Hiroyuki Hachiya

B-mode ultrasound with algorithm based on statistical analysis of signals: evaluation of liver fibrosis in patients with chronic hepatitis C.

OBJECTIVE The purpose of this study was to evaluate the degree of liver fibrosis in patients with chronic hepatitis C by use of a method in which the homogeneity of the tissue texture of the liver on B-mode ultrasound images is analyzed on the basis of results of a statistical chi-square test of the echo amplitudes. The method includes an algorithm for removing small structures, such as cross sections of the thin vessels, in the background texture to minimize differences in analysis results between users. SUBJECTS AND METHODS Analysis was performed on images of 148 patients with histologically proven chronic hepatitis C without cirrhosis. The peak value of the C(m)(2) (modified chi-square distribution) histogram was calculated from B-mode ultrasound images, and the resulting value was compared with the histologic fibrosis grade. RESULTS The peak C(m)(2) histogram value for grade F3 fibrosis was higher than that for grades F0 and F1 (p < 0.0001) and F2 (p = 0.0003). The value for grade F2 was higher than that for grades F0 and F1 (p = 0.0027). The values gradually increased with an increase in liver fibrosis grade, although no difference was found between grades F0 and F1. CONCLUSION The grades of liver fibrosis in patients with chronic hepatitis C are well discriminated with the B-mode ultrasound-based analysis algorithm without discrimination between grades F0 and F1. Findings on conventional ultrasound images may reflect progression of liver fibrosis even in the absence of cirrhosis.

Determination of sound speed in biological tissues based on frequency analysis of pulse response

The sound speed in biological tissues provides important diagnostic and treatment planning information. Conventional methods of sound-speed determination generally require that transducers make physical contact with specimens in order to measure thickness and travel time in the time domain. The physical contact may cause deformation and affect blood flow and the measurement of travel time in the time domain may be sensitive to waveform distortion due to tissue inhomogeneity and surface roughness. A method for determination of the sound speed is proposed in which the sound travel time in the sample and the difference in total travel time from the transducer to the rigid reflector due to the presence of the sample are estimated in the frequency domain and which does not require physical contact of ultrasonic probes to living or freshly excised tissue specimens. Ultrasonic speed measurements in silicone rubber and acrylic resin specimens verified the method validity. The standard deviation of the measurements over a 10- x 10-mm area is less than 4 m/s. Sound-speed distribution measurements of porcine muscle are in agreement with previously published results.

Estimation of Characteristics of Echo Envelope Using RF Echo Signal from the Liver

To realize quantitative diagnosis of liver cirrhosis, we have been analyzing the probability density function (PDF) of echo amplitude using B-mode images. However, the B-mode image is affected by the various signal and image processing techniques used in the diagnosis equipment, so a detailed and quantitative analysis is very difficult. In this paper, we analyze the PDF of echo amplitude using RF echo signal and B-mode images of normal and cirrhotic livers, and compare both results to examine the validity of the RF echo signal.

Relationship Between Speed of Sound in and Density of Normal and Diseased Rat Livers

Speed of sound is an important acoustic parameter for quantitative characterization of living tissues. In this paper, the relationship between speed of sound in and density of rat liver tissues are investigated. The speed of sound was measured by the nondeformable technique based on frequency-time analysis of a 3.5 MHz pulse response. The speed of sound in normal livers varied minimally between individuals and was not related to body weight or age. In liver tissues which were administered CCl4, the speed of sound was lower than the speed of sound in normal tissues. The relationship between speed of sound and density in normal, fatty and cirrhotic livers can be fitted well on the line which is estimated using the immiscible liquid model assuming a mixture of normal liver and fat tissues. For 3.5 MHz ultrasound, it is considered that the speed of sound in fresh liver with fatty degeneration is responsible for the fat content and is not strongly dependent on the degree of fibrosis.

