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Biomedical subjects

W L Davis

Publications and source records attributed to W L Davis.

At least 37 records · Page 2Linked to original sources
PubMed1994

Intracranial MR angiography: comparison of single-volume three-dimensional time-of-flight and multiple overlapping thin slab acquisition techniques.

OBJECTIVE: Time-of-flight (TOF) MR angiography has continued to evolve during the past few years. Signal loss due to flow saturation is a major problem of single-volume (slab) three-dimensional (3D) TOF technique. A multislab 3D TOF method, multiple overlapping thin slab acquisition (MOTSA), shows decreased sensitivity to the effects of flow saturation and therefore should result in better images. SUBJECTS AND METHODS: To evaluate the difference between MOTSA and the traditional single-volume 3D TOF techniques, we performed sequential, location-matched studies in 17 prospectively chosen patients with intracranial vascular abnormalities. All MOTSA and 3D TOF images were obtained after cut-film or 1024 digital angiography. RESULTS: According to specific criteria, abnormalities were better visualized with the MOTSA technique than with the single-volume 3D TOF technique. The difference was most marked in patients with more complex vascular abnormalities. CONCLUSION: We conclude that MOTSA is better than single-volume 3D TOF for showing intracranial abnormalities. The major advantage of MOTSA is decreased sensitivity to flow saturation.

Brain↗
PubMed1994

Evaluation of subclavian steal with two-dimensional phase-contrast and two-dimensional time-of-flight MR angiography.

We describe two MR angiographic methods of diagnosing subclavian steal in each of three patients. By using phase-directional information from a single two-dimensional phase-contrast sequence, we were able to show that the direction of flow in the affected vertebral artery was reversed. The same vertebral artery showed no signal on a 2-D time-of-flight sequence with a concatenated presaturation pulse applied above each section.

Aged↗
PubMed1994

MR imaging and MR angiography in the evaluation of pulsatile tinnitus.

PURPOSE: 1) To evaluate the scope of imaging findings seen with spin-echo MR and MR angiography (MRA) in patients with pulsatile tinnitus; 2) to determine whether MRA adds additional imaging information (to that provided by spin-echo MR) necessary for determining the cause of pulsatile tinnitus; and 3) to suggest MR and MRA imaging techniques for evaluation of patients with pulsatile tinnitus. METHODS: Forty-nine patients with pulsatile tinnitus were evaluated with MR and MRA. Seventeen of these patients had conventional angiography. RESULTS: Vascular lesions or paraganglioma were demonstrated in 28 patients. Of these 28 lesions, the majority were seen best (46%) or only (36%) on MRA. The spectrum of lesions detected included dural arteriovenous fistula (nine), extracranial arteriovenous fistula (three), paraganglioma (five), jugular bulb variants (three), aberrant internal carotid artery (one), internal carotid artery stenosis (one), tortuous internal carotid artery (one), carotid dissection with pseudoaneurysm (one), stenosis of the transverse sinus (two), and arteriovenous malformation (two). CONCLUSIONS: MRA, in conjunction with spin-echo imaging, markedly enhances the ability of MR to diagnose the lesions responsible for pulsatile tinnitus.

Adolescent↗
PubMed1994

Bithalamic hyperintensity on T2-weighted MR: vascular causes and evaluation with MR angiography.

PURPOSE: To determine whether MR angiography can be used to differentiate between the two vascular causes of bithalamic hyperintensity on T2-weighted MR images: "top of the basilar" artery occlusion and deep cerebral vein thrombosis. METHODS: A retrospective review identified six patients with bithalamic T2 hyperintensity of vascular causes. MR angiography was performed in four patients, MR angiography and conventional angiography in one patient, and conventional angiography in one patient. Data pertaining to clinical presentation and hospital course were collected. MR angiographic techniques were multislab overlapping three-dimensional time-of-flight, 2-D time-of-flight, and 2-D phase-contrast. RESULTS: Three cases of top of the basilar artery occlusion and three cases of deep cerebral vein thrombosis were recognized. In all cases, T2 hyperintensity in a vascular distribution suggested cerebral occlusive disease. Infarction involving the thalami and basal ganglia was present in two cases of deep cerebral vein thrombosis. Infarction of the thalami, mesodiencephalic region, and cerebellar hemispheres was present in two cases of basilar artery occlusion. Bithalamic infarction alone was seen in one case of deep cerebral vein thrombosis and one case of basilar artery occlusion. In the five cases in which MR angiography was used, this technique accurately distinguished the vessels involved (arterial or venous). CONCLUSION: MR angiography is a useful adjunct to MR imaging in the evaluation of bithalamic T2 hyperintensity. It does help distinguish between the two vascular causes: top of basilar artery occlusion and deep cerebral vein thrombosis.

