Beyond 30 MHz [applications of high-frequency ultrasound imaging]

Most medical ultrasound imaging systems operate in the frequency range from 3 to 10 MHz and can resolve objects approximately 1 mm in size. In the mid 1980s, new transducer materials led to the development of the first transducers suitable for high-frequency (30-100 MHz) clinical imaging. These high-frequency transducers can provide images of subsurface structures with microscopic resolution. In this article, the authors introduce the basic principles of high-frequency ultrasound imaging and discuss six applications of this new technology: eye imaging, skin imaging, catheter-based intravascular imaging, intra-articular imaging, high-frequency flow imaging, and in-vivo imaging of mouse embryonic development. These examples illustrate a few of the potential applications of high-frequency ultrasound in medicine and biology     

Cytogenetic abnormalities in mesoblastic nephroma: a link to Wilms' tumour?

Cytogenetic analysis of tumour material from a congenital mesoblastic nephroma is reported. Two cell lines were found, one with a normal 46,XY karyotype and the other with a hyperdiploid 51,XY karyotype, including a rearrangement of chromosome 11 at 11p15. This finding is of interest since loss of allelic heterozygosity at polymorphic 11p15 loci has been described in sporadic Wilms' tumour [1], and both cytogenetic [2] and molecular [3] changes of 11p15 are found in the Wiedemann-Beckwith syndrome, a condition with a predisposition to embryonal tumours, particularly Wilms' tumour. Our results lead us to speculate on the implications relating to the pathogenesis of this relatively benign tumour variant with respect to the current understanding of the genetics of Wilms' tumour.     

Silicon-Germanium Nanostructures for Light Emitters and On-Chip Optical Interconnects

In this paper, we review the present status of light emitters based on SiGe nanostructures. In order to be commercially valuable, these light emitters should be efficient, fast, operational at room temperature, and, perhaps most important, compatible with the ldquomainstreamrdquo complementary metal-oxide-semiconductor (CMOS) technology. Another important requirement is in the emission wavelength, which should match the optical waveguide low-loss spectral region, i.e., 1.3-1.6 mum. Among other approaches, epitaxially grown Si/SiGe quantum wells and quantum dot/quantum well complexes produce efficient photoluminescence and electroluminescence in the required spectral range. Until recently, the major roadblocks for practical applications of these devices were strong thermal quenching of the luminescence quantum efficiency and a long carrier radiative lifetime. The latest progress in the understanding of physics of carrier recombination in Si/SiGe nanostructures is reviewed, and a new route toward CMOS compatible light emitters for on-chip optical interconnects is proposed.     

Investigation of cross talk in Kerfless annular arrays for high-frequency imaging

The effect of electromechanical cross talk in high-frequency (> 30 MHz) kerfless annular arrays is investigated. Finite-element model predictions of the radiation patterns from arrays are compared to predictions from an ideal model without cross talk and with experimental measurements. High cross talk in the array causes element broadening and an increase in the amplitude of secondary lobes in the radiation pattern. However, an increase in the pulse ring-down time was not found. This can be attributed to the absence of lateral modes in the kerfless substrate. The level of the pedestal secondary lobes in the two-way radiation pattern increases linearly with the element path difference. The element broadening increases the effective element path difference, which increases the pedestal level for a kerfless annular array above the level for an ideal array. The broadening limits how close to an array one can image compared to the ideal case by reducing the contrast available in the image at small f-numbers. When the element broadening is taken into account by widening the electrode dimensions, the ideal radiation pattern agrees well with the finite-element model and experimental radiation patterns.     

