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In this paper, a new parameter that quantifies the intensity of tissue nonlinear elasticity is introduced as the nonlinear elasticity parameter. This parameter is defined based on the empirical information that the nonlinear elastic behavior of soft tissues exhibits an exponential character. To visualize the quantitative nonlinear elasticity parameter, an ultrasonic imaging procedure involving the three-dimensional finite element method (3-D FEM) is presented. Experimental investigations that visualize the nonlinear elasticity parameter distribution of a chicken gizzard and a pig kidney embedded in a gelatin-based phantom were performed. The values extracted by ultrasound and 3-D FEM were compared with those measured by the direct mechanical compression test. Experimental results revealed that the nonlinear elasticity parameter values extracted by ultrasound and 3-D FEM exhibited good agreement with those measured by the mechanical compression test, and that the intensity of tissue nonlinear elasticity could be visualized quantitatively by the defined nonlinear elasticity parameter.

Since the speed of sound (SOS) reflects tissue characteristics and is expected as an evaluation index of elasticity and water content, the noninvasive measurement of SOS is eagerly anticipated. However, it is difficult to measure the SOS by using an ultrasound device alone. Therefore, we have presented a noninvasive measurement method of SOS using ultrasound (US) and magnetic resonance (MR) images. By this method, we determine the longitudinal SOS based on the thickness measurement using the MR image and the time of flight (TOF) measurement using the US image. The accuracy of SOS measurement is affected by the accuracy of image registration and the accuracy of thickness measurements in the MR and US images. In this study, we address the accuracy improvement in the latter thickness measurement, and present an image-processing-based method for improving the accuracy of thickness measurement. The method was investigated by using in vivo data obtained from a tissue-engineered cartilage implanted in the back of a rat, with an unclear boundary.

Acoustic radiation force (ARF) has been used for evaluating tissue elasticity, and is generated by longer pulse duration (PD) and higher acoustic pressure than those used in the conventional ultrasound devices. Although the use of ARF produces relatively-high temperature rise in living biological tissue, the thermal effect of ARF is uncertain. In addition, considering application to the diagnosis of liver, the thermal effect in combination use of ARF and contrast agents should also be considered. In order to evaluate these effects, we have developed a temperature measurement system using a thermocouple for experiment on living animal. In this study, the temperature rise in living rabbit's liver exposed to ultrasound with ARF was measured and evaluated by using the developed system. As the results, all of maximum temperature rise within regulation limits was below 1.5 °C. In addition, there was no significant difference between temperature rises in the liver with and without contrast agents.

We will report newly developed polymer-based phantom for photoacoustic (PA) imaging systems. Phantoms are important for performance evaluation and calibration of new modalities; however, there is no established method for making phantoms with no long-term change. We have developed skin mimicking phantoms simulating both optical and acoustic properties (i.e. optical scattering and absorption coefficients, and sound velocity). Furthermore, the phantoms are able to give accurate simulation of blood vessels by Inkjet-printing. Newly developed phantoms are consisted of castor oil included acrylic block copolymer and we can fabricate 0.8mm or less thick sheets and pile them using their self-adhesiveness.

This study verified the accuracy of the speed of sound (SOS) measured by the combination method, which calculates the ratio between the thickness values of cartilage measured by using the magnetic resonance imaging (MRI) and the ultrasonic pulse-echo imaging, and investigated in vivo application of this method. SOS specific to an ultrasound imaging device was used as a reference value to calculate the actual SOS from the ratio of cartilage thicknesses obtained from MR and ultrasound images. The accuracy of the thickness measurement was verified by comparing results obtained using MRI and a non-contact laser, and the accuracy of the calculated SOS was confirmed by comparing results of the pulse-echo and transmission methods in vitro. The difference between laser and MRI measurements was 0.05 ± 0.22 mm. SOS values in a human knee measured by the combination method in the medial and lateral femoral condyles were 1650 ± 79 and 1642 ± 78 m/s, respectively (p

Acoustic radiation force (ARF) has been recently used for the tissue elasticity measurement and imaging. On the other hand, it is predicted that the higher temperature rises occur. In vivo measurement of temperature rise in animal experiments is important, whereas the measurement using thermocouples have some problems such as position mismatch of a temperature measuring junction of thermocouple and a focal point of ultrasound and so on. Therefore, in vivo measurement system for solving the above problems was developed in this study. The feasibility of the developed system was verified by the experiments using a tissue mimicking materials (TMM), TMM with a bone mode, an extracted porcine liver and a bone of chicken. Moreover, relations between conditions of ultrasound irradiation and temperature rises were investigated using the system. These results showed that temperature rises at focus on the surface of bone may exceed an allowable temperature rise which WFUMB guideline recommends, even though the acoustic intensity is within the limits of acoustic output regulation in diagnostic ultrasound devices.

