Search PubMed⌕ Search

Biomedical subjects

J E Saunders

Publications and source records attributed to J E Saunders.

At least 19 recordsLinked to original sources
PubMed1992

Acoustic emission and sonoluminescence due to cavitation at the beam focus of an electrohydraulic shock wave lithotripter.

The acoustic emission from cavitation in the field of an extracorporeal shock wave lithotripter has been studied using a lead zirconate titanate piezoceramic (PC4) hydrophone in the form of a 100-mm diameter focused bowl of 120-mm focal length. With this hydrophone directed at the beam focus of an electrohydraulic lithotripter radiating into water, it is possible to identify signals well above the noise level, at the 1-MHz resonance of the hydrophone, which originate at the beam focus. Light emission, attributed to sonoluminescence, is also shown to originate at the focal region of the lithotripter, and the signal obtained from a fast photomultiplier tube directed at the focus has similarities in structure and timing to the detected acoustic signals. The multiple shock emission resulting from a single discharge of an electrohydraulic source is shown to result in two separate bursts of cavitational activity separated by a period of 3-4 ms. The signal burst corresponding to the primary shock has a duration of about 600 microseconds with little noticeable structure. The signal burst associated with the secondary shock has a reproducible structure with two distinct peaks separated by about 200 microseconds depending on the shock amplitude. THe timing and structure of each burst is shown to be in reasonable agreement with the theoretical predictions made by Church (1989) based on the Gilmore model of bubble dynamics. In particular, it is shown that it is possible to obtain precise measurements of the time delay between the separate peaks within the signal burst detected following the secondary shock and this may, as predicted, provide a method of determining the size of bubbles remaining after the primary shock.

Acoustics↗
PubMed1992

Triple fluorochrome labeling of cochlear bone growth.

A new technique is described which measures the extent and time course of intracochlear bone formation after cochlear implantation in an experimental animal model. A series of fluorescent histochemical markers is used to delineate the amount of intracochlear bone deposition during specified time periods.

Animals↗
PubMed1992

A comparison of three commercially available PET imaging systems.

Three commercial positron emission tomography (PET) imagers were assessed using the same test protocol (Positron Corporation 'Posicam', Siemens Ecat 951/31 and the Scanditronix PC 4096-15WB). A cylindrical phantom and a 'Jaszczak' phantom both filled with 18F were employed to measure sensitivity, slice uniformity, transaxial and axial resolution and cold rod contrast. The spread of results were as follows: sensitivity varied from 2.08 to 3.73 kcps kBq-1 ml-1 (77-138 kcps microCi-1 ml-1); radial resolution on axis (at 17.5 cm) varied from 5.0 to 5.9 mm (6.7-8.1 mm); tangential resolution ranged from 5.4 to 5.8 mm (6.7-8.6 mm); axial resolution ranged from 4.6 to 11.5 mm (6.6-13.6 mm); contrast in the middle of a 30 mm diameter rod varied from 98 to 93% and for a 5 mm rod from 37 to 22%. The performance of all three systems approximated reasonably well to the manufacturers' published specifications. The most significant differences were found to be in sensitivity, axial resolution and deadtime correction and can be explained by the choice of crystal size and crystal/photomultiplier configuration.

Evaluation Studies as Topic↗
PubMed1992

Reconstruction of the radical mastoid.

Open cavity techniques (radical mastoidectomy, canal wall down tympanomastoidectomy, modified radical mastoidectomy) are well established surgical procedures for the treatment of chronic otitis media. Despite their effectiveness in exteriorizing cholesteatoma, they are associated with a 20 to 60 percent incidence of persistent intermittent drainage. In an effort to eliminate this problem, we have employed a Palva flap and medial graft technique to reconstruct the mastoid cavity and middle ear space in those patients with chronically draining ears. Between 1987 and 1990, 28 patients underwent this procedure. Twenty-six of these (93%) had complete obliteration of the mastoid cavity and successful tympanic membrane reconstruction. Two of 28 (7%) had a persistent tympanic membrane perforation and intermittent drainage following their surgery. Based on these results, this procedure is effective in eliminating intermittent drainage associated with the open cavity techniques. The indications for this procedure, the specifics of the surgical technique, and the postoperative results are discussed.

Adult↗
PubMed1991

Theoretical predictions of the acoustic pressure generated by a shock wave lithotripter.