Amino Acid Additives Effects on Sweet Potato Starch Thermal Properties

This study assessed the effects of amino acid additives, aspartic acid, leucine, lysine, and methionine, on the thermal characteristics of white‐fleshed and orange‐fleshed Beauregard sweet potato starches. The orange‐fleshed sweet potato (OFSPS) starch began to gelatinize at a lower temperature (56.8°C) than the white‐fleshed sweet potato starch (WFSPS) (70.1°C), but the two starches needed the same amount of energy to gelatinize. Lysine increased the gelatinization temperature of the OFSPS. The addition of leucine, aspartic acid, and methionine had no apparent impact on the OFSPS. The addition of lysine or aspartic acid increased the gelatinization temperatures of the WFSPS. Overall, the two starches used were more affected by charged amino acids than by the neutral ones.     

A prospective randomized single-blind comparative trial of nafarelin acetate with buserelin in long-protocol gonadotrophin-releasing hormone analogue controlled in-vitro fertilization cycles

Matrix metalloproteinases (MMPs) play key roles in tissue remodeling during physiological and pathological processes by degrading various extracellular matrix (ECM) components. Although nine distinct MMPs have been characterized by cDNA cloning, there are thought to be more corresponding to the complexity of the ECM. MMP genes expressed in human tissues and cell lines were analyzed by the polymerase chain reaction (PCR) using degenerate primers that corresponded to the conserved amino acid (aa) sequences of the MMPs. One isolated complementary DNA (cDNA) fragment had sequence homology to the reported MMPs, but was otherwise unique. A human placenta cDNA library (Clontech) was screened using the fragment as a probe and a 3.4-kb cDNA fragment containing a long open reading frame (potentially encoding 582 aa) was isolated. The putative gene product had a common domain structure and the conserved sequence of a MMP, but it had a unique transmembrane (TM)-like structure at the C terminus. It should, therefore, be an TM protein, whereas all the other reported MMPs are secretory proteins. Thus, the gene is thought to be the first of a new subclass of MMPs whose products are potentially expressed on the cell surface.     

A multiorder approach to bod kinetics

Employing a reaeration technique, oxygen uptake curves were obtained for 20 samples from 8 New Jersey, U.S.A. streams. Using a stepwise nonlinear regression approach, rate constants and ultimate BOD values were calculated for equations in which the order of the reaction was assumed to be 1, 1.5, 2, 2.5, 3, 3.5 and 4. There was a tendency for the error mean square to decrease as the reaction order increased from 1 to 4. However, the reduced error was accompanied by an approximate doubling of the ultimate BOD values in going from a first to a fourth order reaction. These ultimate BOD values calculated at the higher reaction orders are in all probability unrealistically high.     

Polymer-coated metal and alloy particles for magnetic recording

Fine particles of cobalt and an iron-cobalt alloy were prepared and encapsulated in a plastic film to protect them from oxidation. The magnetic properties of the coated powders were determined and compared with the properties of coated iron powders studied previously. The thermal degradation of magnetic properties was also investigated. Polymer-coated iron and cobalt powders were incorporated in a Hypalon rubber matrix to obtain additional magnetic property data and to study recording characteristics. The experimental materials exhibited better high-frequency response in magnetic recording than a standard γ-Fe2O3material, and one material had a higher signal output as well.     

A sigma-delta-based sparse synthetic aperture beamformer for real-time 3-D ultrasound

Sigma-delta (ΣΔ) modulation allows delay resolution in ultrasound beamformers to be achieved by simple clock cycle delays applied to the undecimated bitstream, greatly reducing the complexity of the signal processing and the number of bits in the datapath. The simplifications offered by this technique have the potential for low power and portable operation in advanced systems such as 3-D and color Doppler imagers. In this paper, an architecture for a portable, real-time, 3-D sparse synthetic aperture ultrasound beamformer based on ΣΔ modulation is presented, and its simulated performance is analyzed. Specifically, with a 65-element linear phased array and three transmit events, this architecture is shown to achieve a 1.1° beamwidth, a -54-dB secondary lobe level, and a theoretical frame rate of 1700 frames/s at λ/64 delay resolution using a second-order low pass ΣΔ modulator. Finally, a technique for modifying the proposed multi-beam architecture to allow improved analog-to-digital (A/D) resolution by premodulating the input signal for bandpass ΣΔ modulation is also presented