Biomedical subjects
Publications and source records attributed to A D Bond.
Non-centrosymmetric structures are promoted through the use of perfluoroaromatics containing structure-directing CN...X (X = Br, I) supramolecular synthons.
The crystal structure of acetal acid 5 reveals changes in geometry representing progress along the reaction coordinate for acetal cleavage.
The crystal structure of the widely used title fungicidal material, [Cu(C(5)H(4)NOS)(2)], has been determined at 150 (2) K from a microcrystalline fragment using synchrotron radiation. The molecule adopts a trans-square-planar configuration, with the Cu atom sited at a crystallographic centre of inversion.
Hexagonal [(eta 2-Cp)3MnK.1.5thf] 1 and ion-separated [(eta 2-Cp)3Mn]2[Mg(thf)6].2thf 2 are obtained from reactions of CpK and Cp2Mg, respectively, with manganocene, Cp2Mn; they are the first complexes to be structurally characterised containing the [Cp3Mn]- anion.
A general design for a thermal test object (TTO) is proposed. A number of novel features make the design particularly suitable for use as a standardised device for assessing the heating capability of diagnostic ultrasound beams. To assess performance, soft-tissue TTOs have been made containing thin-film thermocouples sandwiched between discs of tissue-mimicking gel. Installed in an appropriate measurement system, these TTOs exhibit excellent thermal and spatial resolution, allowing the ultrasound beam to be located rapidly and reproducibly. The measured temperature rise after 3 minutes of heating has been compared with theoretical predictions based on measured pressure distributions, and agreement is within 10%. Other studies have shown that soft-tissue- and bone-mimicking TTOs can be used to evaluate a wide range of ultrasound fields and that different physical tissue models can be simulated. It is concluded that this design would be suitable for providing reference assessments of the thermal hazard posed by diagnostic ultrasound under standardised conditions.
There are many thousands of Doppler fetal heart beat detectors in medical use and many different detector manufacturers but, until recently, there has been no well-defined quantitative method for measuring the sensitivity of these detectors and, therefore, no way of directly comparing their technical performance under standardised test conditions. At NPL, we have developed a reference test facility for measuring detector sensitivity to meet the needs of manufacturers, and to comply with the requirements of an international standard (IEC 1995) that defines methods of measurement of the sensitivity of fetal heart beat detectors. The test facility has primarily been developed for detectors operating at a transmitted frequency of 2 MHz and with Doppler shifts of up to 1 kHz. The detectors are tested by directing the ultrasound beam at a small moving target being driven at a constant velocity, and then monitoring the output signal from the detector, which will be at the Doppler shift frequency. To determine the sensitivity, attenuators are inserted into the beam until the output signal is reduced to 6 dB above the noise level. The sensitivity is calculated by adding the final signal level above the noise to the total insertion loss of the attenuators in the ultrasound path and the reflection loss of the target. A crucial aspect of this calculation is the knowledge of the target strengths and characteristics. This has already been extensively studied (Preston and Bond 1997) over the frequency range of interest. The NPL test facility developed for undertaking the sensitivity measurements is described, including an assessment of the uncertainties in such a measurement and solutions to problems encountered along the way.
The performance of small-diameter targets suitable for use as oscillating targets for testing the sensitivity of Doppler fetal heartbeat detectors has been systematically studied. Experimental results are presented in the 1.6-3.0 MHz frequency range for the plane-wave reflection loss for a total of 16 targets: spherical balls made of stainless steel; hemispherical-ended rods made of PTFE; and flat-ended rods made of stainless steel, PTFE, polycarbonate, and tungsten carbide. Results show that the fine-structure variation of reflection loss with frequency is greatest in the case of spherical ball targets and least for flat-ended targets. It has been shown that, providing care is taken during manufacture, the reflection loss from a flat-ended target can be predicted using a simple theory based on a plane disc reflector. Tungsten carbide targets consisting of a long rod with a diameter of 1.6 mm tapered down to a cylindrical flat end with a diameter of 0.4, 0.5, and 0.6 mm have been shown to provide reflection losses of between 60 and 40 dB, and to have a smooth variation of reflection loss with frequency. They can also be manufactured in a form that allows no significant interference from the supporting structure and, therefore, are ideal targets to meet the requirements of International Electrotechnical Commission 1266:1995.
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