Search PubMed⌕ Search

Biomedical subjects

D Nicholas

Publications and source records attributed to D Nicholas.

35 records · Page 2Linked to original sources
PubMed1983

B-scan texture classification: a study using physical and theoretical models.

Recent clinical trials, in our own centre and elsewhere, have demonstrated the ability of A- and B-scan texture analysis techniques to provide useful in vivo separation of certain disease conditions. The present paper reports studies, using physical and theoretical models of tissues, aimed at identifying the particular sets of textural features which are most effective in achieving such separations. Using a 3.5 MHz, single element manual scanner, a total of 300 B-scans have been collected from four physical models consisting of gel-embedded 'point' scatterers, with differing mean separations. Additionally, computer modelling has been used to obtain a further 500 B-scans from 14 statistically different scattering situations. The total set of B-scans thus obtained has been subjected to a variety of texture classification procedures which have previously been developed for application in other imaging fields, such as cytology and aerial photography. The results are discussed in terms of: i) the features which are best suited to the classification of B-scans, and ii) the manner in which the resulting classification schemes are sensitive to variables of the ultrasonic scanning instrumentation.

Biometry↗
PubMed1982

The binding of tetanus toxin to retinal cells.

An indirect immunofluorescence assay demonstrated intense binding of tetanus toxin to a minority of cells cultured from neonatal rat retina. These labelled cells were typically spheroid cells bearing long processes. Flat cells and smaller spheroid cells without long processes were essentially unlabelled. A similar assay performed on frozen sections of rat retina showed that tetanus toxin bound intensely to the inner plexiform layer, moderately to the outer plexiform and inner nuclear layers, and only very slightly to the outer nuclear layer. The localization of tetanus toxin bound to frozen sections was confirmed by autoradiography of [125I]tetanus toxin binding. In contrast, the monoclonal antibody A4 bound to all layers of the retina (except that of the outer segments). In cell cultures the monoclonal antibody Ran-2 bound to the flat cells but to neither class of spheroid cells. These data imply that tetanus toxin binds more intensely to retinal neurones than to photoreceptors and other retinal cell types. By assisting identification of cells dissociated from retina, assays of tetanus toxin binding should prove useful in the isolation of specific retinal cell-types.

Animals↗
PubMed1982

Time-frequency-domain analysis: one-dimensional phantom studies.

Two methods have been adopted to date for investigating the interference effects resulting from the scattering of ultrasound by soft mammalian tissues; one involves the conversion of time-domain signals into the frequency-domain, where the broad spectral characteristics of a short acoustic pulse are utilised, whilst the other varies the orientation of the specimen with reference to the incident beam and analyses the interference effects at a specific frequency. It is shown both theoretically and experimentally that the two techniques are equivalent though the former is more seriously restricted by the equipment features. Results are presented on simple linear arrays of nylon monofilaments which indicate the ability of the respective techniques to evaluate scatterer separation. Furthermore a detailed examination of the limitations of the techniques concludes that the monofrequency orientation method is to be preferred and allows for the more accurate determination of scatterer separation. The significance of these findings is discussed with reference to the usage of these techniques for tissue characterisation.

Interferometry↗
PubMed1979

Attenuation of ultrasound in skeletal muscle.

Ultrasonic attenuation in fresh and 5% formalin fixed beef skeletal muscle has been measured, as a continuous function of frequency, in the range 1-8 MHz, for muscle fibre orientations both parallel and normal to the direction of propagation. Good agreement was found in all cases between two independent sets of measurements employing transmission and reflection techniques respectively. The data are consistent with a power law dependence of attenuation coefficient on frequency, with an exponent that is not significantly different from unity. For propagation normal to the fibres attenuation values are found as 1.1 +/- 0.15 and 1.6 +/- 0.15 dB cm-1 MHz-1 for fresh and fixed tissue respectively, the corresponding values for parallel propagation being 2.9 +/- 0.23 and 4.1 +/- 0.25 dB cm-1 MHz-1.

Animals↗
PubMed1979

Ultrasonic diffraction analysis in the investigation of liver disease.

An ultrasonic analytical method has been developed which is capable of remote, in vivo differentiation between various types of soft tissue on the basis of differences in their gross histological structure. The method is analogous to that employed in X-ray crystallography and is referred to as ultrasonic diffraction analysis. A clinical trial of this method in the investigation of liver disease in 70 patients is reported, in which a total of 416 ultrasonic diffraction patterns associated with various liver conditions have been analysed and related to independent follow-up information. The existance of a malignant condition of the liver has been identified in 95% of the cases involving focal metastatic deposits and in all of the 11 cases studied where the livers had diffuse malignant involvement. Cirrhosis and secondary involvement of the liver due to Hodgkin's disease have also been shown to exhibit specific tissue signatures which enable them to be differentiated from other hepatic disorders.

