Feasibility of Bone Assessment with Ultrasonic Backscatter Signals in Neonates

The objective of this study was to assess the value of ultrasonic backscatter signals and the backscatter coefficient (BSC) in the analysis of bone status in neonates and to analyze the relationships between the BSC and gestational age, birth weight, length, head circumference and gender. A total of 122 neonates participated in the study, including 83 premature infants and 39 full-term infants. Their BSCs were measured by ultrasound after birth. The results revealed a significant correlation between the BSC and gestational age (R = 0.47, p < 0.001), birth weight (R = 0.47, p < 0.0001) and length at birth (R = 0.43, p < 0.001) at a frequency of 5.0 MHz. This study suggests that the use of ultrasonic backscattering and the BSC is feasible for assessment of the bone status of neonates.     

Ex vivo Study of Quantitative Ultrasound Parameters in Fatty Rabbit Livers

Nonalcoholic fatty liver disease (NAFLD) affects more than 30% of Americans, and with increasing problems of obesity in the United States, NAFLD is poised to become an even more serious medical concern. At present, accurate classification of steatosis (fatty liver) represents a significant challenge. In this study, the use of high-frequency (8 to 25 MHz) quantitative ultrasound (QUS) imaging to quantify fatty liver was explored. QUS is an imaging technique that can be used to quantify properties of tissue giving rise to scattered ultrasound. The changes in the ultrasound properties of livers in rabbits undergoing atherogenic diets of varying durations were investigated using QUS. Rabbits were placed on a special fatty diet for 0, 3, or 6 weeks. The fattiness of the livers was quantified by estimating the total lipid content of the livers. Ultrasonic properties, such as speed of sound, attenuation, and backscatter coefficients, were estimated in ex vivo rabbit liver samples from animals that had been on the diet for varying periods. Two QUS parameters were estimated based on the backscatter coefficient: effective scatterer diameter (ESD) and effective acoustic concentration (EAC), using a spherical Gaussian scattering model. Two parameters were estimated based on the backscattered envelope statistics (the k parameter and the μ parameter) according to the homodyned K distribution. The speed of sound decreased from 1574 to 1565 m/s and the attenuation coefficient increased from 0.71 to 1.27 dB/cm/MHz, respectively, with increasing fat content in the liver. The ESD decreased from 31 to 17 μm and the EAC increased from 38 to 63 dB/cm³ with increasing fat content in the liver. A significant increase in the μ parameter from 0.18 to 0.93 scatterers/mm³ was observed with increasing fat content in the liver samples. The results of this study indicate that QUS parameters are sensitive to fat content in the liver.     

Ultrasound properties of liver tissue during heating

The objective of this work was to determine changes in the ultrasound properties of heated tissues, with potential application to monitoring of minimally invasive thermal therapy (MITT). Changes in backscatter coefficients and frequency-dependent attenuation coefficients were measured over the frequency range 2.5 MHz to 5 MHz from heated samples of store-bought fresh bovine liver, which was used as a tissue model. Individual liver samples were heated from 37°C to either 50°C, 55°C, 60°C, 65°C or 70°C by warm water. The backscatter coefficient increased during the first 3 min by a factor of 1.09 and 1.11 before the tissue reached 50°C and 55°C, respectively. A decrease in backscatter coefficient followed at 50°C by a factor of 1.12 below the initial level and, at 55°C, the backscatter coefficient dropped below the initial level by a factor of 1.19. The backscatter coefficient decreased within the first 2 min by a factor of 1.22 before the tissue reached 60°C, then increased gradually to a factor of 1.05 below the initial level. At 65°C and 70°C, the changes in backscatter coefficient were highly variable, which may have been due to production of gas microbubbles in the heated tissues. The ultrasound attenuation coefficient increased by as much as 1.48 dB cm⁻¹ over a 30-min period at 70°C. First-order rate parameters derived from the attenuation results revealed one rate process at 50°C and 55°C and two rate processes at 60°C, 65°C and 70°C. An activation energy of 1.00 × 10⁴ cal mol⁻¹ was derived from the second rate constants at 60°C, 65°C and 70°C, which indicates that changes in attenuation may be due to protein denaturation. In conclusion, ultrasound image monitoring of thermal therapy treatment in liver may be feasible; however, the backscatter coefficient changes during heating are small and are of the same order as the variation in these changes from point to point in the tissue.     

