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Biomedical subjects

T J Davis

Publications and source records attributed to T J Davis.

At least 19 recordsLinked to original sources
PubMed2002

Quantitative X-ray projection microscopy: phase-contrast and multi-spectral imaging.

We outline a new approach to X-ray projection microscopy in a scanning electron microscope (SEM), which exploits phase contrast to boost the quality and information content of images. These developments have been made possible by the combination of a high-brightness field-emission gun (FEG)-based SEM, direct detection CCD technology and new phase retrieval algorithms. Using this approach we have been able to obtain spatial resolution of < 0.2 micro m and have demonstrated novel features such as: (i) phase-contrast enhanced visibility of high spatial frequency image features (e.g. edges and boundaries) over a wide energy range; (ii) energy-resolved imaging to simultaneously produce multiple quasi-monochromatic images using broad-band polychromatic illumination; (iii) easy implementation of microtomography; (iv) rapid and robust phase/amplitude-retrieval algorithms to enable new real-time and quantitative modes of microscopic imaging. These algorithms can also be applied successfully to recover object-plane information from intermediate-field images, unlocking the potentially greater contrast and resolution of the intermediate-field regime. Widespread applications are envisaged for fields such as materials science, biological and biomedical research and microelectronics device inspection. Some illustrative examples are presented. The quantitative methods described here are also very relevant to projection microscopy using other sources of radiation, such as visible light and electrons.

Journal Article↗
PubMed2001

Optimization of asymmetric catalysts using achiral ligands: metal geometry-induced ligand asymmetry.

[reaction: see text] Traditionally, asymmetric catalysts have been optimized by modification of resolved chiral ligands. In this Letter, we optimize the asymmetric addition of diethylzinc to aldehydes by modification of achiral methylene bis(phenol) ligands. Upon coordination of the substrate, the achiral ligand becomes asymmetric, a concept termed Metal Geometry-Induced Ligand Asymmetry. The enantioselectivity of the catalyst formed from a single resolved ligand and several achiral ligands ranged from 9% (R) to 83% (S).

Aldehydes↗
PubMed2001

Location of Zn within the Mg12(LaxCe1-x) lattice by X-ray incoherent channelling patterns.

Systematic electron diffraction studies on intermetallic precipitates formed within a lightweight Mg-RE-Zn alloy (RE = La or Ce) identify these to be of structural type Mn(12)Th (space group I4/mmm). Analytical electron microscopy yields an overall composition of Mg(12)(La(x)Ce(1-x)) with x ~ 0.43, with 1 at.% Zn incorporated within the lattice. Variations in characteristic X-ray emission rates, as an electron beam is rocked near zone-axis orientations, are used to form two-dimensional channelling patterns, termed X-ray incoherent channelling patterns. This channelling contrast enables a specific sublattice site that is occupied by Zn to be unambiguously identified within the Mg(12)RE lattice. The particular sublattice site is denoted by the Wyckoff letter f, and is one of the three different Mg sublattice sites f, i and j. Of these three sites, the Wigner-Seitz cell that is centred on the f sublattice site has the largest Mg-RE interatomic distance, and therefore the f site is expected to be favoured for accommodating the substitution of a larger Zn atom.

Journal Article↗
PubMed2001

Snapshots of titanium BINOLate complexes with diverse solid state structures.

[structure: see text]. Many important asymmetric reactions are catalyzed by (BINOLate)Ti species with unknown structures. Reported here are three structures of BINOLate titanium complexes that show an interesting aggregation of (BINOLate)Ti(OiPr)2 with itself and with titanium tetraisopropoxide. These complexes are potential intermediates in the asymmetric addition of alkyl groups to aldehydes.

Journal Article↗
PubMed1999

Correlation of the intercondylar notch width of the femur to the width of the anterior and posterior cruciate ligaments.

