Porphyria cutanea tarda and agricultural pesticides.
Explore the source record for details and available documents.
Agricultural Workers' Diseases↗
Biomedical subjects
A G Collins
Publications and source records attributed to A G Collins.
Magnetic resonance properties of hydrogen: imaging the posterior fossa.
Posterior fossa scans were performed on five healthy volunteers using a nuclear magnetic resonance (NMR) machine constructed by Thorn-EMI Ltd. Three different NMR scanning sequences were used. In the first, a type of saturation-recovery technique was used to produce images strongly dependent on the density of hydrogen nuclei, but with some dependence on the spin-lattice relaxation time (T1). In the second, an inversion-recovery technique was used to produce images with a stronger dependence on the spin-lattice relaxation time. In the third, a spin-echo technique was used to obtain images with a dependence on the spin-spin relaxation time (T2). All three types of NMR image were unaffected by bone artifact. Visualization of brain adjacent to the skull base was obtained without loss of detail due to partial-volume effect from bone. The saturation-recovery images highlighted arteries and veins that were clearly visible without the use of contrast agents. The inversion-recovery images showed remarkable gray-white matter differentiation enabling internal structure to be seen within the brainstem and cerebellum. The trigeminal nerve and ganglion were also seen outside the brain. Experience with the spin-echo technique is limited, but the images at the base of the brain show considerable soft-tissue detail. The NMR images of the posterior fossa in this study were comparable in quality to those obtained from a new rotate-rotate x-ray computed tomography machine and were superior in several respects.
Adult↗
Diazinon and porphyria cutanea tarda.
Cutaneous application of diazinon to rats over a period of 12 weeks gives rise to a condition biochemically indistinguishable from porphyria cutanea tarda. Faecal porphyrin levels are elevated with the appearance of isocoproporphyrin in the faeces. Oral administration of diazinon does not appear to cause any disturbance of porphyrin metabolism.
Administration, Oral↗
Letter: Tinea capitis--a warning.
Explore the source record for details and available documents.
Australia↗
Oil and gas wells--potential polluters of the environment?
Explore the source record for details and available documents.
Environment↗
The significance of moulting in Ecdysozoan evolution.
Three major bilaterian clades first appear in the Early Cambrian fossil record: Deuterostomia, Lophotrochozoa, and Ecdysozoa. The taxa placed in Ecdysozoa are characterized by a moulting habit, unknown in the other major clades. The origin and consequences of moulting are of fundamental importance to the history of the ecdysozoan clade, chiefly because moulting precludes motile ectodermal cilia. Moulting may have originated as an adaptation to permit the enlargement, during growth, of secreted cuticular spines, flanges, and other structures used as ancillary locomotory devices. A combination of phylogenetic and fossil evidence suggests that the early members of these clades were small vermiform paracoelomates that likely lacked indirect-developing planktotrophic larvae. Thus, the evolution of planktotrophic larvae may have been independently achieved at least three times within Bilateria. The nonmoulting clades evolved larvae that swim and feed via ciliated tufts and bands, presumably intercalating these forms within their early developmental systems. Within Ecdysozoa, feeding larvae lacked ciliary feeding tracts and evolved by modification of early instars, employing limbs or setae to generate feeding currents. The setting aside during larval life of cells that give rise to adult features is probably an adaptation associated with metamorphosis.
Animals↗
Defining phyla: evolutionary pathways to metazoan body plans.
Phyla are defined by two sets of criteria, one morphological and the other historical. Molecular evidence permits the grouping of animals into clades and suggests that some groups widely recognized as phyla are paraphyletic, while some may be polyphyletic; the phyletic status of crown phyla is tabulated. Four recent evolutionary scenarios for the origins of metazoan phyla and of supraphyletic clades are assessed in the light of a molecular phylogeny: the trochaea hypothesis of Nielsen; the clonal hypothesis of Dewel; the set-aside cell hypothesis of Davidson et al.; and a benthic hypothesis suggested by the fossil record. It is concluded that a benthic radiation of animals could have supplied the ancestral lineages of all but a few phyla, is consistent with molecular evidence, accords well with fossil evidence, and accounts for some of the difficulties in phylogenetic analyses of phyla based on morphological criteria.
Animal Population Groups↗
Clinical use of rapid T2 weighted partial saturation sequences in MR imaging.
Rapid T2 dependent field echo [partial saturation (PS)] sequences were used in 38 patients with brain tumors, intracerebral hematomas, and cerebral infarction as well as other neurological and abdominal disease. Reduction in the radiofrequency excitation angle (alpha) from 90 to 30 degrees produced an increase in lesion contrast as did change of echo time (TE) from 33 to 59 or 120 ms using repetition time (TR) values in the range of 120-500 ms. The PS sequence showing most lesion contrast was compared with conventional spin echo (SE 1,500/80 and SE 1,500/120) and inversion recovery (IR 1,500/500/44 and IR 1,500/100/44) sequences. Although PS sequences with TE = 39 ms were usually inferior to conventional SE sequences, those with TE = 59 or 120 ms were comparable and in some cases (particularly hematomas) superior. The PS sequences with alpha of approximately 30 degrees, TR of 80-250 ms, and TE of 60-120 ms offer considerable savings in time compared with conventional sequences although more work will be required to explore the limits of this approach and to optimize sequences at different field strengths.
