Biomedical subjects

L J Hahn

Publications and source records attributed to L J Hahn.

53 records · Page 3Linked to original sources

PubMed1990

Whole-body imaging of the distribution of mercury released from dental fillings into monkey tissues.

The fate of mercury (Hg) released from dental "silver" amalgam tooth fillings into human mouth air is uncertain. A previous report about sheep revealed uptake routes and distribution of amalgam Hg among body tissues. The present investigation demonstrates the bodily distribution of amalgam Hg in a monkey whose dentition, diet, feeding regimen, and chewing pattern closely resemble those of humans. When amalgam fillings, which normally contain 50% Hg, are made with a tracer of radioactive 203Hg and then placed into monkey teeth, the isotope appears in high concentration in various organs and tissues within 4 wk. Whole-body images of the monkey revealed that the highest levels of Hg were located in the kidney, gastrointestinal tract, and jaw. The dental profession's advocacy of silver amalgam as a stable tooth restorative material is not supported by these findings.

Animals↗

PubMed1990

Major mandibular reconstruction with vascularized bone graft.

Mandibular reconstruction is one of the most challenging fields in plastic and reconstructive surgery. Deficiencies of the mandible occur in congenital anomalies, trauma, oral and mandibular neoplasms and osteoradionecrosis. Conventional reconstructive aids like bone grafting or insertion of a metallic implant often fail in such situations due to poor local blood supply, deficient oral lining, inadequate skin coverage, large mandibular defects, irradiated fields or infected wounds. A free vascularized bone graft of a osteocutaneous flap overcomes the incompetence of conventional mandible reconstruction. It offers not only a desirable length of vascularized bone, but also has an adequate skin lining for oral mucosa and external tissue deficiencies, as well as a "sandwich reconstruction" for the mandible. The results are usually satisfactory in terms of function and aesthetics. Experience in 8 cases with iliac and scapular osteocutaneous free flaps are presented and discussed in this report. We conclude that a vascularized bone graft, especially the iliac crest, provides reliable and contented results for major mandibular reconstruction.

Adult↗

PubMed1989

Dental "silver" tooth fillings: a source of mercury exposure revealed by whole-body image scan and tissue analysis.

Mercury (Hg) vapor is released from dental "silver" tooth fillings into human mouth air after chewing, but its possible uptake routes and distribution among body tissues are unknown. This investigation demonstrates that when radioactive 203Hg is mixed with dental Hg/silver fillings (amalgam) and placed in teeth of adult sheep, the isotope will appear in various organs and tissues within 29 days. Evidence of Hg uptake, as determined by whole-body scanning and measurement of isotope in specific tissues, revealed three uptake sites: lung, gastrointestinal, and jaw tissue absorption. Once absorbed, high concentrations of dental amalgam Hg rapidly localize in kidneys and liver. Results are discussed in view of potential health consequences from long-term exposure to Hg from this dental material.

Absorption↗

PubMed1989

Angiolipoma of the tongue: report of a case.

Angiolipoma is a rare variety of lipoma in the maxillofacial region. Only eight cases have been documented so far. A case in which an angiolipoma occurred within the tongue of a 49-year-old man is described here. The difference from earlier cases occurring in the tongue is noted. Close follow-up has, as yet, revealed no recurrence.

Hemangioma↗

PubMed1988

Subsets of T lymphocytes in peripheral blood of patients with oral lichen planus.

The T lymphocyte subsets in the peripheral blood were studied in 26 patients with oral lichen planus and in 11 normal controls. Lymphocyte subsets were identified with monoclonal antibodies (Ortho Diagnostic System Inc. Raritan, New Jersey, USA) by an indirect immunofluorescent antibody method. This study shows no significant difference between patients with oral lichen planus and healthy controls. The conclusion is that local immunity, due to the breakdown of skin-associated lymphoid tissue, not a generalized immunologic disorder, is considered to be involved in the pathogenesis of oral lichen planus.

Adult↗

PubMed1988

Noise characteristics for cone beam collimators: a comparison with parallel hole collimator.

In order to evaluate the properties of a cone beam (CB) collimator and three-dimensional filtered backprojection algorithm, the noise characteristics of this collimator configuration were determined and comparisons with a parallel hole (PH) collimator were made. Noise characteristics were evaluated using two approaches: the first consisted of assessing the magnitude of local random fluctuations in the reconstructed images, and the second consisted of assessing the noise texture in these images in the frequency domain by evaluating the noise power spectrum. Data used for these measurements were simulated using Monte Carlo models of SPECT systems equipped with cone beam and parallel hole collimators. Finally, to compare experimentally a specially designed high resolution CB collimator with a high resolution (HRES) PH collimator, measurements of a physical phantom were performed. Results of our studies show better noise magnitude for CB collimators; however, for CB collimators with short focal lengths (40-60 cm) the shape of %RMS noise distributions differs from slice to slice.

Computer Simulation↗

PubMed1987

Peripheral ameloblastoma with metastasis.

Peripheral ameloblastoma is an uncommon clinical entity, while ameloblastoma with distant metastasis is still more unusual. A case of peripheral ameloblastoma with left supraclavicular lymph node metastasis is presented here.

Aged↗

PubMed1987

Nonisotropic attenuation in SPECT: phantom tests of quantitative effects and compensation techniques.

A quantitative study of nonisotropic attenuation in SPECT imaging is presented. The study includes a case where the spatial distribution of the attenuation coefficient is nonuniform, as well as a case where the photon path length in the attenuating medium is variable as a function of direction. The effects are studied using phantoms with known source activity and density distributions. Reconstructed images of the phantoms with and without attenuation compensation are compared with the source distribution. Three methods are used to provide partial attenuation compensation, using effective attenuation coefficients. These coefficients include some of the effects of photon scatter, but scatter is not explicitly treated. One attenuation compensation method involves a multiplicative postprocessing correction using an assumed constant attenuation coefficient. A modification of this technique is implemented using the correct nonuniform attenuation map to determine the multiplication factors. A single-iteration technique is used to provide a more complete compensation. The results indicate that nonuniform attenuation can produce significant distortion in line spread functions and in larger distributed sources. This distortion can alter volume determinations, quantitation measurements, and the shape of small objects, and can cause misplacement of counts into regions of low density. The distortion cannot be eliminated by the multiplicative postprocessing correction, but the single-iteration technique can significantly decrease the distortion.

Models, Structural↗

PubMed1987