Adult↗
PubMed1993

Insulin accelerates the post germinative development of several fat-storing seeds.

The effect of insulin and insulin like growth factors I and II on sunflower, watermelon and cucumber cotyledons has been examined. Each peptide stimulates an increase in the activity of several glyoxysomal enzymes which catalyze the conversion of fat to carbohydrate. These results provide the first evidence for the action of insulin and insulin like growth factors in plants.

Acyl-CoA Dehydrogenase↗
PubMed1993

Superoxide formation preceding flight muscle histolysis in Solenopsis: fine structural cytochemistry and biochemistry.

In Solenopsis spp., muscle histolysis or breakdown is a normal process in females and is initiated in the flight muscles only immediately after a mating flight. Information regarding the presence of the oxyradical scavenging enzyme superoxide dismutase (SOD) and the formation of the radical oxygen intermediate superoxide (SO) during the early stages of flight muscle histolysis in this insect was investigated. In normal fibrillar flight muscles from control animals, SOD was immunolocalized to vesicular and tubular components of the sarcotubular system. Lanthanum tracer studies indicated that some of these SOD-positive structures might be tubulovesicles continuous with the extracellular space. Following the injection of virgin alates with experimental haemolymph obtained from artificially inseminated females, the membrane delimited elements of the sarcotubular system became increasingly swollen and dilated with time (from 60 to 120 minutes postinjection) with a concomitant decrease in SOD activity and an increase in oxyradical formation. Many similar vesicles were lanthanum-positive. SO was not seen in the sarcoplasmic vesicles and tubules of control insects. The biochemical quantification of SO release over a 2-hour period showed a marked increase in oxyradical formation following treatment with the experimental haemolymph in comparison to control insects. Also, the addition of superoxide dismutase depressed SO formation under these conditions. Despite the histochemical and biochemical changes seen in the muscles of experimental insects, by 2 hours post-treatment there was no evidence of muscle necrosis. From these studies on flight muscle histolysis/necrosis in Solenopsis it appears that the formation of oxyradicals might represent an early event in myopathogenesis and subsequent tissue involution. The generation of SO is more than likely to be associated with alterations in the normal structure, biochemistry and permeability of the biomembranes which delimit the sarcotubular system.

Animals↗
PubMed1993

Evaluation of new high-performance calcium polyphosphate bioceramics as bone graft materials.

The purpose of this study was to evaluate the ability of a recently developed porous calcium polyphosphate bioceramic (CPB) to function as a bone graft substitute. After six weeks, postsurgical extraction of the mandibular first and second molars, alveolar ostectomies were performed bilaterally in five dogs. The ridge forms were then restored using the CPB implant material on one side and the autogenous bone obtained from the contralateral ostectomy site on the other. The graft and implant sites were retrieved after 4 months and decalcified and undecalcified sections were prepared for special staining (modified Attwood) and subsequent light microscopy and histomorphometry. In addition, the undecalcified sections were prepared for histometry using backscattered electron imaging (BSEI). Histologically, the CPB implants showed extensive vascularization and cellularity within an "invading" loose connective tissue matrix. On the opposite side, the loose connective tissue of the autografts showed hypovascularity and hypocellularity. Neither the implants nor the autografts showed any histologic evidence of an inflammatory reaction. Using light microscopic histomorphometry, the implants showed a higher incidence of union than the autografts. On BSEI histometry, the CPB implants showed significantly greater new bone formation than the autografts. This study reveals that porous CPB possesses certain characteristics essential for the "ideal" implantable bone substitute necessary for the repair of craniofacial and other bony defects.

Animals↗
PubMed1993

Contrast-to-noise-ratio measurements in three-dimensional magnetic resonance angiography.

