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It has been recognized that tissue stiffness provides useful diagnostic information, as with palpation as a screening for diseases such as cancer. In recent years, shear wave elastography (SWE), a technique for evaluating and imaging tissue elasticity quantitatively and objectively in diagnostic imaging, has been put into practical use, and the amount of clinical knowledge about SWE has increased. In addition, some guidelines and review papers regarding technology and clinical applications have been published, and the status as a diagnostic technology is in the process of being established. However, there are still unclear points about the interpretation of shear wave speed (SWS) and converted elastic modulus in SWE. To clarify these, it is important to investigate the factors that affect the SWS and elastic modulus. Therefore, physical and engineering factors that potentially affect the SWS and elastic modulus are discussed in this review paper, based on the principles of SWE and a literature review. The physical factors include the propagation properties of shear waves, mechanical properties (viscoelasticity, nonlinearity, and anisotropy), and size and shape of target tissues. The engineering factors include the region of interest depth and signal processing. The aim of this review paper is not to provide an answer to the interpretation of SWS. It is to provide information for readers to formulate and verify the hypothesis for the interpretation. Therefore, methods to verify the hypothesis for the interpretation are also reviewed. Finally, studies on the safety of SWE are discussed.

The speed of sound (SoS), which is the propagation speed of longitudinal waves, is expected to be effective for the early detection and monitoring of diseases. Several methods that use handheld probes have been proposed to estimate the SoS. In this study, a modified average SoS estimation method, referred to as the improved focusing method, is proposed to increase the accuracy of average SoS estimation. In the proposed method, a plane wave was transmitted, and the center-element position-dependent variations in the SoS estimation were reduced. Ex vivo experiments were conducted using chicken liver to evaluate the applicability and sensitivity of the proposed method to actual tissues. The livers were subjected to continuous temperature changes to induce changes in the SoS. The results suggest that the improved focusing method measures the average SoS accurately as well as small SoS changes of approximately 1.5 m·s−1·°C−1.

In this study, the longitudinal wave speed (LWS) and shear wave speed (SWS) of the homogeneous agar-glycerol phantoms were ultrasonically measured, and the relationship between the compositions of phantoms and these two speeds was investigated. From the viewpoint of the measurement sensitivity of LWS and SWS, the LWS had the sensitivity to discriminate the differences in the glycerol weight concentration, while the SWS did not exhibit such sensitivity. These results indicate that the LWS can discriminate the composition of tissues different from that by the SWS in clinical diagnosis.

Acoustic radiation force impulse (ARFI) imaging and shear wave elastography use a "push pulse." The push pulse, which is referenced as an ARFI in this study, has a longer duration than that of conventional diagnostic pulses (several microseconds). Therefore, there are concerns regarding thermal safety in vivo. However, few in vivo studies have been conducted using living animals. In this study, to suggest a concept for deciding an ARFI output and cooling time while considering thermal safety, the liver (with and without an ultrasound contrast agent) and femur bone surface of living rabbits were exposed to an ARFI, and the maximum temperature rise, temperature rise for 5-min duration, and cooling time were measured via a thermocouple. While testing within the regulation limits of diagnostic ultrasound outputs, a maximum temperature rise on the femur bone surface exceeded the allowable temperature rise (1.5°C) in the British Medical Ultrasound Society (BMUS) statement. However, using the linear relationships between the pulse intensity integral (PII) of a single pulse and the above three temperature parameters, PII may be determined so that the maximum temperature rise is within the allowable temperature rise in the BMUS statement. The cooling time can be estimated from the PII.

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

The speed of sound (SoS) correlates with tissue properties and has been studied as a promising index for early detection and monitoring of diseases. Although the estimation of average SoS based on the phase aberration correction is the simplest and provides reasonable results for homogeneous media, the estimation error for the inhomogeneous media has not been clarified yet. Therefore, in this study, the backscattered signals of two inhomogeneous media were collected by using a previously developed simulator and the errors of average SoS estimation were analyzed. These results suggested that the statistical properties of the SoS distribution were related to the reliability of the average SoS estimation. In addition, these results may provide important insights for future clinical use of average SoS.