The speed of sound (SOS) is available as an index of elasticity. Using a combination of magnetic resonance imaging (MRI) and ultrasound, one can measure the SOS. In this study, we verified the accuracy of SOS measurements by using a combination of MRI and ultrasound. The accuracy of the thickness measurements was confirmed by comparison of the results obtained with use of MRI with those of a non-contact laser, and the accuracy of the calculated SOS values was confirmed by comparison of the results of the combined method and ultrasound measurements with the transmission method ex vivo. There was no significant difference between thickness measurements by MRI and those with the non-contact laser, and there was a significant linear correlation between SOS measurement results by use of the combined method and those by use of the transmission method. We also showed that the SOS values obtained agreed with those of previously published studies.

The purpose of this study was to develop a new technique for a powerful compact MR elastography (MRE) actuator based on a pneumatic ball-vibrator. This is a compact actuator that generates powerful centrifugal force vibrations via high speed revolutions of an internal ball using compressed air. This equipment is easy to handle due to its simple principles and structure. Vibration frequency and centrifugal force are freely adjustable via air pressure changes (air flow volume), and replacement of the internal ball. In order to achieve MRI compatibility, all parts were constructed from non-ferromagnetic materials. Vibration amplitudes (displacements) were measured optically by a laser displacement sensor. From a bench test of displacement, even though the vibration frequency increased, the amount of displacement did not decrease. An essential step in MRE is the generation of mechanical waves within tissue via an actuator, and MRE sequences are synchronized to several phase offsets of vibration. In this system, the phase offset was detected by a four-channel optical-fiber sensor, and it was used as an MRI trigger signal. In an agarose gel phantom experiment, this actuator was used to make an MR elastogram. This study shows that the use of a ball actuator for MRE is feasible.

Focused ultrasound with acoustic radiation force (ARF) is beginning to be used for imaging and measuring tissue elasticity. On the other hand, it was suggested that the temperature elevation near bone at focus may be significant within the limits of acoustic output regulation in diagnostic ultrasound devices (Herman; 2002). In this study, with the aim of obtaining the relationships between temperature elevations and parameters of ultrasound exposure with ARF, temperature elevations in two kinds of tissue models with or without bone were numerically evaluated. The results showed that the temperature elevation at focus on the surface of bone may exceed an allowable temperature elevation which WFUMB guideline recommends, even though the acoustic intensity is within the limits of acoustic output regulation in diagnostic ultrasound devices.

It is useful for maturity evaluation of regenerating cartilage to measure the temporal change of its stiffness. In this study, a laser and hydrophone-based measurement of ultrasound vibration applied to the measuring object (sample) is investigated for evaluating the stiffness of thin regenerating cartilage sample. Surface particle velocity and acoustic pressure of the sample when applying sinusoidal ultrasound to the sample are measured by a laser Doppler vibrometer and a hydrophone, respectively. Then the acoustic impedance is evaluated by using the measured particle velocity and acoustic pressure. The feasibility of this method was investigated by conducting fundamental experiments using agar-based homogeneous phantoms. Moreover, this method was also applied to in vitro measurements using auricular cartilage samples regenerated in beagles.

Blood viscosity is a promising index for detecting blood abnormality such as thrombosis. However, due to the non- Newtonian property of whole blood, unique evaluations of blood property might be difficult. In this study, the hematocrit (HCT) is evaluated noninvasively based on the ultrasonic estimation of shear rate-viscosity (SV) curve, which is uniquely formed by the HCT. In vivo measurements for healthy subjects revealed the proposed method provided reasonable HCT estimations. As a practical application of this method, the quantitative shear stress estimation in the flow-mediated dilation measurement was also investigated.

