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S D Pye

Publications and source records attributed to S D Pye.

At least 37 records · Page 2Linked to original sources
PubMed1999

Finite beam-width ray model for geometric spectral broadening.

The purpose of the study was to compare measured spectral width and maximum frequency with that predicted from ray models of geometric spectral broadening. Zero and finite beam-width models were used. Spectral data were acquired from a string phantom using two commonly-used linear array systems. Beam width and Doppler aperture sizes were measured using a needle hydrophone. The results showed that the experimentally measured data agreed best with the finite beam-width model. The zero beam-width model was in error by up to 50% for calculated spectral width, and up to 10% for maximum frequency. It is concluded that spectral width and maximum frequency are best calculated using the finite beam-width model, and that ultrasound manufacturers could improve the variation in spectral broadening measured at different locations on a single machine by adjusting the aperture size to give a constant subtended angle and beam width.

Models, Theoretical↗
PubMed1999

The importance of radiometer angular response for ultraviolet phototherapy dosimetry.

The influence of the angular response of radiometer probes on measurements of irradiance in ultraviolet phototherapy has been studied. Irradiance measurements were made using nine ultraviolet (UV) radiometers employed by phototherapy centres in Scotland and Northern Ireland, and compared with measurements made using two spectroradiometers. The light sources used were UVB TL01 fluorescent lamps, arranged in different geometries. Irradiances within TL01 whole body treatment cabinets were assessed based on a comparison with one of the spectroradiometers. The results show variations of 50% in cabinet irradiance measurements made by different radiometers, even when they were calibrated using the same source geometry and spectroradiometer. Differences in radiometer probe design and construction lead to an under- or over-response at angles of incidence greater than zero. Angular responses of different probes were assessed using banks of fluorescent lamps. The differences found are large enough to account for the variations in measurements of cabinet irradiance. The variations in irradiance measurements are significant in terms of planning and monitoring patient exposure during TL01 phototherapy. Accurate dosimetry can only be achieved if radiometer probes have a good cosine response and recommendations are made for better calibration techniques.

Radiometry↗
PubMed1999

Optimizing results of lithotripsy using robust electromagnetic probe.

BACKGROUND AND OBJECTIVE: A significant impediment to the measurement of the pressures and forces created by lithotripter shockwaves has been their destructive properties, which have rendered most measuring devices impractical. We have developed and tested a robust electromagnetic probe to measure cavitational forces in vitro in the focal zones of extracorporeal lithotripters. The probe responds to the pressure gradient generated by the radial motion of cavitation bubbles. MATERIALS AND METHODS: The effects of shockwaves from the Dornier MPL 9000 electrohydraulic lithotripter were measured over the lifetime of multiple electrodes. RESULTS: The pulse energy from the electrodes dropped off rapidly after approximately 50% of the lifetime quoted by the manufacturer. The electrodes were more efficient at higher power settings. As a result, we altered our protocol for the treatment of ureteral stones to use a higher kilovoltage and a second electrode whenever necessary. Stone-free rates after shockwave lithotripsy (SWL) in situ for stones < 11 mm have increased from 68.2% to 83.3%, and the retreatment rate has dropped from 23% to 15%. Despite significantly higher power settings (23.7 kV v 18.7 kV; P < 0.0001), the need for sedoanalgesia has remained relatively constant (26% v 31%). CONCLUSIONS: Measurement of cavitational forces from lithotripters using a robust electromagnetic probe is useful in planning treatment strategy. We have demonstrated a clinically measurable improvement since implementing our new treatment protocol. Because the probe responds directly to cavitational forces, it should also prove useful for the objective comparison of different SWL machines.

Electromagnetic Phenomena↗
PubMed1994

The performance of ultrasound physiotherapy machines in Lothian Region, Scotland, 1992.

Eighty-five ultrasound therapy machines in use in Lothian Region, Scotland were tested for performance and their recalibration was expedited where necessary. The performance characteristics reported are the temporal average acoustic output power, the treatment frequency, pulse timing and treatment timer accuracy. Consideration is also given to the performance of the wide dynamic range radiation force balance that was used to make acoustic power measurements. Of the machines tested, 69% had power outputs that differed by more than 30% from the expected values. The results of power measurements are analysed according to continuous and pulsed output, single and dual frequency treatment heads and year of manufacture. Therapy machines more than 10-12 years old and modern dual frequency treatment heads performed particularly badly. This study suggests that the performance of ultrasound therapy machines has improved little in the last 20 years despite the introduction of IEC 601-2-5 in 1984.