The purpose of this study was to determine if a correlation exists between the intercondylar notch width (NW) of the femur and the width of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). A study group of 124 consecutive patients (mean age 36.6 +/- 15.2 years; 67 men, 57 women) underwent a magnetic resonance imaging evaluation for knee pain but did not have an ACL or PCL tear or arthrosis. A T2 weighted coronal cut was identified and was located at the middle of the tibial spine, which represented the plane where the ACL and PCL cross each other when the knee is in 10 degrees of flexion. The NW and the width of the ACL and PCL were measured at the level of the middle of the popliteal hiatus on a physician-independent console that allowed for digital measurements in millimeters. Our results showed a statistically significant correlation between NW and ACL width (r = 0.87; P < 0.001) and between NW and PCL width (r = 0.75; P < 0.001). The mean ACL width was 6.4 +/- 1.4 mm (range 3-10 mm). The mean PCL width was 10.2 +/- 2.0 mm (range 6-17 mm). The mean ACL width was 5.7 +/- 1.1 mm for women and 7.1 +/- 1.2 mm for men (P < 0.001). The mean PCL width was 9.5 +/- 1.7 mm for women and 10.9 +/- 2.0 for men (P < 0.001). Our results indicate that NW correlates with ACL and PCL width. In addition, ACL and PCL widths are narrower in women than men.

Adolescent↗
PubMed1997

Colonoscopy experience at a family practice residency: a comparison to gastroenterology and general surgery services.

BACKGROUND AND OBJECTIVES: Colonoscopy training is receiving greater emphasis in family practice residencies. However, no standards have been established to measure the adequacy of this training. This study assessed the colonoscopy experience of family practice residents at Louisiana State University Medical Center at Shreveport (LSUMC-S). METHODS: We included all colonoscopies performed by the family practice service between August 1992 and December 1994 and matched them by gender and age with cases from the gastroenterology (GI) and general surgery (GS) services performed during the same time period. Family practice and GI were compared using 143 cases from each service; 166 cases were used to compare family practice to GS. RESULTS: The cecum was intubated in 87% of patients on all services. The average time to complete the procedure was 35 minutes by the family practice service, 44 minutes by GI, and 25 minutes by GS. No significant differences were found between family practice and GI in the number of patients with polyp, normal colon, or biopsy performed. In comparison to GS, there were significantly fewer patients on the family practice service with normal colon and more with multiple polyps and biopsy performed. Significantly more cancers were found by the family practice service than by either GI or GS. There were no complications reported for any of the services. Results compared favorably with data in the current literature. CONCLUSIONS: The colonoscopy experience available to family practice residents at LSUMC-S is acceptable within the parameters studied.

Biopsy↗
PubMed1995

Branches of the tibial nerve: anatomic variations.

Anatomic variations in tibial nerve branches may help explain discrepancies between clinical examination and electrophysiologic tests as to the location of neuronal lesions. Dissection of 20 cadaveric feet (10 pair) along the course of the tibial nerve and its branches confirmed that it bifurcates within 2 cm of the medio-malleolar-calcaneal axis in 90% (18/20) and that it gives off frequent small branches with its accompanying vascular structures. Unlike other studies, however, we found that 60% had multiple calcaneal branches off the tibial nerve and that 20% evidenced previously undescribed accessory innervation to the abductor hallucis muscle from other than the medial plantar nerve.

Foot↗
PubMed1995

External fixation of pediatric femoral fractures.

Fifteen pediatric femoral fractures in 14 patients were treated with external fixation using the EBI Orthofix unilateral external fixator. The average patient age was 8.5 years (range, 3-13 years). There were 7 children with multiple injuries and 7 with isolated fractures. The average duration in the fixator was 63 days; average followup was 34 months. All 15 fractures healed without additional operative intervention. Average angulation at the fracture site was 4.4 degrees in the anteroposterior plane (range, 0 degrees-10 degrees) and 4.6 degrees in the lateral plane (range, 0 degrees-11 degrees). There were 5 pin tract infections, all of which resolved with systemic antibiotics. There was 1 case of refracture in a boy with muscular dystrophy. Ten patients had clinically equal leg lengths, 3 patients had < 1 cm of inequality, and 1 patient had a 1.5 cm discrepancy. External fixation is a well-proven technique for managing pediatric femoral fractures in the child with multiple injuries. It is also an effective means of treating isolated femoral fractures in the pediatric population.

Adolescent↗
PubMed1994

Right coronary ostial atherectomy: a really close shave.

Percutaneous transluminal coronary balloon angioplasty (PTCA) has had limited success with higher complication and restenosis rates in aorto-ostial lesions. Directional coronary atherectomy (DCA) has been advocated as an alternative to PTCA in such lesions. In this report, we describe a potential complication of DCA in right coronary ostial lesions.

