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Biomedical subjects

D J Thomas

Publications and source records attributed to D J Thomas.

At least 217 records · Page 12Linked to original sources
PubMed1983

Nuclear magnetic resonance imaging of posterior fossa tumors.

The results of nuclear magnetic resonance (NMR) examinations in 26 patients with histologic (15 cases) or clinical (11 cases) diagnoses of tumors within the posterior fossa were reviewed and compared with x-ray computed tomography (CT). Most tumors displayed an increase in T1 and T2 relative to brain. All seven benign tumors were seen with both CT and NMR, although one of these cases initially was misdiagnosed on the basis of the CT findings. The extent of these tumors was equally well shown with CT and NMR in three cases but was demonstrated better by NMR in four. Calcification was seen with CT but not with NMR in two of these patients. All 19 malignant tumors were demonstrated with NMR. Two of these were not seen with CT. In 12 patients minimal changes consisting of a poorly defined low-attenuation are or minor displacement of the fourth ventricle were noted with CT, although much more extensive changes were seen with NMR. In three patients the changes were equally well shown with both techniques. In the remaining two cases, the extent of the tumor was defined more accurately with contrast-enhanced CT, where the margin between tumor and surrounding edema was better seen than with NMR. Mass effects were better demonstrated with NMR in 13 patients and equally well shown in six. Bony erosion was better demonstrated with CT in two cases. Hydrocephalus with periventricular edema was seen in five patients; in each it was more clearly demonstrated with NMR. The NMR diagnosis of tumors is discussed and relevant new developments are summarized.

Brain Neoplasms↗
PubMed1983

Clinical NMR imaging of the brain in children: normal and neurologic disease.

The results of initial clinical nuclear magnetic resonance imaging of the brain in eight normal and 52 children with a wide variety of neurologic diseases were reviewed. The high level of gray-white matter contrast available with inversion-recovery sequences provided a basis for visualizing normal myelination as well as delays or deficits in this process. The appearances seen in cases of parenchymal hemorrhage, cerebral infarction, and porencephalic cysts are described. Ventricular enlargement was readily identified and marginal edema was demonstrated with spin-echo sequences. Abnormalities were seen in cerebral palsy, congenital malformations, Hallervorden-Spatz disease, aminoaciduria, and meningitis. Space-occupying lesions were identified by virtue of their increased relaxation times and mass effects. Nuclear magnetic resonance imaging has considerable potential in pediatric neuroradiologic practice, in some conditions supplying information not available by computed tomography or sonography.

Brain↗
PubMed1983

Evoked potential studies of the effects of impact acceleration on the motor nervous system.

The initial results of a continuing investigation into the effects of various levels of impact acceleration on the functional integrity of the motor nervous system are summarized. The results are based on the measurement of alterations in neural transmission along the motor pathway of the Rhesus monkey as revealed by latency and amplitude changes in the motor pathway evoked potential (EP) following the delivery of various levels of impact acceleration to a test vehicle. The EPs were produced by electrical stimulation of and recording from the motor pathway of experimental animals subjected to -Y (lateral impact) acceleration and animals subjected to -X (frontal impact) acceleration. High resolution latency and amplitude measures of the EP recorded from these animals before and after impact were tracked so that the time course of recovery of nerve propagation following impact could be accurately assessed. Analysis of these EP measures revealed that the time course of recovery to preimpact values is directly related to the intensity of the acceleration impulse delivered to the test vehicle.

Acceleration↗
PubMed1982

NMR imaging of the brain using spin-echo sequences.

Eight normal volunteers and 32 patients with a variety of neurological disease were studied with a nuclear magnetic resonance (NMR) scanner using repeated free induction decay (RFID), inversion-recovery (IR) and spin-echo (SE) sequences. The results were compared with X-ray computed tomography (CT). RFID sequences which produce images that reflect changes in proton density displayed very little grey-white matter contrast and relatively small changes in disease. IR sequences which produce images that are dependent on T1 showed a high level of grey-white matter contrast and demonstrated changes in a variety of pathological processes. Although SE scans, which have a strong T2 dependence, had shown no abnormality in previous studies of patients with neurological disease, sequences of this type with longer values of tau displayed abnormalities in cerebral infarction, haemorrhage, herpes encephalitis, multiple sclerosis, cerebral oedema, hydrocephalus, tumours and Wilson's disease. All of these conditions were associated with an increase in T2. Abnormalities were demonstrated in cases of multiple sclerosis and brainstem infarction with NMR scans where no abnormality was seen with CT. More extensive changes were seen with NMR in cases of hemisphere infarction, systemic lupus erythematosis, herpes encephalitis, hydrocephalus (periventricular oedema) and Sturge-Weber disease. The margin between malignant tumour and surrounding oedema was better defined with contrast enhanced CT in four of eight malignant tumours, equally well defined in one, and better defined with NMR in three cases. NMR spin-echo sequences provide a sensitive technique for detecting abnormalities in a variety of neurological disease.