A one-dimensional frequency domain model is used to predict the temporal peak acoustic pressures developed near the beam focus during extracorporeal shock wave lithotripsy (ESWL). The model includes consideration of finite amplitude effects, attenuation, diffraction and dispersion, and results are presented for the case of an electrohydraulic source with the beam geometry of the Dornier HM3 lithotripter. Propagation in castor oil, water and tissue is examined. The model predicts that nonlinear effects enhance the peak positive pressure (p+) at the beam focus in 6 cm of tissue in a Dornier type lithotripter by a factor of about 3 above that which would be expected for linear propagation. The negative peak pressure (p-), conversely, is predicted to be depressed by a factor of about 0.7 below the linear theory prediction. The model also indicates the occurrence of excess absorption due to shock formation. This is shown, for a Dornier HM3 type lithotripter, to cause a reduction in the peak positive pressure gain and a broadening of the focal depth as the output of the source is increased. A threshold aperture pressure is identified for a source with the same beam geometry as the Dornier HM3 below which shock formation does not occur. In this region the pressure gain increases and the focal depth narrows as the source output increases. These effects are characteristic of current commercial piezoelectric and electromagnetic lithotripsy fields.

Humans↗
PubMed1991

Lipomas of the internal auditory canal.

Intracranial lipomas are rare tumors which may occur in the cerebellopontine angle (CPA) or internal auditory canal (IAC). Although seemingly innocuous in other parts of the body, lipomas within the CPA and IAC often involve the surrounding cranial nerves, making attempts at hearing conservation largely unsuccessful. In an attempt to differentiate the IAC lipoma from the more commonly found acoustic schwannoma, the preoperative imaging studies (magnetic resonance and computerized tomography) on five previously unreported cases of IAC lipomas were evaluated. Based on these studies, features were determined that may allow the surgeon to diagnose IAC lipomas preoperatively. These features will be discussed, as well as the surgical and pathological findings.

Adult↗
PubMed1991

Magnetic resonance angiography: technique and skull-base applications.

Cerebral angiography has become essential in the evaluation and management of extensive skull-base lesions. However, with a 2.6 percent incidence of neurologic complications and a 0.3 percent incidence of permanent neurologic deficits associated with cerebral angiography, the procedure is not without risk. Recent advances in magnetic resonance angiography (MRA), allow one to visualize the skull-base vasculature without need of intravenous contrast injection or radiation exposure. Our initial experience in visualizing the normal vascular anatomy and pathology at the base of skull with this new imaging modality is presented. Two different MRA techniques were used: (1) thin-slice two-dimensional gradient echo pulse sequence acquisition with three-dimensional projection reconstruction, and (2) two-dimensional phase contrast angiography. The specifics of these techniques and their usefulness in the evaluation of lesions involving the skull base are discussed and demonstrated.

Adult↗
PubMed1990

Dosimetric intercomparison in the British Institute of Radiology fractionation study of 3F/week versus 5F/week in radiotherapy of laryngo-pharynx cancer.

A dose intercomparison was carried out by the National Physical Laboratory between the seven radiotherapy centres which contributed the largest number of patients to the British Institute of Radiology fractionation study of three fractions per week versus five fractions per week in clinical cancer treatment. Six of the centres showed remarkable agreement within the acceptable limits of error of the measurements. In one centre there appeared to be a physical dose discrepancy of 2.8% which was materially less than could be detected clinically.

Humans↗
PubMed1989

A survey of the acoustic output of commercial extracorporeal shock wave lithotripters.

A survey of the pressures and intensities generated by different commercial extracorporeal shock wave (ESWL) lithotripters is reported. The lithotripters included in the survey are the Dornier HM3, Wolf Piezolith 2200 and 2300, Siemens Lithostar, Technomed Sonolith 2000 and 3000, and EDAP LT-01. Measurements were made using a polyvinylidene difluoride (PVdF) membrane hydrophone in water. The zero crossing frequency of one complete cycle of the focused pulse from ESWL equipment is in the range 0.1 to 1 MHz. Spatial-peak temporal-peak positive and negative pressures up to 114 MPa and 10 MPa, respectively, have been measured and the rise times of the positive pressure half cycle at maximum output settings are 30 ns or less. The mean spatial-peak temporal-average intensity of the lithotripters is 5.0 x 10(2) W m-2 when operated at a pulse repetition frequency of 1 Hz. The spatial-peak pulse-average intensity ranges from 6.6 x 10(7) to 1.24 x 10(9) W m-2. The estimated acoustic energy in a single pulse (at the focus) at the maximum output setting of the lithotripters varies from 2.0 x 10(-3) J to about 9.0 x 10(-2) J. The beam area in the focal plane varies by a factor of 100 on different lithotripters and the temporal-peak pressure at the position of the skin at the entry point of the beam by a factor of 30. Measurement problems associated with hydrophone damage and the uncertainties in the hydrophone calibration at high pressures are discussed and an estimate of the total uncertainty in the absolute measurements of the spatial-peak temporal-peak positive pressure is given as +/- 36%.

