Christiano Bittencourt Machado

MULTIPARAMETRIC HUMAN LIVER FIBROSIS IDENTIFICATION FROM ULTRASOUND SIGNALS

Abstract Classical acoustic parameters (wavespeed, attenuation and backscattering coefficients and mean scatterer spacing) have been used in the characterisation of biological tissue pathologies. Liver fibrosis is a common disease, classified according to the Metavir Scale (from F0: normal, to F4: cirrhosis). The present work evaluates fibrosis discrimination by combining the mentioned parameters and applying a discriminant analysis on ultrasonic backscattering signals from 20 in vitro human liver samples. The highest correct classification percentages (85-90%) happened for parameters combination in groups of there. The limits and potentiality of the study are also discussed. A greater number of samples and non-linear classification methods are presently being pursued.

Ultrasound propagation through bone fractures with reamed intramedullary nailing: results from numerical simulations

Low-intensity pulsed ultrasound stimulation (LIPUS) accelerates fracture healing, enhancing the release of inflammatory mediators and subsequent bone formation. The reamed intramedullary nailing (with the same diameter of the medullary cavity) is a surgical procedure widely used in Medicine. The aim of this work was to study ultrasound propagation inside fractures with and without reamed intramedullary nailing using 2D simulations. It was used a custom-made simulation code applied to numerical models (a 4-mm thick cortical plate, a medullary cavity with radius 4 mm with and without reamed nailing, and fracture gaps varying from 1 to 3 mm). A 1-MHz emitter was positioned above fracture center and fourteen receptor transducers were uniformly placed inside fracture gap. The acquired signals were used to estimate the time-of-flight of the first arriving signal (TOF) and the energy amplitude by means of the root mean square (RMS). TOF was slightly influenced by fracture gap variations. It was observed an increase in RMS values with the presence of metal nailing, due to the reflection in the interface water-metal. The receptors placed near cortical plates received more energy (constructive interference between the direct and lateral waves). For the case of reamed nailing, ultrasound stimulation may be intensified.

In vivo characterization of long-bone in animal model by two ultrasonic scattering parameters: AIB and FSAB

Quantitative Ultrasound (QUS) is a new possibility for non-ionizing diagnosis and monitoring of bone diseases which are usually monitored by radiographs. In this work, an ultrasound (US) pulse-echo method was proposed to in vivo signal acquisition for long bone characterization in an animal model. Two parameters, one related to US backscattering from bone and the other to US reflection at the muscle/bone interface, were calculated in both femurs of seven rats and the results showed that their values statistically belong to the same group. This is indication that the proposed protocol has potential to characterize normal in vivo long bones in animal models.

Influence of temperature on Mean Scattering Spacing estimation of in vitro bovine muscle

Periodicity of structures can be investigated with backscattered ultrasound, usually by applying spectral methods and estimating the Mean Scatterer Spacing (MSS). Biological tissues, such as skeletal muscle, or liver or trabecular bone, can present periodic or quasi-periodic structures. In this work it is studied the behavior of MSS with temperature and frequency for in vitro samples of bovine muscular tissues. MSS was obtained in the range of 37ºC to 43ºC, and between 1 MHz to 10.0 MHz Results show that, for the studied sample, MSS decreased with temperature for the muscle. It seems to be in agreement with the expected physiologic behavior of muscular fibers. Further complementary experiments are being envisaged.

Characterization of pseudarthrosis with ultrasound backscattered signals in rats

PURPOSE To propose a novel model of pseudarthrosis in a small animal and to investigate the ability of backscatter parameters from ultrasound signals in differentiating normal bone from those ones with pseudarthrosis. METHODS Twelve Rattus norvegicus albinus free from pathogenic species (SPF) were randomly divided in two groups, with six animals each. In the Control group a surgical approach to the femur was made, followed by the synthesis of the muscle and skin layers. The Experimental group was submitted to an osteotomy of the femur and a vascularized flap of the fascia lata was interposed in the line of the fractured bone. Then the alignment and bone stabilization were accomplished, by using nylon stitch in U shape introduced in holes made in the proximal and distal fractured bone. Bone samples were scanned with ultrasound and signals were collected for each one to analyze the parameter Apparent Integrated Backscatter - AIB. RESULTS Radiological and anatomopathologic studies revealed the absence of bone consolidation with persistence of fiber-osteoid tissue. Values of the ultrasound parameter AIB from normal bones were statistically different from those with pseudarthrosis. CONCLUSION The experimental model was suitable for pseudarthrosis development in rats and the ultrasound backscatter parameters were able to identify such a bone disease in vitro.

Hepatitis fibrosis characterization by a multiparametric study

The ultrasonic tissue characterization (UTC) is primarily based on radio-frequency (RF) signals’ analysis. The processing of these signals allowed the estimation of different quantitative ultrasonic parameters (backscattered coefficients—ICB-, velocity—SoS, etc). It is known that the RF contains information that can be used to noninvasively characterize the structural and mechanical properties of tissue. Scatterer diameter (or size) from ICB measurements have been already used to discriminate fibrosis from normal tissue. From these findings, our goal was to evaluate the scatterer diameter to test its potential in the discrimination of fibrosis groups (F0, F1, F2, F3, and F4, METAVIR scale) from 20 in-vitro human liver samples, explored at 20 MHz. The mean scatterer diameters (µm) measured were: 42.14–4.90 (F0), 40.18–10.51 (F1), 38.82–6.05 (F3), and 40.30–2.22 (F4). The Kolmogorov-Smirnov test has shown a non-significant level (p > 0.05) indicating that the scatterer size estimation alone cannot different...

The effect of bone fracture unevenness on ultrasound axial transmission measurements: A pilot 2D simulation study

Ultrasound axial transmission (UAT) has been proposed to the diagnosis and follow-up of fracture healing. Some researchers have already pointed out the influence of fracture length, geometry and callus composition on the ultrasound time-of-flight and attenuation, with experimental and simulation studies. The aim of this work was to develop a pilot study on the effect of bone fracture unevenness on UAT measurements. Two-dimensional (2D) numerical simulations of ultrasound wave propagation were run using a custom-made finite-difference time domain code (SimSonic2D). Numerical models were composed of two 4-mm thick bone plates, with fracture lengths varying from 0 to 4 mm. For each case, an upward (UWun) and downward (DWun) unevenness of 0.5, 1.0 and 1.5 mm was implemented in the second plate. The 1-MHz emitter and receptor transducers were placed at 40 mm from each other, 20 mm apart from the center fracture. Two configurations were considered: 1.5 mm above the plates (for the 0-mm unevenness case) and tran...

Evaluating periodicity of trabecular bone phantoms using ultrasound signals

The aim of this work was to characterize the periodicity of a commercial available trabecular bone phantom with ultrasound (US) backscattered signals. Three US frequencies were applied (1.0, 2.25 and 5.0 MHz), and spectral analysis methods were used to estimate the mean scatterer spacing (MSS) of 100 signals/sample from five different samples. The results showed that it is possible to estimate the medium periodicity (trabecular spacings varying from 1.5 to 2.5 mm), and at higher frequencies the average MSS decreased, which is expected because of a higher spatial resolution (identification of the trabecular thickness periodicity). MSS values are in agreement with intertrabecular distances declared by the product supplier.