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Biomedical subjects

L A Ferrari

Publications and source records attributed to L A Ferrari.

9 recordsLinked to original sources
PubMed1988

In vivo acoustic attenuation in liver: correlations with blood tests and histology.

Results of in vivo attenuation measurements in the liver have been obtained in 26 normal controls and in 51 patients with chronic diffuse liver disease. A modified real-time sector scanner was used for narrow-band amplitude attenuation examination. In the control group (people without apparent liver disease), a statistically significant correlation was found between acoustic attenuation in liver and two blood tests reflecting liver function: serum albumin (n = 24, r = 0.67, p = 0.002) and prothrombin time (n = 23, r = 0.63, p = 0.019). There was a statistically significant positive correlation between attenuation and fat for all biopsied patients (n = 51, r = 0.32, p = 0.023) and for patients with minimal fibrosis (n = 25, r = 0.45, p = 0.027). Although no correlation with fibrosis was found for all patients, in the group of patients with minimal fat there was a correlation with portal fibrosis (n = 33, r = 0.37, p = 0.035). This double blind prospective study shows that in the liver: (1) attenuation estimates appear correlated with clinical parameters (blood tests) in normal volunteers, and (2) large changes in fat affect narrow-band acoustic attenuation estimates to a greater degree than severe portal fibrosis in patients with chronic diffuse liver disease. Further research is needed before these estimates can become a clinical tool.

Fatty Liver↗
PubMed1988

Estimate of attenuation coefficient for ultrasonic tissue characterization using time-varying state-space model.

The images generated from ultrasound pulse-echo signals have long been used to aid clinical diagnosis. Recently, there has been a growing interest in quantitatively determining the acoustic parameters of the tissue as a means of classification and diagnosis. For example, the frequency-dependent attenuation is known to be correlated with different diseases in the liver. In this paper we introduce a new technique for estimating the attenuation coefficient. The effect of attenuation on an interrogating signal with a gaussian-shaped spectrum can be obtained by studying the Wigner distribution of reflected rf data based on a one-dimensional signal model. We show that under the condition that the attenuation varies linearly with frequency, the spectral mean of the reflected signal decreases linearly with time. The estimation algorithm models the pulse-echo signal as the output of a second-order time-varying state-space innovations model driven by white noise. The state coupling matrix A and the output coupling vector C vary with time in a known fashion; moreover, they are also functions of an unknown constant parameter theta. The attenuation coefficient, which is one of the elements of theta, can be estimated directly using a recursive system identification algorithm. The algorithm was verified using both computer-generated synthetic data and in-vivo liver data of known diagnosis. The results show correlation between the estimated parameter and the pathological state of the tissue.

Algorithms↗
PubMed1986

Noninvasive evaluation of hepatic fibrosis using frequency demodulation of ultrasound signals.

A new ultrasound image can be produced by frequency demodulation (FM) of the conventional ultrasound signal. This new FM image appeared to produce a more accurate representation of the fine structure of the liver. The individual features of the FM image were correlated with hepatic portal fibrosis and cirrhosis on liver biopsy in 34 patients with minimal hepatic fat and sinusoidal collagen. An overall ultrasound score correlated with portal fibrosis (r = 0.788; P less than 0.001). We conclude that the FM image may be helpful in measuring and following the progression of hepatic fibrosis in patients with chronic liver disease.

Biopsy↗
PubMed1986

Estimation of acoustic attenuation in liver using one megabyte of data and the zero-crossings technique.

Statistical fluctuations due to scatter-induced frequency variations in reflected acoustic pulses are a major problem when estimating acoustic attenuation. Disagreement exists in the ultrasound community as to how much data is sufficient to overcome these statistical fluctuations. The range of attenuation values for normal livers and a tissue equivalent phantom, using 1 megabyte of data per liver and the zero-crossings technique, was investigated. The significance of statistical fluctuations and their effects on attenuation are discussed.

Acoustics↗
PubMed1986

Frequency-demodulated US: evaluation in the liver. Work in progress.

Frequency modulated (FM) imaging is a new ultrasound (US) modality that uses pulse-echo signal instantaneous frequency in addition to the conventional envelope information. Eight features of the FM image in nondiseased livers are described. The technique is evaluated in a study of 34 patients with biopsy-proved diffuse liver disease. Visual grading of FM US image features shows good correlation with levels of biopsy-graded hepatic fibrosis. Patients with diffuse parenchymal liver disease often exhibit evidence of the abnormality when FM liver imaging is used, while such evidence is not as well demonstrated with conventional envelope (AM) imaging.

Humans↗
PubMed1986

The instantaneous frequency of a sinewave squelched bandlimited signal.

We study the instantaneous frequency of a signal which is formed by the summation of a sinewave and a bandlimited signal. We refer to the composite signal as a sinewave squelched or simply a squelched signal. We study the behavior of the squelched signal at its real zeros and extrema. In particular when the sinewave frequency is equal to the largest frequency in the signal's spectrum and its amplitude is greater than the signal's maximum amplitude, the analytic signal corresponding to this resultant signal (hereafter abbreviated as RZ signal) has only real zeros which contain all of the bandlimited signal's information. FM systems often use zero crossing techniques in the demodulation process. For a process with a normal amplitude distribution, we derive a relationship between the zero crossing density of an RZ converted signal and that of the original signal. One application of these analyses is in ultrasonic FM imaging. We give an explanation for the behavior of the FM imaging system as a function of amplitude and frequency of the added cosine.

Image Processing, Computer-Assisted↗
PubMed1986

Induction of doxorubicin resistance in heterogeneous human colon tumor cells by N-methylformamide.

Two clonal subpopulations of cells (termed A and D) obtained originally from a heterogeneous human colon adenocarcinoma were studied in vitro with regard to possible modification of responsivity to graded doses of doxorubicin (ADM) after long-term growth in medium containing the differentiating agent N-methylformamide (NMF). Non-NMF-adapted clone A and D cells exhibited biphasic response curves after exposure to graded doses of ADM (0-1.4 micrograms/ml, 1 hour, 37 degrees C). The inactivation slopes for the initial regions of the survival curves were 0.13 and 0.39 g/ml for clone A and D cells, respectively. NMF-adapted cells, however, exhibited decreased sensitivity to ADM killing as the inactivation slopes for the initial region of the survival curves increased to 0.26 and 0.59 g/ml for clone A and D cells, respectively. The final slopes of the biphasic response curves (doses above about 0.8 micrograms/ml) were not significantly different between clone A and clone D tumor cells in either the non-NMF- or NMF-treated conditions. These data on ADM responses after differentiation induction by NMF indicate that the combination of differentiation-inducing agents with certain chemotherapeutic agents may produce therapeutically undesirable effects and that preclinical data are necessary prior to implementation of possible combined-modality protocols.

Adenocarcinoma↗
PubMed1985

Attenuation estimation with the zero-crossing technique: phantom studies.

Global and local attenuation coefficient estimations were performed in a phantom using a pulse echo method based on the rate of decay of zero crossing density. Focussed and unfocussed 3.5 MHz transducers were used. It was found that good global estimates could be made with either transducer over a 2:1 range of attenuation coefficient. Local estimates exhibit large bias errors and a high degree of variability. This variability diminishes in the focal zone of the focussed transducer and in the far field of the unfocussed transducer.

Mathematics↗