碘化油与高功率聚焦超声破坏肝组织的协同升温效应研究

本实验首次研究生物组织因素（媒质）对高轼率聚焦超声（HIFU）破坏肝组织的影响。采用国产HIFU样机（1．1MHz）．体外观察其靶区在碘化油或蓖麻油不同媒质存在的温度变化。结果显示：不论在高功率（500W/cm2）和低功率（136W/cm2）超声照射下，碘化油使靶区温度升高显著高于无碘的蓖麻油（P=0．0008和P=0．0004）．提示碘比油与HIFU治疗有协同升温作用。用HIFU（1．1MHz，500W/cm2，20s）照射离体肝组织．发现肝内注射碘化油组靶区温度显著高于注射蓖麻油组（P=0．0239），且前者破坏程度和范围均明显大于后者，提示碘化油配合HIFU治疗肝肿瘤具有潜在的增效、定位和导向作用。     

Acoustic properties of lesions generated with an ultrasound therapy system

Methods for quantitative imaging of ultrasound propagation properties were applied to the examination of the acoustic appearance of lesions generated by high intensity focused ultrasound in excised pig livers. Single lesions, about 10 mm maximum diameter by 30 mm long, were created in each of six liver specimens. Two dimensional images (32 by 32 points) of sound speed, mean attenuation coefficient (as a function of frequency in the range 3 to 8.5 MHz) and mean backscattering coefficient (5 to 8 MHz) were obtained in 7 mm thick sections of tissue, cut to include a cross-section through the lesion. Images of these properties, presented alongside surface photographs of the samples, provided a qualitative demonstration that attenuation coefficient was the most useful and backscattering coefficient was the least useful acoustic parameter for visualizing such lesions. Quantitatively the data demonstrated significant increases in attenuation coefficient and sound speed in lesioned liver relative to normal, whereas backscattering was shown not to change in a significant manner except when undissolved gas is the mechanism for increased acoustic scattering. Samples where gas was not fully removed following lesion production gave significant increases in backscattering at the lesion centre, but the shape and size of regions of high backscattering coefficient corresponded poorly with the shape and size of the lesions, unlike attenuation and sound speed for which such correspondence was good.     

高强度聚焦超声定位损伤小型香猪肝脏组织的影像学检查

目的：观察超声在监测高强度聚焦超声（ＨＩＦＵ）损伤肝组织的动态影像学特征,旨在探讨彩超检测ＨＩＦＵ疗效的可行性。方法：采用重庆医科大学医学超声工程研究所自行研制的ＨＩＦＵ治疗样机（１．６ＭＨｚ,１３１５３Ｗ／ｃｍ２）,对２８只小型香猪肝脏组织致超声损伤。于损伤前１天、损伤后即刻、１天、３天、７天、１４天、２１天、２８天分别行彩超观察及解剖活检。结果：ＨＩＦＵ损伤即刻损伤区回声明显增强,３～７天,损伤区回声仍增强,边界更清晰。７～１４天,回声强弱不均,２８天损伤区与正常组织区无明显差异,这些改变与病理检查相一致。结论：超声在监测ＨＩ－ＦＵ疗效方面有重要的应用价值     

Ultrasonic radio-frequency spectrum analysis of normal brain tissue

Acoustic tissue properties can be estimated using texture and/or spectral parameter analysis. Spectral analysis is based on the rf-signals whose frequency-content is commonly neglected in conventional B-mode imaging. Attenuation and backscatter values of normal brain tissue were analyzed. Unprocessed rf-data of 20 patients were sampled intraoperatively after craniotomy using a modified conventional ultrasonic device (Hitachi CS 9600) and analyzed off-line by a custom-made software routine. Before parameter estimation, influences of the diffraction pattern were compensated by means of a correction function obtained using a tissue-mimicking phantom. Attenuation of white matter showed a linear frequency dependence with a slope of 0.94 +/- 0.13 dB cm(-1) MHz(-1). The spectral slope was determined using 10 distinct frequencies between 2.5 and 5.75 MHz. Backscattering properties were analyzed by determining the power spectral density (PSD) and a relative backscatter coefficient (rel BSC) against the values derived from the tissue-mimicking phantom. PSD and rel BSC values were frequency-dependent, with highest PSD values at the probe's center frequency (-75.69 +/- 8.26 dB V(2) Hz(-1)). The corresponding rel BSC value at 5 MHz was determined as 15.39 +/- 8.26 dB. Finally, backscatter coefficients (BSC) of brain tissue were computed using the known BSC of the phantom. The data provided in this study are meant to serve as a base for intended future characterization of brain tissue that potentially allows intraoperative differentiation between normal and pathologic areas and therefore provides the surgeon with additional information for defining the extent of resection in brain more precisely.     

