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Biomedical subjects

D L Daniels

Publications and source records attributed to D L Daniels.

At least 55 records · Page 3Linked to original sources
PubMed1990

The complete AvrII restriction map of the Escherichia coli genome and comparisons of several laboratory strains.

The complete 13 site AvrII restriction map of the genome of E coli strain MG1655 is presented and compared with several other E. coli strains. The map was determined primarily by isolating individual AvrII fragments from pulsed-field gels, and hybridizing these large probes to a battery of mapped E. coli clones in lambda vectors. AvrII restriction patterns for eight other laboratory strains were determined and maps for seven of them deduced from the gel and comparisons between the strain genotypes, the MG1655 map, and AvrII sites in E. coli sequences taken from Genbank.

DNA Restriction Enzymes↗
PubMed1990

The distribution of restriction enzyme sites in Escherichia coli.

A statistical analysis of physical map data for eight restriction enzymes covering nearly the entire genome of E. coli is presented. The methods of analysis are based on a top-down modeling approach which requires no knowledge of the statistical properties of the base sequence. For most enzymes, the distribution of mapped sites is found to be fairly homogeneous. Some heterogeneity in the distribution of sites is observed for the enzymes Pstl and HindIII. In addition, BamHI sites are found to be more evenly dispersed than we would expect for random placement and we speculate on a possible mechanism. A consistent departure from a uniform distribution, observed for each of the eight enzymes, is found to be due to a lack of closely spaced sites. We conclude from our analysis that this departure can be accounted for by deficiencies in the physical map data rather than non-random placement of actual restriction sites. Estimates of the numbers of sites missing from the map are given, based both on the map data itself and on the site frequencies in a sample of sequenced E. coli DNA. We conclude that 5 to 15% of the mapped sites represent multiple sites in the DNA sequence.

DNA, Bacterial↗
PubMed1990

Facial surface coil for MR imaging.

A local-reception counter-rotating-current coil for magnetic resonance imaging at 1.5 T was developed. It consists of two parallel coaxial racetrack-shaped loops. The planes of the loops are orthogonal to the surface of the body, and the space between the loops is open. The separation between the loops allows the device to fit over the nose and mouth for oral-maxillofacial imaging without the threat of occlusion to the patient's air passages. The sensitivity of this coil is similar to that of conventional surface coils of the same dimensions. The two active current elements conform to other anatomic objects including the eyes and anterior portion of the neck.

Face↗
PubMed1990

The use of gadolinium-enhanced magnetic resonance imaging to determine lesion site in traumatic facial paralysis.

Gadolinium-enhanced magnetic resonance imaging has been used to evaluate 20 patients with surgically confirmed facial nerve lesions. When the nerve could be seen, gadolinium-enhanced magnetic resonance imaging accurately revealed the lesion site as well as the known extent, which in some cases was not predicted by topognostic testing. This technique appears to provide accurate lesion-site testing and may have importance in surgical planning. Currently used topognostic tests of facial nerve function are frequently inaccurate and can only determine the most proximal lesion site when there are multiple or extensive lesions. The focal nerve enhancement seen in nerve injury, globally increased signal intensity within the temporal bone after trauma, and increased signal intensity within the dura after surgery can occasionally mask nerve lesions and may be confused with tumors.

Adult↗
PubMed1990

MR imaging of optic nerve lesions: value of gadopentetate dimeglumine and fat-suppression technique.

Eleven patients with known or suspected optic nerve lesions and eight normal subjects were examined with spin-echo technique at 1.5 T with unenhanced T1-weighted imaging, IV gadopentetate-dimeglumine-enhanced T1-weighted imaging, and enhanced T1-weighted imaging with fat suppression. Two pathologically proved and four presumed optic nerve meningiomas demonstrated significant enhancement and were best seen with the fat-suppression technique. None of the three presumed optic nerve gliomas nor the optic nerves of normal subjects demonstrated qualitative enhancement. We conclude that the use of a fat-suppression technique with gadopentetate dimeglumine enhancement improves delineation of enhancing optic nerve lesions. This technique should be useful for evaluating other anatomic regions where enhancing tissue marginates fat.

Adipose Tissue↗
PubMed1990

A case-control study of the impact of improved sanitation on diarrhoea morbidity in Lesotho.

