Posterior view imaging in pulmonary embolism.
Explore the source record for details and available documents.
Humans↗
Biomedical subjects
C J Gibson
Publications and source records attributed to C J Gibson.
The practice of ultraviolet phototherapy in the United Kingdom.
A survey, using a postal questionnaire, was carried out to examine the current practice of UVB phototherapy in dermatology centres in the U.K. The questionnaire was sent to 115 dermatology departments, and sought information regarding the type and age of each machine used for ultraviolet B (UVB) phototherapy, methods of prescribing, recording and terminating patient exposure, and the skin conditions treated. Completed questionnaires were received from 87 of the 115 centres, giving a response rate of 76%. The survey showed that an appreciable number of U.K. phototherapy centres are using equipment which is both old, and suboptimal in producing a therapeutic response. There appeared to be a wide variation in the approach to phototherapy, both in terms of prescribing initial and incremental exposure, and in terminating treatment. The findings suggest that effectiveness and efficiency might be improved, and the risk/benefit ratio of phototherapy further reduced, by some rationalization of treatment protocols.
Dermatology↗
Chromogranin A inhibits retinal dopamine release.
Chromogranin A (CGA), a peripherally active prohormone, is a soluble component in the secretory granules of many endocrine tissues and is cosecreted with their peptide or amine hormones. Using an antibody prepared against purified rat adrenal CGA, immunostaining was localized to the inner and outer plexiform layers of the rat retina and to selected ganglion cells. Exogenous CGA (purified from human adrenals) when applied to perfused rat retina potently inhibited the potassium-induced release of endogenous dopamine (DA). This action was dose-dependent, with an IC50 of 3 nM; at 100 nM CGA retinal DA release was completely abolished.
Animals↗
Rapid filtering of large medical images using one-dimensional convolution kernels.
Many image enhancement algorithms can be implemented by convoluting the image with a predefined kernel function. A class of such functions is identified which has the property that a two-dimensional convolution can be exactly implemented using two successive one-dimensional convolutions along the rows and columns of the image. This leads to a simple and rapid algorithm for image enhancement, which can be applied to implement both low pass and high pass filters. The technique enables large convolution masks to be used without excessive computation time and without the need for large intermediate storage arrays. This approach facilitates the interactive processing of high resolution digital medical images.
Algorithms↗
Tyrosine augments dopamine release in stimulated rat retina.
Endogenous dopamine (DA) release was measured in perfused rat retinae. Perfusion with elevated potassium (40 mM K) resulted in a 5-6-fold increase in DA release over baseline or 11.6 +/- 0.9% of final tissue DA content. When the selective DA D2 receptor agonist quinpirole was added to the perfusion medium (at 1 and 10 microM), K-stimulated DA release was significant decreased compared to controls (to 7.0 +/- 1.6 and 6.14 +/- 1.4%, respectively). Addition of the D2 antagonist (+/-)-sulpiride (10 microM) significantly increased DA release to 19.1 +/- 1.3%. DA could be released with successive pulses of K; an initial 10 min pulse resulted in a 4-5-fold increase in endogenous DA release over basal levels or 11.4% of the final retinal tissue DA content and a 3-fold increase (a 9.3% fractional release) upon a second K stimulation given 50 min later. The ratio of stimulated DA release during the two K pulses was 0.82 +/- 0.04. When L-tyrosine (100 microM) was included in the medium throughout the perfusion, K2/K1 was increased to 1.14 +/- 0.13. Both tissue DA level and release were decreased by the tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine (AMPT). At 10 microM AMPT K-stimulated DA release was reduced by 50% during the first pulse and completely abolished during the second K pulse. At 100 microM both basal and K-stimulated release were significantly reduced. Exposure of dark-adapted retinae to light in L-tyrosine-supplemented perfusion medium resulted in an increased release of DA compared to retinae perfused with tyrosine-free medium.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Wipe tests to assess 99Tcm surface contamination: effects of surface type, swab type and chemical form.
