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No description available.

No description available.

Waveguides occur in a number of areas of medical ultrasonics, one important application being in sonically-sensitive biopsy-needles. The behaviour of the propagation of ultrasound in waveguides is not widely understood. A model of guided sound-wave propagation in the elastic limit, based on Pochhammer's theory, is described. Characteristic equations for both real and imaginary arguments are derived for isotropic solid and hollow cylindrical waveguides and also for transversely-isotropic solid cylindrical waveguides. These equations, which take the form of singular determinants, were solved numerically. The solutions reveal that waveguides are dispersive media and the group and phase velocities of various modes of propagation are presented. In addition, the particle displacements of some of these modes are illustrated. Group velocities of modes in waveguides of different material were measured experimentally using an ultrasound pulse technique and the experimental results are compared with theory. Attenuation of the more dominant modes of propagation was also measured over the frequency range 1.0-5.0 MHz and the phenomenon of selective attenuation is discussed in the light of a number of attenuation models. A systematic study of sound conduction in a variety of waveguides of different radii and material media was undertaken and the effect of heat treatment investigated. The changes in conduction introduced by the latter are explained by changes in the internal grain structure which were observed using methods of metallurgical analysis. Finally, sound propagation was examined for conditions similar to those encountered in biopsy-needle guidance techniques. Other possible applications of waveguides in the field of medical ultrasonics are also considered. These theoretical and experimental studies have provided a fuller understanding of mode propagation in waveguides used in medical ultrasonics.

Raised intracranial pressure (ICP > 20 mm Hg) occurs in at last thirty percent of severely head injured patients and is associated with a significant increase in the number of deaths and severely disabled survivors. A study of the ICP waveform may yield information of relevance to the management of raised ICP either as a predictor of raised ICP or of its underlying cause. An observational study in thirty severely head injured patients was carried out, where fifteen hundred ICP and blood pressure (BP) waveform samples were collected under microcomputer control and analysed through the use of spectral methods in a systems analysis aproach to quantifying pressure transmission across the cerebrovascular bed. The amplitude transfer functions, as a measure of cerebrovascular pressure transmission, were calculated for the first 4 cardiac harmonics from the ICP and BP spectra and were found to cluster into four classes: those with an overall flat amplitude transfer function (curve type 1), and those with an elevated low frequency response (curve type 2), those with an elevated high frequency response (curve type 3) and those exhibiting both an elevated low and an elevated high frequency response (curve type 4). Curve types 2 and 4 (elevated low frequency, elevated low frequency in combination with elevated high frequency) were most often associated with raised ICP (ICP > 20 mm Hg) whereas curve types 1 and 3 (flat, elevated high frequency) were most often associated with ICP less than 15 mm Hg. To aid in the interpretation of these clinically observed forms of cerebrovascular pressure transmission, an expermental investigation into the relationship between cerebrovascular resistance, craniospinal compliance and cerebrovascular pressure transmission was performed. Before such an experimental study could be performed, an improved method of measuring craniospinal compliance was needed. Existing measures of lumped craniospinal compliance such as the volume pressure response method (VPR) were considered too variable chiefly as a result of the sequence using an electronic square wave pressure generator to produce a small (0.05 ml), exact and reproducible transient volume increase into the CSF space. The new method was validated against the VPR method in physical and animal models, where it accurately followed compliance changes and demonstrated significantly less variation between measurements. The experimental studies were then performed in animal models of raised ICP, arterial hypercarbia and arterial hypertension, using the improved compliance technique. The data obtained from those studies were an aid to the interpretation of the four forms of cerebrovascular pressure transmission that were observed in the clinical studies. A flat amplitude transfer function (curve type 1) indicates equal transmission of all harmonics of the arterial pressure waveform through to the CSF space and was found in the experimental studies associated with ICP less than 15 mm Hg and with normal craniospinal compliance normal cerebrovascular resistance and a negative fundamental phase shift. This form of cerebrovascular pressure transmission may characterize a functionally normal cerebrovascular bed.

