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Biomedical subjects

M J Lunt

Publications and source records attributed to M J Lunt.

15 recordsLinked to original sources
PubMed1989

Surface heating of diagnostic ultrasound transducers.

Surface temperatures of a variety of transducers used with common commercial ultrasonic diagnostic equipment have been measured. Transducers operating in imaging mode, in both continuous and pulsed Doppler modes, and in mixed modes were investigated. A total of 30 transducers and scan-heads used with equipment from 10 manufacturers were examined, including a range of array types, mechanical sectors and continuous-wave Doppler transducers. Measurements were made using an infrared radiometer, or a thermocouple probe, with the transducers operating in air. Surface temperatures of 13 transducers operating in imaging mode were found to be in the range 0.0-13.1 degrees C above ambient after 5 min operation. Some transducers operating in pulsed Doppler mode reached considerably higher temperatures. The most extreme example increased the surface temperature by 36.5 degrees C after 1 min and reached a steady-state temperature of almost 80 degrees C. Transducers operating at these temperatures cannot be retained on the skin of a conscious subject without pain, and will cause skin burns within a brief period of time. A linear relationship has been demonstrated between temperature increase and spatial-average acoustic intensity. The rate of increase in air was found to be about 10 times greater for pulsed arrays than for continuous-wave Doppler transducers.

Hot Temperature↗
PubMed1987

Continuous 24 hour ambulatory monitoring of intragastric pH in man.

A system has been developed which permits continuous 24 hour ambulatory recording of intragastric pH under near-physiological conditions. The system utilises a Cecar combination pH electrode connected through a pre-amplifier to an Oxford Medical Systems Medilog 4-24 cassette recorder, and the pH recorded continuously on to tape. The data is replayed at high speed, digitised and then analysed. Sources of error included system drift, system noise and the effect of changes in electrode environment due to saliva, food, loss of fluid contact, temperature variations and electrode time constant. These were found to be small. In contrast, the major changes in pH detected reflect real changes at the electrode tip. These changes can be recorded by the system. Developments in electronics and improvements in both the size and quality of pH electrodes, over the past few decades, has enabled intragastric pH recordings to be made with greater ease. However, a large number of investigators still assess gastric acidity by infrequent, intermittent sampling of gastric secretion through a naso-gastric tube. This new ambulatory system is a significant improvement and its versatility allows studies in acid secretion physiology, pharmacology and pathophysiology.

Electrodes↗
PubMed1983

The effects of pulsed magnetic fields of the type used in the stimulation of bone fracture healing.

The main impression received by us whilst writing this review is the scarcity of technical data in the clinical studies and the total absence of controlled trials. The spatial patterns of the stimulus have not been measured, and no experiments have proved that there is an effect from the magnetic field itself. Control experiments using dummy stimulators must be done, since the orthopaedic management of the stimulated patients is different from conventional management and this may have significant and beneficial clinical effects. There is no clinical study at present which shows a direct therapeutic benefit due solely to the application of the magnetic field component of the overall treatment regime. The in vivo animal experiments suggest that there may be effects due to the magnetic fields used but results are very scarce compared with the accumulated data from direct current stimulation. In vitro studies are far removed from the clinical situation, but could nonetheless prove useful if the opportunity of controlling the stimulus can be taken. In the majority of experiments, approximately spatially uniform magnetic fields have been applied, but temporal changes in the magnetic field and both spatial and temporal variation in electric field lead to non-uniform stimulation. Little attempt has been made to assess or control the induced fields by defining the system geometry. Hence it is still unknown whether effects are due to the magnetic field, the induced extracellular electric field or to fields induced at cellular level by regions of different conductivity. In conclusion, we believe that, unlike steady current work, the pulsed magnetic field treatment of fractures has not been sufficiently well investigated and, although some of the animal experiments suggest significant effects, the benefit of using magnetic fields in the clinical management of non-union and delayed union has still to be proven. Double blind trials are essential and, if these do prove that there is a definite effect of the fields, the mechanisms must then be studied using a combination of theoretical, in vivo and in vitro techniques.

Animals↗
PubMed1980

The optimum frequency and angle of insonation for a Doppler ultrasonic flow velocity meter.

A simple model is used to indicate the optimum ultrasonic frequency and angle of insonation for Doppler studies on vessels at different depths in the body. The criterion taken in determining this optimum frequency is the minimum error in a mean or root mean square frequency meter. The analysis shows that theoretically there is an optimum angle and frequency that depends on the depth of the vessel being examined, and that the optimum frequency is much lower than that normally used.

Blood Flow Velocity↗
PubMed1979

A maximum frequency detector for Doppler blood velocimeters.

The clinical information available from ultrasonic Doppler blood velocimeters may be analysed in several ways, spectral analysis probably being the best. This is, however, a relatively expensive technique when compared with the cost of commerically available Doppler velocimeters. A large part of the diagnostic information present can be obtained from the maximum blood velocity in the vessel at any one time. A relatively inexpensive analogue method of extracting this information from the Doppler signal is described, and the preliminary results obtained on signals derived from peripheral arteries are discussed.

Blood Flow Velocity↗
PubMed1979

A simple radiation balance for measuring ultrasonic power.

The design and construction of a beam balance for measuring the power outputs of therapeutic and diagnostic ultrasonic instruments is described. Power outputs down to 4 mW have been measured using a low magnification microscope.

Calibration↗
PubMed1978

Preliminary report on some ultrasonic methods for detecting carotid artery disease.

The use of both Doppler and pulse-echoultrasonic equipment for detecting carotid artery disease is discussed. The need for new non-invasive techniques, capable of detecting small stenoses, is demonstrated and the development of two techniques (analysis of blood velocity waveforms and the measurement of arterial wall movement) is described. The arterial wall movement showed no change with disease, but analysis of the blood velocity waveforms proved capable of detecting even minor stenosis in some cases. Methods for confirming these preliminary results are discussed.

Adult↗