Characterization of grafted vascular scaffold is essential for evaluating its biocompatibility, maturity and structural intensity. Quantitative elastic modulus measurement of vascular scaffold powerfully assists its characterization because the mechanical property is closely related with the biocompatibility, maturity and structural intensity of the vascular scaffold. We have presented an in vitro or in vivo measurement system for the tissue-engineered vessel before and after grafting in the previous study, we present a novel and modified method for in vivo assessment and follow-up of the vascular scaffold in this study. The measured quantitative elastic modulus is converted into the regeneration score for in vivo assessment. The effectiveness of the proposed evaluation method was validated by in vivo experimental data using canines.

Hemodynamic forces including blood pressure and shear stress affect vulnerable plaque rupture in arteriosclerosis and biochemical activation of endothelium such as NO production. In this study, a method for estimating and imaging shear stress and pressure gradient distributions in blood vessel as the hemodynamic force based on viscosity estimation is presented. Feasibility of this method was investigated by applying to human carotid blood flow. Estimated results of shear stress and pressure gradient distributions coincide with the ideal distributions obtained by numerical simulation and flow-phantom experiment.

Elasticity imaging system development has recently yielded practical systems that can be applied in clinical use. To diagnosis disease progression and precisely differentiate tissue types in elasticity images, we must first clarify the quantitative relationship between tissue viscoelasticity and diseases. However, no database for such a relationship has been yet established. From this viewpoint, we are investigating a three-dimensional tissue viscoelasticity microscope for accumulating quantitative data on tissue mechanical properties. We considered measuring the relatively thick tissue samples in order to preserve the microstructure of tissues and thus to avoid changes of tissue mechanical properties. Our proposed microscopic measurement is based on static methods and obtains Young' s modulus and hysteresis parameter (HP) as viscoelastic properties of tissues. Results of simulation analysis and experiments demonstrated that our basic system could acquire the three-dimensional distributions of the elastic modulus and HP with reasonable resolution and precision.

Quantitative elastic modulus measurements of tissue- engineered (TE) vascular wall are useful for in vivo clinical follow-up because the elastic modulus is closely related with the biocompatibility, maturity and structural intensity of the vascular wall. While we have presented an in vitro measurement system for the TE vessel prior to grafting it in the previous study, we present a novel and specified method for in vivo assessment and follow-up of the TE vascular wall in this paper. Moreover, the regeneration score for in vivo assessment are also presented based on the measured quantitative elastic modulus. The effectiveness of the proposed assessment method was validated by in vivo experiment using canines.

A q-space diffusion MR imaging is able to detect microstructure (10μm ∼ ) dynamically. Recently this method is suggested as investigating neuronal generation and degeneration in spinal cord. The q-space data sets are measured by two-dimensional (2D) multi-slice imaging. In order to perform 2D multi-slice imaging, it is necessary to have a few millimeters of slice thickness and slice gap. Multi-slice imaging by an isotropic voxel in the submicrometer range is difficult. While on the other hand, three-dimensional (3D) MR imaging has the advantage of very thin slices with no slice gap (contiguous slices), and it allows acquisition in a small isotropic voxel compared with 2D multi-slice imaging. For detecting microstructural changes in neuron, q-space data sets should be measured by 3D diffusion imaging which have small isotropic voxel. The purpose of this study was to examine a 3D diffusion-weighted MP-RAGE MR sequence (3D-DWI) for q-space imaging of the plant phantom. In post-processing, q-space analysis were performed and we had several analytic volume map of fresh celery (average displacement, zero-displacement probability, kurtosis). This study we had accomplished to get high resolution q-space map of plant phantom strongly reflected diffusion restriction. We would now like to go on to develop this method by applying rat spinal cord for effectiveness in vivo.

A hemodynamic force imaging method on the basis of viscosity estimation is presented in this paper. Viscosity is estimated by ultrasonic velocity vector measurement and Navier-Stokes equations, and then shear stress and pressure gradient distributions are obtained as hemodynamic forces, in this method. The proposed method was investigated by flow-phantom experiments using two fluids with different viscosity and computer simulations. These results revealed that the proposed method can obtain the quantitative hemodynamic distributions reflecting the viscosity difference, which are close to the ideal ones calculated by simulations.

