Ultrasound attenuation and texture analysis of diffuse liver disease: methods and preliminary results

Abstract

A study was performed to find and test quantitative methods of analysing echographic signals for the differentiation of diffuse liver diseases. An on-line data acquisition system was used to acquire radiofrequency (RF) echo signals from volunteers and patients. Several methods to estimate the frequency-dependent attenuation coefficient were evaluated, in which a correction for the frequency and depth-dependent diffraction and focusing effects caused by the sound beam was applied. Using the estimated value of the attenuation coefficient the RF signals themselves were corrected to remove the depth dependencies caused by the sound beam and by the frequency-dependent attenuation. After this preprocessing the envelope of the corrected RF signals was calculated and B-mode images were reconstructed. The texture was analysed in the axial direction by first- and second-order statistical methods. The accuracy and precision of the attenuation methods were assessed by using computer simulated RF signals and RF data obtained from a tissue-mimicking phantom. The phantom measurements were also used to test the performance of the methods to correct for the depth dependencies. The echograms of 163 persons, both volunteers and patients suffering from a diffuse liver disease (cirrhosis, hepatitis, haemochromatosis), were recorded. The mutual correlations between the estimated parameters were used to preselect parameters contributing independent information, and which can subsequently be used in a discriminant analysis to differentiate between the various diseased conditions.

Precision and accuracy of acoustospectrographic parameters

“…Assuming a homogeneous tissue model, the am plitude spectrum of the backscattered echo signal re ceived in pulse-echo mode, E ( ƒ, z ) , is a random vari able (indicated in bold) with Rayleigh-distributed am plitudes, and an average value, ¡i(f, z ), that can be described by a linear model (Oosterveld et al 1991): (2 ) where E (f, z) is the received amplitude at temporal frequency ƒ of the backscattered echoes of a small tissue volume at depth z, P 2( f ) is the acoustoelectric transfer function of the transducer, D 2(f, z) is the dif fraction spectrogram of the transducer, T (/, z) is the tissue transfer function, and S (f) is the backscatter function.…”

“…The absolute TC (o n foam) was estimated using a method well known in the literature (Insana et al 1983;Oosterveld et al 1991). The procedure is as follows: Place a volume o f the medium in a water tank and orient its planar surface perpendicular to the beam axis.…”

Evaluation of in vivo Liver Tissue Characterization with Spectral RF Analysis versus Elasticity

“…At 3.5MHz, for an average speed of sound of 1500 m/s in human soft tissues, this corresponds to wavelength λ=430µm, which is of the order of magnitude of the liver microstructures. The spectrogram ) , ( z f S of the RF signal at frequency f and at a distance z from the probe is generally modelled as [3][4]: Regarding the generation of non-specular reflection in a homogeneous tissue, the backscattering spectrum is often modeled as…”

Synthetic Aperture Technique Applied to Tissue Attenuation Imaging

“…Liver is the most frequent example. The in vivo characterization of this organ is often restricted to its attenuation properties and it has been proved that the ultrasonic attenuation coefficient increases as the amount of pathological fat in the liver increases (Oosterveld et al, 1991;Lu et al, 1999). Also, the study of excised cancer tissue revealed the differences in acoustic attenuation among cancer types and degrees of pathology.…”