Influence of tissue preparation on the high-frequency acoustic properties of normal kidney tissue

The influence of various tissue preparations on the acoustic properties of normal kidney tissue at high frequencies was investigated. Eight surgically excised normal kidney tissue specimens were classified into three groups: (i) fresh, frozen section, (ii) formalin-fixed, frozen section and (iii) formalin-fixed, paraffin section. Scanning acoustic microscopy operating in the frequency range of 100–200 MHz was used to display the two-dimensional distribution of attenuation constant and sound speed. Our results indicate that (i) there is no significant variation in both acoustic parameters between the three tissue groups, (ii) fixation by 10% formalin produces no significant change in the acoustic parameters, (iii) in fat-free tissue regions, the acoustic parameters are independent of preparation method and (iv) frozen sections must be used to assess the acoustic parameters in fat-rich tissues.     

Development of a Tissue-Mimicking Phantom of the Brain for Ultrasonic Studies

Constructing tissue-mimicking phantoms of the brain for ultrasonic studies is complicated by the low backscatter coefficient of brain tissue, causing difficulties in simultaneously matching the backscatter and attenuation properties. In this work, we report on the development of a polyvinyl alcohol-based tissue-mimicking phantom with properties approaching those of human brain tissue. Polyvinyl alcohol was selected as the base material for the phantom as its properties can be varied by freeze–thaw cycling, variations in concentration and the addition of scattering inclusions, allowing some independent control of backscatter and attenuation. The ultrasonic properties (including speed of sound, attenuation and backscatter) were optimized using these methods with talc powder as an additive. It was determined that the ultrasonic properties of the phantom produced in this study are best matched to brain tissue in the frequency range 1–3 MHz, indicating its utility for laboratory ultrasonic studies in this frequency range.     

Evaluation of lens hardness in cataract surgery using high-frequency ultrasonic parameters in vitro

Ultrasonic parameters of sound velocity and frequency-dependent attenuation ranging from 25 to 45 MHz were measured for the purpose of evaluating the hardness of lenses in cataract surgery (phacoemulsification). Measurements were performed with a 35-MHz ultrasonic transducer on porcine lenses in which artificially cataracts were induced. The hardness of the cataractous lens was also evaluated by mechanical measurement of its elastic properties. The results indicated that the ultrasonic attenuation coefficients in normal porcine lenses were approximately 4.49 +/- 0.05 (mean +/- SD) and 6.32 +/- 0.04 dB/mm at 30 and 40 MHz, respectively. The development progression of the cataracts resulted in the attenuation coefficient increasing linearly to 7.36 +/- 0.25 and 11.1 +/- 0.92 dB/mm, respectively, corresponding to an increase of Young's modulus from 2.6 to 101.2 kPa. The sound velocity concomitantly increased from 1639.8 +/- 4.2 to 1735.6 +/- 10.4 m/s. Evaluation of the relationship between the phacoemulsification energy level and ultrasonic parameters in vitro by surgeons revealed that both the attenuation coefficient and sound velocity were linearly correlated with the phacoemulsification energy (r = 0.941 and 0.915, respectively). These results showed that measuring high-frequency ultrasonic parameters provides surgeons with good capability and reproducibility for selecting the optimal energy level for phacoemulsification.     

实时超声造影定量分析评价大鼠肝纤维化病理分期的实验研究

目的 探讨实时超声造影定量分析技术评价大鼠肝纤维化病理分期的价值.方法 44只大鼠制作肝纤维化模型,6只大鼠作为对照组.于造模的4、8、12周分别随机从造模组取12只,从对照组中取2只行超声造影检查,获得以下参数:造影剂到达肝动脉、门静脉、肝静脉时间(HAAT、PVAT、HVAT);肝实质及门静脉灌注参数:峰值强度(LPPI、PVPI)、达峰时间(LPTP、PVTP)、曲线尖度(LPβ、PVβ)、曲线下面积(LPAUC、PVAUC);计算出肝动脉-肝静脉、门静脉-肝静脉渡越时间(HA-HVTT、Pv-HVTT),门静脉-肝实质峰值强度差(δPI),肝实质-门静脉达峰时间差(δTP).分析对照组及造模组肝纤维化各期定量参数的变化情况.结果 HVAT、PV-HVTT、HA-HVTT、LPPI、LPTP、δPI、δTP差异有统计学意义(P＜0.05),其余参数均无统计学意义.LPTP、δTP对纤维化分期的鉴别能力较好,S≥S2、S≥S3、S≥S4时,曲线下面积分别为0.812、0.860、0.822和0.808、0.857、0.856.结论 实时超声造影定量分析对肝纤维化分期评估有一定价值.     