Calibration↗
PubMed1994

Comparison of the performance of two pulsed dye lasers using a synthetic stone model.

The performance of two pulsed dye laser lithotripters was compared in vitro using a synthetic calculus with gross physical properties similar to natural urinary tract calculi. Synthetic calculi were subjected to 500 shocks at nominal pulse energies of 40, 60, 80, 100 and 120 mJ using a 320 micron. fiber. Three calculi were treated at each energy level on the Technomed Pulsolith and two at each level on the Candela MDL 2000. The pattern of fragmentation was similar with both lithotripters. Increasing the energy level resulted in a linear increase in fragmentation (Pulsolith r = 0.95, MDL 2000 r = 0.99), but fragmentation was greater with the MDL 2000 than with the Pulsolith (6.01 mg/mJ versus 5.00 mg./mJ, p < 0.001). Both lasers fragmented the calculi satisfactorily. We recommend that all users of such lasers acquire a laser meter to allow monitoring of the energy delivered by the fiber tip.

Lithotripsy, Laser↗
PubMed1994

Significance of the thickness of the anal sphincters with age and its relevance in faecal incontinence.

BACKGROUND: Ultrasonographic studies in healthy volunteers showed that the external anal sphincter (EAS) and internal anal sphincter (IAS) thicknesses were inversely related at rest. The functional importance of the two sphincters in continence control was demonstrated in the relationship between the sum of the thicknesses of the two sphincters and the anal canal resting pressure. The aims of the present study were to assess the morphometric appearance of the anal sphincters by endosonography in faecally incontinent patients and to contrast this with that of older healthy subjects. METHODS: Twenty-eight female patients with neurogenic faecal incontinence (FI) were studied. An older group of 7 healthy women, aged 41-75 years, and a young group of 11 nulliparous healthy women, aged 20-23 years, served as control groups. Anal endosonography was performed with a radial rotating endoprobe, with the subject in the left lateral position. Conventional anal manometry was performed in all subjects. RESULTS: The EAS in the FI group was thicker than the EAS in the old (p < 0.04) but did not differ from the EAS in the young. The IAS thickness in the FI group did not differ from that in the older group. In both these groups the IAS was thicker than in the young women (p < 0.01). The anal pressures in the FI group were reduced compared with the normal groups (p < 0.04). There was a direct relationship between the two sphincters in FI (p < 0.001). CONCLUSIONS: The increased thickness of the IAS in the FI group does not seem to compensate for function and results in a failure of the sphincter mechanism to maintain continence, whereas in healthy elderly subjects the increased IAS thickness appears to be compensatory and important for continence control.

Adult↗
PubMed1993

Prostate-specific antigen and prostate gland size in men receiving exogenous testosterone for male contraception.

Steroid regimens containing androgens are being evaluated currently as hormonal contraceptives for men. The possible non-reproductive effects of such treatment were assessed during an efficacy trial using a prototype regime of 200 mg testosterone enanthate i.m. weekly. Prostatic function and size were monitored by regular rectal examination, blood levels of prostate-specific androgen (PSA) were measured in 30 men and prostatic size was measured by trans-rectal ultrasound imaging in a representative subgroup of five subjects for 12 months and for a further 6 months after discontinuation. Despite the sustained rise in serum levels of testosterone, oestradiol and dihydrotestosterone during treatment, there was no detectable increase in prostatic size on rectal examination or any significant change in blood concentrations of PSA. A small but significant increase (14.3 +/- 2.0%) in maximal prostate transverse area was observed in four men while the remaining one showed no change. Our preliminary data demonstrate the feasibility and importance of monitoring prostatic function in the development of androgen-containing male hormonal contraceptives.

Adult↗
PubMed1993

Catheter valves.

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Humans↗
PubMed1993

Anal endosonography in asymptomatic subjects.

