PubMed Health⌕ Search

Biomedical subjects

D S Hickey

Publications and source records attributed to D S Hickey.

At least 19 recordsLinked to original sources
PubMed1990

Non-linear statistical technique applied to data from baboon articular cartilage.

Pattern recognition software was developed and applied together with statistical techniques to articular cartilage data from the knee joint of the baboon. The standard statistical method used for comparison was ANOVA which indicates linear discrimination. In addition a Karhunen-Loève expansion was performed to reduce the dimensionality of the data and provide independent uncorrelated variables. Nearest neighbour analysis, a non-linear method, when combined with bionomial probabilities gave discrimination that was not obtained by ANOVA. Use of pattern recognition and related techniques can improve and extend the analysis of biological data to include non-linear discrimination and classification.

Algorithms↗
PubMed1988

A new urethral catheter.

A new balloon catheter for women with a flexible urethral portion that conforms to the shape of the closed urethra was tested. In sheep control catheters caused epithelial destruction, which was absent with the conformable catheter. A 12 week crossover trial compared control catheters in 52 long stay geriatric patients. Eighty two out of 91 conformable catheters were rated as comfortable compared with 68 of 87 control (p = 0.006). The average length of time in situ was 15.9 days for the conformable catheter compared with 12.9 days for the control (p = 0.001). The average number of bypasses a week with the conformable catheter was 1.1 compared with 1.3 for the control; this difference was not significant. Examination of 249 used catheters showed significantly fewer with intraluminal obstruction with struvite among the conformable than control catheters (1 (0.8%) versus 15 (11.5%); p less than 0.001). This new catheter for women is a substantial improvement over the Foley catheter and (except in urethral stricture) is suitable for all forms of drainage.

Aged↗
PubMed1987

Quantitative tissue characterisation in pancreatic disease using magnetic resonance imaging.

Twenty-nine patients, 27 of whom had either inflammatory disease of the pancreas or pancreatic tumour, were studied by magnetic resonance imaging (MRI) and computed tomography (CT). Six healthy volunteers were studied by MRI alone. The pancreatic T1 and T2 relaxation times were calculated using a multipoint iterative method with data from seven total saturation recovery and six spin echo sequences. Magnetic resonance imaging can demonstrate the normal pancreas and a variety of pathological processes greater than 1-2 cm in size, but with less spatial resolution than CT. The relaxation-time results indicated no significant discrimination between chronic pancreatitis and pancreatic tumour. A significant elevation in the relaxation times was observed, however, in those patients with calcific chronic pancreatitis compared with the non-calcific chronic pancreatitic group and normal controls, suggesting a different pathophysiology for the two subgroups of chronic pancreatitis. The active phase of acute pancreatitis was associated with significantly elevated relaxation times, which returned to normal levels during the resolved phase of the disease. Associated extrapancreatic fluid collections were characterised by their very long relaxation times. The problems associated with spatial resolution, respiratory motion and lack of quantitative tissue characterisation suggest that MRI of the pancreas, using present methods, is unlikely to contribute to the overall management of patients with exocrine pancreatic disease.

Acute Disease↗
PubMed1986

Analysis of magnetic resonance images from normal and degenerate lumbar intervertebral discs.

Degenerate discs can be identified quantitatively by measurement of magnetic resonance (MR) relaxation times. MR images have been recorded from 16-year-old and 82-year-old cadaveric L3-4 discs at the highest resolution attainable with a Picker International MR Imaging System operating at 0.26 Tesla. By recording images with a series of spin-echo and/or saturation-recovery sequences of differing time intervals, the values for sample magnetization, M infinity, and the T1 and T2 relaxation times, have been calculated from each pixel in the MR image. The distribution of M infinity values shows the relative degrees of hydration in different regions of the disc while the corresponding T1 and T2 values are sensitive to the chemical environment of the water molecules. Images from cadaveric discs allowed the nucleus pulposus and annulus fibrosus to be distinguished clearly, and the laminated structure of the annulus could be seen. Loss of water from the nucleus during aging was demonstrated by a reduction and change in the distribution of the M infinity values for an 82-year-old disc, as compared with a 16-year-old disc. Values of T1 and T2 indicated a difference in the chemical environment of water molecules in the nucleus pulposus and annulus fibrosus; the extent of this difference was much greater for younger than for older discs. High-resolution MR images from discs of living subjects showed almost as much detail as those from experimental specimens, but in the latter, the laminated structure of the annulus was resolved.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

A method for increasing the resolution of scanned projection radiography and other digital X-ray systems.

A method for increasing the sampling frequency of digital X-ray systems is described. The method employs discrete, stepwise magnetic deflection of the focal spot and the recombination of the resulting displaced images. The technique was applied to a GE CT/T 8800 scanner operating in "Scout View" mode. The hardware and software modifications were minor. The transverse resolution was shown to improve from 0.63 to 0.9 line pairs per mm, using a test phantom. The effect of the improvement in resolution is also illustrated in the human. The possibility of further improving the resolution of the system is discussed.

Ankle↗
PubMed1986

A method for the clinical measurement of relaxation times in magnetic resonance imaging.

A method for the determination of relaxation times in clinical magnetic resonance images is described. Three components are measured: the spin-lattice (T1) and spin-spin (T2) relaxation times and the proton density (M infinity). These components are separated in the algorithm to give increased tissue discrimination. Multiple data points are used to minimise error and increase reproducibility. Errors that arise in imaging data because of the short sequence repetition periods are considered and a technique for their reduction described. Clinical results obtained using the method are reviewed. These results demonstrate the clinical utility of the technique.