In recent years, non-invasive measurement of tissue stiffness (hardness) using ultrasound elastography has attracted considerable attention. It has been used to evaluate muscle stiffness in the fields of rehabilitation, sports, and orthopedics. However, ultrasonic diagnostic devices with elastography systems are expensive and clinical use of such devices has been limited. In this study, we proposed a novel estimation method for vibration-based shear wave elastography measurement of human skeletal muscle, then determined its reproducibility and reliability. The coefficient of variation and correlation coefficient were used to determine reproducibility and reliability of the method by measuring the shear wave velocities in konjac phantom gels and agar phantom gels, as well as skeletal muscle. The intra-day, day-to-day, and inter-operator reliabilities were good when measuring the shear wave velocities in phantom gels. The intra-day and day-to-day reliabilities were good when measuring the shear wave velocities in skeletal muscle. The findings confirmed adequate reproducibility and reliability of the novel estimation method for vibration-based shear wave elastography. Therefore, the proposed measurement method may be a useful tool for evaluation of muscle stiffness.

In the Original publication of the article Table 3 was published incorrectly.

The elastic modulus of tissue as a useful biomarker of disease detection can be quantitatively evaluated based on shear wave speed (SWS) measurements in shear wave elastography. Although the longitudinal wave speed (LWS) is also expected to be a promising biomarker for disease detection, the elasticity is not always dominant because the LWS is affected by the bulk modulus. In other words, LWS and SWS may reflect different tissue properties. Therefore, in this study, based on the improvement in LWS measurement, the relationship between the composition of a phantom mixed with agar and glycerol and ultrasonically measured LWS and SWS was investigated. The LWS had a good sensitivity in detecting glycerol, while the SWS had a good sensitivity in detecting agar. The calculated Poisson’s ratio had a better sensitivity in detecting agar. In conclusion, a simultaneous measurement of LWS and SWS may help identify the tissue composition.

Speed of sound (SOS), which is the propagation speed of a longitudinal wave, is a promising index for diagnosis. Several methods for SOS measurement and imaging have been proposed. Among them, some methods using the backscattered signals are expected to be useful for the clinical use, but since generally these are ill-posed problem, it is difficult to verify the logical validity. In order to verify the validity of the developed algorithm logically, conducting numerical simulations will be effective prior to the validation using real data. Therefore, in this study, the backscattered wave simulation for SOS measurement and imaging was investigated.

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.

The speed of sound (SOS), which is the propagation speed of longitudinal waves, is a promising index for early detection and monitoring of diseases, and many measurement methods have been proposed. It has already been found that the average SOS can be easily and reasonably estimated for a homogeneous medium based on time-delay processing by utilizing the method using backscattered waves, which enables the use of handheld probes. However, the error caused by the application of the method to an inhomogeneous medium has not yet been clarified. In this study, we investigate the relationship between statistical properties of the SOS distribution and the measurement error through a simulation and a phantom experiment. As a result, it is revealed that if the spatial variation of the SOS distribution is below a certain level, the average SOS can be estimated under the assumption of a homogeneous medium.

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.

Diffusion-magnetic resonance elastography (dMRE) is an emerging practical technique that can acquire diffusion magnetic resonance imaging and MRE simultaneously. However, a signal loss attributable to intravoxel phase dispersion (IVPD) interferes with the calculation of the apparent diffusion coefficient (ADC). This study presents an approach to dMRE that reduces the influence of IVPD by introducing a new pulse sequence. The existing and proposed techniques were performed using a phantom comprising five rods with different elasticities at 60 Hz vibration to investigate the accuracy of previous and proposed dMRE techniques. The measures of ADC and stiffness, obtained by using both dMRE techniques, were compared with conventional spin-echo (SE) diffusion and SE-MRE. Then, we evaluated those differences by using the mean of absolute differences (MAD) in each rod within the phantom. The results of the MAD of the stiffness from both dMRE techniques showed almost no difference. In contrast, the value of the ADC MAD (MAD ≒ 0.16 × 10−3 mm2/s), obtained in the soft region within the phantom with the previous dMRE technique, was large. This value was about 2.7 times that of the value produced by the proposed dMRE technique. This difference must reflect the degree of influence of IVPD in both techniques. These results demonstrate that our dMRE technique is a robust method for addressing the signal loss attributable to IVPD.

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.