High b-value diffusion magnetic resonance imaging (MRI) enables us to detect far smaller architectures, by using q-space analysis, than the resolution in conventional MRI. Average displacement, one of the q-space parameters, quantitatively reflects architecture size and is very useful in observing small changes in microstructures in vivo (e.g., neurodegeneration, tumor heterogeneity, and others). Diffusion-weighted imaging (DWI) is performed by a two-dimensional (2D) multislice method; however, due to finite slice thickness and slice gap, there is a partial-volume effect that makes it difficult to detect the net q-space signal. On the other hand, three-dimensional (3D) MRI, having the advantages of very thin slice thickness and no slice gap (contiguous slices), allows volumetric evaluation acquired in a small isotropic voxel, as compared to 2D multislice imaging. Little is known about the isotropic high-resolution 3D DWI application to q-space analysis. In this study, we have developed and implemented a high b-value 3D DWI sequence, applied q-space analysis to study the reliability of high b-value 3D DWI and obtained a microscopic analytical map with isotropic high resolution and less contamination.

Ultrasonic tissue elasticity imaging, which can visualize diseased tissues based on their stiffness, is a useful technique for breast cancer detection. In general, soft tissues including the breast have nonlinear elasticity and viscoelasticity referred to as high order mechanical properties. These properties make the conventional elasticity evaluations based on strain and Young’s modulus images difficult because these images vary depending on various conditions, in which high order mechanical properties cannot be neglected. For mechanical assessment independent of such conditions, high order mechanical properties must be assessed. Moreover, these properties also change in diseased tissues. Therefore, in this chapter, a method to assess high order mechanical properties is proposed with the aim of improvement of diagnostic ability. In actual breast assessment, cyclic loading and unloading were applied to the body surface by freehand manipulation of an ultrasonic probe; then, the nonlinear elasticity and viscoelastic hysteresis parameters were estimated and visualized based on the surface pressure measured with the pressure sensor, and the local strain distribution was estimated by the combined autocorrelation method. Nonlinear elasticity and hysteresis parameters, which can be estimated by the proposed method, clearly discriminated the breast tumor from the surrounding normal tissue.

It has been reported that the wall shear stress affects the biochemical function of endothelial cell and the development of arteriosclerosis plaque. Therefore, the quantitative estimation of the wall shear stress has possibilities to be useful for the prevention of arteriosclerosis. In this paper, a novel method for the real-time and quantitative estimation of intravascular shear stress distribution is proposed based on the estimates of the viscosity and the shear rate distribution. Experimental investigation, in which two types of fluids with different viscosity coefficient (water, and water mixed by PVA) flowed at a constant flow rate in a silicone tube with a simulated arteriosclerosis plaque, was performed. After estimating the viscosity coefficient and the shear rate distribution based on the ultrasonic measurements of the velocity vector distribution in the tube, the shear stress distributions were obtained. The averaged value of the shear stress distribution estimated in the higher viscosity fluid (water mixed by PVA: 0.3 Pa) became larger than that in the lower viscosity fluid (water: 0.1 Pa). These results reveal that the proposed method is technically valid for the quantitative shear stress estimation.

To overcome the limitation of the conventional Doppler flowmetry, a new method of 3-D velocity vector measurement was proposed. By detecting the gradient of the weighted phase shift distribution on the receiving aperture, the proposed method realizes a single and smaller-sized aperture, and the sensitivity independent of the direction of the transverse flow as compared with the multi-beam techniques. Moreover the real-time measurement can be expected since the conventional autocorrelation technique is utilized for the phase shift extraction. The basic performance of the method was evaluated and the sector scan imaging simulation was executed. The results showed the high feasibility of the proposed method for measuring the 3-D velocity vector. As the future work, a more detailed investigation of the method must be undertaken for a developing practical system.

Evaluations for biocompatibility and structural integrity of the tissue-engineered vessel wall before and after grafting it are important. These are closely related with mechanical properties. Therefore, in vitro and in vivo ultrasonic measurement systems for tissue-engineered vessel wall evaluation was developed based on the ultrasonic elasticity measurement method suited to the evaluation of mechanical properties, in this study. Based on the pressure-strain loops attained by the ultrasound catheter and pressure sensor, elastic modulus and compliance are measured. Feasibility studies for the measurement systems were conducted by using rubber tube phantoms and canine vein. Experimental results revealed that the developed systems could provide equivalent accuracies to standard tension test

