Acoustic characterization of a miniature matrix transducer for pediatric 3D transesophageal echocardiography

This paper presents the design, fabrication and characterization of a miniature PZT-on-CMOS matrix transducer for real-time pediatric 3-dimensional (3D) transesophageal echocardiography (TEE). This 3D TEE probe consists of a 32?×?32 array of PZT elements integrated on top of an Application Specific Integrated Circuit (ASIC). We propose a partitioned transmit/receive array architecture wherein the 8?×?8 transmitter elements, located at the centre of the array, are directly wired out and the remaining receive elements are grouped into 96 sub-arrays of 3?×?3 elements. The echoes received by these sub-groups are locally processed by micro-beamformer circuits in the ASIC that allow pre-steering up to ±37°. The PZT-on-CMOS matrix transducer has been characterized acoustically and has a centre frequency of 5.8 MHz, -6 dB bandwidth of 67%, a transmit efficiency of 6 kPa/V at 30 mm, and a receive dynamic range of 85 dB with minimum and maximum detectable pressures of 5 Pa and 84 kPa respectively. The properties are very suitable for a miniature pediatric real-time 3D TEE probe.     

Sex difference in Aroclor 1254 induction of rat hepatocytes: Consequences for in vitro embryotoxicity and mutagenicity of cyclophosphamide

The sequential culture of rat hepatocytes and post-implantation rat embryos has been proposed as a model for the in vitro testing of pro-teratogens. Comparing this model with a model in which embryos and hepatocytes are cultured simultaneously a striking difference in sensitivity was noted. To address the question of whether this difference could be explained by different sex and/or Aroclor 1254 pretreatment of the rats providing the hepatocytes, an experiment was designed with four groups: male Aroclor 1254 pretreated (M₁), male untreated, pregnant female Aroclor 1254 pretreated (F₁) and pregnant female untreated rats. Hepatocytes were incubated in the presence of cyclophosphamide (CP) and rat embryos were cultured in the media derived from the hepatocyte culture (i.e. the sequential culture model). Additionally, the CP concentrations of the media were analysed and subsequently the media were tested in a bacterial mutagenicity test (Salmonella typhimurium TA1535). With a CP concentration of 300 μ , M₁ produced maximum embryotoxicity and mutagenicity after 4 hr of hepatocytes incubation. All other groups showed no or only a slight increase in embryotoxicity and mutagenicity for all hepatocyte incubations. M₁ was also quickest to eliminate CP from the medium. These results indicate that despite a strong increase in total cytochrome P-450 in both sexes as a result of Aroclor 1254 pretreatment, and in the absence of a significant difference in total cytochrome P-450 between M₁ and F₁, Aroclor 1254 pretreatment has a much more pronounced effect in male rats than in pregnant female rats with regard to the production of embryotoxic and mutagenic metabolites of CP.     

Stereospecific in vitro embryotoxicity of l-homocysteine in pre- and post-implantation rodent embryos

Recently a derangement of homocysteine metabolism has been suggested as a possible risk factor for neural tube defects and recurrent spontaneous abortion. To investigate a possible role of homocysteine in the aetiology of neural tube defects we tested the in vitro embryotoxicity of l-homocysteine by culturing day 10 post coitum post-implantation rat embryos in whole embryo culture (WEC) for 24 hr and day 2 post coitum pre-implantation mouse embryos for 48 hr. With an area under curve (AUC) of 6.3 mm/hr, l-homocysteine significantly reduced the percentage of mouse embryos that developed into blastocysts. In rat WEC, an AUC for l-homocysteine of 3.6 mm/hr reduced the mitotic index of the neural epithelium of the rhombencephalon and the cell density of the mesenchyme adjacent to it, while at an AUC of 7.2 mm/hr l-homocysteine reduced the total morphological score and the number of malformations was increased. Malformations most often seen were transparent rhombencephalon, no or delayed formation of forelimb buds, dysmorphogenesis of the somites, and blister formation dorso-laterally of the place of forelimb bud formation. The embryotoxicity of l-homocysteine was stereospecific since d-homocysteine caused no embryotoxic effects. Also the oxidation product l-homocystine (AUC, 72 mm/hr) and the metabolite l-methionine (AUC, 144 mm/hr) were not embryotoxic. Both stereoisomers of homocysteinethiolactone were embryotoxic at an AUC of 72 mm/hr. The results are discussed in relation to the metabolism of homocysteine and methionine and their possible role in the neurulation process.     

Fast Volumetric Imaging Using a Matrix Transesophageal Echocardiography Probe with Partitioned Transmit–Receive Array

We describe a 3-D multiline parallel beamforming scheme for real-time volumetric ultrasound imaging using a prototype matrix transesophageal echocardiography probe with diagonally diced elements and separated transmit and receive arrays. The elements in the smaller rectangular transmit array are directly wired to the ultrasound system. The elements of the larger square receive aperture are grouped in 4?×?4-element sub-arrays by micro-beamforming in an application-specific integrated circuit. We propose a beamforming sequence with 85 transmit–receive events that exhibits good performance for a volume sector of 60°?×?60°. The beamforming is validated using Field II simulations, phantom measurements and in vivo imaging. The proposed parallel beamforming achieves volume rates up to 59 Hz and produces good-quality images by angle-weighted combination of overlapping sub-volumes. Point spread function, contrast ratio and contrast-to-noise ratio in the phantom experiment closely match those of the simulation. In vivo 3-D imaging at 22-Hz volume rate in a healthy adult pig clearly visualized the cardiac structures, including valve motion.     

Exposure related mutagens in urine of rubber workers associated with inhalable particulate and dermal exposure

Aims: To determine the relation of the inhalation and dermal exposure routes and mutagenic activity in the urine of rubber workers (n = 105).

Methods: Mutagenic activity of ambient total suspended particulate matter (TSPM), surface contamination wipes, and Sunday and weekday urine samples was assessed with S typhimurium YG1041 in the presence of a metabolic activation system. Each subject was grouped into one of two exposure categories for dermal exposure (high (≥25 revertants/cm²), low (<25 revertants/cm²)) based on the mutagenic activity detected on likely skin contact surfaces and into two airborne mutagenic exposure categories (high (≥210 revertants/m³), low (<210 revertants/m³)). The potential influence of skin aberrations and acetylation status (NAT2) on urinary mutagenicity levels was also evaluated.

Results: A non-significant increase of +1605 revertants/g creatinine in urinary mutagenicity during the workweek relative to levels observed on Sunday was observed for the total population. Subsequent multivariate regression analyses, with the subjects' weekday urinary mutagenicity levels as the dependent variable, revealed associations with environmental and mainstream tobacco smoke exposure, with the level of mutagenic contamination on surfaces with which the subjects had likely contact, with the subjects' inhalable particulate exposure level, with observed mild skin aberrations, and when the subjects had a slow acetylation phenotype. Similar associations, although weaker were observed with Sunday urinary mutagenicity levels as well, except for the association with slow acetylation phenotype. Based on measured exposure levels it could be estimated that a high potential for exposure to surface contamination with mutagenic activity increased weekday urinary mutagenicity by about 62% when compared to low exposed workers, while high inhalable particulate exposure levels increased weekday urinary mutagenicity levels by about 21%. Subjects with mild skin aberrations had an additional, non-significant, increase in weekday urinary mutagenic activity compared to subjects without any skin aberrations.

Discussion: Results suggest that the dermal exposure route may contribute more to the level of genotoxic compounds in urine of rubber workers than the inhalation route. Although the study was limited in size, the results warrant further investigation in the importance of and ways to effectively control the dermal exposure route in the rubber industry.