Multidimensional spectral analysis of the ultrasonic radiofrequency signal for characterization of media.

The importance of the analysis of the radiofrequency signal is by now recognized in the field of tissue characterization via ultrasound. The RF signal contains a wealth of information and structural details that are usually lost in the B-Mode representation. The HyperSPACE (Hyper SPectral Analysis for Characterization in Echography) algorithm presented by the authors in previous papers for clinical applications is based on the radiofrequency ultrasonic signal. The present work describes the method in detail and evaluates its performance in a repeatable and standardized manner, by using two test objects: a commercial test object that simulates the human parenchyma, and a laboratory-made test object consisting of human blood at different dilution values. In particular, the sensitivity and specificity in discriminating different density levels were estimated. In addition, the robustness of the algorithm with respect to the signal-to-noise ratio was also evaluated.

Differentiation of Breast Lesions by Use of HyperSPACE: Hyper-Spectral Analysis for Characterization in Echography.

Early diagnosis represents the cornerstone in breast cancer control. Ultrasound is still a valid tool because of its low invasiveness, reduced costs and reduced risk of harm, but better exploitation of its potential is necessary to extract information on tissue features. The proposed method, HyperSPACE (hyper-spectral analysis for characterization in echography), which processes the ultrasonic radiofrequency signal in an N-dimension spectral hyperspace to define several characteristic parameters of the tissue under investigation, was used with the aim of differentiating two types of breast lesion: infiltrating ductal carcinoma and fibroadenoma. The analyzed data set consisted of 2000 radiofrequency frames related to 200 sections of pathologic breast nodules: 104 infiltrating ductal carcinomas and 96 fibroadenomas. The algorithm was trained on single radiofrequency frames related to 50 sections (26 carcinomas, 24 fibroadenomas) to recognize the two pathologies considered, and all the radiofrequency frames related to the other 150 sections were classified, yielding a sensitivity of 92.2%, specificity of 93%, positive predictive value of 93.2% and negative predictive value of 91%. The results were compared with those of RULES (radiofrequency ultrasonic local estimators), a processing method set developed by our group and used by other researchers in clinical and laboratory environments.

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.

A retrospective study to reduce prostate biopsy cores by a real time interactive tool.

OBJECTIVE: Prostate carcinoma (PCa) is one of the most frequent neoplasms, with more than 110.000 new cases/year in Europe. As PCa is not clearly demonstrable at transrectal ultrasound (TRUS), guidelines on TRUS guided biopsy suggest to perform a random tissue sampling (at least 8-12 "cores" depending on gland volume). Although accuracy grows with core number, patient discomfort and adverse event probability grow as well. Thus it would be worth to aim to reduce the number of prostate biopsy cores without loss of diagnostic accuracy. MATERIALS AND METHODS: A retrospective study was performed to evaluate the feasibility of an improved version of a rtCAB tool developed at DEIS (University of Bologna) for the reduction of prostate biopsy cores. rtCAB is an innovative processing technique which enhances TRUS video stream by a live false color overlay image that helps the physician to perform the biopsy by guiding the sampling into target zones. In order to train rtCAB, a monocentric, single operator prostate gland adenocarcinoma database has been built. The database enlists 81 patients, for a total of 743 prostate byoptic (PBx) cores and 14860 ROI. For each patient we collected age, PSA levels, digital rectal examination (DRE) findings, presence or absence of focal lesions, and prostate volume. During TRUS, raw ultrasound data were acquired and associated to each PBx core. For each core we collected both the radio frequency (RF) signal and the histological outcome. RESULTS: The whole system was optimized for reducing the number of false positives while preserving an acceptable number of false negatives. Comparing to a classical PBx approach (8-12 cores), the estimated positive predictive value (PPV) of our method increased from 25% to 40%, with an overall sensitivity of 85%. CONCLUSIONS: Preliminary results show that the proposed tool can provide real-time feedback to the operator during TRUS. Sensitivity and PPV values suggest that a reduction of almost 50% the number of biopsy cores without losing in diagnostic accuracy is feasible. A prospective study is needed to further confirm these preliminary retrospective results.