Examination of the Spatial Correlation of Statistics Information in the Ultrasonic Echo from Diseased Liver

To realize a quantitative diagnosis of liver cirrhosis, we have been analyzing the characteristics of echo amplitude in B-mode images. Realizing the distinction between liver diseases such as liver cirrhosis and chronic hepatitis is required in the field of medical ultrasonics. In this study, we examine the spatial correlation, with the coefficient of correlation between the frames and the amplitude characteristics of each frame, using the volumetric data of RF echo signals from normal and diseased liver. It is found that there is a relationship between the tissue structure of liver and the spatial correlation of echo information.

Estimation of the Scatterer Distribution of the Cirrhotic Liver using Ultrasonic Image.

In the B-mode image of the liver obtained by an ultrasonic imaging system, the speckled pattern changes with the progression of the disease such as liver cirrhosis. In this paper we present the statistical characteristics of the echo envelope of the liver, and the technique to extract information of the scatterer distribution from the normal and cirrhotic liver images using constant false alarm rate (CFAR) processing. We analyze the relationship between the extracted scatterer distribution and the stage of liver cirrhosis. The ratio of the area in which the amplitude of the processing signal is more than the threshold to the entire processed image area is related quantitatively to the stage of liver cirrhosis. It is found that the proposed technique is valid for the quantitative diagnosis of liver cirrhosis.

Extraction of Quantitative Three-Dimensional Information from Ultrasonic Volumetric Images of Cirrhotic Liver

The cirrhotic liver has many fibrotic tissue structures known as nodule structures. Understanding this characteristic in diseased tissue is important for quantitative diagnosis. In this paper, we present a technique to extract quantitative three-dimensional information from a cirrhotic liver. Consecutive two-dimensional images acquired by fan like scanning were processed using constant false alarm rate (CFAR). The 2D processed images are accumulated to obtain 3D information. The nodular structure is clear in the constructed images.

Measurement of Acoustic Property Distributions of Diseased Heart and Liver Tissues.

Acoustic properties of living tissues are an important parameter for quantitative estimation of the tissue structure. It is very important to determine the relationship between the physical and the chemical change of tissue structure and the change of acoustic properties. In this paper, using a new system with high density measuring points, we present the relationship diagram between the speed of sound and attenuation of human heart and liver tissues at 25 MHz. To compare normal and diseased tissues, we investigate the relationship between the sound speed and the attenuation of tissue. A characteristic relationship of the tissue is found in cirrhotic liver and aortic regurgitation tissue.

Target Detectability Using Coded Acoustic Signal in Indoor Environments

An acoustic method in air has the potential to allow for the fast and accurate characterization of objects in air. Nevertheless, it is difficult to identify acoustic signals clearly because of environmental noises and the scattering of signals on the object surface. Therefore, it is required to establish a sensing system, which enables measurements in air. In this paper, we present the object detection using an M-sequence signal in an indoor environment. Using the M-sequence signal enabled the improvement in signal-to-noise (SN) ratio and the stable measurement of reflected waves that cannot be detected using a conventional impulse. The noise and reverberation components are included in the received signals and reflected waves from the target. We confirmed that in the case of a high-order M-sequence signal, target detectability is limited by reverberation. In addition, we eliminated the reverberation component from the received signals using the signals without the target in the reverberation limited case and determined the reflection characteristics of the target.

Evaluation of ultrasonic fiber structure extraction technique using autopsy specimens of liver

It is very important to diagnose liver cirrhosis noninvasively and correctly. In our previous studies, we proposed a processing technique to detect changes in liver tissue in vivo. In this paper, we propose the evaluation of the relationship between liver disease and echo information using autopsy specimens of a human liver in vitro. It is possible to verify the function of a processing parameter clearly and to compare the processing result and the actual human liver tissue structure by in vitro experiment. In the results of our processing technique, information that did not obey a Rayleigh distribution from the echo signal of the autopsy liver specimens was extracted depending on changes in a particular processing parameter. The fiber tissue structure of the same specimen was extracted from a number of histological images of stained tissue. We constructed 3D structures using the information extracted from the echo signal and the fiber structure of the stained tissue and compared the two. By comparing the 3D structures, it is possible to evaluate the relationship between the information that does not obey a Rayleigh distribution of the echo signal and the fibrosis structure.