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Biomedical subjects

W D Robertson

Publications and source records attributed to W D Robertson.

At least 19 recordsLinked to original sources
PubMed2005

Negative ions of ethylene sulfite.

The formation of negative ions in molecular beams of ethylene sulfite (ES, alternately called glycol sulfite or ethylene glycol, C(2)H(4)SO(3)) molecules has been studied using both Rydberg electron transfer (RET) and free electron attachment methods. RET experiments with jet-cooled ES show an unexpected broad profile of anion formation as a function of the effective quantum number (n(*)) of the excited rubidium atoms, with peaks at n(max)(*) approximately 13.5 and 16.8. The peak at n(max)(*) approximately 16.8 corresponds to an expected dipole-bound anion with an electron binding energy of 8.5 meV. It is speculated that the peak at n(max)(*) approximately 13.5 derives from the formation of a distorted C(2)H(4)SO(3)(-) ion. We suggest that quasifree electron attachment promotes the breaking of one ring bond giving a long-lived acyclic anion and term this process incomplete dissociative electron attachment. Theoretical calculations of plausible ionic structures are presented and discussed. Electron beam studies of ES reveal the presence of multiple dissociative attachment channels, with the dominant fragment, SO(2)(-), peaking at 1.3 eV and much weaker signals due to SO(3)(-), SO(-), and (ES-H)(-) peaking at 1.5, 1.7, and 0.9 eV, respectively. All of these products appear to originate from a broad temporary negative ion resonance centered at approximately 1.4 eV.

Journal Article↗
PubMed2004

Geochemical stability of phosphorus solids below septic system infiltration beds.

Review of 10 mature septic system plumes in Ontario, revealed that phosphorus (P) attenuation commonly occurred close to the infiltration pipes, resulting in discrete narrow intervals enriched in P by a factor of 2-4 (. MSc thesis, Dept. Earth Sci., University of Waterloo, Waterloo, Ont.; Ground Water 36 (1995) 1000; J. Contam. Hydrol. 33 (1998) 405). Although these attenuation reactions appeared to be sustainable under present conditions, the potential for remobilization of this P mass, should geochemical conditions change, is unknown. To test the stability of these P solids, dynamic flow column tests were carried out using sediments from three of the previously studied sites (Cambridge, Langton and Muskoka) focusing on sediments from the 'High-P' and underlying (Below) zones. Tests were continued for 166-266 pore volumes (PVs), during which time varying degrees of water saturation were maintained. During saturated flow conditions, relatively high concentrations of PO4 were eluted from the Cambridge and Langton High-P zones (up to 4 and 9 mg/l P, respectively), accompanied by elevated concentrations of Fe (up to 1.4 mg/l) and Mn (up to 4 mg/l) and lower values of Eh (<150 mV). The Below zones from Cambridge and Langton, however, maintained lower concentrations of P (generally<2 mg/l), Fe (<0.2 mg/l) and Mn (<1 mg/l) and maintained higher Eh (>250 mV) during saturated flow conditions. During unsaturated flow, P and Fe declined dramatically in the High-P zones (P<1 mg/l, Fe<0.2 mg/l), whereas concentrations remained about the same during saturated and unsaturated flow in the Below zones. This behavior is at least partly attributed to the development of reducing conditions during saturated flow in the High-P zones, leading to reductive dissolution of Fe (III)-P solids present in the sediments. Reducing conditions did not develop in the Below zones apparently because of lower sediment organic carbon (OC) contents (0.03-0.04 wt.%) compared to the High-P zones (0.2-0.65 wt.%). At the Muskoka site, where the sediments were noncalcareous, low values of P (<0.2 mg/l) were maintained in both the High-P and Below columns and reducing conditions did not develop. Results indicate the possibility of remobilizing P accumulated below septic system infiltration beds should conditions become more reducing. This could occur if sewage loading patterns change, for example when a seasonal use, lakeshore cottage is converted to a permanent dwelling.

Environmental Monitoring↗
PubMed2001

Multicomponent simulation of wastewater-derived nitrogen and carbon in shallow unconfined aquifers. II. Model application to a field site.