Multipulse technique exploiting the intermodulation of ultrasound waves in a nonlinear medium.

In recent years, the nonlinear properties of materials have attracted much interest in nondestructive testing and in ultrasound diagnostic applications. Acoustic nonlinear parameters represent an opportunity to improve the information that can be extracted from a medium such as structural organization and pathologic status of tissue. In this paper, a method called pulse subtraction intermodulation (PSI), based on a multipulse technique, is presented and investigated both theoretically and experimentally. This method allows separation of the intermodulation products, which arise when 2 separate frequencies are transmitted in a nonlinear medium, from fundamental and second harmonic components, making them available for improved imaging techniques or signal processing algorithms devoted to tissue characterization. The theory of intermodulation product generation was developed according the Khokhlov-Zabolotskaya-Kuznetsov (KZK) nonlinear propagation equation, which is consistent with experimental results. The description of the proposed method, characterization of the intermodulation spectral contents, and quantitative results coming from in vitro experimentation are reported and discussed in this paper.

Formation of PCDD and PCDF in the thermal treatment of footwear leather wastes.

The leather waste generated by the footwear industry is considered dangerous due to the presence of trivalent chromium, derived from the salt utilized to tan hides. In Brazil, the majority of this waste is disposed on landfills and only about 3% are recycled. The thermal treatment is an alternative method for purification of such residues. By using this technique it is possible to generate energy and recover the chromium present in the ash for the production of basic chromium sulfate (tanning industry), high carbon ferrochromium or carbon-free ferrochromium (steel industry). In the last 10 years, the gasification and combustion of footwear leather waste have been intensively studied at the Federal University of Rio Grande do Sul. The research experiment for characterization of the emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) were carried out in a semi-pilot unit (350 kW(th)). From new investments the thermal capacity of the unit will increase to 600 kW(th). The unit will produce power from the heat generated in the combustion. The experimental results indicated that during the thermal treatment of footwear leather wastes, the formation mechanism of PCDD/F is the de novo synthesis. Most of PCDD/F were found in the particulate phase (>95%). A kinetic model was used for discussion of the achieved experimental results. The model is based in the carbon gasification, PCDD/F formation, desorption and degradation. From the conclusions obtained in this work will be possible minimize the PCDD/F formation in process of combustion of footwear leather wastes.

Accuracy of a new echographic method (RULES, radiofrequency ultrasonic local estimators) in prostate cancer diagnosis.

BACKGROUND: This study evaluated the accuracy of a new echographic method named RULES (radiofrequency ultrasonic local estimators) in the diagnosis of prostate cancer. PATIENTS AND METHODS: A double-blind prospective study was carried out on 105 patients mean age 66.6 years, prostate specific antigen (PSA) >4 ng/ml with clinical and/or biochemical suspicious of prostate cancer. Patients were submitted to transrectal prostate biopsy (8 to 12 cores) using a traditional echograph connected to a new hardware/ software platform named FEMMINA (fast echographic multiparameter multi image novel apparatus) that processes the echo signal by a RULES (radiofrequency ultrasonic local estimators) algorithm. Histological findings were compared to B-mode and RULES modality. RESULTS: Cancer was detected in 32/105 patients, of which 26/32 were determined as positive with the RULES method. RULES had better positive predictive value, negative predictive value, sensitivity, specificity and accuracy than B-mode. CONCLUSION: Results obtained with RULES are encouraging and, if further confirmed, could help to reduce the number of unnecessary prostatic biopsies.

A novel spectral ultrasonic differentiation method for marking regions of interest in biological tissues. In vivo preliminary results.