A health impact evaluation of the Rural Sanitation Pilot Project in Mohale's Hoek district, Lesotho, was conducted from October 1987 to September 1988. A clinic-based case-control design was used to investigate the impact of improved sanitation on diarrhoea morbidity in young children. The results indicate that under-5-year-olds from households with a latrine may experience 24% fewer episodes of diarrhoea than such children from households without a latrine (odds ratio = 0.76; 95% confidence interval, 0.58-1.01). The impact of latrines on diarrhoea was greater in those households that used more water, practised better personal hygiene, and where the mothers had a higher level of education or worked outside the home. In common with studies conducted in Malawi, Philippines, and Sri Lanka, little evidence was found that the relationship between latrine ownership and diarrhoea was confounded by socioeconomic status or environmental variables. For a sample of cases and controls, data on exposure status (presence or absence of a latrine) that were collected by interview at the clinics agreed closely with those obtained by observation during a home visit.

Case-Control Studies↗
PubMed1989

Gradient recalled echo MR imaging of superior sagittal sinus occlusion.

With T1-weighted gradient recalled echo (GRE) MR images and flow compensation, we studied the superior sagittal sinus in 3 normal volunteers and 3 patients with sinus occlusion. In these images, sites of patency of the superior sagittal sinus were identified due to the high signal intensity of the normal sinus. Tumor invading the sinus was nearly isointense with cerebral gray matter. T1-weighted GRE imaging proves to be an effective technique to evaluate sinus blood flow.

Cerebrovascular Circulation↗
PubMed1989

The use of nutritional status as a second outcome measure in case-control studies of environmental risk factors for diarrhoeal diseases.

Case-control studies are typically used to study the effect of several factors on the risk/incidence rate of a single disease. This paper describes a particular situation in which it is of interest to study the effect of a factor--improved sanitation facilities--on the risk/incidence rate of two 'diseases'--the incidence rate of diarrhoea and the risk of undernutrition. The conditions under which it is valid to perform an analysis of the association between the risk factor (unimproved sanitation) and a second outcome variable (undernutrition) are examined. If the effect of exposure status (improved/unimproved sanitation facilities) on the propensity to report an episode of diarrhoea is independent of the effect of nutritional status it appears that such an analysis may be valid. There must also be no interaction between the risk factor (unimproved sanitation) and the second outcome (undernutrition) with respect to their effects as risk factors for the first outcome variable (diarrhoea incidence rate).

Bangladesh↗
PubMed1989

MR imaging of facial nerve enhancement in Bell palsy or after temporal bone surgery.

The authors evaluated magnetic resonance (MR) images obtained with intravenously administered gadolinium in ten patients who had facial paralysis and no facial nerve tumor. In patients with either Bell palsy (four patients) or facial paralysis after temporal bone surgery (six patients), intratemporal facial nerve enhancement was seen. Facial nerve enhancement on MR images proved to be a nonspecific finding.

Facial Nerve↗
PubMed1989

Gadolinium-enhanced magnetic resonance imaging in temporal bone lesions.

A 2-year experience with an enhancement agent in magnetic resonance imaging (MRI) is examined through case presentations. Characteristics of the agent Gadolinium DTPA/Dimeglumin are reviewed. Radiographic capabilities in enhanced versus unenhanced MRI are compared. Temporal bone lesions, including acoustic neuromas and facial nerve neuromas, are presented. Recent experience with facial nerve enhancement in Bell's palsy is also presented. Greater accuracy in defining small temporal bone lesions and increased delineation of facial nerve involvement appear to be significant benefits with enhanced MRI.

Adult↗
PubMed1989

Contrast enhancement in spinal MR imaging.

We evaluated 44 patients with suspected spinal tumors or previous laminectomies with gadolinium-DTPA MR imaging in order to characterize the enhancement in normal, postoperative, and neoplastic intraspinal tissue. Using the signal intensity of CSF as an internal control, we calculated the percentage increase in signal intensity from pre- to postgadolinium studies. Tumors (astrocytoma, ependymoma, schwannoma) enhanced 70-350%; epidural scar, normal epidural venous plexus, and dorsal root ganglion enhanced up to 200%. Contrast enhancement does not per se distinguish neoplastic from normal tissue. Enhancement with gadolinium-DTPA appeared to increase the conspicuousness of intramedullary tumors but not intraosseous metastases. We believe that gadolinium-enhanced MR imaging is a valuable adjunct to routine MR imaging in the evaluation of intraspinal neoplastic processes and may be useful in delineating normal and postoperative structures in the spinal canal.

