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D J Atkinson

Publications and source records attributed to D J Atkinson.

35 records · Page 2Linked to original sources
PubMed1990

Segmented turboFLASH: method for breath-hold MR imaging of the liver with flexible contrast.

A method called segmented turboFLASH imaging allows high-resolution, multisection, short-inversion-time (TI) inversion-recovery (STIR), T1- or T2-weighted magnetic resonance (MR) studies of the liver to be completed within a breath-hold interval. The method was applied in a phantom and in 19 patients with hepatic lesions. Sequence comparisons were performed among segmented turboFLASH, single-shot turboFLASH, T1-weighted gradient-echo with ultrashort echo time, and T2-weighted spin-echo (SE) techniques. Signal from fat and liver could be nulled with the segmented turboFLASH method, with TIs of 10 and 300 msec, respectively; signal from these tissues could not be eliminated with the single-shot approach. Signal-difference-to-noise ratios and contrast for the best segmented sequences were comparable with those of the best T2-weighted SE and T1-weighted gradient-echo techniques. It is concluded that it is feasible to obtain breath-hold images with arbitrary tissue contrast by means of segmented turboFLASH imaging. The method may prove helpful for the detection and characterization of hepatic lesions and will likely have applications to other anatomic regions such as the chest and pelvis.

Adenoma, Bile Duct↗
PubMed1990

Flow quantification in the superior sagittal sinus using magnetic resonance.

To date, the intracerebral veins and venous sinuses have not been amenable to noninvasive study. We describe a magnetic resonance (MR) technique using "bolus tracking" for rapid imaging and measurement of cerebral venous flow. We specifically applied the technique to the superior sagittal sinus, but it can be used for evaluation of other cerebral venous structures. In 10 healthy subjects and 21 patients referred for MR brain studies, mean flow was 420 ml/min. There was a significant inverse correlation between blood flow and age. There were dynamic changes in cerebral blood flow (CBF) during hyperventilation and hypercapnia. Since the cerebral cortex drains almost exclusively to the superior sagittal sinus, these flow measurements represent an index of global CBF. MR flow quantification provides a new means for assessing dynamic changes in CBF, and may prove useful for monitoring the effects of various disease processes and pharmaceutical agents on CBF.

Adolescent↗
PubMed1990

MR angiography.

Explore the source record for details and available documents.

Angiography↗
PubMed1989

A monoclonal antibody, Py, distinguishes different classes of hippocampal neurons.

A monoclonal antibody, Py, was produced by immunizing mice with a glycoprotein fraction isolated from 3-week-old rat hippocampus. Py antibodies gave strong immunocytochemical staining of the perikarya and dendrites of large neurons in many areas of the rat brain, including the cerebral cortex, hippocampus, cerebellum, brain stem, and olfactory bulb. Immunoelectron microscopy showed the antigen to be predominantly intracellular, although its presence on the neuronal cell surface was not excluded. The antibody gave differential staining of adult hippocampal neurons, large pyramids of field CA3 being strongly immunoreactive, while CA1 pyramids and the dentate granule cells were unstained. Some interneurons were positive in each of the hippocampal fields. In developing hippocampus, the Py antigen appeared by the middle of the first postnatal week, and the adult pattern of staining was achieved by the end of the second week. Immunoblotting showed the antigen to have a relative mobility of 146 kDa with an additional faint band at 166 kDa. Differential Py staining of neurons was seen in dissociated cultures of embryonic hippocampus and in subdissected hippocampal fragments transplanted into adult host brains. This antibody can therefore be used for identification of hippocampal neurons that have been removed from their normal anatomical context.

Animals↗
PubMed1988

FRODO pulse sequences: a new means of eliminating motion, flow, and wraparound artifacts.

Magnetic resonance images of the spine, chest, abdomen, and pelvis are commonly degraded by ghost artifacts. The authors have developed a new technique named FRODO (Flow and Respiratory artifact Obliteration with Directed Orthogonal pulses) to suppress these artifacts. Signal from tissues responsible for the artifacts is eliminated by use of radio frequency pulses specifically optimized for high selectivity to saturate proton magnetization over one or more independently defined slabs (large rectangular volumes) of tissue. Ghost artifacts from pulsatile flow in the heart and blood vessels, as well as from respiratory motion and swallowing, are suppressed. Additional applications of this technique include elimination of intraluminal signal in blood vessels and suppression of wraparound artifact along the phase-encoding axis. Preliminary clinical experience suggests that the FRODO technique, in conjunction with other flow compensation methods, may provide a definitive solution to the problem of motion in spine imaging. FRODO pulse sequences may also prove useful for imaging of blood vessels, heart, abdomen, and other areas where motion, flow, or wraparound artifacts limit image quality.