BACKGROUND: "in vivo" application of a new echographic method able to better identify neoplastic tissue. The aim of this study was to evaluate its accuracy in the diagnosis of prostate cancer. MATERIALS AND METHODS: Double-blind prospective study on 60 patients (pts) submitted to both transrectal ultrasound (TRUS) of prostate with a traditional echograph connected to a new hardware/software platform named FEMMINA (Fast Echographic Multiparameter Multi Image Novel Apparatus) that processes the echo signal by RULES (Radiofrequency Ultrasonic Local EStimators) algorithm and to a prostatic biopsy (8 to 12 cores). Histological findings of biopsies were compared to B-mode and the new ultrasound method. RESULTS: Cancer was detected in 18/60 pts. 14 patients had positive images with RULES, 11 with B-mode modality. The positive predictive value (PPV) and negative predictive value (NPV) of B-mode were 42% and 79% while 77% and 90% of RULES. Sensitivity and specificity of B-mode were 61% and 79% while those of RULES were 77% and 90%. B-mode diagnostic accuracy was 63% and RULES accuracy was 86%. CONCLUSIONS: Results obtained with RULES are encouraging but they need further studies for its application in clinical practice.

Stable and transient subharmonic emissions from isolated contrast agent microbubbles.

Ultrasound contrast agents (UCAs) have been widely studied in recent years in order to improve and develop new, sophisticated imaging techniques for clinical applications. In order to improve the understanding of microbubble-ultrasound interactions, an acoustic dynamic characterization of UCA microbubble behavior was performed in this work using a high frame-rate acquiring and processing system. This equipment is connected to a commercial scanner that provides RF beam-formed data with a frame-rate of 30 Hz. Acquired RF sequences allows us to follow the dynamics of cavitation mechanisms in its temporal evolution during different insonifying conditions. The experimental setup allowed us to keep the bubbles free in a spatial region of the supporting medium, thus avoiding boundary effects that can alter the ultrasound field and the scattered echo from bubbles. The work focuses on the study of subharmonic emission from an isolated bubble of contrast agent. In particular, the acoustic pressure threshold for a subharmonic stable emission was evaluated for a subset of 50 microbubbles at 3.3 MHz and at 5 MHz of insonation frequencies. An unexpected second pressure threshold, which caused the stand still of the subharmonic emission, was detected at 3.3 MHz and 5 MHz excitation frequencies. A transient subharmonic emission, which is hypothesized as being related to the formation of new free gas bubbles, was detected during the ultrasound-induced destruction of microbubbles. An experimental procedure was devised in order to investigate these behaviors and several sequences of RF echo signals and the related spectra, acquired from an isolated bubble in different insonation conditions, are presented and discussed in this paper.

Subharmonic emissions from microbubbles: effect of the driving pulse shape.

The aims of this work are to investigate the response of the ultrasonic contrast agents (UCA) insonified by different arbitrary-shaped pulses at different acoustic pressures and concentration of the contrast agent focusing on subharmonic emission. A transmission setup was developed in order to insonify the contrast agent contained in a measurement chamber. The transmitted ultrasonic signals were generated by an arbitrary wave generator connected to a linear power amplifier able to drive a single-element transducer. The transmitted ultrasonic pulses that passed through the contrast agent-filled chamber were received by a second transducer or a hydrophone aligned with the first one. The radio frequency (RF) signals were acquired by fast echographic multiparameters multi-image novel apparatus (FEMMINA), which is an echographic platform able to acquire ultrasonic signals in a real-time modality. Three sets of ultrasonic signals were devised in order to evaluate subharmonic response of the contrast agent respect with sinusoidal burst signals used as reference pulses. A decreasing up to 30 dB in subharmonic response was detected for a Gaussian-shaped pulse; differences in subharmonic emission up to 21 dB were detected for a composite pulse (two-tone burst) for different acoustic pressures and concentrations. Results from this experimentation demonstrated that the transmitted pulse shape strongly affects subharmonic emission in spite of a second harmonic one. In particular, the smoothness of the initial portion of the shaped pulses can inhibit subharmonic generation from the contrast agents respect with a reference sinusoidal burst signal. It also was shown that subharmonic generation is influenced by the amplitude and the concentration of the contrast agent for each set of the shaped pulses. Subharmonic emissions that derive from a nonlinear mechanism involving nonlinear coupling among different oscillation modes are strongly affected by the shape of the ultrasonic driving pulse.