Computers↗
PubMed1986

Quantitative analysis of intervertebral disc structure.

A reduction in signal intensity from the nucleus can be a feature of intervertebral disc disease. It has been established that T1 and T2 relaxation times of the nucleus decrease with age and that evidence of disc degeneration can be determined before classical clinical features are apparent. A robust multiple point algorithm has been developed which now enables proton density and T1 and T2 values to be computed for each pixel, providing images which are effectively spatial maps of these parameters. Such high resolution maps have provided quantitative data from volunteers, patients and cadavers. These studies have been carried out with specially constructed coils and the cadaveric information compared with cut sections. The spatial maps revealed detailed anatomic structures including the laminae of the annulus and relative levels of hydration. These levels, which are known to be related to the ability of the disc to withstand compressive loads, can now be measured in vivo. Analysis of the proton density and relaxation times in vivo has demonstrated that both water content and the chemical environment in the nucleus change during aging. The results are consistent with changes in the glycosaminoglycan content and fixed charged density measured by other chemical and physical techniques. Such detailed methods can be used to investigate the effects of aging and disease on disc structure and have enabled observations to be made of the effects of stress on the normal disc.

Adolescent↗
PubMed1985

Dynamic shape of the female urethra during micturition. Clinical methods.

Densitometry of the x-ray image provides a suitable technique for clinical quantification of the urethral shape during all stages of voiding. The technique of cystourethrographic densitometry is applied to determine the cross-sectional shape of the human female urethra during various phases of voiding. Errors that may occur because the x-rays are not perpendicularly incident to the urethral plane are considered and a method for their minimization is indicated.

Absorptiometry, Photon↗
PubMed1985

MR imaging of the intervertebral disc: a quantitative study.

The T1 and T2 relaxation times and the proton density of the nucleus pulposus have been measured in 107 normal and 18 surgically proven degenerate intervertebral discs. Data from total saturation recovery and spin echo sequences have been utilised in a robust multi-point method and relaxation times and proton density calculated. The results show that both the T1 and T2 values of the normal nucleus pulposus decrease with age. There was no significant correlation between proton density and age in normal discs. At all ages there was a highly significant difference between the T1 values of normal and degenerate discs. With T2 a highly significant difference in the younger age groups reduced to no distinction in the seventh decade. The observed change in the T1 and T2 values of the nucleus is in agreement with the reduction of water content known to occur with age. Our results indicate that quantitative MR imaging may assist in the diagnosis of intervertebral disc degeneration.

Adolescent↗
PubMed1984

Analysis of circadian rhythms by fitting a least squares sine curve.

A method that fits a least squares sine curve to both point and averaged time series data is described. The method includes a full regression analysis and extends the current "cosinor" approach. Developments include estimation of the linear trend and fitting secondary wave forms.

Aged↗
PubMed1984

Algorithm for the determination of projected urethral lumen cross-sections and shape functions.

A method used to obtain computer graphic representations of projected urethral lumen cross-sections is described. The cross-sectional area of the lumen is measured accurately at all stages of voiding. Two methods of background subtraction are considered, direct subtraction from nonvoiding x-rays and subtraction from a least squares regression line. The projected cross-sections are described by simple shape functions. These shape descriptors increase the technique's potential application by providing a quantitative measure of the projected cross-sections.

Computers↗
PubMed1983

Radial bulging of the annulus fibrosus during compression of the intervertebral disc.

An analysis of the bulging of the annulus fibrosus as a function of the height of the intervertebral disc during compression is presented. The theory was compared with the results of experimental tests on rabbit lumbar discs. When viewed in profile the ventral bulge closely resembled an arc of a circle; at each stage of compression it appeared to extend from the cranial to the caudal extremities of the annulus fibrosus. The radius of curvature of the arc was measured as a function of disc height and the results compared with theoretical predictions. Good agreement was obtained if it was assumed that about half the volume change swept out by the approach of the cranial and caudal end-plates was accommodated by the annular bulge. The lengths of the collagenous fibres reinforcing the outer lamella of the ventral annulus were estimated from the dimensions of the ventral bulge; no appreciable length increase appeared to accompany compression.

Animals↗
PubMed1983

Catheter encrustation by struvite.

Encrusted catheters from 10 female patients were the source of 26 samples of deposits which were examined by X-ray diffraction. Four different types of catheter were represented. The only detectable compound in all of the samples was ammonium magnesium orthophosphate hexahydrate (NH4MgPO4 . 6H2O), which occurs naturally as the mineral struvite.

Aged↗
PubMed1982

Urethral lumen cross-sectional shape: its radiological determination and relationship to function.

This report shows that the urethral lumen cross-sectional shape is complex but slit-like and it is suggested that this shape is related to function. A radiological method for determining urethral shape during micturition has been developed and compared with histological studies. The lumen is markedly non-circular even during micturition. Simple theoretical analysis of preliminary shapes shows that current concepts of urethral flow are incomplete and urethral pressure profile measurements require re-evaluation. The function of accepted sphincter mechanisms requires a slit-like lumen. Lumen shape is a fundamental property of the urethra, the clinical importance of which has yet to be explored.

Adult↗