RATIONALE AND OBJECTIVES: The authors report on the development and preliminary validation of a technique for measuring contrast-to-noise ratio (CNR) at all points along selected vessel segments in the original three-dimensional magnetic resonance angiography (MRA) dataset. METHODS: Contrast-to-noise ratio dependencies on flow rate, field of view, and flip angle were measured on images from a conventional time-of-flight MRA pulse sequence using constant flow in a branching vascular phantom. An estimate of the inherent variability of the technique was obtained from multiple scans of a flow phantom and a human volunteer. RESULTS: The overall standard deviation (SD) of the CNR was found to be approximately 6.1% of the average CNR value for the flow phantom study and 7.3% for the human study. Vessel CNR was found to increase with field of view and was found to become nonuniform for low flow rate and/or high flip angles. CONCLUSION: In general, such CNR measurements allow the investigation of the mechanism of signal loss and general technique optimization in MRA.

Blood Vessels↗
PubMed1993

Overview of MR imaging modalities.

Practical approaches to optimization of the use of gadolinium in MR imaging comprise a range of advances in data-acquisition techniques and pulse sequences that augment tissue contrast and reduce scanning times, increasing throughput and patient comfort. In addition to the effects of magnetic field strengths and manipulation of contrast doses for routine spin-echo (SE) imaging, several approaches are reviewed. These include: fat suppression, which helps to resolve enhancing lesions from tissues with inherently high signal on post-gadolinium T1-weighted imaging; gradient-echo (GRE) and partial radio-frequency (RF) echoplanar techniques, which tend to reduce data acquisition times; MR angiography, which enables elucidation of slow-flow vessels and mass-vessel relationships; and three-dimensional GRE scan displays, which relate lesion location to regional and surface anatomy.

Angiography↗
PubMed1993

Magnetic resonance angiography in pediatric neuroradiology.

Magnetic resonance angiography (MRA) is a novel technique that uses gradient echo pulse sequences and computer postprocessing technology to create vascular-flow images. The technique is easy to apply, noninvasive, and frequently yields information not available by other noninvasive means. The utility and benefits of MRA are amply documented by clinical studies in the neuroimaging literature. This article reviews the techniques of MRA and the current literature in the application of MRA in pediatric imaging. Illustrative cases demonstrating the use of MRA in pediatric neuroradiology are presented. The utilization of MRA in congenital lesions such as aberrant internal carotid artery and arteriovenous malformation and in differing causes of ischemic disease is highlighted. There is an ever-expanding number of applications of MRA in pediatric neuroimaging. Despite the lack of standardized protocols, with a thorough knowledge of the basic principles, MRA can be successfully applied in many imaging situations. The ease of use and noninvasive nature of MRA make it an ideal tool in the evaluation of the pediatric neurovasculature.

Brain Diseases↗
PubMed1992

Evidence for the glyoxylate cycle in human liver.

The enzymatic activities unique to the glyoxylate cycle of higher plants and certain lower invertebrates, isocitrate lyase and malate synthase, have been demonstrated in homogenates prepared from human liver. Human liver can also carry out cyanide-insensitive fatty acid oxidation from palmitate. Utilizing light microscopic immunocytochemistry with an antibody produced against Euglena malate synthase, this enzyme localizes in numerous ovoid granules in human hepatocytes. Also, immunocytochemistry using antibodies produced against rat fatty acyl-CoA oxidase showed that this enzyme was localized in similar structures. With routine cytochemistry, catalase was seen in identical granular bodies. Both catalase and fatty acyl-CoA oxidase are peroxisomal enzymes. The presence of malate synthase in liver homogenates was further confirmed by Western blot analysis. These data suggest that the human liver may be capable of utilizing the carbon backbone of fatty acids for carbohydrate synthesis since the glyoxylate cycle in lower organisms subserves this anabolic function.

Acyl-CoA Oxidase↗
PubMed1991

Immunohistochemical and pharmacokinetic characterization of site-specific immunoconjugate 15A8-glycyl-tyrosyl-(N-epsilon-diethylenetriamine pentaacetic acid)-lysine derived from anti-breast carcinoma monoclonal antibody 15A8.