The purpose of this study was to examine the potential of diffusion-weighted (DW) three-dimensional (3D) MP-RAGE MRI for diffusion-tensor mapping of the rat brain in vivo. A DW-3D-MP-RAGE (3D-DWI) sequence was implemented at 2.0 T using six gradient orientations and a b value of 1000 s/mm2. In this sequence, the preparation sequence with a "90 degrees RF-motion proving gradient (MPG): MPG-180 degrees RF-MPG-90 degrees RF" pulse train (DW driven equilibrium Fourier transform) was used to sensitize the magnetization to diffusion. A centric k-space acquisition order was necessary to minimize saturation effects (T1 contamination) from tissues with short relaxation time. The image matrix was 128x128x128 (interpolated from 64x64x64 acquisitions), which resulted in small isotropic DW image data (voxel size: 0.273x0.273x0.273 mm3). Moreover, 3D-DWI-derived maps of the fractional anisotropy (FA), relative anisotropy (RA) and main-diffusion direction were completely free of susceptibility-induced signal losses and geometric distortions. Two well-known commissural fibers, the corpus callosum and anterior commissure, were indicated and shown to be in agreement with the locations of these known stereotaxic atlases. The experiment took 45 min, and shorter times should be possible in clinical application. The 3D-DWI sequence allows for in vivo 3D diffusion-tensor mapping of the rat brain without motion artifacts and susceptibility to distortion.

Plaque rupture is regarded as one of the main causes of acute coronary syndromes. To prevent plaque rupture and guide a pharmacological treatment, it is important to image the weak (fragile) part of atherosclerotic plaque. Our preliminary experiments revealed the feasibility of a strain image using IVUS (intravascular ultrasound) to discriminate between different types of plaque. For the purpose of obtaining finer and more stable assessments of vulnerable plaque under interventional conditions, we propose a strain power image as an index of tissue deformability by analyzing the time-varying strain profiles obtained from the IVUS data. We also conducted an in vivo test with a new acquisition device that allows us to capture a large scale of RF data. The results demonstrate that strain power imaging has the potential to evaluate the vulnerability of plaques.

Various techniques for tissue elasticity imaging have been proposed in the last decade. For clinical applications, real-time and freehand manipulation of a probe is required. In a previous study, we developed the combined autocorrelation method (CAM), which produces an elasticity image with high-speed processing and accuracy, and achieves a wide dynamic range for strain estimation. In the current study, we extended the CAM clinical uses to be robust for tissue sideslip and suited to freehand compression. We achieved this imaging system by adopting its algorithm and using a commercial ultrasonic scanner and a PC. The echo signals are captured in real time and the strain image frame rate was 10 frames/s. Strain images are superimposed on B-mode images with a translucent color scale. In the clinical measurement, elasticity images for breast and prostate cancer were obtained from more than 50 subjects. Some results yielded an elasticity image, that is, a visualization of the tumor area and detected a non-invasive ductal carcinoma. These results demonstrate that the system can provide high-quality and stable elasticity images in clinical measurement.

The decrease of myocardial wall motion, caused by changes in wall stiffness, often appears in the early stage of ischemic heart disease. Since the myocardium exhibits complex 3-D motion, 3-D assessment of the stiffness distribution is required for accurate diagnosis. Therefore, we propose novel methods to track 3-D motion using a 2-D phased array and to assess myocardial malfunction by visualizing the invariant of a full strain tensor. The feasibilities of the proposed methods were evaluated by numerically simulating short-axis imaging of a 3-D myocardial model. This model includes a hard infarction, located between 1 and 3 o'clock, which is difficult to protect by conventional tissue Doppler and strain-rate imaging. RF signals received at each element on a 2-D phased array were faithfully simulated by convoluting the PSF and the scatter coefficients in the model. When the simulated echoes were processed by the proposed methods, the invariant image obtained by the full strain tensor clearly depicted the hard infarction area where the conventional imaging could not.

Prostate tumor-like areas are often inconspicuous in conventional transrectal ultrasonography (TRUS). Therefore, a needle must be injected into the prostate gland in many places to obtain a biopsy. As an alternative, we propose using a tissue elasticity imaging method for needle biopsy support, based on the principle that cancerous prostate tissue becomes hard. A tissue elasticity image should reduce the number of times a needle must be injected, and decrease the probability of small cancers being overlooked. We developed the tissue elasticity imaging system for prostate glands. As a demonstration, we measured some prostate glands suspected of being cancerous. Although cancer detection is difficult using a conventional B-mode image, the strain image clearly indicates the cancerous area to be hard. A comparison of strain images with needle biopsy results revealed a 94% agreement (15 out of 16) with histological examination in detection of cancer. We therefore concluded that the tissue elasticity imaging method is useful as a prostate needle biopsy support technology.

