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  • 1
    ISSN: 1432-1076
    Keywords: Key words Phenylketonuria ; Positron emission tomography ; Dopamine D2-receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Patients with phenylketonuria (PKU) may suffer from cognitive and neurological deficits which are related to reduced intracerebral concentrations of catecholamines. The function of phenylalanine (Phe) as an inhibitor of the uptake of the precursor amino acid tyrosine (Tyr) through the blood-brain barrier as well as an inhibitor of the expression of dopamine receptors in the brain is under investigation. Positron emission tomography (PET) is a method for quantitatively determining biochemical and physiological processes in vivo. In the current pilot study, l-[1-11C]-Tyr and 18F-fluoro-ethyl-spiperone (FESP) have been used. The metabolic pathway of carboxylic labelled Tyr is mainly incorporation into protein. From the measured tissue and plasma activity as a function of time in combination with a compartimental model the Protein Synthesis Rate (PSR) for Tyr can be calculated. FESP is a ligand which binds irreversibly to the dopamine D2-receptor and has also a low non specific binding, although affinity to the serotonin receptor has been described. The ratio of FESP concentration in striatum and in cerebellum is a measure of the receptor status in vivo. In patients with plasma Phe levels above the maximum therapeutic concentration (〉 700 μmol/l) the PSR for Tyr was decreased as compared to controls and patients with plasma Phe concentrations within the therapeutic range, indicating a decreased availability of Tyr for neurotransmitter synthesis, and hence explaining the reduced cerebral concentration of catecholamines.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0942-0940
    Keywords: Brain tumour ; brain oedema ; blood brain barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A survey is given of the principles underlying the diagnosis of brain tumours. Traditionally diagnosis and localization of brain tumours have been based upon morphological criteria. Currently unsurpassed levels in imaging of anatomical details and topographical relations by the techniques of computed tomography (CT) and magnetic resonance imaging (MRI) have been achieved. The techniques of positron emission tomography (PET) and of magnetic resonance spectroscopy (MRS), which depict also metabolic and blood flow aspects, provide a refinement of our knowledge on the metabolism, structure and pathophysiological relations of a tumour to the surrounding parenchyma. Recent advances in the recording of function-related changes of the cerebral electro-magnetic field allow a better definition of critical functional areas.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0942-0940
    Keywords: Keywords: Brain metastasis; dissemination study; [18F]-FDG whole body PET.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary  Background. In the preoperative diagnosis of malignant brain tumours there is often uncertainty regarding their metastatic or primary nature, requiring dissemination studies. Currently FDG-wbPET is being used for the efficient detection of systemic tumours. It therefore may become a substitute for the conventional dissemination studies if it allows an earlier diagnosis.  Method. In this descriptive and preliminary study a population of 14 patients with suspected or proven metastatic lesions, [18F]-fluoro-2-deoxy-D-glucose whole body positron emission tomography (FDG-wbPET) was conducted and verified by additional conventional dissemination studies.  Findings and their Interpretation. The entire series of dissemination studies required an average of 30 days with a range of 4–73 days. The FDG-wbPET was corroborated by the other dissemination studies in 10 of the 14 patients. In 7 of these 10 patients both PET and dissemination studies showed systemic abnormal findings, but in one case the presence of high pulmonary activity on the FDG-wbPET and the abnormal findings on the chest X-rays proved to be Aspergillus infection at autopsy. In the other 2 cases the negative PET findings corresponded to the absence of systemic dissemination. In 5 cases there was disagreement of the results of the FDG-wbPET with other evidence, among which there were 2 cases of glioblastoma in which systemic metastases were most unlikely, and the foci of activity on the FDG-wbPET had to be considered as false positives. In the remaining 3 cases the systemic presence of high activity on the FDG-wbPET indicated the systemic presence of tumour, whereas the other dissemination studies disclosed no tumour.  Conclusion. The results warrant the use of FDG-wbPET as a screening method for the search of metastases, allowing other studies to be focussed on the lesion. But from the cost/benefit point of view this would make the method less suitable as a substitute for dissemination studies in general, although it may speed up the diagnostic process.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1920