The efficacy of wipe tests for assessing 99Tcm surface contamination was measured. Four types of surface were contaminated with four radiopharmaceuticals and wiped using four types of swab. The fraction of activity removed was measured by direct monitoring for each combination of surface, pharmaceutical and swab. The results obtained showed that wipe tests are neither accurate nor precise. Observed wipe efficacies differed greatly from the customary assumption that 10% of the activity is removed by wiping. Detergent soaked swabs gave a mean efficacy of 40%, although with considerable variation (coefficient of variation 49%). Using these swabs alone the surface type affected efficacy by almost a factor three (floor tile mean efficacy 20%, plastic laminate mean efficacy 57%). In principle this effect might be compensated for by using correction factors according to the surface being swabbed. However, the pharmaceutical type will generally be unknown, and this also affected efficacy by almost a factor of two (eluate mean efficacy 29%, macroaggregated albumin 53%). Overall the results suggest that wipe tests can be used to detect contamination but are unreliable for quantification.
Environmental Monitoring↗
A simple perfusion system for measuring endogenous retinal dopamine release.
A simple superperfusion apparatus for measuring endogenous dopamine (DA) release from rat retina is described. DA release is stimulated by increasing levels of potassium (K) in the superfusion medium and this K-stimulated release is calcium dependent. Exposure of dark-adapted retinae to light also increases endogenous DA release. This system should prove useful in determining what factors may control endogenous DA release in the retina.
Animals↗
Models of renal blood flow and their use in the detection of renal artery stenosis.
First-pass studies of renal blood flow using 99Tcm-DTPA have been analysed in normotensive patients and those with renal artery stenosis. One and two component models of renal blood flow were examined for their ability to discriminate between these two groups. Using a two component model, 5/7 kidneys with proven renal artery stenosis were identified, with 38/40 kidneys in normotensive patients lying within the defined normal range. The two kidneys not detected by this technique both had extremely poor function. This model was also applied to other hypertensive patients referred for routine screening and appears promising in increasing the specificity of the 99Tcm-DTPA study for detecting renal artery stenosis.
Adolescent↗
Exchange of nuclear medicine image files.
Explore the source record for details and available documents.
Diagnostic Imaging↗
Patterns of care for stroke survivors.
Explore the source record for details and available documents.
Cerebrovascular Disorders↗
The design and evaluation of an automated system for monitoring 133Xe in room air.
The radioactive gas 133Xe is widely used for ventilation imaging. This paper describes a system for continuous monitoring of the air concentration of 133Xe. The instrument consisted of a sodium iodide scintillation detector, a scaler/ratemeter and a data logger. The crystal was mounted inside a lead shield and enclosed in a perspex cylinder. A fan at one end of the cylinder drew room air into a shielded active volume via an inlet aperture designed to generate turbulent flow with no stagnant areas. The instrument was rendered relatively insensitive to external radiation by positioning the energy window over the 31 keV peak in the 133Xe spectrum. The detector sensitivity was approximately 2 s-1 per MBq m-3, with a typical background count rate of 0.12 s-1. The system was therefore capable of detecting a concentration of 0.06 MBq m-3 in a one-minute sampling interval. Results collected at five centres demonstrated that the eight-hour time-averaged concentrations were much less than the derived air concentration (DAC) for occupationally exposed persons (mean values 0.4 to 1.5% of the DAC), but that transient concentrations were extremely variable (mean values 7 to 24% of the DAC).
Air Pollutants, Occupational↗
Diurnal alterations in retinal tyrosine level and dopamine turnover in diabetic rats.