A multicomponent reactive transport model as presented by MacQuarrie and Sudicky [MacQuarrie, K.T.B., Sudicky, E.A., this volume. Multicomponent simulation of wastewater-derived nitrogen and carbon in shallow unconfined aquifers: I. Model formulation and performance, J. Contam. Hydrol.] is applied to a well-studied wastewater plume in a sandy aquifer near Cambridge, Ontario. Domestic wastewater is released into the unsaturated zone via a drain field at a depth of about 0.8 m. The physical transport parameters for the model are obtained by simulating a non-reactive solute, while kinetic input data for the nitrogen and carbon reaction network are obtained from the literature. The model shows that the wastewater-loading rate has little influence on the moisture content in the unsaturated zone, thus oxygen diffusion in the air phase is an important transport mechanism. The model results are in general agreement with the field-determined moisture and oxygen profiles near the drain field. The simulation results show that oxidation of ammonium and dissolved organic carbon (DOC) goes to completion in the 1.5-m distance between the drain field and the water table, and that calcite dissolution limits the pH reduction to about 0.2 units. The model-predicted nitrate concentrations in the core of the plume are in the range of 20-25 mg N/l and are in good agreement with the field data. Overall, the results for the major reactive species from the model simulation agree well with the geochemical data obtained below the drain field and it is concluded that the major physical and biochemical processes have been correctly captured in the current model formulation.

Carbon↗
PubMed2001

Numerical simulation of a fine-grained denitrification layer for removing septic system nitrate from shallow groundwater.

One of the most common methods to dispose of domestic wastewater involves the release of septic effluent from drains located in the unsaturated zone. Nitrogen from such systems is currently of concern because of nitrate contamination of drinking water supplies and eutrophication of coastal waters. It has been proposed that adding labile carbon sources to septic distribution fields could enhance heterotrophic denitrification and thus reduce nitrate concentrations in shallow groundwater. In this study, a numerical model which solves for variably saturated flow and reactive transport of multiple species is employed to investigate the performance of a drain field design that incorporates a fine-grained denitrification layer. The hydrogeological scenario simulated is an unconfined sand aquifer. The model results suggest that the denitrification layer, supplemented with labile organic carbon, may be an effective means to eliminate nitrogen loading to shallow groundwater. It is also shown that in noncalcareous aquifers, the denitrification reaction may provide sufficient buffering capacity to maintain near neutral pH conditions beneath and down gradient of the drain field. Leaching of excess dissolved organic carbon (DOC) from the denitrification layer is problematic, and causes an anaerobic plume to develop in simulations where the water table is less than 5-6 m below ground surface; this anaerobic plume may lead to other down gradient changes in groundwater quality. A drain field and denitrification layer of smaller dimensions is shown to be just as effective for reducing nitrate, but has the benefit of reducing the excess DOC leached from the layer. This configuration will minimize the impact of wastewater disposal in areas where the water table is as shallow as 3.5 m.

Eutrophication↗
PubMed2000

Variation in the quality of lumbar spine MR images in Washington State.

PURPOSE: To investigate the variation in quality of lumbar spine magnetic resonance (MR) images as a function of type of ownership of the imaging center, number of studies performed per month, specialty training of the image interpreter, and field strength of the MR unit. MATERIALS AND METHODS: Data were collected from all imaging facilities in western Washington state that received reimbursement from the Washington State Health Care Authority. Three readers with expertise in spine imaging, who were blinded to center and patient identification information, rated the technical image quality of each study. All MR images of the lumbar spine (maximum of six) paid for by the health care authority were evaluated. If a center had performed more than six studies, then six were randomly selected for evaluation. RESULTS: Variation in quality scores among sites was significant (P =.001). Field strength was the strongest predictor of better quality. Poorer quality was associated with for-profit ownership, a larger number of radiologists at the site reading MR images, and a larger percentage of studies checked by a radiologist prior to the end of the examination. CONCLUSION: There was significant variation in the quality of MR images of the lumbar spine, and at least a portion of this variation was attributable to characteristics of the imaging center.

Ambulatory Care Facilities↗
PubMed1996

Sacral plexus: optimal imaging planes for MR assessment.

PURPOSE: To identify the optimal imaging planes for magnetic resonance (MR) evaluation of the sacral plexus (SP) and proximal sciatic nerve (SN). MATERIALS AND METHODS: The SPs of 10 health adult volunteers were prospectively studied with T1-weighted MR imaging with custom-built pelvic phased-array coils. The conspicuity of 12 anatomic characteristics (comprising the SP and their relationship to normal pelvic anatomy) on a series of coronal, axial, and oblique images was graded. Results were evaluated with the Kruskal-Wallis and Wilcoxon signed rank tests. RESULTS: At least two planes were necessary to assess the anatomy of the SP and SN. Analysis of average conspicuity scores showed that the direct coronal and direct axial planes were the best overall and were superior to other imaging planes in the demonstration of the L-4 and L-5 ventral rami, the lumbosacral trunk, the S-1 contribution to the SN, and the SN in the greater sciatic foramen. The sacral coronal plane was best for the visualization of the bony sacrum, sacral foramina, and proximal S-1 to S-4 nerve roots. The remaining imaging planes had limited utility. CONCLUSION: MR imaging with a combination of direct coronal and direct axial planes enables thorough evaluation of all components of the SP and proximal SN.

