Iwaki Akiyama

Speckle Noise Reduction by Superposing Many Higher Harmonic Images

A novel ultrasonic imaging method offering high resolution and high-quality images for clinical diagnosis has been developed. This method produces an image using many higher harmonic components contained in the echoes from the inside of a human body, generated due to ultrasonic nonlinear propagation through biological tissues. A new ultrasonic probe has been designed to detect higher harmonic components efficiently over a broad band produced by nonlinear propagation through biological tissues. This probe has a bilayer structure consisting of a lead zirconate titanate (PZT) transmitter and a polyvinylidene fluoride (PVDF) receiver. Experiments employing the new probe show that the receiving transducer easily detects higher harmonics from the fundamental through the tenth in the spectrum of reflected sound from an agar-gel phantom submerged in water. By scanning the probe, the harmonic images of the fundamental through the ninth harmonic component are successfully obtained. In addition, it is demonstrated that speckle noise can be reduced by averaging many harmonic images.

Multiple-frequency ultrasonic imaging by transmitting pulsed waves of two frequencies.

PurposeThe aim of this study was realization of a broadband measurement system that is capable of effectively carrying out a frequency compound method. In the present method, the secondary wave components of difference and sum frequencies are generated along with the higher harmonic components through the nonlinear interaction of two-frequency ultrasound. A multiple-frequency beam is generated together with the initially radiated frequency components.MethodsFor the structure of a transducer capable of simultaneously radiating two sound waves with different frequencies, a coaxial arrangement of a circular-disc piezoelectric transducer and a ring piezoelectric transducer was designed. The radiating frequencies chosen were 2 and 8 MHz. In addition to the 4-MHz second harmonic sound of the 2-MHz primary sound, sounds of the 6-MHz difference frequency and the 10-MHz sum frequency can be generated.ResultsBy measuring the acoustic pressure distribution, the formation of a multiple-frequency beam was confirmed. The signal-to-noise ratio in an agar-gel phantom image was increased by 5–6 dB with application of the frequency compound method. The validity of the proposed method was demonstrated through the generation of a human finger image. Further, it was found that the influence of the Doppler effect was small enough that almost all the secondary waves were attributable to the nonlinear propagation of sounds.ConclusionsA multiple-frequency sound beam was realized by radiating a two-frequency sound. The effectiveness of the presented method was demonstrated through actual imaging.

Search for Survivors Buried in Rubble by Rescue Radar with Array Antennas - Extraction of Respiratory Fluctuation -

The authors have developed a Doppler-type ground penetrating radar (GPR) unit to find survivors buried in houses that have collapsed in an earthquake or other disaster. The purpose of this study is to improve the dynamic range of radar consisting of an array antenna so that it can quickly identify far-off survivors under rubble. The authors focused on time-variable elements from the respiration of a survivor awaiting rescue in order to remove clutter components, such as the rubble. A healthy individuals respiratory frequency varies from 0.2 Hz to 0.5 Hz, so the authors propose a signal processing method to extract these frequency elements in an effective manner. The authors also examine the effectiveness of this method experimentally.

Development of Multiple-Frequency Ultrasonic Imaging System Using Multiple Resonance Piezoelectric Transducer

The authors have developed a multiple frequency imaging system using a multiple resonance transducer (MRT) consisting of 1–3 composite materials with a low mechanical quality factor Q bonded together. The MRT has a structure consisting of thin and thick piezoelectric plates, two matching layers, and a backing layer. This makes it possible to obtain B-mode images of satisfactory resolution using ultrasonic pulses owing to their short duration. In this paper, the vibration property of the MRT derived through equivalent-circuit analysis is first shown. By utilizing the result, an MRT capable of transmitting ultrasonic pulses for generation of the images of biological tissues with satisfactory resolution is designed and prototyped. Setting the prototype transducer in the mechanical sector probe of commercial ultrasonic diagnosis equipment, the speckle reduction effect is demonstrated using images of various phantoms to mimic biological tissues and a human thyroid.

Development of an ultra-broadband ultrasonic imaging system: prototype mechanical sector device.

PurposeWe constructed an ultra-broadband ultrasonic transducer in a mechanical sector device, and prototyped a system to generate real-time images with higher harmonics. The potential of the system to reduce speckle was also studied.MethodsTo efficiently detect the higher harmonic components in echo signals, in addition to the transmitting transducer, another transducer only for broadband reception is necessary. We constructed a receiving transducer by bonding a polyvinylidene fluoride (PVDF) high-polymer piezofilm to the radiation surface of the transmitting lead zirconate titanate (PZT) transducer. By building this PZT-PVDF bi-layered ultrasonic probe into a mechanical sector scanner of an ultrasonic diagnosis system, an ultra-broadband ultrasonic imaging system capable of real-time imaging was prototyped.ResultsUsing images of phantoms in water acquired using the prototype system, the acquisition of higher harmonic images with less noise up to the fourth order was demonstrated. In addition, we confirmed that the logarithmic summation of harmonic components from the fundamental to the fourth harmonic effectively reduces speckle noise in the images.ConclusionsBy obtaining an echo signal from phantoms using a PZT-PVDF bi-layered ultrasonic mechanical sector probe, real-time imaging was carried out, and the effectiveness of its higher harmonic components from the fundamental to the fourth harmonic was confirmed with respect to speckle reduction.