Abdomen↗
PubMed1985

Serum factors affect Na+ pump activity and DNA synthesis in cultured cerebellar neural cells.

In neurone-enriched cultures derived from early postnatal rat cerebellum and maintained in serum-free medium, addition of serum (10% FCS) evoked a rapid increase in Na+ pump activity (as measured by ouabain-sensitive 86Rb accumulation) by activation of a Na+/H+ exchanger. This effect did not occur with cultured cerebellar astrocytes. In contrast, exposure to serum increased DNA synthesis ([3H]thymidine incorporation) in both cultured cerebellar astrocytes and in the neurone-enriched cultures. However, in the latter cultures this effect was shown by autoradiography to be due to contaminating astrocytes. Thus, in cultured cerebellar neural cells an enhancement of intracellular Na+ accumulation by serum factors may not be linked to initiation of DNA synthesis. Furthermore, raising intracellular Na+ by ouabain exposure actually decreased neural cellular DNA synthesis.

Animals↗
PubMed1985

Effect of thyroid hormone and serum on the development of Na+, K+-adenosine triphosphatase and associated ion fluxes in cultures from rat brain.

The effect of culture conditions, serum supplementation or chemically defined medium and the influence of thyroid hormone were studied on the development of the Na+, K+-adenosine triphosphatase (Na+,K+-ATPase) and on the intracellular content of K+ and Na+ ions in cultures which either were greatly enriched in a neuronal cell type, the cerebellar granule cells, or contained a mixed population of cells (brain reaggregates). Foetal rat brain reaggregates displayed lower Na+,K+-ATPase activity when cultured in chemically defined medium than in the presence of serum. Supplementation of the serum-free medium with thyroid hormone resulted in a rise in the Na+,K+-ATPase activity and [3H]ouabain binding to levels similar to those found in the cultures grown in the serum-containing medium. Thyroid hormone had no significant effect on the Mg2+-ATPase activity and on the intracellular content of Na+ and K+ ions. In the granule cell-enriched cerebellar surface cultures the Na+,K+-ATPase activity was lower when the cells were grown in chemically defined medium compared with the serum-containing medium, and the intracellular Na+ to K+ ratio was higher. Thyroid hormone had no effect on the Na+,K+-ATPase activity, [3H]ouabain binding or Mg2+-ATPase activity. The hormone also failed to influence ATPase activities in cerebellar astrocytes maintained in chemically defined medium. Although thyroid hormone had no effect on the Na+,K+-ATPase activity of cultured cerebellar granule cells, treatment with the hormone resulted in a decrease in the ratio of intracellular Na+ to K+ ion content. The effect of the hormone on the Na+,K+-pump activity in live cells was therefore tested by estimating ouabain-sensitive 86Rb uptake. This was regulated as in other cell types, by the rate of Na+ entry: the Na+-ionophore monensin trebled the rate of 86Rb uptake, which was also increased (+30-100%) by 10% foetal calf serum, the maximal response being obtained by about 20 min exposure to serum. The effect was completely blocked by the Na+/H+ exchange inhibitor amiloride. The factor(s) in the serum responsible for the regulation of the Na+,K+-pump were, however, not the thyroid hormones, which failed to affect 86Rb uptake. On the basis of comparing thyroid hormone effects on the different cultures studied it was concluded that not every type of neural cell is target of the hormone action during development.

Animals↗
PubMed1984

Effects of thyroid status on presynaptic alpha 2-adrenoceptor function and beta-adrenoceptor binding in the rat brain.

The effect of thyroid status on noradrenergic synaptic function in the mature rat brain was examined by measuring presynaptic alpha 2- and post-synaptic beta-adrenoceptors. Repeated triiodothyronine (T3) administration to rats (100 micrograms/kg X 14 days: hyperthyroid) caused an 18% increase in striatal beta-adrenoceptors as shown by [3H]-dihydroalprenolol binding with no change in membranes from cerebral cortex or hypothalamus. In contrast, hypothyroidism (propylthiouracil, PTU X 14 days) produced significant 12% and 30% reductions in striatal and hypothalamic beta-adrenoceptors respectively with no change in the cerebral cortex. Presynaptic alpha 2-adrenoceptor function was measured in the two dysthyroid states using the clonidine-induced hypoactivity model. Experimental hyperthyroidism increased the degree of clonidine-induced hypoactivity, and suggests increased presynaptic alpha 2-adrenoceptor function compared with control rats, whereas hypothyroidism suppressed presynaptic alpha 2-adrenoceptor function. These results show firstly that changes in thyroid status in the mature rat may produce homeostatic alterations at central noradrenergic synapses as reflected by changes in pre- and post-synaptic adrenoceptor function. Secondly, there appear to be T3-induced changes in beta-adrenoceptors in the striatum where changes in dopaminergic neuronal activity have previously been demonstrated.