The elastic properties of tissues are expected to provide novel information for use in diagnosing pathologic changes in tissues and discriminating between malignant and benign tumors. Because it is hard to directly estimate the elastic modulus distribution from echo signals, methods for imaging the distribution of tissue strain under static compression are being widely investigated. Imaging the distribution of strain has proven to be useful for detecting disease tissues on the basis of their differences in elastic properties, although it is more qualitative than elastic modulus distribution. Many approaches to obtaining strain images from echo signals have been proposed. Most of these approaches use the spatial correlation technique, a method of detecting tissue displacement that provides maximum correlation between the echo signal obtained before and the one obtained after compression. Those methods are not suited for real-time processing, however, because of the amount of computation time they require. An alternative approach is a phase-tracking method, which is analogous to Doppler blood flowmetry. Although it can realize the rapid detection of displacement, the aliasing effect prevents its application to the large displacements that are necessary to improve the S/N ratio of the strain image. We therefore developed a more useful technique for imaging tissue elasticity. This approach, which we call the combined autocorrelation (CA) method, has the advantages of producing strain images of high quality with real-time processing and being applicable to large displacements.Numeric simulation and phantom experimentation have demonstrated that this method's capability to reconstruct images of tissue strain distribution under practical conditions is superior to that of the conventional spatial correlation method. In simulation and phantom experimentation, moreover, the image of elastic modulus distribution was also obtained by estimating stress distribution using a three-dimensional tissue model. When the proposed CA method was used to measure breast tumor specimens, the obtained strain images clearly revealed harder tumor lesions that were only vaguely resolved in B-mode images. Moreover, the results indicated the possibility of extracting the pathological characteristics of a tumor, making it useful for determining tumor type. These advantages justify the clinical use of the CA method.

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 .

The relationships between the intravascular wall shear stress, controlled by flow dynamics, and the progress of arteriosclerosis plaque have been clarified by various studies. Since the shear stress is determined by the viscosity coefficient and shear rate, both factors must be estimated accurately. In this paper, an adaptive method for improving the accuracy of quantitative shear rate estimation was investigated. First, the parameter dependence of the estimated shear rate was investigated in terms of the differential window width and the number of averaged velocity profiles based on simulation and experimental data, and then the shear rate calculation was optimized. The optimized result revealed that the proposed adaptive method of shear rate estimation was effective for improving the accuracy of shear rate calculation.

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.

The mechanical properties, or elasticity and viscosity, of tissues reflect the pathological change of tissues caused by lifestyle-related diseases such as cancer and cardiac disease. Therefore, tissue elasticity imaging has been investigated for several years and a practical system applicable to clinical diagnosis has recently been developed. To diagnose the stage of disease progression and differentiate malignant from benign tumors precisely using parameters that represent tissue elasticity and viscosity, it is required to elucidate the quantitative relationship between these parameters and disease. However, no database for such a relationship has been yet established. With the aim of constructing such a database, we undertook to develop a three-dimensional (3D) tissue viscoelasticity microscope, with which we can quantitatively measure the 3D distribution of parameters of tissue elasticity and viscosity. Results of experiments using a phantom model made of konnyaku and acrylamide confirmed that the system could reveal differences in the elasticity and viscosity of tissues.

In this work we report on the development of a novel technique for fat-saturated three-dimensional (3D) diffusion-weighted (DW) MRI sequence based upon 3D magnetization-prepared rapid gradient-echo (3D-MP-RAGE). In order to saturate fat, two kinds of procedures were competed CHESS-DW-3D-MP-RAGE sequence (CHESS -3D-DWI) and DW-3D-MP-WE-RAGE sequence (WE-3D-DWI) “chemical shift selective: CHESS method vs. water-excitation: WE method”. The CHESS-3D-DWI sequence and WE-3D-DWI sequence were compared in terms of their degree of fat suppression. In CHESS-3D-DWI sequence a preparation phase with a “CHESS-90ºRF-motion probing gradient: MPG-180ºRF-MPG-90ºRF” pulse-train was used to sensitize the magnetization to fat-saturated diffusion. In contrast, WE-3DDWI sequence a RAGE-excitation pulse with a “binominal -pulse 1-1 or 1-2-1” was selected to water-excited (fat-saturated) diffusion imaging. These imaging were done during in vivo studies using an animal experiment. From experimental results obtained with a phantom, the effect of diffusion weighting and the effect of fat-saturation were confirmed. Fat-saturation was much better in the WE-3D-DWI sequence than CHESS-3D-DWI sequence. From rat experimental results, fat-saturated diffusion-weighted image data were obtained. This sequence was useful for in vivo imaging., Date of Conference: 22-26 Aug. 2007

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.