Contrast Media↗
PubMed1988

The effect of patient positioning on MR imaging of the internal auditory canal.

Identification of individual cranial nerves and complete exclusion of tumor in the internal auditory canal may be difficult with MR, especially in imperfectly positioned patients. MR studies of the temporal bones in patients and in normal volunteers positioned non-rotated or canted were correlated with corresponding cryomicrotomic sections. Especially in axial images, oblique sectioning of cranial nerves VII and VIII may cause difficulty in identifying individual nerves. A combination of axial and coronal short TR and TE images can be used to confidently exclude intracanalicular tumor in most cases.

Facial Nerve↗
PubMed1988

Insulin stimulates the dephosphorylation and activation of acetyl-CoA carboxylase.

The mechanism underlying the ability of insulin to acutely activate acetyl-CoA carboxylase [acetyl-CoA: carbon-dioxide ligase (ADP-forming), EC 6.4.1.2; AcCoA-Case] has been examined in Fao Reuber hepatoma cells. Insulin promotes the rapid activation of AcCoACase, as measured in cell lysates, and this stimulation persists to the same degree after isolation of AcCoACase by avidin-Sepharose chromatography. The insulin-stimulated enzyme, as compared with control enzyme, exhibits an increase in both citrate-independent and -dependent activity and a decrease in the Ka for citrate. Direct examination of the phosphorylation state of isolated 32P-labeled AcCoACase after insulin exposure reveals a marked decrease in total enzyme phosphorylation coincident with activation. The dephosphorylation due to insulin appears to be restricted to the phosphorylation sites previously shown to regulate AcCoACase activity. All of these effects of insulin are mimicked by a low molecular weight autocrine factor, tentatively identified as an oligosaccharide, present in conditioned medium of hepatoma cells. These data suggest that insulin may activate AcCoACase by inhibiting the activity of protein kinase(s) or stimulating the activity of protein phosphatase(s) that control the phosphorylation state of the enzyme.

Acetyl-CoA Carboxylase↗
PubMed1988

Cervical neural foramina: correlative anatomic and MR imaging study.

Accurate diagnosis of diseases affecting the cervical neural foramina with magnetic resonance (MR) imaging requires an appreciation of the normal anatomic appearance of the foramen. The MR appearance of the foramen was studied in cadavers and healthy volunteers and was correlated with cadaver cryomicrotome sections. With gradient-echo techniques, foraminal soft tissues are highlighted relative to adjacent bone, making gradient-echo images valuable for evaluating the overall size and contents of the neural foramina. Intravenously administered gadolinium DTPA produces enhancement of all foraminal soft tissues, including the dorsal root ganglion. The nerve roots do not enhance with Gd-DTPA. Gradient-echo pulse sequences and intravenous use of Gd-DTPA represent promising techniques for the evaluation of the cervical foramina.

Cervical Vertebrae↗
PubMed1988

MR imaging of the cavernous sinus: value of spin echo and gradient recalled echo images.

A detailed evaluation of the MR appearance of the pituitary gland-cavernous sinus junction has not been described. In a series of coronal T1-weighted spin echo images without and with IV gadolinium, we noted the variable size and signal intensity of cavernous venous spaces adjacent to the pituitary gland and the inconsistent visualization of the dural membrane just lateral to the gland. Correlation of coronal T1-weighted spin echo and gradient recalled echo images (the latter with high-signal-intensity vascular structures) proved to be an effective means of identifying cavernous venous spaces, connective tissue and cranial nerves, and the lateral margins of the pituitary gland, and of differentiating tumor tissue from cavernous venous spaces. Further work is needed to develop criteria to distinguish cavernous sinus compression from actual tumor invasion.

Adenoma↗
PubMed1988

Characteristic features of MR truncation artifacts.

Truncation artifacts occur in MR imaging because Fourier transforms are used to process MR signal data. These artifacts may alter the intensity, shape, and anatomic detail of structures in the spine. Ring artifacts (Gibb phenomenon) occurring near highly contrasting interfaces represent but one manifestation of truncation artifacts visible on MR images. We review truncation phenomena by providing graphic and phantom models. Ways in which truncation artifacts alter the MR appearance of the spine are discussed. We found that truncation phenomena are reduced most effectively by using a 256 x 256 matrix whenever feasible.

Computer Simulation↗