FEMMINA real-time, radio-frequency echo-signal equipment for testing novel investigation methods.

Fast echographic multiparameter multi-image novel apparatus (FEMMINA), is a hardware and software platform dedicated to ultrasonic signal and image processing. FEMMINA is able to operate with sequences of radiofrequency (RF) frames. Its architecture is designed to be modular, expandable, and aimed at implementing different ultrasonic investigation techniques. The first experimental characteristic of this system is in its capability to operate in real time with ultrasonic RF signals, starting from acquisition up to processing, storage, and visualization. The second characteristic is the user-system interactivity that allows one to modify the operation appropriately while observing results. Currently, FEMMINA works in both typical experimental situations to study novel investigation techniques and clinical field to validate the proposed methods in different human districts.

Transient subharmonic and ultraharmonic acoustic emission during dissolution of free gas bubbles.

This work concerns the study of free gas bubble behavior, a basic step in contrast agent study. In order to improve the understanding of microbubble-ultrasound interaction, we propose an acoustic dynamic observation of microbubble behavior performed by a high frame-rate acquiring and processing system. Results from ultrasonic observations of free gas microbubbles are discussed and compared with theoretical simulation. Peculiar radio frequency (RF) echo signals back-propagated from bubbles during dissolution up to their destruction are shown and their behavior is discussed. In particular, the different orders of subharmonic emissions related to changes in bubble sizes during dissolution were observed.

ICARUS: imaging pulse compression algorithm through remapping of ultrasound.

In this work we tackle the problem of applying to echographic imaging those synthetic aperture focusing techniques (SAFT) in the frequency domain commonly used in the field of synthetic aperture radars (SAR). The aim of this research is to improve echographic image resolution by using chirp transmit signals, and by performing pulse compression in both dimensions (depth and lateral). The curved geometry present in the unfocused radio-frequency (RF) ultrasonic image is the main cause of inaccuracy in the direct application of frequency domain SAFT algorithms to echographic imaging. The focusing method proposed in this work, after pulse compression in the depth dimension, performs lateral focusing in the mixed depth-lateral spatial frequency domain by means of a depth variant remapping followed by lateral pulse compression. This technique has the advantage of providing a resolution that is uniform in nonfrequency selective attenuation media, and improved with respect to conventional time domain SAFT, without requiring the acquisition and processing of channel data necessary for the most advanced synthetic transmit aperture techniques. Therefore, the presented method is suitable for easy real-time implementation with current generation hardware.

A novel spectral ultrasonic differentiation method for marking regions of interest in biological tissue: in vitro results for prostate.

OBJECTIVE: The aim of the present study was to evaluate the effectiveness of a new method of spectral analysis of the radiofrequency (RF) ultrasonic echo signal in discriminating neoplastic from non-neoplastic tissue of the prostate gland. MATERIAL AND METHODS: The proposed method was previously set up on ten prostatic glands where cancer had been detected by histology in order to correlate the tumour areas with specific spectral parameters. In the present study sixty prostate specimens of patients undergoing radical retropubic prostatectomy for clinically localized prostate cancer were examined. The surgically removed prostate glands were scanned using an echo signal acquisition apparatus and the spectral parameters were obtained by the wavelet transform. The echographic scans of all cases were then compared with the whole-mount histological sections of the prostate in order to evaluate sensitivity and specificity of the proposed method. RESULTS: The sensitivity and specificity for cancer detection were 93% and 91%, respectively. The specificity was invalidated by the fact that in some of the cases studied, the tumour was located in areas of benign prostatic hyperplasia (BPH). As for the sensitivity, of the three false negative cases two were due to the coexistence of cancer foci and BPH. CONCLUSIONS: Our proposed method, named WAMBLE (Wavelet Analysis Multi Band Local Estimator), is accurate in detecting prostate cancer. Further in vivo studies are warranted to confirm the clinical value of this technique.