Retinal tyrosine level is correlated not only to its serum concentration, but also to the serum tyrosine ratio (the ratio of serum tyrosine to the sum of 5 neutral amino acids, leucine, isoleucine, valine, tryptophan and phenylalanine which compete with it for tissue uptake). In control animals, serum tyrosine ratio, retinal tyrosine, dopamine (DA) and its metabolites, and DOPA synthesis exhibit roughly parallel daily rhythms with night-time lows and peak levels occurring in the early portion of the daily light phase (L + 4 HR). In rats made diabetic by streptozotocin injection serum leucine, isoleucine and valine are elevated, lowering the serum tyrosine ratio and retinal tyrosine level by about 50% throughout the daily cycle. Parameters of DA turnover are still highest in the light phase but normal peak levels are delayed by 4 h until the latter half of the light phase (L + 8 HR). In diabetic rats, the normal increase in retinal DA synthesis and release upon exposure to light may be compromised by the decreased availability of its precursor, tyrosine.
3,4-Dihydroxyphenylacetic Acid↗
Increase in norepinephrine turnover after tyrosine or DL-threo-3,4-dihydroxyphenylserine (DL-threo-DOPS).
The amino acids tyrosine and DL-threo-3,4-dihydroxyphenylserine (DL-threo-DOPS) were compared for their effectiveness in increasing central nervous system norepinephrine (NE) turnover in both saline and DSP-4 pretreated mice. NE was decreased significantly in cortex, hippocampus and cerebellum, and only slightly in hypothalamus and brainstem two weeks after a single intraperitoneal injection of the neurotoxin DSP-4. Levels of the major NE metabolite, 3-methoxyl-4-hydroxyphenylethylene glycol (MHPG), decreased in parallel in these five brain regions. Neither administration of tyrosine (250 mg/kg, as the ethyl ester, i.p.) nor DL-threo-DOPS (200 mg/kg, i.p.) affected regional NE concentration. However, after tyrosine administration, MHPG levels increased significantly in cortex in control mice and in cortex and hippocampus of DSP-4 pretreated mice. In all five brain noradrenergic regions MHPG level increased after DL-threo-DOPS administration and this increase was enhanced (approximately doubled) in DSP-4 pretreated mice. Thus, both amino acids may be useful as precursors of central NE when its level is depleted (e.g. following administration of DSP-4); DL-threo-DOPS producing a generalized increase in brain NE turnover, while increases following tyrosine are specific to those areas in which neuronal activity is increased i.e. cortex and hippocampus.
Animals↗
Effects of the noradrenergic neurotoxin DSP4 on growth and the gonadal steroid- and PMSG-induced release of LH in the prepubertal female rat.
We have examined the effect of DSP4 treatment on PMSG-induced ovulation. A marked attenuation of the stimulatory effects of PMSG (7.5 I.U.) by DSP4 was evidenced by the significantly lower number of corpora lutea present in the ovaries of those animals which ovulated compared to controls. In addition, ovarian weight was lower in the DSP4 group. In a further experiment, we examined the effect of DSP4 on the induction of an LH surge by progesterone (P) in estradiol benzoate (EB) primed rats. DSP4 administration 2 hours prior to P eliminated the LH surge seen in controls. In view of our previous observations that DSP4 can interact with opioid receptors, we attempted to block its inhibitory effect on PMSG and EB/P stimulations. Coinjection of naloxone, an opioid antagonist, only partially prevented the influence of DSP4. It seems likely, therefore, that opioid receptors are not involved in the inhibitory effects of DSP4 described here. In further experiments, we studied the effects of DSP4 on spontaneous sexual maturation in female rats. DSP4 was administered (50 mg/kg, IP) on either day 5, day 23, day 29, or both day 24 and day 26 of life. Growth was inhibited and vaginal opening (VO) was significantly delayed in all except the day 29 group. However, VO occurred at the same body weight as the controls. By the end of the experiment, hypothalamic noradrenaline levels were not significantly different between control and DSP4-treated animals. The lack of an effect of DSP4 on the progression to puberty may be due to sufficient recovery of the central noradrenergic systems during the time course of the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)
Aging↗
Real time 3D display of gated blood pool tomograms.