Animals↗
PubMed1982

Biochemical development of the human brain. III. Benzodiazepine receptors, free gamma-aminobutyrate (GABA) and other amino acids.

Benzodiazepine receptor binding and the concentration of the free tissue GABA, glutamate, glutamine, aspartate, and 13 other amino acids were estimated in specimens of cerebral cortex and cerebellum taken from normal foetuses and from perinatal and postnatal infants and adults postmortem. Compared with the ontogenetic increase, previously reported, in [3H]muscimol binding, that of [3H]flunitrazepam binding developed more rapidly in the cerebellum and less rapidly in the cerebral cortex. The concentration of GABA in both brain parts increased with age more rapidly than did that of glutamate decarboxylase activity. The overall pattern of developmental changes in the amino acid concentrations in the human brain showed many similarities with those reported in the brains of experimental animals. The concentration of the amino acids associated with the tricarboxylic acid cycle increased with age. Although the general downward trend in the levels of essential amino acids (with the exception of Met) was also evident in the human cerebral cortex, this was not the case in the cerebellum where the concentrations of most amino acids were relatively low in the foetus whereas the concentrations exceeded the cerebral cortical levels in the adult.

Adult↗
PubMed1981

Biochemical development of the human brain. II. Some parameters of the GABA-ergic system.

The development of the gamma-aminobutyrate (GABA)-ergic system in the human cerebral cortex and cerebellum was studied in post mortem specimens, by estimating the activity of glutamate decarboxylase (GAD) and the binding capacity for muscimol as markers of GABA-ergic nerve terminals and GABA receptors respectively. The age periods studied were as follows (number of specimens in parentheses): fetal period, 17--24 and 28 weeks, gestational age (GA) (15); perinatal period, 26--42 weeks GA (9); postnatal period, 43--56 and 74 weeks GA (11); adult life, 26, 47, 57--73 years (9). Total protein and DNA were estimated in all specimens. Differences between the cerebral cortex and the cerebellum in the ontogenesis of the GABA-ergic system were revealed. In the cerebral cortex, GAD-specific activity increased progressively during development, but at term had only reached approximately 20% of the adult value, and the trend in the postnatal specimens indicated that the adult level is not reached until some time after 60 weeks GA. The concentration of muscimol binding sites, on the other hand, rose more rapidly than GAD activity with age in the cerebral cortex, attaining adult values by 60 weeks GA and being already at term approximately 45% of the mean adult figure. In the cerebellum, the relative development of pre- and postsynaptic markers was the reverse of that in the cerebral cortex: GAD specific activity had reached the adult value by 60 weeks GA and approximately 40% of this adult level was attained at term, while the muscimol binding site concentration was only about 10% of the adult value at term and was still increasing at 60 weeks GA. The affinity of the receptor for [3H]-muscimol did not change during development, and was the same in cerebral cortex and cerebellum.

Adult↗
PubMed1978

Effect of undernutrition on the regional development of transmitter enzymes: glutamate decarboxylase and choline acetyltransferase.

The effect of undernutrition on the activity of glutamate decarboxylase (GAD) and choline acetyltransferase (ChAc) (markers for the GABA-ergic and the cholinergic transmitter system, respectively) was studied in various parts of the rat brain at the age of 10, 15 and 21 days, and at day 54 following 33 days of rehabilitation. The brain regions investigated were the olfactory bulbs, cerebellum, pons-medulla, hypothalamus, colliculi, cerebral cortex hippocampus and the residual brain. Undernutrition resulted in a marked retardation of the developmental rise of the activities of both enzymes, expressed in terms of either total brain part or unit weight or protein. The effect diminished with age even during the period of nutritional deprivation. In most brain regions the enzyme activities were restored to normal after rehabilitation. In the cerebral cortex the total activity of both enzymes was persistently reduced, although the concentration of GAD exceeded the control levels. A negative correlation was manifested between the activities of GAD and ChAc in the different brain parts (except the cerebellum) during development. The correlation became significant by day 21 in the controls, but only after postweaning rehabilitation of the undernourished rats. The results showed therefore that undernutrition caused a reversible retardation in the development of these two transmitter enzymes, and they suggested that even the balance of the GABA-ergic and cholinergic systems throughout the brain can be restored to normal by rehabilitation.