In this study, the breast carcinoma-reactive monoclonal antibody 15A8 and a site-specific immunoconjugate of the antibody, 15A8-glycyl-tyrosyl-(N-epsilon-diethylenetriamine pentaacetic acid)-lysine (15A8-GYK-DTPA), were characterized by immunohistological methods for reactivity with normal and neoplastic human tissues and normal cynomolgus monkey tissues. In addition, 15A8-GYK-DTPA labeled with 111In was assessed by in vivo imaging and pharmacokinetic studies for localization to human tumor xenografts in nude mice. The native antibody and the site-specific immunoconjugate exhibited similar limited reactivity with normal human tissues. Specifically, epithelial structures, including normal breast epithelium, lung alveoli, bronchial epithelium and glands, liver bile ducts, pancreatic ducts, kidney distal and collecting tubules, epidermal and esophageal epithelium, endometrial glands, and thymic Hassall's corpuscles, were reactive. Normal monkey tissues stained with 15A8 exhibited a similar pattern of reactivities. Antibody 15A8 reacted broadly with epithelium-derived tumors; more than 60% of the cells in all of the breast, colon, non-small cell lung, ovarian, prostate, bladder, and renal carcinomas tested expressed the antigen. In contrast, a variety of nonepithelial neoplasms, including lymphomas, melanomas, sarcomas, and small cell lung carcinomas, were nonreactive. 15A8-GYK-DTPA-111In administered i.v. rapidly localized to and imaged both MX-1 and MCF-7 human breast carcinoma xenografts in nude mice, reaching maximal levels of about 20% of injected dose/g of tumor within 4 days. No unusual localization to any nontumor tissue or organ was seen; the level of radioactivity in the normal tissues and organs was at or below that seen in the blood. Furthermore, the immunoconjugate did not accumulate in xenografts of the antigen-negative breast carcinoma ZR-75-1, which indicates that tumor localization was antigen specific. Pharmacokinetic studies in cynomolgus monkeys suggested that significant amounts of 15A8-GYK-DTPA-111In did not localize to normal epithelia and demonstrated that the immunoconjugate was not toxic. These findings suggest that antibody 15A8 may be useful in the diagnosis and therapy of breast cancer and possibly other carcinomas.

Animals↗
PubMed1991

Cryofixation, ultracryomicrotomy, and X-ray microanalysis of enterocytes from chick duodenum: vitamin-D-induced formation of an apical tubulovesicular system.

New methods of tissue preparation were developed to study the morphology and distribution of calcium ions in duodenal enterocytes from normal, rachitic, and vitamin D-replete (either cholecalciferol [CC] or 1,25-dihydroxycholecalciferol [1,25-DHCC] treated) chicks. Frozen hydrated sections were prepared from cryofixed tissues by ultracryomicrotomy at -125 degrees C. Sections were subsequently freeze-dried by increasing the temperature to -100 degrees C. The latter temperature was maintained throughout both the structural and elemental analyses. In cells from normal, rachitic, and vitamin D-treated [CC] animals the brush border from lanthanum-infused tissues was electron dense and calcium-lanthanum positive by x-ray analysis. In the absence of lanthanum, i.e., sucrose-infused duodena, the microvilli were still calcium positive. In the terminal web region of normal and CC-treated enterocytes, numerous, apparently interconnected, tubules and vesicles were seen. Vacuole-like structures were also seen. Such structures were especially prominent in the enterocytes from the vitamin-treated [CC] animals. Except for the vacuoles, the tubules and vesicles were electron dense in the lanthanum-infused duodena, and clear in sucrose-infused tissues. In both instances, the structures were calcium positive. Similar, but even larger structures were seen below the terminal web. Here however, the tubules and vesicles seemed to be organized into multiple complex interconnecting networks, i.e., tubulo-vesicular complexes. Both the tubules and the vesicles seemed to be interconnected via smaller channel-like entities. The extensiveness of this structure was better appreciated in the enterocytes from lanthanum-infused tissues, where it appeared similar in structure and complexity to an en face view of the sarcoplasmic reticulum of skeletal muscle. These intestinal complexes were less well developed, decreased in number, and quite often absent, in the apical cytoplasm of absorptive cells from rachitic chicks. In the enterocytes from animals treated for 24 hours with 1,25-DHCC, the same highly developed tubulo-vesicular networks were again seen in the enterocyte apical cytoplasm. They were even more developed in the 1,25-DHCC-treated animals. All structures were intensely calcium positive in enterocytes from both the lanthanum- and the sucrose-infused preparations. Numerous endocytotic (pinocytotic) vesicles were seen at the lumenal plasmalemma. Similar structures were also apparent in the terminal web region of the 1,25-DHCC-treated enterocytes. Exocytotic vesicles were seen at the apical aspect of the lateral cell membrane, below the level of the junctional complex. All components of this unique system contained high concentrations of calcium.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Duration of liquid water habitats on early Mars.