Gated radionuclide blood pool tomograms offer the possibility of evaluating the shape, size and function of the cardiac chambers. A modified form of the back-to-front display algorithm has been implemented on a conventional nuclear medicine computer, enabling real time display of three-dimensional shaded surface images of the heart. A surface model was created from conventional blood pool tomograms, and then displayed using depth shading. The mean time required to process 40 tomographic sections was 45 s, and subsequently the heart could be inspected from any aspect with a refresh rate of 2-4 Hz, giving the effect of real time rotation. Rapid oscillation between end-diastolic and end-systolic images allowed wall motion to be assessed, and was combined with interactive selection of the viewing direction using a trackerball. For hard copy images, a surface orientation shading algorithm was used. Kinetic information was incorporated by creating composite hidden surface images from end-diastolic and end-systolic objects, using colour to indicate which surface was visible. It is suggested that these techniques are of value in the visual interpretation of the large amount of data obtained by gated blood pool tomography.
Algorithms↗
Alterations in retinal tyrosine and dopamine levels in rats consuming protein or tyrosine-supplemented diets.
The ad libitum ingestion of casein diets varying in protein content altered serum and retinal levels of tyrosine. The serum tyrosine level rose when protein ingestion was increased from 6 to 24% casein. In rats consuming high-protein diets (40% casein), no further increase in serum tyrosine level occurred, although the levels of other large neutral amino acids, which compete with tyrosine for retinal uptake, continued to rise. The activity of the liver enzyme tyrosine aminotransferase varied directly with the percentage of protein in the diet and may partially explain the failure of chronic high-protein feeding to increase serum tyrosine levels. The retinal tyrosine concentration was significantly correlated with the serum tyrosine level and with the serum tyrosine ratio at all levels of protein intake. Retinal 3,4-dihydroxyphenylalanine synthesis and dopamine (DA) level varied in parallel with the level of the precursor, tyrosine. Addition of pure L-tyrosine (1, 2, or 4%) to normal protein diets resulted in a stepwise increase in serum and retinal tyrosine levels and retinal DA turnover. Alterations of retinal tyrosine level as a result of change in amount of dietary protein or by its addition to the normal diet can influence retinal DA synthesis and release.
3,4-Dihydroxyphenylacetic Acid↗
Increase in mouse brain regional noradrenaline turnover after L-dopa administration.
Noradrenaline (NA) and its major metabolite, 3-methyl-4-hydroxyphenylethylene glycol (MHPG) were measured by HPLC with electrochemical detection in five mouse brain regions after L-dopa treatment. Noradrenaline concentration increased significantly, by 30-40%, in the three terminal regions of the locus coeruleus; cortex, hippocampus and cerebellum, but did not change in hypothalamus and brainstem. In mice whose central NA levels had been depleted by prior treatment with the neurotoxin, DSP-4, remaining NA neurons in these terminal regions were still able to respond with an increase in NA after L-dopa loading. The NA metabolite, MHPG, increased several-fold in all five regions in both saline and DSP-4-pretreated mice. Thus, L-dopa may be a useful precursor of NA in specific brain regions, particularly when NA is depleted.
Animals↗
Inhibition of MAO B, but not MAO A, blocks DSP-4 toxicity on central NE neurons.
The neurotoxin, DSP-4, (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride) specifically and significantly reduces norepinephrine (NE) and its metabolite, 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), in cortical, hippocampal and cerebellar brain regions. Pretreatment with the selective monoamine oxidase (MAO) B inhibitor, deprenyl, and the non-specific MAO inhibitor, pargyline, effectively blocked NE depletion. Pretreatment with the selective MAO A inhibitor, clorgyline, had no effect on central NE DSP-4 toxicity. Thus formation of a toxic metabolite by the action of MAO B may be involved in DSP-4 induced neural damage.
Animals↗