The anal sphincter thickness was measured ultrasonographically in 30 asymptomatic subjects (13 male and 17 female: 23 young and 7 old). The internal anal sphincter (IAS) was measured at its thickest portion in the anal canal, its borders lying between the submucosa and the external and sphincter (EAS). The EAS was measured at the lowermost point in the anal canal, its borders being the IAS and the coccyx. The EAS was thicker in men than in women (p < 0.02). The IAS showed no difference with regard to gender. The EAS became thinner with age (p < 0.005), whereas the IAS appeared thicker with age (p < 0.0002). The EAS thickness correlated inversely with the IAS thickness (p < 0.001). Anorectal manometry showed a correlation between the anal canal resting pressure and the sum of the thickness of the two sphincters (p < 0.001). Thus, although the visualized thickness of the two sphincters vary, they do so proportionally, and their sum reflects their tonic activity.

Adult↗
PubMed1992

Adaptive time gain compensation for ultrasonic imaging.

The quality of ultrasonic images is often adversely affected by incorrect time gain compensation (TGC) settings. TGC set up by the operator is inadequate for two reasons: firstly, one gain function is unlikely to be appropriate for all the scan lines in an image and secondly, the operator may not have sufficient time or experience to optimise it. Adaptive processing offers a solution to this problem; it has the potential both to improve image quality and to let the operators make more effective use of their time. The literature concerned with adaptive TGC is briefly reviewed. A microcomputer-controlled system has been used to develop various algorithms for adaptive TGC. The algorithms operate in real-time and have been tested using a grey-scale test object, and clinically in routine abdominal and obstetric scanning. The imaging characteristics of each algorithm are determined largely by the value of a parameter beta, described in the text. It is concluded that adaptive TGC capable of applying a unique gain function to each part of the image can consistently produce better images than a single gain function set either automatically or manually.

Algorithms↗
PubMed1992

Mechanisms responsible for diminished fragmentation of ureteral calculi: an experimental and clinical study.

We molded 24 synthetic stones (mean weight 680 mg., range 641 to 715) from a commercial mixture of gypsum, silica, cellulose and polyvinyl acetate. Each stone was subjected to 400 shocks on a Wolf 2300 Piezolith and groups of 6 stones were treated in 4 different modes. Mean amounts fragmented were 243 +/- 18 mg. in a free environment, 62 +/- 18 mg. confined loosely in a latex tube, 22 +/- 8 mg. impacted in the tube and 30 +/- 8 mg. impacted alongside a 7F stent. During a 30-month period 118 patients received in situ extracorporeal shock wave lithotripsy for ureteral calculi using the same lithotriptor. The mean stone burden was 11.4 mm. (range 4 to 29). Success was greater for patients with calculi 10 mm. or less than for those with stones greater than 10 mm. (71% versus 51%, p less than 0.05), despite the former group receiving less shocks (5,404 versus 7,491). The influence of size was then excluded by studying the number of shocks delivered per mm. of calculus. Patients receiving 500 to 699 shocks per mm. showed a higher success rate than those receiving a smaller number of shocks per mm. Treatment with a greater number of shocks per mm. did not improve success rate. The experimental study demonstrated that confinement and impaction significantly diminish the rate of fragmentation of calculi. However, the clinical study suggested that there may be an optimum number of shocks per mm. that should be delivered. Treatment beyond this point fails to improve results. The 28% failure rate even in those receiving the highest number of shocks per mm. suggests that large, impacted calculi are unsuitable for treatment with in situ shock wave lithotripsy on this machine.

Adolescent↗
PubMed1992

Cerebral blood-flow velocity and intermittent intracranial pressure elevation during sleep in hydrocephalic children.

The clinical importance of intermittent intracranial pressure (ICP) elevations during sleep in hydrocephalic children is unclear. Eight studies of continuous ICP monitoring with simultaneous cerebral blood-flow velocity (CBFV) measurements were recorded during sleep in seven hydrocephalic children aged between one and 10 years. ICP was measured directly through a frontal reservoir. There were two main patterns of CBFV change in response to raised ICP: a progressive decrease in mean flow velocity and increase in resistance index, suggesting impaired haemodynamic compensation to ICP elevation due to reduced circulatory reserve in patients with limited intracranial compliance; and an increase in mean flow velocity with raised ICP, suggesting that appropriate haemodynamic compensation with increased blood-flow can occur to maintain adequate cerebral perfusion in those with sufficient circulatory reserve. Simultaneous CBFV and ICP measurements may help to identify those with reduced circulatory reserve who are at greater risk of ischaemic insult from episodic increases in ICP.

Blood Flow Velocity↗
PubMed1991

Cerebral blood flow velocity changes after ventricular taps and ventriculoperitoneal shunting.

