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Concept: Acoustic microscopy

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Tissue level structural and mechanical properties are important determinants of bone strength. As an individual ages, microstructural changes occur in bone, e.g., trabeculae and cortex become thinner and porosity increases. However, it is not known how the elastic properties of bone change during aging. Bone tissue may lose its elasticity and become more brittle and prone to fractures as it ages. In the present study the age-dependent variation in the spatial distributions of microstructural and microelastic properties of the human femoral neck and shaft were evaluated by using acoustic microscopy. Although these properties may not be directly measured in vivo, there is a major interest to investigate their relationships with the linear elastic measurements obtained by diagnostic ultrasound at the most severe fracture sites, e.g., the femoral neck. However, before the validity of novel in vivo techniques can be established, it is essential to understand the age-dependent variation in tissue elastic properties and porosity at different skeletal sites. A total of 42 transverse cross-sectional bone samples were obtained from the femoral neck (Fn) and proximal femoral shaft (Ps) of 21 men (mean±SD age 47.1±17.8, range 17-82years). Samples were quantitatively imaged using a scanning acoustic microscope (SAM) equipped with a 50MHz ultrasound transducer. Distributions of the elastic coefficient (c(33)) of cortical (Ct) and trabecular (Tr) tissues and microstructure of cortex (cortical thickness Ct.Th and porosity Ct.Po) were determined. Variations in c(33) were observed with respect to tissue type (c(33Tr)c(33)(Ct.Fn)=35.3GPa>c(33)(Tr.Ps)=33.8GPa>c(33)(Tr.Fn)=31.9GPa), and cadaver age (R(2)=0.28 - 0.46, p<0.05). Regional variations in porosity were found in the neck (superior 13.1%; inferior 6.1%; anterior 10.1%; posterior 8.6%) and in the shaft (medial 9.5%; lateral 7.7%; anterior 8.6%; posterior 12.0%). In conclusion, significant variations in elastic coefficients were detected between femoral neck and shaft as well as between the quadrants of the cross-sections of neck and shaft. Moreover, an age-related increase in cortical porosity and a stiffening of the bone tissue were observed. These findings may explain in part the increase in susceptibility to suffer low energy fractures during aging and highlight the potential of ultrasound in clinical osteoporosis diagnostics.

Concepts: Cerebral cortex, Scanning acoustic microscope, Medical ultrasonography, Acoustic microscopy, Microscopy, Bone, Ultrasound, Acoustics

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The residual stress caused by polymerization shrinkage and thermal contraction of a heat-curing resin containing 4-META on a metal-resin structure was measured by a scanning acoustic microscope. The tensile residual stress in the resin occurred within 70 µm of the adhesion interface with a flat plate specimen. The maximum tensile stress was about 58 MPa at the interface. On a metal plate specimen with retention holes, ring-like cracks in the resin occurred around the retention holes with the adhesive specimen and many linear cracks occurred in the resin vertical to the longitudinal direction of the metal frame with the non-adhesive specimens. There was tensile residual stress on the resin surface at the center of the retention holes of the adhesion specimen, indicating that the stress in the specimen with surface treatment for adhesion was higher than in that without surface treatment.

Concepts: Biology, Ultrasound, Tensile strength, Scanning acoustic microscope, Acoustic microscopy, Microscopes, Acoustics, Microscopy

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Early detection of hepatitis is critical for proper patient management and improving disease prognosis. Ultrasound imaging is ideally suited for early-stage assessments, but conventional ultrasound images based on backscatter do not display quantitative tissue information because conventional ultrasound lacks essential modeling of the complex interaction between ultrasound and liver tissue in normal and diseased states. Therefore, speed-of-sound (SOS) measurements were obtained from three types of rat livers (normal, fatty, and fibrosis). Livers were harvested, fixed, and embedded in paraffin; a single 10-[micro sign]m thin section was obtained using a microtome and placed on a microscope slide. A scanning acoustic microscope incorporating transducers operating at 80- and 250-MHz center frequencies was used to scan the 10-[micro sign]m section. An adjacent 4-[micro sign]m thin section was stained with H&E (normal and fatty livers) or Azan (fibrosis livers). The SOS measured with both transducers displayed the same trend: SOS in fatty liver was lower than in normal liver and SOS in fibrosis liver was higher than in normal liver. SOS differences were greater at 250 MHz because of the improved spatial resolution, which allowed choosing region-of-interests containing only fat or fibrosis tissue. These initial results also were used to correlate the pathologic state with the SOS.

Concepts: Scanning acoustic microscope, Cirrhosis, Microscopes, Acoustic microscopy, Liver, Ultrasound, Microscopy, Acoustics

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A scanning acoustic microscope (SAM) imaging system calculates and color codes speed of sound (SOS). We evaluated the SAM results for lymph node imaging and compared these results with those of light microscopy (LM). SAM showed normal structures and localized/diffuse lesions of the lymph node. Our results revealed that as a rule, soft areas such as cystic necrosis presented less SOS while harder areas such as coagulative necrosis, granulomas, and fibrosis exhibited greater SOS. SOS increased according to stromal desmoplastic reactions and cellular concentration. In neoplastic lesions, statistically significant differences in SOS were observed among scirrhous carcinomas, lymphomas, and medullary carcinomas. SAM provided the following benefits over LM: (1) images reflected the tissue elasticity of each lesion, (2) digitized SOS data could be statistically comparable, (3) images were acquired in a few minutes without special staining, (4) SAM images and echographic images were comparable for clinical ultrasound imaging study.

Concepts: Microscopes, Acoustic microscopy, Anatomical pathology, Lymph node, Cancer, Ultrasound, Acoustics, Microscopy