Ultrasonic characterization of whole cells and isolated nuclei

High frequency ultrasound imaging (20 to 60 MHz) is increasingly being used in small animal imaging, molecular imaging and for the detection of structural changes during cell and tissue death. Ultrasonic tissue characterization techniques were used to measure the speed of sound, attenuation coefficient and integrated backscatter coefficient for (a) acute myeloid leukemia cells and corresponding isolated nuclei, (b) human epithelial kidney cells and corresponding isolated nuclei, (c) multinucleated human epithelial kidney cells and d) human breast cancer cells. The speed of sound for cells varied from 1522 to 1535 m/s, while values for nuclei were lower, ranging from 1493 to 1514 m/s. The attenuation coefficient slopes ranged from 0.0798 to 0.1073 dB mm(-1) MHz(-1) for cells and 0.0408 to 0.0530 dB mm(-1) MHz(-1) for nuclei. Integrated backscatter coefficient values for cells and isolated nuclei showed much greater variation and increased from 1.71 x 10(-4) Sr(-1) mm(-1) for the smallest nuclei to 26.47 x 10(-4) Sr(-1) mm(-1) for the cells with the largest nuclei. The findings suggest that integrated backscatter coefficient values, but not attenuation or speed of sound, are correlated with the size of the nuclei.     

Ultrasonic propagation properties of excised human skin

Eight human skin samples were excised postmortem from the upper and lower back, chest and abdomen from two cadavers. The acoustical speed, attenuation and backscatter were measured as a function of frequency (20 to 30 MHz) at 100 positions on a uniform grid over a cross-sectional slice through each sample with the sound incident in a direction parallel to the skin surface. Measurements were made at 24 ± 0.5°C. Samples were then frozen, cut and stained for histological examination and quantification of fibrous proteins and fat content. The mean attenuation coefficients obtained for whole skin agreed well with previously published results. Employing the model = ₁ƒⁿ where is the attenuation coefficient in decibels per centimeter, ₁ is the value of the attenuation coefficient at 1 MHz and ƒ is frequency raised to the power n, mean values (±1 standard deviation) for epidermis were ₁ = 0.44 ± 0.26 and N = 1.55 ± 0.12, and for dermis ₁ = 0.264 ± 0.17 dB cm⁻¹ and N = 1.69 ± 0.084. Using a similar model the mean backscatter coefficient was defined by μ₁ = (5.01 ± 25.76) × 10⁻⁸Sr⁻¹ cm⁻¹, n = 3.77 ± 1.5 for the epidermis, and μ₁ = (1.79 ± 19.5) × 10⁻⁶ and n = 2.76 ± 1.4 for the dermis. The speed of sound values fell within the range to be found in the literature with a mean value in the epidermis of 1645 m s⁻¹ and in the dermis of 1595 m s⁻¹. Significant, strong correlation existed between the spatially averaged fibrous protein content in the epidermis and dermis and the spatially averaged integrated attenuation measurements. Likewise, strong correlation existed between integrated backscatter and fibrous protein content in the epidermis but not in the dermis. Further research is required to confirm these preliminary findings and to evaluate the role of collagen fibre orientation as a source of variation in the backscattering coefficient of dermis.     

Thermal Fixation of Swine Liver Tissue after Magnetic Resonance-Guided High-Intensity Focused Ultrasound Ablation

The aim of this study was to investigate experimental conditions for efficient and controlled in vivo liver tissue ablation by magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) in a swine model, with the ultimate goal of improving clinical treatment outcome. Histological changes were examined both acutely (four animals) and 1 wk after treatment (five animals). Effects of acoustic power and multiple sonication cycles were investigated. There was good correlation between target size and observed ablation size by thermal dose calculation, post-procedural MR imaging and histopathology, when temperature at the focal point was kept below 90°C. Structural histopathology investigations revealed tissue thermal fixation in ablated regions. In the presence of cavitation, mechanical tissue destruction occurred, resulting in an ablation larger than the target. Complete extra-corporeal MR-guided HIFU ablation in the liver is feasible using high acoustic power. Nearby large vessels were preserved, which makes MR-guided HIFU promising for the ablation of liver tumors adjacent to large veins.     