Toward virtual biopsy through an all fiber optic ultrasonic miniaturized transducer: a proposal.

The present generation of devices based on opto-acoustic and acousto-optic conversion lets us foresee the possibility of realizing complete miniaturized transmitting-receiving transducers, able to generate and detect wideband ultrasounds by laser light. In the present paper, a miniaturized ultrasonic transducer entirely based on fiber optic technology is proposed. Such a device springs from the conjunction between our research, which has produced a highly efficient fiber optic opto-acoustic source, with the results obtained by other researchers concerning the realization of an ultrasonic receiver based on optical interferometry. Making use of the thermo-elastic effect for ultrasound generation, a source of ultrasound can be obtained by coupling a fiber optic to pulsed laser, if a film capable of absorbing laser light is placed onto fiber end. Starting from these remarks, we propose an efficient opto-acoustic source, able to generate pressure pulses with amplitude of the order of 10(4) Pa and bandwidth extending up to 40 MHz and beyond by using graphite materials as absorbing film. This solution makes use of a low-power pulsed laser as optical source possible. An ultrasonic receiving element was realized placing a Fabry-Perot cavity over the tip of a fiber optic. The cavity thickness modulation induced by ultrasonic beam is detected by an interferometer optical technique. We have realized a prototype of a receiving device that exhibits a sensitivity comparable with that of piezoelectric devices (10-100 nV/Pa) and an almost flat bandwidth extending up to 20 MHz or more. The extreme miniaturization of the resulting ultrasonic transducer, together with its wide ultrasonic frequency bandwidth, is the first step toward ultrasonic tissue biopsy. In this paper, before discussing the problem of constructing a complete ultrasonic transducer composed by a transmitter and receiver, the results carried out in these fields during the last decade are reviewed.

Hardware and software platform for real-time processing and visualization of echographic radiofrequency signals.

In this paper the architecture of a hardware and software platform, for ultrasonic investigation is presented. The platform, used in conjunction with an analog front-end hardware for driving the ultrasonic transducers of any commercial echograph, having the radiofrequency echo signal access, make it possible to dispose of a powerful echographic system for experimenting any processing technique, also in a clinical environment in which real-time operation mode is an essential prerequisite. The platform transforms any echograph into a test-system for evaluating the diagnostic effectiveness of new investigation techniques. A particular user interface was designed in order to allow a real-time and simultaneous visualization of the results produced in the different stages of the chosen processing procedure. This is aimed at obtaining a better optimization of the processing algorithm. The most important platform aspect, which also constitutes the basic differentiation with respect to similar systems, is the direct processing of the radiofrequency echo signal, which is essential for a complete analysis of the particular ultrasound-media interaction phenomenon. The platform completely integrates the architecture of a personal computer (PC) giving rise to several benefits, such as the quick technological evolution in the PC field and an extreme degree of programmability for different applications. The PC also constitutes the user interface, as a flexible and intuitive visualization support, and performs some software signal processing, by custom algorithms and commercial libraries. The realized close synergy between hardware and software allows the acquisition and real-time processing of the echographic radiofrequency (RF) signal with fast data representation.

A Doppler system for dynamic vector velocity maps.

The aim of the vector Doppler technique is the quantitative reconstruction of a velocity field independently of the ultrasonic probe axis to flow angle. In particular, vector Doppler is interesting for studying vascular pathologies related to complex blood flows. A problem of vector Doppler is data representation in real-time that should be easy to interpret for the physician. In this work, we present a technique for dynamic display of vector velocity maps and some experimental results obtained in vitro with 2-D vector Doppler on flow phantoms reproducing complex flow conditions. An improvement in the map presentation was obtained by using velocity vector field interpolation. In this work, we considered the problem of spatial sampling for vector Doppler, establishing a relationship between sampling steps and scanning system characteristics. Finally, we developed a novel multimedia solution that uses both interpolated images and sound to discriminate between laminar and turbulent flows.