (SHM) method for mechanical components and structures in composite materials with a focus on carbon-fiber-overwrapped pressure vessels (COPVs) used in the aerospace industry. Two flex arrays of polyvinylidene fluoride (PVDF) interdigital transducers have been designed, realized, and mounted on the COPV to generate guided Lamb waves (mode A0) for damage assessment. We developed a custom electronic instrument capable of performing two functions using the same transducers: passive-mode detection of impacts and active-mode damage assessment using Lamb waves. The impact detection is based on an accurate evaluation of the time of arrival and was successfully tested with low-velocity impacts (7 and 30 J). Damage detection and progression is based on the calculation of a damage index matrix which compares a set of signals acquired from the transducers with a baseline. This paper also investigates the advantage of tuning the active-mode frequency to obtain the maximum transducer response in the presence of structural variations of the specimen, and therefore, the highest sensitivity to damage.

Acoustoseismic Method for Buried-Object Detection by Means of Surface-Acceleration Measurements and Audio Facilities

An experimental setup for acoustoseismic detection of shallow buried objects is presented. The seismic (Rayleigh) waves were generated by exciting an acoustic airborne source by a series of sine-wave bursts, which were designed to cover a frequency range (100-1000 Hz) large enough to distinguish the vibrational characteristics of buried compliant objects. The signals were recorded by means of contact-acceleration microelectromechanical-system sensors moved above different buried objects (compliant and rigid). Signal acquisitions on only sandy soil revealed the natural variability of the outdoor test bed. This variability of soil parameters pointed out the difficulties of buried-object detection based on the amplitude thresholding of the signal spectrum. For this aim, the signals were processed in both time and frequency domains. An audio-channel output was devised to avail of the human hearing apparatus in distinguishing the buried objects according to spatial variations of the acceleration signals obtained by scanning the soil surface.

Silicon micromachined accelerometers for the detection of compliant anti-personnel landmines

Acoustic methods have been recently investigated for the detection of shallow landmines. Some plastic landmines have a compliant case which can made to vibrate by an airborne excitation like a loudspeaker. Our study is based on the possibility to detect landmines by contact or non-contact sensors like accelerometers or phonometers. Phonometers can provide sufficient seismic sensitivity but their response is influenced by direct acoustic wave coupling from the driving source. On the contrary accelerometers are much less influenced by the direct acoustic wave coupling and they have high sensitivity to acquire soil surface vibrations. In our experiments we can measure typical accelerations in order of 2 m/s2 with sensitivity of 800 mV/g. The acceleration signal elaboration and visualization developed in this work demonstrates the suitability of these sensors for acoustic landmine detection study and allows a fast analysis to evaluate the presence of a buried landmine.