To analyse ultrasonic echoes from soft tissues a fast data acquisition system was built. A PDPS/E minicomputer controls a Biomation 8100 transient recorder and an RBBE disk storage unit. The transient recorder can digitise at sample rates up to 100 MHz, with a resolution of up to 8 bits. The design of the transient recorder interface is described, single cycle databreak transfers are used, and three 8-bit bytes of data can be packed into every two computer words. Maintenance facilities in the interface allow detailed testing. An assembly language program allows flexible acquisition of echo data. The transient recorder acquisition parameters may be specified by keyboard commands and stored onfile. Approaches to tissue characterisation are briefly reviewed. One fundamental problem is that interference between echoes from closely spaced scatterers introduces a random element in the echo amplitude. The problem of detecting an array of scatterers surrounded by a different array of scatterers is considered. Simulations based on a discrete scattering model aid the analysis. Signals are synthesised by adding echo pulses with random time delays. Distributions of the average-echo amplitude of synthesised data and liver echo data are compared. The detection of abnormal regions is discussed within the framework of statistical decision theory. The use of moving averages to detect abnormal regions is studied. Level crossing frequencies of various synthesised waveforms are compared with theoretical predictions. The random nature of echo amplitudes can limit the achievable resolution in standard B-scan images. Digital scan converter update algorithms are considered from a statistical viewpoint.

When modern high voltage radiotherapy is used in combination with simple mastectomy for the treatment of breast cancer, the lung apex on the treated side receives up to 4250 cads. Minor changes in overall lung function following such therapy have previously been reported (Emirgil and Heinemann, 1961). These changes are more pronounced when radiation pneumonitis develops, which occurs in about 11% of such patients (Gross, 1977). Two groups of patients were studied, both having had simple mastectomy followed by megavoltage radiotherapy (4250 rads to the axilla and supraclavicular region and 4500 cads to the chest wall by tangential fields, in 10 fractions over four weeks), as part of their treatment of carcinoma of the breast. Overall and regional lung function measurements, chest x-ray and electrocardiograph were carried out in each patient. Overall lung function was assessed by static lung volumes (TLC, VC, RV, RV/TLC%), dynamic lung volumes (FEV1, FVC, FEV1/FVC%), transfer factor of carbon monoxide (TCO), flow volume curves and airways resistance. Regional distribution of ventilation was measured with radioactive Xe133, and regional distribution of perfusion with radioactive Xe133 in the first study and with TC99m macro-aggregated albumin in the second study, using a gamma camera linked on-line to a computer. The first study involved a longitudinal sequential measurement in the same group of ten patients prior to radiotherapy, but after simple mastectomy "control", and at 1, 3, 6, 9 and 12 months after radiotherapy. There were no significant changes in VC, FVC, TCO, Vmaxso, Vmax30 and sGaw after radiotherapy, as compared to control values. However, there was a significant reduction at 5% level in TLC, RV and in FEV1 at 6, 9 and 12 months after radiotherapy, as compared to the control values. Chest x-rays were unchanged in most of these patients. Comparison of regional ventilation between the irradiated lung and non-irradiated "control" lung at the same vertical height showed no changes either before radiotherapy or sequentially at 1, 3, 6, 9 and 12 months thereafter. However, there was a significant reduction in perfusion of the upper zones of the irradiated lung corresponding to the region receiving the radiotherapy in most of these patients. This perfusion reduction was significant at the 5% level at 1 month and at 6 months after radiotherapy, but was not significant thereafter. The second study was a cross-sectional one in a group of 48 patients at an interval of one to fourteen years after radiotherapy, given by the same technique. The chest x-rays showed some changes in 52% of these patients. Their values of TLC, VC and FEV1 were distributed around 100% of the predicted normal value, thus showing normal values, but their TCO was below 100% of the predicted normal value in most. There was no significant change in regional ventilation between the irradiated and the non-irradiated lungs, when compared at the same vertical height, but there was a highly significant reduction in perfusion of the upper zones of the irradiated lung as compared to the non-irradiated "control" lung in the same patient. It is concluded that: 1. This dose and technique of radiotherapy had little effect on overall lung function in these women with normal lungs. 2. However, perfusion to the alveolus was reduced in the irradiated region, without clinical or radiological changes, from as little as one month, to as long as 14 years after radiotherapy in some patients. 3. The earliest effect of radiotherapy appears to be upon the pulmonary vascular bed in the irradiated region.

No description available.

No description available.

No description available.