Adult↗
PubMed1982

Clinical NMR imaging of the brain: 140 cases.

Cranial nuclear magnetic resonance (NMR) scans were performed on 13 healthy volunteers and 140 patients with a broad spectrum of neurologic disease and compared with x-ray computed tomography (CT) scans. The NMR scans included a variety of sequences reflecting proton density, blood flow, T1, and T2 as well as transverse, sagittal, and coronal images. White matter, gray matter, and cerebrospinal fluid were clearly distinguished in the normal brain with inversion-recovery (IR) sequences, and normal progressive myelination was demonstrated in infants and children. Acute hemorrhages displayed short T1 values, but other pathologic processes such as infarction, infection, demyelination, edema, and malignancy were associated with long T1 values. Cysts had very long T1 values (about that of cerebrospinal fluid). Spin-echo (SE) sequences showed increased values of T2 in a variety of conditions and highlighted lesions against the relatively featureless background of the remaining brain. With inversion-recovery scans, different stages of infarction were recognized in the hemispheres. NMR was more useful than CT in demonstrating brainstem infarction. The white matter lesions in demyelinating diseases were well demonstrated with NMR scans. Many more lesions were observed in multiple sclerosis with NMR than with CT. Benign tumors were well seen and usually had shorter T1 values than malignant tumors. Mass effects from tumors were generally better demonstrated with NMR than with CT, including more subtle mass effects such as displacement of the external capsule. Abnormalities were seen in diseases of the basal ganglia, including marked atrophy of the head of the caudate nucleus in Huntington chorea. Advantages of NMR imaging include the high level of gray-white matter contrast, lack of bone artifact, variety of possible sequences, transverse, sagittal, and coronal imaging, sensitivity to pathologic change, and lack of known hazard. Disadvantages include lack of bone detail, limited spatial resolution, lack of contrast agents, and cost. Promising directions for future clinical research include developmental neurology, tissue characterization with T1 and T2, assessment of blood flow, and the development of contrast agents. Much more detailed evaluation will be required, but NMR seems to be a potentially important addition to existing techniques of neurologic diagnosis.

Adolescent↗
PubMed1981

Effect of triethyl tin on myelination in the developing rat.

Myelinogenesis in developing rats was studied following chronic dosing with triethyl tin (TET), at a level of 1.0 mg TET/kg body wt/day. Experiments included starved controls with body weights depressed by 17 to 40% to equal those of the TET-treated groups. Rats at ages of 16, 21, and 30 days showed decreases relative to well-nourished controls in body weight, forebrain weight, myelin yield, cerebroside level, and specific activity of brain 2',3'-cyclic nucleotide-3'-phosphohydrolase when dosed with TET. At 30 days, myelin and cerebroside yields were reduced by approximately 55%, while CNP activity was reduced by less than 20%. No differences in the forebrain myelin protein composition between control, starved, and TET animals were noted. The rate of myelin protein synthesis relative to brain total protein (assayed by incorporation of intracranially injected [3H]glycine into brain homogenate and myelin proteins) was decreased in the TET rats in proportion to the decreased yield of myelin, but no particular myelin protein was preferentially affected. Matching starved controls exhibited similar body weight decreases, less pronounced forebrain weight decreases, and little or no decrease in myelin concentration. There was a relative increase in the myelin protein synthesis rate in the starved rats, indicating preferential utilization of limited protein precursors for myelin protein synthesis. Spinal cord myelin was also decreased in the TET rats, but less severely than in the forebrain. At all ages optic, but not sciatic, nerves showed decreases in myelin concentration with TET treatment. We conclude that TET inhibits forebrain growth and CNS myelination more severely than can be accounted for by a general metabolic insult.

Animals↗
PubMed1981

Factors predisposing to the development of progressive massive fibrosis in coal miners.

