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We previously reported that acoustic radiation force impulse (ARFI) with concomitant administration of perfluorobutane as an ultrasound contrast agent (UCA)-induced arrhythmias at a mechanical index (MI) of 1.8 or 4.0 in a rabbit model. The present study identified the location of arrhythmias with a MI

Ultrasonography-derived carotid artery intima–media thickness (IMT) has been established as an early atherosclerotic imaging biomarker. The IMT reference value of a healthy person is approximately 0.1 × (every 10 years of age) + 0.2 (mm); accordingly, it requires an accuracy of at least 0.1 mm. However, one concern of IMT measurement is intervendor variability. In this study, we aimed to verify the intervendor variability using an IMT phantom. An improved IMT phantom was developed, and it was possible to analyze the IMT by software for all vendors. With the vendor-specific software, the maximum difference between the devices was 0.08 mm, and the difference in quartile range was 0.06 mm. On the other hand, with the vendor-independent offline software, the maximum difference between the devices was 0.16 mm, and the quartile range of variation was 0.06 mm. The intervendor variability assessed using our IMT phantom was less than 0.10 mm, and the on-board vendor-specific software was shown to reduce the difference between the devices significantly compared with the vendor-independent offline software. To further improve the vender difference, adjustment by means of vendor-specific software based on a standardized IMT phantom is warranted.

In cartilage regenerative medicine, autologous chondrocyte implantation (ACI) has been applied clinically for partial defects of joint cartilage or nasal augmentation. To make treatment with ACI more effective and prevalent, modalities to evaluate the quality of transplanted constructs noninvasively are necessary. In this study, we compared the efficacy of several noninvasive modalities for evaluating the maturation of tissue-engineered auricular cartilage containing a biodegradable polymer scaffold. We first transplanted tissue-engineered cartilage consisting of human auricular chondrocytes, atelocollagen gel, and a poly-l-lactic acid (PLLA) porous scaffold subcutaneously into the back of athymic nude rats. Eight weeks after transplantation, the rats were examined by magnetic resonance imaging (MRI), X-ray, and ultrasound as noninvasive modalities. Then, the excised constructs were examined by histological and biochemical analysis including toluidine blue (TB) staining, glycosaminoglycans content, and enzyme-linked immunosorbent assay of type II collagen. Among the modalities examined, transverse relaxation time (T2) and apparent diffusion coefficient of MRI showed quite a high correlation with histological and biochemical results, suggesting that these can effectively detect the maturation of tissue-engineered auricular cartilage. Since these noninvasive modalities would realize time-course analysis of the maturation of tissue-engineered auricular cartilage, this study provides a substantial insight for improving the quality of tissue-engineered cartilage, leading to improvement of the quality and technique in cartilage regenerative medicine.

The speed of sound (SOS) of a longitudinal wave propagating in the living body reflects the tissue properties and is expected as a promising evaluation index for detection of disease, diagnosis and monitoring. However, in general, the interpretation of SOS is complex, because it is influenced mostly by compressibility and multiple factors. In this study, as a study for the interpretation of SOS, the SOS of cartilage was measured in vivo by using a fusion of ultrasound and magnetic resonance imaging (MRI), and the correlations between the SOS and other quantities were investigated. In summary, as a possible interpretation of SOS of cartilage tissue used in this study, it was suggested that the SOS was partly related to water content.

Tissue characterization in terms of the differences in thermo-physical properties of biological tissues was investigated in this study. The objective was to measure the ratio of variation in sound velocity due to ultrasonic heating and to derive the relational expression between the ratio and thermo-physical properties. The ratio of sound velocity variation before and after the temperature rise of tissue samples exposed to ultrasound was measured by ultrasonic pulse echo method. The thermo-physical properties were estimated for a tissue-mimicking material and porcine muscle and fat tissues due to theoretical expression. The transducer for heating had a resonance frequency of 3.2 MHz, and the transducer for measurement of sound velocity variation had a resonance frequency of 5.2 MHz. In the phantom study, the measured values of the temperature rise agreed with the values calculated by a finite element method (FEM). The estimated values of the temperature rise from the sound velocity variations of muscle and fat tissues were 0.36 °C and 1.1 °C, respectively. Also, the estimated values of thermo-physical properties agreed with the reference values within an error of 10%. The thermo-physical properties of the porcine tissues were measured by sound velocity variation due to ultrasonic heating within the safety regulations.