Assessment of In Vitro Dental Implant Primary Stability Using an Ultrasonic Method

Dental implants are used for oral rehabilitation. However, there remain risks of failure that depend on the implant stability. The objective of this study is to investigate whether quantitative ultrasound technique can be used to assess the amount of bone in contact with dental implants. Ten implants are first inserted in the bone samples. The 10 MHz ultrasonic response of each implant is measured using a dedicated device and an indicator I is derived based on the amplitude of the signal. Then, the implant is unscrewed by 2 π radians and the measurement is realized again. A statistical analysis of variance was carried out and revealed a significant effect of the amount of bone in contact with the implant on the values of I (p value < 10^?5). The results indicates the feasibility of quantitative ultrasound techniques to assess implant primary stability in vitro.     

儿童扩张型心肌病的心肌超声背向散射参数研究

目的研究儿童扩张型心肌病心肌超声背向散射参数特点。方法采用超声背向散射积分技术,对20例扩张型心肌病（DCM）患儿及20例健康儿童,于左室长轴观采集室问隔中部及左室后壁心肌背向散射积分数据,包括校正平均背向散射积分（AⅡ％）和背向散射积分周期变化幅度（CVIB）。同时采集常规M型超声参数,并于心腔四腔观及五腔观,行脉冲多勒超声检查获得二尖瓣口和左室流出道血流图,计算左室Ri指数。结果与对照组比较,DCM组左室舒张末内径、收缩末内径、Tei指数、左室后壁AⅡ％增大（P〈0．01）,室间隔、左室后壁CVIB减低（P〈0．01）,背向散射积分曲线形态异常。DCM患儿心肌背向散射参数与左室Tei指数之间无相关性（P〉0．05）。结论扩张型心肌病儿童心肌背向散射参数变化特征：AⅡ％升高、CVIB下降、IBS曲线形态异常;左室Ri指数明显增高,心脏整体功能下降。     

Improving the statistics of quantitative ultrasound techniques with deformation compounding: an experimental study

Many quantitative ultrasound (QUS) techniques are based on estimates of the radio-frequency (RF) echo signal power spectrum. Historically, reliable spectral estimates required spatial averaging over large regions-of-interest (ROIs). Spatial compounding techniques have been used to obtain robust spectral estimates for data acquired over small regions of interest. A new technique referred to as “deformation compounding” is another method for providing robust spectral estimates over smaller regions of interest. Motion tracking software is used to follow an ROI while the tissue is deformed (typically by pressing with the transducer). The deformation spatially reorganizes the scatterers so that the resulting echo signal is decorrelated. The RF echo signal power spectrum for the ROI is then averaged over several frames of RF echo data as the tissue is deformed, thus, undergoing deformation compounding. More specifically, averaging spectral estimates among the uncorrelated RF data acquired following small deformations allows reduction in the variance of the power spectral density estimates and, thereby, improves accuracy of spectrum-based tissue property estimation. The viability of deformation compounding has been studied using phantoms with known attenuation and backscatter coefficients. Data from these phantoms demonstrates that a deformation of about 2% frame-to-frame average strain is sufficient to obtain statistically-independent echo signals (with correlations of less than 0.2). Averaging five such frames, where local scatterer reorganization has taken place due to mechanical deformations, reduces the average percent standard deviation among power spectra by 26% and averaging 10 frames reduces the average percent standard deviation by 49%. Deformation compounding is used in this study to improve measurements of backscatter coefficients. These tests show deformation compounding is a promising method to improve the accuracy of spectrum-based quantitative ultrasound for tissue characterization.     

Ultrasonic attenuation and propagation speed in mammalian tissues as a function of temperature

Ultrasonic attenuation in the frequency range 1–7 MHz, and the speed of sound, were determined experimentally in both fresh and fixed bovine and human soft tissues for various temperatures in the range 5–65°C. At temperatures below 40°C the attenuation coefficient behaves similarly for fixed and fresh tissues where, at high frequencies, it has a negative dependence on temperature, the value at 20°C being about 21% higher than that at 37°C. As the frequency is reduced, the temperature coefficient of attenuation progressively decreases until, after passing a transition frequency (this varies with the tissue specimens but is around 1–2 MHz), a positive dependence on temperature may be observed. At temperatures above about 40°C, the attenuation coefficient of freshly excised tissues increases with temperature, whereas for fixed tissues the attenuation coefficient continues to decrease. These observations help to resolve a possible discrepancy evident in previous reports of the temperature dependence of attenuation. The speed of sound in non-fatty tissues increases with temperature and exhibits a maximum at around 50°C, while for fatty tissues a negative dependence is observed. The implications of this result for improved diagnostic procedures is discussed.