We have employed a simple climate model of early Mars in order to estimate the duration of ice-covered lakes after the onset of freezing conditions on Mars. The critical parameter determining the existence of ice-covered lakes is the existence of peak seasonal temperatures above freezing. The peak temperature occurs at the subsolar point at perihelion. We use the weathering model of Pollack et al. (Icarus 71, 203-224, 1987) to compute the pressure and temperature evolution of the atmosphere. We have included the variability of the solar luminosity. We find that if there was a source of ice to provide meltwater, liquid water habitats could have been maintained under relatively thin ice covers for up to 700 million years after mean global temperatures fell below the freezing point. At this point, the mean annual temperature is 227 K, and the pressure of atmospheric CO2 is about 0.5 bar. Without the presence of stable bodies of liquid water, it is not clear what mechanisms were responsible for the removal of this remaining CO2. From a biological point of view, we find that the duration of liquid water habitats on early Mars exceeds the upper limit on the time required for the origin of life on Mars.

Atmosphere↗
PubMed1991

Copper-zinc superoxide dismutase activity in normal and inflamed human dental pulp tissue.

Information regarding the presence of the free radical scavenging (inactivating, dismutating) enzyme superoxide dismutase in human dental pulp was sought. Free radicals, such as the superoxide anion radical (O2-) and the hydroxyl anion radical (OH.), are powerful biological oxidants produced by phagocytes during the normal tissue response to injury and infection. Also produced is hydrogen peroxide (H2O2), an aggressive oxygen species formed by the reaction of superoxide with itself, i.e., a dismutation in which one molecule of O2- is oxidized by the other. These three reactive oxygen intermediates serve as part of the normal host biological defense mechanism for the inactivation of microorganisms and the breakdown of their toxic products. Both normal and inflamed dental pulps were assayed for the presence of this enzyme. Superoxide dismutase activity was identified in the normal pulpal tissues. There was a slight decrease in activity with age. In the inflamed pulpal tissues, enzyme activity was markedly and significantly increased in comparison to that in the normal tissues. These observations indicate that human dental pulp possesses an endogenous defense mechanism designed to protect the tissue components (cells and matrix) from the toxic effects of the reactive oxygen intermediates. In this regard, the inflammatory response of this specialized and somewhat isolated (compartmentalized) tissue is not unlike that seen in other connective tissues.

Adult↗
PubMed1991

An ultrastructural and immunohistochemical study of human dental pulp: identification of Weibel-Palade bodies and von Willebrand factor in pulp endothelial cells.

Special and specific immunohistochemical techniques as well as routine transmission electron microscopy were used to identify the presence of von Willebrand factor (vWF), a blood clotting factor essential to normal hemostasis, and Weibel-Palade bodies (WPB's), respectively, in the endothelial cells lining the blood vessels from both normal and inflamed human pulpal tissues. In human endothelial cells, WPB's are peculiar and specialized organelles which store vWF. All classes of blood vessels (capillaries, arterioles, arteries, venules, and veins) were vWF positive. The fine structural studies showed similar results with regard to the presence of WPB's. Interestingly, morphometric analyses conducted on the same tissues using either light or transmission electron microscopy showed that significantly more vWF-positive blood vessels were seen in the inflamed tissues. In agreement with the latter observation, transmission electron microscopy showed that more vascular endothelial cells contained WPB's in the inflamed tissues when compared with the normal tissues. From this it appears that during pulpal inflammation, the cascade of events associated with hemostasis may be activated with the increased synthesis and release of vWF by endothelial cells.

Dental Pulp↗