Acoustic radiation force (ARF) impulse can be used to estimate the elasticity of cardiac muscle. The purpose of this study was to evaluate the effect of ARF on the heart with concomitant administration of the ultrasound contrast agent (UCA) perfluorobutane for recently developed elasticity imaging such as shear wave imaging. Ultrasound with ARF was applied to the heart of Japanese white rabbit with or without UCA administration. During the exposure, electrocardiographs were recorded. Following the exposure of ultrasound with a duration of 10 ms and a mechanical index (MI) of 4.0 to the heart, extra waves (QRS complex) were observed only after UCA administration. Although life-threatening arrhythmia was not observed, a greater increase in the frequency of the extra waves was observed following a drip infusion compared with a single (bolus) UCA infusion. In addition, 16.3 % of extra waves were followed by arterial pressure pulse. Cardiac ultrasound with higher MI and longer duration should be carefully considered, particularly with the concomitant use of UCA and higher MI.

Acoustic 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.The 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.The 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.The 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.

Purpose: Commonly used diffusion weighted (DW) imaging such as DW spin echo (SE) type echo planar imaging (DW-SE-EPI) is known to be a snapshot-like acquisition and to have a relatively high signal-to-noise ratio. Spiral MRI sequence (SPIRAL) has characteristics similar to these of EPI, but it has rarely been used for diffusion-weighted imaging (DWI). In vivo DW-SPIRAL of the rat brain has almost never been reported. Our purpose in this study was to examine the potential of SE-type two-dimensional (2D) multi-shot spiral acquisition MRI for apparent diffusion coefficient (ADC) mapping of the rat brain in vivo. Materials and Methods: We made an SE-type DW-2D-spiral MRI sequence (DW-SPIRAL) which was prepared on a 2.0-T animal-experiment MR scanner. Comparing the phantom experimental result of DW-SPIRAL with the phantom experimental result of DW SE-type echo-planar imaging (DW-SE-EPI) and conventional DW spin echo imaging (DW-SE), we estimated the characteristics of DW-SPIRAL and assessed the clinical application of DW-SPIRAL in an animal experiment on the rat brain. Results: There was not much difference between the calculated water/glycerol phantom diffusion coefficient of DW-SPIRAL and the calculated diffusion coefficient of DW-SE. This result shows that the DW-SPIRAL sequence is appropriate for use in diffusion weighted imaging. There were fewer phantom image distortions and ghosting artifacts with DW-SPIRAL than with DW-SE-EPI, and this tendency was similar in the animal experiment on the rat brain. Conclusion: The DW-SPIRAL sequence had been successfully tested in phantom experiments and rat brain experiments. It has been demonstrated that the DW-SPIRAL sequence is capable of producing in vivo rat brain DWI.

Objective Quantitative MR imaging techniques of degenerative cartilage have been reported as useful indicators of degenerative changes in cartilage extracellular matrix, which consists of proteoglycans, collagen, non-collagenous proteins, and water. Apparent diffusion coefficient (ADC) mapping of cartilage has been shown to correlate mainly with the water content of the cartilage. As the water content of the cartilage in turn correlates with its viscoelasticity, which directly affects the mechanical strength of articular cartilage, ADC can serve as a potentially useful indicator of the mechanical strength of cartilage. The aim of this study was to investigate the correlation between ADC and viscoelasticity as measured by indentation testing. Materials and methods Fresh porcine knee joints (n = 20, age 6 months) were obtained from a local abattoir. ADC of porcine knee cartilage was measured using a 3-Tesla MRI. Indentation testing was performed on an electromechanical precision-controlled system, and viscosity coefficient and relaxation time were measured as additional indicators of the viscoelasticity of cartilage. The relationship between ADC and viscosity coefficient as well as that between ADC and relaxation time were assessed. Results ADC was correlated with relaxation time and viscosity coefficient (R2 = 0.75 and 0.69, respectively, p