Ultrasonic imaging of tissue elasticity is useful for the detection of lesions such as cancer in which rigidity changes occur. The viscoelasticity of tissue makes the diagnosis by elasticity imaging difficult because the image quality depends on the rate of deformation, but the differences of viscoelasticity reflect the tissue type and degeneration. In this paper, the ultrasonic imaging of the hysteresis parameter (HP), which characterizes the local viscoelasticity, is presented. Quasi-static and cyclic loading by compression and unloading are applied to the body surface for HP imaging. The ability of HP to distinguish the tissue components and degenerations was confirmed in the results of the direct mechanical test for porcine thigh muscle and kidney. For the porcine kidney and the breast fibroadenoma, the HP images depict different patterns than the conventional B-mode and strain images. From these results, HP imaging has the potential to provide different information from conventional imaging.

Diagnosis of pathologies like atherosclerotic plaque is important for preventing plaque rupture, which induces acute ischemic syndromes. We investigated a method of diagnosing plaque based on elasticity imaging using IVUS that reflects mechanical properties of the tissue of arteries. The aim of this study is to investigate the potential of the developed measurement systems for characterizing coronary arteries. To this end, we conducted in-vivo tests of performance and demonstrated that different types of plaque can be discriminated, revealing the potential of elasticity imaging for diagnosing types of plaque and preventing plaque rupture.

In order to evaluate elasticity distribution based on a 3-D tissue structure, the authors propose a method of measuring 3-D displacement vector distribution based on the multi-beam technique. This method, which utilizes the phase shift at each element on the 2-D array aperture, is referred to as the "weighted phase gradient method (WPGM)". To make the proposed method applicable to the measurement of strain for large displacement (i.e., beyond wavelength), the "combined autocorrelation method", previously proposed by the authors, is incorporated into the WPGM as the phase shift detector. Moreover, the authors attempt to reconstruct the elastic modulus distribution using the measured 3-D displacement vectors. Numerical simulation validated the feasibility of the authors' methods in evaluating the 3-D tissue structure.

A new method of measuring the 3-D velocity vector is proposed. By adopting the 2-D phased array probe and based on the distribution of the weighted phase shift between two successive echoes on the receiving aperture, the proposed method enables us to employ a smaller-sized single aperture compared with the conventional techniques, and real-time measurement can be realized. The basic performance of the method was evaluated and sector scan images were constituted by simulation. The results validate the feasibility and ability of the proposed method in measuring the 3-D velocity vector distribution.

To obtain an accurate strain distribution under a large displacement, beyond ultrasonic wavelength, the authors propose a method of reconstructing the strain distribution by modifying the autocorrelation technique. They call this method the "combined autocorrelation method". The method is capable of rapidly detecting strain in the phase domain processing without aliasing. They also attempt to reconstruct the elastic modulus distribution by solving the inverse problem based on a 3-D finite element tissue model. These methods were applied to obtaining strain and elastic modulus images of a tumor phantom and an extracted breast tissue including a cancer tumor. A tumor with a 10 mm diameter and with poor contrast in a B-mode image was clearly displayed as a region harder than the surrounding soft tissue in the strain and elastic modulus images. These results indicate that the proposed method is a promising means for diagnosing tumors.

In order to measure the 3-D displacement vector distribution induced by static deformations, a ring array transducer with overall 16 elements and with a center frequency of 5.0 MHz was manufactured. In experiments with an agar-based phantom including a spherical inclusion, the 3-D volume data sets of the rf signals were acquired by mechanically scanning the probe, and were used for measuring 3-D displacement vectors and reconstructing the Young's modulus distribution. The experimental results showed that the obtained image was close to the true distribution and 3-D reconstruction produced a more quantitative image with higher contrast than the 2-D reconstruction.

Herein, we present the 3-D displacement vector measurement method utilizing the 2-D array and the reconstruction method of tissue elastic modulus distribution using the measured 3-D displacement vector. Numerical simulation validated the feasibility of the proposed methods in evaluating the 3-D tissue elastic distribution.