Altogether 238 759 miners employed by the National Coal Board were examined in the third of the Board's radiological surveys from 1969 to 1973 inclusive. Excluding those diagnosed as having progressive massive fibrosis (PMF) on that occasion, 210 847 were in collieries still operating at the time of the fourth survey four to five years later 132 728 attended for radiography at the same colliery on the second occasion, and were used to study the attack rate of PMF. In all groups in the age range 35-54 and having category 2 simple pneumoconiosis (SPN) or less, 80% or more had a second radiograph. It was found that the probability of developing PMF increased sharply with rising category of SPN; however, half the cases occurred in men having SPN categories 0 or 1, who were in the majority. Current coalface work had no significant effect on the attack rate. Age increased the attack rate of PMF within each major SPN category (0, 1, 2, and 3), especially the higher categories. All or part of this effect may have been due to the fact that SPN in younger men with categories 1 and 2 tends to lie in the lower range within these categories. Similarly, a lower distribution of SPN within each category associated with a low overall local prevalence may account wholly or in part for the great difference between the attack rates of PMF supervening on each category of SPN in Scotland and South Wales. The rank (quality) of coal mined had no effect on the attack rate.

Adult↗
PubMed1981

Modality effects in short term recognition memory.

Retention was assessed using a four-alternative recognition test in a modified Brown-Peterson paradigm. Performance decreased with the length of the distraction interval at a faster rate when the test modality (auditory or visual) did not match the presentation modality than when test and presentation modalities did match. These results, which were replicated in a second experiment, were interpreted in terms of a dual-access model of the recognition process and a feature conception of memory codes. Also, in Experiment 1, modality-specific encoding was not circumvented by dual-modality presentation (auditory plus visual): dual-modality presentation resulted in performance comparable to that observed following visual presentation. When subjects were instructed to attend to both modalities equally in Experiment 2, the pattern of results reflected a corresponding shift in attentional bias but modality-dependent encoding was circumvented only partially. This result was interpreted as being inconsistent with either the notion of modality-specific processing capacities or dual-code theory.

Adult↗
PubMed1980

Effect of high haematocrit on alertness.

Patients with high-normal or above-normal haematocrit were found to have impaired alertness when compared with a control group matched for age and occupation. On retesting the controls had improved alertness scores attributable to a practice effect; but the patients, when retested after reduction of haematocrit by venesection, had improved significantly more than the controls. Improvement in alertness correlated very well with the increase in cerebral blood flow which followed venesection. Levels of venous haematocrit that are generally accepted as normal may not necessarily be optimum.

Adult↗
PubMed1980

Effect of inorganic lead exposure on myelination in the rat.

The effect of defined lead burdens on myelination of the central and peripheral nervous systems was studied in neonatal Long-Evans rats. Pups were exposed to inorganic lead (100 or 400 mg Pb as lead acetate/kg body wt/day by gastric intubation) from day 2 following birth to 30 days of age. Accumulation of myelin in forebrain was not affected by the 100-mg dosage, but at the 400mg/kg dosage level, myelin accumulation was reduced by approximately 42% on a per gram forebrain basis relative to vehicle-intubated animals. The deficit was over 50% on a per forebrain basis, since there was also a slight reduction in brain weight. This lead effect was observed at both 15 and 30 days of age. Accumulation of myelin in optic nerve (determined on the basis of proteolipid protein concentration) was also reduced by 30% relative to controls by this dosage level. However, myelination in sciatic nerve (determined on the basis of Po protein concentration) was not affected by this exposure regimen. Myelin deficits were greater than could be accounted for by undernutrition secondary to lead exposure and were not due to a developmental delay in the onset of myelination.

Animals↗
PubMed1980

Preservation of autoregulation of cerebral blood flow in autonomic failure.

Cerebral blood flow (CBF) measurements have been made at systolic pressures between 40 and 170 mm Hg in 8 patients with chronic autonomic failure and widespread sympathetic efferent defects. Hypotension was produced by head up tilt. Cerebral autoregulation was preserved over a wide range and only failed at a systolic pressure close to 60 mm Hg, which is below the level at which it fails in normal subjects. Therefore, although autoregulation is probably mediated largely by local myogenic factors, its lower limit appears to be reduced by defective sympathetic function. These findings help to explain the remarkable tolerance of severe postural hypotension in autonomic failure.

Adult↗