Introduction Acoustic Radiation Force Impulse[ARFI] ultrasound elastography has been widely introduced as a diagnostic modality for liver and breast masses. We previously reported that arrhythmias were observed at a mechanical index [MI] of 1.8 with ARFI and concomitant administration of an ultrasound contrast agent[UCA] in rabbits. The aim of this study was to identify the location of the arrhythmias in a heart using a new system (Microsonic co., Tokyo, Japan) which transmits ARFI from the probe used for B-mode imaging of the heart. Methods Under general anesthesia, seven rabbits were exposed to ARFI. Using the new transducer, cardiac B-mode images (4 chamber view, left ventricle long-axis view) were obtained through the intercostal space. We chose three points along the impulse conduction system of the heart: (1) right ventricle, (2) right atrium and (3) left ventricular wall.We confirmed the occurrence of arrhythmias and the shape of arrhythmias with and without UCA (perfluorobutane (SonazoidTM)). (at double the clinical dose). Two minutes after intravenous injection of the UCA, ARFI was transmitted with a 1.0 msec pulse duration delayed 200msec after the R wave. Thirty exposures were synchronized with one exposure per three heart beats. The MI of the ARFI exposure ranged from 0.84 to 1.16. Results Arrhythmias were not observed using ARFI without UCA. For ARFI exposure with UCA, an average of 2.85 arrhythmias were observed (range 0-7). There were no fatal arrhythmias. Arrythmias tend to occur from (1) and (2) rather than (3). The shape of arrhythmias were single ventricular or supraventricular extra-systolic waves. Arrhythmias from the right (1), (2) and left (3) heart had a reversed shape. Discussion Using this new system, the rabbit heart exposed to ARFI had more reliable focal positions. The MI used in this study was similar to that used in clinical setting of ARFI. There was no significant difference in the frequency of arrhythmias among the three points of ARFI exposure. However, reversed shape arrhythmias may indicate that ARFI exposure actually stimulated the right or left-sided impulse conduction system. Conclusion Extra-systolic activity at different origins was observed under similar clinical conditions using ARFI with infusion of an UCA. Ultrasound practitioners should know this adverse reaction, even if the MI is below the previously determined value of 1.9, especially when imaging near the conduction system.

It is recently known that titanium dioxide (TiO 2 ) can be excited by ultrasound and release of OH radicals on the surface. In this study, secretion of an indirect angiogenic factor, tumor necrosis factor-α (TNF-α), from bone marrow mononuclear cells (BM-MNC) incubated on amino group modified TiO 2 nano-particles covalently coated on polyester fabric (TiO 2 /PET) under ultrasonic irradiation was examined in vitro . The cell viability and TNF-α secretion were measured under ultrasound irradiation condition with 255 mW/cm 2 of intensity, which is below the highest output (1 W/cm 2 ) specified in the safety standard for a medical ultrasonic diagnostic apparatus. The living cell number on the TiO 2 /PET and original PET with/without continuous ultrasound irradiation was unchanged statistically by ANOVA test. TNF-α secretion level from BM-MNC remarkably increased on the TiO 2 /PET under ultrasonic irradiation without cell damage. It was, therefore, thought that the high level of TNF-α secretion on the TiO 2 nano-composite by ultrasound irradiation was due to oxidative stress induced from OH radicals on TiO 2 .

Acoustic radiation force (ARF) elastography has recently become available. The previous animal studies have revealed lung injuries induced by diagnostic ultrasound, but the effects on the lung resulting from exposure to ultrasound with ARF are unknown. This study aimed to assess the risk of lung injury associated with ultrasound with ARF. A focused 2.5-MHz transducer that emits ultrasound with ARF was used. A rabbit was anesthetized, and the transducer was placed in the right subcostal region. Exposure settings of mechanical index (MI) 0.80, pulse duration 10 ms, pulse repetition time 5 s, and exposure time 150 s were applied. One red spot (7 × 6 mm) was observed on the surface of the right lung corresponding to the area of exposure. Alveolar hemorrhage was observed microscopically. This lesion was visible across a range of 20–170 μm in depth from the pleural surface. The first example of lung hemorrhage induced by ultrasound with ARF was observed in this study. This observation suggests the possibility of lung injury in humans when ARF elastography is applied with the transducer directed toward the lung. Further studies are needed to determine the safety of this modality.