Humans↗
PubMedDate not supplied

Two-dimensional diffraction scanning of normal and cancerous human hepatic tissue in vitro.

A technique and associated equipment are described which investigate the acoustic signals backscattered from small tissue volumes and interrogated over a solid angle of transmitter/receiver positions. This two-dimensional diffraction technique produces acoustic scatter maps termed, by us "interferograms", which are analysed to determine their usefulness in discriminating between normal, freshly excised liver tissue and cancerous tissue within the intact organ. The "interferograms" are collected at three different narrow-band frequencies and have been used in investigating 26 normal liver and 13 liver tumour samples. The preliminary results indicate that this novel technique has a 97% success in discriminating normal liver from tumour, compared to an 87% success achieved by two observers when scoring conventional sector B-scan images of the same tissue regions.

Humans↗
PubMedDate not supplied

Intubation success rates by air ambulance personnel during 12-versus 24-hour shifts: does fatigue make a difference?

OBJECTIVES: To determine whether the skill performance and psychomotor agility, as measured by the endotracheal intubation success rate, of air ambulance medical personnel would be affected by the potential fatigue incurred when increasing the length of their shifts from 12 to 24 hours. METHODS: This was a retrospective review of all flight and intubation records from a large air medical transport system from 1997, when 24-hour shifts were in place, and six months (March-August) of 1996, during which 12-hour shifts were scheduled. Records of all intubation efforts during both periods, including multiple attempts per patient, and outcomes of all attempts, were recorded. Results of successes and failures were tabulated for both ultimate intubation outcome per patient and all attempts per patient for each calendar day and for the 12 hours between 19:00 and 07:00 when fatigue might play a role. Results from the two study periods were compared using Fisher's exact test. RESULTS: During the six months of 1996, 190 of 199 (95.5%) patients were ultimately successfully intubated. These patients required 237 attempts (80.1% successful). During 1997, 362 of 376 (96.3%) patients were successfully intubated, and required 438 attempts (82.6% successful). There was no statistically significant difference in the number of ultimately successful intubations (p = 0.66) or total intubation attempts (p = 0.37) between 1996 and 1997. Analysis of intubations between 19:00 and 07:00 revealed 81 of 84 (96.4%) patients successfully intubated in 1996, with 81 of 103 (78.6%) attempts successful. During 1997, 173 of 180 (96.1%) patients were ultimately successfully intubated, with 173 of 212 (81.6%) attempts successful. Again, there was no significant difference in the number of successful intubations (p = 0.99) or intubation attempts (p = 0.55) between 1996 and 1997. CONCLUSION: Psychomotor agility of air ambulance medical personnel, as measured by the success rate of endotracheal intubation, was not affected by the potential additional fatigue incurred as a result of increasing shift length from 12 to 24 hours.

Air Ambulances↗
PubMedDate not supplied

Comparing Web and touch screen transaction log files.

BACKGROUND: Digital health information is available on a wide variety of platforms including PC-access of the Internet, Wireless Application Protocol phones, CD-ROMs, and touch screen public kiosks. All these platforms record details of user sessions in transaction log files, and there is a growing body of research into the evaluation of this data. However, there is very little research that has examined the problems of comparing the transaction log files of kiosks and the Internet. OBJECTIVES: To provide a first step towards examining the problems of comparing the transaction log files of kiosks and the Internet. METHODS: We studied two platforms: touch screen kiosks and a comparable Web site. For both of these platforms, we examined the menu structure (which affects transaction log file data), the log-file structure, and the metrics derived from log-file records. RESULTS: We found substantial differences between the generated metrics. CONCLUSIONS: None of the metrics discussed can be regarded as an effective way of comparing the use of kiosks and Web sites. Two metrics stand out as potentially comparable and valuable: the number of user sessions per hour and user penetration of pages.

Adolescent↗
PubMedDate not supplied

Partial genetic characterization of West Nile virus strains, New York State, 2000.

We analyzed nucleotide sequences from the envelope gene of 11 West Nile (WN) virus strains collected in New York State during the 2000 transmission season to determine whether they differed genetically from each other and from the initial strain isolated in 1999. The complete envelope genes of these strains were amplified by reverse transcription-polymerase chain reaction. The resulting sequences were aligned, the genetic distances were computed, and a phylogenetic tree was constructed. Ten (0.7%) of 1,503 positions in the envelope gene were polymorphic in one or more sequences. The genetic distances were 0.003 or less. WN virus strains circulating in 2000 were homogeneous with respect to one another and to a strain isolated in 1999.

Animals↗