PubMed Health⌕ Search

Biomedical subjects

S Jivan

Publications and source records attributed to S Jivan.

13 recordsLinked to original sources

Goldmann applanation tonometer calibration error checks: current practice in the UK.

AIM: Assess current practice and views regarding checking Goldmann applanation tonometers for calibration errors in the United Kingdom. DESIGN: Questionnaire survey. METHODS: A total of 100 ophthalmology residents from England, Wales, and Scotland attending the 2004 Congress of the Royal College of Ophthalmologists, UK, responded to a structured questionnaire. They were asked the following: how often they used different tonometers between clinical sessions; how often they checked their tonometers for errors; and who they felt was responsible for checking tonometers for calibration errors. RESULTS: All respondents were using a different Goldmann tonometer for each clinic: 85% never check tonometers for errors; only 7% perform checks at the start of each clinical session; and 8% would only check the tonometer for calibration errors if they had suspicious or unexpected measurements. A total of 70% of respondents felt that calibration checks are not part of their responsibility. They believe that either nursing staff or other hospital staff should carry out calibration checks and ensure that tonometers are accurate. The remaining 30% felt that calibration checks should be carried out by the doctor using the tonometer. CONCLUSION: Despite evidence that Goldmann tonometers lose accuracy during routine use in clinical practice, only a minority are checking the tonometers for calibration errors. There is no consensus as to who should be responsible for ensuring that tonometer calibration is maintained. We recommend that tonometers should be checked for calibration errors at least on a monthly basis by individuals identified by departmental protocols.

Calibration↗

Water-cooled grid support for high-power irradiation with thin target windows.

A new thin window support system for the accelerator production of positron emitters (e.g. 17F, 18F 11C, 15O) has been developed. The integrated support grid and cooling design has been optimized for 6-13 MeV protons or deuterons. The water-cooled support grid regularly operated at > 100 microA of 6 MeV deuterons and protons. The grid performed without failure at > or = 50 microA of 13 MeV protons on a 3.1 MPa gas target using 25.4 microm aluminum target foil. Transmission for the smallest hole grid of 72% based on uniform parallel beam agreed with the measured yield of 71 +/- 1% compared to the theoretical maximum yield.

Journal Article↗

Pseudomyxoma peritonei.

Pseudomyxoma peritonei is a relatively rare and poorly understood condition in which mucus accumulates within the peritoneal cavity. The presence of cells in the mucin, either inflammatory or neoplastic, distinguishes it from simple acellular mucus ascites caused by mucinous spillage. There is widespread seeding of the peritoneal and omental surfaces with a heavy cancerous glaze. This is principally a complication of borderline or malignant neoplasm of the ovary and/or appendix. This paper describes two cases of previously healthy women who both presented with an acute abdomen, and were diagnosed postoperatively with pseudomyxoma peritonei. In addition, literature on the clinical presentation, diagnostic procedures, and treatment options has been briefly reviewed.

Abdomen, Acute↗

Biochemical variations in the synaptic level of dopamine precede motor fluctuations in Parkinson's disease: PET evidence of increased dopamine turnover.

Motor fluctuations are a major disabling complication in the treatment of Parkinson's disease. To investigate whether such oscillations in mobility can be attributed to changes in the synaptic levels of dopamine, we studied prospectively patients in the early stages of Parkinson's disease with a follow-up after at least 3 years of levodopa treatment. At baseline, 3 positron emission tomography (PET) scans using [11C]raclopride before and after (1 hour and 4 hours) orally administered levodopa were performed on the same day for each patient. Patients who developed "wearing-off" fluctuations during the follow-up period had a different pattern of levodopa-induced changes in [11C]raclopride binding potential (BP) from that observed in patients who were still stable by the end of the follow-up. Thus, 1 hour post-levodopa the estimated increase in the synaptic level of dopamine was 3 times higher in fluctuators than in stable responders. By contrast, only stable responders maintained increased levels of synaptic dopamine in the PET scan performed after 4 hours. These results indicate that fluctuations in the synaptic concentration of dopamine precede clinically apparent "wearing-off" phenomena. The rapid increase in synaptic levels of dopamine observed in fluctuators suggests that increased dopamine turnover might play a relevant role in levodopa-related motor complications.