It is important to evaluate the elasticity of tissue-engineered cartilage, for evaluating its structural strength. However, in vivo evaluation of tissue-engineered cartilage elasticity has not been established. On the other hand, since the speed of sound (SOS) is available for elasticity evaluation, we have proposed in vivo measurement method of SOS using ultrasound and MR images. This method determines the SOS based on the thickness measurement using the MR image and the time-of-flight (TOF) measurement using the ultrasound. In this study, this method was applied to the SOS measurement in tissue-engineered cartilage, and then relation between in vivo SOS and elasticity was investigated. As the result, in vivo SOS had a high correlation with Young's modulus. This result reveals that in vivo evaluation of tissue-engineered cartilage elasticity is available through in vivo SOS measurement.

Acoustic radiation force impulse (ARFI) is a modality for elasticity imaging of various organs using shear waves. In some situations, the heart is a candidate for elasticity evaluation with ARFI. Additionally, an ultrasound contrast agent (UCA) provides information on the blood flow conditions of the cardiac muscle. This study aimed to evaluate ARFI’s effect on the heart concomitantly with UCA administration (i.e., perfluorobutane). Ultrasound with ARFI was applied to the hearts of male Japanese white rabbits (n = 3) using a single-element focused transducer with or without UCA administration. They were exposed to ultrasound for 0.3 ms with a mechanical index (MI) of 1.8. UCA was administered in two ways: a single (bolus) injection or drip infusion. Electrocardiograms were recorded to identify arrhythmias during ultrasound exposure. Extrasystolic waves were observed following ultrasound exposure with drip infusion of UCA. Life-threatening arrhythmia was not observed. The frequency of the extra waves ranged from 4.2 to 59.6 %. With bolus infusion, extra waves were not observed. Arrhythmogenicity was observed during ultrasound (MI 1.8) with ARFI and concomitant administration of UCA in rabbits. Although the bolus administration of UCA was similar to its clinical use, which may not cause extra cardiac excitation, cardiac ultrasound examinations with ARFI should be carefully performed, particularly with concomitant use of UCA.

In order to detect the disease and degeneration of cartilage early, evaluations of acoustic properties are expected, but the physical meaning should be clarified. On the other hand, we have proposed a multimodal method using ultrasound (US) and magnetic resonance (MR) images for in vivo SOS measurement. In this study, the method was applied for the tissue-engineered cartilage, and the SOS was compared with T1, T2, apparent diffusion coefficient (ADC), attenuation coefficient (ATT), and Young’s modulus (YM). All procedures were approved by the Animal Care and Use Committee of our institution. 12-week-old male rats were used, and five different types of tissue-engineered cartilage was subcutaneously implanted in the back of rat (n = 30). Under anesthesia, MR and US images including same cross-sections were acquired separately, by using a MR imager of 2 Tesla and a US device of 13 MHz. At this time, T1, T2, ADC were also measured. The SOS was determined by the thickness measurement using the MR image and the...

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.

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.

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

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.

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.

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.

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.

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.

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.

Abnormal regional wall-motion often appears in the early stages of ischemic heart disease such as angina pectoris and cardiac infarction. Therefore, it is very important to accurately estimate multi-dimensional displacements in order to precisely diagnose ischemic heart disease.

This paper describes a new image reconstruction method for the half-Fourier MR imaging. The signal to noise ration (SNR) is decreased almost one over square root of 2 as same as the conventional half-Fourier MR imaging. It is possible to apply into almost of every MR imaging using Fourier transformation for the image reconstruction such as SE, GRE, Fast-SE, EPI, etc.. Moreover, it is also apply to the spiral imaging and radial scan. The proposed method combined with the keyhole technology, navigator echo and random scanning are useful in practical use.