Biomedical subjects

S L Thomsen

Publications and source records attributed to S L Thomsen.

7 recordsLinked to original sources

PubMed2001

Maintaining the cornea and the general physiological environment in visual neurophysiology experiments.

Neurophysiologists have been investigating the responses of neurons in the visual system for the past half-century using monkeys and cats that are anesthetized and paralyzed, with the non-blinking eyelids open for prolonged periods of time. Impermeable plastic contact lenses have been used to prevent dehydration of the corneal epithelium, which would otherwise occur in minutes. Unfortunately, such lenses rapidly introduce a variety of abnormal states that lead to clouding of the cornea, degradation of the retinal image, and premature termination of the experiment. To extend the viability of such preparations, a new protocol for maintenance of corneal health has been developed. The protocol uses rigid gas permeable contact lenses designed to maximize gas transmission, rigorous sterile methods, and a variety of methods for sustaining and monitoring the overall physiology of the animal. The effectiveness of the protocol was evaluated clinically by ophthalmoscopy before, during, and after the experiments, which lasted 8-10 days. Histopathology and quantitative histology were performed on the corneas following the experiment. Our observations showed that this protocol permits continuous contact lens wear without adversely affecting the corneas. Thus, it is possible to collect data 24 h each day, for the entire duration of the experiment.

Animals↗

PubMed2001

Use of osmotically active agents to alter optical properties of tissue: effects on the detected fluorescence signal measured through skin.

BACKGROUND AND OBJECTIVE: Hyper-osmotic chemical agents were used to study the effects of transient tissue scattering on the remitted fluorescence emission intensity from a target placed under a tissue sample. STUDY DESIGN/MATERIALS AND METHODS: A fluorescent film was placed underneath in vitro and in vivo samples of hamster skin, and the remitted fluorescent signal traveling to the tissue surface was monitored over time as the tissue was treated with an osmotically active agent. RESULTS: The detected fluorescent signal increased as the scattering in tissue samples was substantially reduced. The increase was greater for dimethyl sulfoxide than glucose or glycerol. It was not statistically different between in vivo skin and in vitro skin. CONCLUSION: The study shows how chemical agents can be used to improve the detected signal for a specific optical application. It could be useful in a number of optical therapeutic and diagnostic applications that can benefit from an increase in the penetration depth of light.

Analysis of Variance↗

PubMed2001

Adolescents' interpretations of conditional confidentiality assurances.

PURPOSE: To improve physicians' discussions of confidentiality policies with adolescent patients. METHOD: Fifty-three students completed private semistructured interviews designed to explore adolescents' interpretations of a statement explaining both the protections and limitations of confidentiality. RESULTS: Results suggest strategies for explaining conditional confidentiality in a way adolescents' understand and trust.

Adolescent↗

PubMed2001

Primate retina imaging with polarization-sensitive optical coherence tomography.

Polarization-sensitive optical coherence tomography (PSOCT) is applied to determine the depth-resolved polarization state of light backreflected from the eye. The birefringence of the retinal nerve fiber layer (RNFL) was observed and measured from PSOCT images recorded postmortem in a Rhesus monkey. An image-processing algorithm was developed to identify birefringent regions in acquired PSOCT retinal images and automatically determine the thickness of the RNFL. Values of the RNFL thickness determined from histology and PSOCT were compared. PSOCT may provide a new method to determine RNFL thickness and birefringence for glaucoma diagnostics.

Algorithms↗

PubMed1996

Cervical precancer detection using a multivariate statistical algorithm based on laser-induced fluorescence spectra at multiple excitation wavelengths.

A portable fluorimeter was developed and utilized to acquire fluorescence spectra from 381 cervical sites in 95 patients at 337, 380 and 460 nm excitation immediately prior to colposcopy. A multivariate statistical algorithm was used to extract clinically useful information from tissue spectra acquired in vivo. Two full-parameter algorithms were developed using tissue fluorescence emission spectra at all three excitation wavelengths (161 excitation-emission wavelength pairs) for cervical precancer (squamous intraepithelial lesion [SIL]) detection: a screening algorithm that discriminates between SIL and non-SIL with a sensitivity of 82 +/- 1.4% and specificity of 68 +/- 0.0%, and a diagnostic algorithm that differentiates high-grade SIL from non-high-grade SIL with a sensitivity and specificity of 79 +/- 2% and 78 +/- 6%, respectively. Multivariate statistical analysis was also employed to reduce the number of fluorescence excitation-emission wavelength pairs needed to redevelop algorithms that demonstrate a minimum decrease in classification accuracy. Two reduced-parameter algorithms that employ fluorescence intensities at only 15 excitation-emission wavelength pairs were developed: the screening algorithm differentiates SIL from non-SIL with a sensitivity of 84 +/- 1.5% and specificity of 65 +/- 2% and the diagnostic algorithm discriminates high-grade SIL from non-high-grade SIL with a sensitivity and specificity of 78 +/- 0.7% and 74 +/- 2%, respectively. Both the full-parameter and reduced-parameter screening algorithms discriminate between SIL and non-SIL with a similar specificity (+/-5%) and a substantially improved sensitivity relative to Pap smear screening. A comparison of the full-parameter and reduced-parameter diagnostic algorithms to colposcopy in expert hands indicates that all three have a very similar sensitivity and specificity for differentiating high-grade SIL from non-high-grade SIL.

Algorithms↗

PubMed1995

Laser(-assisted) nerve repair. A review.

Over the last decade low power laser irradiation has been used to repair nerves by photothermal welding. Nineteen animal and clinical experimental studies of laser tissue welding of nerves are reviewed. Possible mechanisms of tissue welding are presented, together with the benefits, limitations, and possible future implications of several techniques used in laser nerve repair. The consensus of these studies is that nerve welding has some advantages over standard suture repair. These advantages include less neuroma- und scar formation and shorter repair time. The major disadvantage of laser nerve repair is the initial inferior tensile strength. In the future, use of dyes or proteins could enhance the welding process by reinforcing the union strength, thus may improve the results of this promising technique.

Animals↗

PubMed1990

Early and late arterial healing response to catheter-induced laser, thermal, and mechanical wall damage in the rabbit.

Pulsed lasers are being promoted for laser angioplasty because of their capacity to ablate obstructions without producing adjacent thermal tissue injury. The implicit assumption that thermal injury to the artery is to be avoided was tested. Thermal lesions were produced in the iliac arteries and aorta of normal rabbits by a) electrical spark erosion, b) the metal laser probe, and c) continuous wave neodymium-yttrium aluminum garnet (Nd-YAG) laser energy through the sapphire contact probe. High-energy doses were used to induce substantial damage without perforating the vessel wall. Thermal lesions (n = 77) were compared with mechanical lesions (n = 22) induced by oversized balloon dilation. Medial necrosis was induced by all four injury methods. Provided no extravascular contrast was observed after the injury, all damaged segments were patent after 1 to 56 days. The progression of healing with myointimal proliferation was remarkably similar for all injuries. At 56 days, the neointima measured up to 370 microns. In conclusion, provided no perforation with contrast extravasation occurred, the normal rabbit artery recovered well from transmural thermal injury. The wall healing response is largely nonspecific.

Angioplasty, Balloon↗