Brain↗

In vivo PET studies of the dopamine D2 receptors in rhesus monkeys with long-term MPTP-induced parkinsonism.

Studies of dopamine (DA) receptor binding in early parkinsonian patients, or in models of Parkinson's disease, have revealed a supersensitivity of the D2-like receptor subtype as compared to age-matched controls. The lack of upregulation in advanced patients is often attributed to the effects of prolonged antiparkinsonian therapy, but the impact of therapy vs. intrinsic mechanisms in untreated patients or animals with long-term lesions of the DA nigrostriatal pathway has been difficult to address. We studied, in vivo, by PET using the DA D2 receptor ligand raclopride, the status of the DA receptors in normal rhesus monkeys and those with acute (3 months) or long-term (10 years) MPTP-induced nigrostriatal lesions. Compared to age-matched controls, there was no change in raclopride binding in MPTP-treated animals without parkinsonian symptoms. There was a significant increase in raclopride binding in the putamen (but not caudate nucleus) of all the animals displaying rigidity, hypo- and bradykinesia. This increase was greater in the animals with acute lesions (32%) than with established, long-term lesions (18%). There was no correlation between the postmortem striatal DA concentrations and in vivo raclopride binding but there was a correlation between PET raclopride binding and [(3)H]raclopride binding in vitro. Complex changes in D2 receptor binding occur in various stages of parkinsonism. Antiparkinsonian therapy is unlikely to be solely responsible for the lack of upregulation found in advanced parkinsonian patients but may be a contributing factor.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

Evaluation of dopaminergic presynaptic integrity: 6-[18F]fluoro-L-dopa versus 6-[18F]fluoro-L-m-tyrosine.

The effectiveness of 6-[18F]fluoro-L-m-tyrosine (6FMT) to evaluate dopamine presynaptic integrity was compared to that of 6-[18F]fluoro-L-dopa (6FDOPA) in vivo by positron emission tomography (PET). Six normal and six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned monkeys received 6FDOPA and 6FMT PET scans on separate occasions with identical scanning protocols. Four measures, the rate of uptake of tracer into striatum using either the arterial input function (Ki) or the activity in the occipital cortex as the input function (Kc), the rate of loss of striatal radioactivity (k(loss)), and an index of "effective turnover" of dopamine (k(loss)/Ki), were obtained for both tracers during extended PET studies. 6-[18F]Fluoro-L-m-tyrosine was as effective as 6FDOPA in separating normals from MPTP-lesioned subjects on the basis of the uptake rate constants Ki and Kc. However, in contrast to 6FDOPA, it was not possible to differentiate the normal from the lesioned animal using k(loss) or k(loss)/Ki for 6FMT. Thus, FMT appears to be a reasonable, highly specific tracer for studying the activity of aromatic dopa decarboxylase enzyme as an index of presynaptic integrity. However, if one is interested in investigating further the metabolic pathway and obtaining an in vivo estimate of the effective turnover of dopamine (after pharmacologic manipulation, for example), 6FDOPA remains the tracer of choice.

Animals↗

An improved HPLC system for the analysis and purification of organic amine radiopharmaceuticals.

This paper describes the separation of lipophilic amine radiopharmaceuticals on normal phase silica using a reversed phase type eluant. This class of compound usually gives very poor peak symmetry on reversed phase columns. However, excellent separation of a number of amines of interest to Positron Emission Tomography, such as spiperone and its derivatives, has been achieved on this system.

Benzazepines↗

The use of C-18 SEP PAK cartridges to simplify routine production of 2-deoxy-2-[18F]fluoro-D-glucose.

The synthesis of 2-deoxy-2[18F]fluoro-D-glucose has been simplified by the use of C-18 SEP PAK cartridges. The fluorinated sugar produced from the reaction of acetyl hypofluorite and tri-acetyl glucal (TAG) was extracted from the neutralized reaction mixture with C-18 SEP PAK cartridges. The product was washed off the cartridge with diethyl ether and hydrolyzed by HCl. After hydrolysis the product was purified by passage through ion retardation resin, alumina and another C-18 cartridge. The radiochemical purity was 98% and the radiochemical yield was 28%, decay corrected to EOB, with a total synthesis time of 50 min from EOB.

Deoxy Sugars↗