Noninvasive 3-D ultrasound of atherosclerotic plaques in the Watanabe rabbit.

We have investigated the ability to quantitate atherosclerosis in the aortic arch of the Watanabe rabbit using noninvasive 3-D ultrasound. Our methodology utilizes postprocessing of videotaped freehand 2-D interrogations to form a compound 3-D data block. Structures may then be segmented on the attributed grey-scale level and volumes measured. Analysis of 3-D reconstructions revealed a low echo structure in the aortic arch of atherosclerotic rabbits, absent in nonatherosclerotic rabbits, at recognized sites of plaque predilection. This structure volume correlated closely with fatty streak volume determined from histology (r = 0.890). During a 30-week study, this structure volume increased in untreated animals, but was blocked by treatment with the antiatherosclerotic agent probucol. Thus, a new 3-D ultrasound methodology has been used noninvasively to detect and quantitate a low echo structure corresponding to fatty streaks in the Watanabe rabbit aortic arch. This new methodology could potentially aid plaque burden quantification in human peripheral arteries.

Three-dimensional freehand ultrasound: image reconstruction and volume analysis.

A system is described that rapidly produces a regular 3-dimensional (3-D) data block suitable for processing by conventional image analysis and volume measurement software. The system uses electromagnetic spatial location of 2-dimensional (2-D) freehand-scanned ultrasound B-mode images, custom-built signal-conditioning hardware, UNIX-based computer processing and an efficient 3-D reconstruction algorithm. Utilisation of images from multiple angles of insonation, "compounding," reduces speckle contrast, improves structure coherence within the reconstructed grey-scale image and enhances the ability to detect structure boundaries and to segment and quantify features. Volume measurements using a series of water-filled latex and cylindrical foam rubber phantoms with volumes down to 0.7 mL show that a high degree of accuracy, precision and reproducibility can be obtained. Extension of the technique to handle in vivo data sets by allowing physiological criteria to be taken into account in selecting the images used for construction is also illustrated.

Active coil isolation in NMR imaging and spectroscopy using PIN diodes and tuned transmission line: a practical approach.

To improve signal-to-noise (S/N) ratios in biological NMR experiments we have regularly employed close-fitting receiver coils. The poor RF (radio-frequency) homogeneity often exhibited by these coils can be partly overcome by using them with large transmitter coils, provided that good between-coil isolation during the RF transmission and receive periods is achieved. With this in mind, we have used combined PIN diodes and tuned line to isolate transmitter and receiver and to remove transmitter noise. A series of experiments reported here demonstrate (a) distortion-free receiver detuning during free-induction decay, (b) the reduced effect of the receiver coil on the transmitter pulse, (c) an increase in S/N from 71:1 to 158:1, and (d) the effectiveness of transmitter noise isolation. Improvements in S/N, isolation, and image homogeneity illustrate the value of utilizing these devices. Hardware to allow PIN diode switching under computer control is described, utilizing mostly nonmagnetic materials and batteries.

A precision isotonic measuring system for isolated tissues.

An isotonic measuring system is described which utilizes an angular position transducer of the linear differential voltage transformer type. Resistance to corrosion, protection against the ingress of solutions, and ease of mounting and setting up were the mechanical objectives. Accuracy, linearity, and freedom from drift were essential requirements of the electrical specification. A special housing was designed to accommodate the transducer to overcome these problems. A control unit incorporating a power supply and electronic filtering components was made to serve up to four such transducers. The transducer output voltage is sufficiently high to drive directly even low sensitivity chart recorders. Constructional details and a circuit diagram are included. Fifty such transducers have been in use for up to four years in these laboratories. Examples of some of the published work done using this transducer system are referenced.

A low-cost modular oxygen-consumption device for small animals.

This paper describes a simple apparatus enabling the O2 consumption of small animals to be monitored. The system consists of a sensitive solid-state pressure transducer linked via a relay to a small peristaltic pump. While the animal breathes air in its closed chamber the CO2 expired is removed by an absorber; hence the pressure falls. The signal is sensed by the transducer triggering the pump to deliver a set volume of O2 to the chamber. The number of pump operations per unit time necessary to keep the system equilibrated is a measure of the O2 consumption rate. Each device is built as a module, up to four being mounted in one assembly controlled by a microcomputer. A balance control, priming switch, pump-volume setting, and electromagnetic counter are built into each front panel. Calibration is achieved be removing a known volume of air from the system with no animal present and counting the number of operations to return the chamber to equilibrium.