Aged↗
PubMed1994

A modified technique for bedside placement of nasoduodenal feeding tubes.

A technique for bedside placement of NDT that was used in our ICU and allowed a significant percentage of feeding tubes to be placed in the duodenum without moving the patient from the ICU setting is reported. We believe that this modification for feeding tube placement is effective and safe and represents an improvement of the previous method.

Duodenum↗
PubMed1982

Coarctation of the aorta from a mediastinal germ cell tumor: a case report.

A 20-yr-old male had compression of the thoracic aorta by a large malignant mediastinal germinoma. The symptoms and signs that simulated coarctation of the aorta included hypertension, markedly decreased femoral pulses, and a systolic murmur that radiated to the back. Following X-ray therapy, the femoral pulses were palpable and the blood pressure became normal. To our knowledge, compression of the aorta by a malignant teratocarcinoma with manifestations mimicking coarctation of the aorta has not been reported.

Adult↗
PubMed1978

Parasitic arterial supply to renal angiomyolipoma.

A case of a large renal angiomyolipoma in a relatively asymptomatic female subject without tuberous sclerosis is presented. The case demonstrates a parasitized blood supply from a lumbar artery and the superior mesenteric artery, in addition to the characteristic angiographic features that have been reported previously. A parasitized blood supply to renal masses has been considered previously to be associated with malignant processes. It is emphasized that parasitization of a blood supply by a renal mass lesion is not definite evidence of malignancy.

Adult↗
PubMed1977

Benign hepatic lesions in women taking oral contraceptives.

Four previously unreported cases of benign hepatic cell lesions in young women taking oral contraceptives are described. A brief review of the literature is presented with emphasis on the clinical symptoms, the findings on angiography and radionuclide scan, and the relation of the lesions to oral contraceptives.

Adult↗
PubMed1977

Immunoglobulin deficiency diseases of the intestine.

Marshak has emphasized the role of the gastrointestinal tract as a major immunologic organ and described the radiologic findings of immunoglobulin deficiency diseases of the small intestine. According to his classification the radiologic findings include multiple nodular defects, edema and increased secretions associated with Giardiasis, a sprue-like pattern, and thickened folds. In this report, the role of the intestine in the immune response is briefly reviewed and several of the radiologic features of immune deficiency diseases and those of benign nodular lymphoid hyperplasia are illustrated.

Adolescent↗
PubMed1975

Haemoglobin synthesis in fused cells.

When primitive erythroid cells from 5-day-old chick embryos are exposed to inactivated Sendai virus they do not undergo haemolysis but fuse with other cells by the normal process of cytoplasmic coalescence. In this way cells actively engaged in the synthesis of haemoglobin may be fused with others that are not. In heterokaryons formed by the fusion of such erythroid cells with cells from established mouse or hamster lines, haemoglobin synthesis initially continues at a high level, but then declines and ceases altogether within a period of about 60 h. This decline affects the synthesis of both haem and globin and reflects the activity of specific regulatory mechanism, for under these conditions other chick proteins continue to be synthesized. The haemoglobin synthesized in the heterokaryons is entirely chick, and not mouse or hamster, haemoglobin.

Animals↗
PubMedDate not supplied

Clinical evaluation of crossed-pin versus lateral-pin fixation in displaced supracondylar humerus fractures.

The radiographs and patient charts of 47 children treated with closed reduction and percutaneous pin fixation of displaced supracondylar humerus fractures were reviewed. Twenty-seven fractures were fixed with crossed medial and lateral pins. Twenty fractures were treated with two parallel laterally placed pins. Baumann's angle on the anteroposterior elbow film and the humerocapitellar angle on the lateral elbow film were independently measured by the three authors on initial postoperative films and on films taken at the time of pin removal. No statistically significant differences regarding maintenance of reduction were found when comparing the two fixation groups. There were two complications in the medial pin group (one cubitus varus and one ulnar nerve injury) and none in the lateral-pin group. We conclude that crossed-pin fixation offers no clinically significant advantage over two laterally placed pins in the treatment of supracondylar humerus fractures.

Bone Nails↗