    Keywords: Key words Gliomas ; Proton magnetic resonance spectroscopy ; Proton magnetic resonance spectroscopic imaging ; Brain oedema ; Positron emission tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In 32 patients with gliomas, one- and two-dimensional proton magnetic resonance spectroscopy (1H-MRS) has been conducted, the latter allowing reconstruction of spectroscopic data into a spectroscopic image (MRSI), showing the distribution of the various metabolite concentrations over the cross-sectional plane. For lack of absolute concentrations, the measured concentrations of phosphocholine (CHOL), N -acetyl-L-aspartate (NAA), and lactate (LAC) were conventionally expressed in ratios relative to that of creatine (CREAT). Compared to normal brain tissue, an increased CHOL/CREAT ratio was found in all groups of tumours, in glioblastomas, high-, middle- and low-grade astrocytomas both at the margin and the core of the tumours, but in oligodendrogliomas only at the margin. This is consistent with an increased phosphocholine turnover in relation to membrane biosynthesis by the proliferating cells. The NAA/CREAT ratio was decreased in all groups of tumours, both in the centre and at the margin, reflecting replacement of functioning neurons by neoplastic cells. The LAC/CREAT ratio was elevated in the core of malignant gliomas, which may be the result of a prevailing glycolysis, characteristic of tumours, possibly in conjunction with hypoxia/ischaemia. In the perifocal oedema, there was neither elevation of the CHOL/CREAT ratio nor decrease of the NAA/CREAT ratio; an increased LAC/CREAT ratio therefore rather reflected ischaemia/hypoxia probably due to locally elevated pressure and compromised regional perfusion. In the normal brain, the metabolite ratios of grey matter did not differ from those of white matter. The frontal lobe and basal ganglia showed lower NAA/CREAT ratios than the other cerebral areas. In 7 patients positron emission tomography was also performed with [18F]fluoro-2-deoxy-D-glucose (18FDG) or L-[1-11C]-tyrosine (11C-TYR); the latter demonstrated a pattern of 11C-TYR uptake similar to that of CHOL elevation in the MRSI.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1920
    Keywords: Key words Gliomas ; cerebral ; Radiotherapy ; Magnetic resonance spectroscopy ; Position emission tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We monitored 10 patients with unresected (9) or partially resected (1) supratentorial gliomas with 11C-tyrosine position emission tomography (TYR-PET) before and after radiotherapy. TYR-PET tumour volumes were measured using a threshold technique. In seven patients the tumour volume decreased after radiotherapy, although all gliomas persisted on TYR-PET images. In eight patients the tumour protein synthesis rate (PSR) was calculated using a dynamic study protocol in combination with a PATLAK analysis. There were no changes in PSR after radiotherapy, but the PSR was calculated on the remaining tumour volume using the same threshold technique as before therapy, i. e. the decrease in tumour volume was not taken into account. In eight patients the PET data were compared with magnetic resonance spectroscopic imaging (1H-MRSI) performed simultaneously. Although there was no statistically significant correlation between TYR-PET volume changes and 1H-MRSI choline level we observed a simultaneous decrease in volume and choline in four patients.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1920
    Keywords: Gliomas ; Proton magnetic resonance spectroscopy ; Proton magnetic resonance spectroscopic imaging ; Brain oedema ; Positron emission tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In 32 patients with gliomas, one- and two-dimensional proton magnetic resonance spectroscopy (1H-MRS) has been conducted, the latter allowing reconstruction of spectroscopic data into a spectroscopic image (MRSI), showing the distribution of the various metabolite concentrations over the cross-sectional plane. For lack of absolute concentrations, the measured concentrations of phosphocholine (CHOL),N-acetyl-L-aspartate (NAA), and lactate (LAC) were conventionally expressed in ratios relative to that of creatine (CREAT). Compared to normal brain tissue, an increased CHOL/CREAT ratio was found in all groups of tumours, in glioblastomas, high-, middle- and low-grade astrocytomas both at the margin and the core of the tumours, but in oligodendrogliomas only at the margin. This is consistent with an increased phosphocholine turnover in relation to membrane biosynthesis by the proliferating cells. The NAA/CREAT ratio was decreased in all groups of tumours, both in the centre and at the margin, reflecting replacement of functioning neurons by neoplastic cells. The LAC/ CREAT ratio was elevated in the core of malignant gliomas, which may be the result of a prevailing glycolysis, characteristic of tumours, possibly in conjunction with hypoxia/ischaemia. In the perifocal oedema, there was neither elevation of the CHOL/CREAT ratio nor decrease of the NAA/CREAT ratio; an increased LAC/CREAT ratio therefore rather reflected ischaemia/hypoxia probably due to locally elevated pressure and compromised regional perfusion. In the normal brain, the metabolite ratios of grey matter did not differ from those of white matter. The frontal lobe and basal ganglia showed lower NAA/CREAT ratios than the other cerebral areas. In 7 patients positron emission tomography was also performed with [18F]fluoro-2-deoxy-D-glucose (18FDG) or L-[1-11C]-tyrosine (11C-TYR); the latter demonstrated a pattern of11C-TYR uptake similar to that of CHOL elevation in the MRSI.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-739X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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