Animals↗
PubMed1975

Effect of undernutrition on metabolic compartmentation of glutamate and on the incorporation of [14C] leucine into protein in the developing rat brain.

The effect of undernutrition on the rate of protein synthesis and the development of metabolic compartmentation of glutamate in the brain was investigated by using [U -14 C] leucine as precursor. In the brain of normal rats the incorporation rate of [14C] leucine into protein was at a maximum during the 3rd week after birth, but in the undernourished animal this rate was markedly lower. The biochemical maturation of the brain, followed in terms of the age-dependent increase in the glutamine/glutamate specific radioactivity ratio, was severly retarded in the undernourished animals, mainly as a result of a marked depression in the conversion of leucine carbon into glutamine. However these biochemical effects of undernutrition were reversible: on rehabilitation from Day 21-35 the rate of conversion of leucine carbon, both into proteins and glutamate and glutamine, was restored to normal.

Animals↗
PubMedDate not supplied

Strategies to improve contrast in turboFLASH imaging: reordered phase encoding and k-space segmentation.

TurboFLASH (fast low-angle shot) sequences enable the acquisition of an image in a fraction of a second. However, unique to T1-weighted ultrafast imaging, the magnetization variation during image acquisition can produce artifacts along the phase-encoding direction. In this study, the signal behavior and nature of these artifacts were analyzed with various acquisition schemes to improve image contrast. The magnetization variation during image acquisition and its filtering effect on the image were simulated for three different approaches to T1-weighted turboFLASH imaging: standard turboFLASH with (a) monotonically ascending phase-encoding steps, (b) reordered phase encoding, and (c) k-space segmentation. Each of the modified data acquisition schemes has advantages. However, for subsecond imaging, reordered phase encoding produced improved image contrast over that of standard turboFLASH, and segmented k-space imaging gave superior tissue contrast compared with that of both standard and reordered turboFLASH, with imaging time that permits breath-hold studies.

Computer Simulation↗
PubMedDate not supplied

Three-dimensional MR imaging and display of intracranial disease: improvements with the MP-RAGE sequence and gadolinium.

Three-dimensional (3D) image rendering was performed in 14 patients who had undergone magnetic resonance (MR) imaging for focal brain lesions. The MR study included the magnetization-prepared rapid gradient-echo (MP-RAGE) sequence with 64 or 128 partitions. Resultant contiguous sections 2.5 or 1.25 mm thick, respectively, were obtained. Images were acquired before and after administration of gadopentetate dimeglumine. Resultant 3D data sets were processed on a commercially available workstation. Correlative surgical observation was performed in four cases. All data sets were successfully processed into 3D images. The precontrast images proved superior to gadolinium-enhanced images for brain surface rendering. Postcontrast images proved superior for reconstruction of tumors and vascular structures. The 64-partition data set proved sufficient for all postprocessing. Coronal orientation was preferred to sagittal orientation for surface rendering because it provided optimal orthogonal orientation of sulcal and gyral brain surface features. Three-dimensional rendition allowed easy superposition of lesion, brain, vessels, and scalp features--all useful for surgical planning. The central sulcus was easily recognized in the midline partitions and traced mediolaterally for projection on the cortical surface. MP-RAGE provides a 3D data set that can be obtained in just over 3 minutes, from which clinically useful 3D renderings are possible. The rapidity of acquisition and capability for 3D rendering provides additional clinical utility.

Adolescent↗
PubMedDate not supplied

First pass MRA of the abdomen: ultrafast, non-breath-hold time-of-flight imaging using Gd-DTPA bolus.

The authors describe a new fast imaging sequence that can produce projection angiograms of the abdominal vessels at a rate of 2 to 3 frames per second. The result is a versatile imaging technique that can track the arrival of a bolus of contrast in major vessels. With very fast data acquisition, gross patient motion is not a problem, and routine vascular projection studies may be performed without the need for breath-holding. This method is compatible with later high-resolution three-dimensional gradient echo studies using contrast agents and may, in fact, be used as an accurate timing protocol to gauge the arrival time of contrast in various segments of the abdominal vessels. Compared with echo planar imaging, this method has the advantages of avoiding susceptibility artifacts and depicting retroperitoneum and other abdominal fat-containing landmarks and does not require extensive hardware modifications for a clinical system.

Abdomen↗