Brain Diseases↗
Four-dimensional chemical shift MR imaging of phosphorus metabolites of normal and diseased human liver.
Four dimensional chemical shift imaging was used to map the relative peak heights of phosphorus metabolites of the liver and overlying skeletal muscle of a normal subject and two patients. The technique provides 31P spectra localised on a voxel-by-voxel basis and may be valuable in mapping heterogeneous structural and metabolic changes in disease.
Adult↗
Use of phosphorus-31 MR spectroscopy to monitor response to chemotherapy in non-Hodgkin lymphoma.
Two patients with non-Hodgkin lymphoma of the femur were examined with 31P magnetic resonance spectroscopy (MRS) and proton magnetic resonance imaging before and during treatment with chemotherapy. Prior to treatment, 31P MRS of the tumor showed that in comparison to normal skeletal muscle, phosphocreatine was reduced, and phosphomonoesters (PME) and phosphodiesters were elevated. The 31P spectrum became similar to that of normal muscle after 40 days of treatment in both cases. Following the initial dose of chemotherapy, an increase in PME relative to adenosine triphosphate was observed within 48 h in one patient. Magnetic resonance showed a change in the soft tissue component of both tumors and 6-12 months later there was no clinical evidence of any recurrence. Magnetic resonance spectroscopy with 31P may prove to be a sensitive technique for monitoring therapeutic response of tumors.
Adult↗
Analysis of the magnitude of susceptibility effects in disease of the brain: implications for MR spectroscopy.
The results of 165 clinical examinations of the brain in which phase mapping was used to display susceptibility effects have been analysed. Significant changes were frequently observed when hemorrhage was a primary or secondary event. A substantial fraction of the examinations, including those of tumor, trauma, hemorrhage, and other patients, showed changes of up to 1 ppm. Spectral interpretation may be made more difficult in many clinical circumstances by susceptibility effects.
Adult↗
Assessment of phase and amplitude effects due to susceptibility variations in MR imaging of the brain.
Susceptibility effects due to the presence of hemorrhage have been observed in a substantial number of patients and are a potential source of artifact in in vivo spectroscopy. The studies so far have concentrated on observations of phase differences, but amplitude variations also exist. This article reviews the degree to which the two are independent and suggests that at least three different pulse sequences are necessary to characterize effects due to local field inhomogeneities arising in clinical studies.
Brain Diseases↗
MR imaging of anisotropically restricted diffusion of water in the nervous system: technical, anatomic, and pathologic considerations.
The use of MR imaging to image anisotropically restricted diffusion (ARD) of water in the nervous system is described. The theoretical basis for the use of the pulsed gradient spin echo sequences is outlined, including an estimate of the range of cell dimensions that can be studied with this technique. The importance of restricted diffusion across myelinated white matter fibre tracts is emphasised and the capacity of MR imaging to demonstrate fibre pathways as a function of their direction is illustrated. Technical developments that have been implemented include 256 x 256 spatial resolution, a wider range of diffusion times Td, and an increased range of diffusion sensitivity parameters b. Effects of these are illustrated together with the use of gradient moment nulling methods, oblique sensitisation, and a smaller set of gradient coils that enable shorter values of echo time to be used with the same value of b. The anatomical basis for ARD imaging is analysed, and association, commissural, and projection fibre tracts are demonstrated in different planes. The published literature on variations of the apparent diffusion coefficient from normal is reviewed and examples where diffusion weighted images revealed information that was not necessarily apparent with conventional sequences are illustrated. These include cases of multiple sclerosis, chronic head injury, progressive multifocal leucoencephalopathy, cerebrovascular disease, astrocytoma, and probable metastases to the brain. Imaging of ARD affords a fascinating conjunction between the microscopic movement of water, the properties of myelinated white matter fibres, gross anatomy of the brain, and changes of the diffusion of water in disease.
Adult↗
Respiratory ordered phase encoding (ROPE): a method for reducing respiratory motion artefacts in MR imaging.
A method of reducing respiratory artefact when using the spin warp technique of magnetic resonance imaging is described. A respiratory signal is used to determine the order in which the rows of the data matrix are measured. The aim is to make the respiratory signal at the time of each phase encoding gradient a slowly varying function of the time integral of the gradient and hence of the row number. Data are collected during each cycle of the imaging sequence; thus the scanning time is not increased.
Humans↗