Acoustics↗
PubMed1989

An experimental shock wave generator for lithotripsy studies.

An electrohydraulic shock wave generator has been constructed to facilitate investigation of the acoustic field generated during extracorporeal shock wave lithotripsy (ESWL). Pressure waveforms at the generator aperture and the beam focus, measured using a PVDF needle hydrophone, are compared with those from a commercial lithotripter, the Dornier HM3.

Acoustics↗
PubMed1989

Inter-subject variability in the metabolism of proguanil to the active metabolite cycloguanil in man.

1. The metabolism of proguanil to the active metabolite cycloguanil has been evaluated in 135 British Troops and 26 Kenyan schoolchildren. 2. Large inter-subject variability was observed in both plasma and urinary concentrations of proguanil and cycloguanil after standard doses of drug. 3. Based on the ratio of proguanil to cycloguanil (P/C) in urine the British troops formed a non-normal distribution. 90% of the population formed a discrete distribution with P/C ranging from 0.5 to 9.0 while the remaining 10% were scattered throughout the distribution to an extreme value of 39. A similar pattern of variability was observed using P/C from a 6 h plasma sample. 4. This variability was due to differences in the ability of individuals to metabolise proguanil to cycloguanil. 5. Thirteen schoolchildren who had experienced malaria during prophylaxis with proguanil and thirteen matched controls each received proguanil (100 mg). We could not discriminate between the two groups based on P/C ratio in either a 6 h plasma or 0-6 h urine sample.

Adolescent↗
PubMed1987

Physical characteristics of Dornier extracorporeal shock-wave lithotriptor.

Measurements of the pressure, noise, and radiation dose levels from a Dornier lithotriptor are reported. The distribution of the peak pressure around the treatment focus was investigated, and the highest pressures were found to occur within an elongated volume. Within the treatment room, noise levels of 80-90 dB were produced during each shock wave, rising to 95 dB by the patient's head. Ear protection for the staff and patient is recommended, and careful room design is necessary to minimize the sound disturbance to adjacent quarters. Measurements of the radiation skin dose received by patients from the x-ray localization system were relatively high and ranged from 2-55 cGy (rad), with a mean of 12 cGy. The operator needs to be aware of these high doses and should take precautions to minimize them.

Ear Protective Devices↗
PubMed1987

Pressure waveforms generated by a Dornier extra-corporeal shock-wave lithotripter.

Pressure waveforms in the acoustic field generated by a Dornier (HM3) shock-wave lithotripter have been measured using a bilaminar shielded PVDF membrane hydrophone in water. Using these waveforms, values of the peak-positive (p+) and peak-negative pressure (p-) at various positions in the field have been estimated. At the focus, p+ is 38.6 MPa (standard deviation = 9.0 MPa) and p- is 10.1 MPa (standard deviation = 1.0 MPa) at 20 kV discharge potential and an electrode separation in the range 1.3 to 2.4 mm. The peak-positive pressure is found to fall to 50% (-6 dB level) at about 60 mm either side of the focus on the major axis of the reflector and on a 10 mm radius circle around the focus in the focal plane. A shot-to-shot variation of +/- 25% in p+ is attributed to the inherent variability of the electrical discharge which may result in changes in the exact position and strength of the acoustic field. The results reported are considered to be more accurate than those of previous measurements due to the relatively flat frequency response of this type of hydrophone.

Acoustics↗
PubMed1987

Acoustic cavitation generated by an extracorporeal shockwave lithotripter.

Evidence is presented of acoustic cavitation generated by a Dornier extracorporeal shockwave lithotripter. Using x-ray film, thin aluminum sheets, and relatively thick metal plates as targets, evidence of liquid jet impacts associated with cavitation bubble collapse was observed. The jet impact was violent enough to puncture thin foils and deform metal plates. Furthermore, numerous jet impacts were generated over a volume of greater than 200 cm3. It is likely that such violent cavitation will also occur in tissue, and observed biological effects (e.g. renal calculus disintegration and tissue trauma) may be related to cavitation damage.

Lithotripsy↗
PubMed1987

F-M 100-Hue total error scores have discrete values.

A proof is presented which shows that the total error scores derived from the Farnsworth-Munsell 100-Hue test are an integer multiple of 4. The one proviso for this relates to the way in which the first and last caps in a box are handled.

Color Perception Tests↗