Transcranial Doppler ultrasonography (TCD) was performed on 14 patients with hydrocephalus (age range 1 day to 12 years old) before and after ventriculoperitoneal shunting. TCD was also performed with simultaneous intracranial pressure (ICP) measurements during ventricular taps through a reservoir in 7 patients. Measurements of the resistance index (RI) = (S-D)/S, peak systolic (S), enddiastolic (D) and time-averaged mean flow velocities were made. After ventricular taps and ventriculoperitoneal shunting there was a significant decrease in RI in all patients. This was due to a greater increase in D compared to S, which suggests a decreased distal cerebrovascular resistance. There was a significant correlation between RI and ICP in the older infants and children and in individual neonates. Successful cerebrospinal fluid diversion reduces ICP and cerebrovascular resistance, thus improving cerebral perfusion. The RI is a reliable index for serial monitoring of cerebrohaemodynamic change in patients with hydrocephalus.

Blood Flow Velocity↗
PubMed1991

Robust electromagnetic probe for the monitoring of lithotriptor output.

The ability to measure the powers and pressures generated by extracorporeal lithotriptors is important for both patient safety and treatment planning. Regular measurements of output have been impossible in the past because there have been no instruments available that could withstand prolonged or repeated exposure to lithotriptor fields. The literature contains reports of various devices that have been used to make measurements of lithotriptor output, and these are briefly described here. The authors report the use of a new electromagnetic probe as a robust monitoring device. It has been tested by comparison with a PVdF coplanar membrane hydrophone, by comparison with the results of disintegrating a series of synthetic stones and by impact measurements. The electromagnetic probe has also been used to monitor the output of a piezoelectric extracorporeal lithotriptor over a 12-month period. Fluctuations in pulse energy of up to 350% were observed.

Electromagnetic Phenomena↗
PubMed1991

Transcranial Doppler (TCD) ultrasound as a noninvasive means of monitoring cerebrohaemodynamic change in hydrocephalus.

Cerebral blood flow velocity (CBFV) measurements by Transcranial Doppler (TCD) ultrasound were performed on 27 patients with hydrocephalus (Group I: neonates, Group II: children). Simultaneous measurements of direct ICP and CBFV were performed during ventricular taps in 16 patients. There was a significant correlation between ICP and Resistance Index (RI = peak systolic-end distolic/peak systolic velocity) overall in Group II patients (p less than 0.02) and in individual neonatal patients (p less than 0.001). After ventricular taps and ventriculo-peritoneal shunting (17 patients) there was a consistent significant decrease in RI due to increased end diastolic velocity in all patients (p less than 0.001). This suggests the RI is a reliable index of cerebrovascular resistance for serial monitoring in individual patients. There was an exponential pattern of decay in RI with CSF volume depletion (volume-flow velocity response) in 50/56 taps which allows calculation of a volume-buffering reserve before perfusion change occurred. Simultaneous ICP/CBFV monitoring during sleep may help to identify patients who are unable to compensate haemodynamically during episodic increase in ICP and are a greater risk of ischaemic insult. TCD is a useful noninvasive technique of monitoring cerebrohaemodynamic change for initial assessment and further management of children with hydrocephalus.

Adolescent↗
PubMed1989

Deconvolution in medical ultrasonics: practical considerations.

Deconvolution can, in principle, enhance the spatial resolution of specular reflectors in medical ultrasonic imaging but, in practice, the resolution improvement offered is offset by the introduction of undesirable artefacts. In this study, several problems related to deconvolution were identified and practical suggestions for minimising artefacts were made. These include: fitting a three-dimensional surface to experimentally measured beam profiles in order to take into account the depth-dependence of the point spread function (PSF); adaptive detail-preserving noise filtering as a preprocessing tool in order to improve the quality of the data and reduce the speckle enhancement artefact; a histogram modification procedure in order to overcome the problems of ringing, over- and undershooting. Processing of a large number of A-scan data obtained from tissue-mimicking phantoms and the abdomens of normal volunteers demonstrated the efficiency of these techniques in reducing artefacts. The performance of deconvolution in terms of resolution improvement was satisfactory when data from resolution test objects were processed but poor with abdominal scans. This difference in performance raises the question as to how similar the PSF in tissue is to the experimentally measured PSF in water or even a tissue-mimicking material.

Abdomen↗