BACKGROUND Transmission and tomographic X-ray measurements are useful in assessing bone structures, but only a few studies have examined cartilage growth because of the poor contrast in conventional X-ray imaging. OBJECTIVE In this study, we attempted to use the linear attenuation coefficient (LAC) as a metric of tissue-engineered cartilage development, which would be useful in high-throughput screening of cartilage products. METHODS Assuming that the LAC is related to the amount of extracellular matrix (ECM) in terms of the density and its atomic components, we measured X-ray absorption through tissue-engineered cartilage constructs. Characteristic X-ray beams from a molybdenum microfocus X-ray tube were employed to avoid beam hardening. The correlation of the LAC with mechanical properties was analyzed for verification. RESULTS The LAC was higher for chondrocyte constructs and lower for fibroblast-dominant constructs and was consistent with the quantification of toluidine blue staining, which is a proof of ECM production. The LAC was positively correlated with the bending modulus but negatively correlated with the dynamic elastic modulus and stiffness, possibly because of the remaining scaffold. CONCLUSIONS The LAC has the potential to be used as a metric of development of tissue-engineered cartilage. However, the calcified regions should be excluded from analysis to avoid decreasing the correlation between the LAC and the amount of ECM.

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.

Mechanical load to the blood vessel wall, such as shear stress and pressure, which occurs in blood flow dynamics, contribute greatly to plaque rupture in arteriosclerosis and to biochemical activation of endothelial cells. Therefore, noninvasive estimations of these mechanical loads are able to provide useful information for the prevention of vascular diseases. Although the pressure is the dominant component of mechanical load, for practical purposes, the pressure gradient is also often important. So far, we have investigated the estimation of the kinematic viscosity coefficient using a combination of the Navier-Stokes equations and ultrasonic velocity measurement. In this paper, a method for pressure gradient estimation using the estimated kinematic viscosity coefficient is proposed. The validity of the proposed method was investigated on the basis of the analysis with the data obtained by computer simulation and a flow phantom experiment. These results revealed that the proposed method can provide a valid estimation of the pressure gradient.

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...

Tissue elasticity imaging technology is expected to be a new technique for breast disease diagnosis. In clinical measurement, high-speed and freehand manipulation of the probe is required for a practical system. Thus, we developed a tissue elasticity imaging system which performs a stable strain measurement with freehand tissue compression based on the extended combined autocorrelation method. The method enables us to obtain tissue strain distribution at high-speed and suppressing errors due to lateral slip of the probe caused by freehand compression. The developed method can estimate the strain images at about 5 frames/s and was applied to breast disease measurement in vivo. Consequently, it is shown that the system is effective not only for the diagnosis of tissue hardness but also to determine the disease expansion area. It is also confirmed that the method can stably estimate the strain during the breast measurement in vivo.

Imaging of tissue elasticity is promising as a technique for visualizing tissue variations such as tumors from the point of view of hardness. Evaluation of the elasticity has hitherto been carried out mainly in the range in which the stress and strain generated within the tissue under infinitesimal deformation are related linearly. Under a finite deformation, such a linear relationship does not hold but a nonlinear phenomenon (strain hardening) takes place, in which Young's modulus increases with the strain. Since such nonlinearity is a property characteristic of the tissue, this paper deals with this nonlinearity and discusses a method of visualizing it and obtaining new information for tissue diagnosis. As a basic study, an experiment is carried out using a phantom containing the gizzard and liver of a fowl. The rate of increase of Young's modulus due to substantial deformation is visualized as a nonlinear parameter. It is found that gelatin and liver, with similar values of Young's modulus, cannot be distinguished by the conventional Young's modulus image but can be distinguished by visualizing the incrementation rate of each Young's modulus. Hence, the nonlinear elastic parameter can be effective for tissue discrimination. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 85(12): 9–18, 2002; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ecjc.10024