Tissue characterization by using fractal dimension of B-scan image

Classification of normal liver and diffuse liver disease, fatty liver and liver cirrhosis, by using the fractal dimension of ultrasound B-scan images is studied. The ruggedness of distribution of texture is classified by fractal dimension. For the fatty liver there are smaller particles in the texture compared with those of normal liver, and they dare distributed uniformly. For this situation the degree of ruggedness is considered to be high. For liver cirrhosis the various sizes of particles are distributed irregularly in the image and thus the state of distribution is considered to be a low degree of ruggedness compared with the fatty liver. For the normal liver the ruggedness is considered to be in between those of fatty liver and liver cirrhosis. Since the degree of ruggedness is varied by values of the fractal dimension, it may be possible to characterize the pathological states of the liver.<<ETX>>

Three dimensional ultrasonic imaging for diagnosis of breast tumor

Three dimensional ultrasonic imaging and digital processing of extraction and construction of breast tumor is proposed for the diagnosis of breast tumors. Since a malignant tumor has uneven shape and complex boundaries, it is possible to evaluate the tumor using characteristics of tumor morphology. The automated extraction of breast tumors and evaluation of the surface of tumor is a significant problem for computer aided diagnosis. The proposed system consists of commercially available ultrasonic diagnosis equipment, a magnetic sensor for location and orientation, and image processing system. The automated extraction of tumor by fuzzy reasoning uses the membership function assumed as Rician distribution function. We apply the method to 20 cases of malignant tumors and 13 cases of benign tumors. As a result we succeeded in constructing the three dimensional breast tumors and displayed the surface rendering image of the extracted tumor. The relation of three kinds of parameter to a degree of surface roughness of the extracted tumor is investigated for diagnosis.

Ultrasonic tomography using arc focusing beam

A novel tomographic reconstruction method for a phased array based on pulsed-echo imaging is proposed. A conventional sector scanning system uses a phased array to form a focusing beam for improvement of lateral resolution. However, the spatial resolution along normal direction to an image plane is not as good as the lateral resolution, since an acoustic lens which is used for the improvement of the resolution has a fixed focal length. The proposed method is based on a narrow phased array which forms an arc focusing beam instead of the point focusing beam. Since the echoes are expressed as an integration of the wavelets from the scatterers on the arc, the amplitude of echoes is a Radon transform of the distribution of the backscattering coefficient on a hemispherical surface. One of the methods to realize the arc focus beam is that a slit is attached in front of the array. Some experimental results on phantoms, using commercially available ultrasonic diagnosis equipment, are shown.

Preliminary Study of Broadband Transducer for Measurement of Bone Characteristics

The purpose of the study is to diagnose bone diseases using the ultrasonic image. We investigate the broadband transducer with a 0.5–5 MHz frequency range. We fabricated two types of transducers with a thin piezoelectric plate bonded with a thick plate resonator. One is an acoustic lens transducer made of flat lead zirconate titanate (PZT) material, and another is a concave transducer made of PZT rod-polymer 1–3 composite material. The application of the transducers to clinical diagnosis involves the measurement of frequency-dependent characteristics of bone by the penetration method. We measured ultrasonic waves radiated from the transducer at the focal point, and performed frequency analysis. As a result, a flat frequency characteristic of the concave transducer was obtained.

Experimental system for in-situ measurement of temperature rise in animal tissue under exposure to acoustic radiation force impulse

PurposeAcoustic radiation force impulse (ARFI) has recently been used for tissue elasticity measurement and imaging. On the other hand, it is predicted that a rise in temperature occurs. In-situ measurement of temperature rise in animal experiments is important, yet measurement using thermocouples has some problems such as position mismatch of the temperature measuring junction of the thermocouple and the focal point of ultrasound. Therefore, an in-situ measurement system for solving the above problems was developed in this study.MethodsThe developed system is composed mainly of an ultrasound irradiation unit including a custom-made focused transducer with a through hole for inserting a thin-wire thermocouple, and a temperature measurement unit including the thermocouple.ResultsThe feasibility of the developed system was evaluated by means of experiments using a tissue-mimicking material (TMM), a TMM containing a bone model or a chicken bone, and an extracted porcine liver. The similarity between the experimental results and the results of simulation using a finite element method (FEM) implied the reasonableness of in-situ temperature rise measured by the developed system.ConclusionThe developed system will become a useful tool for measuring in-situ temperature rise in animal experiments and obtaining findings with respect to the relationship between ultrasound irradiation conditions and in-situ temperature rise.