Adult↗
PubMed1996

The comparison of a rapid screening MR protocol with a conventional MR protocol for lumbar spondylosis.

PURPOSE: To assess the degree of agreement between a rapid T2-weighted fast spin-echo protocol and a detailed protocol for the detection of lumbar spondylosis and to determine the sensitivity and specificity of the rapid protocol with respect to the detailed protocol. MATERIALS AND METHODS: Forty-eight patients with low back pain were studied with both a detailed four-sequence protocol and a two-sequence rapid screening protocol (acquisition time of 28 and 2.5 min for the detailed and screening protocols, respectively). The two protocol groups were numerically graded for the findings of lumbar spondylosis. RESULTS: Agreement for presence or absence of disc abnormality was 87% for the two techniques. The screening protocol showed a disc abnormality in 91% of all disc herniations and 84% of all disc bulges seen on the detailed study. All moderate and severe (grades two and three in this protocol) bulges and herniations were detected by the screening protocol. Foraminal narrowing, annular tear of the disc, degenerative changes of the facet joints, and nerve root swelling were all better shown on the detailed protocol. CONCLUSION: A rapid, two-plane, single-echo fast spin-echo sequence protocol is adequate to detect potentially significant degenerative disease of the lumbar spine. Its 2.5-min acquisition time allows a complete patient study (including patient preparation) to be performed in less than 10-15 min.

Humans↗
PubMed1993

Immunohistochemical study of oral keratoses including lichen planus.

Biopsies of non-ulcerated oral mucosa from 13 patients with oral lichen planus and 12 patients with leukoplakia were immunohistochemically stained using monoclonal antibodies to pan T, pan B, T helper and T suppressor/cytotoxic cells and the stained lymphocytes enumerated using an image analyser. The results show the preponderance of T cells infiltrating both oral lichen planus and leukoplakia. The T helper: T suppressor/cytotoxic cell ratio was the same (1:2) for both oral lichen planus and leukoplakia. A similar proportion of T suppressor/cytotoxic cells was found infiltrating the epithelium. These data indicate that T cell subset analysis is of no value in distinguishing oral lichen planus from other oral keratoses.

Antibodies, Monoclonal↗
PubMed1992

The structure of a complex of bovine alpha-thrombin and recombinant hirudin at 2.8-A resolution.

Crystals of the complex of bovine alpha-thrombin with recombinant hirudin variant 1 have space group C222(1) with cell constants a = 59.11, b = 102.62, and c = 143.26 A. The orientation and position of the thrombin component was determined by molecular replacement and the hirudin molecule was fit in 2 magnitude of Fo - magnitude of Fc electron density maps. The structure was refined by restrained least squares and simulated annealing to R = 0.161 at 2.8-A resolution. The binding of hirudin to thrombin is generally similar to that observed in the crystals of human thrombin-hirudin. Several differences in the interactions of the COOH-terminal polypeptide of hirudin, specifically of residues Asp-55h, Phe-56h, Glu-57h, and Glu-58h, and a few differences in the interactions of the hirudin core, specifically of residues Asp-5h, Ser-19h, and Asn-20h, with thrombin from human thrombin-hirudin suggest that there is some flexibility in the binding of these 2 molecules. Most of the residues in the 9 subsites that bind fibrinopeptide A7-16 to thrombin also interact with the NH2-terminal domain of hirudin. The S1 subsite is a notable exception in that only 1 of its 6 residues, namely Ser-214, interacts with hirudin. The only difference between human and bovine thrombins that appears to influence the binding of hirudin is the replacement of Lys-149E by an acidic glutamate in the bovine enzyme.

Amino Acid Sequence↗
PubMed1992

Ingestion of medication among patients with oral keratoses including lichen planus.

One hundred forty-nine patients attending Edinburgh Dental Hospital had oral keratosis diagnosed clinically and histologically. The keratoses were grouped into erosive and nonerosive lichen planus, other keratoses infiltrated with inflammatory cells, and noninfiltrated keratoses. Drug histories were obtained from each patient on presentation, and the groups were analyzed to assess the association between the ingestion of commonly prescribed drugs and oral keratoses. Patients with infiltrated keratoses took nonsteroidal anti-inflammatory drugs twice as often as patients in the other groups, whereas those with lichen planus more frequently ingested antihypertensive drugs. Patients with erosive lichen planus were 10 times more likely to ingest nonsteroidal anti-inflammatory drugs than those with nonerosive lichen planus (p = 0.01).

Administration, Oral↗
PubMed1991

Carotid and vertebral artery trauma: clinical and angiographic features.