It is important in regenerative medicine to evaluate the maturity of regenerating tissue. In the maturity evaluation of regenerating cartilage, it is useful to measure the temporal change in elasticity because the maturity of regenerating tissue is closely related to its elasticity. In this study, a quantitative elasticity evaluation of extracted regenerating cartilage samples, which is based on the laser Doppler measurement of ultrasonic particle velocity and calibration, was experimentally investigated using agar-based phantoms with different Young's moduli and regenerating cartilage samples extracted from beagles in animal experiments. The experimental results verified the feasibility of the proposed method for the elasticity evaluation of regenerating cartilage samples.

It is important for regenerative medicine to evaluate the maturity of regenerating tissue. In the maturity evaluation of regenerating cartilage, it is useful to measure the temporal change of elasticity because the maturity of regenerating tissue is closely related to its elasticity. In this study, an elasticity evaluation method for the extracted regenerating cartilage sample, which is based on the laser Doppler measurement of ultrasonic particle velocity, was experimentally investigated using agar-based phantoms with different elastic moduli and the regenerating cartilage samples extracted from beagles in animal experiments. In addition, the experimentally-obtained elasticity was compared with the result of a static compression test. These results verified the feasibility of the proposed method in the elasticity evaluation of regenerating cartilage samples.

It has been reported that the hydroxyl (OH) radical is produced by irradiating ultrasound to titanium dioxide (TiO2). On the other hand, infection at the exit site of catheter retained in the body has become a serious problem. Therefore, we are developing a novel anti-infective catheter system in which the exit site of a catheter is covered with an aminated titanium dioxide (AmTiO2) composite, which consists of AmTiO2 nanoparticles immobilized on a substrate and exhibits cell adhesiveness, and the anti-infective effect (OH radical production) is induced by irradiating low-intensity focused ultrasound (LIFU) to the composite. In this study, the ability to activate TiO2 nanoparticles by ultrasound irradiation was verified in a preliminary experiment, and then the feasibilities that the AmTiO2 composite is activated and that the OH radical is produced by LIFU irradiation were verified by dye decomposition experiment and dihydroxybenzoic acid (DHBA) measurement. In addition, as a trigger for activating the AmTiO2 composite by LIFU irradiation and for producing the OH radical, the decrease in cavitation threshold was suggested.

The abnormalities of myocardial wall motion caused by changes in wall stiffness often appear in the early stage of ischemic heart disease. Since the myocardium exhibits complex and large motion, a two-dimensional (2D) or three-dimensional (3D) assessment of stiffness distribution is required for accurate diagnosis. Although a 3D assessment is ultimately required, as a stepped approach for practical use, we propose novel methods for tracking the 2D motion using a one-dimensional (1D) phased array and for assessing myocardial malfunction by visualizing the invariant of a strain tensor. The feasibilities of the proposed methods were evaluated by numerically simulating the short-axis imaging of a 3D myocardial model. This model includes a hard infarction located between 1 and 3 o'clock, which is difficult to detect by conventional tissue Doppler and strain rate imaging, and the motions of the model were assigned by referring to actual myocardial motion. These results revealed that the proposed imaging methods clearly depicted the hard infarction area which conventional imaging could not detect.

For assessing the tissue elastic properties based on 3D information of displacement and strain induced by static deformation, we propose an estimator of 3D displacement vectors. This method is composed of the combination of the weighted phase gradient method (WPG), which utilizes the gradient of the plane obtained from the phase shift at each receiving element on the 2D array, and combined autocorrelation method (CA), which is phase domain processing without aliasing. Large displacements required for highly accurate measurements can be measured by this method. In addition, we develop a tissue elasticity reconstruction method using the measured 3D displacement vectors. Computer simulations reveal that our methods are valid for evaluating the elastic structures of tissues based on 3D information.

Ultrasonic pulse Doppler tomography is generally applied to noninvasive vascular measurement. The present method, however, measures only one component along the beam direction of a three-dimensional (3-D) velocity vector and provides useful information only if the beam direction in relation to the flow velocity vector is known. Images obtained by such systems are not only unsuitable for quantitative evaluation and but also prone to misinterpretation. On the other hand, in terms of real-time data acquisition achieved by scanning 3-D space, a two-dimensional (2-D) array probe is expected to become indispensable for future clinical applications. From this point of view, we have proposed a method of measuring a 3-D velocity vector using the 2-D array probe. In this paper, the principles of the proposed approach are introduced and experimental data obtained using a prototype system and the flow phantom are processed. Experimental results validate the usefulness of the method and its potential for practical use.