Injury to the carotid or vertebral artery is an important clinical entity that requires angiography for definitive diagnosis and evaluation. The common carotid artery may be injured by penetrating trauma while the internal carotid artery is usually damaged by either trivial or blunt trauma. With trivial trauma extracranial internal carotid artery dissection should be considered if there is unilateral headache, Horner's syndrome or delayed transient ischaemic attack, and intracranial dissection if a profound neurological defect occurs immediately following trauma. Injury to the internal carotid artery following blunt trauma includes dissection of the extracranial internal carotid artery, carotid-cavernous fistula and pseudoaneurysm formation. These should be considered in a patient with delayed neurological deficit, mandibular or skull fracture, a constellation of orbital signs or diffuse subarachnoid haemorrhage, respectively. Vertebral artery injury is less frequent. Dissection typically follows abrupt cervical rotation and occurs at C1-2, whereas penetrating trauma may involve either the proximal or distal vertebral artery and occlusion, arteriovenous fistula or pseudoaneurysm may be found. Endovascular techniques may be used in either the carotid or vertebral artery to close fistulae or occlude an extensively damaged vessel.

Adult↗
PubMed1991

Routine contrast enhancement for cranial magnetic resonance imaging: an analysis of its diagnostic value in adults.

This study evaluated the diagnostic value of contrast enhancement in consecutive adults referred for cranial magnetic resonance imaging (MRI). All of the 112 participating patients underwent two sets of studies, first without and then with a contrast medium. Three neuroradiologists independently reviewed the information for each patient. Contrast enhancement contributed diagnostically useful information in 75% of cases: in 4% because undiagnosed lesions became apparent, in 26% because more information was obtained regarding the size, extent or margins of a lesion and in 45% because the lack of contrast enhancement in the area of interest allowed more confident exclusion of disease in patients with compelling clinical findings or demonstrated the nonaggressive nature of a lesion apparent with unenhanced MRI. The authors conclude that contrast enhancement is diagnostically useful for most patients referred for cranial MRI. Although the proportion of cases in which contrast enhancement was useful was much higher than in previous studies conducted in the United States, the authors believe that this finding is due to the high prevalence of disease in the population referred to this Canadian MRI centre.

Adult↗
PubMed1991

Magnetic resonance imaging of the skull base.

Magnetic resonance imaging (MRI) is the principal imaging procedure for assessing skull-base lesions. Superior contrast resolution, increased lesion conspicuity, better definition of the margin of the lesions and multiplanar capability are its main advantages. Computed tomography is currently used to assess skull-base lesions when superior bone detail is required or when MRI cannot be carried out.

Adenoma↗
PubMed1990

Orbital lymphangiomas: clinical, radiologic, and pathologic characteristics.

To assess the value of computed tomography (CT) in evaluation of orbital lymphangioma, the CT findings in 11 patients were retrospectively analyzed and correlated with the clinical, hemodynamic, surgical, and pathologic findings. The lesions were classified by location in three categories: superficial (n = 1), deep (n = 6), or combined (n = 6); the latter were evident earlier in life. The CT findings correlated well with the surgical and histologic findings. Orbital lymphangiomas were poorly defined lesions that crossed anatomic boundaries such as the conal fascia and orbital septum. Some degree of enhancement was the rule, ranging from scattered patchy areas to enhancement of the majority of the lesion. Areas of hemorrhage caused cystlike masses with rim enhancement. Preoperative identification of the vascular enhancing component at CT examination enables the surgeon to resect this area to prevent postoperative hemorrhage. High-resolution CT is of great value in the diagnosis and preoperative treatment planning of orbital lymphangioma.

Adolescent↗
PubMed1990

Graves orbitopathy: correlation of CT and clinical findings.

The clinical and high-resolution computed tomographic (CT) findings in 71 patients (142 orbits) with Graves orbitopathy and 20 healthy patients (40 orbits) were retrospectively reviewed. The orbits with orbitopathy were subgrouped at clinical examination into those with (n = 18) and those without (n = 124) optic neuropathy. Mean extraocular muscle diameters and the calculated muscle diameter index were significantly increased in all orbits with ophthalmopathy, particularly in those with optic neuropathy. Graves orbitopathy affected the superior muscle group (63.4%) more than the medial (61.3%) or inferior (57%) recti. The most common pattern of muscle involvement involved all five measured extraocular muscles. Solitary muscle involvement most frequently involved the superior muscle group (6.3%). Significant enlargements of the retrobulbar optic nerve sheath and superior ophthalmic vein were noted only in orbits with optic neuropathy. Anterior displacement of the lacrimal gland at CT correlated with clinical palpability and occurred more frequently in patients with optic neuropathy. Severe apical crowding was the most sensitive indication of optic neuropathy at CT.

Female↗